Variable Star Network: World Center for Transient Object Astronomy ...

P A SJ: P ubl.A stron.Soc.Japan ,1{??, c 2016. A stronom icalSociety of Japan.

V ariable Star N etw ork: W orld C enter for Transient O bject A stronom y and V ariable Stars TaichiK ato,M akoto U em ura,R yoko Ishioka D epartm ent ofA stronom y, K yoto U niversity,Sakyo-ku, K yoto 606-8502 tkato@ kusastro.kyoto-u.ac.jp, ishioka@ kusastro.kyoto-u.ac.jp, uem ura@ kusastro.kyoto-u.ac.jp

D aisaku N ogam i H ida O bservatory, K yoto U niversity,K am itakara,G ifu 506-1314 nogam i@ kwasan.kyoto-u.ac.jp

arXiv:astro-ph/0310209v1 8 Oct 2003

C hatief K unjaya Institute ofTechnology,B andung,Indonesia kunjaya@ as.itb.ac.id

H ajim e B aba C enter for Planning and Inform ation System s, T he Institute ofSpace and A stronauticalScience (ISA S), Sagam ihara,K anagawa 229-8510 baba@ plain.isas.ac.jp and

H itoshiY am aoka Faculty ofScience,K yushu U niversity, Fukuoka 810-8560 yam aoka@ rc.kyushu-u.ac.jp (R eceived ;accepted )

A bstract VariableStarN etwork (V SN ET )isa globalprofessional-am ateurnetwork ofresearchersin variablestars and related objects,particularly in transient objects,such as cataclysm ic variables,black hole binaries, supernovae and gam m a-ray bursts.T he V SN ET hasbeen playing a pioneering role in establishing the eld oftransientobjectastronom y,by e ectively incorporating m odern advance in observationalastronom y and globalelectronic network,aswellascollaborative progressin theoreticalastronom y and astronom icalcom puting. T he V SN ET isnow one ofthe best-featured globalnetworksin this eld ofastronom y.W e review on the historicalprogress,design concept,associated technology,and a wealth ofscienti c achievem ents powered by the V SN ET . K ey w ords: accretion, accretion disks | astronom ical data bases: m iscellaneous | catalogs | galaxies:B L Lacertaeobjects:general| gam m a rays:bursts| m ethods:data analysis| stars:binaries: eclipsing | stars: binaries: sym biotic | stars: dwarfnovae | stars: em ission-line,B e | stars: novae, cataclysm ic variables | stars: oscillations | stars: pre-m ain sequence | stars: supernovae | stars: variables: other | stars: W olf-R ayet| surveys | X -rays:bursts 1. Introduction 1.1. TransientO bjectA stronom y W ith the progress of m odern physics and astronom y, ouroutlook on the universe isdram atically changing from the stationary universe to the dynam ic, ever changing, universe. T he dynam icalphenom ena in the universe appearas variationsatvarioustim e-scalesranging from the cosm ologicalevolutionary tim escaleto lessthan a m ilisecond. T hese tim e-variationsare becom ing actually observable w ith the advent ofthe m odern observing equipm ent and technology. A m ong them , tim e-variations arising from extrem e gravity as best exem pli ed by black holes, and from degenerate objects, such as w hite dwarfs and neutron stars,havebeen receiving extrem e attention from various eldsofm odern science,asthe naturallaboratory ofgeneralrelativity and quantum m echanics,w hich best representthe glorioussuccessofthe \century ofphysics".

A s can be easily expected from the extrem e conditions, astronom icalphenom ena under strong gravity or in degenerate conditionshave extrem ely shorttim e-scales,and are know n to be usually very unpredictable. T hese astronom ical phenom ena are now generally called \transient phenom ena", or referred to as \transient objects". T he concept oftransientobject astronom y appeared very late in the history of astronom y and now ourishing as a new m odality of astrophysicalresearch.1 T his success greatly owed to the recent great advancem ent ofobserving m odalities,inform ation technology and com putational astrophysics. T he Variable Star N etwork (V SN ET ),the objectiveofthisreview ,isoneoftheearliestand m ostsuccessfulinternationalgroupsthatled to them odern success oftransient object astronom y. 1

A sshow n in A ppendix 1,the V SN E T isthe earliestgroup w hich began using the term transient objects in the present context of astronom icalsigni cance.

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ofthe1986 historicaloutburstofSW U M a wasrelayed via an astronom icaltelegram only w hen the object reached a In the research history of transient object astronom y, historicalbrightness ofV 9,although the outburst was there were two m ajor breakthroughs in the early 1990’s. initially reported 1.5 below the peak brightness. T here T he one is the developm ent ofeasy availability ofC C D s had been very few early stage observations (i.e. w ithin a and personalcom puters, and the other is the advent of day ofthe eventdetection)oftransientobjectsbefore the the internet. T hese two breakthroughs played a key role 1990’s. in establishing transient object astronom y as one of the 1.3. Early Public Electronic C om m unication m ost popular contem porary astronom y topics. From the traditional view point, C C D s were usually T hissituation drastically changed w ith the public availused as a \faint-end" extension ofthe form er photon de- ability ofthe internet. In the early tim es (around 1990{ tection m ethods,e.g. photoelectric and photographic ob- 1991),there were only sporadic internet com m unications servations. T his naturally led to a pursuit of observing on observations,m ainly via personale-m ailsand on public fainter stars on long-exposure C C D im ages (cf. H owell, bulletin board system s.T hisstrategy worked slightly betSzkody 1988; Szkody et al. 1989; H owell et al. 1990; terthan in thepast,thesituation wasbasically unchanged H owellet al.1991). in that m ost ofobservers had to rely on occasionalcom T he founder of the V SN ET was one of the rst to m unications or a slow access to new s m aterials. break thistradition,and wasvirtually the rstperson w ho From thenecessity ofpublicly and electronically dissem system atically turned m odern C C D equipm ent to bright, inating urgentastronom icalphenom ena,thereappeared etransient objects,such as classicalnovae and outbursting m ailexploders(m ailing lists). T he Scandinavian varstars dwarfnovae (the best exam ples being K ato,H irata 1991; list and the (m ainly) professionalnovanetby the A rizona K ato 1991b; K ato, Takata 1991, see the later sections State U niversity team played an early im portant role in for their scienti c achievem ents). T he traditionaltim e- publicly relaying inform ation on transient objects.2 T he resolved observations of classicalnovae and outbursting early-tim e progress ofthese electronic com m unications is dwarfnovae were alm ost restricted to so-called target-of- sum m arized in the vsnet-history list.3 opportunity (T O O )observations.T hebesttraditionalexT hescienti croleofw ide-availability ofthesee-m ailexam ples include the 1978 outburst ofW Z Sge (Patterson, ploders was recognized upon the appearance ofSN 1993J M cG raw 1978; M attei1980;Patterson et al.1981),and in M 81 (R ipero et al. 1993; Pease 1993). T his suthe 1986 outburst of SW U M a (R obinson et al. 1987). pernova showed an unusual early-tim e light curve and T his kind ofobservations was usually severely lim ited by a spectral transition from a type-II to type-Ib superthe telescope tim e allocation,and m any im portant tran- nova (N om oto et al.1993;Swartz et al.1993;Filippenko sient phenom ena (e.g. the 1985 historicallong outburst et al. 1993a; Podsiadlow ski et al. 1993). In com m uniofU G em : C annizzo et al.2002) faded away w ithout re- cating nightly rapid changesand distributing m ostup-toceiving su cient observationalcoverage.Traditionalpro- date observation strategies, the e-m ail exploders played posals for telescope tim e were also lim ited because ofthe a m ore crucialrole than ever. A nother advantage of etransient and unpredictable nature of these phenom ena; m ail exploders as a standardization tool of observations there is no guarantee that there is a suitable transient becam e evident ( gure 1). Early-tim e non-standard obtarget at the tim e ofallocated observation. For this rea- servations were quickly corrected using the updated phoson,system aticobservationalresearch in theseobjectswas tom etric com parison stars,and questionable observations severely restricted to short-period,less unpredictable ob- were exam ined real-tim e to clarify the cause. T his led jects,w ith an enorm ouse ortofworld-w ide coordination to a huge world com pilation ofSN 1993J photom etry up(e.g. V W H yi: Schwarzenberg-C zerny etal.1985;Pringle dates (see gure 2) contributed by a num ber of volunet al.1987;Y Z C nc: van Paradijs et al.1994). teers,including the V SN ET founder.4 T his high-quality, T im ely circulation ofalertson transientobjectsorphe- uniform com pilation ofreal-tim eobservationsgreatly connom ena isalso crucially im portant,particularly forT O O - tributed to real-tim e theoreticalm odeling of this object type observation. B efore the w ide availablity of the in- (e.g. N om oto et al. 1993), spectroscopy (e.g. B aron ternet,the typicalway ofcom m unicating such alerts was et al.1993;Taniguchiet al.1993;C locchiattiet al.1995; a phone call from an observer (usually an am ateur as- Tram m ellet al. 1993a) and photom etry (e.g. van D riel tronom erwatching variable stars)to a variable starorga- et al.1993;W heeler et al.1993). W e published our ow n nization,w hich wastypically relayed (w ith som e delay)to results in O kyudo et al.(1993). W e also contributed to localobserversforcon rm ation.T heinform ation,ifitwas a num ber ofInternationalA stronom icalU nion C irculars recognized asparticularly im portant,wasthen distributed (IA U C s) (K ato, H anzl 1993; Zim m erm ann et al. 1993; to world-w ide observers usually from the C entralB ureau K ing et al. 1993; Filippenko et al. 1993b; Tram m ell ofA stronom icalTelegram s (C B AT ) via telegram s,direct 2 B oth netw orks do not exist at present. phone calls, or slow postcards. It usually took, even in 3 hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/vsnet-history/ best cases,a day or m ore before this crucialinform ation m aillist.htm li. wasrelayed to the actualobserverundertaking a T O O ob- 4 T he nalversion ofthe \photom etry update" is publicly available at hftp://vsnet.kusastro.kyoto-u.ac.jp/pub/vsnet/SN e/ servation.T he early stageoftransientobjectswasusually sn1993j/sn.m agi m issed because ofthis delay. For exam ple,the detection 1.2. N ew W indow to TransientO bjectA stronom y

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F ig. 1. C irculated electronic chart ofSN 1993J (issued on 1993 A pril13) show ing V -band com parison stars for standardization.

et al. 1993b; H u et al. 1993). T he com plete history of tim e ofSN 1993J played an im pressive role: the com prethis SN 1993J story can be also seen in the vsnet-history hensive com pilation ofV 705 C asby Yasuto Takenaka (see gure 3) was cited in a N ature paper (Shore et al.1994) archive. as best authenticated optical record of this nova. T he 1.4. O pening of the Electronic Era of Transient O bject nova waslatereven sym bolically called an electronic nova A stronom y (Pepin 1995),representing the opening ofnew electronic U pon the recognition of the im portance of e-m ail ex- era oftransient object astronom y. ploders on the occasion ofSN 1993J,m ore system atic ef1.5. Establishm entofV SN ET forts were taken to standardize the com m unication and T he inform ation ofthese transient objects and regular data reporting m ethod. In relation to reporting observations,we started w idely dissem inating observations of variable star observations was initially relayed m anually, regular variable star observations, m ainly subm itted to or relayed on existing less speci ed e-m ailexploder systhe Variable Star O bservers League in Japan (V SO LJ),5 tem s. In 1994,ourow n e-m ailexploder system (V SN ET ) and those personally reported to us. People started rec- started working.T hisservicesm oothly took overthe past ognizing the scienti c im portance of w idely dissem inat- m anual e-m ailannouncem ent system s, and im m ediately ing regular observations, w hich can be readily re ected received w ide attention both from am ateur and profeson scheduling new observations. N ew ndings based on sional com m unities. T he establishm ent of the V SN ET w idely reported observations(e.g.superhum p detection of thus becam e the \prototype" of world-w ide am ateura dwarfnova) were also relayed real-tim e,w hich worked professionalcollaborationsbased on publice-m ailcom m uas a positive feedback to originalobservers. T he proto- nication. T his initiative later led to a ourishing V SN ET type of V SN ET -type e-m ail exploders was thus estab- C ollaboration (section 4).T he early history wasreviewed lished in 1993. T he next m ajor astronom ical event at by D . N ogam i et al. (1997) in \Electronic Publishing, this stage of the history was the discovery of N ova C as N ow and the Future", Joint D iscussion 12 of the 23rd 1993 (V 705 C as). T his nova showed considerable degree IA U G eneralA ssem bly. C onsidering the historicalsigni ofearly-tim e uctuations,as wellas a later dust-form ing cance in the adventoftransientobjectastronom y and the episode. D uring allofthe stages ofevolution ofthe nova currentunavailability ofthisdocum entin a solid publicaexplosion,the data circulating strategy established atthe tion,we reproduce the presented contents in A ppendix 1 (in order to preserve the originalcontents, we only cor5 hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/V SO LJ/vsolj.htm li and see hhttp://vsolj.cetus-net.org/i for the V SO LJ V ariable rected m inor typographicalerrors). T he V SN ET m ailing listsystem now hasm orethan 1300 subscribersfrom m ore Star B ulletin page.

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V magnitude

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SN 1993J

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100

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JD - 2449000 F ig. 2. Light curve of SN 1993J, draw n from the \SN 1993J photom etry update" (see text). T he Large and sm alldots represent (nearly) V -band and visualobservations.

Visual magnitude

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V705 Cas 10

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JD - 2449000 F ig. 3. Light curve of V 705 C as (N ova C as 1993), covering the rise and the \great fade", and rebrightening phases, draw n from the observations circulated through the early developm ent of the V SN E T . T he dots and open circles represent visual and photographic/C C D observations,respectively.

the reporting system is described in A ppendix 2. B y globally collecting data,we soon recognized the ne2. V SN E T as a M odern-D ay \E lectronic cessity for setting up a dedicated e-m aillist for reporting observations, vsnet-obs.6 T he alert list vsnet-alert7 was V ariable Star O rganization" prepared at the sam e tim e, w hich has been one of the 2.1. H istoricalD evelopm ent ofthe Electronic Reporting m ost renow ned and reliable sources of noteworthy pheSystem nom ena of variable stars and transient objects, and the D uring the very initialstage ofthe developm ent ofthe m essages in vsnet-alert have been frequently cited in the V SN ET ,wesim ply relayed observationsto thosew ho (po- professionalliterature as the prim ary source of inform atentially)need thedata.H owever,itsoon becam eevident, tion (e.g. D ow nes et al.1997;D ow nes et al.2001;R itter, from the experiences w ith SN 1993J and V 705 C as (sub- K olb 1998;R itter,K olb 2003;K ube et al.2003). section 1.3), that there is a need for a new ly designed 6 hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/vsnet-obs/ reporting system adapted for electronic data exchanges. m aillist.htm li. B ecause of the large num ber of articles, the Since we already had su cient experience w ith relaying online archive is subdivided; see hhttp://w w w .kusastro.kyotou.ac.jp/vsnet/M ail/index.htm li. for the com plete m essage V SO LJ reports to the world-w ide variable star observers, archi ve. it was a naturalsolution to extend the V SO LJ form at to 7 hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/vsnet-alert/ an internationalversion. T his changes were m inim al,by m aillist.htm li. introducing U niversalT im e (U T )-based system and the extension of coding system of observers. T he details of than 50 countries allover the world.

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2.2. Standardization T he V SN ET played an im portant role in standardization ofvariable star observing.T here are severalsteps in standardization: (1) standardization ofreporting form at (see subsection 2.1), (2) standardization of com parison stars, and other m inor steps. In standardizing com parison stars,the V SN ET group also took an initiative in the history of transient object astronom y. T he earliest exam ple includes SN 1993J and classicalnovae, for w hich reliable C C D -based (or som etim es photoelectric) com parison star sequences were determ ined and distributed through the V SN ET lists. B efore this standardizating efforts were taken, the nova researchers had to cope w ith often unreliable early reportsin IA U C s,w hich were often based on various sources ofcom parison stars w ith notoriously diverse photom etric quality. W ith the advent of the V SN ET ,the m odern-day nova observationshave now becom e as reliable as those of other variable stars w ith well-established com parison star sequences. T he V SN ET group hasbeen paying attention to the quality ofthe originaldiscovery reports,and have issued severalm agnitude updatessuperseding theIA U C announcem ents.T hesam e e orthasbeen taken forsupernova photom etry,although the faintness and the large num ber ofthe target objects have m ade ita m ore di cult task than in classicalnovae. In observation of (non-transient) ordinary variable stars,the V SN ET took the initiative to standardize the com parison star m agnitudes to the m odern V system , from variousold system sincluding thetraditionalH arvard visualphotom etric system . T he e ort was initially taken to revise the faint-end m agnitudes for cataclysm ic variables(C V s)and peculiarvariablesusing the C C D cam era at O uda Station,K yoto U niversity (O htaniet al.1992). T hese results were continuously released as \V SN ET charts" through the V SN ET lists (see gure 4). Several independentcontributed e orts,by R afaelB arbera (G rup d’Estudis A stronom ics)8,and Fraser Farrell(A stronom y Society of South A ustralia),9 as well as those by the V SN ET adm inistrator team , were m ade to w rite software packages to graphically display this V SN ET chart form at.B rian Ski hasbeen continuously contributing to the V SN ET in photoelectrically standardizing sequences for selected variable stars; this initiative was globally taken overw ith the C C D works,notably by A rne H enden and B ruce Sum ner.10 T hese standardized sequences and charts have ow n lists vsnet-sequence and vsnet-chart.11 Forthebrightend,wewerethegroup to rstextensively useH ipparcosand Tycho m agnitudesattheearliestepoch (1997)ofthe public release ofthese catalogs.W e im m ediately m ade public variable starchartsbased on H ipparcos and Tycho m agnitudes.12 Since then, this adoption of 8 9 10 11

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hhttp://w w w .astrogea.org/i. hhttp://w w w .assa.org.au/i. hftp://ftp.nofs.navy.m il/pub/outgoing/aah/sequence/sum ner/i. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-sequence/m aillist.htm li and hhttp://w w w .kusastro.kyotou.ac.jp/vsnet/M ail/vsnet-chart/m aillist.htm li. hftp://vsnet.kusastro.kyoto-u.ac.jp/pub/vsnet/charts/H IP T Y C /i

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the standard V -band system (selected for B V colors) for visual photom etry has been gradually becom ing the globalstandard. Since the public release ofTycho-2 catalogue, this standard was extended to a slightly fainter m agnitude.13 For poorly observed faint objects,we also took an initiative (vsnet-chat700,in 1998)14 to calibrate U SN O catalog m agnitudessince the early release ofthe U SN O A 1.0 catalog (M onet et al.1998a). T his calibration has been w idely used,w hen an alternative sequence is not readily available. 2.3. C ollaboration with the V SO LJ From the very beginning ofits history,the V SN ET has been in continuous collaboration w ith the V SO LJ. T he activity includes hosting the V SO LJ alert and discussion m ailing lists, distributing the V SO LJ reports and prediction of variable stars,and hosting the public V SO LJ database and light curves (see subsection 3.2). A part ofstandardization schem es (subsection 2.2) has been developed in collaboration w ith the V SO LJ adm inistrator group (see also A ppendix 2) and through a discussion w ith world-w ide variable star leadersat the International V SO LJ M eeting held in conjunction w ith the 23rd IA U G eneralA ssem bly. T he other pioneering aspect of the V SN ET {V SO LJ collaboration was the introduction of C C D s for C V photom etry. T his work was m ainly done in collaboration w ith M akoto Iida, w ho took the world initiative to m onitor faint C V s w ith a com m ercial C C D . T his collaboration led to fruitful scienti c results (N Y Ser: Iida et al. 1995b; D V D ra: Iida et al.1995a;B C U M a, see hhttp://w w w .kusastro.kyotou.ac.jp/vsnet/D N e/bcum a.htm li). T hese successful resultswere dem onstrated in a num berofinternationalconferences,including thePadova C V C onferencein 1995 and the K eele C V C onference in 1997,and the resultsbecam e gradually digested by the professionalcom m unity. T his pioneering am ateur-professionalcollaboration in transient objectsand C V s nally led to the m ostsuccessfulV SN ET C ollaboration (section 4), and the strategy was taken over, albeit w ith a lesser degree of the original\ avor" ofam ateur-professionalrelations and publicity policy,by a num ber offollow ing world-w ide groupsw ith the sim ilar strategies. 2.4. C ollaboration O bservers

with

the Southern

H em isphere

Since the V SN ET service initially started w ith the coordinating role am ong m ostly northern hem isphere observers,there were initially few reportsfrom the southern observers. W ith the outstanding activity ofthe V SN ET , there arose a num ber of requests from professional astronom ers w ho were planning for T O O observations of southern dwarf novae. T his situation has been gradu13

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hftp://vsnet.kusastro.kyoto-u.ac.jp/pub/vsnet/charts/ T ycho-2/i hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/vsnet-chat/ m sg00700.htm li

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pixel Date: September 14.42, 1996 Exposure Time: 30 s Calibration: (V mag) Device: 60cm Reflector + V -band CCD photometry (Ouda Station, Kyoto University) F ig. 4. E xam ple of V SN E T chart issued in 1996. T he object is G M Sgr (currently renam ed as V 4641 Sgr; note that this chart provided the corrected identi cation against the previous publication). T he availablity ofa chart w ith the correctly identi ed object enabled the discovery ofthe giant outburst in 1999 (see subsection 6.4.1).

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ally and progressively im proved by increasing contributions from the southern observers, particularly by the m em bers ofR oyalA stronom icalSociety ofN ew Zealand (R A SN Z).15 B y now ,these contributions,notably by R od Stubbings,have enabled a num berofrare outburstdetections and early circulation ofthese phenom ena. Together w ith the collaboration w ith southern C C D observers,the scienti c achievem ents of transient object astronom y in the southern hem isphere is explosively grow ing (e.g. m icroquasar V 4641 Sgr: Stubbings, Pearce 1999; U em ura etal.2002d;U em ura etal.2002h,southern SU U M a-type dwarfnovae: K ato et al.2003h;K ato et al.2003b;K ato et al.2003d),w hich w illbe reviewed in later sections. M ostrecently,westarted collaborating w ith theN agoya U niversity team for identifying X -ray transients (see subsection 6.4) w ith the Sim ultaneous-3color InfraR ed Im ager for U nbiased Survey (SIR IU S) cam era installed at the Infrared Survey Facility (IR SF)16 situated at the South A frican A stronom ical O bservatory, Southerland, South A frica. Several scienti c achievem ents have already been issued (K ato et al.2003a;B aba et al.2003a; N agata et al.2003). A work on V 359 C en in collaboration w ith the M icrolensing O bservations in A strophysics (M O A ) project17 team has been also published (K ato et al.2002k). 3. W orld-W ide Service

W eb

and

A nonym ous F T P

3.1. H istoricalD evelopm ent From the very beginning of the V SN ET ,allm essages posted to V SN ET public m ailing lists are opened to the public.A m essagecan berelayed (unlessthesenderotherw isespeci estheusage)to third-party m em bers,orcan be posted to a di erentm ailing list ora public new s service. In the earliest tim es,these m essages were archived (they were som etim es m ade public) at individualreceivers. From the necessity of publicly providing standardized charts and related m aterials (see subsection 2.2),we initially used private anonym ousftp service operated at the D epartm ent of A stronom y, K yoto U niversity. T his was replaced by the o cial V SN ET anonym ous ftp service in 1995 July. C ontributed program s,notably V SN C H T w ritten by R afaelB arbera,to graphically display V SN ET form atchartswere m ade public from the startofthe service. M agnitude sum m aries of selected objects such as new novae,our ow n and contributed C C D im ages ofoutbursting dwarf novae were soon m ade available through the anonym ous ftp service. W e set up the o cial V SN ET W orld-W ide W eb (W W W ) service18 in 1995 June. T he web pages have been continuously updated, particularly in announcing new ly discovered transient object phenom ena. Even during these updates,we have paid alloure ortsto preserve the originalU R Ls for future reference; alm ost all pages 15 16 17 18

hhttp://w w w .rasnz.org.nz/i. hhttp://w w w .saao.ac.za/facilities/irsf/irsf.htm li. hhttp://m oa.scitec.auckland.ac.nz/i. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/i.

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that existed in the past can be tracked w ith the original U R Ls even now . T he other design ofthe V SN ET W W W system was in the com bined usage ofthe W W W and ftp services. In the earliest tim es,not allinternet users were able to use w indow -based brow sers. W e have thus set up two ways (W W W and anonym ous ftp) of access to the desired data. W ith this feature,a user is able to get necessary im ages or program s even w ithout a brow ser or a fast internet connection. T his feature becam e, however, less im portant w ith the w ide availablity of the w indow based brow sers.T he ftp service soon included a com plete archive ofthe V SN ET m ailing list m essages. In 1997 A pril, we started public W W W service of all archivalm essagesposted to the V SN ET lists.T he W W W archive is autom atically updated by using the M H onA rc system .19 W eonceim plem ented theN am azu-based20 fulltextsearch engine on the V SN ET W W W service,butthis wasdiscontinued becausepublicly availablesearch engines now have equivalent functions. 3.2. Public Light C urve A rchive W ith the developm ent of the V SN ET W W W service, we started public light curve archive service in 1996 A ugust.21 T hese light curves are draw n and regularly updated from vsnet-obs reports,w hich were incorporated into the V SN ET database (A ppendix 2). A t present,the regular updates ofthese (static) light curves archive are perform ed by a JavaT M -based lightcurvegeneratorengine w rapping the Linux-based V SN ET database system . T he V SN ET light curve archive also hosts light curvesdraw n from the V SO LJ and A ssociation Francaise des O bservateurs d’Etoiles Variables (A FO EV )22 public database,by courtesy ofthe respective organizations. T hese lightcurvescan be easily reached from the V SN ET top page,as wellas from the A FO EV website. W e also im plem ented individual variable star pages23 generated from the G C V S electronic edition. T hese pages provide handy linksto the lightcurves(V SN ET ,V SO LJ, A FO EV ) and links to the relevant pages and charts on the V SN ET . 3.3. D ata Search Engine and Light C urve G enerator Soon after the establishm ent ofthe data reporting system ,we also im plem ented a C om m on G ateway Interface (C G I)-based data search engine in 1996 June.24 T his service returns the observations of a speci ed variable star selected from the V SN ET public database, w hich is coherently updated from the regularvariable starreportsto the V SN ET . T his type of interactive variable star data brow serwasthe rstone in the world,and becam e a pro19 20

21 22 23 24

hhttp://w w w .m honarc.org/i. T he N am azu full-text W W W -based search engine w as developed by one of the V SN E T adm inistrators, H ajim e B aba. T his is one of the best used system s am ong search engines for non-com m ercial, personal or academ ic uses. See hhttp://w w w .nam azu.org/i for the N am azu project. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/LC s/index.htm li. hhttp://cdsw eb.u-strasbg.fr/afoev/i. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/gcvs/index.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/etc/searchobs.htm li.

