A comprehensive photometric study of dynamically evolved small van den Bergh–Hagen open clusters

Abstract

We present results from Johnson U BV , Kron-Cousins RI and Washington CT 1 T 2photometries for seven van den Bergh-Hagen (vdBH) open clusters, namely, vdBH 1,10, 31, 72, 87, 92, and 118. The high-quality, multi-band photometric data sets wereused to trace the cluster stellar density radial profiles and to build colour-magnitudediagrams (CMDs) and colour-colour (CC) diagrams from which we estimated theirstructural parameters and fundamental astrophysical properties. The clusters in oursample cover a wide age range, from ∼ 60 Myr up to 2.8 Gyr, are of relatively smallsize (∼ 1 − 6 pc) and are placed at distances from the Sun which vary between 1.8 and6.3 kpc, respectively. We also estimated lower limits for the cluster present-day massesas well as half-mass relaxation times (t r ). The resulting values in combination with thestructural parameter values suggest that the studied clusters are in advanced stages oftheir internal dynamical evolution (age/t r ∼ 20 − 320), possibly in the typical phaseof those tidally filled with mass segregation in their core regions. Compared to openclusters in the solar neighbourhood, the seven vdBH clusters are within more massive(∼ 80 − 380M ⊙ ), with higher concentration parameter values (c ∼ 0.75−1.15) anddynamically evolved ones.