IV. 14 HERCULIS, HD 187123, AND HD 2102771. GUILLERMO GONzALEz,2 GEORGE WALLERSTEIN,2 AND STEVEN H. SAAR3. Received 1998 September ...
The Astrophysical Journal, 511:L111–L114, 1999 February 1 q 1999. The American Astronomical Society. All rights reserved. Printed in U.S.A.
PARENT STARS OF EXTRASOLAR PLANETS. IV. 14 HERCULIS, HD 187123, AND HD 2102771 Guillermo Gonzalez,2 George Wallerstein,2 and Steven H. Saar3 Received 1998 September 28; accepted 1998 December 1; published 1998 December 16
ABSTRACT Spectroscopic analyses of 14 Her, HD 187123, and HD 210277, recently reported to harbor planets, reveal that these stars are metal rich. We find [Fe/H] 5 0.50 5 0.05 , 0.16 5 0.05, and 0.24 5 0.05 for 14 Her, HD 187123, and HD 210277, respectively. This is the first spectroscopic analysis of HD 187123; our results for 14 Her and HD 210277 are in agreement with published studies. It is shown that 14 Her and r1 Cnc are nearly identical in their bulk physical characteristics. This result, combined with their extreme metallicities, suggests that their physical parameters have been affected by the process that formed their planets. These two stars join a group of about half a dozen stars in the solar neighborhood with [Fe/H] ≥ 0.4. It is also shown that 51 Peg and HD 187123, which have companions with similar orbital periods and masses, are nearly identical. We find v sin i ≈ 2.0 km s21 for HD 210277 from a high-resolution spectrum. Subject headings: planetary systems — stars: individual (14 Herculis, HD 187123, HD 210277) era and 4096 # 300 pixel UBC-1 CCD resulted in spectra with resolving power near 22,000, S/Ns between 200 and 250, and ˚ . A spectrum of spectral coverage from l 5 6350 to 6920 A 51 Peg was also obtained to compare with our analysis of this star in Paper II. A very high resolution spectrum of HD 210277 (l/Dl 5 125,000; 2 pixels) was obtained with the stellar echelle spectrograph and TI CCD detector (Smith & Giampapa 1987) at the McMath-Pierce solar telescope in 1994 October. Data reduction is described in Osten & Saar (1998); the reduced spec˚ , has S/N ≈ 160. trum, which spans l 5 6163–6182 A All three stars are sharp lined. The line widths are comparable to those of the solar spectrum reflected off Vesta, which was employed in the analyses of Papers I, II, and III. Highresolution spectra and intrinsically sharp lines are essential for the accurate measurement of equivalent widths in the spectra of cool dwarfs.
1. INTRODUCTION
Fuhrmann et al. (1997, 1998), Gonzalez (1997, hereafter Paper I), Gonzalez (1998, hereafter Paper II), and Gonzalez & Vanture (1998, hereafter Paper III) have reported on spectroscopic analyses of the parent stars of extrasolar planets. It was shown in Paper II that the then-known parent stars are, on average, metal rich compared to the metallicity distribution of nearby solar-type stars. Since then, several additional extrasolar planet candidates have been announced by the Lick and Geneva Observatory groups. Herein, we report on LTE Fe-line analyses of three of these: 14 Her (5HD 145675; Marcy, Cochran, & Mayor 1998b), HD 187123 (Butler et al. 1998), and HD 210277 (Marcy et al. 1998a). Knowledge of the elemental abundances of the planet-bearing stars is critical to understanding the empirical relationship between giant planet formation and metallicity. In turn, this information is crucial in guiding the construction of theories of the formation of Jovian-mass planets.
