Electronic Telegram No. 5575 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 M1 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained on June 21 with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala (discovery observations tabulated below). Three 45-s w-band survey images taken in 1".1-1".2 seeing show a condensed head of size 2".2 (full-width-at-half- maximum) with a tail about 8" long in p.a. 280 degrees. 2025 UT R.A. (2000) Decl. Mag. June 21.34360 16 12 04.95 -20 33 14.4 20.9 21.35889 16 12 04.71 -20 33 15.4 20.9 21.36655 16 12 04.53 -20 33 15.8 21.3 Weryk and R. Wainscoat obtained three 60-s gri-band follow-up images of this object on June 24.4 UT with the 3.6-m Canada-France-Hawaii Telescope atop Mauna Kea (queue observer L. Wells; queue coordinator V. Khatu); in the image with the best seeing (0".7), there was a very condensed coma of size about 10" with a broad tail about 6" long spanning p.a. 265-310 degrees. S. Deen (Simi Valley, CA, USA) reports that imaging of this comet (apparently with a 0.43-m reflector at Rio Hurtado, Chile) on June 21.97-21.99 UT shows the object to be clearly cometary, with a diffuse coma of size 4".5 (FWHM) in 0".8 seeing; the magnitude was measured to be V = 20.6. Deen subsequently identified and measured observations of this comet in public archives, as follows. On 2023 Apr. 20.3-20.4, DECam exposures taken with the Cerro Tololo 4-m reflector in 1".1 seeing show a very condensed coma of size 1".5 (FWHM) and no tail (magnitudes r = 21.5, i = 21.4). On 2023 Apr. 24.6, an R-band CFHT image taken in 0".6 seeing shows a condensed coma of size 1".3 (FWHM) and no tail (mag 21.4). On 2023 May 14.3, a z-band DECam image taken in 0".9 seeing shows a condensed coma of size 1".5 (FWHM) and no tail (mag 21.4). On 2023 May 15.5, an R-band CFHT image taken in 0".9 seeing shows a condensed coma of size 1".3 (FWHM) and no tail (mag 21.1). On 2023 June 18.1, an r-band DECam taken in 0".9 seeing shows a very condensed coma of size 1".1 (FWHM) with no tail (mag 21.6). On 2023 June 19.1, an r-band DECam image taken in 1".8 (bad) seeing shows a coma of size 3".0 (FWHM) with no tail (mag 20.8), while a g-band DECam image give mag 21.2. On 2023 June 24.1, a g-band DECam image taken in 1".9 seeing shows a coma of size 2".5 and no tail (mag 21.7). On 2024 May 17.1, an i-band DECam image taken in 1".5 seeing shows a condensed coma of size 2".0 (FWHM) with no tail (mag 20.7). Deen also identified numerous pre-discovery images taken with the 1.5-m Mt. Lemmon reflector, nothing that it appears generally cometary in them, but he can't quantify much because of their relatively low resolution and faintness; below are his measurements of the Mt. Lemmon observations: 2025 UT R.A. (2000) Decl. Apr. 10.46865 16 31 13.70 -19 32 37.4 10.47333 16 31 13.64 -19 32 36.2 10.47802 16 31 13.59 -19 32 37.5 10.48271 16 31 13.53 -19 32 38.2 22.47232 16 28 50.43 -19 43 34.4 22.47805 16 28 50.36 -19 43 