- Installation: pip install FindDouble==0.1
- Navigate to the parent directory where the package was installed and import find_single_stars as fss (for example).
- Using fss.query_the_gaia(), input desired sky RA/Dec coordinate pair as first argument and cone search radius as the second argument. All other arguments are optional. Hour angle string should be in the SIMBAD database format or similar.
- Example function call: fss.query_the_gaia(objloc="11 02 24.8763629208 -77 33 35.667131796",conerad=0.5)
- Refer to the query_the_gaia() docstring for further details on all input arguments.
- Retrieve CSV output catalog file in the same directory the program is located in!
The need for a single, bright star for calibrations arises for many astronomers interested in high-resolution imaging. The purpose of this package is to return a catalog of bright, likely single stars by filtering out multiple star systems.
By default, this package does this by cross-matching the Gaia DR3 catalog with the Washington Double-Star Catalog (WDS) which exists to flag visual binaries. Other catalogs may be passed-in as arguments for additional functionality, though positive cross-match results means those objects will be excluded from the final CSV catalog. It also features user-set options for Renormalized Unit Weight Error (RUWE) and magnitude range to suit the user's needs.
From the Gaia docs:
"The RUWE is expected to be around 1.0 for sources where the single-star model provides a good fit to the astrometric observations. A value significantly greater than 1.0 (say, >1.4) could indicate that the source is non-single or otherwise problematic for the astrometric solution."
By default, the RUWE threshold is set to >1.2.
Specifically, the cross-matching is done by additionally querying the SIMBAD (Set of Identifications, Measurements and Bibliography for Astronomical Data) astronomical database and checking the known identifiers for each object (i.e., if a star has a WDS identifier on SIMBAD, it is rejected).
The final catalog of filtered objects is output in Comma-Seperated Value (CSV) format in the directory the program is located. ([TODO] is this what we want? Should we code in a specified directory?)
The catalog columns include SIMBAD object name, Gaia identifier, RA, Dec, (V or SDSS i or Gaia G) magnitude, RUWE. The objects are sorted by decreasing brightness with increasing row number (i.e., first row contains the brightest star).
Future plans for this project include creating a SQL database to populate with multiple star systems as some of these objects will undoubtedly get through this process. For instance, the resolution capabilities of the instruments used to populate the WDS or the Gaia space telescope are often superceded by larger, ground-based telescopes meaning that unresolved multiple star systems are often serendipitously resolved for ground-based diffraction-limited imaging. For these cases, the object will be input into the database to exclude from future query results leading to increased accuracy over time.
[TODO] make more general by defining more (all?) object identifiers in SIMBAD for additional catalog inputs on command line. This way we only ever need to query Gaia and SIMBAD once, and adding additional catalogs will not slow down the code.