Jun 16, 2014
Henny J.G.L.M. Lamers, University of Amsterdam
"The (NOT-SO) Simple Stellar Populations of the Globular Clusters"
Globular clusters were once thought to be simple stellar populations:with all stars having the same age and the same initial composition. However, in recent year it has become clear that each cluster contains different populations with specific abundance patterns. The most striking ones are multiple main sequences (indicating different He-abundances), the Na-O anti-correlation and the Mg-Al anti-correlation. This has been interpreted as a sign that each cluster had several episodes of star formation, i.e. multiple generations, where each new generation is formed from mass ejected by evolved stars. The proposed polluters are: AGB stars, rapidly rotating massive stars,or interacting massive binaries. This interpretation has several serious problems: a mass budget problem, a gas-retention problem, an IMF problem and a Li-problem. Last year we proposed a new model in which the observations are explained by one single star forming event with the low mass stars,polluted by ejecta from the massive stars of the same event(Bastian et al. 2013, MNRAS 436, 2398) This model overcomes some of the serious shortcomings of the multiple generation models. I will discuss this model and the results of recent studies that support it.