Einstein X-Ray Observations of Planetary Nebulae and their Implications
Central stars of nineteen planetary nebulae were observed for X-ray emission using the Einstein Observatory and four of them were detected. High resolution observations with the Einstein Observatory indicates that the X-ray source in NGC 246 is a point source. These planetary nebulae with positive observations turn out to be the nearest, have the least extinction and also have the largest size of the nebulae around them. It is possible that X-ray emission is observed from these planetary nebulae with larger ages because of the smaller extinction by the nebulae and also due to the settling of heavy elements in the central star which otherwise prevents escape of X-rays by providing opacity.