Non-LTE Modeling of Infrared Molecular Line Emission From Protoplanetary Disks: Evidence for Dust Settling

Details Non-LTE Modeling of Infrared Molecular Line Emission From Protoplanetary Disks: Evidence for Dust Settling Non-LTE Modeling of Infrared Molecular Line Emission From Protoplanetary Disks: Evidence for Dust Settling

Jan 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21542810l&link_type=abstract

American Astronomical Society, AAS Meeting #215, #428.10; Bulletin of the American Astronomical Society, Vol. 42, p.346

Astronomy and Astrophysics

Astronomy

1

Scientific paper

Spitzer IRS spectra of disks around T Tauri stars show emission in the 13.9 and 13.7 um Q branches of HCN and C2H2 (Carr & Najita, 2008). In order to explain these emission features, we made a non-LTE radiative transfer and excitation model of molecular gas and dust in disks. The model assumes the molecules are in rotational LTE, but it includes both radiative and collisional excitation of the vibrational states. We found that the strengths of the emission features are most sensitive to dust settling and/or grain growth, which moves the mid-IR dust photosphere to a larger gas density and column density, where vibrational states can be efficiently collisionally excited. Good fits were obtained by assuming that the dust scale height is 1/2 of the hydrostatic equilibrium gas scale height. To test this explanation, we compared the observed emission strengths with SED indices which are thought to be indicators of dust settling. A good correlation was found, supporting our model and the interpretation of the SEDs.
This work was supported by NSF grant AST-0607312.

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