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arXiv · 2507.21707

Ionic emissions and activity evolution in comet C/2020 F3 (NEOWISE): Insights from long-slit spectroscopy and photometry

K. Aravind·E. Jehin·S. Hmmidouch·M. Vander Donckt·S. Ganesh·P. Rousselot·P. Hardy·D. Sahu·J. Manfroid·Z. Benkhaldoun
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Abstract

Comet C/2020 F3 (NEOWISE) was the brightest comet in the northern hemisphere since C/1995 O1 (Hale-Bopp), providing a unique opportunity to study its composition and spatial distribution of emissions. We conducted narrow-band photometry and long-slit low-resolution spectroscopy to monitor the comet's activity and compositional evolution over several weeks post-perihelion. Narrow-band images (OH, NH, CN, C$_2$, C$_3$, BC, GC, RC) and broad-band images (B, V, Rc, Ic) were acquired with TRAPPIST-North between 22 July and 10 September 2020 to derive production rates, mixing ratios, and dust proxy (Af$\rho$). A long-slit spectrum obtained on 24 July 2020 with HFOSC on the 2-m HCT was used to analyse emission profiles along the sunward and anti-sunward directions. We report production rates and mixing ratios of OH, NH, CN, C$_2$, C$_3$, and NH$_2$, and derive the water production rate using forbidden oxygen line flux. Ionic emissions from N$_2^+$, CO$^+$, CO$_2^+$, and H$_2$O$^+$ were detected at 4$\times$10$^4$ to 1$\times$10$^5$ km from the nucleus in the tailward direction. The average N$_2^+$/CO$^+$ ratio was found to be (3.0 $\pm$ 1.0)$\times$10$^{-2}$, refined to (4.8 $\pm$ 2.4)$\times$10$^{-2}$ using fluorescence modeling. The CO$_2^+$/CO$^+$ ratio was measured to be 1.34 $\pm$ 0.21. These results suggest the comet likely formed in the cold mid-to-outer solar nebula (approx. 50-70 K). Additionally, the average rotation period was estimated as 7.28 $\pm$ 0.79 hours, with a CN outflow velocity of 2.40 $\pm$ 0.25 km/s

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K. Aravind, E. Jehin, S. Hmmidouch, M. Vander Donckt, S. Ganesh, P. Rousselot, P. Hardy, D. Sahu, J. Manfroid, Z. Benkhaldoun. 2025-07-29. Ionic emissions and activity evolution in comet C/2020 F3 (NEOWISE): Insights from long-slit spectroscopy and photometry. https://doi.org/10.1051/0004-6361/202554842

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