30.2 Headers, Keywords, and Group Parameters

IRAF tasks such as imhead or hselect can be used to list the various header keywords. Values of group parameters, on the other hand, can be obtained only with imhead. Table 30.6 provides a listing of all FOS group parameters, with typical values and explanatory comments for each.

Information in FOS Header Keywords

Keyword Type	Information in Keywords	Source
a.) General Information
General data	General structure information for data file in standard FITS style	All headers
Group Parameters: OSS	Acquisition data description, including time of acquisition (modified Julian date), maximum and minimum data values, and axes information	All headers
Group Parameters: PODPS	Observation type and ground-based GIM correction values from GIMP_CORR	Calibrated header files
Generic Conversion Keywords	Existence of science trailer line and reject array	.d0h
FOS Descriptor Keywords	Description of FOS file and GIM correction	All headers
COSTAR Keywords	Positions of the COSTAR FOS M1 mirror	.shh
b.) Engineering Information
Time Conversion Keywords	Spacecraft and Universal time at start of observation	.shh
CDBS Keywords in SHP	Engineering data regarding temperatures, currents, and voltages at various points in the instrument	.shh
CDBS Keywords in UDL	Data acquisition details, such as number of channels used, value of magnetic field deflections used	.ulh
c.) Processing and Calibration Information
Statistical Keywords	Processing information	.shh, .d0h, and calibrated data headers
Calibration Flags and Indicators	Type of observation and configuration of aperture, grating, and detector	.d0h and calibrated data headers
Calibration Reference Files & Tables	Reference files and tables for calfos processing (either used or to be used)	.d0h and calibrated data headers
Calibration Switches	Calibration steps for calfos processing (either used or to be used)	.d0h and calibrated data headers
Pattern Keywords	Magnetic field deflection pattern used in acquiring the data	.d0h and all calibrated data header files
Calibration Keywords	Observing time, user-supplied GIM offset table name, LIVETIME, DEADTIME, position angle of aperture, burst noise rejection limit	.d0h and calibrated data headers
Aperture Position	Aperture position in RA and Dec	.d0h and calibrated data headers
Exposure Information	Exposure information and commanded FGS lock	.d0h and calibrated data headers
d.) Observer-Supplied Observing Information from Phase II Proposal
Support Schedule: Program Info	Information on cover page of proposal and type of output data requested by GO	.shh
Support Schedule: Flags and Indicators	Type of observation requested by GO, for example, the aperture, the detector, the number of channels, etc.	.shh
Proposal Info	Observing strategy, e.g., instrument configuration, target description, and information on flux, exposure, moving target, spatial scan etc.	.shh
Target and Proposal ID	Target and PEP information	.shh
e.) Observing Information Produced in TRANS Stage
Support Schedule: Data Group II	Telescope pointing and instrument configuration on the sky, i.e., target RA and Dec and offset objects, position angle of diode array, OFFSET information, spacecraft velocity, guide stars, etc.	.shh
Onboard Ephemeris Model	Spacecraft ephemeris	.shh

