Issue |
A&A
Volume 372, Number 1, June II 2001
|
|
---|---|---|
Page(s) | 71 - 84 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20010305 | |
Published online | 15 June 2001 |
Multicolour CCD photometry of old open clusters:*
King 5 and Be 20
State Observatory, Manora Peak, Naini Tal - 263 129, India e-mail: pandey, vijay@upso.ernet.in
Corresponding author: A. K. Durgapal, alok@upso.ernet.in
Received:
11
May
2000
Accepted:
6
February
2001
We present multicolour CCD photometry for two poorly
studied open clusters
(King 5 and Be 20). Photometry for a field near King 5 was also
carried out to estimate the contamination by field stars.
The colour magnitude diagrams (CMD) of the clusters show a well
defined main sequence extending to the limit of the photometry, mag. The reddening for King 5, estimated from the
colour-colour diagram, is ~0.82, whereas that for
Be 20 as estimated by comparing theoretical main-sequence (MS) with the
observed MS is 0.10. The morphology of the CMDs indicates that these
clusters are old. The
CMD of Be 20 shows a globular cluster-like horizontal branch.
In case of King 5 the comparison of
observational CMDs with the standard isochrones of VandenBerg
([CITE]) indicates an apparent discrepancy between the shape of the turnoff
and isochrones.
The CMDs of King 5 seem to be better understood in terms of stellar models with convective overshoot.
The comparison of the CMDs with the stellar models by Bertelli et al. ([CITE])
with convective overshoot produces a good fit for a metallicity
and an age = 1 Gyr for King 5 and 5 Gyr for Be 20. An apparent distance modulus
and
15.1 has been estimated for King 5 and Be 20 respectively. They
correspond to a distance of
pc and 9026 ± 480 pc,
respectively. The radial density distribution in King 5 indicates
that there is an excess of low mass stars in the outer region of the
cluster, whereas the density distribution in Be 20 shows a good fit with
the empirical King ([CITE]) model. For both clusters, observations have also been carried out to
search for variable stars.
Key words: Hertzsprung-Russel (HR) diagram / open clusters / individual: King 5; Be 20
© ESO, 2001
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