Strong CO${}^{+}$ and N${}_2^{+}$ Emission in Comet C/2016 R2 (Pan-STARRS)

We report on imaging and spectroscopic observations of comet C/2016~R2 (Pan-STARRS) obtained with the 0.8,m and 2.7,m telescopes of McDonald Observatory in November and December 2017 respectively. The comet was at a heliocentric distance greater than 3,{\sc au} during both sets of observations. The images showed a well-developed tail with properties that suggested it was an ion tail. The spectra confirmed that we were observing well-developed bands of CO${}^{+}$ and N${}_2^{+}$. The N${}_2^{+}$ detection was unequivocally cometary and was one of the strongest bands of N${}_2^{+}$ detected in a comet spectrum. We derived the ratio of these two ions and from that we were able to derive that N${}_2$/CO = 0.15. This is the highest such ratio reported for a comet. Note erratum - N2/CO=0.06 not 0.15.