Electronic Telegram No. 5021 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) 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 = 2022 June 1.64162 TT Peri. = 40.35959 Node = 359.67044 2000.0 q = 4.3746326 AU Incl. = 51.61325 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