Gaia Data Release 2. Summary of the contents and survey properties: We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on as- trophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods. The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the G_BP_ (330-680nm) and G_RP_ (630-1050nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy. The catalogue of radial velocity standard stars (Soubiran et al., 2018A&A...616A...7S) The Radial Velocity Spectrometer (RVS) on board of Gaia having no calibration device, the zero point of radial velocities needs to be calibrated with stars proved to be stable at the level of 300m/s during the Gaia observations. A dataset of about 71000 ground-based radial velocity measurements from five high resolution spectrographs has been compiled. A catalogue of 4813 stars was built by combining these individual measurements. The zero point has been established using asteroids. The resulting catalogue has 7 observations per star on average on a typical time baseline of 6 years, with a median standard deviation of 15m/s. A subset of the most stable stars fulfilling the RVS requirements has been used to establish the zero point of the radial velocities provided in Gaia DR2. The stars not used for calibration are used for the RVS data validation.
Gaia Data Release 1 (DR1) contains astrometric results for more than 1 billion stars brighter than magnitude 20.7 based on observations collected by the Gaia satellite during the first 14 months of its operational phase. For stars in common with the Hipparcos and Tycho-2 catalogues, complete astrometric single-star solutions are obtained by incorporating positional information from the earlier catalogues. For other stars only their positions are obtained, essentially by neglecting their proper motions and parallaxes. The results are validated by an analysis of the residuals, through special validation runs, and by comparison with external data. For about two million of the brighter stars (down to magnitude ~11.5) we obtain positions, parallaxes, and proper motions to Hipparcos- type precision or better. For these stars, systematic errors depending for example on position and colour are at a level of +/-0.3 milliarcsecond (mas). For the remaining stars we obtain positions at epoch J2015.0 accurate to ~10 mas. Positions and proper motions are given in a reference frame that is aligned with the International Celestial Reference Frame (ICRF) to better than 0.1mas at epoch J2015.0, and non-rotating with respect to ICRF to within 0.03mas/yr. The Hipparcos reference frame is found to rotate with respect to the Gaia DR1 frame at a rate of 0.24mas/yr.
A table of the light curves released with Gaia DR2 (about half a million
in total). In each Gaia band (G, BP, RP), we give epochs, fluxes and
their errors in arrays. We do not include the quality flags (DR2: “may
be safely ignored for many general purpose applications”). You can
access them through the associated datalink service if you select
source_id. You will usually join this table with gaia.dr2light.
We have also removed all entries with NaN observation times; hence,
the array lengths in the different bands can be significantly different,
and the indices in transit_ids do not always correspond to the
indices in the time series.
Furthermore, we only give fluxes and their errors here rather than
magnitudes. Fluxes can be turned into magnitude using::
mag = -2.5 log10(flux)+zero point,
where the zero points assumed for Gaia DR2 are
25.6884±0.0018 in G, 25.3514±0.0014 in BP, and
24.7619±0.0019 in RP (VEGAMAG).
This schema contains data re-published from the official
Gaia mirrors (such as ivo://uni-heidelberg.de/gaia/tap) either to
support combining its data with local tables (the various Xlite tables)
or to make the data more accessible to VO clients (e.g., epoch fluxes).
Other Gaia-related data is found in, among others, the gdr2dist, gdr3mock,
gdr3spec, gedr3auto, gedr3dist, gedr3mock, and gedr3spur schemas.
This service exposes about 0.5 million light curves of stars
classified as variable by the Gaia analysis system through the VO SSAP
protocol. The lightcurves are published per-band and are also
available through obscore.
This schema contains data re-published from the official
Gaia mirrors (such as ivo://uni-heidelberg.de/gaia/tap) either to
support combining its data with local tables (the various Xlite tables)
or to make the data more accessible to VO clients (e.g., epoch fluxes).
This schema contains data re-published from the official
Gaia mirrors (such as ivo://uni-heidelberg.de/gaia/tap) either to
support combining its data with local tables (the various Xlite tables)
or to make the data more accessible to VO clients (e.g., epoch fluxes).
Other Gaia-related data is found in, among others, the gdr3mock,
gdr3spec, gedr3auto, gedr3dist, gedr3mock, and gedr3spur schemas.
This is gaia_source from the Gaia Data Release 3, stripped to just
enough columns to enable basic science (but therefore a bit faster and
simpler to deal with than the full gaia_source table).
Note that on this server, there is also The gedr3dist.main, which
gives distances computed by Bailer-Jones et al. Use these in
preference to working with the raw parallaxes.
The full DR3 is available from numerous places in the VO (in
particular from the TAP services ivo://uni-heidelberg.de/gaia/tap and
ivo://esavo/gaia/tap).
This is gaia_source from the Gaia Data Release 3, stripped to just
enough columns to enable basic science (but therefore a bit faster and
simpler to deal with than the full gaia_source table).
Note that on this server, there is also The gedr3dist.main, which
gives distances computed by Bailer-Jones et al. Use these in
preference to working with the raw parallaxes.
This server also carries the gedr3mock schema containing a simulation
of gaia_source based on a state-of-the-art galaxy model, computed by
Rybizki et al.
The full DR3 is available from numerous places in the VO (in
particular from the TAP services ivo://uni-heidelberg.de/gaia/tap and
ivo://esavo/gaia/tap).
This is a “light” version of the full Gaia DR2 gaia_source table,
containing the original astrometric and photmetric columns with just
enough additional information to let careful researchers notice when data
is becomes uncertain and the full error model should be consulted. The
full DR2 is available from numerous places in the VO (in particular from
the TAP services ivo://uni-heidelberg.de/gaia/tap and
ivo://esavo/gaia/tap).
This table also includes a column containing the Renormalized Unit Weight
Error RUWE (GAIA-C3-TN-LU-LL-124-01), a robust measure for the
consistency of the solution.
On this TAP service, there is the table gdr2dist.main containing
distances computed by Bailer-Jones et al (:bibcode:`2018AJ....156...58B`).
If in doubt, use these instead of the parallaxes provided here.
