Electronic Telegram No. 5020 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 P1 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained on Aug. 9 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala; four 45-s w-band survey images show a very condensed coma of size 1".5 (full-width-at- half-maximum) in 1".0 seeing with no obvious tail, but a stacked image suggests a point-spread-function asymmetry along a northeast/southwest axis. The discovery observations are tabulated below along with Pan-STARRS1 observations from Aug. 4 that had been sent earlier under a separate internal designation and were in the Minor Planet Center's "isolated tracklet file", together with July pre-discovery observations identified later. 2021 UT R.A. (2000) Decl. Mag. July 14.55548 0 36 15.35 + 0 24 57.1 20.9 14.56823 0 36 15.31 + 0 25 01.4 21.3 21.56299 0 35 53.21 + 1 02 03.9 20.9 21.57276 0 35 53.15 + 1 02 06.9 20.9 21.58252 0 35 53.11 + 1 02 09.9 21.6 Aug. 4.55928 0 33 13.22 + 2 11 18.2 21.2 4.57200 0 33 12.98 + 2 11 21.8 21.2 4.58471 0 33 12.76 + 2 11 25.4 21.0 4.59745 0 33 12.53 + 2 11 29.1 21.2 9.50939 0 31 38.23 + 2 34 09.6 21.7 9.51880 0 31 38.02 + 2 34 12.2 21.6 9.52821 0 31 37.82 + 2 34 14.8 21.7 9.53764 0 31 37.60 + 2 34 17.3 21.6 Weryk and R. Wainscoat obtained three follow-up 60-s gri-band images with the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea on Aug. 10.53 UT (queue observer H. Januszewski; queue coordinator T. Burdullis) that show this object to be definitely a comet; the very condensed coma showed a size of 1".6 (FWHM) in 1".1 seeing and a straight tail > 12" long in p.a. 205 degrees. After the comet was posted on the MPC's PCCP webpage, H. Sato (Tokyo, Japan) writes that sixteen stacked 60-s CCD exposures taken remotely with a 0.51-m f/6.8 astrograph at Siding Spring on Aug. 12.78 show a moderately condensed coma 6" in diameter with no tail; the magnitude was 20.2 as measured within a circular aperture of radius 4".9. The available astrometry appear on MPEC 2021-Q2. The following parabolic orbital elements by S. Nakano (CBAT) are from 28 observations spanning 2021 July 14-Aug. 12 (mean residual 0".15). These indicate a passage by Jupiter of 2.78 AU on 2021 Oct. 11 UT. 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 = 11.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 08 14 00 29.91 +02 54.1 4.228 4.976 133.1 8.5 20.2 2021 08 24 00 25.11 +03 36.1 4.088 4.938 143.6 7.0 20.1 2021 09 03 00 19.10 +04 14.5 3.973 4.902 154.3 5.1 20.0 2021 09 13 00 12.10 +04 49.6 3.887 4.866 165.1 3.0 19.9 2021 09 23 00 04.48 +05 21.9 3.832 4.832 174.5 1.1 19.9 2021 10 03 23 56.66 +05 51.9 3.810 4.798 170.1 2.1 19.9 2021 10 13 23 49.09 +06 20.7 3.819 4.766 159.3 4.2 19.8 2021 10 23 23 42.22 +06 49.7 3.860 4.735 148.2 6.4 19.8 2021 11 02 23 36.43 +07 19.9 3.927 4.704 137.3 8.2 19.9 2021 11 12 23 31.99 +07 52.9 4.018 4.675 126.5 9.8 19.9 2021 11 22 23 29.04 +08 29.7 4.126 4.647 116.2 11.0 19.9 2021 12 02 23 27.63 +09 11.2 4.248 4.620 106.2 11.8 20.0 2021 12 12 23 27.74 +09 58.2 4.377 4.595 96.6 12.3 20.0 2021 12 22 23 29.28 +10 51.2 4.509 4.571 87.3 12.4 20.1 2022 01 01 23 32.12 +11 50.3 4.641 4.548 78.5 12.2 20.1 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 August 18 (CBET 5020) Daniel W. E. Green