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M. A. Guerrero, Y.-H. Chu, R. A. Gruendl (UIUC)
Two types of X-ray emission are expected in planetary nebulae (PNe): (1) point sources from hot central stars with T\rm eff=100,000--200,000 K; and (2) diffuse emission from shock-heated gas at temperatures > 106 K. Diffuse X-ray emission from PNe, if detected, would lend strong support to the ``two-wind interaction" formation mechanism of PNe.
ROSAT X-ray observations with the Position Sensitive Proportional Counter (PSPC) and the High Resolution Imager (HRI) provide unprecedent sensitivity and resolution for the investigation of X-ray emission from PNe. We have searched the ROSAT archive for observations that contain PNe within the central 40' unvignetted field of view, and found useful ROSAT observations for 82 PNe, of which the exposure time ranges from 1 ks to 90 ks with a median of ~4 ks. Less than 20% of these data have been analyzed and reported previously.
We have used these observations to search for X-ray emission from PNe. For positive detections, we further analyze the spatial and spectral properties of the X-ray emission; for non-detections, we determine the 3\sigma upper limits. In order to disentangle biases in the sample from real physical effects, we have correlated these results with properties of PNe (distance, extinction, and evolutionary status of the central star and nebula). This ROSAT archival study of PNe is the most sensitive, systematic, and exhaustive investigation of X-ray emission from PNe. These results provide not only new insights into the nature of X-ray emission from PNe but also a roadmap for the upcoming X-ray missions AXAF and XMM.
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s follows:
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