In http://uk.arxiv.org/abs/0911.4798, which also came out in Nature this week, Lee et al presents the results of an study of the Calcium abundance in a sample of 8 globular clusters. Why do we care? Well, traditionally globulars are thought to mostly be single stellar populations where all stars formed in a very short time; as Ca is produced by SN II you would expect no variation in Ca abundance in this scenario. But that is not what Lee et al found, indeed they found that in 7 out of their clusters there was clearl evidence for a broadened, or in some cases, double red giant branch. This argues for a more complex formation history for globular clusters and might argue that many of them are the remnant nucleus of accreted dwarf galaxies (this is open to argument though).
Friday, 27 November 2009
Multiple populations in MW globular clusters
In http://uk.arxiv.org/abs/0911.4798, which also came out in Nature this week, Lee et al presents the results of an study of the Calcium abundance in a sample of 8 globular clusters. Why do we care? Well, traditionally globulars are thought to mostly be single stellar populations where all stars formed in a very short time; as Ca is produced by SN II you would expect no variation in Ca abundance in this scenario. But that is not what Lee et al found, indeed they found that in 7 out of their clusters there was clearl evidence for a broadened, or in some cases, double red giant branch. This argues for a more complex formation history for globular clusters and might argue that many of them are the remnant nucleus of accreted dwarf galaxies (this is open to argument though).
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