Vol 18, No 10

A proper motion study of the globular cluster M12 (NGC 6218)

Devesh P. Sariya, Ing-Guey Jiang, Ramakant Yadav


Using astrometric techniques developed by Anderson et al., we determine proper motions (PMs) in the ∼ 14.60 × 16.53 arcmin 2 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 the wide-field imager (WFI) mosaic camera mounted on the ESO 2.2 m telescope. The median value of PM error in both components is ∼ 0.7 mas yr−1 for the stars having V ≤ 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 and BVRI photometry is being provided. One of the possible applications of the catalog is demonstrated by gathering the membership information of the variable stars, blue stragglers and X-ray sources reported earlier in the cluster’s region.


Galaxy: globular clusters — astrometry — catalogs — individual : M12

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