Electronic Telegram No. 5024 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 P4 (ATLAS) An apparently asteroidal object discovered on CCD images taken on Aug. 10 UT with a 0.5-m f/2 Schmidt reflector at Haleakala, 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. The discovery observations are tabulated below. 2021 UT R.A. (2000) Decl. Mag. Aug. 10.53716 1 06 54.69 +55 52 13.6 19.4 10.53899 1 06 54.55 +55 52 16.7 19.2 10.54174 1 06 54.48 +55 52 18.5 19.2 10.55110 1 06 54.31 +55 52 25.0 19.3 10.56350 1 06 54.06 +55 52 33.3 19.3 Following posting on the Minor Planet Center's PCCP webpage, L. Buzzi (Varese, Italy) writes that thirty stacked 60-s CCD exposures taken by on Aug. 15.0 UT with a 0.84-m f/3.5 reflector (measured by A. Aletti and Buzzi) in good conditions show a very condensed coma 5" wide, slightly extended toward p.a. 235 degrees; the total magnitude was given as 19.4. Additional astrometry and reports of cometary appearance appear on MPEC 2021-Q42. The following parabolic orbital elements by S. Nakano (CBAT) are from 148 observations spanning Aug. 10-21 (mean residual 0".4). T = 2022 July 29.86208 TT Peri. = 175.54880 Node = 348.24739 2000.0 q = 1.0822790 AU Incl. = 56.39856 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 10.5 and 2.5n = 8 for the magnitudes. The comet will be poorly placed for observation on the opposite side of the sun near perihelion (with these parameters suggesting a peak total magnitude around 12 at that time). Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 08 14 01 05.55 +56 31.8 4.395 4.622 96.6 12.6 19.0 2021 08 19 01 02.96 +57 27.9 4.294 4.572 99.6 12.6 18.9 2021 08 24 00 59.57 +58 22.6 4.195 4.522 102.5 12.6 18.9 2021 08 29 00 55.33 +59 15.1 4.098 4.472 105.3 12.6 18.8 2021 09 03 00 50.17 +60 04.7 4.004 4.422 108.1 12.5 18.7 2021 09 08 00 44.06 +60 50.7 3.914 4.372 110.6 12.5 18.6 2021 09 13 00 37.00 +61 32.1 3.827 4.321 113.1 12.4 18.5 2021 09 18 00 29.01 +62 08.1 3.744 4.271 115.3 12.3 18.4 2021 09 23 00 20.16 +62 37.7 3.665 4.220 117.2 12.2 18.3 2021 09 28 00 10.57 +63 00.2 3.591 4.168 118.9 12.2 18.2 2021 10 03 00 00.41 +63 14.7 3.521 4.117 120.2 12.1 18.2 2021 10 08 23 49.88 +63 20.8 3.456 4.066 121.3 12.1 18.1 2021 10 13 23 39.25 +63 18.1 3.396 4.014 121.9 12.2 18.0 2021 10 18 23 28.78 +63 06.7 3.341 3.962 122.1 12.3 17.9 2021 10 23 23 18.73 +62 46.8 3.291 3.910 121.9 12.5 17.8 2021 10 28 23 09.32 +62 19.2 3.246 3.857 121.3 12.7 17.7 2021 11 02 23 00.75 +61 44.6 3.205 3.804 120.4 13.0 17.7 2021 11 07 22 53.16 +61 04.0 3.169 3.752 119.0 13.4 17.6 2021 11 12 22 46.65 +60 18.8 3.138 3.698 117.3 13.8 17.5 2021 11 17 22 41.26 +59 30.1 3.110 3.645 115.4 14.2 17.5 2021 11 22 22 37.00 +58 39.2 3.086 3.592 113.2 14.6 17.4 2021 11 27 22 33.83 +57 47.3 3.066 3.538 110.7 15.1 17.3 2021 12 02 22 31.72 +56 55.4 3.048 3.484 108.1 15.6 17.3 2021 12 07 22 30.62 +56 04.6 3.033 3.430 105.4 16.1 17.2 2021 12 12 22 30.47 +55 15.8 3.020 3.375 102.6 16.5 17.1 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 August 21 (CBET 5024) Daniel W. E. Green