Electronic Telegram No. 5226 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/2023 A2 (SWAN) On Jan. 15, Vladimir Bezugly (Dnipro, Ukraine) reported that he found an object that appeared to be moving on low-resolution public website hydrogen Lyman-alpha images obtained during Jan. 6-13 with the Solar Wind Anisotropies (SWAN) camera on the Solar and Heliospheric Observer (SOHO) spacecraft (see CBETs 4068, 4136, 4939; and website URL http://swan.projet.latmos.ipsl.fr/). He estimated the visual magnitude to be about 12 based on the visibility of other comets in SWAN images. He estimates that the object appeared to be about the same brightness every day until Jan. 23 and 24, when it appeared somewhat brighter. Note that SWAN creates daily full-sky scans at the wavelength of hydrogen Lyman_alpha, but its images are at a very poor resolution (not better than about 1 degree). Bezugly's estimated positions are given below: 2023 UT R.A. (2000) Decl. Mag. Jan. 6.5 18 53 + 5 15 12 7.5 18 54 + 4 32 12 8.5 18 55 + 3 49 12 9.5 18 56 + 3 06 12 10.5 18 57 + 2 23 12 11.5 18 58 + 1 40 12 12.5 18 59 + 0 50 12 13.5 18 59 - 0 37 12 14.5 19 03 - 0 31 12 15.5 19 05 - 1 00 12 16.5 19 09 - 1 40 12 17.5 19 11 - 2 16 12 18.5 19 13 - 3 00 12 19.5 19 16 - 4 08 12 21.5 19 18 - 4 51 12 22.5 19 19 - 5 40 12 23.5 19 20 - 6 10 11 24.5 19 22 - 6 58 11 Bezugly posted his suspected discovery in mid-January on the comets-ml discussion group online, which created a lot of effort at confirming the object -- first via other solar-observing cameras and then by ground-based observers once the comet pulled out from intense solar glare, and he notes that the object's reality was confirmed on STEREO-A HI-1A spacecraft images beginning on Feb. 1 by A. Watson, W. Boonplod, and others. However, the position of STEREO-A in space appears to not be known yet with very good precision, so the astrometry are not usable for orbital analysis. Thirty stacked 10-s CCD exposures taken on Jan. 30.9 UT by K. Yoshimoto (Kumage, Yamaguchi, Japan) with a 0.08-m f/4.3 refractor show a diffuse coma 1'.3 in diameter of total magnitude 12.7. 2023 UT R.A. (2000) Decl. Mag. Observer Jan. 30.87286 19 36 24.81 -10 12 55.2 12.7 Yoshimoto 30.87514 19 36 25.38 -10 12 57.4 " 30.87965 19 36 25.99 -10 13 06.3 " M. Mattiazzo (Swan Hill, Victoria, Australia) writes that he was able to image the comet on Feb. 13.8 UT with a Canon 60Da camera (+ Sigma 200-mm- f.l. f/2.8 lens) at Streaky Bay, South Australia; twenty stacked 30-s exposures show a diffuse coma 1' in diameter with a total V magnitude of 12.7. 2023 UT R.A. (2000) Decl. Mag. Observer Feb. 13.80145 20 02 53.90 -18 49 41.7 13.4 Mattiazzo 13.80509 20 02 54.21 -18 49 57.4 12.8 " 13.80909 20 02 55.30 -18 50 15.6 12.7 " M. Masek reports that he obtained CCD images of the comet with a 30-cm reflector at the Pierre Auger observatory, Malargue, Argentina, on three nights with the comet at low altitude (10-12 deg), with his astrometry given below. On Feb. 18.37 UT, he measured total mag 13.9 with a coma diameter of 1'.0. On Feb. 20.37, he estimated total mag 13.9 with a diffuse coma of diameter 1'.0 and a possible elongation toward p.a. 308 deg. His astrometry appears below. 2023 UT R.A. (2000) Decl. Mag. Observer Feb. 15.36792 20 06 01.41 -19 47 16.8 15.3 Masek 15.37297 20 06 02.15 -19 47 28.1 15.1 " 18.36552 20 12 06.71 -21 37 19.8 15.0 " 18.37023 20 12 07.29 -21 37 29.6 15.3 " 20.37013 20 16 16.14 -22 50 54.9 15.2 " 20.37350 20 16 16.70 -22 51 03.3 15.1 " Twelve stacked 60-s CMOS exposures taken remotelly on Feb. 15.38 UT by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 6.5-cm f/3.5 refractor at Rio Hurtado, Chile, show a strongly condensed with a coma of 1'.0 in diameter and no tail; the magnitude was 13.5 as measured within a circular aperture of radius 29".1. Sixteen stacked 60-s exposures taken by Sato on Feb. 19.4 (same instrument) showed the same appearance. 