This data dictionary lists the 53 keywords currently defined in the FITS Standard: (blank) CROTAn EQUINOX NAXISn TBCOLn TUNITn AUTHOR CRPIXn EXTEND OBJECT TDIMn TZEROn BITPIX CRVALn EXTLEVEL OBSERVER TDISPn XTENSION BLANK CTYPEn EXTNAME ORIGIN TELESCOP BLOCKED DATAMAX EXTVER PCOUNT TFIELDS BSCALE DATAMIN GCOUNT PSCALn TFORMn BUNIT DATE GROUPS PTYPEn THEAP BZERO DATE-OBS HISTORY PZEROn TNULLn CDELTn END INSTRUME REFERENC TSCALn COMMENT EPOCH NAXIS SIMPLE TTYPEn --------------------------------------------------------------------- KEYWORD: (blank) REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: none COMMENT: descriptive comment DEFINITION: Columns 1-8 contain ASCII blanks. This keyword has no associated value. Columns 9-80 may contain any ASCII text. Any number of card images with blank keyword fields may appear in a header. KEYWORD: AUTHOR REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: string COMMENT: author of the data DEFINITION: The value field shall contain a character string identifying who compiled the information in the data associated with the header. This keyword is appropriate when the data originate in a published paper or are compiled from many sources. KEYWORD: BITPIX REFERENCE: FITS Standard STATUS: manditory HDU: any VALUE: integer RANGE: -64,-32,8,16,32 COMMENT: bits per data value DEFINITION: The value field shall contain an integer. The absolute value is used in computing the sizes of data structures. It shall specify the number of bits that represent a data value. KEYWORD: BLANK REFERENCE: FITS Standard STATUS: reserved HDU: image VALUE: integer COMMENT: value used for undefined array elements DEFINITION: This keyword shall be used only in primary array headers or IMAGE extension headers with positive values of BITPIX (i.e., in arrays with integer data). Columns 1-8 contain the string, `BLANK ' (ASCII blanks in columns 6-8). The value field shall contain an integer that specifies the representation of array values whose physical values are undefined. KEYWORD: BLOCKED REFERENCE: FITS Standard STATUS: reserved HDU: primary VALUE: logical COMMENT: is physical blocksize a multiple of 2880? DEFINITION: This keyword may be used only in the primary header. It shall appear within the first 36 card images of the FITS file. (Note: This keyword thus cannot appear if NAXIS is greater than 31, or if NAXIS is greater than 30 and the EXTEND keyword is present.) Its presence with the required logical value of T advises that the physical block size of the FITS file on which it appears may be an integral multiple of the logical record length, and not necessarily equal to it. Physical block size and logical record length may be equal even if this keyword is present or unequal if it is absent. It is reserved primarily to prevent its use with other meanings. Since the issuance of version 1 of the standard, the BLOCKED keyword has been deprecated. KEYWORD: BSCALE REFERENCE: FITS Standard STATUS: reserved HDU: image VALUE: real DEFAULT: 1.0 COMMENT: linear factor in scaling equation DEFINITION: This keyword shall be used, along with the BZERO keyword, when the array pixel values are not the true physical values, to transform the primary data array values to the true physical values they represent, using the equation: physical_value = BZERO + BSCALE * array_value. The value field shall contain a floating point number representing the coefficient of the linear term in the scaling equation, the ratio of physical value to array value at zero offset. The default value for this keyword is 1.0. KEYWORD: BUNIT REFERENCE: FITS Standard STATUS: reserved HDU: image VALUE: string COMMENT: physical units of the array values DEFINITION: The value field shall contain a character string, describing the physical units in which the quantities in the array, after application of BSCALE and BZERO, are expressed. The units of all FITS header keyword values, with the exception of measurements of angles, should conform with the recommendations in the IAU Style Manual. For angular measurements given as floating point values and specified with reserved keywords, degrees are the recommended units (with the units, if specified, given as 'deg'). KEYWORD: BZERO REFERENCE: FITS Standard STATUS: reserved HDU: image VALUE: real DEFAULT: 0.0 COMMENT: zero point in scaling equation DEFINITION: This keyword shall be used, along with the BSCALE keyword, when the array pixel values are not the true physical values, to transform the primary data array values to the true values using the equation: physical_value = BZERO + BSCALE * array_value. The value field shall contain a floating point number representing the physical value corresponding to an array value of zero. The default value for this keyword is 0.0. KEYWORD: CDELTn REFERENCE: FITS Standard STATUS: reserved HDU: image VALUE: real COMMENT: coordinate increment along axis DEFINITION: The value field shall contain a floating point number giving the partial derivative of the coordinate specified by the CTYPEn keywords with respect to the pixel index, evaluated at the reference point CRPIXn, in