3. ANALYSIS 2. OBSERVATIONS
3.1. Abundances
Reduced spectra, one for each star (14 Her, HD 187123, and HD 210277), were provided by G. Marcy. They were obtained with the HIRES echelle spectrograph on the Keck telescope as part of the Keck Doppler planet search. The spectra used in the present study were obtained without the iodine absorption cell. The spectral resolving power is near 87,000, and the signal-to-noise ratios (S/Ns) are just above 600. The spectral cov˚ . Additional details of the oberage is from 3900 to 6190 A servations can be found in Butler et al. (1998) and references cited therein. Spectra were obtained with the coude´ spectrograph on the 1.2 m telescope at the Dominion Astrophysical Observatory (DAO) in Victoria, British Columbia for the purpose of determining the lithium abundances. The short focal length cam-
The present method of analysis is the same as that employed in Paper III for r1 Cnc. Briefly, the method makes use of the Kurucz (1993) LTE plane-parallel model atmospheres and Fe i, Fe ii equivalent width measurements to determine the atmospheric parameters: Teff, log g , yt, and [Fe/H], where the symbols have their usual meanings. Due to the different spectral coverage of the Keck spectra compared to those used in Paper III, it was necessary to produce a new line list. For those lines not in Paper III, new gf-values were calculated from an inverted solar analysis using the Kurucz et al. (1984) Solar Flux Atlas. It includes Fe i and Fe ii lines between l 5 4960 and 6165 ˚ . They cover a range in lower excitation potential xl from A 0.09 to 4.65 eV; the measured equivalent widths range from ˚ for 14 Her, l 5 6 to 72 mA ˚ for HD 187123, l 5 21 to 104 mA ˚ for HD 210277. The final line list conand l 5 12 to 87 mA tains 25 Fe i and four Fe ii lines (Table 1). Although the number of Fe ii lines employed is small, the Fe abundances derived from them display small scatter. Lithium abundances were determined from the DAO spectra. The method employed is the same as that described in Papers II and III. The results are log e(Li) ≤ 0.7, log e(Li) 5 1.2 5 0.2, and log e(Li) ≤ 0.8 for 14 Her, HD 187123, and HD
1 Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology, and the National Solar Observatory, Tucson, AZ, administered by AURA, Inc., for the NSF. 2 University of Washington, Astronomy Department, Box 351580, Seattle, WA 98195. 3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138.
L111
L112
PARENT STARS OF EXTRASOLAR PLANETS. IV. TABLE 1 Atomic Data and Equivalent Widths for Program Stars
face gravities for HD 187123 and HD 210277 supports the assumptions that went into the calculation of the evolutionary tracks. The mass and age estimates for 14 Her are based on its close similarity to r1 Cnc (Paper III).
˚) EW(mA Species Fe i . . . . . . .
Fe ii . . . . . .
Vol. 511
l0 ˚) (A
xl (eV)
log gf
14 Her
HD 187123
HD 210277
4961.92 5247.06 5295.32 5373.71 5651.48 5652.33 5677.70 5724.47 5775.09 5814.82 5827.88 5852.22 5853.16 5855.09 5856.10 5956.70 6034.09 6054.14 6079.07 6105.13 6120.25 6151.62 6157.79 6159.44 6165.36 5325.56 5414.08 5425.26 6149.25
3.63 0.09 4.41 4.47 4.47 4.26 4.10 4.28 4.22 4.28 3.28 4.55 1.48 4.61 4.29 0.86 4.31 4.37 4.65 4.55 0.91 2.18 4.07 4.61 4.14 3.22 3.22 3.20 3.89
22.30 24.93 21.52 20.84 21.76 21.73 22.60 22.49 21.11 21.80 23.16 21.18 25.18 21.52 21.56 24.55 22.26 22.20 21.02 21.97 25.88 23.29 21.25 21.87 21.47 23.18 23.54 23.18 22.70
59.7 104.0 54.2 94.7 47.4 60.4 20.9 21.1 92.2 51.2 40.8 76.4 36.7 48.4 61.3 90.1 29.1 32.5 81.7 34.4 25.5 85.6 87.8 37.4 75.7 39.5 35.7 48.3 39.8
31.4 71.5 32.7 67.8 23.2 31.1 8.3 7.5 64.5 27.5 14.7 48.0 10.5 26.7 38.5 56.2 12.1 12.1 54.0 14.9 6.2 56.0 69.8 14.8 51.7 47.1 36.3 47.5 43.6
44.2 87.2 42.9 78.5 29.9 40.6 13.0 12.1 76.0 36.2 25.7 60.9 18.1 35.6 48.8 71.7 17.5 19.2 65.0 24.3 14.5 69.2 81.6 23.7 61.7 42.0 34.8 46.0 39.6
