Electronic Telegram No. 5429 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 TD_22 (LEMMON) An apparently asteroidal object discovered on 2023 Oct. 12 by the Mt. Lemmon Survey (1.5-m reflector; discovery observations tabulated below, from MPEC 2023-U43) has been found to show cometary activity recently as it neared perihelion. 2023 UT R.A. (2000) Decl. Mag. Oct. 12.38144 4 27 21.36 +12 38 05.2 21.5 12.38752 4 27 20.88 +12 38 02.4 12.39268 4 27 20.51 +12 38 01.6 20.7 12.39888 4 27 20.07 +12 37 59.8 20.8 MPS 1974518 also included pre-discovery observations made with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on 2023 Sept. 26.5 UT (magnitude 21.8-22.0) and 2023 Oct. 7.5 (mag 20.9-21.3) that were reported after the discovery was reported. Twelve stacked 60-s CCD exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, on July 4.82 UT show a strongly condensed coma 8" in diameter and no tail; the magnitude was 18.5 as measured within a circular aperture of radius 4".3. CCD images taken remotely on Aug. 2.8 by D. De Martin (Venice, Italy) with the same instrumentation at Siding Spring show a condensed coma of size 10" with no tail. Additional CCD images taken on Aug. 7.14-7.16 by De Martin with a 0.51-m f/6.8 CDK telescope at Nerpio, Spain, show a diffuse coma of size 10" with a broad tail 8" long in p.a. 250 degrees. Further images taken on Aug. 8.1 by De Martin with the same telescope at Nerpio (CMO detector) show a diffuse 11" coma and a broad 10" tail spanning p.a. 240-340 degrees. Twenty-seven stacked 60-s exposures taken on Aug. 7.6 with a 0.20-m f/8 Ritchey-Chretien (+ CMO) by K. Yoshimoto (Kumage, Yamaguchi, Japan) show a very condensed coma 12" in diameter and a faint 12" tail in p.a. 240 deg; the total magnitude was measured as 17.4. A CCD image of this comet taken on 2024 Aug. 12.69 by K. Kadota (Ageo, Japan) with a 0.25-m f/5 reflector yields total mag 16.8. The available astrometry appears on MPEC 2024-P107. The following orbital elements by S. Nakano (Central Bureau) are from 162 observations spanning 2023 Sept. 26-2024 Aug. 10 (mean residual 0".3), indicating an orbital period of 333.8 years. The corresponding "original" and "future" values of 1/a are +0.020602 and +0.021374 (+/- 0.000001) AU**-1, respectively. The comet passed 1.36 AU from Jupiter on 2023 Dec. 6 UT. Epoch = 2024 Sept. 7.0 TT T = 2024 Sept.16.29003 TT Peri. = 32.53340 e = 0.9510225 Node = 5.55611 2000.0 q = 2.3568173 AU Incl. = 170.48961 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. 2024 07 29 00 49.45 +08 33.7 1.856 2.417 111.3 23.0 17.2 2024 08 08 00 20.94 +06 52.4 1.634 2.396 128.0 19.5 16.9 2024 08 18 23 42.06 +04 11.9 1.463 2.378 147.2 13.3 16.6 2024 08 28 22 53.83 +00 31.3 1.369 2.366 167.7 5.2 16.4 2024 09 07 22 01.84 -03 37.6 1.372 2.359 164.6 6.5 16.4 2024 09 17 21 14.24 -07 22.2 1.471 2.357 143.6 14.7 16.6 2024 09 27 20 36.31 -10 12.1 1.644 2.360 124.4 20.5 16.8 2024 10 07 20 08.80 -12 08.9 1.864 2.368 107.7 23.7 17.1 2024 10 17 19 49.99 -13 26.4 2.108 2.381 93.1 24.7 17.4 2024 10 27 19 37.71 -14 17.2 2.359 2.398 80.2 24.1 17.7 2024 11 06 19 30.17 -14 50.3 2.604 2.421 68.4 22.4 17.9 2024 11 16 19 26.00 -15 10.9 2.835 2.448 57.3 19.9 18.2 2024 11 26 19 24.23 -15 22.4 3.046 2.479 46.9 16.9 18.4 2025 03 06 19 35.12 -13 24.3 3.478 2.979 52.4 15.3 19.4 2025 03 16 19 32.13 -13 02.9 3.363 3.042 63.0 16.9 19.5 2025 03 26 19 27.06 -12 41.8 3.232 3.107 74.0 18.0 19.5 2025 04 05 19 19.48 -12 21.4 3.092 3.174 85.5 18.3 19.5 2025 04 15 19 08.95 -12 02.0 2.952 3.242 97.7 17.9 19.5 2025 04 25 18 55.13 -11 43.6 2.821 3.311 110.5 16.5 19.5 2025 05 05 18 37.84 -11 25.9 2.711 3.381 124.1 14.3 19.5 2025 05 15 18 17.30 -11 08.6 2.632 3.452 138.2 11.2 19.5 2025 05 25 17 54.27 -10 51.2 2.596 3.524 152.3 7.7 19.5 2025 06 04 17 30.01 -10 34.1 2.609 3.597 164.4 4.3 19.6 2025 06 14 17 06.11 -10 18.2 2.677 3.670 166.0 3.8 19.8 2025 06 24 16 44.05 -10 05.2 2.796 3.744 155.4 6.5 20.0 2025 07 04 16 24.89 -09 56.9 2.961 3.818 142.6 9.3 20.2 2025 07 14 16 09.10 -09 54.0 3.163 3.893 129.8 11.6 20.4 2025 07 24 15 56.72 -09 57.0 3.393 3.968 117.6 13.1 20.6 2025 08 03 15 47.49 -10 05.5 3.643 4.043 106.1 14.0 20.9 2025 08 13 15 41.01 -10 18.5 3.902 4.119 95.2 14.2 21.1 2025 08 23 15 36.87 -10 35.3 4.165 4.195 84.7 13.9 21.3 2025 09 02 15 34.67 -10 54.9 4.424 4.271 74.7 13.2 21.5 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 August 13 (CBET 5429) Daniel W. E. Green