Abstract
ABSTRACT We obtained time-resolved spectroscopy of seven SU UMa-type dwarf novae and determined orbital periods from velocities of their H-alpha emission lines. The stars and their periods are FO And (0.07161 d=103.1 min), FS Aur (0.0595 d=87.7 min), WX Cet (0.05826 d=82.9 min), AQ Eri (0.06093 d=87.7 min), TY Psc (0.06833 d=98.4 min), CY UMa (0.06957 d=100.2 min), and SS UMi (0.06778 d=97.6 min). This substantially increases the number of well-determined orbital periods Porb for SU UMa stars. The period uncertainties are all < 0.3 percent, sufficent to confront theories accounting for the superhumps observed photometrically during superoutbursts. Combining these periods with others from the literature we show that the correlation between superhump period excess delta-P/Porb and Porb is described by delta-P/Porb = -0.0344+(0.0382 hr-1) X Porb. The correlation is clear, but the scatter is greater than the measurement uncertainties. We also obtained contemporaneous timeseries photometry in the low state for TY Psc, AZ Eri, SS UMi, and CY UMa. TY Psc shows a ~0.2 mag modulation at the orbital period. While the others all show considerable variation, none of them appeared to vary periodically, and none eclipse. The white dwarf photosphere in TY Psc is noticable in the optical spectrum at minimum light.
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