Bibcode
Salaris, M.; Cassisi, S.; Pietrinferni, A.
Bibliographical reference
Astronomy and Astrophysics, Volume 590, id.A64, 10 pp.
Advertised on:
5
2016
Journal
Citations
39
Refereed citations
35
Description
We obtain stringent constraints on the actual efficiency of mass loss
for red giant branch stars in the Galactic globular cluster 47 Tuc, by
comparing synthetic modelling based on stellar evolution tracks with the
observed distribution of stars along the horizontal branch in the
colour-magnitude-diagram. We confirm that the observed, wedge-shaped
distribution of the horizontal branch can only be reproduced by
accounting for a range of initial He abundances, in agreement with
inferences from the analysis of the main sequence, and a red giant
branch mass loss with a small dispersion. We carefully investigated
several possible sources of uncertainty that could affect the results of
the horizontal branch modelling, stemming from uncertainties in both
stellar model computations and cluster properties, such as heavy element
abundances, reddening, and age. We determine a firm lower limit of
~0.17M⊙ for the mass lost by red giant branch stars,
corresponding to horizontal branch stellar masses between
~0.65M⊙ and ~0.73M⊙ (the range driven by
the range of initial helium abundances). We also derive that in this
cluster the amount of mass lost along the asymptotic giant branch stars
is comparable to the mass lost during the previous red giant branch
phase. These results confirm, for this cluster, the disagreement between
colour-magnitude-diagram analyses and inferences from recent studies of
the dynamics of the cluster stars, which predict a much less efficient
red giant branch mass loss. A comparison between the results from these
two techniques applied to other clusters is required to gain more
insights about the origin of this disagreement.