Integrated photometric characteristics of galactic open star clusters

¹ State Observatory, Manora peak, Nainital 263129, Uttaranchal, India e-mail: sneh, pandey, sagar, vijay@upso.ernet.in
² Indian Institute of Astrophysics, Bangalore 560034, India

Corresponding author: S. Lata, sneh@upso.ernet.in

Received: 19 November 2001
Accepted: 19 February 2002

Abstract

Integrated UBVRI photometric parameters of 140 galactic open clusters have been computed. Integrated and 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 values range from -9.0 to -1.0 mag corresponding to a range in total mass of the star clusters from ~25 to . The integrated colours have a relatively narrow range, e.g., 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 and 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 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  mag. No variation has been found of integrated magnitude with galactocentric distance and metallicity.