Electronic Telegram No. 4228
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
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Prepared using the Tamkin Foundation Computer Network


COMET C/2015 YG_1 (NEOWISE)
     J. M. Bauer, Jet Propulsion Laboratory, forwards a report by S. Sonnett
of another comet found on infrared images taken with the Near-Earth Object
Wide-field Infrared Survey Explorer (or NEOWISE; formerly the WISE earth-
orbiting satellite; cf. CBET 4225).  The Minor Planet Center assigned the
minor-planet designation 2015 YG_1 on MPEC 2015-Y48 before it received word
from the NEOWISE team that the object appeared cometary.  The discovery
observations are tabulated below, in which the listed optical-wavelength
magnitude was roughly estimated based on past WISE and NEOWISE cometary
observations.

     2015 UT             R.A. (2000) Decl.       Mag.
     Dec. 17.91253   12 59 13.46   +37 15 12.5   19
          17.91265   12 59 13.32   +37 15 11.5
          18.04369   12 59 14.70   +37 14 19.1
          18.17484   12 59 16.32   +37 13 24.8
          18.30600   12 59 17.42   +37 12 29.7
          18.37158   12 59 18.28   +37 12 03.4

After the object was posted on the Minor Planet Center's NEOCP webpage,
ground-based CCD astrometrists noted the cometary appearance.  V-band
images taken on Dec. 19.4 UT by W. H. Ryan and E. V. Ryan with the Magdalena
Ridge Observatory 2.4-m f/8.9 reflector show a bright, distinct coma of mag
17.5-17.7 with structure and a tail.  M. Schwartz writes that three 320-s
unfiltered exposures taken with the 0.81-m Tenagra II telescope (Nogales, AZ,
U.S.A.) between Dec. 19.51 and 19.54 under reasonably good seeing (FWHM 3")
showed a coma of diameter 10" and a broad tail with length about 20" toward
p.a. 330 degrees.  Eight stacked 60-s exposures taken by H. Sato, Tokyo,
Japan, with an iTelescope 0.43-m f/6.8 astrograph (+ luminance filter) near
Mayhill, NM, USA, on Dec. 19.52 show a strongly condensed coma 50" in
diameter (with w-band magnitude 15.8 as measured within a circular aperture
of radius 28".6) and a fan-like tail about 1' longward pointing northwards.
     The available astrometry (spanning Dec. 17-19), the following
preliminary parabolic orbital elements by G. V. Williams, and an ephemeris
appear on MPEC 2015-Y59.

     T = 2015 Sept.19.0886 TT         Peri. =  84.9818
                                      Node  = 353.1399  2000.0
     q = 1.702570 AU                  Incl. =  51.7104


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

                         (C) Copyright 2015 CBAT
2015 December 21                 (CBET 4228)              Daniel W. E. Green