Electronic Telegram No. 5455 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/2024 T1 (RANKIN) David Rankin, Lunar and Planetary Laboratory, University of Arizona, reports his discovery of a comet with a 7" coma and a 6" tail in p.a. 280 degrees on four 30-s CCD images obtained on Oct. 2.5 UT with the Mt. Lemmon Survey's 1.5-m reflector (discovery observations tabulated below). 2024 UT R.A. (2000) Decl. Mag. Observer Oct. 2.49354 7 35 32.92 +26 01 00.5 19.8 Rankin 2.49824 7 35 33.39 +26 00 57.6 19.7 " 2.50290 7 35 33.87 +26 00 55.2 19.7 " 2.50757 7 35 34.28 +26 00 53.1 19.5 " After the comet was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists elsewhere commented on the cometary appearance. R. Weryk, Department of Physics and Astronomy, University of Western Ontario, writes that four 45-s w-band survey images taken on Sept. 9.6 UT with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala (and present in the MPC's "isolated tracklet file") show a condensed coma of size 1".7 (full-width-at- half-maximum) in 1".2-1".3 seeing with a straight 5" tail in p.a. 280 deg; the cometary activity was not noticed when the observations were submitted to the MPC on Sept. 9. Sixteen stacked 60-s exposures taken on Oct. 3.45-3.46 remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.43-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 no tail; the magnitude was 19.1 as measured within a circular aperture of radius 5".7. The available astrometry appears on MPEC 2024-T181. The following two-body elliptical orbital elements by S. Nakano (Central Bureau) are from 34 observations spanning Sept. 9-Oct. 7 (mean residual 0".3). The orbit depends on the single-night observations from Sept. 9 (a month earlier than the rest of the available astrometry); the orbital period is still uncertain by +/- 0.3 yr. The comet appears to have passed 0.094 AU from Saturn in 2019 February; before that close approach, the comet had q = 3.11 AU and i = 22.9 deg. T = 2024 Sept.30.50238 TT Peri. = 164.89336 e = 0.6586379 Node = 279.73881 2000.0 q = 2.2890700 AU Incl. = 17.61262 a = 6.7056948 AU n = 0.05675948 P = 17.4 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 13.5 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 09 27 07 26.06 +26 49.3 2.335 2.289 74.9 25.0 18.9 2024 10 07 07 42.93 +25 19.5 2.227 2.290 80.7 25.5 18.8 2024 10 17 07 57.93 +23 41.8 2.120 2.294 87.0 25.7 18.7 2024 10 27 08 10.82 +21 58.0 2.015 2.302 93.6 25.5 18.6 2024 11 06 08 21.33 +20 10.0 1.912 2.314 100.8 24.9 18.6 2024 11 16 08 29.21 +18 20.1 1.816 2.329 108.7 23.7 18.5 2024 11 26 08 34.21 +16 30.3 1.727 2.347 117.1 22.0 18.4 2024 12 06 08 36.15 +14 42.9 1.649 2.369 126.3 19.6 18.3 2024 12 16 08 35.01 +13 00.7 1.586 2.394 136.1 16.6 18.3 2024 12 26 08 31.02 +11 26.3 1.541 2.422 146.4 13.0 18.3 2025 01 05 08 24.70 +10 02.6 1.519 2.453 156.8 9.1 18.3 2025 01 15 08 16.96 +08 52.0 1.522 2.487 165.7 5.6 18.4 2025 01 25 08 08.91 +07 55.9 1.552 2.523 167.9 4.7 18.5 2025 02 04 08 01.66 +07 14.2 1.609 2.561 161.0 7.2 18.6 2025 02 14 07 56.14 +06 45.1 1.692 2.602 151.3 10.5 18.8 2025 02 24 07 52.90 +06 25.7 1.798 2.645 141.4 13.5 19.0 2025 03 06 07 52.18 +06 12.7 1.924 2.689 131.8 16.0 19.2 2025 03 16 07 53.92 +06 02.7 2.066 2.735 122.8 17.8 19.4 2025 03 26 07 57.89 +05 52.9 2.220 2.783 114.3 19.1 19.7 2025 04 05 08 03.81 +05 41.1 2.385 2.832 106.2 19.8 19.9 2025 04 15 08 11.38 +05 25.4 2.556 2.883 98.6 20.1 20.1 2025 04 25 08 20.27 +05 05.0 2.732 2.934 91.4 20.0 20.4 2025 05 05 08 30.22 +04 39.0 2.910 2.987 84.5 19.6 20.6 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 October 8 (CBET 5455) Daniel W. E. Green