No Evidence for Chemical Abundance Variations in the Intermediate-age Cluster NGC 1783

TL;DR

This study used Hubble Space Telescope photometry to analyze the intermediate-age star cluster NGC 1783, finding no evidence of chemical abundance variations or multiple stellar populations despite its mass and age.

Contribution

The paper provides the first detailed photometric analysis of NGC 1783, showing it lacks chemical abundance spreads typically associated with multiple populations in similar clusters.

Findings

No broadening of the red giant branch beyond photometric uncertainties.

Color dispersion consistent with a single stellar population.

Supports absence of chemical abundance variations in NGC 1783.

Abstract

We have analyzed multi-passband photometric observations, obtained with the {\it Hubble Space Telescope}, of the massive ($1.8 \times 10^5 M_\odot$), intermediate-age (1.8 Gyr-old) Large Magellanic Cloud star cluster NGC 1783. The morphology of the cluster's red giant branch does not exhibit a clear broadening beyond its intrinsic width; the observed width is consistent with that owing to photometric uncertainties alone and independent of our photometric selection boundaries applied to obtain our sample of red-giant stars. The color dispersion of the cluster's red-giant stars around the best-fitting ridgeline is $0.062 \pm 0.009$ mag, which is equivalent to the width of $0.080 \pm 0.001$ mag derived from artificial simple stellar population tests, that is, tests based on single-age, single-metallicity stellar populations. NGC 1783 is comparably massive as other star clusters that show clear evidence of multiple stellar populations. After incorporating mass-loss recipes from its current age of 1.8 Gyr to an age of 6 Gyr, NGC 1783 is expected to remain as massive as some other clusters that host clear multiple populations at these intermediate ages. If we were to assume that mass is an important driver of multiple population formation, then NGC 1783 should have exhibited clear evidence of chemical abundance variations. However, our results support the absence of any chemical abundance variations in NGC 1783.