| Re: continuum normalized spectra [message #83096 is a reply to message #83002] |
Sun, 03 February 2013 06:33  |
abc
Messages: 46
Registered: March 2011
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On Sunday, February 3, 2013 3:22:54 PM UTC+1, Mats Löfdahl wrote:
> Den söndagen den 3:e februari 2013 kl. 09:09:20 UTC+1 skrev idlhelp:
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>> On Saturday, February 2, 2013 7:42:39 PM UTC+1, David Fanning wrote:
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>>> idlhelp writes:
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>>>> I want to write a program to fit a linear local continuum of absorption line, and plot the spectrum with continuum drawn and the spectrum normalized by the continuum. And than I want to Fit a local continuum using data in the wavelength ranges 1800-1820 and 2020-2040 angstroms.
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>>>> Does anyone know that how can I do that
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>>> Yes, probably. But, not without a hell of a lot more information. :-)
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>>> Cheers,
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>>> David
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>>> --
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>>> David Fanning, Ph.D.
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>>> Fanning Software Consulting, Inc.
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>>> Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
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>>> Sepore ma de ni thue. ("Perhaps thou speakest truth.")
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>> Hi David,
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>> ok so here is the information. This is how I am doing :-)
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>> ; filename - the filename of the input spectrum
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>> ; column - the number of columns in the file
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>> ; row - the number of rows in the file
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>> ; boxsize - the size of the boxcar for the smoothing function
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>> ; dofit - the user keyword
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>> ; dofityes - the variable containing the input parameter
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>> data = fltarr(column, row)
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>> ; open the file as read only
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>> openr,lun,filename,/get_lun
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>> ; read the data from the file into the array
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>> readf,lun,data
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>> ; close the file
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>> close,/all
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>> wave=reform(data(0,*))
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>> flux=reform(data(1,*))
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>> ; This creates a new array containing the results generate
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>> ; by the smooth function.
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>> smoothed_flux = smooth(flux,boxsize)
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>> ; check to see if the user would like to fit the continuum
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>> if keyword_set(dofityes) then begin ; this check the dofit keyword
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>> ; fit velocity and smoothed_flux, using a 1st order polynomial.
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>> result = poly_fit(wave,smoothed_flux,1)
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>> ; generate the continuum with the results from the fit
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>> continuum = result(0) + result(1)*wave
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>> end
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>> But I am not sure that I am doing the continuum normalization to unity in a right way. Because when I make plots the contunum level is higher than the unity.
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> As far as I can see, you don't do any normalization at all. You calculate the fit, but you never operate on the original (or smoothed) spectrum with that fit. I guess you need to divide the spectrum with the fit.
Ahh I forgot, I am dividing the spectrum by the continuum like that
but still the continuum is far from unity
; for continuum normalization
smoothed_flux = smoothed_flux/continuum
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