A detached double degenerate with a 1.4-h orbital period

We have discovered that the detached double degenerate binary WD 0957-666 hasan orbital period of 1.46 hours, rather than the 1.15 day orbital periodreported earlier. This is the shortest period example of such a system yetdiscovered. We obtain a unique period, which fits both our and earlier data. Atthis period the emission of gravitational radiation will cause the binary tomerge within approximately 2.0 x 10*8 years. This system represents apopulation of short orbital period binaries which will merge within a Hubbletime, and so could account for type Ia supernovae, although due to the low massof both stars (0.3 to 0.4 solar masses), it is unlikely to become a supernovaitself. We have detected the companion star and have measured a mass ratio of q= 1.15. This is the third double degenerate for which q has been measured andall three have q close to 1, which is in conflict with the predicted mass ratiodistribution which peaks at 0.7. This system is viewed close to edge on, and weestimate that the probability of this system undergoing eclipses is 15 %.Comment: 7 pages, with 7 encapsulated postscipts figures include