The Dwarf Novae during Quiescence

We present a synthetic spectral analysis of nearly the entire FUV IUE archiveof spectra of DNe in or near quiescence. We have examined all of the systemsfor which S/N permitted an analysis. The study includes 53 systems of all DNsubtypes both above and below the period gap. The spectra were uniformlyanalyzed using synthetic spectral codes for optically thick accretion disks andstellar photospheres along with the best-available distance measurements orestimates. We present newly determined approximate WD temperatures or upperlimits and estimated accretion rates. The average temperature of WDs in DNebelow the period gap is ~18,000K. For WDs in DNe above the period gap, theaverage WD temperature is ~26,000K. There is a flux component, in addition to aWD photosphere, which contributes >60% of the flux in the FUV in 53% of thequiescent DNe in this study. We find that for 41% of the DNe in our sample, aWD photosphere provides >60% of the FUV flux. Accretion rates estimated fromthe FUV alone for the sample of DNe during quiescence ranged from 10^-12Msun/yr to 10^-10 Msun/yr.The additional flux component is almost certainly notan optically thick accretion disk since, according to the disk instabilitymodel, the disk should be optically thin and too cool during DN quiescence tobe a significant FUV continuum emitter. Among the candidates for the secondcomponent of FUV light are the quiescent inner disk, a hot equatorial accretionbelt, and a hot rotating ring. The implications of our study for disk accretionphysics and CV evolution are discussed.Comment: 36 pages, 3 tables, 8 figures, final accepted version of manuscrip