Superhumps in Cataclysmic Binaries. XXII. 1RXS J232953.9+062814

We report photometry of a recently discovered dwarf nova with a remarkably short 64.2 minute orbital period. In quiescence, the star’s light curve is that of a double sinusoid, arising from the “ellipsoidal” distortion of the Roche‐lobe–filling secondary. During superoutburst, common superhumps develop with a period 3%–4% longer than Porb. This indicates a mass ratio M2/M1 = 0.19 ± 0.02, a surprisingly large value in so compact a binary. This implies that the secondary star has a density 2–3 times higher than that of other short‐period dwarf novae, suggesting a secondary enriched by H‐burning prior to the common‐envelope phase of evolution. We estimate i = 50° ± 5°, M1 = 0.63+0.12-0.09 M⊙, M2 = 0.12+0.03-0.02 M⊙, R2 = 0.121+0.010-0.007 R⊙, and a distance to the binary of 180 ± 40 pc.