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

摘要

Context. The Vela Molecular Ridge hosts a number ofyoung embedded star clusters at the same evolutionary stage. Aims. We test whether the fraction of members with acircumstellar disk in a sample of clusters in the cloud D of the VelaMolecular Ridge, is consistent with relations derived for largersamples of star clusters with an age spread. In addition, we constrainthe age of the young embedded star clusters associated with cloud D. Methods. We carried out L(3.78m)photometry using images of six young embedded star clusters associatedwith cloud D of the Vela Molecular Ridge, taken with ISAAC at the VLT.These data are complemented with the available photometry. The 6clusters are of roughly the same size andappear to be at the same evolutionary stage. The fraction of stars witha circumstellar disk was measured in each cluster by counting thefraction of sources found to have a NIR excess in colour-colour ()diagrams. Results. The L photometryallowed us to identify the NIR counterparts of the IRAS sourcesassociated with the clusters. The fraction of stars with acircumstellar disk appears to be constant within the errors for the 6clusters. There is a hint that this is lower for the most massivestars. The age of the clusters is constrained to be 1-2Myr.Conclusions. The fraction of stars with acircumstellar disk in the observed sample is consistent with therelations derived from larger samples of star clusters and with otherage estimates for cloud D. The fraction may be lower for the mostmassive stars. Our results agree with a scenario where all intermediateand low-mass stars form with a disk, whose lifetime is shorter forhigher mass stars. Key words: stars: formation - stars:pre-main sequence - stars: circumstellar matter - ISM: individualobjects: Vela Molecular Ridge- open clusters andassociations: general - infrared: ISM