2.6	Headers, Keywords, and Relationship to Phase II

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:

•	Target name, coordinates, proposal ID, and other proposal level information.

•	Observation and exposure time information such as observation start and duration.

•	Instrument configuration information such as detector, grating, central wavelength setting, and aperture.

•	Readout definition parameters such as subarray parameters.

•	Exposure-specific information such as more detailed timing, world coordinate system information, and Fine Guidance Sensor identification.

•	Calibration information such as the calibration switches and reference files used by the pipeline and parameters derived from the calibration, such as image statistics and wavelength shifts.

The keywords relevant for one COS data type will not necessarily be relevant to another. Accordingly, you will find that the header on a particular file type contains a unique combination of keywords appropriate for that type of observation. Long definitions for the keywords can also be accessed from the following Web page, which provides detailed explanations of the contents and algorithm for populating the keywords. This site also provides sample headers for different COS file types:

http://stdatu.stsci.edu/keyword/.

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. After each calibration step is executed in the COS calibration pipeline, calcos will set the keyword switch to COMPLETE.

Table 2.15:

Selected Header Keywords and Relationship to Phase II Parameters

Header Keyword	Phase II Equivalent	Description
General File Information (Primary Header)
FILENAME		Name of the file
FILETYPE		Type of data found in the file (SCI, ACQ, SPT, ASN_TABLE)
NEXTEND		Number of extensions in the file.
Date		Date file was created
Program Information (Primary Header)
PROPOSID		4 or 5 digit program number.
PR_INV_L PR_INV_F PR_INV_m	PI Last Name PI First Name PI Middle Initial	Last name of principal investigator First name of principal investigator Middle name initial of principal investigator
LINENUM	Visit_Number, Exposure_Number	Indicates the visit and exposure number from the Phase II proposal: Visit_Number, Exposure_Number.
Target Information (Primary Header)
TARGNAME	TargetName	Name of target.
RA_TARG DEC_TARG	RA DEC	Right ascension of the target (deg) (J2000). Declination of the target (deg) (J2000).
POSTARG1 POSTARG2	POSTARG POSTARG	Postarg in axis 1 direction. Postarg in axis 2 direction.
Science Instrument Configuration (Primary Header)
OBSTYPE		Observation type (IMAGING or SPECTROSCOPIC).
OBSMODE	Opmode	Operating mode (ACCUM, TIME-TAG).
EXPTYPE	Opmode	Exposure type (EXTERNAL/SCI, WAVECAL, PHA, DARK, FLAT, ACQ/IMAGE, ACQ/SEARCH, ACQ/PEAKD, ACQ/PEAKXD, ENG DIAG, or MEM DUMP).
DETECTOR	Config	Detector in use (NUV or FUV).
SEGMENT	SEGMENT	FUV detector segment in use (FUVA, FUVB, BOTH, or N/A).
DETECTHV		FUV detector high voltage state (NomAB, NomA, NomB, Off, Low).
SUBARRAY		Data from a subarray (T) or full frame (F).
LAMPUSED		Lamp status, NONE or name of lamp which is on (P1, D1, P2, or D2)
LAMPSET		Spectral calibration lamp current value (milliamps).
LIFE_ADJ		Detector Life time adjustment position. (1-5)
OPT_ELEM	SpElement	Optical element in use (grating or mirror name).
CENWAVE	Wavelength	Central wavelength for grating settings.
APERTURE	Aperture	Aperture name.
PROPAPER	Aperture	Proposed aperture name.
APER_FOV		Aperture field of view description in mm.
FPPOS	FPPOS	Grating offset index (1-4) for spectrum dithers (FPPOS).
TAGFLASH	FLASH	Type of flashed exposures in TIME-TAG (NONE, AUTO, or uniformly-spaced).
EXTENDED	Extended	Is the target extended (Yes or No).
NRPTEXP	NumberOfIterations	Number of repeat exposures in dataset: Default = 1.
EXP_NUM		Exposure number for repeated observations.
SHUTTER		External shutter position (OPEN or CLOSED).
Engineering Parameters (Primary Header)
FPOFFSET		FP offset from nominal, in motor steps.
DEVENTA		Digital event counter, FUV segment A (counts s-1).
DEVENTB		Digital event counter, FUV segment B (counts s-1).
FEVENTA		Fast event counter, FUV segment A (counts s-1).
