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IAUC 8886: 17P

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                                                  Circular No. 8886
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://www.cfa.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)

     This comet (currently near opposition) has been observed to be
undergoing a very large outburst in brightness; based on normal
behavior in recent apparitions, it was predicted to be near total
mag 16 for most of 2007 (H_15 approximately 9.5, from 2007 Comet
Handbook) -- and, indeed, observers have consistently reported it
around mag 16 +/- 1 since last May, L. Buzzi (Varese, Italy, 0.60-m
reflector) reporting the comet at mag 17.8 on Oct. 20.9 UT and G.
Muler (Lanzarate, Spain, 0.20-m reflector) measuring mag 16.8-17.3
on Oct. 23.0.  The first known detection of the current outburst
was communicated by M. Kidger (Herschel Science Centre, European
Space Astronomy Centre, Madrid), who writes that observations by J.
A. Henriquez Santana (Tenerife) on Oct. 24.067 show the comet at
''nuclear" mag 8.4 ("some 9 mag brighter than previously" seen)
with a 0.2-m reflector, and that the comet was brightening by 0.5
mag/hr "over the course of 6 hr"; the outburst was confirmed during
Oct. 24.07-24.09 by Muler and by R. Naves and M. Campas (Barcelona)
with a bright, almost-stellar inner coma (mag R = 7.3 in a 10"
square aperture on Oct. 24.136).  F. Kugel (Banon, France) reports
that unfiltered astrometric CCD images taken by C. Rinner and
himself on Oct. 24.21 with a 0.5-m reflector shows an object of
stellar appearance of mag 7.4 at the predicted position of 17P.
     Following a discussion-group e-mail alert of the outburst,
several other observers have confirmed the outburst.  E. Guido and
G. Sostero (Castellammare di Stabia, Italy, 0.25-m f/3.4 reflector)
write that ten co-added 5-s B-band CCD exposures taken remotely on
Oct. 24.34 with a 0.25-m reflector near Mayhill, NM, show the comet
as a bright, featureless, starlike object of total mag about 4.6.
A. Hale (Cloudcroft, NM) reports viewing the comet as an easy
naked-eye starlike object of mag 4.0 on Oct. 24.50.  S. Yoshida
(Yokohama City, Kanagawa, Japan) reports the comet to be visible
via naked eye even in a large city, at mag 3.5 on Oct. 24.55; with
a 6.6-cm refractor, it looked completely stellar.  Within two hours,
Yoshida adds that the comet had brightened an additional half a
magnitude, to mag 3.0 on Oct. 24.63 as seen via naked eye.  K.
Kadota (Ageo, Saitama-ken, Japan, 0.25-m f/5 reflector) notes that
his CCD image from Oct. 24.61 yields total mag 3.6 and coma
diameter 1'.7 (though starlike with no tail).
     Comet 17P also underwent a large outburst in brightness when
it was first discovered in Nov. 1892 near total visual mag 4 (which
was also about 12 mag over the "normal" brightness); at that time,
it faded by about 3 mag over the following week (e.g., Kronk 2003,
Cometography 2, 694).

                      (C) Copyright 2007 CBAT
2007 October 24                (8886)            Daniel W. E. Green

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