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Astron. Astrophys. 355, 994-1002 (2000)

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Revised Strömgren metallicity calibration for red giants *

Michael Hilker

Departamento de Astronomía y Astrofísica, P. Universidad Católica, Casilla 104, Santiago 22, Chile

Received 10 August 1999 / Accepted 12 November 1999


A new calibration of the Strömgren [FORMULA] diagram in terms of iron abundance of red giants is presented. This calibration is based on a homogeneous sample of giants in the globular clusters [FORMULA] Centauri, M 22, and M 55 as well as field giants from the list of Anthony-Twarog & Twarog (1998). Towards high metallicities, the new calibration is connected to a previous calibration by Grebel & Richtler (1992), which was unsatisfactory for iron abudances lower than -1.0 dex. The revised calibration is valid for CN-weak/normal red giants in the abundance range of [FORMULA][Fe/H][FORMULA] dex, and a color range of [FORMULA] mag.

As shown for red giants in [FORMULA] Centauri, CN-weak stars with Strömgren metallicities higher than -1.0 dex cannot be distinguished in the [FORMULA] diagram from stars with lower iron abundances but higher CN band strengths.

Key words: stars: abundances – stars: chemically peculiar – stars: late-type – Galaxy: globular clusters: individual: ! Cen – Galaxy: globular clusters: individual: M 22

* Based on data collected at the European Southern Observatory, La Silla, Chile

Correspondence to: mhilker@astro.puc.cl

© European Southern Observatory (ESO) 2000

Online publication: March 21, 2000