Multiple stellar populations and their influence on blue stragglers
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abstract
It has become clear in recent years that globular clusters are not simple
stellar populations, but may host chemically distinct sub-populations,
typically with an enhanced helium abundance. These helium-rich populations can
make up a substantial fraction of all cluster stars.
One of the proposed formation channels for blue straggler stars is the
physical collision and merger of two stars. In the context of multiple
populations, collisions between stars with different helium abundances should
occur and contribute to the observed blue straggler population. This will
affect the predicted blue straggler colour and luminosity function.
We quantify this effect by calculating models of mergers resulting from
collisions between stars with different helium abundances and using these
models to model a merger population. We then compare these results to four
observed clusters, NGC 1851, NGC 2808, NGC 5634 and NGC 6093.
As in previous studies our models deviate from the observations, particularly
in the colour distributions. However, our results are consistent with
observations of multiple populations in these clusters. In NGC 2808, our best
fitting models include normal and helium enhanced populations, in agreement
with helium enhancement inferred in this cluster. The other three clusters show
better agreement with models that do not include helium enhancement. We discuss
future prospects to improve the modelling of blue straggler populations and the
role that the models we present here can play in such a study.
