19 Alphabetical listing of all keywords with section references

Below is an alphabetical listing of all keywords used in this document, both new SOLARNET keywords and FITS standard/widely accepted FITS convention keywords.

Keyword origins are defined using a code:

• N: New SOLARNET keywords defined in this document

• S: Keywords defined in the FITS standard (listed in the FITS standard Appendix C)

• P: Keywords defined in Paper I-V and Thompson (2006)[1].

• O: Other keywords in common use before being specified in this document

Keyword requirements are defined as:

• all: Required for all FITS headers

• primary: Required for primary header

• obs: Required for observation headers

• optional: Optional

Solarnet keywords

Keyword	Origin	Description	Required	Section Reference
ANA_NCMP	N	Number of components in the analysis used for parameterized “Type P” data	optional	Appendix IX
AO_LOCK	N	should be used to indicate the status of any adaptive optics. When specified for individual exposures, the value should be either 0 or 1, but as mentioned above, averages may also be specified as appropriate.	optional	5.5, 18.6
AO_NMODE	N	should be used to indicate the number of adaptive optics modes corrected. As mentioned above, averages may also be specified as appropriate. The type of the modes (e.g., Zernike, Karhunen-Loeve, etc.) should be given in the keyword comment.	optional	5.5, 18.6
ATMOS_R0	N	atmospheric coherence length r0. If available, the value of r0 should be stored in the keyword ATMOS_R0. Since there are multiple ways of measuring this value, its only use should be to reflect the quality of the observing conditions whenever the measurements are performed in the same (or similar enough) way.	optional	5.5, 16.0, 18.7, Appendix I, Appendix I-a, Appendix I-b
AUTHOR	S	Who designed the observation	optional	6.0, 15.5
BITPIX	S	Number of bits per pixel. The value of BITPIX is the number of bits per pixel in the data array. The value of BITPIX must be one of the following; 8, 16, 32, 64, -32, -64. The negative values indicate floating point data.	primary
BLANK	S	Value marking undefined pixels before the application of BSCALE, BZERO. Missing or blank pixels in floating-point-valued HDUs should be set to NaN, but missing or blank pixels in integer-valued HDUs must be given the value of BLANK	optional	5.6.2, 15.4
BNAME	N	may be used to provide a human readable explanation of the data contents. This keyword is not mentioned in any FITS standard document, but it is a natural analogy to the CNAMEi keywords used to provide additional description of the WCS coordinate.	optional	5.1, 15.4, 18.5
BNDCTR	N	For radio observations, BNDCTR may be used instead of WAVELNTH to specify a corresponding frequency in Hz.	optional	5.4, 18.6
BSCALE	S	The value of the pixel in the FITS file is given by BZERO + BSCALE * pixel value	optional
BTYPE	N	Description of what the data array represents	obs	5.1, 15.4
BUNIT	S	Units of data array	obs	5.1, 15.4
BZERO	S	The value of the pixel in the FITS file is given by BZERO + BSCALE * pixel value	optional	Appendix IV
CADAVG	N	[s] Average (actual) measurement cadence (frame to frame spacing)	optional	5.3, 18.3
CADENCE	N	[s] Planned/commanded cadence (frame to frame spacing)	optional	5.3, 18.3
CADMAX	N	[s] Maximum frame-to-frame spacing	optional	5.3, 18.3
CADMIN	N	[s] Minimum frame-to-frame spacing	optional	5.3, 18.3
CADVAR	N	[s] Variability of the frame-to-frame spacing	optional	5.3, 18.3
CAMERA	O	Camera name (CAM-xxxx is recommended for other camera keywords).	optional	6.0, 7.2, 15.5
CAMPAIGN	O	Coordinated campaign name/number, including instance number, when applicable	optional	6.0, 15.5
CAR_ROT	P	Carrington rotation number for the reference pixel pointed to by CRPIXj values	optional	3.2
CCURRENT	N	When an Obs-HDU (partially) overlaps in time and space with one or more HDUs stored in other files, CCURRENT (concurrent) may be set to a comma-separated list of its own file name plus the names of all files containing concurrent Obs-HDUs. CCURRENT serves as a pointer to other concurrent (and probably relevant) observations, but it also serves a purpose in grouping search results	optional	15.5, Appendix V-b
CDELTia	P	The increment in the coordinate value along axis i in units of the coordinate value	obs	3.1
CDi_ja	P	Linear-transformation matrix element in the ith row and jth column of the CD matrix	optional
CHECKSUM	P	Checksum of the data array	obs	9.0, 15.1
CHISQAVG	N	Average value of reduced chi-squared over all pixels in the data cube. This is a measure of the goodness of fit, and should ideally be close to 1.0.	optional	Appendix IX
CMP_NPn	N	Number of parameters for component n	optional	Appendix IX
CMPDESn	N	Description of component n	optional	Appendix IX
CMPINCn	N	Indicates whether component n is included (CMPINCn=1) or excluded (CMPINCn=0) in the fit. This allows specification of components that would normally be included but for some reason (e.g., poor S/N ratio) has been left out for this particular data set. If CMPINCn is zero, additive components have a value of zero independent of the parameter values, and multiplicative components have a value of 1. Default value is 1, i.e., the component is included in the fit. The parameters in the data cube should be set to the initial values that would have been used if the component was included. If this is not feasible, the parameters should be set such that the component value would be zero if it had in fact been included.	optional	Appendix IX