8

T .K ato et al.

totype ofthe subsequentsim ilarservices.T hisinteractive data search enginehasbeen w idely used and frequently referred in the professionalliterature. A num ber ofW W W services, including the well-know n \Latest Supernovae" page25 by D avid B ishop,provideslinksto m ostup-to-date com pilations ofvariable star reports by directly referring to the V SN ET data search engine. T his W W W -based data search engine provides the m odern-day extension of the early-tim e m agnitude sum m aries (subsection 1.4). In 1998 M arch,thisV SN ET data search engine furtherm ore started providing a JavaT M applet-based interactive lightcurveinterface,26 w ith w hich a usercan freely brow se the data (both V SN ET and V SO LJ observations) w ith a graphicaluserinterface(G U I).T hiswasoneoftheearliest JavaT M applications in public astronom icalservice. 4. V SN E T C ollaboration 4.1. V SN ET as W orld O bservations ofC V s

C enter

of T im e-Series

A s described in section 2.3, the V SN ET played a pioneering and essentialrole in establishing a new m odality of internet-based am ateur-professionalcollaboration. T his direction was one of the m ain aim s of the V SN ET from the very start ofits internet presence. A m ong various kinds of variable stars, C V s are the \canonical" class oftransient objects,as brie y reviewed in subsection 1.2. W ith the com m on interest in C V s and related system s,the V SN ET am ateur-professionalcollaboration originally m ainly focused on C V s, especially on unpredictable outbursts ofdwarfnovae. T he actualcollaborative studies were done on the existing V SN ET list, m ost frequently on vsnet-alert and vsnet-obs. In m ost cases,real-tim ereportsofvisualdetectionsofoutburstsin dwarfnovae,usually aftersom everi cation processinvolving the V SN ET adm inistrator team ,triggered the actual observing cam paigns.T hisprocesswasusually perform ed w ithin several hours and a day of the detection. T his prom ptreaction to eventtriggersoftransientobjectslater enabled an e cient reaction to gam m a-ray burst (G R B ) triggers(section 6.15).T he unique feature ofthe V SN ET cam paignson transientobjectsis thatthey are a collaborative e ortbetween visualobserversand C C D observers. T he V SN ET is historically the rst organization that realized the high productivity involving traditional visual variable star observations, although this im portance in transient object astronom y had long been stressed and had been a dream am ong researchers. T heearly-tim esuccessfulcooperativeworksinclude:recurrent nova V 3890 Sgr (K ato et al. 1990, phone call), detection of superhum ps in A Q Eri(K ato 1991a,phone calland e-m ail),detection ofsuperhum ps in V 1251 C yg (K ato 1991b; K ato 1995a, phone call and e-m ail), W X C et in 1991 (K ato 1995f independent detection and em ail),EF Peg (K ato,Takata 1991;K ato 2002c,phonecall and e-m ail),H V V ir in 1992 (K ato et al.2001l,e-m ail), 25 26

hhttp://w w w .rochesterastronom y.org/snim ages/i. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/etc/draw obs.htm li.

[Vol.,

SW U M a in 1992 (K ato et al.1992a,phone call). Since then,m ostinform ation isrelayed by e-m ailand e-m ailexploder system s (m ost ofthe works were conducted upon response to real-tim e outburst detection alerts reported through the V SN ET ):V 344 Lyr (K ato 1993),H Y Lup = N ova Lup 1993 (K ato et al.1993b),A K C nc (K ato 1994; M ennickentetal.1996),T Leo (K unjaya etal.1994),K V A nd (K ato et al. 1994), AY Lyr (N ogam i et al. 1994), C Y U M a (K ato 1995b),K V A nd in 1994 (K ato 1995c), FO A nd (K ato 1995d), T T B oo (K ato 1995e), discovery ofER U M a (K ato,K unjaya 1995),w hich w illbe described in subsection 6.1,PU Per (K ato,N ogam i1995), H S V ir (K ato etal.1995d),G O C om (K ato etal.1995c), D H A ql (N ogam i, K ato 1995b), V 1159 O ri (N ogam i et al.1995a),H V A ur (N ogam iet al.1995b),V 725 A ql (N ogam iet al.1995d,ow n detection),R Z LM i(N ogam i et al. 1995c), V 1028 C yg in 1995 (B aba et al. 2000). T his continuous stream of scienti c reports based on the V SN ET am ateur-professionalcooperations brought a great im pact on the com m unity (Liller 1996). D uring this early-epoch collaborative works through the V SN ET ,severalnoteworthy rare (typically once in a decade to severaldecades)phenom ena occurred and were studied in unprecedented detailthrough the V SN ET :A L C om in 1995 (M attei et al. 1995; N ogam i, K ato 1995a: the outburst was detected by an A AV SO m em ber,soon relayed to the V SN ET , w hich enabled the detection of \early superhum ps", w hich are observed only for several nights after the start of the outburst. See K ato etal.1996b;N ogam ietal.1997a foroursum m ariesofthis event).27 T hisinform ation on theV SN ET furtherenabled extensive follow -up studies by di erentgroups(Patterson et al. 1995a; Patterson et al. 1996; Pych, O lech 1995a; Pych,O lech 1995b;H owelletal.1996;Szkody etal.1996). T he 1996{1997 outburst of EG C nc (Schm eer et al. 1996) was a great surprise. T his outburst was detected by Patrick Schm eer, a V SN ET m em ber, and im m ediately relayed through the V SN ET alertsystem . Together w ith theearly detection ofearly superhum ps(M atsum oto, Schm eer1996;M atsum oto etal.1998),the objectshowed an unexpected sequence of post-superoutburst rebrightenings (K ato et al.1997). T his unexpected phenom enon was discovered by ourselves and the collaborative e orts through the V SN ET .28 T his detection ofthe spectacular rebrightening phenom enon,w hich m ostclearly illustrated the power ofreal-tim e inform ation exchange,also led to a num ber ofobservationaland theoreticalpapers (O saki etal.1997;O sakietal.2001;Patterson etal.1998;Szkody et al. 2000; Szkody et al. 2002a). T his im pressive phenom enon exhibited to the public, through the V SN ET , 27

28

T he full details of the phenom enon, m ade public in the K eele C V C onference in 1996 (K ato et al. 1996c), can be seen at hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/D N e/alcom 1.htm li. T he star w as nom inated as the \star of the year" in this conference. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/D N e/egenc.htm li. It w as our greatest pleasure that a num ber of speakers in the W yom ing C V C onference in 1997 presented this V SN E T w ebpage as representing the m ost unusual activity of a dw arf nova.

N o.]

Variable Star N etwork

the \real-tim e science" in the m aking. T he1999 outburstoftherecurrentnova U Sco (Schm eer et al. 1999; gure 5) again illustrated the ability of the international alert network system provided by the V SN ET .29 T he outburst detection was m ade by Patrick Schm eer, and the alert was im m ediately dissem inated through the V SN ET . W ith this quick noti cation, a very stringent upper lim it becam e im m ediately available, w hich was obtained only less than four hours before the outburst detection. T he early new s enabled an A m erican observer to catch the realopticalm axim um (m v = 7.6), w hich was m ore than one m agnitude brighter than had been supposed forthisrecurrentnova.Itisvery likely the delays in delivering inform ation were partly responsible forthe underestim ateofthem axim um m agnitudesin past outbursts. A lm ost allim portant ndings near the m axim um light (w ithin one day of detection) were obtained before the relevantIA U C wasissued.T he V SN ET collaborativestudy on thisoutburstadditionally led to the rsteverdetection ofeclipsesduring the outburst(M atsum oto et al.2003b;H achisu et al.2000a;H achisu et al.2000b). T his outburst again produced a rich scienti c outcom e from various researchers (K ahabka et al. 1999; Lepine et al. 1999; M unari et al. 1999; K iyota 1999; Ikeda etal.2000;A nupam a,D ewangan 2000;Evansetal.2001; Iijim a 2002):w hen com pared to the resultsfrom previous outbursts (1979: B arlow et al.1981;W arner 1979,1987: R osino,Iijim a 1988;Sekiguchietal.1988),the 1999 result could be even referred to as the \victory in the electronic era" oftransient object astronom y. A fter experiences w ith these, and other spectacular transientphenom ena (w hich w illbereviewed in section 6), we setup new lists(vsnet-cam paign30 and othersublists), w hich prim arily dealw ith cam paigns on selected targets. W ith theestablishm entofthesededicated lists,westarted referring to our am ateur-professionalworld-w ide collaboration group as V SN ET C ollaboration. T his (not too tightly bound)group hasbecom eharboring subsequentintensive studiesundertaken in the V SN ET .Figure 6 show s the globaldistribution ofcontributors. 4.2. V SN ET C am paign Lists and Sum m aries T he V SN ET cam paign list and sublists were thus progressively established since 2000, encapsulating a w ide range oftransientastronom icalphenom ena. T he V SN ET cam paign lists are subdivided into categories based on object classes (e.g. vsnet-cam paign-dn for dwarf novae, vsnet-cam paign-xray for X -ray binaries). M ost recently, follow ing the discovery of very unusual objects or phenom ena of public interest, we som etim es set up a separate list focused on single objects (e.g. vsnet-cam paignv4641sgr31 for the m icroquasar V 4641 Sgr (subsection 29 30

31

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/N ovae/usco.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-cam paign/m aillist.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-cam paign-v4641sgr/m aillist.htm li.

9

6.4),vsnet-cam paign-v838m on32 forthem ostunusualstellar explosion (V 838 M on) w ith an astounding light echo, vsnet-cam paign-sn2002ap33 for the nearesthypernova SN 2002ap (see subsection 6.5). T hese new features enabled interested theoreticians to share real-tim e inform ation of these m ostunusualobjects. T he num berofV SN ET cam paign individuallists is 36 (2003 A ugust). Sum m aries of the activities of the V SN ET C ollaboration have been com piled by M akoto U em ura and issued on a weekly basis(V SN ET cam paign new s).34 T his inform ation has been sum m arized as a yearly review of the activity of the V SN ET C ollaboration.35 T hese V SN ET cam paign new s and sum m aries com prise an im portant (authorized) part of the nearly real-tim e contribution from the V SN ET to the other organizations (section 4.3),and are som etim es cited in them selves as a convenient record ofthe activities ofparticular objects. N owadaysthe V SN ET cam paignsare m ore orlesscontinuously undertaken. In orderto inform the currenttargets ofinterest,we have recently set up a noti cation list vsnet-cam paign-targetto cam paign contributors. 4.3. C ontribution to O ther W orld-W ide A lertSystem s From the very start ofthe A stroA lert system 36 m aintained by the Sky Publishing C o.,the V SN ET has been nom inated asoneoftheauthorized inform ation providers. W e now regularly contribute \N ew sfrom V SN ET " to this alert system ,prim arily notifying the transient astronom icalphenom ena ofcurrent interest. W e also occasionally issue alerts on particularly urgent phenom ena and nova discoveries. T he new s have been relayed to the A AV SO , the astro-lm ailing list,and are w idely distributed as the prim ary source of inform ation on transient astronom ical phenom ena. 5. V ariable Star R elated A ctivities In addition to m ain scienti c achievem ents (section 6), the V SN ET group has been engaged in various activities in the eld ofvariable starsand variable star-related m atters. H ere we show our representative activities. 5.1. Variable Star Identi cations T he V SN ET group has been historically engaged in providing updated inform ation to the G eneralC atalogues ofVariable Stars (G C V S:K holopov et al.1985a;Sam us et al. 2000; Sam us’ et al. 2002; Sam us’ et al. 2003; K azarovets et al. 1998) team ,37 and provided a large am ount of variable star identi cations and suggestions, m ainly based on exam ination of the historicalliterature w ith the m odern technology. T he present m ost relevant 32

33

34

35 36 37

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-cam paign-v838m on/m aillist.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-cam paign-sn2002ap/m aillist.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-cam paign-new s/m aillist.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/Sum m ary/i. hhttp://skyandtelescope.com /observing/proam collab/astroalert/i. hhttp://w w w .sai.m su.su/groups/cluster/gcvs/gcvs/i.

T .K ato et al.

Magnitude

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U Sco (1999)

10

15

20 230

240

250

260

270

280

JD - 2451000 F ig. 5. Light curve ofthe 1999 outburst ofthe recurrent nova U Sco from V SN E T observations.

F ig. 6. G lobaldistribution of observers of V SN E T C ollaboration. T he large and sm all\burst" m arks represent regular and occasionalparticipants to C C D photom etric cam paigns. T he num ber of lled squares relative num bers ofrepresent (prim arily) visualor photographic observations from various regions ofthe earth.

lists are vsnet-id and vsnet-gcvs38,w hich dealw ith variable star identi cations and the G C V S revision project, respectively. T he identi cations reported to vsnet-id are also relayed to the SIM B A D 39 o ce. T here is a series ofsolid papers on system atic variable star identi cations (K ato 1999b;K ato 1999c;K ato 1999d;K ato 1999g; K ato 1999h; K ato 1999i; K ato 1999j; K ato 1999k; K ato 2001j).T herehavealso been collaborationsw ith the M ultitudinousIm age-based Sky-survey and A ccum ulative O bservations (M ISA O ) project,40 w hich used their ow n C C D im ages to identify variable objects near the cata38

39 40

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/vsnet-id/ m aillist.htm li and hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/ M ail/vsnet-gcvs/m aillist.htm li. hhttp://sim bad.u-strasbg.fr/Sim badi hhttp://w w w .aerith.net/m isao/i.

loged positions(Yoshida etal.1999a;Yoshida etal.2000b; Yoshida et al. 2000c; Yoshida et al. 2000a; Yoshida et al.1999b). T hese collaborative works were conducted also in collaboration w ith the V SO LJ. In identifying variablestars,ourow n chart-plotting system (A ppendix 4) has played an im portant role. 5.2. N ew Variable Stars T he V SN ET hasbeen providing the role ofa world center of reporting new ly discovered variable stars. T here is a dedicated m ailing list vsnet-newvar.41 T he reported new variable starsare usually checked by the V SN ET adm inistrator group for identi cation w ith other astronom ical sources (e.g. X -ray sources, infrared sources, and 41

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-new var/m aillist.htm li.

N o.]

Variable Star N etwork

em ission-line stars). T hese identi cation processes are also conducted on the public m ailing list. T hese reports on new variablestarson vsnet-newvararenow regarded as the prim ary source oforiginalinform ation by the G C V S team (e.g. K azarovetset al.2000;K azarovetsetal.2001; K azarovetset al.2003). A prelim inary list (new var.cat) of new ly reported, or objects w ith som e peculiarity (w hich can be candidate variable stars)has been updated,and m ade public42 as a reference for those w ho are looking for new variable stars and variablestaridenti cations.Exam ination oftheproperties ofpoorly know n variable stars are also our regular works (m any results have been reported through vsnetgcvs lists,as wellas through som e solid publications such asK ato 2003d;K ato 2003e;K ato 2003f,w hich were based on the A SA S-3 public data;see subsection 5.3). 5.3. C on rm ation ofN ovae C on rm ation of reported nova candidates is another regular work conducted by the V SN ET adm inistrator team ,as wellas scienti c work in novae (subsection 6.2). T hiswork takesadvantageoftheestablished V SN ET software and catalog system s in variable star identi cations (subsection 5.1)and in con rm ing new variablestars(subsection 5.2). T he V SN ET system in screening and conrm ing new ly reported nova candidatesisone ofthe m ost reliable and e cient am ong allthe existing nova con rm ation system s. In particular, the V SN ET team has even succeeded in recognizing novae from otherw ise dism issed new variablestarreports(e.g.V 1548 A ql:U em ura etal.2001e;K ato,Takam izawa 2001).T he recentdiscovery ofV 463 Sct(H aseda 2000;U em ura etal.2000g;K ato et al.2002l) is another exam ple of the reliability of the V SN ET nova identi cation system .43 T he reverse case in that the V SN ET played an im portant role in disqualifying a suspected nova.T he m ost recent exam ple was w ith V 4006 Sgr, w hich was originally reported as a probable nova in IA U C (N akano et al. 2003a). T his object was soon identi ed w ith a know n variable star through the public discussion in the V SN ET .44 T he initialdiscovery announcem ent was subsequently readily corrected w ithin a day ofthe originalannouncem ent (G reen 2003). M ost recently,we refer to the public photom etric realtim e database provided by the A SA S-3 team (Pojm anski 2002)45 for con rm ing southern nova suspects. T he m ost recent successful exam ple includes V 2573 O ph = N ova O ph 2003 (Takao etal.2003).T hisapplication ofA SA S-3 public data is also true for con rm ing new variable stars (e.g. V 2552 O ph = H ad V 98: K ato, H aseda 2003) and better characterizing already know n variable stars (e.g. K ato,Stubbings2003).T he individualvariablestarpages on V SN ET websiteprovidesconvenientlinksto theA SA S3 pages (see subsection 3.2). U pon recognition ofnew novae,theV SN ET team m akes 42 43

44 45

11

an announcem entto nova researchersand thevariablestar com m unity to enable early-tim e con rm ation and follow up observations.T he V SN ET isnow recognized asone of the m ostpowerfulm edia for dissem inating such a kind of alerts to the open com m unity,and is relied on by m any professionalnova researchers. For this purpose, V SN ET takes an \open policy" of any nova (and supernova, variable star etc.) discovery announcem ents, i.e. such announcem ents w ill be im m ediately released and m ade public. T he full reasoning ofthe policy and the actualrecom m ended reporting procedure is described in hhttp://w w w .kusastro.kyotou.ac.jp/vsnet/etc/discovery.htm liand the links from this page. T he V SN ET has a dedicated list for announcing on new novae vsnet-discovery-nova,46 although this kind of inform ation is usually also posted to vsnet-alert from the convention. In any case,readers are strongly recom m ended to refer to the above page before attem pting to m ake an actualnova discovery report. 5.4. C on rm ation ofSupernovae A s wellas con rm ation of nova candidates, con rm ation ofsuspected supernovae is also undertaken from the very beginning ofthe V SN ET .T he rst exam ple was SN 1995D in N G C 2962 (N akano et al.1995),w hich was discovered by R eikiK ushida. T he object was con rm ed on the sam e night in Japan by three individual observers (vsnet-alert 30,31,32,1995 February)47,and the discovery announcem entled the m ulticolorphotom etry starting soon after the discovery (Sadakane et al.1996). Spectroscopic con rm ation of several supernovae has also been reported on the V SN ET lists. T he earliest one was for SN 1995al (vsnet-alert 266, 1995 N ovem ber),48 w hich was distributed wellearlier than the form al publication in IA U C (A yani,K awakita 1995). Such a quick distribution ofspectraltype ofsupernova m ade itpossible to schedule larger telescopes or space-borne instrum ents to observe it. T he nearest type-Ic hypernova SN 2002ap (vsnet-alert 7120, 2002 January)49 was the m ost successfulrecent exam ple (K inugasa et al.2002a,K inugasa et al. 2002b), w hich was followed by m any instrum ents including the Subaru telescope (K awabata et al. 2002) or the X M M -N ew ton (Soria, K ong 2002). Plentiful inform ation,including prediscovery observations(Yam aoka, R ogers2002),hasbeen posted to the specially m ade sublist vsnet-cam paign-sn2002ap. T hese contributionsto early-tim e observation are sum m arized in subsection 6.5,as wellas the scienti c results draw n from them . 46

47

48

hftp://vsnet.kusastro.kyoto-u.ac.jp/pub/vsnet/others/new var.cati.49 See hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/ N ovae/hadv46.htm li for the fullstory. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/N ovae/v4006sgr.htm li hhttp://w w w .astrouw .edu.pl/ gp/asas/asas asas3.htm li

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M vsnet-discovery-nova/m aillist.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M m sg00030.htm li and so on. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M m sg00266.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M m sg00120.htm li.

ail/ ail/vsnet-alert/ ail/vsnet-alert/ ail/alert7000/

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5.5. H osting A nnouncem ents ofExternalO rganizations

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U M a-typedwarfnovae,superoutburstsonly occurapproxim ately once per year,and last for 10 d. T he intervals ofsuperoutbursts (supercycles) are not constant,m aking it di cult to plan a scheduled observation. T he observations ofSU U M a-type dwarfnovae in the past were m ore or less T O O -type observations (subsection 1.2). W e rst prepared a com prehensive list ofcandidates ofSU U M atype dwarf novae, selected by various criteria from the literature and from our ow n observations. T his strategy was in som e way sim ilar to the other projects such as:

T he V SN ET has been playing a role providing an electronic m edium for announcem ents m ade by other variable star-related organizations. T he exam ples include the early announcem ents of A AV SO N ew sletters (vsnet-alert 14, 1995 January), A lert N otices (vsnetalert 58, 1995 M arch), N ew s Flashes (vsnet-alert 344, 1996 February),website announcem ent (vsnet-alert 178, 1995 A ugust),A LEX IS50 transients(vsnet-alert321,1996 February),InternationalT O A D W atch website51 (vsnetH igh-galactic latitude C V search: H owell, alert439,1996 June),websiteforH ungarian A stronom ical Szkody ( 1990) ; Szkody, H owel l ( 1992) ; D rissen A ssociation { Variable Star Section52 (H A A /V SS,vsnet et al.(1994);A ugusteijn,Stehle (1995) 756, 1996 Septem ber), website for C enter for B ackyard Its descendant concept of \Trem endous O utburst A strophysics53 (C B A ,vsnet 872, 1996 N ovem ber), webA m plitude D warf N ovae" (T O A D s): H owell site for B ritish A stronom ical A ssociation, Variable Star et al. (1995); H owell, Szkody (1995); Szkody, Section54 (B A AV SS,vsnet 893,1996 N ovem ber),website H owell(1995);H owell,Skidm ore (2000) for G roup of A m ateur A stronom ers, C zechia, (G A M A , 58 R ecurrent O bject Program m e: e.g. vsnet-alert 596, 1996 N ovem ber), IA U C om m ission 42, Poyner ( 1996) , and t he r el at ed ext ens i ve wor k B ibliography on C lose B inaries55 (B C B ,vsnet 981,1997 by Vanm unster,H owell(1996) January),and num erousannouncem entson callforobservations,electronic publications,and internationalconferA lthough allofthese other projects or works basically ences.56 T he V SN ET website and m ailing lists thus have relied on catalog selections (e.g. H owell et al. 1995) or been a world center of variable star-related announce- were based on the (usually poorly know n) past activim ents. ties. O ur strategy was di erent in that: (1) our selection wasbased on com prehensiveand extensivesearch through 6. Scienti c A chievem ents of V SN E T all available literature (this work was conducted in collaboration w ith the V SO LJ), (2) we had exam ined the 6.1. D warfN ovae Palom ar O bservatory Sky Survey (PO SS) plates and our D warf novae (cf. O saki 1996a) have historically ow n system atic C C D survey to get unique identi cations been the best-studied class of objects by the V SN ET and m ore reliable outburst am plitudes ofthe objects,(3) C ollaboration and its precedent m ailing list-based coop- we applied a theoretical background (e.g. O saki 1985; eration (hereafter referred to the V SN ET C ollaboration O saki 1989; Ichikawa, O saki 1994) for selecting the obthroughout this section). Figure 7 show s a com parison jects,and (4) we had am ateur collaborators to share our oflong-term lightcurvesofthree representative classesof interestin m onitoring faintdwarfnovaew ith a C C D (subdwarf novae (cf. O saki1996a) draw n from the V SN ET section 2.3).T he com bination ofthese factorsbroughtan observations.57 unprecedented success in discovering new SU U M a-type T he early work (up to 1996) alm ost im m ediately dou- dwarf novae. Since the early success story was already bled the num ber of SU U M a-type dwarf novae, by described in subsection 4.1,we m ainly focuson the recent the detection of superhum ps (Vogt 1980; W arner 1985; contributions ofthe V SN ET C ollaboration to this eld. W arner1995c)during theirsuperoutbursts.In typicalSU 50 51 52 53 54 55 56

57

hhttp://nis-w w w .lanl.gov/ asocops/alxhom e/i. hhttp://w w w -astro.physics.ox.ac.uk/ erik/itw /i. hhttp://vcssz.m cse.hu/i. hhttp://cba.phys.colum bia.edu/i. hhttp://w w w .britastro.com /vss/i. hhttp://a400.sternw arte.uni-erlangen.de/ftp/bcb/i. W e now have a dedicated list for conference announcem ents: hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-conference/m aillist.htm li. T hese data ofvarious kinds ofvariable stars are freely available (from the U R L in subsection 3.3),orupon requestto the V SN E T adm inistrator (vsnet-adm @ kusastro.kyoto-u.ac.jp). T here is no specially requested authorization for the usage of these data in scienti c publications other than the usual scienti c m anner of acknow ledgem ent (please refer to the m essage from the data search engine for a recom m ended form of reference). T he data usually cover observations since 1995,and are particularly convenient for m aking correlation analysis w ith other m odern observations (e.g. spectroscopy and m ultiw avelength observations).

