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B.W. Murphy (Butler University), H.N. Cohn, P.M. Lugger (Indiana University), G.A. Drukier (Yale University)
We have developed a new set of dynamically evolving Fokker-Planck models for the collapsed-core globular star cluster M15, which directly address the issue of whether a central black hole is required to fit recent Hubble Space Telescope (HST) observations of the stellar spatial distribution and kinematics. As in our previous work reported by Dull et al., we find that a black hole is not needed. Using local mass-function data from recent HST studies, we have inferred the global stellar mass function. As a consequence of extreme mass segregation, the local mass functions differ from the global mass function at every location. In addition to reproducing the observed mass functions, the models also provide good fits to the star-count and velocity-dispersion profiles, and to the millisecond pulsar accelerations. We address concerns about the large neutron star populations adopted in our previous Fokker-Planck models for M15. We find that good model fits can be obtained with as few as 1000 neutron stars; this corresponds to a retention fraction of 20 percent of the initial population. The models contain a substantial population of massive white dwarfs, that range in mass up to 1.1 solar masses. The combined contribution by the massive white dwarfs and neutron stars provides the gravitational potential needed to reproduce recent HST measurements of the central velocity dispersion profile.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.