THE ROTATION RATE AND SURFACE TEMPERATURE OF THE HOT, ACCRETING WHITE DWARF IN THE DWARF NOVA RX ANDROMEDAE

We obtained Hubble GHRS phase-resolved spectroscopic observations of the dwarf nova RX Andromedae at three times in its outburst cycle: (1) near the end of an extraordinarily deep and long dwarf nova quiescence, 3 months after the last previous outburst; (2) during the rise to outburst; and (3) near the end of a decline from outburst. The spectral wavelength range covered was 1149A to 1435A. All of the spectra are dominated by absorption lines with weak to moderately strong emission wings due to the continued presence of disk material. Uncertainities in line velocities preclude a K 1 determination or mass information. Our best fitting model yielded T wd /1000 = 34.0 ±0.1K, log g = 8.0 ±0.1, and V rot = 600 km/s. The T eff value is very similar to the T eff of the white dwarf in U Gem, but the rotational velocity appears to be higher than U Gem’s value. We report approximate subsolar chemical abundances of Carbon and Silicon for RX And, with C being 0.05 x solar and Si = 0.1 x solar while other elements are at essentially their solar values. However, accurate abundances are complicated by line emission and we cannot exclude that the abundances of all species are essentially at the solar values. We see no evidence of thermonuclear-processed abundance ratios. If the white dwarf mass is 0.8 M (Ritter 1999), then the