The CCD photometric study of the newly identified RS CVn binary star V1034 Hercules
Introduction
V1034 Her. (GSC 0983.1044 = ROTSE 1 J165241.80 + 124905.2) was discovered by Akerlof et al. (2000) as an eclipsing binary star from the ROTSE 1 sky survey. This star was listed in the ROTSE catalogue as a 13th magnitude eclipsing binary star with a period of 0d.40763 and an amplitude of 1.022 magnitudes. After its discovery, Kaiser et al. (2002) observed this star photometrically and determined standard magnitudes and colour indices in V = 12.90, B − V = 0.78, V − Rc = 0.46, Rc − Ic = 0.44 for the variable star at maximum light (phase 0.11). They also obtained the first V light curve of the system. They improved the linear ephemeris of the system and suggested that it is a short period RS CVn type eclipsing binary, which shows asymmetry out of eclipses. Using the B − V = 0.78 colour index at photometric phase 0.11 of the system, they estimated that the primary component is a mid-to-late G spectral type star and the secondary component is an early K spectral type one. By assuming that the mass ratio of the system is equal to one (q = 1), they solved the V light curve and presented the system as a detached configuration, the secondary component having two cool large star spots. Ordway and van Hamme (2004) obtained the BVRI light curves of the system in 2004 and confirmed that the system is a short period RS CVn type eclipsing binary. They also analyzed the light curves with the latest version of the Wilson–Devinney method and suggested a model with spots. They presented these results in the American Astronomical Society Meeting 205 as an unpublished poster. Later, new minima times of the system have been obtained and published by several authors (Diethelm, 2001, Diethelm, 2003, Diethelm, 2004, Krajci, 2005, Bakış et al., 2005, Locher, 2005, Hübscher et al., 2006, Hübscher, 2007).
The particular aims of the present study are: (i) to study the orbital period of V1034 Her., and (ii) to derive the light curve parameters of the system using CCD photometric data. A review of this binary has been presented above. New photometric observations and their reductions are described in Section 2. While the orbital period of the system is studied in Section 3, two different procedures used for analysis of the light curves are outlined in Section 4. Results and discussion are given in the last section.
Section snippets
Observations and reductions
The system was observed at the Çanakkale Onsekiz Mart University Observatory in Turkey. The observations were performed in the observational season of 2006. The journal of observations is shown in Table 1. A 30-cm Cassegrain reflector, equipped with SBIG ST10X-ME CCD camera, was used. This camera gives image scales of 0.45 arcseconds per pixel and provides an observed field of view (FOV) of 12 arcmin × 18 arcmin. All observations were made with V, Rc and Ic filters of the Johnson–Cousin UBVRcIc
Study of the orbital period
During the observations, two primary times and one secondary time of minimum light were obtained. These CCD minima times and their errors, which were determined by using the method of Kwee and van Woerden (1956), are presented in Table 3. We have combined the minima times obtained by previous authors with our values in order to derive a new epoch and period of the system (see Table 3).
As a first step, the (O − C) values were calculated with the following light elements, given by Kaiser et al.
Wilson–Devinney method
We applied the search procedure developed by Zola et al. (1997) in order to model the new light curves of the RS CVn type system V1034 Hercules. In this procedure, Wilson–Devinney (WD) code (Wilson and Devinney, 1971) is supplemented with the Monte Carlo (MC) search method. The search procedure under the MC statistical method generates the solution space in chosen ranges for parameters of the light curve and gives the best fit to the observational light curve by considering that the difference
Results and discussion
We firstly considered the possibility of orbital period variation and derived the new light ephemeris of V1034 Hercules, collecting observed minima times of the system. Although the time range of (O − C) information is rather short – about 20 years, the (O − C) diagram shows a parabolic variation indicating a quite high rate of period increase. Since V1034 Hercules is a detached system, direct mass transfer between the components would not be expected to be the cause of this period change.
Acknowledgements
We would like to thank Professor Edwin Budding for his helpful comments on this study. We also thank Mr. G.H. Lee for checking the English. This work was supported partially by the Çanakkale Onsekiz Mart University Research Foundation under Grant No. 2007/55.
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