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 P·~1.6×10-11. Phase-resolved spectroscopy of ES Cet obtained with the Hobby-Eberly Telescope shows a clear modulation on the photometric period, the assumed orbital 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).