[Iaude] CBET 5354: COMET C/2024 C4

[quai at eps.harvard.edu]

                                                  Electronic Telegram No. 5354
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 C/2024 C4 (ATLAS)
     An apparently asteroidal object discovered on CCD images taken on Feb.
14 UT 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 has been found to show cometary appearance by CCD and CMOS
astrometrists elsewhere.  The discovery observations are tabulated below:

     2024 UT             R.A. (2000) Decl.       Mag.
     Feb. 14.08138   16 55 01.64   -48 34 21.2   17.4
          14.08457   16 55 01.82   -48 34 16.2   17.5
          14.10474   16 55 03.01   -48 33 43.9   16.5
          14.10753   16 55 03.22   -48 33 39.6   17.3

While the object was posted on the Minor Planet Center's NEOCP webpage,
S. Deen (Simi Valley, CA, USA) obtained three 300-s CMOS images remotely on
Feb. 14.2 UT with a "Deep Sky Chile" 0.43-m f/6.8 reflector (+ luminance
filter) located at Rio Hurtado, Chile, which show a diffuse coma of size about
3" (full-width-at-half-maximum) and a broad tail around 9" long spanning p.a.
180-250 degrees; the seeing was estimated as around 1".0.
     Twenty stacked 30-s CMOS exposures taken on Feb. 14.3 UT by K. Yoshimoto
(Kumage, Yamaguchi, Japan) with a "Deep Sky Chile" 0.36-m f/7.2 Corrected
Dall-Kirkham reflector located at Rio Hurtado show this to be definitely a
comet, with a condensed coma 13" in diameter and total mag 16.9, and a broad
tail 13" long in p.a. 225 deg.
     Ten stacked 30-s CCD exposures taken remotely by H. Sato (Tokyo, Japan)
on Feb. 14.37 UT with a "Deep Sky Chile" 0.51-m f/6.8 astrograph at Rio
Hurtado show a strongly condensed comet with an outer coma 17" in diameter
and no tail; the magnitude was 16.4 as measured within a circular aperture of
radius 8".6.  Seven additional stacked CCD exposures taken on Feb. 14.77 by
Sato using a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia,
show a strongly condensed coma 15" in diameter and a broad tail 10" long
spanning p.a. 230-260 degrees; the magnitude was 16.0 as measured within a
circular aperture of radius 7".6.
     Eight 60-s stacked exposures taken remotely by M. Mattiazzo (Swan Hill,
Victoria, Australia) on Feb. 15.26 UT with a Planewave CDK14 reflector (+
luminance filter) located at Rio Hurtado Valley, Chile, show a moderately
condensed coma 20" wide with total broadband G magnitude 15.8 (Gaia reference
stars) and a hint of a tail 10" long in p.a. 230 degrees.  Twenty 30-s
follow-up exposures taken by Mattiazzo on Feb. 16.77 with a Celestron 11
RASA f/2.2 reflector (+ Canon 6D camera) at Swan Hill show a diffuse coma 2'
wide with total V magnitude 14.2 (UCAC4 reference stars).
     T. Prystavski (Lviv, Ukraine) writes that CCD exposures taken remotely
on Feb. 14.74-14.75 UT with a 0.32-m f/9.0 Ritchey-Chretien reflector at
Siding Spring and on Feb. 16.36 with a "Deep Sky Chile" 0.51-m f/6.8 Corrected
Dall-Kirkham telescope at Rio Hurtado show a diffuse comet with a moderately
condensed coma 0'.4 in diameter and a broad tail 0'.5 long in p.a. 227 deg;
the total magnitude was given as 15.9 and 15.7 for the two nights.
     The available astrometry appears on MPEC 2024-D98.  The following
preliminary parabolic orbital elements by S. Nakano (Central Bureau) are from
69 observations spanning 2024 Feb. 14-20 (mean residual 0".4).  The comet is
may have a medium-short-period orbit, but the orbital period is highly
uncertain.

     T = 2024 Jan. 30.86304 TT        Peri. = 322.05035
                                      Node  = 220.80431 2000.0
     q = 1.4784287 AU                 Incl. =  79.45612

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.

