Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sf2a.conf..519o&link_type=abstract
"SF2A-2008: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics Eds.: C. Charbonnel, F. Combes
Astronomy and Astrophysics
Astrophysics
Scientific paper
Silicates are observed in almost every place where dust can survive: in the interstellar medium (ISM), in the Earth mantle, in comets and it is now common knowledge that there are also present in circumstellar disks around young stars. The ISM sub-micron sized silicates are highly amorphous (>99%), while the silicate Mg-rich crystallinity fraction can reach 60% in comets like Hale-Bopp in the Solar System. The silicates have to be exposed to high temperatures to crystallize, and their presence in long-period comets suggests that dust has been heavily processed and transported in the disk. Statistical studies of planet forming disks are keys on understanding if these processes are generic and can occur in other protoplanetary systems. 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 μm, where many crystalline features are present. We find that most of these objects (˜ 70%) show silicate emission features, either attributed to amorphous or crystalline grains. Studying the 10 μm feature, we find that grain growth has occured and their quasi-systematic presence in the disks upper layers indicate ongoing turbulent vertical mixing. We will also show that crystalline dust grains are present in the outer/deeper cold regions of the disk, with typical temperatures of about 100 K, which suggests efficient radial transport mechanisms. Overall, our study shows that vertical and radial transport seem to be generic dynamical processes in disks, challenging theoretical disk evolution and planet formation models.
Augereau J.-Ch.
C2d Irs Team
Monin Jean-Louis
Olofsson Johan
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