Electronic Telegram No. 5290 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 P1 (NISHIMURA) Q.-Z. Ye, Department of Astronomy, University of Maryland, writes that he heard from J. Greaves (Northants, UK) that the orbit of comet C/2023 P1 (cf. CBET 5285) is very similar to orbits of the meteors of the established meteor shower sigma-Hydrids (which is active during Nov. 22-Jan. 18, according to P. Jenniskens). The orbital similarity tests conducted by Greaves using 129 matching video meteor orbits selected from SonotaCo, the Global Meteor Network, CAMS, and EDMOND databases shows a median "D" criterion of D_j < 0.08, where D_j is defined by Jopek (1993, Icarus 106, 603). Calculations by Greaves and Ye using the comet orbit published in MPEC 2023-Q33 shows the theoretical radiant of meteors originating from C/2023 P1 would be around R.A. = 117.0 deg, Decl. = +5.0 deg, with geocentric velocities of 60.3 km/s, and a predicted meteor-shower peak occurring at solar longitude 246.8 deg (around November 30 each year), which is within a few degrees and km/s of the measured radiant of the sigma-Hydrids. It is possible that C/2023 P1 is closely related to the sigma-Hydrids. If this is the case, elevated meteor activity from sigma-Hydrids this year may be possible (even if unlikely), given that its possible parent comet is passing perihelion. Observations are encouraged from the end of November to early December. Observers have indicated that the comet has brightened quite a bit in the past week, with photos posted on the "ICQ Comet Observations" Facebook forum showing the thin ion tail now extending 1.5-2 degrees from the coma. Additional selected visual total-magnitude and coma-diameter estimates reported to the Central Bureau: Aug. 17.13 UT, 9.7, 1'.0 (W. Hasubick, Buchloe, Germany, 44-cm reflector); 22.35, 8.5, -- (J. G. de S. Aguiar, Campinas, Brazil, 25x100 binoculars); 23.47, 7.9, 2'.5 (C. Hergenrother, Tucson, AZ, USA, 30x125 binoculars); 24.36, 8.0, 5' (W. Souza, Sao Paulo, Brazil, 0.15-m reflector); 26.13, 7.6, 4' (V. Gonano, Udine, Italy, 10x50 binoculars); 27.17, 7.3, 5' (J. J. Gonzalez, Leon, Spain, 0.20-m reflector; 0.4-deg tail in p.a. 280 deg). Additional astrometry has been published on MPEC 2023-Q150. The following revised orbital elements by S. Nakano (Central Bureau) are from 388 observations spanning 2023 Aug. 13-28 (mean residual 0".6) and show a departure from a parabola, though the orbital period (around 466 years from this orbit) is still uncertain by perhaps +/- 50 years or more. T = 2023 Sept. 17.64135 TT Peri. = 116.29337 e = 0.9962519 Node = 66.84017 2000.0 q = 0.2251558 AU Incl. = 132.46827 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 8.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2023 08 24 07 48.73 +21 50.0 1.326 0.768 35.2 49.4 7.7 2023 08 29 08 17.98 +23 10.5 1.163 0.649 33.8 60.1 6.8 2023 09 03 08 59.96 +24 09.4 1.009 0.524 30.1 75.0 5.8 2023 09 08 10 01.35 +23 27.6 0.885 0.397 23.1 96.1 4.5 2023 09 13 11 21.33 +18 02.8 0.839 0.279 13.9 119.6 3.2 2023 09 18 12 27.93 +06 30.5 0.939 0.226 12.7 100.6 2.7 2023 09 23 12 51.79 -04 20.2 1.132 0.294 14.2 57.2 4.0 2023 09 28 12 56.39 -11 21.2 1.310 0.415 14.0 35.6 5.5 2023 10 03 12 56.86 -16 10.4 1.459 0.542 13.7 26.0 6.7 2023 10 08 12 56.56 -19 50.6 1.586 0.666 14.3 21.8 7.6 2023 10 13 12 56.20 -22 51.1 1.696 0.784 15.8 20.2 8.3 2023 10 18 12 55.94 -25 26.9 1.791 0.897 17.9 20.0 8.9 2023 10 23 12 55.74 -27 46.6 1.873 1.005 20.7 20.4 9.4 2023 10 28 12 55.53 -29 55.2 1.944 1.110 23.8 21.2 9.8 2023 11 02 12 55.24 -31 56.3 2.006 1.210 27.1 22.0 10.2 2023 11 07 12 54.80 -33 52.2 2.058 1.308 30.7 22.8 10.5 2023 11 12 12 54.09 -35 44.4 2.102 1.403 34.5 23.5 10.8 2023 11 17 12 53.04 -37 34.2 2.139 1.495 38.3 24.2 11.0 2023 11 22 12 51.54 -39 22.2 2.169 1.585 42.3 24.8 11.3 2023 11 27 12 49.47 -41 08.9 2.193 1.673 46.4 25.3 11.5 2023 12 02 12 46.72 -42 54.5 2.211 1.759 50.6 25.7 11.7 2023 12 07 12 43.16 -44 39.1 2.225 1.843 54.8 25.9 11.9 2023 12 12 12 38.64 -46 22.5 2.235 1.925 59.1 26.0 12.0 2023 12 17 12 33.00 -48 03.9 2.241 2.006 63.5 26.0 12.2 2023 12 22 12 26.05 -49 42.5 2.245 2.085 67.9 25.9 12.3 2023 12 27 12 17.64 -51 17.1 2.248 2.164 72.4 25.7 12.4 2024 01 01 12 07.59 -52 46.1 2.250 2.240 76.8 25.3 12.6 2024 01 06 11 55.79 -54 07.5 2.252 2.316 81.2 24.8 12.7 2024 01 11 11 42.15 -55 18.9 2.255 2.391 85.6 24.2 12.8 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 August 29 (CBET 5290) Daniel W. E. Green