EDP Sciences
Free access
Issue
A&A
Volume 402, Number 3, May II 2003
First Science with the ODIN satellite
Page(s) 985 - 1001
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20030296


A&A 402, 985-1001 (2003)
DOI: 10.1051/0004-6361:20030296

Mg isotopic ratios in giant stars of the globular cluster NGC 6752

D. Yong1, F. Grundahl2, D. L. Lambert1, P. E. Nissen2 and M. D. Shetrone3

1  Department of Astronomy, University of Texas, Austin, TX 78712, USA
2  Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark
    e-mail: fgj,pen@phys.au.dk
3  McDonald Observatory, University of Texas, HC 75, Box 1337 MCD, Fort Davis, TX 79734, USA
    e-mail: shetrone@astro.as.utexas.edu

(Received 13 January 2003 / Accepted 27 February 2003 )

Abstract
Mg isotopic abundance ratios are measured in 20 bright red giants in globular cluster NGC 6752 based on very high-resolution ( $R\sim110\,000$), high signal-to-noise spectra obtained with UVES on the VLT. There is a considerable spread in the ratio 24Mg: 25Mg: 26Mg with values ranging from 53:9:39 to 83:10:7. We measured the abundances of O, Na, Mg, Al, and Fe combining our sample with 21 RGB bump stars (Grundahl et al. 2002). The abundances of the samples are consistent and exhibit the usual anticorrelations between O-Na and Mg-Al. A positive correlation is found between 26Mg and Al, a mild anticorrelation is found between 24Mg and Al, while no correlation is found between 25Mg and Al. None of the elemental or isotopic abundances show a dependence on evolutionary status and, as shown by Gratton et al. (2001), the abundance variations exist even in main sequence stars. This strongly suggests that the star-to-star abundance variations are a result of varying degrees of pollution with intermediate mass AGB stars being likely polluters. Consideration of the extremes of the abundance variations provides the composition of the ambient material and the processed material. In the least contaminated stars (lowest Na and Al and highest O and Mg abundances), we infer a Mg isotopic ratio around 80:10:10 and a composition ([O/Fe], [Na/Fe], [Mg/Fe], [Al/Fe]) $\simeq$ (0.6, -0.1, 0.5, 0.0). In the most polluted stars, we find a Mg isotopic ratio around 60:10:30 and a composition ([O/Fe], [Na/Fe], [Mg/Fe], [Al/Fe]) $\simeq$ (-0.1, 0.6, 0.3, 1.2). Even for the least polluted stars, the abundances of 25Mg and 26Mg relative to 24Mg are considerably higher than predicted for ejecta from Z=0 supernovae. Zero metallicity AGB stars may be responsible for these higher abundances. Our measured Mg isotopic ratios reveal another layer to the globular cluster star-to-star abundance variations that demands extensions of our present theoretical knowledge of stellar nucleosynthesis by giant stars.


Key words: galaxies: clusters: general -- galaxies: clusters: individual: NGC 6752 -- stars: abundances -- stars: evolution -- stars: fundamental parameters

Offprint request: D. Yong, tofu,dll@astro.as.utexas.edu

SIMBAD Objects



© ESO 2003

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.