A new interpretation of Serkowski's polarization law
  The basic tenets of the alternative interpretation to be presented here are
that the spectral profiles of the star light polarization peaks observed in the
visible and near IR are a result of the optical properties of silicate grains
in the same spectral range, not of the grain size, provided it remains within
the range of Rayleigh's approximation. The silicate properties are those
obtained experimentally by Scott and Duley \cite{sco} for the non-iron bearing
\bf amorphous \rm forsterite and enstatite. The whole range of observed
Serkowski polarization profiles can be simulated with mixtures made of
forsterite plus an increasing fraction (0 to 0.5) of enstatite as the spectral
peak shifts from 0.8 to 0.3 $\mu$m. Fits to individual observed polarization
spectra are also demonstrated. The optical extinction of silicates in the
vis/IR (the "transparency range") can be understood by analogy with the
thoroughly studied amorphous hydrogenated carbons and amorphous silica. It is
due to structural disorder (dangling bonds and coordination defects) and
impurities, which give rise to electronic states in the forbidden gap of
semi-conductors. Because they are partially localized, their extinction power
is dramatically reduced and has been ignored or simply described by a low, flat
plateau. As their number density depends on the environment, one expects
variations in the ratio of optical extinction coefficients in the visible and
mid-IR.
