Gaia in the UK

Taking the Galactic Census

Gaia Early Data Release 3

Information about the Gaia Early Data Release 3 (Gaia EDR3) is maintained at https://www.cosmos.esa.int/web/gaia/earlydr3 . Gaia EDR3 is scheduled for 3 December 2020. Gaia EDR3 will deliver improved astrometry, with significantly improved parallaxes and proper motions, and mean photometry. The parallax improvement is typically 20% with respect to Gaia DR2, and the proper motions are typically a factor two better than in Gaia DR2.

Gaia Early Data Release 3 in numbers

 Number of sources in Gaia EDR3Number of sources in Gaia DR2Number of sources in Gaia DR1
Total number of sources≈ 1,800,000,000 1,692,919,1351,142,679,769
Number of 5-parameter sources≈ 1,500,000,0001,331,909,7272,057,050
Number of 2-parameter sources≈ 300,000,000361,009,4081,140,622,719
Sources with mean G magnitude≈ 1,800,000,0001,692,919,1351,142,679,769
Sources with mean GBP-band photometry≈ 1,500,000,0001,381,964,755 -
Sources with mean GRP-band photometry≈ 1,500,000,0001,383,551,713 -
Gaia-CRF sources≈ 1,500,000556,8692,191
Sources with radial velocitiesexpected with Gaia DR3 /≈7,210,000 from Gaia DR2 in Gaia EDR37,224,631 -
Variable sourcesexpected with Gaia DR3 / see Gaia DR2550,7373,194
Known asteroids with epoch dataexpected with Gaia DR3 / see Gaia DR214,099 -
Effective temperatures (Teff)expected with Gaia DR3 / see Gaia DR2161,497,595 -
Extinction (AG) and reddening (E(GBP-GRP))expected with Gaia DR3 / see Gaia DR287,733,672 -
Sources with radius and luminosityexpected with Gaia DR3 / see Gaia DR276,956,778 -

Contents of Gaia EDR3

  • The five-parameter astrometric solution - positions on the sky (α, δ), parallaxes, and proper motions - for around 1.5 billion (1.5 109) sources, with a limiting magnitude of about G ≈ 21 and a bright limit of about G ≈ 3. The astrometric solution wil be accompanied with some new quality indicators, like RUWE, and source image descriptors.
  • In addition, two-parameters solutions - positions on the sky (α, δ) - for around 300 million additional sources.
  • G magnitudes for around 1.8 billion sources.
  • GBP and GRP magnitudes for around 1.5 billion sources.
  • Please be aware that the photometric system for the G, GBP, and GRP bands in Gaia EDR3 is different from the photometric system as used in Gaia DR2 and Gaia DR1.
  • Full passband definitions for G, GBP, and GRP. More information will become available on Gaia EDR3 page on ESA website.
  • About 1.5 million celestial reference frame (Gaia-CRF) sources.
  • Cross-matches between Gaia EDR3 sources on the one hand and Hipparcos-2, Tycho-2 + TDSC merged, 2MASS PSC (merged with 2MASX), SDSS DR13, Pan-STARRS1 DR1, SkyMapper DR1, GSC 2.3, APASS DR9, RAVE DR5, allWISE, and URAT-1 data on the other hand.
  • Additionally, a Gaia EDR3 to Gaia DR2 match will be provided.
  • Simulated data from Gaia Object Generator (GOG) and Gaia Universe Model Snapshot (GUMS) will be provided.
  • The commanded scan law covering the Gaia EDR3 data collection period will be provided. Also the major periods where data was not sent to the ground or could not be processed are identified.

To ease the use of the data, the Gaia EDR3 table in the Gaia Archive will be complemented with a set of Gaia DR2 radial velocities.

Background of the data

Gaia DR3 data (both Gaia EDR3 and the full Gaia DR3) are based on data collected between 25 July 2014 (10:30 UTC) and 28 May 2017 (08:44 UTC), spanning a period of 34 months. As a comparison, Gaia DR2 was based on 22 months of data and Gaia DR1 was based on observations collected during the first 14 months of Gaia's routine operational phase.
The reference epoch for Gaia DR3 (both Gaia EDR3 and the full Gaia DR3) is 2016.0. Remember that the reference epoch is different for each Gaia data release (it was was J2015.5 for Gaia DR2 and J2015.0 for Gaia DR1).
Positions and proper motions are referred to the ICRS, to which the optical reference frame defined by Gaia EDR3 is aligned. The time coordinate for Gaia EDR3 is the barycentric coordinate time (TCB).

Gaia Source Identifiers

Sources in the Gaia Catalogue are uniquely identified through the Gaia Source Identifier, i.e., the source_id field in the various tables in the Gaia Archive. The construction of the source identifiers is explained in the Archive documentation (for Gaia DR1, see the data model section). In particular the source_id number contains rough information about the source position on the sky.

As explained in previous announcements, there are various reasons why the identifier of a specific source may change or disappear when going from the Gaia DR1 to the Gaia DR2 source list and on to the Gaia EDR3 source list. Users of Gaia data should thus be aware that the source list for Gaia EDR3 should be treated as independent from Gaia DR2 and from Gaia DR1.
The Gaia source names for EDR3 will all be constructed as follows:

Gaia EDR3 yyy....yy

A table to trace sources from Gaia DR2 to Gaia EDR3 will be provided given that source identifiers used in Gaia DR2 may have changed or disappeared in Gaia EDR3. With each new data release, the source list is becoming progressively more stable and from Gaia DR2 to Gaia EDR3 changes impact less than 5% of the sources.

Gaia EDR3 passbands, data model and additional information

Information about the performance and limitations of Gaia EDR3, Gaia EDR3 passbands, data model, and known issues will be available from Gaia EDR3 page on ESA website.

A draft data model documentation is available for download from ESA's Gaia EDR3 page.

Gaia EDR3 data

The Gaia Archive is the main point of access for the Gaia Early DR3 data, but the data is also served from Gaia partner data centres (CDS, ASDC, ARI, and AIP). Data can be extracted from the Gaia Archive by performing ADQL queries and subsequently downloading the corresponding results tables.

The Gaia EDR3 data set will also be downloadable in compressed CSV-format with the total size of the downloadable data expected to be in the order of 1.3 TB. The increased size, compared to Gaia DR2, is mostly due to the addition of extra information from the Gaia Object Generator (GOG) and Gaia Universe Model Snapshot (GUMS), and due to the increase in the number of sources in the catalogue. The cross-matches with external catalogues will also be made available for bulk download.

 

Page last updated: 21 October 2020