Electronic Telegram No. 5509 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 D1 (GROELLER) Hannes Groeller, Lunar and Planetary Laboratory, University of Arizona, reports his discovery of a comet on CCD images obtained with the 2.25-m Bok reflector at Kitt Peak on Feb. 20; stacked 30-s exposures show a condensed coma of size 3", with a "fuzzy layer around it with a diameter of 4". The discovery observations are tabulated below. 2025 UT R.A. (2000) Decl. Mag. Observer Feb. 20.32842 9 19 56.45 +42 09 00.2 20.6 Groeller 20.33404 9 19 56.29 +42 09 00.0 20.5 " 20.33965 9 19 56.15 +42 08 59.8 20.8 " 20.34526 9 19 56.03 +42 08 59.6 20.7 " After the comet was posted to the Minor Planet Center's PCCP, S. Deen (Simi Valley, CA, USA) writes that he has identified the comet in numerous archival images taken with the same Bok reflector in 2018 and 2019, after finding later observations in 2024-2025 and then also earlier observations in 2022. A g-band images taken on 2018 June 6.20 UT show a moderately condensed coma of size only 2".5 (full-width-at-half-maximum) and mag 23.2 in 2".3 seeing witn no visible tail. An image from 2018 June 7.22 shows a stellar appearance in 1".7 seeing. A g-band image from June 9.21 taken in 1".8 seeing shows a moderately diffuse coma of size 2".4 (FWHM) and mag 23.3 with no tail. An r-band image from 2018 June 18.19 in 1".8 seeing shows a moderately diffuse coma of size 2".2 (FWHM) and mag 22.1 with a possible elongation toward p.a. 235 degrees. An r-band image from 2019 Feb. 9.52 taken in 1".4 seeing shows a moderately diffuse coma of size 2".3 (FWHM) and mag 21.8 with a possible elongation toward p.a. 40 degrees. An r-band image taken on 2019 Feb. 12.31 in 1".8 seeing shows a moderately condensed coma of size 2".1 (FWHM) with no visible tail. An r-band image taken on 2022 Feb. 2.50 by J.-C. Cuillandre with the 3.6-m Canada-France-Hawaii Telescope in 0".6 seeing shows a moderately condensed coma of size 1".4 (FWHM) and mag 21.2 with a very broad 2"-long tail pointing towards p.a. 230 degrees. Two g-band images taken on 2022 May 30.3 with the 8.3-m Subaru Telescope in 0".5 seeing show a moderately condensed coma of size 1".5 (FWHM) and mag 22.3 with a very broad 1".5-long tail pointing towards p.a. 120 degrees. Deen also found numerous pre- discovery images of the comet -- all seeming to be generally non-stellar in appearance -- in photos taken in 2024 and 2025 with the Mt. Lemmon Survey's 1.5-m reflector (from the archive at the NASA/PDS small-bodies node website), as tabulated below. Deen found the 2024-2025 data first, and that allowed him to find the 2022 observations, and from there he was able to find the earlier observations noted above. 