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

Shalmalee Kapse*, Richard de Grijs, Daniel Zucker

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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 δY = 0.003 ± 0.001(Y = 0.300), 0.002 ± 0.001(Y = 0.350), and 0.004 ± 0.002(Y = 0.300), respectively. We determined an upper limit to the NGC 411 nitrogen-abundance variation of Δ[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.
Original languageEnglish
Pages (from-to)6016-6025
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Volume503
Issue number4
DOIs
Publication statusPublished - Jun 2021

Keywords

  • stars: abundances
  • galaxies: star clusters: individual: NGC 411, NGC 1718, NGC 2213
  • Hertzsprung–Russell and colour
  • magnitude diagram

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