Leveraging HST with MUSE: I. Sodium abundance variations within the 2 Gyr-old cluster NGC 1978

Abstract

Nearly all of the well studied ancient globular clusters (GCs), in the Milky Way and in nearby galaxies, show star-to-star variations in specific elements (e.g., He, C, N, O, Na, Al), known as "multiple populations" (MPs). However, MPs are not restricted to ancient clusters, with massive clusters down to $\sim 2$ Gyr showing signs of chemical variations. This suggests that young and old clusters share the same formation mechanism but most of the work to date on younger clusters has focused on N-variations. Initial studies even suggested that younger clusters may not host spreads in other elements beyond N (e.g., Na), calling into question whether these abundance variations share the same origin as in the older GCs. In this work, we combine HST photometry with VLT/MUSE spectroscopy of a large sample of RGB stars (338) in the Large Magellanic Cloud cluster NGC 1978, the youngest globular to date with reported MPs in the form of N-spreads. By combining the spectra of individual RGB stars into N-normal and N-enhanced samples, based on the "chromosome map" derived from HST, we search for mean abundance variations. Based on the NaD line, we find a Na-difference of $\Delta$[Na/Fe]$=0.07\pm 0.01$ between the populations. While this difference is smaller than typically found in ancient GCs (which may suggest a correlation with age), this result further confirms that the MP phenomenon is the same, regardless of cluster age and host galaxy. As such, these young clusters offer some of the strictest tests for theories on the origin of MPs.

10 pages, 9 figures, 1 table. Accepted for publication in MNRAS

References in corpus (17)

• Modules for Experiments in Stellar Astrophysics (MESA)
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IX. The Atlas of Multiple Stellar Populations
• The Data Processing Pipeline for the MUSE Instrument
• Synthetic Stellar Photometry - I. General considerations and new transformations for broad-band systems
• The chemical composition of red giant stars in four intermediate-age clusters of the Large Magellanic Cloud
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. II. The seven stellar populations of NGC7089 (M2)
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XIX. A Chemical Tagging of the Multiple Stellar Populations Over the Chromosome Maps
• Age as a Major Factor in the Onset of Multiple Populations in Stellar Clusters
• Multiple populations in globular clusters and their parent galaxies
• The Search for Multiple Populations in Magellanic Cloud Clusters II: The Detection of Multiple Populations in Three Intermediate-Age SMC Clusters
• The search for multiple populations in Magellanic Clouds clusters - V. Correlation between cluster age and abundance spreads
• The Search for Multiple Populations in Magellanic Cloud Clusters I: Two Stellar Populations in the Small Magellanic Cloud Globular Cluster NGC 121
• A family picture: tracing the dynamical path of the structural properties of multiple populations in globular clusters
• The globular cluster NGC 1978 in the Large Magellanic Cloud
• Photometric characterization of multiple populations in star clusters: The impact of the first dredge-up
• Searching for globular cluster chemical anomalies on the main sequence of a young massive cluster

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