2024 UT R.A. (2000) Decl. Apr. 14.18844 9 15 02.10 +48 39 36.8 14.19409 9 15 02.12 +48 39 35.9 14.19975 9 15 02.16 +48 39 34.9 14.20541 9 15 02.09 +48 39 35.1 June 19.15722 9 16 35.37 +45 10 55.4 19.16157 9 16 35.48 +45 10 53.1 19.16591 9 16 35.59 +45 10 53.1 19.17025 9 16 35.52 +45 10 52.0 Nov. 12.47039 9 46 20.99 +41 21 20.2 12.47561 9 46 21.06 +41 21 20.1 12.48081 9 46 21.02 +41 21 19.7 12.48601 9 46 21.00 +41 21 20.2 Dec. 10.42253 9 43 36.72 +41 41 39.8 10.42776 9 43 36.71 +41 41 39.5 10.43301 9 43 36.68 +41 41 40.5 10.43825 9 43 36.66 +41 41 40.5 2025 UT R.A. (2000) Decl. Jan. 20.32361 9 31 53.15 +42 13 06.3 20.32885 9 31 52.97 +42 13 06.6 20.33408 9 31 52.81 +42 13 06.2 20.33932 9 31 52.71 +42 13 06.8 Feb. 8.14911 9 24 39.08 +42 14 53.7 8.15426 9 24 39.00 +42 14 53.6 8.15941 9 24 38.84 +42 14 53.1 8.16455 9 24 38.81 +42 14 53.7 M. Jaeger writes that thirty 70-s CMOS exposures taken on 2025 Feb. 22.0 UT with a 0.35-m f/4.2 reflector at Martinsberg, Oed, Austria, by G. Rhemann, E. Prosperi, and himself show a 12" coma of mag 20.2 and a 6" tail in p.a. 140 degrees. Additional astrometry appears on MPEC 2025-D83. The following orbital elements by S. Nakano (Central Bureau) are from 58 observations spanning 2018 June 6-2025 Feb. 22 (mean residual 0".5), with corresponding "original" and "future" values of 1/a being +0.000021 and -0.000008 (+/- 0.000007) AU**-1, respectively. There are no close approaches to major planets. Epoch = 2028 May 29.0 TT T = 2028 May 28.26108 TT Peri. = 186.11262 e = 1.0033466 Node = 312.90416 2000.0 q = 14.11261 AU Incl. = 84.45937 The following ephemeris by Nakano from the above orbital elements uses photometric power-law parameters H = 5.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 02 14 09 22.37 +42 12.8 14.261 15.127 150.3 1.9 20.2 2025 02 24 09 18.56 +42 06.1 14.299 15.111 144.0 2.2 20.2 2025 03 06 09 14.99 +41 55.3 14.362 15.095 136.3 2.6 20.2 2025 03 16 09 11.77 +41 40.5 14.450 15.079 127.7 3.0 20.2 2025 03 26 09 09.01 +41 22.2 14.557 15.063 118.8 3.3 20.2 2025 04 05 09 06.77 +41 00.7 14.680 15.048 109.8 3.6 20.3 2025 04 15 09 05.10 +40 36.4 14.814 15.032 100.7 3.8 20.3 2025 04 25 09 04.00 +40 10.0 14.954 15.017 91.6 3.8 20.3 2025 05 05 09 03.49 +39 41.9 15.096 15.001 82.7 3.8 20.3 2025 05 15 09 03.54 +39 12.7 15.236 14.986 73.9 3.7 20.3 2025 05 25 09 04.10 +38 42.7 15.368 14.971 65.2 3.5 20.3 2025 06 04 09 05.14 +38 12.4 15.489 14.956 56.7 3.2 20.3 2025 06 14 09 06.59 +37 42.2 15.597 14.941 48.4 2.9 20.4 2025 09 22 09 30.00 +33 43.0 15.456 14.799 47.7 2.9 20.3 2025 10 02 09 31.81 +33 30.0 15.318 