Electronic Telegram No. 5065 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 C/2021 U4 (LEONARD) G. J. Leonard, Lunar and Planetary Laboratory, University of Arizona, has reported his discovery of another comet to the Minor Planet Center, describing the comet as having a moderately condensed 15" coma with no tail in four co-added 30-s images taken on Oct. 31.3 UT with the Mt. Lemmon 1.5-m reflector (discovery astrometry tabulated below). 2021 UT R.A. (2000) Decl. Mag. Observer Oct. 31.29987 2 40 09.65 -11 30 46.3 19.8 Leonard 31.30506 2 40 07.47 -11 31 05.7 19.7 " 31.31026 2 40 05.26 -11 31 25.3 19.8 " 31.31546 2 40 03.07 -11 31 44.9 19.8 " Four 60-s unfiltered follow-up images taken by K. Wierzchos, Lunar and Planetary Laboratory, with the Steward Observatory 1-m reflector at Mt. Lemmon on Oct. 31.35 UT show a diffuse 8" coma and no tail. Three additional 90-s exposures by Wierzchos on Nov. 1.35 show what appears to be a very subtle elongation of the coma towards the north (but no clear tail) with again a diffuse 8" coma. The available astrometry appears on MPEC 2021-V22 and includes pre- discovery observations found after Leonard's discovery observations were reported to the MPC: with the Mt. Lemmon 1.5-m reflector from Oct. 7 (magnitude given as 20.9-21.5), with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on Oct. 14 (mag 19.9-20.0), and with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala on Oct. 29 (mag 19.5-19.8). The following elliptical orbital elements by S. Nakano (CBAT) are from 26 observations spanning 2021 Oct. 7-Nov. 1 (mean residual 0".3), suggesting an orbital period > 300 yr. T = 2021 Dec. 21.85006 TT Peri. = 237.24175 e = 0.9622980 Node = 241.81134 2000.0 q = 1.7879054 AU Incl. = 152.88116 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 17.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 09 23 05 19.14 +16 55.4 1.693 2.108 99.7 28.0 21.2 2021 09 28 05 10.06 +15 00.9 1.552 2.076 106.8 27.5 21.0 2021 10 03 04 58.38 +12 41.4 1.417 2.046 114.6 26.4 20.7 2021 10 08 04 43.53 +09 50.5 1.290 2.017 123.0 24.5 20.5 2021 10 13 04 24.90 +06 21.5 1.177 1.990 132.2 21.8 20.2 2021 10 18 04 01.96 +02 10.0 1.082 1.963 141.8 18.3 20.0 2021 10 23 03 34.48 -02 41.8 1.010 1.939 150.4 14.7 19.8 2021 10 28 03 02.80 -07 59.6 0.968 1.916 155.1 12.6 19.7 2021 11 02 02 28.18 -13 15.9 0.960 1.894 152.1 14.2 19.6 2021 11 07 01 52.73 -17 58.6 0.984 1.875 143.2 18.5 19.6 2021 11 12 01 18.81 -21 45.5 1.040 1.857 132.4 23.2 19.7 2021 11 17 00 48.27 -24 31.3 1.119 1.841 121.6 27.2 19.9 2021 11 22 00 22.07 -26 23.9 1.217 1.827 111.5 30.2 20.0 2021 11 27 00 00.30 -27 35.7 1.327 1.815 102.4 32.1 20.2 2021 12 02 23 42.61 -28 18.8 1.445 1.805 94.0 33.0 20.4 2021 12 07 23 28.43 -28 42.4 1.567 1.798 86.4 33.2 20.5 2021 12 12 23 17.15 -28 53.2 1.691 1.792 79.3 32.7 20.7 2021 12 17 23 08.22 -28 55.8 1.813 1.789 72.8 31.7 20.8 2021 12 22 23 01.20 -28 53.1 1.933 1.788 66.6 30.3 21.0 2021 12 27 22 55.71 -28 47.3 2.049 1.789 60.8 28.7 21.1 2022 01 01 22 51.47 -28 39.5 2.161 1.792 55.2 26.8 21.2 2022 01 06 22 48.24 -28 30.8 2.266 1.798 49.9 24.7 21.3 2022 01 11 22 45.84 -28 21.8 2.364 1.806 44.9 22.6 21.4 2022 01 16 22 44.11 -28 13.1 2.455 1.816 40.0 20.4 21.5 2022 01 21 22 42.91 -28 04.9 2.539 1.828 35.4 18.2 21.6 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 November 2 (CBET 5065) Daniel W. E. Green