Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...561l.127s&link_type=abstract
The Astrophysical Journal, Volume 561, Issue 1, pp. L127-L130.
Astronomy and Astrophysics
Astronomy
16
Accretion, Accretion Disks, Stars: Abundances, Stars: Dwarf Novae, Stars: Individual: Constellation Name: Vw Hydri, Stars: White Dwarfs
Scientific paper
Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) observations of VW Hydri 2 and 7 days after the end of a superoutburst reveal a heated white dwarf with deep broad Lyα, narrow metallic absorption features and evidence of a hotter Keplerian-broadened component. We confirm the existence of enhanced abundances of odd-numbered nuclear species P, Mn, and Al as well as an N/C ratio indicative of CNO H-burning thermonuclear processing. Our best single-temperature white dwarf reduced χ2 fit to the first spectrum reveals (1) a DAZQ white dwarf with Teff=22,500+/-500 K, logg=8.0, and photospheric abundances C=0.3 solar, N=3.0 solar, O=3.0 solar, Si=0.3 solar, Al=2 solar, Fe=0.5 solar, Mg=3.0 solar, Mn=50 solar, Ni=0.3 solar, P=15 solar, and Ti=0.1 solar. The best-fit white dwarf + accretion belt composite model yields a large improvement in the reduced χ2 value. The accretion belt temperature is 32,000 K and covers a fractional area of 3%, contributing 11% of the flux. The second spectrum 5 days later reveals slightly increased metal abundances except that P is elevated to 20 times solar while Fe has declined to 0.05 times solar. The white dwarf has cooled by ~1000 K, the belt temperature is 32,000 K, and the fractional area and flux contribution of the belt are 5% and 20%, respectively. These STIS observations confirm that a past (prehistoric?) thermonuclear runaway has occurred on the white dwarf in VW Hyi. It is expected that the thermonuclear runaway would be strong enough to produce a nova outburst. Therefore, these two classes of close binaries, namely, dwarf novae and classical novae, are linked and can overlap.
Cheng Fu-Hua
Gansicke Boris
Hubeny Ivan
Sion Edward M.
Sparks Warren M.
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