RADIAL-VELOCITIES OF STARS IN THE GLOBULAR-CLUSTER M14 AND THE CLUSTER DISTANCE

The internal stellar velocity distribution of the globular cluster M4 is evaluated from nearly 200 new radial velocity measurements good to 1 km s(-1) and a rederivation of existing proper motions. The mean rad ial velocity of the cluster is 70.9 +/- 0.6 km s(-1). The velocity dis persion is 3.5 +/- 0.3 km s(-1) at the core, dropping marginally towar ds the outskirts. Such a low internal dispersion is somewhat at odds w ith the cluster's orbit, for which the perigalacticon is sufficiently close to the galactic center that the probability of cluster disruptio n is high; a tidal radius two-thirds the currently accepted value woul d eliminate the discrepancy. The cluster mass-to-light ratio is also s mall, M/L(V) = 1.0 +/- 0.4 in solar units. M4 thus joins M22 as a clus ter of moderate mass and concentration with a mass-to-light ratio amon g the lowest known. The astrometric distance to the cluster is also sm aller than expected, 1.72 +/- 0.14 kpc. This is only consistent with c onventional estimates of the luminosity of horizontal branch stars pro vided an extinction law R = A(V)/E(B-V) approximate to 4 is adopted, a s has been suggested recently by several authors.