English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We investigated the possibility of producing helium enhanced stars inglobular clusters by accreting polluted matter during the pre-main sequencephase. We followed the evolution of two different classes of pre-main sequenceaccreting models, one which neglects and the other that takes into account theprotostellar evolution.  We analysed the dependence of the final central helium abundance, of thetracks position in the HR diagram and of the surface lithium abundanceevolution on the age at which the accretion of polluted material begins and onthe main physical parameters that govern the protostellar evolution. The lateris the beginning of the late accretion and the lower are both the centralhelium and the surface lithium abundances at the end of the accretion phase andin ZAMS (Zero Age Main Sequence). In order to produce a relevant increase ofthe central helium content the accretion of polluted matter should start atages lower than 1 Myr. The inclusion of the protostellar evolution has a strongimpact on the ZAMS models too. The adoption of a very low seed mass (i.e. 0.001M$_{\odot}$) results in models with the lowest central helium and surfacelithium abundances. The higher is the accretion rate and the lower is the finalhelium content in the core and the residual surface lithium. In the worst case-- i.e. seed mass 0.001 M$_\odot$ and accretion rate $\ge 10^{-5}$ M$_\odot$yr$^{-1}$ -- the central helium is not increased at all and the surface lithiumis fully depleted in the first few million years.

Accreting pre-main sequence models and abundance anomalies in globular clusters