Electronic Telegram No. 5454 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) Further to CBET 5445, H. Sato (Bunkyo-ku, Tokyo, Japan) writes that twelve stacked 10-s CMOS exposures taken on Sept. 20.41 UT with a 0.065-m f/3.5 refractor show a strongly condensed coma 3'.2 in diameter and a 30' tail toward p.a. 250 degrees; the magnitude was measured as V = 3.8 within a circular aperture of radius 96".4 comparison star A0-type HIP 51837). K. Yoshimoto, Yamaguchi, Japan, reports the following measured total magnitudes and coma diameters obtained via digital imaging: Sept. 19.84 UT, 4.1:, 1'.2 (180-mm f/2.8 lens + Canon EOS 6D digital camera, G channel; corrected for atmospheric extinction); Sept. 23.84, 3.9, 1'.9 (180-mm f/2.8 lens + Canon EOS Kiss X7i, G channel; 10' tail in p.a. 250 deg); Sept. 25.84, 3.4, 2'.9 (0.08-m f/4.3 refractor + V filter CMOS; tail longer than 1.4 deg in p.a. 257 deg; B-V = +0.66 and V-R = +0.38); Sept. 26.84, 3.2, 2'.8 (135-mm f/2.0 lens + Canon EOS 6D, G channel; tail longer than 1.0 deg in p.a. 258 deg); Sept. 30.84, about 1.9*, 3'.7 (0.08-m f/4.3 refractor + V filter CMOS; tail longer than 40' in p.a. 260 deg). Selected visual total-magnitude and coma-diameter estimates reported to the Central Bureau and the ICQ: Sept. 18.25 UT, 4.1, 2' (V. Gonano, Udine, Italy, 20x80 binoculars); Sept. 19.25, 4.2, 3' (Gonano; 25' tail in p.a. 244 deg); Sept. 20.89, 4.0, 3' (A. Pearce, Nedlands, W. Australia, 15x70 binoculars; 0.5-deg tail in p.a. 253 deg); Sept. 21.88, 3.9, 3' (Pearce; 0.8-deg tail in p.a. 250 deg); Sept. 22.88, 3.7, 3' (Pearce; 1.1-deg tail in p.a. 252 deg); Sept. 23.27, 3.1, 3' (Gonano; 1.2-deg tail in p.a. 254 deg); Sept. 24.14, 3.4, -- (S. J. O'Meara, Maun, Botswana, 8x42 binoculars; 3-deg tail in p.a. 250 deg); Sept. 24.88, 3.3, 2'.5 (Pearce; 2.2-deg tail in p.a. 253 deg); Sept. 25.33, 3.1, 3' (W. Souza, Sao Paolo, Brazil, 10x50 binoculars); Sept. 26.14, 3.1, -- (O'Meara; 2-deg tail in p.a. 253 deg); Sept. 27.15, 2.9, -- (O'Meara); Sept. 28.33, 2.8, 5' (J. G. de S. Aguiar, Campinas, Brazil, 11x80 binoculars); Sept. 28.87, 2.4, -- (Pearce, naked eye); Sept. 29.34, 2.3, 3' (M. Goiato, Aracatuba, Brazil, 7x50 binoculars; 1.5-deg tail in p.a. 260 deg); Sept. 30.33, 2.4, 4' (Aguiar; 1.5-deg tail); Sept. 30.76, 2.3, 15' (C. Wyatt, Walcha, NSW, Australia, naked eye; 9.5-deg tail in p.a. approximately 263 deg); Oct. 1.14, 1.2, -- (O'Meara, naked eye; 10-deg tail in p.a. 260 deg in 8x42 binoculars); Oct. 1.33, 2.0, -- (Souza, naked eye); Oct. 1.79, 1.9, -- (M. Mattiazzo, Swan Hill, Vic., Australia, naked eye; 10-deg tail); Oct. 2.15, 1.4, -- (O'Meara, naked eye; 13-deg tail in p.a. 258 deg in 8x42 binoculars). The following revised orbital elements by S. Nakano (Central Bureau) are from 5112 observations spanning 2022 Apr. 