Issue |
A&A
Volume 469, Number 1, July I 2007
|
|
---|---|---|
Page(s) | 239 - 263 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20066772 | |
Published online | 24 April 2007 |
Evolution of asymptotic giant branch stars*
I. Updated synthetic TP-AGB models and their basic calibration
1
Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 3, 35122 Padova, Italy e-mail: paola.marigo@unipd.it
2
Osservatorio Astronomico di Padova – INAF, Vicolo dell'Osservatorio 5, 35122 Padova, Italy e-mail: leo.girardi@oapd.inaf.it
Received:
20
November
2006
Accepted:
27
February
2007
We present new synthetic models of the TP-AGB evolution.
They are computed for 7
values of initial metal content (Z from 0.0001 to 0.03) and for
initial masses between 0.5 and 5.0 , thus extending the low-
and intermediate-mass tracks of Girardi et al. (2000) to the
beginning of the post-AGB phase. The calculations are performed by
means of a synthetic code that incorporates many recent
improvements, among which we mention: (1) the use of detailed and
revised analytical relations to describe the evolution of
quiescent luminosity, inter-pulse period, third
dredge-up, hot bottom burning, pulse cycle luminosity variations,
etc.; (2) the use of variable molecular opacities – i.e. opacities
consistent with the changing photospheric chemical composition – in
the integration of a complete envelope model, instead of the standard
choice of scaled-solar opacities; (3) the use of formalisms for the
mass-loss rates derived from pulsating dust-driven wind models of C- and
O-rich AGB stars; and (4) the switching of pulsation modes between
the first overtone and the fundamental one along the evolution, which has
consequences in terms of the history of mass loss. It follows that,
in addition to the time evolution on the HR diagram,
the new models also consistently predict variations
in surface chemical compositions,
pulsation modes and periods, and mass-loss rates. The onset and
efficiency of the third dredge-up process are calibrated in order to
reproduce basic observables like the carbon star luminosity functions
in the Magellanic Clouds and TP-AGB lifetimes (star counts) in
Magellanic Cloud clusters.
In this first paper, we describe in detail the model ingredients, basic
properties, and calibration. Particular emphasis is put on
illustrating the effects of using variable molecular opacities.
Forthcoming papers will present the theoretical isochrones
and chemical yields derived from these
tracks and additional tests performed with the aid of a complete population
synthesis code.
Key words: stars: AGB and post-AGB / stars: carbon / stars: mass-loss / stars: general / stars: evolution / stars: abundances
© ESO, 2007
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