[Iaude] CBET 4433: 20170928 : COMET P/2017 S4 = P/2006 UR_111 (SPACEWATCH)

[quai at eps.harvard.edu]

                                                  Electronic Telegram No. 4433
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)
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Prepared using the Tamkin Foundation Computer Network


COMET P/2017 S4 = P/2006 UR_111 (SPACEWATCH)
     E. Lilly, R. J. Wainscoat, and R. Weryk, Institute for Astronomy,
University of Hawaii, report the discovery of another apparent comet on
four w-band CCD exposures taken with the 1.8-m Pan-STARRS1 telescope at
Haleakala on Sept. 24.4 UT (discovery astrometry tabulated below, together
with earlier Pan-STARRS1 observations found subsequently).  The seeing
was variable during the sequence of exposures on Sept. 24, but in each
image the object appears slightly extended compared to nearby stars
(FWHM approximately 1 pixel = 0".25 larger than the stars, which had
FWHM 1".0-1".2); in a stacked image, there is possible evidence for a
broad, low-surface-brightness tail extending towards position angle
approximately 250 degrees.

     2017 UT             R.A. (2000) Decl.       Mag.
     Sept.11.50521   23 52 37.91   + 8 31 23.1   21.3
          11.51665   23 52 37.53   + 8 31 19.0   20.3
          11.52798   23 52 37.15   + 8 31 15.0   20.7
          11.53942   23 52 36.79   + 8 31 10.9   20.7
          16.41616   23 50 00.97   + 8 00 53.7   20.1
          16.42790   23 50 00.57   + 8 00 49.1   20.1
          16.43862   23 50 00.20   + 8 00 45.0   20.1
          16.44933   23 49 59.84   + 8 00 40.9   20.2
          18.30318   23 48 58.89   + 7 48 27.1   18.9
          18.30852   23 48 58.69   + 7 48 25.0   18.7
          18.31385   23 48 58.47   + 7 48 22.9   19.1
          18.31922   23 48 58.36   + 7 48 21.0   19.7
          22.40609   23 46 42.46   + 7 20 17.7   19.0
          22.41661   23 46 42.02   + 7 20 10.3   18.4
          22.41706   23 46 42.04   + 7 20 12.7   18.9
          22.43069   23 46 41.63   + 7 20 05.9   19.2
          24.29124   23 45 39.57   + 7 06 51.7   18.9
          24.29768   23 45 39.37   + 7 06 49.0   19.0
          24.30308   23 45 39.19   + 7 06 46.9   18.9
          24.31131   23 45 38.88   + 7 06 42.9   19.2

On Sept. 16.4 UT, Weryk found the comet to have FWHM around 1".2, vs. 1".1
for neighboring stars, with a small asymmetry towards the same position angle
(about 250 degrees).  Subsequent Pan-STARRS1 observations on Sept. 27.4 show
FWHM around 1".6 (vs. 1".2 for neighboring stars) with a small asymmetry
towards the west perhaps 1" long.
     Three 60-s follow-up CCD exposures (with gri filtering) taken with the
3.6-m Canada-France-Hawaii Telescope on 2017 Sept. 25.40 by Wainscoat and
L. Wells (measured by M. Micheli and Wainscoat) confirm the object as having
cometary appearance, displaying a faint tail extending about 15" toward p.a.
of 245 deg.
     Already on Sept. 24, Weryk suggested that the comet may be identical to
an apparently asteroidal object discovered on 2006 Oct. 19 on Spacewatch
images taken by J. V. Scotti with the Steward Observatory 0.9-m telescope at
Kitt Peak (discovery observations tabulated below, along with other
Spacewatch observations that same month), and which was then given the
minor-planet designation 2006 UR_111 (cf. MPS 184334).

     2006 UT             R.A. (2000) Decl.       Mag.   Observer
     Oct. 11.11335   23 38 55.61   + 5 10 35.8          Scotti
          11.12625   23 38 55.24   + 5 10 30.2            "
          11.13915   23 38 54.89   + 5 10 25.0            "
          19.13172   23 35 43.17   + 4 11 33.5   19.9     "
          19.14468   23 35 42.89   + 4 11 27.8   19.9     "
          19.15766   23 35 42.60   + 4 11 23.0   20.3     "
          21.13856   23 35 03.45   + 3 57 21.6   19.7     "
          21.15149   23 35 03.24   + 3 57 16.2   19.8     "
          21.16442   23 35 02.98   + 3 57 10.7   19.8     "
          23.13113   23 34 27.92   + 3 43 34.3   19.8     "
          23.14407   23 34 27.68   + 3 43 29.1   19.8     "
          23.15701   23 34 27.45   + 3 43 23.8   19.8     "

G. V. Williams has confirmed the linkage.  The available astrometry, the
following linked orbital elements by Williams (from 48 observations spanning
2006 Oct. 11-2007 Jan. 9 and 2017 Sept. 11-27), and an ephemeris appear on
MPEC 2017-S197.

                    Epoch = 2007 June 29.0 TT
     T = 2007 July  2.65430 TT        Peri. = 219.21511
     e = 0.4365805                    Node  = 203.43841 2000.0
     q = 2.7863366 AU                 Incl. =  13.87592
       a =  4.9454034 AU   n = 0.08961929   P =  11.00 years

                    Epoch = 2018 July 21.0 TT
     T = 2018 July  2.50051 TT        Peri. = 219.20867
     e = 0.4378225                    Node  = 203.27695 2000.0
     q = 2.7804234 AU                 Incl. =  13.88255
       a =  4.9458106 AU   n = 0.08960822   P =  11.00 years


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

                         (C) Copyright 2017 CBAT
2017 September 28                (CBET 4433)              Daniel W. E. Green