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                                                  Circular No. 8842
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)

     D. Schleicher, Lowell Observatory, obtained three sets of
narrowband photometry of comet 96P on May 12 (r = 1.07 AU) using
the Hall 1.1-m telescope at Lowell Observatory, with the following
averaged results:  log Q(OH) = 27.33; equivalent log Q(water;
vectorial) = 27.45; log Q(NH) = 25.47; log Q(CN) = 22.4; log Q(C_2)
= 23.7; log Q(C_3) = 22.3; log Af(rho) = 1.5 (cf. IAUC 7342).  The
resulting abundance ratios indicate that, while the NH-to-OH ratio
is on the high side of the normal range, the CN-to-OH ratio is low
by about a factor of 200; C_2 and C_3 are also low but by factors
of 10-20 from "typical" composition (based on A'Hearn et al. 1995,
Icarus 118, 223).  A single observation on May 24 (r = 1.30 AU)
shows production rates having decreased by a factor of 1.7, but to
within uncertainties (3 times for CN and C_3, and much smaller for
other species), production-rate ratios are confirmed.  This
extremely low CN-to-OH ratio for 96P indicates that it is either
compositionally associated with comet C/1988 Y1 (Yanaka; 1988r =
1988 XXIV), which was strongly depleted in CN and C_2 but not NH_2
(Fink 1992, Science 257, 1926), or represents a new compositional
class of comets, since C/1988 Y1 had a much greater depletion of
C_2 (> 100x) than does 96P.

     H. Weaver, Applied Physics Laboratory, Johns Hopkins
University, writes that the New Horizons (NH) spacecraft is making
the first-ever journey down the magnetotail of Jupiter:  "The NH
plasma energetic-particle instruments (PEPSSI and SWAP) have been
measuring interesting spatial structure, particle composition, and
temporal variability during their in situ observations.  We
encourage remote observations of the Jovian system that are
relevant to the magnetosphere during the next few weeks, including
investigations of aurorae, the Io plasma torus, and Io's volcanic
activity.  Observations between now and 2007 June 21, when PEPSSI
and SWAP will be turned off to prepare for the hibernation of the
NH spacecraft, are particularly important.  However, remote
observations somewhat after that time may still be useful for
piecing together a coherent picture of the state of the Jovian
magnetosphere during the NH encounter.  Interested observers may
contact John Spencer (spencer@boulder.swri.edu) for further

                      (C) Copyright 2007 CBAT
2007 June 6                    (8842)            Daniel W. E. Green

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