INTERSTELLAR REDDENING IN THE LOCAL BUBBLE AND LOOP I REGION: INSIGHT FROM STRÖMGREN PHOTOMETRY ANALYSIS AND THREE-DIMENSIONAL MODELING

Abstract

The Sun is located inside an extremely low density region called the Local Bubble (LB). Although they have been studied through a large variety of techniques, the contours of its neutral boundary, defined by a dense wall of interstellar gas and dust, are still an open issue. Our aim is to determine the interstellar reddening in the LB region by means of Stromgren photometry, validating the conclusions through a comparison with high-resolution three-dimensional (3D) hydrodynamical models of the Local and Loop I bubbles' formation and evolution. We have obtained color excesses and distances using the uvbyHβ data of the General Catalogue of Photometric Data, complemented by 820 stars from more recent catalogs, for b ≤ 60°. A set of restrictive exclusion criteria has been applied to eliminate E(b – y) values inappropriate for the study of the interstellar medium (ISM). The final sample has 8492 stars located up to 500 pc from the Sun. Our main results are as follows: (1) the large-scale distribution of the interstellar dust in the LB is highly inhomogeneous; (2) on the Galactic plane, E(b – y) ≥ 0040 is observed at a distance of d ≈ 80-100 pc from l ≥ 270° until l ≤ 45°; (3) the color excess suggests that there are many tunnels and holes in the LB wall; and (4) there is a clear correlation between E(b – y) and the spatial density distribution of the interstellar gas inferred from the simulations.