First Detection of Submillimeter Polarization from T Tauri Stars

We report a first detection of polarization of the 850 mu m continuum emission from two T Tauri stars (TTSs), GM Aur and DG Tau. These are both single and classical TTSs. The emission mostly comes from the compact (r < 100 AU) accretion disks. The polarization (at similar to 3% level at 3 sigma) is interpreted in terms of thermal emission by magnetically aligned dust grains in the disk. Thus these submillimeter polarizations probe the magnetic field structure in the disk, while the previously reported millimeter/submillimeter polarizations of protostars and the transitional objects from the protostars to TTSs trace the magnetic fields in the larger envelope region. In both TTSs, the direction of the magnetic field inferred from our submillimeter polarizations is parallel to the plane of the compact dust disk measured by interferometric observations, suggesting the dominance of a toroidal magnetic field component in the disk. The magnetic evolution of the circumstellar environments is discussed, as well as the constraints on the MHD models of the jets and outflows from young stellar objects.