14.786 56.3 3.2 20.3 2025 10 12 09 33.27 +33 19.6 15.164 14.772 65.2 3.5 20.3 2025 10 22 09 34.32 +33 11.9 14.997 14.759 74.3 3.7 20.2 2025 11 01 09 34.91 +33 06.8 14.823 14.746 83.6 3.8 20.2 2025 11 11 09 35.00 +33 04.1 14.645 14.733 93.2 3.8 20.2 2025 11 21 09 34.56 +33 03.6 14.469 14.720 102.8 3.8 20.1 2025 12 01 09 33.56 +33 05.0 14.300 14.707 112.6 3.5 20.1 2025 12 11 09 32.01 +33 07.7 14.142 14.695 122.5 3.2 20.1 2025 12 21 09 29.92 +33 11.3 14.001 14.682 132.4 2.8 20.1 2025 12 31 09 27.35 +33 15.1 13.882 14.670 142.0 2.4 20.0 2026 01 10 09 24.36 +33 18.3 13.788 14.657 151.2 1.9 20.0 2026 01 20 09 21.05 +33 20.3 13.722 14.645 159.0 1.4 20.0 2026 01 30 09 17.53 +33 20.4 13.687 14.633 163.2 1.1 20.0 2026 02 09 09 13.94 +33 18.2 13.684 14.621 161.2 1.2 20.0 2026 02 19 09 10.39 +33 13.1 13.711 14.609 154.5 1.7 20.0 2026 03 01 09 07.02 +33 05.1 13.767 14.598 145.8 2.2 20.0 2026 03 11 09 03.94 +32 54.0 13.851 14.586 136.4 2.7 20.0 2026 03 21 09 01.25 +32 40.0 13.957 14.575 126.7 3.1 20.0 2026 03 31 08 59.02 +32 23.2 14.083 14.564 117.0 3.5 20.0 2026 04 10 08 57.31 +32 04.0 14.223 14.553 107.3 3.8 20.1 2026 04 20 08 56.13 +31 42.7 14.373 14.542 97.7 3.9 20.1 2026 04 30 08 55.49 +31 19.7 14.527 14.531 88.2 4.0 20.1 2026 05 10 08 55.38 +30 55.2 14.681 14.520 78.9 3.9 20.1 2026 05 20 08 55.77 +30 29.7 14.830 14.509 69.7 3.7 20.1 2026 05 30 08 56.62 +30 03.3 14.970 14.499 60.6 3.5 20.2 2026 06 09 08 57.87 +29 36.5 15.096 14.489 51.7 3.2 20.2 2026 09 27 09 21.77 +25 10.1 15.019 14.384 49.2 3.0 20.1 2026 10 07 09 23.27 +24 53.5 14.873 14.375 58.4 3.4 20.1 2026 10 17 09 24.39 +24 38.8 14.713 14.366 67.8 3.7 20.1 2026 10 27 09 25.10 +24 26.2 14.542 14.358 77.4 3.9 20.1 2026 11 06 09 25.34 +24 15.8 14.364 14.350 87.2 4.0 20.0 2026 11 16 09 25.08 +24 07.4 14.185 14.342 97.1 3.9 20.0 2026 11 26 09 24.31 +24 00.9 14.010 14.334 107.3 3.8 20.0 2026 12 06 09 23.02 +23 56.2 13.843 14.326 117.5 3.5 20.0 2026 12 16 09 21.21 +23 53.0 13.692 14.318 127.9 3.1 19.9 2026 12 26 09 18.94 +23 50.8 13.560 14.310 138.4 2.6 19.9 2027 01 05 09 16.25 +23 49.2 13.451 14.303 149.0 2.0 19.9 2027 01 15 09 13.24 +23 47.7 13.371 14.295 159.4 1.4 19.9 2027 01 25 09 09.99 +23 45.9 13.321 14.288 169.0 0.8 19.9 2027 02 04 09 06.63 +23 43.2 13.303 14.281 172.7 0.5 19.9 2027 02 14 09 03.27 +23 39.3 13.317 14.274 165.2 1.0 19.9 2027 02 24 09 00.04 +23 33.7 13.363 14.268 155.2 1.7 19.9 2027 03 06 08 57.04 +23 26.4 13.439 14.261 144.8 2.3 19.9 2027 03 16 08 54.38 +23 17.1 13.540 14.254 134.5 2.9 19.9 2027 03 26 08 52.14 +23 05.9 13.664 14.248 124.2 3.3 19.9 2027 04 05 08 50.35 +22 52.7 13.805 14.242 114.0 3.7 19.9 2027 04 15 08 49.07 +22 37.8 13.959 