Electronic Telegram No. 5392 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 G6 (ATLAS) A Fitzsimmons reported to the Minor Planet Center the discovery of a comet on CCD images taken on Apr. 10 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, noting that three 110-s exposures show a head of size 5".9 (full-width-at-half-maximum) in 4".6 seeing with a faint tail-like feature extending 13" in p.a. 120 degrees (but adding that the field is very crowded "and background contamination cannot be ruled out"). The discovery observations are tabulated below: 2024 UT R.A. (2000) Decl. Mag. Apr. 10.34864 18 17 04.11 -47 41 51.7 19.1 10.37172 18 17 03.53 -47 41 52.0 18.8 10.39467 18 17 02.98 -47 41 51.8 18.8 After the comet was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists also commented on the cometary appearance, including the following reports sent to the Central Bureau. S. Deen (Simi Valley, CA, USA) reports that he obtained images of this comet with a 0.43-m reflector at Rio Hurtado, Chile, on Apr. 16.1-16.3 UT that show a very condensed head of size 2" (FWHM) in 1".5 seeing with magnitude V = 18.7-18.8; there was also a possible faint tail extending 4".5 in p.a. 160-170 degrees. Ten stacked 60-s exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) using a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, on Apr. 16.8 show a strongly condensed coma 8" in diameter with no tail; the magnitude was 19.0 as measured within a circular aperture of radius 4".3. Twelve 180-s stacked exposures taken on Apr. 19.03-19.05 by A. Aletti, L. Buzzi, F. Bellini, and G. Galli with a 0.36-m f/8.4 reflector at Hakos, Namibia, show a slightly condensed coma 5" wide extended toward the north; the magnitude was measured to be 19.0-19.1. T. Prystavski (Lviv, Ukraine) writes that images obtained with a 0.51-m f/6.8 Corrected Dall-Kirkham telescope located at Rio Hurtado on Apr. 20.3 show a very short, straight tail 0'.14 long in p.a. 322 degrees; the very condensed coma had a size of 0'.1 and total magnitude 19.0. The available astrometry appears on MPEC 2024-J134. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 41 observations spanning 2024 Apr. 10-May 4 (mean residual 0".6). There are no close approaches to any major planets. T = 2026 Feb. 20.83018 TT Peri. = 23.39027 Node = 250.95648 2000.0 q = 6.4346756 AU Incl. = 120.44937 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 7.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 05 10 17 58.54 -47 38.4 7.027 7.764 134.1 5.4 18.4 2024 05 20 17 49.71 -47 25.8 6.895 7.728 143.1 4.5 18.3 2024 05 30 17 40.00 -47 04.5 6.791 7.692 150.8 3.7 18.2 2024 06 09 17 29.78 -46 33.6 6.718 7.657 156.0 3.1 18.2 2024 06 19 17 19.50 -45 52.8 6.678 7.622 156.7 3.0 18.2 2024 06 29 17 09.60 -45 02.9 6.671 7.587 152.4 3.6 18.2 2024 07 09 17 00.46 -44 05.3 6.697 7.553 145.1 4.4 18.2 2024 07 19 16 52.42 -43 02.2 6.752 7.519 136.3 5.4 18.2 2024 07 29 16 45.66 -41 55.9 6.834 7.486 126.8 6.2 18.2 2024 08 08 16 40.29 -40 48.6 6.937 7.453 117.0 7.0 18.2 2024 08 18 16 36.35 -39 42.5 7.057 7.420 107.2 7.5 18.2 2024 08 28 16 33.78 -38 39.0 7.189 7.388 97.4 7.8 18.2 2024 09 07 16 32.50 -37 39.2 7.326 7.356 87.7 7.9 18.3 2024 09 17 16 32.39 -36 43.9 7.464 7.324 78.1 7.7 18.3 2024 09 27 16 33.33 -35 53.1 7.597 7.293 68.7 7.4 18.3 2024 10 07 16 35.18 -35 07.0 7.721 7.262 59.3 6.8 18.3 2024 10 17 16 37.80 -34 25.2 7.831 7.232 50.1 6.1 18.3 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 May 10 (CBET 5392) Daniel W. E. Green