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EUVE spectroscopy of epsilon Canis Majoris (B2 II) from 70 to 730 AWe present spectra of the brightest stellar source of extreme ultraviolet (EUV) radiation longward of 400 A, the B2 II star, epsilon CMa. These data were taken with the three spectrometers aboard the NASA Extreme Ultraviolet Explorer satellite (EUVE) during the first cycle of pointed observations. We report on our initial studies of the continuum and line spectrum of the stellar photosphere in the 320 to 730 A region, and on the wind emission lines observed in the 170-375 A region. This is the first EUV spectrum of an early-type star, and thus makes epsilon CMa the most comprehensively observed B star from the X-ray to infrared regimes. The radiation in both the H Lyman continuum and He I continuum (shortward of 504 A) are found to be significantly greater than predicted by both Local Thermodynamic Equilibrium (LTE) and non-LTE model atmospheres. Since epsilon CMa also exhibits a mid-infrared excess, this points to the outer layers being warmer than the models indicate. The anomalously large Lyman continuum flux, combined with the very low column density measured in the direction toward this star implies that it is the dominant source of hydrogen ionization of the local interstellar medium in the immediate vicinity of the sun. All of the lines predicted to be strong from model atmospheres are present and several wind absorption features are also identified. We have detected emission lines from highly ionized iron that are consistent with the ROSAT Position Sensitive Proportional Counter (PSPC) observations if a multi-temperature emission model is used, and the assumption is made that there is significant absorption beyond that of the neutral phase of the ISM. The spectrum shows strong O III 374 A line emission produced by the Bowen flourescence mechanism, which has not previously been observed in the spectra of hot stars.
Document ID
19950036993
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Cassinelli, J. P.
(Univ. of Wisconsin, Madison, WI United States)
Cohen, D. H.
(Univ. of Wisconsin, Madison, WI United States)
Macfarlane, J. J.
(Univ. of Wisconsin, Madison, WI United States)
Drew, J. E.
(Univ. of Oxford Oxford, United Kingdom)
Lynas-Gray, A. E.
(Univ. of Oxford Oxford, United Kingdom)
Hoare, M. G.
(MPI fuer Astronomie Heidelberg, Germany)
Vallerga, J. V.
(Eureka Scientific, Oakland, CA United States)
Welsh, B. Y.
(Univ. of California, Berkeley, CA United States)
Vedder, P. W.
(Eureka Scientific, Oakland, CA United States)
Hubeny, I.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 16, 2013
Publication Date
January 10, 1995
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 438
Issue: 2
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A68592
Funding Number(s)
CONTRACT_GRANT: NAGW-3834
CONTRACT_GRANT: NAGW-3025
CONTRACT_GRANT: NAGW-2282
Distribution Limits
Public
Copyright
Other

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