EDP Sciences
Free access
Issue
A&A
Volume 414, Number 1, January IV 2004
Page(s) 163 - 174
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20031578


A&A 414, 163-174 (2004)
DOI: 10.1051/0004-6361:20031578

The age of the oldest Open Clusters

M. Salaris1, 2, A. Weiss2 and S. M. Percival1

1  Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD, UK
    e-mail: smp@astro.livjm.ac.uk
2  Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85758, Garching, Germany
    e-mail: weiss@mpa-garching.mpg.de

(Received 15 August 2003 / Accepted 2 October 2003 )

Abstract
We determine ages of 71 old Open Clusters by a two-step method: we use main-squence fitting to 10 selected clusters, in order to obtain their distances, and derive their ages from comparison with our own isochrones used before for Globular Clusters. We then calibrate the morphological age indicator $\delta(V)$, which can be obtained for all remaining clusters, in terms of age and metallicity. Particular care is taken to ensure consistency in the whole procedure. The resulting Open Cluster ages connect well to our previous Globular Cluster results. From the Open Cluster sample, as well as from the combined sample, questions regarding the formation process of Galactic components are addressed. The age of the oldest open clusters (NGC 6791 and Be 17) is of the order of 10 Gyr. We determine a delay by $2.0\pm1.5$ Gyr between the start of the halo and thin disk formation, whereas thin and thick disk started to form approximately at the same time. We do not find any significant age-metallicity relationship for the open cluster sample. The cumulative age distribution of the whole open cluster sample shows a moderately significant ( ${\sim}
2\sigma$ level) departure from the predictions for an exponentially declining dissolution rate with timescale of 2.5 Gyr. The cumulative age distribution does not show any trend with galactocentric distance, but the clusters with larger height to the Galactic plane have an excess of objects between 2-4 and 6 Gyr with respect to their counterpart closer to the plane of the Galaxy.


Key words: Galaxy: disk -- evolution -- open clusters and associations: general -- stellar content

Offprint request: M. Salaris, ms@astro.livjm.ac.uk

SIMBAD Objects



© ESO 2004

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.