A RADIAL-VELOCITY STUDY OF THE DWARF NOVA AR ANDROMEDAE - COMPARISON OF THE QUIESCENT AND OUTBURST STATES

Radial velocity studies of the dwarf nova AR And during quiescence and eruption are presented and compared. These data strongly suggest the orbital period is 0.1640 +/- 0.0005 days, although 1 cycle day(-1) aliases of this period cannot be ruled out unequivocally. Despite being formed in dissimilar disk environments, the quiescent emission and outburst absorption lines yield similar radial velocity amplitudes. The quiescent emission-line amplitude obtained from measurements of H alpha is K-em = 83 +/- 7 km s(-1) The amplitude during outburst, as determined from analysis of the H beta and H gamma absorption lines is slightly lower, but consistent with the quiescent value. Observations obtained on 1991 December 10, similar to 1 week after outburst maximum, yielded K-abs = 74 +/- 10 km s(-1) for both H beta and H gamma. The following night the lines were weaker, the data noiser, and the spectra fewer, resulting in less reliable velocity amplitudes. Nevertheless, the average amplitude of 73 +/- 16 km s(-1) is consistent with the amplitudes determined on the previous night. The similarity between the emission- and absorption-line amplitudes in AR And is a robust result. The derived velocity amplitudes are insensitive to the portion of the line profiles used in the velocity measurements, suggesting that the disk radiation is nearly axisymmetric. This result is corroborated by a Doppler tomogram of the quiescent H alpha data, which shows that the emission is distributed fairly evenly over the surface of the disk. The results presented here add confidence that velocity variations of spectral features from the accretion disk in AR And may provide a reliable tracer of the orbital motion of the white dwarf in this system.