HEASoft and XSPEC are now available as conda packages. See details ....
Dictionary of Commonly Used FITS Keywords
This data dictionary contains FITS keywords that have been widely used
within the astronomical community. It is recommended that these
keywords only be used as defined here. These keywords may be grouped
within the following 7 broad categories:
1. Keywords that describe the data or the FITS file itself:
TITLE FILENAME FILETYPE ROOTNAME
PROGRAM CREATOR CONFIGUR
NEXTEND HDUNAME HDUVER HDULEVEL
TLMINn TLMAXn TDMINn TDMAXn TDBINn
TSORTKEY PROGRAM CREATOR CONFIGUR
HDUCLASS HDUDOC HDUVERS HDUCLASn
2. Keywords that describe the observation:
SUNANGLE MOONANGL
RA DEC RA_NOM DEC_NOM
RA_OBJ DEC_OBJ RA_PNT DEC_PNT PA_PNT
RA_SCX DEC_SCX RA_SCY DEC_SXY RA_SCZ DEC_SCZ
ORIENTAT AIRMASS LATITUDE
OBJNAME OBS_ID
3. Keywords that describe the instrument that took the data:
OBS_MODE DATAMODE
APERTURE DETNAM FILTER FILTERn GRATING GRATINGn
SATURATE
4. Keywords that give the date or duration of the observation:
TIME-OBS TIME-END DATE-END
EXPOSURE EXPTIME TELAPSE ELAPTIME ONTIME LIVETIME
5. Keywords that denote non-standard FITS keyword format conventions:
HIERARCH INHERIT CONTINUE
6. File checksum keywords:
CHECKSUM DATASUM CHECKVER
7. Hierarchical file grouping keywords:
GRPNAME GRPIDn GRPLCn
The keywords are listed alphabetically in the data dictionary; each
entry in this data dictionary has the following format:
KEYWORD: name of the keyword
REFERENCE: URL that documents the keyword
HDU: allowed type of HDU: primary, extension, image, table, or any
DATATYPE: string, logical, integer, or real
UNIT: physical units of the keyword, if any
COMMENT: short description of the keyword
DEFINITION: full description of the keyword
------------------------------------------------------------------------------
------------------------------------------------------------------------------
KEYWORD: AIRMASS
REFERENCE: NOAO
HDU: any
DATATYPE: real
UNIT:
COMMENT: air mass
DEFINITION: The value field shall contain a floating point number
giving the air mass during the observation by a ground based telescope.
The value of the airmass is often approximated by the secant of the
elevation angle and has a value of 1.0 at the zenith and increases
towards the horizon. This value is assumed to correspond to the start
of the observation unless another interpretation is clearly explained
in the comment field.
KEYWORD: APERTURE
REFERENCE:
HDU: any
DATATYPE: string
COMMENT: name of field of view aperture
DEFINITION: The value field shall contain a character string which gives
the name of the instrumental aperture though which the observation was
made. This keyword is typically used in instruments which have a
selection of apertures which restrict the field of view of the detector.
KEYWORD: CHECKSUM
REFERENCE: Checksum
HDU: any
DATATYPE: string
COMMENT: checksum for the current HDU
DEFINITION: The value field of the CHECKSUM keyword shall contain a 16 character
string, left justified starting in column 12, containing the ASCII
encoded complement of the checksum of the FITS HDU (Header and Data
Unit). The algorithm shall be the 32-bit 1's complement checksum and the
ASCII encoding that are described in the checksum proposal. The checksum is accumulated in
FITS datastream order on the same HDU, identical in all respects, except
that the value of the CHECKSUM keyword shall be set to the string
'0000000000000000' (ASCII 0's, hex 30) before the checksum is computed.
KEYWORD: CHECKVER
REFERENCE: Checksum
HDU: any
DATATYPE: string
COMMENT: version of checksum algorithm
DEFINITION: The value field of the CHECKVER keyword shall contain a
string, unique in the first 8 characters, which distinguishes between
any future alternative checksum algorithms which may be defined. The
default value for a missing keyword shall be 'COMPLEMENT' which will
represent the algorithm defined in the current proposal. It is
recommended that this keyword be omitted from headers which implement
the default ASCII encoded 32-bit 1's complement algorithm.
KEYWORD: CONFIGUR
REFERENCE: INTEGRAL
HDU: any
DATATYPE: string
COMMENT: software configuration used to process the data
DEFINITION: The value field shall contain a character string that
uniquely defines the configuration state, or version, of the the
software processing system that generated the data contained in the HDU.
