The helium-rich cataclysmic variable ES ceti

We report photometry of the helium-rich cataclysmic variable ES Ceti during 2001-2004. The star is roughly stable at V ∼ 17.0 and has a light curve dominated by a single period of 620 s, which remains measurably constant over the 3 yr baseline. The weight of evidence suggests that this is the true orbital period of the underlying binary, not a "superhump" as initially assumed. We report GALEX ultraviolet magnitudes that establish a very blue flux distribution (F v ∼ v 1.3) and therefore a large bolometric correction. Other evidence (the very strong He II λ4686 emission and a ROSAT detection in soft X-rays) also indicates a strong EUV source, and comparison to helium atmosphere models suggests a temperature of 130 ± kK. For a distance of 350 pc, we estimate a luminosity of (0.8-1.7) × 10 34 ergs s -1, yielding a mass accretion rate of (2-4) × 10 -9 M⊙ yr -1 onto an assumed 0.7 M⊙ white dwarf. This appears to be about as expected for white dwarfs orbiting each other in a 10 minute binary, assuming that mass transfer is powered by gravitational radiation losses. We estimate mean accretion rates for other helium-rich cataclysmic variables and find that they also follow the expected Ṁ ∼ P 0-5 relation. There is some evidence (the lack of superhumps and the small apparent size of the luminous region) that the mass-transfer stream in ES Cet directly strikes the white dwarf, rather than circularizing to form an accretion disk. © 2005. The Astronomical Society of the Pacific. All rights reserved.