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J/A+A/385/67 HST VI photometry and proper motions in NGC 6528 (Feltzing+, 2002)
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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.
Feltzing S., Johnson R.A.
<Astron. Astrophys. 385, 67 (2002)>
=2002A&A...385...67F (SIMBAD/NED BibCode)
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ADC_Keywords: Clusters, globular ; Photometry ; Proper motions
Keywords: Galaxy: globular clusters: individual: NGC 6528 - Galaxy: bulge -
Galaxy: kinematics and dynamics
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
<mu_l_>=0.006 and <mu_b_>=0.044 arcsec per century. Using stars with
14<V_555_<19 (i.e. the red giant branch and horizontal branch) we
find, for the Galactic bulge, sigma_l_=0.33+/-0.03 and
sigma_b_=0.25+/-0.02 arcsec per century. This give
sigma_l/sigma_b=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.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 81 212 Stellar data derived in this work from WF2-chip
tablea2.dat 81 214 Stellar data derived in this work from WF3-chip
tablea3.dat 81 227 Stellar data derived in this work from WF4-chip
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See also:
J/A+AS/127/167 : V,I CCD photometry of NGC 6528 (Richtler+ 1998)
J/AJ/84/1305 : UBV photometry in NGC 6528 (van den Bergh+, 1979)
Byte-by-byte Description of file: tablea1.dat tablea2.dat tablea3.dat
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Bytes Format Units Label Explanations
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1- 6 F6.3 10mas/yr pmGLON Proper motion in galactic longitude
8- 13 F6.3 10mas/yr pmGLAT Proper motion in galactic latitude
15- 20 F6.3 deg GLON Galactic longitude
22- 27 F6.3 deg GLAT Galactic latitude
29- 34 F6.3 pix pmX Proper motion in x coordinate on the chip
36- 41 F6.3 pix pmY Proper motion in y coordinate on the chip
43- 48 F6.2 pix Xpos X coordinate on the WFPC2 chip
50- 55 F6.2 pix Ypos Y coordinate on the WFPC2 chip
57- 62 F6.3 mag V555mag Magnitude in F555W (HST in-flight system)
64- 68 F5.3 mag e_V555mag Magnitude error in V555mag
70- 75 F6.3 mag I814mag Magnitude in F814W (HST in-flight system)
77- 81 F5.3 mag e_I814mag Magnitude error in I814mag
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Acknowledgements: Sofia Feltzing <sofia@astro.lu.se>
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(End) Patricia Bauer [CDS] 26-Mar-2002