This keyword differs from the CREATOR keyword in that it give the name
and version of the overall processing system and not just the name and
version of a single program.
KEYWORD: CONTINUE
REFERENCE: HEASARC
HDU: any
DATATYPE: none
COMMENT: denotes the CONTINUE long string keyword convention
DEFINITION: The CONTINUE keyword, when followed by spaces in columns 9
and 10 of the card image and a character string enclosed in single
quotes starting in column 11 or higher, indicates that the quoted string
should be treated as a continuation of the character string value in the
previous header keyword. To conform to this convention, the character
string value on the previous keyword must end with the ampersand
character ('&'), but the ampersand is not part of the value string and
should be deleted before concatenating the strings together. The
character string value may be continued on any number of consecutive
CONTINUE keywords, thus effectively allowing arbitrarily long strings to
be written as keyword values.
KEYWORD: CREATOR
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: the name of the software task that created the file
DEFINITION: The value field shall contain a character string giving the
name, and optionally, the version of the program that originally
created the current FITS HDU. This keyword is synonymous with the
PROGRAM keyword. Example: 'TASKNAME V1.2.3'
KEYWORD: DATAMODE
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: pre-processor data mode
DEFINITION: The value field shall contain a character string which
identifies the configuration or mode of the pre-processing software
that operated on the raw instrumental data to generate the data that is
recorded in the FITS file. Example: some X-ray satellite data may be
recorded in 'BRIGHT', 'FAINT', or 'FAST' data mode.
KEYWORD: DATASUM
REFERENCE: Checksum
HDU: any
DATATYPE: string
COMMENT: checksum of the data records
DEFINITION: The value field of the DATASUM keyword shall be a character
string containing the unsigned integer value of the checksum of the
data records of the HDU. For dataless HDU's, this keyword may either be
omitted, or the value field shall contain the string value '0', which
is preferred. A missing DATASUM keyword asserts no knowledge of the
checksum of the data records.
KEYWORD: DATE-END
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: date of the end of observation
DEFINITION: The value field shall contain a character string that gives
the date on which the observation ended. This keyword has the same
format, and is used in conjunction with, the standard DATA-OBS keyword
that gives the starting date of the observation. These 2 keywords may
give either the calendar date using the 'yyyy-mm-dd' format, or may give
the full date and time using the 'yyyy-mm-ddThh:mm:ss.sss' format.
KEYWORD: DEC
REFERENCE: NOAO
HDU: any
DATATYPE: real or string
UNIT: deg
COMMENT: declination of the observed object
DEFINITION: The value field gives the declination of the
observation. It may be expressed either as a floating point number in
units of decimal degrees, or as a character string in 'dd:mm:ss.sss'
format where the decimal point and number of fractional digits are
optional. The coordinate reference frame is given by the RADECSYS
keyword, and the coordinate epoch is given by the EQUINOX keyword.
Example: -47.25944 or '-47:15:34.00'.
KEYWORD: DEC_NOM
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: nominal declination of the observation
DEFINITION: The value field shall contain a floating point number giving
the nominal declination of the pointing direction in units of
decimal degrees. The coordinate reference frame is given by the RADECSYS
keyword, and the coordinate epoch is given by the EQUINOX keyword. The
precise definition of this keyword is instrument-specific, but typically
the nominal direction corresponds to the direction to which the instrument
was requested to point. The DEC_PNT keyword should be used to give the
actual pointed direction.
KEYWORD: DEC_OBJ
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: declination of the observed object
DEFINITION: The value field shall contain a floating point number giving
the declination of the observed object in units of decimal degrees.
The coordinate reference frame is given by the RADECSYS keyword, and the
coordinate epoch is given by the EQUINOX keyword.
KEYWORD: DEC_PNT
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: declination of the pointed direction of the instrument
DEFINITION: The value field shall contain a floating point number giving
the declination of the pointing direction in units of decimal
degrees. The coordinate reference frame is given by the RADECSYS
keyword, and the coordinate epoch is given by the EQUINOX keyword. The
precise definition of this keyword is instrument-specific, but typically
the pointed direction corresponds to the optical axis of the instrument.
This keyword gives a mean value in cases where the pointing axis was not
fixed during the entire observation.
