Population Parameters of Intermediate-Age Star Clusters in the Large Magellanic Cloud. I. NGC 1846 and its Wide Main Sequence Turnoff

Abstract

The Advanced Camera for Surveys on board the Hubble Space Telescope has been used to obtain deep, high-resolution images of the intermediate-age star cluster NGC 1846 in the Large Magellanic Cloud. We present new color-magnitude diagrams (CMDs) based on F435W, F555W, and F814W imaging. We test the previously observed broad main sequence turnoff region for "contamination" by field stars and (evolved) binary star systems. We find that while these impact the number of objects in this region, none can fully account for the large color spread. Our results therefore solidify the recent finding that stars in the main sequence turnoff region of this cluster have a large spread in color which is unrelated to measurement errors or contamination by field stars, and likely due to a ~300 Myr range in the ages of cluster stars. An unbiased estimate of the stellar density distribution across the main sequence turnoff region shows that the spread is fairly continuous rather than strongly bimodal as suggested previously. We fit the CMDs with several different sets of theoretical isochrones, and determine systematic uncertainties for population parameters when derived using any one set of isochrones. We note a degeneracy between age and [alpha/Fe], which can be lifted by matching the shape (curvature) of the full red giant branch in the CMD. We find that stars in the upper part of the main sequence turnoff region are more centrally concentrated than those in any other region of the CMD, including more massive red giant branch and asymptotic giant branch stars. We consider several possible formation scenarios which account for the unusual features observed in the CMD of NGC 1846.

17 pages, 17 figures, in emulateapj format. Figures 1 and 2 have been downgraded in resolution in this version. Accepted for publication in The Astronomical Journal

References in corpus (18)

• The Dartmouth Stellar Evolution Database
• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
• Evidence for the Strong Effect of Gas Removal on the Internal Dynamics of Young Stellar Clusters
• Modeling the color evolution of luminous red galaxies - improvements with empirical stellar spectra
• A double main sequence turn-off in the rich star cluster NGC 1846 in the Large Magellanic Cloud
• Multiple stellar populations in three rich Large Magellanic Cloud star clusters
• Physical parameters of 15 intermediate-age LMC clusters from modelling of HST colour-magnitude diagrams
• Dynamical Evolution of Globular Cluster Systems formed in Galaxy Mergers: Deep HST/ACS Imaging of Old and Intermediate-Age Globular Clusters in NGC 3610
• A Comparison of Optical and Near-Infrared Colours of Magellanic Cloud Star Clusters with Predictions of Simple Stellar Population Models
• The globular cluster NGC 1978 in the Large Magellanic Cloud
• On the origin of double main-sequence turn-offs in star clusters of the Magellanic Clouds
• Captured older stars as the reason for apparently prolonged star formation in young star clusters
• The AGB stars of the intermediate-age LMC cluster NGC 1846 Variability and age determination
• Empirical Corrections for Charge Transfer Inefficiency and Associated Centroid Shifts for STIS CCD Observations
• Complex stellar populations in massive clusters: trapping stars of a dwarf-disc galaxy in a newborn stellar super-cluster
• Horizontal Branch Morphology and Mass Loss in Globular Clusters

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