X-Ray Observations of Planetary Nebulae with the EXOSAT Satellite

Abstract

Twelve planetary nebulae have been observed with X-ray detectors in the Exosat satellite. Eight planetary nebulae are found to emit detectable X-rays, out of which four are reported here for the first time. Six of these are extended nebulae, while two are nebulae of smaller size. The detection of the six older nebulae agrees with the earlier suggestion that the X-rays from the central star are visible when the nebula disperses or when the heavy elements in the central star atmosphere settle down. In the two nebulae NGC 4361 and NGC 1535, the X-ray luminosity is high enough to ionize carbon in the nebula and to allow the X-radiation emerge without absorption.