SIMBAD references

We report on successes and failures in searching for positive superhumps in cataclysmic variables, and show the superhumping fraction as a function of orbital period. Basically, all short-period system do, all long-period systems do not, and a 50% success rate is found at P_orb=3.1±0.2 hr. We can use this to measure the critical mass ratio for the creation of superhumps. With a mass-radius relation appropriate for cataclysmic variables, and an assumed mean white-dwarf mass of 0.75 M_☉, we find a mass ratio q_crit=0.35±0.02. We also report superhump studies of several stars of independently known mass ratio: OU Vir, XZ Eri, UU Aqr, and KV UMa (=XTE J1118+480). The latter two are of special interest, because they represent the most extreme mass ratios for which accurate superhump measurements have been made. We use these to improve the {epsiv}(q) calibration, by which we can infer the elusive q from the easy-to-measure {epsiv} (the fractional period excess of P_superhumpover P_orb). This relation allows mass and radius estimates for the secondary star in any cataclysmic variable (CV) showing superhumps. The consequent mass-radius law shows an apparent discontinuity in radius near 0.2 M_☉, as predicted by the disrupted magnetic braking model for the 2.1-2.7 hr period gap. This is effectively the ``empirical main sequence'' for CV secondaries.