Electronic Telegram No. 4195
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 W1 (GIBBS)
     A. R. Gibbs reports his discovery of a comet on CCD images obtained with
the Catalina Sky Survey's 0.68-m Schmidt telescope (discover observations
tabulated below), with four co-added 30-s exposures showing the object with a
coma 7" across and a broad tail extending for 12" to the west-southwest; the
tail may continue more narrowly in p.a. 230 deg.  Four co-added follow-up 90-s
exposures show an elongated coma of size 8" x 10", elongated in p.a. 240 deg,
with a 23" tail in p.a. 225 deg that is about 30 degrees wide.

     2015 UT             R.A. (2000) Decl.       Mag.   Observer
     Nov. 18.48707    8 44 43.30   + 2 39 09.4          Gibbs
          18.49159    8 44 43.26   + 2 39 11.4   18.7     "
          18.49612    8 44 43.30   + 2 39 14.6            "
          18.50065    8 44 43.26   + 2 39 16.3   18.8     "
          18.51153    8 44 43.29   + 2 39 23.9   18.9     "
          18.51632    8 44 43.26   + 2 39 26.8   18.9     "
          18.52111    8 44 43.21   + 2 39 30.1   18.9     "
          18.52592    8 44 43.23   + 2 39 32.7   18.9     "

After the comet was posted on the Minor Planet Center's PCCP webpage, other
CCD astrometrists commented on the object's cometary appearance.  H. Sato
(Tokyo, Japan) stacked eight 60-s exposures obtained on Nov. 18.73 UT with an
iTelescope 0.51-m f/6.8 astrograph (+ luminance filter) at Siding Spring to
find the comet to be strongly condensed with a faint outer coma 15" in
diameter, with no tail; the w-band magnitude was 19.0 as measured within a
circular aperture of radius 8".8.  V-band images obtained by W. H. Ryan and
E. V. Ryan with the 2.4-m f/8.9 reflector at Magdalena Ridge Observatory on
Nov. 19.4 show a distinct coma (of mag 19.9-20.1) and tail at p.a. about 235
deg.  Images obtained by R. G. Matheny with the Mount Lemmon 1.5-m reflector
on Nov. 19.5 show a coma of size 8" x 10", elongated in p.a. 240 deg, with
a tail about 30 degrees wide pointing generally toward p.a. 225 deg.
     Pre-discovery observations (with no comment about the object's cometary
appearance), which were reported after Gibbs' posting on the NEOCP and PCCP,
were made within about 40 min prior to Gibbs' discovery frames using the
3.5-m Space Surveillance Telescope on Atom Peak in the White Sands Missile
Range, NM, USA; the SST was the telescope used to discover comet C/2015
TQ_209 (cf. CBET 4156).
     The available astrometry, the following preliminary parabolic orbital
elements by G. V. Williams, and an ephemeris appear on MPEC 2015-W43.

     T = 2016 May   3.3582 TT         Peri. =  34.7325
                                      Node  = 115.6938  2000.0
     q = 2.638893 AU                  Incl. =  85.4100


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

                         (C) Copyright 2015 CBAT
2015 November 21                 (CBET 4195)              Daniel W. E. Green