6.1.1. D iscovery ofER U M a Stars In the canonical picture of SU U M a-type dwarf novae, the m ass-transfer (driven by angular m om entum loss from the binary) in these system s was believed to be the result of gravitationalwave radiation (G W R : cf. Paczynski1967;Faulkner1971;Tutukov,Yungelson 1979; Taam et al. 1980; Paczynski, Sienkiew icz 1981), since the fully convective secondary at this ( 2 hr) orbital period (P orb ) is generally considered im probable to sustain m agnetic braking, w hich plays a m ajor role in longer period (P orb 3 hr) C V s (R itter 1976; R itter 1980; W hyte, Eggleton 1980; Paczynski 1981; R appaport et al. 1982; R appaport et al. 1983; Spruit, R itter 1983;Paczynski,Sienkiew icz 1983;Verbunt 1984; Patterson 1984;R itter 1985). Since the angular m om entum loss by G W R is a unique function of com ponent 58

hhttp://w w w .theastronom er.org/recurrent.htm li.

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SS Cyg 8

10

12

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1100

1200

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12

14 1900

2000

2100

2200

2300

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12

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16 1100

1200

1300

1400

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JD - 2450000 F ig. 7. Long-term light curve of three representative classes of dw arf novae (SS C yg,Z C am ,and SU U M a) draw n from V SN E T observations. Portions of the light curves show variation in outburst cycle lengths and quiescent m agnitude (SS C yg), a standstill (Z C am ),and tw o superoutbursts (SU U M a).

14

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m asses and orbitalseparation,and the m asses ofthe prim ary w hite dwarfsand the m ain-sequencesecondary stars only have a sm alldegree of diversity,the SU U M a-type stars were historically considered as an \one param eter system ", i.e. the basic properties are determ ined by a single param eter,P orb . T his concept so w idely prevailed that statistics and classi cations were usually given follow ing this concept (W arner 1995c; Vogt 1993), and that num erical sim ulations im plicitly assum ed this canonical picture (O saki1989).In observations,a search fornew SU U M atype dwarf novae was usually restricted to dwarf novae w ith long recurrence tim es (the best exam ple being the R ecurrent O bject Program m e). O ur discovery,however, ofthe ER U M a stars com pletely changed this picture. ER U M a (= PG 0943+ 521)wasoriginally classi ed asa novalike object(G reen etal.1982)selected from itsultraviolet excess (Palom ar-G reen Survey: G reen et al.1986, see also R ingwald 1993). T his object was,together w ith other PG C V s selected from G reen et al. (1982), regularly m onitored by the V SO LJ m em bers for potential activities. In 1992, M akoto Iida (V SO LJ) noticed that this object show s dwarf nova-like outbursts (Iida 1994, see vsnet-history archive for fulldetails in the public reports circulated in 1992{1993). B ecause ofthe presence of long-lasting states of interm ediate brightness (w hich laterturned outto be superoutbursts),thisstarwasoriginally considered to be a Z C am -type dwarfnova,w hich is characterized by the presense ofstandstills in addition to dwarf nova-type outbursts (see e.g. H ellier 2001a,Sect. 5.4; see also W arner, van C itters 1974; M eyer, M eyerH ofm eister 1983;O ppenheim er et al.1998). In early 1994,follow ing the detection of a bright outburst by G ary Poyner, our C C D observations revealed the presence of superhum ps. C om bined w ith the visual observations electronically reported, this object was nally identi ed as an SU U M a-type dwarf nova w ith an unexpectedly short (43 d) supercycle (Ts). T he shortest Ts before the discovery of ER U M a was 134 d of Y Z C nc (Szkody,M attei1984;van Paradijs et al.1994). It later turned out through a discussion at the Padova C V C onference in 199459 that this object was independently studied at least by two groups:by the R oboScope (H oneycutt 1992) team (R obertson et al. 1995) and by M isselt, Shafter (1995). A m ong allgroups,the V SN ET team was the rst to unam biguously identify the nature ofthis object (K ato,K unjaya 1995). Spectroscopic (T horstensen et al. 1997) as well as photom etric (K ato et al. 1995a) identi cations of the orbital periods later con rm ed this identi cation. O nce this discovery was announced, new m em bers of 59

See also H oneycutt et al. (1995); the object w as originally presented in the conference as the best observational proof for the m ass-transfer burst m odel of dw arf nova outbursts. O ur detection of superhum ps w as presented in a later talk by O saki(1995a),w hich invoked a hot discussion,against the originaltopics to be presented by this talk,regarding the true nature ofE R U M a. A tthe tim e ofthis conference,the tone ofthe audience w as even skepticalabout the presence ofan SU U M a-type dw arfnova w ith such a short supercycle.

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the group of ER U M a stars were im m ediately identi ed through im petuous real-tim e com petitions through the V SN ET public lists: V 1159 O ri (N ogam i et al. 1995a; R obertson etal.1995)and R Z LM i(R obertson etal.1995; N ogam i et al. 1995c). It later turned out that the supercycle of V 1159 O ri was independently recognized by Patterson et al.(1995b),but was only interpreted w ithin the classicalfram ework.T he supercycle ofR Z LM iis exceptionally short (19 d), w hich is the shortest record of supercyclesup to now [see also K ato etal.(1999d)forthe basic observationalreview ,and K ato et al.(2002e);K ato et al. (2003e) for recent discussions of ER U M a stars]. Later additions to these ER U M a stars include D I U M a (K ato et al.1996a),an R Z LM i-like system ,and IX D ra (Ishioka et al.2001b),both ofw hich were discovered by the V SN ET C ollaboration. From the standpointofthe disk-instability m odel,these discoveries im m ediately led to theoreticalinterpretations (O saki1995b;O saki1995d),and signi cantly contributed to the \uni ed theory of dwarf novae" (O saki 1996b; O saki1996a). T hese theoreticalcalculations indicate an unexpectedly (from the canonical picture based on the G W R -driven angularm om entum loss)high m ass-transfer rate (ER U M a: O saki1995b). T he extrem ely short Ts of R Z LM irequires an additional(stillpoorly understood) m echanism (O saki1995d).T histheoreticale ortrecently led to ram i cations of ideas including the e ect of extrem ely low m ass ratio (q = M 2/M 1) (H ellier 2001b) or the e ect of irradiation (B uat-M enard, H am eury 2002), w hich need to be investigated by future work. It has been speculated (H ellier 2001b) that these m echanism s are partly responsible for the m anifestation of the unusual properties of still the still poorly understood W Z Sge-type dwarfnovae,w hich w illbe discussed later (subsection 6.1.2). T he required high m ass-transfer is still a m ystery. A lthough there have been a num ber of suggestions, including the long-term e ect of nova explosions (K ato, K unjaya 1995;Schenkeretal.1998;Patterson 1998;K olb et al.2001),w hich is,in som e sense,a m odern extension ofthe \old" discussion ofthe \nova hibernation" scenario (Shara etal.1986;Prialnik,Shara 1986;Livio,Shara 1987; Livio et al. 1988; D uerbeck 1992; N aylor et al. 1992; M ukai, N aylor 1995), irradiation-induced m ass-transfer feedback (M cC orm ick 1998; M cC orm ick, Frank 1998), none of them has succeeded in explaining the required high m ass-transfer rates in ER U M a. R ecent observations (K ato 2001a; Fried et al. 1999) suggest that the high m ass-transfer rates in ER U M a stars are less likely the result from a secular evolutionary e ect,but m ay be m ore related to the activity cycle in the secondary star (B ianchini1988;B ianchini1990;A k etal.2001).T he origin ofthe unusually high activity ofER U M a starsisstill an open question. From theobservationalside,therehasbeen a system atic search, m ainly conducted by the V SN ET C ollaboration and relevant results com m unicated to the public in real tim e,to nd interm ediate system sbetween ER U M a stars and classical SU U M a-type dwarf novae. Several inter-

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esting objects were recognized as a result: N Y Ser = PG 1510+ 234 (SU U M a-type dwarf nova in the period gap: N ogam iet al.1998b),H S V ir = PG 1341 079 (SU U M a-type dwarfnova w ith very shortoutburstrecurrence tim es: K ato et al.1995d;K ato et al.1998d;M ennickent etal.1999;K ato etal.2001o;M ennickentetal.2001b),SX LM i(low am plitude SU U M a-type dwarf nova: N ogam i et al.1997b;W agner et al.1998;K ato 2001b),C I U M a (SU U M a-type dwarf nova w ith irregular supercycle behavior: N ogam i,K ato 1997),V 1504 C yg (SU U M a-type dwarf nova w ith a short Ts, N ogam i, M asuda 1997), V 503 C yg (unusual SU U M a-type dwarf nova w ith unusual outburst behavior, Ts 89 d: K ato et al. 2002e; H arvey etal.1995),SS U M i(norm alSU U M a-type dwarf nova w ith a short Ts 84.7 d: K ato et al. 1998b; K ato et al.2000a),B F A ra (norm alSU U M a-type dwarfnova w ith the shortest Ts 84.3 d: K ato et al. 2001p; K ato et al. 2003b), V 344 Lyr (large-am plitude SU U M a-type dwarf nova w ith a short supercycle: K ato 1993; K ato et al.2002j),M N D ra = Var73 D ra (SU U M a-type dwarf nova w ith Ts 60 d: N ogam iet al.2003d). T he evolution of superhum ps in ER U M a stars is also know n to be unusual. K ato et al. (1996d) reported the early presence oflarge-am plitude superhum ps, w hich later turned out to be part of an unexpected early phase reversalof superhum ps (K ato et al.2003e). T hisphenom enon resem blestheso-called latesuperhum ps (H aefneretal.1979;Vogt1983;van derW oerd etal.1988; H essm an etal.1992)seen in late stagesofsuperoutbursts in SU U M a stars,but the striking di erence is that they appear in the early stage ofthe superoutburst. T he origin of this phase reversal is not yet understood. G ao et al. (1999) reported som e peculiar features in superhum ps of ER U M a. M asetti, R egos (1997) suggested a possible link between ER U M a stars X -ray transients by com paring the evolution oftheir superhum ps. To sum m arize,the discovery ofER U M a stars brought a revolutionary turning point ofdwarfnova studies: the SU U M a-type dwarfnovae are no longer \one-param eter system s" (see e.g. W arner 1998;N ogam i1998).R esearch on short-P orb C V s (m ainly SU U M a-type dwarfnovae) is continuously broadening,and isnow becom ing oneof\the m ainstream s" ofC V research. 6.1.2. W Z Sge-Type D warfN ovae W Z Sge-type dwarfnovae are a peculiar subtype ofSU U M a-type dwarfnovae.60 T he propertiesofW Z Sge-type 60

H istorically, the concept of W Z Sge-type dw arf novae referred to large-am plitude, rarely outbursting dw arf novae (cf. B ailey 1979; D ow nes, M argon 1981; Patterson et al. 1981; O ’D onoghue et al. 1991). T his extension of this standpoint led to the concept of Trem endous O utburst A m plitude D w arf N ovae (T O A D s),m ainly proposed by H ow ellet al.(1995). W Z Sge-type dw arf novae w ere som etim es even referred to as extrem e T O A D s (cf. H ow ellet al.2003). T he m odern view point, how ever, is that the outburst am plitude is one of the general properties of W Z Sge-type dw arf novae, rather than the definition. W Z Sge-type dw arf novae are now better recognized as an extrem e population of SU U M a-type dw arf novae (K ato et al.2001l, see also the discussion in relation to the \T O A D "

15

dwarfnovae include: (1)long ( 10 yr or m ore)outburst recurrence tim e,(2) large ( 8 m ag) outburstam plitude, (3) very few , or som etim es no, occurrence of (isolated) norm al outbursts, (4) presence of \early superhum ps", w hich are m odulations having periods very close to the orbital periods, during the earliest stage of superoutbursts,and (5)frequentoccurrence ofpost-superoutburst rebrightening (see K ato et al.2001land K ato 2002b for m odern observationalreview s). T hese properties are di cult to explain,even w ith the recent progress of the disk-instability theory, and the W Z Sge-type dwarf novae have been continuously providing challenging problem sto both theoreticiansand observers. O ne of the m ain di culties reside in their extrem ely long recurrence tim es. If one assum es the standard disk-instability m odel,the recurrence tim e islim ited by the di usion tim e in quiescence (Ichikawa,O saki1994; O saki 1996a). In order to avoid a therm al instability resulting from this di usion, one needs to assum e an extrem ely low viscosity param eter in quiescence ( C < 0:00005,Sm ak 1993; C < 0:003,O saki1995c).A lthough the origin of such a low viscosity is becom ing positively resolved by considering a very cold disk w ith a low electronic conductivity (M eyer-H ofm eister et al.1998),there stillexist a num ber ofargum ents to avoid an extrem ely low quiescentviscosity.Forexam ple,Lasota etal.(1995), W arner et al.(1996) assum ed evaporation/truncation of the inner disk to prevent therm al instability to occur. H am eury etal.(1997)and B uat-M enard,H am eury (2002) presented slight m odi cations of these ideas. T he m odels,however,are expected to show m uch shorteroutburst lengths than in the low - C m odel(O saki1995c). Som e m odelsthereby assum e an enhanced m ass-transferduring a superoutburst(asoriginating from Patterson etal.1981 and extended by Patterson et al. 2002), there is, how ever,no concrete observationalevidence supporting this supposed enhanced m ass-transfer(O saki,M eyer2003).A carefulanalysis ofthe observations ofthe 2001 outburst of W Z Sge also supports this lack of m ass-transfer (R . Ishioka et al. in preparation). Som e authors ascribed the existence of a brow n-dwarf secondary star to the origin ofthe required low C (M eyer,M eyer-H ofm eister 1999). T his possibility,together w ith the expectations from the theoreticalview point(e.g. Paczynski1971),led to a w ide interestto search forbrow n dwarfsin W Z Sge-type dwarf novae (H owell et al. 1997; Politano et al. 1998; C iardi et al. 1998; van Teeseling et al. 1999; Patterson 2001; H owell, C iardi 2001; M ennickent et al. 2001a; K ato etal.2002p;M ennickent,D iaz2002;Littlefairetal.2003). A lthough earlierreportstended to suggestthe presence of a brow n dwarf,the evidence islessclearfrom m ore recent detailed studies (Steeghs et al.2001a;K ato et al.2002p; M ennickent, D iaz 2002; H owell et al. 2002; Littlefair et al.2003).M ost recently,the observationallack ofC V s having brow n dwarfsecondaries is even becom ing a serious problem (B arker,K olb 2003). In allaspects ofdiskconcept: K ato etal.2003f). W e therefore prim arily use the term W Z Sge-type dw arfnovae rather than T O A D s.

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F ig. 8. C C D light curve ofthe 2001 outburst ofW Z Sge by the V SN E T C ollaboration.

instability problem s,origin ofdisk viscosity,and late-stage evolution ofcom pact binaries,W Z Sge-type dwarfnovae continue to be key objects. Since the outbursts of W Z Sge-type dwarf novae are quite rare, these objects have best illustrated the ability and the achievem ent of the V SN ET as the real-tim e network. B efore the V SN ET was established,m ost (presum able) W Z Sge-type outbursts were only poorly studied (e.g. A L C om : B ertola 1964,U Z B oo: B ailey 1979, PQ A nd: M cA dam et al. 1988; H urst et al. 1988a; H urst et al.1988b;H urst,Young 1988,G W Lib: M aza, G onzalez 1983,other system s: R ichter 1992). T he establishm entofthe V SN ET hasbeen one ofthe greateststeps toward understanding the W Z Sge-type dwarfnovae. In particular,w ithoutthecollaboration w ith theV SO LJ and w ithoutthe V SN ET alerts,the early partofthe 2001 outburst ofW Z Sge would have stillrem ained a m ystery. T he earliest work on W Z Sge-type dwarf novae was on H V V ir in 1992. A lthough this object was originally recorded asa classicalnova in 1929 (Schneller1931; D uerbeck 1984), we started m onitoring for a future potentialoutburst as a candidate W Z Sge-type dwarfnova (K ato et al. 2001l). T his outburst was discovered by Patrick Schm eer (Schm eer et al. 1992), and was im m ediately relayed through the alert network. T he V SN ET team was the rst to record periodic m odulations (early

superhum ps) in the lightcurve.61 T he nalresulton this superoutburstwaspublished asK ato etal.(2001l),w hich has been chosen as a best m odern reference on new W Z Sge-type starsin Trim ble,A schwanden (2003).A fter 10 yr,the object again went into superoutburst,w hich was observed in detailby the V SN ET C ollaboration (Ishioka et al.2003). T he next object was U Z B oo in 1994 (Iida,York 1994; Szentasko et al. 1994). T he outburst detection was also im m ediately relayed through the V SN ET alert network. D ue to the short visibility, only a prelim inary superhum p period of 0.0619 d was obtained (K ato et al. 2001l), although the post-superoutburst rebrightenings reported through the V SN ET have raised a possible link between W Z Sge-type dwarf novae and soft X -ray transients (SX T s, or X -ray novae,subsection 6.4) (K uulkers et al. 1996). T his suggestion has been m ore substantiated by U em ura et al.(2000c),K uulkers (2000), K uulkers (2001);this relation is becom ing one ofthe m ajor contem porary topics in SX T outbursts. In 1995 and 1996,outstanding W Z Sge-type outbursts of A L C om and EG C nc occurred. T hese outburst detections were im m ediately relayed through the V SN ET , and produced a wealth ofscienti c results as already in61

T his w as im m ediately reported to the C B A T (see vsnet-history archive), but w as not published for an unknow n reason. See K ato et al.2001lm ore details.

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troduced in subsection 4. A L C om again underwent an superoutburst in 2001. A tim ely outburst announcem ent by Steve K err on V SN ET enabled early-tim e observations w hen the object was stillrising. T he detection of grow ing early superhum ps was already reported (Ishioka et al. 2002b), w hich was actually the rst detection of grow ing early superhum ps before the 2001 spectacular outburst ofW Z Sge itself. In late2000,anotherspectacularoutburstofR Z Leo occurred,w hich had long been suspected asa candidate W Z Sge-type dwarfnova (M cN aught1985;M atteietal.1985; C ristiani et al. 1985; R ichter 1985). T he V SN ET C ollaboration succeeded in detecting both early superhum ps and ordinary superhum ps (Ishioka et al. 2000a; Ishioka et al.2001c),giving credence to the W Z Sge-type nature ofthis dwarfnova. T he unexpected outburst ofthe prototype W Z Sge in 2001 was one ofthe greatest astronom icalphenom ena in recent years. It was detected by a Japanese am ateur observer, Tom ohito O hshim a, was im m ediately relayed to the V SN ET ,enabling early coverage(Ishioka etal.2001e; Ishioka et al.2002c;K uulkers et al.2002),w hich was one of the greatest achievem ents of the V SN ET as an alert network (see gure 8). T his outburst produced a burst of scienti c results from a num ber of researchers, both ground-based and satellite-borne: detection of early superhum ps (K ato et al.2001b),grow th ofordinary superhum ps (K ato et al. 2001j; K ato et al. 2001i), spectroscopic detection ofspiralpatterns (Steeghs et al.2001b; B aba et al. 2001) w hose details have been published in B aba et al. (2002), \real-tim e" m odeling of the outburst (C annizzo 2001), C handra observation (W heatley et al. 2001), H ST observation (K nigge et al. 2002), far ultraviolet spectroscopy (Long et al. 2003), infrared spectroscopy (H owellet al.2003),extensive photom etry (Ishioka et al. 2002b; Patterson et al. 2002; R . Ishioka et al. in preparation), and theoretical m odeling of the superhum p light curve (O saki2003). O therW Z Sge-type dwarfnovae observed and reported by the V SN ET C ollaboration include: U W Tri (K ato et al.2001h),LL A nd (K ato 2003b;data cited in H owell, H urst 1994, H owell, H urst 1996), V 2176 C yg (N ovak etal.2001),C G C M a (K ato etal.1999b),V 592 H er(K ato et al.2002p). A m ong them ,V 2176 C yg showed a \dip" phenom enon,noted for rst tim e since the 1995 outburst of A L C om (N ogam i et al. 1997a), and V 592 H er was con rm ed to be a dwarfnova w ith an exceptionally large outburst am plitude. T he V SN ET C ollaboration has rst system atically dem onstrated that allwell-observed W Z Sge-type dwarf novae show \early superhum ps" during the earliest stage oftheir superoutbursts (w hich m ay be the best de ning characteristic ofW Z Sge-type dwarfnovae: K ato 2002b). T hese early superhum ps are usually double-wave (som etim es m ore com plex) variations, w hich have periods extrem ely close to the orbital periods (e.g. Ishioka et al. 2002b). A lthough there is a historical(Patterson et al.1981) and a m odern version (Patterson et al.2002) interpretation,that the phenom enon results from an en-

17

hanced m ass-transfer,itisnow understood asthe resultof som e sortofresonance on the disk (2:1 resonance:O saki, M eyer 2002 or vertical2:1 resonance:K ato 2002b). T he identi cation ofR Z Leo as a W Z Sge-type dwarf nova (Ishioka et al.2001c),is a surprise from this point ofview ,since the superhum p period (0.078529 d) ofR Z Leo is anom alously long com pared to the canonicalpicture of W Z Sge-type dwarf novae. T his identi cation indicates that neither a brow n-dwarf secondary (M eyer, M eyer-H ofm eister 1999) nor an extrem e m ass-ratio, enabling 2:1 resonance(O saki,M eyer2002),m ay be a necessary condition fortheW Z Sge-typeoutburstphenom enon. T hisim plication ispresently underdiscussion forW Z Sgetype dwarfnovae (cf. K ato 2002b; O saki,M eyer 2002). A s concerns early superhum ps,K ato (1997a) detected a sm ooth transition from the orbitalto superhum p period in a m ore usualSU U M a-type dwarfnova,T Leo. T his phenom enon m ay be som ehow related to the evolution of early superhum ps (K ato et al.1996b). Several large-am plitude SU U M a-type dwarf novae share som e com m on properties w ith W Z Sge-type dwarf novae,particularly in the lengthening of the superhum p period. T he periods of the superhum ps are usually not constant,but show a signi cant period derivative (P dot). T he P dot are usually negative in classicalSU U M a-type dwarfnovae (W arner1985;Patterson etal.1993;fora recent progress,see K ato et al.2003h). T his negative P dot is usually considered to be a result of a decrease in the angularvelocity ofprecession ofa shrinking eccentric disk (O saki1985).T he decreasem ay also be a resultofinward propagation of the eccentricity wave (cf. Lubow 1991a; Lubow 1991b;Lubow 1992).A sm allnum berofSU U M atype dwarfnovae,notably m any W Z Sge-type dwarfnovae,are know n to show positive P dot. T hise ectwas rst clearly detected in V 1028 C yg (B aba etal.2000),although this phenom enon rst appeared in solid publications on SW U M a (Sem eniuk et al. 1997; N ogam i et al. 1998a), V 485 C en (O lech 1997b),and on the W Z Sge-type star A L C om (Pych,O lech 1995b;H owellet al.1996;N ogam i etal.1997a).T he SU U M a-type dwarfnovae new ly identi ed by theV SN ET C ollaboration ashaving positiveP dot include: H V V ir (W Z Sge-type star, K ato et al.2001l), W X C et (K ato et al.2001c),EG C nc (W Z Sge-type star, K ato etal.1997),and X Z Eri(U em ura etal.2003c).T he true origin ofthisphenom enon is notyetwellunderstood (B aba et al.2000;K ato et al.2001l;Ishioka et al.2003; K ato et al.2003h;K ato et al.2003b). Post-superoutburst rebrightenings are also a renow ned feature ofthe W Z Sge-type dwarfnovae (K ato etal.1997; Patterson etal.1998;Ishioka etal.2003),forw hich O saki et al.(1997),and O sakiet al.(2001) presented an interpretation based on the slow viscosity decay in the early post-superoutburst state. T his m echanism would require a m ass reservoir in the outer disk (O saki, M eyer 2003), w hose originalobservationalim plication wasproposed by K ato et al.(1998c). T he existence, or non-existence, of post-superoutburst rebrightenings have been system atically studied by the V SN ET C ollaboration in alm ost all SU U M a-type dwarfnova. R ecent exam ples include G O

18

T .K ato et al.

C om (K ato et al. 1995c), W X C et (K ato 1995f; K ato et al. 2001c), V 1028 C yg (B aba et al. 2000), V 725 A ql (U em ura etal.2001c),and in theunusualsystem (seesubsection 6.1.3)EIPsc (U em ura etal.2002e).T he statistics is presented in K ato et al.(1998c). A m issing link between W Z Sge-type dwarfnovae and ordinary SU U M a-type dwarfnovae hasbeen sought. C T H ya (N ogam ietal.1996;K ato etal.1999a)wassuggested to be one such system , though a m ore recent statistical analysis suggests a m ore rigid segregation between W Z Sge-type dwarf novae and ordinary SU U M a-type dwarf novae(K ato etal.2003f).Severalsystem spossibly related to W Z Sge-type dwarf novae have been also studied by the V SN ET C ollaboration: C C Scl= R X J2315.5 3049 (Ishioka et al.2001a). Long P orb SU U M a-type dwarf novae w ith rare outbursts have also been system atically studied by the V SN ET C ollaboration. T he objects include: EF Peg (K ato,Takata 1991;K ato 2002c) and V 725 A ql(N ogam i et al.1995d;U em ura etal.2001c).T he origin ofthe necessary low m ass-transferrate in such long P orb system s is stilla problem .

