Volume 537, January 2012
|Number of page(s)||14|
|Section||Stellar structure and evolution|
|Published online||19 December 2011|
The VLT/VISIR mid-IR view of 47 Tucanae
1 European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
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2 INAF, Oss. Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
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3 Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain
4 Department of Astrophysic, University of La Laguna, 38200 La Laguna, Tenerife, Canary Island, Spain
5 SISSA, via Bonomea, 265, 34136 Trieste, Italy
Received: 9 May 2011
Accepted: 10 October 2011
There is an ongoing debate regarding the onset luminosity of dusty mass loss in population-II red giant stars. We present VLT/VISIR mid-infrared (MIR) 8.6 μm imaging of 47 Tuc, the centre of attention of a number of space-based Spitzer observations and studies. The VISIR high-resolution (diffraction limited) observations allow excellent matching to existing optical Hubble Space Telescope catalogues. The optical-MIR coverage of the inner core of the cluster provide the cleanest possible blending-free sampling of the upper 3 mag of the giant branch. Our diagrams show no evidence of faint giants with MIR-excess. A combined near/mid-infrared diagram additionally confirms the near absence of dusty red giants. Dusty red giants and asymptotic giant stars are confined to the 47 Tuc long-period variable population. In particular, dusty red giants are limited to the upper one N8.6 μm magnitude below the giant branch tip. This particular luminosity level corresponds to ~1000 L⊙, which was suggested in previous determinations to mark the onset of dusty mass loss. Interestingly, starting from this luminosity level we detected a gradual deviation between the colours of red giants and the theoretical isochrones.
Key words: stars: mass-loss / stars: winds, outflows / stars: Population II / globular clusters: individual: 47 Tucanae (NGC 104)
© ESO, 2012
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