Moscow Digital Variables. I

A. L. Manannikov^#1, K. V. Sokolovsky^#2, N. N. Samus^#3, S. V. Antipin^#4

#1. Sternberg Astronomical Institute; #2. Sternberg Astronomical Institute and Astro Space Center of the Lebedev Physical Institute, Russian Academy of Sciences; #3. Institute of Astronomy, Russian Academy of Sciences and Sternberg Astronomical Institute; #4. Sternberg Astronomical Institute and Institute of Astronomy, Russian Academy of Sciences, Moscow, Russia.

Received:   19.12.2006;   accepted:   22.12.2006
(E-mail for contact: kirx@saistud.sai.msu.ru)

Comments:


4. USNO A2.0 1050-06881173 = RXS J13159+2125 was first identified as an AGN by Bade et al. (1998). According to Veron-Cetty & Veron (2006), it is a 17.0(V) mag. Seyfert 1 galaxy at z=0.088. It is listed as a faint radio source (1.25 mJy at 20 cm) in the FIRST catalog (White et al., 1998). SDSS photometry obtained on 2005 March 10, 09:40 UT is available: u=17.25, g=16.92, r=16.43, i=15.81, z=15.68. The object is clearly identified as a galaxy on SDSS images.

5. The light curve of USNO A2.0 1050-06890945 (183 estimates, JD2437047 - 2447647) permits us to consider the new variable as an RR Lyrae type star with some peculiarities. The scatter on the phased light curve is fairly large in maximum (close to phase 0.0), suggesting modulation, like multimodality or Blazhko effect. CCD observations are needed.

7. The variability of BG Com was discovered by Hoffmeister (1964). Meinunger and Wenzel (1968) report the period of 0.305352d for the star, which is inconsistent with our data (175 estimates, JD2437047 - 2447655). Our analysis leads to a period of 0.291706d.

8. ASAS 131954+1954 was first identified as an RR Lyrae variable by the All Sky Automated Survey (Pojmanski et al., 2005). Automatic analysis of the ASAS data gave the period of 0.374985d, but our data suggest P = 0.601167d instead.

14. USNO-A2.0 1050-06926703 = 1RXS J132645.8+210102. Its light curve is similar to those of the Seyfert galaxies RXS J13159+2125 (this paper) and FBQS J161047.7+330337 (Sokolovsky, 2006) obtained from plates of the same telescope, except that here the light variations take place on a longer time scale - of decades rather than of years. No sign of an underlying galaxy is visible on SDSS images, the object is classified as "STAR". The SDSS photometry obtained on 2005 March 10, 09:50 UT is: u=16.85, g=16.54, r=16.53, i=16.65, z=16.59. Spectroscopic observations are required to reveal the true nature of this object, which can also be an X-ray variable star of unrevealed nature.

15. The variability of BK Com was discovered by Hoffmeister (1964). Meinunger and Wenzel (1968)report the period of 0.45219d, which, as in the case of BG Com, is inconsistent with our data (164 estimates, JD2437072 - 2447655). Our analysis suggest a period of 0.825465d.

Remarks:
We present the results of one of our pilot projects of variable-star search using scanned photographic plates. A four-by-four-degree region in Coma Berenices was studied. 247 photographic plates of the field were taken with the 40-cm astrograph in Crimea, they cover 29 years between 1960 and 1989. The plates were scanned by one of the authors (A. Manannikov) at 2400 dpi resolution with the Sternberg Institute's CREO EverSmart Supreme II flatbed scanner. 16 bit-per-channel TIFF images produced by the scanner were converted to FITS format commonly used in astronomical applications by means of custom software developed by A. Lebedev & K. Sokolovsky (available online at ftp://scan.sai.msu.ru/pub/software/tiff2fits/). Further analysis was done in VAST software (Sokolovsky, Lebedev, 2005) which is based on the well-known SExtractor by (Bertin, 2006). A total of 35 variable objects were detected by VAST. Among them, there are 12 known RR Lyrae variables in the globular clusters NGC 5053 and M53, which are not considered here, 8 known variables in the field, and 15 previously unreported variable stars. For 5 stars (BL Com, BN Com, RS Com, RT Com and RV Com), our results are fully consistent with those previously published, and we do not discuss these stars in the present note. Our conclusions about periods of ASAS 131954+1954, BG Com and BK Com significantly differ from those in their earlier studies (see Remarks). Among the newly discovered variables, there are 9 RR Lyrae stars, 2 eclipsing binaries of the W Ursae Majoris type, one high-amplitude SX Phoenicis star, one non-periodic red variable, an optically variable Seyfert 1 galaxy, and a variable X-ray object of unclear nature (probably a Seyfert galaxy or a QSO). All magnitudes in this work were calibrated using photographic blue magnitudes of neighboring USNO-A2.0 stars (Monet et al., 1998). Time series analysis was done with WinEffect software, developed by V. Goranskij.

Acknowledgments: The authors would like to thank A. Lebedev, S. Nazarov, and D. Nasonov for their contribution to development of VAST, D. Kolesnikova for providing us with a nice Matlab tool for plotting phased light curves, and B. Komberg for a useful advice. This research has made use of Aladin interactive sky atlas and SIMBAD database, operated at CDS, Strasbourg, France; NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory of Technology; and publicly available Sloan Digital Sky Survey data (http://sdss.org). N. Samus, S. Antipin and K. Sokolovsky are grateful to RFBR grants 05-02-16289 and 05-02-16688.

References:
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