A DETACHED DOUBLE DEGENERATE WITH A 1.4-H ORBITAL PERIOD

We have discovered that the detached double degenerate binary WD 0957 - 666 has an orbital period of 1.46 h, rather than the 1.15-d orbital period reported earlier. This is the shortest period example of such a system yet discovered. We obtain a unique period, which fits both our data and earlier data. At this period the emission of gravitational r adiation will cause the binary to merge within approximately 2.0 x 10( 8) yr. This system represents a population of short orbital period bin aries which will merge within a Hubble time, and so could account for type Ia supernovae, although, due to the low mass of both stars (0.3 t o 0.4 M-.), it is unlikely to become a supernova itself. We have detec ted the companion star and have measured a mass ratio of q=1.15+/-10.1 0. This is the third double degenerate for which q has been measured, and all three have q similar or equal to 1, which is in conflict with the predicted mass ratio distribution, which peaks at 0.7. This system is viewed close to edge-on, and we estimate that the probability of t his system undergoing eclipses is 15 per cent.