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

TL;DR

This study uses spectroscopy and photometry to analyze the composition, activity, and ionic emissions of comet C/2020 F3 (NEOWISE), revealing insights into its formation environment and physical properties during its perihelion passage.

Contribution

It provides detailed measurements of emission lines, production rates, and ionic ratios, offering new insights into the comet's composition and activity evolution compared to previous observations.

Findings

Detected ionic emissions N₂⁺, CO⁺, CO₂⁺, H₂O⁺ at large distances from nucleus.

Measured N₂⁺/CO⁺ ratio refined to (4.8 ± 2.4)×10⁻², indicating formation in cold solar nebula.

Estimated the comet's rotation period as 7.28 ± 0.79 hours.

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