Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21812502w&link_type=abstract
American Astronomical Society, AAS Meeting #218, #125.02; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
To investigate the importance of physical processes in the stellar atmosphere on the mass loss rates of AGB stars, we have run a substantial grid of dynamical atmosphere models using a code that approximates non-LTE, dust formation, and radiative transfer via one or two parameters each, and using R(L, M, Z, l/H) to investigate the importance of low gravity and metallicity. This gives us six parameters to investigate: Criticial density (for the onset of non-LTE), opacity kappa (determines the photospheric density), Tcondensation and ΔTcondensation (for dust formation), mixing length parameter l/H, and Z, M (for the initial stellar model). We find the location of the Deathline, where dlnM/dt = dlnL/dt, is quite stable, shifting by ΔlogLdeath < 0.1 with variation of any of the parameters inside reasonable limits. We find that the biggest uncertainty in the model-based Deathline is introduced by the uncertainty in R(L, M, Z) represented by varying l/H in the models. The condensation of dust and the non-LTE transfer both have a great effect on the structure of the atmosphere, and affect the outflow velocity in the wind, but neither of these makes a large difference in the predicted Deathline. Observational constraints on the Deathline include the Mira P-L relation and a variety of published empirical mass loss formulae. Research supported by NSF AST0708143.
Wang Qiangguo
Willson Lee Anne M.
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