Structure and mass function of five intermediate/old open clusters
State Observatory, Manora Peak, Naini Tal -263 129, Uttaranchal, India e-mail: alok,pandey@upso.ernet.in
Corresponding author: A. K. Durgapal, alok@upso.ernet.in
Received:
27
February
2001
Accepted:
30
May
2001
The UBVRI data of five northern open star clusters are used to study the
mass function (MF), structure and dynamical state of these clusters. The
clusters under discussion have ages ranging from ~0.6 to 5 Gyr. A
comparison of the density profiles indicates that the
evolution of the core of these clusters is almost the same, whereas the corona
of the clusters are probably affected by the external environment and dynamical evolution.
For the entire cluster region, the slope of the MF of three clusters
(Be 64, Be 69 and King 5) has a value that agrees within the error with the
Salpeter
value, whereas King 7 and Be 20 show a steeper (
) and
almost a flat MF respectively. We find that the slope of the MF of two
clusters (King 5 and King 7) changes significantly from the inner region to the
outer region, becoming steeper at larger radii. The dynamical relaxation time
of the clusters under discussion is less than the age of the clusters,
which indicates that all of these clusters are dynamically relaxed. Thus
the observed mass segregation in three clusters can be attributed to the
dynamical evolution of the clusters. The ratio of the clusters' present
radius to the limiting radius (determined from the relation given
by King [CITE]) can be representated by an exponent law.
Key words: galaxy: open clusters and associations: general
© ESO, 2001