HST Keyword Dictionary

Space Telescope Science Institute

3700 San Martin Drive

Baltimore, MD 21212

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Keyword Definitions for the

Faint Object Spectrograph
Science Data Header

dated 15-APR-94

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APER_FOV: Aperture field of view (arcsec); Datatype: CHARACTER*24 Units: Name; Field of view for the aperture used in the observation. The field of view depends on whether or not the FOS COSTAR mirrors are deployed (indicated by KYDEPLOY=T or F).
APER_ID KYDEPLOY APER_FOV A-1 F 4.30 x 4.30 SINGLE A-1 T 3.66 x 3.71 SINGLE A-2 F 0.50 PAIR SQUARE A-2 T 0.43 PAIR SQUARE A-3 F 0.25 PAIR SQUARE A-3 T 0.21 PAIR SQUARE A-4 F 0.10 PAIR SQUARE A-4 T 0.09 PAIR SQUARE B-1 F 0.50 SINGLE CIRCULAR B-1 T 0.43 SINGLE CIRCULAR B-2 F 0.30 SINGLE CIRCULAR B-2 T 0.26 SINGLE CIRCULAR B-3 F 1.00 SINGLE CIRCULAR B-3 T 0.86 SINGLE CIRCULAR B-4 F BLANK B-4 T BLANK C-1 F 1.00 PAIR SQUARE C-1 T 0.86 PAIR SQUARE C-2 F 0.25 x 2.00 SINGLE SLIT C-2 T 0.21 x 1.71 SINGLE SLIT C-3 F 2.00 BAR OCCULT SQUARE C-3 T 1.71 BAR OCCULT SQUARE C-4 F 0.70 x 2.00 BAR OCCULT C-4 T 0.60 x 1.71 BAR OCCULT

Source : (FOS Handbook)

APER_ID: aperture ID; Datatype: CHARACTER*03 Units: Name; APER_ID Aperture A-2 0.5-PAIR A-3 0.25-PAIR A-4 0.1-PAIR B-1 0.5 B-2 0.3 B-3 1.0 B-4 BLANK C-1 1.0-PAIR C-2 0.25x2.0 C-3 2.0-BAR C-4 0.7x2.0-BAR ERR error

Source : (tguide 7.0-11)

APER_POS: aperture used; Datatype: CHARACTER*8 Units: Name; Aperture position (lower or upper) for observations obtained with paired apertures or "single" for single apertures.
single upper lower

Source :

BACHFILE: background header file; Datatype: CHARACTER*18 Units: FILENAME; The background files contain the default background data used during background subtraction for both object and sky spectra. Background data are stored in a single group with M*N entries where M is the number of diodes plus overscan minus one, and N is the number of X-substeps. Each pixel in the background data file is a single-precision real (REAL*4) count rate value in counts per second.
Source : (calguide)

BAC_CORR: background subtraction; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Subtract the background from sky and object spectra. The observed background is first repaired; bad points (i.e., points at which the data is flagged as lost or garbled in the telemetry process) are filled by linearly interpolating between "good neighbors". Next, the background is smoothed with a median, followed by two iterations of a mean filter before subtraction. Filter widths are contained in table CCS3. If no background was taken, a default reference background, BACHFILE, is used. No smoothing is done to the reference file background, if used. This is a spectroscopy mode calibration step.
Source :(calguide)

BUNIT: brightness units; Datatype: CHARACTER*18 Units: Name; Data units for an image: unitless, counts, counts/s, ergs/cm**2/s/A, or Angstroms. Data quality files are unitless, wavelength files have units of Angstroms, raw science data files have units of counts, calibrated science data files have units of counts/s or ergs/cm**2/s/A.
Source :

CCG2: paired pulse correction parameters; Datatype: CHARACTER*18 Units: FILENAME; Paired-pulse correction table. Deadtime constants are used to correct for the non-linear channel response of each diode. These constants are not expected to change during the lifetime of the FOS. Analysis of prelaunch data indicate that the same constants can be used for both FOS detectors.
Source :(calguide)

