Lithium and oxygen in globular cluster dwarfs and the early disc accretion scenario

Abstract

A new scenario --early disc accretion-- has been recently proposed to explain the discovery of multiple stellar populations in Galactic globular clusters. According to this model, the existence of well defined (anti)-correlations amongst light element abundances (i.e. C, N, O, Na) in the photospheres of stars belonging to the same cluster (and the associated helium enrichment), is caused by accretion of the ejecta of short lived interacting massive binary systems (and single fast rotating massive stars) on fully convective pre-main sequence low- and very low-mass stars, during the early stages of the cluster evolution. We investigated the constraints provided by considering simultaneously the observed spread of lithium and oxygen (and when possible also sodium) abundances for samples of turn-off stars in NGC6752, NGC6121 (M4), and NGC104 (47Tuc), and the helium abundance of their multiple main sequences. These observations provide a very powerful test for the accretion scenario, because the observed O, Li and He abundance distributions at the turn off can be used to constrain the composition (and mass) of the accreted matter, and the timescales of the polluting stars. In case of NGC6752 we could not find a physically consistent solution. In case of M4, spectroscopic errors are too large compared to the intrinsic spread, to constrain the properties of the accreted matter. As for 47Tuc, we could find a physically consistent solution for the abundances of He and O (and Na) in the accreted gas, and predict the abundances of these elements in the accreted matter only if pollution happens with timescales of ~1 Myr, hence polluters are objects with masses of the order of several tens of solar masses (abridged).

8 pages, 8 figures, accepted for publication in A&A

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Cited by in corpus (8)

• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• A General Abundance Problem for All Self-Enrichment Scenarios for the Origin of Multiple Populations in Globular Clusters
• Multiple populations in the old and massive Small Magellanic Cloud globular cluster NGC121
• Revisiting nucleosynthesis in globular clusters: the case of NGC 2808 and the role of He and K
• Globular Cluster Formation at High Density: A model for Elemental Enrichment with Fast Recycling of Massive-Star Debris
• Evolution of long-lived globular cluster stars I. Grid of stellar models with helium enhancement at [Fe/H] = -1.75
• Multiple populations in massive star clusters under the magnifying glass of photometry: Theory and tools
• Pre-main sequence accretion and the formation of multiple populations in Globular Clusters