Electronic Telegram No. 5394 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/2024 J2 (WIERZCHOS) Kacper W. Wierzchos, Lunar and Planetary Laboratory, University of Arizona, reports his discovery of another comet on CCD images obtained on May 11 with the Mt. Lemmon Survey's 1.5-m reflector (discovery observations tabulated below); there was a 5" coma, and a suspected 7" tail spanning p.a. 220-250 degrees in four 30-s unfiltered exposures, but there was a very bright sky background due to strong aurora borealis. 2024 UT R.A. (2000) Decl. Mag. Observer May 11.26844 14 15 42.94 +47 26 27.6 21.2 Wierzchos 11.27403 14 15 42.59 +47 26 29.5 19.9 " 11.27958 14 15 42.11 +47 26 32.1 19.9 " 11.28502 14 15 41.88 +47 26 34.1 20.1 " Follow-up CCD observations obtained by Wierzchos on May 14.2 UT with the 1.0-m reflector of Steward Observatory at Mt. Lemmon show a diffuse 7" coma and no tail (magnitude 19.9-20.2). After the comet was posted to the Minor Planet Center's PCCP webpage, H. Sato (Bunkyo-ku, Tokyo, Japan) reported that twelve stacked 120-s CCD exposures taken remotely on May 12.3 UT with a 0.43-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) show a strongly condensed coma 8" in diameter with no tail; the magnitude was 20.5 as measured within a circular aperture of radius 5".7. Presumably asteroidal pre-discovery images of this comet were subsequently reported to the MPC, which were made with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on Mar. 18.6 UT (mag 21.0-22.0), Mar. 29.6 (mag 21.4), Apr. 20.6 (mag 22.0), and Apr. 26.5 (mag 21.2), and also with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala on Apr. 27.6 (mag 21.1). The available astrometry appears on MPEC 2024-K31. The following unperturbed orbital elements by S. Nakano (Central Bureau) are from 57 observations spanning 2024 Mar. 18-May 19 (mean residual 0".5). There are no close approaches to major planets. T = 2025 Mar. 19.72247 TT Peri. = 143.16322 e = 0.9877339 Node = 189.05375 2000.0 q = 1.8104420 AU Incl. = 79.28734 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 12.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 05 10 14 17.06 +47 17.2 3.501 4.021 114.1 13.3 19.6 2024 05 20 14 06.63 +48 17.8 3.498 3.932 108.1 14.2 19.5 2024 05 30 13 57.02 +48 51.2 3.505 3.842 101.8 15.0 19.4 2024 06 09 13 48.93 +48 59.8 3.519 3.753 95.4 15.6 19.3 2024 06 19 13 42.87 +48 47.4 3.535 3.663 89.1 16.1 19.3 2024 06 29 13 39.14 +48 18.6 3.549 3.574 83.2 16.4 19.2 2024 07 09 13 37.86 +47 37.2 3.558 3.484 77.6 16.6 19.1 2024 07 19 13 39.05 +46 47.1 3.560 3.395 72.5 16.6 19.0 2024 07 29 13 42.59 +45 51.4 3.551 3.305 67.9 16.5 18.9 2024 08 08 13 48.39 +44 52.3 3.531 3.216 63.9 16.4 18.8 2024 08 18 13 56.36 +43 52.0 3.498 3.128 60.6 16.4 18.7 2024 08 28 14 06.39 +42 52.0 3.452 3.039 58.0 16.4 18.6 2024 09 07 14 18.45 +41 53.4 3.393 2.952 56.1 16.5 18.4 2024 09 17 14 32.54 +40 57.3 3.321 2.865 54.9 16.7 18.3 2024 09 27 14 48.66 +40 04.0 3.239 2.779 54.5 17.1 18.1 2024 10 07 15 06.90 +39 14.1 3.147 2.694 54.6 17.6 17.9 2024 10 17 15 27.34 +38 27.6 3.048 2.610 55.2 18.3 17.8 2024 10 27 15 50.10 +37 44.1 2.945 2.528 56.1 19.0 17.6 2024 11 06 16 15.28 +37 02.6 2.841 2.449 57.1 19.9 17.4 2024 11 16 16 42.93 +36 22.0 2.741 2.371 58.0 20.7 17.2 2024 11 26 17 13.01 +35 40.0 2.649 2.296 58.7 21.5 17.0 2024 12 06 17 45.36 +34 54.4 2.568 2.224 58.8 22.3 16.8 2024 12 16 18 19.59 +34 02.8 2.504 2.157 58.3 22.9 16.7 2024 12 26 18 55.16 +33 03.1 2.458 2.093 57.1 23.2 16.5 2025 01 05 19 31.34 +31 54.7 2.432 2.034 55.0 23.3 16.4 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 May 20 (CBET 5394) Daniel W. E. Green