[Iaude] CBET 4543: 20180817 : COMET C/2018 O1 (ATLAS)

quai at eps.harvard.edu quai at eps.harvard.edu
Thu Aug 16 19:39:46 EDT 2018


                                                  Electronic Telegram No. 4543
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/2018 O1 (ATLAS)
     An apparently asteroidal object discovered on July 22 UT (discovery
observations tabulated below) with a 0.5-m f/2 Schmidt reflector at Mauna Loa,
Hawaii, 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.

     2018 UT             R.A. (2000) Decl.       Nag,
     July 22.54515   20 58 02.04   +25 28 22.1   18.7
          22.55244   20 57 57.72   +25 28 06.0   18.7
          22.56451   20 57 50.53   +25 27 43.4   18.5
          22.57295   20 57 45.46   +25 27 27.4   18.6

H. Sato, Tokyo, Japan, writes that twenty stacked 20-s exposures taken on
July 23.4 UT with an iTelescope 0.43-m f/6.8 astrograph (located near Mayhill,
NM, USA) shows a strongly condensed coma 10" in diameter and no obvious tail;
the w-band magnitude was 18.8 as measured within a circular aperture of
radius 7".6.  L. Buzzi, Varese, Italy, finds a compact coma 10" in size that
is softer and larger (by about 20 percent, full-width-at-half-maximum) than
the images of nearby stars, and that the comet is possibly elongated toward
the southwest, in images taken on July 24.0 with a 0.84-m f/3.5 reflector.
P. Birtwhistle, Great Shefford, Berkshire, England, notes that his images
taken on July 31.9 with a 0.40-m f/6 Schmidt-Cassegrain reflector show no tail,
but FWHM measurements of the comet's image appear consistently 25-30 percent
larger than those of nearby stars of similar magnitude in all three sets of
exposures; Birtwhistle obtained additional astrometry on Aug. 9.94-9.97 that
show a similar result.  K. Sarneczky, Konkoly Observatory, reports that three
stacked 20-s unfiltered images taken with the 0.60-m Schmidt telescope at
Piszkesteto, Hungary, on Aug. 3.9 show a slightly diffuse, circular coma
about 10" in diameter with no tail.  H. Weiland writes that four stacked
o-band images taken with the ATLAS discovery telescope on Aug. 6.4 (when the
comet was accidentally re-discovered) show it to be larger than the stellar
point-spread function but with no tail.  R. Weryk also reports that images
taken on Aug. 13.3 with the 1.8-m Pan-STARRS1 Ritchey-Chretien telescope at
Haleakala show a FWHM of about 2" (measured perpendicular to its direction
of motion), larger than the neighboring stars (which are 1".35 +/- 0".04 in
the exposure with the best seeing); he adds that there is a tail at least 6"
long towards the east.
     The available astrometry (including pre-discovery observations made with
the 1.2-m Schmidt telescope at Palomar on July 15.5 and 20.3), the following
elliptical orbital elements by G. V. Williams (from 311 observations spanning
July 15-Aug. 16), and an ephemeris appear on MPEC 2018-Q22.

                    Epoch = 2018 Aug. 30.0 TT
     T = 2018 Aug. 31.5767 TT         Peri. = 162.5081
     e = 0.943963                     Node  =  87.6202  2000.0
     q = 1.558146 AU                  Incl. = 154.0408
       a = 27.805596 AU    n = 0.0067221    P = 146.6 years


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

                         (C) Copyright 2018 CBAT
2018 August 17                   (CBET 4543)              Daniel W. E. Green



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