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35.2 Header Keywords

The header files provide all the information needed to calibrate GHRS data. The headers are divided into groups of keywords that deal with specific types of information (i.e., observing information, engineering information, and processing and calibration information). Table 35.4 lists a few of the important GHRS header keywords.

An HST observation is composed of packets of information sent down to the ground, and each observation packet has an embedded packet format code to identify the packet as SHP, UDL, or science. Each science packet has a packet format code (PKTFMT) that identifies the type of science. The default GHRS calibration switches are set by the PKTFMT keyword value, specified by the type of observation (Target ACQuisition, IMAGE, ACCUM, or RAPID mode). The default calibration switches have been selected to achieve the best possible calibration. The PKTFMT values are set when the observations are scheduled. They are used to determine the values of the science header keywords. This information is stated here for completeness.

The GHRS calibration steps are listed and described in "Recalibrating GHRS Data" on page 36-13.



Important GHRS Header Keywords

Keyword

Description and Values

GCOUNT

Number of data groups

FILETYPE

shp, udl, ext, sci, img, wav, flx

NBINS

Number of substep bins in this pattern

RPTOBS

Expected number of observation repeats

STEPPATT

Step pattern sequence

FP_SPLIT

FP-SPLIT (NO, TWO, FOUR, DSTWO, DSFOUR)

COMB_ADD

Comb-addition (NO, TWO, FOUR, DSTWO, DSFOUR)

FINCODE

Observation termination code

OBSMODE

Observation mode (ACCUM, RAPID, SPYBAL, DEFCAL, ACQ,)

DETECTOR

Detector in use (1 or 2)

GRATING

Grating, echelle, or mirror in use

APERTURE

Aperture name

DATE

Date this file was written (dd/mm/yy)

KZDEPLOY

COSTAR deployed for the HRS (T or F)

APER_FOV

Aperture field of view (arcsec), N/A for cal

FGSLOCK

Commanded FGS lock (FINE, COARSE, GYROS, UNKNO

DATE-OBS

UT date of start of observation (dd/mm/yy)

TIME-OBS

UT time of start of observation (hh:mm:ss)

EXPTIME

Exposure duration (seconds)-calculated



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