Electronic Telegram No. 5384 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 G3 (ATLAS) An apparently asteroidal object discovered on CCD images taken on Apr. 5 UT with a 0.5-m f/2 Schmidt reflector at Rio Hurtado, Chile, 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, after posting on the Minor Planet Center's PCCP webpage. The discovery observations are tabulated below: 2024 UT R.A. (2000) Decl. Mag. Apr. 5.26369 18 15 45.79 -74 35 25.7 19.2 5.28177 18 15 44.96 -74 35 36.7 18.8 5.28591 18 15 45.10 -74 35 39.2 18.7 5.29849 18 15 44.58 -74 35 47.0 18.8 5.30553 18 15 44.41 -74 35 51.3 18.4 K. Yoshimoto, Yamaguchi, Japan, writes that images obtained on Apr. 8.27-8.29 UT with a "Deep Sky Chile" 0.36-m f/7.2 corrected Dall-Kirkham telescope located at Rio Hurtado, Chile, show a nearly stellar head with a faint tail 6" long in p.a. 245 deg; the V magnitude was measured to be 19.3. Twenty-one 300-s exposures taken remotely on Apr. 11.01-11.13 by A. Aletti, L. Buzzi, F. Bellini, and G. Galli using a 0.36-m f/8.4 reflector located at Hakos, Namibia, show a softer aspect (full-width-at-half-maximum 5".3) vs. nearby stars (FWHM 3".9), with a slightly condensed 7" coma but no clear tail; the magnitude was measured to be 18.7. Exposures taken remotely by A. Hale (Cloudcroft, NM, USA) on Apr. 16.03-16.04 with a Las Cumbres Observatory 0.35-m telescope at Sutherland, South Africa, show a condensed coma of size 3" with a straight 7".5 tail in p.a. 300 degrees. The astrometry appears on MPEC 2024-H22. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 87 observations spanning 2024 Apr. 5-17 (mean residual 0".5). There are no close approaches to major planets. T = 2025 Jan. 13.41224 TT Peri. = 108.14863 Node = 220.37853 2000.0 q = 0.0935008 AU Incl. = 116.82222 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 03 31 18 17.19 -73 44.0 4.510 4.711 95.4 12.2 18.7 2024 04 10 18 12.81 -75 23.2 4.293 4.600 101.6 12.3 18.5 2024 04 20 17 59.72 -77 05.8 4.084 4.487 107.3 12.3 18.3 2024 04 30 17 33.54 -78 42.9 3.888 4.372 112.4 12.3 18.1 2024 05 10 16 49.29 -79 57.5 3.707 4.256 116.6 12.2 17.9 2024 05 20 15 47.53 -80 23.2 3.545 4.139 119.6 12.3 17.7 2024 05 30 14 42.23 -79 38.5 3.403 4.020 120.9 12.5 17.5 2024 06 09 13 50.87 -77 45.5 3.285 3.899 120.5 13.0 17.3 2024 06 19 13 18.33 -75 04.8 3.189 3.776 118.2 13.7 17.1 2024 06 29 13 00.55 -71 57.8 3.115 3.652 114.2 14.7 17.0 2024 07 09 12 52.70 -68 40.1 3.062 3.525 108.9 15.8 16.8 2024 07 19 12 51.38 -65 22.8 3.026 3.396 102.6 17.0 16.7 2024 07 29 12 54.42 -62 13.6 3.003 3.264 95.7 18.0 16.5 2024 08 08 13 00.51 -59 17.4 2.990 3.130 88.4 18.9 16.3 2024 08 18 13 08.84 -56 37.3 2.981 2.994 81.0 19.5 16.2 2024 08 28 13 18.87 -54 14.4 2.971 2.854 73.5 19.8 16.0 2024 09 07 13 30.30 -52 08.7 2.957 2.710 66.1 19.9 15.8 2024 09 17 13 42.91 -50 19.3 2.933 2.563 58.9 19.6 15.6 2024 09 27 13 56.57 -48 44.3 2.897 2.412 51.9 19.1 15.4 2024 10 07 14 11.25 -47 21.4 2.844 2.256 45.3 18.4 15.1 2024 10 17 14 26.94 -46 08.1 2.773 2.094 39.0 17.4 14.8 2024 10 27 14 43.70 -45 00.9 2.679 1.927 33.3 16.4 14.4 2024 11 06 15 01.69 -43 56.2 2.562 1.752 28.2 15.5 14.0 2024 11 16 15 21.10 -42 48.7 2.418 1.568 24.1 14.9 13.5 2024 11 26 15 42.35 -41 31.4 2.247 1.374 21.3 15.1 12.9 2024 12 06 16 06.10 -39 53.3 2.045 1.167 19.8 16.6 12.1 2024 12 16 16 33.63 -37 34.6 1.810 0.940 19.3 20.3 11.1 2024 12 26 17 07.76 -33 53.3 1.540 0.686 18.8 27.5 9.6 2025 01 05 17 57.18 -26 56.9 1.225 0.384 15.6 43.5 7.1 2025 01 15 20 15.47 -18 35.4 0.948 0.127 7.3 102.6 2.7 2025 01 25 21 50.41 -31 13.4 1.230 0.487 22.0 49.3 7.9 2025 02 04 22 35.98 -35 58.5 1.498 0.770 27.4 36.1 10.0 2025 02 14 23 08.79 -38 20.2 1.729 1.014 30.7 29.8 11.2 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 April 18 (CBET 5384) Daniel W. E. Green