units of the coordinate specified by the CTYPEn keyword. These units must follow the prescriptions of section 5.3 of the FITS Standard. KEYWORD: COMMENT REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: none COMMENT: descriptive comment DEFINITION: This keyword shall have no associated value; columns 9-80 may contain any ASCII text. Any number of COMMENT card images may appear in a header. KEYWORD: CROTAn REFERENCE: FITS Standard STATUS: reserved HDU: image VALUE: real UNITS: degrees COMMENT: coordinate system rotation angle DEFINITION: This keyword is used to indicate a rotation from a standard coordinate system described by the CTYPEn to a different coordinate system in which the values in the array are actually expressed. Rules for such rotations are not further specified in the Standard; the rotation should be explained in comments. The value field shall contain a floating point number giving the rotation angle in degrees between axis n and the direction implied by the coordinate system defined by CTYPEn. KEYWORD: CRPIXn REFERENCE: FITS Standard STATUS: reserved HDU: image VALUE: real COMMENT: coordinate system reference pixel DEFINITION: The value field shall contain a floating point number, identifying the location of a reference point along axis n, in units of the axis index. This value is based upon a counter that runs from 1 to NAXISn with an increment of 1 per pixel. The reference point value need not be that for the center of a pixel nor lie within the actual data array. Use comments to indicate the location of the index point relative to the pixel. KEYWORD: CRVALn REFERENCE: FITS Standard STATUS: reserved HDU: image VALUE: real COMMENT: coordinate system value at reference pixel DEFINITION: The value field shall contain a floating point number, giving the value of the coordinate specified by the CTYPEn keyword at the reference point CRPIXn. Units must follow the prescriptions of section 5.3 of the FITS Standard. KEYWORD: CTYPEn REFERENCE: FITS Standard STATUS: reserved HDU: image VALUE: string COMMENT: name of the coordinate axis DEFINITION: The value field shall contain a character string, giving the name of the coordinate represented by axis n. KEYWORD: DATAMAX REFERENCE: FITS Standard STATUS: reserved HDU: image VALUE: real COMMENT: maximum data value DEFINITION: The value field shall always contain a floating point number, regardless of the value of BITPIX. This number shall give the maximum valid physical value represented by the array, exclusive of any special values. KEYWORD: DATAMIN REFERENCE: FITS Standard STATUS: reserved HDU: image VALUE: real COMMENT: minimum data value DEFINITION: The value field shall always contain a floating point number, regardless of the value of BITPIX. This number shall give the minimum valid physical value represented by the array, exclusive of any special values. KEYWORD: DATE REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: string COMMENT: date of file creation DEFINITION: The date on which the HDU was created, in the format specified in the FITS Standard. The old date format was 'yy/mm/dd' and may be used only for dates from 1900 through 1999. the new Y2K compliant date format is 'yyyy-mm-dd' or 'yyyy-mm-ddTHH:MM:SS[.sss]'. KEYWORD: DATE-OBS REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: string COMMENT: date of the observation DEFINITION: The date of the observation, in the format specified in the FITS Standard. The old date format was 'yy/mm/dd' and may be used only for dates from 1900 through 1999. The new Y2K compliant date format is 'yyyy-mm-dd' or 'yyyy-mm-ddTHH:MM:SS[.sss]'. KEYWORD: END REFERENCE: FITS Standard STATUS: mandatory HDU: any VALUE: none COMMENT: marks the end of the header keywords DEFINITION: This keyword has no associated value. Columns 9-80 shall be filled with ASCII blanks. KEYWORD: EPOCH REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: real COMMENT: equinox of celestial coordinate system DEFINITION: The value field shall contain a floating point number giving the equinox in years for the celestial coordinate system in which positions are expressed. Starting with Version 1, the Standard has deprecated the use of the EPOCH keyword and thus it shall not be used in FITS files created after the adoption of the standard; rather, the EQUINOX keyword shall be used. KEYWORD: EQUINOX REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: real COMMENT: equinox of celestial coordinate system DEFINITION: The value field shall contain a floating point number giving the equinox in years for the celestial coordinate system in which positions are expressed. KEYWORD: EXTEND REFERENCE: FITS Standard STATUS: reserved HDU: primary VALUE: logical COMMENT: may the FITS file contain extensions? DEFINITION: If the FITS file may contain extensions, a card image with the keyword EXTEND and the value field containing the logical value T must appear in the primary header immediately after the last NAXISn card image, or, if NAXIS=0, the NAXIS card image. The presence of this keyword with the value T in the primary header does not require that