Other
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995hst..prop.5899c&link_type=abstract
HST Proposal ID #5899
Other
Hst Proposal Id #5899 Stellar Populations
Scientific paper
We propose to obtain deep UBV WFPC2 imaging of the central regions of the collapsed-core globular clusters NGC 6284 and NGC 6293. Our CTIO 4 m U-band surface photometry places upper limits of <1" on the core radii of these clusters {Lugger, Cohn, & Grindlay 1995}. WFPC2 imaging will enable us to study the central structure of these dense cluster cores by star count analysis, providing key tests of our theoretical understanding of collisional stellar systems containing binary stars. We will construct color-magnitude diagrams and analyze the radial distributions of individual stellar groups to assess evidence of mass segregation. These observations will be particularly useful for detecting centrally concentrated populations of blue stragglers, bright CVs, and other UV-excess objects. We will fit detailed Fokker-Planck models to these data, as well as carry out nonparametric analyses, in order to test key predictions of the theory of the dynamical evolution of dense stellar systems including globular clusters and galactic nuclei. A particular goal is to distinguish between a small, but resolved core {r_c 1"} and a core that is in a state of deep collapse {r_c << 1"}. The dynamical modeling will constrain the dark remnant populations - particularly of heavy white dwarfs and neutron stars - in the central regions of these clusters. The deep stellar photometry in collapsed cluster cores needed for this program depends critically on the high angular resolution provided by the HST. We are carrying out detailed simulations of HST WFPC2 imaging of collapsed cores based on our Fokker-Planck models, in order to develop optimal techniques for extracting information on cluster structure from these data. The combination of HST star counts for the central regions of the clusters, from the PC and WF frames, with ground-based star counts for the remainder of the clusters from CTIO and WIYN imaging, and large sets of stellar velocities from WIYN multi-object spectroscopy, will allow us to study the global dynamics of these clusters.
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