Electronic Telegram No. 5745 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/2009 Y2 (KOWALSKI) On Sept. 17, Krisztian Sarneczky (Konkoly Observatory) reported the discovery of a comet in twelve 60-s stacked w-band CCD images (limiting mag about 21.5) taken on Sept. 15.0 UT at the Piszkesteto Observatory in Hungary with the 0.60-m Schmidt telescope (discovery observations tabulated below). The comet shows a strongly condensed coma that is "softer" than the nearby faint stars. Thirty 60-s stacked follow-up images taken on the next night (Sept. 16.0) with the same telescope show a well condensed, fan-shaped coma to the north, with size 5" x 7". 2026 UT R.A. (2000) Decl. Mag. Observer Sept.15.04191 4 53 16.46 +41 09 18.4 19.5 Sarneczky 15.05309 4 53 17.37 +41 09 17.3 19.7 " 15.11261 4 53 22.21 +41 09 11.6 19.8 " Twenty stacked 60-s CCD exposures taken by Z. Bognar with the 1.02-m Ritchey-Chretien telescope at Piszkesteto on Sept. 16.1 UT in 0".8 seeing show a clearly cometary appearance: strong central condensation and a faint, diffuse, fan-shaped coma 3".5 x 4" in diameter; the G magnitude was 20.3 as measured within a circular aperture of radius 2". After the comet was posted to the Minor Planet Center's PCCP webpage, T. Kobayashi informed the Central Bureau that this appears to be a recovery of comet C/2009 Y2 (cf. CBET 2088; IAUC 9103). Sixteen stacked 60-s CCD exposures taken remotely with a 0.51-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) by H. Sato (Tokyo, Japan) on 2026 Sept. 18.4 UT show a moderately condensed coma 10" in diameter with no tail; the magnitude was 19.7 as measured within a circular aperture of radius 6".5. Note that the Minor Planet Center announced on MPEC 2026-R15, dated 2026 Sept. 3, the following: "At the same time, beginning December 7, 2026, the MPC will discontinue the practice of assigning a new provisional designation when a previously known comet is recovered. Recovery MPECs will continue to be issued as usual, but they will identify the object as a recovery of the previously designated comet rather than assigning an additional designation for the new apparition. When the orbit is sufficiently well determined and the object meets the requirements for permanent numbering, the comet will be numbered through the usual circular process." This proposed lack of assigning new designations goes against historical practice of the last couple of centuries for the first returns of periodic comets, and apparently was done without proper consultation with the IAU (such matters are usually voted on at the triennial General Assemblies after discussion). The MPC has issued numerous MPECs in the last several years (since 2020) with recovery observations given in their semi-regular "Observations and Orbits of Comets and A/ Objects" MPECs without first issuing recovery MPECs devoted to the recovery comets. The CBAT will continue to call attention to the very important first-recovery apparitions of short-period comets with full recovery details in its CBETs. The residuals for the 2026 Sept. observations of P/2009 Y2 are +2.87 deg in R.A. and -1.37 deg in Decl. from the prediction in NK 1991 (= ICQ Comet Handbook 2026), with a corresponding correction of Delta(T) = -8.8 days. The following linked orbital elements by S. Nakano (Central Bureau) are from 229 observations spanning 2009 Dec. 20-2026 Sept. 19 (mean residual 0".5). The comet passed 2.71 AU from Saturn on 2016 Feb. 29 UT. Epoch = 2010 Mar. 25.0 TT T = 2010 Mar. 30.70227 TT Peri. = 171.96268 e = 0.6401370 Node = 262.12890 2000.0 q = 2.3391043 AU Incl. = 29.92841 a = 6.4999862 AU n = 0.05947513 P = 16.57 years Epoch = 2026 Nov. 16.0 TT T = 2026 Dec. 2.06472 TT Peri. = 172.31584 e = 0.6371864 Node = 262.05313 2000.0 q = 2.3701347 AU Incl. = 29.98325 a = 6.5326505 AU n = 0.05902961 P = 16.70 years Epoch = 2043 July 10.0 TT T = 2043 July 11.12251 TT Peri. = 172.49459 e = 0.6362470 Node = 261.51525 2000.0 q = 2.3722474 AU Incl. = 30.07867 a = 6.5215883 AU n = 0.05917987 P = 16.65 years Epoch = 2060 Mar. 2.0 TT T = 2060 Mar. 10.17658 TT Peri. = 172.17793 e = 0.6374968 Node = 261.38419 2000.0 q = 2.3883497 AU Incl. = 29.99852 a = 6.5884922 AU n = 0.05828074 P = 16.91 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 13.5 and 2.5n = 10 for the magnitudes; this is about 1 mag fainter than observations from the 2009-2010 return. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2026 08 28 04 25.18 +41 12.8 2.425 2.518 83.4 23.5 19.4 2026 09 07 04 41.44 +41 16.4 2.285 2.490 89.5 23.9 19.3 2026 09 17 04 55.95 +41 06.2 2.146 2.464 96.1 23.9 19.1 2026 09 27 05 08.27 +40 41.2 2.010 2.442 103.1 23.6 18.9 2026 10 07 05 17.94 +40 00.2 1.880 2.422 110.8 22.7 18.7 2026 10 17 05 24.49 +39 01.4 1.757 2.405 119.2 21.2 18.5 2026 10 27 05 27.61 +37 42.1 1.645 2.392 128.3 19.0 18.4 2026 11 06 05 27.17 +35 59.3 1.548 2.382 138.4 16.1 18.2 2026 11 16 05 23.38 +33 50.7 1.470 2.374 149.3 12.3 18.1 2026 11 26 05 16.96 +31 16.1 1.416 2.371 160.9 7.8 18.0 2026 12 06 05 09.05 +28 20.1 1.390 2.370 172.5 3.1 18.0 2026 12 16 05 01.01 +25 12.5 1.394 2.373 172.6 3.1 18.0 2026 12 26 04 54.21 +22 06.5 1.428 2.380 161.0 7.8 18.0 2027 01 05 04 49.60 +19 14.8 1.491 2.389 149.2 12.2 18.2 2027 01 15 04 47.72 +16 46.0 1.578 2.402 138.1 15.9 18.3 2027 01 25 04 48.70 +14 43.3 1.686 2.418 127.8 18.8 18.5 2027 02 04 04 52.36 +13 05.7 1.810 2.437 118.3 20.9 18.7 2027 02 14 04 58.45 +11 49.9 1.945 2.459 109.6 22.2 18.9 2027 02 24 05 06.62 +10 51.2 2.089 2.484 101.6 23.0 19.1 2027 03 06 05 16.52 +10 05.1 2.237 2.512 94.1 23.2 19.2 2027 03 16 05 27.87 +09 27.4 2.389 2.542 87.1 23.0 19.4 2027 03 26 05 40.37 +08 54.4 2.542 2.574 80.6 22.5 19.6 2027 04 05 05 53.80 +08 23.3 2.694 2.609 74.4 21.7 19.8 2027 04 15 06 07.96 +07 51.7 2.844 2.646 68.5 20.6 20.0 2027 04 25 06 22.66 +07 17.8 2.990 2.685 62.8 19.5 20.2 2027 05 05 06 37.75 +06 40.3 3.132 2.725 57.4 18.2 20.3 2027 05 15 06 53.11 +05 58.0 3.269 2.768 52.2 16.8 20.5 2027 05 25 07 08.61 +05 10.3 3.399 2.812 47.2 15.3 20.6 2027 06 04 07 24.16 +04 16.8 3.523 2.857 42.4 13.9 20.8 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2026 CBAT 2026 September 23 (CBET 5745) Daniel W. E. Green