SIMBAD references

The unusual variable star AM CVn has puzzled astronomers for over 40 years. This object, both a photometric and spectroscopic variable, is believed to contain a pair of hydrogen deficient white dwarfs of extreme mass ratio, transferring material via an accretion disk. We have examined the phase stability of the dominant photometric variation at 1902.5 µHz, analyzing 289 hours of high speed photometric data spanning 1976 to 1992, and have determined the dominant frequency to be (1902.509802±0.00001) µHz, with {dot}(P) = (+1.71±0.04)x10^–11 s s^–1.