Stellar Physics and Stellar Activity Diffuse X-ray emission from PNe with WR-type central stars U. Rühling, C. Sandin, M. Steffen, D. Schönberner, W.-R. Hamann (Univ. Potsdam), H. Todt (Univ. Potsdam) Planetary nebulæ (PNe) have been identified as weak, diffuse X-ray sources. Recently, we added an observation of PN A66 30 with XMM-Newton. We want to exploit the X-ray emission from PNe with hydrogen-deficient, [WC]-type central stars to constrain their still enigmatic origin. Different scenarios have been proposed, attributing the loss of hydrogen to a "late", "very late", or "AGB final" thermal pulse (LTP, VLTP, and AFTP, respectively). Indicators for stellar evolution The slow AGB wind (green) is swept up by a fast, radiatively driven wind of the successive central star. It forms a planetary nebula (red). The nebula is filled by a shock-heated, X-ray emitting hot bubble. Mostly, the central-star wind is hydrogen-normal (blue). However, for ~10% of all PNe this wind is hydrogen-deficient (turquoise). In case of an AFTP, the fast central-star wind is hydrogen-deficient from the beginning. Thus, the X-ray emitting hot bubble is expected to fill the whole nebula, showing a hydrogen-poor, metal-rich spectrum. In a born-again scenario, on the other hand, the central star wind sets off being hydrogen-normal. Then, another thermal pulse occurs. Only now is the wind hydrogen-deficient. In this case, the X-ray emitting region is expected to be located closer to the central star showing hydrogen-poor LTP/ VLTP composition. Predicted structure of the hot bubble. PNe with central stars of type [WC] or wels. Optical image plus X-ray emission (in blue). Testing evolutionary scenarios To solve the mystery about the origin of hydrogen-deficient central stars of planetary nebulæ, we combine the expertise on stellar winds, radiation hydrodynamic modeling of PNe and X-ray observations. Stellar atmospheres – PoWR With the Potsdam Wolf-Rayet code (PoWR) we can model spectra of expanding, highly non-LTE stellar atmospheres. In the group of W.-R. Hamann at Potsdam University, we analyze a large sample of [WC]type central stars and provide an empirical evolutionary sequence These parameters serve as input for the nebula modeling. Planetary Nebulæ – NEBEL The NEBEL code performes detailed radiation hydrodynamical model calculations that consider the influence of heat conduction. For this project, we included heat conduction of a hydrogen-deficient plasma (for details see poster by C. Sandin). NEBEL calculates X-ray emission for different evolutionary scenarios. X-ray observations We compare NEBEL code predicted X-ray emission for the AFTP/ born-again scenarios with own and archived X-ray observations with XMM-Newton and Chandra. This will shed light on the origin of the hydrogen loss. Combined expertise at AIP and Postdam Univ.