CCS0: aperture parameters; Datatype: CHARACTER*18 Units: FILENAME; A CDBS table containing parameters used to describe the FOS apertures. The relation is filled using data from the project data base tape. Records of aperture parameters are organized by detector and aperture ID. Aperture areas required to scale a sky spectrum taken in one aperture of a paired aperture before subtraction from the object spectrum taken in the other aperture. Values for this relation are required only for the paired apertures.
Source :(calguide)

CCS1: aperture position parameters; Datatype: CHARACTER*18 Units: FILENAME; A CDBS table containing the two Y position values used to determine which of the apertures (upper or lower) was used for a given observation with a paired aperture. The relation is filled using data from the project data base tape. Records of aperture position parameters are organized by detector and disperser.
Source :(calguide)

CCS2: emission line position parameters; Datatype: CHARACTER*18 Units: FILENAME; A CDBS table containing the beginning and ending data point numbers of known emission line regions to be avoided during the smoothing of sky spectra. Records of emission line data points are organized by detector, disperser, first channel (FCHNL), and the number of X-substeps (NXSTEPS). Values for this relation are required only when an observed sky spectrum exists in the data set that is undergoing calibration.
Source : (calguide)

CCS3: filter width parameters; Datatype: CHARACTER*18 Units: FILENAME; A CDBS table containing the mean and median filter widths used to smooth sky and background spectra. Records are organized by detector. Values for this relation are required only when observed sky or background spectra exist in the data set that is undergoing calibration.
Source : (calguide)

CCS4: Wollaston/Waveplate parameters; Datatype: CHARACTER*18 Units: FILENAME; A CDBS table containing the initial position of the waveplate and the measures of the angles of each of two pass directions with respect to the Q=1 coordinate axis of the polarization reference frame. Records are organized by detector, disperser, and polarizer ID. Values for this relation are required only for polarimetry data sets.
Source : (calguide)

CCS5: sky shift parameters; Datatype: CHARACTER*18 Units: FILENAME; A CDBS table containing the offset (in pixels) by which sky spectra be shifted in order to align the wavelength scale with that of object spectra before sky spectra are subtracted from object spectra. Records are organized by detector, aperture, disperser, and the number of X-substeps. Values for this relation are required only when a sky spectrum exists in the data set that is undergoing calibration.
Source : (calguide)

CCS6: wavelength coefficients; Datatype: CHARACTER*18 Units: FILENAME; A CDBS table containing the coefficients used to generate a wavelength scale for FOS spectral data. Records are organized by detector, disperser, aperture, polarizer ID, and pass direction.
Source :(calguide)

CCS7: GIMP-correction coefficients; Datatype: CHARACTER*18 Units: FILENAME; A CDBS table containing the scale factors for the coefficients used to correct for the geomagnetically-induced image motion problem (GIMP) in FOS data. Records are organized by detector. Values for this relation are required only when the data have not had the onboard GIMP correction applied during the observation.
Source :(calguide)

CCS8: background count rates; Datatype: CHARACTER*18 Units: FILENAME; A CDBS table containing the predicted mean background count rates as a function of geomagnetic latitude and longitude. The mean background count rate at the time and position os the observation is interpolated from this table and used to scale the reference background file during calibration. Records are organized by detector and geomagnetic latitude longitude.
Source : (calguide)

CCS9: scattered light parameters; Datatype: CHARACTER*18 Units: FILENAME; A CDBS table containing the beginning and ending channel numbers of spectral regions which, for certain dispersers, have no sensitivity to dispersed light. These regions are used to measure the level of scattered light within the spectrum. Records are organized by detector and disperser.
Source : (calguide)

CNT_CORR: count to count rate conversion; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Convert from raw counts to count rates by dividing each data point by the exposure time and then correcting for disabled diodes. If DEFDDTBL=T, the disabled diodes are taken from the Unique Data Log (UDL), otherwise, the disabled diodes are found in the file DDTHFILE. This is a standard calibration step.
Source :(calguide)

DDTHFILE: disabled diode table header file; Datatype: CHARACTER*18 Units: FILENAME; The disabled diode files contain a disabled diode table for use in the standard case reduction when the Unique Data Log (UDL) is not available. Data are stored in a single group with 512 data values, one for each diode, with a value of zero indicating a disabled diode and a value of one indicating an enabled diode. Data are stored in short integer format (INTEGER*2).
Source : (calguide)

