Magnetic field evolution in Bok globules

Using the Submillimeter Common-User Bolometer Array (SCUBA) at the James Clerk Maxwell Telescope (JCMT), we obtained submillimeter polarization maps of the Bok globules B 335, CB 230, and CB 244 at 850 μm. We find strongly aligned polarization vectors in the case of B 335 and CB 230, indicating a strong coupling of the magnetic field to the dust grains. Based on the distribution of the orientation and strength of the linear polarization we derive the magnetic field strengths in the envelopes of the globules: 134μG (B335), 218μG (CB230), and 257μG (CB244). In agreement with previous submillimeter polarization measurements of Bok globules we find polarization degrees of several percent decreasing towards the centers of the cores. Furthermore, we compare the magnetic field topology with the spatial structure of the globules, in particular with the orientation of the outflows and the orientation of the nonspherical globule cores. In case of the globules B 335 and CB 230, the outflows are oriented almost perpendicular to the symmetry axis of the globule cores. The magnetic field, however, is aligned with the symmetry axis of the prolate cores in the case of the Bok globules B 335 and CB 230, while it is slightly aligned with the outflow axis in the case of the Bok globules CB 26 and CB 54. We discuss the possibility that the different orientations of the magnetic field relative to the outflow directions reflect different evolutionary stages of the single globules. Subject headings: Magnetic fields — Polarization — ISM: individual objects: B 335, CB230, CB244 — ISM: magnetic fields — Submillimeter