Electronic Telegram No. 5228 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/2023 A3 (TSUCHINSHAN-ATLAS) An apparently asteroidal object discovered on CCD images taken on Feb. 22 UT with a 0.5-m f/2 Schmidt reflector at Sutherland, South Africa, 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. The discovery observations are tabulated below: 2023 UT R.A. (2000) Decl. Mag. Feb. 22.08359 15 22 38.19 - 1 22 22.0 18.0 22.08675 15 22 38.17 - 1 22 21.6 18.1 22.09262 15 22 38.11 - 1 22 20.8 18.0 22.10270 15 22 38.06 - 1 22 19.0 18.1 After the comet was posted on the Minor Planet Center's PCCP webpage, and additional observations starting arriving to permit orbit computations, the MPC staff noticed that three single-night observations (tabulated below) that had been made at the Purple Mountain Observatory's XuYi Station on 2023 Jan. 9 were in the MPC's "isolated tracklet file". Further investigation by M. Rudenko and P. Veres (MPC) revealed that the PMO object had been posted to the MPC's NEOCP webpage in January, where it resided until Jan. 30 before being removed as presumed lost (with no additional observations reported). The traditional name used for PMO comets (Tsuchinshan) has thus been used as one of the two names for this comet. 2023 UT R.A. (2000) Decl. Mag. Jan. 9.89711 15 19 15.64 - 2 18 29.4 18.7 9.90663 15 19 15.84 - 2 18 29.1 19.0 9.91614 15 19 15.95 - 2 18 29.4 19.0 The following reports of cometary appearance were reported to the Central Bureau as a result of the object being posted on the MPC's PCCP webpage. Q.-z. Ye writes that pre-discovery images taken on 2022 Dec. 22.55-22.56 UT with the 1.2-m Schmidt telescope at Palomar show a 10" tail pointing toward p.a. 240 degrees; the comet's red magnitude was measured as 19.2-19.6. Six stacked 120-s exposures taken remotely on 2023 Feb. 23.75-23.76 by Hidetaka Sato (Bunkyo-ku, Tokyo, Japan) with a 0.51-m f/6.8 astrograph at Siding Spring show a strongly condensed coma 6" in diameter with no tail; the magnitude was 18.1 as measured within a circular aperture of radius 4".9. M. Mattiazzo (Swan Hill, Victoria, Australia) notes that eight stacked 120-s exposures taken remotely on Feb. 26.38 with a "Deep Sky Chile" iTelescope 0.51-m f/6.8 PlaneWave reflector located at Rio Hurtado Valley, Chile reveal a strongly condensed 4" coma of V magnitude 17.9. K. Kadota, Ageo, Japan, finds only a starlike object of V mag 18.0 on images taken on Feb. 27.75-27.77 with a 0.25-m f/5 reflector. Hirohisa Sato also reports that the object shows only a stellar appearance on fifty stacked 60-s exposures taken by T. Ikemura on Feb. 27.75-27.77 with a 0.38-m f/4.2 reflector at Shinshiro, Japan; the red magnitude was measured to be 18.0. C. Jacques, Belo Horizonte, MG, Brazil, relates that images taken on Feb. 28.17 with a 0.45-m reflector at the SONEAR Observatory, Oliveira, show a very condensed coma of size 11" and no tail. The available astrometry appears on MPEC 2023-D77. The following nearly parabolic orbital elements by S. Nakano (Central Bureau) are from 158 