Publication Date: 2014.
Magnetic fields in accretion disks play a dominant role during the star formation process but have hitherto been observationally poorly constrained. Field strengths have been inferred on T Tauri stars themselves and possibly in the innermost part of the accretion disk, but the strength and morphology of the field in the bulk of the disk have not been observed. Unresolved measurements of polarized emission (arising from elongated dust grains aligned perpendicular to the field) imply average fields aligned with the disks. Theoretically, the fields are expected to be largely toroidal, poloidal, or a mixture of the two, which imply different mechanisms for transporting angular momentum in the disks of actively accreting young stars such as HL Tau. Here we report resolved measurements of the polarized 1.25 mm continuum emission from HL Tau's disk. The magnetic field on a scale of 80 AU is coincident with the major axis (~210 AU diameter) of the disk. From this we conclude that the magnetic field inside the disk at this scale cannot be dominated by a vertical component, though a purely toroidal field does not fit the data well either. The unexpected morphology suggests that the magnetic field's role for the accretion of a T Tauri star is more complex than the current theoretical understanding.
Author affiliation: Stephens, Ian W. . Boston University, Institute for Astrophysical Research; Estados Unidos
Author affiliation: Looney, Leslie W. . University of Illinois, Urbana. Department of Astronomy; Estados Unidos
Author affiliation: Kwon, Woojin . Netherlands Institute for Space Research, Groningen; Países Bajos
Author affiliation: Fernandez Lopez, Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto Argentino de Radioastronomia (i); Argentina
Author affiliation: Hughes, A. Meredith . Wesleyan University. Van Vleck Observatory, Astronomy Department ; Estados Unidos
Author affiliation: Mundy, Lee G. . University of Maryland. Astronomy Department & Laboratory for Millimeter-wave Astronomy; Estados Unidos
Author affiliation: Crutcher, Richard M. . University of Illinois, Urbana. Department of Astronomy; Estados Unidos
Author affiliation: Li, Zhi Yun. University of Virginia. Astronomy Department; Estados Unidos
Author affiliation: Rao, Ramprasad . Academia Sinica. Institute of Astronomy and Astrophysics; Estados Unidos
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas