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Catalog Metadata


The keywords listed below are required or recommended for all FITS files in both primary (P) and extension (E) headers that contain catalogs. Such file headers must also include the basic structural FITS keywords and the list of common keywords.

Keyword HDU Notes
Required Keywords
BUNIT E Brightness unit for array values
RADESYS E Mnemonic for celestial coordinate reference system (typically 'FK5' or the preferred 'ICRS').
<Filt>MAG0 E Flux corresponding to zero magnitude in the <Filt> passband

Catalog Fields

Most of the metadata in catalogs is often in the definition of the database fields, or table column names, units, and numeric types. Below are the recommended fields for source catalogs, where text in brackets is entirely user-defined.

Name DataType Notes
Recommended Fields
SOURCE string Alphanumeric identifier of source
RA double Right ascension coordinate of source
Dec double Declination coordinate of source
<Filt> float Brightness of source in the passband named <Filt>, with NULL value (NaN) indicating no measurement
<Filt>_err float Uncertainty in source brightness.
<Filt>_flag int Applicable, encoded flags that apply to the brightness in the named passband, with the convention that zero indicates no pathologies.


  • Deprecated FITS keywords (such as EPOCH) must not be used.