Electronic Telegram No. 5399 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 J4 (LEMMON) An apparently asteroidal object discovered by K. W. Wierzchos on CCD images obtained on May 11 with the Mt. Lemmon Survey 1.5-m reflector has been found to show cometary appearance elsewhere after posting on the Minor Planet Center's NEOCP and PCCP webpages. Wierzchos flagged the object as a possible near-earth-object candidate, through which it was posted to the NEOCP. The discovery observations are tabulated below. 2024 UT R.A. (2000) Decl. Mag. Observer May 11.41593 19 03 43.51 +44 49 07.2 20.1 Wierzchos 11.42072 19 03 43.25 +44 49 09.9 20.1 " 11.42553 19 03 42.96 +44 49 11.7 20.4 " Ten stacked 120-s CCD exposures taken on May 12.4 UT by H. Sato (Tokyo, Japan) with a 0.43-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) show only a stellar appearance; the magnitude was 19.8 as measured within a circular aperture of radius 5".7. A. F. Tubbiolo reports that eighteen stacked broadband 60-s CCD exposures taken on May 17.5 in 1".2 seeing with the Bok 2.3-m f/9 reflector of Spacewatch and Steward Observatory on Kitt Peak show a coma and tail approximately 15" long in p.a. 140 degrees. Additional exposures taken on May 28.34-28.36 by Tubbiolo show a a tight coma and braad tail approximately 18" long, spanning p.a. 110-170 degrees. The available astrometry appears on MPEC 2024-K128. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 93 observations spanning 2024 May 11-28 (mean residual 0".3). Theese elements indicate that the comet passed 3.77 AU from Uranus in 2015 April. T = 2025 Apr. 27.72117 TT Peri. = 128.07744 Node = 19.31476 2000.0 q = 5.6878424 AU Incl. = 117.53510 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. 2024 05 10 19 05.13 +44 39.6 6.006 6.223 97.7 9.3 19.7 2024 05 20 18 54.38 +45 42.1 5.906 6.195 101.9 9.2 19.7 2024 05 30 18 41.81 +46 30.2 5.821 6.167 105.3 9.1 19.6 2024 06 09 18 27.72 +46 59.8 5.752 6.140 107.9 9.1 19.6 2024 06 19 18 12.65 +47 07.4 5.702 6.114 109.3 9.0 19.6 2024 06 29 17 57.27 +46 51.3 5.673 6.088 109.5 9.1 19.5 2024 07 09 17 42.29 +46 11.5 5.665 6.063 108.4 9.2 19.5 2024 07 19 17 28.35 +45 09.6 5.677 6.039 106.1 9.3 19.5 2024 07 29 17 15.96 +43 49.2 5.708 6.015 102.8 9.5 19.5 2024 08 08 17 05.42 +42 14.4 5.756 5.993 98.6 9.6 19.5 2024 08 18 16 56.87 +40 29.7 5.818 5.971 93.8 9.7 19.5 2024 08 28 16 50.28 +38 39.6 5.890 5.949 88.5 9.8 19.5 2024 09 07 16 45.53 +36 48.1 5.969 5.929 82.9 9.7 19.6 2024 09 17 16 42.45 +34 58.4 6.051 5.909 77.1 9.5 19.6 2024 09 27 16 40.84 +33 13.2 6.132 5.890 71.5 9.3 19.6 2024 10 07 16 40.49 +31 34.5 6.208 5.872 65.9 8.9 19.6 2024 10 17 16 41.21 +30 03.9 6.276 5.854 60.8 8.5 19.6 2024 10 27 16 42.78 +28 42.6 6.333 5.838 56.2 8.1 19.6 2024 11 06 16 45.04 +27 31.3 6.375 5.822 52.3 7.7 19.6 2024 11 16 16 47.81 +26 30.8 6.402 5.807 49.4 7.4 19.6 2024 11 26 16 50.90 +25 41.4 6.410 5.793 47.8 7.2 19.6 2024 12 06 16 54.18 +25 03.3 6.399 5.780 47.5 7.2 19.6 2024 12 16 16 57.46 +24 36.8 6.369 5.768 48.8 7.4 19.6 2024 12 26 17 00.59 +24 21.8 6.319 5.756 51.4 7.7 19.6 2025 01 05 17 03.39 +24 18.3 6.249 5.746 55.2 8.1 19.6 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 May 30 (CBET 5399) Daniel W. E. Green