Mathematics – Probability
Scientific paper
Apr 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...443..124p&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 443, no. 1, p. 124-135
Mathematics
Probability
44
Distance, Globular Clusters, Radial Velocity, Stellar Motions, Velocity Distribution, Astrometry, Horizontal Branch Stars, Kinematics, Mass To Light Ratios, Star Distribution
Scientific paper
The internal stellar velocity distribution of the globular cluster M4 is evaluated from nearly 200 new radial velocity measurements good to 1 km/s and a rederivation of existing proper motions. The mean radial velocity of the cluster is 70.9 +/- 0.6 km/s. The velocity dispersion is 3.5 +/- 0.3 km/s at the core, dropping marginally towards the outskirts. Such a low internal dispersion is somewhat at odds with the cluster's orbit, for which the perigalacticon is sufficiently close to the galactic center that the probability of cluster disruption is high; a tidal radius two-thirds the currently accepted value would eliminate the discrepancy. The cluster mass-to-light ratio is also small, M/LV = 1.0 +/- 0.4 in solar units. M4 thus joins M22 as a cluster of moderate and concentration with a mass-to-light ratio among the lowest known. The astrometric distance to the cluster is also smaller than expected, 1.72 +/- 0.14 kpc. This is only consistent with conventional estimates of the luminosity of horizontal branch stars provided an extinction law R = AV/E(B-V) approximately 4 is adopted, as has been suggested recently by several authors.
Cudworth Kyle McC.
Peterson Ruth C.
Rees Richard F.
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