Searching for chemical abundance variations in young star clusters in the Magellanic Clouds: NGC 411, NGC 1718 and NGC 2213

Abstract

The conventional picture of coeval, chemically homogeneous, populous star clusters -- known as `simple stellar populations' (SSPs) -- is a view of the past. Photometric and spectroscopic studies reveal that almost all ancient globular clusters in the Milky Way and our neighbouring galaxies exhibit star-to-star light-element abundance variations, typically known as 'multiple populations' (MPs). Here, we analyse photometric $Hubble$ $Space$ $Telescope$ observations of three young ($<$2 Gyr-old) Large and Small Magellanic Cloud clusters, NGC 411, NGC 1718 and NGC 2213. We measure the widths of their red-giant branches (RGBs). For NGC 411, we also use a pseudo-colour--magnitude diagram (pseudo-CMD) to assess its RGB for evidence of MPs. We compare the morphologies of the clusters' RGBs with artificially generated SSPs. We conclude that their RGBs do not show evidence of significant broadening beyond intrinsic photometric scatter, suggesting an absence of significant chemical abundance variations in our sample clusters. Specifically, for NGC 411, NGC 1718 and NGC 2213 we derive maximum helium-abundance variations of delta_Y=0.003$\pm$0.001 Y=0.300), 0.002$\pm$0.001 (Y=0.350) and 0.004$\pm$0.002 (Y=0.300), respectively. We determined an upper limit to the NGC 411 nitrogen-abundance variation of $\Delta$[N/Fe] = 0.3 dex; the available data for our other clusters do not allow us to determine useful upper limits. It thus appears that the transition from SSPs to MPs occurs at an age of ~2 Gyr, implying that age might play an important role in this transition. This raises the question as to whether this is indeed a fundamental minimum-age limit for the formation of MPs.

11 pages, 5 Figures

References in corpus (17)

• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• A comprehensive set of simulations studying the influence of gas expulsion on star cluster evolution
• Spectroscopic and Photometric evidence of two stellar populations in the Galactic Globular Cluster NGC6121 (M4)
• Evidence for the Strong Effect of Gas Removal on the Internal Dynamics of Young Stellar Clusters
• A General Abundance Problem for All Self-Enrichment Scenarios for the Origin of Multiple Populations in Globular Clusters
• Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: A Correlation Between Turnoff Width and Early Escape Velocity
• Age as a Major Factor in the Onset of Multiple Populations in Stellar Clusters
• Multiple stellar populations in Magellanic Cloud clusters. V. The split main sequence of the young cluster NGC1866
• The Search for Multiple Populations in Magellanic Cloud Clusters I: Two Stellar Populations in the Small Magellanic Cloud Globular Cluster NGC 121
• On the origin of double main-sequence turn-offs in star clusters of the Magellanic Clouds
• The Na-O anticorrelation in horizontal branch stars. V. NGC 6723
• The difficult early stages of embedded star clusters and the importance of the pre-gas expulsion virial ratio
• The dynamical origin of multiple populations in intermediate-age clusters in the Magellanic Clouds
• An Analysis of the Population of Extended Main Sequence Turn-off Clusters in the Large Magellanic Cloud
• Stellar populations in star clusters
• Chemical Abundances of Two Stars in the Large Magellanic Cloud Globular Cluster NGC~1718

Cited by in corpus (2)

• Multiple stellar populations at less evolved stages-II: no evidence of significant helium spread among NGC 1846 dwarfs
• Decoding the bifurcated red-giant branch as a tracer of multiple stellar populations in the young Large Magellanic Cloud cluster NGC 2173