Published by
EDP Sciences
EDP Sciences Journals List
Subscriber Authentication Point
Home All issues Volume 457/ 3 Article
Free access
Issue A&A
Volume 457, Number 3, October III 2006
Page(s) 995 - 1001
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20065481



A&A 457, 995-1001 (2006)
DOI: 10.1051/0004-6361:20065481

Does the oxygen-sodium anticorrelation in globular clusters require a lowering of the $\mathsf{^{23}}$Na(p, $\mathsf{\alpha)^{20}}$Ne reaction rate?

P. Ventura and F. D'Antona

INAF - Observatory of Rome, via Frascati 33, 00040 MontePorzio Catone (RM) - Italy
    e-mail: [ventura;dantona]@oa-roma.inaf.it

(Received 24 April 2006 / Accepted 3 July 2006)

Abstract
Context.The chemical content of the ejecta of Asymptotic Giant Branch stars (AGBs) is important to understand whether intermediate mass stars played a role in the "self-enrichment scenario", to explain the chemical anomalies observed among Globular Clusters stars. One difficulty of this model is that it is not fully consistent with the observed oxygen-sodium anticorrelation.
Aims.We look for the combinations of the input-physics parameters by which the yields of massive AGBs are sodium-rich and oxygen-poor.
Methods.Many evolutions from the early evolutionary phases until the mass of the envelope drops below ~ $0.5~M_{\odot}$ are calculated for a  $5~M_{\odot}$ Z=0.001 model for various assumptions concerning the extra mixing from the bottom of the envelope and the relevant cross sections involving sodium.
Results.A modest amount of extra mixing from the bottom of the surface convective zone leads to ejecta that are moderately sodium rich and oxygen depleted. A different but appealing modelization allows us to reproduce the observations of stars with a lower oxygen content: extra mixing is not included, but the cross sections of the reaction 23Na $(p, \alpha)$20Ne must be a factor of ~4 lower than the recommended values. If the initial neon content of the star is not solar-scaled but enhanced as the other $\alpha$ elements by a factor ~2, the afore mentioned cross section must be lessened by only a factor ~2.


Key words: stars: abundances -- stars: AGB and post-AGB -- stars: evolution



© ESO 2006

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.