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IAUC 8983: C/2008 L5-L8

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                                                  Circular No. 8983
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 L5-L8 (SOHO)
     Further to IAUC 8982, additional near-sun presumed comets have
been found on SOHO website images:  C/2008 L5 and C/2008 L8 being
Kreutz sungrazers, and the other two belonging to the "Kracht II"
group -- and suggested by R. Kracht to be returning split components
of C/2002 R5 (cf. IAUC 7984), with corresponding two-apparition sets
of orbital elements by B. G. Marsden on MPEC 2008-O23.  K. Battams
writes that C/2008 L5 was small and slightly diffuse (mag about
7.5).  C/2008 L6 was stellar in appearance (mag about 6.5).  C/2008
L7 was tiny and stellar in appearance (mag about 8).  C/2008 L8 was
very diffuse (mag about 8.5).

 Comet        2008 UT       R.A.(2000)Decl.   Inst.  F    MPEC
 C/2008 L5    June 7.246     4 59.7  +20 55   C2     HS   2008-O16
 C/2008 L6        10.038     5 05.5  +23 10   C2     RK   2008-O23
 C/2008 L7        10.038     5 05.8  +23 11   C2     RK   2008-O23
 C/2008 L8        10.229     5 09.8  +21 03   C2     MA   2008-O23

     Z. Sekanina, Jet Propulsion Laboratory, reports that he made
an attempt to constrain the probable time of breakup of the SOHO
comet C/2002 R5 into its fragments, C/2008 L6 and C/2008 L7.  The
approach was based on fitting the geocentric positional offsets of
C/2008 L7 from C/2008 L6, derived from the June 10 astrometric
observations made with the C2 coronagraph (MPEC 2008-O23).  The
low-accuracy data and the short orbital arc available ruled out the
possibility of a more comprehensive modeling, and allowed him only
to conclude that the event occurred most probably between 2 and 10
weeks before the 2002 perihelion, when C/2002 R5 was 0.6 to 1.7 AU
from the sun.  When imaged in 2002, the comet must have been
already double, but the separation distance did not exceed 2" and
the duplicity could not be resolved by either coronagraph.  The rms
residual of these solutions was +/- 3".9, and for the seven used
offsets (of 11 measured) the residuals did not exceed 6".  Another
positive sign of these solutions was a low separation velocity,
reaching submeter-per-second values for the early breakup times and
never getting greater than about 2 m/s.  No outgassing-driven
differential nongravitational accelerations were found to have been
affecting the motions of the fragment comets between 2002 and 2008.
With B. G. Marsden's set of elements for C/2008 L6 (MPEC 2008-O23),
the following orbit is representative of C/2008 L7:  Epoch = 2008
June 23.0 TT, T = 2008 June 10.1704 TT, e = 0.985704, q = 0.045957
AU, Peri. = 58.9343 deg, Node = 359.7975 deg, i = 12.1505 deg
(equinox 2000.0), P = 5.76 years.

                      (C) Copyright 2008 CBAT
2008 September 28              (8983)            Daniel W. E. Green

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