FEVENTB		Fast event counter, FUV segment B (counts s-1).
MEVENTS		NUV MAMA event counter (counts s-1).
Target Acquisition Dataset Identifiers (Primary Header)
ACQSNAME		Rootname of first acquisition search exposure.
ACQINAME		Rootname of first acquisition image exposure.
PEAKXNAM		Rootname of first x-dispersion peakup exposure.
PEAKDNAM		Rootname of first dispersion peakup exposure.
ACQ_NUM		Total number of exposures in acquisition sequence.
Archive Search Keywords (Primary Header)
BandWID		Bandwidth of the data.
SPECRES		Approximate resolving power at central wavelength.
CENTRWV		Central wavelength of the data.
MINWAVE		Minimum wavelength in spectrum.
MAXWAVE		Maximum Wavelength in spectrum.
PLATESC		Plate scale (arcsec/pixel).
Association Keywords (Primary Header)
ASN_ID		Unique identifier assigned to association.
asn_mtyp		Role of the member in the association.
ASN_TAB		Name of the association table.
Exposure Information (in Extension header 1 or greater)
DATE-OBS		UT date of start of observation (yyyy-mm-dd).
TIME-OBS		UT time of start of observation (hh:mm:ss).
EXPTIME		Corrected exposure time (seconds). For FUV exposures, the largest of EXPTIMEA and EXPTIMEB
EXPTIMEA		Corrected FUV Segment A exposure time (seconds).
EXPTIMEB		Corrected FUV Segment B exposure time (seconds).
RawTIME		Exposure time of an individual raw exposure (seconds).
EXPSTART		Exposure start time (Modified Julian Date).
EXPEND		Exposure end time (Modified Julian Date).
EXPSTRTJ		Exposure start time ( Julian Date).
EXPENDJ		Exposure end time (Julian Date).
PLANTIME	TimePerExposure	Planned exposure time (seconds).
Ninterpt		Number of exposure interrupts.
ORIENTAT		Position angle of image y-axis (degrees).
Sunangle		Angle between sun and V1 axis.
moonangl		Angle between moon and V1 axis.
sun_alt		Altitude of the sun above Earth’s limb.
fgslock		Commanded FGS lock (Fine, Coarse, Gyros, Unknown).
gyromode		Number of gyros scheduled for observation.
refframe		Guide star catalog version.
Aperture Information (in Extension header 1 or greater)
RA_APER DEC_APER		RA of reference aperture center. Declination of reference aperture center.
PA_APER		Position angle of reference aperture center.
SHift1a		Wavecal shift determined for FUV segment A or NUV stripe A in dispersion direction (pixels).
SHift1B		Wavecal shift determined for FUV segment B or NUV stripe B in dispersion direction (pixels).
SHift1C		Wavecal shift determined for NUV stripe C in dispersion direction (pixels).
SHift2a		Offset in cross-dispersion direction for FUV segment A or NUV stripe A (pixels).
SHift2b		Offset in cross-dispersion direction for FUV segment B or NUV stripe B (pixels).
SHift2C		Offset in cross-dispersion direction for NUV stripe C (pixels).
SP_LOC_a		Cross-dispersion location at which calcos extracted the FUV segment A or NUV stripe A spectrum.
SP_LOC_B		Cross-dispersion location at which calcos extracted the FUV segment B or NUV stripe B spectrum.
SP_LOC_C		Cross-dispersion location at which calcos extracted the NUV stripe C spectrum.
SP_NOM_A		Nominal location of the spectral extraction region for FUV segment A or NUV stripe A based on the wavecal aperture location.
SP_NOM_B		Nominal location of the spectral extraction region for FUV segment B or NUV stripe B based on the wavecal aperture location.
SP_NOM_C		Nominal location of the spectral extraction region for NUV stripe C based on the wavecal aperture location.
SP_OFF_A		Offset from SP_NOM_A at which the spectrum was found.
SP_OFF_B		Offset from SP_NOM_B at which the spectrum was found.
SP_OFF_C		Offset from SP_NOM_C at which the spectrum was found.
sp_slP_A		Slope of FUV segment A or NUV stripe A spectrum
sp_slp_b		Slope of FUV segment B or NUV stripe B spectrum
sp_slp_c		Slope of NUV stripe C spectrum
sp_HGT_A		Height in pixels of the FUV Segment A spectral extraction region.
SP_HGT_B		Height in pixels of the FUV Segment B spectral extraction region.
Dpixel1a		Fractional part of pixel coordinate for FUV segment A or NUV stripe A (pixels). Average binning error.
