Electronic Telegram No. 4381
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)
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Prepared using the Tamkin Foundation Computer Network


COMET C/2017 F2 (PANSTARRS)
     E. Lilly and R. Weryk, Institute for Astronomy, University of Hawaii,
report the discovery of another comet on images obtained with the 1.8-m
Pan-STARRS1 telescope at Haleakala (discovery observations tabulated below).
The object has a soft appearance, with full-width-at-half-maximum of
approximately 1".7, compared to adjacent stars that had FWHM = 1".4; there is
some evidence for a very faint tail extending for a few arcseconds to the
southwest.

     2017 UT             R.A. (2000) Decl.       Mag.
     Mar. 31.40889   12 01 22.22   +46 20 42.9   21.2
          31.42334   12 01 21.75   +46 20 40.9   21.6
          31.43782   12 01 21.32   +46 20 38.9   21.0

M. Micheli and R. J. Wainscoat report that three 60-s gri-filtered confirming
exposures of the comet were obtained by Wainscoat and D. Woodworth on Apr.
1.26 UT with the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea, which
show clear cometary activity with a broad tail to the west.  After the comet
was posted on the Minor Planet Center's PCCP webpage, R. S. McMillan found
the comet to be more diffuse than surrounding stars with a coma extending
westward on CCD images obtained in 1".8 seeing at Kitt Peak on Apr. 6.45 and
6.46 with the Spacewatch 1.8-m f/2.7 reflector (+ Schott OG-515 filter;
bandpass 515-950 nm); the red magnitude was measured to be 19.9-20.0.
     The available astrometry, the following preliminary elliptical orbital
elements by G. V. Williams (from 24 observations spanning Mar. 31-Apr. 6),
and an ephemeris appear on MPEC 2017-G56.

                    Epoch = 2017 Oct. 14.0 TT
     T = 2017 Oct.  6.5682 TT         Peri. = 130.9563
     e = 0.970816                     Node  =  38.3701  2000.0
     q = 7.029649 AU                  Incl. =  42.6234


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2017 CBAT
2017 April 6                     (CBET 4381)              Daniel W. E. Green