20.4 Headers, Keywords, and Relationship to Phase II

• Target name, coordinates, proposal id, and other proposal level information.
• Observation and exposure timing information such as observation start and duration.
• Instrument configuration information such as detector, grating, central wavelength setting, and filter.
• Readout definition parameters such as binning, gain, subarray parameters.
• Exposure-specific information such as more detailed timing, world coordinate system information, 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, wavelength shifts. The easiest way to quickly identify the observational parameters of a given dataset is to run the task infostis (see Figure 20.3 below) which prints selected header information for STIS FITS images. Wildcard characters or a file list may be used for input (e.g., *.fits or @fitslist).

cl> infostis o3xi03a1m_raw.fits

--------------------------------------------------------------------------------

                                   S  T  I  S

--------------------------------------------------------------------------------

            Rootname: O3XI03A1M                    Detector: CCD

         Proposal ID: 7071                         Obs Type: IMAGING

         Exposure ID: 3.031                        Obs Mode: ACQ

                                                       Lamp: NONE

         Target Name: GD153-1                      Aperture: F28X50LP

     Right Ascension:  12:57:02.3                    Filter: Long_Pass

         Declination: +22:01:53.2               Opt Element: MIRVIS

             Equinox: 2000.0                        CCD amp: D

                                                       Gain: 4

      Axis 1 binning: 1                            CR-split: 1

      Axis 2 binning: 1

            Subarray: yes

     Total Exp. Time: 0.3 sec

    Number of imsets: 3

STIS takes CCD and MAMA spectroscopic and imaging data, as well as acquisitions and acq/peakups. The keywords relevant for one of these data types will not necessarily be relevant to another. Accordingly, you will find that the header on your particular file contains a unique combination of keywords appropriate for your 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 STIS file types:

http://archive.stsci.edu/keyword

Table 20.6 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 populated with one of OMIT, COMPLETE, or PERFORM. Similarly, Table 20.7 summarizes the reference file group of keywords that identify the files used by the pipeline during calibration (see Chapter 21 for a detailed description of pipeline processing).

Selected Keywords and Relationship to Phase II

Keyword	Phase II Equivalent	Description
NEXTEND		Number of image extensions in the file.
Target Information (Primary Header)
TARGNAME	Target Name	Name of target.
RA_TARG DEC_TARG	RA Position DEC	Right ascension of the target (deg) (J2000). Declination of the target (deg) (J2000).
Proposal Information (Primary Header)
PROPOSID		4 digit proposal number
LINENUM		Indicates the visit and exposure number from the phase II proposal; format vv-nnnn, visit number, exposure num..
Summary Exposure Information (Primary Header)
TDATEOBS		UT date of start of first exposure in file (a character string)
TTIMEOBS		UT start time of first exposure in file (a character string); primary header.
TEXPSTRT		Start time (MJD) of 1st exposure in file (a real number).
TEXPEND		End time (MJD) of last exposure in the file (a real number); primary header.
TEXPTIME	Time_per_Exposure	Total exposure time (a real number); summed for an association; primary header.
Science Instrument Configuration (Primary Header)
OBSTYPE		Observation type (IMAGING or SPECTROSCOPIC).
OBSMODE	Opmode	Operating mode (ACQ,ACQ/PEAK,ACCUM,TIME-TAG).
DETECTOR	Config	Detector in use: NUV-MAMA, FUV-MAMA, or CCD.
OPT_ELEM	Sp_Element	Optical element in use (grating name or mirror).
MIRROR	Sp_Element	Mirror element used for imaging observations.
CENWAVE	Centra_Wavelength	Central wavelength for grating settings.
APERTURE	Aperture	Aperture name.
FILTER	Derirved from Aperture	Filter in use.
APER_FOV		Aperture field of view.
WAVEMIN		Minimum wavelength of the data.
WAVEMAX		Maximum wavelength of the data.
PLATESC		Plate scale (arcsec/pixel).
SCLAMP		Lamp status, NONE or name of lamp which is on.
LAMPSET		Spectral cal lamp current value (milliamps).
NRPTEXP	Number_of_Iterations	Number of repeat exposures in set: default 1.
SUBARRAY		Data from a subarray (T) or full frame (F).
CRSPLIT	CR-SPLIT (optional parameter)	Number of cosmic ray split exposures.
Readout Definition Parameters
SIZAXIS1	SIZEAXIS1	Subarray axis 1 size in unbinned detector pixel.
SIZAXIS2	SIZEAXIS2	Subarray axis 2 size in unbinned detector pixel.
BINAXIS1	BINAXIS1	Axis 1 data bin size in unbinned detector pixel.
BINAXIS2	BINAXIS2	Axis 2 data bin size in unbinned detector pixel.
CCDAMP		CCD amplifier read out (A,B,C,D).
CCDGAIN	GAIN (optional parameter)	Commanded gain of CCD.
CCDOFFST		Commanded CCD bias offset.
ATODGAIN		Calibrated CCD amplifier gain value.
Exposure Information (Extension header only)
DATE-OBS		UT date of start of observation (dd/mm/yy); extension header.
TIME-OBS		UT time of start of observation (hh:mm:ss); extension header.
PA_APER		Position angle of slit.
ORIENTAT		Position angle of detector.
CRPIX et al.
DGESTAR		FGS ID(F1,F2,F3) concat. w/ dom. gd. star id.

