Dynamical Models of the Globular Cluster M15
Session 103 -- Open and Globular Clusters
Display presentation, Thursday, 12, 1995, 9:20am - 6:30pm

## [103.10] Dynamical Models of the Globular Cluster M15

B. W. Murphy (Butler U.), H. N. Cohn, P.M. Lugger, J.D. Dull (Indiana U.)

We use evolving multi-mass Fokker-Planck models to investigate the stellar populations of the post-core-collapse globular cluster M15. The models are fit to composite velocity and surface-brightness profiles and to millisecond pulsar accelerations. We adopt an evolved mass function with 6 mass groups that includes neutron stars, white dwarfs, red giants, and main-sequence stars. The models are fit to a number of evolutionary phases, including maximum core bounce and collapse. The best fitting model has a mass-function slope of $x=0.85$ (where 1.35 is the slope of the Salpeter mass function) and a total mass of $4.9\times 10^5$M$_{\odot}$. This model contains approximately $10^4$ neutron stars (3\% of the total mass), of which the majority lie within 6 arcseconds (0.2 parsec) of the cluster center. This finding is similar to that of Drukier (1994, submitted to ApJ ), who finds that NGC~6397 has 4\% of its mass in neutron stars. Our best fitting model indicates that the core of M15 is not currently near maximum bounce. We find that the core radius is less than 1.3 arcseconds (0.07 parsec), roughly 60\% the size attained at maximal bounce. The central velocity dispersion of our best fitting model is 12~km~s$^{-1}$. This is very similar to values found by Phinney (1993, ASP Conf.\ Ser.), Dubath \& Meylan (1994, A\&A ), and Gebhardt et al. (1994, ApJ ) and obviates the need to invoke a massive central black hole.