Testing circumstellar disk lifetimes in young embedded clusters associated with the Vela Molecular Ridge^*

¹ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy e-mail: [fmassi;codella]@arcetri.astro.it
² INAF - Osservatorio Astronomico di Collurania-Teramo, via M. Maggini, 64100 Teramo, Italy e-mail: dicarlo@oa-teramo.inaf.it
³ European Southern Observatory, Karl Schwarzschild str. 2, 85748 Garching, Germany e-mail: ltesti@eso.org
⁴ Departamento de Ingeniera Electrica, Pontificia Universidad Catolica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile e-mail: lvanzi@ing.puc.cl
⁵ Centro de Astronomia e Astrofisica da Universidade de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
⁶ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Hertfordshire, AL10 9AB, UK e-mail: j.gomes@herts.ac.uk

Received: 14 November 2009
Accepted: 23 February 2010

Abstract

Context. The Vela Molecular Ridge hosts a number of young embedded star clusters at the same evolutionary stage.

Aims. We test whether the fraction of members with a circumstellar disk in a sample of clusters in the cloud D of the Vela Molecular Ridge, is consistent with relations derived for larger samples of star clusters with an age spread. In addition, we constrain the age of the young embedded star clusters associated with cloud D.

Methods. We carried out L (3.78 μm) photometry using images of six young embedded star clusters associated with cloud D of the Vela Molecular Ridge, taken with ISAAC at the VLT. These data are complemented with the available HK_s photometry. The 6 clusters are of roughly the same size and appear to be at the same evolutionary stage. The fraction of stars with a circumstellar disk was measured in each cluster by counting the fraction of sources found to have a NIR excess in colour-colour (HK_sL) diagrams.

Results. The L photometry allowed us to identify the NIR counterparts of the IRAS sources associated with the clusters. The fraction of stars with a circumstellar disk appears to be constant within the errors for the 6 clusters. There is a hint that this is lower for the most massive stars. The age of the clusters is constrained to be 1–2 Myr.

Conclusions. The fraction of stars with a circumstellar disk in the observed sample is consistent with the relations derived from larger samples of star clusters and with other age estimates for cloud D. The fraction may be lower for the most massive stars. Our results agree with a scenario where all intermediate and low-mass stars form with a disk, whose lifetime is shorter for higher mass stars.