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Session 122 - The Sun.
Oral session, Thursday, January 18
Salon del Rey South, Hilton

[122.05] Dark Threads and the Coronal Temperature Structure

L. J. November (National Solar Observatory)

High spatial resolution white-light coronal observations from the eclipse of July 11 1991 taken with the 3.6 m Canada-France-Hawaii Telescope on Mauna Kea are the best ever achieved because of the unique opportunity of observing the totally eclipsed sun with a large aperture telescope. Fine relatively dark and bright threads are found in the range of sizes of 1-5 Mm. The relative electron-density depletion and enhancement required to explain the observed thread contrast, assuming that they are isolated cylindrically symmetric structures, is found to be 100threads are fully evacuated. They appear to trace out field lines and probably lie in current sheets. The threads probably indicate directly the presence of non force-free magnetic fields requiring approximately 1 gauss strength to produce their observed contrast. Dark threads having nearly zero internal gas pressure must map the radial variation of the external gas pressure and ambient magnetic field strength. Their radial diameter variation must follow the gas pressure variation near the beta 1 level of the low corona, and the ambient field higher up where the beta is less than 1. If dark threads are constrained from expansion, they will impose an isobaric condition on the ambient which leads to a rapid temperature increase in a hydrostatic corona in thermodynamic balance.

Program listing for Thursday