Gaia science topics at ESA

Gaia's key objective is a detailed study of the Milky Way that will reveal our Galaxy's content, dynamics, current state and formation history. By surveying celestial bodies down to the very faint magnitude 20, Gaia takes in a representative fraction of the Milky Way's population, providing data to tackle unanswered questions about our home galaxy. The all-sky survey of about one billion stars also provides unique insight into many other areas of astronomy. Further details on the main science cases can be found at:

https://www.cosmos.esa.int/web/gaia/science

Some active research lines are listed below, together with contact points.

Astrometry expertise

ESAC plays a key role in the Gaia data processing, in particular the so-called Astrometric Global Iterative Solution (AGIS). This is a central part of the science data analysis for Gaia where the reference frame for the observations is established together with the corresponding instrument calibrations and attitude parameters. Within the framework of the DPAC consortium, extensive work has been devoted to develop new algorithms, run AGIS solutions and analyse the results, in collaboration with science institutes distributed all over Europe.

The software will eventually provide the astrometric solutions (together with instrument and attitude data) for about 100 million stars. Details of the methods and algorithms have been published (Lindegren et al., 2012 A&A 538, A78, 2016 A&A 595A, 4L) including the results of test runs with several million stars. The development effort will continue during and after the mission in order to cope with (as yet unforeseen) complications in the real data.

Contact points: Uwe Lammers (ESAC), Jose Hernandez (ESAC), Alex Bombrun (ESAC)

Archive access

The Gaia Archive, the main Gaia science data distribution hub, is developed and located at ESAC. With Gaia surveying more than a billion sources, data release volumes approach petabyte scales. One key objective in modern archives is to carry out as much processing as possible on the server side, according to the “bring your code to the data” paradigm. The Gaia Archive is likewise experimenting with these concepts.

The system architecture is based on Virtual Observatory standards and provides extensions for authenticated access, persistent uploads, and table sharing. The main contents of the various Gaia Data Releases are included in a single catalogue table named gaia_source, including astrometric parameters and time-averaged photometry and radial velocities. Multi-dimensional data (light curves, spectra, etc.) are served through the DataLink protocol. Continuous studies are made and emphasis is put on enhancing usability of the Archive while data complexity, variety, and volume increases with successive data releases.

Contact points: Héctor Cánovas (ESAC), Jos de Bruijne (ESTEC)

Very bright stars

Very bright stars with magnitudes G<6, i.e. the ~6000 stars observable with the naked eye, are among the best studied astronomical objects. Securing Gaia data for those stars is a unique science opportunity, in particular in what concerns astrometry because no other current or planned observatory can obtain global astrometry at sub-milli-arcsecond level of this stellar sample.

Science cases include but are not limited to:

• Parallaxes and proper motions about 10 more precise than from Hipparcos, e.g. of bright massive stars that are fundamental anchor points for stellar astrophysics.
• Orbit constraints for very bright binary stars (at least 25% of the sample)
• Discover new exoplanets, in particular around very bright A and F stars
• Accurate masses of known exoplanets discovered by radial velocity monitoring

Advanced techniques have been applied to ensure Gaia acquires these key objects. The original Gaia bright limit of G=6 was improved to G=3 by tuning the onboard parameters of the SkyMapper star detection algorithm (Martin-Fleitas et al 2014 Proc. SPIE 9143E 0YM, Sahlmann et al. 2016 Proc. SPIE 9904E 2ES). For the 230 stars brighter than G=3, we are pursuing two solutions to observing them as well. The first consists in forcing the acquisition of full-frame Sky Mapper images and has been in operation since the beginning of Gaia’s nominal mission. The second method uses Virtual Objects whose associated CCD windows are placed at defined locations.

Contact points: Juanma Martín-Fleitas (ESAC), Alcione Mora (ESAC), Cian Crowley (ESAC), Johannes Sahlmann (ESAC), Arancha Delgado (ESAC), Alex Bombrun (ESAC)

Black holes and globular clusters

Merging of massive stars that are ejected from dense stellar clusters leads to the formation of intermediate mass black holes (IMBH) that can be detected by (a) the presence of hypervelocity stars and (b) ultraluminous X-ray sources (Portegies Zwart & McMillan 2002 ApJ 576, 899P, Maccarone 2014 MNRAS 440, 1626M, Rasio et al. (2004)). There are clear signatures of the presence of globular cluster black holes on the basis of strong, highly variable X-ray emission (Maccarone et al. 2008 IAUS 246 336M).

However, the detection of IMBH via the velocity dispersion of the visible stars has been challenging until now: for a cluster of mass Mc containing an IMBH of mass MBH the influence of the IMBH becomes significant only at a fraction 2.5 MBH / Mc of the half-mass radius, affecting only a small number of stars, thus, a mission like Gaia that can determine proper motions and parallaxes for visible stars down to magnitude 20.7 opens revolutionary new methods for detecting black holes in clusters.

The main objective consists of developing a model to detect Intermediate Mass Black Holes (IMBH) based on the study of the dynamic and astrophysical properties of globular clusters. It will be based in two main sources of information: the proper motions from the Gaia Archive, available for most stars from Data Release 2 (DR2), and X-ray observatory data.

