A SYSTEMATIC SURVEY OF HIGH-TEMPERATURE EMISSION IN SOLAR ACTIVE REGIONS

By H. Warren, A. Winebarger, D. Brooks. 2012

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The recent analysis of observations taken with the EUV Imaging Spectrometer and X-Ray Telescope instruments on Hinode suggests that well-constrained measurements of the temperature distribution in solar active regions can finally be made. Such measurements are critical for constraining theories of coronal heating. Past analysis, however, has suffered from limited sample sizes and large uncertainties at temperatures between 5 and 10 MK. Here we present a systematic study of the differential emission measure distribution in 15 active region cores. We focus on measurements in the “inter-moss” region, that is, the region between the loop footpoints, where the observations are easier to interpret. To reduce the uncertainties at the highest temperatures we present a new method for isolating the Fe xviii emission in the AIA/SDO 94 Å channel. The resulting differential emission measure distributions confirm our previous analysis showing that the temperature distribution in an active region core is often strongly peaked near 4 MK. We characterize the properties of the emission distribution as a function of the total unsigned magnetic flux. We find that the amount of high-temperature emission in the active region core is correlated with the total unsigned magnetic flux, while the emission at lower temperatures, in contrast, is inversely related. These results provide compelling evidence that high-temperature active region emission is often close to equilibrium, although weaker active regions may be dominated by evolving million degree loops in the core.

Subfields: Astronomy and Astrophysics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/81af5e17596a6b24668d74ebdfc8aed3e83544e0

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Citations in the corpus

THERMAL DIAGNOSTICS WITH THE ATMOSPHERIC IMAGING ASSEMBLY ON BOARD THE SOLAR DYNAMICS OBSERVATORY: A VALIDATED METHOD FOR DIFFERENTIAL EMISSION MEASURE INVERSIONS (2015, methodology): “If the aim were to accurately measure slopes of DEM curves in the high temperature range (e.g., for constraining coronal heating models), inversions with AIA data may not be the right approach (Warren et al. 2012, also find that slopes of DEMs in the high temperature bins have large uncertainties).”
The multi-thermal emission in solar active regions (2013, methodology): “A number of calcium lines are often used for emission measure purposes (Warren et al. 2012), however, a number of problems have been found here.”