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Session 71 - Globular Clusters.
Display session, Wednesday, January 15
We have obtained UBV\/ WFPC2 imaging of the central regions of the collapsed-core globular clusters NGC 6284 and NGC 6293. We selected these clusters based on our CTIO 4\,m U-band surface photometry, which indicates central power-law cusp profiles without any indication of a resolved core (Lugger, Cohn, amp; Grindlay 1995 [ApJ, 439, 191]). We are carrying out stellar photometry on the WFPC2 frames in order to further study the central structure of the clusters. We have constructed color-magnitude diagrams and are analyzing the radial distributions of individual stellar groups to assess evidence of mass segregation. We find blue straggler populations in both clusters, which are more centrally concentrated than the giant branch stars. NGC 6284 shows a long faint, blue extension of the horizontal branch, while NGC 6293 shows a much less extended horizontal branch. 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 globular cluster dynamical evolution.
Program listing for Wednesday