Electric vector rotations of π/2 in polarized circumstellar SiO maser emission

A. J. Kemball, P. J. Diamond, L. Richter, I. Gonidakis, R. Xue

Research output: Contribution to journalArticlepeer-review


This paper examines the detailed sub-milliarcsecond polarization properties of an individual SiO maser feature displaying a rotation in polarization electric vector position angle of approximately π/2 across the feature. Such rotations are a characteristic observational signature of circumstellar SiO masers detected toward a number of late-type, evolved stars. We employ a new calibration method for accurate circular very long baseline interferometric polarimetry at millimeter wavelengths to present the detailed Stokes {I, Q, U, V} properties for this feature. We analyze the fractional linear and circular polarization as a function of projected angular distance across the extent of the feature and compare these measurements against several theoretical models proposed for sharp rotations of electric vector position angle in polarized SiO maser emission. We find that the rotation is most likely caused by the angle θ between the line of sight and a projected magnetic field crossing the critical Van Vleck angle for maser propagation. The fractional linear polarization profile ml (θ) is well fitted by standard models for polarized maser transport, but we find less agreement for the fractional circular polarization profile mc (θ).

Original languageEnglish (US)
Article number69
JournalAstrophysical Journal
Issue number1
StatePublished - Dec 10 2011


  • masers
  • polarization
  • stars: individual (TX Cam)
  • stars: magnetic field

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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