HST/STIS spectroscopy of the exposed white dwarf in the short-period dwarfnova EK TrA

We present high resolution Hubble Space Telescope ultraviolet spectroscopy of the dwarf nova EK TrA obtained in deep quiescence. The Space Telescope I maging Spectrograph data reveal the broad Ly alpha absorption profile typic al of a moderately cool white dwarf, overlayed by numerous broad emission l ines of He, C, N, and Si and by a number of narrow absorption lines, mainly of C I and Si II. Assuming a white dwarf mass in the range 0.3-1.4 M. we d erive T-eff = 17 500-23 400 K for the primary in EK TrA; T-eff = 18 800 K f or a canonical mass of 0.6 M.. From the narrow photospheric absorption line s, we measure the white dwarf rotational velocity, v sin i = 200 +/- 100 km s(-1). Even though the strong contamination of the photospheric white dwar f absorption spectrum by the emission lines prevents a detailed quantitativ e analysis of the chemical abundances of the atmosphere, the available data suggest slightly sub-solar abundances. The high time resolution of the STI S data allows us to associate the observed ultraviolet flickering with the emission lines, possibly originating in a hot optically thin corona above t he cold accretion disk.