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Session 44 - The Local Diffuse ISM.
Display session, Tuesday, June 11
We present preliminary results of a study of small scale (500-20000 AU) structure in the cold diffuse ISM. We have observed the Na I absorption toward both components of 17 binary or common proper motion systems with the KPNO 0.9 m coude feed telescope and spectrograph at a velocity resolution of \approx 1 km/s. The stars range in spectral type from O6 to A3, and lie between 80 and 1300 pc from the Sun. The separation of the stars in the binaries ranges from \approx 450 AU to as large as \approx 21000 AU, with most of the sample being separated by between 1000 and 3000 AU. In all of the observed binaries, differences were seen in the strength and/or structure of the interstellar Na I absorption profiles. In several cases, including \zeta CrB and HD 36408, components present in the spectrum of one member of the binary are completely absent in the spectrum of the other. We infer that structure on small scales is quite common in the cold diffuse gas sampled by Na I absorption and make a first attempt at characterizing the spatial power spectrum of this clumpiness.
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