EDP Sciences
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Volume 374, Number 2, August I 2001
Page(s) 656 - 661
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20010787

A&A 374, 656-661 (2001)
DOI: 10.1051/0004-6361:20010787

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

B. T. Gänsicke1, P. Szkody2, E. M. Sion3, D. W. Hoard4, S. Howell5, F. H. Cheng3 and I. Hubeny6

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

(Received 3 April 2001 / Accepted 28 May 2001 )

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 ${\rm Ly\alpha}$ 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 $M_{\odot}$ we derive $T_{\rm eff}=17 500$-23 400 K for the primary in EK TrA; $T_{\rm eff}=18 800$ K for a canonical mass of 0.6 $M_{\odot}$. From the narrow photospheric absorption lines, we measure the white dwarf rotational velocity, $v\sin i=200\pm100$ $\rm km s^{-1}$. 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.

Key words: accretion, accretion disks -- stars: individual: EK TrA -- stars: novae, cataclysmic variables -- stars: white dwarfs -- ultraviolet: stars

Offprint request: B. T. Gänsicke, boris@uni-sw.gwdg.de

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