Electronic Telegram No. 5607 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/2025 R3 (PANSTARRS) Yudish Ramanjooloo, Institute for Astronomy, University of Hawaii, reports the discovery of another comet in images obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on images obtained on Sept. 8 UT. Three of four 45-s i-band images taken in 1".2-1".3 seeing show a very diffuse head of size 2".1-2".4 (full-width-at-half-maximum) with no visible tail. The discovery observations are tabulated below. 2025 UT R.A. (2000) Decl. Mag. Sept. 8.46761 1 35 09.53 +38 01 33.1 19.8 8.47923 1 35 08.53 +38 01 37.7 20.2 8.49076 1 35 07.52 +38 01 42.2 20.7 8.50241 1 35 06.56 +38 01 46.4 20.0 R. Weryk, Department of Physics and Astronomy, University of Western Ontario, writes that three 60-s gri-band follow-up images were obtained with R. Wainscoat using the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea on Sept. 17.5 UT (queue observer L. Wells; queue coordinator H. Flewelling) confirm this to be clearly a comet. In the image with the best seeing (0".6), there is a very condensed head of size 1".0 (FWHM) with a broad tail 10" long spanning p.a. 165-225 degrees. After the comet was posted to the Minor Planet Center's PCCP webpage, A. Aletti (Varese, Italy) reported that two-hundred-thirty-four stacked 30-s CCD images taken on Sept. 14.84-14.90 UT with a 0.36-m f/7.5 reflector show a condensed 5" coma with a faint straight 8"-long tail in p.a. 175 degrees. The available astrometry appears on MPEC 2025-S104. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 75 observations spanning Sept. 7-17 (mean residual 0".4). The comet passed 1.60 AU from Uranus in Nov. 2019. T = 2026 Apr. 20.35925 TT Peri. = 162.11495 Node = 38.68622 2000.0 q = 0.5017281 AU Incl. = 124.70205 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 12.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 09 02 01 43.38 +37 18.4 3.112 3.698 118.3 13.9 19.5 2025 09 12 01 29.92 +38 22.6 2.874 3.580 127.8 12.8 19.2 2025 09 22 01 12.06 +39 07.8 2.660 3.460 136.8 11.5 18.9 2025 10 02 00 49.93 +39 22.5 2.477 3.338 143.8 10.2 18.7 2025 10 12 00 24.47 +38 55.2 2.332 3.214 146.8 9.8 18.4 2025 10 22 23 57.54 +37 38.8 2.228 3.089 143.9 10.9 18.2 2025 11 01 23 31.49 +35 35.9 2.166 2.961 135.9 13.5 18.0 2025 11 11 23 08.37 +32 59.3 2.143 2.831 125.1 16.6 17.8 2025 11 21 22 49.40 +30 07.2 2.151 2.699 113.3 19.7 17.6 2025 12 01 22 34.90 +27 17.7 2.182 2.564 101.3 22.2 17.5 2025 12 11 22 24.56 +24 43.7 2.224 2.426 89.6 23.9 17.3 2025 12 21 22 17.79 +22 32.2 2.267 2.285 78.5 25.0 17.1 2025 12 31 22 13.94 +20 46.2 2.304 2.142 68.1 25.2 17.0 2026 01 10 22 12.38 +19 25.5 2.325 1.994 58.4 24.8 16.7 2026 01 20 22 12.60 +18 28.5 2.324 1.844 49.5 23.9 16.5 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 September 18 (CBET 5607) Daniel W. E. Green