Electronic Telegram No. 5310 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 C/2023 S3 (LEMMON) An apparently asteroidal object discovered on Sept. 25 with the 1.5-m reflector at Mt. Lemmon (discovery observations tabulated below) has been found to show cometary appearance by CCD astrometrists elsewhere after it was posted on the Minor Planet Center's PCCP webpage. 2023 UT R.A. (2000) Decl. Mag. Sept.25.45385 5 30 00.50 +23 59 40.2 19.9 25.45900 5 30 00.37 +23 59 35.1 20.4 25.46414 5 30 00.16 +23 59 30.9 20.1 25.46927 5 29 59.99 +23 59 27.7 20.1 Following a request from the Central Bureau, D. Rankin notes that examination of Mt. Lemmon images from Oct. 11.4 UT reveals a highly condensed coma with no tail. L. Buzzi, Varese, Italy, writes that the object appeared stellar (mag 20.1) on CCD exposures taken on Oct. 8.1 by G. Galli and himself with a 0.84-m f/3.5 reflector (measured by Buzzi, Galli, and A. Aletti). Sixteen stacked 60-s exposures taken remotely on Oct. 10.4 by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.51-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) show a strongly condensed coma 8" in diameter with a hint of tail 10" long toward p.a. 260 degrees; the magnitude was 19.2 as measured within a circular aperture of radius 4".9. D. Buczynski reports that images obatined on Oct. 23.0 with a 0.35-m f/6.0 Schmidt-Cassegrain reflector at Tarbatness, Scotland, show only a stellar appearance (mag 18.1-18.3). The available astrometry appears on MPEC 2023-V1. The following elliptical orbital elements by S. Nakano (Central Bureau) are from 325 observations spanning 2023 Sept. 25-Nov. 1 (mean residual 0".4). T = 2024 Jan. 19.63561 TT Peri. = 281.59284 e = 0.9705330 Node = 233.83107 2000.0 q = 0.8299306 AU Incl. = 140.49410 a = 28.1647377 AU n = 0.00659395 P = 149.472 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 16.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2023 10 23 04 36.32 +10 22.7 0.837 1.715 138.6 22.5 17.5 2023 10 28 04 10.86 +04 32.2 0.720 1.650 148.3 18.4 17.0 2023 11 02 03 36.31 -03 15.8 0.628 1.585 155.2 15.2 16.6 2023 11 07 02 51.24 -12 46.8 0.574 1.520 151.2 18.3 16.2 2023 11 12 01 57.00 -22 28.2 0.566 1.455 136.6 27.9 16.1 2023 11 17 00 59.44 -30 11.3 0.604 1.390 119.6 38.2 16.1 2023 11 22 00 06.37 -35 01.7 0.678 1.327 104.0 46.3 16.1 2023 11 27 23 22.56 -37 32.9 0.773 1.264 91.0 51.3 16.3 2023 12 02 22 48.46 -38 40.0 0.881 1.202 80.0 53.9 16.4 2023 12 07 22 22.35 -39 02.7 0.993 1.143 70.6 54.4 16.4 2023 12 12 22 02.13 -39 03.6 1.106 1.086 62.2 53.4 16.5 2023 12 17 21 46.08 -38 54.1 1.216 1.032 54.7 51.1 16.5 2023 12 22 21 32.89 -38 39.8 1.320 0.982 47.8 47.9 16.5 2024 02 20 19 52.72 -32 09.8 1.585 1.008 37.9 37.0 17.0 2024 02 25 19 44.54 -31 08.4 1.521 1.060 43.9 40.3 17.1 2024 03 01 19 35.61 -29 59.6 1.448 1.116 50.3 43.1 17.2 2024 03 06 19 25.62 -28 41.8 1.369 1.175 57.0 45.1 17.2 2024 03 11 19 14.17 -27 12.1 1.285 1.235 64.2 46.4 17.3 2024 03 16 19 00.77 -25 26.8 1.198 1.298 71.9 46.8 17.3 2024 03 21 18 44.88 -23 20.7 1.112 1.361 80.2 46.2 17.3 2024 03 26 18 25.94 -20 47.1 1.028 1.425 89.4 44.4 17.3 2024 03 31 18 03.39 -17 38.3 0.952 1.490 99.6 41.4 17.3 2024 04 05 17 36.87 -13 47.8 0.888 1.555 110.8 37.0 17.3 2024 04 10 17 06.49 -09 14.4 0.842 1.620 122.8 31.3 17.3 2024 04 15 16 33.06 -04 08.4 0.819 1.686 135.1 24.8 17.4 2024 04 20 15 58.25 +01 06.7 0.825 1.751 146.2 18.6 17.5 2024 04 25 15 24.17 +06 00.3 0.859 1.816 153.5 14.3 17.7 2024 04 30 14 52.71 +10 09.0 0.921 1.881 154.4 13.4 18.0 2024 05 05 14 25.13 +13 23.4 1.006 1.945 149.8 15.1 18.3 2024 05 10 14 01.87 +15 46.4 1.110 2.009 142.8 17.7 18.7 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 November 1 (CBET 5310) Daniel W. E. Green