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Register a new userA photometric and spectroscopic study of NSVS 14256825: the second sdOB+dM eclipsing binary
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Added by
Leonardo A. Almeida
Publication date
2012
fields
Physics
and research's language is
English
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We present an analysis of UBVR$_{rm C}$I$_{rm C}$JH photometry and phase-resolved optical spectroscopy of NSVS 14256825, an HW Vir type binary. The members of this class consist of a hot subdwarf and a main-sequence low-mass star in a close orbit ($P_{rm orb} ~ 0.1$ d). Using the primary-eclipse timings, we refine the ephemeris for the system, which has an orbital period of 0.11037 d. From the spectroscopic data analysis, we derive the effective temperature, $T_1 = 40000 pm 500$ K, the surface gravity, $log g_1 = 5.50pm0.05$, and the helium abundance, $n(rm He)/n(rm H)=0.003pm0.001$, for the hot component. Simultaneously modelling the photometric and spectroscopic data using the Wilson-Devinney code, we obtain the geometrical and physical parameters of NSVS 14256825. Using the fitted orbital inclination and mass ratio ($i = 82fdg5pm0fdg3$ and $q = M_2/M_1 = 0.260pm0.012$, respectively), the components of the system have $M_1 = 0.419 pm 0.070 M_{odot}$, $R_1 = 0.188 pm 0.010 R_{odot}$, $M_2 = 0.109 pm 0.023 M_{odot}$, and $R_2 = 0.162 pm 0.008 R_{odot}$. From its spectral characteristics, the hot star is classified as an sdOB star.
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We present the new results of our long-term observational project to detect the small variations in the orbital periods of low-mass and short-period eclipsing binaries. About 120 new precise mid-eclipse times were obtained for three relatively well-known dwarf eclipsing binaries: SDSS J143547.87+373338.5 (P = 0.126 d), NSVS 07826147 (0.162 d), and NSVS 14256825 (0.110 d). Observed-minus-calculated (O-C) diagrams of these systems were analyzed using all accurate timings, and, where possible, new parameters of the light-time effect were calculated. For the first time, we derive (or improve upon previous findings with regard to) the short orbital periods of 13 and 10 years of possible third bodies for SDSS J143547.87+373338.5 and NSVS 07826147, respectively. In these binaries, our data show that period variations can be modeled simply on the basis of a single circumbinary object. For the first two objects, we calculated the minimum mass of the third components to be 17 MJ, and 1.4 MJ respectively, which corresponds to the mass of a brown dwarf or a giant planet. For NSVS 14256825, the cyclical period changes caused by a single additional body cannot be confirmed by our recent eclipse time measurements. More complex behavior connected with two orbiting bodies, or yet unknown effects, should be taken into account.
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