Binaries discovered by the SPY project - I. HE1047-0436: A subdwarf B pluswhite dwarf system

In the course of our search for double degenerate binaries as potential pro genitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (E SO SN Ia Progenitor survey {SPY) we discovered that the sdB star HE1047-043 6 is radial velocity variable. The orbital period of 1.213253 d, a semi-amp litude of 94 km s(-1), and a minimum mass of the invisible companion of 0.4 4 M-. are derived from the analysis of the radial velocity curve. We use an upper limit on the projected rotational velocity of the sdB star to constr ain the system inclination and the companion mass to M >0.71 M-., bringing the total mass of the system closer to the Chandrasekhar limit. However, th e system will merge due to loss of angular momentum via gravitational wave radiation only after several Hubble times. Atmospheric parameters and metal abundances are also derived. The resulting values are typical for sdB star s.