S. Sujatha1,2 , G.S.D. Babu1 and Sharath
Ananthamurthy2
Abstract.
The first CCD photometric UBVRI observations of the open
clusters NGC
1857 (Czernik 20, OCl 427) and Czernik 25 (OCl 493) are presented. The
observations
were obtained on 28 November 2003 with the 2m Himalayan Chandra
Telescope at
Hanle using a LN2 cooled 2k ×2k CCD. The colour excess E(B-V) is found
to be
non-uniform in the line of sight of NGC 1857 ranging between 0.38 and
0.60 mag,
while it is 0.69 mag for Cz 25. Further, the clusters NGC 1857 and Cz 25
are estimated
to be at a distance of 5.75±0.8 kpc and 4.79±0.5 kpc respectively. As
the log (age) of
NGC 1857 is estimated to be in the range of 8.00 to 8.25 and that of Cz
25 is 8.45, they
may be considered to be of intermediate age.
The luminosity function (LF) and the mass function (MF) for both
the clusters
have been derived. The MF slopes for the clusters NGC 1857 and Cz 25 are
-2.39±0.26
and -2.70±0.25 respectively. These values are in fair agreement with
that given by
Salpeter. Mass segregation is observed in both the clusters and it could
be due to the
dynamical evolution of the clusters or the imprint of star formation
process or both.
Keywords: Open clusters, photometry,
distance, age, luminosity function, mass func-
tion and mass segregation
.
1
M.P. Birla Institute of Fundamental Research, Bangalore 560001,
India
2
Department of Physics, Jnana Bharathi Campus, Bangalore University,
Bangalore 560056, India