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 of 878 stars from the Hipparcos catalog. Our results suggest that the structure is highly twisted and fragmented, showing very discrepant distances along the annular region: approximate to 100 pc on the left side and 250 pc on 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 on the left side and showing no relation to its direction on the right side. Altogether, these evidences suggest a highly irregular nature, casting some doubt on the existence of a unique large-scale ring-like structure.