Coagulation and Crystallization of Silicates in Protoplanetary Disks: a c2d Spitzer/IRS Survey


First Author:
Johan Olofsson
Email: olofsson AT obs.ujf-grenoble.fr
LAOG, France
414 rue de la Piscine
38400 - St Martin d'Heres, France
Coauthors:
Augereau, J.-C., LAOG, France
van Dishoeck, E. F., Leiden Observatory, Netherlands
Merín, B., HErschel Science Center, ESA Madrid
Lahuis, F., Space Research Organisation, Netherlands
Dullemond, C. P., MPIA, Heidelberg
Oliveira, I., Leiden Observatory, Netherlands
Blake, G., GPS, Caltech, California
Boogert, A., IPAC, Caltech, California
Brown, J., MPIE, Garching
Evans, N., University of Texas, Austin
Geers, V., Department of AStronomy and Astrophysics, Toronto
Knez, C., Department of AStronomy, Maryland
Monin, J.-L., LAOG, France
Pontoppidan, K., GPS, Caltech, California

Abstract
As part of the Cores to Disks (c2d) Legacy Program, we obtained more than a hundred of Spitzer/IRS spectra of T Tauri stars, in the spectral range 5-35 um where many silicate amorphous and crystalline solid-state features are present. Most of our objects show silicate emission features which allows both a classical study of grain coagulation and an unprecedented statistical analysis of dust crystallization in the planet forming regions in disks around young solar analogs. Analysis of the 10 micron feature indicates that grain growth has occured. Interestingly, the quasi-systematic presence of micron-sized grains in upper disks layers, from where they should have settled out on short time-scales, means that vertical mixing is active. Crystalline silicates appear to be very frequent in disks around TTauri disks and in regions much colder than their presumed formation regions, suggesting efficient outward radial transport mechanisms in disks. Their energy and the frequencies at which they are seen at wavelengths larger than 20 microns are found to be largely uncorrelated to the amorphous 10 micron feature observational properties. This provides support to our proposed compositional fitting approach to the full IRS spectral range to derive the mass fractions of crystalline and large grains in regions of different temperature in the disk. Overall, our study shows that vertical and radial transport seem to be generic dynamical processes in disks, that challenge theoretical disk evolution and planet formation models.
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