The multi-band CCD photometric investigation of short-period eclipsing binary V1044 Her
Introduction
Photometric investigation of contact eclipsing binaries provide key information at an important stellar evolutionary stage (Robertson, Eggleton, 1977, Kaluzny, 1985, Hilditch, King, Mcfarlane, 1988, Shaw, 1994, Zhu, Qian, 2006, Yang, Qian, 2015, etc.). By analyzing photometric light curves (LCs), we can obtain orbital parameters of eclipsing binaries and photospheric starspot parameters. Many eclipsing binaries display a periodic variation of orbital period (Qian, Wang, Zhu, et al., 2014a, Xiang, Xiao, Yu, 2015a, etc.). The explanation for the periodic change might be a third body or a magnetic cycle (Applegate, 1992, Lanza, Rodonò, Rosnonr, 1998, Hoffman, Harrison, McNamara, et al., 2006, etc.).
The eclipsing binary star V1044 Her (GSC 03073-00837) was first discovered as a variable object by Akerlof et al. (2000). Its first unfiltered light curve was obtained by Blattler and Diethelm (2001) and displayed an apparent asymmetry. According to the 77th name-list of variable stars (Kazarovets et al., 2003), it was classified as an EW-type eclipsing binary. Bradstreet et al. (2009) analyzed the light curve of V1044 Her and derived preliminary orbital parameters.
V1044 Her is an intriguing star for studying period variation, LCs evolution and the possible presence of a third body. In this paper, we present our new light curves (LCs) in V and R bands for V1044 Her and our analyses using the updated version of Wilson–Devinney (WD) program (Wilson, Devinney, 1971, Wilson, 1979, Wilson, 1990, Wilson, 1994). We also present our analyses on its period variation for the first time.
Section snippets
New CCD photometric observations
V1044 Her was observed in the VR bands on May 22, 23 and 24, 2015 using the 60-cm reflecting telescope at Xinglong Station of the National Astronomical Observatories of China (NAOC). This telescope was equipped with a 1024 × 1024 pixel CCD and the standard Johnson UBVRI filters. The field of view of the system is 17 × 17 square arcmin Xiang et al. (2015a). The exposure times are 40–60 s and 40–50 s in V and R bands, respectively. We chose comparison and check stars around V1044 Her, which are
Period analyses
We fit our VR LCs using the polynomial fitting method of Kwee and van Woerden (1956), and obtained five new light minimum times and their uncertainties. The fitting program was developed by Nelson (2007). We listed the new minima in Table 3. In order to analyze the period variation for V1044 Her, we need as many light minimum times as possible covering a time period for as long as possible. Therefore, in addition to the five new minimum times, we collected all the available CCD minima times
Orbital parameter analyses
Because our new CCD photometric data have complete phase coverage and high time resolution, we were able to obtain photometric solutions of V1044 Her by analyzing its light curves using the WD program (Wilson and Van Hamme, 2004). V1044 Her is an EW binary (Kazarovets et al., 2003), so we used mode 3 in the program (appropriate for contact binaries). The asymmetry in the light curves can be explained with a hot spot or dark spot on a component star. Because we do not have simultaneous
Orbital parameters
As concluded in the previous section, a hot spot on the primary component (case 3 in our four scenarios) best fits our observed light curves. In this case, the orbital inclination (78.7°) is similar to the result (about 80°) obtained by Bradstreet et al. (2009). The temperature difference between the two components is 198k, which is also similar to the result (200 K) obtained by Bradstreet et al. (2009). The ratios of the luminosity of the primary component to the total light of V1044 Her are
Acknowledgments
This research was supported by the Joint Fund of Astronomy of the National Natural Science Foundation of China and the Chinese Academy of Sciences Grant nos. U1431114, 11263001. This work was also supported by the Joint Fund of Department of Science and Technology of Guizhou Province and Guizou University Grant no. [2014]7642.
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