EDP Sciences

Vol. 611
In section 6. Interstellar and circumstellar matter

Large Interstellar Polarisation Survey. II. UV/optical study of cloud-to-cloud variations of dust in the diffuse ISM

by R. Siebenmorgen, N.V. Voshchinnikov, S. Bagnulo, et al. A&A 611, A5


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The variance of magnetic field strengths and structures is a fundamental issue in the structure of the diffuse interstellar medium. Although Zeeman measurements and infrared polarization provide a picture of the dense phase, the translucent medium remains elusive. This study is a comprehensive survey of approximately 50 lines of sight, using very high resolution UV and optical spectroscopy (resonance transitions for velocity and density information) and optical polarization measurements to decompose the contributors along the lines of sight. In the majority of cases, the contributors are composite and clouds can be separated in velocity and extinction contributions. A substantial fraction, however, are single clouds (about 15% of the sample). Unsurprisingly, the polarization is more randomized with more line-of-sight contributors, but the exceptional detail also makes this study a warning regarding interpretation of single-direction measurements of dust properties.