Ultraviolet observations of AM Her.

Abstract

Observations of AM Her at different flux levels obtained with IUE are presented. From the observations obtained at the lowest flux level, an upper limit to the white dwarf temperature of about 20,000 K, is derived, confirming an earlier temperature determination by Schmidt et al. (1981) from optical spectrophotometry. The increased flux levels at other times are due to moderate heating of a large fraction of the white dwarf surface, rather than to strong heating of small areas around the accretion poles. Comparison with soft X-ray observations shows that the orbital maximum of the soft X-ray lightcurve sometimes occurs during the minimum of the ultraviolet lightcurve. This shows that straightforward interpretation of the varying component of the ultraviolet flux as the tail of blackbody soft X-ray flux is not correct.