DUST EMISSION OF GALACTIC CIRRUS FROM DIRBE OBSERVATIONS

We present the spectral distribution of dust in the diffuse ISM as der ived horn the first release of the DIRBE (Diffuse Infrared Background Explorer) data, in the wavelength range from 3.5 to 240 mu m. Although the spectrum of diffuse regions strongly decreases from 12 mu m towar d shorter wavelengths, it is found that some dust emission is still pr esent in the L and M bands. On average, it corresponds to similar or e qual to 1% of the total IR emission. The comparison with the 3.3 mu m Polycyclic Aromatic Hydrocarbon (PAH) feature emissivity of the diffus e medium in the inner galaxy shows that only a small fraction (8 - 16% ) of the DIRBE L band ISM emission is likely to be produced by the 3.3 mu m feature. Along with the presence of an important dust emission i n the DIRBE M band, where no PAH feature is expected, this implies tha t a continuum component and/or other features from dust also contribut e significantly to the short wavelength emission. The carrier of this emission still has to be identified. Large color variations are observ ed from region to region over most of the DIRBE range, which might ref lect abundance variations of the various dust components.