Simultaneous EUV and IR Observations of the Eclipsing Polar HU Aqr

Abstract

We present simultaneous EUV and infrared (J,K) observations of the polar HU Aqr obtained during August 1998 when the star was in a high mass accretion state. EUV and IR light curves and EUV spectra are presented and compared with previous observations. The accretion region on the white dwarf has increased in temperature (124,000K to 240,000K) and radius (0.04 R$_{WD}$ to 0.06 R$_{WD} $) compared with previous EUV observations made during low mass accretion states. The EUV and IR photometric observations are shown to have a similar appearance as a function o f orbital phase. The EUV photometry shows rapid changes and provides evidence for mass accretion via blobs. The high state IR light curves present an asymmetric double-humped shape with J=14.8 and K=14.1. We applied an ellipsoidal model fit to the observations and the result indicates that the cause of the modulated shape is both due to ellipsoidal variations from the Roche Lobe filling secondary star and a complex flux combination probably dominated at all orbital phases by cyclotron emission. The source of maximum cyclotron emission appears to be in the accretion column high above the white dwarf surface.