The HEASARC Database System

HEASARC Conventions for Virtual Parameters

Virtual parameters are stored in the ZZEXT metabase table. The existence and values of these virtual parameters control how tables are treated by the HEASARC Browse system. The following virtual parameters are utilized and their usage is highly recommended:

default_search_radius
Specfies the default for the Browse cone search radius for this table. The value should be in arcminutes. If the table does not have right ascension and declination columns, then this virtual parameter should not be specified. Note that the default search radius value may be specified as a column name (e.g., the positional error), prefixed by "@", so that it could vary from row to row. The existence of this entry is used by Browse to indicate that this table can be searched by position in a cone.
equinox
Specifies the epoch of the equinox of the right ascension and declination values present in the table. This should normally be a numeric value. In principle Browse can query tables in any equinox; however, in order to support cross-correlations, tables should provide default right ascension and declination columns in J2000 (FK5) coordinates. It is recommended that new tables that are to be ingested which do not have J2000 positions have new columns added to the table with positions in the J2000 standard coordinate frame rather than converting the input columns. As a result, this virtual parameter value is almost always "2000". If the table does not have right ascension and declination columns, then this virtual parameter should not be specified.
right_ascension
Specifies the name of the field in the table which contains the right ascension values. Traditionally, this is almost always "ra". If the table does not have a right ascension column, then this virtual parameter should not be specified.
declination
Specifies the name of the field in the table which contains the declination values. Traditionally, this is almost always "dec". If the table does not have a declination column, then this virtual parameter should not be specified.
target_name
Specifies the name of the field in the table which contains the names of the astronomical objects or targets. This is usually "name". If the table does not have a name column, then this virtual parameter should not be specified.
start_time
Specifies the name of the field in the table which contains the (starting) date/time of the observation or event in MJD format. If the table does not contain temporal data, then this virtual parameter should not be specified.
end_time
Specifies the name of the field in the table which contains the date/time that the observation ended in MJD format. If the table does not contain temporal data or if the table only contains one time field, then this virtual parameter should not be specified.
frequency_regime
Specifies the frequency regime that the data in the table belongs to. Tables may have multiple frequency_regime virtual parameters and values if the data contained therein is multiwavelength. Possible values:
  • EUV
  • Gamma-ray
  • Infrared
  • Optical
  • Radio
  • Ultraviolet
  • X-ray
  • Physics
"Physics" is obviously not a frequency regime, but the HEASARC has traditionally specified this value when dealing with tables containing physics-related data.
observatory_name
Specifies the name of the observatory or mission from which the data table originated. The HEASARC convention is to use all uppercase for these names. If the table contains non-mission-specific or non-observatory-specific data, a generic classification may be used. For example,
  • GALAXY CATALOG
  • GAMMA-RAY BURSTS
  • GENERAL CATALOG
  • MASTER CATALOG
  • NEBULA CATALOG
  • PHYSICS DATA
  • RADIO CATALOG
  • STAR CATALOG
table_priority
Specifies the order of tables within a mission/observatory grouping in Browse table listings. Values should be real numbers, with lower numbers meaning they are listed before higher numbers.
table_author
Specifies the author(s) of the table. Use "HEASARC" for internal tables. Use institution names such as SAO or STScI for external project tables. Use a comma-separated list of authors' surnames for external, non-project-related tables. For more than 4 authors or so, use "Smith et al." where "Smith" is the primary author. Use semicolons to separate lists of authors, if the table is a compilation of multiple sources with different sets of authors.
table_type
Specifies the type of table. In Browse users can select the table types of interest. Possible values:
Object
"Object" catalogs typically have one entry per astronomical object.
Observation
"Observation" catalogs typically have multiple entries per object.
Proposal
"Proposal" tables contain mission-specific data about the proposals submitted by guest observers.
Physics
"Physics" tables contain physics data.
System
"System" tables comprise the metabase portion of the Next-Generation HEASARC DBMS and their names typically start with "zz".
row_type
Specifies the content of each row in the table. There is currently no set list of possible values, but an effort should be made to utilize existing types as much as possible. Note that multiple row_type virtual parameter names/values may be specified, if appropriate. Typical values:
  • AGN
  • Atomic Datum
  • CV
  • Cluster of Galaxies
  • Compilation Source
  • Extragalactic Source
  • Extragalactic Supernova
  • Extragalactic Variable Star
  • GRB
  • Galaxy
  • Galaxy Group
  • Image
  • Lightcurve
  • Nebula
  • Nova
  • Observation
  • Observation Information
  • Optical Counterpart
  • Proposal
  • Proposed Target
  • Publication
  • Pulsar
  • Radio Counterpart
  • Redshift
  • SNR
  • Solar Flare
  • Spectrum
  • Star
  • Star Cluster
  • Supernova
  • Survey Source
  • Transient
  • Variable Star
  • White Dwarf
  • XRB
unique_key
Specifies the field (or fields, if multiple fields are needed, in which case a comma-delimited list is used) which comprises the unique (primary) key of the table. Browse no longer utilizes this virtual parameter, so it is no longer necessary; however, it may still be useful in understanding what each row in the database table logically comprises. Tables now have a special, hidden field, '_unique_id' added to them when they are ingested which is used to provide a unique identifier.
w3browse_display
If the value is "N", then Browse will not display the table in its table listings, effectively hiding the table from users. No other value is currently recognized. Note that queries may still be made against this table if the user formats the URL manually or uses the batch interface.
catalog_bibcode
Specifies the ADS bibcode or the CDS table specifier for this table. In the case off the latter, angle brackets ("<", ">") are used to differentiate the CDS table specifiers from ADS bibcodes.

All virtual parameter names are automatically converted to lowercase by the HDBingest software, effectively making all virtual parameter names case-insensitive; however, virtual parameter values are case-sensitive.


Documentation prepared by the HEASARC Database Group

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Last modified: Tuesday, 18-Oct-2005 15:23:15 EDT