DEADTIME: accumulator close time (unit=7.8125 microsec); Datatype: INTEGER*4 Units: 7.8125 microsecon; The amount of time spent transferring accumulated counts to memory at the close of each accumulation (livetime) period.
Source :

DECAPER1: declination of the aperture (deg); Datatype: REAL*8 Units: DEGREES; Source :

DEC_APER: declination of aperture (deg); Datatype: REAL*8 Units: DEGREES; The declination of the reference position of the aperture used for the group data. For WFPC group data, the aperture is indicated by the value of the group keyword DETECTOR. For other SIs the aperture is that indicated by the standard header packet keyword APEROBJ.
Source :

DEFDDTBL: UDL disabled diode table used (T/F); Datatype: LOGICAL*1 Units: T/F; This flag indicates whether or not the list of disabled diodes stored in the Unique Data Log (UDL) is to be used to correct for the effects of disabled diodes during the count to count-rate conversion process in the calibration pipeline (CALFOS). If DEFDDTBL=F, a calibration reference file containing disabled diode information (DDTHFILE) will be used instead of the UDL.
Source : (ICD-47)

DETECTOR: detector in use: amber, blue; Datatype: CHARACTER*05 Units: Name; Indicates which of the two FOS detectors (AMBER or BLUE) was used for the observation.
Source :

DQ1HFILE: first data quality initialization header file; Datatype: CHARACTER*18 Units: FILENAME; Data quality initialization files contain a priori information about the effect of the FOS's diode arrays on the quality of output data values. The files contain data quality flag values for intermittent noisy and dead channels. Data quality initialization data are stored in a single group with M*N entries where M is the number of diodes plus overscan minus one, and N is the number of X-substeps. Data quality initialization data are stored in single-precision real format (REAL*4).
Source : (calguide)

DQ2HFILE: second data quality initialization header file; Datatype: CHARACTER*18 Units: FILENAME; Data quality initialization file applied to data from the second aperture of paired-aperture observations and the second pass direction of polarimetry observations.
Source : (calguide)

ERR_CORR: propagated error computation; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Compute the propagated error at each point in the spectrum. The photon statistical errors in the original data are carried through the reductions. The errors are scaled at each calibration step. Thus, the standard errors have the same units as the calibrated data. This step is a spectroscopy mode calibration step.
Source :(calguide)

EXPOSURE: exposure time per pixel (seconds); Datatype: REAL*4 Units: SECONDS; Total exposure time per pixel for a data group since the previous memory clear.
Source : (FOS Handbook)

FCHNL: first channel; Datatype: INTEGER*4 Units: CHANNEL NUMBER; The first channel (diode) to be processed: 0,2,4,...,510 or -1 for error.
Source :[qexposure.fchnl]

FGWA_ID: FGWA id; Datatype: CHARACTER*03 Units: NAME; Identifies the dispering element (grating or prism) used in the observation.
Disperser FGWA_ID G130H H13 G190H H19 G270H H27 G400H H40 G570H H57 G780H H78 G160L L15 G650L L65 PRISM PRI MIRROR CAM or ERR for error.

Source :[qexposure.fgwa_id]

FL1HFILE: first flat-field header file; Datatype: CHARACTER*18 Units: FILENAME; Flat field files contain diode and photocathode sensitivity data used to correct spectra for fine structure sensitivity variations. Flat field data are stored in single-precision real format (REAL*4).
Source : (calguide)

FL2HFILE: second flat-field header file; Datatype: CHARACTER*18 Units: FILENAME; Flat field file applied to data from the second aperture of paired-aperture observations and the second pass diretion of polarimetry observations.
Source : (calguide)

FLT_CORR: flat fielding; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Remove diode-to-diode sensitivity variations and fine structure by multiplying by the flat field response. The object spectra and sky spectra (if obtained) are flat-fielded. This process requires the use of the flat field response file, FL1HFILE. A second flat field file, FL2HFILE, is required for paired aperture or spectropolarimetry observations. This step is a spectroscopy mode calibration step.
Source :(calguide)

