This page (revision-12) was last changed on 27-Nov-2017 16:52 by Peter Young

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NarrowWorksheet6
NarrowWorksheet6

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At line 3 changed one line
Generally the EIS emission lines have a Gaussian shape and, by fitting a Gaussian function to the spectrum, one can derive line intensity, line width and velocity maps. The high sensitivity of EIS means that for many lines it is possible to perform good quality fits at each pixel in the image. The routine eis_auto_fit in Solarsoft takes the output from eis_getwindata (Worksheet 5) and fits a single Gaussian to each pixel in the image. It is called as
Generally the EIS emission lines have a Gaussian shape and, by fitting a Gaussian function to the spectrum, one can derive line intensity, line width and velocity maps. The high sensitivity of EIS means that for many lines it is possible to perform good quality fits at each pixel in the image. The routine eis_auto_fit in Solarsoft takes the output from eis_getwindata (Worksheet 5) and fits a single Gaussian to each pixel in the image. The calling procedure is:
At line 5 changed one line
IDL> eis_auto_fit, wd, fit, refwvl=195.12
IDL> eis_wave_corr, l1name, offset
IDL> eis_auto_fit, wd, fit, offset=offset
At line 7 changed one line
refwvl is used to specify a reference wavelength for the emission line, so that velocities can be calculated. Reference wavelengths for lines can be obtained from the CHIANTI database, e.g.,
The first command is used to determine the wavelength offset at each spatial pixel due to the tilt of the EIS slit and orbit variation of emission line centroids. Correcting for these effects yields a much more accurate velocity map.
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IDL> which_line,’fe_12’,195
The output from eis_auto_fit is an IDL structure called 'fit'. Intensity, velocity and line width arrays can be extracted from fit by doing:
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If a wavelength window contains more than one emission line, then it is possible to use a reduced wavelength range with the wvlpix= keyword. E.g., wvlpix=[194.9,195.4] to use only pixels between 194.9 and 195.4 Å.
int=eis_get_fitdata(fit,/int)
vel=eis_get_fitdata(fit,/vel)
wid=eis_get_fitdata(fit,/wid)
At line 19 removed one line
The results of the fitting process can be checked using the widget-based routine eis_fit_viewer:
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IDL> eis_fit_viewer, wd, fit
The top 3 graphic windows in the GUI show line intensity, line velocity and line width (FWHM). Note the vertical bands in the velocity window – this is due to the orbital variation of the lines on the detector (see Worksheet 7a).
With the ‘Zoom’ button depressed, the mouse can be used to draw a ‘rubber-band’ box to zoom into the images. With the ‘Pixel’ button depressed, the line profile from the selected pixel will be drawn in the bottom-left graphic window.
The bottom-right window shows a histogram of the selected images pixels for either intensity, velocity or line width.
This page (revision-12) was last changed on 27-Nov-2017 16:52 by Peter YoungTop