EXTRAGALACTIC SYMBIOTIC SYSTEMS .4. THE SUPERSOFT X-RAY SOURCE SMC-3

We present a consistent model for the UV and supersoft X-ray emission from the symbiotic nova SMC3 (= RX J0048.4-7332). Following the presen t picture of symbiotic stars, the model consists of radiation from a h ot star and an emission nebula excited by that star. The observations were compared to theoretical models in which the hot star's emission i s calculated with the help of hydrostatic and Wolf-Rayet-type non-LTE model atmospheres. Our analysis clearly shows evidence for mass loss r ates of several 10(-6) M(circle dot)/yrThe minimum effective temperatu re compatible with both the observed UV and X-ray flux is about 260 00 0 K, which is higher than in any other star analyzed with sophisticate d NLTE model atmospheres. Since the hydrostatic surface is hidden by t he stellar wind no upper limit for the temperature can be determined. However, we were able to determine the total luminosity of a symbiotic nova with reasonable accuracy (L(SMC3) = 10(4.05+/-0.05) L(circle dot )). This value is well below the Eddington limit (approximate to 50 00 0 L(circle dot)). In order to reproduce the observed energy distributi on a carbon-to-helium ratio > 2.10(-4)-leading to an absorption edge a t 0.39 keV-is necessary.