CMPMULn	N	Indicates whether component n is multiplicative (CMPMULn=1), in which case it is to be applied to the result of all previous components n-1, n-2, etc. This can be used for e.g., extinction functions. Default value is 0.	optional	Appendix IX
CMPNAMn	N	Name of component n, typically used to identify/label the emission line fitted	optional	Appendix IX
CMPSTRn	N	Used by SSW’s cfit routines for the string to be included in composite function names. E.g., the function string for a Gaussian is ‘g’, and ‘p1’ for a first-order polynomial. An automatically generated composite function of the two would be called ‘cf_g_p1_’.	optional	Appendix IX
CMPTYPn	N	Component type, e.g., - ‘Polynomial’, a polynomial of order CMP_NPn - 1. - ‘Gaussian’, a Gaussian - ‘SSW comp_bgauss’, a broadened Gaussian, see SSW routine comp_bgauss - ‘SSW comp_voigt’, a Voigt profile, see SSW routine comp_voigt - … etc. If you need additional component types, contact prits-group@astro.uio.no.	optional	Appendix IX
CNAMEia	P	Name of the coordinate axis i	obs	5.1
COMMENT	S	May be used to include the relevant parts of the OBS_LOG, and any other relevant comments about the HDU that may be useful for the interpretation of the data.	optional	2.4, 5.5
COMP_ALG	N	Name of the compression algorithm used	optional	5.5, 18.7
COMPQUAL	N	set to a number between 0.0 and 1.0, where 1.0 indicates lossless compression (if any) and 0.0 indicates “all information is lost”. In practice, however, the actual value is not crucial, as long as a higher value corresponds to a higher data quality. If there is a choice between different compression algorithms for this instrument, the name of the algorithm should be given in COMP_ALG - starting with either ‘Lossy’ or ‘Lossless’, then typically a concatenation of all instrument-specific compression-related keywords, separated with slashes.	optional	5.5, 18.7
CONSTEXT	N	constant mask ([x,y,t,p]) - if the constant mask value (x,y,t,p)=1, parameter p has been kept constant/frozen at the stored value during the fitting process for point (x,y,t). When the constant mask extension is not present, it is assumed that all parameters have been fitted freely (between the specified min and max values) at all times unless PCONSna=1.	optional	Appendix IX
CONTINUE	P	May be used to continue a keyword value that is too long to fit in a single 80-character record	optional	8.2, 15.5, 17.0, 18.4, 18.10, 18.13, Appendix I, Appendix II, Appendix IV, Appendix VII
CPDISia	N	Prior distortion function type. Distortion correction for axis i.	optional
CPERRia	N	Maximum value of prior distortion correction for axis i	optional
CQDISia	P	Posterior distortion function type. Distortion correction for axis i.	optional	Appendix VI
CQERRia	P	Maximum value of posterior distortion correction for axis i	optional	Appendix VI
CRDERia	P	Random error in Coordinate i, which must be non-negative.	optional	3.1
CREATOR	O	Name of software pipeline that produced the FITS file	optional	8.1, 18.10, Appendix IV
CROTAia	O	The amount of rotation from the standard coordinate system to a different coordinate system. Further use of this of this keyword is deprecated, in favor of the newer formalisms that use the CDi_j or PCi_j keywords to define the rotation.	optional	3.0
CRPIXja	P	Location of the reference point in the image for Axis j corresponding to rj. Note that the reference point may lie outside the image and that the first pixel in the image has pixel coordinates (1.0, 1.0, …)	obs	3.1, 3.2
CRVALia	P	Worldcoordinate value at the reference point of Axis i.	obs	3.1
CSYERia	P	Systematic error in Coordinate i, which must be non-negative.	optional	3.1
CTYPEia	P	Type of coordinate i	obs	3.1, 4.1, 5.1, 5.4
CUNITia	P	Physical units of CRVAL and CDELT for Axis i. Note that units should always be specified. Units for celestial coordinate systems defined in this Standard must be degrees.	obs	5.4
CWDISia	N	Weighted distortion function type. Distortion correction for axis i.	optional	Appendix VI
CWERRia	N	Maximum value of weighted distortion correction for axis i	optional	Appendix VI
DATAEXT	N	the original data/Obs-HDU ([x,y,lambda,t])	optional	Appendix IX, Appendix VII
DATAKURT	O	Kurtosis of the data array	optional	5.6, 18.8
DATAMAD	N	Median absolute deviation of the data array	optional	5.6, 18.8
DATAMAX	S	Maximum value of the data array	optional	5.6, 18.8, Appendix III
DATAMEAN	O	Mean of the data array	optional	5.6, 18.8
DATAMEDN	O	Median of the data array	optional	5.6, 18.8
DATAMIN	S	Minimum value of the data array	optional	5.6, 18.8, Appendix III
DATANMAD	N	Normalized median absolute deviation of the data array	optional	5.6, 18.8
DATANPnn	N	Normalized Percentiles from DATAPnn, of the nn percentile (where nn is e.g., 01, 02, 05, 10, 25, 50, 75, 90, 95, 98, and 99).	optional	5.6
