Electronic Telegram No. 4225
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/2015 X8 (NEOWISE)
[Editor's note:  This text replaces that on CBET 4224 (discovery details).]
     On Dec. 18, J. Bauer reported to the Minor Planet Center astrometry
measured from images of an unknown extended object that was found on infrared
images taken with the Near-Earth Object Wide-field Infrared Survey Explorer
(or NEOWISE; formerly the WISE earth-orbiting satellite; cf. IAUC 9118).  The
truncated satellite-centered discovery astrometry is tabulated below, with
the listed optical-wavelength magnitude having been roughly estimated based
on past NEOWISE cometary observations.

     2015 UT            R.A. (2000) Decl.       Mag.
     Dec. 14.63534    12 29 57     +32 42.8     16
          14.76637    12 29 45     +32 53.7
          14.83195    12 29 39     +32 59.2
          14.96311    12 29 27     +33 10.2
          15.09427    12 29 15     +33 21.3

After the object was posted on the Minor Planet Center's PCCP webpage,
ground-based CCD astrometrists have confirmed the cometary appearance.  H.
Sato, Tokyo, Japan, writes that eleven stacked 20-s exposures taken with an
iTelescope 0.43-m f/6.8 astrograph (+ luminance filter) at Nerpio, Spain, on
Dec. 18.2 UT show the object to be strongly consensed with a round outer coma
25" in diameter and no tail; the w-band magnitude was 15.9 as measured within
a circular aperture of radius 12".6.  Ten stacked 60-s CCD images taken by C.
Jacques, E. Pimentel, and J. Barros with an iTelescope 0.61-m f/6.5 reflector
at the Sierra Remote Observatory near Auberry, CA, USA, on Dec. 18.5 show a
strong central condensation 51" in diameter surrounded by a diffuse coma
that was measured to be 2'11" in diameter, with red magnitude 17.2-17.4.
A. Hale, Cloudcroft, NM, USA, reports that he followed the comet visually
for about an hour with a 0.41-m reflector; he notes that the comet was very
vague and diffuse with just the very slightest central brightening and
without condensation, and he measured total visual magnitude 12.8 with coma
diameter 2'.4 on Dec. 18.49.
     The available astrometry (spanning Dec. 14-18), the following
preliminary parabolic orbital elements by G. V. Williams, and an ephemeris
appear on MPEC 2015-Y20.

     T = 2015 Oct. 25.5236 TT         Peri. =  22.2043
                                      Node  = 190.7933  2000.0
     q = 1.211900 AU                  Incl. = 155.0360


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

                         (C) Copyright 2015 CBAT
2015 December 19                 (CBET 4225)              Daniel W. E. Green