2013A&A...553A..18S

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 (ASAS102322-3737.0). 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=0.13927d, an inclination of i=65.86°, a mass ratio q=0.34, a radial velocity semiamplitude K₁=81.0km/s, 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=28400 K, logg=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=0.16M_☉. ASAS102322-3737.0 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.