Electronic Telegram No. 5676 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 P/2026 AH_19 = P/2017 B4 (PANSTARRS) On Jan. 15, Kacper Wierzchos, Lunar and Planetary Laboratory, University of Arizona, reported his discovery of an apparent comet with a 3" condensed coma and a straight 7" tail in p.a. 280 degrees in mosaic CCD images obtained with the Bok 2.25-m reflector at Kitt Peak (astrometry tabulated below). He obtained four 30-s exposures and four confirming 60-s exposures with a Schott OG-515 filter. 2026 UT R.A. (2000) Decl. Mag. Observer Jan. 13.44715 10 35 56.39 +20 27 00.2 21.2 Wierzchos 13.45275 10 35 56.38 +20 27 03.6 21.1 " 13.45833 10 35 56.36 +20 27 07.7 21.0 " 13.46392 10 35 56.35 +20 27 11.2 21.0 " 14.45080 10 35 54.72 +20 37 34.1 21.6 Pan-STARRS1 14.47458 10 35 54.65 +20 37 49.2 21.8 " 14.48655 10 35 54.57 +20 37 57.0 21.9 " 15.41784 10 35 51.36 +20 47 51.6 20.9 Wierzchos 15.42343 10 35 51.34 +20 47 55.3 21.0 " 15.42901 10 35 51.32 +20 47 58.7 21.1 " 15.43460 10 35 51.31 +20 48 02.2 21.2 " 15.45796 10 35 51.17 +20 48 17.2 21.5 " 15.45893 10 35 51.16 +20 48 17.8 21.1 " 15.45990 10 35 51.13 +20 48 18.4 21.1 " 15.46086 10 35 51.14 +20 48 19.0 21.3 " After Wierzchos' Jan. 15 observations (above) were posted to the Minor Planet Center's PCCP webpage, R. Weryk (Physics and Astronomy, University of Western Ontario) took note and identifyed it with an independent discovery in images obtained on Jan. 14 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala (also tabulated above) and then also with additional Bok-telescope images obtained by Wierzchos on Jan. 13 (also tabulated above) that appeared with a third preliminary object designation in the MPC's "isolated tracklet file". This allowed Weryk to identify this single object with two additional nights worth of observations obtained on 2025 Dec. 15.6 and 25.6 UT with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala. On four stacked 45-s w-band survey images taken on Dec. 15 in 1".4-1".7 seeing, Weryk found no coma but a possible tail about 2" long in p.a. 240 degrees. The December observations appear on MPEC 2026-F198. When Weryk realized that these were all observations of comet P/2017 B4 (cf. CBET 4355), he notified both the MPC and the Central Bureau of this on Jan. 15. Unfortunately, the MPC did nothing about this recovery until Mar. 25, when MPEC 2026-F198 was published, and R. Pike (MPC) informs the Central Bureau that it was apparently inadvertently given the minor-planet designation 2026 AH_19 around the time that the daily MPEC 2026-D36 was published (with an orbit from a 32-day arc but no observations were evidently published) on Feb. 18; in other words, the presence of the comet on the PCCP in January and two reported observations of apparently cometary appearance were somehow lost by the MPC. Already on Jan. 21, S. Nakano (Central Bureau) reported an orbit by T. Kobayashi (Oizumi, Gunma-ken, Japan) linking the December and January observations with P/2017 B4, with all of those observations apparently having been posted at the PCCP webpage then. Nakano added that the residuals of those observations from his prediction on NK 4110 were +410" in R.A. and -35" in Decl., with a corresponding correction of Delta(T) = -0.35 day. Revised linked orbital elements by Nakano now from 124 observations spanning 2016 Dec. 22-2026 Mar. 12 (mean residual 0".5) are tabulated below. The comet passed 0.64 AU from Jupiter on 2020 Aug. 7 UT. Epoch = 2007 Oct. 27.0 TT T = 2007 Nov. 13.27404 TT Peri. = 16.19977 e = 0.3564285 Node = 121.54917 2000.0 q = 2.8351195 AU Incl. = 20.15520 a = 4.4052908 AU n = 0.10659632 P = 9.23 years Epoch = 2017 Feb. 16.0 TT T = 2017 Jan. 27.11924 TT Peri. = 16.19207 e = 0.3577206 Node = 121.54616 2000.0 q = 2.8169279 AU Incl. = 20.18152 a = 4.3858292 AU n = 0.10730662 P = 9.18 years Epoch = 2025 Nov. 21.0 TT T = 2025 Dec. 2.00033 TT Peri. = 11.45924 e = 0.3551782 Node = 119.47125 2000.0 q = 2.8163991 AU Incl. = 21.05518 a = 4.3677167 AU n = 0.10797480 P = 9.13 years Epoch = 2034 Dec. 24.0 TT T = 2035 Jan. 11.35170 TT Peri. = 11.29476 e = 0.3541106 Node = 119.48039 2000.0 q = 2.8238067 AU Incl. = 21.03743 a = 4.3719660 AU n = 0.10781741 P = 9.14 years Epoch = 2044 Mar. 6.0 TT T = 2044 Mar. 16.07579 TT Peri. = 11.50003 e = 0.3531805 Node = 119.38811 2000.0 q = 2.8358610 AU Incl. = 21.01793 a = 4.3843157 AU n = 0.10736219 P = 9.18 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 14.5 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2026 02 09 10 27.95 +25 30.3 1.891 2.848 162.6 5.9 20.4 2026 02 19 10 22.18 +27 18.5 1.894 2.857 163.8 5.5 20.4 2026 03 01 10 16.12 +28 49.7 1.926 2.868 157.8 7.5 20.5 2026 03 11 10 10.68 +29 58.1 1.984 2.880 148.8 10.3 20.6 2026 03 21 10 06.66 +30 41.6 2.065 2.893 139.2 13.0 20.7 2026 03 31 10 04.61 +31 00.8 2.166 2.907 129.7 15.3 20.8 2026 04 10 10 04.79 +30 58.3 2.282 2.923 120.6 17.2 20.9 2026 04 20 10 07.21 +30 37.3 2.410 2.939 112.1 18.5 21.1 2026 04 30 10 11.73 +30 01.0 2.547 2.956 104.0 19.3 21.2 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2026 CBAT 2026 March 26 (CBET 5676) Daniel W. E. Green