DATANRMS	N	Normalized root mean square of the data array	optional	5.6, 18.8
DATAPnn	N	Percentiles of the data array, of the nn percentile (where nn is e.g., 01, 02, 05, 10, 25, 50, 75, 90, 95, 98, and 99).	optional	5.6
DATARMS	O	Root mean square of the data array	optional	5.6, 18.8
DATASKEW	O	Skewness of the data array	optional	5.6, 18.8
DATASUM	O	Sum of the data array, for checksum purposes	obs	9.0, 15.1
DATATAGS	N	Used for any additional search terms that do not fit in any of the other keywords.	optional	6.0, 15.5
DATE	S	FITS file creation date in UTC	obs	2.2, 13.0, 15.1, 18.2
DATE-AVG	P	used to give the average date of the observation. However, there is no unambiguous definition of the average when applied to observations with varying cadence or varying exposure times	optional	4.0, 18.2
DATE-BEG	P	referring to the start time of the data acquisition in the time system specified by the TIMESYS keyword, which has the default of ‘UTC’.	obs	2.2, 4.0, 4.1, 13.0, Appendix III
DATE-END	P	End time of the data aquisition	optional	4.0, 18.2, Appendix III
DATE-OBS	S	Date of the observation, in the time system specified by the TIMESYS keyword, which has the default of ‘UTC’. The DATE-OBS keyword is used to indicate the date of the observation, and it should be set to the date of the first exposure in the observation. Note that we do not recommend using the DATE-OBS keyword mentioned in the FITS Standard, since this is not explicitly defined there, and has a history of somewhat ambiguous use (see Paper IV).	optional	4.0
DATEREF	P	Time coord. zero point (time reference, mandatory) set to the zero point of the WCS time coordinate. I.e., for pixels that have the CTYPEi=’UTC’ coordinate equal to zero, the time is the value given in DATEREF. In most cases the values of DATEREF and DATE-BEG will be identical, but note that according to the FITS standard, DATE-BEG is not a default value for DATEREF, thus DATEREF may not be omitted.	obs	4.0, 4.1, 14.0, 15.2, Appendix I, Appendix I-a, Appendix III
DETECTOR	O	Name of detector	optional	6.0, 7.2, 15.5, 18.12, Appendix IV
DPja	P	Primary Distorion parameter for axis j	optional	Appendix VI
DQia	P	Posterioir distortion parameter for axis i	optional	Appendix VI
DSUN_AU	N	Distance to Sun (in Astronomical Units)	optional	3.2, 18.1
DSUN_OBS	P	Distance to Sun (in meters)	optional	3.2, 4.0, 15.3.3
DWia	N	Weighted distortion function type. Distortion correction for axis i. The DWia records describe the association of coordinates between the distortion array and the data cube whose coordinates are to be corrected.	optional	Appendix VI, Appendix VI-a
ELEV_ANG	N	This keyword should be used to quote the telescope’s elevation angle at the time of data acquisition, in degrees.	optional	5.5, 18.7
EXT_EXT	N	External extension placeholder extension path and name.	optional	Appendix VII
EXTEND	S	The EXTEND keyword is used to indicate that the file contains one or more extensions. The value of EXTEND must be set to ‘T’ (true) if the file contains one or more extensions, and ‘F’ (false) if it does not. The default value of EXTEND is ‘T’.	primary
EXTLEVEL	S	Level of extension, starting with 1 for the first extension after the primary HDU, 2 for the second extension, etc.	optional
EXTNAME	S	All HDUs - including the primary HDU - in SOLARNET FITS files must contain the string-valued keyword EXTNAME, and each EXTNAME value must be unique within the file. EXTNAME must not contain the characters comma or semicolon except as prescribed for the variable-keyword mechanism, the pixel list mechanism and the meta-observation mechanism. In addition, EXTNAME must not start with a space, but any trailing spaces are ignored. Finally, the CONTINUE Long String Keyword Convention must not be used with EXTNAME, since this is a reserved keyword defined in the FITS standard.	obs	2.1, 2.2, 5.5, 5.6.2, 8.2, 12.0, 17.0, Appendix I, Appendix I-a, Appendix I-b, Appendix II, Appendix III, Appendix III-a, Appendix IV, Appendix IX, Appendix VII
EXTVER	S	Version of the extension, starting with 1 for the first version of a given extension type, 2 for the second version, etc.	optional	2.1
FILENAME	P	FITS filename	obs	15.1, Appendix IV, Appendix V-a
FILEVERP	N	File Version Pattern. The keyword FILEVERP (file version pattern) should be specified to highlight a version identifier included in the file name. E.g., a file named solo_SPICE_sit-V01-2395.fits and the subsequent version solo_SPICE_sit-V02-2395.fits should both have FILEVERP=’solo_SPICE_sit-V*-2395.fits’, where the asterisk identifies where the file version occurs in the file name. Using an asterisk means that the file version should be interpreted lexically, whereas a percentage sign should be used when the version number is not a fixed number of decimals. E.g., with file names file_V2.fits and file_V12.fits, using FILEVERP=’file_V%.fits’ would ensure that the second file recognized as having a higher version number (thus superseding the first file).	optional	Appendix V-a
FILTER	O	Name(s) of the filter(s) used during the observation.	optional	6.0, 7.2, 15.5, 18.12
