Occultation of a GSC star by Pluto on July 19-20
A-M.Lagrange (May 27  2002)
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An exceptionnal observation for July 19/20 : an occultation of a
GSC (GSC 0565101777) star by Pluton (see text from last week). The
centrality crosses over Paranal which might (still tbc) observe the
central flash.

The maximum duration of the occultation will be 3mn. The absolute
occultation time is known with a 2mn uncertainty. Also, data should be
recorded prior and after the oiccultation to ensure a good statistics
on the photometry outside the occultation. Hence 20 mn of observations
centered on the occultation time is reasonnable.  In order to avoid
possible problems close to the occultation time, the servoing will not
be made on the GSC star itself, but on a R=15,6 magnitude star located
at ra= 255.074631 dec= -12.694848 J2000, ie 21 arcsec au south-east of
GSC.

Also, a 10 minutes image of Pluton and Charon once clearly separated
from the star (motion 2.8 arcsec/heure) should be recorded, to perform
a good relative photometry between GSc and pluton. This is
particularly important to check whether or not the star has
disappeared completely or not during the occultation (aerosols). For
us this will also allow to check the differential tracking of NAOS,
which has been tested only once.

K band. 2,3 microns. Individual exposure times of 0.1 second are
needed.
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