Electronic Telegram No. 5300 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 Q1 (PANSTARRS) P. Veres, Minor Planet Center, writes that he linked together five previously unlinked sets of one-night observations spanning Aug. 20-Sept. 20 that were in the MPC's "isolated tracklet file". After noticing a nearly parabolic orbit for the fit of these observations, Veres asked R. Weryk (Department of Physics and Astronomy, University of Western Ontario) to check the images obtained with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala. Weryk reports finding a weakly active comet on two nights: On Aug. 20.6 UT, three 45-s w-band survey images show a very condensed head of size 1".0 (full-width-at-half-maximum) in 0".85 seeing with no tail. Four 45-s w-band survey images taken on Sept. 17.4 show a very condensed head of size 1".4 (FWHM) in 1".1 seeing with no tail. Weryk also identified pre-discovery Pan-STARRS1 images from July 25.6 (mag 22.5-23.0) and Pan-STARRS2 images from July 26.6 (mag 22.1) and 29.6 (mag 22.7-22.8). The discovery observations are tabulated below. 2023 UT R.A. (2000) Decl. Mag. Aug. 20.55451 0 40 52.32 - 0 49 25.5 22.0 20.56726 0 40 52.05 - 0 49 24.9 22.3 20.57997 0 40 51.75 - 0 49 24.3 22.0 After the comet was posted on the MPC's PCCP webpage, H. Sato (Bunkyo-ku, Tokyo, Japan) reported that twenty-three stacked 60-s CCD exposures obtained on Sept. 23.7 UT with a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, show a strongly condensed coma 6" in diameter with no tail; the magnitude was 20.4 as measured within a circular aperture of radius 4".9. The available astrometry appears on MPEC 2023-T8. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 46 observations spanning 2023 July 25-Sept. 27 (mean residual 0".5). The comet will pass 2.75 AU from Jupiter on 2024 Jan. 19 UT. T = 2024 Dec. 2.31277 TT Peri. = 84.43277 Node = 7.16416 2000.0 q = 2.5798246 AU Incl. = 36.64700 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. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2023 09 13 00 29.65 -00 43.5 4.130 5.100 162.7 3.4 20.2 2023 09 23 00 23.35 -00 44.3 4.026 5.024 173.6 1.3 20.1 2023 10 03 00 16.58 -00 44.8 3.952 4.949 173.8 1.2 20.0 2023 10 13 00 09.73 -00 43.4 3.911 4.873 162.8 3.5 20.0 2023 10 23 00 03.24 -00 38.3 3.899 4.797 151.5 5.7 19.9 2023 11 02 23 57.51 -00 27.8 3.916 4.722 140.3 7.7 19.9 2023 11 12 23 52.87 -00 11.0 3.956 4.647 129.3 9.5 19.8 2023 11 22 23 49.55 +00 13.2 4.016 4.571 118.6 10.9 19.8 2023 12 02 23 47.71 +00 45.2 4.089 4.496 108.3 12.0 19.8 2023 12 12 23 47.37 +01 25.1 4.171 4.422 98.3 12.7 19.8 2023 12 22 23 48.53 +02 12.8 4.256 4.347 88.7 13.1 19.8 2024 01 01 23 51.10 +03 08.2 4.341 4.273 79.5 13.1 19.7 2024 01 11 23 54.99 +04 10.9 4.421 4.199 70.7 12.8 19.7 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 5300) Daniel W. E. Green