The N$_2$ Production Rate in Comet C/2016 R2 (PanSTARRS)

TL;DR

This study measures the N$_2$ production rate in comet C/2016 R2 (PanSTARRS) using N$_2^+$ emission lines, providing the first direct scalelengths and revealing the highest N$_2$ production rate observed in a comet.

Contribution

It presents the first direct measurement of N$_2$ scalelengths and quantifies the N$_2$ production rate in comet C/2016 R2, highlighting its exceptionally high N$_2$ output.

Findings

N$_2$ production rate is approximately 1×10^{28} molecules/sec.

N$_2$/CO ratio is about 0.09.

N$_2$ production varies by ±20% over three nights.

Abstract

Observations of comet C/2016 R2 (PanSTARRS) have revealed exceptionally bright emission bands of N$_2^+$, the strongest ever observed in a comet spectrum. Alternatively, it appears to be poor in CN compared to other comets, and remarkably depleted in H$_2$O. Here we quantify the N$_2$ production rate from N$_2^+$ emission lines using the Haser model. We derived effective parent and daughter scalelengths for N2 producing N2+. This is the first direct measurement of such parameters. Using a revised fluorescence efficiency for N2+, the resulting production rate of molecular nitrogen is inferred to be Q(N$_2$) ~ 1 $\times 10^{28}$ molecules.s-1 on average for 11, 12, and 13 Feb. 2018, the highest for any known comet. Based on a CO production rate of Q(CO) ~ 1.1 $\times 10^{29}$ molecules.s-1, we find Q(N$-2$)/Q(CO)~0.09, which is consistent with the N$_2^+$/CO$^+$ ratio derived from the observed intensities of N$_2^+$ and CO$^+$ emission lines. We also measure significant variations in this production rate between our three observing nights, with Q(N$_2$) varying by plus or minus 20% according to the average value