2011AJ....142..163M

The internal proper motion dispersion of NGC 6266 was measured using Hubble Space Telescope Wide Field Planetary Camera 2 images with an epoch difference of eight years. The dispersion was found to be 0.041±0.001 arcsec century^–1. This value was then equated to the cluster's radial velocity dispersion of 13.7±1.1 km/s to yield a distance to NGC 6266 of 7054 ±583 pc. Based on this distance we find that the NGC 6266 RR Lyrae stars have M_V= 0.51±0.18 mag. This magnitude is in good agreement with that predicted by the M_V versus [Fe/H] relation found by Benedict et al. Using an average [Fe/H] of -1.25 for NGC 6266, their relation predicts M_V= 0.49 ±0.06. Based on the RR Lyrae M_V versus age relation determined by Chaboyer et al., we estimate that NGC 6266 has an age of 11.4±2.2 Gyr.