Contact points: Mercedes Ramos-Lerate (ESAC), Asier Abreu (ESAC)

Young stars and stellar groups

Gaia astrometry, photometry, and spectroscopy, including derived astrophysical parameters, are a goldmine for the study of young stars and stellar groups in the Milky Way. Gaia scientists at ESA have a broad and varied interest in studying star-formation processes from spiral-arm scales down to young stellar groups and eruptive stars. Such studies touch topics ranging from for instance the dynamics and kinematics to structure and stellar content, including runaway stars. In addition, studies have been made of Gaia’s science return, including combining space and/or ground-based astrometry (Carte du Ciel, Hipparcos, and Gaia). Example papers involving Gaia scientists include:

Kóspál et al. (2012) https://ui.adsabs.harvard.edu/abs/2012A%26A...541A..71K/abstract 

De Bruijne & Eilers (2012) https://ui.adsabs.harvard.edu/abs/2012A%26A...546A..61D/abstract 

De Bruijne et al. (2015) https://ui.adsabs.harvard.edu/abs/2015A%26A...576A..74D/abstract 

Antoja et al. (2016) https://ui.adsabs.harvard.edu/abs/2016A%26A...589A..13A/abstract

Manara et al. (2016) https://ui.adsabs.harvard.edu/abs/2016A%26A...591L...3M/abstract

Antoja et al. (2017) https://ui.adsabs.harvard.edu/abs/2017A%26A...602L..13A/abstract

Zari et al. (2017) https://ui.adsabs.harvard.edu/abs/2017A%26A...608A.148Z/abstract

Reino et al. (2018) https://ui.adsabs.harvard.edu/abs/2018MNRAS.477.3197R/abstract 

Lehtinen et al. (2018) https://ui.adsabs.harvard.edu/abs/2018A%26A...616A.185L/abstract 

Manara et al. (2018) https://ui.adsabs.harvard.edu/abs/2018A%26A...615L...1M/abstract 

Voirin et al. (2018) https://ui.adsabs.harvard.edu/abs/2018A%26A...610A..64V/abstract 

Canovas et al. (2019) https://ui.adsabs.harvard.edu/abs/2019A%26A...626A..80C/abstract

Schoettler et al. (2019) https://ui.adsabs.harvard.edu/abs/2019MNRAS.487.4615S/abstract 

De Jong et al. (2020) https://ui.adsabs.harvard.edu/abs/2020A%26A...642A.205D/abstract

Schoettler et al. (2020) https://ui.adsabs.harvard.edu/abs/2020MNRAS.495.3104S/abstract

Jerabkova et al. (2021) https://ui.adsabs.harvard.edu/abs/2021A%26A...647A.137J/abstract

Contact points: Héctor Cánovas (ESAC), Jos de Bruijne (ESTEC), Timo Prusti (ESTEC), Tereza Jerabkova (ESTEC)

Extrasolar planets and substellar systems

Exoplanet host stars exhibit positional changes caused by the orbiting companion that can in principle be detected with the help of astrometric measurements in an absolute reference frame. This orbital motion is superimposed to parallax and proper motion but usually is much smaller in amplitude. Historically, the typical amplitudes of exoplanet host stars were therefore beyond the reach of available
instrumentation. Because of its unprecedented accuracy, the Gaia mission is now about to add astrometry to the mainstream of exoplanet characterisation techniques. Gaia data can be used for giant exoplanet discovery and characterisation, with particular scientific relevance for dynamical studies of planetary systems, and their combination with external datasets, e.g. Hipparcos or ground-based astrometry, has already proven to be very powerful. Similarly, multiplicity studies of ultracool dwarfs (very low-mass stars and brown dwarfs) at separations < 1AU have for long been hampered by the relative faintness of those objects and the associated observational limitations. Gaia astrometry will characterize hundreds of ultracool binary orbits and significantly improve our knowledge on the occurrence and properties of compact ultracool binaries.

Recent publications:
Sahlmann et al. (2021): https://ui.adsabs.harvard.edu/abs/2021MNRAS.500.5453S/abstract
Sahlmann et al. (2020): https://ui.adsabs.harvard.edu/abs/2020MNRAS.495.1136S/abstract
Nielsen et al. (2020): https://ui.adsabs.harvard.edu/abs/2020AJ....159...71N/abstract
Kiefer et al. (2019): https://ui.adsabs.harvard.edu/abs/2019A%26A...631A.125K/abstract
Lazorenko & Sahlmann (2018): https://ui.adsabs.harvard.edu/abs/2018A%26A...618A.111L/abstract

Contact: Johannes Sahlmann (ESAC)

Gaia's optical reference frame as geometric calibrator for imaging instruments

The geometric calibration of space and ground-based imaging instruments is necessary for their efficient operation, e.g. for pointing and target acquisition, and its quality directly affects the astrometric accuracy of derived products. Gaia's all-sky, dense, and accurate optical reference frame has a multitude of applications, e.g. monitoring and correction of optical and atmospheric distortion, that are enhancing the scientific output of imaging surveys for a variety of astrophysical applications. 

Recent publications:
Sahlmann (2020): https://ui.adsabs.harvard.edu/abs/2020jwst.rept.7082S/abstract
Sahlmann et al. (2020): https://ui.adsabs.harvard.edu/abs/2020MNRAS.495.1136S/abstract
Sahlmann et al. (2019): https://ui.adsabs.harvard.edu/abs/2019tel..rept....1S/abstract
Lazorenko & Sahlmann (2019): https://ui.adsabs.harvard.edu/abs/2019A%26A...629A.113L/abstract

Contact: Johannes Sahlmann (ESAC)