Electronic Telegram No. 5267 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 H3 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained on Apr. 28 with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala (discovery observations tabulated below). Four 45-s w-band survey images taken in 1".3 seeing show a condensed head of size 1".9 (full-width-at-half-maximum) with and point-spread asymmetry that suggests a short tail toward the northwest. 2023 UT R.A. (2000) Decl. Mag. Apr. 28.39582 14 26 19.97 -13 34 06.0 20.8 28.40795 14 26 19.64 -13 34 04.8 21.1 28.42011 14 26 19.35 -13 34 03.4 20.8 28.43227 14 26 19.05 -13 34 02.2 21.1 Weryk adds that four 45-s w-band survey-images taken on May 12.4 UT with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala show a condensed head of size 2".0 (FWHM) in 1".3 seeing, again with a PSF asymmetry towards p.a. 315 degrees. Y. Ramanjooloo, University of Hawaii, writes that three 240-s unfiltered follow-up exposures taken on May 28.34-28.35 with the University of Hawaii 2.2-m reflector at Mauna Kea in 2".1 seeing show a slightly fuzzy, diffuse coma of size 3".0 (FWHM) and no tail. Additional Pan-STARRS1 observations from Mar. 31.6 (mag 21.2-21.5) were found in the Minor Planet Center's "isolated tracklet file", as well as Pan-STARRS2 observations from Apr. 15.4 (mag 20.9-21.4). Weryk subsequently identified pre-discovery Pan-STARRS2 observations from Mar. 16.6 (mag 20.7-21.5) and Pan-STARRS2 observations from Apr. 21.5 (mag 20.4-20.6). The available astrometry appears on MPEC 2023-K195. The following orbital elements by S. Nakano (Central Bureau) are from 47 observations spanning 2023 Mar. 16-May 28 (mean residual 0".2). Nakano notes that the orbital period is uncertain by about one week, adding that if this orbit is correct, the comet would have passed 0.005 AU from Uranus in 1938 November, with the previous orbital elements being T = 1924 Oct. 29, q = 6.19 AU, e = 0.62, Peri. = 37.4 deg, Node = 226.4 deg, i = 46.1 deg (equinox J2000.0), a = 16.3 AU, P = 66 years Epoch = 2024 Feb. 20.0 TT T = 2024 Feb. 18.84671 TT Peri. = 193.30759 e = 0.6160430 Node = 55.10315 2000.0 q = 5.2327694 AU Incl. = 2.48888 a = 13.6285289 AU n = 0.01958983 P = 50.31 years 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. 2023 05 16 14 19.42 -13 05.4 4.511 5.483 162.3 3.2 20.2 2023 05 26 14 16.04 -12 51.9 4.552 5.466 151.9 5.0 20.2 2023 06 05 14 13.39 -12 42.2 4.617 5.449 141.6 6.6 20.2 2023 06 15 14 11.66 -12 37.1 4.705 5.433 131.6 8.0 20.2 2023 06 25 14 10.96 -12 37.4 4.811 5.418 121.9 9.2 20.3 2023 07 05 14 11.39 -12 43.5 4.931 5.403 112.5 10.0 20.3 2023 07 15 14 12.93 -12 55.2 5.062 5.389 103.4 10.6 20.4 2023 07 25 14 15.58 -13 12.3 5.198 5.375 94.6 10.9 20.4 2023 08 04 14 19.28 -13 34.5 5.337 5.362 86.0 10.9 20.5 2023 08 14 14 23.96 -14 01.0 5.475 5.350 77.6 10.7 20.5 2023 08 24 14 29.55 -14 31.4 5.608 5.338 69.4 10.2 20.6 2023 09 03 14 35.97 -15 05.0 5.735 5.327 61.4 9.6 20.6 2023 09 13 14 43.13 -15 40.9 5.852 5.316 53.6 8.8 20.6 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 May 30 (CBET 5267) Daniel W. E. Green