TY - JOUR
T1 - Dynamical Model Calculations of AGB Star Winds Including Time Dependent Dust Formation and Non-LTE Radiative Cooling
AU - Schirrmacher, V.
AU - Woitke, P.
AU - Sedlmayr, E.
PY - 2000
Y1 - 2000
N2 - Stars on the Asymptotic Giant Branch (AGB) are pulsating objects in a
late evolutionary stage. The stellar pulsation creates sound waves which
steepen up to shock waves in the upper atmosphere and lead to a time
dependent levitation of the outer atmosphere. Thereby, the stellar
pulsation triggers and facilitates the formation of dust close to the
star. The dust is accelerated by radiation pressure and drags the gas
outwards due to frictional forces which is identified to provide the
basic mass loss mechanism. A longstanding problem concerning the
modelling of these physical processes is the influence of the
propagating shock waves on the temperature structure of the wind, which
strongly influences the dust formation. We have therefore improved our
numerical models of AGB-star envelopes by including (i) a detailed
calculation of non-LTE radiative heating and cooling rates,
predominantly arising from atomic and molecular lines and (ii) atomic
and molecular exitation aswell as ionisation and dissociation in the
equation of state. First results, presented here, show that the cooling
time scales behind the shock waves are usually rather short, but the
binding energies of molecular hydrogen provide an important energy
buffer capable to delay the radiative heating or cooling. Thus
considerable deviations from radiative equilibrium may occur in the
important inner dust forming layers.
AB - Stars on the Asymptotic Giant Branch (AGB) are pulsating objects in a
late evolutionary stage. The stellar pulsation creates sound waves which
steepen up to shock waves in the upper atmosphere and lead to a time
dependent levitation of the outer atmosphere. Thereby, the stellar
pulsation triggers and facilitates the formation of dust close to the
star. The dust is accelerated by radiation pressure and drags the gas
outwards due to frictional forces which is identified to provide the
basic mass loss mechanism. A longstanding problem concerning the
modelling of these physical processes is the influence of the
propagating shock waves on the temperature structure of the wind, which
strongly influences the dust formation. We have therefore improved our
numerical models of AGB-star envelopes by including (i) a detailed
calculation of non-LTE radiative heating and cooling rates,
predominantly arising from atomic and molecular lines and (ii) atomic
and molecular exitation aswell as ionisation and dissociation in the
equation of state. First results, presented here, show that the cooling
time scales behind the shock waves are usually rather short, but the
binding energies of molecular hydrogen provide an important energy
buffer capable to delay the radiative heating or cooling. Thus
considerable deviations from radiative equilibrium may occur in the
important inner dust forming layers.
M3 - Article
VL - 17
JO - Astronomische Gesellschaft Abstract Series
JF - Astronomische Gesellschaft Abstract Series
ER -