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Paper: Optical Absorption Line Observations of Small Scale Interstellar Structure
Volume: 365, SINS — Small Ionized and Neutral Structures in the Diffuse Interstellar Medium
Page: 40
Authors: Lauroesch, J.T.
Abstract: Recent optical absorption line studies (primarily studying the NaI D lines) have provided convincing evidence for pervasive small-scale structure in the diffuse interstellar medium on scales of order 1000 AU through observations of members of multiple star systems and clusters. Such spectra reveal that absorption components change in strength, velocity, and even number from sightline to sightline. However, these variations do not imply that the interstellar medium consists of a multitude of very small cloudlets since the vast majority of components are seen toward all stars in a system. Instead it appears that these variations arise in what appear to be sheets of gas within which the physical conditions vary. Using temporal variations in interstellar absorption lines it has been found that in some cases there can be significant structure on AU scales. Our survey of 40 stars suggests that this phenomenon is not as pervasive as the variations noted on larger ( 1000 AU) scales. While the majority of the known variable sightlines are associated with the Orion-Eridanus H I shell, this phenomenon is not limited to that region.
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