X-Ray Properties of Symbiotic Stars: I. The Supersoft Symbiotic Novae RR Tel and SMC3 (=RX J0048.4-7332)

We searched the ROSAT archive for pointed PSPC observations covering positions of symbiotic stars. 16 systems are detected. We find three distinct types of energy distributions, one of which is supersoft. This class consists of seven objects, among them two symbiotic novae, RR Tel and SMC3, which are discussed in more detail in this paper. The supersoft emission is produced by photospheric emission from the hot star. For RR Tel the ROSAT and IUE observations are simultaneously reproduced with a white dwarf type atmosphere with T _eff=142 000 K. SMC3 can only be fitted with a WR-type atmosphere with considerable mass loss (dot M ∼ 10^{ - 5} M_ odot /yr), and a temperature in excess of T _eff ≳ 260 000 K.