Chronology of the halo globular cluster system formation
Received 28 February 1997 / Accepted 16 June 1997
Using up-to-date stellar models and isochrones we determine the age of 25 galactic halo clusters. The clusters are distributed into four groups according to metallicity. We measure the absolute age of a reference cluster in each group, and then find the relative ages of the other clusters relative to this one. This combination yields the most reliable results. We find that the oldest cluster group on average is Gyr or Gyr old, depending on whether we include Arp2 and Rup106. The average age of all clusters is about 10.5 Gyr. Questions concerning a common age for all clusters and a relation between metallicity and age are addressed. The groups of lower metallicity appear to be coeval, but our results indicate that globally the sample has an age spread, and age and metallicity are correlated but not with a simple linear relation.
Key words: Galaxy: formation - Galaxy: halo - globular clusters: general - stars: evolution
Send offprint requests to: M. Salaris (firstname.lastname@example.org)
© European Southern Observatory (ESO) 1997
Online publication: April 8, 1998