First wavefront sensor for GRAVITY installed at Paranal Observatory
The first out of four wavefront sensors for the GRAVITY instrument has been successfully installed at the ESO Paranal Observatory in Chile. GRAVITY is a 2nd generation near-infrared instrument for the Very Large Telescope Interferometer (VLTI) that will combine the light of the four 8.2m-telescopes to achieve a much higher resolution than it would be possible with a single telescope. Alternatively, GRAVITY can also combine the light of the four smaller 1.8m auxiliary telescopes.
A major science goal of GRAVITY is the observation of objects in the immediate environment of the supermassive black hole in the center of our Milky Way – objects which might even fall into the black hole. Furthermore, GRAVITY will allow studies of young stellar objects and evolved stars with unrivaled sensitivity.
In order to achieve the highest possible sensitivity and resolution one has to cancel out the blurring effect of atmospheric turbulence above each of the unit telescopes with an Adaptive Optics System (AO) of fast deformable mirrors. Therefore, GRAVITY consists of the Beam Combiner Instrument (BCI) in the VLTI laboratory and of four infrared wavefront sensors to analyse the atmospheric turbulences. The wavefront sensors are located in the four telescope´s Coude-Rooms, respectively, and are named Coude Infrared Adaptive Optics (CIAO). Observations in the infrared are beneficial both for the operation of AO and for the detection and study of celestial objects behind interstellar dust clouds.
The BCI has been installed already in autumn 2015 at Paranal and tests with the auxiliary telescopes are still ongoing. The CIAO wavefront sensors are built under the responsibility of the Max Planck Institute for Astronomy in close cooperation with ESO and the GRAVITY consortium under the lead of MPE (Max Planck Institute for Extraterrestrial Physics) as PI institute.
Each CIAO system gets the light from the Star Separator System inside the Coude rooms and guides it through its internal warm optics to the infrared detector within a cold cryostat. To correct the atmospheric perturbations of the incoming wavefront, the CIAO system communicates directly with the deformable mirror.
The installation period of the first CIAO system took 24 days starting mid February 2016. After a 15 days period of assembly, integration and internal alignment in the integration hall the instrument was brought to the Coude Room of Unit Telescope 1 on 2nd March 2016. After another 8 days the system was fully functional and aligned with respect to the Star Separator. Currently, the scientific verification is ongoing, including system optimisation and the first on-sky performance tests in early April 2016.
Parallel to the installation activities at Paranal with the first system, the second unit was tested and the assembly and alignment of systems 3 and 4 at MPIA are ongoing. The second CIAO system will be installed at Paranal in April/May 2016. With two wavefront sensors in place, the first interferometric tests with the BCI can start. CIAO system 3 and 4 will be installed and commissioned at Paranal from mid August till early October 2016 including commissioning with the Beam Combiner Instrument.
MPIA-News Release (January 13, 2016):