35.0 22.48377 16 28 50.31 -19 43 35.6 22.48950 16 28 50.19 -19 43 34.9 May 19.37177 16 21 43.49 -20 06 13.0 19.37225 16 21 43.49 -20 06 12.8 19.37715 16 21 43.41 -20 06 13.0 19.37763 16 21 43.43 -20 06 13.7 19.38251 16 21 43.28 -20 06 13.4 19.38299 16 21 43.25 -20 06 13.3 19.38835 16 21 43.18 -20 06 13.0 June 6.28876 16 16 22.97 -20 20 42.6 6.29359 16 16 22.93 -20 20 42.3 19.28821 16 12 38.65 -20 31 28.8 19.29398 16 12 38.52 -20 31 29.9 19.29974 16 12 38.46 -20 31 29.7 19.30554 16 12 38.39 -20 31 30.2 Additional astrometry appears on MPEC 2025-M132, including pre-discovery observations made with the 2.25-m Bok reflector at Kitt Peak on 2021 May 18.4 UT (mag 21.6-22.0). The following orbital elements by S. Nakano (Central Bureau) are from 62 observations spanning 2021 May 18-2025 June 26 (mean residual 0".4), with corresponding "original" and "future" values of 1/a being +0.000115 and +0.000150 (+/- 0.000009) AU**-1, respectively. There are no close approaches to major planets. Epoch = 2029 Aug. 12.0 TT T = 2029 Aug. 1.80733 TT Peri. = 230.37919 e = 1.0002724 Node = 66.92561 2000.0 q = 10.83448 AU Incl. = 64.83001 The following ephemeris by Nakano from the above orbital elements uses the formula total magnitude = 4.5 + 5 log Delta + 8.0 log r. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 06 14 16 14.13 -20 27.0 12.340 13.312 162.4 1.3 19.0 2025 06 24 16 11.37 -20 35.5 12.375 13.283 152.3 2.0 18.9 2025 07 04 16 08.88 -20 44.6 12.436 13.255 142.2 2.7 19.0 2025 07 14 16 06.76 -20 54.3 12.521 13.226 132.2 3.3 19.0 2025 07 24 16 05.06 -21 04.9 12.626 13.198 122.3 3.7 19.0 2025 08 03 16 03.85 -21 16.5 12.747 13.169 112.5 4.1 19.0 2025 08 13 16 03.15 -21 29.1 12.879 13.141 102.8 4.3 19.0 2025 08 23 16 02.99 -21 43.0 13.018 13.113 93.2 4.4 19.0 2025 09 02 16 03.36 -21 57.9 13.158 13.085 83.7 4.4 19.0 2025 09 12 16 04.25 -22 14.1 13.295 13.057 74.2 4.3 19.0 2025 09 22 16 05.64 -22 31.3 13.424 13.030 64.9 4.0 19.1 2025 10 02 16 07.48 -22 49.5 13.542 13.002 55.5 3.6 19.1 2025 10 12 16 09.74 -23 08.5 13.644 12.975 46.3 3.2 19.1 2026 01 20 16 41.26 -26 43.6 13.353 12.706 47.3 3.3 19.0 2026 01 30 16 43.71 -27 05.7 13.192 12.680 56.8 3.7 18.9 2026 02 09 16 45.75 -27 27.7 13.016 12.654 66.4 4.1 18.9 2026 02 19 16 47.30 -27 49.7 12.829 12.628 76.1 4.4 18.9 2026 03 01 16 48.30 -28 11.4 12.635 12.603 85.9 4.5 18.8 2026 03 11 16 48.72 -28 32.8 12.439 12.577 95.7 4.5 18.8 2026 03 21 16 48.53 -28 53.8 12.247 12.552 105.6 4.4 18.7 2026 03 31 16 47.71 -29 14.2 12.063 12.526 115.6 4.1 18.7 2026 04 10 16 46.28 -29 33.8 11.892 12.501 125.5 3.7 18.7 2026 04 20 16 44.27 -29 52.3 11.739 12.476 135.5 3.2 18.6 2026 04 30 16 41.75 -30 09.5 11.608 12.451 145.5 2.6 18.6 2026 05 10 16 38.81 -30 25.2 11.502 12.426 155.3 1.9 18.6 2026 05 20 16 35.55 -30 39.3 11.424 12.402 164.4 1.3 18.5 2026 05 30 16 32.10 -30 51.7 11.376 12.377 170.7 0.8 18.5 2026 06 09 16 28.60 -31 02.5 11.358 12.353 168.2 1.0 18.5 2026 06 19 16 25.19 -31 11.7 11.369 