A photometric and spectroscopic study of NSVS 14256825: the second sdOB+dM eclipsing binary

We present an analysis of UBVRCICJH 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 (Porb similar to 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, , for the hot component. Simultaneously modelling the photometric and spectroscopic data using the WilsonDevinney code, we obtain the geometrical and physical parameters of NSVS 14256825. Using the fitted orbital inclination and mass ratio (i= 82 degrees.5 +/- 0 degrees.3 and q=M2/M1= 0.260 +/- 0.012, respectively), the components of the system have M1= 0.419 +/- 0.070 M-circle dot, R1= 0.188 +/- 0.010 R-circle dot, M2= 0.109 +/- 0.023 M-circle dot and R2= 0.162 +/- 0.008 R-circle dot. From its spectral characteristics, the hot star is classified as a subdwarf OB (sdOB) star.