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 How to create a accurate WCS with some simple method
   
Matrix
 05/12/2015 03:18AM (Read 1093 times)  
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Hello, everyone! Today I encounter a second question: I found the WCS and RA/DEC did not have a right correspondence in my fits file. And this cause a problem: when I want to know the target star, I move the mouse to the accurate RA/DEC (from the header), but it may not be the target star. So I want to create a accurate WCS, I heard SCAMP can do some work in this problem, but I don't know how to do it? Can anyone tell me some procedures in detail? Thanks a lot to you.

 
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fitz
 05/12/2015 04:02PM  
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The thing to remember is that there is no standard definition of the RA/DEC header keywords, and that these have no defined relation to the WCS itself. Depending on the instrument/control system, RA/DEC may refer to the (unprecessed) coordinates of an object in the field, a pointing value for the telescope, the center position of a dither field, etc. So, before deciding the WCS is wrong, you should test the readout of coords to see whether a cursor put on an object corresponds to some known object or whether there is a systematic offset, and necessarily whether the WCS ties to the RA/DEC keywords in some logical way.

The astromatic.net forums can be used to discuss SCAMP, for computing a WCS in IRAF see the "Creating a Mosaic WCS" document (https://iraf.net/irafdocs/astrom.php) for an overview, you'll need to adjust this a but for a single-frame image.

 
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Matrix
 05/13/2015 08:43AM  
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Thank you, fits. There is few difference between celestial coordinates of some known stars on the fits and celestial coordinates of these stars on the SDSS DR12 finding tool. I don't know which one I should use to create the accurate wcs. Additional, for IRAF to create right wcs, I don't know how to collect the pixel coordinates and the celestial coordinates I should choose which.

 
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