||Dust Production from Sub-Solar to Super-Solar Metallicity in
Thermally Pulsing Asymptotic Giant Branch Stars
||497, Why Galaxies Care about AGB Stars III: A Closer Look in Space and Time
||Nanni, A.; Bressan, A.; Marigo, P.; Girardi, L.; Javadi, A.; van Loon, J. Th.
||We discuss the dust chemistry and growth in the circumstellar envelopes
(CSEs) of Thermally Pulsing Asymptotic Giant Branch (TP-AGB) star
models, computed with the COLIBRI code, at varying initial
mass and metallicity (Z = 0.001, 0.008, 0.02, 0.04, 0.06).
A relevant result of our analysis deals with silicate production in
M stars. We show that, in order to reproduce the observed trend
between terminal velocities and mass-loss rates in Galactic M giants,
one has to significantly reduce the efficiency of chemisputtering by
H2 molecules, usually considered the most effective dust destruction
mechanism. This conclusion is in agreement with the most recent
laboratory results, which show that silicates may condense already at
Tcond∼1400 K, rather than only at Tcond∼1000 K,
as obtained by models that include chemisputtering.
From analysis of the total dust ejecta, we find that the dust-to-gas
ratios of the total ejecta from intermediate-mass stars are much less
dependent on metallicity than usually assumed. In a broader context,
our results are suitable for studying the dust enrichment of the
interstellar medium provided by TP-AGB stars in both nearby and