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

TL;DR

This study combines photometric and spectroscopic data to analyze the NSVS 14256825 binary system, refining its orbital parameters and physical characteristics of its components, including the classification of the hot star as an sdOB type.

Contribution

The paper provides a detailed combined photometric and spectroscopic analysis of NSVS 14256825, accurately determining its physical parameters and classifying the hot component as an sdOB star, which is novel for this system.

Findings

Orbital period refined to 0.11037 days.

Hot component's temperature is 40000 K.

Component masses and radii are precisely measured.

Abstract

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, $\log g_1 = 5.50\pm0.05$, and the helium abundance, $n(\rm He)/n(\rm H)=0.003\pm0.001$, 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 ($i = 82\fdg5\pm0\fdg3$ and $q = M_2/M_1 = 0.260\pm0.012$, 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.