Electronic Telegram No. 5616 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 2025 S1 = P/2005 T5 (BROUGHTON) G. J. Leonard recovered comet P/2005 T5 (cf. IAUC 8621) accidentally on CCD images obtained by on Sept. 24 UT with the Mount Lemmon Survey 1.5-m reflector. He reported it to the Minor Planet Center as a recovery, and D. Rankin then acquired follow-up CCD observations on the following night with the 1-m Steward Observatory reflector at Mt. Lemmon, which showed a condensed coma about 4" across with a straight tail about 6" long in p.a. about 260 degrees. 2025 UT R.A. (2000) Decl. Mag. Observer Sept.24.40940 2 30 27.28 - 2 00 54.1 19.6 Leonard 24.41457 2 30 27.13 - 2 00 53.9 19.5 " 24.41973 2 30 27.01 - 2 00 53.6 19.7 " 24.42489 2 30 26.88 - 2 00 53.8 19.6 " 25.28910 2 30 05.86 - 2 00 34.2 19.4 Rankin 25.29736 2 30 05.67 - 2 00 34.1 19.5 " 25.30747 2 30 05.42 - 2 00 33.9 19.3 " T. Kobayashi then identified observations of this comet in the Minor Planet Center's "isolated tracklet file" (which is available publicly) that had been made on 2024 July 1.5 UT with the Pan-STARRS1 1.8-m Ritchey- Chretien reflector at Haleakala (mag given as 21.5-21.8), and those were included on MPEC 2025-S299. Following a request by the Central Bureau, R. Weryk (Department of Physics and Astronomy, University of Western Ontario) identified additional images of this comet with both the Pan-STARRS1 and the Pan-STARRS2 1.8-m Ritchey-Chretien reflectors at Haleakala. On 2024 June 12, Pan-STARRS1 images showed the comet only faintly visible in poor (2".0-2".5) seeing. Four 45-s w-band survey images from 2024 July 1 show a fuzzy head of size 1".7 (full-width-at-half-maximum) in 1".4-1".5 seeing, with no tail. Three 45-s Pan-STARRS1 w-band survey images taken on 2024 July 6 in 1".4-1".5 seeing show essentially a stellar appearance. Four 45-s Pan-STARRS2 w-band survey images taken on 2025 Aug. 26 in 1".0-1".2 seeing show a head of size 1".5 (FWHM) with a tail 14" long toward p.a. 250 degrees; a similar appearance was visible in both Pan-STARRS1 and Pan-STARRS2 images on 2025 Sept. 15 and 28. Additional astrometry by Weryk is tabulated below (only the last of the 2025 Sept. 15 observations was with Pan-STARRS1; the rest of the 2025 observations were obtained with Pan-STARRS2): 2024 UT R.A. (2000) Decl. Mag. July 6.49289 20 52 54.96 -43 25 11.7 21.7 6.50131 20 52 54.68 -43 25 15.0 21.8 6.50976 20 52 54.42 -43 25 17.9 21.3 2025 UT R.A. (2000) Decl. Mag. Aug. 26.55468 2 33 56.00 - 2 15 07.2 20.6 26.56613 2 33 56.10 - 2 15 06.6 20.7 26.57760 2 33 56.20 - 2 15 05.9 20.6 26.58915 2 33 56.30 - 2 15 05.3 20.6 Sept.15.53924 2 33 16.64 - 2 03 46.3 20.5 15.55158 2 33 16.45 - 2 03 46.1 20.4 15.56395 2 33 16.27 - 2 03 45.9 20.2 15.57632 2 33 16.05 - 2 03 45.6 19.7 15.62821 2 33 15.28 - 2 03 44.5 20.5 28.45816 2 28 41.74 - 1 59 14.6 19.4 Ten stacked 60-s CCD exposures taken remotely on 2025 Sept. 28.38 UT by H. Sato (Tokyo, Japan) with a 0.51-m f/6.8 astrograph located at Rio Hurtado, Chile, show a strongly condensed coma 5" in diameter with a fan-like tail 30" long spanning p.a. 230-270 degrees; the magnitude was 19.8 as measured within a circular aperture of radius 2".9. The residuals for the 2024 July 1 observations were +0.24 deg in R.A. and +0.03 deg in Decl. (and +0.26 deg in R.A. and +0.23 deg in Decl. for the 2025 Sept. observations) from the prediction in NK 1400 (and in the ICQ's 2025 Comet Handbook), with a corresponding correction of Delta(T) = -1.32 day. The following linked observations by S. Nakano (Central Bureau) are from 118 observations spanning 2005 Aug. 26-2025 Sept. 28 (mean residual 0".6). The comet will pass 1.18 AU from Jupiter on 2042 Dec. 19 UT. Epoch = 2005 Nov. 6.0 TT T = 2005 Nov. 3.57375 TT Peri. = 304.52738 e = 0.5524022 Node = 57.06854 2000.0 q = 3.2467844 AU Incl. = 21.37304 a = 7.2537990 AU n = 0.05044938 P = 19.534 years Epoch = 2025 June 14.0 TT T = 2025 June 13.73532 TT Peri. = 304.85715 e = 0.5516916 Node = 56.99771 2000.0 q = 3.2535746 AU Incl. = 21.38525 a = 7.2574472 AU n = 0.05041134 P = 19.55 years Epoch = 2044 Dec. 11.0 TT T = 2044 Nov. 30.03113 TT Peri. = 307.06063 e = 0.5514354 Node = 56.37506 2000.0 q = 3.1826164 AU Incl. = 21.16009 a = 7.0951122 AU n = 0.05215130 P = 18.90 years 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. The comet appears to be about a magnitude fainter than in 2005. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 09 02 02 34.59 -02 10.0 2.651 3.303 122.3 15.0 19.3 2025 09 12 02 33.98 -02 05.0 2.561 3.315 131.6 13.1 19.2 2025 09 22 02 31.37 -02 01.7 2.488 3.330 141.1 10.9 19.2 2025 10 02 02 26.94 -01 57.4 2.436 3.345 150.8 8.4 19.2 2025 10 12 02 21.06 -01 49.1 2.408 3.362 159.7 5.9 19.2 2025 10 22 02 14.25 -01 34.3 2.407 3.380 165.6 4.2 19.2 2025 11 01 02 07.20 -01 10.7 2.435 3.400 163.9 4.6 19.2 2025 11 11 02 00.58 -00 37.0 2.491 3.421 156.2 6.7 19.3 2025 11 21 01 55.00 +00 06.9 2.575 3.442 146.6 9.1 19.4 2025 12 01 01 50.93 +01 00.5 2.683 3.466 136.5 11.3 19.5 2025 12 11 01 48.61 +02 02.5 2.812 3.490 126.6 13.1 19.7 2025 12 21 01 48.15 +03 11.5 2.957 3.515 117.0 14.4 19.8 2025 12 31 01 49.52 +04 26.1 3.116 3.542 107.7 15.3 20.0 2026 01 10 01 52.59 +05 44.7 3.284 3.569 98.8 15.8 20.1 2026 01 20 01 57.21 +07 06.3 3.457 3.597 90.2 15.9 20.3 2026 01 30 02 03.20 +08 29.7 3.631 3.626 81.9 15.6 20.4 2026 02 09 02 10.38 +09 54.0 3.805 3.657 73.9 15.0 20.5 2026 02 19 02 18.59 +11 18.3 3.974 3.688 66.2 14.2 20.7 2026 03 01 02 27.68 +12 41.9 4.137 3.719 58.7 13.2 20.8 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 October 1 (CBET 5616) Daniel W. E. Green