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descendants ofa certain class ofC V s w ith hydrogen-rich appearance (cf. W ebbink 1984;Tutukov,Yungelson 1996; N elem ans et al. 2001; Yungelson et al. 2002). T his object, given its proxim ity and relatively heavy com ponent m asses, is also considered to be an excellent candidate for next generation experim ents of directly detecting gravitationalwave radiation (H ils, B ender 2000; Strohm ayer 2002). In clarifying thenatureofEIPsc,properm otion studies played an independent im portant role in identifying the objectasa nearby object.T his nding wassoon con rm ed by later researchers (B iggs, W alsh 2001), and the sam e technique has been applied to di erent sorts of objects by the V SN ET C ollaboration (R X J2309.8+ 2135: K ato, Yam aoka 2002,V 379 Peg: K ato et al.2002u,C W M on: K ato et al.2003j). T his application of astrom etry soon becam e the globalstandard in studying C V s and related system s (K ato et al. 2001t, see also recent entries of a survey of proper m otions in D ow nes et al. online C V catalog62 ). H elium C V shave been one ofthe bestobserved targets by the V SN ET C ollaboration. A m ong them , C R B oo has been identi ed as the rst \helium ER U M a star" w ith a supercycle of46.3 d (cf. subsection 6.1.1)by K ato et al.(2000c). T he V SN ET team also joined a cam paign to study superhum ps in C R B oo (Patterson et al.1997). K ato et al.(2000d) identi ed a sim ilar supercycle in the helium C V ,V 803 C en.K ato etal.(2001m )furtheridentied standstillsin V 803 C en,w hich wereinitially suggested for C R B oo in K ato et al.(2000c). K ato et al.(2001k) laterdetected a transition ofC R B oo to a state ofa short supercycle (14.7 d),w hich they called \the second supercycle".T hisphenom enon isstilldi cultto explain.K ato et al.(2003i) studied V 803 C en for its long-term behavior and its 2003 June superoutburst, and revealed that the object (and probably also C R B oo) show s outburst behavior sim ilar to W Z Sge. From these studies, both C R B oo and V 803 C en have been well-established \helium counterparts" to hydrogen-rich SU U M a-type dwarf novae, in contrast to the traditional V Y Scl-type (variable m ass-transferrate from the secondary,see subsection 6.3.3)explanation ofhigh and low statesin these system s (W arner 1995a;W oudt,W arner 2003b). T his interpretation is perfectly in line w ith the dwarf nova-type interpretation (T sugawa,O saki1997),although this interpretation was not originally correctly applied to observation (Patterson et al.1997;Patterson et al.2000b). O utburst detections ofother helium dwarfnovae (e.g. K L D ra = SN 1998di)have been also announced through the V SN ET ,and provided necessary fundam entals63 for detailed research (e.g. Jha et al. 1998b; Sam us 2000b; W ood et al.2002).

6.1.3. U ltra-Short Period System s and H elium C ataclysm ic Variables From the standard evolutionary scenario of com pact binaries, there should be a \period m inim um " (e.g. Paczynski1971) at w hich the m ass-losing secondary star becom es degenerate and the binary period starts to lengthen. T his period is observationally determ ined to be 1.3 hr,w hich is about 10% longer than the theoreticalpredictions(Paczynski1971;K olb,B ara e 1999;K ing et al.2001;K ing et al.2002). T his discrepancy has not been yet resolved, although several attem pts have been m ade (e.g. R envoize et al.2002; B arker,K olb 2003) to reconcile theory w ith observation. T here exist, however, hydrogen-rich system s w ith periods well below this theoretical m inim um period. T he \classical" object is V 485 C en (A ugusteijn et al. 1993; A ugusteijn et al. 1996; O lech 1997b); the faintness of this object, however, prevented a detailed observational study. In the past few years, the V SN ET team found a hydrogen-rich,nearby bright system (EI Psc = 1R X S J232953.9+ 062814)having a short period com parable to V 485 C en (U em ura et al. 2001b; U em ura et al. 2002f; U em ura et al. 2002e). B oth the radial-velocity study (T horstensen et al. 2002b) and the superhum p period analysis(U em ura et al.2002e;Skillm an et al.2002)independently con rm ed that the secondary star ofthis system ism ore m assive than w hatisexpected forthisorbital period,suggesting that the m ass donoris an evolved core w ith a thin hydrogen envelope.From this nding,U em ura et al.(2002f)suggested,follow ing the evolutionary calculations by Podsiadlow skiet al.(2003),that both EI Psc 6.1.4. Eclipsing D warfN ovae Since C V s are close binary system s, high-inclination and V 485 C en can be ancestors of helium C V s (or A M C V n stars,W arner 1995a;Solheim 1995) consisting ofa system s show eclipses. T he presence of eclipses in C V s w hite dwarfand a m ass-losing helium w hite dwarf.Ifthis 62 hhttp://icarus.stsci.edu/ dow nes/cvcat/i. interpretation is con rm ed,this objectwould becom e the 63 hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/D N e/kldra.htm li. rst direct observational evidence that helium C V s are

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historically provided m ost crucialinform ation about the geom etry and fundam entalphysics of the accretion disk or the accretion stream (W alker 1954; W alker 1955; K raft 1958;G reenstein,K raft 1959;K raft 1962;W arner, N ather 1971) and the clari cation of the cause of outbursts (O saki1974;Sm ak 1976;Sm ak 1984;K rzem inski, Vogt 1985). In recent years, the eclipse m apping technique (H orne 1985) has been used to geom etrically resolve the accretion disk by num erically m odeling the eclipse light curve (and som etim es line variations) of C V s (H orne, Stiening 1985; M arsh, H orne 1987; W ood et al. 1989a; B aptista,Steiner 1991;B aptista,Steiner 1993).T his and analogousm ethodshavealso been used to study the tim eevolution of the accretion disk during dwarf nova outbursts (H orne, C ook 1985; W ood et al. 1989b; R utten et al.1992;W olf et al.1993;B obinger et al.1997),discuss the presence ofa spiralpattern (w hich m ay be theoretically predicted spiral shocks: Sawada et al. 1986; Spruit et al. 1987; M atsuda et al. 1990; M atsuda et al. 2000) in dwarf novae (B aptista, C atalan 2001; B aptista, C atalan 2000; B aptista et al. 2000), for m apping ofthe superoutbursting disks,(B ruch etal.1996),to spectrally resolve the accretion disk (R utten et al.1993; R utten et al. 1994), and to directly obtain physicalparam eters of the accretion disk (Vrielm ann et al. 1999; Vrielm ann et al.2002). T he V SN ET C ollaboration played an im portantrole in studying eclipsing C V s,especially eclipsing dwarfnovae. T he initiale orts were m ade to follow the eclipses ofthe rising phase ofan IP Peg outburst (N ogam i1996). T he V SN ET alert lists provided an initiative role of system atic studies w hen the northern new eclipsing dwarfnova EX D ra (= H S 1804+ 6753)wasdiscovered (N ogam i1996). T hisaction wassoon extended to observerareoutburstsof an eclipsing SU U M a-type dwarfnova,D V U M a (N ogam i et al. 2001b). T he 1995 outburst of H T C as was also spectacular. T his is a well-know n eclipsing dwarf nova (cf. Patterson 1981;Zhang et al.1986;W ood et al.1995; M ukaiet al.1997). In 1995,the V SN ET team received a requestforan opticalground-based cam paign coordinated w ith the H ubble Space Telescope (H ST ).T he observation by the V SN ET team succeeded in correcting the eclipse ephem eris,w hich is readily re ected on the H ST observing schedule, w hen the object suddenly jum ped into an outburst! T hanks to this coincidence, we were able to obtain eclipse inform ation only two dayspriorto the outburstm axim um ,w hich precluded the enhancem entofthe hot spot as expected from the m ass-transfer burst (B aba et al.1999). T he eclipses during this outburst was also followed by another group (Ioannou et al. 1999), w ho observed this object in response to this outburst detection. T he results ofeclipse m apping,together w ith later outburstobservations,have been recently reported (B aba et al.2003b). IR C om (= S 10932),a system very sim ilarto H T C as, has also been extensively studied by the V SN ET team . In particular,we detected the 1996 January outburst,and succeeded in taking the earliesteclipse observations(K ato

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etal.2002a),T he true nature ofthisobjecthad rem ained unclearbefore(R ichter,G reiner1995;R ichteretal.1997). T he real-tim e circulation of this outburst detection and eclipse inform ation enabled a third-party follow -up observations (R ichter et al.1996). In m ost recent years, the V SN ET C ollaboration discovered a deeply eclipsing bright SU U M a-type dwarf nova (IY U M a = T m z V 85) in the northern hem isphere (U em ura etal.2000d;U em ura etal.2000b;Sam us2000a). For the rst tim e in history,this observation yielded the sim ultaneous discovery ofsuperhum ps and eclipses. T his system ,the only brightnorm alSU U M a-type dwarfnovae suitably situated for northern telescopes, has been proposed asthe bestcandidate objectfornextgeneration detectors on huge telescopes (cf. M oon et al.2001;Steeghs etal.2003;R eynoldsetal.2003).T hisand thesubsequent outbursts were followed by a num ber of team s, resulting in rich physicalinsights (Patterson et al.2000a;W u et al.2001;Stanishev et al.2001;R olfe et al.2001;R olfe etal.2002;Sm ak 2003).W ith strong em ission linesofH eii and C iii/N iii in outburst (W u et al.2001; such objects are know n to be quite rare:M orales-R ueda,M arsh 2002), this object is a good candidate for spatially resolving a superoutbursting disk by the em ission-line eclipse m apping m ethod (M akita, M ineshige 2002), as well as w ith classicalD opplertom ography ofthe velocity eld (M arsh, H orne 1988). W e also succeeded in identifying the supercycle (K ato et al.2001n). T he other outstanding object is D V U M a, w hich was observed during the entire stage of the 1999 D ecem ber superoutburst follow ing the outburst report by T im o K innunen.64 T hisobservation rstfully covered the early evolution ofeclipses in this rarely outbursting system . In 2002 February,a collaborative e ort on G Y C nc = R X J0909.8+ 1849 led to the discovery of the eclipsing nature of this dwarf nova (G ansicke et al. 2000; K ato et al. 2000f; Shafter et al. 2000; T horstensen 2000). Eclipse observations during the 2001 N ovem ber outburst revealed the noticeable absence ofthe hotspotduring the late stage ofan outburst (K ato et al.2002f). T his observation suggested that G Y C nc m ay be the rst long-P orb object sharing com m on properties w ith H T C as and IR C om . R ecent detailed outburst (or superoutburst) observations of eclipsing dwarf novae include: X Z Eri(U em ura et al. 2003c) and O U V ir (R . Ishioka et al. in preparation). B oth stars show prom inent superhum ps as well as eclipses. X Z Eri is the rst eclipsing SU U M a-type dwarf nova w ith a positive period derivative (U em ura et al.2003c). O U V ir is another object continuously receiving world-w ide attention (Vanm unster et al. 2000b; M ason et al. 2002), for w hich we succeeded in determ ining the rst reliable orbitaland superhum p periods. V 2051 O ph is another eclipsing C V , w hich had been thought to be a low - eld polar (W arner, C ropper 1983; W enzel 1984; W arner, O ’D onoghue 1987) for w hich the V SN ET C ollaboration rst provided unam biguous clari64

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/D N e/dvum a9912.htm li.

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cation ofits SU U M a-type nature by securely detecting superhum ps and supercycles (K iyota, K ato 1998; K ato et al. 2001n). W ith the help by this clear identi cation,this object has also been receiving specialattention both w ith ground-based and satellite-borne observations (B aptista et al.1998; B ruch 2000; Steeghs et al. 2001c; Vrielm ann et al.2002) T herecovery and clari cation ofthenatureofthe\lost" dwarfnova V 893 Sco is another noteworthy achievem ent by the V SN ET C ollaboration.T his object had long been lost, w hen K atsum i H aseda (V SO LJ) reported an outbursting object (at a nom inally di erent position from that ofthe originally reported V 893 Sco) to the V SN ET . A fter careful research of the discovery m aterial, as a part ofcon rm atory process ofa new variable star (subsection 5.2), this new ly reported object was eventually identi ed w ith the lost V 893 Sco (K ato et al. 1998a). T his was only the beginning of the story; the object soon turned out to be the brightest,and presum ably one of the nearest, eclipsing dwarf novae below the period gap (T horstensen 1999; M atsum oto et al. 2000; B ruch et al. 2000). T his object has been extensively studied since its recovery (M ason et al.2001;K ato et al.2002h). C W M on (K ato etal.2003j)show sgrazing eclipsesduring certain stages ofoutbursts. Together w ith the transient appearance ofpulsed signals,the presence ofa prem axim um halt in the outburst light curve and relatively strong X -ray radiation,this object has been suspected to be an interm ediate polar (see also subsection 6.3.1). 6.1.5. Super-Q uasi-Periodic O scillations Q uasi-periodic oscillations (Q PO s) are short-period, quasi-periodicoscillationsw idely observed in accreting binary system s including C V s (cf. W arner 1995b). Q PO s in C V s are usually subdivided into two classes. O ne is dwarfnova oscillations(D N O s)observed during outbursts ofdwarfnovae.D N O shaveshortperiods(usually 19{29s) and long coherence tim es (R obinson 1973;Szkody 1976; Patterson 1981; H ildebrand et al. 1980). T he other is Q PO s, w hich have longer (40 to several hundred seconds) and shorter coherence tim es (usually less than 10 wave num bers). W e discovered a potentially new class ofQ PO s (super-Q PO s)during the 1992 superoutburst of SW U M a (K ato et al. 1992a). T hese super-Q PO s have long (several hundred seconds) periods and long coherent tim es (m ore than severaltens ofwave num bers). In som ecases(K ato etal.1992a),theam plitude can bequite large (up to 0.2 m ag). T he m ost outstanding feature of super-Q PO s is that they are observed only during certain stagesofSU U M a-type superoutbursts. In SW U M a (1992) and EF Peg (K ato 2002c),the super-Q PO s were observed during thegrow ing stageofsuperhum ps.A sim ilar,butlessstriking,probable appearance ofsuper-Q PO s was also recorded by the V SN ET C ollaboration during the early stage ofan superoutburst ofN SV 10934 (K ato et al.2003d). D uring the 2000 superoutburst of SW U M a, sim ilar super-Q PO stem porarily appeared during thedecay phase

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of a superoutburst (vsnet-alert 4331).65 T hese observationssuggestthattheappearanceofsuper-Q PO sisclosely related to the grow th and decay of superhum ps, or related to the existence ofheating/cooling waves(Yam asaki et al.(1995) proposed that som e sort ofQ PO s can be an excitation oftrapped oscillationsaround the discontinuity ofphysicalparam eters). D i erent interpretations have also been suggested. For exam ple,W arner,W oudt(2002)suggested thatthesuperQ PO s m ay be a result of interaction between the weak m agnetism ofthe w hite dwarfand som e kind ofwave in the inneraccretion disk.A lthough thisexplanation would be com patible w ith the suggested presenceofa weak m agnetic eld in SW U M a (Shafter et al. 1986; R obinson et al.1987;Szkody et al.1988;R osen et al.1994),there would be a need for a di erent m echanism to explain w hy these super-Q PO s only appear only during tem porary stages ofsuperoutbursts. In EF Peg (K ato 2002c), a rapid decrease in the periods of super-Q PO s was recorded. From this nding, K ato (2002c) suggested a rapid rem ovalof angular m om entum from an orbiting blob in the accretion disk,via a reasonable viscosity in a turbulent disk. T he origin of super-Q PO sisstillan open question,buttheirprom inent pro le is expected to provide crucial inform ation about the origin ofQ PO s in C V s (W arner,W oudt 2002). 6.1.6. Low States in D warfN ovae A lthough som e nova-like C V s (V Y Scl-type stars,subsection 6.3.3) are best know n to show \low states",during w hich m ass-transfer from the secondary is reduced (W arner 1995b;R obinson et al.1981),this phenom enon has not been clearly con rm ed to occur in dwarfnovae. A lthough there have been claim s for \low states" (H T C as: Zhang et al. 1986; W ood et al. 1995; R obertson, H oneycutt 1996, IR C om : R ichter, G reiner 1995; K ato et al.2002a,W W C et: R ingwald et al.1996; B Z U M a: K aluzny 1986), it is not evident w hether or not these phenom ena directly re ect a reduced m ass-transfer from the secondary, since the state change in the disk (especially the viscosity param eter) would reproduce sim ilar phenom ena. Extensive studies on selected well-observed dwarf novae (e.g. H oneycutt et al. 1998; O ppenheim er etal.1998)havefound no evidence forthe long-term variation ofm ass-transfer. D uring the extensive work by the V SN ET C ollaboration, we discovered that the Z C am star R X A nd underwent a deep fading in 1996 Septem ber (vsnet-obs 3750).66 T his fading (and the lack of outbursts) lasted until 1997 January, w hich yielded the rst unam biguous detection of a tem porarily reduced m ass-transfer in dwarf novae. T his phenom enon was thoroughly studied by K ato et al. (2002i). C areful research on the historical light curve indicated that sim ilar phenom ena were sporadically observed in R X A nd (K ato et al. 2002i; Schreiber et al. 2002), but had 65 66

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/D N e/sw um a00.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/obs3000/ m sg00750.htm li.

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(K ato et al.2002m ),IW A nd (unusualZ C am star: been overlooked m ainly because of the confusion of the K ato et al.2003c), true quiescent identi cation, and the lack of real-tim e (e) Q uiescent dwarfnovae: U V Per (K ato 1990b),G O circulation of inform ation. T he V SN ET C ollaboration C om (K ato,H irata 1990a) succeeded in detecting such a phenom enon through real(f) C lassi cation: B F Eri(K ato 1999a;K ato,U em ura tim e, regular m onitoring of light curves of dwarf novae, 2000a),LX A nd (U em ura etal.2000e;K ato 2002f), and through a prom pt reaction w hen an anom alous H P A nd (w ith Subaru,N ogam iet al.2003b) change was observed (the deep quiescence of R X A nd (g) Statistics and com pilation: N ogam iet al.(1997b); was originally con rm ed by our ow n C C D observation). K ato et al.(2003f) T his is another aspect how e ectively the V SN ET alert network worked, besides other outburst-type transient M ost ofthe work was done w ith the help ofthe alert events. T his detection, announced world-w ide, thereby led to a prom ptH ST observation (Sion etal.2001),w hich network and thecollaboration described in subsections2.3 revealed the presence ofa hot w hite dwarf. K ato (2003c) and 4.1. further reported the detection of short fading episodes in R X A nd and SU U M a, w hich m ay be a result of 6.1.8. O ther G lobalC ontributions A s the V SN ET has been m ediating an enorm ous num tem porary reduction ofm ass-transfer rate. ber ofoutburst alerts ofdwarfnovae since its very early history, these alerts, as well as long-term observations, 6.1.7. O ther D warfN ova W orks O ther dwarf nova-related works, not covered by the contributed to world-w ide dwarfnova studies by di erent above subsections,by the V SN ET C ollaboration include: team s. Since they are so num erous,we only listrepresentative ones: (a) D warfnovae in the period gap: G X C as,V 419 Lyr V 485 C en: O lech (1997a);O lech (1997b) (N ogam iet al.1998c) (see subsection 6.1.1 for N Y PV Per: Vanm unster (1997) Ser and M N D ra) T U C rt: M ennickent et al.(1998) (b) T im e-variation in m ore usualSU U M a-type dwarf K S U M a: W atanabe (1998a);O lech et al.(2003b) novae and candidates: AW G en (K ato 1996b),R Z K V D ra: Vanm unster et al.(2000a) Sge (K ato 1996a), V 1113 C yg (K ato et al. 1996e; W Y Tri: Vanm unster (2001) K ato 2001h),C C C nc (K ato,N ogam i1997a;K ato K X A ql: Tappert,M ennickent (2001) et al. 2002o), V Z Pyx (K ato, N ogam i 1997b), X Y Psc: H enden et al.(2001) C Y U M a (K ato 1997b; K ato, M atsum oto 1999a), A H H er: Spogliet al.(2001);Spogliet al.(2002) PU Per (K ato,M atsum oto 1999b),A Q Eri(K ato, C V s in the 2M A SS survey: H oard et al.(2002b) M atsum oto 1999c; K ato 2001g), C T H ya (K ato V 844 H er: T horstensen et al.(2002c) et al.1999a),V 364 Peg (K ato,M atsum oto 1999d), V 2051 O ph: Vrielm ann et al. (2002); Vrielm ann, Q W Ser (K ato, U em ura 1999b; N ogam i et al. O utt (2003) 2003c), B Z U M a (K ato 1999e), C I G em (K ato, Q Z Ser: T horstensen et al. (2002a), another peSchm eer 1999), T Y Vul (K ato, U em ura 1999d), culiar dwarf nova discovered by K atsum i H aseda K V D ra (N ogam i et al. 2000), V 844 H er (K ato, (H ad V 04),and announced in collaboration w ith the U em ura 2000b), Q Y Per (K ato et al. 2000e), T Y V SN ET (subsection 5.2) Psc (K unjaya et al. 2001; K unjaya et al. 2003), IP Peg:B aptista et al.(2002) V 630 C yg (N ogam iet al.2001a),V 369 Peg (K ato, R X J0944.5+ 0357:M ennickent et al.(2002) U em ura 2001c),U V G em ,FS A nd,A S Psc (K ato, V 1504 C yg: Pavlenko,D udka (2002) U em ura 2001f), R X C ha (K ato et al. 2001a), Y Z G Z C nc: Tappert,B ianchini(2003) C nc (K ato 2001f),IR G em (K ato 2001i),FT C am V 1141 A ql: O lech (2003) (K ato et al. 2001t; K ato 2002d), G Z C nc, N SV Q W Ser: O lech et al.(2003a) 10934 (K ato et al.2001r; K ato et al.2002b), D M FS A ur: Tovm assian et al.(2003) D ra (K ato et al. 2002n), SU U M a (K ato 2002a), EM C yg: Spogliet al.(2003) D M Lyr (N ogam iet al.2003a) short-period dwarf novae: T horstensen, (c) T im e-variation in SS C yg-type dwarfnovae: V 1008 Fenton (2003) H er (K ato, U em ura 1999c), V 1101 A ql (K ato faint C V s survey: M ason,H owell(2003) et al.1999c),D K C as (K ato, U em ura 2001a),H H SU U M a stars: Patterson et al.(2003) C nc = T m z V 36 (K ato, U em ura 2001e), IS D el (K ato 2001c),IZ A nd (K ato 2001e),D X A nd (K ato, N ogam i2001a),A H Eri(K ato,N ogam i2001b),C G 6.2. N ovae and RecurrentN ovae D ra (K ato,N ogam i2001c), 6.2.1. C lassicalN ovae and Related O bjects (d) Standstills of Z C am -type dwarf novae: V W From the beginning of the V SN ET , novae and reVul (K ato 1999f), AT C nc (N ogam i et al. 1999, cur rent novae have been w idely studied as one of the D oppler tom ography; K ato et al. 2001q), Z C am cl as sical representatives of transient objects. T he ear(K ato 2001d),H L C M a (K ato 2002e),FX C ep (K ato l i es t observations include the recurrent nova V 3890 Sgr etal.2001f),V 363 Lyr(K ato etal.2001g),EY C yg (1990), w hose exact identi cation was clari ed by us

22

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(K ato et al. 1990). T he next advancem ent was w ith V 838 H er(N ova H er1991),w hoseeclipsing natureand exact orbitalperiod was clari ed by our observation (K ato, H irata 1991). T his is the rst classicalnova w hose evolution ofeclipses was caught from the early decline stage of the outburst (Leibow itz 1993; Szkody, Ingram 1994; Ingram etal.1992).T he\nova ofthecentury" (Starr eld, Shore 1994) V 1974 C yg (N ova C yg 1992) was followed w ith the advent ofthe e-m ailalert list (see vsnet-history m essages).T his nova later turned out to be a perm anent superhum per system (Sem eniuk et al. 1994; Sem eniuk et al.1995;R etter et al.1997;Skillm an et al.1997). T he V SN ET C ollaboration later contributed to the internationalobserving cam paignsofthe superhum ps(A .R etter et al.,in preparation). T he next m ajor step was w ith V 705 C as (N ova C as 1993),as introduced in subsection 1.4. A fter this nova, the V SN ET has continuously provided public pages on individualnovae,67 w hich are referenced as a prim ary resource on recent novae. V 723 C as (N ova C as 1995) has been one of the best studied novae in the V SN ET history. T he object was discovered by M inoru Yam am oto, w hose reportim m ediately triggered early follow -up observations (H irosawa et al.1995). Severalearly reports discussed against the classicalnova-type classi cation (e.g. M unarietal.1995a).W ewerethe rst,w ith theenorm ous am ountofinform ation collected by theV SN ET ,to predict that the object is a prem axim um phase slow nova resem bling H R D el(vsnet223).68 T hisprediction waslaterconrm ed by a num berofworks(O hsim a etal.1996;M unari et al. 1996; Iijim a, R osino 1996; Iijim a, R osino 1997; Iijim a et al.1998). A lthough it was not a classical nova, V 4334 Sgr (Sakurai’s object) in 1996 brought a m ajor breakthrough in \stellar evolution in realtim e" (D uerbeck et al.1996; D uerbeck, B enetti 1996). T his star is one of the best studied and discussed variable stars since the late 1990’s (D uerbeck etal.1997;A rkhipova,N oskova 1997;A splund et al. 1997; A rkhipova et al. 1998a; Evans et al. 1998; A rkhipova et al. 1999b; K ipper, K lochkova 1999a; K erber 1999; K erber 2001; A splund et al. 1999; Pavlenko et al. 2000; D uerbeck et al. 2000; Pavlenko, D uerbeck 2001; Shenavrin, Yudin 2001; H erw ig 2001; Tatarnikov et al. 2001; D uerbeck 2002; C layton 2002; Je ery, Pollacco 2002; K am ath, A shok 2002; Law lor, M acD onald 2002; Lynch et al.2002; K au et al.2003). T he V SN ET not only relayed this breathtaking discovery ofa nalhelium ash object,but also prom ptly provided prediscovery observations by K esao Takam izawa (vsnetalert 341)69 ( nally published by Takam izawa 1997), w hich has been frequently referenced and em ployed for theoreticalm odeling. See subsection 6.7 for its relation w ith R C rB -like stars (cf. Law lor,M acD onald 2003). In recent years,the V SN ET C ollaboration has been is67 68

69

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/N ovae/novae.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet/m sg00223.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/vsnet-alert/ m sg00341.htm li.

