AGORA: Alignment of Gaia optical and radio reference frames

• Applicants: Dr.-Ing. Robert Heinkelmann; Professor Dr.-Ing. Harald Schuh
• Subject Area: Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography ; Astrophysics and Astronomy
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 461911643

Since 2014, the Gaia satellite scans the observable universe in optical wavelengths with high precision. This astrometric mission of ESA (European Space Agency) establishes several records: with the second data release (DR2) there have been more than 1.7 billion objects included with unprecedented relative precision. For applications on Earth and on board of satellites and spacecraft, the Gaia data can only be utilized properly, if they can be referred to the corresponding reference systems with high precision. Relevant reference frames for geodesy, astronomy and space flight, the ITRF, that represents the Earth surface, and the solar system ephemerides are accessible via the International Celestial Reference Frame (ICRF) through the space geodetic technique VLBI (very long baseline interferometry). Project AGORA grants the access to Gaia data by establishing precisely the time-variable orientation of Gaia with respect to ICRF. Based on the legacy VLBI networks and the new VLBI Global Observing System (VGOS) of the IVS (International VLBI Service for Geodesy and Astrometry) a consistent celestial reference frame will be determined, which is accurate enough to meet the requirements for the orientation during the entire duration of the Gaia mission. Active galactic nuclei and their optical counterparts, the hosting radio galaxies, are objects that are available in the Gaia catalogue as well as in the ICRF. These are therefore very suitable for establishment of the mutual orientation. All radio galaxies, however, are extremely faint in optical wavelength and thus do not provide enough precision for orientation of the bright fraction of Gaia objects. In project AGORA, VLBI observations of radio stars are planned and will be analysed for providing the proper orientation of bright Gaia objects. Since radio stars are extremely faint in radio wavelengths, their observation has to be done with special relative measurement techniques. After completion of the project, transformation parameters of Gaia data will be available for applications in the reference systems mentioned above. Thereby, ground-based optical observations and other applications, such as the attitude control of satellites, can be utilized based on Gaia data with substantially improved accuracy.

• DFG Programme: Research Grants