FLX_CORR: flux scale generation; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Convert the object spectra to absolute flux units. The object spectra are converted to flux units by multiplying by the inverse sensitivity vector. This routine requires the inverse sensitivity file IV1HFILE. A second inverse sensitivity file, IV2HFILE, is required for paired- aperture or spectropolarimetry observations. This calibration step converts the count rates to units of ergs/cm**2/sec/Angstrom. This step is a spectroscopy mode calibration step.
Source :(calguide)

GMF_CORR: scale reference background; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Scale the reference background file to a mean expected count rate based on the geomagnetic position of the spacecraft at the time of the observation. The reference background data are scaled before subtracting them from the object and sky spectra. This routine requires the background count rates table CCS8.
Source : (calguide)

GRNDMODE: ground software mode; Datatype: CHARACTER*18 Units: Name; LED-FLAT-FIELD-MAP (IMAGE) TIME-RESOLVED (PERIOD) TIME-TAGGED (TAG) RAPID-READOUT (RAPID) TARGET ACQUISITION (ACQ,ACQ/BINARY,ACQ/PEAK,ACQ/FIRMWARE) SPECTROSCOPY (no polarizer) SPECTROPOLARIMETRY (with polarizer)

Source :

HEADER: science header line exists; Datatype: LOGICAL*1 Units: T/F; Source :

INTS: number of integrations; Datatype: INTEGER*4 Units: Counts; The number of repetitions of the livetime/deadtime cycle, whereby electrons are counted in the selected diode accumulators with no changes in magnetic deflection.
Source : (FOS Handbook)

IV1HFILE: first inverse sensitivity header file; Datatype: CHARACTER*18 Units: FILENAME; Inverse sensitivity files contain data used to convert count rate data to an absolute flux scale. Inverse sensitivity data are stored in single-precision real format (REAL*4) and have units of (ergs/cm**2/s/A)/(counts/s).
Source : (calguide)

IV2HFILE: second inverse sensitivity header file; Datatype: CHARACTER*18 Units: FILENAME; Inverse sensitivity data applied to the second aperture of paired-aperture observations and the second pass direction of polarimetry observations.
Source : (calguide)

KYDEPLOY: COSTAR deployed for FOS (T or F); Datatype: LOGICAL*1 Units: TRUE/FALSE; The logical KYDEPLOY keywords are to be set to True only if the COSTAR arm for the FOS has been deployed. There are two conditions under which this keyword should be set to False. Before the servicing mission, a database flag will have to be set to instruct PODPS not to extract the COSTAR mirror positions from the SHP (the telemetry positions will still correspond to HSP data), set the DEPLOY keywords to False and set the mirror position keywords to a default value (99999). Once COSTAR is installed in HST, the database flag will be set to indicate that the COSTAR SHP entries are valid. PODPS should then populate the DEPLOY keywords based on the SHP position telemetry values. If any of the telemetered values for a given SI are the default value (99999), then the DEPLOY keyword for that SI should be set to false. This will allow for the possibility of deploying some COSTAR arms and not others.
Source :

LIVETIME: accumulator open time (unit=7.8125 microsec); Datatype: INTEGER*4 Units: 7.8125 microsecon; Time interval during which counts are accumulated before being transfered to memory.
Source :

MAXCLK: maximum clock count; Datatype: INTEGER*4 Units:; Source :

MAXWAVE: maximum wavelength (angstroms); Datatype: REAL*4 Units: ANGSTROMS; Maximum wavelength value for calibrated images.
Source :

MINWAVE: minimum wavelength (angstroms); Datatype: REAL*4 Units: ANGSTROMS; Minimum wavelength value for calibrated images.
Source :

MIR_REVR: is the image mirror reversed; Datatype: LOGICAL*4 Units: T/F; Source :

