New Clues to the Cause of Extended Main Sequence Turn-Offs in Intermediate-Age Star Clusters in the Magellanic Clouds

Abstract

We use the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope (HST) to obtain deep, high resolution images of two intermediate-age star clusters in the Large Magellanic Cloud of relatively low mass ($\approx$ $10^4$ $M_{\odot }$) and significantly different core radii, namely NGC2209 and NGC2249. For comparison purposes, we also re-analyzed archival HST images of NGC1795 and IC2146, two other relatively low mass star clusters. From the comparison of the observed color-magnitude diagrams with Monte Carlo simulations, we find that the main sequence turnoff (MSTO) regions in NGC2209 and NGC2249 are significantly wider than that derived from simulations of simple stellar populations, while those in NGC1795 and IC2146 are not. We determine the evolution of the clusters' masses and escape velocities from an age of 10 Myr to the present age. We find that the differences among these clusters can be explained by dynamical evolution arguments if the currently extended clusters (NGC2209 and IC2146) experienced stronger levels of initial mass segregation than the currently compact ones (NGC2249 and NGC1795). Under this assumption, we find that NGC2209 and NGC2249 have estimated escape velocities $V_{\mathrm{esc}}$ $\ge$ 15 km s${}^{-1}$ at an age of 10 Myr, large enough to retain material ejected by slow winds of first-generation stars, while the two clusters that do not feature extended MSTOs have $V_{\mathrm{esc}}$ $\le$ 12 km s${}^{-1}$ at that age. These results suggest that the extended MSTO phenomenon can be better explained by a range of stellar ages rather than a range of stellar rotation velocities or interacting binaries.

arXiv comment9 pages (in emulateapj format), 4 figures, accepted for publication in ApJ

References in corpus (30)

• Stellar population synthesis at the resolution of 2003
• Evolution of asymptotic giant branch stars II. Optical to far-infrared isochrones with improved TP-AGB models
• Drizzle: A Method for the Linear Reconstruction of Undersampled Images
• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• Massive binaries as the source of abundance anomalies in globular clusters
• Star formation through gravitational collapse and competitive accretion
• Age Determination of Six Intermediate-age SMC Star Clusters with HST/ACS
• The Effect of Stellar Rotation on Colour-Magnitude Diagrams: On the apparent presence of multiple populations in intermediate age stellar clusters
• Black holes and core expansion in massive star clusters
• Massive AGB models of low metallicity: the implications for the self-enrichment scenario in metal poor Globular Clusters
• Multiple stellar populations in three rich Large Magellanic Cloud star clusters
• A model for the Globular Cluster extreme anomalies
• Discovery of two distinct red clumps in NGC419: a rare snapshot of a cluster at the onset of degeneracy
• Population Parameters of Intermediate-Age Star Clusters in the Large Magellanic Cloud. I. NGC 1846 and its Wide Main Sequence Turnoff
• Population Parameters of Intermediate-Age Star Clusters in the Large Magellanic Cloud. II. New Insights from Extended Main Sequence Turnoffs in 7 Star Clusters
• Effects of Primordial Mass Segregation on the Dynamical Evolution of Star Clusters
• Can rotation explain the multiple main sequence turn-offs of Magellanic Cloud star clusters?
• Obscured AGB stars in the Magellanic Clouds II. Near-infrared and mid-infrared counterparts
• The effects of rotation on the main-sequence turnoff of intermediate-age massive star clusters
• Population Parameters of Intermediate-Age Star Clusters in the Large Magellanic Cloud. III. Dynamical Evidence for a Range of Ages Being Responsible for Extended Main Sequence Turnoffs
• Two-Dimensional Hydrodynamic Models of Super Star Clusters with a Positive Star Formation Feedback
• And in the Darkness Bind Them: Equatorial Rings, B[e] Supergiants, and the Waists of Bipolar Nebulae
• The star formation history of the SMC star cluster NGC419
• The Extended Main-Sequence Turn-off Clusters of the Large Magellanic Cloud - Missing links in Globular Cluster Evolution
• A Deep, Wide-Field, and Panchromatic View of 47 Tuc and the SMC with HST: Observations and Data Analysis Methods
• The Contributions of Interactive Binary Stars to Double Main Sequence Turn-Offs and Dual Red Clump of Intermediate-Age Star Clusters
• Combined Effects of Binaries and Stellar Rotation on the Color-Magnitude Diagrams of Intermediate-Age Star Clusters
• The star formation history of the Large Magellanic Cloud star cluster NGC1751
• The effects of differential reddening and stellar rotation on the appearance of multiple populations in star clusters: the case of Trumpler 20
• A new Extended Main Sequence Turnoff star cluster in the Large Magellanic Cloud