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suing scienti cresults,aswellasearly announcem entsand identi cations, on individual novae: V 2487 O ph (N ova O ph 1998,recurrent nova candidate: N akano et al.1998; H achisu et al.2002),V 4444 Sgr (N ova Sgr 1999,the possibility ofthis being a recurrentnova has been discussed: K ato et al. 2004), V 463 Sct (N ova Sct 2000, fast nova w ith an unusually prom inent prem axim um halt: U em ura et al. 2000g; K ato et al. 2002l), V 445 Pup (N ova Pup 2000, unusual nova w ith no indication of hydrogen features: K ato et al. 2000b; K ato, H aseda 2000; K ato, N akam ura 2001; N akano et al. 2001; M . U em ura et al. in preparation), V 1548 A ql (N ova A ql 2001, slow nova initially reported as a m ore usualvariable star: U em ura et al.2001e;K ato,Takam izawa 2001),V 1178 Sco (N ova Sco 2001, object originally confusedly reported to be a novalike object, later turned out to be a genuine nova w ith early stage oscillations:H aseda etal.2001;K anatsu etal.2001;K ato,Fujii2001),V 2540 O ph (N ova O ph 2002, large-am plitudeslow nova w ith strong post-outburstoscillations: Sekiet al.2002;K ato etal.2002q).T he V SN ET C ollaboration also joined m ultiwavelength cam paigns on novaew ith satellites(e.g.V 4743 Sgr:W agneretal.2003). T he V SN ET has recently been relaying discovery, independent and prediscovery detections ofnovae,as wellas spectroscopic con rm ation and early photom etric observations: V 2274 C yg (N ova C yg 2001: Sato et al.2001), V 4643 Sgr (N ova Sgr 2001: K ato et al. 2001d), V 4740 Sgr (N ova Sgr 2001 N o. 3: W est et al.2001);V 4741 Sgr (N ova Sgr 2002: Liller et al.2002a;Liller et al.2002b), V 4742 Sgr(N ova Sgr2002 N o. 2:Yam aoka etal.2002d), V 4743 Sgr (N ova Sgr 2002 N o. 3: H aseda et al. 2002; W est et al. 2002), V 4744 Sgr (N ova Sgr 2002 N o. 4: Yam aoka et al.2002b),V 4745 Sgr (N ova Sgr 2003: K ato et al.2003g; K ato, Fujii 2003), Possible N ova (2002) in N G C 205 (Yam aoka etal.2002a),PossibleN ova (2003)in Scutum : (N akano et al.2003b). T he discovery ofa very unusualeruptive object (V 838 M on,B row n et al.2002;W agner et al.2002;D ella Valle, Iijim a 2002) was relayed through the V SN ET alert system during itsearly stageoferuption,enabling early-stage observations (B edient 2002a;B edient 2002b). T he identi cation ofthe object w ith G SC ,IR A S and 2M A SS objects was reported (K ato et al.2002s).T he early stage of this object was m ost unusual, show ing an M -type spectrum at outburst m axim um . O n 2002 February 2, the object underwent a second m ajor brightening,w hich was quickly relayed via the V SN ET alert system worldw ide, and the starbecam e world-popularw ithin a day. T he object subsequently showed a prom inent light echo w hen it faded (by the obscuration by the form ing dust). T here have been a num ber ofworksbased on these observations (K im eswenger et al.2002;M unariet al.2002;G oranskii et al.2002;Sobotka et al.2002;B ond et al.2003;C rause etal.2003;W isniew skietal.2003),w hich m oreorlessem ployed V SN ET observationsand ndingsw hen discussing the peculiarity ofthis object. T he origin ofthis eruption is stilla m ystery. B ased on an idea proposed by Soker, Tylenda (2003),K ato (2003a)tried to explain the historicalm ysterious eruption ofC K Vul.

N o.]

Variable Star N etwork

6.2.2. RecurrentN ovae and SupersoftX -Ray Sources T he last two decades have dram atically changed our view of recurrent novae. T he discovery of recurrent outbursts of V 394 C rA in 1987 (Liller et al. 1987; D uerbeck 1988;Sekiguchiet al.1989),V 745 Sco in 1989 (Liller 1989; D uerbeck 1989; Sekiguchi et al. 1990b), V 3890 Sgr in 1990 (Jones, Pearce 1990; G onzalezR iestra 1992;H arrison et al.1993) and N ova LM C 1990 N o. 2 (Sekiguchiet al.1990a;Shore et al.1991) resulted in a dram aticincreaseofourknow ledgein recurrentnovae (cf. Shara 1989;A nupam a 1992;Sekiguchi1995). A notherepoch ofrecurrentnova discoveriesarrived like a urry in the late 1990’s and early 2000’s. A llofthese recurrent nova outbursts were m ediated via V SN ET and followed in detail. T he initialobject in this series ofrecurrent nova outbursts was U Sco in 1999, w hose early history was described in detail in subsection 4.1. T his outburst of U Sco rst enabled eclipse observations in realtim e during outburst [the eclipsing nature ofU Sco was revealed only in 1990 (Schaefer 1990);the 1999 outburst was the rst outburst since this discovery;see also K ato (1999l) for the retrospective detection ofan eclipse during the1987 outburst].T hisobservation led to the rst detection ofthe period change in thissystem (M atsum oto etal.2003b).T his nding severely constrained the m asstransfer rate in quiescence (H achisu et al.2000a;H achisu etal.2000b),w hich m akesU Sco the m ostprom ising candidate for an im m ediate precursorofa type-Ia supernova (H achisu et al.2000a). T he next object in this series was C I A ql. T his object had long been suspected to be a dwarfnova based on the (apparently) sm all outburst am plitude of the 1917 outburst(D uerbeck 1987).B ased on thispotentialidenti cation,the object had been m onitored by am ateur variable starobservers,notably by V SO LJ m em bersand by m em bers ofthe R ecurrent O bject Program m e (see subsection 6.1). T he proposed quiescent counterpart,however,was found to be an eclipsing binary w hich did not show C V characteristics (M ennickent,H oneycutt 1995). T he sam e conclusion had been reached w ith snapshot spectroscopy (Szkody,H owell1992),show ing no indication ofhydrogen em ission lines.W ith thisinform ation,alm ostallobservers stopped m onitoring for an outburst, although there was the unexplained presence ofa H eiiem ission line (G reiner et al.1996). T he new s of a possible nova detection by K esao Takam izawa on lm s taken on 2000 A pril 28 arrived at the V SN ET on A pril29. T he reported position was extrem ely close to that of C I A ql. M inoru Yam am oto independently detected this phenom enon, and reported it to be a brightening ofC I A ql. A fter carefulexam ination of the identi cation,this possible nova is identi ed as a recurrentoutburst ofC IA ql,83 years after the 1917 discovery (Takam izawa et al.2000;Yam aoka et al.2000).70 T he nova-type nature of the outburst was soon claried w ith spectroscopy (U em ura, K ato 2000), con rm 70

T he object w as later found to be positively recorded one day earlier (Liller 2000). A n outburst in 1941{1942 w as also later found in the plate archive (Schaefer 2001).

23

ing that C I A qlis a new recurrent nova. B eing already know n as an eclipsing binary, the evolution of the outburstlightcurve and the eclipse pro le were precisely followed (M atsum oto et al.2001;M atsum oto et al.2003a). In particular,a dip-like sudden fading in 2000 N ovem ber was noted (M atsum oto, K ato 2000). W ith these observational constraints, H achisu, K ato (2001) succeeded in m odeling the light curve, w hich was further re ned and extended (H achisu,K ato 2003b;H achisu,K ato 2003c)to explain the unique high/low transitions in the supersoft X -ray source R X J0513.9 6951 in the LM C . Its galactic counterpart,V Sge,has been very recently identi ed (H achisu,K ato 2003a).T hese objectsare now considered to beprom ising candidatesforprecursorsoftype-Ia supernovae (e.g.H achisu etal.1999b;H achisu,K ato 2003c;for earlierand othersuggestions,see e.g.H achisu etal.1989; H achisu et al. 1996; della Valle, Livio 1996; H achisu etal.1999a).T he discoveriesand m odern detailed observationsofU Sco and C IA qloutburststhus provided rm observationalevidence for recurrent novae and supersoft X -ray sources as im m ediate precursors of type-Ia supernovae. O ther representative works (outside the V SN ET ) on C IA qlincludephotom etry (Schm eja etal.2000),spectroscopy (K issetal.2001;B urlak,Esipov 2001),C handra X -ray observation (G reiner, D i Stefano 2002), m odeling (Lederle,K im eswenger 2003),re-exam ination ofthe 1917 outburst (W illiam s 2000). T he next discovery ofthe series was on IM N or (possible nova in 1920) in 2002 January. T he outburst detection by W illiam Liller(Liller2002)wasquickly relayed to the V SN ET ,and enabled early astrom etric work to rst rm ly identify the quiescentcounterpartand itsrecurrent nova nature (D uerbeck et al. 2002; R etter et al. 2002). T he light curve of IM N or was published m ore than 50 years after the 1920 outburst (Elliot, Liller 1972). T here had been a suggestion of identi cation w ith the U H U R U X -ray source 2U 1536 52,w hich was later conrm ed to be spurious (W ycko ,W ehinger 1979,see also K ato 2002g). A lthough the outburst light curve in 1920 resem bled that of a slow recurrent nova T Pyx (Elliot, Liller 1972),the unusually faint quiescence inferred from W ycko ,W ehinger (1979) had been a m ystery. T he exactidenti cation w ith a new outburstsolved thism ystery, by the detection ofa considerable variation in quiescence (K ato et al.2002t). T his suggestion was later con rm ed by the detection ofa short period variation w ith eclipselike fadings (W oudt,W arner 2003a). K ato et al.(2002t) suggested,from the lightcurve and spectroscopic appearance, that both C I A ql and IM N or are m em bers of a new class ofrecurrent novae having interm ediate properties between classicalnovae and fast recurrentnovae. 6.3. O ther C ataclysm ic Variables 6.3.1. Interm ediate Polars Interm ediate polars (IPs), w hich are a class of m agnetic C V s (M C V s) having a m agnetic w hite dwarfasynchronously rotating w ith the orbital m otion (som etim es referred to as D Q H er stars: for recent review s, see e.g. K ing, Lasota 1990; Patterson 1994; H ellier 1996;

24

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B uckley 2000; chapters 8 and 9 in H ellier 2001a). A lthough m any \classical" IPs are novalike system s w ith therm ally stable accretion disks, there are a num ber of IPs show ing transient outbursts. Som e ofthem look like dwarf novae (subsection 6.1), including well-know n objects such as G K Per (W atson et al. 1985; B ianchini et al. 1986; H utchings, C ote 1986; N orton et al. 1988; Patterson 1991), D O D ra (som etim es called Y Y D ra, see K holopov et al. 1985b, K holopov, Sam us 1988 for the o cialnom enclature,Patterson et al.1992;H aswell et al.1997),EX H ya (W arner,M cG raw 1981;Jablonski, B usko 1985;H eise et al.1987;H ellier et al.1987). T here has been a long-standing discussion w hether these IP outbursts originate from disk-instabilities or from m asstransfer bursts (H ellier et al.1989;H ellier,B uckley 1993; H ellier etal.2000).T he m odern understanding is thatat leastsom e ofthem are betterunderstood asm ass-transfer events (T V C ol: H ellier,B uckley 1993),w hile others can be understood as disk-instability events (G K Per: K im et al.1992;Y iet al.1992). R apid circulation ofoutburst alerts are extrem ely im portant for short-period system s, because these IP outbursts are usually very brief (usually less than 1 d) and require prom pt follow -up observations (e.g. T V C ol: Szkody,M ateo 1983;Szkody,M ateo 1984;Schwarz et al.1988;H ellier,B uckley 1993;R etter et al.2003,EX H ya: B ateson et al. 1986; B ateson, Jones 1987; B ond etal.1987;Fujino etal.1987;H ellieretal.1989;R einsch, B euerm ann 1990; Jones 1994; H ellier et al. 2000, D O D ra: W enzel 1983b; W enzel 1983a; H urst et al. 1985; M cN aught et al.1985;H azen 1986;D yck,Schm eer 1988; K ato, D yck 1988). A lthough these outburst detections have historically been relayed via IA U C s,they were not usually rapid enough to enable early-stageobservationsof these outbursts. T he V SN ET C ollaboration has played a role in detecting, and rapidly relaying these IP outbursts. Since IP outbursts tend to cluster (cf. B ateson et al.1986,M .U em ura et al. in preparation),rapid electronic announcem ents of these outbursts have dram atically increased the chance of detailed follow -up observations, including sim ultaneous observations w ith satellites. T he m ost rem arkable recent exam ple includes X ray/opticalsim ultaneousobservationsoftwo outburstsof D O D ra (Szkody etal.2002b),w hoseopticalcoveragewas based on observations by the V SN ET C ollaboration. T he IP outbursts for w hich the V SN ET C ollaboration played an im portant role of early noti cation include G K Per in 1996 (Ishida et al. 1996; M orales-R ueda etal.1996;N ogam ietal.2002),in 1999,w hoseoccurrence was notably predicted by a V SN ET m em ber, T sutom u W atanabe (vsnet-future 2),71 and real rise observed in detailby the V SN ET C ollaboration (vsnet-alert 2652).72 T hese two outbursts were ofspecialim portance because detailed m odern tim e-resolved C C D observations set a stringentlim iton the expected occurrence ofeclipsesdur71

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ing outburst(K im et al.1992).T hese outbursts also provided an opportunity to study tim e-resolved spectroscopy of the Q PO s (M orales-R ueda et al. 1996), as well as X -ray/opticaldetections of long-period Q PO s (M oralesR ueda et al.1999;N ogam ietal.2002).M ulticolorobservations ofthe 1996 outburst also provided observational constraints on the outburst m odels (N ogam iet al.2002). T he 2002 outburst of G K Per provided an opportunity to study m agnetic accretion (B ianchiniet al.2003). T he long-term visualdata,including the data reported to the V SN ET ,have been used for analysis ofoutburst properties (Sim on 2002). In m ost recent years, the V SN ET C ollaboration has succeeded in characterizing outburst properties of the unusual short-period interm ediate polar H T C am (Tovm assian et al. 1998). T he outbursts are extrem ely brief(W atanabe1998b),show ing precipitousdeclinesduring the late part ofoutburst. From the tim e-di erence of outburst m axim um and the m axim um appearance ofIP pulsesduring the2001 outburst,Ishioka etal.(2002a)concluded that the outburst was triggered by a dwarfnovatype disk instability phenom enon.T he existence ofa precipitouslaterdeclinecan beexplained by thetruncation of the inner accretion disk. T he 2001 outburst ofH T C am was also studied by another group (K em p et al. 2002). T he outburstofH T C am thus hasbeen one ofm ilestones in the study ofIP-dwarfnova relation. K ato,Starkey (2002) reported short-period,nearly coherent,Q PO s in V 592 C as,a nova-like star in the period gap.T hisobjecthasbeen suggested to be a unique object in the period gap show ing both propertiesofsuperhum ps and occasionalIP-like,nearly coherent,photom etric oscillations.Severalotherdwarfnovae have been suspected of IP-type signature,and were brie y discussed in the relevant parts ofsubsection 6.1. 6.3.2. Polars B rightpolars(M C V sw ith synchronously rotating w hite dwarfs) have been regularly m onitored by the V SN ET C ollaboration. M any polars,notably A M H er ( gure 9) and V 834 C en,occasionally show low states,w hose occurrence hasbeen noti ed through the V SN ET alertsystem . Long-term C C D m onitoring offaintpolarshave been regularly reported by B erto M onard. C oordinated m ulti-wavelength observations have been conducted on severaloccasions. T he targets include A M H er,A R U M a,ST LM i,V V Pup,A N U M a and EF Eri. Som e ofthese collaborative studieshasbeen already published as a solid paper (H oard et al.2002a). 6.3.3. V Y Scl-Type Stars V Y Scl-type starsare novalike C V sw ith occasionallow states, or fading episodes (cf. W arner 1995b; R obinson et al. 1981; see gure 10 for the V SN ET light curve of M V Lyr). In som e system s, these low states occur very infrequently (the bestexam ple being T T A ri: B ortle et al.1980; Fuhrm ann 1981; Shafter et al.1982; H udec

Variable Star N etwork

Visual magnitude

N o.]

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12 13 14 15 16 50000

50500

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F ig. 9. Light curve ofA M H er from V SN E T observations.

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16 50000

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JD - 2400000 F ig. 10. Light curve ofthe V Y Scl-type star M V Lyr from V SN E T observations.

et al.1984;Shafter et al.1985;H utchings,C ote 1985).73 Such low states provide a unique opportunity to study the w hite dwarf atm osphere or to directly detect the secondary star (e.g. Jam eson et al. 1982a; Jam eson et al. 1982b). From the view point of disk-instability m odel,the decreasing m ass-transferrate would produce a dwarfnova-typedisk instability ifthereisno specialm echanism to suppress the instability (H oneycutt et al.1994; K ing, C annizzo 1998). O bservations, however, tend to show sm ooth m onotonousdeclines(H oneycuttetal.1994; G reiner 1998). T his m akes a clear contrast to the \low states" in dwarfnovae (cf. 6.1.6).T here m ustbe a m echanism in V Y Scl-type starsto som ehow therm ally stablizing the disk w hen the m ass-transferis reduced (cf. Leach etal.1999).D ense observationalcoverage ofV Y Scl-type starsisthereforehighly needed im m ediately afterthestart 73

A lthough there w as an interpretation ofthis object as a Z C am type dw arfnova perm anently atstandstill(K rautteretal.1981), w hich w asadopted by the G C V S team ,itisgenerally considered as a V Y Scl-type star w ith an occasional dram atic decrease of m ass-transfer.

oftheir declines. It is also know n that V Y Scl-type stars tend to show superhum ps (cf. Patterson 1999). Since the m assratios (q) of V Y Scl-type stars are not usually considered su ciently sm allto enable excitation ofthe 3:1 resonance to produce superhum ps (cf. H irose, O saki 1990; W ood et al. 2000; W hitehurst, K ing 1991; M olnar, K obulnicky 1992;M urray 1998),there is apparently the need for an explanation ofthe cause ofthe superhum ps. M urray etal.(2000)considered the variation in the m asstransfer rate in V Y Scl-type stars,and presented a working hypothesis w hy V Y Scl-type stars,w ith interm ediate q,can show superhum ps.T hishypothesisalso needsto be tested by m ore observations ofV Y Scl-type stars during di erent brightness states. T he V SN ET C ollaboration succeeded in early announcing a rare fading of V 751 C yg, w hose V Y Scl-type nature was suspected m ore than 20 years ago (R obinson etal.1974)buthad no com parable fading in recentyears. T he 1997 fading ofV 751 C yg was originally reported to the V SN ET by Laszlo Szentasko,and itsprogresswasfol-

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V SN ET hasbeen providing inform ation aboutX -ray transientsw hich enablesprom ptobservations,notonly foropticalobservers,but also for X -ray,U V ,IR ,and radio observers.B esides these recentstudies,the earliestwork by theauthorsincludeinfrared quiescentobservation ofV 404 C yg = G S 2023+ 338 (K ato,H irata 1990b),w hich rstrevealed the existence ofthe photom etric period of5.76 hr. A nother outstanding early resultwas the discovery ofsuperhum ps and orbitalvariation in the outbursting X -ray transientG R O J0422+ 32 = V 518 Per(K ato etal.1992b; K ato et al.1993a;K ato et al.1995b). T his observation has been one ofthe m ostcom prehensive studies ofsuperhum ps in \classical" soft X -ray transients up to now (cf. O ’D onoghue,C harles 1996). H ere we focus on the soft X -ray transients for w hich the V SN ET collaboration conducted intense world-w ide cam paigns.SoftX -ray transientsarealso called X -ray novae,w hosecom m on characteristicswereestablished in the m id-1990’s(Tanaka,Lew in 1995;C hen etal.1997):T heir light curves are typically described w ith a Fast R ise and an ExponentialD ecay (FR ED ).T he e-folding tim e is 30{ 40 d during the decay phase.In the FR ED -type outburst, a re are,or a secondary m axim um is observed 50 d after the outburstm axim um . T he outburstsare considered to occur due to a sudden increase ofm ass accretion rate in an accretion disk (M ineshige, W heeler 1989; H uang, W heeler 1989). R adialvelocity studies ofthe secondary star have revealed that a dozen of soft X -ray transients contains stellar-m ass black holes. Soft X -ray transients thus provide an ideallaboratory ofthe accretion physics onto the black hole,and they are called black hole X -ray transients. In the fram ework of classical soft X -ray transients, the opticaland X -ray em issions originate from the outer and the inner region of the accretion disk, respectively. Sim ultaneousopticaland X -ray observationsthereforeenable us to study the evolution of the accretion disk and the m echanism ofits activity. T he V SN ET collaboration enablesusto obtain dense sam plesthroughoutoutbursts. W ith these observations, we sum m arize the progress of studies of classical soft X -ray transients in subsection 6.4.3. O n the other hand, severalrecent transients have exhibited characteristicsw hich aredi cultto explain w ithin the classicalfram ework.T he prom pt observations by the V SN ET collaboration has played an im portant role, in 6.4. X -Ray Binaries and X -Ray Transients particular, for the research on the lum inous fast tranX -ray binariesare close binary system sw hich consistof sients (U em ura et al. 2002h) and rapid optical variaa com pact object and a norm alstar. T he m ass accretion tions (U em ura etal.2000c;U em ura etal.2002d;U em ura from the norm alstar onto the com pact object generates et al. 2004a). W e sum m arize our studies on these new strong X -ray em ission. A num ber ofX -ray binaries have classes ofactivity in subsections 6.4.1 and 6.4.2. been discovered as transients (cf. Liu et al.2001). T heir outbursts can be observed in all wavelengths, hence si- 6.4.1. FastX -ray transients,V 4641 Sgr and C I C am m ultaneous m ulti-wavelength observations have played a It has been proposed that the outburst ofclassicalsoft key role to revealthe nature ofX -ray binaries and X -ray X -ray transients is induced by therm alinstability ofthe transients (e.g. O rosz,B ailyn 1997; H ynes et al.2000). accretion disk (M ineshige,W heeler1989;H uang,W heeler T heir outburst cycle is generally longer than a year,and 1989). T his m odel can explain the large e-folding tim e in som e cases,longer than decades. Prom pt observations during their decay phase by considering a strong X -ray of an early outburst phase are hence im portant. T he irradiation w hich stabilizes the outer disk. T his standard lowed in detail by the V SN ET C ollaboration m em bers, notably w ith C C D photom etry at O uda Station. T his fading not only presented authentication ofV 751 C yg as a genuine V Y Scl-type star, but also enabled X -ray observations w hich led to the discovery of transient supersoft X -ray em ission (G reiner et al.1999; G reiner 2000). T his observation, suggesting a possible extension of lum inous supersoft X -ray sources (SSX S) toward a lessm assive w hite dwarf,led to a revolutionary change in our view ofV Y Scl-typestars.O therrarelow statesofV Y Scltype stars announced through the V SN ET C ollaboration include LQ Peg (= PG 2133+ 115)in 1999 (the second historical fading: W atanabe 1999a; K ato, U em ura 1999a; Schm idtke et al. 2002) and B Z C am in 1999 (the second historical fading: W atanabe 2000; W atanabe 2001; K ato,U em ura 2001b;G reiner etal.2001).T he 1999 fading of B Z C am is notable in that transient superhum ps were detected during the fading (K ato,U em ura 2001b), w hich m ay give support for the explanation by M urray et al.(2000). T he V SN ET C ollaboration also succeeded in presenting the rst-ever light curve of V 504 C en (K ato, Stubbings 2003),w hich hasbeen suspected to be a V Y Scl-type star from spectroscopy (K ilkenny,Lloyd Evans1995),buthad no solid photom etric record qualifying the V Y Scl-type nature. W ell-know n V Y Scl-type stars, such as M V Lyr, have long been best-observed targets by the V SN ET C ollaboration.Som e ofthese long-term observationswere em ployed to qualify the light curves ofV Y Scl-type stars (G reiner 1998). T he well-know n V Y Scl-type star K R A urwasintensively studied by the V SN ET C ollaboration (K ato et al.2002g),w hich led to the detection ofshortterm variations having power-law type tem poralproperties. T he other notable object is V 425 C as, w hose low state in 1998 was announced by T im o K innunen through the V SN ET , w hich led to our ow n discovery of shortterm (2.65 d),large-am plitude (up to 1.5 m ag)variations (K ato et al.2001s). Such a type of variation had never been never in any class ofhydrogen-rich C V s,and K ato etal.(2001s)suggested thatthey are dwarfnova-type instabilities in a m oderately stabilized disk. T his discovery was introduced as the \shortest period dwarf nova" in A strophysics in 2002 (Trim ble,A schwanden 2003).

