Proper Motions and Internal Dynamics in the Core of the Globular Cluster M71

TL;DR

This study uses adaptive optics imaging to measure proper motions in the core of globular cluster M71, revealing its internal dynamics and setting limits on a potential central black hole.

Contribution

It provides the first detailed proper motion measurements in M71's core, including dispersion and anisotropy analysis, and constrains the presence of a central black hole.

Findings

Proper motion dispersion is 179 microarcsec/yr.

No evidence of anisotropy in stellar motions.

Upper limit on central black hole mass is ~150 solar masses.

Abstract

We have used Gemini North together with the NIRI-ALTAIR adaptive optics imager in the H and K bands to explore the core of the Galactic globular cluster M71 (NGC 6838). We obtained proper motions for 217 stars and have resolved its internal proper motion dispersion. Using a 3.8 year baseline, the proper motion dispersion in the core is found to be 179 +/- 17 microarcsec/yr. We find no evidence of anisotropy in the motions and no radial variation in the proper motions with respect to distance from the cluster center. We also set an upper limit on any central black hole to be ~150 Msun at 90% confidence level.