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Peremennye Zvezdy (Variable Stars) 28, No. 2, 2008 Received 15 November 2007; accepted 21 February 2008.
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Article in PDF |
GSC 2805-00766 is a new W UMa variable
S. Kleidis1,2, I. Rozakis1,2, S. Tsantilas3
- Zagori Observatory, Epirus, Greece;
e-mail: steliosklidis@gmail.com
- Helliniki
Astronomiki Enosi, Athens, Greece
- Astronomy Dept., Athens University, Athens, Greece
| Multi-night CCD observations of the previously unknown variable GSC 02805-00766 reveal its nature as a contact binary. We present its light elements and light curve. |
The star GSC 2805-00766 (coordinates for equinox 2000.0:
,
) is in
the field of CC And and was found to vary by I. Rozakis during CCD
observations in autumn 2005. It was monitored by S. Kleidis in
autumn/winter 2006 and autumn 2007 for fifteen nights.
A 30 cm SCT telescope, ST-7 XMEI CCD camera and Schuler
photometric 
and 
filters were used. The data set of 28th
December 2006 was taken through a clear filter. Five primary
minima in 2006 and one secondary minimum in 2007 were recorded and
are presented in the Table. All images were flat-fielded, bias and
dark frames were subtracted according to standard procedures. We
used the calibration and photometry software AIP4WIN V1.25 (Berry
and Burnell, 2003). Times of minima and period calculated using
Peranso period analysis software (Vanmunster, 2006) and software
written by Robert Nelson (Nelson, 2007). The data are available
electronically.
The comparison stars used were Comp1 = GSC 2805-00633 (adopted
magnitude 
from the GSC catalogue), Comp2 =
GSC 2805-01419 and Comp3 = GSC 2805-00807. Unfortunately, all
three are about two magnitudes brighter than the variable,
limiting the precision of the observations. The average nightly
standard deviation for the check stars was 0
02-003 in
and 0012-0017 in . The light curves and electronic
tables of observations contain differential magnitudes
.
Table. Times of Minimum Light
| JD Hel. 2450000+ |
Min | O–C (days) |
 |
Filter |
| 3980.51609 | I | -0.00966 | -31 | |
| 3995.49103 | I | 0 | 0 | |
| 4008.53186 | I | 0.00655 | 27 | |
| 4024.45861 | I | 0.00252 | 60 | |
| 4098.30620 | I | -0.01079 | 213 | Clear |
| 4350.56045 | II | 0.00606 | 735.5 | |
The weighted average of period values was 0
48276 and further
refined through O-C diagram to 048275. The ephemeris is:
 |
 |
|
Fig. 1.
The phased light curve of GSC 2805-00766
|
Fig. 2.
The phased light curve of GSC 2805-0766
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To measure the star's calibrated magnitudes, we arranged a short
, observing run on 16th October, 2007. The magnitude of the
variable at phase 0.458 was estimated as
(
), as measured with respect of two standard
Landolt fields using PhotoRed software (B.D. Warner, http://www.minorplanetobserver.com/) for reductions. The
amplitude is about 03 in and 035 in filters. The
phased light curves in both filters are given in Fig. 1 and
Fig. 2, they are typical for W UMa systems. The almost equal
depths of primary and secondary minima suggest close temperatures,
however due to the faintness of the new variable and the absence
of spectroscopic data, it is impossible to calculate an accurate
light curve solution at this time. The finder chart for the new
variable, along
with comparison stars used, can be found in Fig. 3.
 |
Fig. 3. Finder chart of GSC 2805-00766 |
Acknowledgements: This research made use of the SIMBAD and VizieR databases operated at the Centre de Données Astronomiques (Strasbourg) in France. The authors wish to thank Dr. Helen Rovithis-Livaniou (Section of Astronomy, Astrophysics and Mechanics, Physics Dept., University of Athens, Greece) for her advice. We thank Patrick Wils (Vereniging Voor Sterrenkunde, Belgium) and Manolis Zoulias (Academy of Athens, Research Center for Astronomy) for their help in preparing this paper.
References:
Berry, R., Burnell, J., 2005, Handbook of Astronomical Image Processing, Willmann-Bell
Vanmunster, T., 2006, http://www.peranso.com
Nelson R.H., 2007, http://members.shaw.ca/bob.nelson/software1.htm