Electronic Telegram No. 5034 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 R4 (WIERZCHOS) Kacper W. Wierzchos, Lunar and Planetary Laboratory, University of Arizona, reports his discovery of a comet on CCD images obtained with the Mount Lemmon 1.5-m reflector in southern Arizona (discovery observations tabulated below); the comet showed a 6" coma and a straight 12" tail in p.a. 225 degrees. 2021 UT R.A. (2000) Decl. Mag. Observer Sept. 6.40246 0 23 09.13 +27 46 32.3 21.1 Wierzchos 6.40817 0 23 08.96 +27 46 36.3 " 6.41388 0 23 08.75 +27 46 40.7 20.6 " 6.41959 0 23 08.54 +27 46 45.3 20.9 " 6.46138 0 23 06.92 +27 47 15.3 20.3 " 6.46563 0 23 06.79 +27 47 17.7 20.7 " 6.46980 0 23 06.62 +27 47 20.5 20.4 " Single-night observations were made on Sept. 4.4 UT (at mag 21.3-21.6) with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala, HI, USA, without the Pan-STARRS team noting cometary appearance (and submitted to the Minor Planet Center under a separate designation in real time); R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports that a subsequent review of those four 45-s w-band survey images show a diffuse coma of size 2".4 (full-width-at-half-maximum) in 1".3 seeing, with a straight 6" tail in p.a. 210 degrees. After the comet was posted on the MPC's PCCP webpage, H. Sato (Tokyo, Japan) found that twenty stacked 60-s CCD exposures taken on Sept. 7.4 show a strongly condensed coma 8" in diameter and a hint of a tail 10" long toward p.a. 190 degrees; the magnitude was 20.4 as measured within a circular aperture of radius 5".7. The available astrometry appear on MPEC 2021-R256. The following preliminary elliptical orbital elements by S. Nakano (CBAT) are from 33 observations spanning 2021 Sept. 4-11 (mean residual 0".4). The orbital period is uncertain by more than a month. No previous observations were found in a search of archival astrometry. T = 2021 Oct. 13.65455 TT Peri. = 56.54102 e = 0.5858483 Node = 321.24497 2000.0 q = 2.3256926 AU Incl. = 21.03372 a = 5.6155571 AU n = 0.07406530 P = 13.31 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 16.0 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 08 14 00 29.77 +22 10.8 1.670 2.384 123.5 20.8 20.9 2021 08 19 00 29.59 +23 29.0 1.622 2.375 127.2 19.9 20.8 2021 08 24 00 28.73 +24 44.5 1.578 2.366 130.9 18.9 20.7 2021 08 29 00 27.20 +25 56.4 1.538 2.359 134.5 17.8 20.7 2021 09 03 00 25.01 +27 03.8 1.503 2.352 138.0 16.7 20.6 2021 09 08 00 22.19 +28 05.7 1.473 2.346 141.4 15.5 20.5 2021 09 13 00 18.81 +29 01.1 1.447 2.341 144.5 14.4 20.5 2021 09 18 00 14.97 +29 49.5 1.427 2.336 147.2 13.5 20.5 2021 09 23 00 10.80 +30 30.0 1.412 2.333 149.3 12.7 20.4 2021 09 28 00 06.44 +31 02.4 1.403 2.330 150.7 12.1 20.4 2021 10 03 00 02.06 +31 26.3 1.400 2.328 151.3 11.9 20.4 2021 10 08 23 57.82 +31 42.1 1.402 2.326 150.9 12.0 20.4 2021 10 13 23 53.92 +31 50.2 1.409 2.326 149.7 12.5 20.4 2021 10 18 23 50.50 +31 51.7 1.422 2.326 147.8 13.2 20.4 2021 10 23 23 47.69 +31 47.4 1.440 2.327 145.2 14.1 20.5 2021 10 28 23 45.60 +31 38.5 1.462 2.329 142.3 15.1 20.5 2021 11 02 23 44.28 +31 26.3 1.490 2.332 139.0 16.2 20.5 2021 11 07 23 43.81 +31 11.9 1.522 2.335 135.6 17.3 20.6 2021 11 12 23 44.18 +30 56.5 1.558 2.339 132.0 18.3 20.7 2021 11 17 23 45.40 +30 41.1 1.598 2.344 128.5 19.3 20.7 2021 11 22 23 47.44 +30 26.6 1.641 2.350 124.9 20.2 20.8 2021 11 27 23 50.25 +30 13.5 1.688 2.357 121.3 21.0 20.9 2021 12 02 23 53.81 +30 02.4 1.737 2.364 117.8 21.6 20.9 2021 12 07 23 58.06 +29 53.7 1.790 2.372 114.3 22.2 21.0 2021 12 12 00 02.95 +29 47.6 1.845 2.381 110.9 22.7 21.1 2021 12 17 00 08.44 +29 44.4 1.902 2.391 107.6 23.1 21.2 2021 12 22 00 14.47 +29 43.9 1.961 2.401 104.3 23.4 21.3 2021 12 27 00 20.99 +29 46.3 2.021 2.412 101.1 23.6 21.4 2022 01 01 00 27.96 +29 51.2 2.084 2.423 97.9 23.7 21.4 2022 01 06 00 35.34 +29 58.7 2.148 2.436 94.8 23.7 21.5 2022 01 11 00 43.10 +30 08.7 2.213 2.448 91.7 23.7 21.6 2022 01 16 00 51.19 +30 20.8 2.280 2.462 88.7 23.5 21.7 2022 01 21 00 59.59 +30 34.8 2.347 2.476 85.7 23.3 21.8 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 5034) Daniel W. E. Green