YOUNG OPEN CLUSTERS AS PROBES OF THE STAR-FORMATION PROCESS .1. AN ATLAS OF OPEN CLUSTER PHOTOMETRY

We have obtained CCD photometry, in the UBV system, for 23 open cluste rs in order to explore the star formation history of the Cassiopeia re gion of the Perseus spiral arm of our Galaxy. Magnitudes and colors of 35,788 stars were measured, making this the most comprehensive, homog eneous single study of open cluster properties in one part of the Gala xy. This paper presents an atlas of open cluster photometry that serve s as the database for an investigation of cluster properties such as t heir ages, distances, reddenings, sizes, and richnesses. This informat ion provides insight into the spatial and temporal formation sequence of the clusters and allows an investigation of the stellar content of the clusters to be undertaken.