Electronic Telegram No. 5285 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 P1 (NISHIMURA) Hideo Nishimura, Kakegawa, Japan, reports his discovery of a diffuse comet with a 5' coma on three 30-s exposures (limiting mag 15) taken on Aug. 12.78 UT using a 200-mm f/3 lens mounted on a Canon EOS 6D digital camera. Nishimura subsequently found the comet on pre-discovery exposures that he took the previous night. The report came to the Central Bureau via S. Nakano (CBAT) and via I. Endoh (National Astronomical Observatory of Japan, Tokyo). Nishimura's astrometry is tabulated below. 2023 UT R.A. (2000) Decl. Mag. Observer Aug. 11.76854 7 04 09.47 +18 52 24.3 11.0 Nishimura 11.76888 7 04 09.60 +18 52 27.7 " 11.76921 7 04 10.09 +18 52 26.6 " 11.79992 7 04 14.52 +18 52 42.0 " 12.77992 7 06 58.28 +19 05 11.5 10.4 " 12.78035 7 06 58.56 +19 05 10.8 10.5 " 12.78076 7 06 58.93 +19 05 16.8 10.3 " News of the comet circulated rapidly online before it was posted on the Minor Planet Center's PCCP webpage. Below are observations sent directly to the Bureau (some via the "ICQ Comet Observations" Facebook forum, which contains numerous images of the comet). Thirty stacked 30-s CMOS exposures taken by K. Yoshimoto (Hirao, Kumage, Yamaguchi, Japan) on Aug. 13.8 UT with a 0.20-m f/8 Ritchey-Chretien reflector show a condensed coma 3'.6 in diameter of total mag 10.0 and no tail. S. Deen (Simi Valley, CA, USA) writes that CMOS images obtained on Aug. 14.4 UT with a 0.43-m reflector at Rio Hurtado, Chile, show a very diffuse coma with a diameter exceeding 100" and showing no obvious central condensation, adding that the center is elongated along p.a. 64/244 degrees and measuring about 5" x 10" in size (very slightly sharper in the solar direction, and more diffuse in the anti-solar direction); an ion tail extends at least 180" away from the center of the coma toward p.a. 267 degrees. CCD images taken remotely A. Pearce (Nedlands, W. Australia) with a 0.25-m f/3.4 reflector located at the Utah Desert Remote Observatory (Beryl Junction, UT, USA) on Aug. 14.49 show a coma diameter of approximately 1'.5 of total mag 9.5 with a tail approximately 8' long in p.a. 265 deg. Sixteen stacked 20-s CCD exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) on Aug. 14.49 with a 0.51-m f/6.8 astrograph located at Beryl Junction show a strongly condensed object with an outer coma 3'.0 in diameter and a faint ion tail 11' long toward p.a. 270 deg; the magnitude was 10.8 as measured within a circular aperture of radius 90".2. Twenty stacked 20-s exposures taken by M. Mattiazzo (Swan Hill, Victoria, Australia) with a Canon 6D camera and a Celestron 11 f/2.2 Rowe-Ackermann Schmidt Astrograph on Aug. 14.83-14.84 show a strongly condensed coma 3' wide with total mag 10.4 (UCAC4 comparison-star V magnitudes). CCD images taken on Aug. 15.1 by M. Jaeger