Star clusters with dual red clumps

Abstract

A few star clusters in the Magellanic Clouds exhibit composite structures in the red-clump region of their colour-magnitude diagrams. The most striking case is NGC419 in the SMC, where the red clump is composed of a main blob as well as a distinct secondary feature. This structure is demonstrated to be real and corresponds to the simultaneous presence of stars which passed through electron degeneracy after central-hydrogen exhaustion and those that did not. This rare occurrence in a single cluster allows us to set stringent constraints on its age and on the efficiency of convective-core overshooting during main-sequence evolution. We present a more detailed analysis of NGC419, together with a first look at other populous LMC clusters which are apparently in the same phase: NGC1751, NGC1783, NGC1806, NGC1846, NGC1852 and NGC1917. We also compare these Magellanic Cloud cases with their Galactic counterparts, NGC752 and NGC7789. We emphasise the extraordinary potential of these clusters as absolute calibration marks on the age scale of stellar populations.

contributed talk at IAUS 266 'Star clusters: basic galactic building blocks', eds R. de Grijs and J. Lepine. A high resolution version of Fig. 1 is available in http://stev.oapd.inaf.it/~lgirardi/NGC419_hr.pdf

References in corpus (7)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• Age Determination of Six Intermediate-age SMC Star Clusters with HST/ACS
• The Effect of Stellar Rotation on Colour-Magnitude Diagrams: On the apparent presence of multiple populations in intermediate age stellar clusters
• Multiple stellar populations in three rich Large Magellanic Cloud star clusters
• Discovery of two distinct red clumps in NGC419: a rare snapshot of a cluster at the onset of degeneracy
• The extended star formation history of the star cluster NGC 2154 in the Large Magellanic Cloud
• Homogeneous photometry and star counts in the field of 9 Galactic star clusters

Cited by in corpus (2)

• The star formation history of the SMC star cluster NGC419
• Testing the intrinsic scatter of the asteroseismic scaling relations with Kepler red giants