Changes in the .fits header...

Posted by wvinton on May 24, 2017; 8:33pm
URL: http://astroimagej.170.s1.nabble.com/Changes-in-the-fits-header-tp683.html

Karen: First of all, I'm eternally grateful for your creation of this program, and your immediate responses on the forum!

Now, here's a question I can't find an answer to in the documentation.... It appears that when I use the data processor to calibrate images with biases, darks and flats, that some values in the .fits header get changed. I have not done an extensive study to see which ones - but the most obvious is the AIRMASS.  For example, in one of my original science images, the AIRMASS was 1.00611; after calibration the value was 16.803.  Scanning through some of my other image headers (which all started out with AIRMASS values around 1.006) I see values that go up as high as 386, and some end up as -1.00.

So, I'm puzzled by this. Is this an unavoidable part of calibration? When I calibrate should I uncheck the "General" under FITS header updates?

Also, if I do something like a mean combine of a stack of images to enhance SNR, the FITS header is completely zapped, ("No valid FITS header").

 Is there any way to keep the header categories intact during something like a mean combine of a stack?

Thanks again for everything!

Bill V