Electronic Telegram No. 5353 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/2024 C3 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on Feb. 9 UT (discovery observations tabulated below); four 45-s w-band survey images taken in 1".3-1".7 seeing showed a diffuse head of size 1".7 (full-width-at- half-maximum) with a possible tail 3" long towards p.a. 270 degrees. 2024 UT R.A. (2000) Decl. Mag. Feb. 9.46625 11 36 55.05 + 9 08 36.3 21.7 9.48979 11 36 54.60 + 9 08 37.5 21.4 9.50172 11 36 54.38 + 9 08 37.9 21.9 Weryk was then able to find several apparently asteroidal pre-discovery images of the comet with the Pan-STARRS2 telescope on 2023 Mar. 18.3 UT (at mag 20.9-22.2) and 2023 Dec. 17.6 (mag 21.2-22.3), as well as images taken on 2023 Mar. 25.3 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala (when the comet was at mag 21.4-22.1). Y. Ramanjooloo, Institute for Astronomy, University of Hawaii (UH), writes that four 120-s follow-up exposures were obtained in 1".5-1".7 seeing using the UH 2.2-m reflector at Mauna Kea on 2024 Feb. 20.5, which show a condensed head of size about 2".1 (FWHM) and a tail about 3".9 long toward p.a. 300 deg. After the comet was posted on the Minor Planet Center's PCCP webpage, H. Sato (Tokyo, Japan) reported that ten stacked CCD exposures taken remotely on 2024 Feb. 10.4 UT with a "Deep Sky Chile" 0.51-m f/6.8 astrograph located at Rio Hurtado, Chile, show only a stellar appearance for this comet; the magnitude was 21.4 as measured within a circular aperture of radius 2".2. Twelve additional 120-s exposures taken remotely by Sato on Feb. 13.7 with a 0.51-m f/6.8 astrograph at Siding Spring, NSW, Australia, show a strongly condensed coma 4" in diameter, elongated toward p.a. 315 degrees; the magnitude was 21.0 as measured within a circular aperture of radius 3".2. The available astrometry appears on MPEC 2024-D97. The following orbital elements by S. Nakano (Central Bureau) are from 44 observations spanning 2023 Mar. 18-2024 Feb. 20 (mean residual 0".3). There are no close approaches to major planets. Epoch = 2023 Oct. 23.0 TT T = 2023 Nov. 8.50923 TT Peri. = 159.68486 e = 0.4228724 Node = 359.70521 2000.0 q = 6.7124425 AU Incl. = 22.46972 a = 11.6307773 AU n = 0.02484797 P = 39.67 years Epoch = 2063 Sept. 3.0 TT T = 2063 Sept.11.62277 TT Peri. = 160.86025 e = 0.4354626 Node = 359.25241 2000.0 q = 6.7071183 AU Incl. = 22.52850 a = 11.8807342 AU n = 0.02406795 P = 40.95 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. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 02 20 11 33.34 +09 16.7 5.793 6.727 159.5 3.0 20.4 2024 03 01 11 29.44 +09 25.1 5.753 6.730 169.6 1.5 20.4 2024 03 11 11 25.29 +09 33.0 5.745 6.734 174.2 0.9 20.4 2024 03 21 11 21.14 +09 38.9 5.767 6.737 165.8 2.1 20.4 2024 03 31 11 17.26 +09 41.6 5.819 6.741 155.5 3.5 20.5 2024 04 10 11 13.86 +09 40.1 5.899 6.745 145.1 4.9 20.5 2024 04 20 11 11.14 +09 33.9 6.003 6.749 134.8 6.1 20.5 2024 04 30 11 09.22 +09 22.7 6.129 6.754 124.8 7.0 20.6 2024 05 10 11 08.18 +09 06.3 6.270 6.759 115.0 7.8 20.6 2024 05 20 11 08.05 +08 44.8 6.423 6.764 105.5 8.3 20.7 2024 05 30 11 08.82 +08 18.6 6.584 6.770 96.2 8.6 20.7 2024 06 09 11 10.44 +07 47.9 6.748 6.775 87.2 8.6 20.8 2024 06 19 11 12.87 +07 13.1 6.911 6.781 78.5 8.4 20.8 2024 06 29 11 16.02 +06 34.7 7.069 6.788 69.9 8.1 20.9 2024 07 09 11 19.81 +05 53.0 7.220 6.794 61.5 7.6 20.9 2024 07 19 11 24.18 +05 08.4 7.360 6.801 53.3 6.9 21.0 2024 07 29 11 29.02 +04 21.2 7.486 6.808 45.1 6.1 21.0 2024 11 26 12 37.50 -06 00.1 7.462 6.912 52.9 6.5 21.1 2024 12 06 12 41.74 -06 44.2 7.333 6.922 61.8 7.2 21.0 2024 12 16 12 45.35 -07 25.0 7.192 6.932 70.9 7.7 21.0 2024 12 26 12 48.24 -08 02.1 7.044 6.943 80.1 8.0 21.0 2025 01 05 12 50.34 -08 35.1 6.891 6.954 89.6 8.1 20.9 2025 01 15 12 51.58 -09 03.5 6.738 6.965 99.3 8.0 20.9 2025 01 25 12 51.90 -09 27.1 6.590 6.977 109.3 7.7 20.8 2025 02 04 12 51.29 -09 45.4 6.451 6.988 119.4 7.1 20.8 2025 02 14 12 49.79 -09 58.3 6.328 7.000 129.7 6.2 20.8 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 February 21 (CBET 5353) Daniel W. E. Green