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) ali ases of this period cannot be ruled out unequivocally. Despite being f ormed in dissimilar disk environments, the quiescent emission and outb urst absorption lines yield similar radial velocity amplitudes. The qu iescent emission-line amplitude obtained from measurements of H alpha is K-em = 83 +/- 7 km s(-1) The amplitude during outburst, as determin ed from analysis of the H beta and H gamma absorption lines is slightl y lower, but consistent with the quiescent value. Observations obtaine d on 1991 December 10, similar to 1 week after outburst maximum, yield ed K-abs = 74 +/- 10 km s(-1) for both H beta and H gamma. The followi ng night the lines were weaker, the data noiser, and the spectra fewer , resulting in less reliable velocity amplitudes. Nevertheless, the av erage amplitude of 73 +/- 16 km s(-1) is consistent with the amplitude s determined on the previous night. The similarity between the emissio n- and absorption-line amplitudes in AR And is a robust result. The de rived velocity amplitudes are insensitive to the portion of the line p rofiles used in the velocity measurements, suggesting that the disk ra diation is nearly axisymmetric. This result is corroborated by a Doppl er tomogram of the quiescent H alpha data, which shows that the emissi on is distributed fairly evenly over the surface of the disk. The resu lts presented here add confidence that velocity variations of spectral features from the accretion disk in AR And may provide a reliable tra cer of the orbital motion of the white dwarf in this system.