HST/STIS spectroscopy of the exposed white dwarf in the short-period dwarf nova EK TrA^*

¹ Universitäts-Sternwarte, Geismarlandstr. 11, 37083 Göttingen, Germany
² Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195, USA
³ Department of Astronomy & Astrophysics, Villanova University, Villanova, PA 19085, USA
⁴ Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile
⁵ Astrophysics Group, Planetary Science Institute, 620 North 6th Avenue, Tucson, AZ 85705, USA
⁶ Laboratory for Astronomy and Solar Physics, NASA/GSFC, Greenbelt, MD 20711, USA

Corresponding author: B. T. Gänsicke, boris@uni-sw.gwdg.de

Received: 3 April 2001
Accepted: 28 May 2001

Abstract

We present high resolution Hubble Space Telescope ultraviolet spectroscopy of the dwarf nova EK TrA obtained in deep quiescence. The Space Telescope Imaging Spectrograph data reveal the broad absorption profile typical of a moderately cool white dwarf, overlayed by numerous broad emission lines of He, C, N, and Si and by a number of narrow absorption lines, mainly of CI and SiII. Assuming a white dwarf mass in the range 0.3-1.4 we derive - K for the primary in EK TrA; K for a canonical mass of 0.6 . From the narrow photospheric absorption lines, we measure the white dwarf rotational velocity, . Even though the strong contamination of the photospheric white dwarf absorption spectrum by the emission lines prevents a detailed quantitative analysis of the chemical abundances of the atmosphere, the available data suggest slightly sub-solar abundances. The high time resolution of the STIS data allows us to associate the observed ultraviolet flickering with the emission lines, possibly originating in a hot optically thin corona above the cold accretion disk.