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This proposal is an extention of MC_DIFFU.
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We still do not know if PAHs (or other carbon dominated solid elements)
exist in environments as deficient in metal as in the case of the SMC.
From the ultraviolet observations, the SMC mean extinction curve shows
a very weak bump at 0.22 microns compared to the galactic curve.
This observational fact is thought to be related to the underabundance of
carbon in the interstellar dust in these irregular galaxies compared to
the solar neighborhood. From the IRAS observations on the SMC one observes
a very weak mid-infrared (12 and 25 microns) emission.
There seems to be a tight correlation between the ratio nu*I(12 microns)
to far-infrared and the abundance O/H, which suggests that the weakness of
the 12 microns emission is due to a metallicity effect. The search of the
PAH features in the Magellanic Clouds will permit a more quantitative
analysis in the frame of models accounting for the underabundance of carbon
in the dust grain population.
We propose supplementary observations to the previous MC_DIFFU in the SMC.
The principal goals of this proposal are:
1) a sensitive photometry over a broad range of wavelengths to
constrain the models of grain population (composition and
size distribution).
2) the detection of the near infrared features at 7.7 and 11.3
microns.
3) comparison between the far infrared emission and HI
distribution.