at Martinsberg, Oed, Austria, with a 0.4-m reflector show a 4'.5 coma of total mag 10.4 with a 10' tail in p.a. 275 degrees. Visual total-magnitude and coma-diameter estimates: Aug. 14.16 UT, 9.3, 4' (J. J. Gonzalez Suarez, Alto del Castro, Leon, Spain, 0.20-m reflector; altitude 11 degrees); Aug. 15.35, 10.8, -- (J. G. de S. Aguiar, Campinas, Brazil, 0.27-m reflector; cirrus clouds; altitude 16 deg); Aug. 15.45, 10.2, 3' (A. Hale, Cloudcroft, NM, USA, 0.41-m reflector). The available astrometry appears on MPEC 2023-P87. The following parabolic orbital elements by Nakano are from 60 observations spanning Aug. 11-2023 Aug. 15 (mean residual 1".5). T = 2023 Sept. 18.00203 TT Peri. = 117.18755 Node = 67.63345 2000.0 q = 0.2215244 AU Incl. = 130.67933 The comet has been < 40 degrees from the sun since late April. The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 9.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2023 08 04 06 45.48 +17 22.9 1.966 1.210 30.6 25.3 11.1 2023 08 09 06 56.94 +18 18.7 1.818 1.108 32.6 29.5 10.7 2023 08 14 07 10.52 +19 21.2 1.664 1.003 34.1 34.6 10.1 2023 08 19 07 27.19 +20 31.6 1.505 0.893 35.1 40.7 9.5 2023 08 24 07 48.55 +21 49.7 1.342 0.779 35.2 48.5 8.8 2023 08 29 08 17.38 +23 10.2 1.180 0.660 33.9 58.7 7.9 2023 09 03 08 58.36 +24 11.0 1.027 0.535 30.5 72.9 6.9 2023 09 08 09 57.95 +23 39.6 0.901 0.406 23.7 93.1 5.6 2023 09 13 11 16.51 +18 41.8 0.847 0.285 14.7 116.5 4.3 2023 09 18 12 25.25 +07 19.2 0.933 0.222 12.4 102.6 3.6 2023 09 23 12 51.14 -04 04.2 1.121 0.284 14.0 58.7 4.9 2023 09 28 12 56.06 -11 30.3 1.298 0.406 14.0 36.7 6.4 2023 10 03 12 56.52 -16 35.1 1.447 0.535 14.1 27.1 7.6 2023 10 08 12 56.17 -20 26.3 1.573 0.659 14.9 22.9 8.5 2023 10 13 12 55.78 -23 35.3 1.682 0.779 16.5 21.3 9.3 2023 10 18 12 55.48 -26 18.1 1.777 0.893 18.7 21.0 9.9 2023 10 23 12 55.25 -28 43.8 1.860 1.002 21.5 21.3 10.4 2023 10 28 12 55.02 -30 57.8 1.931 1.107 24.6 21.9 10.8 2023 11 02 12 54.70 -33 03.8 1.994 1.209 27.9 22.6 11.2 2023 11 07 12 54.22 -35 04.3 2.047 1.307 31.4 23.3 11.5 2023 11 12 12 53.48 -37 00.9 2.092 1.403 35.1 23.9 11.8 2023 11 17 12 52.38 -38 54.8 2.130 1.496 38.9 24.5 12.0 2023 11 22 12 50.81 -40 46.9 2.162 1.587 42.8 25.0 12.3 2023 11 27 12 48.65 -42 37.4 2.188 1.675 46.8 25.4 12.5 2023 12 02 12 45.79 -44 26.8 2.208 1.762 50.9 25.8 12.7 2023 12 07 12 42.08 -46 15.0 2.224 1.847 55.1 25.9 12.9 2023 12 12 12 37.35 -48 01.7 2.237 1.930 59.3 26.0 13.0 2023 12 17 12 31.44 -49 46.4 2.246 2.011 63.6 26.0 13.2 2023 12 22 12 24.16 -51 27.9 2.253 2.092 67.9 25.8 13.3 2023 12 27 12 15.31 -53 05.0 2.258 2.170 72.2 25.6 13.5 2024 01 01 12 04.74 -54 36.0 2.263 2.248 76.5 25.2 13.6 2024 01 06 11 52.29 -55 58.9 2.269 2.325 80.8 24.7 13.7 2024 01 11 11 37.89 -57 11.1 2.275 2.400 85.1 24.1 13.8 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 August 15 (CBET 5285) Daniel W. E. Green