Electronic Telegram No. 5028 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 Q4 (FULS) David Carson Fuls, Lunar and Planetary Laboratory, University of Arizona, reports his discovery of a comet on CCD images taken with the Mt. Lemmon 1.5-m reflector on Aug. 26 (discovery observations tabulated below). Fuls noted a coma of diameter 5".5 and a tail 9" long in p.a. 270 degrees. 2021 UT R.A. (2000) Decl. Mag. Observer Aug. 26.29857 19 17 09.52 +50 31 46.5 20.0 Fuls 26.30385 19 17 09.47 +50 31 45.0 20.2 " 26.30913 19 17 09.37 +50 31 42.9 20.3 " 26.31442 19 17 09.32 +50 31 41.3 20.1 " 26.33663 19 17 08.96 +50 31 33.8 20.2 " 26.35006 19 17 08.93 +50 31 28.8 20.4 " 26.36405 19 17 08.78 +50 31 24.2 20.8 " K. Wierzchos obtained follow-up observations of the comet with the 1.5-m Mt. Lemmon reflector on Aug. 27.25 UT, which show a condensed coma of diameter 5" and a broad tail 11" long spanning p.a. 210-260 degrees. After the comet was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists also have commented on the cometary appearance. One-hundred-twenty 30-s exposures taken on Aug. 29.0 UT by L. Buzzi, Varese, Italy, with a 0.84-m f/3.5 reflector (and measured by A. Aletti) show a condensed coma 7" wide with a straight tail 12" long in p.a. 290 degrees. Twenty-four stacked 60-s exposures taken remotely by H. Sato, Tokyo, Japan, using a 0.43-m f/6.8 astrograph located near Mayhill, NM, USA, on Aug. 29.2 show a strongly condensed, fuzzy coma 8" in diameter with no tail; the magnitude was 20.1 as measured within a circular aperture of radius 5".7. R. Weryk, Department of Physics and Astronomy, University of Western Ontario, writes that four 45-s i-band survey images obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on Aug. 29.4 UT show a diffuse coma of size 1".8 (full-width-at-half-maximum) in 1".2 seeing with no tail. E. Guido, Castellammare di Stabia, Italy, relates that thirty stacked 120-s unfiltered exposures taken remotely by a large group of observers on Aug. 29.9 with a "Telescope Live" 0.7-m f/8 Ritchey-Chretien telescope located at Oria, Spain, show a compact coma about 8" arcsec in diameter elongated toward p.a. 275 degrees; the magnitude was given as 19.3-19.5. The available astrometry appears on MPEC 2021-Q102; included are numerous pre-discovery Pan-STARRS observations (reported after the PCCP posting) going back to 2020 May 19.6 UT (mag 22.4) that include four nights in May 2020, two nights in June 2020, one observation each on 2020 July 1.5 (mag 22.2) and 2020 Aug. 1.5 (mag 21.9), several observations on 2020 Aug. 18.3 (mag 21.1-21.4) and on 2020 Sept. 23, and a single observations on 2020 Oct. 26.24 (mag 21.9) -- as well as Pan-STARRS1 observations on 2021 July 25.5. Mt. Lemmon observations of the comet were also subsequently identified from 2021 June 16.4. The following orbital elements by S. Nakano (CBAT) are from 78 observations spanning 2020 Apr. 27-2021 Aug. 30 (mean residual 0".4); the corresponding original and future values of 1/a are +0.000133 and +0.000288 AU**-1, respectively (mean error +/- 0.000006). The comet will pass 2.45 AU from Saturn on 2025 Apr. 30 UT. Epoch = 2023 June 25.0 TT T = 2023 June 10.66635 TT Peri. = 147.01173 e = 1.0030503 Node = 183.33225 2000.0 q = 7.5647821 AU Incl. = 71.47505 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 7.