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

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 degrees, a mass ratio q = 0.34, a radial velocity semiamplitude K-1 = 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-circle dot, close to the canonical mass of such objects. The companion is a late M-dwarf with a mass of M-comp = 0.16 M-circle dot. 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.