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

TL;DR

This study investigates how the environment of star clusters influences dust production by massive AGB stars, showing that UV irradiation can significantly reduce dust formation, impacting galactic dust input estimates.

Contribution

It combines N-body cluster simulations with stellar evolution and circumstellar models to quantify UV effects on dust formation in massive AGB stars within clusters.

Findings

Approximately 30% of massive AGB stars leave clusters and join the field.

UV irradiation can penetrate deep into circumstellar envelopes, inhibiting dust formation.

The galactic dust input rate from AGB stars may be overestimated without considering UV effects.

Abstract

We examine the fraction of massive asymptotic giant branch (AGB) stars remaining bound in their parent star clusters and the effect of irradiation of these stars by intracluster ultraviolet (UV) field. We employ a set of N-body models of dynamical evolution of star clusters 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 circumstellar environment (CSE). The initial stellar masses of clusters are varied from $50\rm M_\odot$ to $10^{5}\rm M_\odot$. Results derived for individual clusters are combined using a mass distribution function for young star clusters. We find that about 30% of massive AGB stars initially born in clusters become members of the field population, while the rest evolves in star clusters. 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 absence of dust shielding, the UV photons penetrate in the CSE deeper than $10R_*$ in 64% and deeper than $2 R_*$ in 42% of all massive AGB stars. If this suppresses following dust formation, the current injection rate of silicate dust from AGB stars in the local Galaxy decreases from $2.2 \times 10^{-4}\rm M_\odot\,kpc^{-2}\,Gyr^{-1}$ to $1.8 \times 10^{-4}\rm M_\odot\,kpc^{-2}\,Gyr^{-1}$ at most. A lower revised value of 40% for the expected fraction of presolar silicate grains from massive AGB stars is still high to explain the non-detection of these grains in meteorites.