\bf Hubble Space Telescope HRS Spectroscopy of U GEMINORUM in Quiescence: Rotation of the White Dwarf
Session 63 -- Intrinsic and Cataclysmic Variables
Display presentation, Thursday, 9:20-4:00, Heller Lounge Room

[63.09] \bf Hubble Space Telescope HRS Spectroscopy of U GEMINORUM in Quiescence: Rotation of the White Dwarf

E.M. Sion, M. Huang (Villanova U.), K. Long (STScI), P. Szkody (U. Wash.), K. Horne (STScI)

of U Gem in quiescence, on September 23, 1992, 24 days after the start of its outburst of 29 August, 1992 and 8 days after the return to optical quiescence. The observation was made using the G160M disperser and covered the region 1370 \AA\ to 1402 \AA. We report the detection of the first fully resolved line profile (Si IV 1393, 1402 resonance doublet) of a cataclysmic variable white dwarf. The profile is unsaturated, both line cores are resolved and the wings of the profiles appear too broad for the central depths, suggesting that rotational broadening is contributing significantly as well as collisional broadening. The components have widths of approximately 2\AA. If the widths are dominated by rotational broadening, then an upper limit v sin i = $\sim$ 500 km/s is implied. The line centers are red-shifted to a velocity of 148 km/s. A preliminary fit, using theoretical profiles by I. Hubeny for T$_{eff}$ = 30,000K, log g = 7, requires a silicon abundance greater than solar in order to match the observed profiles. The results of more extensive profile fitting will be presented. The absence of O V 1371 provides an important constraint on the oxygen abundance and temperature of any heated equatorial region still present at the time of our observation.

Support of this work was provided by NASA through grant GO3836.0191A from the Space Telescope Institute.