Charting the Interstellar Magnetic Field causing the Interstellar Boundary Explorer (IBEX) Ribbon of Energetic Neutral Atoms

Abstract

The interstellar magnetic field (ISMF) near the heliosphere is a basic part of the solar neighborhood that can only be studied using polarized starlight. Results of an ongoing survey of polarized starlight are analyzed with the goal of linking the interstellar magnetic field that shapes the heliosphere to the nearby field in interstellar space. New results for the direction of the nearby ISMF, based on a merit function that utilizes polarization position angles, identify several magnetic components. The dominant interstellar field, B_pol, is aligned with the direction L,B= 36.2,49.0 (+/-16.0) degrees and is within 8 degrees of the IBEX Ribbon ISMF direction. Stars tracing B_pol have the same mean distance as stars that do not trace B_pol, but show weaker polarizations consistent with lower column densities of polarizing grains. The variations in the polarization position angle directions indicate a low level of magnetic turbulence. B_pol is found after excluding polarizations that trace a separate magnetic structure that apparently is due to interstellar dust deflected around the heliosphere. Local interstellar cloud velocities relative to the LSR increase with the angles between the LSR velocities and ISMF, indicating that the kinematics of local interstellar material is ordered by the ISMF. Polarization and color excess data are consistent with an extension of Loop I to the solar vicinity. Polarizations are consistent with previous findings of more efficient grain alignment in low column density sightlines. Optical polarization and color excess data indicate the presence of nearby interstellar dust in the BICEP2 field. Color excess E(B-V) indicates an optical extinction of A_V about 0.59 mag in the BICEP2 field, while the polarization data indicate that A_V is larger than 0.09 mag. The IBEX Ribbon ISMF extends to the boundaries of the BICEP2 region.