Electronic Telegram No. 4360
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
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Prepared using the Tamkin Foundation Computer Network


COMET 73P/SCHWASSMANN-WACHMANN
[Editor's note:  this text replaces that on CBET 4359 (minor typo)]
     After having been last observed astrometrically on 2012 Jan. 1 at its
previous apparition (MPC 78774), and following its next known observation on
2016 Feb. 13 at Lowell Observatory (MPC 98768), the brightest component of
comet 73P has been observed since 2016 Oct. 10 at numerous observatories
worldwide while brightening to total magnitude about 12.  A secondary
component has been found in recent days and denoted component BT (following
on the previous newly confirmed component, BS, that was seen in April and
May 2006; cf. MPEC 2006-K18).  This is the first secondary component observed
at this apparition after dozens were detected at its 2006 return (cf. IAUCs
8703, 8704, 8709), and only component C was identified as having been seen
at the 2011 return.  The available astrometry of component BT with orbital
elements by G. V. Williams and an ephemeris appear on MPEC 2017-C79.
Component BT has Delta(T) = +0.11 day with respect to the primary component.
     Following are CCD observations of the primary component and the new
secondary component that have been reported to the Central Bureau.  K.
Kadota, Ageo, Japan, found magnitude 12.0 for component BT and mag 13.9 for
the primary component on Feb. 10.85 UT (0.25-m f/5 reflector).  F. Kugel,
Banon, France, notes that T. Noel had detected component BT on Feb. 10.35 and
alerted Kugel, who then obtained images together with C. Rinner on Feb. 11.22
with a 0.4-m f/3 reflector, which showed the secondary component to be at red
magnitude 13.7 in an aperture of size 5".5, compared to mag 15.5 for the
primary component in the same aperture; component BT was located 48".6 in
p.a. 317 degrees from the primary, and the secondary showed a circular coma of
size around 0'.5 with magnitude 11.3 in an aperture of size 12".  Unfiltered
images obtained by A. Maury and J.-F. Soulier with a 0.4-m f/5.4 Ritchey-
Chretien reflector at San Pedro de Atacama, Chile, on Feb. 11.32-11.39 show
component BT to be stellar in appearance with magnitude 12.6 in an aperture
of radius 0'.33, while the primary component had a coma diameter of about 26"
and a tail about 40" long in p.a. 285 deg; they measured the magnitude of BT
to be 13.2 in an aperture of radius 6".2, compared to mag 15.0 for the
primary component in the same aperture.  E. Bryssinck, Kruibeke, Belgium,
writes that unfiltered images taken by F. J. Hambsch and himself on Feb. 11.36
with a 0.4-m f/6.8 reflector at San Pedro de Atacama, Chile, shows component
BT as a stellar object of red mag 12.9 (vs. 14.8 for the primary component) in
an aperture of radius 5".5, with BT located 37" in p.a. 298 degrees from the
primary; the primary showed a coma diameter of 32" and a tail 21" long in
p.a. 287 deg.


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

                         (C) Copyright 2017 CBAT
2017 February 13                 (CBET 4360)              Daniel W. E. Green