Evidence of a thermonuclear runaway and proton-capture material on a white dwarf in a dwarf nova

Edward M. Sion, F. H. Cueno, Warren M. Sparks, Paula Szkody, Min Huang, Ivan - Hubeny

Research output: Contribution to journalArticle

39 Citations (Scopus)

Abstract

We present Hubble Space Telescope Goddard High-Resolution Spectrograph G160M spectra of the white dwarf in VW Hydri, exposed during quiescence, 1 month after the end of a normal dwarf nova outburst. Our spectra, covering the wavelength interval 1236-1272 Å, were obtained at orbital phase 0.06-1.60; they reveal strong photospheric Si II λλ1260, 1265 absorption features and a previously unidentified broad feature centered around 1250 Å. This feature is due to a blend of phosphorus lines. From line-shift measurements we determine a gravitational redshift of 58 ± 33 km s-1, yielding a white dwarf mass Mwd = 0.86-0.32+0.18 M (this is only the second gravitational redshift determined for a cataclysmic variable white dwarf), white dwarf radius Rwd = 6.5-1.5+3.1 × 108 cm, and gravity log g = 8.43-0.54+0.31. Our best-fitting synthetic spectra yield white dwarf effective temperature Td = 22,000 K and a rotational velocity Vrot = 400 km s-1. The chemical abundances, in number relative to solar, are, for C, 0.5; N, 5.0; O, 2.0; Fe, 0.5; Si, 0.1; P, 900; and all other metals, 0.3. The abundance of phosphorus being 900 solar, coupled with the elevated aluminum abundance reported by Sion and coworkers, suggest nucleosynthetic production of these odd-numbered nuclei from proton capture on the even-numbered nuclei during a CNO thermonuclear runaway (TNR) on the white dwarf. It is clear that the white dwarf has undergone a runaway sometime in the past, the first such evidence of a TNR in a dwarf nova. A TNR on a slowly accreting 0.86 M white dwarf should produce a classical nova explosion. If our interpretation is correct, then we have found the first direct spectroscopic link between a dwarf nova and a classical nova by using the white dwarf surface chemical abundance. This is also the first direct evidence of proton capture-processed material in the atmosphere of a white dwarf. Nova explosions on more numerous, lower mass C-O white dwarfs may therefore account for some fraction of the short-lived radionuclide 26Al in the Galaxy. This nuclide is observed from its Galactic gamma-ray line emission and is postulated to have an important role in the heating of small bodies in the solar system.

Original languageEnglish (US)
JournalAstrophysical Journal
Volume480
Issue number1 PART II
StatePublished - 1997
Externally publishedYes

Fingerprint

protons
phosphorus
explosions
explosion
nuclei
cataclysmic variables
nuclides
Hubble Space Telescope
outburst
solar system
radioactive isotopes
spectrographs
radionuclide
coverings
aluminum
gamma rays
gravity
gravitation
galaxies
heating

Keywords

  • Novae, cataclysmic variables
  • Stars: individual (VW Hydri)
  • White dwarfs

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Sion, E. M., Cueno, F. H., Sparks, W. M., Szkody, P., Huang, M., & Hubeny, I. . (1997). Evidence of a thermonuclear runaway and proton-capture material on a white dwarf in a dwarf nova. Astrophysical Journal, 480(1 PART II).

Evidence of a thermonuclear runaway and proton-capture material on a white dwarf in a dwarf nova. / Sion, Edward M.; Cueno, F. H.; Sparks, Warren M.; Szkody, Paula; Huang, Min; Hubeny, Ivan -.

In: Astrophysical Journal, Vol. 480, No. 1 PART II, 1997.

