Astron. Astrophys. 333, L23-L26 (1998)

Letter to the Editor

Twisted magnetic field lines around protostars

J.S. Greaves and W.S. Holland

Joint Astronomy Centre, 660 N. A'ohoku Place, University Park, Hilo, Hawaii 96720, USA

Received 16 September 1997 / Accepted 26 February 1998

Abstract

Polarized dust emission from six star-forming cloud cores has been detected, at wavelengths of 450 to 1100 µm. The data are used to measure net magnetic field directions as a function of beam size, and in two sources the field is found to twist through very large angles (60- ). For the low-mass protobinary IRAS16293-2422, one field direction is along the circumbinary disk, while another is aligned between the two bipolar outflows. This is the first observational evidence of bent field lines around protostars. For the high-mass W75N source, the data indicate a centrally contracted field. The dust core occupies the most compressed part of the field, and the field lines are bent by large angles, .

In the highest angular resolution observations ( beam at 450 µm), the deduced magnetic field direction is parallel to the outflow axis, in all three sources observed. This suggests the highest-resolution observations may be tracing the components of the magnetic field that constrain the outflowing gas.

Key words: polarization stars: formation ISM: magnetic fields

Send offprint requests to: J.S. Greaves

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Contents

• 1. Introduction
• 2. Observations
• 3. Results
• 4. Discussion
  • 4.1. The magnetic field around IRAS16293-2422
  • 4.2. A model for W75N
  • 4.3. Magnetic collimation of outflows
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998
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