An Illustration of Modeling Cataclysmic Variables: HST, FUSE, and SDSS Spectra of SDSS J080908.39+381406.2

Abstract

FUSE, HST, and SDSS spectra of the cataclysmic variable SDSS J080908.39+381406.2 provide a spectral flux distribution from 900 to 9200 Å. This data set is used to illustrate procedures for calculating and testing system models. The spectra are not contemporaneous; it is necessary to assume that the combined spectra are representative of the system. The illustrations are based on a system with a 1.0 M_⊙ white dwarf, a 0.30 M_⊙, 3500 K, Roche lobe-filling secondary star, and an accretion disk extending to the tidal cutoff radius. Assuming a similar accretion state for the nonsimultaneous spectra, the best standard model fit is with a mass transfer rate of 3.0 × 10^(-9)M_⊙ yr^(-1). Extensive simulations demonstrate that the accretion disk must be truncated at its inner edge if the temperature profile follows the standard model, but truncated models face severe objections, which we address. Following additional simulation tests, we obtain a model accretion disk with a temperature profile comparable to the profile for SW Sex as determined from tomographic image reconstruction. This model fits the discovery SDSS spectrum well but has a flux deficit in the UV and FUV. Emission from a white dwarf is a plausible source of additional flux. Adding this source to the disk synthetic spectrum produces FUV flux that can explain the observed flux. An additional (archival) SDSS spectrum is fainter by about 0.3 mag in the optical. Additional analysis showed that UV residuals from a model fitting the archival optical wavelength spectrum are unacceptably large. Contemporaneous spectra from all wavelength regions would be necessary for a reliable system model. Our discussion illustrates how this conclusion follows from the system models.

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