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Retrieve header key with gethead

A quick note on gethead of WCSTools – as I have needed many times (but obviously not that many to remember it!). Rather straightforward use: gethead HEADER_KEY image.fits (as simple as possibly!) If HEADER_KEY contains empty spaces then use double quotes, e.g. “HIERARCH TEL AIRM END”. Reminder: you have to have installed already the WCSTools! […]

IRAF’s error message 502 and pixel value replacement

While running a data reduction of IR observations with IRAF, the ccdproc printed this error: ERROR (502, “floating point invalid operation”) which means that some values of the image used (the flat image in this case) are not suitable for the performing mathematical actions (like division with 0s). Moreover the IR ccds have many bad […]

IRAF’s error message 1121 with hedit

Although hedit of IRAF is supposed to handle the keywords of a fits file (add, remove) its behaviour can be misleading sometimes. An error like this: ERROR (1121, “FXF: EOF encountered while reading FITS file (something.fits)”) means that after altering the keywords in the header the EOF of the header has been placed wrongly. The […]

Extracting spectra from AAOmega observations

AAOmega (at Anglo-Australian Observatory) observations can be reduced with 2dfdrv4 tool pretty much very easilly. But the reduction ‘s final output is a combined fits image which includes all spectra from the 400 fibers. So, the user has to extra by himself/herself the spectra individually and this has been frustrating (at least for me…). 1. […]

Reading fits headers within Starlink (.sdf files)

Starlink has its own image format (the NDF format, .sdf extension) which is not perhaps so convenient as the fits format. Nevertheless, there are ways to read the contents of the fits headers of your .sdf files, depending on the program you are working with. With KAPPA you can use the command: $ fitslist file.sdf […]