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picture cannot,however,explain two atypicaloutbursts, that is, the fast transients V 4641 Sgr (H jellm ing et al. 2000; U em ura et al. 2002h) and C I C am (B elloni et al. 1999).T heiroutburstduration wasonly a few days,w hich istoo shortto be interpreted w ith the viscousdecay ofthe classicalsoft X -ray transients. O n 1998 M arch 31,the A ll-Sky M onitor (A SM ) ofthe R ossiX -R ay T im ing Explorer(R X T E)detected a new X ray transientnam ed X T E J0421+ 560 (Sm ith etal.1998). W eweream ong the rstto pointoutthepresenceofa supposed sym biotic starC IC am (B ergneretal.1995)w ithin the error (vsnet-alert 1621).74 T his inform ation was im m ediately relayed to X -ray and opticalobserversthrough the V SN ET ,and the proposed identi cation wassecurely con rm ed w ith the discovery ofan outbursting object at the location ofC I C am (H jellm ing,M ioduszew ski1998). C ontrary to classicalX -ray transients,this objectstarted a rapid fading w ith an e-folding tim e of 0:5 d just after outburst m axim um (B elloniet al.1999). Its X -ray spectrum can be described by an absorbed power-law m odel w ith high-energy cuto ,w hich is atypicalfor X -ray transients(B ellonietal.1999).O pticalobservationsreported to the V SN ET show that C I C am brightened to 8.8 m ag on A pril 3,75 and faded by 2 m ag w ithin two days. Spectroscopicobservationsrevealed thatC IC am isa B [e]{ X -ray binary (B ellonietal.1999).T he nature ofthe com pactobjectisstillunknow n (B ellonietal.1999;O rlandini et al.2000;H ynes et al.2002;R obinson etal.2002).T he V SN ET C ollaboration furtherobtained quiescentobservations,w hich revealed the presence ofweak activity (K ato, U em ura 2001d). V 4641 Sgr is a variable w hose opticalspectrum is that ofan A -type star (D ow nes et al.1995;note that the object was not correctly identi ed in the literature untilwe published a reliable chart, see subsection 2.2). In 1999 A ugust, T sutom u W atanabe, a m em ber of the V SO LJ, noticed that the object entered an active state in the opticalrange (W atanabe 1999b). T his state was characterized by the presence oflarge-am plitude variation having a possible periodicity of 2.5 d (K ato et al. 1999e). O n Septem ber 15,the state was term inated by a short outburst reaching 8.8 m ag independently detected by R od Stubbingsand the K yoto team ,follow ing B erto M onard’s detection ofa brightening preceding thisevent(vsnet-alert 3475,3477,3478;Stubbings,Pearce 1999).76 A llthese reports were im m ediately circulated through the V SN ET alert network; the resultant vigileventually enabled the historicaldetection ofthisperfectly unexpected giantoutburst. Follow ing our noti cation,a corresponding X -ray outburst was found in the backlog recorded w ith the R X T E/A SM ; the X -ray outburst was not discovered \real-tim e" even w ith X -ray all-sky m onitor. T he X -ray 74

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See hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ alert1000/m sg00621.htm li. See hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/X ray/ cicam .htm li. See hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/X ray/ gm sgr.htm li for the fullstory.

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outburst,afterreaching an astonishing ux of12 C rab at the X -ray m axim um , rapidly faded and returned to the pre-outburstlevelw ithin only 2 hours(Sm ith etal.1999). T he duration ofthe opticaloutburst was also short ( 5 d) (U em ura et al. 2002h). T he V SN ET collaboration team perform ed prom pt observation of this short X -ray outburst, and revealed that the optical variation exhibited anti-correlation againstthe X -ray variation (U em ura et al. 2002h). Spectroscopic observations revealed that V 4641 Sgr consists ofa black hole and a late B -type star (O rosz et al.2001). A s reported below ,V 4641 Sgr experienced active phasesin the nextcouple ofyears(U em ura et al. 2002d; U em ura et al. 2004a; R upen et al. 2003), however,no com parable outburst to the 1999 Septem ber giant one has been yet observed. W hile theirbinary com ponentsaretotally di erent,the short outbursts of V 4641 Sgr and C I C am have several com m on characteristics: First, spatially resolved radio jets were associated w ith the outburst in both system s (H jellm ing et al. 1998; H jellm ing et al. 2000). Second, the peak lum inosities reached the Eddington lum inosity (R obinson et al. 2002; R evnivtsev et al. 2002b). T heir high lum inosity im plies that supercritical accretion occurred. Since the m atter falls w ith alm ost free-falltim e scale in the supercritical accretion, the problem of the short duration of the outbursts can be reconciled. T he optical{X -ray anti-correlation of V 4641 Sgr m ay be understood w ith the scenario thatthe optically-thick supercritical accretion ow absorbed the X -ray em ission and re-em itted the opticalem ission (R evnivtsev et al.2002a; U em ura et al.2002h). It is,however,stillunknow n how the supercriticalaccretion was induced. 6.4.2. Short-term ,non-therm alopticalvariations In the classical picture, the optical em ission is therm alem ission from the outer portion ofthe accretion disk w here the tem perature is relatively low ( 104 K ). T he observed tim e scale of optical variations is hence long, such assuperhum ps(e.g.O ’D onoghue,C harles1996)and orbital period variations (e.g. K ato et al. 1995b). T he black hole binary system , G X 339-4 is, however,know n to show rapid opticalvariations ofthe tim e scale ofseconds (M otch et al.1982;M otch et al.1983). Such short tim e scale variations indicate that they originate from an inner portion of the accretion ow . T hey are proposed to be cyclo-synchrotron em ission from the inner region (M otch et al. 1982), however, the m echanism to generate the em ission and variations is poorly know n. T he V SN ET collaboration team has recently observed optical rapid variationsoftwo sources,thatis,X T E J1118+ 480= K V U M a (U em ura et al.2000c) and V 4641 Sgr (U em ura et al.2002d;U em ura et al.2004a). X T E J1118+ 480 was discovered w ith the R X T E/A SM on 2000 M arch 29 (R em illard et al. 2000). W e discovered an optical counterpart at 12.92 m ag on M arch 30 (U em ura et al. 2000f). T he optical light curve showed so m any uctuations that U em ura et al. (2000c) suggested the presence of optical rapid variations. Spruit, K anbach 2002 detected opticalshort-term (a few tens of

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F ig. 11. \O ptical ash" from V 4641 Sgr observed on 2002 July 7.

seconds) variations w hich correlate w ith the X -ray variations. T hese rapid opticalvariations are also proposed to be synchrotron em ission from the inner accretion ow (Spruit,K anbach 2002).Since X T E J1118+ 480 rem ained at a low /hard state throughout the outburst, the inner region is considered to be lled not by the standard disk, but by the advection dom inated accretion ow (A D A F: N arayan, Y i 1994). In the A D A F region, the gas density is so low that the m agnetic pressure is dom inant (M ineshige et al.1995). T he opticalrapid variations are probably generated at shock regions in such an inner region,w hich are form ed by m agnetic reconnections or collisions of blobs in the m agnetically-dom inated accretion ow (U em ura et al.2002d). A fter the lum inous,short outburst in 1999 Septem ber, V 4641 Sgr experienced a new active phase in 2002 and 2003. T he V SN ET collaboration succeeded in detecting rapid opticalvariations during the 2002 active state ( gure 11), w hose detailed features and interpretation are reported in U em ura et al.(2004a)in this volum e.

cretion disk (O saki1985)orthe inward propagation ofthe eccentricity wave (Lubow 1992). Itisproposed thatthe re areisinduced by the grow ing tidaldissipation (Ichikawa et al.1994;Truss et al.2002). T his m odel was developed based on the fact that superhum ps appeared only after the re are (O ’D onoghue, C harles 1996).O n the other hand,superhum ps appeared even before the re are in X T E J1118+ 480 (U em ura etal.2002g).T he V SN ET collaboration obtained a dense sam ple around the re areofX T E J1859+ 226,w hich isreported in U em ura et al.2004c in this issue. W e detected periodic variations,w hich m ay be superhum ps,even before the re are of X T E J1859+ 226. T hese observations are unfavorable for the above scenario for the re are. It is also proposed that strong X -ray irradiation onto the outer accretion disk m ay induce the re are (e.g. K ing, R itter 1998).

6.4.4. H igh-M ass X -Ray Binaries SS 433 = V 1343 A qlis an active high-m ass X -ray binary (H M X B ) w ith relativistic jets,and the nature ofthe binary system is still m ysterious in m any aspects. Its 6.4.3. C lassicalsoftX -ray transients Superhum ps,w hich have been originally studied in SU opticalm agnitude isfrequently m onitored by V SN ET obU M a-type dwarf novae, are also observed in soft X -ray servers,and rem arkable (brightening or fading) behavior transients (e.g. O ’D onoghue,C harles 1996). To observe is reported via vsnet-cam paign-xray w hen it occurs. In 1995,1998,and 2000,sim ultaneousm ulti-wavelength the evolution of superhum ps was di cult in the case of soft X -ray transients because oftheir rare outbursts,rel- observationswereorganized by theA SC A team ofR IK EN atively long orbital period, and long durations of out- (N .K awaietal.,in preparation)in orderto determ ine an burstsm ade a dense sam pling throughoutoutburstsdi - accurate ephem eris of the eclipse and to com pare light cult. O urintense cam paign ofX T E J1118+ 480,however, curves in the X -ray and opticalwavelengths,w hich yield rst revealed the evolution of superhum ps in soft X -ray a clue to understand the em itting regions in the binary transients (U em ura et al.2002g). T he superhum p period system . In these cam paigns,V SN ET played the role ofa was rst 0.43% longer than the orbitalperiod,and then m edium for exchanging inform ation on the opticalparts, decreased during the m ain outburst. Superhum ps in SU such as calls for optical inform ation, explanation of the U M a-type dwarfnovae also exhibit this behavior,w hich background,and practicalconditionsand notesforobsercan be interpreted by the contraction ofthe ellipticalac-

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vation (e.g. vsnet 103,for the 1995 cam paign).77 6.5. Supernovae O ur contributions to the spectroscopic type determ ination of supernovae are sum m arized in table 1. C on rm atory observations,identi cationsand sim ilaractivities reported in IA U C s are also listed in table 2. W e also run them ailing listvsnet-cam paign-sn,78 w hich isnow w idely know n asthem ostreliableand up-to-dateinform ation ofsupernovae. T he \Latest Supernovae" page (subsection 3.3)hasbeen collaborating w ith it,w hich also providesU SN O -A 2.0 (M onetetal.1998b)based chartsm ade by O dd Trondalforalm ostevery supernova brighterthan 20th m agnitude. T he charts gives blue and red m agnitudesforphotom etric reference stars,the latteroneshave been w idely used for \C R " m easurem ents (see A ppendix 2.1). B esidesobjectsdescribed in thesubsections1.3 and 5.4, here we m ention here rem arkable exam ples. SN 1997efin U G C 4107 wasdiscovered by Yasuo Sano, one of the m ost active participants of V SN ET (N akano et al. 1997). It was originally announced as \possible supernova", because its spectra was quite unusual and could notconvincingly be classi ed asthatofa supernova (G arnavich et al.1997b). Further spectroscopic observationsrevealed thatitwaslikely an explosion w ith m assive (several M ) ejecta. T he object consequently received the designation ofSN 1997ef(H u et al.1997,Filippenko, M artin 1997). Filippenko,M artin (1997) and G arnavich et al. (1997a) suggested that it was likely be an explosion of a stripped very m assive star, a suggestion supported by theoreticalm odeling (Iwam oto et al.2000). It is the rst exam ple ofthe so-called \type-Ic hypernova", a concept developed after the suggested association SN 1998bw w ith G R B 980425 (G alam a et al.1998,Iwam oto et al.1998),SN 2002ap (see subsection 5.4),and the unam biguous identi cation ofthe supernova signature (SN 2003dh)in G R B 030329 (see subsection 6.15). SN 1997eiwasdiscovered by M asakatsu A oki(N akano, A oki 1997) in N G C 3963. T he rst spectroscopy reported in IA U C indicated that it is a type-Ia supernova (G arnavich et al.1997c). O ur spectroscopy showed som e peculiarity, then we reported that it could be a peculiar type-Ia supernova (A yani, Yam aoka 1997). From later spectroscopic observations, it nally turned out to be a type-Ic supernova (W ang et al. 1998, Filippenko, M oran 1998). T he SN 1998T case taughtusthe im portance ofidentication. Itwasproduced in a pairofinteracting galaxies, and som e catalogues ofgalaxies gave discrepant designationsforthem .T heblobby natureofthehostgalaxiesalso led to m isidenti cations ofthe supernova.T he discussion on vsnet-chat,including the consultation ofthe N G C /IC project 79,led us to a correctidenti cation ofthe galaxy, 77

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w hich was accom panied by precise astrom etry (Yam aoka et al.1998). SN 1998bu in M 96 was discovered by M arko V illi. It was the nearest supernova since SN 1993J in M 81. T he rstspectroscopy reported in IA U C wasa high-dispersion one,w hich could only determ ine the depth of the interstellar absorption w ithin our G alaxy and the host galaxy (M unariet al.1998). O ur spectrum revealed that it is a type-Ia supernova,and this report was naturally posted to vsnet-alert 178580. It was distributed earlier than the relevant IA U C (A yani et al. 1998), w hich also included other spectroscopy (M eikle et al. 1998). In response to the type determ ination,the C O M PT EL instrum ent was pointed towards SN 1998bu in order to detect the line ray of56 C o decay,w hich had been detected only from SN 1991T ,the peculiar lum inous type-Ia supernova. D espite SN 1998bu is as close to us as SN 1991T ,the -ray lines wasnotdetected (G eorgiietal.2002),w hich m ay suggest a diversity am ong type-Ia supernovae in the line -ray,as wellas in the light curves (R iess et al.1996) and in the spectra (N ugent et al.1995). T he rst spectroscopic observation of SN 1998es indicated that it is an intrinsically bright type-Ia supernova like SN 1991T (Jha et al.1998a). O ur report con rm ed it,giving in addition the spectralevolution and the interstellar extinction (A yani,Yam aoka 1998c). SN 1999dn was a case sim ilar to SN 1997ei. O ur spectrum suggested that it was of type Ic w ith week H ei lines (A yaniet al.1999). T he sam e IA U C also contained two spectroscopic observations, one of w hich (Turatto et al.1999) reached the sam e conclusion, but the other suggested it was oftype Ia (Q iu et al.1999). Later spectroscopy revealed thatSN 1999dn isan interm ediateevent between type Ib and type Ic (Pastorello et al.1999). SN 2000ch was a very sublum inous supernova. It was originally announced as a variable star in eld of N G C 3432 (Papenkova, Li 2000). W e noticed that the object can be seen on the D SS im ages since 1998 (vsnetchat 2908),81 (Yam aoka 2000). O n the other hand,spectroscopy of this object (W agner et al. 2000) suggested that it is located w ithin N G C 3432. From these ndings, Filippenko (2000) assigned the supernova designation of this object, resem bling the \type-V " SN 1961V . T he com m entofthe discoverer(vsnet-chat2944)82 nally supported this classi cation. SN 2001bfwasyetanotherexam plesim ilarto SN 1997ei and SN 1999dn. D espite ofits low signal-to-noise ratio, our spectrum clearly showed a deep Siii absorption feature,from w hich we estim ated that it is a type-Ia supernova (K awakita et al.2001a). A nother group suggested that it is of type Ic (Phillips, K risciunas 2001),but the laterspectralevolution revealed thatitisindeed a type-Ia supernova (C hornock et al.2001). 80

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SN 2002ao was a slightly di erent case. T he rst report on IA U C quoted the resem blance w ith type-IIb supernovae (G al-Yam et al.2002a,G al-Yam et al.2002b). W e estim ated thatitisoftype Ic (K inugasa etal.2002d), w hich is consistent w ith a later report (Filippenko, C hornock 2002) indicating the resem blance w ith SN Ic 1999cq. T he rapid decline (Yam aoka et al. 2002c) of SN 2002ao was another com m on feature w ith SN 1999cq (M atheson et al.2000). O ther IA U C issues in relation w ith the activity ofthe V SN ET adm inistrators include IA U C 7033 (SN 1998eg: H urst et al. 1998), IA U C 8101 (SN 2003cg: H irose, Yam aoka 2003), and IA U C 8171 (SN 2003gs: Evans et al.2003). 6.6. Sym biotic Variables B right sym biotic variables (cf. A llen 1984; K enyon 1986;B elczynskiet al.2000;M unari,Zw itter 2002) have been well-observed by m any m em bers of the V SN ET C ollaboration (see gure 12). T hese observations provided a num ber of detections of outbursts and eclipses, w hich were im m ediately relayed to m ore specialized researchersfor detailed study. T he eclipse phenom enon in the outbursting object FN Sgrwasdiscovered through theV SN ET regularactivity.83 T his work was sum m arized by W atanabe et al.(2000). T he outburstand possible eclipse phenom enon in V 343 Ser = A S 289 was discovered by K esao Takam izawa (= T m z V 17, vsnet-obs 8957)84 and M inoru W akuda. T he nalpublication is by Takam izawa et al.(1998). V 1413 A ql= A S 338 is another object w hose eclipsing sym biotic nature (cf. gure 13) was revealed by am ateur astronom ers(W akuda 1988).85 T heoutburstsand eclipses were regularly announced in V SN ET , w hich have been followed by a num ber of researchers (e.g. Esipov et al. 2000;K olotilov et al.2001). K ato (2000) reported the sim ilarity oflight curves between C H C yg and the supersoft X -ray sources (V Sge and R X J0513.9 6951)based on V SN ET observations. T he 1997 and 2000 outbursts ofZ A nd were reported in vsnet-alert938,86 and vsnet-alert5232,5233,87 respectively.T hese outburstsenabled,m ore orlessow ing to the V SN ET alerts,m odern observationsofthis classicalsym bioticbinary (Sokoloski,B ildsten 1999;Skopaletal.2000; Skopal2003;Tom ov et al.2003). Ishioka etal.(2001d)system atically studied short-term variations of V 694 M on = M W C 560. D uring the entire period ofobservations,the objectshowed pronounced ickering activity. T his work has been referred to as one 83 84

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hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/Sym bio/fnsgr.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/obs8000/ m sg00957.htm li. See hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/docs/ v1413aql.htm li fora fullstory. See also Schulte-Ladbeck (1985), M unari(1992),M unariet al.(1993). hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-alert/m sg00938.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ alert5000/m sg00232.htm li and hhttp://w w w .kusastro.kyotou.ac.jp/vsnet/M ail/alert5000/m sg00233.htm li.

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ofthe m ost intensive photom etric observations ofths peculiar sym biotic variable (Schm id et al. 2001; see also Sokoloskiet al.2001 for a recent survey work). W e now have a dedicated m ailing list for sym biotic stars vsnetsym bio88 for inform ing about recent activities, particularly announcem ents ofoutbursts and eclipses,ofsym biotic variables. 6.7. R C oronae Borealis Stars and Related O bjects R C rB stars are hydrogen-de cient carbon stars w hich show occasional fadings caused by dust form ation (C layton 1996). A representative light curve of R C rB from V SN ET observations is show n in gure 14. Early announcem ents of the fadings of R C rB stars can provide the best opportunities to study the form ation m echanism of dust in these stars. B efore the V SN ET era,these fadings had been only w idely announced only w hen the objects had unm istakably faded (typically below 1 m ag below their usualm axim um );the early decline stage had been usually overlooked. T he real-tim e com m unication via the V SN ET public lists broke this historical lim itation. T he m ost dram atic instance was w ith the rst-ever fading ofFG Sge (also know n as a nalhelium ash object) in 1992 late A ugust{Septem ber (cf. history partly recorded in vsnet-history 200, 202). It was only w hen the object had already faded by 1 m ag w hen IA U C s were issued (Papousek,G ranslo 1992; W aagen et al. 1992; W oodward et al. 1992). T his detection of a possible fading (1992 A ugust 30) reported by N obuhiro M akiguchi(V SO LJ,see subsection 2.3) was im m ediately attended by a num ber of world-w ide observers. T his fading was the rst one of the series of fadings successively occurring up tp now (cf. Iijim a, Strafella 1993;Iijim a 1996;Iben,Livio 1993;Jurcsik 1993; Stone etal.1993;W oodward etal.1993;A rkhipova 1994; Sim on 1994;van G enderen 1994;K ipper et al.1995;van G enderen, G autschy 1995; A rkhipova 1996; A rkhipova, Esipov 1996;A rkhipova etal.1994;A rkhipova etal.1996; A rkhipova et al. 1998b; A rkhipova et al. 1998c; A rkhipova et al. 1999a; K ipper, K lochkova 1999b; G onzalez et al.1998; Jurcsik,M ontesinos 1999; K ipper, K lochkova 2001). T he discovery ofthe fading in FG Sge broughta breakthrough in the understanding oflate-tim e low -m ass stellar evolution: our understanding ofFG Sge had been slow and lim ited before this phenom enon (cf. C ow ley et al.1985;A ikawa 1985;A rkhipova et al.1991; although the unusualnature ofthisobjectwasrecognized m ore than 30 yr ago and had long been discussed from di erent standpoints, including binary hypothesis and a therm al pulse in stellar evolution (e.g. K ukarkin 1960; Furtig, W enzel 1962; H erbig, B oyarchuk 1968; W enzel, Furtig 1971; Paczynski 1970; Paczynski 1971; Sparks, K utter 1973; C hristy-Sackm ann, D espain 1974; Langer et al. 1974; C ohen et al. 1980; K urtz 1986; Feibelm an, B ruhweiler 1990). It is now w idely believed that FG Sge,V 605 A ql,and V 4334 Sgr (cf. subsection 6.2.1),as 88

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-sym bio/m aillist.htm li.

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T able 1. Spectroscopy ofsupernovae.

SN nam e Type V SN ET article R elevant IA U C 1995al Ia alert 266 6256 (A yani,K awakita 1995) 1997ei Ic alert 1399 6800 (A yani,Yam aoka 1997) 1998an Ia alert 1684 6878 (A yani,Yam aoka 1998a) 1998aq Ia alert 1681 6878 (A yani,Yam aoka 1998b) 1998bu Ia alert 1785 6905 (A yaniet al.1998) 1998es Ia,pec alert 2394 7059 (A yani,Yam aoka 1998c) 1999bg II alert 2816 7137 (A yani,Yam aoka 1999a) 1999dn Ib/c alert 3380 7244 (A yaniet al.1999) 1999gn II alert 3842 7336 (A yani,Yam aoka 1999b) 1999gq II alert 3862 7339 (A yani,Yam aoka 1999c) 2001bf Ia alert 5873 7625 (K awakita et al.2001a) 2001bg Ia alert 5871 7622 (K awakita et al.2001b) 2001dp Ia alert 6299 7683 (M igliardiet al.2001) 2002ao Ic cam p-sn 339 7810 (G al-Yam et al.2002a) 2002ap Ic,pec alert 7120 7811 (K inugasa et al.2002a) 2002bj II(n?) cam p-sn 363 7844 (K inugasa et al.2002e) 2002bo Ia alert 7241 7848 (K inugasa et al.2002c) 2002bu IIn alert 7259 7864 (A yaniet al.2002) 2002fk Ia alert 7516 7976 (A yani,Yam aoka 2002) 2003J II cam p-sn 534 8048 (A yaniet al.2003) 2003K Ia cam p-sn 534 8048 (A yaniet al.2003) alert for vsnet-alert,chat for vsnet-chat, cam p-sn2002ap for vsnet-cam paign-sn2002ap, cam p-sn for vsnet-cam paign-sn,

R em ark see sec. 5.4. see text.

see text. see text. see text.

see text.

see text. see sec. 5.4. lum inous

T able 2. Identi cation,astrom etry and follow -up ofsupernovae.

SN nam e 1998T 1999et 2000M 2000P

V SN ET articles chat 775,779,780,786,787 alert 4320 alert 4363,4365,4366,4368,4369

2000ch

chat 2908,2941,2944

2000cm

alert 4944,chat 3035

2001dp 2002ao 2002ap 2002dm

alert 6317 alert 7190 cam p-sn2002ap 154 cam p-sn 440

2002ed

alert 7441,cam p-sn 454

2003ez A bbreviations sam e as in table 1.

R elevant IA U C s R em ark 6859 (Yam aoka et al.1998) see text. 7344 (Yam aoka,Yam am oto 2000) 7373 (D im aiet al.2000) 7378 (C olas et al.2000), 7379 (corrigendum ) 7415 (Papenkova,Li2000), see text. 7417 (W agner et al.2000), 7419 (Yam aoka 2000), 7421 (Filippenko 2000) 7436 (M ueller,R ykoski2000), 7437 (Jha et al.2000a), 7438 (Jha et al.2000b) 7683 (M igliardiet al.2001) 7836 (Yam aoka et al.2002c) see text. 7836 (Yam aoka,R ogers2002) prediscovery 7921 (Sanders et al.2002), 7923 (Yam aoka,Sanders 2002) 7940 (M onard,Li2002), 7943 (Yam aoka 2002) 8141 (Papenkova,Li2003), 8142 (Yam aoka,A yani2003)

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F ig. 12. Light curve ofC H C yg from V SN E T observations.

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F ig. 14. Light curve ofR C rB from V SN E T observations.

