AM CVn stars in the UCT CCD CV survey

Abstract

High speed photometry of the helium-transferring binary ES Cet - taken over a two-year period (2001 October - 2003 October) - shows a very stable photometric period of 620.211437 +/- 0.000038 s, with a tentative indication of curvature in the O-C diagram suggesting a change in period at a rate of dP/dt ~ 1.6x10^-11. Phase-resolved spectroscopy of ES Cet obtained with the Hobby-Eberly Telescope shows a clear modulation on the photometric period. We have followed a newly identified AM CVn star (`2003aw') photometrically through its 2003 February/March outburst during which it varied in brightness over a range of V = 16.5 - 20.3; we find a superhump period of 2041.5 +/- 0.3 s. Questions are raised about the reality of the detected spin-up in RX J0806 (Hakala et al. 2003; Strohmayer 2003).