Astronomy and Astrophysics, volume 309, 267-274 (1996/5-1)
The magnetic field structure around protostars. Submillimetre polarimetry of VLA 1623 and S 106-IR/FIR.
HOLLAND W.S., GREAVES J.S., WARD-THOMPSON D. and ANDRE P.
Abstract (from CDS):
We present 800µm polarization observations of the young low-mass candidate protostar VLA 1623, and of the high-mass young stellar object S 106-IR and its companion candidate protostar S 106-FIR. The polarized emission due to aligned dust grains has been used to derive the magnetic field direction around both sources. In the case of VLA 1623 we find that the field direction is almost exactly perpendicular to the extremely well-collimated CO outflow. This suggests that the large-scale magnetic field in the cloud cannot be responsible for the collimation of the outflow. However, the data may be consistent with a recent magneto-hydrodynamic model where the field follows stream lines through the central plane of a `cored apple' accretion structure. In S 106 our observations indicate a magnetic field along the dust lane connecting the IR/FIR sources, and perpendicular to the bipolar HII region. A model consistent both with these data, and previous Zeeman measurements, is presented, in which the large-scale magnetic field is poloidal, but is either twisted into a toroidal morphology, or highly `pinched-in', in the flattened dust lane. We also present a synopsis of recent submillimetre polarimetry observations of young disk/outflow sources. For high-mass objects, the data are consistent with super-critical collapse models, and there is evidence for varying degrees of field compression. There is also a correlation of net field orientation with source distance, which is explained by the inclusion of varying amounts of ambient cloud material within the telescope beam. For the few low-mass objects for which data is available, the polarization is less affected by ambient material, and there is some evidence that different outflow models may apply in different sources.
polarization - stars: formation - ISM: individual: ρ Oph - ISM: individual: S 106 (NAME SH 2-106 IR), (NAME SH 2-106 FIR) - ISM: magnetic fields - radio continuum: ISM
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