A few comments below. Also @sageyu123 as he has been working on the FITS headers.
What do "com_x" and "com_y" stand for? Perhaps something like "refra_shift_x" and "refra_shift_y" would be more intuitive? I also think there is no need for adding "fitted" to the keyword name. Also it is worthwhile to specify the unit of these values using the standard keyword such as "BUNIT = arcsec"
FITS keyword "REFRA" = "1" to "REFRA_COR" = True?
Perhaps add "REFRA_VER = 1.0" to indicate the version of the refraction correction, in case we need to update it in the future.
The coefficient keywords can also be more specific, such as PX0 -> REFRA_PX0, etc.
just to remind myself. https://github.com/suncasa/suncasa-src/issues/272