210277, respectively. The Li abundance for 51 Peg is ≤1.2, consistent with the result of Paper II. The results of the analyses are given in Table 2. The calculation of the uncertainties and the contribution from systematic errors are discussed in Paper III; systematic errors should be negligible in the present study, since these stars are similar to the Sun (except 14 Her). It was shown in Paper III that our analysis of r1 Cnc, which is about 500 K cooler than the Sun, probably does not suffer from significant systematic errors. As we did in Paper III, we refrain from quoting formal uncertainties in [Fe/H] less than 0.05 dex. The masses and ages have been determined in the same way as in Paper II. Using the Hipparcos parallaxes (Perryman 1997) and the stellar evolutionary grids of Schaller et al. (1992) and Schaerer et al. (1993a, 1993b), we have calculated the masses and ages for HD 187123 and HD 210277 (Table 2). Because of the large parallaxes and hence small distances, neither the Lutz & Kelker (1973) nor extinction corrections need be applied. The theoretical surface gravities are log g 5 4.38 5 0.05 for HD 187123 and log g 5 4.35 5 0.03 for HD 210277. The close agreement between the observed and theoretical sur-
3.2. Line Profile Analysis The line profile modeling technique employed in the present study is described in Saar & Osten (1997). In brief, we use a simple Milne-Eddington line model whose fundamental parameters are determined from fits to lines in the Kurucz et al. (1984) Solar Flux Atlas and then scaled to match the star being modeled. The intensity profiles are integrated over the stellar disk using 15 limb angles (with equal projected area) and 60 azimuthal sectors. Values for v sin i , zRT (the radial-tangential macroturbulent velocity dispersion), and the line strength change (relative to the Sun) are then solved for, using a conjugate gradient algorithm to achieve the best fit. We adopted the Teff and log g determined from the abundance analysis for consistency. Four lines (Fe i ll6165 and 6173, Ca i l6166, and Ni i l6175) were modeled. Due to the moderate S/N, the best determined quantity is the “total broadening” 2 0.5 (Saar & Osten 1997) of vtot 5 [( v sin i) 2 1 zRT ] ≈ 4.2 5 0.3 21 km s , with a tendency toward slightly better fits with higher zRT values. The best fit was for v sin i 5 2.0 5 0.4 km s21 and zRT 5 3.7 5 0.3 km s21 (reduced xn2 5 1.3, with 6 degrees of freedom). Note that the present method of line profile analysis (using disk integration and a simple line model) differs from that of Paper II (which used convolutions and a more detailed model). The two methods yield comparable estimates for v sin i, as evidenced by a comparison between the results of Paper II and Henry et al. (1997) for 47 UMa and 70 Vir. However, due to the differences in the methods and in the lines used, the estimates for zRT differ (comparing 47 UMa, 70 Vir, and the Sun, zRT ≈ 0.7 km s21 smaller by the present method). 4. DISCUSSION
4.1. Comparison with Previous Studies The present work is the first published analysis of HD 187123. This is not surprising, given its faintness (mv 5 7.9). Both 14 Her and HD 210277, being much brighter (mv ∼ 6.6), have been studied previously. Of the seven super–metal-rich nearby dwarfs listed by Taylor (1996, Table 4), two harbor planets: r1 Cnc and 14 Her. Taylor cites four studies that have included 14 Her; there is general agreement among them in that Teff is between 5300 and 5400 K and [Fe/H] is greater than 0.30. He assigns [Fe/H] 5 0.414 5 0.096 and 0.380 5 0.072 to r1 Cnc and 14 Her, respectively. Favata, Micela, & Sciortino (1997) reported on a spectroscopic analysis of a volume-limited sample of G and K dwarfs
TABLE 2 Spectroscopically Determined Physical Parameters of the Program Stars Star
Teff (K)
log g
yt (km s21)
[Fe/H]a
MVb
Agec (Gyr)
Massc (M,)
14 Her . . . . . . . . . . . HD 187123 . . . . . . HD 210277 . . . . . .
5300 5 90 5830 5 40 5540 5 60
4.27 5 0.16 4.40 5 0.07 4.35 5 0.10
0.80 5 0.12 1.00 5 0.08 0.85 5 0.08
0.50 5 0.05 0.16 5 0.05 0.24 5 0.05
5.32 5 0.03 4.43 5 0.08 4.90 5 0.05
∼6 411 20.5 12 5 2
∼1.05 1.08 5 0.04 0.92 5 0.02
a b c
The formal uncertainties in [Fe/H] for HD 187123 and HD 210277 are 0.03 and 0.04 dex, respectively. Calculated from the Hipparcos parallaxes. Based Schaller et al. (1992) and Schaerer et al. (1993a, 1993b) evolutionary tracks.
