Electronic Telegram No. 5203 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/2022 W2 (ATLAS) A. Fitzsimmons reports the discovery of a comet on CCD images taken on 2022 Nov. 24 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, with the object appearing non-stellar in four individual 30-s exposures; it showed a size of 7".6 (full-width-at-half-maximum) in 4".6 seeing. The discovery observations are tabulated below. 2022 UT R.A. (2000) Decl. Mag. Nov. 24.23624 18 37 12.05 +76 45 16.8 19.1 24.24168 18 37 12.87 +76 45 15.8 18.9 24.24530 18 37 13.13 +76 45 14.3 18.9 24.26172 18 37 14.72 +76 45 13.2 18.7 After the comet was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists have also commented on the object's appearance. Pre- discovery (and presumably asteroidal) images of the comet were subsequently identified by Q.-z. Ye in exposures taken with the ZTF camera on the Palomar 1.2-m f/2.4 Schmidt telescope on 2022 Nov. 5.1 UT (at mag R = 19.2), 16.1 (R = 19.0), and 23.1 (i = 18.7). Twelve stacked 60-s exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.61-m f/6.5 astrograph located at the Sierra Remote Observatory near Auberry, CA, USA, on 2022 Nov. 22.10 showed only a stellar appearance; the magnitude was 19.1 as measured within a circular aperture of radius 3".8. Sixteen 120-s images taken with 0.3-m f/4 reflector by M. Jaeger at Martinsberg, Oed, Austria, on Nov. 27.78 show a strongly condensed coma of size 7" and total mag 18.9 with a broad tail 11" long toward p.a. 30-95 deg. F. D. Romanov, Yuzhno-Morskoy, Nakhodka, Russia, writes that fifty-three stacked 60-s unfiltered exposures taken remotely with a 0.36-m f/6.2 Schmidt-Cassegrain located at the Abbey Ridge Observatory at Stillwater Lake, NS, Canada, centered at Nov. 29.95 show a condensed coma of diameter 7" and mag 19.1 with no tail. Seven 120-s unfiltered exposures taken on Dec. 1.74-1.77 by F. Kugel with a 0.4-m f/2.8 reflector at Dauban, France, show a 7" coma of mag 18.8-19.3. L. Buzzi, Varese, Italy, writes that two-hundred-forty 30-s exposures taken and measured by A. Aletti on Dec. 6.8 with a 0.36-m f/7.5 reflector show a very condensed coma 7" wide (full-width-at-half-maximum size 4".0 in 3".1 seeing) with magnitude 18.9. Twenty-five stacked 120-s unfiltered exposures taken by E. Bryssinck, Kruibeke, Belgium, with a 0.4-m f/3.8 reflector on Dec. 12.91 show a strong central condensation with a faint coma of size 10" and magnitude 18.9 as measured within a circular aperture of radius 5".5. The available astrometry appears on MPEC 2023-A28. The following nearly parabolic orbital elements by S. Nakano (Central Bureau) are from 195 observations spanning 2022 Nov. 5-2023 Jan. 9 (mean residual 0".4) and indicate that the comet passed 3.35 AU from Jupiter on 2021 Aug. 17 UT. T = 2023 Mar. 8.57195 TT Peri. = 123.22680 e = 0.9901839 Node = 320.45437 2000.0 q = 3.1229178 AU Incl. = 63.53033 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 11.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2022 12 07 19 00.69 +76 39.6 2.909 3.246 101.1 17.3 17.9 2022 12 17 19 26.00 +77 01.1 2.874 3.221 101.7 17.4 17.9 2022 12 27 19 58.84 +77 42.5 2.845 3.199 102.1 17.5 17.8 2023 01 06 20 41.67 +78 37.8 2.824 3.179 102.1 17.6 17.8 2023 01 16 21 38.00 +79 35.5 2.812 3.163 101.8 17.7 17.7 2023 01 21 22 12.30 +79 59.5 2.810 3.155 101.4 17.8 17.7 2023 01 26 22 50.75 +80 16.5 2.811 3.149 100.9 17.9 17.7 2023 01 31 23 32.67 +80 23.2 2.816 3.143 100.2 18.0 17.7 2023 02 05 00 16.64 +80 16.8 2.824 3.138 99.3 18.1 17.7 2023 02 10 01 00.68 +79 55.5 2.835 3.134 98.3 18.2 17.7 2023 02 15 01 42.84 +79 18.9 2.850 3.130 97.1 18.2 17.7 2023 02 20 02 21.69 +78 28.0 2.869 3.127 95.8 18.3 17.7 2023 02 25 02 56.59 +77 24.8 2.892 3.125 94.2 18.4 17.8 2023 03 02 03 27.48 +76 11.4 2.919 3.124 92.5 18.5 17.8 2023 03 07 03 54.70 +74 49.9 2.949 3.123 90.7 18.5 17.8 2023 03 12 04 18.74 +73 22.2 2.983 3.123 88.7 18.5 17.8 2023 03 17 04 40.12 +71 49.9 3.021 3.124 86.6 18.5 17.9 2023 03 22 04 59.29 +70 14.3 3.062 3.126 84.4 18.5 17.9 2023 03 27 05 16.63 +68 36.6 3.106 3.128 82.1 18.4 17.9 2023 04 01 05 32.47 +66 57.7 3.153 3.131 79.6 18.3 18.0 2023 04 06 05 47.04 +65 18.3 3.203 3.135 77.1 18.1 18.0 2023 04 11 06 00.55 +63 38.9 3.255 3.140 74.5 17.9 18.0 2023 04 16 06 13.17 +61 59.9 3.309 3.145 71.9 17.6 18.1 2023 04 21 06 25.04 +60 21.8 3.365 3.151 69.2 17.3 18.1 2023 04 26 06 36.26 +58 44.9 3.423 3.158 66.4 17.0 18.2 2023 05 01 06 46.91 +57 09.3 3.482 3.165 63.6 16.6 18.2 2023 05 06 06 57.06 +55 35.3 3.541 3.174 60.8 16.1 18.3 2023 05 11 07 06.76 +54 02.9 3.601 3.183 58.0 15.6 18.3 2023 05 16 07 16.08 +52 32.1 3.661 3.192 55.1 15.1 18.4 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 January 10 (CBET 5203) Daniel W. E. Green