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This paper presents a component-level comparison of the polarized v=1 J =1-0,v=2 J=1-0 and v=1 J=2-1 SiO maser emission towards the supergiant star VY CMaat milliarcsecond-scale, as observed using the VLBA at $\lambda=7$mm and$\lambda=3$mm. An earlier paper considered overall maser morphology andconstraints on SiO maser excitation and pumping derived from these data. Thegoal of the current paper is to use the measured polarization properties ofindividual co-spatial components detected across multiple transitions toprovide constraints on several competing theories for the transport ofpolarized maser emission. This approach minimizes the significant effects ofspatial blending. We present several diagnostic tests designed to distinguishkey features of competing theoretical models for maser polarization. The numberof coincident features is limited by sensitivity however, particularly in thev=1 J=2-1 transition at 86 GHz, and deeper observations are needed. Preliminaryconclusions based on the current data provide some support for: i)spin-independent solutions for linear polarization; ii) the influence ofgeometry on the distribution of fractional linear polarization with intensity;and, iii) $\pi/2$ rotations in linear polarization position angle arising fromtransitions across the Van Vleck angle ($\sin^2{\theta}=2/3$) between the maserline-of-sight and magnetic field. There is weaker evidence for severalenumerated non-Zeeman explanations for circular polarization. The expected 2:1ratio in circular polarization between J=1-0 and J=2-1 predicted by standardZeeman theory cannot unfortunately be tested conclusively due to insufficientcoincident components.

monthly notices of the royal astronomical society

Simultaneous VLBA polarimetric observations of the v=$\{$1,2$\}$ J=1-0  and v=1, J=2-1 SiO maser emission toward VY CMa II: component-level  polarization analysis