Table C.1.
FITS header keywords required by CRISPEX
| Keyword | SN | SG | SJ | Description and use |
|---|---|---|---|---|
| BITPIX | X | X | X | Number of bits per pixel; is converted to IDL datatype and used to initialize variables holding the data slices |
| NAXISi | X | X | X | Numbered variables specifying the size of each dimension |
| BTYPE | X | X | X | Description of data type, e.g., intensity, temperature, pressure, etc.; used for plot labeling and user feedback |
| BUNIT | X | X | X | Data units, e.g., erg cm−2 s−1 sr−1, K, m s−1, etc.; used for plot labeling and user feedback |
| BSCALE | X | — | X | Data scaling factor; used in combination with BZERO to descale the data |
| BZERO | X | — | X | Data scaling offset; used in combination with BSCALE to descale the data |
| CDELTi | X | X | X | Pixel size of each dimension in terms of CUNITi; used for WCS transformations (pixel-to-WCS and vice versa) |
| CRPIXi | X | X | X | Reference pixel of each dimension; used for WCS transformations |
| CRVALi | X | X | X | Reference pixel value of each dimension in terms of CUNITi; used for WCS transformations |
| CTYPEi | X | X | X | Description of data type of each dimension; used for plot labeling and user feedback (the CTYPEi corresponding to the X-axis is also checked for containing ’TAB’, to determine further processing) |
| CUNITi | X | X | X | Data unit of each dimension (e.g., arcsec, Ångström, seconds, etc.); used for plot labeling and user feedback |
| PCi_j | X | X | X | Elements of the PC-matrix; used in WCS transformations |
| OBSID | — | X | X | IRIS observing program ID; provided in user feedback |
| STARTOBS | P | X | X | Date and time of observations start; used to determine the timing in UTC when combined with second (first) auxiliary extension data of a SG (SJI) file. |
| DATE_OBS | X | X | X | Date and time of observations start; used if STARTOBS is not defined |
| INSTRUME | X | X | P | Instrument that produced the data; used to (un)set the non-equidistant spectral warping switch for IRIS SG data (unset if not equal to ’IRIS’) |
| NWIN | — | X | — | Number of diagnostics compressed in the wavelength dimension |
| WSTARTi | — | X | — | Starting index of each diagnostic; used in combination with WWIDTHi to determine diagnostic boundaries within the spectral dimension |
| WWIDTHi | — | X | — | Width in pixels of each diagnostic; used in combination with WSTARTi to determine diagnostic boundaries within the spectral dimension |
| WDESCi | — | X | — | Label of each diagnostic; used in labeling plots and control panel selection options |
| TWAVEi | — | X | — | Central wavelength of each diagnostic; used to determine the Doppler velocity |
| TDESC1 | — | — | X | Label of detector; used for control panel labeling of SJI functions |
| TELESCOP | P | — | X | Telescope name; used for control panel labeling of SJI functions |
| TIME | — | — | X | Time since STARTOBS, keyword indicates the row-index of the extension data array; used to determine the timing in UTC |
| XCENIX | — | — | X | Time-dependent central FOV X-value in CUNIT1 (row-index); used to determine the SJI CRVAL1 |
| YCENIX | — | — | X | Time-dependent central FOV Y-value in CUNIT2 (row-index); used to determine the SJI CRVAL2 |
| PCi_j IX | — | — | X | Time-dependent PC-matrix elements (row-index); used determine the SJI CRPIX/2, and by extension CRVAL1/2 |
| SLTPX1IX | — | — | X | Time-dependent slit center X-pixel (row-index); used to determine the SJI CRPIX1 and CRVAL1 |
| SLTPX2IX | — | — | X | Time-dependent slit center Y-pixel (row-index); used to determine the SJI CRPIX2 and CRVAL2 |
Notes. Columns 2–4 indicate whether a particular keyword is required (marked X), present but not required / actively used (marked P), or absent (marked —) for the SOLARNET (SN), IRIS spectrograph (SG), and slit-jaw image (SJ) files, respectively. The keywords above the horizontal line are from the main data extension header; those below the line correspond to the first auxiliary extension header. For tabulated WCS coordinates, the keywords CDELTi, CRPIXi, and CRVALi are defined differently, along with PSi_j and PVi_j, they are used to find the relevant data in binary extensions (see Greisen et al. 2006).
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