The study of the color-magnitude diagram of globular clusters gives a large amount of information regarding their age, composition, location and history, as well as information on the galactic evolution. In particular the study of the remote globular clusters is important to describe the actual and past structure of the outer halo of the Galaxy.
The Palomar clusters are a group of sparse, low-mass globular clusters identified by Abel (1955). They generally lie at large galactocentric distance and have a low integrated absolute magnitude, very low surface brightness, large core and tidal radii and predominantly red horizontal branch populations.
Palomar 13 is a typical representative of the Palomar class clusters. A preliminary study of the cluster was published by Ciatti et al. (1965). In 1985 Ortolani, Rosino and Sandage have published the B and V magnitudes of 122 stars which have been determined by examining plates obtained at the prime focus of the Hale telescope by means of a PDS microphotometer.
This paper presents the first CCD photometry of the central (
) region of Palomar 13 performed in the BV Johnson photometric
system and a photometry of the wide-field (
) in the
Thuan-Gunn system. The purpose of our work is to study some details of the
color-magnitude diagram and to determine the absolute and differential age of the
cluster.