A cometary fluorescence model of cyanogen in the near-infrared
Notice bibliographique
Résumé
While the cyano radical (CN) is a well-known and prominent feature in cometary optical spectra, its origin remains poorly understood. In particular, although hydrogen cyanide (HCN) is considered the primary parent molecule of CN, it is not abundant enough to account for the observed amounts of the radical (Fray et al., 2005). As a result, cyanogen (C2N2) has been proposed as a secondary potential parent molecule.Among the major breakthroughs achieved by the Rosetta mission, the discovery of around 40 new molecular species—previously undetected in comets—by the ROSINA mass spectrometer has considerably improved our understanding of cometary chemical diversity. Cyanogen was among the most recently identified molecules in the coma of 67P (Hänni et al., 2021). Although the low derived mixing ratios suggest it is unlikely to produce CN in sufficient amounts on its own, further investigation of its abundance in other comets is essential to better constrain its potential role as a CN precursor and to improve our understanding of cometary chemistry.In this context, we investigated the presence of cyanogen in near-infrared cometary spectra. In the HITRAN database (Gordon et al., 2022), only the far-infrared ν5 band of C2N2 (Fayt et al., 2012) is currently included, and no spectroscopic data are available above 310 cm-1. Notably, one of the molecule's fundamental vibrational bands, ν3, centered at 2158 cm-1 (4.63 μm), has never been studied at high spectral resolution. This band is particularly interesting as it lies within the M-infrared atmospheric window, a region relatively free from atmospheric emission lines of H2O and CO2.We present here, for the first time, a high-resolution analysis of line positions and intensities in the ν3 band region of C2N2, based on laboratory infrared spectra. From this, we derived molecular parameters for both the ground and excited vibrational states using PGOPHER (Western, 2017).This spectroscopic analysis enabled the construction of the first line-by-line fluorescence model of cyanogen. Excitation rates for individual lines of the ν3 band in cometary comae are also presented (Fig. 1).Finally, we present an upper limit for the abundance of cyanogen in comet C/2022 E3 (ZTF), observed in 2023 with JWST (Milam et al., 2023). We discuss how future instruments such as METIS on the ELT could further improve this limit, or even allow a detection of cyanogen in a bright comet. Figure 1: Emission g-factors of C2N2 expressed in photons s-1 molecule-1 at T=50 K. This work is part of the COSMIC project (Computation and Spectroscopy of Molecules in the Infrared for Comets), funded by the EIPHI Graduate School. https://gradschool.eiphi.ubfc.fr/?p=3710 References Fayt A., Joly A., Benilan Y., Manceron L., Kwabia-Tchana F., Guillemin J.-C., 2012, Frequency and intensity analyses of the far infrared ν5 band system of cyanogen (C2N2) and applications to Titan, Journal of Quantitative Spectroscopy and Radiative Transfer 113, 1195-1219.Fray N., Bénilan Y., Cottin H., Gazeau M.-C., Crovisier J., 2005, The origin of the CN radical in comets: A review from observations and models. Planetary and Space Sciences 53(12), 1243–1262.Gordon I.E., Rothman L.S., Hargreaves R.J. et al., 2022, The HITRAN2020 molecular spectroscopic database, Journal of Quantitative Spectroscopy and Radiative Transfer 277.Hänni N., Altwegg K., Balsiger H. et al., 2021, Cyanogen, cyanoacetylene, and acetonitrile in comet 67P and their relation to the cyano radical, Astronomy And Astrophysics, 647.Milam S. N., Roth N. X., Villanueva G.L., Wong I., Kelley M. S. P., Bockelée-Morvan D., Hammel H. B., 2023, Asteroids, Comets, Meteors Conference 2023, LPI Contrib. No 2851.Western C.M., 2017, PGOPHER: A program for simulating rotational, vibrational and electronic spectra, Journal of Quantitative Spectroscopy and Radiative Transfer 186, 221-242.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,001 |
| Bibliométrie | 0,001 | 0,000 |
| Études des sciences et des technologies | 0,001 | 0,002 |
| Communication savante | 0,001 | 0,004 |
| Science ouverte | 0,003 | 0,001 |
| Intégrité de la recherche | 0,003 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,013 | 0,003 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».