Electronic Telegram No. 5050 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 R7 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained with the Pan-STARRS2 (Sept. 5.43-5.45 UT) and Pan-STARRS1 (Sept. 5.6) 1.8-m Ritchey- Chretien reflectors at Haleakala. The discovery astrometry is tabulated below, together with pre-discovery Pan-STARRS1 observations from Aug. 7 that were identified later. The cometary appearance was only marginally seen on Sept. 5. 2021 UT R.A. (2000) Decl. Mag. Aug. 7.52371 1 22 14.38 +20 01 14.1 22.4 7.53800 1 22 13.84 +20 01 11.3 21.6 7.55226 1 22 13.25 +20 01 07.6 21.4 7.56647 1 22 12.71 +20 01 04.7 21.7 Sept. 5.42575 0 57 44.17 +17 22 53.2 22.0 5.43787 0 57 43.42 +17 22 47.7 21.7 5.45005 0 57 42.65 +17 22 42.7 21.9 5.60109 0 57 33.27 +17 21 36.4 21.4 5.60195 0 57 33.21 +17 21 35.8 21.3 Weryk notes that three 60-s follow-up gri-band images obtained by Weryk and R. Wainscoat with the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea on Sept. 7.4 UT (queue observer L. Wells; coordinator H. Flewelling) show a very condensed coma of size 1".0 (full-width-at-half-maximum) in 0".6 seeing, with a straight 1" tail in p.a. 45 degrees. After the object was posted to the Minor Planet Center's NEOCP webpage, twenty-one stacked 60-s CCD 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 UT show only a stellar appearance; the magnitude was 21.4 as measured within a circular aperture of radius 5".7. Thirty stacked 120-s CCD exposures taken on Oct. 1.03-1.06 by L. Buzzi and L. Demetz (measured by A. Aletti, L. Buzzi, and G. Galli) using a 0.50-m f/6.9 astrograph located at Nerpio, Spain, show a very condensed coma 4" wide, slightly extended toward p.a. 60 degrees; the coma (mag 21.5) was about 1".1 larger than stars of similar brightness. The available astrometry appears on MPEC 2021-T162. The following parabolic orbital elements by S. Nakano (CBAT) are from 47 observations spanning 2021 Aug. 7-Oct. 7 (mean residual 0".3). T = 2021 Apr. 16.27882 TT Peri. = 140.15559 Node = 170.12619 2000.0 q = 5.6451305 AU Incl. = 158.86912 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 12.5 and 2.5n = 7 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 09 23 00 38.55 +14 57.4 4.798 5.762 162.2 3.1 21.2 2021 10 03 00 27.17 +13 21.9 4.788 5.777 170.3 1.7 21.2 2021 10 13 00 16.03 +11 41.5 4.821 5.792 165.6 2.5 21.3 2021 10 23 00 05.62 +10 00.5 4.896 5.809 154.4 4.2 21.3 2021 11 02 23 56.29 +08 23.1 5.010 5.826 142.3 6.0 21.4 2021 11 12 23 48.30 +06 52.6 5.157 5.845 130.1 7.4 21.4 2021 11 22 23 41.79 +05 31.7 5.332 5.864 118.2 8.5 21.5 2021 12 02 23 36.77 +04 21.5 5.525 5.883 106.6 9.2 21.6 2021 12 12 23 33.20 +03 22.5 5.731 5.904 95.3 9.6 21.7 2021 12 22 23 30.96 +02 34.4 5.941 5.925 84.3 9.5 21.8 2022 01 01 23 29.90 +01 56.4 6.148 5.947 73.7 9.1 21.9 2022 01 11 23 29.87 +01 27.4 6.347 5.970 63.3 8.5 21.9 2022 01 21 23 30.70 +01 06.3 6.531 5.994 53.2 7.6 22.0 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 October 8 (CBET 5050) Daniel W. E. Green