Calibration Switch Keywords

Keyword	Ref. File Keywords	Explanation	Spectra	Images	CCD	MAMA
STATFLAG	N/A	Calculate image statistics?	·	·	·	·
DQICORR	BPIXTAB	Initialize data quality image	·	·	·	·
LORESCORR	N/A	Convert MAMA image to low-res	·	·		·
DARKCORR	DARKFILE	Dark image correction	·	·	·	·
FLATCORR	LFLTFILE	Flatfield corrections	·	·	·	·
	PFLTFILE
	DFLTFILE
SGEOCORR	SDSTFILE	Small-scale distortion correction	·	·	·	·
RPTCORR	N/A	Add individual repeat observations	·	·	·	·
ATODCORR	ATODTAB	A-to-D correction	·	·	·
BLEVCORR	N/A	Correct for CCD bias level (overscan)	·	·	·
BIASCORR	BIASFILE	Bias image (structure) correction	·	·	·
CRCORR	CRREJTAB	Cosmic ray rejection	·	·	·
EXPSCORR	N/A	Process individual observations after CRCORR	·	·	·
SHADCORR	SHADFILE	Shutter shading correction	·	·	·
PHOTCORR	PHOTTAB	Populate header photometric keywords		·	·	·
GEOCORR	N/A	Geometric correction		·	·	·
X2DCORR	SDCTAB	Rectify 2-D spectral image	·		·	·
	DISPTAB		·		·	·
	INANGTAB		·		·	·
	APDESTAB		·		·	·
	MOFFTAB		·		·	·
	SPTRCTAB		·		·	·
X1DCORR	SPTRCTAB	Extract 1-D Spectrum	·		·	·
	XTRACTAB
BACKCORR	XTRACTAB	Subtract spectral background	·		·	·
DISPCORR	DISPTAB	Apply dispersion solution	·		·	·
	INANGTAB
	APDESTAB
	MOFFTAB
WAVECORR	N/A		·		·	·
FLUXCORR	APERTAB	Convert to absolute flux	·		·	·
	PHOTTAB
HELCORR	N/A	Convert to heliocentric wavelengths	·			·
DOPPCORR	N/A	Doppler correction needed? (TIMETAG mode only)	·			·
GLINCORR	N/A	Global detector non-linearities	·			·
LFLGCORR	N/A	Flag pixels for local and global non-linearities	·			·

Reference File Keywords

Keyword	File Suffix	Format	Explanation	Spectra	Images	CCD	MAMA
BPIXTAB	_bpx	Table	Bad pixel	·	·	·	·
ATODTAB	_a2d	Table	A-to-D correction	·	·	·
CCDTAB	_ccd	Table	CCD parameters	·	·	·
BIASFILE	_bia	Image	Bias (structure)	·	·	·
CRREJTAB	_crr	Table	Cosmic ray rejection parameters	·	·	·
SHADFILE	_ssc	Image	Shutter shading correction	·	·	·
DARKFILE	_drk	Image	Dark	·	·	·	·
LFLTFILE	_lfl	Image	Low-order flat	·	·	·	·
PFLTFILE	_pfl	Image	Pixel-to-pixel flat	·	·	·	·
DFLTFILE	_dfl	Image	Delta-flat	·	·	·	·
SDSTFILE	_ssd	Image	Small-scale distortion correction	·	·		·
MLINTAB	_lin	Table	Flux linearity table	·	·		·
PHOTTAB	_pht	Table	Photometric conversion	·	·	·	·
APERTAB	_apt	Table	Aperture throughput	·		·	·
LAMPTAB	_lmp	Table	Template CAL lamp spectra	·		·	·
APDESTAB	_apd	Table	Aperture descriptions	·		·	·
IDCTAB	_idc	Table	Image distortion correction		·	·	·
SDCTAB	_sdc	Table	2-D spectrum distortion correction	·		·	·
INANGTAB	_iac	Table	Incident angle correction	·		·	·
MOFFTAB	_moc	Table	MAMA Offset correction	·			·
DISPTAB	_dsp	Table	Dispersion coefficients	·		·	·
SPTRCTAB	_1dt	Table	1-D Spectrum trace	·		·	·
XTRACTAB	_1dx	Table	1-D Extraction parameter	·		·	·