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Long-term evolution of AGB wind envelopes: Insights from hydrodynamical models

Published online by Cambridge University Press:  25 May 2016

M. Steffen ,
D. Schönberner  and
R. Szczerba
M. Steffen
Affiliation:
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
D. Schönberner
Affiliation:
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
R. Szczerba
Affiliation:
N. Copernicus Astronomical Center, Rabianska 8, 87-100 Torun, Poland

Abstract

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Up to now, hydrodynamical models of dust-driven AGB winds do not generally take into account the ‘long-term’ changes of the stellar parameters (on stellar evolution time scales of 103 to 105 yrs), although it is well known that the luminosity and (very likely) the mass loss rate undergo significant variations when so called ‘thermal pulses’ occur on the upper AGB. In this review we demonstrate that time-dependent radiation hydrodynamics calculations are needed to understand the formation, structure, and spectral energy distribution of detached dust shells detected by IRAS and ISO. Combined with appropriate models, these observations can reveal part of the previous mass loss history on the AGB and allow an empirical check of presently adopted mass loss laws.

Based on insights from hydrodynamical simulations, we discuss the two competing scenarios that have been put forward to explain the origin of the very thin molecular shells recently discovered around some carbon stars. We find that the signature of a short mass loss ‘eruption’ broadens quickly with time due to the related velocity gradient across the shell. Hence, this scenario is not considered a likely explanation of detached CO shells. On the other hand, the alternative mechanism, interaction of winds, is shown to be capable of producing very thin shells of greatly enhanced gas density in the dusty outflows from AGB stars by sweeping up matter at the interface between both type of winds.

Type
Part 4. Circumstellar Envelopes
Information
Symposium - International Astronomical Union , Volume 191: Asymptotic Giant Branch Stars , 1999 , pp. 379 - 388
Copyright
Copyright © Astronomical Society of the Pacific 1999 

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