Monitoring the activity and composition of comet C/2017K2 (PanSTARRS) with TRAPPIST telescopes
Authors: Hmiddouch Said , Jehin Emmanuel , Moulane Youssef , Jabiri Abdelhadi , Vander Donckt Mathieu , Benkhaldoun Zouhair 
Published: September 2022

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