Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001pasp..113.1222s&link_type=abstract
The Publications of the Astronomical Society of the Pacific, Volume 113, Issue 788, pp. 1222-1226.
Astronomy and Astrophysics
Astronomy
2
Accretion, Accretion Disks, Stars: Novae, Cataclysmic Variables, Stars: Individual (Uu Aquilae), Stars: White Dwarfs
Scientific paper
We present a high-gravity, solar composition model atmosphere and model accretion disk study of the U Gem type dwarf nova UU Aql. We have identified the far-UV signature of the underlying white dwarf for the first time. Our best-fit model atmosphere to the observed far-UV spectrum in quiescence is 27,000+/-1000 K. The solar abundance high-gravity photosphere provides a consistent explanation for the sharp absorption lines due to metals in the white dwarf's atmosphere. This interpretation is also consistent with the predicted 20,000-30,000 K small, hot, far-UV source (smaller than an accretion disk) proposed by Patterson & Raymond. Model accretion disk fits do not account for the sharp absorption lines and continuum slope. The best-fit accretion disk corresponds to Mwd=0.8 Msolar, i=60deg, and M=10-9.5 Msolar yr-1. Optically thick disk models at accretion rates lower than 1×10-9.5 Msolar yr-1 are ruled out because of marked flux deficiency shortward of 1400 Å. Theoretical arguments are presented that rule out accretion rates as high as 1×10-9.5 Msolar yr-1 during dwarf nova quiescence. While we can rule out the quiescent disk as being a significant UV flux contributor, we believe the heated white dwarf accounts for the majority of the far-UV flux. The white dwarf is only the fifth accretor among U Gem systems with a known surface temperature. The temperatures of all five accretors lie between 25,000 and 35,000 K.
Sion Edward M.
Stump Michael
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