Astrophys. J., 814, 112 (2015/December-1)
Charting the interstellar magnetic field causing the interstellar boundary explorer (IBEX) ribbon of energetic neutral atoms.
FRISCH P.C., BERDYUGIN A., PIIROLA V., MAGALHAES A.M., SERIACOPI D.B., WIKTOROWICZ S.J., ANDERSSON B.-G., FUNSTEN H.O., McCOMAS D.J., SCHWADRON N.A., SLAVIN J.D., HANSON A.J. and FU C.-W.
Abstract (from CDS):
The interstellar magnetic field (ISMF) near the heliosphere is a fundamental component of the solar galactic environment that can only be studied using polarized starlight. The results of an ongoing survey of the linear polarizations of local stars are analyzed with the goal of linking the ISMF that shapes the heliosphere to the nearby field in interstellar space. We present new results on the direction of the magnetic field within 40 pc obtained from analyzing polarization data using a merit function that determines the field direction that provides the best fit to the polarization data. Multiple magnetic components are identified, including a dominant interstellar field, BPOL, that is aligned with the direction l, b = 36.°2, 49.°0 (±16.°0). Stars tracing BPOL have the same mean distance as stars that do not trace BPOL, but show weaker average polarizations consistent with a smaller column density of polarizing material. BPOL is aligned with the ISMF traced by the IBEX Ribbon to within 7.6–7.6+14.9 degrees. The variations in the polarization position angle directions derived from the data that best match BPOL indicate a low level of magnetic turbulence, ∼9°±1°. The direction of BPOL is obtained after excluding polarization data tracing a separate magnetic structure that appears to be associated with interstellar dust deflected around the heliosphere. The velocities of local interstellar clouds relative to the Local Standard of Rest (LSR) increase with the angles between the LSR velocities and BPOL, indicating that the kinematics of local interstellar material is ordered by the ISMF. The Loop I superbubble that extends close to the Sun contains dust that reddens starlight and whose distance is determined by the color excess E(B - V) of starlight. Polarizations caused by grains aligned with respect to BPOL are consistent with the location of the Sun in the rim of the Loop I superbubble. An angle of 76.827.6_+23.5 between BPOL and the bulk LSR velocity the local interstellar material indicates a geometry that is consistent with an expanding superbubble. The efficiency of grain alignment in the local interstellar medium has been assessed using stars where both polarization data and hydrogen column density data are available. Nearby stars appear to have larger polarizations than expected based on reddened sightlines, which is consistent with previous results, but uncertainties are large. Optical polarization and color excess E(B - V) data indicate the presence of nearby interstellar dust in the BICEP2 field. Color excess E(B - V) indicates an optical extinction of AV> 0.6 in the BICEP2 field, while the polarization data indicate that AV> 0.09 mag. The IBEX Ribbon ISMF extends to the boundaries of the BICEP2 region.
dust, extinction - ISM: clouds - ISM: magnetic fields - polarization - Sun: heliosphere
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