Electronic Telegram No. 5542 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 D1 (LEMMON) An apparently asteroidal object with a nearly parabolic orbit was found on CCD images taken on 2024 Feb. 16 with the Mt. Lemmon survey's 1.5-m reflector (observations tabulated below). After about a month on the Minor Planet Center's NEOCP and PCCP webpages, only a single unconfirmed report of possible cometary appearance was received, and the MPC issued MPEC 2024-E161 with the designation A/2024 D1. 2024 UT R.A. (2000) Decl. Mag. Feb. 16.30735 10 44 07.71 +47 57 47.5 21.9 16.31263 10 44 07.52 +47 57 49.6 21.2 16.31796 10 44 07.35 +47 57 50.5 21.5 16.32339 10 44 07.20 +47 57 52.2 21.6 That one report was from R. Weryk, Department of Physics and Astronomy, University of Western Ontario, who indicated that this object was "probably a comet" from pre-discovery images obtained on 2023 Dec. 28.6 UT with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala, in which the point-spread function seems to be extended above that of neighboring stars in four 120-s z-band images; a stack of the three best images show a possible coma of size about 1".5 (full-width-at-half-maximum) and mag 22.3-22.7 in 1".0-1".3 seeing. Weryk also identified pre-discovery Pan-STARRS1 observations of this object with no certain features on 2023 Dec. 27.5 (mag 21.3-22.7), 2024 Jan. 2.65 (mag 22.2), and 2024 Jan. 23.56 UT (mag 22.1), as well as Pan-STARRS2 images also on 2024 Jan. 6.54 (mag 19.6). K. Wierzchos, University of Arizona, writes that four 30-s survey CCD exposures taken on 2025 Feb. 24 with the 2.25-m Bok reflector (+ Schott OG-515 filter) at Kitt Peak show a condensed coma of size 6" with a straight tail 13" long in p.a. 165 degrees. The available astrometry appears on MPEC 2025-H119. The following orbital elements by S. Nakano (Central Bureau) are from 56 observations spanning 2023 Dec. 27-2025 Feb. 28 (mean residual 0".3), with corresponding "original" and "future" values of 1/a being +0.000045 and +0.000048 (+/- 0.000011) AU**-1, respectively. Epoch = 2027 Dec. 21.0 TT T = 2027 Dec. 3.76620 TT Peri. = 125.81996 e = 1.0014446 Node = 179.64177 2000.0 q = 6.6900177 AU Incl. = 132.44941 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 8.5 and 2.5n = 7.5 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 03 26 09 16.06 +61 29.9 8.860 9.209 107.5 5.9 20.5 2025 04 05 09 08.04 +61 19.7 8.944 9.167 99.8 6.2 20.5 2025 04 15 09 01.58 +61 02.3 9.036 9.125 92.0 6.3 20.5 2025 04 25 08 56.74 +60 39.9 9.129 9.084 84.3 6.3 20.5 2025 05 05 08 53.52 +60 14.4 9.221 9.043 76.7 6.2 20.5 2025 05 15 08 51.80 +59 47.5 9.306 9.001 69.5 6.0 20.5 2025 05 25 08 51.44 +59 20.7 9.382 8.960 62.6 5.8 20.5 2025 06 04 08 52.30 +58 55.0 9.444 8.920 56.2 5.4 20.5 2025 06 14 08 54.20 +58 31.4 9.491 8.879 50.5 5.1 20.5 2025 09 02 09 29.15 +58 01.3 9.145 8.562 52.0 5.3 20.3 2025 09 12 09 33.98 +58 26.1 9.015 8.523 57.9 5.7 20.3 2025 09 22 09 38.44 +58 59.2 8.870 8.485 64.4 6.1 20.2 2025 10 02 09 42.37 +59 41.0 8.713 8.446 71.3 6.4 20.2 2025 10 12 09 45.55 +60 31.8 8.549 8.408 78.5 6.7 20.1 2025 10 22 09 47.76 +61 31.9 8.382 8.370 86.0 6.8 20.0 2025 11 01 09 48.69 +62 40.9 8.214 8.333 93.4 6.8 20.0 2025 11 11 09 47.99 +63 58.1 8.052 8.296 100.8 6.7 19.9 2025 11 21 09 45.23 +65 22.1 7.900 8.259 108.0 6.5 19.9 2025 12 01 09 39.90 +66 50.7 7.762 8.222 114.6 6.3 19.8 2025 12 11 09 31.44 +68 20.7 7.643 8.186 120.4 6.0 19.8 2025 12 21 09 19.29 +69 47.8 7.546 8.149 125.0 5.7 19.7 2025 12 31 09 03.07 +71 06.9 7.473 8.114 127.8 5.5 19.7 2026 01 10 08 42.79 +72 12.4 7.428 8.078 128.6 5.5 19.7 2026 01 20 08 19.14 +72 59.0 7.409 8.043 127.2 5.6 19.6 2026 01 30 07 53.65 +73 23.3 7.417 8.008 123.9 5.9 19.6 2026 02 09 07 28.40 +73 24.7 7.448 7.973 119.0 6.2 19.6 2026 02 19 07 05.42 +73 05.5 7.501 7.939 112.9 6.6 19.6 2026 03 01 06 46.09 +72 30.2 7.571 7.905 106.2 6.9 19.6 2026 03 11 06 30.98 +71 44.4 7.654 7.871 99.0 7.2 19.6 2026 03 21 06 20.00 +70 52.9 7.746 7.837 91.6 7.3 19.7 2026 03 31 06 12.72 +69 59.8 7.840 7.804 84.3 7.3 19.7 2026 04 10 06 08.56 +69 08.3 7.934 7.772 77.1 7.2 19.7 2026 04 20 06 06.95 +68 20.3 8.023 7.739 70.1 7.0 19.7 2026 04 30 06 07.39 +67 37.3 8.102 7.707 63.6 6.7 19.7 2026 05 10 06 09.45 +67 00.1 8.169 7.676 57.6 6.4 19.7 2026 05 20 06 12.77 +66 29.2 8.222 7.644 52.3 6.0 19.7 2026 08 08 06 54.77 +66 33.9 7.944 7.409 54.9 6.4 19.5 2026 08 18 06 58.76 +67 08.6 7.825 7.381 60.6 6.9 19.5 2026 08 28 07 01.60 +67 51.5 7.693 7.354 66.8 7.3 19.4 2026 09 07 07 02.92 +68 42.5 7.550 7.327 73.5 7.6 19.4 2026 09 17 07 02.19 +69 41.4 7.400 7.301 80.4 7.8 19.3 2026 09 27 06 58.74 +70 47.0 7.248 7.275 87.6 7.9 19.3 2026 10 07 06 51.73 +71 57.6 7.097 7.250 94.8 7.9 19.2 2026 10 17 06 40.06 +73 10.1 6.952 7.225 102.0 7.8 19.2 2026 10 27 06 22.56 +74 19.4 6.818 7.200 108.8 7.5 19.1 2026 11 06 05 58.27 +75 18.4 6.700 7.177 115.1 7.2 19.0 2026 11 16 05 27.15 +75 58.3 6.601 7.153 120.4 6.8 19.0 2026 11 26 04 51.07 +76 10.1 6.527 7.130 124.3 6.6 19.0 2026 12 06 04 13.91 +75 48.3 6.478 7.108 126.4 6.4 18.9 2026 12 16 03 40.06 +74 53.4 6.458 7.086 126.4 6.4 18.9 2026 12 26 03 12.42 +73 31.7 6.466 7.065 124.1 6.6 18.9 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 April 25 (CBET 5542) Daniel W. E. Green