Electronic Telegram No. 5052 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 S4 (TSUCHINSHAN) An apparently asteroidal object reported by Hai-bin Zhao on CCD images taken on Sept. 29 with the 1.04-m f/1.8 Schmidt telescope at the XuYi station of the Purple Mountain Observatory (discovery observations tabulated below) has been found to show cometary appearance on pre-discovery Pan-STARRS images. 2021 UT R.A. (2000) Decl. Mag. Observer Sept.29.77171 1 20 11.78 +14 39 39.3 20.5 Zhao 29.78586 1 20 11.53 +14 39 39.1 19.7 " 29.80000 1 20 11.26 +14 39 38.4 20.4 " R. Weryk, Department of Physics and Astronomy, University of Western Ontario, writes that four stacked 45-s w-band survey exposures taken on Sept. 8.44-8.47 UT with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala show a very condensed coma of size 1".4 (full-width-at-half-maximum) in 0".9 seeing, with no tail. Four stacked 60-s w-band survey exposures taken on Sept. 30.35-30.38 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala show a very condensed coma of size 1".5 (FWHM) in 1".1 seeing, again with no tail. The available astrometry appears on MPEC 2021-T167. The following preliminary orbital elements by S. Nakano (CBAT) are from 33 observations spanning 2021 Sept. 8-Oct. 7 (mean residual 0".5). T = 2023 Dec. 25.03844 TT Peri. = 71.48983 e = 0.9366509 Node = 5.43970 2000.0 q = 6.7831768 AU Incl. = 17.42430 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 8.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 09 23 01 22.17 +14 42.2 7.593 8.511 154.8 2.9 19.8 2021 10 03 01 19.21 +14 37.9 7.506 8.475 164.8 1.8 19.8 2021 10 13 01 16.02 +14 30.9 7.448 8.439 173.1 0.8 19.8 2021 10 23 01 12.78 +14 22.0 7.421 8.404 170.5 1.1 19.7 2021 11 02 01 09.69 +14 12.2 7.424 8.368 161.0 2.2 19.7 2021 11 12 01 06.92 +14 02.6 7.456 8.333 150.6 3.3 19.7 2021 11 22 01 04.65 +13 54.4 7.516 8.298 140.2 4.4 19.7 2021 12 02 01 03.00 +13 48.4 7.598 8.264 129.8 5.3 19.7 2021 12 12 01 02.07 +13 45.7 7.700 8.229 119.5 6.0 19.8 2021 12 22 01 01.93 +13 46.8 7.816 8.195 109.4 6.5 19.8 2022 01 01 01 02.59 +13 52.1 7.942 8.161 99.5 6.8 19.8 2022 01 11 01 04.05 +14 02.0 8.073 8.128 89.7 6.9 19.8 2022 01 21 01 06.27 +14 16.5 8.204 8.094 80.2 6.9 19.8 2022 01 31 01 09.21 +14 35.3 8.330 8.061 70.9 6.6 19.9 2022 02 10 01 12.81 +14 58.4 8.448 8.028 61.8 6.2 19.9 2022 02 20 01 16.99 +15 25.3 8.554 7.996 52.9 5.7 19.9 2022 03 02 01 21.68 +15 55.6 8.645 7.964 44.2 5.0 19.9 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 5052) Daniel W. E. Green