Imaging the magnetic field in the atmosphere of TX Camelopardalis

Recent advances in very long baseline interferometry (VLBI) allow full interferometric imaging, in both linear and circular polarization, of the 43 GHz SiO maser emission in the immediate circumstellar environment of late-type stars. The SiO masers act as unique probes of the magnetic field in the near circumstellar environment and provide information on the stellar field morphology of distant stars at unprecedented angular resolution. This technique allows direct imaging of the magnetic field in the extended atmospheres of distant stars. We report on such observations of the nu = 1, J = 1-0 SiO maser emission toward the Mira variable TX Cam, finding a mean magnetic field strength of B sec theta similar to 5-10 G, where theta is the angle between the line of sight and the magnetic field, as well as evidence for an orderly field topology over significant portions of the maser shell. The implied field geometry and implications for possible mass-loss mechanisms are discussed.