Issue |
A&A
Volume 385, Number 1, April I 2002
|
|
---|---|---|
Page(s) | 67 - 86 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20011771 | |
Published online | 15 April 2002 |
A new, cleaner colour-magnitude diagram for the metal-rich globular cluster NGC 6528 *,**
Velocity dispersion in the Bulge, age and proper motion of NGC 6528
1
Lund Observatory, Box 43, 221 00 Lund, Sweden
2
Institute of Astronomy, Madingley Road, CB3 0HA Cambridge, UK e-mail: rjohnson@eso.org
Corresponding author: S. Feltzing, sofia@astro.lu.se
Received:
20
July
2001
Accepted:
11
December
2001
Using two epochs of HST/WFPC2 images of the metal-rich
globular cluster NGC 6528 we derive the proper motions of the stars
and use them to separate the stars belonging to NGC 6528 from those of
the Galactic bulge. The stellar sequences in the resulting
colour-magnitude diagram for the cluster are significantly better
determined than in previously published data. From comparison of the
colour-magnitude diagram with the fiducial line for NGC 6553 from
Zoccali et al. ([CITE]) we conclude that the two globular clusters have
the same age. Further, using α-enhanced stellar isochrones,
NGC 6528 is found to have an age of Gyr. This fitting of
isochrones also give that the cluster is 7.2 kpc away from us. From
the measured velocities both the proper motion of the cluster and the
velocity dispersion in the Galactic bulge are found. NGC 6528 is
found to have a proper motion relative to the Galactic bulge of
= 0.006 and
= 0.044 arcsec per century. Using
stars with ~14
(i.e. the red giant branch and
horizontal branch) we find, for the Galactic bulge,
and
arcsec per century. This
give
, consistent both with previous
proper motion studies of K giants in the Galactic bulge as well as
with predictions by models of the kinematics of bulge stars.
Key words: Galaxy: globular clusters: individual: NGC 6528 / Galaxy: bulge / Galaxy: kinematics and dynamics
© ESO, 2002
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