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J. H. Howell, P. Guhathakurta (UCSC), A. Sarajedini (Wesleyan U.), R.L. Gilliland, M.D. Albrow (STScI), T.M. Brown (NCAR), D. Charbonneau (NCAR/CfA), A.S. Burrows (UA), W.D. Cochran, N. Baliber (U. Texas), P.D. Edmonds (SAO), S. Frandsen, H. Bruntt (U. Aarhus), D.N.C. Lin, S.S. Vogt, P. Choi (UCSC), G.W. Marcy (UCB), M. Mayor, D. Naef (Obs. Geneve), E.F. Milone, C.R. Stagg, M.D. Williams (U. Calgary), S. Sigurdsson (PSU), D.A. VandenBerg (U. Victoria)
The 8.3~d HST experiment described by R. L. Gilliland, et al. (see their poster) is aimed at detecting planetary transits in the globular cluster 47~Tucanae. An important by-product is a set of extremely deep WFPC2 images in F555W (V) and F814W (I) of the dense cluster core region. The effective exposure times in each of these bands is over 100,000~s, and extensive sub-pixel dithers between individual exposures supports the creation of 4\times oversampled images in which the FWHM of the point spread function is \lesssim70~mas (PC) and \lesssim140~mas (WF CCDs). Limited use is made of the shorter exposure time F336W (U) data.
This poster describes a study of mass segregation in the core of 47~Tuc using this extremely deep WFPC2 data set. Luminosity functions are constructed in a sequence of radial bins, and are compared with theoretical luminosity functions (Bergbusch & VandenBerg 1992) based on a variety of power-law stellar mass functions. The degree of mass segregation is characterized by the slope x of the best fitting stellar mass function, where x=+1.35 is the Salpeter value. The mass function slope is found to vary from x~5 in the cluster center to x~2 at the edge of the WFPC2 field of view, r~00'', indicating extreme mass segregation in the core of 47 Tuc. The results are coupled with image simulations and results derived from a set of archival short WFPC2 exposures to assess the effect of faint end incompleteness in the latter data set.
Funding has been provided via a NASA/STScI grant for GO-8267.
The author(s) of this abstract have provided an email address for comments about the abstract: jhhowell@ucolick.org