Monitoring the activity and composition of comet C/2017K2 (PanSTARRS) with TRAPPIST telescopes

<p><span dir="ltr" role="presentation">We report on the results of a long photometry and monitoring of comet C/2017 K2 (PanSTARRS), </span><span dir="ltr" role="presentation">hereafter 17K2, with the TRAPPIST telescopes [1]. 17K2 is an Oort cloud comet discovered by </span><span dir="ltr" role="presentation">the Pan-STARRS survey in 2017 [2], at a large heliocentric distance of 16 au.</span> <span dir="ltr" role="presentation">The comet was </span><span dir="ltr" role="presentation">later identified in archival imagery to be active at 23.8 au from the Sun, the second most distant</span><span dir="ltr" role="presentation"> discovery of an active comet [3]. It has been claimed that 17K2 is a rare CO-rich comet [4]. We </span><span dir="ltr" role="presentation">started observing 17K2 with TRAPPIST-North on October 25, 2017 using broad-band</span><span dir="ltr" role="presentation"> filters when the comet was at 15 au from the Sun with a magnitude of 18. We started collecting </span><span dir="ltr" role="presentation">broad and narrow-band images [5] with TRAPPIST-South on September 9, 2021 (r</span><span dir="ltr" role="presentation">h</span><span dir="ltr" role="presentation">=5.4 au) </span><span dir="ltr" role="presentation">when the comet became visible and bright from the southern hemisphere. The comet will reach</span><span dir="ltr" role="presentation"> its perihelion on December 19, 2022 at r</span><span dir="ltr" role="presentation">h</span><span dir="ltr" role="presentation">=1.8 au, and we will monitor its activity on both sides </span><span dir="ltr" role="presentation">of perihelion. As writing this abstract, we detected emission of CN, C</span><span dir="ltr" role="presentation">2</span><span dir="ltr" role="presentation">, and C</span><span dir="ltr" role="presentation">3</span> <span dir="ltr" role="presentation">radicals as well as </span><span dir="ltr" role="presentation">the dust continuum in four bands. By fitting the observed gas profiles with Haser model [6] after </span><span dir="ltr" role="presentation">subtraction of the dust continuum, we derived the gas production rates for a different detected </span><span dir="ltr" role="presentation">species. From the continuum and broad-bands images, we computed the Af</span><span dir="ltr" role="presentation">&#961;</span> <span dir="ltr" role="presentation">parameter, and a</span><span dir="ltr" role="presentation"> dust production proxy [7].</span> <span dir="ltr" role="presentation">In this work, we will show the magnitude evolution of this comet</span><span dir="ltr" role="presentation"> over 4 years (2017-2022), as well as the gas and dust activity for several months as a function of </span><span dir="ltr" role="presentation">heliocentric distances.</span></p> <p><span dir="ltr" role="presentation">References<br role="presentation" />[1] E. Jehin et al. 2011, The Messenger, 145, 2-6.<br role="presentation" />[2] Kaiser, N., Aussel, H., Burke, B. E., et al. 2002, Proc. SPIE, 4836, 154.<br role="presentation" />[3] Meech, K. J., Kleyna, J. T., Hainaut, O., et al. 2017, ApJL, 849, L8<br role="presentation" />[4] Yang, B., Jewitt, D., Zhao, Y., et al. 2021, ApJL, 914, L17<br role="presentation" />[5] Farnham, T. L., Schleicher, D. G., A&#8217;Hearn, M. F. 2000, Icarus, 147, 180<br role="presentation" />[6] L. Haser. 1957, Bulletin de l&#8217;Acad &#769;emie Royale de Belgique, Vol. 43, 740-750.<br role="presentation" />[7] Michael F. A&#8217;Hearn et al. 1984, The Astronomical Journal, Vol. 89, 579-591.</span></p>