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First Detection of Near-infrared Line Emission from Organics in Young Circumstellar Disks

Mandell, Avi M. and Bast, Jeanette and van Dishoeck, Ewine F. and Blake, Geoffrey A. and Salyk, Colette and Mumma, Michael J. and Villanueva, Geronimo (2012) First Detection of Near-infrared Line Emission from Organics in Young Circumstellar Disks. Astrophysical Journal, 747 (2). Art. No. 92. ISSN 0004-637X. doi:10.1088/0004-637X/747/2/92.

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We present an analysis of high-resolution spectroscopy of several bright T Tauri stars using the CRIRES spectrograph on the Very Large Telescope and NIRSPEC spectrograph on the Keck Telescope, revealing the first detections of emission from HCN and C_2H_2 in circumstellar disks at near-infrared wavelengths. Using advanced data reduction techniques, we achieve a dynamic range with respect to the disk continuum of ~500 at 3 μm, revealing multiple emission features of H_2O, OH, HCN, and C_2H_2. We also present stringent upper limits for two other molecules thought to be abundant in the inner disk, CH_4 and NH_3. Line profiles for the different detected molecules are broad but centrally peaked in most cases, even for disks with previously determined inclinations of greater than 20°, suggesting that the emission has both a Keplerian and non-Keplerian component as observed previously for CO emission. We apply two different modeling strategies to constrain the molecular abundances and temperatures: we use a simplified single-temperature local thermal equilibrium (LTE) slab model with a Gaussian line profile to make line identifications and determine a best-fit temperature and initial abundance ratios, and we compare these values with constraints derived from a detailed disk radiative transfer model assuming LTE excitation but utilizing a realistic temperature and density structure. Abundance ratios from both sets of models are consistent with each other and consistent with expected values from theoretical chemical models, and analysis of the line shapes suggests that the molecular emission originates from within a narrow region in the inner disk (R < 1 AU).

Item Type:Article
Related URLs:
URLURL TypeDescription
Mandell, Avi M.0000-0002-8119-3355
van Dishoeck, Ewine F.0000-0001-7591-1907
Blake, Geoffrey A.0000-0003-0787-1610
Salyk, Colette0000-0003-3682-6632
Additional Information:© 2012 American Astronomical Society. Received 2011 September 30; accepted 2012 January 1; published 2012 February 17. Based partially on observations collected at the European Southern Observatory Very Large Telescope under program ID 179.C-0151, program ID 283.C-5016, and program ID 082.C-0432 (P.I.: Pontopiddan). A.M.M. is supported by the Goddard Center for Astrobiology. J.E.B. is supported by grant 614.000.605 from Netherlands Organization of Scientific Research (NWO). E.v.D. acknowledges support from an NWO Spinoza Grant and from Netherlands Research School for Astronomy (NOVA). The authors are very grateful to Klaus Pontoppidan for his central role in the CRIRES observations and for making his RADLite program available. They also thank Daniel Harsono for help with the disk modeling, and the anonymous referee for helpful suggestions for improving the manuscript. This research made use of the ESO/ST-ECF Science Archive Facility. Some of the results herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
Funding AgencyGrant Number
Goddard Center for AstrobiologyUNSPECIFIED
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)614.000.605
Nederlandse Onderzoekschool voor de Astronomie (NOVA)UNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords: line: profiles; planets and satellites: formation; protoplanetary disks; stars: low-mass
Issue or Number:2
Record Number:CaltechAUTHORS:20120515-070249087
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Official Citation: First Detection of Near-infrared Line Emission from Organics in Young Circumstellar Disks Avi M. Mandell et al. 2012 ApJ 747 92
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:31458
Deposited By: Ruth Sustaita
Deposited On:15 May 2012 15:14
Last Modified:09 Nov 2021 19:53

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