Mass functions and photometric binaries in nine open clusters

TL;DR

This study analyzes the mass functions and binary star content in nine open clusters using CCD photometry, revealing mass segregation, the decay of MF slopes with age, and a high binary fraction, with implications for initial mass function variations.

Contribution

It provides homogeneous measurements of mass functions, binary content, and mass segregation in nine open clusters, highlighting the variation of MF slopes with cluster age and location.

Findings

MF slopes range from -1.1 to -2.1, differing from Salpeter's value.

Outer regions show steeper MFs indicating mass segregation.

Photometric binary content is approximately 40%.

Abstract

Using homogeneous CCD photometric data from the 105-cm Kiso Schmidt telescope covering a 50' x 50' field, we study the mass functions (MFs) of nine open clusters. The ages and Galactocentric distances of the target clusters vary from 16 - 2000 Myr and 9-10.8 kpc, respectively. The values of MF slopes vary from -1.1 to -2.1. The classical value derived by Salpeter (1955) for the slope of the IMF is \Gamma = -1.35. The MFs in the outer regions of the clusters are found to be steeper than in the inner regions, indicating the presence of mass segregation in the clusters.The MF slopes (in the outer region as well as the whole cluster) undergo an exponential decay with the evolutionary parameter \tau (= age/ relaxation time). It seems that the evaporation of low-mass members from outer regions of the clusters is not significant at larger Galactocentric distances. It is concluded that the initial mass function (IMF) in the anticentre direction of the Galaxy might have been steeper than the IMF in the opposite direction. A comparison of the observed CMDs of the clusters with synthetic CMDs gives a photometric binary content of ~40%.