Electronic Telegram No. 5238
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 C/2023 C2 (ATLAS)
     An apparently asteroidal object discovered on CCD images taken on Feb. 1
UT with a 0.5-m f/2 Schmidt reflector at Rio Hurtado, Chile, in the course of
the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS) search program has
been found to show cometary appearance by CCD astrometrists elsewhere after
it was posted on the Minor Planet Center's PCCP webpage.  The discovery
observations are tabulated below:

     2023 UT             R.A. (2000) Decl.       Mag.
     Feb.  1.25410   11 05 31.33   -48 04 42.0   19.1
           1.27741   11 05 30.45   -48 04 50.0   19.2
           1.29240   11 05 30.11   -48 04 54.1   19.1
           1.30052   11 05 29.79   -48 04 55.3   19.0

Thirteen stacked 120-s exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo,
Japan) using a 0.51-m f/6.8 astrograph located at Siding Spring on Feb. 3.74-
3.75 UT show a stellar appearance; the magnitude was 20.0 as measured within a
circular aperture of radius 4".4.  E. Bryssinck, Kruibeke, Belgium, writes
that thirteen stacked 180-s luminance-filtered exposures taken on Feb. 28.12
by M. Rocchette, E. Guido, G. Milani, A. Valvasori, and himself remotely with
a "Telescope Live" 0.61-m f/6.7 reflector located at Rio Hurtado Chile, show
a central condensation with a coma 9" in diameter and magnitude 19.0 as
measured within a circular aperture of radius 5".
     The available astrometry appears on MPEC 2023-F141.  The following
parabolic orbital elements by S. Nakano (Central Bureau) are from 68
observations spanning Feb. 1-Mar. 19 (mean residual 0".4).

     T = 2024 Nov. 16.45194 TT        Peri. = 357.44471
                                      Node  = 301.02744 2000.0
     q = 2.3670192 AU                 Incl. =  48.31651

The following ephemeris by the undersigned from the above orbital elements
uses photometric power-law parameters H = 8.5 and 2.5n = 8 for the magnitudes.

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase  Mag.
2023 01 16    11 11.82   -46 27.1    6.624    6.838    98.4     8.2  19.3
2023 01 26    11 08.37   -47 30.1    6.443    6.762   104.8     8.1  19.2
2023 02 05    11 03.58   -48 23.4    6.272    6.687   110.8     7.9  19.1
2023 02 15    10 57.60   -49 04.6    6.114    6.611   116.3     7.7  19.0
2023 02 25    10 50.68   -49 31.8    5.971    6.535   120.9     7.5  18.9
2023 03 07    10 43.19   -49 43.3    5.846    6.459   124.4     7.3  18.8
2023 03 17    10 35.57   -49 38.9    5.740    6.383   126.6     7.2  18.7
2023 03 27    10 28.30   -49 18.9    5.653    6.306   127.2     7.2  18.7
2023 04 06    10 21.84   -48 45.2    5.586    6.230   126.2     7.4  18.6
2023 04 16    10 16.55   -48 00.4    5.539    6.153   123.8     7.8  18.5
2023 04 26    10 12.69   -47 07.5    5.508    6.076   120.1     8.2  18.5
2023 05 06    10 10.40   -46 10.3    5.494    5.999   115.6     8.7  18.4
2023 05 16    10 09.71   -45 11.9    5.493    5.921   110.4     9.2  18.4
2023 05 26    10 10.61   -44 15.6    5.503    5.844   104.8     9.6  18.3
2023 06 05    10 13.01   -43 24.0    5.521    5.766    98.9    10.0  18.3
2023 06 15    10 16.79   -42 39.1    5.544    5.688    93.0    10.3  18.3
2023 06 25    10 21.83   -42 02.6    5.569    5.610    87.1    10.4  18.2
2023 07 05    10 28.01   -41 35.5    5.595    5.532    81.2    10.5  18.2
2023 07 15    10 35.20   -41 18.5    5.618    5.454    75.5    10.4  18.1
2023 07 25    10 43.31   -41 12.0    5.637    5.375    70.0    10.2  18.1
2023 08 04    10 52.24   -41 16.3    5.649    5.297    64.8    10.0  18.1


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

                         (C) Copyright 2023 CBAT
2023 March 26                    (CBET 5238)              Daniel W. E. Green