Dynamical Modeling of NGC 6397: Simulated HST Imaging

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Session 103 -- Open and Globular Clusters
Display presentation, Thursday, 12, 1995, 9:20am - 6:30pm

[103.08] Dynamical Modeling of NGC 6397: Simulated HST Imaging

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

The proximity of NGC~6397 (2.2~kpc) provides an ideal opportunity to test current dynamical models for globular clusters with the HST Wide-Field/Planetary Camera (WFPC2)\@. We have used a Monte Carlo algorithm to generate ensembles of simulated Planetary Camera (PC) $U$-band images of NGC~6397 from evolving, multi-mass Fokker-Planck models. These images, which are based on the post-repair HST-PC point-spread function, are used to develop and test analysis methods for recovering structural information from actual HST imaging. We have considered a range of exposure times up to $2.4\!\times\!10^4$\,s, based on our proposed HST Cycle~5 observations.

Our Fokker-Planck models include energy input from dynamically-formed binaries. We have adopted a 20-group mass spectrum extending from 0.16 to 1.4~$M_\odot$. We use theoretical luminosity functions for red giants and main sequence stars. Horizontal branch stars, blue stragglers, white dwarfs, and cataclysmic variables are also included. Simulated images are generated for cluster models at both maximal core collapse and at a post-collapse bounce. We are carrying out stellar photometry on these images using ``DAOPHOT-assisted aperture photometry'' software that we have developed. We are testing several techniques for analyzing the resulting star counts, to determine the underlying cluster structure, including parametric model fits and the nonparametric density estimation methods. Our simulated images also allow us to investigate the accuracy and completeness of methods for carrying out stellar photometry in HST Planetary Camera images of dense cluster cores.

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