Dpixel1b		Fractional part of pixel coordinate for FUV segment B or NUV stripe B (pixels). Average binning error.
Dpixel1c		Fractional part of pixel coordinate for NUV stripe C (pixels). Average binning error.
TIME-TAG Parameters (in Extension header 1 or greater)
Bufftime	BUFFER-TIME	Onboard memory half-buffer-fill time.
overflow		Number of science data overflows.
nbadevnt		Total number of events deleted in screening (NUV).
NBADEVTA		Total number of events deleted in screening (FUV, segment A).
NBADEVTB		Total number of events deleted in screening (FUV, segment A).
nevents		Total number of events in raw data (NUV).
NEVENTSA		Total number of events in raw data (FUV, segment A).
NEVENTSB		Total number of events in raw data (FUV, segment B).
FUV TIME-TAG Parameters (in Extension header 1 or greater)
tbrst_a tbrst_b		Time lost to bursts on FUV segment A (seconds). Time lost to bursts on FUV segment B (seconds).
tbadt_a tbadt_b		Time lost to BADTCORR screening on FUV segment A (sec). Time lost to BADTCORR screening on FUV segment B (sec).
npha_a npha_b		Number of events lost due to pulse height screening on segment A. Number of events lost due to pulse height screening on segment B.
nbrst_a nbrst_b		Number of events lost due to burst screening on segment A. Number of events lost due to burst screening on segment B.
Nbadt_a Nbadt_b		Number of events flagged by BADTCORR for segment A. Number of events flagged by BADTCORR for segment B.
Nout_a Nout_b		Number of events outside the active area for segment A. Number of events outside the active area for segment B.
NUV TIME-TAG Parameters (in Extension header 1 or greater)
Nbadt		Number of events flagged by BADTCORR.
TBADT		Time lost to BADTCORR screening (sec).
TAFGFLASH Parameters (in Extension header 1 or greater)
numflash		Integer number of flashes.
lmpduri		Duration of flash i, seconds.
lmp_oni		Lamp turn-on time for flash i, seconds since EXPSTART.
lmpoffi		Lamp turn-off time for flash i, seconds since EXPSTART.
lmpmedi		Median time of flash i, seconds since EXPSTART.
Velocity Reference Frame Conversion (in Extension header 1 or greater)
v_helio		Geometric to heliocentric velocity.
v_lsrstd		Heliocentric to standard solar LSR.
Doppler Correction Parameters (in Extension header 1 or greater)
orbitper		Orbital period used onboard for Doppler correction.
dopper		Doppler shift period (seconds).
doppmagv		Doppler shift magnitude (Km/sec).
doppon		Doppler correction flag (T or F).
doppzero		Commanded time of zero Doppler shift (MJD).
Instrument Doppler Correction Parameters (in Extension header 1 or greater)
orbtperT		Orbital period used onboard for Doppler correction.
DopmagT		Doppler shift magnitude (low-res pixels).
dopponT		Doppler correction flag (T or F).
doppzeroT		Commanded time of zero Doppler shift (MJD).
Global Count Parameters (in Extension header 1 or greater)
Globrate		Global count rate (NUV).
GLOBRT_A		Global count rate (FUV, segment A).
GLOBRT_B		Global count rate (FUV, segment B).
globlim		Was global linearity level exceeded (NUV).
GLOBLIMA		Was global linearity level exceeded for FUV segment A.
GLOBLIMB		Was global linearity level exceeded for FUV segment B.
Subarray Readout Parameters (in Extension header 1 or greater)
nsubarry1		Number of subarrays (1-8)
corner[n]x		Subbarray N axis1 corner pt in unbinned detector pixels.
Corner[n]y		Subarray N axis2 size in unbinned detector pixels.
size[n]y		Subarray N axis1 corner pt in unbinned detector pixels.
size[n]x		Subarray N axis2 size in unbinned detector pixels.
Stim Pulse Parameters (in Extension header 1 or greater; for FUV data only)
stimrate		Approximate STIM pulse injection rate.
stima_lx stima_ly stima_rx stima_rY		Segment A Left STIM pulse X centroid in raw data. Segment A Left STIM pulse Y centroid in raw data. Segment A Right STIM pulse X centroid in raw data. Segment A Right STIM pulse Y centroid in raw data.
stimB_lx stimB_ly stimB_rx stimb_rY		Segment B Left STIM pulse X centroid in raw data. Segment B Left STIM pulse Y centroid in raw data. Segment B Right STIM pulse X centroid in raw data. Segment B Right STIM pulse Y centroid in raw data.