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well as som e unusual R C rB stars (cf. V 348 Sgr, e.g. C layton 2002) com prise a sequence of nal helium - ash objects (cf. Law lor,M acD onald 2003). T he dram atic fading of ES A ql, w hich had been suspected to be an R C rB -type star, was rst announced through the V SN ET alert network; Peter W illiam s was the rst to detect this object getting fainter than 14.0 on 2001 M arch 22. B ased on this inform ation, C layton et al.(2002) succeeded in clarifying the R C rB -type nature ofthis object. T he other R C rB -type star recognized through the V SN ET activity is V 2552 O ph = H ad V 98 (K ato, H aseda 2003,R ao,Lam bert 2003;see subsection 5.3). W e now have a dedicated m ailing list for R C rB stars and related objects vsnet-rcb,89 w hich is best em ployed by the researchers of this eld. M ore recent announcem ents ofrare R C rB -type fadingsinclude the 2003 fading of V 3795 Sgr (vsnet-rcb 585).90 A lthough the attem pt wasnotvery successful,R osenbush (2001)tried to predict future light curve ofR C rB using V SN ET observations. 6.8. Be Stars A m ong recentphenom ena in B e stars(B -typeem issionlinestars),thecaseof Scorpiiisstillfresh in ourm em ory. T he star, w hich had been considered as a non-variable B -type star,underwent a dram atic change in 2000 July. Sebastian O tero,a V SN ET m em ber,visually noticed a 0.1 m ag brightening in Scorpiiand issued an alert through the V SN ET (vsnet-be 2).91 T he supposed transition to a B e star was subsequently con rm ed by spectroscopic observations(Fabregatetal.2000).T he starfurtherbrightened to a m axim um ofV 1.8 around 2000 July 30. Such a dram atic change in a brightnaked-eye starisextrem ely rare. T he only com parable precedent phenom enon was C assiopeiae in 1937, w hich brightened to V 1.6. T his new s was w idely distributed through public new s m edia, asoriginating from theV SN ET ,and becam etheoneofthe m ostpopularastronom icalphenom ena in thatyear.T his object,after reaching a tem poralm inim um just follow ing the initialpeak,continues to show rem arkable activities up to 2003 (O tero etal.2001;G andetetal.2002).O n severaloccasions in 2002 and 2003,the star even brightened close to V 1.5,even slightly surpassing in brightnessthe historicalevent of C assiopeiae. In the afterm ath of this event, visual m onitoring of bright B e stars has been conducted by a num ber of V SN ET m em bers,m ost intensively by O tero. T hese observations have detected ofnum ber ofoutbursts,e.g. in C entauri(cf. B aade et al.2001) and ! C anis M ajoris (cf. O tero 2002).T he V SN ET runsdedicated listson the B e-starphenom enon,vsnet-be92 and vsnet-cam paign-be.93 89

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hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M m aillist.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M m sg00585.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M m sg00002.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M m aillist.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M

ail/vsnet-rcb/ ail/vsnet-rcb/ ail/vsnet-be/ ail/vsnet-be/ ail/

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6.9. W olf{Rayet Stars W olf{R ayet(W R )starsare m assive,lum inous,and hot stars w hich have lost their hydrogen envelope, and are considered to be im m ediate precursors of som e kinds of supernovae, and likely G R B s. In spite of their astrophysicalim portance,W R stars were less conspicuous objects in term s ofopticalvariability. T he only know n categories of variability in W R stars had been occasional short-period obscuration by dust production,instabilities in thew ind,orpossiblepulsation (seeW illiam setal.1990; W illiam s 1995;Veen et al.1998 for recent references). T his situation dram atically changed by the discoveries of the two m ost actively variable W R stars by the V SN ET team (W R 104 = H ad V 82 = V 5097 Sgr: K ato et al. 2002d, W R 106 = H ad V 84 = V 5101 Sgr: K ato etal.2002c).B oth objectswere initially reported asvariable starsby K atsum iH aseda,detected during his search for novae. T he variables soon turned out to be identical w ith know n W R stars. In particular,W R 104 is a wellknow n binary consisting of a late-type W R star and an O B star.T hem ostrem arkablefeaturein thisobjectisthe presenceofa \dusty pinw heelnebula" (Tuthilletal.1999; Tuthilletal.2002)co-rotating w ith theinterferom etricbinary. T he im portance ofthe detection oflarge-am plitude optical variation was im m ediately recognized and com m unicated via V SN ET alert network. Such a large variation in W R 104 required a non-classicalinterpretation (K ato et al.2002d). W ith these conspicuous discoveries, the V SN ET signi cantly broadened the scope ofvariability studies of W R stars, and this eld is now becom ing one ofthe contem porary topics in studying the W R -type activity. C om bined w ith the recent advance in G R B astronom y,the im portanceoffundam entalunderstanding of various phenom ena in W R stars w illbe a m atter ofkey im portance. 6.10. Pre-m ain Sequence Stars Som e pre-m ain sequence starsshow dram atic outbursts (FU O ristars: FU O R s) and sm aller outbursts (EX Lup stars: EX O R s), probably originating from som e kind of instabilities in the circum stellar disk (e.g. K awazoe, M ineshige 1993). O utbursts of these objects were occasionally followed by the V SN ET C ollaboration.T he best exam ple wasthe 1995 outburstofV 1143 O ri(B aba etal. in preparation). O utbursts ofV 1118 O rihave also been occasionally reported (e.g. H ayakawa et al.1998). A m ong pre-m ain sequence stars, H erbig A e/B e stars have been one of the best observed objects by V SN ET m em bers. T he recent discovery ofa likely H erbig A e/B e star w ith large-am plitude variation,M isV 1147,has been w idely studied through the V SN ET (M . U em ura et al. in preparation).O therobjectsofthis class,wellobserved and tim ely inform ed through theV SN ET ,includeU X O ri, R R Tau, C Q Tau, A B A ur, R Z Psc and W W Vul (see gure 15). R em arkable variations in these objects have been relayed through a dedicated listofpre-m ain sequence vsnet-cam paign-be/m aillist.htm li.

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variables,vsnet-orion,94 and utilized for detailed follow - ofEK A nd (Yoshida et al.2003),and period variation in T U M i(Szatm ary et al.2003). up studies. N um erous new variable stars reported in vsnet-newvar 6.11. Peculiar Variable Stars (subsection 5.2)havebeen studied in detail,and havebeen Som e peculiar (or unique) variable stars were also reported in a num erous num ber of papers published in studied by the V SN ET C ollaboration. T he m ost strik- Inform ation B ulletin on Variable Stars (IB V S). C as,originally classi ed as a yellow sem iregularvariing objects include V 651 M on (the central star of the planetary nebula N G C 2346). T his binary system con- able, is now considered to be a low -tem perature countaining a B -type subdwarf underwent a totally unex- terpart (yellow hypergiants: de Jager 1998; Israelian pected fading in 1981{1985 (for a sum m ary ofthis event, et al. 1999; de Jager et al. 2001; Stothers, C hin 2001) see C ostero et al. 1986). A lthough no sim ilar phe- of the extrem ely lum inous hot hypergiants (lum inous nom enon was recorded in the century-long past photo- blue variables: LB V s). T his object occasionally undergraphicrecords,theobjectunderwentanotherunexpected goes tem porary optical fadings caused by huge m assfading episode in 1996{1997. T his phenom enon was de- loss events, usually once in decade(s) ( gure 18). T he tected by D anie O verbeek,and im m ediately reported to m ost spectacular recent event occurred in 2000 (Lobel the V SN ET (vsnet-alert548).95 Follow ing thisannounce- et al. 2003). Independent detections, including that by m ent,K ato etal.(2001e)succeeded in recording the phe- one of the authors (T K ), of this phenom enon were cirnom enon in detail. T here wasa sharply de ned transient culated through the V SN ET (vsnet-alert 5186, 5187),96 clearing (brightening) even during this fading,w hich was w hich enabled rst dense optical coverage of this kind ascribed to a sharply de ned,sm all(severaltim es 1011 of phenom enon. U pon recognition of the astrophysical cm )lucentstructurew ithin theobscuring body.See gure signi cance of this event,we set up a dedicated m ailing listvsnet-cam paign-rhocasin 2000 A ugust.97 T heseobser16 for the recent light curve. vations have provided the prim ary resource on this rare 6.12. Pulsating Variables event,and are referenced on Lobel’s dedicated page on A lthough pulsating variableswere only occasionally se- C assiopeiae.98 In 2003 therewasa sm allsignatureofa line lected as intensive targets ofthe V SN ET C ollaboration, variation sim ilarto theprecursoreventin 2000.T hisnew s the V SN ET public data archive (cf. gure 17),as wellas wasw idely announced through vsnet-cam paign-rhocasand the V SO LJ database,have been frequently used in period the object has been intensively observed. analysis,and correlation studies w ith other observational 6.13. Eclipsing Binaries m odalities. T hese referencesto the V SN ET /V SO LJ data A lthough classical (other than C V -type or sym bihave been so num erousthatwe only listm ostrecentones: historicalarchive for C ephei(Ski 2001),evolution of otic type) binaries are usually not intensive targets R H ya (Zijlstra, B edding 2002), dust form ation in L2 for the V SN ET C ollaboration, there have been sevPup (B edding et al. 2002), possible chaotic behavior in eral calls for observations, particularly for long-period R C yg (K iss, Szatm ary 2002), period determ ination of 96 hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/alert5000/ V 648 O ph (K azarovets,Pastukhova 2002),non-variability m sg00186.htm li and hhttp://w w w .kusastro.kyoto-u.ac.jp/ 94

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F ig. 17. Light curve ofthe RV Tau-type star R Sct from V SN E T observations.

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T .K ato et al.

eclipsing binaries (e.g. O W G em , EE C ep). V isual and C C D /photoelectric observations,as wellas com parison star sequence inform ation, have been exchanged on V SN ET lists. T he discovery of eclipses in the bright naked-eye star Velorum was one of the breaking new s m ediated through theV SN ET (seealso O tero etal.2000). A dedicated list for Velorum observations has been set up,vsnet-cam paign-deltavel.99 T he V SN ET runs dedicated lists on eclipsing binaries, vsnet-ecl100 w hich are now recognized as one of worldw ide networks exchanging inform ation in eclipsing binaries. K azuo N agai (V SO LJ) has been sum m arizing the tim es ofm inim um ofeclipsing binaries reported to vsnetecl. 6.14. Blazars B lazars (B L Lac objects and optically violently variable quasars)are also one ofthe targets oflong-term and intensive observing cam paign. W e run a dedicated list vsnet-cam paign-blazar101 for exchanging inform ation on blazar activities and upcom ing collaboration w ith other world-w ide blazar groups. From the very establishm ent of the W hole Earth B lazar Telescope (W EB T : V illata et al. 2002b),102 we have been continuously in collaboration w ith this group. In addition to continuous visualm onitoring cam paigns on strongly activeblazars,such asO J 287,M arkarian 421, 3C 279,quick electronic circulation and prom pt feedback via the V SN ET discussion group led to the notable discovery ofunexpectedly large,short-term intranight variation of B L Lac in 1997.103 T his intensive observation was initiated by a report ofa bright state of B L Lac in IA U C (M attox et al.1999),w hich initially revealed \outbursts" every ve to ten days. Follow ing this stage,the object entered a m ore active phase in m id-July to early A ugust. D uring this stage, real-tim e com parisons of visual observations through the V SN ET discussion group revealed substantialdiscrepanciesdepending on observers’ longitudes. T hese discrepancies,w hich were m uch larger than w hathad been recognized asblazarm icrovariability, were initially considered as a result ofan inhom ogeneous m agnitude system . T his possibility was soon disproved by the real-tim e distribution ofthe m odern photoelectric com parison starm agnitudes.B y the end of1997 July,the incredible short-term variation (0.8 m ag in four hours)in B L Lac had becom e a doubtless phenom enon. In response to these visual observations, the K yoto U niversity team obtained long tim e-resolved C C D photom etry at O uda Station, revealing the unprecedented com plexity and fast variation in the light curve. A sim ilar conclusion was reached w ith tim e-resolved C C D pho99

100

101

102 103

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-cam paign-deltavel/m aillist.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/vsnet-ecl/ m aillist.htm li. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-cam paign-blazar/m aillist.htm li. hhttp://w w w .to.astro.it/blazars/w ebt/i. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/B LLA C /bllac.htm li.

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tom etry by Tonny Vanm unster, w hich was also rapidly com m unicated via V SN ET . T he variation has a powerlaw tem poralproperties,analogousto those ofA G N variability (although the variation in B L Lac was m uch m ore violentand rapid),w hich can betracked dow n to vem inutes. T hisis one ofthe shortesttim e scaleseverrecorded in blazar opticalvariation (M atsum oto et al.1999). T he early results by the V SN ET team were presented at the 23rd IA U G eneralA ssem bly held in K yoto held in 1997 A ugust. Since then,severalstudies have been perform ed in collaboration w ith the W EB T (R avasio et al.2002;V illata et al.2002a). Long-term light curves ofselected blazars from V SN ET observationshave been w idely used forcorrelation w ith m ultiwavelength data. 6.15. G am m a-Ray Bursts T he V SN ET collaboration team hastried to search opticalafterglow s ofG R B s and reported their detection or upper-lim its of m agnitudes. Earlier announcem ents of B eppo Satellite per A stronom ia X (B eppoSA X ) G R B detectionswere reported to vsnet-alert.Since 2000 June,we set up a dedicated list for G R B announcem ents (vsnetgrb).104 T his m ailing list is currently em ployed to distribute satellite-borne alerts, as a secondary distribution node ofthe G R B C oordinatesN etwork (G C N ).105 A public m ailing list vsnet-grb-info,106 originally extended from vsnet-grb, currently provides G C N C ircular inform ation as well as our ow n observations by the V SN ET C ollaboration. Table 3 sum m arizes our ow n G R B afterglow observations (not allobservations are listed),w hich is an extension oftable 1 in Yam aoka et al.(2003b). See the corresponding G C N C irculars for m ore details. H ere we sum m arize oursigni cantdetections and their im portance in G R B astronom y: G R B010222: O ur observation of the afterglow of G R B 010222 covered a period around the jet break (U em ura et al.2001a). T his is the rst detection ofthe G R B afterglow in Japan.107 T his observation encouraged observers having sm alltelescopes in Japan to try observations ofG R B afterglow s. G R B020331: W e succeeded in observing an early afterglow w ith R c = 17:9 (17.5{18.7;1- lim its) 64 m in after the burst(K ato etal.2002r).T hisisthe earliestobservation for this afterglow .O ur observation revealed that the lightcurve can be described w ith a single power-law from the early phase ( 1 hr) ofthe afterglow . G R B021004: O w ing to the prom pt identi cation by the H ET E-2 satellite (Shirasaki2002), we rst revealed the continuousbehaviorofthe G R B afterglow around 1 hraf104

105 106

107

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/vsnet-grb/ m aillist.htm li. hhttp://gcn.gsfc.nasa.gov/i. hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/ vsnet-grb-info/m aillist.htm li. T he rst detection w ith a Japanese telescope w as the infrared afterglow ofG R B 000926 observed w ith the Subaru telescope in H aw aii(K obayashiet al.2000).

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T able 3. G R B A fterglow s observed by the K yoto team .

G R B nam e 001025A 001025B 001212 010214 010220 010222

A lert type IPN IPN IPN SA X SA X SA X

011030 011130 020124 020331 020812

SA X H ET E H ET E H ET E H ET E

020813 020819 020903 021004 030227 030329

H ET E H ET E H ET E H ET E H ET E H ET E

Epoch (d) 1.7 1.6 2.0 0.29 1.5 0.23 0.55 0.28 0.47 0.079 0.033 0.018 0.038 0.36 0.14 0.18 0.036 0.046 0.053

Telescope (cm ) M agnitudey 60 > 18.0 60 > 19.0 25 > 17.5 30 > 18.0 30 > 17.5 30 17.8 30 19.3 25 > 16.0 25 OF 25,30 OF 25,30 17.9 60 > 21.2 25,30 > 19.1 60 19 60 > 15.0 25 O F or > 17.5 25,30 16.3 25 > 18.0 25,30 12.6

G C N C ircular 866 (U em ura et al.2000a) unpublished 902 (Ishioka et al.2000b) 948 (U em ura et al.2001d) unpublished 984 (U em ura et al.2001a) unpublished unpublished unpublished 1363 (K ato et al.2002r) 1515 (O hashiet al.2002) 1521 (U em ura et al.2002a) unpublished unpublished 1537 (U em ura et al.2002b) 1566 (U em ura et al.2002c) 1899 (U em ura et al.2003a) 1989 (U em ura 2003), 1994 (U em ura et al.2003f), 2147 (Yam aoka et al.2003a) 2252 (U em ura et al.2003b) 2370 (Im ada et al.2003)

030528 H ET E 0.004 25 > 16.0 030823 H ET E 1.24 60 > 20.5 D ay after the burst detection. y U n ltered C C D or R c m agnitude. O F = opticalcounterpartout ofthe eld ofview . terthe burst(U em ura etal.2002c;U em ura etal.2003d). A n early afterglow wasalso observed in G R B 990123 (Sari, Piran 1999a),however,our observation covered a period corresponding to an observing gap of the early afterglow light curve of G R B 990123. In the light curve of G R B 021004,the initial fading phase was term inated by a short plateau phase that lasted for about 2 hours from 0.024 to 0.10 d after the burst (U em ura et al. 2003d). T he object then entered an ordinary power-law fading phase.W eproposethattheplateau phaseisevidencethat the m axim um ofthe synchrotron em ission from a forward shock region appears around 0:1 d after the burst,as expected from theoreticalcalculations(Sari,Piran 1999b; K obayashi,Zhang 2003). T he initialfading phase can be interpreted aspartoftheoptical ash,w hich wasrecorded in G R B 990123. Ifthis is the case,the color ofthe afterglow would have dram atically changed from blue to red around the m axim um ,w hile no colorinform ation isavailable in this early phase (Sariet al.1998). D etections the color change in the early phase w illbe an im portant future step for G R B astronom y. O n the other hand, the feature around 0.1 d afterthe burstcan be one ofa series ofbum ps observed 1 d after the burst (N akar et al.2003; Lazzatiet al.2002;Fox et al.2003;Schaefer et al.2003; Li,C hevalier 2003).

of the G R B afterglow (Vanderspek et al. 2003; G reiner et al.2003;C aldwellet al.2003). W e detected a bright, 12th-m ag optical afterglow 76 m in after the burst (Peterson,Price 2003;Torii2003;U em ura et al.2003f). W ith theinternationalcollaboration through theV SN ET , we obtained an 11 hr continuous light curve ofthis afterglow (U em ura et al.2003e). O ur observation revealed that the afterglow experienced repetitive m odulations even in the early phase ofourobservation.In conjunction w ith public data reported to the G C N C irculars,the light curve was rich in unexpectedly com plicated structures throughout 6 days after the burst. It is a surprise that the am plitude of m odulations was alm ost constant w ith tim e. T his feature of m odulations is di cult to be understood w ith density variations of the interstellar m edium (N akar et al. 2003). T he energy in the shock region m usthavechanged w ith tim e,w hilethem echanism to generate additionalenergy is an open issue (U em ura et al. 2004b). T he V SN ET team also contributed to a anothercollaborative work on the earlieststage afterglow (Toriiet al.2003). 7. C onclusion

Variable Star N etwork (V SN ET ) is a global professional-am ateur network of researchers in variG R B030329: T he world-fam ous \m onster G R B " able stars and related objects, particularly in transient G R B 030329 ( gure 19)occurred closestto us(z = 0:168), objects,such ascataclysm ic variables,black hole binaries, w hich gave a chance forusto study the detailed structure

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F ig. 19. Fading afterglow of G R B 030329. T he im ages w ere taken by the V SN E T C ollaboration. T he individualim ages (from left top to right bottom ) correspond to 1.27,3.37,8.18 and 28.65 hr after the gam m a-ray burst.

supernovae and gam m a-ray bursts. T he V SN ET has been playing a pioneering role in establishing the eld of transient object astronom y, by e ectively incorporating m odern advance in observational astronom y and global electronic network, as well as collaborative progress in theoreticalastronom y and astronom icalcom puting. T he V SN ET is now one ofthe best-featured globalnetworks in this eld of astronom y. W e review on the historical progress,design concept,associated technology. W e also review on the breathtaking scienti c achievem ents, as wellas regular variable star works,particularly focusing on dwarfnovae (discovery ofER U M a stars,worksin W Z Sge-type dwarf novae, m ore usual SU U M a-type dwarf novae,eclipsing dwarfnovae),black hole X -ray transients (discoveries of an unexpected violent outburst of V 4641 Sgr,rapid opticalvariations from the sam e object),and recent achievem ents in gam m a-ray bursts. W e are grateful to Seiji M asuda and K atsura M atsum oto,w ho greatly contributed to the activities of theV SN ET adm inistratorgroup.W earegratefulto m any V SN ET m em bers w ho have been continuously supporting our activity. W e are grateful to Em ile Schweitzer (A FO EV ),K eiichiSaijo and M akoto W atanabe (V SO LJ) for kindly allow ing us to use A FO EV and V SO LJ public database for draw ing light curves. W e are also grateful to D ave M onet for m aking U SN O A 1 C D -R O M s readily available for us. T his work is partly supported by a grant-in-aid [13640239,15037205 (T K ),14740131 (H Y )]

from theJapaneseM inistry ofEducation,C ulture,Sports, Science and Technology. Part of this work is supported by a R esearch Fellow ship of the Japan Society for the Prom otion of Science for Young Scientists (M U , R I). T his research has m ade use of the astronom ical catalogs at A stronom icalD ata C enters operated by N ational A stronom ical O bservatory, Japan, and N A SA . T his research hasalso m ade use ofthe D igitized Sky Survey producted by ST ScI,the ESO Skycat tool,the V izieR catalogueaccesstool,and theElectronicEdition oftheG C V S. A ppendix 1. P oster P resented at the 23rd IA U G eneral A ssem bly D evelopm ent of a M ailing List on V ariable Stars, V SN E T (D aisaku N ogam i,TaichiK ato, H ajim e B aba,C hatiefK unjaya) A bstract A sthecom puterenvironm enthasbeen developing drastically these years, the style of astronom ical study has been changed.T hekey wordsofthesechangesarethought to be \real-tim e" and \interactivity". Suspecting that they havepotentialto m adean greate ecton thestudy of transientobjects(cataclysm ic variables,X -ray binary,supernovae,and so on),we setup the m ailing list,V SN ET , in 1994. O ur policy on V SN ET since the start is that V SN ET isworld-w idely opened to any kindsofresearchers

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including professionals and am ateurs,observers and theorists. Subscribers have increased as tim e goes and now are over 400 from over 40 countries. A lthough V SN ET started asa m ailing list,it atpresentconsists of ve subm aling lists,vsnet:vsnet-alert,vsnet-obs,vsnet-chat,and vsnet-chart,and each of these lists works independently for di erent purposes. U sing the di erent characteristics ofthesesub-liststo advantage,varioustypesofstudy have been proposed and carried out. V SN ET w ill be developed further w ith cooperation ofsubscribers.Ifyou have any com m ents or questions, please feel free to contact w ith V SN ET adm inistrators(vsnet-adm @ kusastro.kyotou.ac.jp). Introduction T he com puter environm ent is m aking rem arkable progress w ith developm ent ofthe infrastructure and the m achine power. T he W orld-W ide W eb (W W W ,B ernersLee et al. 1992) is explosively com ing into w ide as well, redraw ing the com m on sense on the inform ation distribution. T hese have an great a ect on the astronom icalstudy, forexam ple,1)thecom plicated rapid controloftelescopes (adaptive optics,etc.) becom es possible, 2) the scale of sim ulations are getting m uch larger,3) editors ofvarious journals encourage the electronic subm ission,4) the electronic publication ofpapers on W W W or by C D -R O M is discussed and partly realized , 5) IA U circulars are distributed by e-m ail, 6) preprints are usually distributed by e-m ail or on web pages (e.g. http://w w w .lanl.gov, G insparg 1996),7)the search ofpapershasbecom e quite easy by the foundation ofthe A strophysics D ata System (N A SA ,A ccom azziet al. 1995),and so on. T hekey wordsofthisrevolution arethoughtto be\realtim e" and \interactivity". Is there a possibility for these characteristics to be quite useful in the study of transient objects? W e had an eye on the m ailing list since the system m akes it possible to share m uch inform ation am ong m uch people quite quickly and can be used interactively by m uch people. T hen, in July 1994, we started a m ailing list, V SN ET (vsnet@ kusastro.kyoto-u.ac.jp),m ainly on cataclysm ic variables,supernovae,X -ray binaries,and so on, w ith a policy thatwe aim to m ake a contribute to the astronom icalcom m unity by providing a m echanism to m ake inform ation shared and a room to discussallaspectsofthe astronom y concerning those transientobjectsam ong subscribers from allover the world irrespective ofthe status (an am ateur or a professional),the style ofastronom ical study (an observer or a theorist),and other properties. H istory ofV SN ET T he rst m em ber of V SN ET is several tens of am ateurs belongs to am ateur associations (T he A m erican A ssociation of Variable Stars (A AV SO , see http://w w w .aavso.org/), A ssociation Francaise des O bservateursd’EtoilesVariables(A FO EV ),Variable Star O bserverLeaguein Japan (V SO LJ),and so on)and a few tensofprofessionals.Subscribers,then,have increased by

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m ouse-to-m ouse advertising and ourinvitation to authors of papers in astronom icaljournals. N ow the num ber of subscribers from about 50 countries exceeds 400, w hich m eans that m ajor part ofresearchers in this eld has already subscribed. A t rst, all e-m ails other than adm inistrative ones for subscription and unsubscription were distributed to all subscribers. H owever, accepting a request m ainly from theorists that they do not need daily data but want to know nal results deduced from observations, we m odi ed the system of V SN ET to divide V SN ET to three sub-m ailing lists in O ctober 1994, 1) vsnetobs(vsnet-obs@ kusastro.kyoto-u.ac.jp)forreporting daily observations, 2) vsnet-alert (vsnet-alert@ kusastro.kyotou.ac.jp) for alert on the discovery of supernovae, novae, rare outbursts, discovery of new variable star, dram atic change of know n variable stars, and so on, and 3) vsnet (vsnet@ kusastro.kyoto-u.ac.jp) for the generalinform ation not suited for the form er two lists, for exam ple, com plied data, nding charts,preprints,callsforobservations for internationalco-observation cam paigns,and so on. In orderto referto an old log correctly,serialnum bersin the subject were added as [vsnet-obs 1997]since January 1995. In June 1995, the V SN ET W eb pages (http://w w w .kusastro.kyoto-u.ac.jp/vsnet/) were opened.You can see allarticleseverposted to V SN ET on W W W .You can see lightcurvesdraw n from observations distributed via vsnet-obs in the recom m ended form at, too. T he m ost im portant results am ong vsnet-alert logs and public inform ation like conference announcem ent are gathered on the top page alm ost daily up-dated. M any useful tools developed and provided by various groups are available on the pages as well. A t the sam e tim e we started V SN ET anonym ous ftp service (ftp.kusastro.kyoto-u.ac.jp/vsnet/) w here you can get objects alm ost sam e as on W W W . In January 1997,we m ade an addition of a new subm ailing-list of vsnet-chat (vsnet-chat@ kusastro.kyotou.ac.jp) in order to discuss various subjects. T hough V SN ET was used nearly only for distribution of inform ation,this m odi cation w idened the usage ofV SN ET . H aving the background as m entioned here,V SN ET at present consists of four sub-m ailing-lists (vsnet, vsnetalert,vsnet-obs,and vsnet-chat) as wellas V SN ET W eb pages and anonym ous ftp service. H owever, one of the sub-lists,vsnet,is now closed,since com m ercialinform ations never related to astronom y, so-called SPA M , were posted again and again. T his type ofproblem ,although com m on to allm ailing lists,is hard to com pletely solve. T he num ber ofe-m ailposted to vsnet-obs,vsnet-alert, and vsnet-chat is 20-40, a few , 5 per day, although changing from day to day. Tables show severale-m ails posted to V SN ET andfigures show light curves available on W W W .

