Evidence for Absorption of EUV Radiation by the Accretion Column: Modeling of EUVE Light Curves of AM HER Systems

We present extreme ultraviolet (EUV) light curves for a number of AM Her systems observed by the Extreme Ultraviolet Explorer (EUVE). In order to understand the physical structures responsible for the EUV emissions, we have developed a software model to generate synthetic light curves. For several systems we find a small, symmetric, raised spot on the white dwarf (WD) is the only shape consistent with the data. Residuals from simple geometric model fits indicate that a large fraction of the EUV-bright light curve in each system is seen in absorption. The addition of a cylindrically symmetric absorber of uniform density that intersects the accretion spot accounts for the missing flux. We conclude that the observed absorption is due to the accretion column immediately above the EUV accretion spot, and that the column is inclined away from the WD surface normal vector in the direction of the white dwarf rotation. Our analyses of the phase-folded spectra give insight into the nature of the absorbing material. This work has been supported by NASA contract NAS5-29298.