A Study of Stellar Spins in 15 Open Clusters

TL;DR

This study investigates the spin-axis orientations of stars in 15 open clusters, finding most are consistent with random orientations, supporting turbulence dominance over ordered rotation in star formation.

Contribution

It provides the first ensemble analysis of stellar spin distributions across multiple open clusters, combining spectroscopic and photometric data for a comprehensive assessment.

Findings

80% of clusters have isotropic spin distributions

97% of individual stars are consistent with random orientations

No unambiguous evidence of stellar spin alignment found

Abstract

We analyze spectroscopic and photometric data to determine the projected inclinations of stars in 11 open clusters, placing constraints on the spin-axis distributions of six clusters. We combine these results with four additional clusters studied by Healy & McCullough (2020) and Healy et al. (2021) to perform an ensemble analysis of their spins. We find that eight out of ten constrained clusters (80%) have spin-axis orientations consistent with isotropy, and we establish a lower limit of four out of ten (40%) isotropic clusters at 75% confidence, assuming no correlation of spins between clusters. We also identify two clusters whose spin-axis distributions can be better described by a model consisting of an aligned fraction of stars combined with an isotropic distribution. However, the inclination values of these stars may be influenced by systematic error, and the small number of stars modeled as aligned in these two clusters precludes the interpretation that their stellar subsets are physically aligned. Overall, no cluster displays an unambiguous signature of spin alignment, and 97% of the stars in our sample are consistent with isotropic orientations in their respective clusters. Our results offer support for the dominance of turbulence over ordered rotation in clumps and do not suggest alignment of rotation axes and magnetic fields in protostars.