Electronic Telegram No. 5292 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/2023 KF_3 = P/2010 YK_3 An apparently asteroidal object discovered with the Mt. Lemmon 1.5-m reflector on CCD images obtained on 2023 May 24 (and given the minor-planet designation 2023 KF_3) has been found to be cometary -- apparently first by D. Rankin about a month after the observations were reported to the Minor Planet Center. The discovery observations are tabulated below. 2023 UT R.A. (2000) Decl. Mag. Observer May 24.43798 22 04 10.04 - 9 27 11.3 20.6 Rankin 24.44321 22 04 10.32 - 9 27 09.2 20.1 " 24.44841 22 04 10.61 - 9 27 06.8 19.8 " 24.45361 22 04 10.89 - 9 27 04.6 20.3 " A. Hale (Cloudcroft, NM, USA) writes that CCD images obtained on 2023 Aug. 9.9 UT with a 0.35-m f/3 Cassegrain reflector at Las Cumbres Observatory (LCO), Sutherland, South Africa, shows a condensed coma of size 12" with a straight tail 22" long in p.a. 245 degrees. Additional images taken by Hale with the same telescope on Aug. 20.85-20.86 show a condensed coma 12" in size (and mag 16.9) with a straight tail 40" long in p.a. 240 degrees. Further images taken remotely by Hale with an LCO 0.35-m f/3 Cassegrain reflector at McDonald Observatory on Sept. 6.18 show a diffuse 13" coma of mag 16.4 (with a strong central condensation roughly 4" in diameter and a straight, broad 24" tail about 12" in width toward p.a. 225 degrees. [Corrigendum: on CBET 5246, the observation made by Hale on 2023 Apr. 11.37 was made with a Las Cumbres Observatory telescope, not a Las Campanas Observatory reflector.] Fifteen stacked 60-s CCD exposures taken remotely on Aug. 10.6 UT by K. Yoshimoto (Kumage, Yamaguchi, Japan) using a 0.51-m f/6.8 reflector at Siding Spring Observatory show a condensed coma 24" in diameter of total mag 16.8 with a tail 1'.0 long in p.a. 240 deg. A. Fitzsimmons, Queen's University, Belfast, writes that J. Robinson noticed cometary appearance in eight individual 30-s exposures taken on Aug. 12.3 UT with a 0.5-m f/2 Schmidt reflector at Rio Hurtado, Chile, in the course of the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS) search program; the comet's head showed a size of 7".2 (full-width-at-half- maximum) in 4".3 seeing, and a stacked image with total exposure time 240 s shows a tail 20" long in p.a. 235 degrees. Linkage was then made to an apparently asteroidal object discovered on CCD images obtained at the end of 2010 with the LINEAR survey's 1-m f/2 reflector (discovery observations tabulated below), when it was given the minor-planet designation 2010 YK_3 (cf. MPS 363422). 2010 UT R.A. (2000) Decl. Mag. Dec. 31.29494 5 38 37.79 +25 03 15.4 19.4 31.30872 5 38 37.23 +25 03 13.8 19.6 31.32210 5 38 36.57 +25 03 11.8 19.7 Jan. 5.27163 5 35 17.09 +24 52 03.8 19.5 5.28478 5 35 16.64 +24 52 00.5 20.1 5.31119 5 35 15.54 +24 51 56.5 19.6 5.32444 5 35 14.97 +24 51 55.9 20.0 K. Ly (El Monte, CA, USA) writes that he has looked closely at additional images of 2010 YK_3 that were subsequently found in images obtained with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala on 2010 Nov. 30 and 2010 Dec. 25. A single 45-s i-band exposure taken on 2010 Nov 30.57 showed the comet with a