Hi-C Observations and the Structure of Coronal Loops
Abstract:Despite nearly four decades of study since the launch of Skylab, the physical structure of coronal loops remains an enigma. Loops are guided by the magnetic field and, in the common EUV emission lines, appear to be composed of stranded structures reminiscent of field lines. This stranded structure appears to have constant or nearly-constant width, at odds with naive understanding of flux tube behavior in a field gradient. Possible explanations range from physical solutions such as twisted magnetic structure or peculiar properties of separators and quasi-separators, to observation effects that invoke finite resolution or anisotropy of the field containing each strand. The uncertainty affects many aspects of basic coronal physics, because some of the possible explanations for stranded structure have strong implications for other mysteries such as the anomalously tall scale height of the EUV corona.
The Hi-C EUV images are the highest resolution coronal images to date, and offer new insights into the structure of coronal loops. We present an overview of research to date, show results from a detailed analysis of several dozen well-presented loops that are visible in the Hi-C data set, and speculate on the implications for the rest of the corona.