We present a compilation of PRONAOS-based results concerning the temperature dependence of the dust submillimeter spectral index , including data from Galactic cirrus , star-forming regions , dust associated to a young stellar object , and a spiral galaxy .
We observe large variations of the spectral index ( from 0.8 to 2.4 ) in a wide range of temperatures ( 11 to 80 K ) .
These spectral index variations follow a hyperbolic-shaped function of the temperature , high spectral indices ( 1.6-2.4 ) being observed in cold regions ( 11-20 K ) while low indices ( 0.8-1.6 ) are observed in warm regions ( 35-80 K ) .
Three distinct effects may play a role in this temperature dependence : one is that the grain sizes change in dense environments , another is that the chemical composition of the grains is not the same in different environments , a third one is that there is an intrinsic dependence of the dust spectral index on the temperature due to quantum processes .
This last effect is backed up by laboratory measurements and could be the dominant one .

We also briefly present a joint analysis of WMAP dust data together with COBE/DIRBE and COBE/FIRAS data .