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Open Clusters in 2MASS Photometry. II. Mass Function and Mass Segregation

Bukowiecki Ł., Maciejewski G., Konorski P., Niedzielski A.

Acta Astronomica

2012

Vol. 62, No. 3

281--296

This is a continuation of our study of open clusters based on the 2-Micron All Sky Survey photometry. Here we present the results of the mass function analysis for 599 known open clusters in the Milky Way. The main goal of this project is a study of the dynamical state of open clusters, the mass segregation effect and an estimate of the total mass and the number of cluster members. We noticed that the cluster size (core and overall radii) decreases along dynamical evolution of clusters. The cluster cores evolve faster than the halo regions and contain proportionally less low-mass stars from the beginning of the cluster dynamical evolution. We also noticed, that the star density decreases for the larger clusters. Finally, we found an empirical relation describing the exponential decrease of the mass function slope with the dynamical evolution of clusters.

Open Clusters in 2MASS Photometry. I. Structural and Basic Astrophysical Parameters

Bukowiecki Ł., Maciejewski G., Konorski P., Strobel A.

Acta Astronomica

2011

Vol. 61, No. 3

231--246

The main goal of our project is to obtain a complete picture of individual open clusters from homogeneous data and then search for correlations between their astrophysical parameters. The near-infrared JHKS photometric data from the 2-Micron All Sky Survey were used to determine new coordinates of the centers, angular sizes and radial density profiles for 849 open clusters in the Milky Way. Additionally, age, reddening, distance, and linear sizes were also derived for 754 of them. For these open clusters our results are in satisfactory agreement with the literature data. The analyzed sample contains open clusters with ages in the range from 7 Myr to 10 Gyr. The majority of these clusters are located up to 3 kpc from the Sun, less than 0.4 kpc from the Galactic plane and 6-12 kpc from the Galactic center. The majority of clusters have core radii of about 1.5 pc and the limiting radii of the order of 10 pc. We notice that in the near-infrared, open clusters seem to be greater than in optical bands. We notice that a paucity of clusters is observed at galactic longitudes range from 140° to 200° which probably reflects the real spatial distribution of open clusters in the Galaxy. The lack of clusters was also found in earlier studies.