HST Keyword Dictionary

Space Telescope Science Institute

3700 San Martin Drive

Baltimore, MD 21212

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Keyword Definitions for the

This is version 11.4, dated 16-NOV-1987

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APERAREA
aperature area 
Datatype: REAL*4              
Units:    ARCSECONDS^2
Area of the aperture used, in square arc seconds. This keyword is filled by calibration software only when the target is an extended source.

Source :

APERTOBJ
aperture in use - object data 
Datatype: CHARACTER*10        
Units:

Source :

APERTSKY
aperture in use - sky data 
Datatype: CHARACTER*10        
Units:

Source :

APERTURE
name of the aperture used for this file 
Datatype: CHARACTER*10        
Units:

Source :

BDEXPFLG
bus director expander flag 
Datatype: INTEGER*2           
Units:

Source :

BUNIT
brightness units: COUNTS or DN (analog data) 
Datatype: CHARACTER*18        
Units:

Source :

CCP0
aperture area table name 
Datatype: CHARACTER*18        
Units:    FILENAME
A CDBS table containing the names and areas of all the HSP's apertures and are used by the HSP calibration. Each entry contains an aperture name and an aperture area, which is used to convert HSP count rates into count rates per square arc-second. This information is loaded only from the Project Data Base Tape. See ICD-47 for further information.

Source :

COMPTAB
the HST components table 
Datatype: CHARACTER*18        
Units:    FILENAME
See PHOTMODE and related photometry keywords.

Source :

CVCOFSET
scaled CVC offset 
Datatype: REAL*4              
Units:
Current-to-voltage converter (CVC) offset, in DN. This keyword is filled by the calibration software only for digital data files.

Source :(calhsp)

DARKRATE
scaled cathode dark rate 
Datatype: REAL*4              
Units:    COUNTS/SEC
Dark counts due to the detector, in counts/second, calculated by the calibration sofware

Source :(calhsp)

DATA_FMT
data format: byte, word, lwrd, alog, all 
Datatype: CHARACTER*04        
Units:

Source :

DATA_SRC
data source: star, sky, area scan 
Datatype: CHARACTER*09        
Units:

Source :

DATA_TYP
data type: digital, analog 
Datatype: CHARACTER*07        
Units:

Source :

DEADTIME
deadtime correction 
Datatype: CHARACTER*08        
Units:

Source :

DEADTM
deadtime 
Datatype: REAL*4              
Units:    SECONDS
Deadtime used in calculating pair-pulse correction for digital data, in seconds. This keyword is filled by the calibration software only for digital data files.

Source :(calhsp)

DEC_APER
declination of the aperture (deg) 
Datatype: REAL*8              
Units:    DEGREES

Source :

DELAY
delay between integrations (seconds) 
Datatype: REAL*4              
Units:

Source :

DETECTOB
detector in use (0-5) - object data 
Datatype: INTEGER*2           
Units:
This holds the number of the detector that was used for data from the object during this observation. It is one of the five image dissector tubes (numbered from 1 to 5), including the two CsTe photocathodes, the two bialkali cathodes, and the photomultiplier tube. 
		0:	none                                                                       
		1:	POL                                                                        
		2:	UV1                                                                        
		3:	VIS                                                                        
		4:	UV2                                                                        
		5:	PMT

Source :[qexposure.detectob]

DETECTOR
detector used for this file 
Datatype: INTEGER*2           
Units:
HRS: detector in use (1-2): WFPC: the ccd number of the data

Source :

DETECTSK
detector in use (0-5) - sky data 
Datatype: INTEGER*2           
Units:
This holds the number of the possible detector that was used for data from the sky (or background) during this observation. It is one of the five image dissector tubes (numbered from 1 to 5), including the two CsTe photocathodes, the two bialkali cathodes, and the photomultiplier tube. When MODE is SCP or ARS, this field will contain the null value (-1).

Source :[qexposure.detectsk]

DET_CHR
retrieve detector characteristics 
Datatype: CHARACTER*08        
Units:
Retrieve detector characteristics. This keyword is not currently used, and it is not updated to COMPLETE by the calibration.

Source :(calguide)

EX_EFFIC
scaled extended source cathode efficiency 
Datatype: REAL*4              
Units:    UNITLESS
Extended source sensitivity relative to that of the reference aperture, unitless. This keyword is filled by the calibration software only when the target is an extended source.

