Electronic Telegram No. 5053 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 T1 (LEMMON) An apparently asteroidal object discovered with the Mt. Lemmon 1.5-m reflector on Oct. 2 (discovery observations tabulated below) and posted on the Minor Planet Center's NEOCP webpage has been found to show cometary appearance by CCD astrometrists elsewhere. 2021 UT R.A. (2000) Decl. Mag. Oct. 2.20822 23 53 01.81 +44 29 43.5 20.0 2.21351 23 53 00.50 +44 29 40.4 20.0 2.21881 23 52 59.13 +44 29 36.7 19.8 2.22411 23 52 57.78 +44 29 33.0 20.0 2.34385 23 52 27.40 +44 28 11.9 19.5 2.34669 23 52 26.61 +44 28 10.1 19.5 2.34963 23 52 25.84 +44 28 07.8 20.1 2.35268 23 52 25.11 +44 28 05.9 20.0 The following reports were received by the Central Bureau after the comet was posted on the MPC's PCCP webpage. Fourteen stacked 60-s exposures taken remotely by H. Sato, Tokyo, Japan, with a 0.43-m f/6.8 astrograph located near Mayhill, NM, USA, on Oct. 3.26 UT show a strongly condensed coma 6" in diameter with no tail; the magnitude was 19.7 as measured within a circular aperture of radius 5".7. E. Bryssinck, Kruibeke, Belgium, writes that thirty stacked 90-s unfiltered CCD images taken with a 0.4-m f/3.8 reflector on Oct. 4.83-4.87 show a condensed coma of size 8" with a hint of a tail 12" long in p.a. 317 degrees; the magnitude was 19.8 as measured within a circular aperture of radius 5".5. The available astrometry appears on MPEC 2021-T168 and includes pre- discovery observations obtained on Sept. 15.34 UT by the Catalina Sky Survey (magnitude 20.4). The following parabolic orbital elements by S. Nakano (CBAT) are from 59 observations spanning Sept. 15-Oct. 6 (mean residuals 0".6). Nakano cautions that these preliminary elements are heavily dependent on the two Sept. 15 observations, which appear to be inferior measurements (and with no astrometry between Sept. 15 and Oct. 2). T = 2021 Oct. 14.21645 TT Peri. = 51.54729 Node = 56.82406 2000.0 q = 3.0584134 AU Incl. = 140.35264 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 13.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 09 23 00 32.16 +45 34.5 2.284 3.066 133.8 13.7 18.7 2021 09 28 00 10.90 +45 09.0 2.255 3.063 136.7 13.0 18.7 2021 10 03 23 49.71 +44 20.6 2.240 3.060 138.3 12.6 18.6 2021 10 08 23 29.29 +43 10.6 2.241 3.059 138.2 12.6 18.6 2021 10 13 23 10.22 +41 42.4 2.256 3.058 136.6 13.0 18.7 2021 10 18 22 52.90 +40 00.1 2.286 3.059 133.6 13.7 18.7 2021 10 23 22 37.54 +38 08.8 2.329 3.060 129.5 14.5 18.7 2021 10 28 22 24.18 +36 13.0 2.384 3.061 124.8 15.5 18.8 2021 11 02 22 12.76 +34 16.9 2.450 3.064 119.6 16.4 18.8 2021 11 07 22 03.14 +32 23.6 2.525 3.067 114.2 17.1 18.9 2021 11 12 21 55.14 +30 35.7 2.608 3.071 108.7 17.8 19.0 2021 11 17 21 48.58 +28 54.7 2.696 3.076 103.2 18.2 19.1 2021 11 22 21 43.27 +27 21.5 2.790 3.082 97.7 18.5 19.1 2021 11 27 21 39.04 +25 56.7 2.886 3.089 92.4 18.6 19.2 2021 12 02 21 35.76 +24 40.2 2.984 3.096 87.1 18.5 19.3 2021 12 07 21 33.28 +23 31.9 3.083 3.104 82.0 18.3 19.4 2021 12 12 21 31.50 +22 31.6 3.181 3.112 77.1 18.0 19.5 2021 12 17 21 30.30 +21 38.9 3.278 3.122 72.2 17.5 19.5 2021 12 22 21 29.60 +20 53.3 3.373 3.132 67.6 16.9 19.6 2021 12 27 21 29.32 +20 14.2 3.464 3.143 63.0 16.2 19.7 2022 01 01 21 29.40 +19 41.4 3.552 3.155 58.7 15.4 19.7 2022 01 06 21 29.78 +19 14.3 3.635 3.167 54.5 14.6 19.8 2022 01 11 21 30.40 +18 52.7 3.713 3.180 50.5 13.8 19.9 2022 01 16 21 31.21 +18 35.9 3.786 3.193 46.8 13.0 19.9 2022 01 21 21 32.18 +18 23.8 3.853 3.208 43.2 12.1 20.0 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 October 8 (CBET 5053) Daniel W. E. Green