CCD photometry of the distant Southern globular cluster NGC 5824

Abstract

CCD observations have been used to generate a V,(B-V) colour-magnitude diagram for the distant globular cluster NGC 5824. The sample consists of 285 stars reaching V= 20.5, and a well-defined blue horizontal branch is observed for the first time. Assuming a reddening of E(B-V)= 0.13, the colour of the giant branch at the level of the horizontal branch is determined to be (B-V)_o,g=O.77 and the apparent distance modulus (V-M_v)= 18.0 ± 0.2. From these, a value of [Fe/H] = -1.7 and a heliocentric distance of 33 (±3) kpc have been estimated for the cluster. This yields a galacto- centric distance of 25 kpc which, when combined with Hesser, Shawl & Meyer's recent radial-velocity determination, enables the representative point of the cluster to be plotted in Lynden-Bell's velocity-distance diagram where its location is consistent with a conventional value of the mass of our Galaxy.