Patrick Wils

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

We report the discovery of a bright (mV = 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 reflectio n 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 are 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 (Teff = 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 MsdB = 0.46M⊙, close to the canonical mass of such objects. The companion is a late M-dwarf with a mass of Mcomp = 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. caused by a substellar companion.