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The Interstellar and Circumstellar Environment of White Dwarfs
conference contribution
posted on 2023-05-23, 07:03 authored by Barstow, MA, Dobbie, PD, Holberg, JBWe 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.
History
Publication title
The Local Bubble and Beyond Lyman-Spitzer-ColloquiumVolume
506Editors
Dieter Breitschwerdt, Michael Freyberg, Joachim TrümperPagination
69-74ISBN
978-3-540-64306-7Department/School
School of Natural SciencesPublisher
SpringerPlace of publication
Berlin HeidelbergEvent title
IAU Colloquium No. 166Event Venue
Garching, GermanyDate of Event (Start Date)
1997-04-21Date of Event (End Date)
1997-04-25Rights statement
Copyright 1998 SpringerRepository Status
- Restricted