Electronic Telegram No. 5333 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 A1 (ATLAS) A new comet has been discovered on CCD images obtained 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. A. Fitzsimmons reported that four 30-s images taken on Jan. 3.2 UT show the object as being "slightly soft" with a size of 6".3 (full-width-at-half-maximum) in 4".3 seeing. The discovery observations are tabulated below: 2024 UT R.A. (2000) Decl. Mag. Jan. 3.20752 7 05 23.35 -65 42 33.4 18.8 3.21123 7 05 22.85 -65 42 33.3 18.7 3.24216 7 05 20.04 -65 42 26.2 18.8 3.24854 7 05 19.31 -65 42 25.2 18.8 After the object was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists have commented on the object's appearance, as follows. Eight stacked 60-s exposures taken remotely by Hidetaka Sato (Bunkyo-ku, Tokyo, Japan) using a 0.51-m f/6.8 astrograph located at Rio Hurtado on Jan. 4.30 UT show a strongly condensed coma 8" in diameter with a hint of tail 5" long toward p.a. 300 degrees; the magnitude was 18.5 as measured within a circular aperture of radius 4".3. Exposures taken remotely by A. Hale (Cloudcroft, NM, USA) on Jan. 5.1 using a 0.35-m reflector located at Sutherland, South Africa, show the object to be slightly non-stellar, with a small hint of diffuseness, when compared to stars of similar brightness, and no tail. Twenty-one 60-s exposurse taken in 3".4 seeing by A. Aletti, F. Bellini, L. Buzzi, and G. Galli on Jan. 10.9 remotely using a 0.36-m f/8.4 Ritchey-Chretien reflector located at Hakos, Namibia, show a slightly condensed coma of size 4".8 (FWHM) that extends toward the north. The available astrometry appears on MPEC 2024-B78. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 93 observations spanning 2024 Jan. 3-19 (mean residual 0".4). T = 2025 June 13.86526 TT Peri. = 353.31775 Node = 112.15936 2000.0 q = 3.8754626 AU Incl. = 94.44347 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. 2023 12 02 07 50.27 -65 43.4 6.076 6.063 84.6 9.3 18.2 2023 12 07 07 44.63 -65 56.4 6.027 6.033 85.7 9.4 18.1 2023 12 12 07 38.36 -66 05.3 5.978 6.004 86.8 9.4 18.1 2023 12 17 07 31.54 -66 09.6 5.929 5.974 87.9 9.5 18.1 2023 12 22 07 24.26 -66 08.8 5.881 5.945 88.9 9.5 18.0 2023 12 27 07 16.66 -66 02.3 5.834 5.915 90.0 9.6 18.0 2024 01 01 07 08.86 -65 50.0 5.787 5.886 90.9 9.6 18.0 2024 01 06 07 01.01 -65 31.4 5.742 5.857 91.9 9.7 17.9 2024 01 11 06 53.26 -65 06.4 5.698 5.828 92.7 9.7 17.9 2024 01 16 06 45.77 -64 35.0 5.655 5.798 93.5 9.7 17.9 2024 01 21 06 38.65 -63 57.2 5.615 5.769 94.1 9.8 17.8 2024 01 26 06 32.03 -63 13.3 5.577 5.740 94.6 9.8 17.8 2024 01 31 06 25.99 -62 23.7 5.541 5.712 95.0 9.9 17.8 2024 02 05 06 20.59 -61 28.6 5.507 5.683 95.3 9.9 17.7 2024 02 10 06 15.86 -60 28.6 5.476 5.654 95.3 10.0 17.7 2024 02 15 06 11.84 -59 24.1 5.448 5.625 95.3 10.1 17.7 2024 02 20 06 08.52 -58 15.8 5.423 5.597 95.0 10.1 17.7 2024 02 25 06 05.88 -57 04.1 5.400 5.568 94.6 10.2 17.6 2024 03 01 06 03.90 -55 49.7 5.381 5.540 94.1 10.3 17.6 2024 03 06 06 02.55 -54 33.0 5.364 5.512 93.3 10.4 17.6 2024 03 11 06 01.79 -53 14.7 5.351 5.483 92.4 10.4 17.6 2024 03 16 06 01.59 -51 55.2 5.340 5.455 91.4 10.5 17.5 2024 03 21 06 01.90 -50 35.0 5.333 5.427 90.2 10.6 17.5 2024 03 26 06 02.68 -49 14.7 5.327 5.400 88.8 10.6 17.5 2024 03 31 06 03.89 -47 54.6 5.325 5.372 87.3 10.7 17.5 2024 04 05 06 05.49 -46 35.2 5.325 5.344 85.7 10.8 17.5 2024 04 10 06 07.46 -45 16.7 5.327 5.317 84.0 10.8 17.4 2024 04 15 06 09.75 -43 59.6 5.331 5.289 82.2 10.8 17.4 2024 04 20 06 12.33 -42 44.3 5.336 5.262 80.3 10.8 17.4 2024 04 25 06 15.17 -41 30.8 5.343 5.235 78.4 10.9 17.4 2024 04 30 06 18.25 -40 19.5 5.352 5.208 76.4 10.8 17.4 2024 05 05 06 21.54 -39 10.6 5.361 5.181 74.4 10.8 17.4 2024 05 10 06 25.02 -38 04.2 5.370 5.154 72.3 10.8 17.3 2024 05 15 06 28.66 -37 00.5 5.380 5.127 70.2 10.7 17.3 2024 05 20 06 32.44 -35 59.7 5.390 5.101 68.2 10.6 17.3 2024 05 25 06 36.34 -35 01.8 5.399 5.075 66.1 10.5 17.3 2024 05 30 06 40.35 -34 06.8 5.408 5.049 64.1 10.4 17.3 2024 06 04 06 44.45 -33 14.9 5.416 5.023 62.1 10.3 17.3 2024 06 09 06 48.62 -32 26.0 5.422 4.997 60.2 10.2 17.3 2024 06 14 06 52.84 -31 40.3 5.427 4.971 58.4 10.0 17.2 2024 06 19 06 57.10 -30 57.6 5.431 4.945 56.7 9.9 17.2 2024 06 24 07 01.39 -30 18.0 5.432 4.920 55.0 9.7 17.2 2024 06 29 07 05.70 -29 41.4 5.431 4.895 53.5 9.6 17.2 2024 07 04 07 10.00 -29 07.9 5.427 4.870 52.2 9.5 17.2 2024 07 09 07 14.29 -28 37.3 5.420 4.845 51.0 9.4 17.2 2024 07 14 07 18.56 -28 09.6 5.411 4.820 50.0 9.3 17.1 2024 07 19 07 22.78 -27 44.8 5.398 4.796 49.2 9.2 17.1 2024 07 24 07 26.95 -27 22.7 5.382 4.772 48.6 9.2 17.1 2024 07 29 07 31.06 -27 03.3 5.363 4.748 48.3 9.2 17.1 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 January 21 (CBET 5333) Daniel W. E. Green