Electronic Telegram No. 5527 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/2025 D6 (ATLAS) An apparently asteroidal object discovered on CCD images taken on Feb. 26.3 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. The discovery observations are tabulated below: 2025 UT R.A. (2000) Decl. Mag. Feb. 26.27486 13 12 11.44 -43 42 42.0 18.4 26.27634 13 12 11.16 -43 42 41.8 18.9 26.27769 13 12 10.94 -43 42 40.1 18.7 26.27815 13 12 10.78 -43 42 39.8 18.7 26.28087 13 12 10.17 -43 42 38.8 18.8 26.28133 13 12 10.10 -43 42 37.8 18.9 26.30708 13 12 04.50 -43 42 20.1 18.7 Eight stacked 60-s CCD exposures taken remotely on Mar. 1.7 UT by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, show onlly a stellar appearance; the magnitude was 18.7 as measured within a circular aperture of radius 4".9. A. Hale (Cloudcroft, NM, USA) reports that single 180-s CCD exposures taken remotely on Mar. 2.13 UT with a 0.35-m f/3 Cassegrain reflector located at Cerro Tololo show what appears to be a small, condensed faint coma of size 6" surrounding a dense star-like interior (mag 18.9-19.1) with no tail. An additional single 180-s CCD exposure taken by Hale on Mar. 19.8 with a 0.35-m f/3 Cassegrain reflector located at Sutherland, South Africa, shows a condensed but clearly diffuse coma of size 6" (mag 18.4-19.2) with no tail. CMOS exposures taken remotely by T. Prystavski (Lviv, Ukraine) using an iTelescope 0.25-m f/3.8 Newtonian reflector at Rio Hurtado, Chile, on Mar. 10.3 show a noticeable cometary appearance (total mag 18.4). Thirty 30-s stacked CCD exposures taken by Prystavski on Mar. 12.4 with an iTelescope 0.51-m f/6.8 "corrected Dall-Kirkham" telescope located at Rio Hurtado show a fuzzy coma of size about 0'.2 (total mag 18.5) with no tail. The available astrometry appears on MPEC 2025-F22. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 105 observations spanning Feb. 26-Mar. 20 (mean residual 0".5). The comet passed 2.87 AU from Saturn on 2022 Nov. 17 and will pass 1.62 AU from Jupiter on 2026 June 21 UT. T = 2024 Dec. 11.54740 TT Peri. = 285.44793 Node = 151.47873 2000.0 q = 2.5046969 AU Incl. = 145.79425 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 13.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 02 14 13 51.30 -45 04.9 2.235 2.600 100.3 21.9 18.1 2025 02 19 13 36.61 -44 43.9 2.150 2.615 106.9 21.2 18.0 2025 02 24 13 20.19 -44 06.4 2.072 2.631 113.7 20.1 17.9 2025 03 01 13 02.25 -43 08.3 2.002 2.648 120.6 18.8 17.9 2025 03 06 12 43.21 -41 46.4 1.943 2.666 127.5 17.2 17.8 2025 03 11 12 23.61 -39 58.7 1.897 2.685 134.1 15.4 17.8 2025 03 16 12 04.07 -37 45.2 1.865 2.704 140.1 13.7 17.8 2025 03 21 11 45.20 -35 08.0 1.850 2.725 144.8 12.2 17.8 2025 03 26 11 27.52 -32 11.9 1.852 2.746 147.5 11.2 17.8 2025 03 31 11 11.39 -29 03.0 1.872 2.768 147.7 11.1 17.9 2025 04 05 10 57.04 -25 48.5 1.909 2.791 145.4 11.7 18.0 2025 04 10 10 44.52 -22 35.1 1.963 2.815 141.2 12.9 18.1 2025 04 15 10 33.81 -19 28.4 2.033 2.839 135.8 14.3 18.2 2025 04 20 10 24.78 -16 32.2 2.115 2.865 129.8 15.6 18.3 2025 04 25 10 17.28 -13 49.1 2.209 2.890 123.6 16.8 18.4 2025 04 30 10 11.16 -11 20.3 2.313 2.917 117.4 17.9 18.5 2025 05 05 10 06.27 -09 06.0 2.424 2.944 111.3 18.6 18.7 2025 05 10 10 02.45 -07 05.8 2.542 2.972 105.3 19.1 18.8 2025 05 15 09 59.55 -05 18.7 2.663 3.000 99.4 19.4 18.9 2025 05 20 09 57.46 -03 43.6 2.788 3.029 93.8 19.5 19.1 2025 05 25 09 56.07 -02 19.5 2.915 3.058 88.3 19.3 19.2 2025 05 30 09 55.29 -01 05.3 3.042 3.088 83.0 19.0 19.3 2025 06 04 09 55.03 +00 00.2 3.169 3.118 77.9 18.5 19.5 2025 06 09 09 55.23 +00 57.9 3.295 3.149 72.9 17.9 19.6 2025 06 14 09 55.82 +01 48.7 3.419 3.180 68.0 17.2 19.7 2025 06 19 09 56.75 +02 33.4 3.540 3.212 63.2 16.4 19.8 2025 06 24 09 57.97 +03 12.8 3.657 3.244 58.5 15.5 19.9 2025 06 29 09 59.44 +03 47.4 3.771 3.276 53.8 14.5 20.0 2025 07 04 10 01.13 +04 17.7 3.881 3.309 49.3 13.5 20.1 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 March 20 (CBET 5527) Daniel W. E. Green