Electronic Telegram No. 5393 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/2024 J1 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala on May 1 (discovery observations tabulated below). Four stacked 45-s w-band survey images taken on May 1 in 1".3-1".5 seeing show a diffuse head of size 1".9 (full-width-at- half-maximum) with a short tail 4" long toward p.a. 45 degrees. 2024 UT R.A. (2000) Decl. Mag. May 1.31557 12 30 26.83 -22 29 47.3 20.8 1.32680 12 30 26.48 -22 29 44.3 21.0 1.33841 12 30 26.15 -22 29 41.7 21.0 1.34964 12 30 25.80 -22 29 38.7 20.9 Two stacked 60-s follow-up w-band Pan-STARRS1 images taken on May 2.3 UT in 1".25 seeing show a condensed coma of size 1".8 (FWHM) with a 5" tail toward p.a. 45 degrees. Weryk further notes that four 60-s gri-band follow-up observations were obtained with the 3.6-m Canada-France-Hawaii telescope at Mauna Kea on May 4.26 (PI R. Wainscoat; queue observer A. Acohido; queue coordinator T. Burdullis) in 0".7 seeing, showing a very condensed coma of size 1".4 (FWHM) and a broad tail 5" long spanning p.a. 350-75 degrees. Weryk subsequently identified pre-discovery Pan-STARRS1 observations of the comet taken on Mar. 19.48 and Apr. 1.4 (mag 20.7-20.9). Pre-discovery observations obtained with the Mt. Lemmon 1.5-m reflector obtained on Apr. 29.2 were also reported later (mag 20.3-20.7). After the comet was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists commented on the comet's appearance. Sixteen stacked 60-s exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, on May 2.45-2.46 UT show a strongly condensed coma 7" in diameter with no tail; the magnitude was 19.6 as measured within a circular aperture of radius 6".6. S. Deen (Simi Valley, CA, USA) writes that two 30-min exposures taken with a 0.43-m reflector at Rio Hurtado, Chile, on May 2.1 UT show the object to be "distinctly cometary" with a condensed coma of size around 3" (FWHM) in 2" seeing, with no clear tail. The available astrometry appears on MPEC 2024-J133. The following elliptical orbital elements by S. Nakano (Central Bureau) are from 24 observations spanning 2024 Mar. 19-May 4 (mean residual 0".2). The comet passed 0.48 AU from Jupiter in 1974 June. T = 2023 Nov. 11.20342 TT Peri. = 200.33910 e = 0.3074578 Node = 321.95380 2000.0 q = 2.6366295 AU Incl. = 13.15693 a = 3.8071753 AU n = 0.13267826 P = 7.43 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 15.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 05 10 12 27.27 -21 54.0 1.970 2.834 142.0 12.7 20.1 2024 05 20 12 25.86 -21 16.7 2.068 2.855 133.0 15.0 20.2 2024 05 30 12 26.84 -20 47.3 2.182 2.876 124.2 17.0 20.4 2024 06 09 12 30.05 -20 28.4 2.310 2.898 115.7 18.4 20.5 2024 06 19 12 35.28 -20 20.9 2.447 2.921 107.7 19.4 20.7 2024 06 29 12 42.26 -20 24.7 2.591 2.945 100.1 19.9 20.8 2024 07 09 12 50.76 -20 39.1 2.740 2.969 92.8 20.0 21.0 2024 07 19 13 00.56 -21 03.0 2.891 2.993 85.8 19.8 21.1 2024 07 29 13 11.46 -21 34.9 3.042 3.018 79.0 19.3 21.3 2024 08 08 13 23.31 -22 13.6 3.192 3.044 72.4 18.5 21.4 2024 08 18 13 35.98 -22 57.6 3.338 3.069 66.0 17.5 21.5 2024 08 28 13 49.36 -23 45.7 3.479 3.096 59.7 16.4 21.6 2024 09 07 14 03.36 -24 36.5 3.614 3.122 53.6 15.0 21.7 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 May 10 (CBET 5393) Daniel W. E. Green