ORBITAL PERIODS FOR 7 DWARF NOVAE OF THE SU-URSAE-MAJORIS SUBCLASS FROM RADIAL-VELOCITIES AT MINIMUM LIGHT

We obtained time-resolved spectroscopy of seven SU UMa-type dwarf nova e and determined orbital periods from velocities of their Her emission lines. The stars and their periods are FO And (0.07161 d=103.1 min), FS Aur (0.0595 d=85.7 min), WX Cet (0.05826 d=83.9 min), AQ Eri (0.060 93 d=87.7 min), TY Psc (0.06833 d=98.4 min), CY UMa (0.06957 d=100.2 m in), and SS UMi (0.06778 d=97.6 min). This substantially increases the number of well-determined orbital periods P-orb for SU UMa stars. The period uncertainties are all <0.3 per cent, sufficient to confront th eories accounting for the superhumps observed photometrically during s uperoutbursts. Combining these periods with others from the literature we show that the correlation between superhump period excess Delta P/ P-orb and P-orb is described by Delta P/P-orb=-0.0344+(0.0382 hr(-1))X P(orb). The correlation is clear, but the scatter is greater than the measurement uncertainties. We also obtained contemporaneous time-serie s photometry in the low state for TY Psc, AQ Eri, SS UMi, and CY UMa. TY Psc shows a similar to 0.2 mag modulation at the orbital period. Wh ile the others all show considerable variation, none of them appeared to vary periodically, and none eclipse. The white-dwarf photosphere in TY Psc is noticeable in the optical spectrum at minimum light.