Rotationally Broadened Synthetic Spectra for HST and IUE Observations of Exposed White Dwarfs in Cataclysmic Variables

In many dwarf novae during quiescence, the underlying white dwarf dominates the flux in the far-UV. By observing these exposed degenerate stars with the HST Goddard High Resolution Spectrograph and Faint Object Spectrograph (GHRS and FOS), the white-dwarf rotation rates can be determined or constrained by fitting synthetic spectra broadened by rotation. Using TLUSTY and SYNSPEC, we present a grid of rotationally broadened white-dwarf synthetic spectra, convolved with the resolution of the GHRS, FOS, and IUE low-resolution short-wavelength prime (SWP) spectra. We examine the predicted appearance of accreted solar-composition white-dwarf atmospheres in the context of determining or constraining the white-dwarf rotational velocities. We present model grids that demonstrate this capability, and the first application of these grids to the SWP low-resolution spectra of the white dwarf in the nova-like variable TT Ari, exposed during the very low brightness state of that system. We also rule out the possibility that the absence of Ly-alpha absorption in many cataclysmic variables in quiescence could be due to rotational velocities of the white dwarf near breakup. (Author)