FT_LOCK	N	The keyword FT_LOCK is used to indicate the status of any feature tracking FT_LOCK=0 (no feature tracking lock) or FT_LOCK=1 (feature tracking lock) for individual exposures, with appropriate averages as mentioned above.	optional	5.5, 18.6
GEOX_OBS	P	[m] Observer’s non-fixed geographic X coordinate	optional	3.2, 15.3.2
GEOY_OBS	P	[m] Observer’s non-fixed geographic Y coordinate	optional	3.2, 15.3.2
GEOZ_OBS	P	[m] Observer’s non-fixed geographic Z coordinate	optional	3.2, 15.3.2
GRATING	O	Name of the grating used during the observation	optional	6.0, 7.2, 15.5
HASH_SW	N	Commit hash of software applied	optional	8.1, 18.10
HGLN_OBS	P	Observer’s heliographic longitude	optional	3.2, 4.0, 15.3.3
HGLT_OBS	P	Observer’s heliographic latitude	optional	3.2, 4.0, 15.3.3
HISTORY	S	History of the file, including all changes made to the file since its creation. The HISTORY keyword is a string-valued keyword that may be repeated as many times as necessary to record the history of the file. The first occurrence of the HISTORY keyword should contain a brief description of the contents of the file, and subsequent occurrences should contain a description of any changes made to the file.	optional
iCRVLn	P	The reference value of the coordinate axis i in the data cube, which is the value of the coordinate axis i at the reference pixel. The reference pixel is the pixel at which the WCS coordinate values are CRVALn. The reference value is the value of the coordinate axis at the reference pixel.	optional	Appendix I-a
iCTYPn	P	The type of the coordinate axis i in the data cube, which is the physical quantity that the coordinate axis represents. The type is specified by the keyword CTYPEi, where i is the axis number in the data cube. The type is a string that is a valid FITS keyword value, e.g., ‘RA—TAN’ for a tangent-plane projection in right ascension.	optional
INCLEXT	N	component inclusion mask ([x,y,t,n]) - if (x,y,t,n)=0, component n has not been included for point (x,y,t). When not present, it is assumed that all components have been included at all times.	optional	Appendix IX
INFO_URL	N	should point to a human-readable web page describing “everything” about the data set - what it is, how to use it, links to e.g., user guides, instrument/site/telescope descriptions, descriptions of caveats, information about data rights, preferred acknowledgements, whom to contact if you have questions, and repositories of observing/engineering logs.	optional	9.0, 18.11
INST_TYP	N	Instrument type (e.g., imager, spectrograph)	optional
INSTRUME	S	Instrument name	optional	6.0, 7.2, 15.5, 18.12
jCRPXn	P	The reference pixel of the coordinate axis j in the data cube	optional	Appendix I-a
LEVEL	O	Data level of fits file	optional	8.0, 8.1, 18.10
METADIM	N	Dimension that has been splot for constituent HDUs. E.g., when splitting an array [x,y,t] into time chunks, METADIM=3. Note than an accompanying auxiliary HDU with e.g., dimensions [t,z] would set METADIM=1. Auxiliary HDUs whose data array dimensions does not contain the split dimension (e.g., flatfields) do not need to contain the METADIM keyword. It is allowed to have METADIM > NAXIS to account for lost trailing singular dimensions. E.g., if constituent HDUs have dimensions [x,y,lambda] and METADIM=5, the resulting stitched HDU will have five dimensions e.g., [x,y,lambda,1,t].	optional	17.0, Appendix III
METADIMn	N	Indicate which dimensions have been split. . It is then possible to construct Meta-HDUs resulting from aggregating Constituent HDUs along one or more dimensions. I.e., if an original HDU with dimensions [1000, 2000, 3000] has been split into 100 files/HDUs with dimensions [100,2000,300], the Constituent HDUs would have METADIM1=1 and METADIM2=3.	optional	Appendix III-a
METAFILS	N	List of filenames of constituent HDUs. The filenames should be separated by commas, and the list should be ordered in the same way as the HDUs are ordered in the Meta-HDU.	optional	17.0, Appendix III
MISSION	N	Mission name	optional	6.0, 15.5
MOSAICID	N	For mosaic observations, the keyword MOSAICID can be used to tie individual observations together.	optional	7.4, 18.12
NAPRXPIX	N	the number of pixels with approximated values (used by e.g., SolO/SPICE)	optional	5.6.1, 18.9
NAXIS	S	Number of data axes	obs	3.1, 15.2, Appendix III, Appendix IV, Appendix VII
NAXISn	S	The NAXISn keywords must be present for all values n = 1,… , NAXIS, in increasing order of n, and for no other values of n. 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. A value of zero for any of the NAXISn signifies that no data follow the header in the HDU (however, the random-groups structure described in Sect. 6 has NAXIS1 = 0, but will have data following the header if the other NAXISn keywords are non-zero). If NAXIS is equal to 0, there shall not be any NAXISn keywords.	obs	Appendix VII
NBIN	N	In order to provide a simple way to determine the combined binning factor (for archive searches), the keyword NBIN should be set to the product of all specified NBINj keywords.	optional	5.2, 7.2, 15.4, 18.12
