Tracers of stellar mass-loss. I. Optical and near-IR colours and surface brightness fluctuations

TL;DR

This study models optical and near-IR colours and surface brightness fluctuations of stellar populations, including dusty envelopes of TP-AGB stars, to understand mass-loss effects and predict mid-IR SBF as a diagnostic tool.

Contribution

It introduces new stellar population synthesis models incorporating dust-enshrouded TP-AGB stars with variable mass-loss rates, validated against observational data.

Findings

Optical and near-IR colours and SBFs cannot detect changes in mass-loss rates.

Mid-IR SBF measurements can identify mass-loss variations.

Models support the link between metallicity and mass-loss in TP-AGB stars.

Abstract

We present optical and IR integrated colours and SBF magnitudes, computed from stellar population synthesis models that include emission from the dusty envelopes surrounding TP-AGB stars undergoing mass-loss. We explore the effects of varying the mass-loss rate by one order of magnitude around the fiducial value, modifying accordingly both the stellar parameters and the output spectra of the TP-AGB stars plus their dusty envelopes. The models are single burst, and range in age from a few Myr to 14 Gyr, and in metallicity between $Z$ = 0.0001 and $Z$ = 0.07; they combine new calculations for the evolution of stars in the TP-AGB phase, with star plus envelope SEDs produced with the radiative transfer code DUSTY. We compare these models to optical and near-IR data of single AGB stars and Magellanic star clusters. This comparison validates the current understanding of the role of mass-loss in determining stellar parameters and spectra in the TP-AGB. However, neither broad-band colours nor SBF measurements in the optical or the near-IR can discern global changes in the mass-loss rate of a stellar population. We predict that mid-IR SBF measurements can pick out such changes, and actually resolve whether a relation between metallicity and mass-loss exists.