Tentative Identification of Interstellar Dust in Heliosphere Nose

Observations of polarization toward nearby stars in the upwind direction made by Tinbergen (1982) are consistent with an origin associated with interstellar dust grains entrained in interstellar magnetic fields wrapped around the heliosphere nose. The region of maximum polarization is centered around ecliptic coordinates (λ,β) = (295,0), corresponding to (l,b) = (20,–21). The direction of maximum polarization is offset along the ecliptic longitude by ∼35 from the heliosphere nose. An offset is also seen between the region with the best aligned dust grains, λ=281→330, and the inflowing interstellar dust grains observed by Ulysses and Galileo, and in this region polarization strength anti-correlates with ecliptic latitude. These offsets support an interpretation whereby the maximum polarization occurs in a direction perpendicular to the interstellar field lines, the region of consistent polarization angle shows the deflection of small grains, and the inflow of larger grains shows the undeflected grain population. An interstellar field direction towards l∼100, and inclined to the ecliptic by ∼60 would be consistent with these data. The offsets in the aligned dust direction, and separate upwind directions for inflowing dust, He, and H, are understood if the filtration factors for each species depend on gyroradius, so that observed upwind directions respond to heliosheath asymmetries introduced by the draped interstellar magnetic field. The presence of interstellar dust grains captured in the heliosheath represents a potentially important, but weak, large scale contamination of the cosmic microwave background signal. Subject headings: polarization, solar system: general, ISM: dust, cosmology: cosmic microwave background