NBINj	N	Binning should be specified by the keywords NBINj, where j is the dimension number (analogous to the NAXISj keywords). E.g., for an observational data cube with dimensions (x,y,lambda,t) where 2x2 binning has been performed in the y and lambda directions (as is sometimes done with slit spectrometers), NBIN2 and NBIN3 should be set to 2. The default value for NBINj is 1, so NBIN1 and NBIN4 may be left unspecified.	optional	5.2, 15.4
NDATAPIX	N	the number of usable pixels NTOTPIX - NLOSTPIX - NSATPIX - NSPIKPIX	optional	5.6.1, 18.9
NLOSTPIX	N	the number of lost pixels due to telemetry/acquisition glitches	optional	5.6.1, 18.9
NMASKPIX	N	the number of dust-affected/hot/cold/padded pixels etc.	optional	5.6.1, 18.9
NSATPIX	N	the number of saturated pixels	optional	5.6.1, 18.9
NSPIKPIX	N	the number of identified spike pixels	optional	5.6.1, 18.9
NSUMEXP	N	the number of summed exposures	optional	5.2, 15.4
NTOTPIX	N	the number of potentially usable pixels. the number of data cube pixels minus NMASKPIX	optional	5.6.1, 18.9
OBS_DESC	O	Description of observation. A string describing the observation, e.g., “Sit and stare on AR10333”. Should be identical to OBSTITLE when no more suitable value is available.	optional	6.0, 15.5
OBS_HDU	N	Whether the HDU is an observational HDU (1) or not (0).	obs	2.2, 8.0, 13.0, Appendix IV, Appendix IX
OBS_LOG	N	Location of the log file that is relevant to this observation, if available, given as a URL.	optional	5.5, 9.0, 18.7
OBS_MODE	O	Name of predefined settings used during observation. A string (from a limited/discrete list) uniquely identifying the mode of operation.	optional	6.0, 7.2, 15.5
OBS_TYPE	N	Type of observatory. A string (from a limited/discrete list) uniquely identifying the type of observatory.	optional
OBS_VR	N	[km/s] Observer’s outward velocity w.r.t. Sun	optional	3.2, 15.6
OBSERVER	S	Who acquired the data	optional	6.0, 15.5
OBSGEO-X	P	[m] Observer’s fixed geographic X coordinate	optional	3.2, 15.3.1
OBSGEO-Y	P	[m] Observer’s fixed geographic Y coordinate	optional	3.2, 15.3.1
OBSGEO-Z	P	[m] Observer’s fixed geographic Z coordinate	optional	3.2, 15.3.1
OBSRVTRY	N	Name of the observatory	optional	6.0, 15.5
OBSTITLE	O	Title of observation. A more generic/higher-level description, e.g., “Flare sit-and-stare”, “High cadence large raster”), which often corresponds to OBS_MODE, though not necessarily as a oneto-one relationship. Used by IRIS and SPICE, corresponds to Hinode OBS_DEC. Should be identical to OBS_DESC or OBS_MODE when no more suitable value is available.	optional	6.0, 15.5
ORIGIN	S	set to a character string identifying the organization or institution responsible for creating the FITS file.	obs	8.0, 15.1
PARENTXT	N	Identifies parent extension(s), path(s), file name(s), and extension name(s), likely using external extension reference syntax	optional	8.0, Appendix IX, Appendix VII
PCi_ja	P	a linear transformation matrix between data cube dimension j and coordinate axis i, which can be used to specify rotations, shear, transpositions and reflections.	optional	3.1
PCONSna	N	Optional functional keyword for parameters in parameterized components. Set to 1 if pa has been kept constant during fitting.	optional	Appendix IX
PCT_APRX	N	the percentage of pixels with approximated values (used by e.g., SolO/SPICE) (NAPRXPIX/NTOTPIX*100)	optional	5.6.1, 18.9
PCT_DATA	N	the percentage of usable pixels (NDATAPIX/NTOTPIX*100)	optional	5.6.1, 18.9
PCT_LOST	N	the percentage of lost pixels due to telemetry/acquisition glitches (NLOSTPIX/NTOTPIX*100)	optional	5.6.1, 18.9
PCT_MASK	N	the percentage of dust-affected/hot/cold/padded pixels etc. (NMASKPIX/NTOTPIX*100)	optional	5.6.1, 18.9
PCT_SATP	N	the percentage of saturated pixels (NSATPIX/NTOTPIX*100)	optional	5.6.1, 18.9
PCT_SPIK	N	the percentage of identified spike pixels (NSPIKPIX/NTOTPIX*100)	optional	5.6.1, 18.9
PDESCna	N	Optional functional keyword for parameters in parameterized components. Parameter desciption	optional	Appendix IX
PINITna	N	Optional functional keyword for parameters in parameterized components. Initial value of parameter	optional	Appendix IX
PIXLISTS	N	PIXLISTS must declare the EXTNAME of the extension containing the pixel list, followed by a semicolon, then a comma-separated list of any pixel attribute names. When multiple pixel lists are used, this is signalled by adding a comma, the EXTNAME of the next pixel list extension followed by a semicolon, etc. Note that even when a pixel list does not contain any attributes, a comma is needed before the EXTNAME of any subsequent pixel list.	optional	17.0, Appendix II, Appendix IV
PIXTYPE	N	Pixel Type	optional	17.2, Appendix II
PLANNER	O	Observation planner	optional	6.0, 15.5, 16.0
PMAXna	N	Optional functional keyword for parameters in parameterized components. Maximum value of parameter	optional	Appendix IX
PMINna	N	Optional functional keyword for parameters in parameterized components. Minimum value of parameter	optional	Appendix IX
PNAMEna	N	Optional functional keyword for parameters in parameterized components. Parameter name	optional	Appendix IX
POINT_ID	N	Pointing ID serves to separate otherwise identical observations into groups in a logical way.	optional	7.1, 7.2, 7.3, 15.9, 18.12, Appendix V-b
