HS1136+6646: A Hot DA0.5+K6V Young Post-CE Pre CV Binary

Abstract

Photometric and spectroscopic observations of HS 1136+6646 have been obtained, revealing a newly formed post-common envelope binary star containing a DAO.5 primary and a K6V secondary. H I, He II, Ca I, and Mg II are all in emission due to irradiation of the K6V secondary by the hot white dwarf. These lines are observed to disappear near inferior conjunction. An orbital period of 0.8314 ± 0.0005 days has been determined by phasing radial velocities, equivalent widths of the emission lines, and photometric measurements. Radial velocity measurements reveal an amplitude of KWD = 105 ± 20 km s ^-1 for the white dwarf and K _K6V = 125 ± 8 km s⁺¹ for the secondary star. Low amplitude oscillations with a period of 116 minutes have been observed in all photometric observations. The amplitude varies with the maximum being around 0.05 mag. The oscillations appear to be independent of the orbital phase and are possibly associated with the rotation of the white dwarf star. FUSE data shows the white dwarf to have a T _eff = 110,000 K and log g = 7 – 7.5. The extremely high temperature white dwarf and relatively early spectral type of the secondary star indicate that the binary system is one of the earliest post-CE object known, having an age around 10⁵ years.