Electronic Telegram No. 5040 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 M1 = P/2008 QP20 (LINEAR-HILL) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the accidental recovery of comet P/2008 QP20, for its third recorded apparition (cf. CBET 4832 for the 2016 recovery), in images obtained on Aug. 17 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala, Hawaii; four 45-s w-band survey images taken in 1".3 seeing show a very condensed coma of size 1".5-1".6 (full-width-at-half-maximum) and a straight tail 2" long in p.a. 240 degrees. Weryk also identified the comet in numerous other 2021 Pan-STARRS1 images, and his astrometry is tabulated below. 2021 UT R.A. (2000) Decl. Mag. June 18.58966 22 57 30.23 - 7 10 07.5 22.9 July 13.47929 23 12 58.28 - 4 11 53.8 22.1 20.52460 23 15 04.48 - 3 28 32.5 22.8 31.57186 23 15 55.71 - 2 28 56.4 22.3 31.58366 23 15 55.66 - 2 28 53.2 22.1 Aug. 4.48849 23 15 27.77 - 2 10 37.2 21.9 4.50051 23 15 27.61 - 2 10 34.0 21.5 4.51252 23 15 27.46 - 2 10 30.8 21.7 4.52454 23 15 27.29 - 2 10 27.6 21.6 12.49816 23 13 12.07 - 1 38 16.1 21.7 12.51066 23 13 11.75 - 1 38 13.0 21.5 12.52316 23 13 11.43 - 1 38 10.4 21.7 17.50449 23 10 55.70 - 1 21 38.1 21.4 17.51643 23 10 55.29 - 1 21 36.0 21.3 17.52832 23 10 54.89 - 1 21 33.8 21.2 17.54026 23 10 54.48 - 1 21 31.6 21.5 The 2016 return presumably gets the designation P/2016 10. The residuals of the recovery observation on 2021 June 18 was -12" in R.A. and -10" in Decl. from the prediction on CBET 4832, with a corresponding correction of Delta(T) = +0.01 day. The following orbital elements by S. Nakano (CBAT) confirm the 2016 recovery and are from 489 observations spanning three apparitions, 2008-2021 (mean residual 0".9). Nakano notes that the distribution of the residuals in 2008 are slightly poor, suggesting that there may be some non-gravitational effects on the comet's motion. The comet passed 1.44 AU from Jupiter on 2017 July 20 UT. No other observations were identified in archival astrometry files. Epoch = 2008 Oct. 21.0 TT T = 2008 Nov. 2.69997 TT Peri. = 72.03756 e = 0.5063140 Node = 325.15440 2000.0 q = 1.7231327 AU Incl. = 7.74983 a = 3.4903414 AU n = 0.15114793 P = 6.52 years Epoch = 2015 May 18.0 TT T = 2015 May 17.28154 TT Peri. = 72.35226 e = 0.5063906 Node = 324.96924 2000.0 q = 1.7233739 AU Incl. = 7.74184 a = 3.4913719 AU n = 0.15108102 P = 6.52 years Epoch = 2022 Jan. 21.0 TT T = 2022 Jan. 2.14859 TT Peri. = 75.53962 e = 0.4913081 Node = 322.07317 2000.0 q = 1.8062355 AU Incl. = 7.52190 a = 3.5507458 AU n = 0.14730744 P = 6.69 years Epoch = 2028 Sept.26.0 TT T = 2028 Sept.16.98608 TT Peri. = 75.68743 e = 0.4900315 Node = 321.99051 2000.0 q = 1.8148442 AU Incl. = 7.51305 a = 3.5587378 AU n = 0.14681150 P = 6.71 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 14.0 and 2.5n = 15 for the pre-perihelion magnitudes and H = 14.0 and 2.5n = 10 for the post-perihelion magnitudes (following CBET 4832). Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 08 14 23 12.59 -01 32.9 1.231 2.180 152.5 12.4 19.5 2021 08 24 23 07.09 -01 04.1 1.149 2.135 162.8 8.0 19.2 2021 09 03 22 59.59 -00 45.8 1.088 2.093 172.5 3.6 19.0 2021 09 13 22 51.09 -00 35.9 1.052 2.052 171.2 4.3 18.8 2021 09 23 22 43.01 -00 30.4 1.038 2.013 160.8 9.4 18.6 2021 10 03 22 36.73 -00 24.2 1.046 1.977 150.0 14.7 18.5 2021 10 13 22 33.35 -00 12.2 1.073 1.944 139.6 19.4 18.5 2021 10 23 22 33.54 +00 09.9 1.115 1.914 130.0 23.5 18.5 2021 11 02 22 37.41 +00 44.7 1.169 1.887 121.3 26.7 18.5 2021 11 12 22 44.82 +01 33.7 1.233 1.863 113.4 29.2 18.5 2021 11 22 22 55.41 +02 37.3 1.303 1.843 106.3 30.9 18.6 2021 12 02 23 08.72 +03 54.8 1.378 1.828 99.9 32.1 18.6 2021 12 12 23 24.38 +05 25.0 1.458 1.816 94.1 32.7 18.7 2021 12 22 23 41.99 +07 06.3 1.541 1.809 88.7 32.9 18.8 2022 01 01 00 01.23 +08 56.1 1.627 1.806 83.7 32.8 18.9 2022 01 11 00 21.86 +10 52.2 1.716 1.808 79.0 32.3 17.7 2022 01 21 00 43.63 +12 51.8 1.808 1.814 74.6 31.5 17.9 2022 01 31 01 06.37 +14 52.0 1.902 1.825 70.4 30.6 18.0 2022 02 10 01 29.96 +16 50.1 1.999 1.839 66.3 29.4 18.2 2022 02 20 01 54.23 +18 43.4 2.098 1.858 62.3 28.1 18.3 2022 03 02 02 19.08 +20 29.3 2.200 1.881 58.4 26.7 18.5 2022 03 12 02 44.39 +22 05.7 2.303 1.907 54.5 25.1 18.6 2022 03 22 03 10.03 +23 30.7 2.408 1.937 50.7 23.5 18.8 2022 04 01 03 35.88 +24 42.7 2.513 1.969 46.8 21.7 18.9 2022 04 11 04 01.80 +25 40.9 2.618 2.005 42.9 19.9 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 18 (CBET 5040) Daniel W. E. Green