[Iaude] CBET 4321: 20160916 : COMET C/2016 R3 (BORISOV)

quai at eps.harvard.edu quai at eps.harvard.edu
Fri Sep 16 09:56:15 EDT 2016

                                                  Electronic Telegram No. 4321
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

     Gennady Borisov reports his discovery of a diffuse comet with a coma
diameter of 16" on three unfiltered 70-s exposures obtained on Sept. 11.06 UT
through a 0.3-m f/1.5 Genon astrograph at the MARGO observatory (near
Nauchnij, Crimea).  The total red magnitude of the comet was 16.0 as measured
in a circular aperture of size 0'.5.  The discovery observations are tabulted
below, along with follow-up observations from the following night.

     2016 UT             R.A. (2000) Decl.       Mag.   Observer
     Sept.11.06676    9 45 21.07   +27 53 36.3   16.0   Borisov
          11.07516    9 45 24.56   +27 53 31.2   16.0     "
          11.08356    9 45 27.74   +27 53 27.0   16.0     "
          12.06029    9 52 16.14   +27 42 51.3   16.0     "
          12.06456    9 52 18.12   +27 42 51.0   16.0     "
          12.07168    9 52 21.11   +27 42 45.7   16.0     "

After the object was posted on the Minor Planet Center's PCCP webpage, other
CCD astrometrists have confirmed the object's cometary appearance.  H. Sato,
Tokyo, Japan, stacked twelve 20-s exposures taken on Sept. 12.5 UT with an
iTelescope 0.61-m f/6.5 astrograph (+ luminance filter) at the Sierra Remote
Observatory, Auberry, CA, USA, to find a strongly condensed coma 8" in
diameter with a hint of tail was 20" long toward p.a. 260 degrees; the w-band
magnitude was 17.9 as measured within a circular aperture of radius 5".0.  P.
Birtwhistle, Great Shefford, Berkshire, England, writes that images obtained
with a 0.40-m f/6 Schmidt-Cassegrain reflector in twilight (with clouds
interfering) on Sept. 13.2 show the comet to be very diffuse 15" coma with a
poorly defined central condensation; the magnitude was measured to be 17.5
in a photometric aperture with 12".8 radius.  The comet appeared similarly to
Birtwhistle on Sept. 14.2 in worse observing conditions, and the magnitude
was given as 17.0; on Sept. 15.2, the very diffuse coma was as large as 30"
in diameter with no tail, and the magnitude given as 17.7.  J.-F. Soulier
obtained unfiltered images with a 0.30-m f/3.8 Newtonian reflector at
Maisoncelles, France, on Sept. 14.14-14.16 that show a diffuse 35" coma with
no tail; the red magnitude was 18.0 in a photometric aperture of radius 6".5.
A. Hale, Cloudcroft, NM, USA, reports that he detected the comet visually
at altitude 14 degrees in zodiacal light and early twilight with a 0.41-m
reflector on Sept. 14.48, finding total magnitude about 12.9 with a 1'.4 coma.
     The available astrometry, the following preliminary parabolic orbital
elements by G. V. Williams, and an ephemeris appear on MPEC 2016-S03.

     T = 2016 Oct. 10.9706 TT         Peri. = 117.8863
                                      Node  =  78.6961  2000.0
     q = 0.448367 AU                  Incl. =  53.0108

M. Meyer, Limburg, Germany, has suggested similarity of the orbital elements
of this comet with those of comet C/1915 R1 (Mellish), for which a parabolic
orbit was published by Einaarson and Alter (1915, Lick Obs. Bull. 8, 151)
based on only three observations (which was then compared to other available
observations).  Williams notes that the available observations for C/2016 R3
are consistent with intermediate-period orbits with periods as short as 50
years, possibly even 30 years.  A new orbit by Williams for C/1915 R1, based
on seven observations spanning 1915 Sept. 19-23 is given below for comparison:

     T = 1915 Oct. 13.6001 TT         Peri. = 116.1746
                                      Node  =  77.5290  2000.0
     q = 0.464924 AU                  Incl. =  52.3278

Attempts by Williams and S. Nakano to definitively link the 1915 and 2016
apparitions (for zero, 1, 2, and 3 potential missed returns between 1915 and
2016) have not been successful.

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

                         (C) Copyright 2016 CBAT
2016 September 16                (CBET 4321)              Daniel W. E. Green

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