POLCANGL	N	If the polarimetric reference frame is not aligned with any set of WCS coordinate names, a rotation of the reference frame given in POLCCONV can be specified in POLCANGL. The rotation, specified in degrees, should be applied to the POLCCONV-specified system around its third axis. The rotation is counter-clockwise as seen from a point with a positive third-axis coordinate value, taking the sign from POLCCONV into account. I.e., specifying a positive angle with POLCCONV=’(…, …, +HPRZ) ‘ specifies a counter-clockwise rotation as seen from Earth, whereas zwith POLCCONV=’(…, …, -HPRZ) ‘ would specify a clockwise rotation as seen from Earth.	optional	5.4.1, 15.8
POLCCONV	N	The axes must be explicitly specified by the keyword POLCCONV in the form ‘(+/-x, +/-y, +/-z)’ where x, y, and z are valid WCS coordinate names. E.g., POLCCONV=’(+HPLT,-HPLN,+HPRZ)’ means that the reference system’s x axis is parallel to the HPLT axis (Solar North), and y is antiparallel to the HPLN axis, with z pointing towards the observer.	optional	5.4.1, 15.8
PRBRAna	N	Optional pipeline processing keyword. Branch name of code use in processing step n	optional	8.2
PRENVn	N	specify the operating environment of the pipeline such as the hardware (CPU type) and the operating system type/version, compiler/interpreter versions, compiler options, etc.6 The default value of a PRENVn keyword is the value of PRENVn in the previous processing step, so for a pipeline that has been run from beginning to end in a single environment, only PRENV1 will have to be specified.	optional	8.2
PRHSHna	N	Optional pipeline processing keyword. Convenience keyword to easily find the exact git commit for a library that has been used. Note that it does not replace PRVERna, because PRHSHna is not a number that increases with the maturity of the libraries (but such a number can be constructed, see above)	optional	8.2
PRLIBna	N	Optional pipeline processing keyword. Library name used in processing step n	optional	8.2
PRLOGn	N	Optional pipeline processing keyword. used to include a processing log in case messages/warnings from the processing may be of importance.	optional	8.2
PRMODEn	N	Optional pipeline processing keyword. Meant for pipelines that may be run with different trade-offs between e.g., signal to noise ratio versus spatial resolution or contrast. This should already be apparent from the other keywords, but PRMODEn provides a much simpler way of identifying data processed in a particular way (e.g., “BALANCED” or “HIGH CONTRAST”). Note that a single observation may be registered multiple times in an SVO with different values of PRMODEn - but then a PRMODEnspecific identifier in the file name is necessary in order to ensure uniqueness.	optional	8.2, Appendix V-a
PROJECT	N	Name(s) of the project(s) affiliated with the data	optional	6.0, 15.5
PRPARAn	N	Optional pipeline processing keyword. The PRPARAn keyword can be used in different ways 1. As a plain comma-separated listing of parameters and their values, signalled by the first character matching the regular expression ‘[A-Za-z_$]’ 2. As a JSON string, signalled by the first character being an opening curly bracket 3. As an XML specification, signalled by the first character being a ‘<’ 4. As the EXTNAME of an ASCII table, signalled by the first character being a ‘[’	optional	8.2
PRPROCn	N	Optional pipeline processing keyword. Name of Processing Procedure used in processing step n	optional	8.2
PRPVERn	N	Optional pipeline processing keyword. Version of processing pipeline used in processing step n	optional	8.2
PRREFn	N	Optional pipeline processing keyword. Reference to the processing step n	optional	3.1, 8.2
PRSTEPn	N	should specify the nature of the processing steps, if any, that has been applied to the data. Each PRSTEPn may contain a comma separated list if multiple processing steps are inseparable. The number n specifies the step number and should reflect the order in which the steps have been performed	optional	8.1, 8.2
PRVERna	N	Optional pipeline processing keyword. Version of code used in processing step n for library a	optional	8.2
PTRAna	N	Optional functional keyword for parameters in parameterized components. Linear transformation coefficient A.	optional	Appendix IX
PTRBna	N	Optional functional keyword for parameters in parameterized components. Linear transformation constant B.	optional	Appendix IX
PUNITna	N	Optional functional keyword for parameters in parameterized components. The units for parameter a of component n, specified according to the FITS Standard Section 4.3, e.g., ‘nm’ or ‘km/s’.	optional	Appendix IX
RELEASE	N	Public release date of data. Proprietary data should be marked by setting the keyword RELEASE to the date at which the data can be freely distributed.	optional	9.0, 18.11
RELEASEC	N	Email address of data release administrator. The keyword RELEASEC may be used to give contact information for one or more people (name/email addresses, comma separated) administering the release details.	optional	9.0, 18.11
REQUESTR	N	Who requested this particular observation.	optional	6.0, 15.5
