Probing Grain Alignment in Circumstellar Envelopes with Optical Polarimetry

Dust induced polarization is a powerful and versatile method of tracing magnetic fields in the ISM of our and external galaxies. However, to fully take advantage of the method, we need to quantitatively understand the mechanisms responsible for the alignment and randomization of the grains causing the polarization. To separate the effects of grain mineralogy, we have initiated a program to study the polarization and grain alignment in the circumstellar envelopes (CSE) of asymptotic giant branch stars, using optical, far infrared and sub-mm wave polarimetry. While the latter two have the advantage of allowing mapping, optical polarimetry avoids interpretation complications due to line-of-sight grain temperature and emissivity - at the cost of having to use faint background stars. I will discuss recent observations from Lick/Kast and Keck/LRISp of, primarily, the CSE of IRC+10 216, probing the alignment mechanism and grain properties of its carbon dust.