Stellar Spins in the Pleiades, Praesepe, and M35 Open Clusters

TL;DR

This study investigates stellar spin orientations and internal kinematics in three open clusters, finding evidence for isotropic and aligned spins, and detecting significant rotation in Praesepe.

Contribution

It provides the first detailed analysis of stellar inclination distributions and internal kinematics in multiple open clusters, highlighting possible spin alignments and cluster rotation.

Findings

Isotropic and moderate spin alignment are consistent with Pleiades and Praesepe data.

M35 shows a mix of isotropic and aligned spins, possibly due to systematic errors or physical groupings.

Significant plane-of-sky rotation detected in Praesepe, with a mean velocity of 0.132 km/s.

Abstract

We analyze spectroscopic and photometric data to determine the projected inclinations of stars in three open clusters: the Pleiades, Praesepe, and M35. We determine the $\sin i$ values of 42, 35, and 67 stars in each cluster, respectively, and from their distributions we find that isotropic spins and moderate alignment are both consistent with the Pleiades and Praesepe data. While it is difficult to distinguish between these scenarios for a single cluster, an ensemble of such distributions may facilitate a distinction. The M35 inclination distribution is most consistent with a superposition of isotropic and anisotropic spins, the source of which could be systematic error or a physical grouping of aligned stars. We also study internal cluster kinematics using radial velocities and proper motions. Our kinematics analysis reveals significant plane-of-sky rotation in Praesepe, with a mean velocity of $0.132 \pm 0.022$ km s$^{-1}$ in a clockwise direction.