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Hubble Space Telescope observations of the dwarf Nova Z Chamaeleontis through two eruption cyclesWe have obtained the first high-speed photometry of the eclipsing dwarf nova Z Cha at ultraviolet wavelengths with the Hubble Space Telescope (HST). We observed the eclipse roughly every 4 days over two cycles of the normal eruptions of Z Cha, giving a uniquely complete coverage of its outburst cycle. The accretion disk dominated the ultraviolet light curve of Z Cha at the peak of an eruption; the white dwarf, the bright spot on the edge of the disk, and the boundary layer were all invisible. We were able to obtain an axisymmetric map of the accretion disk at this time only by adopting a flared disk with an opening angle of approximately 8 deg. The run of brightness temperature with radius in the disk at the peak of the eruption was too flat to be consistent with a steady state, optically thick accretion disk. The local rate of mass flow through the disk was approximately 5 x 10(exp -10) solar masses/yr near the center of the disk and approximately 5 x 10(exp -9) solar masses/yr near the outer edge. The white dwarf, the accretion disk, and the boundary layer were all significant contributors to the ultraviolet flux on the descending branches of the eruptions. The temperature of the white dwarf during decline was 18,300 K less than T(sub wd) less than 21,800 K, which is significantly greater than at minimum light. Six days after the maximum of an eruption Z Cha has faded to near minimum light at ultraviolet wavelenghts, but was still approximately 70% brighter at minimum light in the B band. About one-quarter of the excess flux in the B band came from the accretion disk. Thus, the accretion disk faded and became invisible at ultraviolet wavelengths before it faded at optical wavelenghts. The disk did, however, remain optically thick and obscured the lower half of the white dwarf at ultraviolet and possibly at optical wavelenghts for 2 weeks after the eruption ended. By the third week after eruptiuons the eclipse looked like a simple occultation of an unobscured, spherical white dwarf by a dark secondary star. The center of the accretion disk was, therfore, optically thin at ultraviolet wavelenghts and the boundary layer was too faint to be visible.
Document ID
19950053595
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Robinson, E. L.
(Univ. of Texas, Austin, TX United States)
Wood, Janet H.
(Univ. of Texas, Austin, TX United States)
Bless, R. C.
(Univ. of Wisconsin, Madison, WI United States)
Clemens, J. C.
(Univ. of Texas, Austin, TX United States)
Dolan, J. F.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Elliot, J. L.
(MIT, Cambridge, MA United States)
Nelson, M. J.
(Univ. of Wisconsin, Madison, WI United States)
Percival, J. W.
(Univ. of Wisconsin, Madison, WI United States)
Taylor, M. J.
(Univ. of Wisconsin, Madison, WI United States)
Van Citters, G. W.
(NSF, Washington, DC United States)
Date Acquired
August 16, 2013
Publication Date
October 4, 1995
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 443
Issue: 1
ISSN: 0004-637X
Subject Category
Astronomy
Accession Number
95A85194
Funding Number(s)
CONTRACT_GRANT: NAS5-26555
CONTRACT_GRANT: CRG-93-0354
CONTRACT_GRANT: NAG5-1613
Distribution Limits
Public
Copyright
Other

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