Electronic Telegram No. 5648 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/2025 W4 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained on Nov. 23 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala (discovery observations tabulated below). Four stacked 45-s w-band survey images taken in 1".4-1".8 seeing show a head of size 2".0 (full-width-at-half-maximum) but with no obvious coma and a straight tail > 90" long in p.a. 260 degrees. 2025 UT R.A. (2000) Decl. Mag. Nov. 23.51400 4 52 00.83 +22 03 13.5 20.6 23.52770 4 52 00.03 +22 03 11.1 21.2 23.54134 4 51 59.23 +22 03 09.1 20.9 23.55496 4 51 58.46 +22 03 06.7 21.0 Weryk adds that two stacked 60-s w-band follow-up images taken with the same telescope on Nov. 26.37 UT in 1".2-1".4 seeing show the head to have a size of 1".7 (FWHM) but again no obvious coma and a clear tail 85" long toward p.a. 265 degrees. Weryk subsequently identified pre-discovery Pan-STARRS1 images from Sept. 5.6 (at mag 22.2-22.6), as well as Pan-STARRS2 images from Sept. 20.53-20.56 (mag 22.2-22.7) and Sept. 30.52-30.56 (mag 21.8). Weryk later reported that three 90-s gri-band images were obtained on Dec. 11.32 with the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea (queue observer J. Nagasako; queue coordinator H. Flewelling) in 1".0-1".1 seeing show a very condensed head of size around 1".4 (FWHM) with a tail > 180" long in p.a. 265 degrees. After the object was posted on the MPC's PCCP webpage, S. Deen (Simi Valley, CA, USA) reports that he obtained two 15-min CMOS exposures on Nov. 25.2 UT with a 0.43-m reflector at Rio Hurtado, Chile that show a fairly diffuse head without any obvious central condensation and a 25"-long straight tail nearly as bright as the head of the comet in p.a. 255 degrees. Deen also identified Mt. Lemmon archival images from Oct. 26.4 at mag 21.6 with a slightly more distinct/compact nuclear condensation and a 45"-long tail towards p.a. 265 deg (his astrometry tabulated below). Deen was unable to find the comet in Mt. Lemmon images from Oct. 4 that contained the predicted position. MPEC 2025-Y30 includes a single night of four observations reported without comment from the Mt. Lemmon Survey 1.5-m reflector on Nov. 15.3 that were identified in the Minor Planet Center's "isolated tracklet file"; Deen adds that these images show the tail 25" long in p.a. 263 degrees and similarly bright to its faint, extended nuclear condensation (he estimated total mag 20.7 on the Nov. 15.32 image). 2025 UT R.A. (2000) Decl. Mag. Oct. 26.37979 5 06 31.16 +22 51 14.8 21.6 26.38492 5 06 31.14 +22 51 13.6 26.39006 5 06 31.07 +22 51 13.9 A search by Deen of earlier archival images produced no detections; a search of its predicted position in a very dense star field from a Subaru Telescope image taken on 2020 Aug. 13 show nothing to magnitude V = 24. M. Jaeger, Vienna, reports that thirty-four 90-s CMOS images obtained on Dec. 14.9 UT with a 0.35-m f/4.2 reflector at Martinsberg, Oed, Austria, show a highly condensed coma of size 5" and mag 19.7, and a straight 40"-long tail in p.a. 264 degrees whose first 10" of length was noticeably brighter. The available astrometry appears on MPEC 2025-Y30. The following orbital elements by S. Nakano (Central Bureau) are from 79 observations spanning 2025 Sept. 