Magnetic Structure of a Dark Bok Globule

Abstract

The thermal dust continuum emission at 848 ≠≠mu;m from the globule CB 068, a Class 0 young stellar object (YSO), reveals strong linear polarization percentage values (up to 11%) in two polarized-intensity regions located on either side of the center, away from the twin CO outflows. At the 5% polarized intensity level, the two highly polarized regions have a radial separation of 0.01 pc from the center of the Bok globule. The two polarized regions are located on either side of the axis of the twin CO outflows, with polarization contours paralleling the outflows. The linear polarization orientation leads us to deduce that, in the inner part of the polarized-intensity regions, the electric field vector roughly follows the boundary of a pseudodisk or bar (the pseudodisk or bar was previously detected both in dust and in ammonia emission). The linear polarization orientation, within a radius of 0.03 pc, can be matched roughly to an infalling halo-to-disk magnetic field morphology, excluding the regions of the external envelope and near the CO outflows. On a 0.04 pc scale, our model predictions for CB 068 give a pseudodisk diameter of about 8800 AU. We predict a magnetic field strength (over 0.03 pc) of about 150 ≠≠mu;G, which comes about from the Chandrasekhar-Fermi method (via the ratio of the line of sight velocity dispersion to the polarization angle dispersion).