科研之友
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摘要
Following work by Wunsch and collaborators, we investigate a self-enrichment scenario for second-generation star formation in globular clusters wherein wind material from the first-generation massive stars rapidly radiatively cools. Radiative energy loss allows retention of fast winds within the central regions of clusters, where it fuels star formation. Secondary star formation occurs in similar to 3-5 Myr, before supernovae, producing uniform iron abundances in both populations. We derive the critical criteria for radiative cooling of massive star winds and the second-generationmass as a function of cluster mass, radius and metallicity. We derive a critical condition on M/R, above which second-generation star formation can occur. We speculate that above this threshold the strong decrease in the cluster wind energy and momentum allows ambient gas to remain from the cluster formation process. We reproduce large observed second-generation fractions of similar to 30-80 per cent if wind material mixes with ambient gas. Importantly, the mass of ambient gas required is only of order the first generation's stellar mass. Second-generation helium enrichment Delta Y is inversely proportional to mass fraction in the second generation; a large second generation can form with Delta Y similar to 0.001-0.02, while a small second generation can reach Delta Y similar to 0.16. Like other self-enrichment models for the second generation, we are not able to simultaneously account for both the full range of the Na-O anticorrelation and the second-generation fraction.
- 出版日期2017-8
