Electronic Telegram No. 5118 Central Bureau for Astronomical Telegrams Mailing address: Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network COMET P/2020 WJ_5 (LEMMON) An apparently asteroidal object discovered on images obtained on 2020 Nov. 18 UT (discovery observations tabulated below, as published with the minor-planet designation 2020 WJ_5 on MPS 1307506) with the Mt. Lemmon Survey 1.5-m reflector was found to show cometary activity in late 2020 and beyond (but only now being announced as a comet, belatedly, although it does appear and the ICQ's 2021 Comet Handbook). 2020 UT R.A. (2000) Decl. Mag. Nov. 18.50399 9 41 57.44 - 2 20 17.2 20.7 18.50925 9 41 57.53 - 2 20 18.3 20.5 18.51448 9 41 57.67 - 2 20 19.5 20.6 18.51973 9 41 57.77 - 2 20 20.6 20.7 18.53913 9 41 58.13 - 2 20 24.4 20.8 R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reported on 2020 Dec. 10 that Mark Huber noticed this object (found independently in four 45-s w-band survey images obtained on 2020 Dec. 10.6 UT with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala) to be cometary in appearance, with a condensed coma of size 1".7 (full-width-at= half-maximum) in 1".3 seeing with a clear tail extending for about 5" in p.a. 300 degrees. Y. Ramanjooloo, Institute for Astronomy, University of Hawaii, reported on 2021 Jan. 11 that 2020 WJ_5 showed a very condensed coma of mag 20.4 and size 2".3 (FWHM) in 1".4 seeing, with a thin, curved tail 4" long in p.a. 298 degrees, as seen in four 45-sec w-band Pan-STARRS1 exposures taken on 2021 Jan. 11.5. H. Sato, Tokyo, Japan, writes that 2020 WJ_5 appeared stellar at mag 19.9 on his CCD images obtained remotely with a 0.51-m f/6.8 astrograph at Siding Spring, NSW, on 2021 Jan. 13.6. However, eight stacked 120-s exposures taken remotely by Sato on 2022 Mar. 25.3 with a 0.43-m f/6.8 astrograph near Mayhill, NM, USA, show a strongly condensed coma 12" in diameter with a 15" tail toward p.a. 280 degrees; the magnitude was 17.9 as measured within a circular aperture of radius 6".3. The available astrometry appears on MPEC 2022-H121. The following orbital elements by S. Nakano (Central Bureau) are from 228 observations spanning 2020 Nov. 18-2022 Apr. 26 (mean residual 0".4). The observations in 2022 April are off by +0.16 deg in R.A. and +0.03 deg in Decl. from the orbit in the ICQ's 2021 Comet Handbook. The comet passed 1.11 AU from Jupiter on 1992 Mar. 19 and perhaps 2.05 AU from Saturn in 1936 Dec. Epoch = 2006 Sept.22.0 TT T = 2006 Sept. 7.24240 TT Peri. = 338.81349 e = 0.1721465 Node = 177.91909 2000.0 q = 5.0213884 AU Incl. = 22.24275 a = 6.0655517 AU n = 0.06597792 P = 14.94 years Epoch = 2021 July 5.0 TT T = 2021 July 3.86164 TT Peri. = 338.46525 e = 0.1713716 Node = 177.81221 2000.0 q = 4.9870994 AU Incl. = 22.29052 a = 6.0184994 AU n = 0.06675315 P = 14.76 years Epoch = 2036 Apr. 17.0 TT T = 2036 Apr. 6.84183 TT Peri. = 337.35386 e = 0.1715008 Node = 177.64120 2000.0 q = 5.0198482 AU Incl. = 22.26084 a = 6.0589660 AU n = 0.06608552 P = 14.91 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 10.0 and 2.5n = 8 for the magnitudes. The brightness of this comet is rather odd, if one takes the astrometric magnitudes seriously -- rising with a steeper index than would be expected for a comet this far from the sun. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2022 04 11 11 57.08 +02 54.3 4.127 5.066 157.3 4.4 18.7 2022 05 01 11 51.46 +04 18.7 4.305 5.077 135.9 7.9 18.8 2022 05 21 11 49.96 +05 08.0 4.565 5.089 116.0 10.3 19.0 2022 06 10 11 52.99 +05 20.7 4.871 5.102 97.4 11.4 19.1 2022 06 30 12 00.18 +05 01.5 5.190 5.116 80.2 11.3 19.2 2022 07 20 12 10.84 +04 17.2 5.495 5.130 63.9 10.2 19.4 2022 08 09 12 24.18 +03 15.0 5.762 5.144 48.4 8.5 19.5 2022 08 29 12 39.51 +02 01.4 5.973 5.159 33.4 6.2 19.6 2022 12 07 14 05.30 -03 25.9 5.897 5.244 44.8 7.6 19.6 2022 12 27 14 19.89 -03 44.0 5.663 5.263 61.4 9.4 19.5 2023 01 16 14 31.77 -03 35.1 5.385 5.282 78.7 10.5 19.4 2023 02 05 14 40.00 -02 56.4 5.092 5.301 96.9 10.6 19.3 2023 02 25 14 43.77 -01 48.5 4.813 5.321 115.9 9.6 19.2 2023 03 17 14 42.71 -00 17.4 4.586 5.341 135.4 7.5 19.1 2023 04 06 14 37.30 +01 24.2 4.445 5.362 154.0 4.7 19.1 2023 04 26 14 29.13 +02 58.2 4.412 5.383 163.2 3.1 19.1 2023 05 16 14 20.60 +04 06.3 4.494 5.404 151.5 5.1 19.1 2023 06 05 14 14.08 +04 37.8 4.679 5.426 133.3 7.8 19.2 2023 06 25 14 11.21 +04 31.7 4.941 5.448 114.9 9.7 19.4 2023 07 15 14 12.59 +03 54.4 5.248 5.470 97.3 10.6 19.5 2023 08 04 14 18.08 +02 54.8 5.568 5.493 80.5 10.5 19.6 2023 08 24 14 27.14 +01 42.1 5.873 5.515 64.6 9.5 19.8 2023 09 13 14 39.10 +00 24.1 6.141 5.539 49.4 7.9 19.9 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2022 CBAT 2022 April 30 (CBET 5118) Daniel W. E. Green