THE ACCRETING WHITE DWARF IN SS CYGNI REVEALED

Journal Article · Sun Jun 20 04:00:00 EDT 2010 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/716/2/L157· OSTI ID:21450948

Sion, Edward M; Godon, Patrick; Myzcka, Janine ^[1]

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1. Astronomy and Astrophysics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085 (United States)

We have carried out a combined Hubble Space Telescope (HST/GHRS) and Far Ultraviolet Spectroscopic Explorer (FUSE) analysis of the prototype dwarf nova SS Cygni during quiescence. The FUSE and HST spectra were obtained at comparable times after outburst and have matching flux levels where the two spectra overlap. In our synthetic spectral analysis, we have used SS Cygni's accurate HST fine guidance sensor parallax giving d = 166 pc, a newly determined mass for the accreting white dwarf (WD) of M{sub wd} = 0.81 M{sub sun} (lower than the previous widely used 1.2 M{sub sun}) and the reddening (E{sub B-V}) values 0.04 and 0.07 derived from the 2175 A absorption feature in the IUE LWP spectra. From the best-fit model solutions to the combined HST + FUSE spectral energy distribution, we find that the WD is reaching a temperature T{sub eff}{approx} 45,000-55,000 K in quiescence, assuming log(g) = 8.3 with a solar composition accreted atmosphere. The exact temperature of the WD depends on the reddening assumed and the inclusion of a quiescent low mass accretion rate accretion disk. Accretion disk models alone fit badly in the FUSE range while, and if we take the distance to be a free parameter, the only accretion disk model that fits well is for a discordant distance of at least several hundred parsecs and an accretion rate ({approx}10{sup -8} M{sub sun} yr{sup -1}), which is unacceptably high for a dwarf nova in quiescence. We discuss the implications of the WD's temperature on the time-averaged accretion rate and long-term compressional heating models.

• OSTI ID: 21450948
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 716; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
ACCRETION DISKS
BINARY STARS
DWARF STARS
ELECTROMAGNETIC RADIATION
ENERGY SPECTRA
ERUPTIVE VARIABLE STARS
FAR ULTRAVIOLET RADIATION
MASS
NOVAE
RADIATIONS
SENSORS
SORPTION
SPECTRA
STARS
TELESCOPES
ULTRAVIOLET RADIATION
VARIABLE STARS
WHITE DWARF STARS