Integrated photometric characteristics of galactic open star clusters

Abstract

Integrated UBVRI photometric parameters of 140 galactic open clusters have been computed. Integrated I(V − R)o and I(V − I)o colours as well as integrated parameters for 71 star clusters have been obtained for the first time. These, in combination with published data, altogether 352 objects, are used to study the integrated photometric characteristics of the galactic open clusters. The I(Mᵥ ) values range from −9.0 to −1.0 mag corresponding to a range in total mass of the star clusters from ∼25 to 4×10⁴ M☉. The integrated colours have a relatively narrow range, e.g., I(B − V )o varies from −0.4 to 1.2 mag. The scatter in integrated colours at a given integrated magnitude can be understood in terms of differences in fraction of red giants/supergiants in the clusters. The observed integrated magnitudes and colours agree with the synthetic ones, except the dependences of I(V − R)o and I(V − I)o colours for clusters younger than ∼100 Myrs and also of the integrated magnitudes of oldest clusters. The large sample provides the most accurate age dependence of integrated magnitudes and colours determined so far. The luminosity function of the I( Mᵥ ) has a peak around −3.5 mag and its slope indicates that

only ∼1% of the open clusters in the galactic disc are brighter than I( Mᵥ ) = −11 mag. No variation has been found of integrated magnitude with galactocentric distance and metallicity.