HST multiband photometry of the globular cluster NGC 6388

Abstract

We present color-magnitude diagrams (CMD) of the globular cluster NGC 6388 based on HST multiband photometry (F255W, F336W, F439W, F555W). In this paper we focus our attention on the peculiar horizontal branch of this cluster. After a careful reddening correction, we fitted the observed CMD with theoretical models. For the first time we demonstrated that the HB of this very metal rich globular cluster extends beyond Te > 30.000 K, showing clear evidence of a population of blue hook (D'Cruz et al.2000, Brown et al. 2001) stars. Moreover, we could demonstrate that the HB tilt (slope) is not a reddening effect and is present in all the photometric bands.