Issue |
A&A
Volume 441, Number 2, October II 2005
|
|
---|---|---|
Page(s) | 573 - 588 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20053108 | |
Published online | 19 September 2005 |
The evolution of planetary nebulae
III. Internal kinematics and expansion parallaxes
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: [deschoenberner;rjacob;msteffen]@aip.de
Received:
22
March
2005
Accepted:
11
July
2005
A detailed theoretical study of the basic internal kinematics of
planetary nebulae is presented, based on 1D radiation-hydrodynamics
simulations of circumstellar envelopes around central stars of
0.595 and 0.696 . By means of observable quantities like radial
surface-brightness distributions and emission-line profiles computed from
the models, a comparison with real objects was performed and revealed
a reasonable agreement. This allowed to draw important conclusions
by investigating the kinematics of these models in detail.
Firstly, it is shown that the determination of kinematical
ages, normally considered to be simple if size and expansion
rate of an object are given, can seriously be flawed. Secondly, the
expansion law of a planetary nebula is different from what is
assumed for deriving spatio-kinematical models.
Thirdly and most importantly, our
hydrodynamical models help to correctly use existing angular expansion
measurements for distance determinations. The mere combination of the
angular expansion rates with the spectroscopic expansion velocities
leads always to a serious underestimate of the distance,
the degree of which depends on the evolutionary state of the object.
The necessary correction factor varies between 3 and 1.3.
Individual correction factors can be estimated with an accuracy
of about 10% by matching our hydrodynamical models to real objects.
As a result, revised distances for a few objects with
reliable angular expansion rates are presented.
But even these corrected distances are not always satisfying: they still
appear to be inconsistent with other distance determinations
and, even more disturbing, with the accepted theory of post-asymptotic
giant branch evolution.
As a byproduct of the angular expansion measurements, the
transition times from the vicinity of the asymptotic giant branch
to the planetary-nebula regime could be estimated. They appear
to be shorter than assumed in the present evolutionary calculations.
Key words: hydrodynamics / radiative transfer / planetary nebulae: general / stars: AGB and post-AGB
© ESO, 2005
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