Electronic Telegram No. 4067
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 D1 (SOHO)
     K. Battams, Naval Research Laboratory, reports that Worachate Boonplod
found images of a comet in public SOHO/LASCO C3 satellite images (geocentric
discovery position tabulated below); Battams notes that the comet's image
appeared tiny at first (just above the noise at mag about 9) and gradually
brightened as it neared the sun, but was surprised to see that it then
dramatically brightened to magnitude about 1.5 as it crossed into the C2
field-of-view -- when a short, faint tail appeared (Feb. 19) and remained
visible for the rest of the comet's visible passage (fading to mag around 6
by the time it left LASCO's field-of-view (Feb. 21.77 UT).

     2015 UT            R.A. (2000) Decl.        Mag.
     Feb. 18.00423    21 39 55     - 6 32.5      9.1

     M. Knight, Lowell Observatory, has analyzed the SOHO images and
reports that the comet was first visible late on Feb. 17 right at the
detection limit in C3 (mag about 9.5-10), and peak brightness occurred
around Feb. 19.9 at an apparent V magnitude of about 1.3.  It showed much
more cometary appearance during the second half of the visible apparition,
and the tail seemed more distinct as it was fading.
     The reduced SOHO astrometry, the following parabolic orbital elements
by G. V. Williams, and an ephemeris for possible ground-based recovery
observations appear on MPEC 2015-D73.  Pre- and post-perihelion solutions
were required to fit the observations; together with the appearance of the
tail near perihelion and rapid brightening, it is possible that some large
physical change (perhaps splitting) occurred around that time.

From 210 pre-perihelion observations (Feb. 18-19):

     T = 2015 Feb. 19.7514 TT         Peri. = 235.9476
                                      Node  =  96.1211  2000.0
     q = 0.028306 AU                  Incl. =  69.9509

From 211 post-perihelion observations (Feb. 19-21):

     T = 2015 Feb. 19.7471 TT         Peri. = 234.7391
                                      Node  =  96.0501  2000.0
     q = 0.028115 AU                  Incl. =  70.2855


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2015 CBAT
2015 February 24                 (CBET 4067)              Daniel W. E. Green