Electronic Telegram No. 5495 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 A3 (TSUCHINSHAN) Zhijian Xu reports the discovery of a comet in three 60-s unfiltered survey images taken on Jan. 5 using the 1.04-m f/1.8 Schmidt telescope at the Xuyi Observatory of Purple Mountain Observatory (Tsuchinshan) in the course of the "China Near Earth Object Survey Telescope" (CNEOST) search program. The object was initially submitted as an asteroidal target by the CNEOST automated system and was later recognized on three 60-s stacked CCD exposures to show a diffuse 4" coma with a 5"-long tail in p.a. 117 degrees. The discovery observations are tabulated below. 2025 UT R.A. (2000) Decl. m1 Jan. 5.82197 10 31 09.04 + 7 50 24.9 19.6 5.83964 10 31 08.90 + 7 50 23.4 19.5 5.85732 10 31 08.73 + 7 50 22.9 19.4 Xu then contacted A. M. Abdelaziz et al. in Egypt for follow-up observations, and twenty stacked 120-s CCD exposures taken by Abdelaziz, M. S. Aboueisha, and M. Ismail with the the Kottamia 1.9-m telescope on 2025 Jan. 8.0 UT show a 2" coma with a straight 7"-long tail in p.a. 118 degrees. After the comet was posted on the Minor Planet Center's PCCP webpage, R. Weryk (Department of Physics and Astronomy, University of Western Ontario) reported that three 45-s w-band pre-discovery images obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on 2025 Jan. 4.5 UT in 1".6-1".9 seeing show a very diffuse coma of size about 5" (and mag 20.1- 20.2) with no tail. The available astrometry appears on MPEC 2025-A178 and includes pre- discovery observations from Pan-STARRS2 on 2024 Dec. 25.5 UT (mag 20.0-20.4) and Dec. 28.52-28.56 (mag 20.0-20.4), and from Pan-STARRS1 on Dec. 29.5. The following two-body orbital elements by S. Nakano (Central Bureau) are from 32 observations spanning 2024 Dec. 25-2025 Jan. 12 (mean residual 0".4). There are no close approaches to any major planets. T = 2026 Mar. 27.39219 TT Peri. = 223.50109 e = 0.4348425 Node = 322.43402 2000.0 q = 5.7648229 AU Incl. = 9.98156 a = 10.2003833 AU n = 0.03025376 P = 32.58 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 9.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 01 05 10 31.26 +07 50.7 5.476 6.130 128.0 7.3 19.5 2025 01 15 10 29.46 +07 49.7 5.342 6.114 138.5 6.1 19.4 2025 01 25 10 26.76 +07 53.9 5.232 6.099 149.4 4.7 19.4 2025 02 04 10 23.32 +08 02.4 5.147 6.084 160.3 3.1 19.3 2025 02 14 10 19.37 +08 14.0 5.092 6.070 171.3 1.4 19.3 2025 02 24 10 15.18 +08 27.5 5.068 6.056 176.6 0.6 19.3 2025 03 06 10 11.04 +08 41.3 5.074 6.042 166.1 2.3 19.3 2025 03 16 10 07.26 +08 53.8 5.111 6.028 155.2 4.0 19.3 2025 03 26 10 04.09 +09 03.8 5.175 6.015 144.5 5.5 19.3 2025 04 05 10 01.73 +09 10.3 5.263 6.002 134.1 6.9 19.3 2025 04 15 10 00.32 +09 12.4 5.371 5.989 124.0 8.0 19.4 2025 04 25 09 59.94 +09 09.6 5.495 5.977 114.1 8.8 19.4 2025 05 05 10 00.62 +09 01.7 5.630 5.965 104.6 9.4 19.5 2025 05 15 10 02.32 +08 48.7 5.771 5.953 95.5 9.7 19.5 2025 05 25 10 04.98 +08 30.5 5.916 5.942 86.6 9.8 19.6 2025 06 04 10 08.54 +08 07.4 6.059 5.931 77.9 9.6 19.6 2025 06 14 10 12.91 +07 39.6 6.197 5.920 69.6 9.3 19.6 2025 06 24 10 17.98 +07 07.4 6.328 5.910 61.4 8.7 19.7 2025 07 04 10 23.66 +06 31.0 6.448 5.899 53.4 8.0 19.7 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 January 15 (CBET 5495) Daniel W. E. Green