Observations of Rapid Blue Variables-IX. AM CVN (HZ 29)

Photometric observations with 1- and 3-s time resolution demonstrate the existence of rapid flickering in AM CVn. Mean light curves confirm the existence of a double-humped light curve with a period near 18 min. Using our data, and previously published observations by Ostriker & Hesser, and Krzeminski, we derive a mean period of 1051·0505 s but show that there is some phase jitter about this period. Periodogram analyses show the existence of long-lived coherent periodicities in the range 115–120 s. A binary star model is suggested for AM CVn, with an orbital period of 18 min. It is proposed that AM CVn represents a late stage of evolution of a cataclysmic variable star, in which all hydrogen has been removed from the system.