|Authors||C. Maraston1, M. Kissler-Patig2, J.P. Brodie3, P. Barmby4, J.P. Huchra4|
|Affiliation||1Universitäts-Sternwarte der Ludwig-Maximilians-Universität, Scheinerstr.~1, 81679 München, Germany|
2European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
3University of California Observatories / Lick Observatory, University of California, Santa Cruz, CA 95064, USA
4Havard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
|Accepted by||Astronomy and Astrophysics|
For the present analysis we present models for Simple Stellar Populations which include the contribution of the AGB stellar phase, calibrated with the young and intermediate age star clusters of the Magellanic Clouds. The comparison with the colour distribution of the NGC 7252 star clusters shows that they are indeed intermediate age clusters undergoing the AGB phase transition. The AGB phase transition is observed for the first time outside the Local Group.
Most of the studied clusters span the very narrow age range 300 -500 Myr, and likely have metallicities 0.5 - 1 ZO. A very important exception is the cluster W32, which has already completed its AGB epoch, its colours being consistent with an age of ~ 1 - 2 Gyr. This impacts on the duration of the merger-induced starburst.
The strengths of the magnesium and iron lines in the spectrum of the best observed cluster W3, and in the spectrum of the diffuse central light of NGC 7252, do not show an overabundance in alpha-elements, in contrast to the bulk stellar population of elliptical galaxies.