Using a Differential Emission Measure and Density Measurements in an Active Region Core to Test a Steady Heating Model

Abstract

The frequency of heating events in the corona is an important constraint on the coronal heating mechanisms. Observations indicate that the intensities and velocities measured in active region cores are effectively steady, suggesting that heating events occur rapidly enough to keep high temperature active region loops close to equilibrium. In this paper, we couple observations of Active Region 10955 made with XRT and EIS on Hinode to test a simple steady heating model. First we calculate the differential emission measure of the apex region of the loops in the active region core. We find the DEM to be broad and peaked around 3 MK. We then determine the densities in the corresponding footpoint regions. Using potential field extrapolations to approximate the loop lengths and the density-sensitive line ratios to infer the magnitude of the heating, we build a steady heating model for the active region core and find that we can match the general properties of the observed DEM for the temperature range of 6.3 < Log T < 6.7. This model, for the first time, accounts for the base pressure, loop length, and distribution of apex temperatures of the core loops. We find that the density-sensitive spectral line intensities and the bulk of the hot emission in the active region core are consistent with steady heating. We also find, however, that the steady heating model cannot address the emission observed at lower temperatures. This emission may be due to foreground or background structures, or may indicate that the heating in the core is more complicated. Different heating scenarios must be tested to determine if they have the same level of agreement.

MHD modeling of coronal loops: the transition region throat

“…Then, we heated our loop with a large-scale slowly-changing (quasi-steady) heating (e.g., Winebarger et al 2011;Warren et al 2010a,b). We focussed on the structure of the moss in active regions, i.e., the thin loop layers at temperature ranging between about 0.1 MK and 1 MK, that are generally interpreted as the footpoints of hotter loops.…”

“…Our scope is to study what level of variability is expected in the moss at the base of a high-pressure loop. We check, for instance, whether the loop heating drives variations in the loop and in particular of its cross section in the transition region, by considering the situation in which the loop is heated as smoothly as possible (e.g., Winebarger et al 2011;Warren et al 2010a,b).…”

The multi-thermal emission in solar active regions

“…Tripathi et al 2011;Warren et al 2012) but did not analyse in detail the thermal structure of the 3 MK loops. Winebarger et al (2011) calculated the differential emission measure (DEM) of the apex region of the hot core loops, and found the DEM to be broad and peaked around 3 MK.…”

“…Various studies on moss emission have been performed, to try and gain an insight into the physics of the 3 MK loops (see, e.g. Tripathi et al 2010Tripathi et al , 2012Winebarger et al 2011). We will discuss moss characteristics in a separate paper, but note that any measurement of coronal structures needs to avoid regions where moss is present.…”

Doppler shift of hot coronal lines in a moss area of an active region

“…However, in the case of hot coronal loops, there is observational support for both steady heating (Antiochos et al 2003;Warren et al 2008Warren et al , 2010Winebarger et al 2008Winebarger et al , 2011) and impulsive heating (Tripathi et al 2010b(Tripathi et al , 2011Bradshaw & Klimchuk 2011;Viall et al 2012). Because of the unresolved nature of hot coronal loops (Tripathi et al 2009) it is not possible to isolate a single loop and study its characteristics.…”