Main Objective: Coordinated EIS/IRIS observations focused on Fe XII lines in both instruments, as well as neighbouring Fe XI and XIII for diagnostics of the non-Maxwellian kappa-distributions and electron density.
Scientific Justification: This submission is a modified version of IHOP 343. The proposers are attempting to see if the Fe XII 192 / 1349 A ratio confirms the presence of non-Maxwellians in another AR with larger signal-to-noise than we got Del Zanna et al. (2022). This ratio is currently the best available diagnostic.
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This IHOP is proposed to acquire joint observations to probe the diagnostics for the non-Maxwellian distributions from Hinode/EIS and IRIS. The target will be a limb active region and this will be a Target-of-Opportunity (ToO) HOP.
We note that the previous IHOP 316 was run for multiple days. The data were analyzed, however we found that no IRIS Fe XII emission was present off-limb at the heights observable with the COMP instrument (i.e., about 40 arc sec above the limb). Therefore, we had no overlap between IRIS and EIS. Signal in IRIS at low heights at limb was present though. To ensure an overlap, the observations should be performed on an active region approaching the solar limb, partially covering the limb and AR core with both EIS and IRIS.
The assumption of a Maxwellian distribution is common in the analysis of solar spectra. However, this assumption may be incorrect if the emitting plasma is heated dynamically e.g. by nanoflares. A possible signature of such dynamic heating in the solar corona would be the presence of non-Maxwellian distributions. The kappa-distributions, characterized by a high-energy tail, have been diagnosed in a transient coronal loop observations made by EIS in Fe XI and Fe XII (Dudik et al. 2015, ApJ, 807, 123) and are also commonly observed in the solar wind (e.g. Maksimovic et al. 1997, Zouganelis 2008). Such distributions should result in an increase in the intensity of the coronal forbidden lines compared to the EUV ones (Dudik et al. 2014, A&A, 570, A124), an effect detectable by coordinated EIS and IRIS observations by using the Fe XII lines.
In order to disentangle the effect of kappa-distributions from the effects of the electron density and differential emission measure (DEM), observations of additional EUV lines by EIS are needed for density and DEM diagnostics. These additional lines can also be used for diagnostics of κ from EIS lines alone.
The proposers will examine data from SDO and STEREO-A to determine, ahead of an observing plan, whether the observations should go ahead, and at which position angle on the limb. Given this point in the solar cycle, however, active regions are still expected to be present. |
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