RESEXT	N	Optional functional keyword for parameters in parameterized components. the HDU containing the analysis results ([x,y,t,p]).	optional	Appendix IX
RESIDEXT	N	Optional functional keyword for parameters in parameterized components. Residuals from the fitting process ([x,y,lambda,t]) which may in some cases be an important factor in the verification e .g., to discover emission lines that have not been considered during the fitting	optional	Appendix IX
RESOLVPW	N	Resolving power for spectrometric data	optional	5.4, 18.6
RESPAPPL	N	Response function applied	optional	5.4, 18.6
RESPONSE	N	Response function used	optional	5.4, 18.6
ROT_COMP	N	set to 1 if automated solar rotation compensation was in effect during the observation, and to 0 if not.	optional	5.5, 18.6
ROT_FORM	N	The formula specified is meant to be human-readable, not machine readable, thus e.g., ‘ A sin(…)’, using parameter names that are common within your community. An explanation in the comments may be useful. The units should be degrees per day. More important, though is that the coordinate variation is reflected in the WCS description of the data, using cross terms between the time coordinate and spatial coordinates in the PCi_j matrix or by tabulating the coordinates.	optional	5.5, 18.6
ROT_MODL	N	The keyword ROT_MODL should be set to specify the rotation model used for rotation compensation4. It can refer to specific, predefined models such as ALLEN (Allen, Astrophys. Quantities, 1979), HOWARD (Howard et al.), SIDEREAL, SYNODIC, CARRINGTON, SNODGRASS or aaa.a - arcseconds per hour (units [arcsec/h]). See also the SolarSoft routine diff_rot.pro. If other models have been used, please contact prits-group@astro.uio.no, or set ROT_MODL to FORMULA, and specify the formula in the keyword ROT_FORM.	optional	5.5, 18.6
RSUN_ARC	O	[arcsec] apparent photospheric solar radius in arc seconds	optional	3.2
RSUN_REF	P	[m] Reference solar radius in meters. For observations (instruments) where the plate scale/pointing is derived from measurements of the apparent solar radius versus the physical size, the keywords RSUN_REF should be used to report the reference value for the physical radius used in the calculations (see Thompson 2010, Section 8).	optional	3.1, 18.7
SETTINGS	N	Additional instrument/acquisition settings	optional	6.0, 7.2, 15.5
SIGMADAT	N	standard deviation values of the data as a formula, a lookup table, or as an extension with explicit values	optional	5.5, Appendix IX
SIMPLE	S	set to T if the file is in FITS format, and to F if not.	primary
SLIT_WID	N	[arcsec] Slit width	optional	5.4, 7.2, 15.7
SOLAR_B0	O	[deg] Heliographic latitude of the observer. Note that the Solar B angle is identical to HGLT_OBS, and although it is a duplication of information, it may be reported also in SOLAR_B0 for convenience.	optional	3.2
SOLAR_EP	O	apparent angle from observer location between celestial north and ecliptic north	optional	3.2
SOLAR_P0	O	apparent angle from observer location between celestial north and solar north	optional	3.2
SOLARNET	N	Fully SOLARNET-compliant=1.0, partially=0.5	obs	2.2, 2.3, 13.0, 17.0, Appendix I, Appendix II, Appendix III, Appendix IX
SOLNETEX	N	List of keywords that are used in conflict with SOLARNET-defined meanings. This mechanism may sometimes be necessary to ensure backwards compatibility with existing utilities. Keywords listed in SOLNETEX will be ignored by SOLARNET-aware utilities. The SOLNETEX mechanism must not be applied to FITS standard keywords.	optional	2.2, 16.0
SPECSYS	P	Spectral reference frame	optional	3.2, 15.6
SVO_GRP	N	SVO_GRP may be used to achieve the opposite, to tie observations together even if they have different POINT_IDs and/or have other differing characteristics. Heuristically, a shared value for SVO_GRP signals that if you are interested in this observation, you are probably interested in all of these observations (with the same SVO_GRP value).	optional	7.3, 18.12
SVO_SEPn	N	To guide archive designers in the process of presenting grouped observations, we introduce the keywords SVO_SEPn, with n spanning from 1 to 5. SVO_SEP1 should have a comma-separated list of keywords giving the most fine grained grouping, and SVO_SEP5 should have a commaseparated list of keywords giving the coarsest sensible grouping. Normally, the first keyword should be POINT_ID, and it may be the only keyword. Not all SVO_SEPn keywords need to be defined, but they should be populated starting with SVO_SEP1.	optional	7.2
TCTYPn	P	Binary table columns storing pixel indices must have TCTYPn equal to ‘PIXEL’ and TTYPEn equal to ‘DIMENSIONk’, where k is the dimension number in the referring HDU’s data cube. The column storing pixel types must have TTYPEn equal to ‘PIXTYPE’. Any attribute columns must have TTYPEn equal to the name of the attached attribute contained in that column.	optional	17.2, Appendix II
TDESCn	N	TDESCn may be used to give a description of the contents of the binary table column.	optional	18.13
TDIMn	S	TDIMn may be used to give the dimensions of the binary table column.	optional	Appendix IV
TELCONFG	N	Telescope configuration	optional	6.0, 15.5
