A new abundance calibration for the Washington system and some early results

D. GEISLER, J.J. CLARIÁ, .MINNITI

Santiago3

Congreso; Primera Reunión Astronómica Sur-Andina; 1992

ESO

A revised metal abundance calibration is presented for the Washington photometric system which represents a significant improvemente over previous calibrations. New solar abundance fiducial relations in the color-color diagrams are derived. Observations of a large sample of globular cluster giants demonstrate, and allow correction for, an unsuspected decrease in metallicity sensitivity for cooler giants. A new abundance index, C-T1, and a new temperature index, M-T2, are introduced. Various combinations of abundance and temperature indices are investigated. We confirm that the Washington system offers a unique combination of efficiency and accuracy for determining metallicity in late-type giants over the full range of stellar abundances, although the system loses sensitvity for the coolest metal-poor stars.