Superhumps in Cataclysmic Binaries. XXIV. Twenty More Dwarf Novae

We report precise measures of the orbital and superhump period in 20 more dwarf novae. For 10 stars, we report new and confirmed spectroscopic periods—signifying the orbital period Po—as well as the superhump period Psh. These are GX Cas, HO Del, HS Vir, BC UMa, RZ Leo, KV Dra, KS UMa, TU Crt, QW Ser, and RZ Sge. For the remaining 10, we report a medley of Po and Psh measurements from photometry; most are new, with some confirmations of previous values. These are KV And, LL And, WX Cet, MM Hya, AO Oct, V2051 Oph, NY Ser, KK Tel, HV Vir, and RX J1155.4−5641. Periods, as usual, can be measured to high accuracy, and these are of special interest since they carry dynamical information about the binary. We still have not quite learned how to read the music, but a few things are clear. The fractional superhump excess ε[= (Psh - Po)/Po] varies smoothly with Po. The scatter of the points about that smooth curve is quite low, and can be used to limit the intrinsic scatter in M1, the white dwarf mass, and the mass‐radius relation of the secondary. The dispersion in M1 does not exceed 24%, and the secondary‐star radii scatter by no more than 11% from a fixed mass‐radius relation. For the well‐behaved part of ε(Po) space, we estimate from superhump theory that the secondaries are 18% ± 6% larger than theoretical ZAMS stars. This affects some other testable predictions about the secondaries: at a fixed Po, it suggests that the secondaries are (compared with ZAMS predictions) 40% ± 14% less massive, 12% ± 4% smaller, 19% ± 6% cooler, and less luminous by a factor of 2.5(7). The presence of a well‐defined mass‐radius relation, reflected in a well‐defined ε(Po) relation, strongly limits effects of nuclear evolution in the secondaries.