Other
Scientific paper
Oct 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995mnras.276.1382r&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 276, Issue 4, pp. 1382-1390.
Other
17
Accretion, Accretion Discs, Stars: Magnetic Fields, Stars: Variables: Other, X-Rays: Stars
Scientific paper
We present data for four AM Her stars which were observed in an intermediate or low brightness state. We show that as the luminosity of the blackbody component decreases so does the energy balance ratio L_bb,bol/(L_tb,bol+L_cyc). Indeed, AM Her in an intermediate state shows a soft X-ray deficiency over the standard shock model of Lamb & Masters and does not follow the correlation between the coupling radius and the energy balance ratio found by Ramsay et al. for systems in a high state. ST LMi in a low state shows a much reduced bremsstrahlung temperature compared to its high state. We hypothesize that as the overall accretion rate decreases the fraction of the gas which shocks above the surface of the white dwarf becomes smaller. Instead, much of the accreting gas cools via Coulomb collisions and cyclotron emission. At low accretion rates, the thermalized component of the accretion energy emitted at the surface of the white dwarf is too cool to be observed in the ROSAT band above the cut-off imposed by interstellar absorption.
Cropper Mark
Mason Keith O.
Ramsay Gavin
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