ROSAT X-RAY OBSERVATIONS OF 4 PLANETARY-NEBULAE

We report ROSAT Position Sensitive Proportional Counter (PSPC) observa tions of four planetary nebulae. The observations show that all four n ebulae have two-component spectra. A two-component model consisting of a blackbody and a Raymond-Smith thermal plasma is fitted to the obser ved ROSAT PSPC spectra of NGC 1535, Abell 36, and NGC 7293. For all th ree cases, the temperatures of the blackbody component are apparently higher than those of the stellar photospheres, indicating nonblackbody atmospheres. In all cases, the temperatures of the high-energy compon ent can be attributed to a hot plasma associated with the possible ste llar coronae or the ''hot bubbles'' predicted by the interacting winds model. The spectral energy distribution of NGC 1535 is constructed an d modeled by incorporating our X-ray spectrum into existing data in UV , optical, near-infrared, and far-infrared wavelengths.