SNe Ia with low total-to-selective extinction ratio values, RV, also show peculiar continuum polarization wavelength dependencies, raising towards blue, with polarization peaks at short wavelengths (λmax ≲ 0.4 μm, Serkowski et al. 1975), while for comparison, normal sight lines in the Milky Way have polarization peaks at λmax ~ 0.55 μm. It is not well understood why SNe Ia sight lines display such different polarization profiles compared to what we observe in the Milky Way. Possible explanations are that the composition of interstellar dust in SNe Ia host galaxies is different from the dust in our Galaxy, or that there is circumstellar dust with an enhanced abundance of small grains, which was ejected from the progenitor system before the explosion, causing such peculiar polarization profiles.
Some post-AGB stars (proto-planetary nebula, PPN) have as well polarization curves rising towards the blue, which are produced by CSM scattering. These polarization curves are remarkably similar to those observed towards highly reddened SNe Ia (Cikota et al. 2017). We suggest that also these polarization curves observed towards highly reddened SNe Ia, might be produced by CSM dust scattering. Furthermore, we speculate that those SNe Ia might explode within a PPN.