Electronic Telegram No. 5235 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 P/2016 N7 = P/2020 O1 (LEMMON-PANSTARRS) K. Ly (El Monte, CA, USA) and S. Deen (Simi Valley, CA, USA) report the identification of observations of comet P/2020 O1 (cf. CBET 4820) in publicly available CCD images obtained in 2016 with the 8.2-m Subaru reflector atop Mauna Kea. The astrometry below was measured by Ly, who noticed the comet's active nature also in 2016. Deen reports an essentially stellar nuclear condensation on July 3, with a long, straight, thin tail 40" long in p.a. 248 degrees, noting that the fade from the nuclear condensation to the tail is remarkably abrupt (the 'edge' of the nuclear conodensatin is just as sharp ahead and behind, contrary to the asymmetrical appearance seen in typical comae). The comet appears entirely asteroidal in the Aug. 1 images in 0".5 seeing; there is no visible tail to > 3 magnitudes fainter than the comet's nuclear condensation. (These observations had been inadvertently published on MPEC 2022-Y114 without noting that this represents pre-discovery observations at a second apparition, permitting the numbering of this comet.) 2016 UT R.A. (2000) Decl. Mag. July 3.56813 23 30 55.08 + 0 04 05.7 23.2 3.57859 23 30 55.40 + 0 04 07.5 23.2 3.58896 23 30 55.72 + 0 04 09.1 23.1 3.59937 23 30 56.05 + 0 04 11.1 23.2 Aug. 1.44949 23 36 45.23 + 0 12 15.4 1.56820 23 36 43.84 + 0 11 57.8 The 2016 observations show residuals of -35" in R.A. and -10" in Decl. from an orbit in NK 4860, with a corresponding correction of Delta(T) = +0.03 day. The following linked orbital elements by S. Nakano (Central Bureau) are from 91 observations spanning 2016-2021 (mean residual 0".5), and this confirms the identify of the comet in single-night observations made on 2021 July 22 with the Hubble Space Telescope (cf. MPC 142043). There are no close approaches to major planets, meaning that the orbit remains stable over long periods of time. Epoch = 2016 Jan. 13.0 TT T = 2016 Jan. 15.33940 TT Peri. = 105.08460 e = 0.1185305 Node = 176.05154 2000.0 q = 2.3317835 AU Incl. = 5.22248 a = 2.6453367 AU n = 0.22907761 P = 4.30 years Epoch = 2020 Apr. 21.0 TT T = 2020 May 4.24039 TT Peri. = 104.94152 e = 0.1198137 Node = 176.01149 2000.0 q = 2.3293080 AU Incl. = 5.22214 a = 2.6463807 AU n = 0.22894206 P = 4.30 years Epoch = 2024 Sept. 7.0 TT T = 2024 Aug. 20.31462 TT Peri. = 104.38178 e = 0.1185968 Node = 175.96804 2000.0 q = 2.3320561 AU Incl. = 5.22506 a = 2.6458449 AU n = 0.22901161 P = 4.30 years Epoch = 2028 Dec. 15.0 TT T = 2028 Dec. 11.93010 TT Peri. = 104.89976 e = 0.1161796 Node = 175.88684 2000.0 q = 2.3386024 AU Incl. = 5.23271 a = 2.6460153 AU n = 0.22898949 P = 4.30 years Epoch = 2033 Mar. 24.0 TT T = 2033 Apr. 4.15253 TT Peri. = 105.31109 e = 0.1171114 Node = 175.86027 2000.0 q = 2.3363363 AU Incl. = 5.23321 a = 2.6462414 AU n = 0.22896014 P = 4.30 years Epoch = 2037 July 1.0 TT T = 2037 July 19.96497 TT Peri. = 104.35559 e = 0.1183376 Node = 175.83297 2000.0 q = 2.3328399 AU Incl. = 5.23709 a = 2.6459560 AU n = 0.22899719 P = 4.30 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 15.5 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2023 02 25 09 27.60 +10 48.0 1.880 2.846 164.5 5.3 21.4 2023 03 07 09 20.16 +11 44.1 1.918 2.837 152.7 9.2 21.4 2023 03 17 09 14.59 +12 32.5 1.982 2.827 141.3 12.7 21.5 2023 03 27 09 11.36 +13 10.5 2.066 2.817 130.5 15.6 21.6 2023 04 06 09 10.68 +13 36.4 2.166 2.807 120.3 17.9 21.7 2023 04 16 09 12.47 +13 50.0 2.278 2.797 110.9 19.6 21.8 2023 04 26 09 16.56 +13 51.6 2.397 2.787 102.1 20.7 21.8 2023 05 06 09 22.70 +13 41.6 2.520 2.776 93.8 21.3 21.9 2023 05 16 09 30.58 +13 21.0 2.643 2.765 86.1 21.4 22.0 2024 03 31 17 30.20 -17 21.1 1.896 2.394 107.5 23.5 20.7 2024 04 10 17 36.74 -16 53.5 1.774 2.386 115.7 22.2 20.5 2024 04 20 17 40.64 -16 22.1 1.661 2.379 124.5 20.4 20.4 2024 04 30 17 41.66 -15 48.7 1.560 2.371 133.8 17.9 20.2 2024 05 10 17 39.68 -15 15.3 1.475 2.365 143.7 14.7 20.1 2024 05 20 17 34.86 -14 44.2 1.408 2.359 153.9 10.9 20.0 2024 05 30 17 27.73 -14 17.8 1.362 2.354 164.0 6.8 19.9 2024 06 09 17 19.14 -13 58.3 1.341 2.349 170.7 4.0 19.8 2024 06 19 17 10.28 -13 48.0 1.345 2.344 166.4 5.8 19.8 2024 06 29 17 02.36 -13 48.0 1.372 2.341 156.7 9.9 19.9 2024 07 09 16 56.38 -13 58.7 1.422 2.338 146.4 13.9 20.0 2024 07 19 16 53.05 -14 19.5 1.491 2.335 136.5 17.4 20.1 2024 07 29 16 52.64 -14 48.5 1.576 2.334 127.2 20.3 20.2 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 March 22 (CBET 5235) Daniel W. E. Green