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Overview of the GES Science Archive

Summary

The GES Science Archive comprises calibrated one- and two-dimensional spectra for stars observed in the Gaia-ESO Survey (GES), and a variety of astrophysical parameters (heliocentric radial velocity, effective temperature, surface gravity, metallicity etc) derived from these spectra. As the survey progresses interim releases, internal to the GES Consortium, are made available to Consortium members. These releases are listed on the Data Releases page.

GES is a public spectroscopic survey of approximately 100,000 stars, systematically covering all the major components of the Milky Way, from the halo to star-forming regions and providing the first homogeneous overview of the distributions of kinematics and elemental abundances. The target stars were observed using the FLAMES spectrograph on the ESO VLT at Paranal in Chile. The survey was conducted in support of the ESA Gaia astrometric satellite, but will have numerous other uses.

• Constituent programmes of the Gaia-ESO Survey,
• Organisation of the GES Science Archive,
• Querying the GES Science Archive,
• Radial velocities in the GES Science Archive.

Constituent programmes of the Gaia-ESO Survey

The Gaia-ESO Survey (GES) includes stars representative of the main components of the Galaxy: inner and outer bulge, inner and outer thick and thin discs, the halo and known halo streams. There is a special focus on open clusters of all ages and on solar neighbourhood field stars, as these trace both stellar and Galactic evolution, complement the Gaia astrometry, and will benefit most from the most precise Gaia data. Specifically, the Survey includes the following components or programmes:

• Bulge Survey,

• Halo/Thick Disc Survey,

• Outer Thick Disc, 2-4 kpc from the Sun,

• Thin Disc Dynamics,

• Solar Neighbourhood,

• Open Clusters.

Organisation of the GES Science Archive

All the data for the GES Science Archive are maintained in a single database (strictly speaking a single database schema in the jargon of relational database systems). The archive is presented to the user as a collection of tables, which can be searched to identify stars and results of interest and from which results can be extracted. The principal tables in the GES Science Archive are:

• Target The master list of all the stars observed in the Survey.

• Spectrum A master list of all the spectra of target stars acquired during the Survey. There are more spectra than target stars because most stars will be observed more than once.

• RecommendedAstroAnalysis Astrophysical analysis results for the various spectra included in the Survey: the astrophysical parameters (effective surface temperature, log surface gravity etc) recommended by GES Working Group 15 (WG15). The list has been compiled by WG15 by homogenising and selecting from the values returned by the other spectrum analysis working groups. The recommended results are the ones that must be used in publications, as prescribed in the PI publication policy. See Known Issues for additional information regarding use of recommended parameters.

• WgRecommendedAstroAnalysis Astrophysical analysis parameters for the various spectra included in the Survey: the computed astrophysical parameters (effective surface temperature, log surface gravity etc) recommended by each of the individual spectrum analysis Working Groups within GES, based on the results returned by their analysis nodes. The WG recommended results undergo inter-WG homogenisation by WG15 to arrive at the final recommended parameters presented in RecommendedAstroAnalysis. Note that WgRecommendedAstroAnalysis does not include WG15 values.

• AstroAnalysis For the various spectra included in the release the complete set of individual astrophysical analysis parameters and results provided by every spectrum analysis node working within each WG, together with the WG and WG15 recommended values. (Note that every spectrum in the release will usually be analysed by different analysis nodes using several different and independent techniques, leading to several estimates of each parameter.) That is, AstroAnalysis includes the results of every analysis of every spectrum in the release, made by all the nodes in all the working groups of Survey, where available, or default values where nodes were unable to compute a value. It also includes all the WG and WG15 recommended values (above).

• LineList Atomic and molecular line data provided by the Line list group and used consistently by all Working Groups in calculating line-by-line abundances in their analyses in conjunction with model atmospheres. Note that the same set of atomic and molecular data are used consistently throughout the GES analyses

• SpecFrame A master list of all the the SpecFrames in the Survey. A SpecFrame contains a set of one-dimensional spectra extracted from all the fields or pointings in the Survey. (The Survey uses multi-object spectrographs so each pointing of an instrument typically yields a set of spectra.)

Information for each target star
The information listed for each Target star is primarily intended to allow the star to be identified and located (both in the Survey and on the sky), and consists of its celestial coordinates (expressed as J2000 equatorial coordinates), names or catalogue numbers and some basic astrophysical data.

Information for each spectrum
The information available for each Spectrum includes:

• A link back to the Target star, to allow the spectrum to be identified.

• The date the Spectrum was acquired.

• A fully reduced, calibrated, one-dimensional spectrum, with errors. This spectrum can be retrieved as a FITS file. A detailed description of the file format is available here. Spectra are stored in the archive as components of the appropriate SpecFrame, but are retrieved as individual files.

• Recommended astrophysical parameters derived from each spectrum. (Note that these parameters are per Spectrum, not per Target star. They do not necessarily link back to the individual spectra because offsets may have been applied to the parameters derived from that spectrum.

• Astrophysical parameters derived from each individual analysis of each spectrum. (Note that every spectrum in the Survey will usually be analysed using several different and independent techniques, leading to several estimates of each parameter.)

• Each Spectrum is linked to the TwoDFrame from which it was extracted, so its provenance can be investigated, and links to further tables allow the instrumental setup, configuration settings and software items used to derive the TwoDFrame to be listed.

Database organisation
As mentioned, all the data for the GES Data Archive are maintained in a single database schema and the archive is presented to the user as a collection of tables. It actually consists of not just tables but also views ('virtual tables' generated on-the-fly from real tables), indices and constraints, though these are not usually directly visible to the user.

• Use the schema browser to explore the contents and layout of the tables in the archive.

Querying the GES Science Archive

Users can search the GES Science Archive to retrieve astrophysical parameters and spectra for stars included in the GES survey. The following method of searching the database is currently available:

• Freeform query - submit an SQL query directly.

The following methods will be added in future releases:

• Individual star - search for data on an individual, named star, identified by its name or celestial coordinates,
• List of stars - search for data on a user-supplied list of stars, with the stars again identified by name or celestial coordinates,

Where SQL is the Structured Query Language, the standard language for searching relational databases. SQL queries allow inter alia the database to be searched for stars classified as being of a given type or stars with astrophysical parameters lying within given ranges. Note that the GES data archive is hosted as a relational database running on Microsoft SQL Server 2008. SQL queries submitted to the archive must be expressed in SQL Server's dialect of SQL, Transact-SQL or T-SQL, rather than any other dialect of SQL.

For further details see querying the archive.