On the Disalignment of Interstellar Grains

Several mechanisms have been proposed to explain the alignment of grains withthe interstellar magnetic field, including paramagnetic dissipation, radiativetorques, and supersonic gas-grain streaming. These must compete withdisaligning processes, including randomly directed torques arising fromcollisions with gas atoms. I describe a novel disalignment mechanism for grainsthat have a time-varying electric dipole moment and that drift across themagnetic field. Depending on the drift speed, this mechanism may yield a muchshorter disalignment timescale than that associated with random gas atomimpacts. For suprathermally rotating grains, the new disaligning process may bemore potent for carbonaceous dust than for silicate dust. This could result inefficient alignment for silicate grains but poor alignment for carbonaceousgrains.Comment: 19 pages, 3 figures, submitted to Ap