Probing Small-Scale Interstellar Structure At High Column Densities

Details Probing Small-Scale Interstellar Structure At High Column Densities Probing Small-Scale Interstellar Structure At High Column Densities

Feb 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000noao.prop..160l&link_type=abstract

NOAO Proposal ID #2000A-0160

Computer Science

Scientific paper

We propose to obtain very high resolution (~ 1.7 km s^- 1) observations of interstellar K I absorption toward the components of 5 multiple star systems as part of an ongoing program to more thoroughly understand recent evidence of ubiquitous small-scale structure in the diffuse ISM. Based upon KPNO Coude observations, Watson & Meyer (1996) have found interstellar Na I line profile variations toward 17 out of 17 binaries, indicative of ISM structure on scales of 500 to 29,000 AU. Using KPNO Coude Feed measurements of interstellar K I line profiles, Lauroesch & Meyer (1999) detected significant differences between components of multiple star systems in 3 out of 5 cases. However, Na I cannot be used to trace structure at high column densities, due to line saturation. Given its lower cosmic abundance, K I provides a useful probe of high column density sightlines. These differences suggest that the small- scale structure traced by Na I for low column density sightlines is present at some level in clouds of all column densities. However, the current sample size is too small for statistical analyses of the characteristics of structure and its variations. Our proposed observations are designed to supplement the undersampled high column density regime with systems previously selected, but not observed due to poor weather. Observations of these systems will double the size of the sample, allowing us to refine our conclusions about the presence of variations at various column densities and hence the mass fraction of the interstellar material involved.

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