have subtracted the fitted curves from the original data (see Figure 4). ... Figure 4: Example of the binarity effect subtraction for MX Pav. ... W Ursae Majoris 117.
ISSN 1845–8319
SEARCHING FOR PULSATING STARS IN ECLIPSING BINARIES IN THE OMC–VAR CATALOGUE J. ALFONSO-GARZÓN, A. MOYA, B. MONTESINOS, J. M. MAS-HESSE and A. DOMINGO Centro de Astrobiología (CSIC-INTA), Madrid, Spain Abstract. The first catalogue of variable sources observed by OMC (OMC–VAR hereafter) contains light curves for 5263 variable stars, out of which we have been able to detect periodicities for 1137 objects. A large variety of objects can be found in the catalogue, but the most frequent ones in the present compilation are pulsating stars and eclipsing binaries. We have performed an analysis to find eclipsing systems showing evidences of pulsations in one of their components some preliminary results are shown. Key words: eclipsing binaries - pulsating stars - catalogue - photometry
1.
Introduction
The INTEGRAL Optical Monitoring Camera (OMC, Mas-Hesse et al., 2003), observes the optical emission from the prime targets of the gamma ray instruments on-board the INTEGRAL ESA mission: SPI (gamma ray spectrometer) and IBIS (gamma ray imager), with the support of the JEMX monitor in the X-ray domain. OMC provides photometry in the Johnson V band (centred at 5500 Å) and it is able to monitor sources from V ≃ 7 mag (to avoid saturation effects) to V ≃ 16-17 mag (magnitude limit for a 3σ source detection). Typical observations are done by performing a sequence of different integration times, allowing for photometric uncertainties below 0.1 mag for objects with V ≤ 16. Currently, the OMC database (Gutiérrez et al., 2004) contains light curves for more than 60 000 sources (with more than 50 photometric points each). 2.
OMC–VAR: The First Catalogue of Optically Variable Sources Observed by OMC
The first catalogue of variable sources observed by OMC (Alfonso-Garzón et al., 2012) contains photometric information about optical variability for Cent. Eur. Astrophys. Bull. 37 (2013) 1, 187–194
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5263 sources distributed all over the sky (see Figure 1). In the catalogue we provide for each object the median of the visual magnitude, the magnitude at maximum and minimum brightness in the light curve during the observational window, the period, when found, as well as the complete intrinsic and period-folded light curves, together with some supplementary data. The list of object data and full set of figures with finder charts and light curves are available at the CDS via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/ A+A/548/A79 +90
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Figure 1: Distribution in galactic coordinates of all the sources in the catalogue. The green crosses represent pulsating stars, the red filled points correspond to eclipsing binaries, the brown pluses are eruptive stars, the orange complex pluses represent rotating stars, the inverted dark blue filled triangles represent cataclysmic variables, the light blue filled stars are X-ray binaries, the yellow filled points correspond to objects simply classified as variable stars, the purple filled pentagons represent extragalactic objects and the empty purple squares are other types of objects. Colours will only be available in the electronic version.
The values of the median magnitudes range from 7.10 to 16.27. In Figure 2 (left), we show the histogram of the median magnitudes with a peak at around 12.3 mag. The distribution of the periods derived is plotted in Figure 2 (right). Typical values vary between a few hours and 10 days, with a peak at around 15 h. To determine what sources were periodic and to derive their periods, an algorithm based on the Phase Dispersion Minimization (PDM) technique 188
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Figure 2: Left: Histogram of the magnitudes of the sources in OMC–VAR. The fraction of sources for which we determined a period are represented with dark bars. Right: Histogram of the periods derived.
Figure 3: Histogram of the different groups of variability types present in the catalogue. There is a significant number of objects which are unclassified, or just classified as variable objects. In dark colour are represented the sources for which we have determined a period in this work. Cent. Eur. Astrophys. Bull. 37 (2013) 1, 187–194
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(Stellingwerf, 1978) was developed. With this method we determined periods for 1337 sources. The distribution of periods we found is also plotted in Figure 2. We show in Figure 3 the histogram corresponding to the different groups of objects that can be found in the catalogue. There are eclipsing binaries, pulsating stars, eruptive stars, rotating stars, cataclysimic binaries, X-ray binaries, Be stars, extragalactic objects and other kind of variable objects. 3.
