2008/08/24 by Harry P. Warren, Ignacio Ugarte-Urra, Ignacio Ugarte‐Urra +4 · 5 citations
Biochemistry, Genetics and Molecular Biology · Physics and Astronomy · #Geomagnetism and Paleomagnetism Studies #Solar and Space Plasma Dynamics #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/592960
Submitted to ApJL
arxiv created 2008/08/24 · openalex publication_date 2008/09/16 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/01
Previous solar observations have shown that coronal loops near 1 MK are difficult to reconcile with simple heating models. These loops have lifetimes that are long relative to a radiative cooling time, suggesting quasi-steady heating. The electron densities in these loops, however, are too high to be consistent with thermodynamic equilibrium. Models proposed to explain these properties generally rely on the existence of smaller scale filaments within the loop that are in various stages of heating and cooling. Such a framework implies that there should be a distribution of temperatures within a coronal loop. In this paper we analyze new observations from the EUV Imaging Spectrometer (EIS) on Hinode . EIS is capable of observing active regions over a wide range of temperatures (Fe VIII-Fe XVII) at relatively high spatial resolution (1''). We find that most isolated coronal loops that are bright in Fe XII generally have very narrow temperature distributions (σ T ≲ 3 × 10 5 K), but are not isothermal. We also derive volumetric filling factors in these loops of approximately 10%. Both results lend support to the filament models.