TELESCOP	S	Telescope/Sensor name	optional	6.0, 15.5
TEXPOSUR	N	The integration time for a single exposure	optional	5.2, 15.4
TFORMn	S	TFORMn may be used to give the format of the binary table column.	optional
TIMESYS	P	Time scale of the time-related keywords.	optional	4.0, 18.2
TKEYSn	N	The naming conventions for column-specific keywords (starting with T and allowing for 3-digit column numbers) leaves only 4 letters to carry meaning, which easily leads to the creation of very awkward column-specific keyword names. To alleviate this problem for keywords that must have different values for different columns, the column-specific keyword TKEYSn is introduced, listing pairs of keyword names and values inside a string. The CONTINUE Long String Keyword Convention may of course be used to improve readability and add comments.	optional	Appendix IV
TPCn_na	P	Optional keyword for pixel list mechanism for flagging pixels.	optional	Appendix II
TPXLSn	N	Optional keyword for pixel list mechanism for flagging pixels. TPXLSn replaces PIXLISTS	optional	Appendix IV
TTYPEn	S	TTYPEn may be used to give the name of the binary table column.	optional	5.6.2, 17.2, Appendix I, Appendix II, Appendix IV, Appendix VII
TVARKn	N	Optional keyword for pixel list mechanism for flagging pixels. TVARKn replaces VAR_KEYS	optional	Appendix IV
TZEROn	S	This indexed keyword shall be used, along with the TSCALn keyword, to linearly scale the values in the table Field n to transform them into the physical values that they represent using Eq. 7. 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. This keyword must not be used for A-format fields. TZEROn replaces BZERO.	optional	Appendix IV
UCD	N	UCD (Unified Content Descriptor) is a standard for describing the content of data in a machine-readable way. It is a string that describes the physical quantity represented by the data in the column.	optional	5.1, 18.5
VAR_KEYS	N	VAR_KEYS must declare the EXTNAME of the extension containing the variance keys, followed by a semicolon, then a comma-separated list of any variance key names. When multiple variance keys are used, this is signalled by adding a comma, the EXTNAME of the next variance key extension followed by a semicolon, etc. Note that even when a variance key does not contain any attributes, a comma is needed before the EXTNAME of any subsequent variance key.	optional	17.0, Appendix I, Appendix I-d, Appendix IV, Appendix VII
VELOSYS	P	[floating point; default:: none]. Relative radial velocity between the observer and the selected standard of rest in the direction of the celestial reference coordinate. Units must be m/s. The CUNITia keyword is not used for this purpose since the WCS Version a might not be expressed in velocity units.	optional	3.2, 15.6
VERS_CAL	N	Version of calibration pack applied	optional	8.1, 18.10
VERS_SW	N	Version of software applied	optional	8.1, 18.10
VERSION	N	FITS file processing generation/version. VERSION should be set to the processing version of the file, an integer that should be increased whenever a reprocessing is performed in order to improve the data set (e.g., with a better flatfield, better detection of cosmic rays, more complete telemetry, etc). The version numbers in files published through an SVO may increase by more than one for each new published “generation”, allowing the use of intermediate values for internal/experimental use.	optional	8.0, 18.10
WAVEBAND	N	Human-readable description of the waveband	optional	5.4, 18.6
WAVECOV	N	The total wavelength coverage if multiple filters (-, etc.)	optional	5.4, 18.4
WAVELNTH	O	The characteristic wavelength of the observation	optional	5.4, 18.6, Appendix IV
WAVEMAX	N	[Angstrom] Maximum wavelength covered by filter	optional	5.4, 15.6, 18.4
WAVEMIN	N	[Angstrom] Minimum wavelength covered by filter	optional	5.4, 15.6, 18.4
WAVEREF	N	Wavelength related kwds in vacuum	optional	5.4, 15.6
WAVEUNIT	O	Wavelength related kwds have unit: 10^(WAVEUNIT) m	optional	5.4, 15.6
WCSAXES	P	Number of physical axes. The number of physical coordinates is normally equal to NAXIS but may be larger or smaller as optionally specified in WCSAXES.	optional	3.1, 15.2, Appendix III
WCSNAMEa	P	WCS name for axis a	optional	Appendix I-d
WCSNn	P	WCS name for axis n	optional	17.1, Appendix I-b
XDIMENm	N	The dimension number(s), counting left to right starting with 1, of dimensions that was absorbed/removed during the fitting process.	optional	Appendix IX
XNAXIS	N	Number of axes in external extension	optional	Appendix IX, Appendix VII
XNAXISn	N	Number of axes in external extension n	optional	Appendix IX, Appendix VII
XPOSURE	P	[s] Total effective exposure time	optional	5.2, 5.5, 7.2, 15.4, Appendix V-c
XTENSION	S	The name of the extension containing the data. The name is a string that is a valid FITS keyword value, e.g., ‘DATA’ for the data extension.	optional
XTYPEm	N	the CTYPEi of the mth dimension absorbed by the fitting process.	optional	Appendix IX

Number of keywords: 223

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[1]

Some of the WCS keywords defined in these papers are also defined in the FITS standard Table 22