PX Andromedae: Superhumps and variable eclipse depth

Abstract

Results of a photometric study of the SW Sex novalike PX And are presented. The periodogram analysis of the observations obtained in October 2000 reveals the presence of three signals with periods of 0.142, 4.8 and 0.207 days. The first two periods are recognized as "negative superhumps" and the corresponding retrograde precession period of the accretion disk. The origin of the third periodic signal remains unknown. The observations in September-October 2001 point only to the presence of "negative superhumps" and possibly to the precession period. The origin of the "negative superhumps" is discussed and two possible mechanisms are suggested. All light curves show strong flickering activity and power spectra with a typical red noise shape. PX And shows eclipses with highly variable shape and depth. The analysis suggests that the eclipse depth is modulated with the precession period and two possible explanations of this phenomenon are discussed. An improved orbital ephemeris is also determined: T_min[HJD]=49238.83662(14)+0.146352739(11)E.