Binary White Dwarfs in the Supernova Ia Progenitor Survey

We report results of a systematic radial velocity survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae: SPY (ESO Supernovae Ia Progenitor surveY). More than 1000 white dwarfs (WDs) and pre-white dwarfs were observed with the VLT. The aim of SPY is to perform a statistically significant test of the DD scenario. We give an overview of the project and follow-up results. The sample is used for two tests of the contempo- rary picture of close binary evolution leading to DDs. It is shown that the SPY observations of low mass He-core WDs (HeWDs) are inconsistent with the idea that they all reside in close binary systems. We carry out a model atmosphere analysis of WDs residing in double-lined binaries and estimate individual cooling ages. For a number of systems the younger (and hotter) component is the less massive one, as expected. However, for some systems the mass ratio is inverted.