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To probe the nature of stellar evolution in dense environments, we study thedense core of the globular cluster Messier 13 using pre-refurbishment PlanetaryCamera-I images obtained with the Hubble Space Telescope. We find 15 bluestraggler star candidates and 10 other possible blue stragglers in this regionof M13. Their specific frequency is in the range 0.04-0.07, comparable to whatis observed near the centers of other dense clusters. A comparison betweenM13's observed V band stellar luminosity function and a theoretical model(Bergbusch & Vandenberg 1992) for the luminosity function of an old, metal-poorcluster shows that the model predicts too few of the brightest red giants(V~12.5-15) by a factor of two relative to subgiants/turnoff stars (> 6 sigmaeffect). The radial distributions of the red giants, blue stragglers, andsubgiants are consistent with one another. Stars in the blue horizontal branchof M13, however, appear to be centrally depleted relative to other stellartypes.  We combine data from three dense `King model clusters', M13, M3, and 47 Tuc,and two post core collapse clusters, M30 and M15, and compare the distributionsof various stellar types as a function of (r/r_half light) and (r/r_core). Thehorizontal branch stars in the combined sample appear to be centrally depletedrelative to the giants (97% significance) - this depletion is only marginal (<about 1.5 sigma) in each of the clusters taken individually. The bluestragglers in the combined sample are centrally concentrated relative to thegiants.Comment: 28 pages, Latex (aaspp4 style file), 7 figures, to be published in  AJ, Feb. 199

Globular Cluster Photometry with the Hubble Space Telescope.VI.WF/PC-I Observations of the Stellar Populations in the Core of M13 (NGC 6205)