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Long-term photometric study of a faint W UMa binary in the direction of M31

Yogesh Chandra Joshi, Rukmini Jagirdar


We carry out a re-analysis of the photometric data in Rc I c bands which were taken during the Nainital Microlensing Survey from 1998 to 2002 with the aim to detect gravitational microlensing events in the direction of M31. Here, we do photometric analysis of a faint W UMa binary CSS_J00425.3 + 410629 identified in the target field. The orbital period of this star is found to be 0.266402±0.000018d. The photometric mass ratio, q, is found to be 0.28 ± 0.01. The photometric light curves are investigated using the Wilson-Devinney (WD) code and absolute parameters are determined using empirical relations which provide masses and radii of the binary as M1 = 1.19 ± 0.09M, M2 = 0.33 ± 0.02M and R1 = 1.02±0.04R, R2 = 0.58±0.08R respectively based on Rc band data. Quite similar values are found by analyzing Ic band data. From the photometric light curve examination, the star is understood to be a low mass-ratio overcontact binary of A-subtype with a high fill-out factor of about 47%. The binary system is found to be located approximately at a distance of 2.64 ± 0.03 kpc having a separation of 2.01 ± 0.05 R between the two components.


methods: observational — techniques: photometric — binaries: eclipsing — stars: funda- mental parameters

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