KEYWORD: DEC_SCX
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: declination of the X spacecraft axis
DEFINITION: The value field shall contain a floating point number giving
the declination of the space craft (or telescope platform) X axis
during the observation in decimal degrees. The coordinate reference
frame is given by the RADECSYS keyword, and the coordinate epoch is
given by the EQUINOX keyword. This keyword gives a mean value in cases
where the axis was not fixed during the entire observation.
KEYWORD: DEC_SCY
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: declination of the Y spacecraft axis
DEFINITION: The value field shall contain a floating point number giving
the declination of the space craft (or telescope platform) Y axis
during the observation in decimal degrees. The coordinate reference
frame is given by the RADECSYS keyword, and the coordinate epoch is
given by the EQUINOX keyword. This keyword gives a mean value in cases
where the axis was not fixed during the entire observation.
KEYWORD: DEC_SCZ
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: declination of the Z spacecraft axis
DEFINITION: The value field shall contain a floating point number giving
the declination of the space craft (or telescope platform) Z axis
during the observation in decimal degrees. The coordinate reference
frame is given by the RADECSYS keyword, and the coordinate epoch is
given by the EQUINOX keyword. This keyword gives a mean value in cases
where the axis was not fixed during the entire observation.
KEYWORD: DETNAM
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: name of the detector used to make the observation
DEFINITION: The value field shall contain a character string giving the
name of the detector within the instrument that was used to
make the observation. Example: 'CCD1'
KEYWORD: ELAPTIME
REFERENCE: UCOLICK
HDU: any
DATATYPE: real
UNIT: s
COMMENT: elapsed time of the observation
DEFINITION: The value field shall contain a floating point number
giving the difference between the stop and start times of the
observation in units of seconds. This keyword is synonymous with the
TELAPSE keyword.
KEYWORD: EXPOSURE
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: s
COMMENT: exposure time
DEFINITION: The value field shall contain a floating point number giving
the exposure time of the observation in units of seconds. The exact
definition of 'exposure time' is mission dependent and may, for example,
include corrections for shutter open and close duration, detector dead
time, vignetting, or other effects. This keyword is synonymous with the
EXPTIME keyword.
KEYWORD: EXPTIME
REFERENCE: NOAO
HDU: any
DATATYPE: real
UNIT: s
COMMENT: exposure time
DEFINITION: The value field shall contain a floating point number giving
the exposure time of the observation in units of seconds. The exact
definition of 'exposure time' is mission dependent and may, for example,
include corrections for shutter open and close duration, detector dead
time, vignetting, or other effects. This keyword is synonymous with the
EXPOSURE keyword.
KEYWORD: FILENAME
REFERENCE: NOAO
HDU: any
DATATYPE: string
COMMENT: name of the file
DEFINITION: The value field shall contain a character string giving the
the host file name used to record the original data.
KEYWORD: FILETYPE
REFERENCE: ???
HDU: any
DATATYPE: string
COMMENT: type of file
DEFINITION: The value field shall contain a character string giving the
file type suffix of the host file name. The full file name typically
consists of the root name (see ROOTNAME) followed by a file type
suffix, separated by the period ('.') character.
KEYWORD: FILTER
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: name of filter used during the observation
DEFINITION: The value field shall contain a character string which gives
the name of the filter that was used during the observation to
select or modify the radiation that was transmitted to the detector.
More than 1 filter may be listed by using the FILTERn indexed keyword.
The value 'none' or 'NONE' indicates that no filter was used.
KEYWORD: FILTERn
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: name of filters used during the observation
DEFINITION: The value field of this indexed keyword shall contain a
character string which gives the name of one of multiple
filters that were used during the observation to select or modify the
radiation that was transmitted to the detector. The value 'none' or
'NONE' indicates that no filter was used.
KEYWORD: GRATING
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: name of the grating used during the observation.
DEFINITION: The value field shall contain a character string which gives
the name of the defraction grating that was used during the
observation. More than 1 grating may be listed by using the GRATINGn
indexed keyword. The value 'none' or 'NONE' indicates that no grating
was used.
KEYWORD: GRATINGn
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: name of gratings used during the observation.
DEFINITION: The value field of this indexed keyword shall contain a
character string which gives the name of one of multiple
defraction gratings that were used during the observation. The value
'none' or 'NONE' indicates that no grating was used.
