Deep and Wide Photometry of Two Open Clusters NGC 1245 and NGC 2506: Dynamical Evolution and Halo

TL;DR

This study uses deep wide-field photometry to analyze the structure and dynamical evolution of two old open clusters, revealing mass segregation, evaporation, and potential tidal features.

Contribution

Introduces a new method for assigning cluster membership probabilities combining spatial and colour-magnitude data, applied to analyze cluster dynamics.

Findings

Both clusters show signs of mass segregation and dynamical relaxation.

Evidence suggests evaporation of low-mass stars in the clusters.

Possible tidal tail detected in NGC 1245, but not confirmed.

Abstract

We studied the structure of two old open clusters, NGC 1245 and NGC 2506, from a wide and deep VI photometry data acquired using the CFH12K CCD camera at CFHT. We devised a new method for assigning cluster membership probability to individual stars using both spatial positions and positions in the colour-magnitude diagram. From analyses of the luminosity functions at several cluster-centric radii and the radial surface density profiles derived from stars with different luminosity ranges, we found that the two clusters are dynamically relaxed to drive significant mass segregation and evaporation of some fraction of low-mass stars. There seems to be a signature of tidal tail in NGC 1245 but the signal is too low to be confirmed.