5-Dec. 16 (mean residual 0".5). There are no close approaches to major planets. Nakano was unable to identify earlier observations in archival astrometry. Epoch = 2000 Dec. 2.0 TT T = 2000 Nov. 27.06391 TT Peri. = 171.22907 e = 0.2154363 Node = 237.51140 2000.0 q = 2.0226041 AU Incl. = 1.29781 a = 2.5779985 AU n = 0.23811134 P = 4.14 years Epoch = 2005 Jan. 30.0 TT T = 2005 Jan. 15.18872 TT Peri. = 170.96667 e = 0.2146545 Node = 237.48447 2000.0 q = 2.0242779 AU Incl. = 1.29750 a = 2.5775633 AU n = 0.23817165 P = 4.14 years Epoch = 2009 Mar. 30.0 TT T = 2009 Mar. 11.26380 TT Peri. = 171.72784 e = 0.2124743 Node = 237.40214 2000.0 q = 2.0303317 AU Incl. = 1.29868 a = 2.5781149 AU n = 0.23809521 P = 4.14 years Epoch = 2013 Apr. 18.0 TT T = 2013 May 2.37220 TT Peri. = 171.95484 e = 0.2135102 Node = 237.36289 2000.0 q = 2.0274212 AU Incl. = 1.29989 a = 2.5778100 AU n = 0.23813746 P = 4.14 years Epoch = 2017 June 16.0 TT T = 2017 June 20.38890 TT Peri. = 171.65274 e = 0.2136033 Node = 237.29985 2000.0 q = 2.0271595 AU Incl. = 1.29956 a = 2.5777822 AU n = 0.23814132 P = 4.14 years Epoch = 2021 Aug. 14.0 TT T = 2021 Aug. 12.18791 TT Peri. = 171.98156 e = 0.2105483 Node = 237.16027 2000.0 q = 2.0357210 AU Incl. = 1.29749 a = 2.5786517 AU n = 0.23802087 P = 4.14 years Epoch = 2025 Oct. 12.0 TT T = 2025 Oct. 4.50352 TT Peri. = 172.29022 e = 0.2110743 Node = 237.12112 2000.0 q = 2.0343947 AU Incl. = 1.29823 a = 2.5786898 AU n = 0.23801560 P = 4.14 years Epoch = 2029 Dec. 10.0 TT T = 2029 Nov. 23.38892 TT Peri. = 172.06362 e = 0.2121342 Node = 236.99609 2000.0 q = 2.0316020 AU Incl. = 1.29845 a = 2.5786143 AU n = 0.23802605 P = 4.14 years Epoch = 2033 Dec. 29.0 TT T = 2034 Jan. 13.32901 TT Peri. = 171.99847 e = 0.2097060 Node = 236.81475 2000.0 q = 2.0384227 AU Incl. = 1.29669 a = 2.5793220 AU n = 0.23792810 P = 4.14 years Epoch = 2038 Feb. 26.0 TT T = 2038 Mar. 8.40916 TT Peri. = 172.32752 e = 0.2095655 Node = 236.77498 2000.0 q = 2.0388790 AU Incl. = 1.29713 a = 2.5794409 AU n = 0.23791165 P = 4.14 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 17.0 and 2.5n = 7.5 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 11 21 04 54.24 +22 09.3 1.084 2.051 163.8 7.7 19.5 2025 12 01 04 44.90 +21 43.8 1.074 2.059 176.0 1.9 19.5 2025 12 11 04 35.26 +21 16.6 1.089 2.068 171.5 4.1 19.6 2025 12 21 04 26.97 +20 51.6 1.129 2.078 159.3 9.6 19.6 2025 12 31 04 21.38 +20 33.3 1.191 2.090 147.8 14.5 19.8 2026 01 10 04 19.19 +20 24.2 1.273 2.103 137.1 18.6 19.9 2026 01 20 04 20.54 +20 25.0 1.372 2.117 127.2 21.7 20.1 2026 01 30 04 25.26 +20 34.6 1.482 2.132 118.2 24.0 20.3 2026 02 09 04 32.96 +20 50.7 1.603 2.148 109.8 25.6 20.5 2026 02 19 04 43.19 +21 10.8 1.730 2.165 102.2 26.5 20.7 2026 03 01 04 55.55 +21 32.0 1.861 2.183 95.0 26.9 20.9 2026 03 11 05 09.66 +21 52.0 1.996 2.202 88.3 26.8 21.1 2026 03 21 05 25.18 +22 08.5 2.131 2.222 81.9 26.4 21.2 2026 03 31 05 41.83 +22 19.8 2.265 2.242 75.9 25.6 21.4 2026 04 10 05 59.36 +22 24.5 2.398 2.263 70.1 24.6 21.6 2026 04 20 06 17.54 +22 21.5 2.529 2.284 64.5 23.4 21.7 2026 04 30 06 36.19 +22 10.1 2.655 2.305 59.1 22.0 21.8 2026 05 10 06 55.14 +21 50.0 2.777 2.328 53.8 20.5 22.0 2026 05 20 07 14.26 +21 20.9 2.893 2.350 48.6 18.8 22.1 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 December 18 (CBET 5648) Daniel W. E. Green