Interstellar polarization and grain alignment: the role of iron and silicon

We compiled the polarimetric data for a sample of lines of sight with known abundances of Mg, Si, and Fe. We correlated the degree of interstellar polarization P and polarization efficiency (the ratio of P to the colour excess E(B - V) or extinction A(V)) with dust phase abundances. We detect an anticorrelation between P and the dust phase abundance of iron in non silicate-containing grains [Fe(rest)/H](d), a correlation between P and the abundance of Si, and no correlation between P/E(B - V) or P/A(V) and dust phase abundances. These findings can be explained if mainly the silicate grains aligned by the radiative mechanism are responsible for the observed interstellar linear polarization.