Electronic Telegram No. 5256 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 H1 (PANSTARRS) Yudish Ramanjooloo, Institute for Astronmy, University of Hawaii, reports the discovery of another comet in images obtained on Apr. 17 UT with the Pan- STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala (discovery observations tabulated below. The four 45-s w-band survey discovery images reveal a diffuse coma of size 2".6 (full-width-at-half-maximum) in 1".5-1".6 seeing, with no tail. 2023 UT R.A. (2000) Decl. Mag. Apr. 17.34826 12 18 57.80 -30 04 19.4 20.8 17.35977 12 18 57.49 -30 04 17.6 20.7 17.37125 12 18 57.24 -30 04 15.5 20.9 17.38278 12 18 56.96 -30 04 13.5 20.7 Ramanjooloo adds that three 60-s and one 180-s follow-up exposures taken with the 2.2-m University of Hawaii telescope at Mauna Kea on Apr. 29.3 UT show a diffuse coma of size 3".1 (FWHM) in 2".3 seeing with a possible broad tail perhaps 3"-4" long toward p.a. 315 degrees. R. Weryk, Department of Physics and Astronomy, University of Western Ontario, writes that three 60-s gri-band follow-up images obtained with the 3.6-m Canada-France-Hawaii Telescopes at Mauna Kea on Apr. 21.4 (queue observer C. Cunningham; queue coordinator E. Bertin) show a diffuse coma of size 1".7 (FWHM) in 1".0 seeing with a straight tail 8" long toward p.a. 315 degrees. After the comet was posted to the Minor Planet Center's PCCP webpage, H. Sato (Bunkyo-ku, Tokyo, Japan) relates that he obtained eight stacked 120-s CCD exposures remotely on Apr. 18.3 UT with a "Deep Sky Chile" 0.51-m f/6.8 astrograph located at Rio Hurtado, Chile, showing a strongly condensed coma 4" in diameter with no tail; the magnitude was 20.4 as measured within a circular aperture of radius 2".2. The available astrometry appears on MPEC 2023-J101. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 25 observations spanning Apr. 17-May 6 (mean residual 0".2). There are no close approach to any major planets. T = 2024 Nov. 27.61031 TT Peri. = 333.86195 Node = 292.64629 2000.0 q = 4.4373524 AU Incl. = 21.77595 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 9.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2023 04 06 12 23.54 -30 31.0 5.565 6.481 154.4 3.8 19.7 2023 04 16 12 19.48 -30 08.0 5.516 6.428 153.2 4.0 19.7 2023 04 26 12 15.85 -29 38.3 5.494 6.375 148.6 4.7 19.6 2023 05 06 12 12.90 -29 04.2 5.498 6.322 141.8 5.7 19.6 2023 05 16 12 10.82 -28 28.0 5.525 6.269 134.0 6.7 19.6 2023 05 26 12 09.75 -27 52.0 5.572 6.217 125.6 7.6 19.6 2023 06 05 12 09.78 -27 18.5 5.635 6.165 117.2 8.4 19.6 2023 06 15 12 10.92 -26 49.1 5.711 6.113 108.7 9.1 19.6 2023 06 25 12 13.16 -26 25.2 5.797 6.062 100.3 9.5 19.6 2023 07 05 12 16.45 -26 07.7 5.888 6.011 92.1 9.7 19.6 2023 07 15 12 20.72 -25 57.1 5.980 5.960 84.0 9.8 19.6 2023 07 25 12 25.92 -25 53.7 6.071 5.910 76.1 9.6 19.6 2023 08 04 12 31.95 -25 57.4 6.156 5.860 68.4 9.3 19.6 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 May 12 (CBET 5256) Daniel W. E. Green