Physics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........6r&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF CHICAGO, 1995.Source: Dissertation Abstracts International, Volume: 56-03, Section: B, page: 1
Physics
Scientific paper
Surface brightness profiles, luminosity functions, and radial velocities of individual globular cluster stars from the literature are used in conjunction with proper motions from published and unpublished Yerkes studies to construct dynamical models for eight Galactic globular clusters (47 Tuc, M2, M4, M5, M15, M22, M92, and NGC 6397). These are multi-mass, anisotropic King-type models, following the formalism of Gunn & Griffin (AJ, 84, 752 (1979)). Cluster rotation is taken into account in a simple fashion, as the available velocity data for some clusters are inadequate to justify detailed modeling of the rotation. The radial velocity and proper motion dispersions in each cluster have been related via the models to derive distances to the clusters that are independent of interstellar absorption or any standard candle arguments. The distances thus obtained are mostly in agreement with previous determinations, with the exception of 47 Tuc, where the simple rotation correction is probably inadequate. M15 and NGC 6397 could also be affected by a small systematic error, since for these clusters a King-type model does not accurately describe the entire surface brightness or velocity profile. The result for NGC 6397 is also suspect due to the preliminary nature of the currently available proper motions. A small distance to M4 and thus a high ratio of total to selective absorption (R~3.8) in its direction is strongly supported. The derived distances (supplemented by previous determinations for M3 and M13) are used to investigate the horizontal branch M_{V }-(Fe/H) relation, which is found to be M V(HB) = 0.22(Fe/H) + 0.96 if 47 Tuc, M15, and NGC 6397 are excluded on the grounds of probable systematic errors, and M_{V }(HB) = 0.00(Fe/H) + 0.66 if M15 and NGC 6397 are included. Both derivations give large error bars for the slope of the relation and are sensitive to the adopted (Fe/H) of M4, but the value of M_{V }(HB) can be well constrained at (Fe/H) = -1.6, and is found to be 0.61+/-0.04. .
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