[Top] [Prev] [Next] [Bottom]

30.2 Headers, Keywords, and Group Parameters

Header files provide much of the information needed to reduce FOS data. A description of each keyword is generally provided in the header itself. Some important header parameters, such as exposure timing information, background correction, or scattered light correction, have different values for each group of data within the file. Such parameters are termed group parameters. Table 30.4 is a description of the different topics covered in the various header files. The header files used most often are the standard header packet (.shh), the science data header file (.d0h), and the calibrated science data header file (.c1h). Most of the information needed to understand the data is found among the header keyword types that describe general information (Table 30.4a) and among the processing and calibration information (Table 30.4c) sections of the headers. Table 30.5 lists many important header keywords used to interpret FOS data.

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)



[Top] [Prev] [Next] [Bottom]

stevens@stsci.edu
Copyright © 1997, Association of Universities for Research in Astronomy. All rights reserved. Last updated: 01/14/98 14:29:35