On circumstellar disks: Spitzer identifies two possible evolutionary paths

Paula S. Teixeira1*, Charles J. Lada2, Massimo Marengo2, and Elizabeth Lada3
1European Southern Observatory, Karl-Schwarzschild-Str.2, D-85748 Garching, Germany
2Harvard-Smithsonian Center for Astrophysics, 60 Garden Street M.S. 72, MA 02138 USA
3Department of Astronomy, University of Florida, Gainesville, FL 32611-2055, USA

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Multi-wavelength surveys have vastly improved our understanding of many astrophysical objects, in particular, circumstellar disks. We present our results for the disk population of the young cluster NGC2264. Our study was based on data obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer on board the Spitzer Space Telescope combined with previously published optical data. We divide the disk population into 3 classes based on their spectral energy distribution shapes: optically thick disks, homologously depleted anemic disks, and radially depleted transition disks. We find that there are two distinct evolutionary paths for disks: a homologous one, where the disk emission decreases uniformly in NIR and mid-infrared wavelengths (anemic disks) and throughout which most sources pass, and a radially differential one where the emission from the inner region of the disk decreases more rapidly than from the outer region (transition disks). Whether a disk evolves in a homologously or radially depleted fashion is still unknown and may depend on the nature of planet formation in the disk.

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Keywords : methods: observational - infrared: stars - stars: formation - (stars:) circumstellar matter - (stars:) planetary systems: protoplanetary discs