Can star cluster environment affect dust input from massive AGB stars?

Abstract

We examine the fraction of massive asymptotic giant branch (AGB) stars remaining bound in their parent star clusters (SCs) and the effect of irradiation of these stars by an intracluster ultraviolet (UV) field. We employ a set of N-body models of dynamical evolution of SCs rotating in a galactic potential at the solar galactocentric radius. The cluster models are combined with stellar evolution formulae, a library of stellar spectra, and simple models for SiO photodissociation in the circumstellar environment (CSE). The initial stellar masses of clusters are varied from to . Results derived for individual clusters are combined using a mass distribution function for young SCs. We find that about 30% of massive AGB stars initially born in clusters become members of the field population, while the rest evolve in SCs. They are irradiated by strong intracluster UV radiation, resulting in the decrease of the photodissociation radius of SiO molecules, in many stars down to the dust formation zone. In the absence of dust shielding, the UV photons penetrate in the CSE deeper than in 64% and deeper than in 42% of all massive AGB stars. If this suppresses subsequent dust formation, the current injection rate of silicate dust from AGB stars in the local Galaxy decreases from to at most. A lower revised value of 40% for the expected fraction of presolar silicate grains from massive AGB stars is still too high to explain the non-detection of these grains in meteorites.