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The Unique Passage of Comet C/2020 F3 (NEOWISE): Deep Investigations of its Organic and Isotopic Composition as Revealed by iSHELL at NASA/IRTF

Presentation #111.01 in the session “Comet Comae: C/2020 F3 (NEOWISE)”.

Published onOct 26, 2020
The Unique Passage of Comet C/2020 F3 (NEOWISE): Deep Investigations of its Organic and Isotopic Composition as Revealed by iSHELL at NASA/IRTF

In July 2020, we acquired comprehensive high-resolution spectra of Oort cloud comet C/2020 F3 (NEOWISE) right after its perihelion that occurred on 3 July 2020. Daytime observations, as part of an awarded DDT observing campaign targeting three Oort Cloud comets, were conducted using iSHELL — the near-IR high resolution immersion echelle spectrograph on NASA/IRTF (Mauna Kea, Hawaii). Comet C/2020 F3 (NEOWISE) was observed on 8 July (Rh = 0.34 au), on 13, 19, 30 and 31 July 2020 (Rh = 0.83 au), as it moved from perihelion on July 3rd (Rh = 0.29 au). Many cometary emission lines were detected across the four customized instrument settings (L1, Lp1, Lp2 and M1), covering the 1–5 μm wavelength range. A plethora of water emission lines detected in settings L1-custom and M1 provided an exceptional opportunity to retrieve accurate measures of independent rotational temperatures for ortho- and para-H2O, thereby reducing systematic uncertainty in the derived ortho-para ratio and nuclear spin temperature. We also conducted a deep search for mono-deuterated water (HDO) in setting Lp2, leading to isotopic D/H characterization; results will be presented. Fluorescent emissions from CO, OCS, HCN, C2H2, NH3, NH2, H2CO, CH4, C2H6 and CH3OH were detected. These species are relevant to astrobiology, owing to questions regarding the origin of pre-biotic organics and water on terrestrial planets. The brightness of comet F3 (NEOWISE) combined with the extraordinary capabilities of iSHELL provided unique results. The individual iSHELL settings cover very wide spectral range with very high accuracy, eliminating many sources of systematic errors when retrieving molecular abundances; future comparisons amongst comets will clarify the nature and meaning of cosmogonic indicators derived from chemical and isotopic compositions.


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