Stroemgren photometry of the Bulge: the Baade's Window and the globular   cluster NGC 6522
  We present Ca-uvby Stroemgren photometry of the Baade's Window, including the Galactic globular cluster NGC 6522. We separate field and cluster stars by adopting color-color planes and proper motions. We then estimate the global metallicity of red-giants (RGs) in NGC 6522 by using a new theoretical metallicity calibration of the Stroemgren index hk presented in Calamida et al. (2011). We find that metallicities estimated by adopting the hk index and the (Ca-y) color are systematically more metal-rich than metallicities estimated with hk and the (u-y), (v-y) and (b-y) colors. Current evidence indicate that the hk metallicity index is affected not only by the Calcium abundance, but also by another source of opacity. 
A. Calamida, G. Bono, C. E. Corsi, G. Iannicola, V. Ripepi, B.   Anthony-Twarog, B. Twarog, M. Zoccali, R. Buonanno, S. Cass...
astro-ph.SR