New Constraints on the Star Formation History of the Star Cluster NGC 1856

Abstract

We use the Wide Field Camera 3 onboard the Hubble Space Telescope to obtain deep, high-resolution photometry of the young (age ~ 300 Myr) star cluster NGC1856 in the Large Magellanic Cloud. We compare the observed colour-magnitude diagram (CMD), after having applied a correction for differential reddening, with Monte Carlo simulations of simple stellar populations (SSPs) of various ages. We find that the main sequence turn-off (MSTO) region is wider than that derived from the simulation of a single SSP. Using constraints based on the distribution of stars in the MSTO region and the red clump, we find that the CMD is best reproduced using a combination of two different SSPs with ages separated by 80 Myr (0.30 and 0.38 Gyr, respectively). However, we can not formally exclude that the width of the MSTO could be due to a range of stellar rotation velocities if the efficiency of rotational mixing is higher than typically assumed. Using a King-model fit to the surface number density profile in conjunction with dynamical evolution models, we determine the evolution of cluster mass and escape velocity from an age of 10 Myr to the present age, taking into account the possible effects of primordial mass segregation. We find that the cluster has an escape velocity Vesc ~ 17 km/s at an age of 10 Myr, and it remains high enough during a period of ~ 100 Myr to retain material ejected by slow winds of first-generation stars. Our results are consistent with the presence of an age spread in NGC1856, in contradiction to the results of Bastian & Silva-Villa (2013).

17 pages, 14 figures. Re-submitted to MNRAS after addressing all the comments by the referee

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Cited by in corpus (15)

• Rotating Stellar Models Can Account for the Extended Main Sequence Turnoffs in Intermediate Age Clusters
• A high fraction of Be stars in young massive clusters: evidence for a large population of near-critically rotating stars
• Multiple stellar populations in Magellanic Cloud clusters. V. The split main sequence of the young cluster NGC1866
• Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: Stellar Rotation diminishes, but does not eliminate, Age Spreads
• Multiple stellar populations in NGC 1866. New clues from Cepheids and Colour-Magnitude Diagram
• Asteroseismology of the young open cluster NGC 2516 I: Photometric and spectroscopic observations
• Young LMC clusters: the role of red supergiants and multiple stellar populations in their integrated light and CMDs
• 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
• The overlooked role of stellar variability in the extended main sequence of LMC intermediate-age clusters
• Stellar populations in star clusters
• A discovery of young stellar objects in older clusters of the Large Magellanic Cloud
• Extinction in the Large Magellanic Cloud Bar around NGC1854, NGC1856, and NGC1858
• The wide upper main sequence and main sequence turnoff of the ~ 800 Myr old star cluster NGC1831
• On the Precision of Full-Spectrum Fitting of Simple Stellar Populations. IV. A Systematic Comparison with Results from Colour-Magnitude Diagrams