8.2. Cloudlets in Filaments

Messinger et al. (1997) have studied the variations of linear polarization percentages and position angles at wavelengths from 0.36 µm up to 2.0 µm, of 3 stars located behind the filamentary Taurus Molecular Cloud-1, located way off the Galactic Plane. They assigned the observed variations to cloudlets (subclouds) located within the filament. Each cloudlet has a gas density ~ 10⁴ cm^-3, radius ~ 0.1 pc, gas temperature ~ 10 K, and a mass ~ 2M, and may harbor a site of low-mass star formation inside. They used a deconvolution technique, separating the Stokes parameters Q and U into a linear sum of cloudlets 1 and 2, to subtract a low-density foreground cloudlet 1 from the higher-density cloudlets 2 and 3, and thus obtain grain information inside each cloudlet. The data for the heavily reddeded star HD 29647 imply grains inside cloudlet 2 to be 1.3 times larger than grains outside (~ 0.1 µm), with icy mantles on the grains, and to have an internal magnetic field roughly perpendicular to the elongation of the overall filament TMC-1. The low-density filament has a magnetic field parallel to the galactic magnetic field outside the filament.