tycho

This module defines the interface to the Tycho 2 star catalog.

Catalog Description

The Tycho2 is a bright star catalog containing positions, proper motions, and photometry for the 2.5 million brightest stars in the sky based solely on observations from the Hipparcos satellite. This corresponds to nearly complete coverage down to a visual magnitude magnitude of about 11.0.

The Tycho 2 catalog uses a csv text file to store the stars. It is not very efficient for querying either large or small numbers of stars. It also does not include blended stars (stars that are close enough together to appear as a single source in an image). If you need faster retrieval and/or blended stars then you should use the giant_catalog instead.

For a more thorough description of the Tycho2 star catalog see https://www.cosmos.esa.int/web/hipparcos/tycho-2.

Use

The Tycho 2 catalog can be used anywhere that a star catalog is required in GIANT. It is stored in 3 csv files plus an index csv that takes about 500 MB of disk space. If you attempt to initialize the class and point it to a directory that does not contain the Tycho 2 data it will ask you if you want to download the catalog (note that the Tycho 2 data is not included by default so if you have not downloaded it yourself you will definitely need to). If you answer yes, be aware that it may take a very long time to download.

Once you have initialized the class (and downloaded the data files), then you can access the catalog as you would any GIANT usable catalog. Simply call query_catalog() to get the GIANT records for the stars as a dataframe with columns according the GIANT_COLUMNS. This class also provides a helper method, query_catalog_raw(), which can be used to retrieve the raw catalog entries (instead of the GIANT entries).

Classes

Tycho2

This class provides access to the Tycho 2 star catalog.

Methods

query_catalog	This method queries stars from the catalog that meet specified constraints and returns them as a DataFrame with columns of GIANT_COLUMNS.
query_catalog_raw	This method queries stars from the catalog that meet specified constraints and returns them as a DataFrame where the columns are the raw catalog columns.
retrieve_record	This method can be used to retrieve a single star by ID from the tycho 2 main catalog or first supplement file.
empty_frame	This simple helper function returns an empty dataframe with the appropriate columns.
nan_frame	This simple helper function returns a dataframe with a single NaN filled row.
convert_to_giant_format	This static method converts raw tycho2 records into GIANT records so they can be used in star id.