• García-Hernández, D. A.
• Dellagli, F.
• Di Criscienzo, M.
• Schneider, R.
• Rossi, C.
• Ventura, P.

Abstract

The O-rich asymptotic giant branch (AGB) stars experience strong mass-loss with efficient dust condensation and they are major sources of dust in the interstellar medium. Alumina dust (Al<SUB>2</SUB>O<SUB>3</SUB>) is an important dust component in O-rich circumstellar shells and it is expected to be fairly abundant in the winds of the more massive and O-rich AGB stars. By coupling AGB stellar nucleosynthesis and dust formation, we present a self-consistent exploration on the Al<SUB>2</SUB>O<SUB>3</SUB> production in the winds of AGB stars with progenitor masses between ̃3 and 7 M<SUB>☉</SUB> and metallicities in the range 0.0003 ≤ Z ≤ 0.018. We find that Al<SUB>2</SUB>O<SUB>3</SUB> particles form at radial distances from the centre between ̃2 and 4 R<SUB>*</SUB> (depending on metallicity), which is in agreement with recent interferometric observations of Galactic O-rich AGB stars. The mass of Al<SUB>2</SUB>O<SUB>3</SUB> dust is found to scale almost linearly with metallicity, with solar metallicity AGBs producing the highest amount (about 10<SUP>-3</SUP> M<SUB>☉</SUB>) of alumina dust. The Al<SUB>2</SUB>O<SUB>3</SUB> grain size decreases with decreasing metallicity (and initial stellar mass) and the maximum size of the Al<SUB>2</SUB>O<SUB>3</SUB> grains is ̃0.075 μm for the solar metallicity models. Interestingly, the strong depletion of gaseous Al observed in the low-metallicity hot bottom burning (HBB) AGB star HV 2576 seems to be consistent with the formation of Al<SUB>2</SUB>O<SUB>3</SUB> dust as predicted by our models. We suggest that the content of Al may be used as a mass (and evolutionary stage) indicator in AGB stars experiencing HBB....

Topics

• impedance spectroscopy
• grain
• grain size