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28 March 2024
 
  » arxiv » astro-ph/0012457

 Article overview


The O-Na and Mg-Al Anticorrelations in Turn-Off and early Subgiants in Globular Clusters
R.G. Gratton ; P. Bonifacio ; A. Bragaglia ; E. Carretta ; V. Castellani ; M. Centurion ; A. Chieffi ; R. Claudi ; G. Clementini ; F. D’Antona ; S. Desidera ; P. Francois ; F. Grundahl ; S. Lucatello ; P. Molaro ; L. Pasquini ; C. Sneden ; F. Spite ; O. Straniero ;
Date 21 Dec 2000
Subject astro-ph
AbstractHigh dispersion spectra (R>40,000) for a quite large number of stars at the main sequence turn-off and at the base of the subgiant branch in NGC6397 and NGC6752 were obtained with the UVES on Kueyen (VLT UT2). The [Fe/H] values we found are -2.03+/-0.02+/-0.04 and -1.42+/-0.02+/-0.04 for NGC6397 and NGC6752 respectively, where the first error bars refer to internal errors and the second ones to systematic errors. In both clusters the [Fe/H] obtained for TO-stars agree perfectly (within a few per cents) with that obtained for stars at the base of the RGB. The [O/Fe]=0.21+/-0.05 value we obtain for NGC6397 is quite low, but it agrees with previous results obtained for giants in this cluster; also, the star-to-star scatter in both O and Fe is very small, indicating that this small mass cluster is chemically very homogenous. On the other side, our results show clearly and for the first time that the O-Na anticorrelation (up to now seen only for stars on the red giant branches of globular clusters) is present among unevolved stars in the globular cluster NGC6752, a more massive cluster than NGC6397. A similar anticorrelation is present also for Mg and Al, and C and N. It is very difficult to explain the observed Na-O, and Mg-Al anticorrelation in NGC6752 stars by a deep mixing scenario; we think it requires some non internal mechanism.
Source arXiv, astro-ph/0012457
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