Electronic Telegram No. 5079 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 R8 (SHEPPARD) D. Tholen, Institute for Astronomy, University of Hawaii, writes that Scott Sheppard has discovered a faint comet in their "Hyper Suprime-Cam" CCD images taken in early September with the 8.2-m f/2.2 Subaru reflector at Mauna Kea; the head of the comet is trailed in these long, sidereally-tracked exposures (290 s on Sept. 5; 250 s on Sept. 6), making it difficult to describe the morphology of the near-nucleus region, but there is a tail extending about 15" in position angle 240 deg. The discovery observations are tabulated below. 2021 UT R.A. (2000) Decl. Mag. Observer Sept. 5.54775 23 20 51.79 - 4 09 35.3 21.6 Sheppard 6.48120 23 20 16.13 - 4 14 58.1 21.8 " Tholen asked R. Weryk (Department of Physics and Astronomy, University of Western Ontario) to look for possible Pan-STARRS images of the comet. Weryk found images of the comet on six nights that were taken with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala (Aug. 12-Oct. 6, with magnitudes ranging from 22.7-23.5 on Aug. 12.5 UT to 21.3 on Sept. 9.5 to 21.6-22.0 on Oct. 6.3) and on two nights with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on Sept. 30.32-30.35 (mag 22.0-22.6) and Oct. 4.4 (mag 22.3), noting that the object was quite marginal in almost all images, although the Sept. 30 images look somewhat "fuzzy" -- in which four 45-s w-band survey images show the head to have a size of about 2" (full-width-at- half-maximum) in 1".3-1".4 seeing, with no obvious tail. After the comet was posted to the Minor Planet Center's PCCP webpage, H. Sato (Tokyo, Japan) has noted that sixty stacked 60-s CCD exposures taken remotely on Dec. 7.1 UT with a 0.43-m f/6.8 astrograph located near Mayhill, NM, USA, show a stellar appearance; the magnitude was 22.3 as measured within a circular aperture of radius 5".7. The available astrometry appears on MPEC 2021-X149. The following orbital elements by S. Nakano (CBAT) are from 25 observations spanning 2021 Aug. 12-Dec. 7 (mean residual 0".3); the first of Sato's observations was omitted. There are no close approach to major planets. Epoch = 2016 July 31.0 TT T = 2016 July 14.37211 TT Peri. = 191.18410 e = 0.2940498 Node = 167.08200 2000.0 q = 2.1301774 AU Incl. = 2.20166 a = 3.0174616 AU n = 0.18803620 P = 5.24 years Epoch = 2021 Sept.23.0 TT T = 2021 Oct. 7.47352 TT Peri. = 190.77845 e = 0.2940196 Node = 167.02544 2000.0 q = 2.1310487 AU Incl. = 2.20308 a = 3.0185662 AU n = 0.18793299 P = 5.24 years Epoch = 2026 Dec. 26.0 TT T = 2027 Jan. 5.74939 TT Peri. = 190.82303 e = 0.2922775 Node = 167.00221 2000.0 q = 2.1376952 AU Incl. = 2.20284 a = 3.0205273 AU n = 0.18774999 P = 5.25 years Epoch = 2032 Mar. 29.0 TT T = 2032 Apr. 9.45784 TT Peri. = 190.93010 e = 0.2866069 Node = 166.78917 2000.0 q = 2.1588457 AU Incl. = 2.20038 a = 3.0261656 AU n = 0.18722552 P = 5.26 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 18.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 11 22 23 19.06 -05 51.0 1.620 2.151 108.7 25.8 22.2 2021 12 02 23 29.19 -04 50.4 1.739 2.160 101.3 26.6 22.4 2021 12 12 23 41.03 -03 37.2 1.862 2.171 94.3 26.9 22.5 2021 12 22 23 54.26 -02 13.6 1.989 2.184 87.8 26.7 22.7 2022 01 01 00 08.62 -00 41.9 2.118 2.199 81.5 26.3 22.9 2022 01 11 00 23.91 +00 56.1 2.247 2.215 75.4 25.5 23.0 2022 01 21 00 39.94 +02 38.3 2.376 2.232 69.6 24.4 23.2 2022 01 31 00 56.60 +04 23.1 2.502 2.251 64.0 23.2 23.3 2022 02 10 01 13.79 +06 08.8 2.626 2.272 58.5 21.7 23.4 2022 02 20 01 31.41 +07 53.8 2.747 2.293 53.1 20.2 23.6 2022 03 02 01 49.41 +09 36.7 2.862 2.316 47.8 18.5 23.7 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 December 7 (CBET 5079) Daniel W. E. Green