SPHERE/IRDIS: final performance assessment of the dual-band imaging and long slit spectroscopy modes
Résumé
The near-infrared imager and spectrograph IRDIS is one of the three science sub-systems of VLT/SPHERE dedicated to the detection and characterization of giant exoplanets at large orbital radii. It offers a wide range of observational modes including dual-band imaging (DBI) with very low differential aberrations, and long slit spectroscopy (LSS) coupled with a classical Lyot coronagraph at low (R = ~50) and medium (R = ~330) resolution. Over the course of 2012 and 2013, IRDIS has been extensively tested in laboratory during the integration and optimization of the SPHERE system. At the beginning of 2014, the instrument has been shipped to Chile and has been reintegrated at the Paranal observatory. We present here a detailed summary of the performance of the DBI and LSS modes obtained in laboratory. We provide a wide range of results covering different observing conditions and setups for the DBI mode, and we show that the instrument reaches the technical specifications in terms of contrast. We also identify some of the limitations that prevent going down much further in contrast while testing in the laboratory. For the LSS mode, we present results obtained both at low and medium resolution in the main setups that will be offered to future users. We demonstrate that the LSS mode will provide a useful characterization tool for the planets detected in DBI mode. Finally, we present the first results obtained on-sky during the first commissioning run of SPHERE at the VLT.