J. P. Naiman, E. Ramirez-Ruiz, D. N. C. Lin
The discovery of multiple evolutionary sequences has challenged the paradigm that globular clusters (GCs) host simple stellar populations. In addition, spectroscopic studies of GCs show a spread in light-element abundances, suggesting that multiple sequences can be formed from gaseous ejecta processed in evolved cluster stars. If multiple sequences originate from within GCs, then it should be determined how such stellar systems retain gas, form new stars within them and subsequently evolve. Here we expand upon previous studies and carry out hydrodynamical simulations that explore a wide range of cluster masses, compactness, metallicities and stellar age combinations in order to determine the ideal conditions for gas retention. We find that up to 6.4% of the mass of the star cluster can be made up of retained stellar wind gas at the time star formation is triggered. However, we show that multiple episodes of star formation can take place during the lifetime of a star cluster in particular for times $\gtrsim 1$ Gyr, thus leading to a sizable enhancement in the total number of new stars. The fact that this favorable star formation time interval coincides with the asymptotic giant branch (AGB) phase seems to give further credence to the idea that, at least in some GCs, there are stars which have formed from material processed by a previous generation of stars. The ability of extended heating sources, such as pulsar outflows or accretion onto compact objects, to hamper gas retention is illustrated via a simple numerical treatment.
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http://arxiv.org/abs/1206.5002
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