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 P_orb. 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 shortperiod 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_-0.09^+0.12 M_⊙, M₂ = 0.12_-0.02^-0.03 M_⊙, R₂ = 0.121_-0.007^-0.010 R., and a distance to the binary of 180 ± 40 pc.