Comet 2I/2019 q4 (borisov)

Fitzsimmons, A. ; Opitom, C. ; Yang, B. ; Moulane, Y. ; Meech, K. ; Kleyna, J. ; Keane, J. ; Jehin, E. ; Snodgrass, C. ; Micheli, M. 

Abstract

A. Fitzsimmons, Queen's University, Belfast; C. Opitom, O. Hainaut, B. Yang, and Y. Moulane, European Southern Observatory; K. Meech, J. Kleyna, and J. Keane, University of Hawaii; E. Jehin, Universite de Liege; C. Snodgrass, University of Edinburgh; and M. Micheli, Near-Earth-Object Coordination Centre, European Space Agency, report that they obtained additional spectroscopy (cf. CBETs 4670, 4672) of comet 2I/Borisov with the 4.2-m William Herschel Telescope (+ ISIS spectrograph) on Oct 2.2 and 13.2 UT. CN emission is observed extending up to 30" from the nucleus (60000 km at the comet). CN production rates of 1.9 x 10E24 and 2.1 x 10E24 molecules/s were measured on these dates (respectively), assuming a standard Haser model, a molecular velocity of 0.5 km/s, and nominal Schleicher and A'Hearn scalelengths. There was no detection of C_2 emission, with a 3-sigma upper limit to the production rate of 6 x 10E23 molecules/s. From additional observations performed with the 2.5-m Isaac Newton Telescope (+IDS spectrograph) on Sept. 30.2 and Oct. 1.2 UT, they also measure a CN production rate of 1.8 x 10E24 molecules/s and a 3-sigma upper limit for the C_2 production rate of 9 x 10E23 molecules/s, in agreement with the WHT measurements. These C_2 upper limits are significantly below the reported detection by Kareta et al. (their paper posted at website URL https://arxiv.org/1910.03222), and confirm this comet is depleted in C_2 relative to CN when compared to most solar-system comets.