NGC 6397: A case study in the resolution of post-collapse globular cluster cores

Model surface brightness profiles based on Fokker-Planck simulations have been used to assess the high resolution surface brightness profile of the globular cluster NGC 6397 of Lauzeral et al. (1992). The profile is well fitted by the model in the maximum-expansion phase of a gravothermal oscillation with a core radius of 0.06 pc (6’'), but an unresolved core cannot be ruled out. A core this size is also expected in highly evolved clusters including significant numbers of primordial binaries. A more massive cluster will provide better statistics, as would star counts. The greater distance of the other globular clusters and the requirements of star counting will demand very high resolution observations to definitively resolve cores this size.