Electronic Telegram No. 4221
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
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Prepared using the Tamkin Foundation Computer Network


COMET P/2015 X6 (PANSTARRS)
     E. Lilly and R. Weryk report the discovery of another comet in three
w-band exposures taken with the 1.8-m Pan-STARRS1 telescope on Haleakala (the
Dec. 7 discovery observations tabulated below), the object described as having
an extended coma with FWHM approximately 1".6 in 1".0 seeing, with evidence
of a faint tail extending towards the northeast.

     2015 UT             R.A. (2000) Decl.       Mag.
     Dec.  7.27311    1 48 29.28   + 4 43 20.1   21.4
           7.28505    1 48 29.16   + 4 43 21.8   21.6
           7.29698    1 48 29.00   + 4 43 23.6   21.5

M. Micheli reports on three 60-s follow-up CCD exposures taken with the 3.6-m
Canada-France-Hawaii Telescope at Mauna Kea by R. J. Wainscoat and L. Wells
on Dec. 8.3 UT, which show the object to be clearly cometary, with a sharp 6"
tail at p.a. 175 deg with an elongated coma (FWHM of about 1".3, compared to
0".6 for nearby stars); the red magnitude was measured to be 20.7-20.8.
After the object was posted on the Minor Planet Center's NEOCP and PCCP
webpages, other CCD astrometrists also noted the object's cometary appearance.
V-band images taken by W. H. Ryan and E. V. Ryan with the Magdalena Ridge
Observatory 2.4-m f/8.9 reflector on Dec. 8.24-8.26 UT show a short, thin,
prominent tail at p.a. about 70 deg.  H. Sato, Tokyo, Japan, writes that
fifteen stacked 60-s exposures taken with an iTelescope 0.51-m astrograph (+
luminance filter) at Siding Spring on Dec. 10.4 show the comet to be strongly
consensed with a faint coma 8" in diameter and no tail; the w-band magnitude
was 20.8 as measured within a circular aperture of radius 4".9.
     The available astrometry, the following elliptical orbital elements by
G. V. Williams, and an ephemeris appear on MPEC 2015-X180.

     T = 2016 Feb.  8.7318 TT         Peri. = 315.9376
     e = 0.119109                     Node  = 107.7521  2000.0
     q = 2.321313 AU                  Incl. =   4.5303
       a =  2.635187 AU    n = 0.2304024    P =   4.28 years


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2015 CBAT
2015 December 16                 (CBET 4221)              Daniel W. E. Green