The Hipparcos satellite

The Gaia satellite

Space astrometry at Lund Observatory:

Astrometric radial velocities

Stellar multiplicity

Galactic research

Lund Observatory
Local events
Lund University

Research on Gaia

Gaia - The Galactic Census Project: The galactic astrophysics mission Gaia, launched by the European Space Agency in December 2013, will survey the stellar content of a large part of the Milky Way Galaxy, with the ultimate goal to trace the origin and evolution of our galaxy and understand its present structure. The satellite is a unique and powerful optical space observatory, combining large-scale photometric and radial-velocity surveys with determinations of stellar distances and transverse motions through microarcsecond astrometry for more than a billion stars brighter than V = 21. Parallax and proper motion accuracies are such that the space densities and kinematics of common tracer stars (e.g. K giants) can be accurately mapped across the whole Galaxy. For more information on the mission and its current status, please refer to the main science portal for Gaia.

Recent and current work on Gaia: Lund Observatory has a major long-term commitment in the development and implementation of software for part of 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. Lund Observatory provides the basic algorithms and some of the software for AGIS, which are implemented at one of the Gaia Data Processing Centres, located at the European Space Astronomy Centre (ESAC) outside of Madrid. The scientific team in Lund collaborates intensely with the technical teams at ESAC to develop and refine the software used to calculate the astrometric solutions (together with instrument and attitude data) for about 100 million stars. Methods and algorithms published before the launch (Lindegren et al., A&A 538, A78, 2012) are continually improved as more data become available and the attitude and calibration models become more sophisticated after confrontation with the real data. The first release of Gaia data (Gaia DR1) in September 2016 successfully demonstrated the validity of concepts that had been developed over many years in Lund and elsewhere.

The group also develops algorithms and software for improved error analysis in the future Gaia Archive. A theoretical foundation for this was developed in the thesis work of Dr. Berry Holl (A&A 543, A14, 2012; A&A 543, A15, 2012).

The combination of Gaia data with other astrometric catalougues or prior information from Galactic models were considered in the PhD project of Dr. Daniel Michalik. Ideas developed in this work proved to be instrumental for providing the first accurate astrometric results in Gaia DR1, in particular the so-called Tycho-Gaia Astrometric Solution (TGAS).

The reference frame and fundamental physics aspects of Gaia were studied as part of the PhD project of Rajesh K. Bachchan. The use of Gaia data for exoplanet detection was studied in a project with Dr. Pieor Ranalli. The exploitation of Gaia data for Galactic studies is actively pursued by severala researchers in Lund, in particular Dr. Paul McMillan and PhD student Daniel Mikkola.

The historical involvement of Lund Observatory in the mission: Gaia was originally proposed in October 1993 by Lindegren, Perryman (ESTEC) et al. as a concept for an ESA cornerstone mission. Called GAIA, an acronym for Global Astrometric Interferometer for Astrophysics, it envisaged using two optical interferometers with 30 cm apertures and 3 m baselines, capable of measuring some 50 million stars brighter than V = 15-16 mag to an accuracy of about 20 microarcsec. (The 1993 proposal can be found here.) Soon after, it was realized that that a much better performance could be achieved with a direct imaging system, using filled apertures and a mosaic of CCDs operated in TDI mode, rather than the complex fringe detection method described in the 1993 proposal. These ideas had already earlier in 1993 been developed by E. Høg, Lindegren and others for the Roemer mission proposed to ESA as a medium-size mission. After further studies by scientists together with ESA and industry, a mature concept was presented in 2000 to the ESA advisory bodies and eventually approved as a future mission in the ESA programme. Gaia was then no longer an interferometer, and in fact incorporated many features from the Roemer concept, but it retained its proper name Gaia - which is therefore not an acronym. A summary description of the project as it was at the time of approval in 2000 can be found here. Since then the project has continued to evolve considerably, and the reader should consult the official Gaia information sheets for up-to-date information.

Early mission studies (Lindegren, Söderhjelm, Holmberg, Quist): Studies performed by the Lund group during the Concept and Technology Study phase (up to 2000) include predictions of star counts and the detection of binaries, brown-dwarf and planetary companions, and the determination of orbits and masses.  It has been shown, for instance, that Gaia will measure the individual stellar masses for many thousand stars, and that the mission will provide a nearly complete census of brown-dwarf companions to stars within 100 pc from the Sun. The impact of Gaia for the determination of astrometric radial velocities has been examined.  The main mission accuracy analysis was performed in Lund, using semi-analytical tools developed here and subsequently refined as a consequence of the industrial studies.  Numerous technical studies of optics and detector performance have been carried out, e.g. modelling the effects of charge transfer inefficiency due to radiation-induced charge trapping.  Aspects of the data analysis for Gaia have been studied, including data-base architectures for an observatory-type facility.

Lund Observatory, Box 43, SE-22 100 Lund, Sweden
Visiting adress: Sölvegatan 27
Phone: +46 46 22 27300, Fax: +46 46 22 24614
Publisher: Anders Johansen
Last updated: 2017 July 30