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Are Unidentified Extreme-Ultraviolet Sources the Closest Neutron Stars?Unidentified extreme-ultraviolet (EUV) sources, detected in the EUVE and ROSAT WFC all-sky surveys, could be isolated old neutron stars, accreting material from the interstellar medium (ISM). The closest neutron stars, which are located in the local ISM bubble of unusually low density, are faint and cool (L approximately 10(exp 27) erg/s, T approximately < 6 eV). The extreme-UV spectrum of these sources is very sensitive to the H I column density, since a large fraction of the energy is emitted just below the hydrogen Lyman edge. The EUVE sources with large count rates in the long-wavelength bandpass (600 A) seem to be the most promising candidates. These sources should have low H I column density (N(sub H I) approximately < 10(exp 18) sq cm), constraining their distances to a few tens of parsecs. Otherwise, their spectra would be significantly modified by ISM absorption, and inevitably they would appear stronger in the short-wavelength (100 A, 200 A) EUVE bandpasses. If these unidentified objects are familiar EUV sources rather than neutron stars, i.e. white dwarfs, late-type stars or cataclysmic variables, they are expected to be identifiable, and generally brighter than V approximately 14.
Document ID
20000000247
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Shemi, A.
(Wise Observatory Tel Aviv, Israel)
Date Acquired
August 19, 2013
Publication Date
January 1, 1995
Publication Information
Publication: Monthly Notices of the Royal Astronomical Society
Volume: 275
Subject Category
Space Radiation
Funding Number(s)
CONTRACT_GRANT: NAG5-2913
Distribution Limits
Public
Copyright
Other

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