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Astron. Astrophys. 358, 943-955 (2000)

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Comparison between observed and theoretical Red Giant Branch luminosity functions of galactic globular clusters *

M. Zoccali and G. Piotto

Dipartimento di Astronomia - Università di Padova, Padova, Italy (zoccali,piotto@pd.astro.it)

Received 25 January 2000 / Accepted 26 April 2000


V-band luminosity functions (LF) have been obtained for the upper main-sequence (MS), sub-giant branch (SGB) and red giant branch (RGB) of 18 galactic globular clusters (GGC) from HST data. A comparison with four sets of theoretical models has been performed. In contrast with what was found in several previous works, a good general agreement has been found between the observed and theoretical LF at any metallicity [M/H][FORMULA]. Possible discrepancies at higher metallicity, in the upper part of the RGB, need to be confirmed with further observational data and by extending all the models to the most metal rich regime. The SGB shape has been used to set an upper limit to the cluster age, and consequently a lower limit on the cluster distance. A discussion on the still open problem of the mismatch between the observed and theoretical RGB bump location is also presented.

Key words: stars: distances – stars: evolution – stars: luminosity function, mass function – stars: Population II – Galaxy: globular clusters: general

* Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555, and on observations retrieved from the ESO ST-ECF Archive.

Send offprint requests to: M. Zoccali (zoccali@pd.astro.it)

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© European Southern Observatory (ESO) 2000

Online publication: June 20, 2000