Binaries discovered by the SPY project. I. HE 1047-0436: A subdwarf B white dwarf syste

In the course of our search for double degenerate binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SNIa Progenitor surveY { SPY) we discovered that the sdB star HE1047−0436 is radial velocity variable. The orbital period of 1.213253 d, a semi-amplitude of 94 kms−1, and a minimum mass of the invisible companion of 0:44M 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 constrain the system inclination and the companion mass to M > 0:71M , bringing the total mass of the system closer to the Chandrasekhar limit. However, the 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 stars.