We report the clear detection of C2 and of abundant NH2 in the first prominently active interstellar comet, 2I/Borisov. We observed 2I on three nights in November 2019 at optical wavelengths 4800--9300 \AA with the Multi-Unit Spectroscopic Explorer (MUSE) integral-field spectrograph on the ESO/Very Large Telescope. These data, together with observations close in time from both 0.6-m TRAPPIST telescopes, provide constraints on the production rates of species of gas in 2I's coma. From the MUSE detection on all epochs of several bands of the optical emission of the C2 Swan system, a rich emission spectrum of NH2 with many highly visible bands, and the red (1-0) bandhead of CN, together with violet CN detections by TRAPPIST, we infer production rates of Q(C2) = 1.1×1024 mol s−1, Q(NH2) = 4.8×1024 mol s−1 and Q(CN) = (1.8±0.2)×1024 mol s−1. In late November at 2.03~au, 2I had a production ratio of C2/CN=0.61, only barely carbon-chain depleted, in contrast to earlier reports measured further from the Sun of strong carbon-chain depletion. Thus, 2I has shown evolution in its C2 production rate: a parent molecule reservoir has started sublimating. At Q(NH2)/Q(CN) = 2.7, this second interstellar object is enriched in NH2, relative to the known Solar System sample.
@article{arxiv.2001.11605,
title = {Interstellar comet 2I/Borisov as seen by MUSE: C$_2$, NH$_2$ and red CN detections},
author = {Michele T. Bannister and Cyrielle Opitom and Alan Fitzsimmons and Youssef Moulane and Emmanuel Jehin and Darryl Seligman and Philippe Rousselot and Matthew M. Knight and Michael Marsset and Megan E. Schwamb and Aurélie Guilbert-Lepoutre and Laurent Jorda and Pierre Vernazza and Zouhair Benkhaldoun},
journal= {arXiv preprint arXiv:2001.11605},
year = {2020}
}