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acters.Since a fulldescription ofthe form atused in these data or lesm ay notbe necessary to allreaders,the m inT he m ajor usages ofV SN ET are 1) to forecast the be- im alrequirem ents to interpret the data w hich are m ade havior ofvariable stars from daily observations available available through the V SN ET W orld-W ide W eb service. via vsnet-obs and plot a strategy of the observation, 2) Each line contains the follow ing item s. to check the status ofa variable star in opticalon vsnet(a) N am e ofthe object obs at the tim e ofthe observations in U V or X -ray,3) to (b) T im e ofthe observation in decim als ofU T publish new results on vsnet-alert (discoveries of super(c) O bserved m agnitude novae, determ ination of superhum p period in SU U M a(c’) M agnitude system (C C D /photoelectric)or lm and type dwarf novae, and so on), 4) to call the follow -up lter (photographic) observationsoftransientobjectsdetected in U V orX -ray, (d) O bserver’scode 5)to callthe co-operation forinternationalco-observation cam paigns,6) to notify conferences new ly held,7) to disT hese item s were designed to express originalobservacuss various subjects ranging from the rst step of the tionsasexactly aspossible (m ainly in term sofsigni cant observation to theoreticalinterpretations ofnew interest- digits). C om parison stars,charts used,or any other text ing phenom ena, and so on. For reference, tables list a inform ation can be w ritten as a com m ent follow ing the part ofsubjects ofe-m ails posted to V SN ET .T hese us- item (d);they are usually used for future reference or exages would be born in the active environm ent under the am ination,and notdirectly used atpresentin the V SN ET com plex of\real-tim e",\interactivity",and the V SN ET regular database m anagem ent. policy. Each item is separated by one or m ore space characIn addition, new original applications of V SN ET are ters(A SC IIcode 20 in hexadecim al)and doesnotcontain appreciated alltim e,and,actually,w illbe proposed.W e, spaces w ithin the item . V SN ET adm inistrators, would be m uch glad if studies com pleted on use of V SN ET contribute to the progress (a) N am e ofthe O bject of astrophysics. If you have any questions, requests, T hisisan identi erfortheobject.Ifthenam eisunique and suggestions, please do not hesitate to com m unicate enough to discrim inate the objectfrom othercelestialobw ith V SN ET adm inistrators(vsnet-adm @ kusastro.kyotojects, any expression is basically allowed; the use of the u.ac.jp). nam es listed in the G eneralC atalogue of Variable Stars Part of this work was supported by a R esearch (G C V S), B eyer nam es, num bers in the N ew catalogue Fellow ship of the Japan Society for the Prom otion of ofSuspected Variable Stars (N SV ),and D urchm usterung num bers (B D , C D , C PD ), however, is strongly recom Science for Young Scientists (D .N .). m ended. W hen there is no speci c relevant catalog,the R eferences use ofG SC and U SN O identi er can be used. For G C V S and B eyer nam es,three-letter IA U code of A ccom azzi,A .,Eichhorn,G .,G rant,C .S.,M urray,S. cons tellation (in upper-case letters) precedes the nam e of S.,and K urtz,M .J.1995,V istas in A stronom y 39,63 t he s tar in the constellation. G reek letters are w ritten in B erners-Lee, T . J., et al. 1992, in \Electronic t he s t andard English expressions. N etworking:R esearch,A pplicationsand Policy" (M eckler Publishing,W estport),Vol. 2,N o.1,p52 Exam ples: A N D R for R A nd, G insparg,P.1996,http://xxx.lanl.gov/blurb/ O R Ialpha for B etelgeuse ( O ri) pg96unesco.htm l Translation of reported nam es into standard expresA ppendix 2. V SN E T D ata R eporting System sions,w hen necessary,is perform ed either autom atically orm anually using the A LIA S database.T hisprocessparA s described in subsection 2.1,the V SN ET data han- ticularly becom es necessary w hen new G C V S nam es are dling, database m anaging, and data analysis tools are released in the form ofregularnam e-listupdates,orw hen m ostly com m on to the ones developed for the V SO LJ a new G C V S designation is given for a new nova. A ll database project (K ato 1990a), and later adapted for the nam e translation rules are centralized in the A LIA S w ider range of observations. T he program s were origi- databaseand re ected on the entireV SN ET system ,elim nally w ritten form icrocom putersrunning on M S-D O ST M , inating additionale ortsto m odify individualobservation and later ported to Linux. T he follow ing inform ation is reports or expressions in V SN ET circulars. T his is an m ainly an excerptfrom K ato (1990a),partly rew ritten for great advantage of the V SN ET database m anaging prothe recent changes for the V SN ET m anagem ent. cess, and a new ly released nam e-list update (containing som e hundreds ofnew ly designated variable stars)can be A .2.1. Electronic Form atofO bservations usually re ected w ithin a day oftherelease.O bserversare T he V SN ET reporting form at is an U T extension of allowed to continueusing theold expressionsaslong asthe the V SO LJ electronic reporting form at,w hose design was expressionscan be uniquely and autom atically translated established in 1987. T he standard form at V SN ET obser- into the new expressions. vations are com posed oflines separated by new -line charV SN ET :N ow and Future

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(b) T im e ofthe O bservation In order to facilitate detecting errors by eye,tim es are expressed in the follow ing decim alform at using U T C . Exam ple: 20030701.123 (2003 July 1.123 U T C ). N o heliocentric or barycentric corrections are introduced at this stage. T he conversion to TA I or T D (in any expression including Julian D ate),or helio-(or bary)centric corrections are left to data analysis software and users. T hese m easures are partly because w idely used software packages at the observer’send are know n to frequently contain problem s. T he other reason is that leap secondsdo not allow to distribute xed tables for conversion beforehand. (c) O bserved M agnitude D ecim al points are explicitly used to show the significant digits. U pper lim it observation (non-detection) is expressed by a pre x ‘< ’. Expression m ay be followed by one of‘:’ or ‘?’ to show uncertainty. (c’) M agnitude System ,Film and Filter If the observation is visually perform ed, this item is not necessary. O therw ise,the code ofthe m agnitude system (or the lm and the lter ifthe observation is done photographically) follow s the item (c) w ithout placing a space. W ell-de ned standard photoelectric system s (e.g. Johnson-C ousinsU ,B ,V ,R c,Ic,R j,Ij)system sare used as in usual sense. O ther V SN ET -speci c codes include \C " (unspeci ed un ltered C C D m agnitude),\C R " (unltered C C D m agnitude calibrated on R c-band) and \p" (unspeci ed photographic m agnitude). T he com plete list ofthe codesrepresenting the lm sand ltersatpresentis available at the V SN ET website.108 Exam ple: < 15.5R c (fainter than 15.5 in R c-band) (d) O bserver’s code T he code is usually a three-letter code, as canonically used by the A m erican A ssociation ofVariable Star O bservers(A AV SO )109 and the V SO LJ.T he code m ay be im m ediately followed by a period m ark (‘.’) and the organization code. W hen there isno xed a liation forthe observer,the V SN ET m anagergroup issuesa code,w hich schem e also enables archiving historicalor literature observations. W ith this form at,each line ofobservation has allinform ation in itself;any operation ofm oving linesin a data le (such assorting)doesnota ectthepropertiesofthedata. T he above design ofelectronic data hasgreatly facilitated overallaspects of the follow ing electronic data m anagem ent,and thispioneering concepthasbeen taken overby a num ber ofworld-w ide variable star organizations. 108 109

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/etc/form at.htm li. hhttp://w w w .aavso.orgi.

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A ppendix 3. D esign of the V SN E T D atabase M ost of program s are w ritten in the language C , and were originally com piled w ith Turbo-C (B orland International). M any of m achine-independent source codes (handling text-based data) can be com piled by A N SI C (A N SI X 3.159) com pilers (such as gcc) w ithout m uch correction. In the actual V SN ET database m anagem ent,these codesare eithercom piled on W indow sT M /D O S personalcom puters,orLinux workstations. M ostofthe text-based worksare currently done on Linux workstations. B esides storing originaldata as text les (as reported in vsnet-obs),they are also incorporated into an observationaldatabase in rew ritable m edia allow ing random access. Severalinteresting graphic program sand data analysisprogram srun in thism ode.T he m axim um num berof observations handled at one tim e depends only on capacity ofthe m edia and the addressing capacity ofthe operating system . For exam ple,we now handle dynam ic and random access to the entire V SN ET observations, consisting ofm ore than 1.2 m illion visualobservations( 130 M B ) ofrandom ly accessible data,and we have registered m ore than 1.3 m illion C C D observationssubm itted to the V SN ET C ollaboration. W e have also con rm ed that a com bination test of the V SN ET , V SO LJ and A FO EV public data (about3 m illion observation)hasyielded satisfactory e ciency ofhandling a hugevolum e ofrandom ly accessible data. In addition to the observationaldatabase,there also existothersystem databasesincluding VA RT Y PE (database on individualvariable star types),and A LIA S (nam e resolver database). A program m er on this system can inquire these databases for the type of variability or the standard expression ofthe nam e for the object speci ed by a given identi er. A .3.1. Structure ofthe D atabase B ecause the num ber ofthe data or the objects is very large,and both random and sequentialaccessesare necessary foreasy operation on thelightcurves,weadopted the com bination ofB + tree and bidirectionallinear list. T his basic structure ofthe database was originally established in 1989 to fully incorporate the V SO LJ database. C om plete data ofobservations(otherthan rem arks)are stored in a le equivalent to an index le ofan relational database,and there is no need for reading an additional data le. T he size of a storage block is 16 kilobytes, but this can be m odi ed upon di erent com pilation. T he m ain m em ory is dynam ically allocated to sim ulate a virtualm em ory in order to m inim ize access to the storage m edia. W ith thisfeature,the m ain database m odule only requires an order ofa few hundreds ofm egabytes of actualm em ory. T he kernelofthe database m odule is w ritten transparently to theupperm odules,so upperm odules haveonly to passthe key orthe virtualaddressto the kernelto inquire the nextorthe previousdata. T he m odules are w ritten to enable sim ultaneous handling of m ultiple databases (e.g. observationaldatabase and VA RT Y PE)

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w ithoutinterference.T hedatabasefunctionsareprepared circ autom atically produces V SN ET C V C irculars. asa form ofC -languagebased application interface(A PI), butweskipped thedetailsofindividualA PIsbecausethey A .3.4. D ata Processing are too technicalto be presented in this paper. B esides draw ing light curves, there also exist several kinds of scienti c data-analysis program s. Som e require A .3.2. Basic C om m and O perations databases and others require only data les in the text B asic useroperationsto the database can be perform ed form at. A few sam ples are show n here. M any of the TM by com m and-line tasks on M S-D O S or Linux. T he general-purpose program s(m ostly w ith source codes) are m ost frequently used and basic com m ands include: available from the V SN ET website \Toolsand Program s" section.110 inittree creates a new database. m rg m erges a text le to a database. H eliocentric and Barycentric C orrections vdel deletesdata speci ed by a text le from a database. vm rg m ergesan observationaldata lein thestandard forW e have im plem ented both conventional heliocentric m at to the observationaldatabase,and lists potencorrectionsforthe observed JD s,by using the well-know n tialerrors by referring to the previously registered N ewcom b’sexpansion ofthe planets. W e have also im pledata and VA RT Y PE database. m ented barycentriccorrectionsby num erically integrating vcut lists data ofa given objectfor a given chronological the D E 200 ephem eris produced by N A SA .T he original period. source code ofthe D E 200 ephem eris was im ported from vren replaces an identi er for an object by another. a software package w ritten by M r. N ovas. vlist lists alldata in a database. liststar lists allstars in a database. Period A nalysis Tools seltype selects data from a text le by specifying types of W e have our ow n im plem entations ofD iscrete Fourier variability,by referring to the VA RT Y PE database. chknew checks observation data le if they contain new ly Transform (D FT ),PhaseD ispersion M inim ization (PD M : reported objects by com parison w ith the existing Stellingwerf 1978), D iscrete W avelet Transform (D W T : Foster 1996) and other period analysis tools. T he PD M observationaldatabase.. chkstd checks observation data le for gram m ar,and lists package was ported to W indow sT M by A ndreas W ijaya, discordant data and potential errors by referring and has been conveniently used by m any users. to the previously registered data and VA RT Y PE C V C irculars database. looktype returns the variable star type by referring to the C V C irculars were originally prepared m onthly and isVA RT Y PE database. sued by theV SO LJ,from theobservationsreported by the settype sets or m odi es the variable star type in the end of the next m onth. In the m odern V SN ET service, VA RT Y PE database. these circulars are issued alm ost daily to fully incorpocalias convertsa variable starnam e to the standard nam e rate the daily changes in the rapidly varying C V s. T he by referring to A LIA S database. corresponding list is vsnet-cvcirc.111 alias sets or m odi es the entry in the A LIA S database C V C irculars contain inform ation about all reported (this com m and has a di erent nam e on Linux beoutbursts and standstills of dwarf novae in the form of cause of the collision w ith the shell built-in com nightly averages, and nightly averages of other peculiar m and). objects(C V sotherthan dwarfnovae,X -ray binaries,sym M ost basic operations on the V SN ET data are done biotic variables,eruptive variable such as R C rB stars,S w ith these basic com m ands,and are frequently used as a D or stars,FU O ristars,and supernovae,active galactic nucleiand other objects ofspecialinterest). com bination regulated by a shellscript. U npredictable variations ofbrightness ofthese objects A .3.3. D ata A nalysis A pplication Program s m ake it extrem ely di cult to check observations as auM ost ofthese program suse a G U I.T hese packages are tom atically done for pulsating variables. Together w ith architecture-speci c, and presently run in lim ited envi- faintnessofthese objects(w hich im pliesexistence oflarge ronm ents(e.g. N EC PC 9801 m achines),although e orts num ber of negative observations), cross checks between di erent observersare indispensable. havebeen taken to portthese applicationsto W indow sT M T he present program circ, referring to a list of m ore operating system ,or to w rite an equivalent w rapper G U I applicationsw ritten in JavaT M .Figure 20 show sa sam ple than 1000 objectscontaining theirproperties(typeofvariability,norm alrange ofvariation,ephem erides ofeclipses im age by grp interactive light curve viewer program . etc.),checks allobservations using databases. T he list is grp displays light curves,and enables interactive zoom updated by the editorw henevernew inform ation becom es ing,data selection,data editing. available in order to m aintain circulars up-to-date. autogrp displays and prints light curves autom atically. A n 110 hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/etc/prog.htm li. TM equivalent package w ritten in Java is presently 111 hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/vsnetused to produce V SN ET online light curves. cvcirc/m aillist.htm li.

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F ig. 20. Sam ple im age by grp interactive light curve view er program . T he light curve is B L Lac from V SN E T observations. W hite and red m arks represent positive and upper lim it observations,respectively. T he program enables interactive G U I-based operation on photom etric database constructed on the database engine described in A ppendix 3.1.

T he results are then listed as a le in the prototypical form ofC V C irculars,containing thereportsofpotentially discordant data (or rapid intrinsic changes) w ith special m arks. T he present version can handle m ore than tens ofthousands ofobservations per m onth,and produces a circular in a m inute. T he sam e program ,slightly m odi ed to produce longterm averages,is used to produce V SN ET M ira C irculars vsnet-m iracirc.112 A ppendix 4. C hart-P lotting Identi cation P rogram

and

Star

W hen identifying variable stars and locating the C C D eld of view , chart-plotting and star identi cation program s are very useful,particularly w hen the network resource was unavailable. For this purpose,one ofthe authors (T K ) developed in 1990 a chart-plotting com puter program , w hen m achine-readable G uide Star C atalog (G SC )1.0 (Laskeretal.1990)wasreleased.T he program was designed to run on a stand-alone personalcom puter running on M S-D O ST M non-extended (less than 640 K B ) m em ory. Since the distribution form ofG SC 1.0 wascom posed of huge A SC IItableson two C D -R O M s(1.2 G B ),and since 112

hhttp://w w w .kusastro.kyoto-u.ac.jp/vsnet/M ail/vsnetm iracirc/m aillist.htm li.

theobjectswererandom ly arranged w ithin individual les covering 2{3 degrees square,it was an absolute requirem ent to com pressthese data and m ake them quickly and random ly accessible. In this software,we subdivided the entire G SC data into 0.5 degree bins in declination,and sorted the objects w ithin the sam e bin according to right ascension. In order to com press the data, we used binary les w hich can be directly m apped in C structure. In order to avoid redundancy in right ascensions and enable quick random access,we used a separate jum p table w hich recordsthe lepositionsofgiven coordinatem eshes. Individualentries in the 0.5-deg bins only contain residuals to the m esh coordinates. In originalcom pression of G SC 1.0,each catalog entry corresponded to 5 bytes. B y com bining theinform ation ofcoordinatem esh in thejum p table and the individualentries,one can obtain the fully decoded coordinates. T hese functions (including sequentialreading functionsofa given box)wereim plem ented as transparentA PIs,m any ofw hich were designed to take a pointer to the display function as a call-back function. W ith this com pression, the entire G SC 1.0 (disregarding the object nam es,plate num bers) can be com pressed into 100 M B .T his program was one ofthe earliestchartplotting software packages that used G SC as source catalogs and im plem ent encoded com pressed catalogs, and the design wastaken overin varioussuccessivethird-party applications. T he program is also able to display G C V S and N SV variable star catalogs,and IR A S PSC objects,

44

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w hich were com pressed in a sim ilar m anner em ployed in G SC com pression. T he program was later updated to accom m odate G SC 1.1 (Lasker et al. 1996) and U SN O A 1.0 (M onet et al. 1998a)catalogsin 1998,and othercatalogs(w ith variablelength object labels). W ith the increase of capacity of storage m edia,the present version uses 12 bytes for one G SC 1.1 fullentry and 8 bytes for one U SN O A 1.0 entry. W ith this com pression m ethod, the entire U SN O A 1.0 data (m ore than 4.8 108 objects) can be stored in 4 G B storage and can be quickly and random ly accessed. T he present version is equipped w ith a function to handle the 2M A SS point source catalog in the sam e m anner. T he program also handles a nam e resolver by using the sam e database engine described in A ppendix 3.1. T he entire program is presently ported to W indow sT M and Linux using xlib graphic library (see gure 21 for an exam ple). W ith thisprogram and A PIs,onecan very quickly identify new and know n variable stars either interactively or in a batch. O nline V SN ET charts w ith H ipparcos and Tycho m agnitudes(subsection 2.2)have been prepared w ith this software operated in a batch m ode. T he objectdatabases have been regularly updated,especially w hen a nam e lists for new variable stars is released. T he source codes are available upon request to the author. R eferences A ikaw a,T .1985,A p& SS,116,401 A k,T .,O zkan,M .T .,& M attei,J.A .2001,A & A ,369,882 A llen,D .A .1984,Publ.A stron.Soc.A ustralia,5,369 A nupam a,G .C .1992,PA SP,104,308 A nupam a,G .C .,& D ew angan,G .C .2000,A J,119,1359 A rkhipova,V .P.1994,Pis’m a A Zh,20,919 A rkhipova,V .P.1996,Pis’m a A Zh,22,828 A rkhipova,V .P.,& Esipov,V .F.1996,Pis’m a A Zh,22,264 A rkhipova,V .P.,et al.1998a,Pis’m a A Zh,24,297 A rkhipova,V .P.,Esipov,V .F.,& Sokol,G .V .1998b,Pis’m a A Zh,24,431 A rkhipova, V . P., Esipov, V . F., Sokol, G . V ., & Shugarov, S.Y .1999a,A stron.Letters,25,739 A rkhipova,V .P.,& N oskova,R .I.1997,Pis’m a A Zh,23,709 A rkhipova,V .P.,N oskova,R .I.,Esipov,V .F.,& Sokol,G .V . 1999b,A stron.Letters,25,615 A rkhipova,V .P.,Zaitseva,G .V .,Ikonnikova,N .P.,N oskova, R .I.,& Shugarov,S.Y .1994,Pis’m a A Zh,20,916 A rkhipova,V .P.,Zaitseva,G .V .,Ikonnikova,N .P.,N oskova, R .I.,& Shugarov,S.Y .1996,Pis’m a A Zh,22,836 A rkhipova,V .P.,Zaitseva,G .V .,Ikonnikova,N .P.,N oskova, R .I.,Sokol,G .V .,& Shugarov,S.Y .1998c,Pis’m a A Zh, 24,427 A rkhipova, V . P., Zaitseva, G . V ., & N oskova, R . I. 1991, A stron.T sirk.,1547,9 A splund, M ., G ustafsson, B ., Lam bert, D . L., & K am esw ara R ao,N .1997,A & A ,321,L17 A splund, M ., Lam bert, D . L., K ipper, T ., Pollacco, D ., & Shetrone,M .D .1999,A & A ,343,507 A ugusteijn, T ., & Stehle, R .1995, in C ataclysm ic Variables, ed. A . B ianchini, M . della Valle, & M . O rio (D ordrecht: K luw er A cadem ic Publishers), 103 A ugusteijn, T ., van der H ooft, F., de Jong, J. A ., & van Paradijs,J.1996,A & A ,311,889

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F ig. 21. Sam ple chart ofV 4743 Sgr (N ova Sgr 2002 N o. 3). T he nova progenitor is m arked.

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K ato,T .1999d,Inf.B ull.Variable Stars,4764 K ato,T .1999e,Inf.B ull.Variable Stars,4768 K ato,T .1999f,Inf.B ull.Variable Stars,4769 K ato,T .1999g,Inf.B ull.Variable Stars,4788 K ato,T .1999h,Inf.B ull.Variable Stars,4789 K ato,T .1999i,Inf.B ull.Variable Stars,4790 K ato,T .1999j,Inf.B ull.Variable Stars,4791 K ato,T .1999k,Inf.B ull.Variable Stars,4799 K ato,T .1999l,V SO LJ Variable Star B ull.,33,3 K ato,T .2000,Inf.B ull.Variable Stars,4918 K ato,T .2001a,PA SJ,53,L17 K ato,T .2001b,Inf.B ull.Variable Stars,5071 K ato,T .2001c,Inf.B ull.Variable Stars,5092 K ato,T .2001d,Inf.B ull.Variable Stars,5093 K ato,T .2001e,Inf.B ull.Variable Stars,5102 K ato,T .2001f,Inf.B ull.Variable Stars,5104 K ato,T .2001g,Inf.B ull.Variable Stars,5107 K ato,T .2001h,Inf.B ull.Variable Stars,5110 K ato,T .2001i,Inf.B ull.Variable Stars,5122 K ato,T .2001j,Inf.B ull.Variable Stars,5137 K ato,T .2002a,A & A ,384,206 K ato,T .2002b,PA SJ,54,L11 K ato,T .2002c,PA SJ,54,87 K ato,T .2002d,Inf.B ull.Variable Stars,5316 K ato,T .2002e,Inf.B ull.Variable Stars,5243 K ato,T .2002f,Inf.B ull.Variable Stars,5346 K ato,T .2002g,IA U C irc.,7791 K ato,T .2003a,A & A ,399,695 K ato,T .2003b,PA SJ,subm itted K ato,T .2003c,PA SJ,in press (astro-ph/0308086) K ato,T .2003d,V SO LJ Variable Star B ull.,in press K ato,T .2003e,V SO LJ Variable Star B ull.,in press K ato,T .2003f,V SO LJ Variable Star B ull.,in press K ato,T .,B aba,H .,& N ogam i,D .2002a,PA SJ,54,79 K ato, T ., B olt, G ., N elson, P., M onard, B ., Stubbings, R ., Pearce,A .,Yam aoka,H .,& R ichards,T .2003b,M N R A S, 341,901 K ato,T .,D jam aluddin,T .,H irata,R .,& Saito,M 1990,IA U C irc.,5007 K ato,T .,et al.2002b,A & A ,396,929 K ato,T .,& D yck,G .1988,IA U C irc.,4575 K ato,T .,& Fujii,M .2001,Inf.B ull.Variable Stars,5150 K ato,T .,& Fujii,M .2003,IA U C irc.,8132 K ato, T ., G arradd, G ., Stubbings,R ., Pearce, A ., & N elson, P.2001a,Inf.B ull.Variable Stars,5117 K ato, T ., H anson, G ., Poyner, G ., M uyllaert, E., R eszelski, M ., & D ubovsky, P. A . 2000a, Inf. B ull. Variable Stars, 4932 K ato,T .,& H anzl,D .1993,IA U C irc.,5747 K ato,T .,& H aseda,K .2000,IA U C irc.,7553 K ato,T .,& H aseda,K .2003,Inf.B ull.Variable Stars,5417 K ato,T .,H aseda,K .,Takam izaw a, K .,K azarovets,E.V .,& Sam us,N .N .1998a,Inf.B ull.Variable Stars,4585 K ato,T .,H aseda,K .,Takam izaw a,K .,& Yam aoka,H .2002c, A & A ,393,L69 K ato,T .,H aseda,K .,Yam aoka,H .,& Takam izaw a,K .2002d, PA SJ,54,L51 K ato,T .,& H irata,R .1990a,Inf.B ull.Variable Stars,3489 K ato,T .,& H irata,R .1990b,Inf.B ull.Variable Stars,3529 K ato,T .,& H irata,R .1991,IA U C irc.,5262 K ato,T .,H irata,R .,& M ineshige,S.1992a,PA SJ,44,L215 K ato,T .,Ishioka,R .,& U em ura,M .2002e,PA SJ,54,1029 K ato,T .,Ishioka,R .,& U em ura,M .2002f,PA SJ,54,1023 K ato,T .,Ishioka,R .,& U em ura,M .2002g,PA SJ,54,1033

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