14.236 104.0 3.9 20.0 2027 04 25 08 48.30 +22 21.1 14.121 14.230 94.2 4.0 20.0 2027 05 05 08 48.04 +22 03.0 14.285 14.224 84.5 4.0 20.0 2027 05 15 08 48.26 +21 43.4 14.446 14.219 75.0 3.9 20.0 2027 05 25 08 48.93 +21 22.6 14.600 14.213 65.7 3.7 20.0 2027 06 04 08 50.00 +21 00.8 14.744 14.208 56.4 3.4 20.1 2027 06 14 08 51.43 +20 38.0 14.872 14.203 47.3 3.0 20.1 2027 10 02 09 14.39 +16 10.3 14.748 14.155 52.1 3.2 20.1 2027 10 12 09 15.59 +15 49.1 14.599 14.151 61.6 3.6 20.0 2027 10 22 09 16.41 +15 29.3 14.437 14.148 71.2 3.8 20.0 2027 11 01 09 16.80 +15 11.0 14.266 14.145 81.0 4.0 20.0 2027 11 11 09 16.72 +14 54.4 14.091 14.142 91.0 4.0 19.9 2027 11 21 09 16.16 +14 39.7 13.916 14.139 101.1 3.9 19.9 2027 12 01 09 15.09 +14 26.8 13.747 14.136 111.4 3.7 19.9 2027 12 11 09 13.53 +14 15.8 13.590 14.134 121.8 3.4 19.9 2027 12 21 09 11.51 +14 06.5 13.449 14.131 132.4 2.9 19.8 2027 12 31 09 09.07 +13 58.9 13.330 14.129 143.1 2.4 19.8 2028 01 10 09 06.29 +13 52.7 13.238 14.127 153.8 1.8 19.8 2028 01 20 09 03.26 +13 47.7 13.174 14.125 164.6 1.1 19.8 2028 01 30 09 00.08 +13 43.4 13.142 14.123 174.7 0.4 19.8 2028 02 09 08 56.86 +13 39.5 13.143 14.121 172.6 0.5 19.8 2028 02 19 08 53.72 +13 35.7 13.176 14.120 162.2 1.2 19.8 2028 02 29 08 50.77 +13 31.6 13.239 14.119 151.6 1.9 19.8 2028 03 10 08 48.11 +13 26.9 13.331 14.117 141.0 2.5 19.8 2028 03 20 08 45.81 +13 21.4 13.448 14.116 130.6 3.1 19.8 2028 03 30 08 43.94 +13 14.7 13.585 14.115 120.3 3.5 19.9 2028 04 09 08 42.54 +13 06.8 13.737 14.114 110.2 3.8 19.9 2028 04 19 08 41.63 +12 57.5 13.900 14.114 100.3 4.0 19.9 2028 04 29 08 41.21 +12 46.6 14.069 14.113 90.5 4.1 19.9 2028 05 09 08 41.26 +12 34.3 14.237 14.113 80.9 4.1 20.0 2028 05 19 08 41.76 +12 20.3 14.401 14.113 71.5 3.9 20.0 2028 05 29 08 42.67 +12 04.7 14.556 14.113 62.2 3.6 20.0 2028 06 08 08 43.94 +11 47.6 14.698 14.113 53.1 3.3 20.0 2028 06 18 08 45.52 +11 29.0 14.824 14.113 44.1 2.9 20.1 2028 09 26 09 06.27 +07 22.7 14.790 14.123 46.9 3.0 20.0 2028 10 06 09 07.57 +06 55.9 14.658 14.125 56.1 3.4 20.0 2028 10 16 09 08.51 +06 29.7 14.511 14.127 65.5 3.7 20.0 2028 10 26 09 09.04 +06 04.3 14.353 14.129 75.1 3.9 20.0 2028 11 05 09 09.13 +05 40.2 14.187 14.132 84.8 4.0 20.0 2028 11 15 09 08.75 +05 17.5 14.019 14.134 94.7 4.0 19.9 2028 11 25 09 07.89 +04 56.6 13.855 14.137 104.7 3.9 19.9 2028 12 05 09 06.55 +04 37.7 13.698 14.140 114.8 3.6 19.9 2028 12 15 09 04.74 +04 21.1 13.556 14.142 124.9 3.3 19.9 2028 12 25 09 02.52 +04 06.9 13.431 14.145 135.1 2.8 19.8 2029 01 04 08 59.94 +03 55.1 13.331 14.149 145.1 2.3 19.8 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 February 24 (CBET 5509) Daniel W. E. Green