Electronic Telegram No. 5301 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 R2 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala (discovery observations tabulated below). The object appeared only marginally cometary in the discovery images, but three 60-s gri-band follow-up images obtained on Sept. 11.61 UT with the 3.6-m Canada-France-Hawaii Telescope on Mauna Kea (queue observer L. Wells) confirm the cometary nature; there is a very condensed coma of size 1".6 (full-width-at-half-maximum) in 1".0 seeing with a broad tail > 4" long spanning p.a. 230-300 degrees. 2023 UT R.A. (2000) Decl. Mag. Sept.10.58966 3 15 42.86 + 0 29 27.3 20.6 10.60129 3 15 42.82 + 0 29 23.2 20.6 10.61287 3 15 42.79 + 0 29 18.8 20.6 Y. Ramanjooloo (University of Hawaii) adds that four additional 45-s w-band Pan-STARRS2 images obtained on Sept. 19.6 UT in 1".5 seeing show a diffuse coma of size 2".5 (FWHM) with no apparent tail. After the comet was posted on the Minor Planet Center's PCCP webpage, H. Sato (Bunkyo-ku, Tokyo, Japan) reported that eight stacked 120-s CCD exposures obtained at Siding Spring on Sept. 13.78 with a 0.51-m f/6.8 astrograph show a strongly condensed coma 8" in diameter with a hint of a tail 5" long toward p.a. 150 degrees; the magnitude was 19.9 as measured within a circular aperture of radius 4".9. The available astrometry appears on MPEC 2023-T7. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 120 observations spanning 2023 Sept. 10-29 (mean residual 0".4). The comet passed 1.09 AU from Jupiter on 2023 June 29 UT. T = 2024 Aug. 12.48466 TT Peri. = 337.11135 Node = 189.04584 2000.0 q = 0.9080865 AU Incl. = 30.78356 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 11.5 and 2.5n = 8 for the magnitudes. The comet will be on the far side of the sun at perihelion. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2023 09 13 03 15.59 +00 14.6 3.959 4.566 121.5 10.8 19.8 2023 09 23 03 14.12 -00 52.5 3.741 4.464 130.9 9.8 19.6 2023 10 03 03 11.07 -02 07.2 3.543 4.360 140.3 8.4 19.4 2023 10 13 03 06.41 -03 27.5 3.369 4.256 149.1 6.9 19.2 2023 10 23 03 00.28 -04 50.0 3.223 4.151 155.9 5.6 19.0 2023 11 02 02 52.93 -06 10.3 3.106 4.045 158.3 5.2 18.8 2023 11 12 02 44.80 -07 23.8 3.021 3.938 154.6 6.2 18.7 2023 11 22 02 36.45 -08 25.7 2.966 3.830 146.7 8.1 18.5 2023 12 02 02 28.51 -09 12.4 2.939 3.721 137.0 10.4 18.4 2023 12 12 02 21.55 -09 41.8 2.935 3.611 126.7 12.6 18.3 2023 12 22 02 16.09 -09 53.2 2.950 3.500 116.4 14.6 18.2 2024 01 01 02 12.47 -09 47.7 2.977 3.387 106.3 16.2 18.1 2024 01 11 02 10.86 -09 27.1 3.010 3.273 96.7 17.4 18.0 2024 01 21 02 11.37 -08 53.6 3.045 3.158 87.5 18.1 17.9 2024 01 31 02 13.94 -08 09.5 3.076 3.042 78.8 18.5 17.8 2024 02 10 02 18.52 -07 16.9 3.100 2.925 70.7 18.6 17.7 2024 02 20 02 25.02 -06 17.8 3.112 2.806 63.0 18.3 17.6 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 October 3 (CBET 5301) Daniel W. E. Green