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

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$\ddot{I}$). 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

14 pages, 18 figures, 5 tables; Accepted for publication in A&A