!!This is EIS Discussion Area page.\\


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!A Comment on Using  Fe XII 195 for Studying Nonthermal Widths and Doppler Shifts

Fe XII 195 is a core line and is present in almost every EIS study. It has been noted, however, that there is a subtle contribution of Fe XII 195.18 to the wing of the observed line profile. This component is density sensitive and can make an important contribution to the line in active regions. The intensity of this component is generally very small (<15% of the total), it does, however, alter the calculation of the line width and centroid. A two Gaussian fit can be performed on the observed line profile but it is necessary to constrain it. One scheme is to set the line widths of both components to be equal and to fix the difference between the two line centroids to be 0.06 Angstroms. This is not difficult to implement in MPFIT.

The following images illustrate the differences between a single Gaussian fit (top), a two Gaussian fit (middle), and a single Gaussian fit (bottom) to the Fe XII 192.394, which appears to be unblended. The single Gaussian fit suggests larger nonthermal widths and Doppler shifts in the active region than are seen in the two Gaussian fit or in the Fe XII 192.394 line.

[{Image src = 'compare_fits.jpg' width='600'}]

Here is an example profile fit. The image is the intensity in Fe XII 195.18.

[{Image src = 'display_fe_12_195_180.jpg' width='600'}]

A detailed discussion on this can be found in the following [paper|http://adsabs.harvard.edu/abs/2009A%26A...495..587Y] by Peter Young. Also note that you can view higher resolution images by looking at the "Attach" tab.

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!A Comment on the Temperature of Formation for Fe VIII

It has been noted that Fe VIII and Si VII rasters look nearly identical [(Young et al. 2007)|http://adsabs.harvard.edu/abs/2007PASJ...59S.857Y] but the  temperature of formation for the two ions are seperated by about 0.2 dex. This image illustrates this by comparing Mg, Si, and Fe images in this temperature range. These data suggest that the Fe VIII and perhaps Fe IX are formed at higher temperatures than suggested by the ionization balance calculations of [Mazzotta et al. (1998)|http://adsabs.harvard.edu/abs/1998A%26AS..133..403M].

[{Image src = 'compare_rasters.jpg' width='600'}]

Note that you can view higher resolution images by looking at the “Attach” tab. 

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!Deconvolving coronal features from the He II 256 blend

He II 256.32 is a self-blend of two He II lines and is also blended with four coronal lines. This section provides some information for those hoping to accurately extract the He II component from the blend.

* [Off-limb spectra|HeIIOffLimb]


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!Missing exposures and bright exposures

Since the change to S-band operations in 2008 it has been common to see missing exposures when forming rasters from EIS data. Another feature has been the appearance of anomalously bright exposures. The link below shows examples from one raster data-set.

[PRY_footpoints_HI2 raster on, 11-Dec-2009, 19:50|BadExposureExample]