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We study the alignment of grains subject to both radiative torques andpinwheel torques while accounting for thermal flipping of grains. By pinwheeltorques we refer to all systematic torques that are fixed in grain body axes,including the radiative torques arising from scattering and absorption ofisotropic radiation. We discuss new types of pinwheel torques, which aresystematic torques arising from infrared emission and torques arising from theinteraction of grains with ions and electrons in hot plasma. We show that bothtypes of torques are long-lived, i.e. may exist longer than gaseous dampingtime. We compare these torques with the torques introduced by E. Purcell,namely, torques due to H$_2$ formation, the variation of accommodationcoefficient for gaseous collisions and photoelectric emission. Furthermore, werevise the Lazarian & Draine model for grain thermal flipping. We calculatemean flipping timescale induced by Barnett and nuclear relaxation for bothparamagnetic and superparamagnetic grains, in the presence of stochastictorques associated with pinwheel torques, e.g. the stochastic torques arisingfrom H$_2$ formation, and gas bombardment. We show that the combined effect ofinternal relaxation and stochastic torques can result in fast flipping forsufficiently small grains and, because of this, they get thermally trapped,i.e. rotate thermally in spite of the presence of pinwheel torques. Forsufficiently large grains, we show that the pinwheel torques can increase thedegree of grain alignment achievable with the radiative torques by increasingthe magnitude of the angular momentum of low attractor points and/or by drivinggrains to new high attractor points.

Radiative torques alignment in the presence of pinwheel torques