A&A 371, 1012-1017 (2001)
DOI: 10.1051/0004-6361:20010451

Magnetic field structure in the outer OH maser envelope of VX Sagittarii

M. Szymczak¹, R. J. Cohen² and A. M. S. Richards<sup>2

1</sup>  Torun Centre for Astronomy, Nicolaus Copernicus University, ul. Gagarina 11, 87100 Torun, Poland
²  Jodrell Bank Observatory, University of Manchester, Macclesfield, Cheshire, SK11 9DL, UK

(Received 29 January 2001 / Accepted 15 March 2001 )

Abstract
The OH 1612 MHz maser transition from the supergiant star VX Sgr has been imaged in all Stokes parameters using MERLIN. Numerous elliptically polarised components are distributed in a roughly symmetric envelope of a size similar to that measured in total maser intensity. The polarisation vectors are generally tangential to the circumstellar envelope, indicating a globally ordered magnetic field at the distance of about 1400 au from the supergiant. It is suggested that a predominance of projected radial magnetic lines and a displacement between the red- and blue-shifted parts of the envelope can be explained with a dipole field tilted at 20-30 to the line of sight.

Key words: masers -- polarisation -- stars: magnetic fields -- stars: circumstellar matter -- stars: supergiants -- stars: individual: VX Sgr

Offprint request: M. Szymczak, msz@astro.uni.torun.pl

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© ESO 2001

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