A Proper Motions Study of the Globular Cluster M12 (NGC 6218)

TL;DR

This study measures proper motions in the globular cluster M12 using ground-based astrometry over 11 years, providing a detailed membership catalog to distinguish cluster members from field stars and analyze stellar populations.

Contribution

It applies advanced astrometric techniques to produce a comprehensive proper motion catalog for M12, aiding in membership determination and stellar population studies.

Findings

Proper motions with median error of 0.7 mas/yr for stars brighter than V=20 mag

Membership probabilities for 3725 stars are provided

Catalog includes coordinates, proper motions, and photometry for cluster analysis

Abstract

Using astrometric techniques developed by Anderson et al., we determine proper motions (PMs) in 14.60 arcmin X 16.53 arcmin area of the kinematically "thick-disk" globular cluster M12. The cluster's proximity and sparse nature makes it a suitable target for ground-based telescopes. Archive images with time gap of 11.1 years were observed with wide-field imager (WFI) mosaic camera mounted on ESO 2.2 m telescope. The median value of PM error in both components is 0.7 mas/yr for the stars having V less than or equal to 20 mag. PMs are used to determine membership probabilities and to separate field stars from the cluster sample. In electronic form, a membership catalog of 3725 stars with precise coordinates, PMs, BVRI photometry is being provided. One of the possible applications of the catalog was shown by gathering the membership information of the variable stars, blue stragglers and X-ray sources reported earlier in the cluster's region.