Pre-main sequence accretion and the formation of multiple populations in Globular Clusters

Abstract

We investigate the viability of a model in which the chemical anomalies among Globular Cluster stars are due to accretion of gas onto the protostellar discs of low mass stars. This model has been suggested as a way to reduce the large initial cluster masses required by other models for the formation of multiple stellar generations. We numerically follow the evolution of the accreting stars, and we show that the structure of the seed star does not remain fully convective for the whole duration of the accretion phase. Stellar populations showing discrete abundances of helium in the core, that seem to be present in some clusters, might be formed with this mechanism only if accretion occurs before the core of the stars become radiative (within 2-3Myr) or if a thermohaline instability is triggered, to achieve full mixing after the accretion phase ends. We also show that the lithium abundances in accreted structures may vary by orders of magnitude in equal masses obtained by accreting different masses. In addition, the same thermohaline mixing which could provide a homogeneous helium distribution down to the stellar center, would destroy any lithium surviving in the envelope, so that both helium homogeneity and lithium survival require that the accretion phase be limited to the first couple of million years of the cluster evolution. Such a short accretion phase strongly reduces the amount of processed matter available, and reintroduces the requirement of an extremely large initial mass for the protocluster.

8 pages, 5 figures. Accepted for publication on Monthly Notices of the RAS

References in corpus (7)

• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• On the self-enrichment scenario of galactic globular clusters: Constraints on the IMF
• Chemical Transport and Spontaneous Layer Formation in Fingering Convection in Astrophysics
• The Chemical Evolution of Helium in Globular Clusters: Implications for the Self-Pollution Scenario
• The Chemical Evolution of Globular Clusters I. Reactive Elements and Non-Metals
• Lithium and oxygen in globular cluster dwarfs and the early disc accretion scenario

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
• Multiple populations in globular clusters: the distinct kinematic imprints of different formation scenarios
• Radial distributions of sub-populations in the globular cluster M15: a more centrally concentrated primordial population
• Evolution of long-lived globular cluster stars I. Grid of stellar models with helium enhancement at [Fe/H] = -1.75
• Monte Carlo simulations of multiple populations in globular clusters: constraints on the cooling flow vs. accretion scenario using million bodies simulations
• Protostellar accretion in low mass metal poor stars and the cosmological lithium problem
• A Multi-Wavelength Study of the Segue 3 Cluster
• Cool stars as tracers of multiple stellar populations in the Galactic globular cluster 47 Tuc