{ital EUVE} observations of U Geminorum in outburst

Journal Article · Tue Oct 01 04:00:00 EDT 1996 · Astrophysical Journal

DOI:https://doi.org/10.1086/177832· OSTI ID:467177

Long, K S ^[1]; Mauche, C W ^[2]; Raymond, J C ^[3]; Szkody, P ^[4]; Mattei, J A ^[5]

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1. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218 (United States)
2. Lawrence Livermore National Laboratory, L-41, P.O. Box 808, Livermore, California 94450 (United States)
3. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States)
4. Department of Astronomy, University of Washington, Seattle, Washington 98195 (United States)
5. American Association of Variable Star Observers, 25 Birch Street, Cambridge, Massachusetts 02138 (United States)

We have observed U Gem during the peak and declining phases of a wide outburst in 1993 December with the {ital Extreme} {ital Ultraviolet} {ital Explorer} ({ital EUVE}) satellite. At peak, U Gem was one of the brightest EUV sources in the sky. The spectrum of the source is complex. Fitted to a blackbody spectrum, the apparent temperature at peak is {approximately}140,000 K, the luminosity is {approximately}4{times}10{sup 34}({ital D}/90 pc){sup 2} ergss{sup {minus}1}, and the minimum size of the emitting region is comparable to that of the white dwarf (WD). If the EUV emission arises primarily from the boundary layer, then the boundary layer luminosity in U Gem is comparable to the disk luminosity. The EUV source is partially eclipsed at orbital phases 0.6{endash}0.8. The eclipse spectrum, which we associate with a wind emerging from the vicinity of the white dwarf, is dominated by emission features. The identification of these emission features with transitions expected in a relatively cool ({ital T}{lt}160,000 K), photoionized plasma helps to resolve a controversy concerning the ionization state of winds of dwarf novae. The EUV lines arise from the dominant ionization states of the wind, and their strengths suggest that the wind mass-loss rate, at least in U Gem, is a substantial fraction of the WD accretion rate. {copyright} {ital 1996 The American Astronomical Society.}

• Research Organization: Lawrence Livermore National Laboratory
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 467177
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 469; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
BINARY STARS
ECLIPSE
EXTREME ULTRAVIOLET SPECTRA
IONIZATION
LUMINOSITY
MASS TRANSFER
NOVAE
ORBITS
STELLAR ATMOSPHERES
STELLAR WINDS
TEMPERATURE DISTRIBUTION
WHITE DWARF STARS