[Iaude] CBET 4524: 20180611 : COMET C/2018 EN_4 (NEOWISE)

quai at eps.harvard.edu quai at eps.harvard.edu
Mon Jun 11 10:33:07 EDT 2018


                                                  Electronic Telegram No. 4524
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 EN_4 (NEOWISE)
     An apparently asteroidal object with a comet-like orbit that was found
on infrared images taken on Mar. 9 with the Near-Earth Object Wide-field
Infrared Survey Explorer (or NEOWISE; formerly the WISE earth-orbiting
satellite; cf. CBET 4225) has been found to show cometary activity by ground-
based CCD astrometrists.  The discovery observations are tabulated below as
published first on MPEC 2018-F12, in which the listed optical-wavelength
magnitude was roughly estimated based on past WISE and NEOWISE cometary
observations.

     2018 UT             R.A. (2000) Decl.      Mag.
     Mar.  9.08775    6 34 15.16   -11 44 43.0   20
           9.15320    6 34 12.44   -11 40 59.7
           9.21865    6 34 09.78   -11 37 16.2
           9.41552    6 34 02.04   -11 26 04.1
           9.67733    6 33 51.52   -11 11 10.5

H. Sato, Tokyo, Japan, found a 10" coma on four stacked 60-s exposures taken
on May 13.18 UT with an iTelescope 0.61-m f/6.5 astrograph at the Sierra
Remote Observatory near Auberry, CA, USA; the w-band magnitude was 18.5 as
measured within a circular aperture of radius 5".0.  Twelve stacked 60-s
exposures taken by Sato with an iTelescope 0.43-m f/6.8 astrograph near
Mayhill, NM, USA, on May 14.1 showed a round coma 10" in diameter with a
fan-like tail 20" long spanning p.a. 90-135 degrees; the w-band magnitude was
18.0 as measured within a circular aperture of radius 5".7.  Exposures taken
as on May 14.1 by Sato on May 17.1 showed a strongly condensed coma 15" in
diameter with a fan-like tail 15" long spanning p.a. 90-170 degrees; the
w-band magnitude was 18.5 as measured within a circular aperture of radius
7".6.  Sato obtained additional observations and stacked ten 60-s exposures
on June 1.15 and 3.15 (same instrumentation near Mayhill) that showed a
strongly condensed coma 30" in diameter (clearly larger than in May); the
w-band magnitude was 17.8 on June 1.15 and 17.4 on June 3.15 as measured
within a circular aperture of radius 15".3.
     M. Micheli, J. Kleyna, K. Meech, and J. Keane obtained two 120-s r-band
exposures EN4 using the Canada-France-Hawaii Telescope at Mauna Kea on May
17.2 UT (queue observer L. Wells) that show a broadm faint tail about 10"
long toward the southeast; the coma is only marginally extended (full-width-
at-half-maximum of about 1".0, compared to 0".8 for nearby stars).  M. Jaeger,
Vienna, Austria, writes that images taken by E. Prosperi, S. Prosperi, W.
Vollmann, and himself with a 0.3-m f/4 reflector at Stixendorf on June 4.9
show a 15" coma of mag 18.5, with a central condensation visible that was a
little softer than stars of the same brightness.  L. Buzzi, Varese, Italy,
reports that stacked images obtained with a 0.84-m f/3.5 reflector in good
seeing on June 9.9 show a 10" round coma with no tail; he adds that his
images taken on Mar. 13.8 with the same telescope (and a total exposure time
of 50 minutes in moderate seeing) show only a stellar appearance.
     Additional astrometry, the following revised orbital elements by G. V.
Williams, and an ephemeris appear on MPEC 2018-L53.

                    Epoch = 2018 June 11.0 TT
     T = 2018 June  7.78136 TT        Peri. =  35.01391
     e = 0.9213777                    Node  = 136.16554 2000.0
     q = 1.4479234 AU                 Incl. =  81.56186
       a = 18.4161880 AU   n = 0.01247109   P =  79.03 years


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

                         (C) Copyright 2018 CBAT
2018 June 11                     (CBET 4524)              Daniel W. E. Green



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