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 Background subtraction from spectra
   
Francesca
 07/16/2014 10:23AM (Read 1567 times)  
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Junior

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Registered: 06/01/2010
Posts: 15
Hi,

I am using the "background" task in iraf to subtract the background from some 2d spectra. I am using the task in interactive mode because I would like to change the fit windows along the spectrum wavelength. This is what I do: once the task is launched, I insert a column (i.e. a lambda) in the graphical window and obtain the profile along the spatial direction. Then I select the windows typing 's', and I type 'f' to obtain the fit; then I move to another column, I delete the previous windows with 'z', I select new windows with 's', and then I type 'f', and so on. Nevertheless, when I exit the task and check the result (I display the subtracted 2d spectrum), it looks like the background has been subtracted along the ENTIRE spectrum using just the last windows choice. My question is: is it indeed possible to model the background adopting different window setups along the columns (lambda), or instead just one choice for the windows is allowed? I am doing something wrong?

Many thanks,

Francesca


 
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valdes
 07/25/2014 05:31PM  
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Active Member

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Registered: 11/11/2005
Posts: 728
Hi,

I'm afraid the logic of the interactive mode in this task, which can confuse people, is that your are setting up the parameters to use and the 'f' is just to see what it would look like. So, in fact, the last parameters you set interactively is what is used. What you should really be doing is building up a window list. This is possible, I may not remember the details without trying it, by just using the s key repeatedly without clearing it. Note that you can also just make the window list as a parameter. It thing the format is a "range list" which is something like wave-wave,wave-wave,.... Remember what you are setting is the windows for background and not the regions to exclude from the fit.

I hope this makes sense. If you still can't figure it out I can refresh my memory and give you a more concrete recipe. Again, the task is behaving as it was designed but it can be counter-intuitive if you have a different picture in your mind.

Frank Valdes

 
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