Low Wind Effect, the main limitation of the SPHERE instrument

The SPHERE instrument (Beuzit, et al., 2010) is dedicated to the direct imaging of extra-solar planets. This kind of observation allows one to study the photons emitted by the planet’s atmosphere itself, or reflected by its surface. The search for bio-markers is therefore made possible. The SPHERE instrument has been installed and commissioned at VLT Paranal Observatory during 2014 and now routinely delivers high contrast images to the exoplanet community. This paper presents a study of the main actual limitation of the SPHERE instrument, as known as the Low Wind Effect [LWE]. This effect has been discovered on SPHERE during commissioning period. Its effect is a strong degradation of the instrument PSF, preventing instrument to perform high contrast imaging. It happens during particularly low wind conditions (below 1m/s at the telescope level) which happens one night out of five.