High-speed photometry of AM CVn stars

We present high-speed photometry of three AM CVn stars discovered in the last few years (ES Cet, '2003aw' and SDSS J1240). ES Cet has a very stable photometric modulation with a single period of 620.2117 (+/- 0.0002) s (Espaillat et al. 2005) which is identical to its sFectroscopic period. The 2-sigma upper limit on the period derivative (15) of ES Cet is < 1.5 x 10(-11), based on a 3-year observational baseline. Since the discovery of '2003aw' in a supernova search, this AM CVn star has been observed during two outbursts and has a superhump modulation of P-sh = 2041.5 +/- 0.3 s. At quiescence, 2003aw is fairly faint (V similar to 20.4 mag) and no orbital period has yet been derived for this system. Two of the AM CVn stars (V803 Cen and CR Boo) show rapid oscillations similar to the (longer-period) dwarf nova oscillations and quasi-periodic oscillations seen in hydrogen-rich high-M CVs (Warner 2004).