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Free access article

Issue A&A
Volume 448, Number 2, March III 2006
Page(s) 597 - 611
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20054275

A&A 448, 597-611 (2006)
DOI: 10.1051/0004-6361:20054275

The magnetic field in the star-forming region Cepheus A

from H $\mathsf{_2}$O maser polarization observations
W. H. T. Vlemmings1, P. J. Diamond1, H. J. van Langevelde2, 3 and J. M. Torrelles4

1  Jodrell Bank Observatory, University of Manchester, Macclesfield, Cheshire, SK11 9DL, UK
    e-mail: wouter@jb.man.ac.uk
2  Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
3  Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands
4  Instituto de Ciencias del Espacio (CSIC)-IEEC, C/ Gran Capitá, 2-4, 08034 Barcelona, Spain

(Received 29 September 2005 / Accepted 13 October 2005 )

Abstract
We present linear and circular polarization observations of the H2O masers in 4 distinct regions spread over 1 $\times$ 2 arcsec around the HW2 high-mass young stellar object in the Cepheus A star-forming region. We find magnetic fields between 100-600 mG in the central maser region, which has been argued to trace a circumstellar disk. The masers further from HW2 have field strengths between 30-100 mG. In all cases the magnetic field pressure is found to be similar to the dynamic pressure, indicating that the magnetic field is capable of controlling the outflow dynamics around HW2. In addition to several H2O maser complexes observed before, we also detect a new maser filament, $\simeq$1$\arcsec$ ($\simeq$690 AU) East of HW2, which we interpret as a shocked region between the HW2 outflow and the surrounding medium. We detect a linear polarization gradient along the filament as well as a reversal of the magnetic field direction. This is thought to mark the transition between the magnetic field associated with the outflow and that found in the surrounding molecular cloud. In addition to the magnetic field we determine several other physical properties of the maser region, including density and temperatures as well as the maser beaming angles.


Key words: star: formation -- masers -- polarization -- magnetic fields

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