Source :

GRAPHTAB
the HST graph table 
Datatype: CHARACTER*18        
Units:    FILENAME
See PHOTMODE and related photometry keywords.

Source :

HIGHVOLT
scaled high voltage factor 
Datatype: REAL*4              
Units:
Scaling factor relative to the reference volatge, unitless, calculated by the calibration software

Source :(calhsp).

INT_TIME
time of integration (in 1/1.024 microseconds) 
Datatype: INTEGER*4           
Units:

Source :

LINES
number of lines in a group 
Datatype: INTEGER*4           
Units:

Source :

MIR_REVR
is the image mirror reversed 
Datatype: CHARACTER*          
Units:

Source :

MODE
instrument mode SCP, SSP, ARS 
Datatype: CHARACTER*03        
Units:                        
		  SCP = single color photometry,                                              
                 SSP = star/sky photometry,                                     
                 ARS = area scan,                                               
                 DUM = a dump;

Source :[qexposure.mode]

ORIENTAT
the orientation of the image (deg) 
Datatype: CHARACTER*          
Units:

Source :

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]

PRE_AMP
scaled tube pre-amp contribution 
Datatype: REAL*4              
Units:    COUNTS/SEC
Pre-amplifier noise, in counts/seconds. Calculated by the calibration software.

Source :(calhsp)

PTSRCFLG
point source flag (P=point, E=extended) 
Datatype: CHARACTER*01        
Units:                        
		P = Point (default),                                                          
		E = Extended.

Source :[qexposure.pt_src_flg]

PT_EFFIC
scaled point source cathode efficiency 
Datatype: REAL*4              
Units:
Point source sensitivity relative to that of the reference aperture, unitless. This keyword is filled by the calibration software only when the target is a point source.

Source :

RA_APER
right ascension of the 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 :

SAMPTIME
time of integration (in seconds) 
Datatype: REAL*4              
Units:

Source :

TIMEBIAS
instrument time bias (in 1/1.024 microseconds) 
Datatype: INTEGER*4           
Units:
The value of the time biases that is used to correct the integration time for internal instrument delays. The timebias is a function of the particular HSP data format (BYTE, WORD, LWRD, ALOG, or ALL) and the instrument mode (SCP, ARS, SSP1, or SSP2). (cgptme)

Source :

TRUE_CNT
compute the true count rates 
Datatype: CHARACTER*08        
Units:
Compute the true count rates. This switch applies only to digital data, it has no effect on analog data. True counts are corrected according to the following equation: 
		z = (y-d-e)/(h*r)                                                             
	Where:                                                                         
		z is the final calibrated true count rate,                                    
		y is the observed count rate,                                                 
		d is the dark signal,                                                         
		e is the pre-amplifier noise,                                                 
		h is the high-voltage factor, and                                             
		r is the relative sensitivity.
If the target is an extended source (i.e., the value of the header keyword PTSRCFLG is "E"), z is further divided by the aperture area.

Source :(calguide)

TRUE_PHC
compute the true photocurrents 
Datatype: CHARACTER*08        
Units:
Compute the true photocurrents. This switch applies only to analog data, it has no effect on digital data. True photocurrents are corrected by the following equation: 
		z = ((y-i)/g - d - e)/(h*r)                                                   
	Where:                                                                         
		z is the final calibrated true count rate,                                    
		y is the observed digital number,                                             
		i is the CVC offset,                                                          
		g is the gain factor,                                                         
		d is the dark signal,                                                         
		e is the pre-amplifier noise,                                                 
		h is the high-voltage factor, and                                             
		r is the relative sensitivity.
If the target is an extended source (i.e., the value of the header keyword PTSRCFLG is "E"), z is further divided by the aperture area.

Source :(calguide)

TUBEGAIN
scaled tube gain factor 
Datatype: REAL*4              
Units:
Gain factor used to convert digital numbers (DN) in the analog mode to count rates, in DN/(counts/second). This keyword is filled by the calibration software only for analog data files.

Source :(calhsp)

VGAIND
gain setting 
Datatype: INTEGER*2           
Units:
Gain setting of the object or sky depending on data source. (cgpsdh)

Source :

WORDS
number of HSP samples in a line 
Datatype: INTEGER*2           
Units:

Source :

HST Keyword Dictionary: 3/15/94: (rose@stsci.edu)