EDP Sciences
Free access
Volume 448, Number 2, March III 2006
Page(s) L37 - L41
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200600012
A&A 448, L37-L41 (2006)
DOI: 10.1051/0004-6361:200600012


On the origin of the high helium sequence in $\mathsf{\omega}$ Centauri

A. Maeder and G. Meynet

Geneva Observatory, 1290 Sauverny, Switzerland
    e-mail: [andre.maeder;georges.meynet]@obs.unige.ch

(Received 19 December 2005 / Accepted 21 January 2006 )

The blue Main Sequence (bMS) of $\omega$ Cen implies a ratio of helium to metal enrichment  $\Delta Y/\Delta Z \approx 70$, which is a major enigma. We show that rotating models of low metallicity stars, which account for the anomalous abundance ratios of extremely metal poor stars, are also useful for understanding the very high $\Delta Y/\Delta Z$ ratio in $\omega$ Cen. Models of massive stars with moderate initial rotation velocities produce stellar winds with large He- and N-excesses, but without the large C- (and O-) excesses made by very fast rotation, in agreement with the observed chemical abundance ratios in $\omega$ Cen.

It is still uncertain whether the abundance peculiarities of $\omega$ Cen result from the fact that the high velocity contributions of supernovae escaped the globular cluster, usually considered as a tidally stripped core of a dwarf galaxy. Another possibility is a general dominance of wind ejecta at very low Z, due to the formation of black holes. Some abundance and isotopic ratios like $\rm Mg/Al$, $\rm Na/Mg$, $\rm Ne/N$, $\rm ^{12}C/^{13}C$, $\rm ^{16}O/^{18}O$ and $\rm ^{17}O/^{18}O$ may allow us to further discriminate between these scenarios and between the AGB and massive star contributions.

Key words: stars: $\omega$ Centauri -- helium -- stars: evolution

SIMBAD Objects

© 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.