[Iaude] CBET 4768: COMET C/2020 H6

[quai at eps.harvard.edu]

                                                  Electronic Telegram No. 4768
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/2020 H6 (ATLAS)
     James Robinson, Queens University, Belfast, reports the discovery of
a comet by Alan Fitzsimmons and himself on individual images from taken on
Apr. 22 UT with a 0.5-m f/2 Schmidt reflector at Haleakala, Hawaii, in the
course of the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS) search
program.  The comet's head showed a size of 7".6 (full-width-at-half-
maximum), compared to nearby field stars with FHWM 5".4.

     2020 UT             R.A. (2000) Decl.       Mag.
     Apr. 22.34303   11 55 23.71   -49 22 30.8   18.1
          22.34626   11 55 23.54   -49 22 28.9   18.8
          22.35186   11 55 23.37   -49 22 25.8   18.8
          22.36251   11 55 23.10   -49 22 19.2   18.6

After the comet was posted on the Minor Planet Center's PCCP webpage, other
CCD astrometrists have commented on the cometary appearance.  H. Sato, Tokyo,
Japan, found a stellar appearance on eight stacked 60-s exposures taken on
Apr. 24.64 UT with a 0.51-m f/6.8 astrograph at Siding Spring, NSW; the
magnitude was 18.5 as measured within a circular aperture of radius 4".9.
P. Camilleri reports that images obtained by J. Oey, R. Groom, and himself
with the Perth Observatory 0.34-m f/5 reflector on Apr. 26.51-26.58 show a
possible very condensed coma of size 5" in five 120-s exposures; similar
exposures taken in average seeing on Apr. 29.6 suggest an essentially
stellar image.  Ten stacked 120-s unfiltered exposures taken remotely by
A. Valvasori and E. Guido with an iTelescope 0.50-m f/6.8 astrograph at
Siding Spring on Apr. 28.44-28.45 show a compact coma about 10" in diameter
that is slightly elongated toward p.a. 330 degrees.
     The available astrometry appear on MPEC 2020-J23.  The following
preliminary parabolic orbital elements by S. Nakano, Sumoto, Japan, are
from 50 observations spanning Apr. 22-May 2 (mean residual 0".38).

     T = 2021 Oct.  1.1775 TT         Peri. =  20.4263
                                      Node  = 213.7597  2000.0
     q = 4.696624 AU                  Incl. =  79.8868

The following ephemeris by the undersigned from the above orbital elements
uses photometric power-law parameters H = 8.0 and 2.5n = 8 for the magnitudes.

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase  Mag.
2020 03 12    12 21.03   -54 11.1    5.842    6.417   121.5     7.6  18.3
2020 03 17    12 17.77   -53 51.7    5.776    6.392   124.4     7.4  18.3
2020 03 22    12 14.42   -53 27.7    5.716    6.367   127.1     7.2  18.2
2020 03 27    12 11.06   -52 59.4    5.661    6.342   129.5     7.0  18.2
2020 04 01    12 07.74   -52 26.6    5.611    6.318   131.6     6.8  18.1
2020 04 06    12 04.52   -51 49.7    5.566    6.293   133.2     6.7  18.1
2020 04 11    12 01.47   -51 08.7    5.528    6.269   134.3     6.6  18.1
2020 04 16    11 58.63   -50 24.0    5.496    6.245   134.9     6.5  18.1
2020 04 21    11 56.04   -49 35.9    5.470    6.221   134.9     6.6  18.0
2020 04 26    11 53.75   -48 44.9    5.451    6.196   134.4     6.7  18.0
2020 05 01    11 51.78   -47 51.4    5.438    6.172   133.3     6.8  18.0
2020 05 06    11 50.15   -46 55.9    5.431    6.149   131.7     7.0  18.0
2020 05 11    11 48.87   -45 58.9    5.431    6.125   129.7     7.3  18.0
2020 05 16    11 47.96   -45 00.9    5.436    6.101   127.2     7.6  18.0
2020 05 21    11 47.40   -44 02.4    5.447    6.078   124.5     7.9  18.0
2020 05 26    11 47.21   -43 03.9    5.464    6.054   121.4     8.2  17.9
2020 05 31    11 47.38   -42 05.8    5.486    6.031   118.1     8.5  17.9
2020 06 05    11 47.88   -41 08.6    5.513    6.008   114.7     8.8  17.9
2020 06 10    11 48.71   -40 12.7    5.544    5.984   111.1     9.1  17.9
2020 06 15    11 49.85   -39 18.2    5.578    5.961   107.4     9.4  17.9
2020 06 20    11 51.29   -38 25.6    5.617    5.938   103.6     9.6  17.9
2020 06 25    11 53.01   -37 35.0    5.658    5.916    99.8     9.7  17.9
2020 06 30    11 54.99   -36 46.6    5.701    5.893    95.9     9.9  17.9
2020 07 05    11 57.23   -36 00.7    5.747    5.871    92.0    10.0  17.9
2020 07 10    11 59.69   -35 17.2    5.793    5.848    88.1    10.0  18.0


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

                         (C) Copyright 2020 CBAT
2020 May 3                       (CBET 4768)              Daniel W. E. Green