Probing mass segregation in the globular cluster NGC 6397

Abstract

In this study, we present a detailed study of mass segregation in the globular cluster NGC 6397. First, we carry out a photometric analysis of projected European SouthernObservatory (ESO)– Very Large Telescope (VLT) data (between 1 and 10 arcmin from the cluster centre), presenting the luminosity function corrected by completeness. The luminosity function shows a higher density of bright stars near the central region of the data with respect to the outer region. We calculate a deprojected model (covering the whole cluster), estimating a total number of 193 000 ± 19 000 stars. The shapes of the surface brightness and density-number profiles versus the radial coordinate r (instead of the projected coordinate R) lead to a decreasing luminosity and thus mass for an average star, up to 1 arcmin, quantifying the mass segregation. The deprojected model does not show evidence of mass segregation outside this region.