HST Observations of Mass Segregation in the Globular Cluster NGC 6397
Session 103 -- Open and Globular Clusters
Display presentation, Thursday, 12, 1995, 9:20am - 6:30pm

## [103.09] HST Observations of Mass Segregation in the Globular Cluster NGC 6397

Craig Sosin, Ivan R.\ King, and Adrienne M.\ Cool (UC Berkeley)

We have observed three fields near the center of the post-core-collapse globular cluster NGC 6397 in $B$ and $V$, using the Faint Object Camera on the repaired Hubble Space Telescope ({\it HST}). We present accurate photometry of stars on the main sequence down to a $V$ magnitude of 24, corresponding to a stellar mass of $\sim 0.16$ ${\rm M}_{\sun}$. We present the mass function of the cluster center, and compare it with the mass function of a field five arcminutes out (Paresce, De Marchi, \& Romaniello 1994). We find a very striking degree of mass segregation:\ the main sequence near the center is dominated by stars near the turnoff mass, and few low-mass stars are present at all, compared with the outer field. This first deep observation of the center of a cusp cluster with the refurbished HST shows the remarkable extent to which energy exchanges between high- and low-mass stars have affected the stellar distribution, and demonstrates the potential of the telescope for resolving fundamental issues in cluster dynamics.