The Three Dimensional Structure of EUV Accretion Regions in AM Herculis Stars: Modeling of EUV Photometric and Spectroscopic Observations

摘要

We have developed a model of the high-energy accretion region for magneticcataclysmic variables and applied it to {it Extreme Ultraviolet Explorer}observations of 10 AM Herculis type systems. The major features of the EUVlight curves are well described by the model. The light curves exhibit a largevariety of features such as eclipses of the accretion region by the secondarystar and the accretion stream, and dips caused by material very close to theaccretion region. While all the observed features of the light curves arehighly dependent on viewing geometry, none of the light curves are consistentwith a flat, circular accretion spot whose lightcurve would vary solely fromprojection effects. The accretion region immediately above the WD surface is asource of EUV radiation caused by either a vertical extent to the accretionspot, or Compton scattering off electrons in the accretion column, or, verylikely, both. Our model yields spot sizes averaging 0.06 R$_{WD}$, or $f sim 1imes 10^{-3}$ the WD surface area, and average spot heights of 0.023R$_{WD}$. Spectra extracted during broad dip phases are softer than spectraduring the out-of-dip phases. This spectral ratio measurement leads to theconclusion that Compton scattering, some absorption by a warm absorber,geometric effects, an asymmetric temperature structure in the accretion regionand an asymmetric density structure of the accretion columnare all importantcomponents needed to fully explain the data. Spectra extracted at phases wherethe accretion spot is hidden behind the limb of the WD, but with the accretioncolumn immediately above the spot still visible, show no evidence of emissionfeatures characteristic of a hot plasma.