THE OLD OPEN CLUSTER, BERKELEY-66

We have performed V and I CCD observations of the previously unstudied open cluster Berkeley 66 (Be 66) with the Kitt Peak National Observat ory 2.1 m telescope. We find Be 66 to be an old cluster, with an age o f 3-4 Gyr, based on isochrone fits to the color-magnitude diagram and from the ''morphological age index'' (MAI) of Janes & Phelps [AJ, 108, 1773 (1994)]. At a Galactocentric distance of 12.9 kpc, Be 66 is amon g the distant old open clusters and is therefore useful for studies of the Galactocentric radial abundance gradient. Using our adopted dista nce of 5.2 kpc for Be 66, we find that the cluster is 21 pc above the Galactic plane and that it is a relatively large cluster, with a deriv ed radius of 1.8-3.5 pc, depending on how the radius is defined. An es timate of the minimum mass of the cluster is 750 M.. Although field st ar contamination in the cluster color-magnitude diagram is great, ther e is some indication that a blue straggler population may exist in Be 66. (C) 1996 American Astronomical Society.