Electronic Telegram No. 5233 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 E1 (ATLAS) An apparently asteroidal object discovered on CCD images taken on Mar. 1 UT with a 0.5-m f/2 Schmidt reflector at Sutherland, South Africa, 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. P. Veres, Minor Planet Center, linked the one-night ATLAS astrometry from Mar. 1 with a second night of astrometry of a previously unlinked apparently asteroidal object found in Feb. 26 CCD images obtained with the ATLAS 0.5-m reflector located at Rio Hurtado, Chile, and archived in the MPC's "isolated tracklet file". From this two-night linkage, Veres then found earlier, fainter images of the same object in the ITF made on Feb. 4.4 UT by G. J. Leonard with the Mt. Lemmon Survey's 1.5-m reflector (at mag 19.1-20.4), followed by images obtained on Jan. 22.6 with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala (at mag 20.9-21.0), and finally images obtained by R. A. Mastaler with the Bok 2.25-m reflector at Kitt Peak on 2022 Dec. 25.5 (mag 21.5-21.8). The discovery observations are tabulated below, together with the Feb. 26 ATLAS observations from Rio Hurtado: 2023 UT R.A. (2000) Decl. Mag. Feb. 26.26723 12 49 54.91 + 8 41 37.5 19.3 26.27039 12 49 54.92 + 8 41 43.1 19.3 26.30281 12 49 55.14 + 8 42 33.9 19.1 26.32699 12 49 55.42 + 8 43 17.2 19.5 Mar. 1.00405 12 50 19.82 +10 00 21.7 18.8 1.00630 12 50 19.79 +10 00 25.6 19.0 1.00946 12 50 19.76 +10 00 30.3 18.4 1.01489 12 50 19.82 +10 00 40.3 18.8 The highly eccentric orbit that Veres found from the above observations led him to post the object to the MPC's PCCP webpage, which resulted in the finding of cometary activity by CCD astrometrists elsewhere. R. Weryk, University of Western Ontario, writes that the Pan-STARRS2 from Jan. 22 (mentioned above) suggest only slight cometary activity (if any); three 45-s w-band survey images taken in seeing of 1".7 or better show the object to have a size of 1".8 with no discernible coma and no tail. A. Valvasori, Padulle, Italy, notes that ninety stacked, 60-s unfiltered exposures taken by E. Guido and himself on Mar. 4.94 UT with a 0.30-m f/4 reflector located at the ALMO Observatory in Padulle show a coma about 5" in diameter and of mag 18.7-19.3. One-hundred-twenty 15-s exposures taken on Mar. 5.1 by L. Buzzi (Varese, Italy) with a 0.84-m f/3.5 reflector (and measured by Buzzi and A. Aletti) show a weak cometary appearance with a very condensed 6" coma that is only slightly larger than nearby stars (in good seeing but with moonlight interference), with a faint and short extension toward the northeast; the magnitude was measured as 18.9. E. Bryssinck, Kruibeke, Belgium, relates that twenty 60-s luminance-filtered exposures taken by M. Rocchetto, Guido, G. Milani, Valvasori, and himself on Mar. 10.3 remotely with a "Telescope Live" 0.61-m f/6.8 reflector located at Rio Hurtado in disturbing moonlight show a central condensation with a small coma of size 5".5 and magnitude of 18.5 in an aperture of radius 5".3. The available