Hubble Space Telescope GHRS spectroscopy of U geminorum during two outbursts

Edward M. Sion, Fuhua Cheng, Paula Szkody, Min Huang, Judi Provencal, Warren Sparks, Brian Abbott, Ivan - Hubeny, Janet Mattei, Harry Shipman

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

We obtained 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: N v (1238 Å, 1242 Å), Si III (1300 Å), and He II (1640 Å). The spectrum corresponding to the early decline phase of outburst 1 is essentially featureless except for weak N v 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 N v absorption velocity versus orbital phase traces the motion of the white dwarf, but the He II 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 × 10-10 M yr-1 and 2 × 10-9 M yr-1. Implications are discussed.

Original languageEnglish (US)
Pages (from-to)907-912
Number of pages6
JournalAstrophysical Journal
Volume483
Issue number2 PART I
DOIs
StatePublished - 1997
Externally publishedYes

Fingerprint

Hubble Space Telescope
outburst
spectroscopy
accretion
orbital velocity
optical disks
profiles
accretion disks
low speed
spectrographs
boundary layers
boundary layer
prototypes
gratings
shell
continuums
wavelength
high resolution
radiation
wavelengths

Keywords

  • Accretion, accretion disks
  • Novae, cataclysmic variables
  • Stars: emission-line, Be
  • Stars: individual (U Geminorum)
  • Ultraviolet: stars

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Sion, E. M., Cheng, F., Szkody, P., Huang, M., Provencal, J., Sparks, W., ... Shipman, H. (1997). Hubble Space Telescope GHRS spectroscopy of U geminorum during two outbursts. Astrophysical Journal, 483(2 PART I), 907-912. https://doi.org/10.1086/304269

Hubble Space Telescope GHRS spectroscopy of U geminorum during two outbursts. / Sion, Edward M.; Cheng, Fuhua; Szkody, Paula; Huang, Min; Provencal, Judi; Sparks, Warren; Abbott, Brian; Hubeny, Ivan -; Mattei, Janet; Shipman, Harry.

In: Astrophysical Journal, Vol. 483, No. 2 PART I, 1997, p. 907-912.

Research output: Contribution to journalArticle

Sion, EM, Cheng, F, Szkody, P, Huang, M, Provencal, J, Sparks, W, Abbott, B, Hubeny, I, Mattei, J & Shipman, H 1997, 'Hubble Space Telescope GHRS spectroscopy of U geminorum during two outbursts', Astrophysical Journal, vol. 483, no. 2 PART I, pp. 907-912. https://doi.org/10.1086/304269
Sion EM, Cheng F, Szkody P, Huang M, Provencal J, Sparks W et al. Hubble Space Telescope GHRS spectroscopy of U geminorum during two outbursts. Astrophysical Journal. 1997;483(2 PART I):907-912. https://doi.org/10.1086/304269
Sion, Edward M. ; Cheng, Fuhua ; Szkody, Paula ; Huang, Min ; Provencal, Judi ; Sparks, Warren ; Abbott, Brian ; Hubeny, Ivan - ; Mattei, Janet ; Shipman, Harry. / Hubble Space Telescope GHRS spectroscopy of U geminorum during two outbursts. In: Astrophysical Journal. 1997 ; Vol. 483, No. 2 PART I. pp. 907-912.
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N2 - We obtained 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: N v (1238 Å, 1242 Å), Si III (1300 Å), and He II (1640 Å). The spectrum corresponding to the early decline phase of outburst 1 is essentially featureless except for weak N v 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 N v absorption velocity versus orbital phase traces the motion of the white dwarf, but the He II 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 × 10-10 M⊙ yr-1 and 2 × 10-9 M⊙ yr-1. Implications are discussed.

AB - We obtained 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: N v (1238 Å, 1242 Å), Si III (1300 Å), and He II (1640 Å). The spectrum corresponding to the early decline phase of outburst 1 is essentially featureless except for weak N v 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 N v absorption velocity versus orbital phase traces the motion of the white dwarf, but the He II 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 × 10-10 M⊙ yr-1 and 2 × 10-9 M⊙ yr-1. Implications are discussed.

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