diffuse coma extending at least 8" in diameter with no tail; a magnitude of i = 18.5 was measured in a 5".5-diameter circular aperture. Another 45-s i-band exposure taken on the same night was of too-poor quality to show any clear cometary features. A pair of 45-s i-band exposures taken on 2010 Dec 25.53-25.54 showed the comet again with a diffuse coma extending at least 7" in diameter and having no tail; its magnitude was i = 18.3 as measured in a 5".5-diameter circular aperture. This linkage allowed further pre-discovery observations to be identified, including the following single-night Spacewatch observations from 1996 (cf. MPS 1914917): 1996 UT R.A. (2000) Decl. Mag. June 23.41195 21 50 43.51 -10 10 01.5 23.43964 21 50 43.80 -10 09 55.1 23.46902 21 50 44.18 -10 09 49.4 20.7 Additional astrometry appears on MPEC 2023-R42. No name has yet been assigned to this comet. The following linked orbital elements by S. Nakano (Central Bureau) are from 205 observations spanning 1996-2023 (mean residual 0".4). The comet passed 0.87 AU from Jupiter on 1995 May 7 UT. Epoch = 1997 Feb. 1.0 TT T = 1997 Jan. 15.78853 TT Peri. = 94.93615 e = 0.6289499 Node = 284.33026 2000.0 q = 2.0841467 AU Incl. = 4.78050 a = 5.6168879 AU n = 0.07403898 P = 13.31 years Epoch = 2010 June 13.0 TT T = 2010 May 26.73248 TT Peri. = 94.84197 e = 0.6280168 Node = 283.63055 2000.0 q = 2.1213950 AU Incl. = 4.78893 a = 5.7029323 AU n = 0.07236970 P = 13.62 years Epoch = 2023 Dec. 2.0 TT T = 2023 Dec. 20.29410 TT Peri. = 94.95909 e = 0.6279845 Node = 283.34162 2000.0 q = 2.1234083 AU Incl. = 4.79088 a = 5.7078491 AU n = 0.07227621 P = 13.64 years Epoch = 2037 May 22.0 TT T = 2037 May 19.78358 TT Peri. = 95.04170 e = 0.6281026 Node = 282.60655 2000.0 q = 2.0955926 AU Incl. = 4.78968 a = 5.6348672 AU n = 0.07368491 P = 13.38 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 12.0 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2023 08 04 22 32.51 -03 20.9 1.529 2.472 152.1 11.1 16.9 2023 08 14 22 28.63 -03 10.5 1.444 2.428 162.0 7.4 16.6 2023 08 24 22 23.27 -03 12.3 1.382 2.386 171.1 3.7 16.5 2023 09 03 22 17.26 -03 23.8 1.344 2.347 171.6 3.6 16.3 2023 09 13 22 11.58 -03 40.9 1.330 2.310 162.5 7.5 16.3 2023 09 23 22 07.25 -03 58.8 1.339 2.276 152.1 11.9 16.2 2023 10 03 22 05.14 -04 12.1 1.369 2.244 142.0 15.9 16.2 2023 10 13 22 05.75 -04 16.9 1.417 2.216 132.5 19.4 16.2 2023 10 23 22 09.32 -04 09.9 1.479 2.192 123.5 22.2 16.3 2023 11 02 22 15.78 -03 49.4 1.552 2.171 115.3 24.4 16.3 2023 11 12 22 24.88 -03 14.8 1.635 2.153 107.7 26.0 16.4 2023 11 22 22 36.31 -02 26.0 1.725 2.140 100.6 27.0 16.5 2023 12 02 22 49.73 -01 23.7 1.820 2.130 94.1 27.5 16.6 2023 12 12 23 04.79 -00 09.1 1.919 2.125 87.9 27.6 16.7 2023 12 22 23 21.22 +01 16.3 2.022 2.123 82.1 27.3 16.8 2024 01 01 23 38.75 +02 50.7 2.127 2.126 76.6 26.7 16.9 2024 01 11 23 57.17 +04 32.2 2.234 2.133 71.3 25.9 17.0 2024 01 21 00 16.31 +06 18.9 2.342 2.144 66.2 24.8 17.2 2024 01 31 00 36.02 +08 08.6 2.451 2.159 61.3 23.6 17.3 2024 02 10 00 56.20 +09 59.4 2.561 2.177 56.5 22.2 17.4 2024 02 20 01 16.77 +11 49.2 2.670 2.200 51.8 20.7 17.6 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 September 8 (CBET 5292) Daniel W. E. Green