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IAUC 8825: (134340)

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                                                  Circular No. 8825
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)


(134340) PLUTO
     M. J. Person, J. L. Elliot, A. A. S. Gulbis, and C. A. Zuluaga,
Massachusetts Institute of Technology; B. A. Babcock, A. J. McKay,
J. M. Pasachoff, and S. P. Souza, Williams College; W. B. Hubbard,
C. A. Kulesa, and D. W. McCarthy, University of Arizona; S. D. Kern,
Space Telescope Science Institute; S. E. Levine, U.S. Naval
Observatory; A. S. Bosh, Boston University; E. V. Ryan and W. H.
Ryan, Magdalena Ridge Observatory; and A. Meyer and J. Wolf, SOFIA,
report observations on Mar. 18 UT of an occultation by (134340)
Pluto of the star/event called P445.3 by McDonald and Elliot (2000,
A.J. 120, 1599; see also
http://occult.mit.edu/research/occultations/Pluto/P445.3-preds/).
The occultation was observed from five sites by their consortium
(as well as by others).  A preliminary astrometric solution based
on the light curves from all of the stations places Pluto's shadow
north of pre-event predictions.  Based on this solution, the
closest approach distance of the center of Pluto's shadow to their
successful observation sites are as follows:  Mount Hopkins, 1319
km; Magdalena Ridge, 1192 km; Fremont Peak, 1019 km; USNO Flagstaff
Station, 1102 km; and Mt. Graham, 1258 km.  All closest-approach
distances are south of Pluto's center in the shadow plane,
perpendicular to the direction to the star and shifted by the same
amount within the uncertainties.  The formal error on the
astrometric solution is +/- 4 km, but error bars of +/- 15 km
account for possible systematic effects.  The half-light shadow
radius from this solution is 1207 +/- 15 km, consistent with the
shadow radius of 1208 +/- 10 km from 2006 (Elliot et al., A.J., in
press).
     McCarthy, Kulesa, Hubbard, Kern, Person, Elliot, and Gulbis
further write that the 6.5-m MMT telescope imaged a grazing
occultation of the star P445.3 by (134340) Pluto on Mar. 18.453 UT,
revealing substantial scintillation effects caused by Pluto's
atmosphere.  High-signal-to-noise (> 100/frame) observations were
obtained simultaneously by the PISCES camera in the H band (0.3-s
integrations) and by the POETS camera in the optical (0.25-s
integrations).  Data from both cameras reveal over a dozen highly
correlated scintillations in Pluto's atmosphere with high signal-
to-noise and temporal widths (about 10 s), which appear to increase
with depth in Pluto's atmosphere.  Similar effects have been
reported in occultations by Neptune (Hubbard et al. 1988, Ap.J. 325,
490) and are expected in this case based on previous Pluto
observations (Elliot et al., op.cit.) and the slowly moving shadow
(about 7 km/s).  The MMT observations were obtained in excellent
seeing conditions (FWHM about 1" at 1.6 microns) and present
uniquely-high signal-to-noise.

                      (C) Copyright 2007 CBAT
2007 March 31                  (8825)            Daniel W. E. Green

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