KEYWORD: HDUCLASS
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: general identifier for the classification of the data
DEFINITION: The value field shall contain a character string that identifies
the domain to which the associated HDUCLASn keywords apply. This keyword
typically identifies the institution or project that has defined the allowed
set of values for the associated hierarchical HDUCLASn keywords.
KEYWORD: HDUCLASn
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: hierarchical classification of the data
DEFINITION: The value fields of this hierarchical set of indexed keywords
shall contain character strings that classify the type of data contained
in the HDU. The HDUCLAS1 keyword gives the highest, most general data
classification, and the HDUCLAS2 and higher keywords provide progressively
more detailed subclassifications of the data.
KEYWORD: HDUDOC
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: reference to document describing the data format
DEFINITION: The value field shall contain a character string that gives a
reference to a document that describes the allowed values
that may be assigned to the HDUCLASn data classification keywords.
KEYWORD: HDULEVEL
REFERENCE: ???
HDU: any
DATATYPE: integer
COMMENT: hierarchical level of the HDU
DEFINITION: This keyword is synonymous to the standard EXTLEVEL keyword
except that it may also be used in the primary header. It is
recommended that the HDULEVEL and EXTLEVEL keywords should not both be
given in the same HDU header, but if they are, then the HDULEVEL
keyword will have precedence.
KEYWORD: HDUNAME
REFERENCE: ???
HDU: any
DATATYPE: string
COMMENT: descriptive name of the HDU
DEFINITION: This keyword is synonymous to the standard EXTNAME keyword
except that it may also be used in the primary header. It is
recommended that the HDUNAME and EXTNAME keywords should not both be
given in the same HDU header, but if they are, then the HDUNAME keyword
will have precedence.
KEYWORD: HDUVER
REFERENCE: ???
HDU: any
DATATYPE: integer
COMMENT: version number of the HDU
DEFINITION: This keyword is synonymous to the standard EXTVER keyword
except that it may also be used in the primary header. It is
recommended that the HDUVER and EXTVER keywords should not both be
given in the same HDU header, but if they are, then the HDUVER keyword
will have precedence.
KEYWORD: HDUVERS
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: specific version of the document referenced by HDUDOC
DEFINITION: The value field shall contain a character string that gives
the specific version of the document referenced by HDUDOC.
KEYWORD: HIERARCH
REFERENCE: ESO
HDU: any
DATATYPE: none
COMMENT: denotes the HIERARCH keyword convention
DEFINITION: The HIERARCH keyword, when followed by spaces in columns 9
and 10 of the FITS card image, indicates that the ESO HIERARCH keyword
convention should be used to interpret the name and value of the
keyword. The HIERARCH keyword formally has no value because it is not
followed by an equals sign in column 9. Under the HIERARCH convention
the actual name of the keyword begins in column 11 of the card image and
is terminated by the equal sign ('=') character. The name can contain
any number of characters as long as it fits within columns 11 and 80 of
the card image and also leaves enough space for the equal sign separator
and the value field. The name can contain any printable ASCII text
character, including spaces and lower-case characters, except for the
equal sign character which serves as the terminator of the name field.
Leading and trailing spaces in the name field are not significant, but
embedded spaces within the name are significant. The value field follows
the equals sign and must conform to the syntax for a free-format value
field as defined in the FITS Standard. The value field may be null, in
which case it contains only space characters, otherwise it may contain
either a character string enclosed in single quotes, the logical
constant T or F, an integer number, a floating point number, a complex
integer number, or a complex floating point number. The value field may
be followed by an optional comment string. The comment field must be
separated from the value field by a slash character ('/'). It is
recommended that the slash character be preceeded and followed by a
space character. Example: "HIERARCH Filter Wheel = 12 / filter
position". In this example the logical name of the keyword is 'Filter
Wheel' and the value is 12.
KEYWORD: INHERIT
REFERENCE: STScI
HDU: extension
DATATYPE: logical
COMMENT: denotes the INHERIT keyword convention
DEFINITION: The presence of this keyword with a value = T in an
extension header indicates that the keywords contained in the primary
header (except the FITS Mandatory keywords, and any COMMENT, HISTORY or
'blank' keywords) are to be inherited, or logically included in that
extension header.
KEYWORD: LATITUDE
REFERENCE: UCOLICK
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: geographic latitude of the observation
DEFINITION: The value field shall contain a floating point number
giving the geographic latitude from which the observation was made
in units of degrees.
