The Noah Project: detection of the spin-orbit beat period of BY Camelopardalis

BY Camelopardalis is one of only three known asynchronous AM Herculis-type cataclysmic variables (CVs). The slightly different spin and orbital periods lead to a predicted beat period of about two weeks. We collected at least one orbit worth of observations of BY Cam on each of 46 nights over a period of four months to detect and study the beat phenomena. We detected a period of 7.26 d both in the O-C values of the photometric variation and in the amplitude of a sine wave fit to individual orbits of data. This period most likely represents half of the true beat period of 14.52 d. We also measured a photometric period of 0.137111 d, shorter than the previously suggested spin periods, from our large data set. Smaller sections of data showed a period closer to the previously published spin period. The photometric variation is caused by the white dwarf spin, but the accretion spot slips on the white dwarf surface over the course of a beat period, causing the shorter photometric period. Given the observed beat and photometric periods, we obtain a white dwarf spin period of 0.1384339+/-0.000003 d, consistent with previous measurements. A search of a subset of the data for periodicities from 6 to 40 min showed significant power in this range consistent with shot noise, flickering and broad peaks around 10 and 15 min.