Silicon depletion in the interstellar medium

Abstract

We report interstellar silicon ( Si ) depletion and dust-phase column densities of Si along 131 Galactic sight lines using archival observations. The data were corrected for differences in the assumed oscillator strength. This is a much larger sample than previous studies but con fi rms the majority of results, which state that the depletion of Si is correlated with the average density of hydrogen along the line of sight ( () á ñ n H ) as well as the fraction of hydrogen in molecular form ( f ( H 2 )) . We also fi nd that the linear part of the extinction curve is independent of Si depletion. Si depletion is correlated with the bump strength ( c 3 / R V ) and the FUV curvature ( c 4 / R V ) suggesting that silicon plays a signi fi cant role in both the 2175 Å bump and the FUV rise.