Context : SiO maser emission occurs in the extended atmosphere of evolved stars and can be studied at high angular resolution .
As compact , high brightness components they can be used as important tracers of the dynamics at distances close to the central star .
The masers also serve as probes of the evolutionary path from spherically symmetric AGB stars to aspherical PNe .
Very long baseline interferometry ( VLBI ) observations of Mira variables indicate that SiO masers are significantly linearly polarized with linear polarization fraction up to 100 \% .
However , no information is available at high angular resolution for SiO masers in higher mass loss OH/IR stars .
Theory indicates a different SiO pumping mechanism in higher mass loss evolved stars .

Aims : We extend the VLBI SiO maser studies to OH/IR stars .
The observations enable us to understand the SiO pumping mechanisms in higher mass loss evolved objects and compare those with Mira variables .
Additionally , polarimetric observations of SiO masers help us to understand the magnetic field strength and morphology and to distinguish between conflicting polarization theories .

Methods : The 43 GHz SiO maser observations of the OH/IR star OH 44.8-2.3 were performed with the VLBA in full polarization spectral line mode .
Auxiliary EVLA observations were performed to allow for the absolute calibration of the polarization angle .
The Zeeman splitting was measured by cross correlating the right and left circular polarization spectra as well as the S-curve fitting .
Additionally , we analyzed the 1612 MHz OH maser observations of OH 44.8-2.3 from the VLA archive .

Results : The SiO masers of OH 44.8-2.2 form a ring located at \sim 5.4 AU around the star .
The masers appear to be highly linearly polarized with fractional linear polarization up to 100 \% .
The linear polarization vectors are consistent with a dipole field morphology in this star .
We report a tentative detection of circular polarization of \sim 0.7 \% for the brightest maser feature .
The magnetic field measured for this feature corresponds to 1.5 \pm 0.3 G. Additionally , the distribution of the 1612 MHz OH maser emission could indicate an elongated morphology .

Conclusions :