AAS 202nd Meeting, May 2003
Session 24 When Do Planets Form?
Topical Oral, Tuesday, May 27, 2003, 8:30-10:00am and 10:45am-12:30pm, 204

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[24.06] Evolution of Circumstellar Disks in Young Stellar Clusters

E.A. Lada (University of Flordia)

Knowledge of the frequency and mass distributions of cicumstellar disks in clusters is key to understanding the processes involved in the formation and evolution of circumstellar disks and any planetary systems. For example, in the youngest clusters, determination of the disk frequency is a measure of the probability of disk formation around newly formed stars. In addition, the investigation of the variation of disk frequency and disk mass with cluster age provide a direct measure of the lifetimes of the disks and hence the duration for planet building. I will discuss the results of sensitive and homogeneous surveys in young stellar clusters. These surveys were conducted at both near-infrared (JHKL), and 1.3 mm continuum wavelengths and are sensitive to inner and outer disks respectively. Disks appear common in the youngest clusters. However, there is a clear variation in both the inner and outer disk fractions among the clusters studied. Comparison of the mm and NIR observations of the same clusters reveal that the variation in the fraction of detected millimeter sources from cluster to cluster is similar to the variation in the fraction of NIR excess sources for these clusters. This implies that the inner and the outer disks are coupled and that the decrease in these fractions is a result of evolution. Our NIR observations of clusters provide an estimate of the inner disk lifetime, t < 6Myr. Our mm observations imply an even shorter lifetime for massive planet forming disks of t< 3Myr. Comparison of the mm luminosity distributions among the clusters reveal that the most massive disks are not present in clusters with low disk fractions indicating that either all disks fade systematically or that the most massive disks evolve more rapidly in clusters. Finally, it appears that the cluster environments play a role in making circumstellar disk evolution very rapid. Since most stars in our Galaxy probably form in clusters, these results place important constraints on theories of planet formation.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.