12.329 159.9 1.6 18.5 2026 06 29 16 22.01 -31 19.6 11.410 12.305 150.5 2.3 18.5 2026 07 09 16 19.17 -31 26.7 11.476 12.281 140.8 3.0 18.5 2026 07 19 16 16.78 -31 33.2 11.565 12.257 131.1 3.6 18.5 2026 07 29 16 14.93 -31 39.6 11.674 12.234 121.4 4.1 18.5 2026 08 08 16 13.66 -31 46.3 11.798 12.210 111.7 4.4 18.6 2026 08 18 16 13.02 -31 53.7 11.933 12.187 102.2 4.7 18.6 2026 08 28 16 13.02 -32 02.1 12.073 12.164 92.7 4.8 18.6 2026 09 07 16 13.64 -32 11.6 12.215 12.141 83.4 4.7 18.6 2026 09 17 16 14.87 -32 22.5 12.354 12.118 74.1 4.6 18.6 2026 09 27 16 16.68 -32 35.0 12.485 12.095 65.0 4.3 18.6 2026 10 07 16 19.02 -32 48.9 12.604 12.073 56.0 3.9 18.7 2026 10 17 16 21.82 -33 04.5 12.708 12.050 47.0 3.5 18.7 2027 01 25 17 00.18 -36 56.7 12.468 11.836 48.3 3.6 18.6 2027 02 04 17 03.23 -37 26.6 12.318 11.816 57.4 4.0 18.5 2027 02 14 17 05.79 -37 57.5 12.153 11.796 66.6 4.4 18.5 2027 02 24 17 07.79 -38 29.3 11.978 11.775 75.9 4.7 18.5 2027 03 06 17 09.14 -39 01.7 11.796 11.756 85.2 4.8 18.4 2027 03 16 17 09.80 -39 34.6 11.613 11.736 94.7 4.8 18.4 2027 03 26 17 09.71 -40 07.4 11.433 11.716 104.1 4.7 18.3 2027 04 05 17 08.86 -40 39.8 11.262 11.697 113.5 4.5 18.3 2027 04 15 17 07.25 -41 11.1 11.103 11.678 122.9 4.1 18.3 2027 04 25 17 04.91 -41 40.9 10.961 11.659 132.1 3.7 18.2 2027 05 05 17 01.91 -42 08.4 10.840 11.640 140.9 3.1 18.2 2027 05 15 16 58.36 -42 33.0 10.743 11.621 149.0 2.6 18.2 2027 05 25 16 54.39 -42 54.2 10.673 11.603 155.6 2.1 18.2 2027 06 04 16 50.16 -43 11.8 10.631 11.584 159.1 1.8 18.1 2027 06 14 16 45.86 -43 25.5 10.618 11.566 158.1 1.9 18.1 2027 06 24 16 41.67 -43 35.6 10.633 11.548 153.1 2.3 18.1 2027 07 04 16 37.77 -43 42.3 10.675 11.531 145.9 2.8 18.1 2027 07 14 16 34.32 -43 46.2 10.742 11.513 137.6 3.4 18.1 2027 07 24 16 31.46 -43 48.0 10.831 11.496 128.9 3.9 18.2 2027 08 03 16 29.28 -43 48.4 10.939 11.479 119.9 4.4 18.2 2027 08 13 16 27.86 -43 48.1 11.061 11.462 110.9 4.7 18.2 2027 08 23 16 27.24 -43 48.0 11.193 11.445 102.0 5.0 18.2 2027 09 02 16 27.42 -43 48.6 11.331 11.429 93.0 5.1 18.2 2027 09 12 16 28.38 -43 50.4 11.470 11.412 84.2 5.0 18.3 2027 09 22 16 30.10 -43 53.9 11.606 11.396 75.5 4.9 18.3 2027 10 02 16 32.53 -43 59.4 11.736 11.380 66.9 4.6 18.3 2027 10 12 16 35.61 -44 07.0 11.854 11.365 58.5 4.3 18.3 2027 10 22 16 39.26 -44 17.0 11.958 11.349 50.4 3.9 18.3 2027 11 01 16 43.42 -44 29.4 12.045 11.334 42.6 3.4 18.3 2028 01 20 17 24.56 -47 36.9 11.929 11.220 42.2 3.4 18.3 2028 01 30 17 29.26 -48 11.3 11.814 11.206 50.0 3.9 18.3 2028 02 09 17 33.51 -48 48.0 11.683 11.193 58.1 4.3 18.2 2028 02 19 17 37.21 -49 27.0 11.538 11.180 66.5 4.6 18.2 2028 02 29 17 40.26 -50 08.1 11.384 11.168 74.9 4.9 18.2 2028 03 10 17 42.55 -50 50.9 11.224 11.155 83.5 5.1 18.1 2028 03 20 17 43.99 -51 35.1 11.063 11.143 92.1 5.1 18.1 2028 03 30 17 44.51 -52 20.1 10.904 11.131 100.6 5.1 18.1 2028 04 09 17 44.03 -53 05.2 10.752 11.119 109.0 4.9 18.0 2028 04 19 17 42.54 -53 49.4 10.612 11.108 117.2 4.6 18.0 2028 04 