The shortest period sdB plus white dwarf binary CD-30 11223 (GALEX J1411-3053)

We report on the discovery of the shortest period binary comprising a hot subdwarf star (CD-30 11223, GALEX J1411-3053) and a massive unseen companion. Photometric data from the All Sky Automated Survey show ellipsoidal variations of the hot subdwarf primary and spectroscopic series revealed an orbital period of 70.5 minutes. The large velocity amplitude suggests the presence of a massive white dwarf in the system (M_2/M_sun > 0.77) assuming a canonical mass for the hot subdwarf (0.48 M_sun), although a white dwarf mass as low as 0.75 M_sun is allowable by postulating a subdwarf mass as low as 0.44 M_sun. The amplitude of ellipsoidal variations and a high rotation velocity imposed a high-inclination to the system (i > 68 deg) and, possibly, observable secondary transits (i > 74 deg). At the lowest permissible inclination and assuming a subdwarf mass of ~0.48 M_sun, the total mass of the system reaches the Chandrasekhar mass limit at 1.35 M_sun and would exceed it for a subdwarf mass above 0.48 M_sun. The system should be considered, like its sibling KPD 1930+2752, a candidate progenitor for a Type Ia supernova. The system should become semi-detached and initiate mass transfer within ~30 Myr.