Electronic Telegram No. 5023 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/2021 P2 (PANSTARRS) [Editor's note: this text replaces that on CBET 5021 (orbital elements)] R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala on Aug. 7, when a stack of four 45-s w-band survey images showed a coma size of 1".5 (full- width-at-half-maximum) in 1".35 seeing (worst image) with no obvious tail. The discovery observations, along with pre-discovery Pan-STARRS1 astrometry from June, are tabulated below. 2021 UT R.A. (2000) Decl. Mag. June 19.58688 1 17 01.35 +17 11 42.2 21.6 19.59139 1 17 01.35 +17 11 42.8 21.0 19.59593 1 17 01.35 +17 11 43.8 21.3 19.60047 1 17 01.32 +17 11 44.2 21.5 Aug. 7.52435 1 01 45.86 +18 57 00.9 21.5 7.53865 1 01 45.32 +18 57 01.8 21.4 7.55291 1 01 44.78 +18 57 02.6 21.5 7.56712 1 01 44.24 +18 57 03.2 21.7 Weryk writes that four stacked 60-s w-band follow-up images taken on Aug. 9.5 UT show a coma size of 1".45 +/- 0".04 (FWHM) in 1".1 seeing (worst image) with no obvious tail; four stacked 60-s w-band follow-up images taken on Aug. 10.5 show a coma of size 1".4 (FWHM) in 0".9-1".2 seeing. Weryk and R. Wainscoat obtained follow-up images on Aug. 11.51 with the 3.6-m Canada- France-Hawaii Telescope at Mauna Kea (queue observer H. Januszewski; queue coordinator M. B. Laychak) in 1".1 seeing; three 60-s gri-band images were taken, but a single image shows a coma of size 1".6 (FWHM) and a possible tail/asymmetry towards p.a. 115 degrees. The available astrometry appears on MPEC 2021-Q28. The following parabolic orbital elements by S. Nakano (CBAT) are from 27 observations spanning 2021 June 19-Aug. 11 (mean residual 0".2), with the caution that this orbit is heavily reliant on the one-night June observatinos that are uncomfortably far separated from the August observations. Nakano was unable to find additional observations in archival astrometray. T = 2023 Jan. 21.64146 TT Peri. = 76.52684 Node = 31.99640 2000.0 q = 5.0690412 AU Incl. = 150.02256 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 11.0 and 2.5n = 7.5 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 08 14 00 57.45 +19 00.9 5.848 6.412 119.8 7.9 20.9 2021 08 24 00 49.66 +19 00.2 5.664 6.369 130.7 6.9 20.8 2021 09 03 00 40.61 +18 50.2 5.504 6.325 141.6 5.7 20.7 2021 09 13 00 30.48 +18 30.2 5.375 6.282 152.2 4.3 20.6 2021 09 23 00 19.61 +18 00.2 5.281 6.240 161.3 3.0 20.6 2021 10 03 00 08.37 +17 21.1 5.226 6.198 164.9 2.4 20.5 2021 10 13 23 57.24 +16 34.6 5.211 6.157 159.6 3.2 20.5 2021 10 23 23 46.65 +15 43.3 5.235 6.116 149.8 4.7 20.5 2021 11 02 23 36.98 +14 50.4 5.295 6.075 138.6 6.2 20.5 2021 11 12 23 28.51 +13 58.8 5.385 6.035 127.2 7.5 20.5 2021 11 22 23 21.43 +13 11.3 5.500 5.996 115.8 8.5 20.5 2021 12 02 23 15.78 +12 29.8 5.632 5.957 104.6 9.2 20.6 2021 12 12 23 11.54 +11 55.9 5.774 5.919 93.7 9.6 20.6 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 August 19 (CBET 5021) Daniel W. E. Green NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 August 20 (CBET 5023) Daniel W. E. Green