extensions be present. KEYWORD: EXTLEVEL REFERENCE: FITS Standard STATUS: reserved HDU: extension VALUE: integer RANGE: [1:] DEFAULT: 1 COMMENT: hierarchical level of the extension DEFINITION: The value field shall contain an integer, specifying the level in a hierarchy of extension levels of the extension header containing it. The value shall be 1 for the highest level; levels with a higher value of this keyword shall be subordinate to levels with a lower value. If the EXTLEVEL keyword is absent, the file should be treated as if the value were 1. This keyword is used to describe an extension and should not appear in the primary header. KEYWORD: EXTNAME REFERENCE: FITS Standard STATUS: reserved HDU: extension VALUE: string COMMENT: name of the extension DEFINITION: The value field shall contain a character string, to be used to distinguish among different extensions of the same type, i.e., with the same value of XTENSION, in a FITS file. This keyword is used to describe an extension and should not appear in the primary header. KEYWORD: EXTVER REFERENCE: FITS Standard STATUS: reserved HDU: extension VALUE: integer RANGE: [1:] DEFAULT: 1 COMMENT: version of the extension DEFINITION: The value field shall contain an integer, to be used to distinguish among different extensions in a FITS file with the same type and name, i.e., the same values for XTENSION and EXTNAME. The values need not start with 1 for the first extension with a particular value of EXTNAME and need not be in sequence for subsequent values. If the EXTVER keyword is absent, the file should be treated as if the value were 1. This keyword is used to describe an extension and should not appear in the primary header. KEYWORD: GCOUNT REFERENCE: FITS Standard STATUS: mandatory HDU: extension VALUE: integer COMMENT: group count DEFINITION: The value field shall contain an integer that shall be used in any way appropriate to define the data structure, consistent with Eq. 5.2 in the FITS Standard. This keyword originated for use in FITS Random Groups where it specifies the number of random groups present. In most other cases this keyword will have the value 1. KEYWORD: GROUPS REFERENCE: FITS Standard STATUS: mandatory HDU: groups VALUE: logical COMMENT: indicates random groups structure DEFINITION: The value field shall contain the logical constant T. The value T associated with this keyword implies that random groups records are present. KEYWORD: HISTORY REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: none COMMENT: processing history of the data DEFINITION: This keyword shall have no associated value; columns 9-80 may contain any ASCII text. The text should contain a history of steps and procedures associated with the processing of the associated data. Any number of HISTORY card images may appear in a header. KEYWORD: INSTRUME REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: string COMMENT: name of instrument DEFINITION: The value field shall contain a character string identifying the instrument used to acquire the data associated with the header. KEYWORD: NAXIS REFERENCE: FITS Standard STATUS: mandatory HDU: any VALUE: integer RANGE: [0:999] COMMENT: number of axes DEFINITION: The value field shall contain a non-negative integer no greater than 999, representing the number of axes in the associated data array. A value of zero signifies that no data follow the header in the HDU. In the context of FITS 'TABLE' or 'BINTABLE' extensions, the value of NAXIS is always 2. KEYWORD: NAXISn REFERENCE: FITS Standard STATUS: mandatory HDU: any VALUE: integer RANGE: [0:] COMMENT: size of the axis DEFINITION: The value field of this indexed keyword shall contain a non-negative integer, representing the number of elements along axis n of a data array. The NAXISn must be present for all values n = 1,...,NAXIS, and for no other values of n. A value of zero for any of the NAXISn signifies that no data follow the header in the HDU. If NAXIS is equal to 0, there should not be any NAXISn keywords. KEYWORD: OBJECT REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: string COMMENT: name of observed object DEFINITION: The value field shall contain a character string giving a name for the object observed. KEYWORD: OBSERVER REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: string COMMENT: observer who acquired the data DEFINITION: The value field shall contain a character string identifying who acquired the data associated with the header. KEYWORD: ORIGIN REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: string COMMENT: organization responsible for the data DEFINITION: The value field shall contain a character string identifying the organization or institution responsible for creating the FITS file. KEYWORD: PCOUNT REFERENCE: FITS Standard STATUS: mandatory HDU: extension VALUE: integer COMMENT: parameter count DEFINITION: The value field shall contain an integer that shall be used in any way appropriate to define the data structure, consistent with Eq. 5.2 in the FITS Standard. This keyword was originated for use with FITS Random Groups and represented