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase  Mag.
2024 01 11    15 49.03   -60 43.5    1.860    1.505    53.8    31.8  16.3
2024 01 16    16 02.98   -59 16.1    1.824    1.493    54.9    32.6  16.2
2024 01 21    16 15.28   -57 42.5    1.783    1.485    56.4    33.5  16.1
2024 01 26    16 26.06   -56 02.7    1.738    1.480    58.3    34.5  16.1
2024 01 31    16 35.44   -54 16.3    1.689    1.478    60.5    35.5  16.0
2024 02 05    16 43.52   -52 22.7    1.635    1.480    63.2    36.5  15.9
2024 02 10    16 50.35   -50 20.9    1.579    1.485    66.2    37.4  15.9
2024 02 15    16 55.96   -48 09.4    1.519    1.494    69.5    38.3  15.8
2024 02 20    17 00.39   -45 46.8    1.456    1.506    73.2    39.0  15.7
2024 02 25    17 03.63   -43 10.8    1.392    1.520    77.3    39.4  15.7
2024 03 01    17 05.69   -40 19.1    1.327    1.538    81.8    39.6  15.6
2024 03 06    17 06.53   -37 08.8    1.262    1.559    86.6    39.4  15.5
2024 03 11    17 06.11   -33 36.9    1.199    1.582    91.9    38.9  15.5
2024 03 16    17 04.37   -29 40.2    1.139    1.609    97.6    37.8  15.4
2024 03 21    17 01.28   -25 15.9    1.083    1.637   103.8    36.2  15.4
2024 03 26    16 56.82   -20 22.7    1.035    1.668   110.3    34.1  15.4
2024 03 31    16 50.98   -15 01.1    0.996    1.700   117.0    31.6  15.3
2024 04 05    16 43.79   -09 15.4    0.968    1.735   123.7    28.7  15.3
2024 04 10    16 35.31   -03 13.8    0.953    1.771   129.9    25.7  15.4
2024 04 15    16 25.70   +02 51.4    0.953    1.809   135.3    23.0  15.5
2024 04 20    16 15.17   +08 45.7    0.969    1.849   139.0    20.9  15.6
2024 04 25    16 04.00   +14 15.4    1.000    1.889   140.8    19.7  15.7
2024 04 30    15 52.50   +19 10.4    1.045    1.931   140.4    19.4  15.9
2024 05 05    15 41.00   +23 24.6    1.103    1.974   138.4    19.8  16.1
2024 05 10    15 29.84   +26 56.7    1.172    2.018   135.1    20.7  16.3
2024 05 15    15 19.30   +29 48.5    1.251    2.063   131.3    21.6  16.5
2024 05 20    15 09.63   +32 04.2    1.336    2.108   127.2    22.5  16.7
2024 05 25    15 00.98   +33 48.6    1.428    2.154   123.0    23.2  16.9
2024 05 30    14 53.45   +35 06.8    1.525    2.201   118.9    23.8  17.2
2024 06 04    14 47.05   +36 03.2    1.625    2.248   114.8    24.2  17.4
2024 06 09    14 41.80   +36 41.9    1.727    2.296   111.0    24.4  17.6
2024 06 14    14 37.66   +37 06.2    1.832    2.344   107.3    24.4  17.8
2024 06 19    14 34.55   +37 19.1    1.938    2.392   103.7    24.4  18.0
2024 06 24    14 32.40   +37 22.9    2.045    2.441   100.3    24.2  18.2
2024 06 29    14 31.13   +37 19.5    2.151    2.490    97.1    23.9  18.3
2024 07 04    14 30.65   +37 10.4    2.258    2.539    93.9    23.5  18.5
2024 07 09    14 30.90   +36 56.8    2.364    2.589    90.9    23.1  18.7
2024 07 14    14 31.82   +36 39.8    2.470    2.638    88.0    22.6  18.8
2024 07 19    14 33.32   +36 20.3    2.574    2.688    85.3    22.1  19.0
2024 07 24    14 35.35   +35 58.8    2.677    2.738    82.6    21.6  19.1
2024 07 29    14 37.86   +35 36.1    2.778    2.788    80.0    21.0  19.3
2024 08 03    14 40.80   +35 12.4    2.877    2.838    77.6    20.4  19.4
2024 08 08    14 44.13   +34 48.3    2.975    2.888    75.2    19.8  19.6
2024 08 13    14 47.82   +34 24.1    3.071    2.938    72.9    19.3  19.7
2024 08 18    14 51.83   +34 00.2    3.164    2.988    70.8    18.7  19.8
2024 08 23    14 56.13   +33 36.7    3.255    3.038    68.7    18.1  19.9
2024 08 28    15 00.69   +33 14.0    3.344    3.088    66.7    17.5  20.0
2024 09 02    15 05.49   +32 52.1    3.430    3.138    64.9    16.9  20.1
2024 09 07    15 10.51   +32 31.3    3.514    3.187    63.1    16.4  20.3


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

                         (C) Copyright 2024 CBAT
2024 February 21                 (CBET 5354)              Daniel W. E. Green