The calibration of the RGB Tip as a Standard Candle

Free access article

Issue		A&A Volume 424, Number 1, September II 2004


Page(s)		199 - 211
Section		Stellar structure and evolution
DOI		http://dx.doi.org/10.1051/0004-6361:20035910

A&A 424, 199-211 (2004)
DOI: 10.1051/0004-6361:20035910

Extension to Near Infrared colors and higher metallicity

M. Bellazzini¹, F. R. Ferraro², A. Sollima^{1, 2}, E. Pancino¹ and L. Origlia¹

¹ INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
e-mail: michele.bellazzini@bo.astro.it
² Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
e-mail: francesco.ferraro3@unibo.it

(Received 19 December 2003 / Accepted 28 April 2004 )

Abstract
New empirical calibrations of the Red Giant Branch Tip in the I, J, H and K bands based on two fundamental pillars, namely $\omega$ Centauri and 47 Tucanae, have been obtained by using a large optical and near infrared photometric database.

Our best estimates give $M_I^{\rm TRGB}= -4.05 \pm 0.12$ , $M_J^{\rm TRGB}= -5.20 \pm 0.16$ , $M_H^{\rm TRGB}= -5.94 \pm 0.18$ and $M_K^{\rm TRGB}= -6.04 \pm 0.16$ at $[M/H]\simeq-1.5$ ( $\omega$ Cen) and $M_I^{\rm TRGB}= -3.91 \pm 0.13$ , $M_J^{\rm TRGB}= -5.47 \pm 0.25$ , $M_H^{\rm TRGB}= -6.35 \pm 0.30$ and $M_K^{\rm TRGB}= -6.56 \pm 0.20$ at $[M/H]\simeq-0.6$ (47 Tuc).

With these new empirical calibrations we also provide robust relations of the TRGB magnitude in the I, J, H, and K bands as a function of the global metallicity. It has also been shown that our calibrations self-consistently provide a distance modulus of the Large Magellanic Cloud in good agreement with the standard value ( $(m-M)_0\simeq 18.50$ )).

Key words: distance scale -- globular clusters: individual: NGC 5139; NGC 104 -- stars: Population II -- Magellanic Clouds

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