The interstellar cloud surrounding the Sun: a new perspective
  Aims: We offer a new, simpler picture of the local interstellar medium, made
of a single continuous cloud enveloping the Sun. This new outlook enables the
description of a diffuse cloud from within and brings to light some unexpected
properties. Methods: We re-examine the kinematics and abundances of the local
interstellar gas, as revealed by the published results for the ultraviolet
absorption lines of MgII, FeII, and HI. Results: In contrast to previous
representations, our new picture of the local interstellar medium consists of a
single, monolithic cloud that surrounds the Sun in all directions and accounts
for most of the matter present in the first 50 parsecs around the Sun. The
cloud fills the space around us out to about 9 pc in most directions, although
its boundary is very irregular with possibly a few extensions up to 20 pc. The
cloud does not behave like a rigid body: gas within the cloud is being
differentially decelerated in the direction of motion, and the cloud is
expanding in directions perpendicular to this flow, much like a squashed
balloon. Average HI volume densities inside the cloud vary between 0.03 and 0.1
cm-3 over different directions. Metals appear to be significantly depleted onto
grains, and there is a steady increase in depletion from the rear of the cloud
to the apex of motion. There is no evidence that changes in the ionizing
radiation influence the apparent abundances. Secondary absorption components
are detected in 60% of the sight lines. Almost all of them appear to be
interior to the volume occupied by the main cloud. Half of the sight lines
exhibit a secondary component moving at about -7.2 km/s with respect to the
main component, which may be the signature of a shock propagating toward the
cloud's interior.
