The origin of multiple populations in globular clusters: clues from dwarf galaxies
Astronomy and astrophysics
Friday 08 May 2015
to 11:30 at
Soeren Larsen (University of Nijmegen)
Globular star clusters were once viewed as archetypical examples of simple stellar populations: systems of stars with a single age and chemical composition, reflecting the properties of the gas cloud out of which they formed. This view has been challenged, however, by observations which show that the abundances of light elements (with atomic number up to 13, aluminium) can vary by large amounts from star to star in globular clusters. Furthermore, in typically about half of the stars in a globular cluster, these elements are found in combinations that are unique to globular cluster stars. These stars appear to have been "polluted" by a mechanism that only operates in globular clusters. Various scenarios have been proposed to account for these observations, including formation of a second generation of stars out of polluted ejecta from asymptotic giant branch stars or massive main sequence stars, or by accretion of ejecta from massive interacting binaries onto discs around low-mass stars. I will discuss recent observational tests of these scenarios, including 1) constraints on the amount of mass loss from GCs via observations of the Fornax dwarf spheroidal galaxy, 2) the spatial distribution of stellar populations within GCs, and 3) the (lack of) evidence for on-going star formation in young massive clusters.