Observations of small-scale interstellar structure in dense atomic gas

We present high-resolution (R ∼ 170,000) Kitt Peak National Observatory coudé feed telescope observations of the interstellar K i l7698 line toward five multiple star systems with saturated Na i components. We compare the K i absorption-line profiles in each of the two (or three) lines of sight in these systems and find significant differences between the sight lines in three out of the five cases. We infer that the small-scale structure traced by previous Na i observations is also present in at least some of the components with saturated Na i absorption lines, and thus the small-scale structures traced by the neutral species are occurring at some level in clouds of all column densities. We discuss the implications of that conclusion and a potential explanation by density inhomogeneities.