The Orbital Period Distribution of Cataclysmic Variables Found by the SDSS

The orbital period is one of the most accessible observables of a cataclysmic variable. It has been a concern for many years that the orbital period distribution of the known systems does not match that predicted by evolutionary theory. The sample of objects discovered by the Sloan Digital Sky Survey has changed this: it shows the long-expected predominance of short-period objects termed the `period spike'. The minimum period remains in conflict with theory, suggesting that the angular momentum loss mechanisms are stronger than predicted.