  We have used HST/COS to obtain a series of 4 FUV (915-2148A) spectroscopic
observations of the prototypical dwarf nova U Geminorum during its cooling
following a two-week outburst. Our FUV spectral analysis of the data indicates
that the white dwarf (WD) cools from a temperature of 41,500 K, 15 days after
the peak of the outburst, to 36,250 K, 56 days after the peak of the outburst,
assuming a massive WD (log(g)=8.8) and a distance of 100.4 pc. These results
are self-consistent with a 1.1 solar mass WD with a 5,000 km radius. The
spectra show many absorption lines of but no emission features. We find
supra-solar abundances of nitrogen confirming the anomalous high N/C ratio. The
FUV lightcurve reveals a 5% modulation with the orbital phase, showing dips
near phase 0.25 and 0.75, where the spectra exhibit an increase in the depth of
some absorption lines and in particular strong absorption lines from Si, Al,
and Ar. The phase dependence we observe is consistent with material overflowing
the disk rim at the hot spot, reaching a maximum elevation near phase 0.75,
falling back at smaller radii near phase 0.5 where it bounces off the disk
surface and again rising above the disk near phase 0.25. There is a large
scatter in the absorption lines' velocities, especially for the silicon lines,
while the carbon lines seem to match more closely the orbital velocity of the
WD. This indicates that many absorption lines are affected by- or form in- the
overflowing stream material veiling the WD, making the analysis of the WD
spectra more difficult.
