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M.A. Guerrero (IAA, CSIC), Y.-H. Chu, R.A. Gruendl (UIUC), M. Meixner (STScI)
Planetary nebulae (PNe) consist of the stellar material ejected by low- and intermediate-mass stars (1-8 M\odot) at the end of the asymptotic giant branch phase (AGB). As such a star evolves off the AGB phase, the copious mass-loss strips off the stellar envelope and exposes the hot stellar core that ionizes the nebular material. The central stars of PNe present fast stellar winds with terminal velocities 1000-4000 km s-1, while fast collimated outflows with velocities up to 1000 km s-1 are also observed in PNe. The interactions of the fast stellar wind and/or collimated outflows with nebular material can give rise to diffuse X-ray emission from PNe.
Diffuse X-ray emission has been detected only in young PNe previously. To investigate the evolution of hot gas in PN interiors, we obtained \emph{XMM-Newton} observations of NGC 2392 (the Eskimo Nebula) and NGC 3242 (the Ghost of Jupiter), two evolved elliptical PNe. Diffuse X-ray emission is detected in both nebulae. In both cases, the hot gas is confined within the innermost shell, the X-ray spectrum can be described by a thin plasma emission model with temperature ~2\times106 K, and the X-ray luminosity is ~1\times1031 ergs s-1. Furthermore, the X-ray spectrum of NGC 3242 shows evidence of enhanced nitrogen abundance, while the X-ray morphology of NGC 2392 hints a possible association with its fast collimated outflows.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.