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S. Stanimirovic (UC Berkeley), J. M. Weisberg, Z. Pei, K. Tuttle, J. T. Green (Carleton College)
The presence of structure on AU-scales in the cold neutral medium was inferred by numerous VLBI absorption measurements and multi-epoch HI absorption measurements towards pulsars. Yet, the origin of these features has been a puzzle since their discovery in 1976. Observations suggest over-dense and over-pressured blobs of gas, being far from pressure equilibrium with the surrounding medium, but still frequently observed in the interstellar medium. To study properties of these features we have recently undertaken a multi-epoch HI absorption experiment, with the Arecibo telescope, towards six pulsars. Our observations show that the AU-sized structure is not ubiquitous in the interstellar medium and could be a rare phenomenon. The new HI data are used to address several theoretical models and learn about conditions that are most conducive to development and maintenance of the AU-size structure.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.