Electronic Telegram No. 5337 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/2015 HG_16 = P/2023 W2 (PANSTARRS) According to MPEC 2024-B134, comet P/2015 HG_16 (cf. CBET 4270) was recovered by J. Maikner on CCD images obtained on 2023 Nov. 19 UT with a 0.30-m f/3.8 Riccardi-Honders telescope at New Ringgold, PA, USA (no remarks about appearance). The recovery observations are tabulated below. 2023 UT R.A. (2000) Decl. Mag. Observer Nov. 19.14985 2 29 02.36 + 7 37 34.4 20.4 Maikner 19.17300 2 29 01.35 + 7 37 36.1 20.2 " 19.19616 2 29 00.34 + 7 37 38.1 20.3 " On 2023 Dec. 6, MPEC 2023-X98 published nine of Maikner's observations from 2023 Nov. 17, 19, and 20 (with no indication that this was a recovery apparition); the Nov. 17 observations have large residuals and may not be real or may be of another object. M. Rudenko, Minor Planet Center, writes that three additional sets of single-night observations (2023 Dec. 7, 8, and 16) that appear on MPEC 2024-B134 were found in the MPC's "isolated tracklet file". The residuals of Maikner's 2023 Nov. 19 observations were -274" in R.A. and -210" in Decl. from the prediction in NK 4189 and the ICQ's 2023 Comet Handbook, with a corresponding correction of Delta(T) = +0.47 day. The following linked orbital elements by S. Nakano (Central Bureau) are from 57 observations spanning 2015 Jan. 14-2023 Dec. 16 (mean residual 0".8). The comet passed 2.34 AU from Saturn on 2000 June 10 and 0.0664 AU from Jupiter on 2006 Nov. 12 UT. Previous orbital elements were T = 2005 Aug. 9, q = 4.859 AU, e = 0.380, Peri. = 129.8 deg (equinox J2000.0), Node = 62.8 deg, i = 18.8 deg, a = 7.837 AU, P = 21.9 years. Epoch = 2014 July 2.0 TT T = 2014 June 29.00506 TT Peri. = 48.15722 e = 0.3462740 Node = 59.52702 2000.0 q = 3.1318120 AU Incl. = 18.86840 a = 4.7907102 AU n = 0.09399489 P = 10.49 years Epoch = 2024 Oct. 17.0 TT T = 2024 Oct. 16.58651 TT Peri. = 46.74086 e = 0.3465579 Node = 57.05783 2000.0 q = 3.1234071 AU Incl. = 19.00511 a = 4.7799291 AU n = 0.09431307 P = 10.45 years Epoch = 2035 Mar. 14.0 TT T = 2035 Mar. 22.49191 TT Peri. = 47.13920 e = 0.3463952 Node = 56.94364 2000.0 q = 3.1170788 AU Incl. = 19.01037 a = 4.7690573 AU n = 0.09463576 P = 10.42 years Epoch = 2045 Sept.17.0 TT T = 2045 Sept. 6.20743 TT Peri. = 47.16094 e = 0.3451324 Node = 56.90894 2000.0 q = 3.1428357 AU Incl. = 18.97500 a = 4.7991925 AU n = 0.09374580 P = 10.51 years Curiously, MPC 123463 published three ATLAS observations that were supposedly of this comet, obtained on 2018 July 14 with a measured magnitude of 16.9-17.0 (when the predicted parameters below would suggest magnitude 23.5), but the residuals are large and those observations surely do not belong to this comet. The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 13.5 and 2.5n = 8 for the magnitudes, which represent both apparitions reasonably well. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 01 11 02 13.12 +10 42.0 3.108 3.491 104.8 15.8 20.3 2024 01 21 02 15.98 +11 40.9 3.231 3.467 95.6 16.4 20.4 2024 01 31 02 20.61 +12 45.4 3.356 3.445 86.8 16.6 20.4 2024 02 10 02 26.84 +13 54.3 3.480 3.422 78.5 16.4 20.5 2024 02 20 02 34.53 +15 06.6 3.600 3.401 70.5 15.9 20.5 2024 03 01 02 43.52 +16 21.2 3.714 3.380 62.9 15.1 20.6 2024 03 11 02 53.67 +17 37.1 3.819 3.359 55.6 14.1 20.6 2024 03 21 03 04.85 +18 53.4 3.914 3.340 48.6 12.9 20.7 2024 03 31 03 16.96 +20 09.1 3.998 3.321 41.8 11.6 20.7 2024 09 07 07 31.95 +32 04.9 3.590 3.132 55.5 15.4 20.2 2024 09 17 07 47.36 +32 20.6 3.472 3.128 62.0 16.5 20.2 2024 09 27 08 02.04 +32 37.7 3.348 3.125 68.6 17.4 20.1 2024 10 07 08 15.83 +32 58.0 3.220 3.124 75.5 18.0 20.0 2024 10 17 08 28.53 +33 23.3 3.089 3.123 82.7 18.5 19.9 2024 10 27 08 39.97 +33 55.4 2.958 3.124 90.2 18.6 19.8 2024 11 06 08 49.88 +34 36.0 2.829 3.126 98.0 18.3 19.7 2024 11 16 08 58.00 +35 26.7 2.705 3.128 106.2 17.7 19.6 2024 11 26 09 04.07 +36 27.8 2.589 3.132 114.7 16.6 19.5 2024 12 06 09 07.80 +37 39.1 2.484 3.137 123.4 15.2 19.4 2024 12 16 09 08.94 +38 58.4 2.395 3.142 132.3 13.4 19.4 2024 12 26 09 07.40 +40 21.4 2.324 3.149 140.9 11.4 19.3 2025 01 05 09 03.24 +41 42.4 2.276 3.157 148.5 9.4 19.3 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 January 26 (CBET 5337) Daniel W. E. Green