The first set of IRIS MgII h and k spectral feature data is available here. The ZIP file is here.

 

The input calibrated data can be accessed here.

 

The singly ionized Magnesium h and k lines are a source of strong ultraviolet emission in the spectrum of the sun. Each of these lines has features in their profiles that have been identified as k1r, k2r, k3, k2v, k1v, h1r, h2r, h3, h2v, and h1v. The measurement of their wavelengths, intensities, and spacial locations is the purpose of this project. The k1r, k1v, h1r, and h1v features are not included in this current project.

 

We start with a portion of the sun that is being observed in 'Sit-and-Stare' mode (see Figure 1) at a particular time. Different data sets may have a different time interval between successive images/spectra. In this figure, the thin black vertical line is the entrance slit for the spectrograph. Notice that the slit intersects a sunspot about 2/3 of the way from the bottom of the image.

 

 

Figure 1

 

 

The spectrograph produces spectra at many different wavelength bands of interest, one of them being a band that covers the Mg II k and h lines, which are at approximately 2796.4A and 2803.5A respectively. Figure 2 shows a typical h spacial-spectrum. The x-axis corresponds to wavelength and the y-axis correponds to spacial location along the slit.

 

 

 

Figure 2

 

 

Figure 3 shows the identified spectral line features. The red, green, and blue points identify the h2r, h3, and h2v features, respectively. The x-axis is wavelength (in angstroms) and the y-axis is the number of vertical arcseconds away from the center of the sun. Compare this to the input data (Figure 2) and you'll see that the algorithm is generally doing a fairly good job at feature identification.

 

Figure 3

 

 

Figure 4 shows a typical line profile for the h line, identifying the three features that will be measured. Figure 5 is the same data, but zoomed in to show just the spectral features and their calculated pixel positions.

 

Figure 4

 

 

 

 

Figure 5

 

 

The algorithm scans the profile and calculates the difference in intensities between adjactent points. When the difference flips between a positive difference and a negative difference, a peak has been found. When the difference flips from negatice to positive, a trough has been found. The exact location where the difference has a value of zero is the location of the peak or the trough. Figure 6 shows the differences. The black dots indicate where the differences are zero. There is a 1/2 pixel offset between Figure 5 and Figure 6 values because the intensity differences are measured from the "centers" of the pixels while the intensities themselves are measured from the "edges" of the pixels.

 

Figure 6

 

 

Because of various factors, not all line features can be measured. These features disappear, for example, in the location of the sunspot. This algorithm is looking for a peak-trough-peak sequence and will fail proper identification if this sequence is not encountered (for instance if it finds a trough before the first peak, or if just a single peak is found).

 

Once the pixel location of the peak or trough has been calculated, it is translated into an spacial offset (in arcseconds away from the center of the sun) and wavelength (in angstroms), by using the "CRVAL1" and "CDELT1" metadata values provided in the FITS headers. The intensity of the peak or trough is also measured and reported.

 

This is done separately for the k and h lines.

 

Currently, the software will only work with 'Sit-and-Stare' input data.