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Astron. Astrophys. 329, 937-942 (1998)

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On the calibration of Red Giant Branch metallicity indicators
in globular clusters:
new relations based on an improved abundance scale

Eugenio Carretta and Angela Bragaglia

Osservatorio Astronomico di Bologna, Via Zamboni 33, I-40126 Bologna, Italy (carretta@astbo3.bo.astro.it, angela@astbo3.bo.astro.it)

Received 8 July 1997 / Accepted 22 August 1997


We present an improved calibration of photometric metallicity indicators, derived from the new metallicity scale for Globular Clusters presented by Carretta & Gratton (1997) and based on direct high resolution spectroscopy of 160 stars in 24 globular clusters.

We have carefully recalibrated the traditional abundance indices based upon the red giant branch (RGB) morphology, both in the [FORMULA] and [FORMULA] planes, namely the dereddened colour at the luminosity level of the horizontal branch (HB), and the magnitude difference between the HB and the RBG at a given dereddened colour.

Finally, we give new accurate relations to employ in the Simultaneous Metallicity Reddening method by Sarajedini (1994), also tied to the Carretta & Gratton (1997) abundance scale.

Key words: stars: abundances – globular clusters: general

Send offprint requests to: E. Carretta

© European Southern Observatory (ESO) 1998

Online publication: December 16, 1997