LISM structure — Fragmented superbubble shell?

Abstract

Small scale structure in local interstellar matter (LISM) is considered. Overall morphology of the local cloud complex is inferred from Ca II absorption lines and observations of H I in white dwarf stars. Clouds with column densities ranging from 2–100 × 10¹⁷ cm⁻² are found within 20 pc of the Sun. Cold (50 K) dense (∼10⁵ cm⁻³) small (5–10 au) clouds could be embedded and currently undetected in the upwind gas. The Sun appears to be embedded in a filament of gas with thickness ≤0.7 pc, and cross-wise column density ≤ 2 × 10¹⁷ cm⁻². The local magnetic field direction is parallel to the filament, suggesting that the physical process causing the filamentation is MHD related. Enhanced abundances of refractory elements and LISM kinematics indicate outflowing gas from the Scorpius-Centaurus Association. The local flow vector and λ Sco data are consistent with a 4,000,000 year old superbubble shell at ∼−22 km s⁻¹, which is a shock front passing through preshock gas at ∼−12 km s⁻¹, and yielding cooled postshock gas at ∼−26 km s⁻¹in the upwind direction. A preshock magnetic field strength of 1.6 μG, and postshock field strength of 5.2 μG embedded in the superbubble shell, are consistent with the data.