Cited by in corpus (34)

• Constraining the thermally-pulsing asymptotic giant branch phase with resolved stellar populations in the Small Magellanic Cloud
• Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: A Correlation Between Turnoff Width and Early Escape Velocity
• The VMC Survey - XIV. First results on the look-back time star-formation rate tomography of the Small Magellanic Cloud
• Multiple stellar populations in Magellanic Cloud clusters. VI. A survey of multiple sequences and Be stars in young clusters
• Apparent Age Spreads in Clusters and the Role of Stellar Rotation
• Multiple stellar populations in Magellanic Cloud clusters. III. The first evidence of an extended main sequence turn-off in a young cluster: NGC1856
• Multiple stellar populations in Magellanic Cloud clusters. IV. The double main sequence of the young cluster NGC1755
• NGC 1866: First Spectroscopic Detection of Fast Rotating Stars in a Young LMC Cluster
• No Evidence for Significant Age Spreads in Young Massive LMC Clusters
• Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: Stellar Rotation diminishes, but does not eliminate, Age Spreads
• Combined Effects of Rotation and Age Spreads on Extended Main Sequence Turn Offs
• Controversial Age Spreads from the Main Sequence Turn-Off and Red Clump in Intermediate-Age Clusters in the LMC
• Disappearance of the extended main sequence turn-off in intermediate age clusters as a consequence of magnetic braking
• The Morphology of the Sub-Giant Branch and Red Clump Reveal No Sign of Age Spreads in Intermediate Age Clusters
• Dynamical masses and mass-to-light ratios of resolved massive star clusters -- II. Results for 26 star clusters in the Magellanic Clouds
• On the Interpretation of Sub-Giant Branch Morphologies of Intermediate-Age Star Clusters with Extended Main Sequence Turnoffs
• New Constraints on the Star Formation History of the Star Cluster NGC 1856
• A systematic study of effects of stellar rotation, age spread and binaries on color-magnitude diagrams with extended main-sequence turn-offs
• The Minimum Mass of Rotating Main Sequence Stars and its Impact on the Nature of Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters in the Magellanic Clouds
• A New Approach to Convective Core Overshooting: Probabilistic Constraints from Color-Magnitude Diagrams of LMC Clusters
• The radial distributions of the two main-sequence components in the young massive star cluster NGC 1856
• The effects of the overshooting of the convective core on main-sequence turnoffs of young- and intermediate-age star clusters
• An Analysis of the Population of Extended Main Sequence Turn-off Clusters in the Large Magellanic Cloud
• On the Precision of Full-spectrum Fitting of Simple Stellar Populations. I. Well-sampled Populations
• Hubble Space Telescope survey of Magellanic Cloud star clusters. Binaries among the split main sequences of NGC 1818, NGC 1850, and NGC 2164
• Harnessing the Hubble Space Telescope Archives: A Catalogue of 21,926 Interacting Galaxies
• Strömgren metallicities for intermediate-age and old star clusters
• On the Precision of Full-Spectrum Fitting of Simple Stellar Populations. IV. A Systematic Comparison with Results from Colour-Magnitude Diagrams
• The wide upper main sequence and main sequence turnoff of the ~ 800 Myr old star cluster NGC1831
• The Effects of Binary Stars on the Color-Magnitude Diagrams of Young-Age Massive Star Clusters
• New age-metallicity diagnostic diagram for the Washington photometric system
• The VISCACHA Survey: XIII. The extended main-sequence turn-off in intermediate-age low-mass clusters
• The broadening of the main sequence in the open cluster M38
• Synthetic clusters of massive stars to test stellar evolution models