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

Abstract

We report on $BVI$ CCD photometry to $V=22.0$ for 3 fields centered on the region of the Galactic star clusters Ruprecht~4, Ruprecht~7 and Pismis~15 and on 3 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 et al. (1993). 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.