astrometry appears on MPEC 2023-E59. The following elliptical orbital elements by S. Nakano (Central Bureau) are from 93 observations spanning 2022 Dec. 25-2023 Mar. 11 (mean residual 0".5); the orbital period is still uncertain, but there are no close approaches to the outer major planets. The comet will pass 0.37 AU from the earth on 2023 Aug. 18 UT. Epoch = 2023 June 25.0 TT T = 2023 July 1.10987 TT Peri. = 105.89235 e = 0.9469392 Node = 164.57443 2000.0 q = 1.0266612 AU Incl. = 38.31413 a = 19.3487566 AU n = 0.01158042 P = 85.1 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 15.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2023 02 25 12 49.66 +08 07.1 1.258 2.149 145.6 15.1 18.7 2023 03 02 12 50.44 +10 30.4 1.174 2.091 149.9 13.7 18.4 2023 03 07 12 50.62 +13 14.1 1.097 2.033 153.5 12.6 18.2 2023 03 12 12 50.17 +16 18.8 1.027 1.976 155.8 11.9 17.9 2023 03 17 12 49.05 +19 43.8 0.966 1.918 156.0 12.2 17.7 2023 03 22 12 47.24 +23 27.1 0.914 1.861 153.9 13.6 17.5 2023 03 27 12 44.74 +27 25.0 0.870 1.803 149.8 16.2 17.2 2023 04 01 12 41.61 +31 32.5 0.835 1.746 144.2 19.5 17.0 2023 04 06 12 37.90 +35 43.5 0.809 1.690 137.9 23.4 16.9 2023 04 11 12 33.74 +39 51.7 0.789 1.633 131.1 27.5 16.7 2023 04 16 12 29.26 +43 51.1 0.777 1.578 124.3 31.7 16.5 2023 04 21 12 24.69 +47 36.9 0.770 1.523 117.6 35.8 16.4 2023 04 26 12 20.28 +51 06.2 0.766 1.469 111.2 39.7 16.3 2023 05 01 12 16.34 +54 17.6 0.766 1.416 105.2 43.3 16.1 2023 05 06 12 13.16 +57 11.8 0.767 1.365 99.6 46.7 16.0 2023 05 11 12 11.01 +59 50.3 0.768 1.316 94.5 49.9 15.9 2023 05 16 12 10.20 +62 15.1 0.769 1.269 89.9 52.8 15.8 2023 05 21 12 11.03 +64 28.7 0.768 1.225 85.8 55.5 15.6 2023 05 26 12 13.84 +66 33.7 0.765 1.183 82.2 58.0 15.5 2023 05 31 12 18.98 +68 32.7 0.759 1.146 79.1 60.3 15.4 2023 06 05 12 26.87 +70 27.8 0.750 1.112 76.5 62.5 15.2 2023 06 10 12 38.12 +72 20.4 0.737 1.084 74.5 64.5 15.1 2023 06 15 12 53.74 +74 11.2 0.721 1.060 73.0 66.4 15.0 2023 06 20 13 15.37 +75 59.7 0.702 1.043 72.1 68.0 14.9 2023 06 25 13 45.68 +77 43.4 0.678 1.032 71.9 69.5 14.8 2023 06 30 14 28.74 +79 15.7 0.652 1.027 72.3 70.6 14.7 2023 07 05 15 29.22 +80 22.7 0.622 1.029 73.4 71.3 14.6 2023 07 10 16 46.99 +80 40.3 0.590 1.037 75.2 71.4 14.5 2023 07 15 18 09.20 +79 43.1 0.555 1.052 78.0 70.9 14.4 2023 07 20 19 18.20 +77 20.8 0.520 1.073 81.7 69.6 14.3 2023 07 25 20 08.19 +73 36.8 0.485 1.099 86.6 67.3 14.3 2023 07 30 20 42.71 +68 33.1 0.451 1.130 92.7 63.8 14.2 2023 08 04 21 06.66 +62 06.3 0.420 1.166 100.4 58.8 14.2 2023 08 09 21 23.58 +54 12.1 0.395 1.206 109.7 52.3 14.1 2023 08 14 21 35.83 +44 53.9 0.379 1.249 120.5 44.4 14.2 2023 08 19 21 44.96 +34 34.3 0.375 1.295 132.4 35.3 14.3 2023 08 24 21 52.00 +23 56.9 0.385 1.343 144.4 26.0 14.5 2023 08 29 21 57.65 +13 54.1 0.410 1.393 155.3 17.6 14.7 2023 09 03 22 02.40 +05 05.0 0.450 1.445 163.1 11.7 15.0 2023 09 08 22 06.56 -02 14.1 0.502 1.499 165.2 9.9 15.4 2023 09 13 22 10.39 -08 05.7 0.565 1.553 161.8 11.7 15.8 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 March 12 (CBET 5233) Daniel W. E. Green