Electronic Telegram No. 5088 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 Y1 (ATLAS) An apparently asteroidal object discovered on CCD images taken on 2021 Dec. 26.3 UT with a 0.5-m f/2 Schmidt reflector at Mauna Loa, Hawaii, in the course of the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS) search program has been found to show cometary appearance by CCD astrometrists elsewhere after the comet was posted on the Minor Planet Center's PCCP webpage. The discovery observations are tabulated below. 2021 UT R.A. (2000) Decl. Mag. Dec. 26.28500 1 22 11.22 +56 15 19.9 18.9 26.28823 1 22 11.26 +56 15 19.0 18.8 26.28915 1 22 11.31 +56 15 18.2 18.7 26.29425 1 22 11.28 +56 15 14.8 18.7 26.30485 1 22 10.96 +56 15 06.9 18.8 Ten stacked 60-s CCD exposures taken remotely by H. Sato, Tokyo, Japan, on 2021 Dec. 29.3 UT with a 0.43-m f/6.8 astrograph located near Mayhill, NM, USA, show a strongly condensed coma 10" in diameter with no tail; the magnitude was 18.9 as measured within a circular aperture of radius 5".7. L. Buzzi, Varese, Italy, writes that thirty stacked 60-s exposures taken on Dec. 31.0 with a 0.84-m f/3.5 reflector show a 9" coma and no tail in a crowded star field, the comet's head being about 1" larger than nearby stars (full-width-at-half-maximum). Forty-five stacked 60-s exposures taken by Buzzi on Dec. 31.8 (measured by A. Aletti, G. Galli, and Buzzi) show an 8" coma of mag 18.8 with a hint of a tail a few arcseconds long toward p.a. 60 degrees. E. Bryssinck, Kruibeke, Belgium, reports that twenty stacked luminance-filtered 90-s exposures obtained remotely on 2022 Jan. 3.98 by a large group of observers with a "Telescope Live" 0.7-m f/8 Ritchey-Chretien reflector located at Oria, Spain, show a coma of size about 6" x 10", elongated in p.a. 118 degrees but with no obvious tail; the magnitude was 18.9 in an aperture of radius 5".3. The available astrometry (including two separate nights reported by M. Holbrook from images taken at Pleasant Groves, AL, USA, and found by M. Rudenko in the MPC's "isolated tracklet file" from 2021 Nov. 8.1 and 24.0 UT, with the magnitude reported as 18.8-19.2 and 18.3-19.0, respectively, but reported as two separated objects with no additional information) appears on MPEC 2022-A50. The following parabolic orbital elements by S. Nakano (CBAT) are from 131 observations spanning 2021 Nov. 8-2022 Jan. 6 (mean residual 0".4). T = 2023 May 1.00574 TT Peri. = 245.82308 Node = 244.75854 2000.0 q = 2.0333964 AU Incl. = 77.19980 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 8.5 and 2.5n = 8 (because numerous astrometric observations give the comet's magnitude as 17-18). Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2022 01 01 01 21.98 +55 07.2 5.000 5.475 114.0 9.4 17.9 2022 01 11 01 23.31 +53 10.7 5.028 5.392 106.6 10.1 17.9 2022 01 21 01 26.55 +51 20.5 5.068 5.309 98.8 10.6 17.8 2022 01 31 01 31.42 +49 39.0 5.118 5.226 90.8 10.9 17.8 2022 02 10 01 37.69 +48 07.4 5.173 5.143 82.8 11.0 17.8 2022 02 20 01 45.12 +46 46.5 5.227 5.059 74.8 10.9 17.7 2022 03 02 01 53.52 +45 36.1 5.279 4.976 67.0 10.6 17.7 2022 03 12 02 02.75 +44 35.7 5.323 4.892 59.3 10.1 17.6 2022 03 22 02 12.66 +43 44.4 5.357 4.807 52.0 9.4 17.6 2022 04 01 02 23.12 +43 01.1 5.378 4.723 44.9 8.6 17.5 2022 04 11 02 34.05 +42 24.8 5.383 4.638 38.3 7.7 17.5 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2022 CBAT 2022 January 7 (CBET 5088) Daniel W. E. Green