Superhumps in Cataclysmic Binaries. XXIV. Twenty More Dwarf Novae

We report precise measures of the orbital and superhump period in twenty moredwarf novae. For ten stars, we report new and confirmed spectroscopic periods -signifying the orbital period P_o - as well as the superhump period P_sh. Theseare GX Cas, HO Del, HS Vir, BC UMa, RZ Leo, KV Dra, KS UMa, TU Crt, QW Ser, andRZ Sge. For the remaining ten, we report a medley of P_o and P_sh measurementsfrom 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, HVVir, and RX J1155.4-5641. Periods, as usual, can be measured to high accuracy, and these are of specialinterest since they carry dynamical information about the binary. We still havenot quite learned how to read the music, but a few things are clear. Thefractional superhump excess epsilon [=(P_sh-P_o)/P_o] varies smoothly with P_o.The scatter of the points about that smooth curve is quite low, and can be usedto limit the intrinsic scatter in M_1, the white dwarf mass, and themass-radius relation of the secondary. The dispersion in M_1 does not exceed24%, and the secondary-star radii scatter by no more than 11% from a fixedmass-radius relation. For the well-behaved part of epsilon(P_o) space, weestimate from superhump theory that the secondaries are 18+-6% larger thantheoretical ZAMS stars. This affects some other testable predictions about thesecondaries: at a fixed P_o, it suggests that the secondaries are (comparedwith ZAMS predictions) 40+-14% less massive, 12+-4% smaller, 19+-6% cooler, andless luminous by a factor 2.5(7). The presence of a well-defined mass-radiusrelation, reflected in a well-defined epsilon(P_o) relation, strongly limitseffects of nuclear evolution in the secondaries.