2023 UT R.A. (2000) Decl. Mag. Observer Feb. 15.37893 20 06 02.84 -19 47 39.7 Sato 15.38427 20 06 03.58 -19 47 52.7 13.5 " 19.36885 20 14 10.90 -22 14 04.2 " 19.37329 20 14 11.35 -22 14 12.7 " 19.37783 20 14 11.98 -22 14 23.2 13.5 " K. Kadota (Ageo, Japan) reports that his CCD observations obtained on Feb. 15.86 UT with a 0.25-m f/5 reflector show a faint, diffuse object of diameter about 1' (total magnitude 13.8) with no tail in bright twilight at a low altitude of about 5 degrees. 2023 UT R.A. (2000) Decl. Mag. Observer Feb. 15.85326 20 06 59.70 -20 05 14.8 Kadota 15.85528 20 06 59.76 -20 05 21.2 13.8 " Additional astrometry appears on MPEC 2023-D49. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 47 observations spanning 2023 Jan. 30-Feb. 22 (mean residual 3".2). There are no close approaches to major planets. A general solution from the same 47 observations gives e = 0.995 with a mean error of +/- 3".1. T = 2023 Jan. 20.41678 TT Peri. = 142.64616 Node = 94.48595 2000.0 q = 0.9482577 AU Incl. = 94.70658 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 11.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2022 09 18 09 12.44 +57 06.6 2.462 2.186 62.4 24.0 15.7 2022 09 28 09 56.22 +59 12.9 2.236 2.061 67.0 26.6 15.3 2022 10 08 10 52.59 +60 59.8 2.022 1.937 70.7 29.1 14.8 2022 10 18 12 04.02 +61 43.2 1.830 1.812 73.1 31.8 14.4 2022 10 28 13 26.64 +60 19.0 1.670 1.687 73.7 34.4 13.9 2022 11 07 14 47.88 +55 58.3 1.553 1.564 72.1 37.1 13.5 2022 11 17 15 56.23 +48 51.9 1.485 1.444 68.0 39.4 13.1 2022 11 27 16 49.23 +40 04.3 1.470 1.328 61.8 40.9 12.8 2022 12 07 17 29.79 +30 49.0 1.499 1.219 54.1 40.9 12.6 2022 12 17 18 01.55 +21 55.9 1.561 1.122 45.7 38.9 12.4 2022 12 27 18 27.39 +13 45.7 1.638 1.040 37.1 34.8 12.2 2023 01 06 18 49.31 +06 18.0 1.716 0.982 29.2 29.2 12.1 2023 01 16 19 08.91 -00 36.5 1.780 0.951 22.7 23.5 12.1 2023 01 26 19 27.45 -07 07.9 1.823 0.953 19.5 20.1 12.1 2023 01 31 19 36.65 -10 17.7 1.836 0.966 19.6 20.0 12.2 2023 02 05 19 45.95 -13 24.7 1.842 0.987 21.0 21.0 12.3 2023 02 10 19 55.46 -16 29.8 1.842 1.015 23.4 22.7 12.4 2023 02 15 20 05.28 -19 33.8 1.837 1.049 26.4 24.7 12.5 2023 02 20 20 15.49 -22 37.3 1.828 1.088 29.9 26.9 12.6 2023 02 25 20 26.17 -25 41.2 1.814 1.132 33.6 29.0 12.7 2023 03 02 20 37.42 -28 46.1 1.798 1.180 37.6 30.8 12.8 2023 03 07 20 49.32 -31 52.5 1.780 1.231 41.7 32.4 13.0 2023 03 12 21 02.01 -35 00.7 1.762 1.285 45.8 33.7 13.1 2023 03 17 21 15.62 -38 10.8 1.743 1.341 50.0 34.6 13.2 2023 03 22 21 30.31 -41 22.6 1.726 1.398 54.1 35.2 13.4 2023 03 27 21 46.27 -44 35.2 1.712 1.457 58.2 35.6 13.5 2023 04 01 22 03.74 -47 47.7 1.700 1.517 62.2 35.6 13.6 2023 04 06 22 23.01 -50 57.9 1.693 1.578 66.0 35.4 13.7 2023 04 11 22 44.42 -54 03.6 1.690 1.640 69.8 35.0 13.9 2023 04 16 23 08.34 -57 01.5 1.693 1.701 73.3 34.4 14.0 2023 04 21 23 35.15 -59 48.1 1.702 1.764 76.5 33.6 14.1 2023 04 26 00 05.16 -62 19.1 1.718 1.826 79.5 32.8 14.3 2023 05 01 00 38.52 -64 30.2 1.741 1.888 82.2 31.9 14.4 2023 05 06 01 15.04 -66 17.4 1.770 1.951 84.5 31.0 14.6 2023 05 11 01 54.06 -67 37.6 1.806 2.013 86.4 30.0 14.7 2023 05 16 02 34.41 -68 29.9 1.849 2.076 88.0 29.1 14.9 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 February 23 (CBET 5226) Daniel W. E. Green