VizieR Catalogs

VizieR Catalogs#

VizieR is an astronomical catalog service hosted by the Centre de Données astronomiques de Strasbourg (CDS), home to more than 25,000 catalogs. There are two ways to access VizieR catalogs with LSDB:

  1. VizieR HATS service — for catalogs listed at vizcat.cds.unistra.fr: load them directly with lsdb.open_catalog.

  2. astroquery — for any other VizieR catalog: fetch with astroquery and load into LSDB via lsdb.from_dataframe.

1. VizieR HATS service#

The CDS VizieR HATS service provides experimental HATS-on-the-fly access to a subset of VizieR catalogs. Catalogs available through this service can be loaded directly with lsdb.open_catalog.

Note

This service is in beta. Please keep in mind the following:

  • Only catalogs listed at vizcat.cds.unistra.fr/hats are accessible. If the catalog you need is not there, use the astroquery section below.

  • Do not use this service to retrieve full large catalogs such as 2MASS, AllWISE, or Gaia. For those, use data.lsdb.io or convert the original catalog data with the hats-import package.

The hats:n parameter in the URL controls the partition size:

  • Use hats:n=10000 when expecting to retrieve around 10,000 objects or fewer (e.g. a small cone search).

  • Use hats:n=1000000 (recommended default) for cross-matching and other large-scale tasks.

1.1. Example: load the Gaia DR3 AGN catalog#

The Gaia DR3 AGN catalog (I/358/vagn) is available on the VizieR HATS service. Load it with LSDB:

import lsdb

cat = lsdb.open_catalog("https://vizcat.cds.unistra.fr/hats:n=1000000/I/358/vagn/")

For a small cone search, use a smaller partition size to reduce data transfer:

import lsdb

cat = lsdb.open_catalog("https://vizcat.cds.unistra.fr/hats:n=10000/I/358/vagn/")
result = cat.cone_search(ra=187.0, dec=2.0, radius_arcsec=3600).compute()

2. Fetching from VizieR with astroquery#

For catalogs not available on the VizieR HATS service, use astroquery to fetch data and lsdb.from_astropy to load it into LSDB.

Warning

This approach is only suitable for small datasets (fewer than ~1 million rows). For large VizieR catalogs, use data.lsdb.io or convert the original data with the hats-import package.

2.1. Requirements#

pip install astroquery

For more installation options, see the astroquery documentation.

2.2. Example: load the Gaia DR3 microturbulence catalog#

The Gaia DR3 microturbulence catalog (I/358/vmicro) is an example of a small catalog that can be fetched from VizieR with astroquery:

import lsdb
from astroquery.vizier import Vizier

# Request _RAJ2000 and _DEJ2000 explicitly; "**" includes all native columns.
# Most VizieR catalogs provide these computed columns (degrees, J2000),
# and they are recommended as the ra/dec columns when creating HATS catalogs.
vizier = Vizier(row_limit=-1, columns=["_RAJ2000", "_DEJ2000", "**"])
tables = vizier.get_catalogs("I/358/vmicro")

cat = lsdb.from_astropy(tables[0], ra_column="_RAJ2000", dec_column="_DEJ2000", catalog_name="vmicro")
cat.write_catalog("./vmicro")

We recommend saving the result as a HATS catalog immediately so you can reload it later without re-fetching:

cat = lsdb.open_catalog("./vmicro")

For a complete worked example including cross-matching, see the ZTF BTS × NGC tutorial.