Physics
Scientific paper
Jul 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004hst..prop10194g&link_type=abstract
HST Proposal ID #10194
Physics
Hst Proposal Id #10194 Hot Stars
Scientific paper
Accretion inflows and outflows are fundamental phenomena in a wide variety of astrophysical environments, such as Young Stellar Objects, galactic binaries, and AGN. Observationally, cataclysmic variables {CVs}, interacting white dwarf/main sequence binaries, are particularly well suited for the study of accretion processes. Furthermore, CVs that are born with a donor more massive than the white dwarf are potential progenitors of supernovae type Ia. We are currently carrying out a STIS UV spectroscopic snapshot survey of CVs to fully exploit the diagnostic potential of these objects for our understanding of accretion physics. We analyze the STIS spectra with state-of-the-art accretion disc model spectra {SYNSPEC}, testing our current knowledge of accretion disk structure, and thereby, providing new insight into the currently poorly understood process of viscous dissipation. In addition, we use our parameterised wind model PYTHON for the analysis of the radiation driven accretion disc wind spectra, assessing the fundamental question whether the mass loss rate correlates with the disc luminosity. Our survey data also identify a number of systems in which the white dwarf significantly contributes to the UV flux, permitting an analysis of the impact of mass accretion on the evolution of these compact stars. Finally, anomalous N/C emission line flux ratios unmistakably identify CVs that started out with a donor more massive than the white dwarf but failed to reach the Chandrasekhar limit. Determining the number of these "failed SNIa" will provide crucial input for the population models of this type of system, and, consequently, improve the predictions on the number of white dwarf binaries that actually do overcome the Chandrasekhar limit. While the data obtained so far are of excellent quality, the number of targets that have been observed so far is too small for a statistically significant analysis. We propose here to extend this survey into Cycle 13, building a homogenous database of accretion disc and wind outflow spectra covering a wide range of mass transfer rates and binary inclinations, and sampling the N/C abundances of at least 100 CVs.
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