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 08 14 19 20.18 +51 34.0 8.247 8.612 107.9 6.4 19.6 2021 08 24 19 17.62 +50 44.4 8.225 8.583 107.5 6.5 19.5 2021 09 03 19 15.99 +49 46.4 8.213 8.555 106.5 6.5 19.5 2021 09 13 19 15.39 +48 41.7 8.212 8.527 104.9 6.5 19.5 2021 09 23 19 15.87 +47 32.2 8.222 8.499 102.7 6.6 19.5 2021 10 03 19 17.45 +46 19.9 8.240 8.471 100.0 6.7 19.5 2021 10 13 19 20.08 +45 06.9 8.268 8.444 96.8 6.7 19.5 2021 10 23 19 23.71 +43 55.0 8.303 8.417 93.2 6.8 19.5 2021 11 02 19 28.25 +42 45.8 8.344 8.391 89.3 6.8 19.5 2021 11 12 19 33.61 +41 40.9 8.390 8.365 85.1 6.8 19.5 2021 11 22 19 39.68 +40 41.6 8.438 8.339 80.9 6.7 19.5 2021 12 02 19 46.36 +39 48.8 8.488 8.313 76.5 6.6 19.5 2021 12 12 19 53.53 +39 03.5 8.536 8.288 72.2 6.5 19.5 2021 12 22 20 01.09 +38 26.0 8.580 8.263 68.1 6.3 19.5 2022 01 01 20 08.94 +37 56.8 8.620 8.239 64.1 6.2 19.5 2022 01 11 20 16.97 +37 36.0 8.653 8.215 60.6 6.0 19.5 2022 01 21 20 25.09 +37 23.5 8.678 8.191 57.5 5.8 19.5 2022 01 31 20 33.20 +37 19.1 8.692 8.168 55.0 5.7 19.5 2022 02 10 20 41.20 +37 22.4 8.696 8.145 53.3 5.6 19.5 2022 02 20 20 49.02 +37 33.1 8.687 8.122 52.4 5.5 19.5 2022 03 02 20 56.56 +37 50.3 8.666 8.100 52.4 5.6 19.5 2022 03 12 21 03.74 +38 13.7 8.632 8.078 53.3 5.7 19.4 2022 03 22 21 10.48 +38 42.2 8.585 8.057 55.1 5.8 19.4 2022 04 01 21 16.69 +39 15.1 8.526 8.036 57.7 6.0 19.4 2022 04 11 21 22.30 +39 51.5 8.454 8.015 60.9 6.3 19.4 2022 04 21 21 27.22 +40 30.3 8.372 7.995 64.8 6.5 19.3 2022 05 01 21 31.39 +41 10.5 8.279 7.975 69.1 6.8 19.3 2022 05 11 21 34.72 +41 50.7 8.178 7.956 73.8 7.0 19.3 2022 05 21 21 37.15 +42 29.8 8.071 7.937 78.8 7.2 19.2 2022 05 31 21 38.64 +43 06.3 7.958 7.919 84.1 7.3 19.2 2022 06 10 21 39.14 +43 38.5 7.843 7.901 89.5 7.4 19.2 2022 06 20 21 38.68 +44 05.0 7.729 7.883 95.0 7.4 19.1 2022 06 30 21 37.28 +44 24.0 7.616 7.866 100.5 7.3 19.1 2022 07 10 21 35.01 +44 33.9 7.509 7.849 105.9 7.2 19.0 2022 07 20 21 32.03 +44 33.2 7.409 7.833 111.1 7.0 19.0 2022 07 30 21 28.51 +44 20.7 7.320 7.817 115.9 6.7 19.0 2022 08 09 21 24.67 +43 55.7 7.245 7.801 120.0 6.5 18.9 2022 08 19 21 20.77 +43 17.8 7.185 7.786 123.3 6.2 18.9 2022 08 29 21 17.08 +42 27.5 7.142 7.772 125.5 6.1 18.9 2022 09 08 21 13.83 +41 25.8 7.119 7.758 126.3 6.0 18.9 2022 09 18 21 11.26 +40 14.3 7.116 7.744 125.6 6.1 18.9 2022 09 28 21 09.51 +38 55.3 7.133 7.731 123.5 6.2 18.9 2022 10 08 21 08.70 +37 31.0 7.170 7.719 120.1 6.4 18.9 2022 10 18 21 08.88 +36 04.2 7.225 7.707 115.5 6.7 18.9 2022 10 28 21 10.07 +34 37.4 7.298 7.695 110.0 7.0 18.9 2022 11 07 21 12.24 +33 12.8 7.386 7.684 103.9 7.2 18.9 2022 11 17 21 15.32 +31 52.6 7.484 7.673 97.3 7.3 19.0 2022 11 27 21 19.23 +30 38.2 7.592 7.663 90.4 7.4 19.0 2022 12 07 21 23.88 +29 31.1 7.704 7.653 83.4 7.3 19.0 2022 12 17 21 29.16 +28 31.9 7.818 7.644 76.3 7.2 19.0 2022 12 27 21 34.98 +27 41.2 7.929 7.635 69.2 6.9 19.1 2023 01 06 21 41.24 +26 59.2 8.035 7.627 62.3 6.6 19.1 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 September 2 (CBET 5028) Daniel W. E. Green