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One key feature of the interacting stellar winds model of the formation ofplanetary nebulae (PNe) is the presence of shock-heated stellar wind confinedin the central cavities of PNe. This so-called hot bubble should be detectablein X-rays. Here we present XMM-Newton observations of NGC 3242, amultiple-shell PN whose shell morphology is consistent with the interactingstellar winds model. Diffuse X-ray emission is detected within its inner shellwith a plasma temperature ~2.35\times10^6 K and an intrinsic X-ray luminosity~2\times10^30 ergs s^(-1) at the adopted distance of 0.55 kpc. The observedX-ray temperature and luminosity are in agreement with "ad-hoc" predictions ofmodels including heat conduction. However, the chemical abundances of theX-ray-emitting plasma seem to imply little evaporation of cold material intothe hot bubble, whereas the thermal pressure of the hot gas is unlikely todrive the nebular expansion as it is lower than that of the inner shell rim.These inconsistencies are compounded by the apparent large filling factor ofthe hot gas within the central cavity of NGC 3242. Subject headings: planetarynebulae: individual (NGC 3242)

Physical Structure of the Planetary Nebula NGC 3242 from the Hot Bubble to the Nebular Envelope