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Todays colloquium: Star clusters - links between stellar and galactic astrophysics (Soeren Larsen)

Submitter: Adam Deller
Description: Several nearby star-forming galaxies host young star clusters with masses well above 100,000 solar masses. Unlike most Milky Way open clusters, these clusters are rich enough that the post-main sequence phases are well populated even at young ages. The challenge is that the degree of stellar crowding is extremely high, but it is nevertheless possible to extract photometry of individual stars in several such clusters and compare with stellar evolutionary models. On the one hand, this allows us to study the stellar content of the clusters, and test whether the colour-magnitude diagrams (CMDs) are well explained by standard stellar isochrones. On the other hand, the availability of resolved imaging allows us to put the analysis of integrated spectroscopy of the clusters on a much firmer basis. I will first discuss our recent results on the CMDs of several massive clusters, which are found to be poorly approximated by single isochrones. Possible explanations include age spreads and/or effects of binary stellar evolution. I will critically examine the case for age spreads in star clusters and discuss some of its implications. I will then briefly discuss our ongoing efforts to model the integrated light of star clusters, with the ultimate aim of carrying out detailed chemical analysis of star clusters in external galaxies.

Image: A young star cluster in M83, with optical imaging (HST) and spectroscopy (VLT/X-Shooter).
Copyright: S. Larsen
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