Electronic Telegram No. 5397 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 G7 (ATLAS) An apparently asteroidal object discovered on CCD images taken on Apr. 3 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 the object was posted to the Minor Planet Center's PCCP webpage. The discovery observations are tabulated below: 2024 UT R.A. (2000) Decl. Mag. Apr. 3.34729 22 07 44.95 -61 32 18.8 19.4 3.37231 22 07 45.75 -61 32 28.8 19.4 3.37508 22 07 45.79 -61 32 31.1 19.2 3.39451 22 07 46.29 -61 32 39.2 19.4 6.33363 22 09 00.30 -61 52 48.5 19.5 6.34336 22 09 00.70 -61 52 52.5 19.0 6.34613 22 09 00.68 -61 52 54.6 19.4 6.35591 22 09 00.88 -61 52 58.1 19.2 6.35868 22 09 00.93 -61 52 59.8 17.9 6.41272 22 09 02.29 -61 53 23.9 19.2 Eight stacked 60-s exposures taken remotely on Apr. 7.4 UT by H. Sato (Bunkyo-ku, Tokyo, Japan) with a "Deep Sky Chile" 0.51-m f/6.8 astrograph located at Rio Hurtado, Chile, show a moderately condensed coma 7" in diameter with no tail; the magnitude was 19.1 as measured within a circular aperture of radius 3".6. Eight stacked 60-s follow-up exposures taken by Sato on May 7.8 with a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, again show a strongly condensed coma 7" in diameter and no tail; the magnitude was 18.6 as measured within a circular aperture of radius 6".6. Exposures taken on Apr. 21.8 by T. Prystavski (Lviv, Ukraine) using a 0.51-m f/4 Corrected Dall-Kirkham telescope at Siding Spring show a coma of size 10".8 with total mag 19.2, with an apparently elongation toward p.a. 82 degrees. The available astrometry appears on MPEC 2024-K41. The following parabolic orbital elements are from 45 observations spanning Apr. 3-May 11 (mean residual 0".4). The comet passed 1.95 AU from Uranus in 2015 October. T = 2025 Feb. 9.05670 TT Peri. = 289.50338 Node = 191.92206 2000.0 q = 6.0322610 AU Incl. = 131.51635 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 8.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 05 10 22 14.35 -67 06.1 6.077 6.330 100.0 9.0 18.8 2024 05 20 22 10.72 -69 05.5 5.946 6.309 106.6 8.8 18.8 2024 05 30 22 02.88 -71 12.7 5.830 6.289 112.6 8.6 18.7 2024 06 09 21 49.04 -73 22.6 5.735 6.270 117.6 8.2 18.7 2024 06 19 21 26.75 -75 27.1 5.663 6.252 121.3 8.0 18.6 2024 06 29 20 53.32 -77 14.5 5.616 6.234 123.4 7.8 18.6 2024 07 09 20 07.46 -78 29.5 5.597 6.217 123.5 7.8 18.6 2024 07 19 19 13.03 -78 57.5 5.606 6.200 121.7 8.0 18.6 2024 07 29 18 19.65 -78 34.1 5.640 6.184 118.1 8.3 18.6 2024 08 08 17 36.19 -77 28.6 5.699 6.169 113.2 8.7 18.6 2024 08 18 17 05.31 -75 57.4 5.779 6.155 107.2 9.0 18.6 2024 08 28 16 45.22 -74 14.8 5.875 6.142 100.6 9.3 18.7 2024 09 07 16 33.17 -72 30.8 5.983 6.129 93.6 9.4 18.7 2024 09 17 16 26.84 -70 51.6 6.098 6.117 86.3 9.4 18.7 2024 09 27 16 24.53 -69 20.7 6.216 6.106 79.1 9.3 18.8 2024 10 07 16 25.09 -67 59.7 6.331 6.095 71.9 9.0 18.8 2024 10 17 16 27.71 -66 49.5 6.439 6.086 65.0 8.5 18.8 2024 10 27 16 31.79 -65 50.3 6.537 6.077 58.5 8.0 18.8 2024 11 06 16 36.91 -65 01.8 6.620 6.069 52.6 7.5 18.9 2024 11 16 16 42.72 -64 23.8 6.686 6.062 47.5 6.9 18.9 2024 11 26 16 48.93 -63 55.6 6.732 6.055 43.6 6.4 18.9 2024 12 06 16 55.30 -63 37.1 6.757 6.049 41.1 6.2 18.9 2024 12 16 17 01.58 -63 27.7 6.759 6.045 40.5 6.1 18.9 2024 12 26 17 07.53 -63 27.1 6.738 6.041 41.8 6.2 18.9 2025 01 05 17 12.92 -63 35.1 6.694 6.037 44.9 6.6 18.9 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 May 21 (CBET 5397) Daniel W. E. Green