No. 2, 1999
GONZALEZ ET AL.
drawn from the Gliese catalog. Basing their temperature on photometric color indices and the Fe abundance on the equivalent widths of 11 Fe i lines, they derive Tef f 5 5625 K and [Fe/H] 5 0.22 5 0.04 for HD 210277. Wyse & Gilmore (1995) derive [Me/H] 5 0.11 from its Stro¨mgren colors. Fuhrmann (1998) reports the following results of a detailed spectroscopic analysis of HD 210277: Tef f 5 5541 5 80 K, log g 5 4.42 5 0.10, yt 5 0.73 5 0.20 km s21, and [Fe/H] 5 0.26 5 0.07. All of these results are in agreement with ours. 4.2. Metallicity Trends The present results continue to confirm the trend found in other recent studies of the parent stars of extrasolar planets: most of the parent stars are metal rich (relative both to the Sun and to nearby stars). Excluding the high-velocity star HD 1147624 and the solar-metallicity star 70 Vir, which have the most massive companions that may be brown dwarfs, the mean metallicity of the stars with planets is 0.19 5 0.07. If these two stars are included, the mean is reduced to 0.10 5 0.09, mainly due to the low metallicity of HD 114762. For 66 nearby G dwarfs, the sample of Favata et al. (1997) has a mean [Fe/H] of 20.23, with only 8% of the stars showing [Fe/H] ≥ 10.05. The most important finding of the present study is the fact that r1 Cnc and 14 Her are nearly identical. Their bulk physical parameters are the same to within the uncertainties of the estimates, except MV, which differ only by 0.15 mag; the physical parameters of r1 Cnc, as determined in Paper III, are Tef f 5 5250 5 70 K, log g 5 4.40 5 0.15, yt 5 0.80 5 0.09 km s21, and [Fe/H] 5 0.45 5 0.05. These two are possibly the most metal-rich stars in the solar neighborhood. These facts together suggest that their physical parameters were affected by the process that formed their planets. There are two leading hypotheses to explain the relationship between high metallicity and the presence of planets. The first holds that high metallicity favors the formation of rocky planets and large rocky cores of gas giants simply as a result of the presence of more solid material in the protoplanetary disk of the forming star. The second suggestion—originally formulated to explain the high lithium content of certain stars by Alexander (1967)—holds that the high metallicity of stars with planets is due to the capture of rocky material by the star, thus enhancing the heavy element content in the stellar atmosphere. To date, no critical observation to differentiate between the two hypotheses has been reported. Any proposed model must account for the following key observations of 14 Her and r1 Cnc: (1) very high metallicities, (2) nearly identical bulk physical parameters: Tef f ∼ 5300 K, log g ∼ 4.35, yt 5 0.80 km s21, and [Fe/H] ∼ 0.5, and (3) different orbital periods and masses of their planets. Also suggestive is the very close similarity between the 51 Peg and HD 187123 systems. Not only are the parent stars 4 We should note that HD 114762 was discovered in a survey with different criteria compared to the other extrasolar planet candidates; it was the only star to show small amplitude Doppler variations in a large low-precision velocity survey (Latham et al. 1989), so the probability that HD 114762 is a nearly pole-on system is not insignificant. However, our minimum mass estimates for HD 114762 and 70 Vir are similar (see Table 12 of Paper II).
L113
nearly identical in every measurable way, but their companions are also very similar. The minimum companion masses are 0.45MJ for 51 Peg (Marcy et al. 1997) and 0.52MJ for HD 187123 (Butler et al. 1998), and their orbital periods are 3.1 and 4.2 days, respectively. This could just be a coincidence. It would be interesting to see if this pattern continues as new systems are discovered. The Li abundance in HD 187123 is similar to that in the Sun, 16 Cyg A (which to date does not display Doppler variations above the measurement uncertainties), r CrB, and 51 Peg. The upper limit for 14 Her is similar to that in r1 Cnc. The upper limit for HD 210277 is much less than the detection in 70 Vir, which has a similar temperature. If the planet capture theory is correct, then HD 187123 and 51 Peg may have enhanced their Li by the capture of a planet. If the other stars with low Li—14 Her, r1 Cnc, and HD 210277—captured planets, they may have done so shortly after their births so as to have had time to deplete their Li, as has the Sun (relative to the chondritic meteorite Li abundance). Castro et al. (1997) present the results of their analyses of five stars in the solar neighborhood with [Fe/H] ≥ 10.4 and claimed that they are the most metal-rich stars currently known, but they were not able to assign this group to a specific population in the Milky Way. We can now add 14 Her and r1 Cnc to this select list. It is notable that three stars in their sample have Tef f ∼ 5400 K and [Fe/H] ∼ 0.45: BD 21073166, HD 99109, and HD 126614. The two brighter stars, HD 99109 and HD 126614, should be searched for Doppler variations. 4.3. Rotational and Macroturbulent Velocities of HD 210277 Combining v sin i with R 5 1.06 5 0.04 R, (from MV and Teff) and a rotational period estimated from Ca ii HK emission (Prot ≈ 39 days; Shirts & Marcy 1998), the implied sin i is 1.5 5 0.3. Hence, if this estimate of the rotation period is correct, then our v sin i estimate is slightly too large. Note, however, that this value of Prot is not a direct measurement, but is based on the mean Ca ii flux. If HD 210277 is in a low part of its magnetic cycle, then the Ca ii flux will be smaller than typical and the predicted Prot will be too large. The inferred equatorial velocity (∼v sin i ) is consistent with an old star. The zRT lies between that of an inactive mainsequence star (zRT ≈ 3 km s21; Gray 1992; Saar & Osten 1997) and a subgiant (zRT ≈ 4.5 km s21; Gray 1992) at the Teff of HD 210277, consistent with the star’s slightly evolved state (R ≈ 1.06 R,, age ≈12 Gyr). Significant improvement in the accuracy of the line profile analysis can be achieved with modest gains in the S/N ratio (≥200). We also encourage observers to obtain high-resolution spectra of HD 187123. Due to its low temperature and very high metallicity, an accurate line profile analysis of 14 Her would be more difficult. We are grateful to Geoff Marcy for offering his HIRES Keck spectra for analysis. We also thank the anonymous referee for several helpful comments. This research has made use of the Simbad database, operated at CDS, Strasbourg, France. The research has been supported in part by the Kennilworth Fund of the New York Community Trust and by NSF grants AST9528563 and AST-9731652.