stima0lx stima0ly stima0rx stima0rY		Reference location of Segment A Left STIM pulse X coordinate. Reference location of Segment A Left STIM pulse Y coordinate. Reference location of Segment A Right STIM pulse X coordinate. Reference location of Segment A Right STIM pulse Y coordinate.
stimB0lx stimB0ly stimB0rx stimB0rY		Reference location of Segment B Left STIM pulse X coordinate. Reference location of Segment B Left STIM pulse Y coordinate. Reference location of Segment B Right STIM pulse X coordinate. Reference location of Segment B Right STIM pulse Y coordinate.
stimaslx stimasly stimasrx stimasrY		RMS width of Segment A Left STIM pulse X coordinate. RMS width of Segment A Left STIM pulse Y coordinate. RMS width of Segment A Right STIM pulse X coordinate. RMS width of Segment A Right STIM pulse Y coordinate.
stimBslx stimBsly stimBsrx stimBsrY		RMS width of Segment B Left STIM pulse X coordinate. RMS width of Segment B Left STIM pulse Y coordinate. RMS width of Segment B Right STIM pulse X coordinate. RMS width of Segment B Right STIM pulse Y coordinate.
Pulse Height Parameters (in Extension header 1 or greater for FUV data only)
phalowra phalowrb		Pulse height screening lower limit for segment A. Pulse height screening lower limit for segment B.
phauppra phaupprB		Pulse height screening upper limit for segment A. Pulse height screening upper limit for segment B.
Image Statistics and Data Quality Flags (in Extension header 1 or greater)
ngoodpix		Number of good pixels (NUV).
NGOOD_A		Number of good pixels (FUV, segment A).
NGOOD_B		Number of good pixels (FUV, segment B).
sdqflags		Serious data quality flags. (Can be modified as a calcos parameter see Section 3.4.19)
goodmax		Maximum value of good pixels (NUV).
GOODMAXA		Maximum value of good pixels (FUV, segment A).
GOODMAXB		Maximum value of good pixels (FUV, segment B).
goodmean		Mean value of good pixels (NUV).
GOODMN_A		Mean value of good pixels (FUV, segment A).
GOODMN_B		Mean value of good pixels (FUV, segment B).
softerrs		Number of soft error pixels (DQF=1).
Deadtime Correction Keywords (in Extension header 1 or greater)
deadrt deadrt_A deadrt_b		Count rate used for the NUV dead time correction (cps) Count rate used in the FUV Segment A dead time correction (cps) Count rate used in the FUV Segment B dead time correction (cps)
deadmt deadmt_a deadmt_b		NUV Deadtime correction method (DATA, DEVENTS, or MEVENTS) FUVA Deadtime correction method (DATA, DEVENTS, or MEVENTS) FUVB Deadtime correction method (DATA, DEVENTS, or MEVENTS)
TIME-TAG Events Orientation Keywords (in Extension header 1 or greater)2
tctyp2 tctyp3		Axis type for dimension 1. Axis type for dimension 2.
tcrvl2 tcrvl3		Sky coordinates of 1st axis. Sky coordinate of 2nd axis.
tcdlt2 tcdlt3		Axis 1 degrees per pixels. Axis 2 degrees per pixels.
tcrpx2 tcrpx3		Axis 1 pixel of tangent plane direction. Axis 2 pixel of tangent plane direction.
talen2 talen3		Length of axis 1. Length of axis 2.
tc2_2 tc2_3 tc3_2 tc3_3		Partial of first axis coordinate with respect to x. Partial of first axis coordinate with respect to y. Partial of second axis coordinate with respect to x. Partial of second axis coordinate with respect to y.
Tcuni2 tcuni3		Units of first coordinate value. Units of second coordinate value.
World Coordinate System and Related Parameters (in Extension header 1 or greater)
wcsaxes		Number of World Coordinate System axes.
crpix1 crpix2		x-coordinate of reference pixel. y-coordinate of reference pixel.
crval1 crval2		First axis value at reference pixel. Second axis value at reference pixel.
ctype1 cytpe2		The coordinate type for the first axis. The coordinate type for the second axis.
cd1_1 cd1_2 cd2_1 cd2_2		Partial of first axis coordinate with respect to x. Partial of first axis coordinate with respect to y. Partial of second axis coordinate with respect to x. Partial of second axis coordinate with respect to y.
cunit1 cunit2		Units of first coordinate value. Units of second coordinate value.
ltv1 ltv2		Offset in X to subsection start. Offset in Y to subsection start.
ltm1_1 ltm2_2		Reciprocal of sampling rate in X. Reciprocal of sampling rate in Y.

