Controversial Age Spreads in Intermediate-Age Starclusters

31 Oct

Screen Shot 2015-10-31 at 1.28.49 AMMost star clusters at an intermediate age (1-2 Gyr) in the Magellanic Clouds show a puzzling feature in their color-magnitude diagrams. The main sequence turn-off of these clusters is much broader than  expected.  One (highly-debated) interpretation of this feature is that age spreads of the order 200-500 Myr exist within individual clusters.

We analyze  12 clusters that show an extended turn-off using data taken with the Hubble Telescope. We fit the star formation history of the turn-off  and the red clump independently with two different models.  In most of the cases, the age spreads inferred from the red clumps are smaller than the ones resulting from the turn-off region. The width of the main sequence turn-off feature is correlated with the age of the clusters in a way which would be unexplained in the “age spread” interpretation, but which may be expected if stellar rotation is the cause of the spread at the turn-off.

F. Niederhofer, N. Bastian, V. Kozhurina-Platais, M. Hilker, S. E. de Mink, I. Cabrera-Ziri, C. Li, B. Ercolano, “Controversial Age Spreads from the Main Sequence Turn-Off and Red Clump in Intermediate-Age Clusters in the LMC”, accepted for publication in A&A