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A new calibration of the RGB Tip as a Standard Candle

Michele Bellazzini, Francesco R. Ferraro, Elena Pancino

astro-pharXiv:astro-ph/0110645

Abstract

We have obtained an accurate estimate of the absolute I magnitude of the Tip of the Red Giant Branch (MI(TRGB)) for the globular cluster Omega Cen, based (a) on the largest photometric database ever assembled for a globular, by Pancino et al. (2000), and (b) on a direct distance estimate for , recently obtained by Thompson et al.(2001) from a detached eclipsing binary. The derived value MI(TRGB) = -4.04 0.12 provides, at present, the most accurate empirical zero-point for the calibration of the -- [Fe/H] relation, at [Fe/H] ~ -1.7.

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