Research output: Contribution to journalArticle

Sion, EM, Cueno, FH, Sparks, WM, Szkody, P, Huang, M & Hubeny, I 1997, 'Evidence of a thermonuclear runaway and proton-capture material on a white dwarf in a dwarf nova', Astrophysical Journal, vol. 480, no. 1 PART II.
Sion, Edward M. ; Cueno, F. H. ; Sparks, Warren M. ; Szkody, Paula ; Huang, Min ; Hubeny, Ivan -. / Evidence of a thermonuclear runaway and proton-capture material on a white dwarf in a dwarf nova. In: Astrophysical Journal. 1997 ; Vol. 480, No. 1 PART II.
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abstract = "We present Hubble Space Telescope Goddard High-Resolution Spectrograph G160M spectra of the white dwarf in VW Hydri, exposed during quiescence, 1 month after the end of a normal dwarf nova outburst. Our spectra, covering the wavelength interval 1236-1272 {\AA}, were obtained at orbital phase 0.06-1.60; they reveal strong photospheric Si II λλ1260, 1265 absorption features and a previously unidentified broad feature centered around 1250 {\AA}. This feature is due to a blend of phosphorus lines. From line-shift measurements we determine a gravitational redshift of 58 ± 33 km s-1, yielding a white dwarf mass Mwd = 0.86-0.32+0.18 M⊙ (this is only the second gravitational redshift determined for a cataclysmic variable white dwarf), white dwarf radius Rwd = 6.5-1.5+3.1 × 108 cm, and gravity log g = 8.43-0.54+0.31. Our best-fitting synthetic spectra yield white dwarf effective temperature Td = 22,000 K and a rotational velocity Vrot = 400 km s-1. The chemical abundances, in number relative to solar, are, for C, 0.5; N, 5.0; O, 2.0; Fe, 0.5; Si, 0.1; P, 900; and all other metals, 0.3. The abundance of phosphorus being 900 solar, coupled with the elevated aluminum abundance reported by Sion and coworkers, suggest nucleosynthetic production of these odd-numbered nuclei from proton capture on the even-numbered nuclei during a CNO thermonuclear runaway (TNR) on the white dwarf. It is clear that the white dwarf has undergone a runaway sometime in the past, the first such evidence of a TNR in a dwarf nova. A TNR on a slowly accreting 0.86 M⊙ white dwarf should produce a classical nova explosion. If our interpretation is correct, then we have found the first direct spectroscopic link between a dwarf nova and a classical nova by using the white dwarf surface chemical abundance. This is also the first direct evidence of proton capture-processed material in the atmosphere of a white dwarf. Nova explosions on more numerous, lower mass C-O white dwarfs may therefore account for some fraction of the short-lived radionuclide 26Al in the Galaxy. This nuclide is observed from its Galactic gamma-ray line emission and is postulated to have an important role in the heating of small bodies in the solar system.",
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AU - Sion, Edward M.

AU - Cueno, F. H.

AU - Sparks, Warren M.

AU - Szkody, Paula

AU - Huang, Min

AU - Hubeny, Ivan -

PY - 1997

Y1 - 1997

N2 - We present Hubble Space Telescope Goddard High-Resolution Spectrograph G160M spectra of the white dwarf in VW Hydri, exposed during quiescence, 1 month after the end of a normal dwarf nova outburst. Our spectra, covering the wavelength interval 1236-1272 Å, were obtained at orbital phase 0.06-1.60; they reveal strong photospheric Si II λλ1260, 1265 absorption features and a previously unidentified broad feature centered around 1250 Å. This feature is due to a blend of phosphorus lines. From line-shift measurements we determine a gravitational redshift of 58 ± 33 km s-1, yielding a white dwarf mass Mwd = 0.86-0.32+0.18 M⊙ (this is only the second gravitational redshift determined for a cataclysmic variable white dwarf), white dwarf radius Rwd = 6.5-1.5+3.1 × 108 cm, and gravity log g = 8.43-0.54+0.31. Our best-fitting synthetic spectra yield white dwarf effective temperature Td = 22,000 K and a rotational velocity Vrot = 400 km s-1. The chemical abundances, in number relative to solar, are, for C, 0.5; N, 5.0; O, 2.0; Fe, 0.5; Si, 0.1; P, 900; and all other metals, 0.3. The abundance of phosphorus being 900 solar, coupled with the elevated aluminum abundance reported by Sion and coworkers, suggest nucleosynthetic production of these odd-numbered nuclei from proton capture on the even-numbered nuclei during a CNO thermonuclear runaway (TNR) on the white dwarf. It is clear that the white dwarf has undergone a runaway sometime in the past, the first such evidence of a TNR in a dwarf nova. A TNR on a slowly accreting 0.86 M⊙ white dwarf should produce a classical nova explosion. If our interpretation is correct, then we have found the first direct spectroscopic link between a dwarf nova and a classical nova by using the white dwarf surface chemical abundance. This is also the first direct evidence of proton capture-processed material in the atmosphere of a white dwarf. Nova explosions on more numerous, lower mass C-O white dwarfs may therefore account for some fraction of the short-lived radionuclide 26Al in the Galaxy. This nuclide is observed from its Galactic gamma-ray line emission and is postulated to have an important role in the heating of small bodies in the solar system.

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