Significant age range in massive star cluster excluded by tight sub-giant-branch morphology

Chengyuan LiRichard de GrijsLicai Deng

Science lead the way.以化成天下。

Multiple stellar populations in Magellanic Cloud clusters, an ordinary feature for intermediate age globulars in the LMC?

--- Milone et al.2009

~300 Myr age spread

Multiple stellar populations in Magellanic Cloud clusters, an ordinary feature for intermediate age globulars in the LMC?

--- Milone et al.2009

NGC 1868: 320 Myr age spreadLi et al. 2014

How to detect multiple stellar populations in Galactic Globular Clusters?

• Multiple or Broadened• Main Sequence(s),• Sub-giant branch(es), • Red-giant branch(es) • Horizontal-branch(es)

Omega-Centauri: Villanova et al.2007

Extended Main-Sequence Turn-Off should link to a broadened Sub-giant-branch, but where is it?

NGC 1651: Li et al. 2014, Nature, accepted

Extended Main-Sequence Turn-Off should link to a broadened Sub-giant-branch, but where is it?

NGC 1651: Li et al. 2014, Nature, accepted

Age spread: 450 Myr (eMSTO), SSP (SGB)

Is this feature unique for NGC 1651?

NGC 2155SL 674Piatta et al. 2014

Multiple stellar populations in Magellanic Cloud clusters, an ordinary feature for intermediate age globulars in the LMC?

--- Milone et al.2009Single stellar population suggested by tight sub-giant-branch,

an ordinary feature for intermediate age globulars in the LMC? --- Li et al.2014

Questions: Why sub-giant-branch is ideal?1, It direct link to turn-off region.2, It easy to learn, do not experience significant mass loss.3, It ideally get rid of the effect from fast rotating.

Narrow sub-giant-branch ideal single stellar population

Why there is no one found this feature for a long time? (set by Luis)1, Not every clusters show clear sub-giant-branch.2, Bias.3, People already began action (Nate Bastian group, 2014, prepare to submit)

Science lead the way.以化成天下。

The Significance: 1, Single stellar population still hold for intermediate-age star clusters.2, No additional physics is needed to prevent gas from collapsing into star forming.3, No need for us to expect a tremendous massive origin.4, Stellar rotating seems important for intermediate-age star clusters.

Thanks!