Composition and quantities of dust produced by AGB-stars and returned to the interstellar medium

Abstract

The composition of the dust mixture and the amounts of dust returned into the interstellar medium during the evolution of low and intermediate mass stars on the AGB is calculated by simple models for dust-forming stellar winds with M-, S-, and C-star chemistry. These models consider the most abundant dust species formed in circumstellar dust shells, i.e. olivine- and pyroxene-type silicate grains and iron grains in the case of M-stars, iron grains in the case of S-stars, and carbon, SiC, and iron grains in the case of C-stars. The wind models are combined with calculations of synthetic AGB-evolution to consistently determine the variation of the dust injection rate into the interstellar medium from AGB-stars with initial mass and metallicity as the stars evolve along the AGB and change their chemical surface compositions due to repeated dredge-up episodes. Numerical results are presented for initial stellar masses from 1 to 7 M ○. and for metallicities between Z = 0.001 and Z = 0.04, which can then be used to calculate chemical evolution models for the dust content of galaxies.