Peremennye Zvezdy (Variable Stars) 28, No. 9, 2008 Received 28 October; accepted 15 December.

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RS CVn STARS AMONG VARIABLES WITH POSSIBLE CW CLASSIFICATION IN THE ASAS-3 SURVEY

L.N. Berdnikov¹, E.N. Pastukhova²

Sternberg Astronomical Institute, Moscow State University, Russia; e-mail: berdnik@sai.msu.ru

Institute of Astronomy, Russian Academy of Sciences, Russia; e-mail: pastukhova@sai.msu.ru

Classical Cepheids are very important as distance indicators as well as for studies of stellar evolution, structure and kinematics of our Galaxy. An extensive program of Cepheid studies is under way in the Sternberg Astronomical Institute and Institute of Astronomy (Russian Academy of Sciences) (Samus et al. 2007). Population II Cepheids are also of astrophysical interest, and some of them enter our programs of observations. We are interested in the largest possible volume of our Cepheid sample and in clear separation of Population I and Population II Cepheids from objects of other nature resembling them by periods and light-curve shapes.

Recently, thousands of new variable stars were discovered in the ASAS-3 automatic survey (Pojmanski 2002). Many of them have ASAS-3 classification as Cepheids or possible Cepheids. However, our trial observations of objects from the ASAS-3 variable star catalog revealed that some stars had photometric behavior incompatible with their Cepheid classification. Most of them can be identified with Galactic X-ray sources and thus, most probably, are RS CVn variables.

In this study, we analyzed the complete list of stars in the ASAS-3 variable-star catalog with Population II (CW) classification as the main one or as an alternative possibility. Among stars we were able to identify with known X-ray sources of the following catalogs: 1RXS (Voges et al. 1999, 2000), 1RXH (ROSAT Consortium 2000), 1WGA (White et al. 2000), and 2E (Harris 1994), 109 objects have light curves (from ASAS-3 data) permitting us to consider them RS CVn variables.

The list of our RS CVn candidates is presented in the Table. The lines of the Table contain: coordinates (right ascension and declination) from the 2MASS catalog; the X-ray catalog identification; the ASAS-3 catalog identification; the star's variability period from the ASAS-3 catalog; our revised period value (if available); the GCVS/NSV designation and GCVS type (if available). The revised periods are often twice shorter than those suggested in the ASAS-3 catalog.

Note that the star ASAS-3 032406+0729.5 is probably an eclipsing RS CVn star, the only case in our sample. Alternatively, it could even be an EW variable with the period 067645. The ASAS-3 data give no possibility to rule out any of these options.

The star ASAS-3 082250+0151.6 (NSV 17868) was correctly identified as an RS CVn variable in Henry et al. (1995). The period given for this star in the Table is from the cited paper, we retained the star in the Table for the sake of completeness.

Acknowledgements: The authors gratefully acknowledge support for this work by research funding awarded through the Russian Foundation of Basic Research (RFBR, grants 07-02-00380 and 08-02-00375), through the Program of Support for Leading Scientific Schools of Russia, and through the program "Origin and Evolution of Stars and Galaxies" of the Presidium of Russian Academy of Sciences. Thanks are due to the Editor, N.N. Samus, for valuable suggestion towards improvement of the manuscript.

References:

Harris, D.E., Forman, W., Gioa, I.M., et al., 1994, VizieR On-line Data Catalog: IX/13

Henry, G.W., Fekel, F.C., Hall, D.S., 1995, Astron. J., 110, 2926

Pojmanski, G., 2002, Acta Astron., 52, 397

ROSAT Consortium, 2000, VizieR On-line Data Catalog: IX/28A

Samus, N.N., Antipin, S.V., Berdnikov, L.N., et al., 2007, Odessa Astron. Publ., 20, 197

Voges, W., Aschenbach, B., Boller, Th., et al., 1999, VizieR On-line Data Catalog: IX/10A

Voges, W., Aschenbach, B., Boller, Th., et al., 2000, VizieR On-line Data Catalog: IX/29

White, N.T., Giommi, P., Angelini, L., 2000, VizieR On-line Data Catalog: IX/31

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