[en] 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. <P />S. Nakano, Sumoto, Japan, writes that he has computed the asymptotic points of 2I/Borisov; the original asymptotic point from whence the comet came on its way to the solar system is located at R.A. = 2h11m.2m, Decl. = +59d26' (equinox J2000.0), which is in the constellation Cassiopeia. The comet is headed toward the future asymptotic point at R.A. = 18h21m.5, Decl. = -51d59' (which is in Telescopium). <P />Twenty-seven stacked 40-s unfiltered images taken in moonlight by T. Chen (and measured by the undersigned) with a 30-cm f/7.2 reflector at Ngari, Tibet, in the course of the BIST survey on Oct. 16.95 UT show total magnitude 16.1 in a 50"-diameter photometric aperture.; there is a condensed, brighter inner coma of diameter about 4" and a fainter outer coma of diameter about 10", with a very faint, diffuse, fan tail perhaps 25" long centered in p.a. about 320 degrees. Stacked BIST images taken on Oct. 14.91 in 2".5 seeing show a less-condensed, irregular coma with inner diameter about 6" and total mag 17.2 in a 30" aperture; the faint, diffuse fan tail was measured to be centered at p.a. approximately 313 deg.