FOS Header -Keywords

Keyword	Description and Comments
General Information from Header File-usually in .d0h or .c1h
GCOUNT	Number of groups in data file
YTYPE	Nature of observation, important for paired aperture observations. (Not real values in d0h file). Values are OBJ, BKG, or SKY
YPOSn	Location of diode center in Y-base units, of the nth group, useful for interpreting ACQ/BIN data. If there is only one group then YPOS is the Y-base of that one group. Not populated with real values in the .d0h file
YBASE	YPOS of group #1
XBASE	XDAC units needed to center aperture on the diode array for group #1
DEFDDTBL	UDL disabled diode table to be used (value: T) or DDTHFILE table to be used (value: F)
BUNIT	Flux units of the data. Values: COUNTS, COUNTS/SEC, ERGS/SEC/ CM^2/A, or ANGSTROM
FILLCNT	Number of sequences of filled data
ERRCNT	Number of sequences with bad data
INSTRUME	Instrument used for the observation. This will be FOS.
ROOTNAME	Rootname of the observation set. Will start with letter "y"
FILETYPE	Type of data in the file: SHP is science header packet, UDL is unique data log, SDQ is raw science data quality, WAV is wavelength, FLX is calibrated flux, ERR is calibrated flux error, MOD is CALFOS special mode processed data, SCI is object, sky, or background science data, OBJ is object data, BKG is background data, CDQ is calibration data quality, SKY is sky data, NET is sky-subtracted object data
GRNDMODE	Ground software mode of FOS. Can be SPECTROSCOPY, TARGET ACQUISITION, IMAGE, RAPID-READOUT, SPECTRO-POLARIMETRY, or TIME-RESOLVED
DETECTOR	Detector in use for the observation. AMBER or BLUE
APER_ID	Aperture used for the observation; A-1 corresponds to the 4.3\xfd , A-2 to the 0.5\xfd pair (square), A-3 to the 0.25 pair (square), A-4 to the 0.1 pair (square), B-1 to the 0.5\xfd (round), B-2 to the 0.3\xfd (round), B-3 to the 1.0\xfd (round), B-4 is blank, C-1 to the 1.0\xfd pair (square), C-2 to the 0.25\xfd x2.0\xfd slit, C-3 to the 0.7\xfd x2.0\xfd bar, and C-4 to the 2.0\xfd bar apertures respectively
POLAR_ID	Polarization waveplate used for the observation. A is the waveplate A, B is the waveplate B and C is no polarizer used (clear)
FGWA_ID	Filter and grating used for the observation. Hxx means Gxx0H filter, L15 means G160L, L65 means G650L, PRI means PRISM, and CAM means camera (mirror).
POLANG	Initial angular position of the polarizer in degrees
FCHNL	First diode used in observation (first diode in array is designated as zero)
NCHNLS	Number of diodes used in the observation, useful for interpreting ACQ/BIN data and exposure time. Usually 512 (except target acquisition and other specific modes, see below)
OVERSCAN	Number of overscans used in the observation, useful for interpreting ACQ/BIN data and exposure time. Usually 5. FOS reference files and calibration support only OVERSCAN=5.
NXSTEPS	Number of X substeps used in the observation, useful for interpreting ACQ/BIN data and exposure time. Usually 4
MINWAVE	Minimum wavelength in Å. (Not populated in .c0h file)
MAXWAVE	Maximum wavelength in angstroms. (Not populated in .c0h file)
YFGIMPEN	Onboard GIM correction enabled. T or F
KYDEPLOY	COSTAR mirror deployment for the FOS. T or F
Exposure Time Information-usually in .d0h or .c1h
FPKTTIME	Time of first data packet sent to the SDF, i.e., approximate time of the end of the group exposure. The units are modified Julian date. Each group has its own unique FPKTIME, accurate to about 1/8 second.
LPKTTIME	Approximate time of the last data packet sent to the SDF. The units are modified Julian date.
DATE-OBS	FPKTTIME of group 1 converted to standard notation for date
TIME-OBS	FPKTTIME of group 1 converted to standard notation for time, truncated to integer value; thus these are only accurate to 1/8 of a second
EXPSTART	Exposure start time in modified Julian date
EXPOSURE	Exact exposure time per pixel in seconds for each group. Note that this keyword is not populated with real values in the d0h file
Pattern Keywords for Exposure Times-usually in .c0h or .c1h
LIVETIME	Time, in units of 7.8125 microseconds, during which accumulator is open
DEADTIME	Time, in units of 7.8125 microseconds, in which accumulator is closed
INTS	Number of repetitions of the live time/dead time cycle
YSTEPS	Number of Y substeps used in the observation. Usually 1
NPAT	Number of patterns used per readout
SLICES	Number of repeats of the magnetic field deflection sequence. Usually 1
NREAD	Number of readouts per memory clear. For the ACCUM mode this is usually the number of groups. For RAPID mode this is 1
NMCLEARS	Number of memory clears per obs. 1 for ACCUM, number of groups for RAPID mode when NMCLEARS > 1
Aperture Orientation Information-usually .shh and .d0h of acquisition image
OPMODE	Operation mode of the FOS for the observation. Can be: ACQ, ACQ/BIN, ACQ/PEAK, ACQ/FIRMWARE, IMAGE, ACCUM, RAPID or PERIOD
PA_APER	Position angle of the aperture in degrees
RA_APER1	RA of aperture center in degrees
DECAPER1	Dec of aperture center in degrees

FOS Group Parameter Keywords

Keyword	Typical Value	Alternate Name in Header	Description
CRVAL1	1.	PTYPE1	Reference pixel value
CRPIX1	1.	PTYPE2	Pixel number of reference pixel
CD1_1	1.	PTYPE3	Pixel increment
DATAMIN	1.946443E-14	PTYPE4	Minimum value in the data
DATAMAX	1.118037E-13	PTYPE5	Maximum value in the data
RA_APER	297.4443291667	PTYPE6	Right ascension of aperture (deg)
DEC_APER	48.961	PTYPE7	Declination of aperture (deg)
FILLCNT	0	PTYPE8	Number of segments containing fill
ERRCNT	0	PTYPE9	Error count of the data
FPKTTIME	50441.0428552372	PTYPE10	Time of the first packet (Modified Julian Date)
LPKTTIME	50441.0428653645	PTYPE11	Time of the last packet (Modified Julian Date)
CTYPE1	PIXEL	PTYPE12	First coordinate type
APER_POS	SINGLE	PTYPE13	Aperture used
PASS_DIR	0	PTYPE14	Polarization pass direction
YPOS	-1597.	PTYPE15	y-position on photocathode (Y-bases)
YTYPE	OBJ	PTYPE16	Observation type: OBJ, SKY, BCK
EXPOSURE	62.5	PTYPE17	Exposure time per pixel (seconds)
X_OFFSET	0.	PTYPE18	x_offset for GIMP correction (diodes)
Y_OFFSET	0.	PTYPE19	y_offset for GIMP correction (defl.units)
SCT_VAL	0.1351963	PTYPE20	Scattered light correction value (cts/sec/pixel)
SCT_ERR	0.01424327	PTYPE21	Scattered light correction error (cts/sec/pixel)