Electronic Telegram No. 5036 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/2021 R3 (PANSTARRS) [Editor's note: this text replaces that on CBET 5033 (astrometry list).] An apparently asteroidal object discovered in very poor seeing on survey images taken on Sept. 5 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala, Hawaii, has been found to show cometary appearance by several CCD observers after the comet was posted on the Minor Planet Center's PCCP webpage. The discovery astrometry is tabulated below, together with pre-discovery Pan-STARRS1 observations identified later dating back to July 9 (and including also three observations obtained on Aug. 30.4 UT with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala). 2021 UT R.A. (2000) Decl. Mag. July 9.55425 22 21 20.18 - 2 16 00.3 22.1 9.56617 22 21 19.97 - 2 15 53.1 22.1 9.57807 22 21 19.78 - 2 15 46.8 22.0 9.59002 22 21 19.58 - 2 15 39.4 22.1 14.50129 22 19 46.15 - 1 29 52.7 21.5 14.51295 22 19 45.88 - 1 29 46.1 21.8 14.52464 22 19 45.58 - 1 29 40.3 21.5 14.53631 22 19 45.31 - 1 29 33.5 21.1 17.60782 22 18 27.93 - 1 02 15.4 22.2 Aug. 3.45577 22 07 40.45 + 1 05 56.0 20.9 3.46736 22 07 39.86 + 1 06 00.4 21.2 7.33308 22 04 28.22 + 1 29 28.5 21.5 7.34598 22 04 27.53 + 1 29 33.0 21.6 7.35884 22 04 26.86 + 1 29 37.5 21.7 11.41975 22 00 53.97 + 1 51 37.6 20.6 11.43298 22 00 53.24 + 1 51 41.5 21.5 11.44618 22 00 52.51 + 1 51 45.8 20.9 12.36833 22 00 03.15 + 1 56 22.4 21.0 12.38010 22 00 02.50 + 1 56 26.0 21.1 13.53638 21 58 59.62 + 2 02 00.9 20.5 13.54713 21 58 59.02 + 2 02 04.1 20.9 25.44049 21 48 09.53 + 2 47 02.6 21.3 25.46443 21 48 08.19 + 2 47 06.4 20.9 30.35210 21 43 53.13 + 2 59 22.7 21.5 30.36367 21 43 52.51 + 2 59 24.3 21.3 30.37528 21 43 51.91 + 2 59 25.8 21.4 Sept. 5.31938 21 39 05.22 + 3 10 05.7 21.4 5.33194 21 39 04.63 + 3 10 06.7 21.2 5.34444 21 39 04.04 + 3 10 07.6 21.4 5.35698 21 39 03.44 + 3 10 08.9 21.4 M. Jaeger posted on the ICQ Comet Observations Facebook page that sixteen stacked 200-s exposures taken on Sept. 5.9 UT with a 0.30-m reflector at Stixendorf, Austria, show a possible coma of size 10". R. Weryk, Department of Physics and Astronomy, University of Western Ontario, writes that R. Wainscoat and he confirmed this object to be a comet on three 60-s gri-band exposures taken on Sept. 6.4 with the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea (queue observer L. Wells; coordinator N. Manset); there was a very condensed coma of size 0".9 (full-width-at-half-maximum) in 0".6 seeing with a broad 4" tail spanning p.a. 140-220 degrees. Twenty stacked 60-s exposures taken remotely by H. Sato (Tokyo, Japan) with a 0.43-m f/6.8 astrograph located near Mayhill, NM, USA, on Sept. 7.3 show a strongly condensed coma 8" in diameter and no tail; the magnitude was 20.8 as measured within a circular aperture of radius 5".7. The available astrometry appears on MPEC 2021-R255. The following elliptical orbital elements by S. Nakano (CBAT) are from 59 observations spanning 2021 July 9-Sept. 10 (mean residual 0".3), which indicate that the comet passed 0.36 AU from Jupiter in 2002 Sept. UT. No other observations of this comet were identified in archival astrometry. T = 2021 May 27.13139 TT Peri. = 3.00669 e = 0.3319765 Node = 304.24814 2000.0 q = 2.5251104 AU Incl. = 19.92847 a = 3.7799724 AU n = 0.13411308 P = 7.35 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 15.0 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 08 14 21 58.58 +02 04.2 1.588 2.572 162.4 6.8 20.1 2021 08 24 21 49.45 +02 42.8 1.594 2.585 165.1 5.8 20.1 2021 09 03 21 40.89 +03 06.5 1.627 2.598 160.2 7.6 20.2 2021 09 13 21 33.83 +03 18.3 1.684 2.613 151.6 10.6 20.3 2021 09 23 21 28.98 +03 22.8 1.764 2.630 142.2 13.5 20.4 2021 10 03 21 26.67 +03 24.4 1.863 2.647 132.8 16.1 20.6 2021 10 13 21 26.99 +03 27.0 1.978 2.666 123.8 18.1 20.7 2021 10 23 21 29.80 +03 34.0 2.106 2.685 115.2 19.6 20.9 2021 11 02 21 34.84 +03 47.4 2.243 2.706 107.0 20.5 21.1 2021 11 12 21 41.84 +04 08.7 2.388 2.728 99.2 21.0 21.2 2021 11 22 21 50.50 +04 38.6 2.536 2.750 91.8 21.0 21.4 2021 12 02 22 00.52 +05 17.3 2.686 2.774 84.7 20.7 21.6 2021 12 12 22 11.68 +06 04.8 2.836 2.798 77.8 20.1 21.7 2021 12 22 22 23.75 +07 00.7 2.983 2.823 71.1 19.3 21.9 2022 01 01 22 36.55 +08 04.2 3.127 2.849 64.7 18.2 22.0 2022 01 11 22 49.93 +09 14.9 3.266 2.875 58.4 16.9 22.2 2022 01 21 23 03.78 +10 31.8 3.398 2.902 52.3 15.6 22.3 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 September 12 (CBET 5036) Daniel W. E. Green