Fundamental Parameters, Integrated Red Giant Branch Mass Loss, and Dust Production in the Galactic Globular Cluster 47 Tucanae

McDonald, I.; Boyer, M. L.; van Loon, J. Th.; Zijlstra, A. A.; Hora, J. L.; Babler, B.; Block, M.; Gordon, K.; Meade, M.; Meixner, M.; Misselt, K.; Robitaille, T.; Sewiło, M.; Shiao, B.; & Whitney, B.
2011, The Astrophysical Journal Supplement, 193, 23

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.


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Copyright © 2012 Karl D. Gordon All Rights Reserved