AAS 201st Meeting, January, 2003
Session 40. Normal and Dwarf Novae
Poster, Tuesday, January 7, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[40.16] A preliminary model of the intermediate polar YY Dra from FUSE spectra

A.P. Linnell (Univ. Washington), D.W. Hoard (SSC/IPAC), P. Szkody (Univ. Washington)

YY Dra is an intermediate polar with orbital period 3h 58m. The WD has magnetic poles lying close to the equator (Szkody et al. 2002); the WD spin period is 529s (Haswell et al. 1996). We have obtained phase-resolved FUSE spectra of the YY Dra system, and have determined a mean FUSE spectrum. We have measured flux values at spin maximum, spin minimum, and mean flux values from the HST plots by Haswell et al. (1996), and have combined these with the corresponding FUSE spectra.

The BINSYN program suite (Linnell & Hubeny 1996) has been used to calculate synthetic spectra of the WD, based on the Haswell et al. (1996) system parameters. The distance determination by Mateo et al. (1991) establishes an absolute flux calibration factor to superpose synthetic spectra on the observed spectra. An initial comparison between the spot minimum spectrum, and the model WD, but without model hot spots, shows that the WD {\rm Teff} must be less than 20kK.

We represent the hot spots as flat, circular regions on the WD photosphere, separated by 180{\arcdeg} in longitude. With one spot located on the WD central meridian, as seen by the observer, we explored the tradeoff between spot angular radius and spot {\rm Teff} in fitting the FUSE+HST spot maximum flux. The best fit was with a spot {\rm Teff} of 80kK on a WD of 16kK {\rm Teff}. A comparison of the same model, but with the spots at the WD limb, and a simulation with no spots shows substantial differences and demonstrates that the spots must be visible at the WD limb. We empirically vary the spot size as function of angular distance from the central meridian to fit the observed light variation. The paper reports satisfactory fits to the observational data. We expect that re-extraction of the phase-resolved spectra with the latest FUSE pipeline software will improve the spectra S/N and allow further refinement of the model.

The author(s) of this abstract have provided an email address for comments about the abstract: linnell@astro.washington.edu

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