The Search for Pulsating Components in Eclipsing Binaries
Asteroseismology aims to understand the pulsation physics in order to probe the interior parts of all kinds of stars. Only a fraction of the theoretically predicted modes are observed, which results in many free parameters in the pulsation models. It is indeed important to infer the fundamental stellar properties of the pulsator from other methods. One way is to study the pulsating components of binary (multiple) systems in great detail, since binary (multiple) systems with well-characterized components supply additional constraints for a more reliable modelling. About 70% of all stars of the Solar neighbourhood are members of binary or multiple systems (67% for G-M stars (Mayor et al., 2001), 75% for O-B stars (Mason et al., 2001). Yet, these facts are usually ignored in the study of stellar pulsation. There is, however, strong evidence that binarity affects the pulsation properties in specific cases (e.g. the eccentric binaries HD 177863 (De Cat and Aerts, 2002) and HD 209295 (Handler et al., 2002). It is thus essential to understand the possible link(s) between binarity and pulsation(s) (Lampens, 2006). Eclipsing binaries are particularly powerful tools in astrophysics, since their accurate observation enables to derive the fundamental properties (masses, radii, luminosities, effective temperatures) of each component. In order to study pulsations in the components of our eclipsing systems, we have modelled the folded light curves with polyfit (Prša et al., 2008), we have subtracted the fitted curves from the original data (see Figure 4). The residuals obtained have been analysed for periodic signals by calculating the Fourier periodogram (see Figure 5), avoiding the intervals when eclipses occur. With this method we have confirmed some previous eclipsing systems with a pulsator as one of their components. An illustrative example is shown in Figures 4 and 5. 190
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Figure 4: Example of the binarity effect subtraction for MX Pav. This is a known Algol eclipsing with a δ-Scuti component. Top: Unfolded light curve. Middle: Phase-folded light curve using the orbital period. The model obtained with polyfit is overplotted. The dashed lines represent the limits of the eclipses we have considered and the solid lines correspond to the limits of the areas that have been excluded from the Fourier analysis. Bottom: Residuals after subtracting the binarity effect and excluding the eclipsing areas.
1133 objects in our catalogue are classified as eclipsing binaries in the Variable Star Index (VSX; Watson 2006; Watson et al. 2012). We have made the above analysis for the sources in Table I that have a value of the orbital period. With this method we have found 13 candidates to contain pulsating Cent. Eur. Astrophys. Bull. 37 (2013) 1, 187–194
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Table I: Eclipsing binaries in OMC–VAR and period information available.
Eclipsing type Algol Beta Lyrae W Ursae Majoris Other
All 728 191 117 96
with POM C 272 145 100 23
with PV SX 703 184 108 61
Figure 5: Fourier analysis of the residuals after the binarity subtraction for MX Pav. The previously known pulse frequency of 13.22 cycles per day has been confirmed with OMC data.
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components. We are now characterizing the components of these systems and determining the nature of the oscillations, combining the OMC light curves with ground-based multicolour photometry and high-resolution spectroscopy obtained in August-September 2012 for some of the objects. Acknowledgements This project is being funded by Spanish MINECO under grants AYA200803467 and AYA2011-24780/ESP. References Alfonso-Garzón, J., Domingo, A., Mas-Hesse, J. M., and Giménez, A.: 2012, Astron. Astrophys. 548, A79. De Cat, P. and Aerts, C.: 2002, Astron. Astrophys. 393, 965. Gutiérrez, R., Solano, E., Domingo, A., and García, J.: 2004, in . D. E. F. Ochsenbein, M. G. Allen (ed.), Astronomical Data Analysis Software and Systems (ADASS) XIII, Vol. 314 of Astronomical Society of the Pacific Conference Series, p. 153. Handler, G., Balona, L. A., Shobbrook, R. R., Koen, C., Bruch, A., RomeroColmenero, E., Pamyatnykh, A. A., Willems, B., Eyer, L., James, D. J., and Maas, T.: 2002, Mon. Not. R. Astron. Soc. 333, 262. Lampens, P.: 2006, in C. Aerts and C. Sterken (eds.), Astrophysics of Variable Stars, Vol. 349 of Astronomical Society of the Pacific Conference Series, p. 153. Mas-Hesse, J. M., Giménez, A., Culhane, J. L., Jamar, C., McBreen, B., Torra, J., Hudec, R., Fabregat, J., Meurs, E., Swings, J. P., Alcacera, M. A., Balado, A., Beiztegui, R., Belenguer, T., Bradley, L., Caballero, M. D., Cabo, P., Defise, J. M., Díaz, E., Domingo, A., Figueras, F., Figueroa, I., Hanlon, L., Hroch, F., Hudcova, V., García, T., Jordan, B., Jordi, C., Kretschmar, P., Laviada, C., March, M., Martín, E., Mazy, E., Menéndez, M., Mi, J. M., de Miguel, E., Muñoz, T., Nolan, K., Olmedo, R., Plesseria, J. Y., Polcar, J., Reina, M., Renotte, E., Rochus, P., Sánchez, A., San Martín, J. C., Smith, A., Soldan, J., Thomas, P., Timón, V., and Walton, D.: 2003, Astron. Astrophys. 411, L261. Mason, B. D., Gies, D. R., and Hartkopf, W. I.: 2001, in D. Vanbeveren (ed.), The Influence of Binaries on Stellar Population Studies, Vol. 264 of Astrophysics and Space Science Library, p. 37. Mayor, M., Udry, S., Halbwachs, J. L., and Arenou, F.: 2001, in H. Zinnecker and R. Mathieu (eds.), The Formation of Binary Stars, Vol. 200 of IAU Symposium, p. 45. Cent. Eur. Astrophys. Bull. 37 (2013) 1, 187–194
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Prša, A., Guinan, E. F., Devinney, E. J., DeGeorge, M., Bradstreet, D. H., Giammarco, J. M., Alcock, C. R., and Engle, S. G.: 2008, Astrophys. J. 687, 542. Stellingwerf, R. F.: 1978, Astrophys. J. 224, 953. Watson, C., Henden, A. A., and Price, A.: 2012, VizieR Online Data Catalog 1, 2027. Watson, C. L.: 2006, Society for Astronomical Sciences Annual Symposium 25, 47.
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