GRAVITY is a 2nd generation near-infrared VLTI instrument that combines the light of the four unit or four auxiliary telescopes of the ESO Paranal observatory in Chile.

In order to cancel out the effect of atmospheric turbulence for each unit telescope and to be able to see beyond dusty layers, GRAVITY needs infrared wavefront sensors when operating with the unit telescopes. Therefore GRAVITY consists of the Beam Combiner Instrument (BCI) located in the VLTI laboratory and a wavefront sensor in each unit telescope Coude room, thus aptly named Coude Infrared Adaptive Optics (CIAO). The BCI has been installed in autumn 2015 on Paranal and testing with the auxiliary telescopes is ongoing. Four CIAO wavefront-sensors have been installed in 2016.

The first CIAO system has been successfully installed at the Paranal in February/March 2016.

After a 15 day period of assembly, integration and internal alignment in the integration hall the instrument had been transported to the Coude Room of UT1 on 2nd March 2016. The transport and the installation can be seen in this time laps video After another 8 days the system was fully functional and aligned with respect to the Star Separator System. A small photo-story on the Assembly and Integration activities can be found here. After system optimisation and verification, the first on-sky performance testing will be done in early April 2016. The second CIAO system has been installed at Paranal in April/May 2016. With two wavefront sensors in place, the first interferometric tests with the BCI could be done. CIAO system 3 and 4 have been installed and commissioned in one long run from mid August till early October 2016 at Paranal including commissioning with the Beam Combiner Instrument.

Since then, many observations have been done with GRAVITY leading to a large number of excellent publications. In December 2020, ESO has granted PAC to Gravity, this means the instrument is now officially accepted and maintained by ESO.

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