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B.W. Murphy, C.A. Moore, T.E. Trotter (Butler University), H.N. Cohn, P.M. Lugger (Indiana University)
We have fit dynamically evolving Fokker-Planck models to the globular star cluster 47~Tuc (Ngc~104). Using mass-function and star-count data from the Hubble Space Telescope, we have determined the global stellar mass function down to 0.1 M\odot. In addition to the mass function and star-count data, the velocity-dispersion profile and millisecond pulsar acceleration are well fit by the model. The best-fitting model is a pre-core-collapse model that mimics the behavior of a cluster with a sizable population of primordial binaries. These Fokker-Planck models are far more successful than are King-Mitchie model for fitting the full set of observational data. The best-fitting model has a mass function with power-law indices of 1.35, -1.0, 0.5, and -1.0 (where 1.35 is the Salpeter index) over the mass intervals of 60 to 1.0 M\odot, 1.0 to 0.55 M\odot, 0.55 to 0.25 M\odot, and 0.35 to 0.1 M\odot, respectively. The total mass of the cluster is 1.1\times 106 M\odot, the half-mass radius is 7 parsecs, and the core radius is 0.2 parsecs. The model contains a large number (4.6% of the total cluster mass) in nonluminous objects of 1.4 M\odot. If most of these objects are neutron stars, the large inferred number suggest that either the upper main sequence mass function was flatter that the Salpeter mass function or that the progenitor stellar mass range for neutron star formation may extend to lower masses in low-metallicity systems than in high metallicity systems.
The author(s) of this abstract have provided an email address for comments about the abstract: murphy@butler.edu