The intermediate-age open clusters Ruprecht 4, Ruprecht 7 and Pismis 15

Abstract

We report on <i>BVI</i> CCD photometry to V = 22.0 for three fields centred on the region of the Galactic Star clusters Ruprecht 4, Ruprecht 7 and Pismis 15 and on three displaced control fields. Ruprecht 4 and Pismis 15 have never been studied before, and we provide, for the first time, estimates of their fundamental parameters, namely, radial extent, age, distance and reddening. Ruprecht 7 (Berkeley 33), however, was studied by Mazur, Kaluzny & Krzeminski. We find that the three clusters are all of intermediate age (0.8-1. 3 Gyr), and with a metallicity close to or lower than solar.