|Author||Petre, R. ♦ Shipman, H. L. ♦ Canizares, C. R.|
|Source||United States Department of Energy Office of Scientific and Technical Information|
|Subject Keyword||CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS ♦ COSMIC X-RAY SOURCES ♦ WHITE DWARF STARS ♦ X RADIATION ♦ ABUNDANCE ♦ STAR MODELS ♦ ULTRAVIOLET SPECTRA ♦ VISIBLE SPECTRA ♦ COSMIC RAY SOURCES ♦ DWARF STARS ♦ ELECTROMAGNETIC RADIATION ♦ IONIZING RADIATIONS ♦ MATHEMATICAL MODELS ♦ RADIATIONS ♦ SPECTRA ♦ STARS ♦ Astrophysics & Cosmology- Quasi-Stellar, Radio, & X-Ray Sources- (-1987)|
|Abstract||Observations 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 59 references.|
|Learning Resource Type||Article|
|Publisher Department||NASA, Goddard Space Flight Center, Greenbelt, MD ♦ Delaware Univ., Newark ♦ MIT, Cambridge, MA|
|Publisher Place||United States|
|Organization||NASA, Goddard Space Flight Center, Greenbelt, MD ♦ Delaware Univ., Newark ♦ MIT, Cambridge, MA|
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