Observations of Active Region Loops with the EUV Imaging Spectrometer on Hinode

摘要

Previous solar observations have shown that coronal loops near 1 MK aredifficult to reconcile with simple heating models. These loops have lifetimesthat are long relative to a radiative cooling time, suggesting quasi-steadyheating. The electron densities in these loops, however, are too high to beconsistent with thermodynamic equilibrium. Models proposed to explain theseproperties generally rely on the existence of smaller scale filaments withinthe loop that are in various stages of heating and cooling. Such a frameworkimplies that there should be a distribution of temperatures within a coronalloop. In this paper we analyze new observations from the EUV ImagingSpectrometer (EIS) on \textit{Hinode}. EIS is capable of observing activeregions over a wide range of temperatures (\ion{Fe}{8}--\ion{Fe}{17}) atrelatively high spatial resolution (1\arcsec). We find that most isolatedcoronal loops that are bright in \ion{Fe}{12} generally have very narrowtemperature distributions ($\sigma_T \lesssim 3\times10^5$ K), but are notisothermal. We also derive volumetric filling factors in these loops ofapproximately 10%. Both results lend support to the filament models.