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The Interstellar and Circumstellar Environment of White Dwarfs

Citation

Barstow, MA and Dobbie, PD and Holberg, JB, The Interstellar and Circumstellar Environment of White Dwarfs, The Local Bubble and Beyond Lyman-Spitzer-Colloquium, 21-25 April 1997, Garching, Germany, pp. 69-74. ISBN 978-3-540-64306-7 (1998) [Refereed Conference Paper]

Copyright Statement

Copyright 1998 Springer

DOI: doi:10.1007/BFb0104696

Abstract

We have studied the EUV spectra of 13 DA white dwarfs, observed by the EUVE satellite, paying attention to the possible sources of absorbing material along the lines-of-sight in both the local interstellar medium and in the photospheres of the stars themselves. The range of interstellar column densities seen are consistent with our previous understanding of the local distribution of material. Absorption from interstellar He II is found in the direction of five stars, allowing us to measure directly the He ionization fraction and estimate, indirectly, that of H. The weighted mean ionization fractions along these lines-of-sight are 0.27 0.04 and 0.35 0.1 respectively. Where He ii is directly detected, the observed ionization fractions are not correlated with direction or with the volume/column density of material along the line-of-sight. Furthermore, the limits on the amount of He II established in all other directions completely encompass the range of observed values. Indeed, all the data can be consistent with more or less constant He and H ionization fractions throughout the local ISM. However, observation of very hot DA stars, indicating higher He ii columns, might contradict this picture if the material is not photospheric or circumstellar.

Item Details

Item Type:Refereed Conference Paper
Keywords:astronomy, astrophysics, relativity and cosmology
Research Division:Physical Sciences
Research Group:Astronomical and Space Sciences
Research Field:Stellar Astronomy and Planetary Systems
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Physical Sciences
Author:Dobbie, PD (Dr Paul Dobbie)
ID Code:81195
Year Published:1998
Deposited By:Mathematics and Physics
Deposited On:2012-11-26
Last Modified:2013-08-13
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