Isodensitometry of Omega Centauri and 47 Tucanae

Abstract

We present details of procedure on equidensitometry of globular clusters using the Sabattier technique in photography. Equidensitometry of Omega Centauri and 47 Tuc shows that both clusters become more elliptical beyond r = 2' from the centre when compared to their form close to the centre. Omega Centauri shows a second minimum in ellipticity around 5' from the centre. All clusters for which data on their ellipticity are available exhibit small values close to the centre and a little away from the centre, with a maximum in between. It is suggested that this is the result of peculiarties in the distribution of giant, sub-giant and horizontal branch stars in the cluster. The exact centre of Omega Centauri is given with respect to two bright stars in the field. Multiband equidensitometry of Omega Centauri shows that there is no asymmetric absorption by interstellar dust over the cluster.