MOD_CORR: ground software mode dependent reductions; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Perform ground software mode-dependent reductions for time-resolved, spectropolarimetry, and rapid-readout observations. The following processing steps are performed in addition to the standard case and spectroscopy mode calibration steps. Rapid-Readout: The total and its statistical error for each frame are calculated. Time-Resolved: The average of all slices (bins) and the differences from the average for each slice (bin) of the last frame of time-resolved data are computed. Spectropolarimetry: The spectropolarimetry reductions require the Wollaston and Waveplate parameter table, CCS4, and the retardation reference file, RETHFILE. On an initial pass, the reference data is read. On all calls to the special processing routine, the flux and errors are saved for use on the last call---in which the processing is done. The Stokes parameters, linear and circular polarization, and the polarization angle (theta) for FOS polarimetry data are computed. Interference is corrected using the coefficients in CCS4 and theta is changed to sky coordinates by adding PANGAPER. If you are truly interested in how this works, talk to Rich Allen.
Source :(calguide)

NCHNLS: number of channels; Datatype: INTEGER*4 Units: CHANNELS; The number of channels to be processed: 2,4,...,512 or -1 for error.
Source :[qexposure.nchnls]

NMCLEARS: number of memory clears per acquisition; Datatype: INTEGER*4 Units: Count; A memory clear zeroes all locations in the science data array to allow input of new data.
Source : (FOS Handbook)

NOISELM: burst noise rejection limit; Datatype: INTEGER*4 Units: Counts; If burst noise rejection mode is enabled, the sum of the counts is examined at each closing of the accumulators before being transfered to memory. A value greater than the commanded reject limit (NOISELM) will cause the data to be rejected as burst noise. The FOS microprocessor keeps track of the number of rejected integrations in a rejection array which is indexed by x-step, overscan, y-step, and slice.
Source : (FOS Handbook)

NPAT: number of patterns per readout; Datatype: INTEGER*4 Units: Count; A pattern is a completed series of slices; all memory locations allocated for the science data array (and the reject array, if applicable) are filled after completion of the first pattern. Counts in subsequent patterns will be added to the corresponding previous values in the science data array.
Source : (FOS Handbook)

NREAD: number of readouts per memory clear; Datatype: INTEGER*4 Units: Count; A readout consists of sending the science data to the NSSC-1 computer for either storage on the tape recorder or telemetry to the ground. Readouts are non-destructive, and typically will be performed at regular intervals (nominally four minutes) without memory clears in order to protect against loss of data. The last readout contains all the data accumulated since the previous memory clear.
Source : (FOS Handbook)

NXSTEPS: number of x steps; Datatype: INTEGER*4 Units: Count; The number of xsteps per ystep: 1,...,32 or -1 for error. X-steps are magnetic field deflections of the electrons in the dispersion (x) direction. The default value for X-step is 4, the so-called "quarter stepping" that will place the electrons on the next diode after 4 steps. The data go into new memory locations with each X-step. The reason for x-stepping is to satisfy the Nyquist sampling criterion, which requires X-step greater than or equal to 2.
Source : (FOS Handbook)

OFFS_TAB: GIMP offsets (post-pipeline processing only); Datatype: CHARACTER*18 Units: FILENAME; A user-supplied table of X- and Y-offset values to be used when performing the groundbased GIMP-correction during post-pipeline calibration processing. This method offers an alternative to using offset values based on the geomagnetic position of the spacecraft at the time of the observation.
Source : (calguide)

OFF_CORR: GIMP correction; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Correct count rate spectra for the geomagnetically-induced image motion problem (GIMP). This routine the GIMP-correction scale factors table CCS7, or (for post-pipeline processing only) a user-supplied table of X- and Y-offset values. This step is a spectroscopy mode calibration step and is performed only if the onboard GIMP correction was not enabled for the observation.
Source : (calguide)

ORIENTAT: the orientation of the image (deg); Datatype: REAL*4 Units: Degrees; Source :

OVERSCAN: overscan number; Datatype: INTEGER*4 Units: COUNT; The overscan number: 1,2,3,4,...,256 or -1 for error. The overscan parameter indicates the number of times to repeat the addition of counts into the memory array, with an offset of one memory location at each overscan. Each offset is accompanied by a corresponding magnetic deflection in the x-direction so that data from a given photocathode location falls into the same memory location independent of the diode which sampled it. The purpose is to average out the response of different diodes, including dead ones.
Source : (FOS Handbook)

