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[127.01] The Local Bubble's O VI Resonance Line Emission Challenges Expectations

R. L. Shelton (The Johns Hopkins University)

Based on its 1/4 keV X-ray emission, the Local Bubble surrounding the solar neighborhood is thought to be a large (~70 pc) bubble of very highly ionized gas. Whether it is a 10⁶ K bubble wrapped in a cooler (few times 10⁵ K) transition zone or a tepid, overionized bubble, the Local Bubble is thought to contain a large column density of O VI ions and to radiate strongly in the O VI resonance lines. However, our observations place very tight upper limits on its O VI resonance line intensity (2 sigma values of 420 and 540 photons/s/cm²/sr in the 1032 and 1038 Angstrom lines, respectively). The resulting upper limit on the doublet intensity is far less than that expected from the most current models of the Local Bubble. The disagreement raises fundamental questions about the physics of transition zones in the first type of model and raises concerns about the ionization state in the second type of model.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.