ACS image header keywords are described in Tables 2.6
. When printing the header, note that the keywords are grouped together by type, for example, "Target Information," "Science Instrument Configuration," "Calibration Switches," and "Calibration Reference files." There are also convenience functions for querying header keywords. For more information, see the Astropy documentation
Extension or group header keywords (FITS extensions > 0), as shown in Table 2.7
, contain parameter values that are specific to the image group (however, many primary header keyword values are also accessible when querying an image group header).