Detection of small scale structure in metal lines at the extreme solar limb

Abstract

We describe a tangential limb spectrum at 5870 Å which geometrically probes the high photosphere through the low chromosphere. Velocity and brightness structures with sizes ranging from 500 to 1500 km are present in the stronger emission lines. Such structure is consistent between the Fe i and Ba ii lines, and emission knots in these lines coincide with continuum bright streaks. But no correlation is evident between structure in the He i D₃ line, emission in the Na i D₂ line, and emission in the Fe i and Ba ii lines as a group. Two classes of near-horizontal velocity structure are seen in the height range from 0 to 500 km above the limb: υ ⪝ 1 km s⁻¹ for the weaker metals and υ ∼ 7–10 km s⁻¹ for the Na i line. Differences in line opacity are suggested as the cause of the low correlation between the fine structure in the various lines.