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 Wavelength units on NIR spectra
   
massey
 04/10/2017 09:58PM (Read 119 times)  
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Registered: 02/10/2006
Posts: 158
I have some NIR spectra taken with FIRE on Magellan that I reduced with their IDL pipeline. When I splot the spectra, they look fine, and the units on the X axis are Angstroms--all well and good! But, when I wspect the spectra to a text file, the uni-69 13 01.95ts are clearly the log of the wavelength in angstroms. Here's what the fits header says:

CDELT1 = 1.81081307382E-05 /
CRPIX1 = 1 /
CTYPE1 = 'LINEAR ' /
DC-FLAG = 1 /
CRVAL1 = 3.91592865169 /

So, I'm extremely puzzled. How does splot know how to do the right thing and convert this to angstroms? Why isn't wspect as smart?

thanks!


 
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valdes
 04/25/2017 10:14PM  
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Registered: 11/11/2005
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Hi Phil,

Your answer is implicit in your question. Why doesn't wspect know what to do? Because, unfortunately, it wasn't written that way. To be less factious, splot and many of the onedspec tasks use a library of routines that provide units conversion features and recognize various ways that headers are encoded. A lot of effort went into understanding the many ways people and observatories properly and improperly define units in image headers. wspect text is not in that category and is actually a pretty simple task that is a wrapper around the basic wtextimage and listpixels tasks and is not a onedspec tool in the same sense.

Frank

 
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