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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.