[Iaude] CBET 5337: COMET P/2015 HG_16 = P/2023 W2

[quai at eps.harvard.edu]

                                                  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 at eps.harvard.edu (alternate cbat at 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