# Stellar rotation bifurcation caused by tidal locking in the open cluster NGC 2287?

## TL;DR

This study analyzes stellar rotation velocities in the young open cluster NGC 2287, suggesting that tidal locking in binary systems may cause the observed split in the main sequence by creating a dichotomy in stellar rotation rates.

## Contribution

It provides evidence that tidal locking in binary systems can explain the bifurcation of the main sequence in NGC 2287, a novel interpretation for this phenomenon.

## Key findings

- Distribution of stellar rotation velocities shows a dichotomy.
- Tidal locking likely influences a subset of stars in the cluster.
- The cluster may have an unusually high number of short-period binaries.

## Abstract

We present a detailed analysis of the projected stellar rotational velocities of the well-separated double main sequence (MS) in the young, $\sim200$Myr-old Milky Way open cluster NGC 2287 and suggest that stellar rotation may drive the split MSs in NGC 2287. We find that the observed distribution of projected stellar rotation velocities could result from 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. The slow rotators are likely stars that initially rotated rapidly but subsequently slowed down through tidal locking induced by low-mass-ratio binary systems. However, the cluster may have a much larger population of short-period binaries than is usually seen in the literature, with relatively low secondary masses.