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

Abstract

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,more » 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}« less

Authors:
;  [1];  [2];  [1];  [3];  [4];  [1];  [5];  [6];  [3]
  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)
Publication Date:
OSTI Identifier:
542146
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 483; Journal Issue: 2; Other Information: PBD: Jul 1997
Country of Publication:
United States
Language:
English
Subject:
66 PHYSICS; NOVAE; ULTRAVIOLET SPECTRA; DWARF STARS; STAR ACCRETION; MASS TRANSFER; PHOTON TRANSPORT; LINE WIDTHS; PHOTOIONIZATION

Citation Formats

Sion, E M, Cheng, F, Szkody, P, Huang, M, Provencal, J, Sparks, W, Abbott, B, Hubeny, I, Mattei, J, and Shipman, H. {ital Hubble Space Telescope} GHRS spectroscopy of U Geminorum during two outbursts. United States: N. p., 1997. Web. doi:10.1086/304269.
Sion, E M, Cheng, F, Szkody, P, Huang, M, Provencal, J, Sparks, W, Abbott, B, Hubeny, I, Mattei, J, & Shipman, H. {ital Hubble Space Telescope} GHRS spectroscopy of U Geminorum during two outbursts. United States. https://doi.org/10.1086/304269
Sion, E M, Cheng, F, Szkody, P, Huang, M, Provencal, J, Sparks, W, Abbott, B, Hubeny, I, Mattei, J, and Shipman, H. 1997. "{ital Hubble Space Telescope} GHRS spectroscopy of U Geminorum during two outbursts". United States. https://doi.org/10.1086/304269.
@article{osti_542146,
title = {{ital Hubble Space Telescope} GHRS spectroscopy of U Geminorum during two outbursts},
author = {Sion, E M and Cheng, F and Szkody, P and Huang, M and Provencal, J and Sparks, W and Abbott, B and Hubeny, I and Mattei, J and Shipman, H},
abstractNote = {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}},
doi = {10.1086/304269},
url = {https://www.osti.gov/biblio/542146}, journal = {Astrophysical Journal},
number = 2,
volume = 483,
place = {United States},
year = {Tue Jul 01 00:00:00 EDT 1997},
month = {Tue Jul 01 00:00:00 EDT 1997}
}