2012MNRAS.423..478A

We present an analysis of UBVR_CI_CJH 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_orb ∼ 0.1 d). Using the primary-eclipse timings, we refine the ephemeris for the system, which has an orbital period of 0.110 37 d. From the spectroscopic data analysis, we derive the effective temperature, T₁= 40 000±500 K, the surface gravity, log g₁= 5.50±0.05, and the helium abundance, ν(He)/ν(H) = 0.003± 0.001, 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= 82°.5±0°.3 and q=M₂/M₁= 0.260±0.012, respectively), the components of the system have M₁= 0.419±0.070 M_☉, R₁= 0.188±0.010 R_☉, M₂= 0.109±0.023 M_☉ and R₂= 0.162±0.008 R_☉. From its spectral characteristics, the hot star is classified as a subdwarf OB (sdOB) star.

Based on observations carried out at the Observatório do Pico dos Dias/Laboratório Nacional de Astrofìsica (OPD/LNA) in Brazil.