Multiple stellar populations in Magellanic Cloud clusters. V. The split main sequence of the young cluster NGC1866

Abstract

One of the most unexpected results in the field of stellar populations of the last few years, is the discovery that some Magellanic-Cloud globular clusters younger than ~400 Myr, exhibit bimodal main sequences (MSs) in their color-magnitude diagrams (CMDs). Moreover, these young clusters host an extended main sequence turn off (eMSTO) in close analogy with what is observed in most ~1-2 Gyr old clusters of both Magellanic Clouds. We use high-precision Hubble-Space-Telescope photometry to study the young star cluster NGC1866 in the Large Magellanic Cloud. We discover an eMSTO and a split MS. The analysis of the CMD reveals that (i) the blue MS is the less populous one, hosting about one-third of the total number of MS stars; (ii) red-MS stars are more centrally concentrated than blue-MS stars; (iii) the fraction of blue-MS stars with respect to the total number of MS stars drops by a factor of ~2 in the upper MS with F814W <~19.7. The comparison between the observed CMDs and stellar models reveals that the observations are consistent with ~200 Myr old highly-rotating stars on the red-MS, with rotation close to critical value, plus a non-rotating stellar population spanning an age interval between ~140 and 220 Myr, on the blue-MS. Noticeable, neither stellar populations with different ages only, nor coeval stellar models with different rotation rates, properly reproduce the observed split MS and eMSTO. We discuss these results in the context of the eMSTO and multiple MS phenomenon.

11 pages, 11 figures, accepted for publication in MNRAS

References in corpus (14)

• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• 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
• Iron and s-elements abundance variations in NGC5286: comparison with anomalous globular clusters and Milky Way satellites
• Ground-Based CCD Astrometry with Wide Field Imagers. I. [Observations just a few years apart allow decontamination of field objects from members in two Globular clusters.]
• Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: A Correlation Between Turnoff Width and Early Escape Velocity
• Populations of rotating stars III. SYCLIST, the new Geneva Population Synthesis code
• Discovery of two distinct red clumps in NGC419: a rare snapshot of a cluster at the onset of degeneracy
• Multiple stellar populations in Magellanic Cloud clusters. III. The first evidence of an extended main sequence turn-off in a young cluster: NGC1856
• No evidence of chemical anomalies in the bimodal turnoff cluster NGC 1806 in the LMC
• The halo+cluster system of the Galactic globular cluster NGC1851
• The exclusion of a significant range of ages in a massive star cluster
• Accretion of pristine gas and dilution during the formation of multiple-population globular clusters
• New Constraints on the Star Formation History of the Star Cluster NGC 1856

Cited by in corpus (10)

• NGC 1866: First Spectroscopic Detection of Fast Rotating Stars in a Young LMC Cluster
• Stars caught in the braking stage in young Magellanic Clouds clusters
• Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: Stellar Rotation diminishes, but does not eliminate, Age Spreads
• Discovery of Extended Main Sequence Turn-offs in Four Young Massive Clusters in the Magellanic Clouds
• Detailed chemical composition of classical Cepheids in the LMC cluster NGC 1866 and in the field of the SMC
• Hubble Space Telescope analysis of stellar populations within the globular cluster G1 (Mayall II) in M31
• Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud IV: Evidence for Multiple Populations in Hodge 11 and NGC 2210
• Young LMC clusters: the role of red supergiants and multiple stellar populations in their integrated light and CMDs
• The effects of the overshooting of the convective core on main-sequence turnoffs of young- and intermediate-age star clusters
• On the photometric signature of fast rotators