Binaries discovered by the SPY project. III. HE 2209-1444: A massive, short period double degenerate

In the course of our search for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY – SPY) we discovered HE2209−1444 to be a double-lined system consisting of two DA white dwarfs. From the analysis of the radial velocity curve we determined the period of the system to be P = 6h38m47s. The semi-amplitudes for both individual components are 109 km s−1 each. A model atmosphere analysis enabled us to derive individual temperatures for both components (8490 K and 7140 K, resp.) and masses of 0.58 M for each component. The total mass of the system is 1.15 ± 0.07 M . The system will lose angular momentum due to gravitational wave radiation and therefore will merge within 5 Gyrs – less than a Hubble time. HE 2209−1444 is the second massive, short period double degenerate detected by SPY. Its total mass is about 20% below the Chandrasekhar mass limit and therefore it does not qualify as a potentional SN Ia progenitor. However, together with our previous detections it supports the view that Chandrasekhar mass systems do exist.