Electronic Telegram No. 5296 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/2023 S1 Y. Ramanjooloo, Institute for Astronomy, University of Hawaii, reports the discovery of a comet in images obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on Sept. 20 (discovery observations tabulated below); three 45-s w-band exposures show a condensed head of size 2".1 (full-width-at-half-maximum) in 1".3 seeing with a faint, straight tail 11".5 long and about 5" wide spanning p.a. 223-237 degrees. 2023 UT R.A. (2000) Decl. Mag. Sept.20.60443 2 28 54.43 +26 21 00.3 20.3 20.61228 2 28 54.25 +26 21 01.2 20.5 20.62011 2 28 54.11 +26 21 01.8 20.5 Pre-discovery observations were subsequently reported to the Minor Planet Center that had been obtained on Sept. 15.4 UT (Mt. Lemmon, mag 19.5-19.7), on Sept. 17.5 (Pan-STARRS2, mag 20.3-20.4), and on Sept. 19.5 (Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala, mag 20.2-20.5). Also, three observations made by T. Maroti with a 0.28-m f/2.2 reflector on Sept. 20.0 at Csokako, Hungary, were found in the MPC's "isolated tracklet file"; Maroti gave the magnitude as 18.4-19.4. After the object was posted on the MPC's PCCP webpage, H. Sato (Bunkyo-ku, Tokyo, Japan) reported that eight stacked 120-s CCD exposures taken remotely on Sept. 21.32 with a 0.51-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) showed a strongly condensed coma 6" in diameter with no tail; the magnitude was 19.5 as measured within a circular aperture of radius 4".9. T. Prystavski (Lviv, Ukraine) reports total mag 19.7 and a 0'.2 tail in p.a. 229 degrees on Sept. 25.44 from five 120-s CCD exposures obtained remotely with an iTelescope 0.51-m reflector at Beryl Junction (image posted on the "ICQ Comet Observations" Facebook forum). The available astrometry appears on MPEC 2023-S264. The following orbital elements by S. Nakano (Central Bureau) are from 81 observations spanning 2023 Sept. 15-29 (mean residual 0".4) and still have much uncertainty due to the comet having passed only 0.0017 AU from Jupiter (whose radius is 0.00048 AU) around 2021 June 8 UT. Prior to the 2021 encounter, the comet's previous orbital elements were T = 1998 Jan. 16 TT, q = 4.994 AU, e = 0.429, Peri. = 205.2 deg, Node = 143.7 deg, i = 10.3 deg, a = 8.748 AU, P = 25.9 years. These suggest that the comet also passed 0.81 AU from Jupiter around 1916. Epoch = 2025 Feb. 14.0 TT T = 2025 Feb. 26.77752 TT Peri. = 180.20696 e = 0.3132301 Node = 317.30430 2000.0 q = 2.6345674 AU Incl. = 9.15771 a = 3.8361718 AU n = 0.13117679 P = 7.514 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 11.0 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2023 09 13 02 30.81 +26 06.5 3.124 3.795 125.2 12.5 19.3 2023 09 23 02 28.08 +26 24.3 2.989 3.767 135.1 10.8 19.1 2023 10 03 02 23.55 +26 31.1 2.873 3.738 145.2 8.8 19.0 2023 10 13 02 17.46 +26 25.4 2.780 3.710 155.2 6.5 18.9 2023 10 23 02 10.24 +26 07.0 2.714 3.681 164.1 4.2 18.8 2023 11 02 02 02.54 +25 36.8 2.677 3.653 167.6 3.4 18.8 2023 11 12 01 55.06 +24 57.3 2.670 3.624 161.8 4.9 18.7 2023 11 22 01 48.51 +24 12.6 2.692 3.595 152.2 7.4 18.7 2023 12 02 01 43.46 +23 27.4 2.740 3.566 141.7 9.9 18.7 2023 12 12 01 40.30 +22 46.0 2.810 3.537 131.1 12.1 18.7 2023 12 22 01 39.22 +22 12.0 2.899 3.508 120.9 13.9 18.8 2024 01 01 01 40.25 +21 47.7 3.002 3.478 111.1 15.3 18.8 2024 01 11 01 43.30 +21 34.1 3.113 3.449 101.7 16.2 18.8 2024 01 21 01 48.24 +21 31.3 3.230 3.420 92.7 16.7 18.9 2024 01 31 01 54.89 +21 38.6 3.347 3.391 84.1 16.8 18.9 2024 02 10 02 03.06 +21 55.1 3.462 3.362 76.0 16.5 19.0 2024 02 20 02 12.61 +22 19.4 3.571 3.333 68.2 16.0 19.0 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 September 30 (CBET 5296) Daniel W. E. Green