2010MNRAS.406.1570P -
Mon. Not. R. Astron. Soc., 406, 1570-1582 (2010/August-2)
Revisiting ΔY/ΔZ from multiple main sequences in globular clusters: insight from nearby stars.
PORTINARI L., CASAGRANDE L. and FLYNN C.
Abstract (from CDS):
For nearby K dwarfs, the broadening of the observed main sequence (MS) at low metallicities is much narrower than expected from isochrones with the standard helium-to-metal enrichment ratio ΔY/ΔZ ∼ 2. Though the latter value fits well the MS around solar metallicity, and agrees with independent measurements from Hii regions as well as with theoretical stellar yields and chemical evolution models, a much higher ΔY/ΔZ ∼ 10 is necessary to reproduce the broadening observed for nearby subdwarfs. This result resembles, on a milder scale, the very high ΔY/ΔZ estimated from the multiple MSs in ωCen and NGC 2808. Although not `inverted' as in ω Cen, where the metal-rich MS is bluer than the metal-poor one, the broadening observed for nearby subdwarfs is much narrower than stellar models predict for a standard helium content. We use this empirical evidence to argue that a revision of lower MS stellar models, suggested from nearby stars, could significantly reduce the helium content inferred for the subpopulations of those globular clusters. A simple formula based on empirically calibrated homology relations is constructed for an alternative estimate of ΔY/ΔZ in multiple MSs. We find that, under the most favourable assumptions, the estimated helium content for the enriched populations could decrease from Y ≃ 0.4 to as low as Y ≃ 0.3.
Abstract Copyright:
© 2010 The Authors. Journal compilation © 2010 RAS
Journal keyword(s):
stars: abundances - stars: fundamental parameters - subdwarfs - globular clusters: individual (ω Cen, NGC 2808) - Hertzsprung-Russell and colour-magnitude diagrams
Simbad objects:
5
Full paper
View the references in ADS
To bookmark this query, right click on this link: simbad:2010MNRAS.406.1570P and select 'bookmark this link' or equivalent in the popup menu