Double Degenerates from the Supernova IA Progenitor Survey (SPY)

Close binary systems consisting of two white dwarfs (double degenerates — DDs) are considered possible progenitors of Supernovae type Ia. The SPY project (Napiwotzki et al., these proceedings) surveys a large sample of white dwarfs for radial velocity (RV) variations. DDs are the result of close binary evolution, but the theoretical modeling of this evolution depends heavily on some not well known parameters (Nelemans et al., 2001). Therefore, an important way to calibrate these parameters is by comparison of observed system parameters such as periods and mass ratios of DDs with results of theoretical calculations. We present follow-up observations of four DDs found by the SPY project, which allowed us to derive radial velocity curves and system parameters. Two systems are of particular interest because they have double lined spectra.