Open a Spectrum...
A spectrum is similar to a cut in a 2D image. If you open a file that corresponds to a 1D spectrum (using the tool "Open"), you get such an image
If you select a straight horizontal line along this image (at any vertical position), and ask to "plot the profile", you end up with the following spectrum (it has been stretched to allow a comparison with the 2D image) : dark band in 2D are related to "absorption lines", i.e. a serie of consecutive pixels with lower intensity
If you open the same file, but using the tool "Open a spectrum", the above window is opened directly.
Within this window, you may :
- see all values as an array using "List"
- "Save" those values as a text file
- "Copy" those values to paste them into a different document (spreadsheet or texte)
- modify the axis :
"Axis properties" allow to define the title, the min and max values to be displayed (this is recommanded rather than the use of a zoom)
"Set scale" : by default, the horizontal axis shows channel (i.e. number of pixel). Most files corresponding to a spectrum provide information about wavelength.
If you want to visualize this information, click "set scale". In the pop-up window, specify whether you want
channel / wavelength / frequency
velocity : velocity is defined through the Doppler effect, by comparing the observed wavelength to a reference wavelngth :
v=c(l/l0-1). If l >l0, v >0. So, you have to define a reference wavelength (in nanometers) if you want to visualize velocity
If you open a radio spectra created with EU-HOU MW, the reference wavelength is known. You just need to ask for a velocity scale.
- Create a "baseline", generally for radio spectra.
A pop-up window will ask you to define two intervals, and a fit to the data within those intervals is made as a polynome. You define the order of the polynome in the same window.
The fit, called a baseline, is displayer. You may then substract it to the observed spectrum.
You may "Reset" if you are not satisfied with the result.
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