The N-2 production rate in comet C/2016 R2 (PanSTARRS)

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 H2O. Here, we quantify the N-2 production rate from N-2(+) emission lines using the Haser model. We derived effective parent and daughter scale lengths for N-2 producing N-2(+). This is the first direct measurement of such parameters. Using a revised fluorescence efficiency for N; , the resulting production rate of molecular nitrogen is inferred to be Q(N-2) similar to 1 x 10(28) molecule s(-1) on average for 2018 February 11, 12, and 13, the highest for any known comet. Based on a CO production rate of Q(CO) similar to 1.1 x 10(29) molecules s(-1), we find Q(N-2)/Q(CO) similar to 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 per cent according to the average value.