The Donor Stars of Cataclysmic Variables

We carefully consider observational and theoretical constraints on the global properties of secondary stars in cataclysmic variable stars (CVs). We then use these constraints to construct and test a complete, semi-empirical donor sequence for CVs with orbital periods Porb � 6 hrs. All key physical and photometric parameters of CV secondaries (along with their spectral types) are given as a function of Porb along this sequence. This provides a benchmark for observational and theoretical studies of CV donors and evolution. The main observational basis for our donor sequence is an empirical mass-radius relationship for CV secondaries. Patterson and co-workers have recently shown that this can be derived from superhumping and/or eclipsing CVs. We independently revisit all of the key steps in this derivation, including the calibration of the period excess-mass ratio relation for superhumpers and the use of a single representative primary mass for most CVs. We also present an optimal techique for estimating the parameters of the mass-radius relation that simultaneously ensures consistency with the observed locations of the period gap and the period minimum. We present new determinations of these periods, finding Pgap,+ = 3.18 ± 0.04 hrs

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