PASS_DIR: polarization pass direction; Datatype: INTEGER*4 Units: Direction index; The waveplate plus Wollaston prism assemblies split the incoming beam into a pair of spectra corresponding to orthogonal directions of polarization. The first pass direction (PASS_DIR=1) spectrum corresponds the ordinary ray, and the second pass direction (PASS_DIR=2) spectrum corresponds to the extra-ordinary ray. One exposure is composed of an observation of the spectrum from each pass direction and is accomplished by alternately deflecting one of the two spectra onto the diode array.
Source : (FOS Handbook)

PA_APER: position ang of aperture used with target (deg); Datatype: REAL*4 Units: DEGREES; This value is computed before the observation, rather than spacecraft measured. This is the angle from North, towards East, of the +Y-axis of the Science Instrument Corrected System (SICS) coordinates for the aperture designated by APEROBJ. The direction of North is taken at the target even when he target is not centered in the FOV. For FOC, the zoomed FOV have the SICS Y-axis aligned with the direction of increasing pixel. In the group data, the Y-axis (for the CD matrix and ORIENTAT) is always the direction of increasing line. For these zoomed FOC apertures, that can be identified as those with a Z in the fourth caharcter in APEROBJ, the value of PA_APER will be 90 degrees larger than the ORIENTAT value in the group data. For FOS, in the right-handed XY coordinate system of the detector, this is the angle one rotates the image clockwize in order for North to coincide with +Y. The FOS APEROBJ values that end in "BAR" have a PA_APER value 90 degrees larger than ORIENTAT.
Source :[qobservation.aper_angle]

PKTFMT: packet format code; Datatype: INTEGER*4 Units: Code; The packet format code indicates the instrument data accumulation mode.
PKTFMT OPMODE 64 WAVECAL 80 IMAGE 81 Discriminator/Noise test 96 Spectroscopy (ACCUM) 97 Spectropolarimetry (ACCUM) 98 TIME-TAGGED (TAG) 99 RAPID-READOUT (RAPID) 100 TIME-RESOLVED (PERIOD) (synchronous) 101 TIME-RESOLVED (PERIOD) (asynchronous) 112 ACQ/FIRMWARE (raw data) 113 ACQ/FIRMWARE (filtered data) 114 ACQ/FIRMWARE (raw + filtered data) 115 ACQ 128 ACQ/BINARY 129 ACQ/PEAK

Source :

POLANG: initial angular position of polarizer; Datatype: REAL*4 Units: DEGREES; Position angle of the polarizer at the start of the observation.
Source :

POLAR_ID: polarizer id; Datatype: CHARACTER*01 Units: Name; Name of the polarizer in use (if any) for the observation.
A: polarizer A; B: polarizer B; C: no polarizer; E: error.

Source :

PPC_CORR: paired pulse correction; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Correct the raw count rates for saturation in the detector electronics using table CCG2, which contains the paired-pulse correction parameters. On the first call, the paired pulse parameters are read from table CCG2. The following equation is used:
x = y/(1-yt) Where: x -- is the true count rate, y -- is the observed count rate, t = q0 if y is less than or equal to F, and t = q0 + q1 * (y - F) if y is greater than F. q0, q1, and F are coefficients in CCG2.
This is a standard calibration step.
Source :(calguide)

RA_APER: right ascension of aperture (deg); Datatype: REAL*8 Units: DEGREES; The right ascension of the reference position of the aperture used for the group data. For WFPC group data, the aperture is indicated by the value of the group keyword DETECTOR. For other SIs the aperture is that indicated by the standard header packet keyword APEROBJ.
Source :

RA_APER1: right ascension of the aperture (deg); Datatype: REAL*8 Units: DEGREES; Source :

RETHFILE: waveplate retardation header file; Datatype: CHARACTER*18 Units: FILENAME; The FOS retardation files contain values computed from the retardation of the waveplate used during spectropolarimetric calibration to create observation matrix f(w). Retardation data are stored in separate groups corresponding to pass direction for polarizers A and B. Retardation data are stored in REAL*4 format.
Source : (calguide)

