Electronic Telegram No. 5383 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 G2 (ATLAS) An apparently asteroidal object discovered on CCD images taken on Apr. 8 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 it was posted to the Minor Planet Center's PCCP webpage due to its nearly parabolic orbit. The discovery observations are tabulated below: 2024 UT R.A. (2000) Decl. Mag. Apr. 8.32961 13 11 46.85 -78 23 51.9 18.6 8.34785 13 11 42.53 -78 23 45.6 18.8 8.36604 13 11 38.35 -78 23 39.8 18.9 S. Deen (Simi Valley, CA, USA) writes that he obtained four 600-s exposures with a 0.43-m reflector located at Rio Hurtado, Chile, on Apr. 9.12-9.15 UT that show obvious cometary activity with a coma of size 3".5 in 2".5 seeing, along with a tail about 10" long in p.a. 160 degrees; the measured V magnitude was 19.1-19.3. Eight stacked 60-s exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) with a "Deep Sky Chile" 0.51-m f/6.8 astrograph located at Rio Hurtado on Apr. 9.37 show a strongly condensed coma 7" in diameter with no tail; the magnitude was 18.8 as measured within a circular aperture of radius 3".6. Twenty-three 180-s exposures taken remotely by A. Aletti, L. Buzzi, F. Bellini, and G. Galli on Apr. 12.1 with a 0.36-m f/8.4 reflector located at Hakos, Namibia, show a condensed coma 8" wide (full- width-at-half-maximum 5".0 in 3".7 seeing); the magnitude was measured to be 18.5-18.8. T. Prystavski (Lviv, Ukraine) writes that ten stacked 120-s exposures taken on each of two nights (Apr. 12.5 and 13.6) with a 0.32-m f/9 Ritchey-Chretien telescope at Siding Spring, NSW, Australia, show an apparently stellar head of total mag 19.1-19.2 with an apparent "spike" (tail) toward p.a. 175 degrees. The available astrometry appears on MPEC 2024-H20. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 50 observations spanning 2024 Apr. 8-16 (mean residual 0".3). There are no close approaches to major planets. T = 2025 June 13.93448 TT Peri. = 328.89517 Node = 171.38175 2000.0 q = 5.3399077 AU Incl. = 122.13455 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 8.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 03 31 13 45.34 -78 55.2 5.911 6.240 104.7 8.9 18.2 2024 04 10 13 05.31 -78 14.4 5.794 6.204 109.7 8.7 18.2 2024 04 20 12 30.25 -76 56.2 5.695 6.167 113.7 8.6 18.1 2024 04 30 12 03.21 -75 06.2 5.616 6.132 116.5 8.5 18.0 2024 05 10 11 44.30 -72 52.6 5.561 6.097 117.8 8.4 18.0 2024 05 20 11 32.25 -70 23.7 5.529 6.062 117.4 8.5 18.0 2024 05 30 11 25.45 -67 47.0 5.523 6.029 115.5 8.7 18.0 2024 06 09 11 22.57 -65 08.8 5.540 5.995 112.1 9.0 17.9 2024 06 19 11 22.57 -62 34.0 5.578 5.963 107.5 9.4 17.9 2024 06 29 11 24.68 -60 06.7 5.635 5.931 102.1 9.7 17.9 2024 07 09 11 28.35 -57 49.8 5.707 5.900 96.0 9.9 17.9 2024 07 19 11 33.17 -55 45.4 5.790 5.869 89.5 10.0 18.0 2024 07 29 11 38.84 -53 54.5 5.879 5.839 82.8 9.9 18.0 2024 08 08 11 45.12 -52 17.6 5.971 5.810 76.0 9.8 18.0 2024 08 18 11 51.83 -50 54.8 6.061 5.782 69.3 9.4 18.0 2024 08 28 11 58.81 -49 45.6 6.146 5.754 62.8 9.0 18.0 2024 09 07 12 05.96 -48 49.3 6.220 5.728 56.6 8.4 18.0 2024 09 17 12 13.14 -48 05.1 6.282 5.702 50.9 7.9 18.0 2024 09 27 12 20.25 -47 32.0 6.327 5.676 45.9 7.3 18.0 2024 10 07 12 27.20 -47 09.0 6.355 5.652 42.0 6.8 18.0 2024 10 17 12 33.87 -46 55.2 6.362 5.628 39.4 6.5 18.0 2024 10 27 12 40.14 -46 49.4 6.348 5.605 38.5 6.3 18.0 2024 11 06 12 45.89 -46 50.7 6.312 5.584 39.5 6.5 18.0 2024 11 16 12 50.98 -46 58.0 6.254 5.562 42.3 6.9 17.9 2024 11 26 12 55.24 -47 10.0 6.173 5.542 46.7 7.4 17.9 2024 12 06 12 58.50 -47 25.6 6.071 5.523 52.2 8.1 17.9 2024 12 16 13 00.56 -47 43.3 5.951 5.505 58.7 8.8 17.8 2024 12 26 13 01.22 -48 01.4 5.814 5.487 66.0 9.4 17.7 2025 01 05 13 00.25 -48 17.8 5.663 5.471 73.8 9.9 17.7 2025 01 15 12 57.45 -48 30.0 5.504 5.455 82.0 10.3 17.6 2025 01 25 12 52.68 -48 34.8 5.340 5.440 90.6 10.4 17.5 2025 02 04 12 45.86 -48 28.7 5.177 5.427 99.5 10.3 17.4 2025 02 14 12 37.07 -48 07.4 5.021 5.414 108.4 10.0 17.4 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 April 17 (CBET 5383) Daniel W. E. Green