M. A. Guerrero, N. Ruiz, W. -R. Hamann, Y. -H. Chu, H. Todt, D. Schoenberner, L. Oskinova, R. A. Gruendl, M. Steffen, W. P. Blair, J. A. Toala
The planetary nebula (PN) A 30 is believed to have undergone a very late
thermal pulse resulting in the ejection of knots of hydrogen-poor material.
Using multi-epoch HST images we have detected the angular expansion of these
knots and derived an age of 850+280-150 yr. To investigate the spectral and
spatial properties of the soft X-ray emission detected by ROSAT, we have
obtained Chandra and XMM-Newton deep observations of A 30. The X-ray emission
from A 30 can be separated into two components: a point-source at the central
star and diffuse X-ray emission associated with the hydrogen-poor knots and the
cloverleaf structure inside the nebular shell. To help us assess the role of
the current stellar wind in powering this X-ray emission, we have determined
the stellar parameters and wind properties of the central star of A 30 using a
non-LTE model fit to its optical and UV spectrum. The spatial distribution and
spectral properties of the diffuse X-ray emission is highly suggestive that it
is generated by the post-born-again and present fast stellar winds interacting
with the hydrogen-poor ejecta of the born-again event. Charge-exchange
reactions between the ions of the stellar winds and neutral material of the
born-again ejecta seem the most likely mechanism for the production of diffuse
X-ray emission. Shock-heated plasma may also contribute to this emission, as
the hydrogen-poor knots are ablated by the stellar winds, in which case
efficient mass-loading of the stellar winds is needed to raise the density and
damp the velocity of the stellar winds to reproduce the spectral properties of
the diffuse emission. The origin of the X-ray emission from the central star of
A 30 is puzzling: shocks in the present fast stellar wind and photospheric
emission can be ruled out, while the development of a new, compact hot bubble
confining the fast stellar wind seems implausible.
View original:
http://arxiv.org/abs/1202.4463
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