Computer Science
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........43g&link_type=abstract
PhD Dissertation, Indiana Univ. Bloomington, IN United States
Computer Science
3
Globular Clusters, Stellar Models, Fokker-Planck Equation, Stellar Evolution, Collapse, Hubble Space Telescope, Mass Distribution, Pulsars
Scientific paper
I have used the multi-mass Fokker-Planck method including energy input from dynamically formed binaries to generate dynamical models of globular star clusters that evolve through core collapse into post collapse core oscillations. I have made fits of these models to observations that include velocity data and Hubble Space Telescope (HST) imaging data for the prototypical 'collapsed-core' cluster, M15. While standard King-type models have previously been successful in describing the observed distribution of light, they cannot produce the high stellar velocities seen in the core of M15. With 9 percent of the cluster mass in heavy, nonluminous remnants, my models are able to reproduce both of these features and also have a mass distribution sufficiently concentrated to account for the observed line-of-sight accelerations of the millisecond pulsars PSR 2127+11A,D. From my best fitting model for M15, I have generated ensembles of 10 synthetic HST images of globular clusters at both extremes of the core oscillation cycle -- maximal core collapse and post-collapse core bounce. I have compared centers determined from the images using total-light autocorrelation, residual-light autocorrelation and the equibarycentric method and find that the equibarycenter provides the best measure of the true cluster center. Using these centers, I have constructed surface-brightness and surface-density profiles from each image in an attempt to determine the input cluster structure. By computing slopes of surface-brightness profiles from individual images and ensemble averages, I conclude that surface-brightness data cannot be used to determine whether or not a globular cluster is presently in deep core collapse or a post-collapse core bounce. Slopes of surface-density profiles show more significant variation between collapsed-model images and expanded-model images, but will require better resolution than is currently available from the HST to yield conclusive results. Model density profiles indicate that the true structure of M15 would best be discerned by measuring the central distribution of the heaviest components of the cluster, either by directly detecting blue stragglers or by obtaining accurate measurements of stellar velocities for approximately 100 stars in the central 2 arcseconds.
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