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Space Telescope Science Institute |
COS Data Handbook v.3 |
help@stsci.edu |
As with previous HST instruments, the FITS header keywords in COS data files store important information characterizing the observations and telemetry received during the observations, and describe the post-observation processing of your dataset. Each keyword follows FITS conventions and is no longer than eight characters. Values of keywords can be integer, real (floating-point), boolean, and character strings. Several keywords are HST and COS specific. Knowledge of the keywords and where to find them is an important first step in understanding your data. By examining your file headers, using either catfits, imhead, hselect, thselect or hedit, in STSDAS you will find detailed information about your data including:Keywords that deal with a particular topic, such as the instrument configuration, are grouped together logically throughout the headers. Table 2.15 lists a useful subset of these groups of keywords, indicates the name of the grouping, and where applicable, shows their relationship to the corresponding information from the Phase II proposal.Table 2.16 summarizes the possible calibration switch keywords, and indicates whether they are present for a particular observation; it also indicates the reference file keyword corresponding to the particular calibration step. A calibration switch keyword is initially populated with values of OMIT, PERFORM or N/A in the raw uncalibrated science data (with the exception of XTRACTALG, which has values of ‘BOXCAR’ or ‘TWOZONE’ to select the extraction algorithm to be used). After each calibration step is executed in the COS calibration pipeline, calcos will set the keyword switch to COMPLETE.
Exposure type (EXTERNAL/SCI, WAVECAL, PHA, DARK, FLAT, ACQ/IMAGE, ACQ/SEARCH, ACQ/PEAKD, ACQ/PEAKXD, ENG DIAG, or MEM DUMP). Number of repeat exposures in dataset: Default = 1. Cross-dispersion location at which calcos extracted the FUV segment A or NUV stripe A spectrum. Cross-dispersion location at which calcos extracted the FUV segment B or NUV stripe B spectrum. Cross-dispersion location at which calcos extracted the NUV stripe C spectrum. Offset from SP_NOM_A at which the spectrum was found. Offset from SP_NOM_B at which the spectrum was found. Offset from SP_NOM_C at which the spectrum was found. Subarray Readout Parameters1 (in Extension header 1 or greater) TIME-TAG Events Orientation Keywords (in Extension header 1 or greater)2
Table 2.16: Spectroscopic Calibration Switch Keywords
XTRACTALG1
Table 2.17: Imaging Calibration Switch Keywords
Table 2.18: Reference File Keywordsc