Fundamental parameters, integrated RGB mass loss and dust production in the Galactic globular cluster 47 Tucanae

TL;DR

This study investigates the fundamental parameters, mass loss, and dust production in post-main-sequence stars of 47 Tucanae, confirming its distance and age, and analyzing dust formation onset in bright giants through spectral energy distribution fitting.

Contribution

It provides a detailed analysis of mass loss and dust production in 47 Tucanae using SED fitting, clarifying the luminosity threshold for dusty mass loss in giant stars.

Findings

Dusty mass loss begins at ~1000 Lsun.

No significant difference in RGB mass loss compared to omega Centauri.

Dust production is observed only in the brightest giants.

Abstract

Fundamental parameters and time-evolution of mass loss are investigated for post-main-sequence stars in the Galactic globular cluster 47 Tucanae (NGC 104). This is accomplished by fitting spectral energy distributions (SEDs) to existing optical and infrared photometry and spectroscopy, to produce a true Hertzsprung--Russell diagram. We confirm the cluster's distance as 4611 (+213, -200) pc and age as 12 +/- 1 Gyr. Horizontal branch models appear to confirm that no more RGB mass loss occurs in 47 Tuc than in the more-metal-poor omega Centauri, though difficulties arise due to inconsistencies between the models. Using our SEDs, we identify those stars which exhibit infrared excess, finding excess only among the brightest giants: dusty mass loss begins at a luminosity of ~ 1000 Lsun, becoming ubiquitous above 2000 Lsun. Recent claims of dust production around lower-luminosity giants cannot be reproduced, despite using the same archival Spitzer imagery.