Electronic Telegram No. 5268
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 K1 (ATLAS)
     N. Erasmus, South African Astronomical Observatory, reports the discovery
of a comet on CCD images taken on May 27.1 UT with a 1-m telescope at
Sutherland, South Africa, in the course of the "Asteroid Terrestrial-Impact
Last Alert System" (ATLAS) search program.  The comet then showed an
asymmetrical diffuse coma extending out 10"-15" with the largest part toward
p.a. 270-285 degrees.  The discovery observations are tabulated below:

     2023 UT             R.A. (2000) Decl.       Mag.
     May  27.09383   22 58 48.05   -61 49 58.9   18.6
          27.09532   22 58 47.83   -61 50 02.1   17.6
          27.10174   22 58 47.31   -61 50 17.3   17.7
          27.11319   22 58 46.22   -61 50 43.2   17.7

After the comet was posted on the Minor Planet Center's PCCP webpage, other
CCD astrometrists also commented on the cometary appearance.  L. Buzzi writes
that eighteen stacked 60-s exposures taken by A. Aletti, F. Bellini, G. Galli,
and himself (and measured by Aletti) on May 29.14-29.16 with a 0.36-m f/8.4
reflector located at Hakos, Namibia, show a condensed coma 11" wide and a
broad, faint tail 30" long centered at p.a. 255 degrees.  Twelve stacked 30-s
exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) on May 29.82
with a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia,
show a strongly condensed coma 12" in diameter with a fan-like tail 20" long
spanning p.a. 200-265 degrees; the magnitude was 17.6 as measured within a
circular aperture of radius 6".5.  T. Prystavski, Lviv, Ukraine, obtained
images with a "Deep Sky Chile" 0.51-m f/6.8 corrected Dall-Kirkham telescope
located at Rio Hurtado, Chile, on June 1.4 that show a coma 0'.3 in diameter
of total mag 16.8 and a tail 0'.5 long in p.a. 272 degrees.
     The available astrometry appears on MPEC 2023-L19.  The following
parabolic orbital elements by S. Nakano (Central Bureau) are from 56
observations spanning 2023 May 27-June 2 (mean residual 0".5).

     T = 2023 Sept. 7.77896 TT        Peri. = 337.56536
                                      Node  = 223.72415 2000.0
     q = 2.0377765 AU                 Incl. = 137.99408

The following ephemeris by the undersigned from the above orbital elements
uses photometric power-law parameters H = 13.0 and 2.5n = 8 for the
magnitudes.

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase  Mag.
2023 05 16    23 07.62   -55 52.0    2.185    2.450    92.7    24.3  17.8
2023 05 21    23 05.05   -58 19.8    2.069    2.418    97.5    24.5  17.6
2023 05 26    23 00.25   -61 09.7    1.957    2.388   102.3    24.5  17.5
2023 05 31    22 52.00   -64 22.7    1.851    2.358   107.2    24.3  17.3
2023 06 05    22 38.03   -67 57.9    1.754    2.329   111.8    23.8  17.2
2023 06 10    22 13.81   -71 50.0    1.666    2.302   116.1    23.3  17.0
2023 06 15    21 29.70   -75 41.9    1.592    2.275   119.8    22.8  16.9
2023 06 20    20 07.62   -78 46.7    1.533    2.250   122.6    22.4  16.7
2023 06 25    18 02.86   -79 28.2    1.492    2.225   123.9    22.3  16.6
2023 06 30    16 12.68   -76 52.8    1.470    2.202   123.7    22.6  16.6
2023 07 05    15 09.00   -72 15.2    1.467    2.181   121.7    23.4  16.5
2023 07 10    14 34.83   -66 52.1    1.484    2.160   118.3    24.5  16.5
2023 07 15    14 15.63   -61 22.3    1.519    2.141   113.7    25.8  16.6
2023 07 20    14 04.41   -56 05.3    1.571    2.124   108.4    27.0  16.6
2023 07 25    13 57.79   -51 11.0    1.637    2.108   102.7    28.0  16.7
2023 07 30    13 54.02   -46 44.0    1.714    2.093    96.8    28.8  16.7
2023 08 04    13 52.11   -42 45.1    1.800    2.080    90.9    29.2  16.8
2023 08 09    13 51.49   -39 13.2    1.892    2.069    85.1    29.2  16.9
2023 08 14    13 51.79   -36 06.0    1.988    2.060    79.4    28.9  17.0
2023 08 19    13 52.78   -33 21.0    2.087    2.052    73.9    28.3  17.1
2023 08 24    13 54.29   -30 55.6    2.187    2.046    68.5    27.4  17.2
2023 08 29    13 56.20   -28 46.9    2.286    2.041    63.3    26.2  17.3
2023 09 03    13 58.41   -26 52.8    2.383    2.039    58.1    24.9  17.4
2023 09 08    14 00.87   -25 11.0    2.477    2.038    53.1    23.3  17.4
2023 09 13    14 03.52   -23 39.8    2.567    2.039    48.2    21.6  17.5


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

                         (C) Copyright 2023 CBAT
2023 June 6                      (CBET 5268)              Daniel W. E. Green