Electronic Telegram No. 5264 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 H2 (Lemmon) An apparently asteroidal object discovered on CCD images obtained on Apr. 23 with the Mt. Lemm0n Survey 1.5-m reflector (discovery observations tabulated below) has been found to show cometary activity by CCD astrometrists elsewhere after it was posted on the Minor Planet Center's PCCP webpage. 2023 UT R.A. (2000) Decl. Mag. Apr. 23.27971 14 09 31.46 +38 04 52.6 20.7 23.28403 14 09 30.82 +38 04 58.4 20.8 23.28836 14 09 30.32 +38 05 04.3 21.3 23.29274 14 09 29.79 +38 05 10.9 23.30088 14 09 28.69 +38 05 21.5 20.6 23.30301 14 09 28.40 +38 05 24.6 21.1 23.30512 14 09 28.14 +38 05 27.1 21.2 R. Weryk, Department of Physics and Astronomy, University of Western Ontario, has identified pre-discovery images of this object in images obtained on Mar. 26.6 UT with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala (at mag 21.9-22.2) and on Apr. 18.43-18.46 with the Pan-STARRS2 1.8-m Ritchey- Chretien reflector at Haleakala (at mag 20.9-21.6); conditions were too poor to ascertain any activity. Twenty-four stacked 60-s CCD exposures taken on Apr. 26.4 by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.51-m f/6.8 astrograph located at the Utah Desert Remote Observatory near Beryl Junction, UT, USA, show only a stellar appearance; the magnitude was 20.5 as measured within a circular aperture of radius 4".9. Q.-z. Ye, Department of Astronomy, University of Maryland, writes that observations obtained on May 14.19 using the 4.3-m Lowell Discovery Telescope at Happy Jack, AZ, USA, show a coma that is 12" in diameter with no tail. The available astrometry appears on MPEC 2023-K122. The following nearly parabolic orbital elements by S. Nakano (Central Bureau) are from 71 observations spanning 2023 Mar. 26-May 22 (mean residual 0".4); Nakano cautions on the dependence on the single-night observatino on Mar. 26 (three weeks earlier than the rest). T = 2023 Oct. 29.17906 TT Peri. = 150.65268 e = 0.9963267 Node = 217.03957 2000.0 q = 0.8942436 AU Incl. = 113.74884 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 14.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2023 05 16 13 14.69 +44 39.2 2.195 2.706 109.5 20.6 19.7 2023 05 26 12 50.42 +46 04.5 2.219 2.584 99.3 22.8 19.5 2023 06 05 12 28.80 +46 42.2 2.255 2.462 89.3 24.3 19.4 2023 06 15 12 10.90 +46 44.3 2.295 2.338 79.7 25.3 19.3 2023 06 25 11 57.07 +46 23.0 2.330 2.213 70.7 25.7 19.1 2023 07 05 11 47.12 +45 49.1 2.353 2.086 62.4 25.6 18.9 2023 07 15 11 40.56 +45 10.2 2.358 1.959 54.9 25.1 18.7 2023 07 25 11 36.88 +44 32.2 2.341 1.831 48.3 24.5 18.4 2023 08 04 11 35.56 +43 59.3 2.297 1.702 43.0 24.0 18.2 2023 08 14 11 36.18 +43 34.6 2.224 1.575 39.2 24.0 17.8 2023 08 24 11 38.41 +43 21.0 2.117 1.449 37.3 25.0 17.4 2023 09 03 11 42.05 +43 21.2 1.974 1.326 37.6 27.6 17.0 2023 09 13 11 47.05 +43 37.9 1.794 1.209 39.9 32.3 16.4 2023 09 23 11 53.71 +44 14.4 1.575 1.102 44.0 39.3 15.8 2023 10 03 12 03.01 +45 14.3 1.318 1.010 49.4 48.7 15.1 2023 10 13 12 17.97 +46 42.3 1.025 0.941 55.4 60.8 14.3 2023 10 23 12 48.60 +48 43.7 0.704 0.901 61.3 75.5 13.4 2023 10 28 13 20.23 +49 49.4 0.539 0.895 63.5 83.9 12.8 2023 11 02 14 21.70 +49 58.6 0.378 0.897 64.5 93.2 12.0 2023 11 07 16 27.26 +42 45.0 0.241 0.908 63.2 103.1 11.1 2023 11 12 19 09.69 +10 24.9 0.197 0.929 66.3 102.6 10.7 2023 11 17 20 47.34 -18 43.0 0.291 0.957 75.1 87.7 11.7 2023 11 22 21 35.25 -30 10.4 0.441 0.992 77.6 76.6 12.7 2023 11 27 22 01.90 -35 13.0 0.604 1.033 76.8 68.5 13.5 2023 12 02 22 18.96 -37 54.4 0.769 1.079 74.7 61.8 14.2 2023 12 07 22 31.21 -39 31.9 0.932 1.129 72.1 56.1 14.8 2023 12 12 22 40.83 -40 35.4 1.091 1.183 69.3 51.1 15.3 2023 12 17 22 48.95 -41 18.9 1.245 1.239 66.3 46.7 15.7 2023 12 22 22 56.18 -41 49.7 1.394 1.298 63.4 42.7 16.1 2023 12 27 23 02.89 -42 11.9 1.536 1.358 60.6 39.1 16.5 2024 01 01 23 09.29 -42 28.4 1.673 1.419 57.8 35.9 16.8 2024 01 06 23 15.53 -42 40.7 1.803 1.481 55.2 33.0 17.1 2024 01 11 23 21.70 -42 50.2 1.927 1.545 52.7 30.4 17.4 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 May 24 (CBET 5264) Daniel W. E. Green