Fundamental Parameters, Integrated Red Giant Branch Mass Loss, and Dust Production in the Galactic Globular Cluster 47 Tucanae
van Loon, J. Th.; Hora, J. L.; Zijlstra, A. A.; Boyer, M. L.; Gordon, K.; Meixner, M.; Misselt, K.; Babler, B.; Meade, M.; McDonald, I.; Whitney, B.; Shiao, B.; Sewiło, M.; Robitaille, T.; Block, M.
United Kingdom, United States
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 d = 4611+213 -200 pc and age as 12 ± 1 Gyr. Horizontal branch models appear to confirm that no more red giant branch mass loss occurs in 47 Tuc than in the more metal-poor ω Centauri, though difficulties arise due to inconsistencies between the models. Using our SEDs, we identify those stars that exhibit infrared excess, finding excess only among the brightest giants: dusty mass loss begins at a luminosity of ~1000 L sun, becoming ubiquitous above L = 2000 L sun. Recent claims of dust production around lower-luminosity giants cannot be reproduced, despite using the same archival Spitzer imagery.