High-resolution Spectroscopy of Feige 24 in the Extreme-ultraviolet

We report the first high-resolution (R = 4000) spectroscopic observation of the binary DA white dwarf Feige 24 in the extreme-ultraviolet band 220-250 A. A stellar atmosphere model assuming a homogeneous element distribution yields a best fit to the data that excludes a significant abundance of phot...

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Bibliographic Details
Published inThe Astrophysical journal Vol. 730; no. 2; pp. 115 - jQuery1323909900630='48'
Main Authors Kowalski, M. P, Barstow, M. A, Wood, K. S, Yentis, D. J, Fritz, G. G, Lapington, J. S, Barbee, T. W, Berendse, F. B, Cruddace, R. G
Format Journal Article
LanguageEnglish
Published Bristol IOP Publishing 01.04.2011
IOP
Subjects
ABSORPTION
ABUNDANCE
Astronomy
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
DISTRIBUTION
Earth, ocean, space
Exact sciences and technology
EXTREME ULTRAVIOLET RADIATION
HELIUM
HYDROGEN
IONIZATION
LAYERS
SPECTROSCOPY
STELLAR ATMOSPHERES
TELESCOPES
WHITE DWARF STARS
Lower bound
Spectroscopy
White dwarf stars
Atmosphere model
stars: evolution
Stellar abundance
Stellar evolution
Star models
stars: abundances
Stellar atmospheres
Absorption line
Upper bound
white dwarfs
Ionization
techniques: spectroscopic
Solar neighborhood
ultraviolet: stars
Spectroscopical observation
Interstellar matter
local interstellar matter
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Summary:We report the first high-resolution (R = 4000) spectroscopic observation of the binary DA white dwarf Feige 24 in the extreme-ultraviolet band 220-250 A. A stellar atmosphere model assuming a homogeneous element distribution yields a best fit to the data that excludes a significant abundance of photospheric helium. The upper limit on the photospheric helium abundance is 2.5 X 10--6 (90% confidence), equivalent to a lower limit of 1.2 X 10--13 M on the overlying layer of hydrogen. An ionized interstellar He component (3.9 X 1017 cm--2) is clearly present along the line of sight, which implies an He ionization fraction of 0.72, considerably higher than is typical of the local interstellar medium. However, some of this material may be associated with circumstellar gas, which has been detected by analysis of the C IV absorption line doublet in a Hubble Space Telescope/Space Telescope Imaging Spectrograph spectrum.
Bibliography:ObjectType-Article-1
SourceType-Scholarly Journals-1
ObjectType-Feature-2
content type line 23
BNL-97921-2012-JA
DE-AC02-98CH10886
USDOE SC OFFICE OF SCIENCE (SC)
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/730/2/115