C.D.S. - SIMBAD4 rel 1.7 - 2020.08.04CEST22:05:58

2002A&A...393..215V - Astronomy and Astrophysics, volume 393, 215-223 (2002/10-1)

Yields from low metallicity, intermediate mass AGB stars: Their role for the CNO and lithium abundances in Globular Cluster stars.


Abstract (from CDS):

We present the results of extensive computation of the Thermal Pulse phase AGB evolution of stars of metallicities in mass fraction 2x10–4≤Z≤0.01, for those masses in the range 2.5≤M/M≤ 6, which suffer the Hot Bottom Burning (HBB) phase. The evolution is fully computed, by assuming a mass loss rate consistent with the observations of the Magellanic Clouds lithium-rich stars, and modelling convection with the Full Spectrum of Turbulence model by Canuto and Mazzitelli. The results are discussed in the framework of their importance for the evolution of proto-Globular Clusters, whose spectra show that the stars are very probably formed from matter contaminated by the ejecta of these stars, or have accreted it after formation. The main results we find are the following: 1) for metallicities Z≤10–3, masses above ∼4M suffer complete CNO cycling in HBB, so that they show at the surface the result of this process, and the oxygen abundance is reduced; 2) most models suffer the third dredge up. Although carbon is processed to nitrogen by HBB, the oxygen burning is so strong in the lowest metallicities (2x10–4) that carbon becomes more abundant than oxygen: in other words, low-metallicity intermediate mass stars may show up as carbon stars due to the drastic oxygen burning; 3) if Globular Cluster stars are contaminated by matter processed through these phases, we must expect a non negligible helium enhancement in their composition: from a Big Bang abundance Y=0.24, e.g., we might expect an abundance Y=0.28. This may have no practical consequences if pollution concerns only the external parts of the stars, but is very important if the stars formed as a whole from a helium rich environment. 4) The lithium yields, although not important for galactic chemical evolution, are very interestingly close to the initial Big Bang abundance: processing by HBB is the only way in which we can obtain substantial amounts of gas which have gone through full CNO burning, but preserve a reasonable abundance of lithium.

Abstract Copyright:

Journal keyword(s): stars: AGB and post-AGB - ISM: abundances - globular clusters: general

Simbad objects: 6

goto Full paper

goto View the reference in ADS

Number of rows : 6

N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
1 NGC 104 GlC 00 24 05.359 -72 04 53.20   5.78 4.09     ~ 3555 0
2 HE 0024-2523 Pe* 00 27 27.6485410349 -25 06 28.291081599 15.067 15.32 14.91     CEMP-s 65 0
3 M 13 GlC 16 41 41.634 +36 27 40.75     5.8     ~ 2012 0
4 M 92 GlC 17 17 07.39 +43 08 09.4     6.52     ~ 1908 0
5 NGC 6397 GlC 17 40 42.09 -53 40 27.6   7.39 5.17     ~ 1804 1
6 NGC 6752 GlC 19 10 52.11 -59 59 04.4   6.96 6.28     ~ 1811 0

    Equat.    Gal    SGal    Ecl

To bookmark this query, right click on this link: simbad:objects in 2002A&A...393..215V and select 'bookmark this link' or equivalent in the popup menu


© Université de Strasbourg/CNRS

    • Contact