Electronic Telegram No. 5461 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 T3 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in four 45-s w-band survey images obtained on Oct. 10 with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala (discovery observations tabulated below). In the image with the best seeing (1".1), Weryk found a condensed head of size 1".5 (full- width-at-half-maximum) with a broad, 6"-long tail spanning p.a. 195-255 deg. 2024 UT R.A. (2000) Decl. Mag. Oct. 10.54002 3 55 35.17 -30 18 39.9 20.0 10.55065 3 55 34.81 -30 18 40.3 20.2 10.56127 3 55 34.44 -30 18 40.5 19.9 10.57188 3 55 34.08 -30 18 40.9 20.3 10.63514 3 55 31.93 -30 18 42.4 20.3 10.63580 3 55 31.91 -30 18 42.4 20.1 Weryk subsequently identified the comet in four 45-s w-band pre-discovery Pan-STARRS2 survey exposures taken on Sept. 8.6 UT and also in four 45-s w-band pre-discovery Pan-STARRS1 exposures taken on Sept. 30.6. In the Sept. 8 image taken in the best seeing (1".2), Weryk found a condensed head of size 1".6 (FWHM) and mag 20.0-20.8 with a broad, 6"-long tail spanning p.a. 210-250 degrees. In the Sept. 30 image taken in the best seeing (1".3) with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala, Weryk found a condensed coma of size 1".8 (FWHM) and mag 20.2-20.6 with a broad, 6"-long tail spanning p.a. 195-255 degrees. Weryk adds that he measured two 90-s images of the comet obtained on Oct. 13.5 by J. Fairlamb with the University of Hawaii 2.2-m telescope; in the image with the best seeing (1".0-1".1), the head showed a size of 1".7-1".8 (FWHM) and mag 19.9 with a broad 10"-long tail spanning p.a. 230-260 degrees. After the comet was posted on the Minor Planet Center's PCCP webpage, H. Sato (Bunkyo-ku, Tokyo, Japan) reported that ten stacked 60-s CCD exposures taken remotely on Oct. 11.34 UT with a "Deep Sky Chile" 0.51-m f/6.8 astrograph located at Rio Hurtado, Chile, show a strongly condensed coma 7" in diameter with no tail; the magnitude was 19.5 as measured within a circular aperture of radius 3".6. The available astrometry appears on MPEC 2024-U17. The following two- body elliptical orbital elements by S. Nakano (Central Bureau) are from 19 observations spanning 2024 Sept. 8-Oct. 16 (mean residual 0".2). Nakano calls attention to the lack of observations between the first night (Sept. 8) and the second night (Sept. 30). There are no close approaches to major planets. This orbit indicates a semi-major axis of 85 AU and a period of 783 yr. T = 2025 Mar. 15.91944 TT Peri. = 337.04926 e = 0.9562865 Node = 74.80964 2000.0 q = 3.7138554 AU Incl. = 53.49867 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 12.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 09 27 04 01.23 -30 00.7 3.432 3.996 117.5 12.9 19.5 2024 10 07 03 57.42 -30 16.0 3.332 3.965 122.9 12.2 19.4 2024 10 17 03 51.65 -30 18.3 3.248 3.935 127.5 11.6 19.3 2024 10 27 03 44.23 -30 02.4 3.182 3.908 131.1 11.1 19.2 2024 11 06 03 35.61 -29 23.6 3.137 3.882 133.0 10.8 19.2 2024 11 16 03 26.43 -28 18.8 3.115 3.858 133.0 10.8 19.2 2024 11 26 03 17.41 -26 47.5 3.117 3.835 130.8 11.2 19.1 2024 12 06 03 09.21 -24 51.2 3.143 3.814 126.7 12.0 19.1 2024 12 16 03 02.41 -22 33.8 3.193 3.796 121.1 12.8 19.2 2024 12 26 02 57.34 -20 00.5 3.264 3.779 114.5 13.7 19.2 2025 01 05 02 54.19 -17 16.4 3.353 3.764 107.2 14.5 19.2 2025 01 15 02 52.99 -14 26.7 3.458 3.750 99.7 15.0 19.3 2025 01 25 02 53.63 -11 35.6 3.574 3.739 91.9 15.3 19.3 2025 02 04 02 55.99 -08 46.0 3.699 3.730 84.2 15.2 19.4 2025 02 14 02 59.88 -06 00.4 3.827 3.723 76.5 14.9 19.5 2025 02 24 03 05.11 -03 20.2 3.957 3.718 68.9 14.4 19.5 2025 03 06 03 11.52 -00 46.3 4.085 3.715 61.5 13.6 19.6 2025 03 16 03 18.94 +01 40.7 4.208 3.714 54.2 12.5 19.7 2025 03 26 03 27.22 +04 00.6 4.323 3.715 47.0 11.3 19.7 2025 04 05 03 36.24 +06 13.5 4.429 3.718 39.9 9.9 19.8 2025 04 15 03 45.88 +08 19.3 4.524 3.723 33.0 8.4 19.8 2025 04 25 03 56.04 +10 18.5 4.607 3.730 26.2 6.8 19.9 2025 05 05 04 06.62 +12 11.2 4.675 3.739 19.5 5.2 19.9 2025 05 15 04 17.52 +13 57.8 4.728 3.751 13.1 3.5 20.0 2025 05 25 04 28.68 +15 38.6 4.766 3.764 7.4 2.0 20.0 2025 06 04 04 40.00 +17 14.2 4.787 3.779 5.5 1.5 20.0 2025 06 14 04 51.41 +18 45.1 4.793 3.796 9.8 2.6 20.0 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 October 19 (CBET 5461) Daniel W. E. Green