9-2024 Sept. 30 (mean residual 0".5), with corresponding "original" and "future" values of 1/a being -0.000005 and -0.000046 (+/- 0.000001) AU**-1, respectively. The Sept. 2024 astrometry show some large residuals (+/- 2" in Decl), possibly due to the low altitude of the comet. Epoch = 2024 Oct. 17.0 TT T = 2024 Sept.27.74194 TT Peri. = 308.49307 e = 1.0000920 Node = 21.55932 2000.0 q = 0.3914189 AU Incl. = 139.11072 The following ephemeris by the undersigned from the above orbital elements extendes that on CBET 5404 and uses photometric power-law parameters H = 6.0 and 2.5n = 7.5 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 10 17 15 37.39 +01 15.8 0.517 0.637 33.9 119.2 3.1 2024 10 27 17 32.15 +03 26.5 0.805 0.830 53.7 74.9 4.9 2024 11 06 18 18.40 +03 52.3 1.152 1.022 56.3 53.9 6.4 2024 11 16 18 43.47 +04 03.9 1.491 1.207 53.8 41.4 7.5 2024 11 26 19 00.63 +04 18.9 1.808 1.386 49.4 32.7 8.3 2024 12 06 19 14.16 +04 41.4 2.101 1.557 44.4 26.3 9.1 2024 12 16 19 25.69 +05 12.5 2.367 1.723 39.3 21.2 9.6 2024 12 26 19 35.93 +05 52.0 2.606 1.883 34.8 17.3 10.1 2025 01 05 19 45.22 +06 40.2 2.817 2.039 31.1 14.4 10.6 2025 01 15 19 53.66 +07 36.6 3.000 2.190 28.8 12.5 10.9 2025 01 25 20 01.29 +08 41.0 3.154 2.337 28.5 11.6 11.3 2025 02 04 20 08.09 +09 53.1 3.280 2.480 30.4 11.6 11.5 2025 02 14 20 13.97 +11 12.6 3.380 2.621 34.0 12.2 11.8 2025 02 24 20 18.85 +12 39.0 3.454 2.758 39.1 13.1 12.0 2025 03 06 20 22.58 +14 11.8 3.505 2.892 45.2 14.1 12.2 2025 03 16 20 25.01 +15 50.2 3.534 3.024 51.9 15.0 12.3 2025 03 26 20 25.98 +17 33.3 3.545 3.153 59.2 15.8 12.5 2025 04 05 20 25.29 +19 19.7 3.541 3.280 66.9 16.3 12.6 2025 04 15 20 22.74 +21 07.2 3.527 3.405 74.9 16.5 12.7 2025 04 25 20 18.16 +22 53.4 3.506 3.529 83.0 16.4 12.8 2025 05 05 20 11.40 +24 34.6 3.485 3.650 91.3 16.0 12.9 2025 05 15 20 02.40 +26 06.3 3.469 3.769 99.5 15.3 13.0 2025 05 25 19 51.26 +27 23.7 3.463 3.887 107.4 14.4 13.1 2025 06 04 19 38.24 +28 21.5 3.473 4.003 114.7 13.3 13.2 2025 06 14 19 23.88 +28 55.2 3.503 4.118 120.9 12.2 13.3 2025 06 24 19 08.84 +29 02.3 3.557 4.232 125.7 11.2 13.5 2025 07 04 18 53.92 +28 42.2 3.638 4.344 128.4 10.6 13.6 2025 07 14 18 39.90 +27 57.2 3.748 4.454 128.7 10.3 13.7 2025 07 24 18 27.37 +26 51.7 3.884 4.564 126.7 10.3 13.9 2025 08 03 18 16.76 +25 31.1 4.046 4.672 122.7 10.5 14.1 2025 08 13 18 08.26 +24 01.2 4.230 4.779 117.3 10.9 14.2 2025 08 23 18 01.87 +22 27.2 4.432 4.886 110.9 11.1 14.4 2025 09 02 17 57.49 +20 53.3 4.650 4.991 104.0 11.3 14.6 2025 09 12 17 54.93 +19 22.9 4.877 5.095 96.8 11.3 14.7 2025 09 22 17 53.99 +17 58.2 5.110 5.198 89.4 11.1 14.9 2025 10 02 17 54.44 +16 40.8 5.345 5.300 82.0 10.8 15.1 2025 10 12 17 56.08 +15 31.7 5.577 5.401 74.7 10.3 15.2 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 October 2 (CBET 5454) Daniel W. E. Green