Hot White Dwarfs in the Local Interstellar Medium: Hydrogen and Helium Interstellar Column Densities and Stellar Effective Temperatures from Extreme-Ultraviolet Explorer Spectroscopy

1995 ◽  
Vol 455 ◽  
pp. 574 ◽  
Author(s):  
Jean Dupuis ◽  
Stephane Vennes ◽  
Stuart Bowyer ◽  
Anil K. Pradhan ◽  
Peter Thejll
Keyword(s):  
Interstellar Medium ◽  
White Dwarfs ◽  
Extreme Ultraviolet ◽  
Local Interstellar Medium ◽  
Effective Temperatures

scholarly journals Extreme Ultraviolet Observations of Hot White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 66-85 ◽  
Author(s):  
Stuart Bowyer
Keyword(s):  
Interstellar Medium ◽  
White Dwarfs ◽  
Thermal Emission ◽  
Extreme Ultraviolet ◽  
Upper Atmosphere ◽  
Wavelength Band ◽  
Upper Limits ◽  
Effective Temperatures ◽  
Ultraviolet Observations ◽  
The Universe

The term extreme ultraviolet (EUV or XUV) is employed in upper atmosphere physics and in solar work where it usually denotes the wavelength band between 100 and 1000 Å. Since thermal emission with 30,000 ≲ T ≲ 300,000 K peaks in this band, it might be expected that studies at these wavelengths would be especially useful for objects with effective temperatures in this range. In fact9 few such studies have been carried out. The reason for this anomaly is that very few EUV studies have been made at all, particularly because of unreasonably pessimistic estimates of the opacity of the interstellar medium and partially because of instrumental difficulties encountered at these wavelengths. The first search for extreme ultraviolet emitting objects was carried out in 1975 with instrumentation on the Apollo spacecraft in the Apollo-Soyuz mission. Four of approximately thirty preselected objects were detected with this instrumentation. The objects detected unquestionably are more a reflection of the prejudices of the investigators than they are a sampling of the contents of the universe. Nonetheless, two of the four objects detected were hot white dwarfs: HZ 43 and Feige 24. In addition, upper limits which turned out to be extremely useful were obtained on the Sirius A/B system. These results, plus more recent results obtained on hot white dwarfs will be discussed in this review.

scholarly journals The Interstellar and Circumstellar Environment of White Dwarfs

1997 ◽  
Vol 166 ◽  
pp. 69-74
Author(s):  
M.A. Barstow ◽  
P.D. Dobbie ◽  
J.B. Holberg
Keyword(s):  
Interstellar Medium ◽  
White Dwarfs ◽  
Column Density ◽  
Line Of Sight ◽  
Local Distribution ◽  
Local Interstellar Medium ◽  
Weighted Mean ◽  
Ionization Fraction ◽  
Absorbing Material ◽  
Circumstellar Environment

AbstractWe 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.

Extreme ultraviolet observations of G191-B2B and the local interstellar medium with the Hopkins Ultraviolet Telescope

1993 ◽  
Vol 404 ◽  
pp. 663 ◽  
Author(s):  
Randy A. Kimble ◽  
Arthur F. Davidsen ◽  
William P. Blair ◽  
Charles W. Bowers ◽  
W. Van Dyke Dixon ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Extreme Ultraviolet ◽  
Local Interstellar Medium ◽  
Ultraviolet Observations
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