giant_catalogue

This module defines the interface to the default GIANT star catalogue.

Catalogue Description

The default GIANT star catalogue is a blending of the UCAC4 and Tycho2 catalogues into a stripped down sqlite3 database. This makes retrieval of stars very fast instead of using the UCAC4 or Tycho2 catalogue files themselves and also includes blended stars (stars that are so close together they will appear as a single star in most cameras). This catalogue includes stars down to about 16th magnitude and should be sufficient for nearly all stellar OpNav needs.

The current implementation of the database storing this catalogue is a single table with a primary index column of rnm, which contains the unique ID of the provided star from the UCAC4 catalogue. For blended stars, the index number becomes the negative of the unique ID of the brightest star in the group. In addition to the index, the following columns are provided

Column	Units	Type	Description
source	N/A	string	The original catalogue source of the star (UCAC4 or Tycho2)
zone	N/A	integer	The UCAC4 zone number for the star, if applicable
rnz	N/A	integer	The star number in the UCAC4 zone if applicable
ra	deg	double	The right ascension of the star in degrees
dec	deg	double	The declination of the star in degrees
distance	km	double	The distance to the star in km. If not known then this is replaced with the average distance to a star
ra_proper_motion	deg/yr	double	The proper motion of the right ascension of the star in degrees per SI year
dec_proper_motion	deg/yr	double	The proper motion of the declination of the star in degrees per SI year
mag	mag	double	The visual magnitude of the star. This is the APASM_V magnitude if available, otherwise the MAGM (model magnitude) from the UCAC4 catalogue.
ra_sigma	deg	double	The right ascension uncertainty in units of degrees
dec_sigma	deg	double	The declination uncertainty in units of degrees
distance_sigma	km	double	The distance uncertainty in units of kilometers. For stars for which this is not known it is set to a large number
ra_pm_sigma	deg/yr	double	The right ascension proper motion uncertainty in degrees per SI year.
dec_pm_sigma	deg/yr	double	The declination proper motion uncertainty in degrees per SI year.

While this implementation mirrors the GIANT_COLUMNS currently, and probably will in the future, it isn’t guaranteed to stay that way. In addition, while this is currently a blend of the UCAC4 and Tycho2 catalogues, in the future it will likely be built from the GAIA DR2 catalogue since this provides much more accurate stars positions/magnitudes for many more stars.

Use

The GIANT catalogue can be used anywhere that a star catalogue is required in GIANT and is generally the default catalogue that is used if you do not override it. It is stored in a sqlite file in a directory called data in the same directory hosting this file, though it is possible to override this if desired (which you may want to do if you need different versions of the catalogue for different cameras). To access the default catalogue simply initialize this class with no arguments and then call query_catalogue() to retrieve the star records that you want.

This implementation also provides 2 helper methods that can retrieve the original star record from either the Tycho 2 or UCAC4 catalogue (if the star exists in them and is not a blended star). These are get_ucac4_record() and get_tycho2_record(). They take in a pandas DataFrame of stars retrieved from this catalogue and return a dataframe with the original records for those stars. This can be useful if you need more information about a star than what GIANT typically considers. Just note that these methods will require that the entire UCAC4/Tycho2 star catalogues be downloaded if they aren’t already.

This module also provides a few functions that can be used to build a new version of this catalogue, build_catalogue(), find_star_pairs(), and blend_stars(). Typically you won’t interact with these directly and instead will use the script build_catalogue which provides a command line interface, however they’re provided for those who are interested in what they do or in doing some more advanced things.

Classes

GIANTCatalogue

This class provides access to the default GIANT star catalogue built from the UCAC4 and Tycho2 Catalogues.

Function

blend_stars	Blends groups of stars together into a single "apparent" star as viewed by a camera.
build_catalogue	Build a sqlite3 catalogue from the UCAC catalogue for faster query times.
find_star_pairs	This identifies possible star pairs based on separation.