Electronic Telegram No. 5355 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/2023 X7 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on 2023 Dec. 10 UT (discovery observations tabulated below). No activity could be discerned then, but activity was found subsequently. 2023 UT R.A. (2000) Decl. Mag. Dec. 10.38833 5 52 53.01 -40 52 37.0 20.4 10.39944 5 52 52.55 -40 52 35.5 20.5 10.41050 5 52 52.15 -40 52 34.3 20.6 10.42158 5 52 51.71 -40 52 33.0 20.6 Weryk writes that two 60-s Pan-STARRS2 w-band follow-up images taken on 2024 Feb. 4.25 UT in 1".8-1".9 seeing show a diffuse coma of size about 2".6 (full-width-at-half-maximum) with a broad tail 3" long spanning p.a. 70-150 degrees. Y. Ramanjooloo, Institute for Astronomy, University of Hawaii (UH), adds that three 300-s follow-up exposures taken with the UH 2.2-m telescope on 2024 Feb. 20.2 in 1".4-1".8 seeing show a very condensed head of size 2".2 (FWHM) with a possible faint and short tail towards the southeast. After the object was posted on the Minor Planet Center's PCCP webpage, H. Sato (Bunkyo-ku, Tokyo, Japan) reported that nine stacked 120-s CCD exposures taken with a 0.51-m f/6.8 astrograph at Siding Spring, NSW, Australia, on 2023 Dec. 11.5 UT show only a stellar appearance; the magnitude was 19.9 as measured within a circular aperture of radius 4".3. Sato adds that ten stacked 60-s CCD exposures taken with a "Deep Sky Chile" 0.51-m f/6.8 astrograph located at Rio Hurtado, Chile, on 2024 Jan. 6.1 show a strongly condensed coma 7" in diameter with no tail; the magnitude was 19.8 as measured within a circular aperture of radius 3".6. The available astrometry appears on MPEC 2024-D102. The following orbital elements by S. Nakano (Central Bureau) are from 69 observations spanning 2023 Dec. 10-2024 Feb. 20 (mean residual 0".4), with corresponding "original" and "future" values of 1/a being +0.000274 and +0.000973 (+/- 0.000055) AU**-1, respectively. The comet will pass 2.17 AU from Jupiter on 2025 Aug. 26 UT. Epoch = 2025 May 5.0 TT T = 2025 May 15.17903 TT Peri. = 354.39714 e = 1.0027811 Node = 119.19972 2000.0 q = 4.8201441 AU Incl. = 69.07984 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 10.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 02 20 05 20.50 -31 34.6 5.706 5.934 98.6 9.5 20.0 2024 03 01 05 20.60 -29 35.0 5.752 5.891 93.2 9.7 20.0 2024 03 11 05 22.01 -27 34.1 5.807 5.849 87.5 9.8 20.0 2024 03 21 05 24.63 -25 34.6 5.867 5.807 81.7 9.8 20.0 2024 03 31 05 28.34 -23 38.6 5.929 5.766 75.8 9.7 20.0 2024 04 10 05 33.02 -21 47.7 5.992 5.725 69.9 9.5 20.0 2024 04 20 05 38.55 -20 03.2 6.052 5.685 64.0 9.1 19.9 2024 04 30 05 44.80 -18 26.1 6.107 5.645 58.4 8.7 19.9 2024 05 10 05 51.66 -16 56.9 6.155 5.606 53.0 8.3 19.9 2024 05 20 05 59.01 -15 36.0 6.194 5.568 48.0 7.8 19.9 2024 05 30 06 06.75 -14 23.6 6.222 5.531 43.5 7.2 19.9 2024 07 29 06 55.91 -09 59.2 6.091 5.322 37.5 6.7 19.7 2024 08 08 07 03.72 -09 40.0 6.014 5.290 41.0 7.2 19.7 2024 08 18 07 11.16 -09 26.5 5.920 5.259 45.4 7.9 19.6 2024 08 28 07 18.14 -09 17.7 5.810 5.229 50.6 8.6 19.6 2024 09 07 07 24.56 -09 12.9 5.687 5.199 56.5 9.3 19.5 2024 09 17 07 30.29 -09 11.0 5.550 5.171 63.0 10.0 19.4 2024 09 27 07 35.23 -09 10.8 5.401 5.144 69.9 10.5 19.4 2024 10 07 07 39.25 -09 10.9 5.243 5.117 77.3 11.0 19.3 2024 10 17 07 42.21 -09 09.6 5.079 5.092 85.1 11.2 19.2 2024 10 27 07 44.00 -09 05.1 4.912 5.067 93.3 11.3 19.1 2024 11 06 07 44.50 -08 55.3 4.746 5.044 101.9 11.1 19.0 2024 11 16 07 43.64 -08 37.8 4.585 5.022 110.8 10.6 18.9 2024 11 26 07 41.39 -08 10.3 4.434 5.000 120.0 9.8 18.8 2024 12 06 07 37.78 -07 30.4 4.298 4.980 129.3 8.8 18.7 2024 12 16 07 32.94 -06 36.4 4.182 4.961 138.4 7.6 18.7 2024 12 26 07 27.11 -05 27.1 4.092 4.943 146.7 6.3 18.6 2025 01 05 07 20.61 -04 02.6 4.030 4.927 153.0 5.2 18.6 2025 01 15 07 13.88 -02 24.3 4.002 4.911 155.1 4.8 18.5 2025 01 25 07 07.34 -00 34.9 4.006 4.897 152.0 5.4 18.5 2025 02 04 07 01.45 +01 22.0 4.044 4.884 145.0 6.7 18.5 2025 02 14 06 56.56 +03 22.4 4.112 4.872 136.1 8.1 18.6 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 February 22 (CBET 5355) Daniel W. E. Green