SIMBAD references

We have detected 800µm polarization at the flux peak and positions around the outflow sources DR 21 and NGC 7538-IRS 11. For both sources the direction of the polarization vectors is extremely uniform and the dispersion is small. This implies that, within the reslution of our observations, the magnetic field is both uniform in direction and strong. The direction of the magnetic field around DR 21 does not appear to be aligned with either the direction of the outflow axis or the major axis of the submm circumstellar dust structure. For NGC 7538-IRS 11 the magnetic field is aligned with the outflow axis, implying that within the resolution of our observations (14 arcsec FWHM) the circumstellar magnetic field is poloidal. The direction of the molecular outflows, magnetic fields and dust ridges for both IRS 11 and its neighbour IRS1 (60 arcsec/0.9 parsec to the north) are in identical directions. As IRS1 and IRS 11 are linked by an arm of submm emission and form an elongated dust ridge that is orthogonal to the ambient magnetic field of the NGC 7538 region, part of the cloud may have collapsed along the magnetic field lines to produce the core from which IRS1 and IRS 11 have formed. For both DR 21 and NGC 7538-IRS 11 the percentage polarization at the position of the flux peak is low compared to the surrounding points. This has been noted for several other outflow sources and is commonly referred to as a polarization `hole'. The most plausible explanation is a change in the magnetic field alignment in the vicinity of the outflow source. There is a marked increase in the observed percentage polarization from DR 21 at higher wavelengths. This implies the grain composition cannot be predominantly silicate, but instead is mainly graphite/metallic, and may require grains of different magnetic susceptibility or varying elongation to also be at different temperatures along the observed line of sight.