{ital Hubble Space Telescope} GHRS spectroscopy of U Geminorum during two outbursts

Journal Article · Tue Jul 01 04:00:00 EDT 1997 · Astrophysical Journal

DOI:https://doi.org/10.1086/304269· OSTI ID:542146

Sion, E M; Cheng, F ^[1]; Szkody, P ^[2]; Huang, M ^[1]; Provencal, J ^[3]; Sparks, W ^[4]; Abbott, B ^[1]; Hubeny, I ^[5]; Mattei, J ^[6]; Shipman, H ^[3]

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1. Department of Astronomy and Astrophysics, Villanova University, Villanova, Pennsylvania 19085 (United States)
2. Department of Astronomy, University of Washington, Seattle, Washington 98195 (United States)
3. Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States)
4. Nuclear and Hydrodynamic Applications Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
5. Code 681, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States)
6. American Association of Variable Star Observers, Cambridge, Massachusetts 02138 (United States)

We obtained {ital Hubble Space Telescope} Goddard High-Resolution Spectrograph medium-resolution (G160M grating) phase-resolved spectroscopic observations of the prototype dwarf nova U Geminorum during different stages of two different outbursts. The spectral wavelength ranges were centered on three different line regions: NV (1238 {Angstrom}, 1242 {Angstrom}), SiIII (1300 {Angstrom}), and HeII (1640 {Angstrom}). The spectrum corresponding to the early decline phase of outburst 1 is essentially featureless except for weak NV absorption and narrow interstellar lines, while the spectrum at the peak of outburst 2 reveals broad emission peaks separated by narrow central absorption. The double-peaked emission-line profile structure with low-velocity central absorption seen in the second outburst suggests a disk origin, but the emission velocity widths appear narrower than the widths of the optical disk emission features. We interpret the high-excitation emission lines, with central absorption below the continuum, to be due to photoionized material (coronal?) above the disk plane with the thickened outer disk absorbing the boundary layer or inner disk radiation. The possibility of a wind origin for the profiles is also discussed, as well as the possibility of an ejected optically thin shell. The NV absorption velocity versus orbital phase traces the motion of the white dwarf, but the HeII absorption velocity appears to deviate from the white dwarf motion. We present the results of synthetic accretion disk spectral fitting to the data of both outbursts and derive accretion rates for the two outbursts of 6{times}10{sup {minus}10}M{sub {circle_dot}}yr{sup {minus}1} and 2{times}10{sup {minus}9}M{sub {circle_dot}}yr{sup {minus}1}. Implications are discussed. {copyright} {ital 1997} {ital The American Astronomical Society}

• OSTI ID: 542146
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 483; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
DWARF STARS
LINE WIDTHS
MASS TRANSFER
NOVAE
PHOTOIONIZATION
PHOTON TRANSPORT
STAR ACCRETION
ULTRAVIOLET SPECTRA