Electronic Telegram No. 5009 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 O3 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another apparent comet in images obtained with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala, Hawaii (discovery astrometry tabulated below); he notes that the object looks "soft" in poor seeing, suggestive of being a possible comet. 2021 UT R.A. (2000) Decl. Mag. July 26.48098 23 27 10.79 +27 47 30.1 19.8 26.49180 23 27 10.50 +27 47 31.9 20.0 26.50264 23 27 10.20 +27 47 33.7 19.9 26.60836 23 27 07.40 +27 47 48.3 19.6 26.60901 23 27 07.39 +27 47 48.5 20.2 After the object was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists have commented on the cometary appearance. E. Guido, Castellammare di Stabia, Italy, writes that fifteen stacked 240-s exposures taken remotely by a large group of observers on July 30.3 UT with a "Telescope Live" 0.61-m f/6.5 astrograph located at El Sauce, Chile, show a compact coma about 8" in diameter with magnitude 18.8-19.7. Twelve stacked 60-s exposures taken remotely by H. Sato, Tokyo, Japan, using a 0.61-m f/6.5 astrograph located at the Sierra Remote Observatory near Auberry, CA, USA, on July 31.5 show a stellar appearance; the magnitude was 19.7 as measured within a circular aperture of radius 3".7. Images taken on Aug. 1.0 by L. Buzzi and L. Demetz with a 0.51-m f/6.7 astrograph of the Skygems Telescope Network in Namibia yield mag 19.1, but seeing conditions prevented any unambiguous assessment of cometary nature. Twelved stacked 120-s luminance-filtered exposures taken remotely on Aug. 1.05 by E. Bryssinck, Kruibeke, Belgium, using a Skygems 0.51-m f/6.7 astrograph in Namibia show a coma about 8" across with no tail; the magnitude was 19.7 in an aperture of radius 5".5. The available astrometry appears in MPEC 2021-P05. The following parabolic orbital elements by S. Nakano (CBAT) are from 52 observations spanning July 26-Aug. 1 (mean residual 0".3). T = 2022 Apr. 21.25884 TT Peri. = 300.00160 Node = 189.08401 2000.0 q = 0.2868490 AU Incl. = 56.69738 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 11.0 and 2.5n = 8 for the magnitudes. The comet may reach total visual mag 6-7 in late April 2022, but it will then be only 15-20 degrees from the sun. The extended ephemeris below from such preliminary elements is provided for planning purposes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 07 05 23 32.19 +26 33.0 4.317 4.554 97.0 12.8 19.4 2021 07 10 23 31.72 +26 53.9 4.190 4.499 101.1 12.8 19.3 2021 07 15 23 30.84 +27 12.9 4.065 4.443 105.3 12.7 19.2 2021 07 20 23 29.54 +27 29.7 3.941 4.387 109.6 12.6 19.1 2021 07 25 23 27.79 +27 43.9 3.820 4.331 113.8 12.4 19.0 2021 07 30 23 25.57 +27 55.0 3.701 4.274 118.1 12.1 18.9 2021 08 04 23 22.87 +28 02.5 3.586 4.217 122.4 11.7 18.8 2021 08 09 23 19.69 +28 05.9 3.474 4.160 126.6 11.3 18.7 2021 08 14 23 16.03 +28 04.6 3.367 4.102 130.8 10.8 18.5 2021 08 19 23 11.91 +27 58.0 3.266 4.044 134.9 10.2 18.4 2021 08 24 23 07.35 +27 45.8 3.169 3.985 138.7 9.6 18.3 2021 08 29 23 02.40 +27 27.2 3.079 3.927 142.2 9.1 18.2 2021 09 03 22 57.10 +27 02.1 2.995 3.867 145.2 8.6 18.1 2021 09 08 22 51.54 +26 29.9 2.919 3.807 147.5 8.2 18.0 2021 09 13 22 45.79 +25 50.6 2.850 3.747 148.9 8.0 17.9 2021 09 18 22 39.95 +25 04.2 2.788 3.687 149.1 8.0 17.8 2021 09 23 22 34.13 +24 11.1 2.735 3.626 148.1 8.4 17.7 2021 09 28 22 28.42 +23 11.7 2.689 3.564 146.0 9.0 17.6 2021 10 03 22 22.92 +22 06.7 2.651 3.502 143.0 9.9 17.5 2021 10 08 22 17.74 +20 56.9 2.620 3.440 139.3 10.9 17.4 2021 10 13 22 12.96 +19 43.3 2.597 3.376 135.0 12.1 17.3 2021 10 18 22 08.66 +18 27.2 2.580 3.313 130.3 13.3 17.2 2021 10 23 22 04.89 +17 09.5 2.570 3.249 125.4 14.5 17.1 2021 10 28 22 01.70 +15 51.4 2.565 3.184 120.3 15.6 17.1 2021 11 02 21 59.11 +14 33.8 2.565 3.119 115.1 16.7 17.0 2021 11 07 21 57.16 +13 17.7 2.569 3.053 110.0 17.8 16.9 2021 11 12 21 55.84 +12 04.0 2.576 2.986 104.8 18.7 16.9 2021 11 17 21 55.16 +10 53.1 2.585 2.919 99.7 19.5 16.8 2021 11 22 21 55.10 +09 45.7 2.596 2.851 94.6 20.2 16.7 2021 11 27 21 55.64 +08 42.1 2.608 2.782 89.6 20.8 16.6 2021 12 02 21 56.77 +07 42.4 2.619 2.713 84.7 21.2 16.6 2021 12 07 21 58.47 +06 47.0 2.630 2.643 79.9 21.5 16.5 2021 12 12 22 00.72 +05 55.7 2.639 2.571 75.3 21.7 16.4 2021 12 17 22 03.49 +05 08.7 2.646 2.500 70.7 21.8 16.3 2021 12 22 22 06.77 +04 25.8 2.651 2.427 66.2 21.8 16.2 2021 12 27 22 10.52 +03 46.9 2.652 2.353 61.8 21.6 16.1 2022 01 01 22 14.75 +03 11.8 2.649 2.278 57.5 21.4 16.0 2022 01 06 22 19.44 +02 40.4 2.643 2.202 53.4 21.0 15.9 2022 01 11 22 24.58 +02 12.5 2.631 2.125 49.3 20.5 15.7 2022 01 16 22 30.15 +01 47.8 2.615 2.047 45.3 20.0 15.6 2022 01 21 22 36.17 +01 26.1 2.593 1.967 41.5 19.4 15.4 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 August 1 (CBET 5009) Daniel W. E. Green