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A Spitzer Survey of Mid-infrared Molecular Emission from Protoplanetary Disks. I. Detection Rates

Pontoppidan, Klaus M. and Salyk, Colette and Blake, Geoffrey A. and Meijerink, Rowin and Carr, John S. and Najita, Joan (2010) A Spitzer Survey of Mid-infrared Molecular Emission from Protoplanetary Disks. I. Detection Rates. Astrophysical Journal, 720 (1). pp. 887-903. ISSN 0004-637X.

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We present a Spitzer InfraRed Spectrometer search for 10-36 μm molecular emission from a large sample of protoplanetary disks, including lines from H_(2)O, OH, C_(2)H_2, HCN, and CO2. This paper describes the sample and data processing and derives the detection rate of mid-infrared molecular emission as a function of stellar mass. The sample covers a range of spectral type from early M to A, and is supplemented by archival spectra of disks around A and B stars. It is drawn from a variety of nearby star-forming regions, including Ophiuchus, Lupus, and Chamaeleon. Spectra showing strong emission lines are used to identify which lines are the best tracers of various physical and chemical conditions within the disks. In total, we identify 22 T Tauri stars with strong mid-infrared H2O emission. Integrated water line luminosities, where water vapor is detected, range from 5 × 10^(–4) to 9 × 10^(–3) L_☉ sun, likely making water the dominant line coolant of inner disk surfaces in classical T Tauri stars. None of the five transitional disks in the sample show detectable gaseous molecular emission with Spitzer upper limits at the 1% level in terms of line-to-continuum ratios (apart from H_2), but the sample is too small to conclude whether this is a general property of transitional disks. We find a strong dependence on detection rate with spectral type; no disks around our sample of 25 A and B stars were found to exhibit water emission, down to 1%-2% line-to-continuum ratios, in the mid-infrared, while more than half of disks around late-type stars (M-G) show sufficiently intense water emission to be detected by Spitzer, with a detection rate approaching 2/3 for disks around K stars. Some Herbig Ae/Be stars show tentative H_(2)O/OH emission features beyond 20 μm at the 1%-2% level, however, and one of them shows CO_2 in emission. We argue that the observed differences between T Tauri disks and Herbig Ae/Be disks are due to a difference in excitation and/or chemistry depending on spectral type and suggest that photochemistry may be playing an important role in the observable characteristics of mid-infrared molecular line emission from protoplanetary disks.

Item Type:Article
Related URLs:
URLURL TypeDescription
Pontoppidan, Klaus M.0000-0001-7552-1562
Salyk, Colette0000-0003-3682-6632
Blake, Geoffrey A.0000-0003-0787-1610
Carr, John S.0000-0002-6695-3977
Additional Information:© 2010 American Astronomical Society. Received 2010 March 30; accepted 2010 June 21; published 2010 August 13. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA. Support for K.M.P. was provided by NASA through Hubble Fellowship grant no. 01201.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. Research support for J.S.C. was also provided by 6.1 base funding at the Naval Research Laboratory. The authors acknowledge valuable discussions with Uma Gorti, Ilaria Pascucci, and Ewine van Dishoeck.
Funding AgencyGrant Number
NASANAS 5-26555
Space Telescope Science Institute01201.01
Naval Research Laboratory6.1 base funding
Subject Keywords:astrochemistry; protoplanetary disks; stars: pre-main sequence
Issue or Number:1
Classification Code:PACS: 97.21.+a; 98.38.Dq; 97.20.Jg; 95.85.Jq; 97.20.Ge; 97.10.Fy
Record Number:CaltechAUTHORS:20100927-105452689
Persistent URL:
Official Citation:Klaus M. Pontoppidan et al 2010 ApJ 720 887 doi: 10.1088/0004-637X/720/1/887
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20162
Deposited By: Jason Perez
Deposited On:27 Sep 2010 23:23
Last Modified:09 Dec 2019 21:59

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