A&A Supplement series, Vol. 127, January II 1998, 167-179
Received October 11, 1995; accepted April 29, 1997
T. Richtler - E.K. Grebel - A. Subramaniam - R. Sagar
Send offprint request: T. Richtler, Bonn
Sternwarte der Universität Bonn, Auf dem Hügel 71,
D-53121 Bonn, Germany
richtler@astro.uni-bonn.de
Indian Institute of Astrophysics, 560034 Bangalore, India
purni@iiap.ernet.in, sagar@iiap.ernet.in
Astronomisches Institut der Universität Würzburg, Am Hubland, D-97074
Würzburg, Germany grebel@astro.uni-wuerzburg.de
Uttar Pradesh State Observatory, Naini Tal, India
We present CCD photometry in V and I for the metal-rich globular cluster NGC 6528. A comparison with previous photometry reveals discrepancies of the order 0.1 to 0.2 mag in V, emphasizing the need for independent photometry. As found previously, the giant branch (or the asymptotic giant branch, which cannot be distinguished) of the cluster extends to V-I = 7. Population synthesis in V-I must take these red stars into account in order to understand integrated red colours of bulge populations. Currently available theoretical isochrones do not reproduce the shape of the RGB/AGB. The derivation of reliable values for reddening, distance and metallicity of NGC 6528 is hampered by uncertainties in the extrapolation to high metallicity, which dominate the absolute error rather than the photometric uncertainty does. Together with other properties (old age derived from HST data, high radial velocity), this object is more likely a member of the bulge than of the disk population.
keywords: Galaxy: globular clusters: general; individual: NGC 6528 -- galaxy abundances -- stars: late-type -- HR diagram