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The Nitrogen Carrier in Inner Protoplanetary Disks

Pontoppidan, Klaus M. and Salyk, Colette and Banzatti, Andrea and Blake, Geoffrey A. and Walsh, Catherine and Lacy, John H. and Richter, Matthew J. (2019) The Nitrogen Carrier in Inner Protoplanetary Disks. Astrophysical Journal, 874 (1). Art. No. 92. ISSN 1538-4357. doi:10.3847/1538-4357/ab05d8.

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The dominant reservoirs of elemental nitrogen in protoplanetary disks have not yet been observationally identified. Likely candidates are HCN, NH_3, and N_2. The relative abundances of these carriers determine the composition of planetesimals as a function of disk radius due to strong differences in their volatility. A significant sequestration of nitrogen in carriers less volatile than N2 is likely required to deliver even small amounts of nitrogen to the Earth and potentially habitable exoplanets. While HCN has been detected in small amounts in inner disks (<10 au), so far only relatively insensitive upper limits on inner disk NH_3 have been obtained. We present new Gemini-TEXES high-resolution spectroscopy of the 10.75 μm band of warm NH_3, and use two-dimensional radiative transfer modeling to improve previous upper limits by an order of magnitude to [NH_3/H_(nuc)] < 10^(−7) at 1 au. These NH_3 abundances are significantly lower than those typical for ices in circumstellar envelopes ([NH_3/H_(nuc)]∼3×10^(−6)). We also consistently retrieve the inner disk HCN gas abundances using archival Spitzer spectra, and derive upper limits on the HCN ice abundance in protostellar envelopes using archival ground-based 4.7 μm spectroscopy ([HCN_(ice)]/[H_2O_(ice)] < 1.5%–9%). We identify the NH_3/HCN ratio as an indicator of chemical evolution in the disk, and we use this ratio to suggest that inner disk nitrogen is efficiently converted from NH_3 to N_2, significantly increasing the volatility of nitrogen in planet-forming regions.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Pontoppidan, Klaus M.0000-0001-7552-1562
Salyk, Colette0000-0003-3682-6632
Banzatti, Andrea0000-0003-4335-0900
Blake, Geoffrey A.0000-0003-0787-1610
Walsh, Catherine0000-0001-6078-786X
Lacy, John H.0000-0001-6783-2328
Richter, Matthew J.0000-0002-8594-2122
Additional Information:© 2019 The American Astronomical Society. Received 2018 October 7; revised 2019 February 8; accepted 2019 February 9; published 2019 March 27. We are grateful to the referee for a constructive report that helped to clarify the paper. K.M.P. and A.B. acknowledge financial support by a NASA Origins of the solar system grant No. OSS 11-OSS11-0120, a NASA Planetary Geology and Geophysics Program under grant NAG 5-10201. This work is based in part on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnologa e Innovacin Productiva (Argentina), and Ministrio da Cincia, Tecnologia e Inovao (Brazil). This work is also based in part on observations obtained at the European Southern Observatory, Paranal, Chile, within the observing program 164.I-0605. This work is also based in part 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. C.W. acknowledges support from the University of Leeds and the Science and Technology Facilities Council (grant No. ST/R000549/1). This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration, 2018). This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Facilities: Gemini - , VLT - , Spitzer - .
Group:Astronomy Department
Funding AgencyGrant Number
NASAOSS 11-OSS11-0120
NASANAG 5-10201
Association of Universities for Research in Astronomy (AURA)UNSPECIFIED
Gemini PartnershipUNSPECIFIED
University of LeedsUNSPECIFIED
Science and Technology Facilities Council (STFC)ST/R000549/1
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:ISM: molecules – planets and satellites: composition – planets and satellites: formation – protoplanetary disks
Issue or Number:1
Record Number:CaltechAUTHORS:20190327-102302441
Persistent URL:
Official Citation:Klaus M. Pontoppidan et al 2019 ApJ 874 92
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:94208
Deposited By: Tony Diaz
Deposited On:27 Mar 2019 17:51
Last Modified:16 Nov 2021 17:03

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