Pontoppidan, KM, Salyk, C, Banzatti, A et al. (4 more authors) (2019) The nitrogen carrier in inner protoplanetary disks. Astrophysical Journal, 874 (1). 92. ISSN 0004-637X
Abstract
The dominant reservoirs of elemental nitrogen in protoplanetary disks have not yet been observationally identified. Likely candidates are HCN, NH₃ and N₂. 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 exo-planets. While HCN has been detected in small amounts in inner disks (<10 au), so far only relatively insensitive upper limits on inner disk NH₃ have been obtained. We present new Gemini-TEXES high resolution spectroscopy of the 10.75 μm band of warm NH₃, and use 2-dimensional radiative transfer modeling to improve previous upper limits by an order of magnitude to [NH₃/Hnuc]<10−7 at 1 au. These NH₃ abundances are significantly lower than those typical for ices in circumstellar envelopes ([NH₃/Hnuc]∼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 ([HCNice]/[H₂Oice]<1.5−9\%). We identify the NH₃/HCN ratio as an indicator of chemical evolution in the disk, and use this ratio to suggest that inner disk nitrogen is efficiently converted from NH₃ to N₂, significantly increasing the volatility of nitrogen in planet-forming regions.
Metadata
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Copyright, Publisher and Additional Information: | © 2019. The American Astronomical Society. All rights reserved. Uploaded in accordance with the publisher's self-archiving policy. | ||||
Keywords: | ISM: molecules – planets and satellites: composition – planets and satellites: formation – protoplanetary disks | ||||
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Institution: | The University of Leeds | ||||
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Physics and Astronomy (Leeds) > Astrophysics (Leeds) | ||||
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Depositing User: | Symplectic Publications | ||||
Date Deposited: | 22 Feb 2019 16:32 | ||||
Last Modified: | 11 Apr 2019 09:44 | ||||
Status: | Published | ||||
Publisher: | Institute of Physics Publishing | ||||
Identification Number: | https://doi.org/10.3847/1538-4357/ab05d8 | ||||
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