Astronomy & Astrophysics

Free access article

Issue		A&A Volume 399, Number 2, February IV 2003
Page(s)		773 - 787
Section		The Sun
DOI		10.1051/0004-6361:20021638

A&A 399, 773-787 (2003)
DOI: 10.1051/0004-6361:20021638

Structure of the DM Tau Outer Disk: Probing the vertical kinetic temperature gradient

E. Dartois¹, A. Dutrey² and S. Guilloteau³

¹ Institut d'Astrophysique Spatiale, UMR 8617, Bât. 121, Campus Paris XI, 91405 Orsay, France
² Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France
³ Institut de Radio Astronomie Millimétrique, 300 Rue de la Piscine, 38406 Saint Martin d'Hères, France

(Received 20 August 2002 / Accepted 6 November 2002 )

Abstract
We use high angular and spectral resolution ( ${\sim} 1''$ & 0.1 km s ^-1) images in $^{\rm CO}$ , $^{\rm CO}$ $J=2\!\rightarrow\! 1$ , $J=1\!\rightarrow\! 0$ and ${\rm C}^{\rm O}$ $J=2\!\rightarrow\! 1$ coming from the IRAM interferometer to probe the vertical temperature distribution in the disk of DM Tau. We investigate here a new method based on the different opacities of the CO isotopomers to sample the temperature disk structure at various vertical scales inside the disk. Typically, the $^{\rm CO}$ transitions are sampling at 2-4 scale heights, while the $^{\rm CO}$ data are more likely tracing 1 scale height for the J=2-1, and the disk mid-plane for the J=1-0 line. At the disk scale at which the IRAM observations are sensitive ( $R\geq 50$ -60 AU), the analysis reveals a vertical temperature gradient. The outer layers where $\tau$ ( $^{\rm CO}$ $J=2\!\rightarrow\! 1$ $) \simeq 1$ are warmer ( ${\sim} 30$ K) than the inner layers probed by $^{\rm CO}$ and ${\rm C}^{\rm O}$ data ( ${\sim} 13$ -20 K). These findings are consistent with the structure expected for flared irradiated disks around TTauri stars. We also observe that the outer radius of the disk is smaller in $^{\rm CO}$ and ${\rm C}^{\rm O}$ than in $^{\rm CO}$ . These differences in truncation radius are in agreement with photodissociation effects. We also note that the dynamical mass determination from CO is weakly affected by the temperature gradient.

Key words: stars: individual: DM Tauri -- stars: circumstellar matter -- stars: pre-main sequence -- radio-lines: stars

Offprint request: E. Dartois, emmanuel.dartois@ias.u-psud.fr

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