Space Telescope Science Institute
WFC3 Data Handbook 2.1 May 2011
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WFC3 Data Handbook > Chapter 2: WFC3 Data Structure > 2.4 Headers and Keywords

Both the primary and extension headers in a WFC3 science data file contain keywords. These keywords store a wide range of information about the observations themselves (e.g., observing mode, exposure time, detector, etc.), as well as any processing done or to be done on the data.
The primary header keywords apply to all extensions in the FITS file. The extension headers carry extension-specific keywords, i.e., information relevant only to the image in a particular extension. For example, observation parameters, calibration switches, and reference file names are stored in the primary header. Exposure time and World Coordinate System information, on the other hand, are stored in the extension headers because this information can vary from one set of extensions to another.
In Table 2.7 and Table 2.8, we list the WFC3 keywords that appear in the primary header and SCI extension header, respectively. Columns 1 and 2 give the name of the keyword and a short description. The third column gives the format used for the value of the keyword: “L” for boolean values, “C” for characters, “R” for real values and “I” for integer values, followed by the precision of the value. Columns 4 and 5 show to which detector the keyword applies.
Table 2.9 lists the keywords that appear in the headers of the ERR, DQ, SAMP, and TIME extensions belonging to an imset in a WFC3 data file. Note that the SAMP and TIME extensions apply only to IR data.
MultiDrizzle adds up to ~50 keywords which are not listed in this handbook.
The pattern keywords refer to the different dithering strategies and patterns available for the WFC3 detector which are discussed in greater detail later in
Section 4.2.
Table 2.7: WFC3 primary header keywords.
the HST graph table
the HST components table
Table 2.8: WFC3 SCI extension header keywords.
Table 2.9: WFC3 extension header keywords (Imset extensions 2-5).

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