Hubble Space Telescope high resolution spectroscoy of the exposed white dwarf in the dwarf nova VW Hydri in quiescence: A rapidly rotating white dwarf

Details Hubble Space Telescope high resolution spectroscoy of the exposed white dwarf in the dwarf nova VW Hydri in quiescence: A rapidly rotating white dwarf Hubble Space Telescope high resolution spectroscoy of the exposed white dwarf in the dwarf nova VW Hydri in quiescence: A rapidly rotating white dwarf

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...445l..31s&link_type=abstract

Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 445, no. 1, p. L31-L34

Astronomy and Astrophysics

Astronomy

34

Astronomical Spectroscopy, Boundary Layers, Dwarf Novae, Hubble Space Telescope, Spectrum Analysis, Stellar Rotation, Ultraviolet Astronomy, White Dwarf Stars, Absorption Spectra, Far Ultraviolet Radiation, High Resolution, Photosphere

Scientific paper

We obtained a far-ultraviolet spectrum of the dwarf nova VW Hyi in quiescence, with the Hubble Space Telescope Goddard High Resolution Spectrograph covering the region of the Si iv lambda(lambda)1393, 1402 resonance doublet. The broad, shallow Si iv doublet feature is fully resolved, has a total equivalent width of 2.8 A, and is the first metal absorption feature to be clearly detected in the exposed white dwarf. Our synthetic spectral analysis, using a model grid constructed with the code TLUSTY, resulted in a reasonable fit to a white dwarf photosphere with Teff = 22,000 +/- 2000 K, log g = 8.0 +/- 0.3, an approximately solar Si/H abundance, and a rotational velocity, v sin i approximately equal to 600 km/s. This rotation rate, while not definitive because it is based upon just one line transition, is 20% of the Keplerian (breakup) velocity of the white dwarf and hence does not account for the unexpectedly low boundary-layer luminosity inferred from the soft-X-ray/extreme ultra-violet bands where most of the boundary-layer luminosity should be radiated. The predicted boundary-layer luminosity for a 0.6 solar mass white dwarf accreting at the rate 10-10 solar mass/yr and rotating at 600 km/s, corresponding to VW Hyi in quiescence, is 2 x 1032 ergs/s when proper account is taken of the rotational kinetic energy going into spinning up the white dwarf. If the boundary-layer area is equal to that of the white dwarf, then Tbl = 24,000 K. This is essentially identical to the photspheric luminosity and temperature determined in far-ultraviolet photospheric analyses. If the boundary-layer area is 10-3 of the white dwarf surface area, then Tbl = 136,000 K.

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