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Linear polarization of hydroxyl masers in circumstellar envelope outer regions

Published online by Cambridge University Press:  24 July 2012

P. Wolak ,
M. Szymczak  and
E. Gérard
P. Wolak
Affiliation:
Toruń Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, 87-100 Toruń, Poland email: wolak@astro.uni.torun.pl
M. Szymczak
Affiliation:
Toruń Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, 87-100 Toruń, Poland email: wolak@astro.uni.torun.pl
E. Gérard
Affiliation:
GEPI, UMR 8111, Observatoire de Paris, 5 place J. Janssen, 92195 Meudon Cedex, France
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Abstract

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A recent polarimetric survey of OH masers in a large sample of AGB and post-AGB stars revealed widespread occurrence of polarized features. We made a statistical analysis of the polarization properties of this large data set. We discuss the alignment of polarization position angles between the extreme blue- and red-shifted parts of the 1612 MHz spectrum. The average polarization angle of OH masers from the opposite sides of the envelope agrees within 20° for 80% of the sources in the sample. For two objects monitored over ~6 years the polarization position angle at 1612 MHz is constant within measurement uncertainties: this suggests a stable and a very regular structure of the circumstellar magnetic fields. Alternatively, this could indicate a galactic origin of the field which may be amplified by the stellar wind in the outermost parts of the envelopes.

Keywords

masers – polarization – circumstellar matter – magnetic field – stars: AGB and post-AGB
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 8 , Symposium S287: Cosmic Masers - from OH to H0 , January 2012 , pp. 59 - 63
Copyright
Copyright © International Astronomical Union 2012

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