Multiple stellar populations at less evolved stages: detection of chemical variations among main-sequence dwarfs in NGC 1978

Abstract

Multiple stellar populations (MPs) with different chemical compositions are not exclusive features of old GCs (older than 10 Gyr). Indeed, recent studies reveal that younger clusters ($\sim$2--6 Gyr-old) in the Magellanic Clouds also exhibit star-to-star chemical variations among evolved stars. However, whether MPs are present among less evolved dwarfs of these intermediate-age clusters is still unclear. In this work, we search for chemical variations among GK-type dwarfs in the $\sim$2 Gyr-old cluster NGC 1978, which is the youngest cluster with MPs. We exploit deep ultraviolet and visual observations from the Hubble Space Telescope to constrain the nitrogen (N) and oxygen (O) variations among MS stars. To do this, we compare appropriate photometric diagrams that are sensitive to N and O with synthetic diagrams of simple stellar populations and MPs. We conclude that the G- and K-type MS stars in NGC\,1978 host MPs. Our statistical analysis shows that the fraction of N-rich stars ranges from $\sim$40\% to $\sim$80\%, depending on the detailed distributions of nitrogen and oxygen.

arXiv comment16 pages, 10 figures, ApJ accepted

References in corpus (44)

• The chemical composition of the Sun
• On the variation of the Initial Mass Function
• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• Modules for Experiments in Stellar Astrophysics (MESA): Binaries, Pulsations, and Explosions
• Embedded Clusters in Molecular Clouds
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• MESA Isochrones and Stellar Tracks (MIST) 0: Methods for the construction of stellar isochrones
• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• Determining stellar atmospheric parameters and chemical abundances of FGK stars with iSpec
• The ACS Survey of Galactic Globular Clusters. XII. Photometric Binaries along the Main-Sequence
• Massive binaries as the source of abundance anomalies in globular clusters
• Modern stellar spectroscopy caveats
• Super-Massive Stars as a Source of Abundance Anomalies of Proton-Capture Elements in Globular Clusters
• Abundance patterns of multiple populations in Globular Clusters: a chemical evolution model based on yields from AGB ejecta
• A unique model for the variety of multiple populations formation(s) in globular clusters: a temporal sequence
• Statistics of N-body Simulations I. Equal Masess Before Core Collapse
• Dynamical Evolution and Spatial Mixing of Multiple Population Globular Clusters
• Nitrogen abundances in giant stars of the globular cluster NGC 6752
• Age as a Major Factor in the Onset of Multiple Populations in Stellar Clusters
• The star cluster formation history of the LMC
• Multiple populations in globular clusters and their parent galaxies
• Extended main sequence turnoff as a common feature of Milky Way open clusters
• The possible role of stellar mergers for the formation of multiple stellar populations in globular clusters
• The Search for Multiple Populations in Magellanic Cloud Clusters III: No evidence for Multiple Populations in the SMC cluster NGC 419
• The exclusion of a significant range of ages in a massive star cluster
• 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
• Two Groups of Red Giants with Distinct Chemical Abundances in the Bulge Globular Cluster NGC 6553 Through the Eyes of APOGEE
• Consequences of Dynamical Disruption and Mass Segregation for the Binary Frequencies of Star Clusters
• The HST Large Programme on NGC6752. II. Multiple populations at the bottom of the main sequence probed in NIR
• C and N abundances of MS and SGB stars in NGC 1851
• Four stellar populations and extreme helium variation in the massive outer-halo globular cluster NGC 2419
• Sodium abundances of AGB and RGB stars in Galactic globular clusters II. Analysis and results of NGC 104, NGC 6121 and NGC 6809
• The Dynamics of Multiple Populations in the Globular Cluster NGC 6362
• Hierarchical structures in the Large and Small Magellanic Clouds
• Globular cluster formation with multiple stellar populations from hierarchical star cluster complexes
• No Evidence for Chemical Abundance Variations in the Intermediate-age Cluster NGC 1783
• When does the onset of multiple stellar populations in star clusters occur? Detection of enriched stellar populations in NGC 2121
• When does the onset of multiple stellar populations in star clusters occur-III: No evidence of significant chemical variations in main-sequence stars of NGC 419
• Searching for globular cluster chemical anomalies on the main sequence of a young massive cluster
• Multiple Stellar Populations of Globular Clusters from Homogeneous Ca--CN--CH Photometry. V. $c{n}_{\mathrm{JWL}}^{\prime }$ as a Surrogate $c{n}_{\mathrm{JWL}}$ Index and NGC 6723
• When does the onset of multiple stellar populations in star clusters occur-II: No evidence of multiple stellar populations in Lindsay 113

Cited by in corpus (7)

• Stellar collisions in globular clusters: the origin of multiple stellar populations
• Evidence of globular cluster abundance anomalies in the SMC intermediate-age cluster Kron 3
• Multiple stellar populations at less evolved stages-II: no evidence of significant helium spread among NGC 1846 dwarfs
• Driving factors behind multiple populations
• Low-density star cluster formation: discovery of a young faint fuzzy on the outskirts of the low-mass spiral galaxy NGC 247
• Multiple stellar populations at less evolved stages-III: a possible helium spread in NGC 2210
• APOGEE chemical abundances of stars in the MW satellites Fornax, Sextans, Draco and Carina