Star clusters constitute a principal link between the theories of stellar evolution and the observable universe. Open clusters are important tools to analyze the properties of the galactic disk and to test the theories of galactic and stellar evolution. The comparison between the HR diagram of the observed clusters and the isochrones, computed by means of evolutionary models, provides a test of stellar structure and evolution. The comparison provides an opportunity to ascertain whether or not convective overshoot plays an important role in the evolution.
Only about one third of the open clusters of the Milky Way have well studied HR diagrams to estimate their ages and other parameters and most of them are much younger than the galaxy. Most of the open clusters are destroyed by interaction with molecular clouds on time scales of a few hundred million of years or less (Spitzer 1958). Janes & Adler (1982) and Pandey et al. (1987) found that the median age of clusters is about yrs. However, some open clusters survive for billions of year and few may be as old as the disk.
There is currently much interest shown by various groups to determine the accurate age for intermediate age and old open clusters (see e.g., Kaluzny 1990, 1994; Janes & Phelps 1990; Twarog et al. 1993; Phelps et al. 1994; Carraro & Chiosi 1994) because the determination of age of clusters would allow us to set a lower limit to the age of the galactic disk. The understanding of their properties (age, metallicity and kinematics) is mandatory for many studies, such as the history of star formation in the galactic disk, the formation and structure of the disk.
With the aim to contribute to the progress in our understanding of this population we have undertaken an observational program to obtain reliable UBVRI CCD photometry of those clusters which are unstudied or poorly studied.
In this paper, we present CCD UBVRI photometry for the open clusters Be 64 (, , ) and Be 69 (, , ), for which no previous photometric studies could be found in the literature and compare their colour - magnitude diagrams (CMDs) with the theoretical ones.