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THE ASTRONOMER Electronic Circular No 2968      2013 Dec 05 15.49UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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COMET C/2013 V3 (Nevski): OUTBURST
Mark Kidger and John Murrell have reported an outburst of this comet. John
indicated on Nov 16 it was possibly 5 magnitudes brighter than the ephemeris
of the Minor Planet Center.

Mark Kidger: This comet appears to have had a small post-perihelion
outburst, as indicated by the following R magnitudes calibrated against
CMC14 and the equivalent geocentric distance-corrected magnitudes for an
effective 100000km aperture.

2013 November
23.05, 13.73, Fernando Limón (MPC I99, Argentina), 11.49 25.25, 14.18,
Francisco Soldán (MPC Z74, Seville), 12.06 29.25, 14.42, Faustino García
(MPC J38, Asturias), 12.19 30.20, 14.36, Juanjo González (MPC J01,
Asturias), 12.06

2013 December
02.10, 13.64, Ramón Naves & Montse Campàs (MPC 213, Barcelona), 11.17 03.20,
13.54, Limón, 11.23 04.10, 13.92, Naves & Campàs, 11.60

COMET C/2012 S1 (ISON)
Dan Green, Central Bureau: The comet's nucleus apparently disrupted near
perihelion, with the comet's head fading from perhaps a peak brightness of
visual mag -2 some hours before perihelion to well below mag +1 before
perihelion. M. Knight, Lowell Observatory, finds that the comet peaked
around visual mag -2.0 around Nov.
28.1 UT, adding that the brightest feature in the coma of the comet faded
steadily after perihelion from about mag 3.1 in a 95"-radius aperture when
the comet first appeared from behind the SOHO coronagraph occulting disk on
Nov.28.92 to about mag 6.5 on Nov. 29.98.  K. Battams, Naval Research
Laboratory, writes that, based on LASCO C3 images of Nov. 30.912UT, there is
no visible nucleus or central condensation; what remains is very diffuse,
largely transparent to background stars, and fading; it appears that
basically a cloud of dust remains from the nucleus.
 
Z. Sekanina, Jet Propulsion Laboratory, reports that, from the position of
the northeastern boundary of the comet's fan-shaped tail in three images
taken with the C3 coronagraph onboard the SOHO spacecraft between 0.7 and
1.9 days after perihelion (Nov. 29.46 to 30.66 UT), he finds that the
comet's production of dust terminated about 3 hours before perihelion.
Although this result is preliminary, it is unlikely to be significantly in
error, because the position angles of a perihelion emission are off in the
three images by 14-22 deg, and those of post-perihelion emissions still
more. The estimated time of terminated activity is consistent with the
absence of any feature that could be interpreted as a condensation around an
active nucleus in the 20 or so images taken with the C2 on Nov. 28.8-29.0 UT
(0.8 to 5.4 hr after perihelion) and with the appearance of a very sharp tip
(replacing a rounded head) at the comet's sunward end in the C2 images
starting about 4 hr before perihelion and continuing until its disappearance
behind the occulting disc around Nov. 28.74 UT (or some 50 minutes before
perihelion).  The time of terminated activity is here interpreted as the end
of nuclear fragmentation, a process that is likely to have begun shortly
before a sudden surge of brightness that peaked nearly 12 hr prior to
perihelion. 

Guy M Hurst