X‐Ray Lines from Hot Flows around White Dwarfs: Application to SS Cygni

Rather than accreting via a disk, some White Dwarfs (WDs) in quiescent DwarfNovae (DN) could accrete via an Advection-Dominated Accretion Flow (ADAF)possibly responsible for the X-ray Bremsstrahlung emission observed. Such a hotaccretion flow is also expected to produce characteristic thermal lineemission. Using SS Cyg as a specific example, we show that knowing a priori theinclination and the WD mass in quiescent DN makes X-ray line diagnosticspowerful probes of the flow structure in these systems. Current X-rayinstruments can discriminate, from their width, between lines emitted from aflow with a Keplerian rotation rate and those emitted at a substantiallysub-Keplerian rate. This could be used to observationally test the property ofenergy advection, which is at the origin of the partial radial pressure supportby the hot gas and the sub-Keplerian rotation rate in an ADAF.Comment: 16 pages, 3 figures, accepted for publication in Ap