Worksheet 5 - Extracting window data to a structure (eis_getwindata)#
For many purposes it is useful to extract window data to a structure. This is done as follows:
IDL> wd=eis_getwindata(filename,195.12,/refill)
where filename is that of the calibrated (level-1) data file. Note that the routine automatically looks in the same directory for the error file and reads this too.
Specifying 195.12 means the routine will find the window that contains the wavelength 195.12 Å (the strong Fe XII line).
The /refill option implements an interpolation method that assigns a realistic intensity and error value to missing data points. It is described in detail in EIS Software Note #13
.
The returned structure contains an intensity array and error array, as well as a lot of useful auxiliary information. To see the structure tags do:
IDL> help,wd,/str
note that the HDR tag contains the complete header structure for the data-set.
Exercise #
- Use the IDL command ploterr to plot out a spectrum for spatial pixel (70,70) from the data window with overplotted error bars.
- Create an intensity image from wd by summing in the wavelength direction (see Worksheet 2), and then plot the image. What do you notice about the image compared to that in Worksheet 2?
- Choose spatial pixel (70,70) and use the IDL GAUSSFIT routine to fit the spectrum (including errors); use a linear background, i.e., NTERMS=5. What is the intensity and width of the line? Are there any missing data for this line profile? If yes, what should you do about them?
- With the Fe XII 195 window, do the following:
IDL> plot_image,rebin(wd.int(*,*,20),80,256)
can you explain what is seen here?