Electronic Telegram No. 5418 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 L5 (ATLAS) An apparently asteroidal object discovered on CCD images taken on June 14.94-14.96 UT with a 0.5-m f/2 Schmidt reflector at Sutherland, South Africa, in the course of the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS) search program has been found to show cometary appearance by CCD astrometrists elsewhere. The discovery observations are tabulated below: 2024 UT R.A. (2000) Decl. Mag. June 14.94445 17 08 35.68 -38 02 46.9 17.6 14.94764 17 08 35.21 -38 02 46.6 17.6 14.95319 17 08 34.36 -38 02 45.8 17.7 14.96322 17 08 32.87 -38 02 45.3 17.7 H. Sato (Bunkyo-ku, Tokyo, Japan) writes that seven stacked 60-s exposures taken remotely on June 16.66 UT with a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, show a strongly condensed object with an outer coma 10" in diameter and no tail; the magnitude was 17.1 as measured within a circular aperture of radius 5".4. T. Prystavski (Lviv, Ukraine) notes that images obtained on June 26.4 with a 0.51-m f/6.8 Corrected Dall-Kirkham telescope at Siding Spring show the comet to be only a star-like object of mag 17.6 in a dense star field. F. D. Romanov (Yuzhno-Morskoy, Nakhodka, Russia) relates that seventeen stacked 60-s exposures taken remotely on July 18.1 with an iTelescope 0.5-m f/6.8 reflector (+ Luminance filter) at the "Deep Sky Chile" observatory (Rio Hurtado Valley, Chile) show a condensed coma 9" in diameter with a straight 7" tail in p.a. 80 deg; the magnitude was measured as 17.8. The available astrometry appears on MPEC 2024-O15. The following orbital elements by S. Nakano (Central Bureau) are from 142 observations spanning 2024 June 14-July 18 (mean residual 0".4) and indicate that the comet passed 0.0034 AU from Saturn on 2022 Jan. 24 UT. Prior to that close encounter, the comet had orbital elements T = 1883 July 11, q = 7.240 AU, e = 0.738, Peri. = 250.8 degrees, Node = 137.4 deg, i = 157.6 deg (equinox J2000.0), a = 27.65 AU, P = 145.4 years. The comet will pass 0.60 AU from Jupiter on 2026 Aug. 18 UT. The corresponing "future" value of 1/a is -0.009156 (+/- 0.000238) AU**-1. Epoch = 2025 Mar. 26.0 TT T = 2025 Mar. 10.39265 TT Peri. = 290.51680 e = 1.0373672 Node = 139.17750 2000.0 q = 3.4323213 AU Incl. = 166.57327 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 06 19 16 58.58 -37 55.1 3.243 4.220 161.7 4.3 17.1 2024 06 29 16 34.48 -37 17.9 3.249 4.168 151.1 6.8 17.0 2024 07 09 16 12.38 -36 19.7 3.300 4.118 138.6 9.4 17.0 2024 07 19 15 53.32 -35 08.7 3.390 4.068 125.8 11.7 17.0 2024 07 29 15 37.72 -33 53.5 3.508 4.020 113.3 13.4 17.1 2024 08 08 15 25.56 -32 41.3 3.648 3.974 101.4 14.5 17.1 2024 08 18 15 16.53 -31 36.5 3.797 3.928 89.9 14.9 17.2 2024 08 28 15 10.21 -30 41.6 3.950 3.885 79.0 14.8 17.2 2024 09 07 15 06.16 -29 57.3 4.097 3.843 68.4 14.1 17.2 2024 09 17 15 03.97 -29 23.5 4.233 3.802 58.3 13.0 17.3 2024 09 27 15 03.27 -28 59.3 4.351 3.763 48.5 11.5 17.3 2024 12 26 15 19.42 -29 52.8 4.194 3.504 40.4 10.5 17.0 2025 01 05 15 19.05 -30 13.5 4.032 3.486 50.3 12.5 16.9 2025 01 15 15 17.06 -30 34.2 3.848 3.471 60.5 14.3 16.7 2025 01 25 15 12.97 -30 53.1 3.647 3.458 71.2 15.6 16.6 2025 02 04 15 06.21 -31 07.8 3.436 3.448 82.5 16.5 16.5 2025 02 14 14 56.16 -31 14.2 3.221 3.440 94.3 16.6 16.3 2025 02 24 14 42.22 -31 06.7 3.014 3.435 106.9 16.0 16.2 2025 03 06 14 23.96 -30 36.7 2.823 3.433 120.3 14.4 16.0 2025 03 16 14 01.40 -29 34.4 2.663 3.433 134.3 12.0 15.9 2025 03 26 13 35.36 -27 50.7 2.546 3.435 148.5 8.7 15.8 2025 04 05 13 07.48 -25 22.5 2.482 3.441 160.4 5.6 15.8 2025 04 15 12 39.99 -22 17.6 2.480 3.449 162.2 5.1 15.8 2025 04 25 12 14.95 -18 53.0 2.540 3.459 151.9 7.9 15.8 2025 05 05 11 53.70 -15 29.3 2.655 3.472 138.2 11.2 15.9 2025 05 15 11 36.71 -12 22.5 2.815 3.488 124.4 13.8 16.1 2025 05 25 11 23.79 -09 41.4 3.008 3.506 111.3 15.6 16.2 2025 06 04 11 14.45 -07 28.4 3.222 3.526 99.0 16.5 16.4 2025 06 14 11 08.09 -05 42.0 3.445 3.549 87.5 16.6 16.6 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 July 20 (CBET 5418) Daniel W. E. Green