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Observing Carbon and Oxygen Carriers in Protoplanetary Disks at Mid-infrared Wavelengths

Anderson, Dana E. and Blake, Geoffrey A. and Cleeves, L. Ilsedore and Bergin, Edwin A. and Zhang, Ke and Schwarz, Kamber R. and Salyk, Colette and Bosman, Arthur D. (2021) Observing Carbon and Oxygen Carriers in Protoplanetary Disks at Mid-infrared Wavelengths. Astrophysical Journal, 909 (1). Art. No. 55. ISSN 0004-637X. doi:10.3847/1538-4357/abd9c1.

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Infrared observations probe the warm gas in the inner regions of planet-forming disks around young Sun-like T Tauri stars. In these systems, H₂O, OH, CO, CO₂, C₂H₂, and HCN have been widely observed. However, the potentially abundant carbon carrier CH₄ remains largely unconstrained. The James Webb Space Telescope (JWST) will be able to characterize mid-infrared fluxes of CH₄ along with several other carriers of carbon and oxygen. In anticipation of the JWST mission, we model the physical and chemical structure of a T Tauri disk to predict the abundances and mid-infrared fluxes of observable molecules. A range of compositional scenarios are explored involving the destruction of refractory carbon materials and alterations to the total elemental (volatile and refractory) C/O ratio. Photon-driven chemistry in the inner disk surface layers largely destroys the initial carbon and oxygen carriers. This causes models with the same physical structure and C/O ratio to have similar steady-state surface compositions, regardless of the initial chemical abundances. Initial disk compositions are better preserved in the shielded inner disk midplane. The degree of similarity between the surface and midplane compositions in the inner disk will depend on the characteristics of vertical mixing at these radii. Our modeled fluxes of observable molecules respond sensitively to changes in the disk gas temperature, inner radius, and total elemental C/O ratio. As a result, mid-infrared observations of disks will be useful probes of these fundamental disk parameters, including the C/O ratio, which can be compared to values determined for planetary atmospheres.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Anderson, Dana E.0000-0002-8310-0554
Blake, Geoffrey A.0000-0003-0787-1610
Cleeves, L. Ilsedore0000-0003-2076-8001
Bergin, Edwin A.0000-0003-4179-6394
Zhang, Ke0000-0002-0661-7517
Schwarz, Kamber R.0000-0002-6429-9457
Salyk, Colette0000-0003-3682-6632
Bosman, Arthur D.0000-0003-4001-3589
Alternate Title:Observing Carbon & Oxygen Carriers in Protoplanetary Disks at Mid-infrared Wavelengths
Additional Information:© 2021. The American Astronomical Society. Received 2020 November 7; revised 2021 January 4; accepted 2021 January 6; published 2021 March 4. The authors thank the anonymous reviewer for providing helpful suggestions. D.E.A. acknowledges support from the Virginia Initiative on Cosmic Origins (VICO) Postdoctoral Fellowship. L.I.C. gratefully acknowledges support from the David and Lucile Packard Foundation, the Virginia Space Grant Consortium, Johnson & Johnson's WiSTEM2D Award, and NSF AAG grant No. AST-1910106. G.A.B. acknowledges support from the NASA XRP program (NNX16AB48G). Software: Astropy (Astropy Collaboration et al. 2013; Price-Whelan et al. 2018), Matplotlib (Hunter 2007), Numpy (van der Walt et al. 2011), Pandas (Reback et al. 2021), parallel (Tange 2018), slabspec (Salyk 2020).
Funding AgencyGrant Number
Virginia Initiative on Cosmic Origins (VICO)UNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Virginia Space Grant ConsortiumUNSPECIFIED
Johnson and JohnsonUNSPECIFIED
Subject Keywords:Astrochemistry; Protoplanetary disks
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Astrochemistry (75); Protoplanetary disks (1300)
Record Number:CaltechAUTHORS:20210308-084803380
Persistent URL:
Official Citation:Dana E. Anderson et al 2021 ApJ 909 55
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108337
Deposited By: Tony Diaz
Deposited On:08 Mar 2021 20:51
Last Modified:16 Nov 2021 19:11

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