BARNETT RELAXATION IN THERMALLY ROTATING GRAINS

We present an exact formulation of the physics of Barnett relaxation. Our formulation is based on a realistic kinetic model of the relaxatio n mechanism, which includes the alignment of the grain angular momentu m in body coordinates by Barnett dissipation, disalignment by thermal fluctuations, and coupling of the angular momentum to the gas via gas damping. We solve the Fokker-Planck equation for the measure of intern al alignment using numerical integration of the equivalent Langevin eq uation for Brownian rotation. The accuracy of our results is calibrate d by comparing our numerical solutions with exact analytic results obt ained for special cases. We describe an analytic approximation for the measure of alignment that fits our numerical results for cases of pra ctical interest.