KEYWORD: LIVETIME
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: s
COMMENT: exposure time after deadtime correction
DEFINITION: The value field shall contain a floating point number giving
the total integrated exposure time in units of seconds corrected for
detector 'dead time' effects which reduce the net efficiency of the
detector. The ratio of LIVETIME/ONTIME gives the mean dead time
correction during the observation, which lies in the range 0.0 to 1.0.
KEYWORD: MOONANGL
REFERENCE: STScI
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: angle between the observation and the moon
DEFINITION: The value field shall contain a floating point number giving
the angle between the direction of the observation (e.g., the optical
axis of the telescope or the position of the target) and the moon,
measured in degrees.
KEYWORD: NEXTEND
REFERENCE: STScI
HDU: primary
DATATYPE: integer
COMMENT: Number of standard extensions
DEFINITION: The value field shall contain an integer giving the
number of standard extensions contained in the FITS file. This
keyword may only be used in the primary array header.
KEYWORD: OBJNAME
REFERENCE: NOAO
HDU: any
DATATYPE: string
COMMENT: IAU name of observed object
DEFINITION: The value field shall contain a character string giving a
name for the observed object that conforms to the IAU astronomical
object naming conventions. The value of this keyword is more
strictly constrained than for the standard OBJECT keyword which in practice
has often been used to record other ancillary information about the
observation (e.g. filter, exposure time, weather conditions, etc.).
KEYWORD: OBS_ID
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: unique observation ID
DEFINITION: The value field shall contain a character string which
uniquely identifies the dataset contained in the FITS file. This is
typically a sequence number that can contain a mixture of numerical and
character values. Example: '10315-01-01-30A'
KEYWORD: OBS_MODE
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: instrumental mode of the observation
DEFINITION: The value field shall contain a character string which gives
the observing mode of the observation. This is used in cases where the
instrument or detector can be configured to operate in different modes
which significantly affect the resulting data. Examples: 'SLEW',
'RASTER', or 'POINTING'
KEYWORD: ONTIME
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: s
COMMENT: integration time during the observation
DEFINITION: The value field shall contain a floating point number giving
the total integrated exposure time of the observation in units of
seconds. ONTIME may be less than TELAPSE if there were intevals during
the observation in which the target was not observed (e.g., the shutter
was closed, or the detector power was turned off).
KEYWORD: ORIENTAT
REFERENCE: STScI
HDU: image
DATATYPE: real
COMMENT: position angle of image y axis (deg. E of N)
DEFINITION: The value field shall contain a floating point number giving
the position angle of the y axis of the detector projected on the sky,
in degrees east of north. This keyword is synonymous with the CROTA2 WCS
keyword.
KEYWORD: PA_PNT
REFERENCE: UCOLICK
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: position angle of the pointing
DEFINITION: The value field shall contain a floating point number
giving the position angle of the relevant aspect of telescope pointing
axis and/or instrument on the sky in units of degrees east of north.
It commonly applies to the orientation of a slit mask.
KEYWORD: PROGRAM
REFERENCE: UCOLICK
HDU: any
DATATYPE: string
COMMENT: the name of the software task that created the file
DEFINITION: The value field shall contain a character string giving the
name, and optionally, the version of the program that originally
created the current FITS HDU. This keyword is synonymous with the
CREATOR keyword. Example: 'TASKNAME V1.2.3'
KEYWORD: RA
REFERENCE: NOAO
HDU: any
DATATYPE: real or string
UNIT: deg
COMMENT: R.A. of the observation
DEFINITION: The value field gives the Right Ascension of the
observation. It may be expressed either as a floating point number in
units of decimal degrees, or as a character string in 'HH:MM:SS.sss'
format where the decimal point and number of fractional digits are
optional. The coordinate reference frame is given by the RADECSYS
keyword, and the coordinate epoch is given by the EQUINOX keyword.
Example: 180.6904 or '12:02:45.7'.
The value field shall contain a character string giving the
Right Ascension of the observation in 'hh:mm:ss.sss' format. The decimal
point and fractional seconds are optional. The coordinate
reference frame is given by the RADECSYS keyword, and the coordinate
epoch is given by the EQUINOX keyword. Example: '13:29:24.00'
KEYWORD: RA_NOM
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: nominal R.A. of the observation
DEFINITION: The value field shall contain a floating point number giving
the nominal Right Ascension of the pointing direction in units of
decimal degrees. The coordinate reference frame is given by the RADECSYS
keyword, and the coordinate epoch is given by the EQUINOX keyword. The
precise definition of this keyword is instrument-specific, but typically
the nominal direction corresponds to the direction to which the instrument
was requested to point. The RA_PNT keyword should be used to give the
actual pointed direction.
