Mineral formation in stellar winds

V. Formation of calcium carbonate

Institut für Theoretische Astrophysik, Universität Heidelberg, Albert-Überle-Str. 2, 69120 Heidelberg, Germany e-mail: gail@ita.uni-heidelberg.de

Received: 18 August 2004
Accepted: 1 October 2004

Abstract

An emission band around m found in a few IR spectra from highly evolved stars was proposed to be due to the presence of carbonate dust grains in the circumstellar material (Kemper et al. [CITE], Nature, 415, 295). This contribution presents the results of a model calculation for the condensation of calcite (CaCO₃) in the stellar wind of AGB stars. It is shown that the quantities of carbonate dust formed relative to the quantities of silicate dust are negligibly small. This results from the fact that carbonates form at a much lower temperature than the silicate dust components. Carbonate dust formation then is suppressed by the strong acceleration of the wind material by radiation pressure on the silicate dust and the subsequent rapid dilution of the wind material. This makes it highly improbable that carbonate dust can be formed in stellar outflows.