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1

For FUV data subarrays 1-3 refer to segment A, and subarrays 4-7 refer to segment B.

2

The values for these keywords are currently deleted from the output files except for NUV Imaging.

Table 2.16: Spectroscopic Calibration Switch Keywords

EXPTYPE	EXTERNAL/SCI EXTERNAL/CAL				WAVECAL		DARK		FLAT
DETECTOR	FUV		NUV		FUV	NUV	FUV	NUV	FUV	NUV
OBSMODE	TIME- TAG	ACCUM	TIME- TAG	ACCM	TIME- TAG	TIME- TAG	TIME- TAG	TIME- TAG	TIME- TAG	TIME-TAG
Module
BRSTCORR	Omit1	N/A	N/A	N/A	Omit1	N/A	Omit1	N/A	Omit1	N/A
BADTCORR	Perform	N/A	Perform	N/A	Perform	Perform	Perform	Perform	Perform	Perform
PHACORR	Perform	Perform	N/A	N/A	Perform	N/A	Perform	N/A	Perform	N/A
RANDCORR	Perform	Perform	N/A	N/A	Perform	N/A	Perform	N/A	Perform	N/A
RANDSEED	-1	-1	N/A	N/A	-1	N/A	-1	N/A	-1	N/A
TEMPCORR	Perform	Perform	N/A	N/A	Perform	N/A	Perform	N/A	Perform	N/A
GEOCORR	Perform	Perform	N/A	N/A	Perform	N/A	Perform	N/A	Perform	N/A
IGEOCORR	Perform	Perform	N/A	N/A	Perform	N/A	Perform	N/A	Perform	N/A
DOPPCORR	Perform	Perform	Perform	Perform	N/A	N/A	N/A	N/A	N/A	N/A
DEADCORR	Perform	Perform	Perform	Perform	Perform	Perform	Perform	Perform	Perform	Perform
FLATCORR	Omit2	Omit	Perform	Perform	Omit	Perform	Omit	Omit	Omit	Omit
DQICORR	Perform	Perform	Perform	Perform	Perform	Perform	Perform	Perform	Perform	Perform
WAVECORR	Perform	Perform	Perform	Perform	Perform	Perform	Omit	Omit	Omit	Omit
X1DCORR	Perform	Perform	Perform	Perform	Perform	Perform	Omit	Omit	Omit	Omit
BACKCORR	Perform	Perform	Perform	Perform	Perform	Perform	Omit	Omit	Omit	Omit
FLUXCORR	Perform	Perform	Perform	Perform	N/A	N/A	Omit	Omit	Omit	Omit
TDSCORR	Perform	Perform	Perform	Perform	N/A	N/A	Omit	Omit	Omit	Omit
HELCORR	Perform	Perform	Perform	Perform	N/A	N/A	Omit	Omit	Omit	Omit
STATFLAG	T	T	T	T	T	T	T	T	T	T

---

1

BRSTCORR is set to Omit until further information about FUV bursts has been determined on-orbit.

2

FLA.

Table 2.17: Imaging Calibration Switch Keywords

EXPTYPE	EXTERNAL/SCI EXTERNAL/CAL		WAVECAL	DARK	FLAT	ACQ/IMAGE
DETECTOR	NUV		NUV	NUV	NUV	NUV
OBSMODE	TIME-TAG	ACCUM	TIME-TAG	TIME-TAG	TIME-TAG	ACCUM
Modules
BADTCORR	Perform	N/A	Perform	Perform	Perform	N/A
FLATCORR	Perform	Perform	Perform	Omit	Omit	Perform
DEADCORR	Perform	Perform	Perform	Perform	Perform	Perform
DQICORR	Perform	Perform	Perform	Perform	Perform	Perform
PHOTCORR	Perform	Perform	Perform	Omit	Omit	Perform
TDSCORR	Perform	Perform	Perform	Omit	Omit	Perform
STAFLAG	T	T	T	T	T	T

Table 2.18: Reference File Keywords

Reference File	Description
HVTAB	High voltage level table
BRSTTAB	Burst parameter table
BRFTAB	Baseline reference frame reference table
BADTTAB	Bad time interval reference table
PHATAB	Pulse height discrimination reference table
GEOFILE	Geometric distortion table
WALKTAB	Y walk correction table
DEADTAB	Deadtime reference file
FLATFILE	Pixel to pixel flat-field reference file
LAMPTAB	Template calibration lamp spectra table
WCPTAB	Wavecal parameters table
DISPTAB	Dispersion coefficient reference table
BPIXTAB	Bad pixel table
GSAGTAB	Gain sag table
XTRACTAB	1-D Spectral extraction information table
FLUXTAB	Photometric throughput table
TDSTAB	Time-dependent sensitivity correction table
SPWCSTAB	Spectroscopic World Co-ordinate System table