Electronic Telegram No. 4324
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau@eps.harvard.edu (alternate cbat@iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


COMET C/2016 S1 (PANSTARRS)
     Robert Weryk and Eva Lilly report the discovery of another apparent comet
in four r-band exposures obtained with the 1.8-m Pan-STARRS1 telescope at
Haleakala on Sept. 21 UT (discovery observations tabulated below); the comet
has a FWHM of about 1".4 (in 1".0 seeing), and there is a suspected short tail
extending towards the southwest for about 2".

     2016 UT             R.A. (2000) Decl.       Mag.
     Sept.21.57243    4 57 47.35   -25 58 58.0   19.4
          21.58212    4 57 47.43   -25 59 17.2   19.4
          21.59179    4 57 47.51   -25 59 36.5   19.5
          21.60147    4 57 47.58   -25 59 56.0   19.6

R. J. Wainscoat and P. Forshay obtained three 60-s w-band follow-up exposures
on Sept. 25.64 UT with the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea,
tracked at the object's predicted motion, which show an extended core (FWHM of
1".3, vs. 0".75 for nearby stars) in the direction perpendicular to the
motion; a broad tail is clearly seen extending to the west for at least 10"
(measurements by M. Micheli and Wainscoat).  After the object was posted on
the Minor Planet Center's PCCP webpage, other CCD astrometrists have also
commented on the cometary appearance.  H. Sato (Tokyo, Japan) writes that
stacked 60-s exposures taken with iTelescope 0.51-m f/6.8 astrographs (+
luminance filter) near Mayhill, NM, USA, on Sept. 22.48 and at Siding Spring,
NSW, Australia, on Sept. 23.60 show the comet to be strongly condensed with a
coma 12" in diameter and magnitude 17.9 as measured within circular apertures
of radii 6".5 and 8".8, respectively; on Sept. 22, the coma was slightly
elongated toward p.a. 200 degrees.  Sato obtained eight additional stacked
60-s exposures with a 0.40-m f/3.5 astrograph at Siding Spring on Sept. 23.7
that show a strongly condensed coma 10" in diameter with no tail and mag 17.5
as measured within a circular aperture of radius 6".4.  Eight stacked 180-s
images taken by L. Buzzi, P. Concari, S. Foglia, G. Galli, and M. Tombelli
with an iTelescope 0.15-m f/7 refractor at Siding Spring on Sept. 26.65-26.66
reveal an elongated shape of size 6" x 10", elongated toward p.a. 300 deg.
Unfiltered CCD images taken by A. Maury and J.-F. Soulier on Sept. 28.2-28.3
with a 0.4-m f/8 Ritchey-Chretien reflector at San Pedro de Atacama, Chile,
show a coma of size about 16" and a tail about 18" long in p.a. 270 deg; they
measured red mag 18.4 in an aperture of readius 6".2.
     The available astrometry, the following preliminary elliptical orbital
elements by G. V. Williams (from 46 observations spanning Sept. 21-29), and an
ephemeris appear on MPEC 2016-S93.

     T = 2017 Mar. 11.6136 TT         Peri. = 272.2089
     e = 0.753105                     Node  = 227.8788  2000.0
     q = 2.433961 AU                  Incl. =  94.9299
       a =  9.858268 AU    n = 0.0318422    P =  30.95 years


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

                         (C) Copyright 2016 CBAT
2016 September 29                (CBET 4324)              Daniel W. E. Green