Tidal-locking-induced stellar rotation dichotomy in the open cluster NGC 2287?

Abstract

Stars spend most of their lifetimes on the `main sequence' (MS) in the Hertzsprung--Russell diagram. The obvious double MSs seen in the equivalent color--magnitude diagrams characteristic of Milky Way open clusters pose a fundamental challenge to our traditional understanding of star clusters as `single stellar populations.' The clear MS bifurcation of early-type stars with masses greater than $\sim 1.6M_{\odot }$ is thought to result from a range in the stellar rotation rates. However, direct evidence connecting double MSs to stellar rotation properties has yet to emerge. Here, we show through analysis of the projected stellar rotational velocities ($v\sin i$, where $i$ represents the star's inclination angle) that the well-separated double MS in the young, $\sim 200Myr$-old Milky Way open cluster NGC 2287 is tightly correlated with a dichotomous distribution of stellar rotation rates. We discuss whether our observations may reflect the effects of tidal locking affecting a fraction of the cluster's member stars in stellar binary systems. We show that the slow rotators could potentially be initially rapidly rotating stars that have been slowed down by tidal locking by a low mass-ratio companion in a cluster containing a large fraction of short-period, low-mass-ratio binaries. This demonstrates that stellar rotation drives the split MSs in young, $⪅300$Myr-old star clusters. However, special conditions, e.g., as regards the mass-ratio distribution, might be required for this scenario to hold.

15 pages, 8 figures, 1 table. Accepted for publication in ApJ

References in corpus (16)

• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Multiple stellar populations in three rich Large Magellanic Cloud star clusters
• The Age and Age Spread of the Praesepe and Hyades Clusters: a Consistent, ~800 Myr Picture from Rotating Stellar Models
• Bayesian Ages for Early-Type Stars from Isochrones Including Rotation, and a Possible Old Age for the Hyades
• Populations of rotating stars III. SYCLIST, the new Geneva Population Synthesis code
• Spin alignment of stars in old open clusters
• Multiple stellar populations in Magellanic Cloud clusters. III. The first evidence of an extended main sequence turn-off in a young cluster: NGC1856
• Rotating Stellar Models Can Account for the Extended Main Sequence Turnoffs in Intermediate Age Clusters
• NGC 1866: First Spectroscopic Detection of Fast Rotating Stars in a Young LMC Cluster
• 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
• The exclusion of a significant range of ages in a massive star cluster
• Stars caught in the braking stage in young Magellanic Clouds clusters
• Discovery of Extended Main Sequence Turn-offs in Four Young Massive Clusters in the Magellanic Clouds
• Stellar rotation and the extended main sequence turnoff in the open cluster NGC 5822
• Dissecting the Extended Main Sequence Turn-off of the Young Star Cluster NGC1850

Cited by in corpus (15)

• Stellar mergers as the origin of the blue main-sequence band in young star clusters
• The PLATO field selection process I. Identification and content of the long-pointing fields
• How stellar rotation shapes the colour magnitude diagram of the massive intermediate-age star cluster NGC 1846
• Exploring the role of binarity in the origin of the bimodal rotational velocity distribution in stellar clusters
• Exploring the stellar rotation of early-type stars in the LAMOST Medium-Resolution Survey. I. Catalog
• The role of binarity and stellar rotation in the split main sequence of NGC 2422
• When does the onset of multiple stellar populations in star clusters occur-III: No evidence of significant chemical variations in main-sequence stars of NGC 419
• The Stellar "Snake" I: Whole Structure and Properties
• On the origin of the split main sequences of the young massive cluster NGC 1856
• Binary-driven stellar rotation evolution at the main-sequence turn-off in star clusters
• On aging star clusters using red supergiants independent of the fraction of interacting binary stars
• Exploring the Stellar Rotation of Early-type Stars in the LAMOST Medium-resolution Survey. III. Evolution
• Extended Main Sequences in Star Clusters
• The impact of stellar rotations and binaries on the shape of upper main sequence near turn off in open cluster NGC\,6067
• Stellar rotation bifurcation caused by tidal locking in the open cluster NGC 2287?