Electronic Telegram No. 5045 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 R6 (GROELLER) Hannes Groeller, Lunar and Planetary Laboratory, University of Arizona, reported the discovery of a comet on images obtained with the 1.5-m reflector at Mt. Lemmon, AZ, USA, with four co-added 30-s exposures showing a condensed 4" coma and a broad 4" tail spanning p.a. 240-270 degrees. The discovery astrometry is tabulated below. 2021 UT R.A. (2000) Decl. Mag. Observer Sept.12.45894 2 35 09.72 - 6 51 30.6 20.2 Groeller 12.46374 2 35 09.82 - 6 51 35.7 20.2 " 12.46855 2 35 09.90 - 6 51 40.9 20.1 " 12.47335 2 35 10.02 - 6 51 46.5 20.4 " 12.49924 2 35 10.53 - 6 52 16.0 20.2 " 12.50150 2 35 10.57 - 6 52 18.6 20.1 " 12.50261 2 35 10.61 - 6 52 19.7 20.0 " After the comet was posted to the Minor Planet Center's PCCP webpage, pre-discovery observations of this object that were obtained on Aug. 31.54- 31.58 UT (at mag 20.9-21.1) with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala, and on Sept. 4.6 (at mag 21.0-21.4) in images obtained with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala, were found in the MPC's "isolated tracklet file". R. Weryk, Department of Physics and Astronomy, University of Western Ontario, writes that the quality of the Aug. 31 Pan-STARRS2 images is too poor to assess any potential cometary activity; the comet appears essentially stellar on the four 45-s w-band Sept. 4 Pan-STARRS1 survey images (the best image in 1".1 seeing showing the head to be perhaps 0".1 larger with no tail). The following additional reports of cometary appearance have been sent to the Central Bureau by CCD observers. Sixteen stacked 60-s exposures taken remotely by H. Sato, Tokyo, Japan, on Sept. 13.48 UT with a 0.43-m f/6.8 astrograph located near Mayhill, NM, USA, show a stellar appearance; the magnitude was 20.8 as measured within a circular aperture of radius 5".7. Twenty stacked 60-s exposures taken as above by Sato on Sept. 17.4 show a strongly condensed coma 6" in diameter with a hint of tail 6" long toward p.a. 280 degrees; the magnitude was 20.1 as measured within a circular aperture of radius 5".7. Seventy-nine 60-s exposures taken with a 0.60-m f/4 reflector at San Marcello Pistoiese, Italy, on Sept. 19.1 by P. Bacci and M. Maestripieri (measured by Bacci, L. Tesi, and G. Fagioli) show a tail about 12" long in p.a. 275 degrees; the total magnitude was given as 19.7. The available astrometry appears on MPEC 2021-S113. The following elliptical orbital elements by S. Nakano (CBAT) are from 64 observations spanning 2021 Aug. 31-Sept. 28 (mean residual 0".3). No additional observations were found in a search of archival astrometry. T = 2021 Oct. 31.86215 TT Peri. = 220.72010 e = 0.5933335 Node = 176.11601 2000.0 q = 2.5521926 AU Incl. = 34.92835 a = 6.2758853 AU n = 0.06268903 P = 15.72 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 14.0 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 09 23 02 37.71 -10 18.0 1.726 2.572 139.4 14.7 19.3 2021 10 03 02 37.82 -13 40.5 1.679 2.563 145.0 12.9 19.2 2021 10 13 02 35.89 -16 56.1 1.656 2.557 147.9 12.0 19.2 2021 10 23 02 32.45 -19 50.7 1.660 2.553 147.1 12.2 19.2 2021 11 02 02 28.21 -22 12.6 1.688 2.552 143.1 13.5 19.2 2021 11 12 02 24.04 -23 54.2 1.738 2.554 137.1 15.3 19.3 2021 11 22 02 20.80 -24 53.3 1.808 2.558 130.1 17.2 19.4 2021 12 02 02 19.14 -25 12.5 1.893 2.565 122.9 18.8 19.5 2021 12 12 02 19.48 -24 56.7 1.990 2.575 115.7 20.2 19.6 2021 12 22 02 22.01 -24 12.6 2.097 2.587 108.8 21.1 19.7 2022 01 01 02 26.66 -23 06.5 2.210 2.602 102.2 21.7 19.9 2022 01 11 02 33.33 -21 44.2 2.328 2.619 95.9 21.9 20.0 2022 01 21 02 41.79 -20 10.7 2.449 2.639 89.9 21.9 20.2 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 September 28 (CBET 5045) Daniel W. E. Green