Isothermal and Multithermal Analysis of Coronal Loops Observed With Atmospheric Imaging Assembly. Ii. 211 Å Selected Loops

Abstract

An important component of coronal loop analysis involves conflicting results on the cross-field temperature distribution. Are loops isothermal or multithermal? The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory was designed in part to answer this question. AIA has a series of coronal filters that peak at different temperatures and cover the entire active region temperature range. These properties should make AIA ideal for multithermal analysis, but recent results have shown that the response functions of two of the filters, AIA 94 and 131 Å, are missing a significant number of low-temperature emission lines. Here we analyze coronal loops from several active regions that were chosen in the 211 Å channel of AIA, which has a peak response temperature of log T = 6.3. The differential emission measure (DEM) analysis of the 12 loops in our sample reveals that using data from the 131 Å AIA filter distorts the results, and we have no choice but to do the analysis without these data. The 94 Å data do not appear to be as important, simply because the chosen loops are not visible in this channel. If we eliminate the 131 Å data, however, we find that our DEM analysis is not well constrained on the cool temperature end of six of our loops. The information revealed by our 211 selected loops indicates that additional atomic data are required in order to pin down the cross-field temperature distribution.

Differential Emission Measure Analysis of Multiple Structural Components of Coronal Mass Ejections in the Inner Corona

“…Since the plasma is prohibited from moving across magnetic field lines, the energy released by magnetic reconnection is difficult to transfer into the CME LF. Therefore, during the magnetic reconnection, the CME flux rope is heated but the LF remains about the same temperature as the quiet coronal loops (e.g., T ∼ 1.0-3.0 MK; Schmelz et al 2010Schmelz et al , 2011aSchmelz et al , 2011b.…”

“…Finally, we note that a cool line component was missing in the old response function of AIA 94 Å passband (Foster & Testa 2011;Schmelz et al 2011b) and there were also concerns about the accuracy of the 131 Å response function (Schmelz et al 2011b). We use the revised response functions (updated on 2012 January 30), in which the cool lines have been added to 94 and 131 Å passbands, to avoid the issue of the missing cool line component.…”

“…In this work, we use the "xrt_dem_iterative2.pro" routine in SSW package to compute the DEM. This code was originally designed for Hinode/X-ray Telescope data Weber et al 2004), and here is modified slightly to work with AIA data (see also Schmelz et al 2010Schmelz et al , 2011aSchmelz et al , 2011bWinebarger et al 2011). For more details and tests of this method, see the Appendix.…”

On the Origin of the Extreme-Ultraviolet Late Phase of Solar Flares

“…Using all six coronal passbands of AIA images, we measure the EM of the late phase loop arcade and derive the electron density; it is found that the density is ∼(2-10) × 10 9 cm −3 for the first event and ∼(4-10) × 10 9 cm −3 . Note that a detailed discussion of the EM method is beyond the scope of this paper, and one can refer to the recent studies of Schmelz et al (2011) andCheng et al (2012) for details. In any case, our density estimation is semiquantitative, which is relatively insensitive to the EM models used.…”

The Cold Shoulder: Emission Measure Distributions of Active Region Cores

“…We also used the ionization balance calculations of Bryans et al (2009) We use two different EMD methods in our multithermal analysis. The first, DEM_manual (Schmelz et al 2011a(Schmelz et al , 2011c, is a forward folding technique with a manual manipulation of the EMD. The best fit is determined from a χ 2 minimization of the differences between the observed and predicted line fluxes.…”