Condensation of MgS in outflows from carbon stars

Abstract

The basic mechanism responsible for the widespread condensation of MgS in the outflows from carbon rich stars on the tip of the AGB is discussed with the aim of developing a condensation model that can be applied in model calculations of dust formation in stellar winds. The different possibilities how MgS may be formed in the chemical environment of outflows from carbon stars are explored by some thermochemical calculations and by a detailed analysis of the growth kinetics of grains in stellar winds. The optical properties of core-mantle grains with a MgS mantle are calculated to demonstrate that such grains reproduce the structure of the observed 30 $\mu$m feature. These considerations are complemented by model calculations of circumstellar dust shells around carbon stars. It is argued that MgS is formed via precipitation on silicon carbide grains. This formation mechanism explains some of the basic observed features of MgS condensation in dust shells around carbon stars. A weak secondary peak at about 33 ... 36 $\mu$m is shown to exist in certain cases if MgS forms a coating on SiC.

9 pages, 7 figures

References in corpus (2)

• Spitzer spectroscopy of carbon stars in the Small Magellanic Cloud
• Solar heavy element abundance: constraints from frequency separation ratios of low-degree p modes

Cited by in corpus (7)

• Carbon-rich dust past the asymptotic giant branch: aliphatics, aromatics, and fullerenes in the Magellanic Clouds
• Chemical equilibrium in AGB atmospheres: Successes, failures, and prospects for small molecules, clusters, and condensates
• The role of Pop III stars and early black holes in the 21cm signal from Cosmic Dawn
• SiS formation in the interstellar medium through Si+SH gas phase reactions
• A study of carbon-rich post-AGB stars in the Milky Way to understand the production of carbonaceous dust from evolved stars
• Chemistry of nebulae around binary post-AGB stars: A molecular survey of mm-wave lines
• Molecular gas in 21 and 30 micron sources: the 2\,mm and 1.3\,mm spectra of IRAS\,21318+5631 and 22272+5435