HST observations of the pulsating white dwarf GD 358

¹ Instituto de Física, Universidade Federal do Rio Grande do Sul, 91501-900 Porto-Alegre, RS, Brazil e-mail: barbara@if.ufrgs.br
² Sloan Digital Sky Survey, Apache Pt. Observatory, PO Box 59, Sunspot, NM 88349, USA
³ Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712, USA
⁴ Institut für Theoretische Physik und Astrophysik, Universität Kiel, 24098 Kiel, Germany

Received: 2 July 2004
Accepted: 20 October 2004

Abstract

We used time-resolved ultraviolet spectroscopy obtained with the FOS and STIS spectrographs of the Hubble Space Telescope (HST), together with archival IUE observations to measure the effective temperature (), surface gravity () and distance (d) of the pulsating DB white dwarf GD 358 with unprecedented accuracy, and to show that the temperature did not change during the 1996 sforzando, when the star changed basically to a single mode pulsator. We also measured for the first time for a DBV the spherical harmonic degree () for two modes, with and , which was only possible because the stellar light curve was dominated by a single mode in 1996. The independent spectra provide the following values:  K, and   pc. The ultraviolet spectroscopic distance is in better agreement with the seismological value, than the one derived by parallax.