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Gaia DR4 time series data: from still to film

Figure 1. Infographic highlighting the different time series that will be published with Gaia's data release 4: astrometry time series, photometry time series, and spectroscopy time series. Even in some cases derived astrophysical parameter time series will be available. Gaia data release 4 will be based on 66 months of data, obtained from mid 2014 to early 2020. Credits: ESA/Gaia/DPAC - CC BY-SA 3.0 IGO. Acknowledgements: created by V. Reichel in collaboration with T. Roegiers and J. de Bruijne.

With Gaia data release 4, the full Gaia time series data for the first 5.5 years of observations becomes available to the community. 2.8 billions sources will be released for which a total of 142 billion detections exist. The infographic in Figure 1 captures the various time series that will be published, ranging from position time series, photometry time series and time series of both RVS spectra and BP/RP spectra. From these time series, also derived astrophysical parameter time series are obtained. A true wealth of new data to explore our Milky Way!

Position time series

The time series of positions allow to trace the motion of a source on the sky (the proper motion) and determine the parallax of the source, which gives an indication of its distance. Sometimes a companion of the source causes an additional wobble of the observed main source. This companion can have different sizes. In this way, Gaia spots exoplanets, neutron stars, black holes, double stars and even triple systems. In the first panel in Figure 1 the grey line depicts the proper motion, the orange line shows the proper motion plus parallax, and the dark blue/green line shows the combination of proper motion, parallax and a highly exaggerated additional wobble for a companion. Observe how the source was scanned by Gaia over time, the colour of the dark blue/green line is linked to the observation time.

Photometry time series

Photometry time series are available for all sources as is highlighted in the mid panel in Figure 1. In December Gaia publishes time series of brightness (G magnitude) as well as time series in the blue photometer (BP) band and red photometer (RP) band. Photometry time series allow to investigate when a source brightens or dims unexpectedly. They also allow to investigate the variability of a source. Is something moving in front of the source, like for example an exoplanet? Is the main source being deformed due to a companion star? Or is there perhaps a case of microlensing observed? Gaia's data processing pipelines run classifications for various variable stars, give indications for companions with the main source, but also sent alerts for sudden brightening or dimming observed. The outcomes of all of these pipelines can be found in the Gaia archive with the publication of Gaia Data Release 4.

Time series of spectra

Each time Gaia scanned over a source with its photometer, it captured a BP and RP spectrum. Similarly, each time Gaia scanned over a source of sufficient brightness with its spectrometer, it captured an RVS spectrum. A time series of spectra is hence available for most of Gaia's sources. Epoch radial velocities are derived by the Gaia Data Processing and Analysis Consortium for sources with a G_RVS below or equal to magnitude 14. All of these will be published in Gaia's data release 4, planned on 2 December 2026.

From the astrometry, photometry and spectroscopy obtained on the sources, the astrophysical parameters are derived for many sources. Having time series on all of the above means that in some cases, also time series of stellar parameters will be published. Stay tuned to learn more on Gaia's upcoming data release 4.