29 17 40.03 -54 31.7 10.487 11.096 125.1 4.3 18.0 2028 05 09 17 36.56 -55 11.0 10.380 11.085 132.3 3.9 17.9 2028 05 19 17 32.24 -55 46.3 10.295 11.074 138.6 3.5 17.9 2028 05 29 17 27.23 -56 16.6 10.233 11.064 143.4 3.1 17.9 2028 06 08 17 21.75 -56 41.0 10.197 11.053 146.0 2.9 17.9 2028 06 18 17 16.07 -56 59.3 10.187 11.043 146.0 3.0 17.9 2028 06 28 17 10.45 -57 11.4 10.201 11.033 143.3 3.2 17.9 2028 07 08 17 05.18 -57 17.6 10.241 11.023 138.6 3.5 17.9 2028 07 18 17 00.50 -57 18.6 10.303 11.014 132.4 3.9 17.9 2028 07 28 16 56.62 -57 15.4 10.385 11.005 125.4 4.3 17.9 2028 08 07 16 53.71 -57 09.1 10.484 10.996 117.9 4.7 17.9 2028 08 17 16 51.84 -57 00.9 10.597 10.987 110.2 5.0 18.0 2028 08 27 16 51.09 -56 51.8 10.719 10.979 102.3 5.2 18.0 2028 09 06 16 51.44 -56 42.8 10.848 10.970 94.3 5.3 18.0 2028 09 16 16 52.88 -56 34.9 10.979 10.962 86.4 5.3 18.0 2028 09 26 16 55.34 -56 28.7 11.108 10.954 78.6 5.1 18.0 2028 10 06 16 58.77 -56 24.6 11.231 10.947 71.0 5.0 18.1 2028 10 16 17 03.06 -56 23.2 11.346 10.939 63.6 4.7 18.1 2028 10 26 17 08.14 -56 24.5 11.448 10.932 56.6 4.4 18.1 2028 11 05 17 13.92 -56 28.9 11.536 10.926 50.0 4.0 18.1 2028 11 15 17 20.28 -56 36.4 11.607 10.919 44.1 3.6 18.1 2029 01 14 18 05.18 -58 29.4 11.607 10.885 41.0 3.4 18.1 2029 01 24 18 12.78 -58 59.9 11.536 10.880 46.3 3.8 18.1 2029 02 03 18 20.12 -59 33.9 11.449 10.875 52.4 4.1 18.1 2029 02 13 18 27.07 -60 11.3 11.346 10.871 59.0 4.5 18.1 2029 02 23 18 33.49 -60 52.1 11.231 10.867 66.0 4.8 18.0 2029 03 05 18 39.27 -61 36.2 11.108 10.863 73.2 5.0 18.0 2029 03 15 18 44.25 -62 23.5 10.979 10.859 80.5 5.2 18.0 2029 03 25 18 48.29 -63 13.5 10.848 10.856 87.8 5.3 18.0 2029 04 04 18 51.25 -64 05.7 10.718 10.853 95.1 5.3 17.9 2029 04 14 18 52.97 -64 59.4 10.594 10.850 102.2 5.2 17.9 2029 04 24 18 53.32 -65 53.6 10.478 10.847 109.0 5.0 17.9 2029 05 04 18 52.20 -66 47.2 10.374 10.845 115.4 4.8 17.9 2029 05 14 18 49.52 -67 38.6 10.285 10.842 121.2 4.6 17.8 2029 05 24 18 45.29 -68 26.5 10.213 10.841 126.1 4.3 17.8 2029 06 03 18 39.60 -69 09.3 10.160 10.839 129.9 4.1 17.8 2029 06 13 18 32.66 -69 45.5 10.128 10.838 132.3 4.0 17.8 2029 06 23 18 24.82 -70 14.0 10.116 10.836 133.1 3.9 17.8 2029 07 03 18 16.51 -70 34.1 10.127 10.836 132.2 4.0 17.8 2029 07 13 18 08.26 -70 45.7 10.157 10.835 129.7 4.1 17.8 2029 07 23 18 00.60 -70 49.1 10.207 10.835 125.9 4.4 17.8 2029 08 02 17 54.00 -70 45.4 10.275 10.834 121.1 4.6 17.8 2029 08 12 17 48.81 -70 35.7 10.358 10.835 115.6 4.8 17.9 2029 08 22 17 45.28 -70 21.7 10.454 10.835 109.6 5.0 17.9 2029 09 01 17 43.53 -70 04.7 10.560 10.836 103.3 5.2 17.9 2029 09 11 17 43.57 -69 46.1 10.672 10.837 96.7 5.3 17.9 2029 09 21 17 45.36 -69 27.1 10.788 10.838 90.2 5.3 17.9 2029 10 01 17 48.79 -69 08.7 10.904 10.839 83.6 5.3 18.0 2029 10 11 17 53.72 -68 51.5 11.018 10.841 77.2 5.2 18.0 2029 10 21 18 00.02 -68 36.2 11.125 10.843 71.0 5.0 18.0 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 June 27 (CBET 5575) Daniel W. E. Green