Polarisation of Class II Methanol Masers

We have used the University of Tasmania Mt Pleasant 26-m radio telescope to investigate the polarisation characteristics of a sample of strong 6.7GHz methanol masers, the first spectral line polarisation observations to be undertaken with this instrument. As part of this process we have developed a new technique for calibrating linear polarisation spectral line observations. This calibration method gives results consistent with more traditional techniques, but requires much less observing time on the telescope. We have made the first polarisation measurements of a number of 6.7GHz methanol masers and find linear polarisation at levels from a few to 10% in most of the sources we observed, consistent with previous results. We also investigated the circular polarisation produced by Zeeman splitting in the 6.7GHz methanol maser G9.62þ0.20 to get an estimate of the line of sight magnetic field strength of 35 7mG. Additional keywords: masers — polarisation Received 2011 June 17, accepted 2011 September 12, published online 2011 October 26