First detection of submillimeter polarization from T Tauri stars

We report a first detection of polarization of the 850 mu m continuum emiss ion 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 grain s in the disk. Thus these submillimeter polarizations probe the magnetic he ld structure in the disk, while the previously reported millimeter/submilli meter polarizations of protostars and the transitional objects from the pro tostars to TTSs trace the magnetic fields in the larger envelope region. In both TTSs, the direction of the magnetic field inferred from our submillim eter polarizations is parallel to the plane of the compact dust disk measur ed by interferometric observations, suggesting the dominance of a toroidal magnetic field component in the disk. The magnetic evolution of the circums tellar environments is discussed, as well as the constraints on the MHD mod els of the jets and outflows from young stellar objects.