KEYWORD: RA_OBJ
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: R.A. of the observed object
DEFINITION: The value field shall contain a floating point number giving
the Right Ascension of the observed object in units of decimal degrees.
The coordinate reference frame is given by the RADECSYS keyword, and the
coordinate epoch is given by the EQUINOX keyword.
KEYWORD: RA_PNT
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: R.A. of the pointed direction of the instrument
DEFINITION: The value field shall contain a floating point number giving
the Right Ascension of the pointing direction in units of decimal
degrees. The coordinate reference frame is given by the RADECSYS
keyword, and the coordinate epoch is given by the EQUINOX keyword. The
precise definition of this keyword is instrument-specific, but typically
the pointed direction corresponds to the optical axis of the instrument.
This keyword gives a mean value in cases where the pointing axis was not
fixed during the entire observation.
KEYWORD: RA_SCX
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: R.A. of the X spacecraft axis
DEFINITION: The value field shall contain a floating point number giving
the Right Ascension of the space craft (or telescope platform) X axis
during the observation in decimal degrees. The coordinate reference
frame is given by the RADECSYS keyword, and the coordinate epoch is
given by the EQUINOX keyword. This keyword gives a mean value in cases
where the axis was not fixed during the entire observation.
KEYWORD: RA_SCY
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: R.A. of the Y spacecraft axis
DEFINITION: The value field shall contain a floating point number giving
the Right Ascension of the space craft (or telescope platform) Y axis
during the observation in decimal degrees. The coordinate reference
frame is given by the RADECSYS keyword, and the coordinate epoch is
given by the EQUINOX keyword. This keyword gives a mean value in cases
where the axis was not fixed during the entire observation.
KEYWORD: RA_SCZ
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: R.A. of the Z spacecraft axis
DEFINITION: The value field shall contain a floating point number giving
the Right Ascension of the space craft (or telescope platform) Z axis
during the observation in decimal degrees. The coordinate reference
frame is given by the RADECSYS keyword, and the coordinate epoch is
given by the EQUINOX keyword. This keyword gives a mean value in cases
where the axis was not fixed during the entire observation.
KEYWORD: ROOTNAME
REFERENCE: ???
HDU: any
DATATYPE: string
COMMENT: rootname of the file
DEFINITION: The value field shall contain a character string giving the
root of the host file name. The full file name typically consists of the
root name followed by a file type suffix (see FILETYPE), separated by
the period ('.') character.
KEYWORD: SATURATE
REFERENCE: STScI
HDU: any
DATATYPE: integer
COMMENT: Data value at which saturation occurs
DEFINITION: The value field shall contain an integer giving the data
value at which the detector becomes saturated. This keyword value may
differ from the maximum value implied by the BITPIX in that more bits
may be allocated in the FITS pixel values than the detector can
accommodate.
KEYWORD: SUNANGLE
REFERENCE: STScI
HDU: any
DATATYPE: real
UNIT: deg
COMMENT: angle between the observation and the sun
DEFINITION: The value field shall contain a floating point number giving
the angle between the direction of the observation (e.g., the optical
axis of the telescope or the position of the target) and the sun,
measured in degrees.
KEYWORD: TDBINn
REFERENCE: CXC
HDU: table
DATATYPE: real
COMMENT: default histogram bin size for the column
DEFINITION: The value field of this indexed keyword shall contain a
floating point number specifying the suggested bin size when producing a
histogram of the values in column n. This keyword is typically used in
conjunction the TLMINn and TLMAXn keywords when constructing a histogram
of the values in column n, such that the histogram ranges from TLMINn to
TLMAXn with the histogram bin size given by TDBINn. This keyword may
only be used in 'TABLE' or 'BINTABLE' extensions.
KEYWORD: TDMAXn
REFERENCE: HEASARC
HDU: table
DATATYPE: real
COMMENT: maximum physical value in the column
DEFINITION: The value field of this indexed keyword shall contain a
floating point number specifying the maximum valid physical value
represented in column n of the table, exclusive of any special values.
This keyword may only be used in 'TABLE' or 'BINTABLE' extensions and
is analogous to the DATAMAX keyword used for FITS images.