the number of parameters preceding each group. It has since been used in 'BINTABLE' extensions to represent the size of the data heap following the main data table. In most other cases its value will be zero. KEYWORD: PSCALn REFERENCE: FITS Standard STATUS: reserved HDU: groups VALUE: real DEFAULT: 1.0 COMMENT: parameter scaling factor DEFINITION: This keyword is reserved for use within the FITS Random Groups structure. This keyword shall be used, along with the PZEROn keyword, when the nth FITS group parameter value is not the true physical value, to transform the group parameter value to the true physical values it represents, using the equation, physical_value = PZEROn + PSCALn * group_parameter_value. The value field shall contain a floating point number representing the coefficient of the linear term, the scaling factor between true values and group parameter values at zero offset. The default value for this keyword is 1.0. KEYWORD: PTYPEn REFERENCE: FITS Standard STATUS: reserved HDU: groups VALUE: string COMMENT: name of random groups parameter DEFINITION: This keyword is reserved for use within the FITS Random Groups structure. The value field shall contain a character string giving the name of parameter n. If the PTYPEn keywords for more than one value of n have the same associated name in the value field, then the data value for the parameter of that name is to be obtained by adding the derived data values of the corresponding parameters. This rule provides a mechanism by which a random parameter may have more precision than the accompanying data array elements; for example, by summing two 16-bit values with the first scaled relative to the other such that the sum forms a number of up to 32-bit precision. KEYWORD: PZEROn REFERENCE: FITS Standard STATUS: reserved HDU: groups VALUE: real DEFAULT: 0.0 COMMENT: parameter scaling zero point DEFINITION: This keyword is reserved for use within the FITS Random Groups structure. This keyword shall be used, along with the PSCALn keyword, when the nth FITS group parameter value is not the true physical value, to transform the group parameter value to the physical value. The value field shall contain a floating point number, representing the true value corresponding to a group parameter value of zero. The default value for this keyword is 0.0. The transformation equation is as follows: physical_value = PZEROn + PSCALn * group_parameter_value. KEYWORD: REFERENC REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: string COMMENT: bibliographic reference DEFINITION: The value field shall contain a character string citing a reference where the data associated with the header are published. KEYWORD: SIMPLE REFERENCE: FITS Standard STATUS: mandatory HDU: primary VALUE: logical COMMENT: does file conform to the Standard? DEFINITION: The SIMPLE keyword is required to be the first keyword in the primary header of all FITS files. The value field shall contain a logical constant with the value T if the file conforms to the standard. This keyword is mandatory for the primary header and is not permitted in extension headers. A value of F signifies that the file does not conform to this standard. KEYWORD: TBCOLn REFERENCE: FITS Standard STATUS: mandatory HDU: ASCII_table VALUE: integer RANGE: [1:] COMMENT: begining column number DEFINITION: The value field of this indexed keyword shall contain an integer specifying the column in which field n starts in an ASCII TABLE extension. The first column of a row is numbered 1. KEYWORD: TDIMn REFERENCE: FITS Standard STATUS: reserved HDU: BINTABLE VALUE: string COMMENT: dimensionality of the array DEFINITION: The value field of this indexed keyword shall contain a character string describing how to interpret the contents of field n as a multidimensional array, providing the number of dimensions and the length along each axis. The form of the value is not further specified by the Standard. A proposed convention is described in Appendix B.2 of the FITS Standard in which the value string has the format '(l,m,n...)' where l, m, n,... are the dimensions of the array. KEYWORD: TDISPn REFERENCE: FITS Standard STATUS: reserved HDU: table VALUE: string COMMENT: display format DEFINITION: The value field of this indexed keyword shall contain a character string describing the format recommended for the display of the contents of field n. If the table value has been scaled, the physical value shall be displayed. All elements in a field shall be displayed with a single, repeated format. For purposes of display, each byte of bit (type X) and byte (type B) arrays is treated as an unsigned integer. Arrays of type A may be terminated with a zero byte. Only the format codes in Table 8.6, discussed in section 8.3.4 of the FITS Standard, are permitted for encoding. The format codes must be specified in upper case. If the Bw.m, Ow.m, and Zw.m formats are not readily available to the reader, the Iw.m display format may be used instead, and if the ENw.d and ESw.d formats are not available, Ew.d may be used. The meaning of this keyword is not defined for fields of type