Compressional Heating of Accreting White Dwarfs in CV's

Abstract

In recent years several Dwarf Novae (DN) systems have been observed in quiescence, when the accretion rate is low and the WD photosphere can be directly detected. The WDs are observed to cool after the DN outburst from high effective temperatures to lower effective temperatures (T_eff) thought to be indicative of the thermal state of the deep interior of the WD. Sion has argued that the most likely energy source for this quiescent luminosity is the gravitational compression of the WD interior, which rejuvenates an otherwise cold WD into a much hotter state. We are undertaking a theoretical study of the compressional heating of WD's, extending down to the very low time averaged accretion rates, ~10^{-11}M_sun/yr, applicable to the post-turnaround CV's (the ``TOADS''). Nuclear burning is unstable at these 's, so we have incorporated the recurrent heating and cooling of the WD throughout the classical novae limit cycle. In addition to self-consistently finding the range of T_eff as a function of during the cycle, we also self-consistently find the ignition masses. Comparing these theoretical masses to the observed ejected masses will tell us whether the WD mass in CV's is secularly increasing or decreasing. We close by comparing our results to the accumulated observations of quiescent DN and making predictions for the colors of low CV's in quiescence that are applicable to searches for faint CVs in the field and galactic globular clusters.