Electronic Telegram No. 4136
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 P3 (SWAN)
     M. Mattiazzo, Swan Hill, Victoria, Australia, reports that he noticed a
moving object on low-resolution public website hydrogen Lyman-alpha images
obtained during Aug. 3 and 4 with the Solar Wind Anisotropies (SWAN) camera on
the Solar and Heliospheric Observer (SOHO) spacecraft (see CBET 4068 and
website URL http://swan.projet.latmos.ipsl.fr/), and he confirmed the object
as a comet on images obtained on Aug. 9.383 UT with a Canon 60Da camera (+
Sigma 200-mm-f.l. f/2.8 lens) from an observing location at Castlemaine, Qld.;
the comet's appearance on his images was slightly condensed with a coma
diameter of 2' and "photometric magnitude" 11.8.  He subsequently found a
possible earlier detection on July 28; he assumed 12h UT on each date (the
SOHO website does not specify times within a day) and provides the following
approximate positions from the poor-scale SWAN images:

     2015 UT         R.A. (2000) Decl.
     July 28.5     11 31        +31 30
     Aug.  3.5     11 56        +22 15
           4.5     12 05        +20 00

Mattiazzo's astrometry from his confirming camera images:

     2015 UT             R.A. (2000) Decl.
     Aug.  9.38326   12 24 21.72   +12 05 09.1
           9.39375   12 24 24.99   +12 03 55.6
           9.40301   12 24 28.07   +12 02 59.3

He adds that the comet is situated in Virgo, near the Virgo supercluster of
galaxies.  After the comet was posted on the Minor Planet Center's PCCP
webpage, other CCD astrometrists have commented on the object's cometary
appearance.  A. Maury and J.-F. Soulier write that their unfiltered images
taken on Aug. 9.97-9.99 UT with a 0.4-m f/8 Ritchey-Chretien reflector at
San Pedro de Atacama, Chile, show a circular coma of diameter 1'.15 and no
visible tail.  H. Sato, Tokyo, Japan, notes that his images taken with an
iTelescope 0.51-m f/6.8 astrograph (+ luminance filter) near Mayhill, NM,
USA, on Aug. 10.1 show the comet to be strongly condensed with an outer coma
2'.0 in diameter with w-band magnitude 11.9 as measured within a circular
aperture of radius 63"; no tail was visible in 24 stacked 10-s exposures.
R. Weryk found the object with a tail extending for approximately 10"
toward p.a. approximately 100 degrees in two z-band images taken on Aug.
10.25 with the 1.8-m Pan-STARRS1 telescope at Haleakala.  E. Guido and N.
Howes report that thirteen stacked 15-s images taken remotely on Aug. 10.37
with an iTelescope 0.50-m f/6.8 astrograph at Siding Spring show a bright
coma about 1' in diameter.  Images taken by C. Jacques, E. Pimentel, and J.
Barros with a 0.45-m f/2.9 reflector at the SONEAR Observatory, Oliveira,
Brazil, on Aug. 10.9 reveal a sharp central condensation surrounded by a
coma 90" in diameter in six stacked 60-s images.
     A. Hale, Cloudcroft, NM, USA, reports total visual magnitude 12.2
and coma diameter 2'.3 with a 0.41-m reflector on Aug. 10.14 UT.
     The available astrometry, the following very preliminary parabolic
orbital elements by G. V. Williams, and an ephemeris appear on MPEC 2015-P25.

     T = 2015 July 27.2617 TT         Peri. = 131.8065
                                      Node  =  86.9127  2000.0
     q = 0.714631 AU                  Incl. =  59.3232


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

                         (C) Copyright 2015 CBAT
2015 August 11                   (CBET 4136)              Daniel W. E. Green