P in the Standard but may be defined in conventions using such fields. KEYWORD: TELESCOP REFERENCE: FITS Standard STATUS: reserved HDU: any VALUE: string COMMENT: name of telescope DEFINITION: The value field shall contain a character string identifying the telescope used to acquire the data associated with the header. KEYWORD: TFIELDS REFERENCE: FITS Standard STATUS: mandatory HDU: table VALUE: integer RANGE: [0:999] COMMENT: number of columns in the table DEFINITION: The value field shall contain a non-negative integer representing the number of fields in each row of a 'TABLE' or 'BINTABLE' extension. The maximum permissible value is 999. KEYWORD: TFORMn REFERENCE: FITS Standard STATUS: mandatory HDU: table VALUE: string COMMENT: column data format DEFINITION: The value field of this indexed keyword shall contain a character string describing the format in which field n is encoded in a 'TABLE' or 'BINTABLE' extension. KEYWORD: THEAP REFERENCE: FITS Standard STATUS: reserved HDU: BINTABLE VALUE: integer COMMENT: offset to starting data heap address DEFINITION: The value field of this keyword shall contain an integer providing the separation, in bytes, between the start of the main data table and the start of a supplemental data area called the heap. The default value shall be the product of the values of NAXIS1 and NAXIS2. This keyword shall not be used if the value of PCOUNT is zero. A proposed application of this keyword is presented in Appendix B.1 of the FITS Standard. KEYWORD: TNULLn REFERENCE: FITS Standard STATUS: reserved HDU: table VALUE: integer or string COMMENT: value used to indicate undefined table element DEFINITION: In ASCII 'TABLE' extensions, the value field for this indexed keyword shall contain the character string that represents an undefined value for field n. The string is implicitly blank filled to the width of the field. In binary 'BINTABLE' table extensions, the value field for this indexed keyword shall contain the integer that represents an undefined value for field n of data type B, I, or J. The keyword may not be used in 'BINTABLE' extensions if field n is of any other data type. KEYWORD: TSCALn REFERENCE: FITS Standard STATUS: reserved HDU: table VALUE: real DEFAULT: 1.0 COMMENT: linear data scaling factor DEFINITION: This indexed keyword shall be used, along with the TZEROn keyword, when the quantity in field n does not represent a true physical quantity. The value field shall contain a floating point number representing the coefficient of the linear term in the equation, physical_value = TZEROn + TSCALn * field_value, which must be used to compute the true physical value of the field, or, in the case of the complex data types C and M, of the real part of the field with the imaginary part of the scaling factor set to zero. The default value for this keyword is 1.0. This keyword may not be used if the format of field n is A, L, or X. KEYWORD: TTYPEn REFERENCE: FITS Standard STATUS: reserved HDU: table VALUE: string COMMENT: column name DEFINITION: The value field for this indexed keyword shall contain a character string, giving the name of field n. It is recommended that only letters, digits, and underscore (hexadecimal code 5F, ('_') be used in the name. String comparisons with the values of TTYPEn keywords should not be case sensitive. The use of identical names for different fields should be avoided. KEYWORD: TUNITn REFERENCE: FITS Standard STATUS: reserved HDU: table VALUE: string COMMENT: column units DEFINITION: The value field shall contain a character string describing the physical units in which the quantity in field n, after any application of TSCALn and TZEROn, is expressed. The units of all FITS header keyword values, with the exception of measurements of angles, should conform with the recommendations in the IAU Style Manual. For angular measurements given as floating point values and specified with reserved keywords, degrees are the recommended units (with the units, if specified, given as 'deg'). KEYWORD: TZEROn REFERENCE: FITS Standard STATUS: reserved HDU: table VALUE: real DEFAULT: 0.0 COMMENT: column scaling zero point DEFINITION: This indexed keyword shall be used, along with the TSCALn keyword, when the quantity in field n does not represent a true physical quantity. The value field shall contain a floating point number representing the true physical value corresponding to a value of zero in field n of the FITS file, or, in the case of the complex data types C and M, in the real part of the field, with the imaginary part set to zero. The default value for this keyword is 0.0. This keyword may not be used if the format of field n is A, L, or X. KEYWORD: XTENSION REFERENCE: FITS Standard STATUS: mandatory HDU: extension VALUE: string COMMENT: marks beginning of new HDU DEFINITION: The value field shall contain a character string giving the name of the extension type. This keyword is mandatory for an extension header and must not appear in the primary header. For an extension that is not a standard extension, the type name must not be the same as that of a standard extension.