Electronic Telegram No. 4100
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director:  Daniel W. E. Green; 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 J2 (PANSTARRS)
     E. Lilly and R. Weryk, Institute for Astronomy, University of Hawaii,
report the discovery of another apparent comet in three w-band exposures taken
with the 1.8-m Pan-STARRS1 telescope at Haleakala on May 15.5 UT (discovery
observations tabulated below); the object shows a prominent tail with
approximately 8" long extending towards p.a. approximately 300 degrees.

     2015 UT             R.A. (2000) Decl.       Mag.
     May  15.48694   16 10 05.44   -23 22 05.6   19.6
          15.49789   16 10 05.12   -23 22 07.0   19.7
          15.50882   16 10 04.80   -23 22 08.7   19.6

Wainscoat and M. Micheli add that three 60-s r-band follow-up exposures were
taken of the object with the 3.6-m Canada-France-Hawaii Telescope on May 16.5
UT (queue observer D. Woodworth), which show the object clearly cometary in
appearance, with a broad, low-surface-brightness tail that extends from the
nuclear condensation for at least 10" toward p.a. approximately 300 degrees.
     After the comet was posted on the Minor Planet Center's PCCP webpage,
other CCD astrometrists have also noted the object's cometary appearance.
J. Lacruz, Madrid, Spain, reports that sixty stacked 60-s exposures taken with
a 0.40-m Ritchey-Chretien reflector on May 17.0 UT show the comet to be
diffuse with a fan-shaped coma 9" across with an apparent tail in p.a. 320
deg.  A. Maury and J.-F. Soulier finds that images taken on May 17.1 with a
0.4-m f/8 Ritchey-Chretien reflector at San Pedro de Atacama show a 11" x 13"
coma and a tail 15" long in p.a. 310 deg; they measured the comet's brightness
in a 6".2 radius to be 18.8.  W. H. Ryan communicates that his R-band images
taken on May 18.33-18.36 with the Magdalena Ridge Observatory 2.4-m f/8.9
reflector show a distinct tail at p.a. about 300 deg, and he finds the
comet's magnitude to be 18.6-18.9.  H. Sato, Tokyo, Japan, writes that four
stacked 60-s exposures taken with an iTelescope 0.51-m f/6.8 astrograph (+
luminance filter) at Siding Spring on May 18.6 UT show the comet to be
strongly condensed with a coma 10" in diameter and no tail; the w-band
magnitude was 20.2 as measured within a circular aperture of radius 6".6.
     The available astrometry, the following preliminary parabolic orbital
elements by G. V. Williams, and an ephemeris appear on MPEC 2015-K18.

     T = 2015 Oct. 17.8168 TT         Peri. = 208.0670
                                      Node  =  57.2873  2000.0
     q = 4.448423 AU                  Incl. =  18.7941


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

                         (C) Copyright 2015 CBAT
2015 May 19                      (CBET 4100)              Daniel W. E. Green