[Iaude] CBET 5338: COMET P/2023 Y3 = P/2017 BQ_100 (ATLAS)

[quai at eps.harvard.edu]

                                                  Electronic Telegram No. 5338
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/2023 Y3 = P/2017 BQ_100 (ATLAS)
     A. Fitzsimmons reported on 2023 Dec. 19 that L. Denneau found an object
discovered on CCD images taken on 2023 Dec. 19.0 UT with a 0.5-m f/2 Schmidt
reflector at Sutherland, South Africa, in the course of the "Asteroid
Terrestrial-Impact Last Alert System" (ATLAS) search program to be possibly
diffuse in four individual 30-s exposures; Fitzsimmons measured the head to
have a size of 8".5 (FWHM) in 5".3 seeing, with an extension visible toward
p.a. 310 degrees in a co-added image.  The discovery observations are
tabulated below:

     2023 UT             R.A. (2000) Decl.       Mag.
     Dec. 18.98291    7 21 11.73   +13 13 03.9   18.9
          18.98472    7 21 11.63   +13 13 04.2   18.7
          18.98787    7 21 11.56   +13 13 04.3   18.9
          19.00861    7 21 10.82   +13 13 09.7   18.8

The Minor Planet Center subsequently identified three ATLAS observations of
this comet at mag 19.0-19.2 that had been made on 2023 Dec. 13 with a 0.5-m
f/2 Schmidt reflector at Rio Hurtado, Chile, in the MPC's "isolated tracklet
file".  After the comet was posted to the MPC's PCCP webpage, other observers
commented on the object's cometary appearance to the Central Bureau, as
listed below.
     R. Weryk, Department of Physics and Astronomy, University of Western
Ontario, reports finding the comet in CCD images obtained on 2023 Nov. 17.6 UT
with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala; two 45-s
w-band survey images taken in 1".4 seeing show a very condensed head of size
1".7 (FWHM) with a clear 4" tail in p.a. 275 degrees.  Weryk adds that three
45-s w-band survey images taken on 2023 Nov. 20.5 with the Pan-STARRS1 1.8-m
Ritchey-Chretien reflector at Haleakala in 1".4 seeing show a very condensed
coma of size 1".7 (FWHM) and a clear 4" tail in p.a. 275 degrees.  Weryk then
identified the comet with an apparently asteroidal object that was discovered
on 2017 Jan. 28 with the Pan-STARRS1 telescope (discovery observation
tabulated below) and had been designated 2017 BQ_100 when it was announced on
MPS 766268 on 2017 Feb. 12, when it had a five-day arc (four nights) and
produced an un-noteworthy orbit; he adds that four 45-s w-band survey images
taken in 1".0 seeing on 2017 Jan. 28 show a very sharp point-spread function
(very condensed head of size 1".0 FWHM), but the comet also exhibits a clear
tail 10" long in p.a. 270 degrees.  The 2017 discovery observations are
tabulated below.

     2017 UT             R.A. (2000) Decl.       Mag.
     Jan. 28.49125    8 46 14.92   +18 06 09.7   20.8
          28.50412    8 46 14.35   +18 06 16.4   20.8
          28.51709    8 46 13.78   +18 06 23.2   20.7
          28.53002    8 46 13.22   +18 06 29.8   20.9

     Eight stacked 60-s CCD exposures taken remotely on 2023 Dec. 20.3 UT by
Hidetaka Sato (Bunkyo-ku, Tokyo, Japan) with a "Deep Sky Chile" 0.51-m f/6.8
astrograph located at Rio Hurtado, Chile, show a strongly condensed coma 5"
in diameter with a 10" tail extending toward p.a. 285 degrees; the magnitude
was 19.1 as measured within a circular aperture of radius 2".8.
     Two-hundred stacked 30-s CCD exposures taken at Varese, Italy, on 2023
Dec. 24.9 UT by A. Aletti (and measured by Aletti and M. Auteri) with a 0.36-m
f/7.5 reflector in 3".8 seeing show a slightly condensed coma of size 4".7
(FWHM), extended toward the west.
     Hirohisa Sato has measured sixteen stacked 60-s CCD exposures taken on
2024 Jan. 11.66 UT at Shinshiro, Japan, by T. Ikemura with a 0.38-m f/4.2
reflector, which reveal a condensed coma about 13" in diameter of total mag
18.2 with no tail.
     S. Deen (Simi Valley, CA, USA) has identified the comet in two publicly
available 90-s i-band DECam exposures obtained on 2017 Jan. 28.24 UT by S.
Bocquet, J. Frieman, and T. Li with the Cerro Tololo 4-m reflector.  Deen sees
no apparent coma in the images, but there is a very faint, straight 11" tail
toward p.a. 267 degrees.
     The available astrometry appears on MPEC 2024-B139.  The following linked
orbital elements by S. Nakano (Central Bureau) are from 436 observations
spanning 2015 Sept. 18-2024 Jan. 22 (mean residual 0".4).  There are no close
approaches to major planets.

