Electronic Telegram No. 4112
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 M1 (PANSTARRS)
     R. Weryk and R. Wainscoat, Institute for Astronomy, University of Hawaii,
report the discovery of a comet moving across a very crowded star field in
three w-band exposures taken with the 1.8-m Pan-STARRS1 telescope at Haleakala
on June 20.5 UT (discovery observations tabulated below); the object's full-
width-at-half-maximum (1".7) was slightly larger than those for nearby stars
(seeing 1".2).

     2015 UT             R.A. (2000) Decl.       Mag.
     June 20.45177   19 29 59.24   -22 10 38.2   19.8
          20.47456   19 29 57.67   -22 11 38.4   19.8
          20.48592   19 29 56.88   -22 12 08.4   19.7

The object was posted on the Minor Planet Center's PCCP webpage.  D. J. Tholen
writes that follow-up images taken by P. Forshay with the 3.6-m Canada-France-
Hawaii Telescope on June 21.5 UT (measured by Wainscoat and himself) shows the
comet to be clearly non-stellar with a tail extending at least 20" to the
northwest, with a hint of an antitail; the red magnitude was measured to be
19.2-19.3.  Stacked unfiltered CCD images taken by A. Maury and J.-F. Soulier
with a 0.4-m f/8 Ritchey-Chretien reflector at San Pedro de Atacama, Chile, on
June 21.3 also show cometary appearance, with a 15" coma and no tail.
H. Sato, Tokyo, Japan, writes that sixteen stacked 30-s exposures taken on
June 21.8 with an iTelescope 0.70-m f/6.6 astrograph (+ luminance filter) at
Siding Spring show the comet to be moderately condensed with a faint coma 12"
in diameter, with magnitude 18.0 as measured within a circular aperture of
radius 6".5.
     The available astrometry, the following preliminary parabolic orbital
elements by G. V. Williams, and an ephemeris appear on MPEC 2015-M45.

     T = 2015 May  16.2065 TT         Peri. = 164.2385
                                      Node  = 100.3060  2000.0
     q = 2.095602 AU                  Incl. =  57.4399


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2015 CBAT
2015 June 22                     (CBET 4112)              Daniel W. E. Green