FITS Header fields data origins

[Patrick]

Hello,
Can someone please explain where the data for following FITS header fields originates?:

RA
DEC
OBJECTRA
OBJECTDEC

I have images where the two RA values are the same (as are the two DEC values).

Regards,
Patrick

[fabdev]

Hello, they are both the approximate center of the image. They are not standard, but widely used.
Astroart writes both to help other programs which may support only one. They are read from the telescope.
Reference:
https://heasarc.gsfc.nasa.gov/docs/fcg/common_dict.html
https://heasarc.gsfc.nasa.gov/docs/heas ... tsExt.html

[Patrick]

Thank you - very helpful.
RA and DEC used by IRAF
Regards,
Patrick