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Common Metadata

The keywords listed below are required (or in a few cases, recommended) in all FITS files (and in some cases, all FITS extensions) of any type that contain images, spectra, or light curves. Recommended keywords, if absent, will be derived and inserted prior to ingest. Note that the list below does not include the basic structural FITS keywords (SIMPLE, NAXIS, etc.) that are required for valid FITS HDUs. Most FITS writing applications already know how to insert structural keywords into FITS headers.

The extension column refers to the primary (P) header or, for multi-extension (MEF) files, one or more extensions (E). Depending upon the organization of the data (e.g., if image data arrays appear in an extension), any given Primary keyword may instead belong in an Extension.

Keyword HDU Notes
Required Keywords
DATE-BEG P or E ISO-8601 formatted DateTime for start of observation, in the time system specified by TIMESYS. May use MJD-BEG in addition or instead. For catalogs, this time should reflect the time of the earliest observation of the entries.
DATE-END P or E ISO-8601 formatted DateTime for end of observation, in the time system specified by TIMESYS. For catalogs, this time should reflect the time of the latest observation of the entries.
EQUINOX E Equinox of the celestial coordinate system. This keyword must not be used if RADESYS = 'ICRS'
HLSPTARG P Designation of the target(s) or field(s) for this HLSP
INSTRUME P Designation of instrument used for this observation
MJD-BEG P or E Start time of observation, expressed as MJD. May use DATE-BEG in addition or instead. For catalogs, this time should reflect the time of the earliest observation of the entries.
MJD-END P or E End time of exposure, expressed as MJD, in the time system specified by TIMESYS. For catalogs, this time should reflect the time of the earliest observation of the entries.
MJD-MID P or E Mid-time of exposure, expressed as MJD, in the time system specified by TIMESYS. For catalogs, this time should reflect the time of the earliest observation of the entries.
OBSERVAT P Observatory used to obtain this observation.
TELESCOP P Designation of telescope used for this observation
TIMESYS P or E Character string code for time scale of time-related keywords.
XPOSURE P or E Duration of exposure, corrected for dead time
Recommended Keywords
HLSPID P The identifier (acronym) for this HLSP collection
HLSPLEAD P Full name of HLSP project lead
HLSPNAME P Name for HLSP project name, long form
HLSPVER P Version identifier for this HLSP product
LICENSE P License for use of these data, with the value 'CC BY 4.0'
LICENURL P Data license URL, with the value 'https://creativecommons.org/licenses/by/4.0/'
PROPOSID P Observatory program/proposal identifier, if applicable
REFERENC P Bibliographic identifier (ADS bibcode or DOI) for reference where these data were published
TELAPSE P or E Time elapsed between start- and end-time of observation

Notes:

  • Keyword records are listed in the above table alphabetically by name for ease of reference; contributor teams may choose the order of most keywords.
  • Deprecated FITS keywords (such as EPOCH) must not be used.