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IAUC 8987: C/2008 O4, C/2008 O5,, C/2008 O6; 205P

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IAUC number

                                                  Circular No. 8987
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)

COMETS C/2008 O4, C/2008 O5, AND C/2008 O6 (SOHO)
     Further to IAUC 8986, additional near-sun presumed comets have
been found on SOHO website images; C/2008 O5 is a Kreutz sungrazer,
and C/2008 O6 belongs to no known group.  C/2008 O5 was stellar in
appearance in C3 images (mag about 6.5-7.0), and small and slightly
diffuse in C2 images.  C/2008 O6 was stellar in appearance and
quite bright (mag about 6.5).  Contrary to the inference on IAUC
8985, C/2008 O4 also belongs to no known group, and the last
sentence of the first paragraph (regarding C/2008 O4) should be
replaced with the following:  C/2008 O4 was small and condensed,
being brightest at the edge of the C2 field-of-view (mag perhaps
7.5) and becoming fainter as it approached the occulter.

 Comet       2008 UT       R.A.(2000)Decl.   Inst.  F    MPEC
 C/2008 O5   July 17.196    7 29.8  +18 29   C3/2   BZ   2008-S68
 C/2008 O6        17.571    7 52.8  +23 59   C3/2   HS   2008-T10

     Z. Sekanina, Jet Propulsion Laboratory, reports that both
companion nuclei (IAUC 8978) are fragments of long lifetimes.
While their brightness may fluctuate and will generally decrease
with time on account of increasing heliocentric and geocentric
distances, they are not expected to disintegrate soon.  Nucleus 'B',
the one closer to the principal nucleus 'A', is found to have
separated from it in the second half of 2006, about 700 days before
perihelion, when the comet was 4.8 AU from the sun, while the more
distant companion 'C' appears to have detached from 'A' at the very
end of 1998, at 5.5 AU from the sun and slightly more than 3 years
before the previous perihelion, which occurred on 2002 Jan. 21.0.
The nongravitational decelerations relative to 'A' are derived to
be 3.1 +/- 1.0 and 4.3 +/- 0.1 x 10**(-5) units of solar
gravitational acceleration for 'B' and 'C', respectively, and their
separation velocities are calculated to have been 0.11 +/- 0.05 and
0.7 +/- 0.4 m/s.  The comet has a history of splitting long before
perihelion (Sekanina 1979, Icarus 38, 306).  The predicted
separation distance and position angle for 'B' relative to 'A' are
as follows (2008, 0h TT):  Oct. 1, 68", 265 deg; 21, 62", 269 deg;
Nov. 10, 54", 270 deg; 30, 48", 269 deg; Dec. 20, 42", 268 deg.
The predicted separation distance and position angle for 'C'
relative to 'A' are:  Oct. 1, 619", 266.2 deg; 11, 568", 267.5 deg;
21, 518", 268.3 deg; 31, 470", 268.6 deg; Nov. 10, 425", 268.6 deg;
20, 384", 268.3 deg; 30, 347", 268.0 deg; Dec. 10, 314", 267.6 deg;
20, 284", 267.4 deg.

                      (C) Copyright 2008 CBAT
2008 October 2                 (8987)            Daniel W. E. Green

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