NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
An X-ray survey of hot white dwarf stars - Evidence for a m(He)/n(H) versus Teff correlationObservations of 13 white dwarf and subdwarf stars using the Einstein Observatory High Resolution Image are reported. Included are stars of classes DA, DB, DAV, sDO, and sDB, with optically determined effective temperatures in the range 10,000-60,000 K. X-ray emission was detected from two of the 13: the very hot (55,000 K) DA1 star WD 2309 + 105 (= EG 233), with a count rate one-fifth that of HZ 43, and the relatively cool (26,000 K) DA3 star WD 1052 - 273 (=GD 125). The effective temperatures determined from ultraviolet and optical observations were used to place limits on the He content of the white dwarf photospheres, presuming that trace photospheric He is the missing opacity source which quenches the thermal X-rays in these stars. When presently obtained results were combined with those available from the literature evidence was found for a correlation between Teff and n(He)/n(H), in which HZ 43 is a conspicuous exception to the general trend. Both this correlation and the exceptional behavior of HZ 43 are qualitatively accounted for by a radiative acceleration model, in which the rate of upward movement of the He is a function of temperature and surface gravity
Document ID
19860051391
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Petre, R.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Shipman, H. L.
(Delaware, University Newark, United States)
Canizares, C. R.
(MIT Cambridge, MA, United States)
Date Acquired
August 12, 2013
Publication Date
May 1, 1986
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 304
ISSN: 0004-637X
Subject Category
Astrophysics
Funding Number(s)
CONTRACT_GRANT: NAG8-494
CONTRACT_GRANT: NSF AST-81-15095
CONTRACT_GRANT: NAG5-348
CONTRACT_GRANT: NSF AST-83-43067
Distribution Limits
Public
Copyright
Other
No Preview Available