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c2d Spitzer IRS Spectra of Disks around T Tauri Stars. III. [Ne II], [Fe I], and H_2 Gas-Phase Lines

Lahuis, Fred and van Dishoeck, Ewine F. and Blake, Geoffrey A. and Evans, Neal J., II and Kessler-Silacci, Jacqueline E. and Pontoppidan, Klaus M. (2007) c2d Spitzer IRS Spectra of Disks around T Tauri Stars. III. [Ne II], [Fe I], and H_2 Gas-Phase Lines. Astrophysical Journal, 665 (1). pp. 492-511. ISSN 0004-637X.

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We present a survey of mid-infrared gas-phase lines toward a sample of 76 circumstellar disks around low-mass pre-main-sequence stars from the Spitzer "Cores to Disks" legacy program. We report the first detections of [Ne II] and [Fe I] toward classical T Tauri stars in ~20% and ~9% of our sources, respectively. The observed [Ne II] line fluxes and upper limits are consistent with [Ne II] excitation in an X-ray irradiated disk around stars with X-ray luminosities L_X = 10^(29)-10^(31) erg s^(-1). [Fe I] is detected at ~10^(-5) to 10^(-4) L_⊙, but no [S I] or [Fe II] is detected down to ~10^(-6) L_⊙. The [Fe I] detections indicate the presence of gas-rich disks with masses of ≳ 0.1 M_J. No H_2 0-0 S(0) and S(1) disk emission is detected, except for S(1) toward one source. These data give upper limits on the warm (T ~ 100-200 K) gas mass of a few Jovian masses, consistent with recent T Tauri disk models that include gas heating by stellar radiation. Compact disk emission of hot (T ≳ 500 K) gas is observed through the H_2 0-0 S(2) and/or S(3) lines toward ~8% of our sources. The line fluxes are, however, higher by more than an order of magnitude than those predicted by recent disk models, even when X-ray and excess UV radiation are included. The [Ne II]/H_2 0-0 S(2) ratios for these sources are similarly lower than predicted, consistent with the presence of an additional hot molecular gas component not included in current disk models. Oblique shocks of stellar winds interacting with the disk can explain many aspects of the hot gas emission but are inconsistent with the nondetection of [S I] and [Fe II] lines.

Item Type:Article
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URLURL TypeDescription
van Dishoeck, Ewine F.0000-0001-7591-1907
Blake, Geoffrey A.0000-0003-0787-1610
Evans, Neal J., II0000-0001-5175-1777
Pontoppidan, Klaus M.0000-0001-7552-1562
Additional Information:© 2007 The American Astronomical Society. Received 2007 March 6; accepted 2007 April 15. The authors would like to thank Jes Jørgensen for making the Spitzer IRAC mosaics and Hideko Nomura for communicating her latest disk model results. Astrochemistry in Leiden is supported by a NWO Spinoza grant and a NOVA grant. Support for this work, part of the Spitzer Legacy Science Program, was provided by NASA through contracts 1224608, 1230779, and 1256316 issued by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. We thank the Lorentz Center in Leiden for hosting several meetings that contributed to this paper.
Funding AgencyGrant Number
Subject Keywords:circumstellar matter; infrared : ISM; planetary systems : protoplanetary disks; stars : evolution; stars : low-mass, brown dwarfs; surveys
Issue or Number:1
Record Number:CaltechAUTHORS:20100924-135737154
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Official Citation:Fred Lahuis et al 2007 ApJ 665 492 doi: 10.1086/518931
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20130
Deposited By: Tony Diaz
Deposited On:24 Sep 2010 22:10
Last Modified:09 Dec 2019 21:33

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