Optical Polarization Mapping toward the interface between the Local
  Cavity and Loop I
  The Sun is located inside an extremely low density and quite irregular volume
of the interstellar medium, known as the Local Cavity (LC). It has been widely
believed that some kind of interaction could be occurring between the LC and
Loop I, a nearby superbubble seen in the direction of the Galactic Center. As a
result of such interaction, a wall of neutral and dense material, surrounded by
a ring shaped feature, would be formed at the interaction zone. Evidence of
this structure was previously observed by analyzing the soft X-ray emission in
the direction of Loop I. Our goal is to investigate the distance of the
proposed annular region and map the geometry of the Galactic magnetic field in
these directions. On that account, we have conducted an optical polarization
survey to 878 stars from the Hipparcos catalogue. Our results suggest that the
structure is highly twisted and fragmented, showing very discrepant distances
along the annular region: approximately 100 pc to the left side and 250 pc to
the right side, independently confirming the indication from a previous
photometric analysis. In addition, the polarization vectors' orientation
pattern along the ring also shows a widely different behavior toward both sides
of the studied feature, running parallel to the ring contour in the left side
and showing no relation to its direction in the right side. Altogether, these
evidence suggest a highly irregular nature, casting some doubt on the existence
of a unique large-scale ring-like structure.
