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Title:
HST VI photometry and proper motions in NGC 6528 (Feltzing+, 2002)
Authors:
Feltzing, S.; Johnson, R. A.
Publication:
VizieR On-line Data Catalog: J/A+A/385/67. Originally published in: 2002A&A...385...67F
Publication Date:
03/2002
Origin:
SIMBAD
Keywords:
Clusters: globular, Photometry, Proper motions
Comment:
tablea1.dat 212x81 Stellar data derived in this work from WF2-chip; tablea2.dat 214x81 Stellar data derived in this work from WF3-chip; tablea3.dat 227x81 Stellar data derived in this work from WF4-chip
Bibliographic Code:
2002yCat..33850067F

Abstract

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. (2001AJ....121.2638Z) we conclude that the two globular clusters have the same age. Further, using alpha-enhanced stellar isochrones, NGC 6528 is found to have an age of 11+/-2Gyr. This fitting of isochrones also give that the cluster is 7.2kpc 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 <mul>=0.006 and <mub>=0.044 arcsec per century. Using stars with 14<V555<19 (i.e. the red giant branch and horizontal branch) we find, for the Galactic bulge, sigmal=0.33+/-0.03 and sigmab=0.25+/-0.02 arcsec per century. This give sigmal/sigmab=1.32+/-0.16, 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. (3 data files).

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