Fundamental parameters, integrated red giant branch mass loss, and dust production in the galactic globular cluster 47 Tucanae

摘要

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 _⊙, becoming ubiquitous above L = 2000 L _⊙. Recent claims of dust production around lower-luminosity giants cannot be reproduced, despite using the same archival Spitzer imagery.