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==> In this proposal, more time is being requested for FBOULANG.WISMDUST
==> This proposal requests an upgrade from Priority 3 for FBOULANG.WISMDUST
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Dust grains in low density gas are subjected to sputtering and shattering in
fast supernovae shocks.  Although there has been extensive modelling of the
dust destruction, still little is known about the grains which survive.  Jones
et al.  (1996) have modeled the effect of the destruction processes on the
size distribution of grains.  They predict that fast J shocks are efficient in
grinding large dust grains into smaller particles.  Two recent results
providing information about dust in low density gas may be confirming this
prediction.  (1) Analysis of DIRBE data has brought evidence for a large
enhancement of the abundance of very small grains around the nearby star
Spica.  Spica is located in a low density region of the ISM within the Loop I
bubble centered on the Sco-Cen association.  With this location it is
tentalizing to associate the enhanced abundance with a shock.  (2) Using
ISOCAM we have detected extended emission around a halo star, HD149881,
located at a z-height of 1.2 kpc.  This detection suggests the presence of
PAHs in the Galactic halo.  Since matter in the halo must have been expulsed
up to high z heights by some energetic events the detection could indicate
that PAHs can be produced by shock processing of large grains.  We propose new
observations to complement these results and confirm them on one additonal
Galactic Halo star.  We also ask for a time upgrade to extend a statistical
search for dust in the Galactic halo.  The proposed observations should have
important implications on the understanding of the dust life-cycle and the
evolution of interstellar gas in between the different phases of the
interstellar medium.