The Effect of Binarity on Stellar Rotation - Beyond the Reach of Tides

TL;DR

This study compares rotation periods of single and close binary solar-type stars in a young cluster, revealing that binary primaries rotate faster due to factors beyond tidal effects, likely related to early stellar evolution processes.

Contribution

It demonstrates that binarity influences stellar rotation rates independently of tidal synchronization, highlighting the role of early accretion and star-disk interactions.

Findings

Binary primary stars rotate faster than single stars.

Differences are statistically significant at 99.9% confidence.

Tidal effects are excluded as the cause of faster rotation.

Abstract

We present a comparison between the rotation period distributions of solar-type single stars and primary stars in close binaries (0.1 AU ~< a ~< 5 AU) in the young (150 Myr) open cluster M35 (NGC 2168). We find that the primary stars in the close binaries rotate faster than the single stars, on average. The differences in the means and medians between the period distributions are statistically significant at the 99.9% level or higher. The faster rotation among the primary stars in close binaries is not due to tidal synchronization as tidally evolved stars are excluded from the comparison. We discuss this result in the context of different early-evolution accretion processes and star-disk interactions for single stars and stars in close binaries.