observations spanning 2022 Dec. 22-2023 Feb. 28 (mean residual 0".3), with corresponding "original" and "future" values of 1/a being +0.000496 and +0.000456 (+/- 0.001704) AU**-1, respectively. There is no close approach to any of the outer major planets. The comet will pass 0.47 AU from the earth on 2024 Oct. 13 UT. Epoch = 2024 Oct. 17.0 TT T = 2024 Sept.28.23711 TT Peri. = 308.54555 e = 0.9998961 Node = 21.57176 2000.0 q = 0.3909142 AU Incl. = 139.09511 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. Its current brightness suggests that the comet may reach total visual mag 3 near perihelion but will be at very small solar elongations for weeks before, until weeks after, perihelion -- and likely not easily visible from the earth until it is closer to 4th magnitude and pulling out of the solar glare three weeks after perihelion in Oct. 2024. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2022 09 18 14 42.12 +01 00.8 9.314 8.637 45.3 4.7 19.3 2022 09 28 14 44.51 +00 32.8 9.335 8.556 37.0 4.0 19.3 2022 10 08 14 47.33 +00 05.4 9.334 8.475 29.1 3.3 19.3 2022 10 18 14 50.50 -00 21.1 9.309 8.393 22.0 2.5 19.2 2022 10 28 14 53.95 -00 46.0 9.258 8.311 16.7 2.0 19.2 2022 11 07 14 57.59 -01 08.9 9.181 8.228 15.2 1.8 19.1 2022 11 17 15 01.34 -01 29.3 9.077 8.145 18.5 2.2 19.1 2022 11 27 15 05.11 -01 46.7 8.947 8.062 24.9 2.9 19.0 2022 12 07 15 08.79 -02 00.8 8.791 7.978 32.5 3.8 18.9 2022 12 17 15 12.29 -02 11.1 8.611 7.894 40.9 4.7 18.9 2022 12 27 15 15.50 -02 17.3 8.410 7.809 49.6 5.5 18.8 2023 01 06 15 18.30 -02 19.1 8.191 7.724 58.6 6.2 18.7 2023 01 16 15 20.59 -02 16.1 7.955 7.638 67.8 6.8 18.6 2023 01 26 15 22.24 -02 08.3 7.709 7.552 77.2 7.3 18.5 2023 02 05 15 23.14 -01 55.5 7.455 7.466 86.8 7.6 18.3 2023 02 15 15 23.18 -01 37.8 7.200 7.379 96.6 7.6 18.2 2023 02 25 15 22.26 -01 15.4 6.948 7.292 106.6 7.5 18.1 2023 03 07 15 20.30 -00 48.7 6.704 7.204 116.6 7.1 18.0 2023 03 17 15 17.26 -00 18.4 6.475 7.115 126.8 6.4 17.9 2023 03 27 15 13.14 +00 14.5 6.265 7.026 136.9 5.6 17.8 2023 04 06 15 07.98 +00 48.8 6.079 6.937 146.7 4.5 17.6 2023 04 16 15 01.92 +01 23.1 5.922 6.847 155.5 3.5 17.5 2023 04 26 14 55.13 +01 55.7 5.795 6.756 161.4 2.7 17.5 2023 05 06 14 47.86 +02 24.8 5.702 6.665 161.3 2.8 17.4 2023 05 16 14 40.40 +02 48.9 5.642 6.574 155.2 3.7 17.3 2023 05 26 14 33.04 +03 06.7 5.614 6.481 146.4 5.0 17.2 2023 06 05 14 26.10 +03 17.2 5.614 6.388 136.5 6.3 17.2 2023 06 15 14 19.81 +03 20.3 5.639 6.295 126.4 7.5 17.1 2023 06 25 14 14.38 +03 15.7 5.684 6.201 116.2 8.5 17.1 2023 07 05 14 09.96 +03 03.9 5.744 6.106 106.2 9.2 17.1 2023 07 15 14 06.61 +02 45.5 5.813 6.010 96.3 9.7 17.1 2023 07 25 14 04.36 +02 21.3 5.885 5.914 86.7 9.9 17.0 2023 08 04 14 03.20 +01 52.2 5.955 5.817 77.3 9.8 17.0 2023 08 14 14 03.08 +01 18.9 6.019 5.719 68.1 9.5 17.0 2023 08 24 14 03.93 +00 42.3 6.071 5.620 59.2 8.9 16.9 2023 09 03 14 05.66 +00 03.2 6.109 5.521 50.4 8.1 16.9 2023 09 13 14 08.20 -00 37.7 6.129 5.421 41.8 7.1 16.8 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 February 28 (CBET 5228) Daniel W. E. Green