                    Epoch = 2017 Feb. 16.0 TT
     T = 2017 Mar.  7.09161 TT        Peri. =  10.78533
     e = 0.3186256                    Node  = 128.52705 2000.0
     q = 2.5488954 AU                 Incl. =  12.49113
       a =  3.7408147 AU   n = 0.13622436   P =   7.24 years

                    Epoch = 2024 May  10.0 TT
     T = 2024 May   1.97317 TT        Peri. =  13.18078
     e = 0.3434593                    Node  = 127.27143 2000.0
     q = 2.3936061 AU                 Incl. =  12.52524
       a =  3.6457850 AU   n = 0.14158508   P =   6.96 years

                    Epoch = 2031 May  14.0 TT
     T = 2031 Apr. 25.20362 TT        Peri. =  13.43030
     e = 0.3426015                    Node  = 127.21007 2000.0
     q = 2.3992822 AU                 Incl. =  12.51986
       a =  3.6496620 AU   n = 0.14135954   P =   6.97 years

                    Epoch = 2038 Apr.  7.0 TT
     T = 2038 Apr. 14.83698 TT        Peri. =  13.11416
     e = 0.3406883                    Node  = 127.16133 2000.0
     q = 2.4142214 AU                 Incl. =  12.51308
       a =  3.6617302 AU   n = 0.14066128   P =   7.01 years

The following ephemeris by the undersigned from the above orbital elements
uses photometric power-law parameters H = 13.0 and 2.5n = 10 for the
magnitudes.

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase  Mag.
2024 01 11    07 04.69   +15 26.8    1.523    2.500   171.7     3.2  17.9
2024 01 21    06 57.02   +16 40.2    1.526    2.482   162.6     6.8  17.9
2024 01 31    06 50.71   +17 55.7    1.556    2.466   151.4    11.0  17.9
2024 02 10    06 46.67   +19 09.0    1.609    2.452   140.5    14.8  17.9
2024 02 20    06 45.50   +20 16.7    1.682    2.439   130.1    18.1  18.0
2024 03 01    06 47.43   +21 16.5    1.770    2.427   120.5    20.6  18.1
2024 03 11    06 52.36   +22 07.2    1.869    2.417   111.5    22.5  18.2
2024 03 21    07 00.08   +22 47.8    1.977    2.409   103.3    23.7  18.3
2024 03 31    07 10.23   +23 17.7    2.089    2.403    95.7    24.4  18.4
2024 04 10    07 22.47   +23 36.6    2.204    2.398    88.5    24.7  18.5
2024 04 20    07 36.46   +23 43.9    2.320    2.395    81.9    24.5  18.6
2024 04 30    07 51.84   +23 39.6    2.435    2.394    75.7    24.1  18.7
2024 05 10    08 08.32   +23 23.6    2.548    2.394    69.8    23.3  18.8
2024 05 20    08 25.66   +22 56.2    2.658    2.396    64.1    22.3  18.9
2024 05 30    08 43.61   +22 17.8    2.765    2.401    58.7    21.2  19.0
2024 06 09    09 01.99   +21 28.8    2.867    2.406    53.5    19.8  19.1
2024 06 19    09 20.64   +20 30.1    2.964    2.414    48.5    18.4  19.2


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2021 CBAT
2021 January 27                  (CBET 5338)              Daniel W. E. Green