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Astron. Astrophys. 348, L17-L20 (1999)


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Letter to the Editor

On the formation of warm molecular layers

P. Woitke, Ch. Helling, J.M. Winters and K.S. Jeong

Institut für Astronomie und Astrophysik, TU Berlin, Sekr. PN 8-1, Hardenbergstrasse 36, D-10623 Berlin, Germany (woitke@physik.tu-berlin.de)

Received 16 April 1999 / Accepted 5 July 1999

Abstract

The levitation of the outer atmospheres of AGB stars by pulsations is proposed as possible mechanism to form "warm molecular layers". We compare the amounts of CO, H2O, CO2 and SO2 molecules found in an oxygen-rich dynamical model atmosphere with the values derived from recent ISO observations. In the model, the molecules are present in a layered structure behind shock waves which leads to a substantial increase of the column densities in comparison with static models. By additional non-LTE investigations, we calculate the vibrational and rotational excitation temperatures of these molecules and discuss the respective deviations from the kinetic gas temperature in view of the interpretation of the observations.

Key words: infrared: stars – molecular processes – hydrodynamics – stars: late-type – stars: circumstellar matter


© European Southern Observatory (ESO) 1999

Online publication: July 16, 1999

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