Electronic Telegram No. 5030 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 R1 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery by Mark Huber (University of Hawaii) of a comet in four 45-s w-band survey images obtained with the Pan-STARRS1 1.8-m Ritchey- Chretien reflector at Haleakala on Sept. 4.4 UT (discovery observations tabulated below). The comet shows a condensed coma of size 2".0 (full-width- at-half-maximum) in 1".6 seeing, with a straight 8" tail in p.a. 250 degrees in the discovery images. 2021 UT R.A. (2000) Decl. Mag. Sept. 4.35526 23 47 01.75 - 5 03 09.1 20.6 4.36610 23 47 01.50 - 5 03 11.5 20.8 4.37699 23 47 01.25 - 5 03 13.6 20.6 4.38782 23 47 01.00 - 5 03 15.8 21.0 4.51051 23 46 58.11 - 5 03 40.8 20.6 4.51119 23 46 58.10 - 5 03 40.9 20.5 After the comet was posted on the Minor Planet Center's PCCP webpage, M. Jaeger (Vienna) reported on the "ICQ Comet Observations" Facebook page that twenty stacked 180-s exposures taken on 2021 Sept. 5.96 UT with a 30-cm reflector at Stixendorf, Austria, show a 6".5 coma of mag 20.5 and a 20" tail in p.a. 250 degrees. Pre-discovery Pan-STARRS1 observations were identifed subsequently on six nights spanning 2020 Aug. 10-Sept. 16 (mag generally 21.5-22.5), via Pan-STARRS2 observations on 2020 Sept. 12 (at mag 22), and Pan-STARRS1 observations on eight additional nights spanning 2021 July 20-Aug. 27 (mag generally 20.5-21.5 during that interval). The available astrometry appear on MPEC 2021-R150. The following elliptical orbital elements by S. Nakano (CBAT) are from 70 observations spanning 2020 Aug. 10-2021 Sept. 5 (mean residual 0".3). these indicate that the comet passed 0.99 AU from Saturn in 1976 Oct. and 1.81 AU from Jupiter on 2020 Oct. 25 UT. Nakano was unable to find additional archival observations of this comet. Epoch = 2021 Dec. 12.0 TT T = 2021 Dec. 17.58978 TT Peri. = 220.31497 e = 0.4200264 Node = 143.40871 2000.0 q = 4.8855916 AU Incl. = 5.52130 a = 8.4238179 AU n = 0.04031258 P = 24.45 years Epoch = 2045 May 20.0 TT T = 2045 June 1.21826 TT Peri. = 220.48450 e = 0.4013826 Node = 142.86102 2000.0 q = 4.8716846 AU Incl. = 5.57100 a = 8.1382272 AU n = 0.04245309 P = 23.22 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 12.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 08 14 23 53.55 -03 58.3 4.070 4.926 144.1 6.9 20.6 2021 08 24 23 50.93 -04 26.4 3.989 4.920 154.4 5.1 20.5 2021 09 03 23 47.54 -04 58.6 3.933 4.914 164.9 3.1 20.5 2021 09 13 23 43.62 -05 32.6 3.906 4.909 174.8 1.1 20.5 2021 09 23 23 39.53 -06 06.0 3.909 4.905 172.1 1.6 20.5 2021 10 03 23 35.62 -06 36.4 3.940 4.900 161.7 3.7 20.5 2021 10 13 23 32.22 -07 01.5 4.000 4.897 151.0 5.7 20.5 2021 10 23 23 29.64 -07 19.7 4.085 4.894 140.5 7.4 20.6 2021 11 02 23 28.08 -07 29.8 4.192 4.891 130.1 8.9 20.6 2021 11 12 23 27.70 -07 31.3 4.318 4.889 120.0 10.1 20.7 2021 11 22 23 28.56 -07 24.1 4.457 4.887 110.2 10.9 20.8 2021 12 02 23 30.64 -07 08.7 4.606 4.886 100.7 11.4 20.8 2021 12 12 23 33.90 -06 45.4 4.760 4.886 91.5 11.6 20.9 2021 12 22 23 38.25 -06 15.2 4.916 4.886 82.5 11.5 21.0 2022 01 01 23 43.58 -05 38.7 5.068 4.886 73.8 11.1 21.0 2022 01 11 23 49.78 -04 56.8 5.215 4.887 65.3 10.5 21.1 2022 01 21 23 56.73 -04 10.3 5.354 4.889 57.1 9.7 21.2 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 September 8 (CBET 5030) Daniel W. E. Green