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
Item Type: | Article |
---|---|
Authors/Creators: |
|
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 |
Dates: |
|
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) |
Funding Information: | Funder Grant number Science & Technology Facilities Council (STFC) ST/R000549/1 |
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: | 10.3847/1538-4357/ab05d8 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:142879 |