KEYWORD: TDMINn
REFERENCE: HEASARC
HDU: table
DATATYPE: real
COMMENT: minimum physical value in the column
DEFINITION: The value field of this indexed keyword shall contain a
floating point number specifying the minimum valid physical value
represented in column n of the table, exclusive of any special values.
This keyword may only be used in 'TABLE' or 'BINTABLE' extensions and
is analogous to the DATAMIN keyword used for FITS images.
KEYWORD: TELAPSE
REFERENCE: HEASARC
HDU: any
DATATYPE: real
UNIT: s
COMMENT: elapsed time of the observation
DEFINITION: The value field shall contain a floating point number
giving the difference between the stop and start times of the
observation in units of seconds. This keyword is synonymous with the
ELAPTIME keyword.
KEYWORD: TIME-END
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: time at the end of the observation
DEFINITION: The value field shall contain a character string that gives
the time at which the observation ended. This keyword is used in
conjunction with the DATE-END keyword to give the ending time of the
observation; the DATE-END keyword gives the ending calendar date, with
format 'yyyy-mm-dd', and TIME-END gives the time within that day using
the format 'hh:mm:ss.sss...'. This keyword should not be used if the
time is included directly as part of the DATE-END keyword value with the
format 'yyyy-mm-ddThh:mm:ss.sss'.
KEYWORD: TIME-OBS
REFERENCE: HEASARC
HDU: any
DATATYPE: string
COMMENT: time at the start of the observation
DEFINITION: The value field shall contain a character string that gives
the time at which the observation started. This keyword is used in
conjunction with the standard DATE-OBS keyword to give the starting
time of the observation; the DATE-OBS keyword gives the starting
calendar date, with format 'yyyy-mm-dd', and TIME-OBS gives the time
within that day using the format 'hh:mm:ss.sss...'. This keyword should
not be used if the time is included directly as part of the DATE-OBS
keyword value with the format 'yyyy-mm-ddThh:mm:ss.sss'.
KEYWORD: TITLE
REFERENCE: ROSAT
HDU: any
DATATYPE: string
COMMENT: title for the observation or data
DEFINITION: The value field shall contain a character string giving a
title that is suitable for display purposes, e.g., for annotation on
images or plots of the data contained in the HDU.
KEYWORD: TLMAXn
REFERENCE: HEASARC
HDU: table
DATATYPE: real
COMMENT: maximum legal value in the column
DEFINITION: The value field of this indexed keyword shall contain a
floating point number specifying the upper bound of the legal range of
physical values that may be represented in column n of the table. The
column may contain values that are greater than this legal maximum value
but the interpretation of such values is not defined here. The value of
this keyword is typically used as the maxinum value when constructing a
histogram of the values in the column. This keyword may only be used
in 'TABLE' or 'BINTABLE' extensions.
KEYWORD: TLMINn
REFERENCE: HEASARC
HDU: table
DATATYPE: real
COMMENT: minimum legal value in the column
DEFINITION: The value field of this indexed keyword shall contain a
floating point number specifying the lower bound of the legal range of
physical values that may be represented in column n of the table. The
column may contain values that are less than this legal minimum value
but the interpretation of such values is not defined here. The value of
this keyword is typically used as the mininum value when constructing a
histogram of the values in the column. This keyword may only be used
in 'TABLE' or 'BINTABLE' extensions.
KEYWORD: TSORTKEY
REFERENCE: HEASARC
HDU: table
DATATYPE: string
COMMENT: defines the sort order of a table
DEFINITION: The value field shall contain a character string that
defines the order in which the rows in the current FITS ASCII or binary
table extension have been sorted. The character string lists the name
(as given by the TTYPEn keyword) of the primary sort column, optionally
followed by the names of any secondary sort column(s). The presence of
this keyword indicates that the rows in the table have been sorted
first by the values in the primary sort column; any rows that have the
same value in the primary column have been further sorted by the values
in the secondary sort column and so on for all the specified columns.
If more than one column is specified by TSORTKEY then the names must be
separated by a comma. One or more spaces are also allowed between the
comma and the following column name. By default, columns are sorted in
ascending order, but a minus sign may precede the column name to
indicate that the rows are sorted in descending order. This keyword may
only be used in 'TABLE' or 'BINTABLE' extensions. Example: TSORTKEY =
'TIME, RA, DEC'.