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Astron. Astrophys. 336, L77-L80 (1998)

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Letter to the Editor

Theoretical vs. semi-empirical relative ages of globular clusters

L. Pulone 1, 2, M. Salaris 3, 4, A. Weiss 3 and R. Buonanno 1

1 Osservatorio Astronomico di Roma, Via dell'Osservatorio 2, I-00040 Monte Porzio Catone (Roma), Italy
2 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
3 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, D-85748 Garching, Germany
4 Astrophysics Research Institute, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK

Received 14 May 1998 / Accepted 7 July 1998


Theoretical relative ages of galactic globular clusters have recently been challenged by a semi-empirical relation. It was used to point out that tested sets of isochrones were unable to reproduce the relation and yield internally inconsistent relative ages. We find that differential cluster ages derived with the isochrones by Salaris & Weiss (1998) are reliable and internally consistent. We also show that this consistency depends on using the lower absolute ages determined by SW98, which therefore receive more empirical support. Moreover, we discuss the effect of the clusters absolute age on the evaluation of their differential ages, and its connection with the question of their age dispersion.

Key words: stars: evolution – population II – galaxy: evolution – globular clusters: general

Send offprint requests to: L. Pulone
Correspondence to: L. Pulone

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© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998