A new bright eclipsing hot subdwarf binary from the ASAS and SuperWASP surveys

¹ Dr. Remeis-Observatory & ECAP, Astronomical Institute, Friedrich-Alexander University Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
e-mail: veronika.schaffenroth@sternwarte.uni-erlangen.de
² Institute for Astro- and Particle Physics, University of Innsbruck, Technikerstr. 25/8, 6020 Innsbruck, Austria
³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
⁴ Vereniging voor Sterrenkunde, Belgium
⁵ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Heverlee, Belgium
⁶ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
⁷ Carnes Hill Observatory, 34 Perisher St., 2171 Horningsea Park, NSW, Sydney, Australia

Received: 14 December 2012
Accepted: 1 March 2013

Abstract

We report the discovery of a bright (m_V = 11.6 mag), eclipsing, hot subdwarf binary of spectral type B with a late main sequence companion from the All Sky Automated Survey (ASAS 102322-3737.0). Such systems are called HW Vir stars after the prototype. The lightcurve shows a grazing eclipse and a strong reflection effect. An orbital period of P = 0.13927 d, an inclination of i = 65.86°, a mass ratio q = 0.34, a radial velocity semiamplitude K₁ = 81.0 km s^-1, and other parameters were derived from a combined spectroscopic and photometric analysis. The short period can only be explained by a common envelope origin of the system. The atmospheric parameters (T_eff = 28 400 K, log g = 5.60) are consistent with a core helium-burning star located on the extreme horizontal branch. In agreement with that we derived the most likely sdB mass to be M_sdB = 0.46 M_⊙, close to the canonical mass of such objects. The companion is a late M-dwarf with a mass of M_comp = 0.16 M_⊙. ASAS 102322-3737.0 is the third brightest of only 12 known HW Virginis systems, which makes it an ideal target for detailed spectroscopic studies and long-term photometric monitoring to search for period variations, e.g., those caused by a substellar companion.