L114
PARENT STARS OF EXTRASOLAR PLANETS. IV.
Vol. 511
REFERENCES Alexander, J. B. 1967, Observatory, 87, 238 Butler, R. P., Marcy, G. W., Vogt, S. S., & Apps, K. 1998, PASP, 110, 1389 Castro, S., Rich, R. M., Grenon, M., Barbuy, B., & McCarthy, J. K. 1997, AJ, 114, 376 Favata, F., Micela, G., & Sciortino, S. 1997, A&A, 323, 809 Fuhrmann, K. 1998, A&A, 338, 161 Fuhrmann, K., Pfeiffer, M. J., & Bernkopf, J. 1997, A&A, 326, 1081 ———. 1998, A&A, 336, 942 Gonzalez, G. 1997, MNRAS, 285, 403 (Paper I) ———. 1998, A&A, 334, 221 (Paper II) Gonzalez, G., & Vanture, A. D. 1998, A&A, 339, L29 (Paper III) Gray, D. F. 1992, The Observation and Analysis of Stellar Photospheres (Cambridge: Cambridge Univ. Press) Henry, G. W., Baliunas, S. L., Donahue, R. A., Soon, W. H., & Saar, S. H. 1997, ApJ, 474, 503 Kurucz, R. L. 1993, Kurucz CD-ROM 13 (Cambridge: Smithsonian Astrophysical Observatory) Kurucz, R. L., Furenlid, I., Brault, J., & Testerman, L. 1984, Solar Flux Atlas from 296 to 1300 nm (Sunspot: National Solar Observatory) Latham, D. W., Mazeh, T., Stefanik, R. P., Mayor, M., & Burki, G. 1989, Nature, 339, 38
Lutz, T. E., & Kelker, D. H. 1973, PASP, 85, 573 Marcy, G. W., Butler, R. P., Vogt, S. S., & Liu, M. 1998a, ApJ, submitted Marcy, G. W., Butler, R. P., Williams, E., Bildsten, L., Graham, J. R., Ghez, A. M., & Jernigan, J. G. 1997, ApJ, 481, 926 Marcy, G. W., Cochran, W. D., & Mayor, M. 1998b, in Protostars and Planets IV, ed. V. Manings (Tucson: Univ. Arizona Press), in press Osten, R. A., & Saar, S. H. 1998, MNRAS, 295, 257 Perryman, M. A. C., ed. 1997, The Hipparcos and Tycho Catalogue (ESA SP1200; Noordwijk: ESA) Saar, S. H., & Osten, R. A. 1997, MNRAS, 284, 803 Schaerer, D., Charbonnel, C., Meynet, G., Maeder, A., & Schaller, G. 1993a, A&AS, 102, 339 Schaerer, D., Meynet, G., Maeder, A., & Schaller, G. 1993b, A&AS, 98, 523 Schaller, G., Schaerer, D., Meynet, G., & Maeder, A. 1992, A&AS, 96, 269 Shirts, P., & Marcy, G. W. 1998, PASP, submitted Smith, M. A., & Giampapa, M. S. 1987, in Cool Stars, Stellar Systems, and the Sun, ed. J. Linsky & R. Stencel (Berlin: Springer), 477 Taylor, B. J. 1996, ApJS, 102, 105 Wyse, R. F. G., & Gilmore, G. 1995, AJ, 110, 2771
