Measurements of the magnetic field geometry and strength in Bok globules

In order to study the influence and structure of the magnetic field in the early phases of low-mass star formation, we obtained polarization maps of t hree Bok globules at a wavelength of 850 mum, using the Submillimeter Commo n-User Bolometer Array at the James Clerk Maxwell Telescope. We observed th e following sources : CB 26, a globule with a nearly dispersed dense core c ontaining a source with a circumstellar disk; CB 54, a deeply embedded youn g stellar cluster; and DC 253-1.6 (CG 30), a protostellar double core. We f ind strongly aligned polarization vectors in the case of CB 26 and DC 253-1 .6, while the vector orientations in the case of CB 54 are more or less ran domly distributed. The degree of polarization, amounting to several percent , was found to decrease toward the center in each source. In the case of CB 54 and DC 253-1.6, the degree of polarization similarly depends on the cor responding intensity. Assuming dichroic emission by aligned nonspherical gr ains as the polarization mechanism, where the magnetic field plays a role i n the alignment process, we derive magnetic field strengths and structures from the observed polarization patterns. In the case of the double core DC 253-1.6, we discuss the correlation between the fragmentation process and t he magnetic field direction.