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Gaia Data Release 2 : an astronomical data mine

Apr 25 2018

Map of the full sky, built from apparent luminosity measurements of 1,3 billion stars in the Gaia DR2 catalogue. At each point in the sky, Gaia magnitudes have been converted into fluxes to simulate the color of the corresponding pixel. Our Galaxy, the Milky Way, is seen edge-on. Both Magellanic Clouds are visible in the lower right. Credits : T. Boch, Observatoire astronomique de Strasbourg.

Light curves for an RR-Lyræ variable star from the Gaia DR2 catalogue. Gaia is equipped with three different filters, measuring three magnitudes for each star. Each symbol corresponds to one observation. Time (expressed as a phase) is on the abscissas axis, luminosity (expressed in magnitudes) on the vertical axis. Credits : T. Boch, Observatoire astronomique de Strasbourg.

Astronomers worldwide are eagerly awaiting for April 25 2018. This is the date the European Space Agency (ESA) will publish the second catalogue derived from observations and measurements made by the Gaia astrometric space mission. The Gaia DR2 (Gaia Data Release 2) is the result of 22 months of observations (2014 July 25 – 2016 May 23), and contains positions of nearly 1.7 billion stars.

The main goal of the Gaia mission is to measure parallaxes and proper motions of stars with unprecedented accuracy. The parallax of an object yields its distance. And the new Gaia catalogue is expected to revolutionize astronomy, with measurements of parallaxes, proper motions and colors for 1.3 billion stars ! This is a major breakthrough compared to the first Gaia catalogue published in 2016 (listing only 2 million parallaxes), or over the HIPPARCOS mission (a satellite that measured parallaxes of 100,000 nearby stars in the '90s).

Gaia makes multiple observations of each star, building up 'light curves' for half a million variable stars. Gaia DR2 will also provide radial velocities for 7 million stars, surface temperature measurements for 161 million stars, and new measurements for 14,000 minor solar system bodies (mainly asteroids) and half a million quasars (distant extragalactic point sources). This catalogue is an extraordinary astronomical data mine that astronomers will use to make discoveries in many sub-disciplines of astrophysics in the coming years.

The raw data from the Gaia satellite, observing from its location 1.5 million kilometers away from Earth, are processed by the DPAC consortium of about 450 scientists and engineers from over 20 countries, in order to produce catalogues suited for scientific exploitation. Data are available through the ESA's Gaia Archive, but also partner data centers, including the Centre de Données astronomiques de Strasbourg (CDS).

Handling a catalogue of more than one billion sources is not trivial, and researchers will be able to use CDS tools to optimize their usage of Gaia data. The Gaia DR2 catalogue has been integrated in VizieR, the CDS catalogue service (containing over 17,000 catalogues), and can be queried to retrieve subsets at any sky coordinates. Gaia data are also integrated in the CDS X-match service that allows combination of data from multiple catalogues, including those exceeding 1 billion rows.

The Aladin sky atlas can be used to visualize a spatial density map of Gaia sources, and overlay a progressive version of the Gaia DR2 catalogue generated at CDS : starting from a full-sky view, one can zoom in anywhere and retrieve more Gaia sources locally, without downloading the full 1Tbyte catalogue. And last but not least, the CDS will provide visualization of the 500,000 available light curves.

External links :

Gaia data at CDS

Gaia DR2 at ESA

Media contact :

Sébastien Derriere,, 03 68 85 24 24

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