The Cooling White Dwarf in VW Hydri after Normal Outburst and Superoutburst: HST Evidence of a Sustained Accretion Belt

Details The Cooling White Dwarf in VW Hydri after Normal Outburst and Superoutburst: HST Evidence of a Sustained Accretion Belt The Cooling White Dwarf in VW Hydri after Normal Outburst and Superoutburst: HST Evidence of a Sustained Accretion Belt

Nov 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...471l..41s&link_type=abstract

Astrophysical Journal Letters v.471, p.L41

Astronomy and Astrophysics

Astronomy

42

Stars: Novae, Cataclysmic Variables, Stars: White Dwarfs, Stars: Individual Constellation Name: Vw Hydri

Scientific paper

Hubble Faint Object Spectrograph (FOS) observations of VW Hyi one day after the end of a normal dwarf nova outburst reveal a heated white dwarf with deep, broad Ly alpha , narrow metallic absorption features, and evidence of a hotter Keplerian-broadened component manifested in quiescence as a broad continuum hump. Our best reduced chi 2 fit to the data reveals (1) a DAZQ white dwarf with Teff = 22,500 +/- 500 K, log g = 8, and photospheric abundances C = 0.5 solar, N = 5.0 solar, O = 2.0 solar, Si = 0.2 solar, Fe = 0.5 solar, with all other metals being 0.3 solar, and (2) a rapidly spinning accretion belt with Vrot = 3350 km s-1, Tbelt = 26,000 +/- 1000 K, log g = 6.0, and a fractional belt area of approximately 11%. Our earlier FOS spectrum obtained 10 days after superoutburst reveals a cooler DAZQ white dwarf (20,500 +/- 1000 K), relatively lower metal abundances, and a smaller fractional area (3%) for the accretion belt. Thus, 1 day after a normal outburst, the white dwarf is ~2000 K hotter, the accretion belt fractional area is a factor of 3 greater, the accretion belt temperature appears to be cooler than at 10 days post-superoutburst, and the accreted atmosphere has relatively higher metal abundances. Finally, the accretion belt maintained during quiescence may provide a natural explanation for the 14 s soft X-ray oscillations, requires a deeper source of heating (compression and shear mixing), and implies a lower limit to the viscous spin-down timescale of 10 days.

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