ASCA X-Ray Spectra of Non-Magnetic Catclysmic Variables

We present the results of a uniform analysis of all the ASCA X-ray observations of non-magnetic cataclysmic variables. The collection includes 13 objects. We believe that the ASCA spectra of 8 of these objects are presented here for the first time. After experimenting with a variety of models, we find that 2-temperature, thermal plasma models (by Mewe, Kaastra, & Liedahl, or by Raymond & Smith) provide the best description of the observed spectra. The resulting temperatures lie mostly between 4 and 10 keV, which is somewhat higher than what was found in previous such ``surveys'' with the Einstein and ROSAT X-ray observatories, but in reasonable agreement with older, EXOSAT observations. In 6 objects we measure an absorbing column density significantly above the Galactic value, which we interpret to result in material intrinsic to the binary. We also investigate the temporal variability properties of the sources by looking for correlations between the flux and hardness ratio, and we search for periodic signals by computing power spectra. We compare these results with models of X-ray emission from white dwarf boundary layers, as well as with models of hot coronae surrounding the accreting white dwarfs, and with recent models of advection dominated accretion flows.