SCT_CORR: scattered light correction; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Subtract contribution of scattered light from object and sky spectra. This routine measures the level of scattered from spectral regions that have no sensitivity to dispersed light and subtracts that value from the object and sky spectra. This correction can only be performed for data obtained using detector/disperser combinations that contain regions of no sensitivity within the recorded spectra. This routine requires the scattered light parameters table CCS9, which contains the beginning and ending diode numbers of the no sensitivity region for each detector/disperser combination. This is a spectroscopy mode calibration step.
Source : (calguide)

SCT_ERR: scattered light correction error; Datatype: REAL*4 Units: COUNTS/S; Uncertainty in the mean scattered light value. Computed as:
( sum ( C - |C| )**2 ) sct_err = sqrt ( ------------------ ) ( total * (total-1) ) where C -- is the pixel value in counts/s |C| -- is the mean pixel value over the no sensitivity region sum -- is the sum over all pixels in the no sensitivity region total -- is the total number of pixels in the no sensitivity region

Source : (calguide)

SCT_VAL: scattered light correction value; Datatype: REAL*4 Units: COUNTS/S; The mean value of the scattered light computed during the SCT_CORR calibration step. This value is subtracted from every pixel in the object and sky count rate spectra.
Source : (calguide)

SKY_CORR: sky subtraction; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Subtract the sky from the object spectrum. If the sky was observed, the flat-fielded sky spectrum is smoothed with a median filter once and a mean filter twice, except in known regions of emission lines. The spectrum is then scaled by the aperture size, and shifted so that the wavelength scales of the object and sky are matched. The sky spectrum is then subtracted from the object spectra. This routine requires table CCS3 containing the filter widths, the aperture size table, CCS0, the emission line position table, CCS2, and the sky shift table, CCS5. This step is a spectroscopy mode calibration step.
Source :(calguide)

SLICES: number of time slices; Datatype: INTEGER*4 Units: Count; A single slice consists of an entire deflection sequence, where a deflection sequence is composed of all magnetic deflections necessary satisfy NXSTEPS, OVERSCAN, and YSTEPS. A deflection sequence can be repeated up to SLICES number of times; the data from each repetition goes into a new set of memory locations.
Source : (FOS Handbook)

TRAILER: reject array exists; Datatype: LOGICAL*1 Units: T/F; Indicates whether or not a reject array (TRAILER file) exists for the observation.
Source :

WAV_CORR: wavelength scale generation; Datatype: CHARACTER*08 Units: PERFORM/OMIT; Compute a vacuum wavelength scale for each object or sky spectrum. Wavelengths are computed using coefficients stored in table CCS6. This is computed differently for the gratings and for the prism. This step is a spectroscopy mode calibration step.
Source :(calguide)

XBASE: X-deflection base; Datatype: INTEGER*4 Units: 1/32 diode width; The X deflection base value in units of 1/32 of the diode width. The default is zero. This may be used to move an image away from the region of a dead diode, to adjust the X deflection scaling, and to permit viewing of the photocathode mask edge region. The range is -2048 to +2047 (equivalent to +/- 64 diodes).
Source : (FOS Handbook)

XPITCH: X-deflection pitch between diode; Datatype: INTEGER*4 Units:; Source :

X_OFFSET: x_offset for GIMP correction (diodes); Datatype: REAL*4 Units: DIODES; X offset value used during groundbased GIMP correction. Either computed from the geomagnetic position of the spacecraft at the time of the observation or read from the user-supplied OFFS_TAB input table.
Source : (calguide)

YBASE: Y-deflection base; Datatype: INTEGER*4 Units: 1/256 diode heigh; The Y deflection base value in units of 1/256 of the diode height. Default values are set from a table of premeasured values, depending on the aperture, grating wheel and polarizer settings, and the value of YSTEPS. The range is -2048 to +2047 (equivalent to +/- 8 diode heights).
Source : (FOS Handbook)

