47 Tucanae: The spectroscopic versus color-magnitude diagram age discrepancy

Citation
A. Vazdekis et al., 47 Tucanae: The spectroscopic versus color-magnitude diagram age discrepancy, ASTROPHYS J, 549(1), 2001, pp. 274-280
Citations number
43
Categorie Soggetti
Space Sciences
Journal title
ASTROPHYSICAL JOURNAL
ISSN journal
0004637X → ACNP
Volume
549
Issue
1
Year of publication
2001
Part
1
Pages
274 - 280
Database
ISI
SICI code
0004-637X(20010301)549:1<274:4TTSVC>2.0.ZU;2-D
Abstract
We investigate current problems in obtaining reliable ages for old stellar systems based on stellar population synthesis modeling of their integrated spectra. In particular, we address the large ages derived for the globular cluster 47 Tuc, which is at odds with its color-magnitude diagram (CMD) age . Using a new age indicator, H gamma (sigma <130), which is particularly ef fective at breaking the degeneracy between age and metallicity, we confirm the discrepancy between the spectroscopic age and the CMD age of 47 Tuc, in that the spectroscopic age is much older. Nebular emission appears unlikel y to be a source for weakening the observed Balmer lines. We then explore a number of key parameters affecting the temperature of turnoff stars, which are the main contributors to the Balmer lines for old metal-rich stellar p opulations. We find that <alpha>-enhanced isochrones with atomic diffusion included not only provide a good Dt to the CMD of 47 Tuc but also lead to a spectroscopic age in better agreement with the CMD age.