Color gradients in four king type globular clusters: NGC 2298, NGC 6402, NGC 6934, and NGC 7089

We present CCD surface photometry for four globular clusters: NGC 2298, NGC 6402, NGC 6934 and NGC 7089. Our photometry was aimed at the central ∼ 3 arcmin region in each cluster. We show that the surface brightness distributions of these clusters are well described by the isothermal King (1966) models. Our color analysis shows that NGC 7089 exhibits a remarkable color gradient in which the central region is bluer than the outer parts by the amplitude in B - V ∼ 0.1 mag/□″. Color gradients have also been detected in the central regions of NGC 6402 and NGC 6934, although the variation does not extend to outer part. No gradient has been detected in NGC 2298. Similar color gradients have been previsouly observed exclusively in highly concentrated systems classified as post core collapse clusters.