Hubble space telescope spectroscopy of the unexpected 2001 July outburst of the dwarf nova WZ sagittae

Edward M. Sion, Boris T. Gänsicke, Knox S. Long, Paula Szkody, Fu Hua Cheng, Steve B. Howell, Patrick Godon, William F. Welsh, Sumner Starrfield, Christian Knigge, Warren M. Sparks

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

We present Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph E140M spectra of the dwarf nova WZ Sge, following the early superoutburst of 2001 July. Our four far-ultraviolet (FUV) spectra, obtained over a time span of 4 months, monitor changes in the hot component of the system during the decline phase. The spectra cover the wavelength interval 1150-1708 Å. They reveal Stark-broadened Lyα and He II (1640) absorption and absorption lines due to metals (Si, C, N, Al) from a range of ionization states. Single-temperature white dwarf models provide reasonable qualitative agreement with the HST spectra. We find that the white dwarf appears to dominate the spectra from October through December. However, it is not clear that the absorption lines of metals form in the white dwarf photosphere. Therefore, the derived abundances and rotational velocity must be viewed with caution. Only a modest improvement in the fits to the data results when an accretion belt component is included. If the FUV spectra arise from the white dwarf alone, then we measure a cooling in response to the outburst of at least 11, 000 K (29, 000-18, 000 K). The absence of broad underlying absorption features due to metals at this stage suggests slow rotation (∼200 km s -1). It is possible that the white dwarf envelope has expanded due to the heating by the outburst or that the relatively narrow absorption features we observe are forming in an inflated disk atmosphere or curtain associated with the outburst.

Original languageEnglish (US)
Pages (from-to)1137-1150
Number of pages14
JournalAstrophysical Journal
Volume592
Issue number2 I
DOIs
StatePublished - Aug 1 2003

Fingerprint

Hubble Space Telescope
outburst
spectroscopy
ultraviolet spectra
metals
metal
curtains
photosphere
spectrographs
monitors
envelopes
telescopes
ionization
intervals
cooling
atmospheres
accretion
heating
wavelength
atmosphere

Keywords

  • Novae, cataclysmic variables
  • Stars: individual (WZ Sagittae)
  • White dwarfs

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Sion, E. M., Gänsicke, B. T., Long, K. S., Szkody, P., Cheng, F. H., Howell, S. B., ... Sparks, W. M. (2003). Hubble space telescope spectroscopy of the unexpected 2001 July outburst of the dwarf nova WZ sagittae. Astrophysical Journal, 592(2 I), 1137-1150. https://doi.org/10.1086/375855

Hubble space telescope spectroscopy of the unexpected 2001 July outburst of the dwarf nova WZ sagittae. / Sion, Edward M.; Gänsicke, Boris T.; Long, Knox S.; Szkody, Paula; Cheng, Fu Hua; Howell, Steve B.; Godon, Patrick; Welsh, William F.; Starrfield, Sumner; Knigge, Christian; Sparks, Warren M.

In: Astrophysical Journal, Vol. 592, No. 2 I, 01.08.2003, p. 1137-1150.

Research output: Contribution to journalArticle

Sion, EM, Gänsicke, BT, Long, KS, Szkody, P, Cheng, FH, Howell, SB, Godon, P, Welsh, WF, Starrfield, S, Knigge, C & Sparks, WM 2003, 'Hubble space telescope spectroscopy of the unexpected 2001 July outburst of the dwarf nova WZ sagittae', Astrophysical Journal, vol. 592, no. 2 I, pp. 1137-1150. https://doi.org/10.1086/375855
Sion EM, Gänsicke BT, Long KS, Szkody P, Cheng FH, Howell SB et al. Hubble space telescope spectroscopy of the unexpected 2001 July outburst of the dwarf nova WZ sagittae. Astrophysical Journal. 2003 Aug 1;592(2 I):1137-1150. https://doi.org/10.1086/375855
Sion, Edward M. ; Gänsicke, Boris T. ; Long, Knox S. ; Szkody, Paula ; Cheng, Fu Hua ; Howell, Steve B. ; Godon, Patrick ; Welsh, William F. ; Starrfield, Sumner ; Knigge, Christian ; Sparks, Warren M. / Hubble space telescope spectroscopy of the unexpected 2001 July outburst of the dwarf nova WZ sagittae. In: Astrophysical Journal. 2003 ; Vol. 592, No. 2 I. pp. 1137-1150.
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AU - Cheng, Fu Hua

AU - Howell, Steve B.

AU - Godon, Patrick

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AB - We present Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph E140M spectra of the dwarf nova WZ Sge, following the early superoutburst of 2001 July. Our four far-ultraviolet (FUV) spectra, obtained over a time span of 4 months, monitor changes in the hot component of the system during the decline phase. The spectra cover the wavelength interval 1150-1708 Å. They reveal Stark-broadened Lyα and He II (1640) absorption and absorption lines due to metals (Si, C, N, Al) from a range of ionization states. Single-temperature white dwarf models provide reasonable qualitative agreement with the HST spectra. We find that the white dwarf appears to dominate the spectra from October through December. However, it is not clear that the absorption lines of metals form in the white dwarf photosphere. Therefore, the derived abundances and rotational velocity must be viewed with caution. Only a modest improvement in the fits to the data results when an accretion belt component is included. If the FUV spectra arise from the white dwarf alone, then we measure a cooling in response to the outburst of at least 11, 000 K (29, 000-18, 000 K). The absence of broad underlying absorption features due to metals at this stage suggests slow rotation (∼200 km s -1). It is possible that the white dwarf envelope has expanded due to the heating by the outburst or that the relatively narrow absorption features we observe are forming in an inflated disk atmosphere or curtain associated with the outburst.

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