13.3 Tutorials for Gaia DR2

In order to educate and support users retrieving and manipulating Gaia DR2 data, a number of tutorials has been created. All of them can be found on the help pages of the Archive (https://www.cosmos.esa.int/web/gaia-users/archive/help). The following tutorials exist as of March 2019:

  • ’Simple query form’: this tutorial explains how to extract Gaia DR2 data for single objects (making benefit of the Simbad name resolver), how to do cone searches or box queries on the sky, how to perform conditional queries, for instance in a limited magnitude range, and how to retrieve data for a list of objects in a file. This tutorial is also available in video format.

  • ’Getting started’, also known as ’White dwarfs exploration’: this tutorial walks the user through a realistic use case in which a VizieR table with infrared Spitzer photometry for white dwarfs is uploaded to the Archive and cross-matched with Gaia DR2. The resulting, merged table is then used to create several colour-magnitude and colour-colour diagrams in TOPCAT.

  • ’Cluster analysis’ (either in GUI or in Python format): this tutorial explains how to query the Archive for the Pleiades cluster, based on positions and proper motions, how to retrieve the average parallax of the members using ADQL, and how to cross-match the member list with the 2MASS catalogue that is available in the Archive for user convenience.

  • ’ICRF-2 sources’: this tutorial investigates, mostly using TOPCAT, the positional differences between Gaia measurements and ICRF-2 positions of those ICRF-2 sources that are contained in Gaia DR1.

  • ’DataLink and lightcurves’: this tutorial explains how to retrieve Gaia DR2 epoch photometry (lightcurves) for variable stars, both through the Massive Data service and through TAP.

  • ’Query timeouts’: this tutorial addresses common pitfalls and provides several tips to write efficient queries (’Be careful with on-the-fly computations’, ’Use indexed fields’, ’Use additional restrictions’, ’Use random samples’, ’Use histograms’, ’Divide the query into pieces’, and ’Ask for longer execution time quota’ as last resort). There is also an FAQ on data access at https://www.cosmos.esa.int/web/gaia/archive-tips.

  • ’On the use of Gaia parallaxes’: this tutorial, linked to Luri et al. (2018), refers to a set of Python and R examples (https://github.com/agabrown/astrometry-inference-tutorials) that implement the recommended use of (Gaia) astrometry, and in particular parallaxes, in astronomical data analysis or Bayesian inference problems (’Infer distance to a single source’, ’Infer distance to and size of a cluster’, ’Infer distance and tangential velocity of a source’, ’Luminosity calibration’, and ’The period-luminosity relation’).

  • ’AstroPy TAP+ client’: two Python packages exist, one for accessing the Archive (astroquery.gaia, https://astroquery.readthedocs.io/en/latest/gaia/gaia.html) and one for accessing any TAP or TAP+ compliant service (astroquery.utils.tap, https://astroquery.readthedocs.io/en/latest/utils/tap.html).

  • ’Java TAP+ client’: this tutorial explains how to use the Java TAP+ client, both as an open-source example and directly as an external library to wrap possible complexities of the authenticated TAP features.

  • ’Command-line TAP access’: this tutorial explains command-line TAP access, both for non-authenticated and for authenticated users.

  • ’ADQL’: this tutorial provides a concise introduction to ADQL, lists the ESA-provided additional ADQL functions, and provides links for further reading.

  • ’Epoch propagation’: this tutorial explains how to use the fully-reversible time transformation of the six-element vector (celestial positions, parallax, proper motions, and radial velocity) and their associated errors and correlation coefficients, using the ADQL functions EPOCH_PROP, EPOCH_PROP_POS, ASTROMETRIC_PARAMETERS, EPOCH_PROP_ERROR, ASTROMETRIC_PARAMETER_ERROR, and RADIAL_VELOCITY.

  • ’Using job results within ADQL’: this query explains the TAP+ mechanism allowing to use job results directly in an ADQL query.

  • ’ADQL queries’: this tutorial provides several Gaia DR1 / Gaia DR2 ADQL query examples, including ’ConeSearch sorted by distance’, ’Cone search filtered by magnitude, ordered by magnitude’, ’TGAS catalogue filtered by magnitude and parallax’, ’ADQL positional cross-match: Hipparcos versus Gaia’, ’Built-in positional cross-match: Hipparcos versus Gaia’, ’TGAS Healpix maps: source density, average good observations, and excess noise’, ’Red clump stars: absolute magnitudes in Hipparcos colour bins’, ’Red clump stars’, ’TGAS-2MASS Hertzsprung-Russell diagram (individual objects)’, ’TGAS-2MASS Hertzsprung-Russell diagram (histogram)’, ’RR Lyrae phase-folded light curve reconstruction, including errors’, ’Cepheids: light curve retrieval for all stars’, ’RR Lyrae: light curve retrieval for all stars’, ’Cepheids: number of data points and estimated parameters’, ’RR Lyrae: number of data points and estimated parameters’, and ’Proper-motion propagation: Pleiades TGAS field at epoch 1950’.

Should you have any question, please check the Gaia frequently-asked questions (FAQ; https://www.cosmos.esa.int/web/gaia/faqs) or contact the Gaia Helpdesk (https://www.cosmos.esa.int/web/gaia/gaia-helpdesk).