YFGIMPEN: onboard GIMP correction enabled (T/F); Datatype: LOGICAL*1 Units: T/F; Data obtained after April 5, 1993 have the option of using the onboard GIMP-correction scheme. Data obtained without the onboard correction require the groundbased pipeline calibration correction. The onboard GIMP correction is applied on a finer grid than the groundbased correction, and is applied in both the dispersion (x) and spatial (y) directions of the diode array. The onboard GIMP correction is calculated and applied every 30 seconds.
Source :

YFGIMPER: error in onboard GIMP correction (YES/NO); Datatype: CHARACTER*03 Units: YES/NO; Indicates whether or not an error occured during application of the onboard GIMP correction.
Source :

YLINSFRM: packets per frame; Datatype: INTEGER*4 Units: count; Source :

YPITCH: Y-deflection pitch; Datatype: INTEGER*4 Units:; Source :

YPOS: y-position on photocathode; Datatype: REAL*4 Units: 1/256 diode heigh; YPOS specifies the position (in the y or spatial direction) on the photocathode from which the spectrum is read. Each disperser produces its spectrum at a different location on the photocathode. The photoelectrons from the region of the photocathode where the image is expected are then accelerated to the diode array to be accumulated and recorded. The photocathode extends from -2048 to +2047 Y-base units. Spectra recorded in different Y-STEPS within one observation sequence can have different values of YPOS (e.g. object and sky spectra observed through the upper and lower portions of a paired aperture).
Source : (FOS Handbook)

YRANGE: y range; Datatype: INTEGER*4 Units: 1/32 YBASE unit; YRANGE selects the range over which the y-deflections for an observation sequence will occur. Successive YSTEP increments are offset (always in in the +Y direction) by (YRANGE*32)/YSTEPS.
Source : (FOS Handbook)

YSPACE: yrange * 32 / ysteps; Datatype: REAL*4 Units: 1/256 diode heigh; The spacing, in YBASE units, between successive YSTEPS in a deflection sequence. The YSPACE has legal values, ranging from 0 to 4080, of (N x 32) / YSTEPS, where N (the YRANGE) is an integer from 0 to 255. YSPACE is normally set, for star-sky or star-sky-bkg step patterns in ACCUM mode, to correspond to the spacing between images from the upper and lower apertures of the paired apertures. YSPACE is also automatically set to correspond to the spacing between the two spectra produced by the polarizer when a POLSCAN is performed.
Source : (FOS Handbook)

YSTEP1: first ystep data type: OBJ, SKY, BCK, NUL; Datatype: CHARACTER*03 Units: Name; Source type for the spectral data obtained at YSTEP position 1.

YSTEP2: second ystep data type: OBJ, SKY, BCK, NUL; Datatype: CHARACTER*03 Units: Name; Source type for the spectral data obtained at YSTEP position 2.

YSTEP3: third ystep data type: OBJ, SKY, BCK, NUL; Datatype: CHARACTER*03 Units: Name; Source type for the spectral data obtained at YSTEP position 3.

YSTEPS: number of y steps; Datatype: INTEGER*4 Units: count; A Y-step is a magnetic deflection of electrons at right angles to the dispersion direction. The value, YBASE, is set at the beginning of an observation and is the base for the entire y-deflection sequence, ending after YSTEPS deflection increments. The purposes of y-stepping include mapping the photocathode and switching between the two spectra from the polarizer or paired apertures.
Source : (FOS Handbook)

YTYPE: observation type: OBJ, SKY, BCK; Datatype: CHARACTER*4 Units: Name; This is a group parameter that specifies the source type for the spectral data contained in each data group of an image. Each group usually corresponds to data obtained at a particular YSTEP position. Either object (OBJ), sky (SKY), or background (BCK).
Source :

YWRDSLIN: science words per packet; Datatype: INTEGER*4 Units: count; Source :

Y_OFFSET: y_offset for GIMP correction (defl.units); Datatype: REAL*4 Units: Deflection units; Y offset value used during groundbased GIMP correction. Either computed from the geomagnetic position of the spacecraft at the time of the observation or read from the user-supplied OFFS_TAB input table. Note that the Y_OFFSET value is computed by the groundbased GIMP correction scheme, but is NOT applied to the data. Source : (calguide)
Source :

HST Keyword Dictionary: 15-APR-94: (rose@stsci.edu)