ESPRESSO instrument control software and electronics: commissioning in Paranal

The ESPRESSO (Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations) spectrograph, after the preliminary tests carried out at the Astronomical Observatory of Geneva (Switzerland), has been shipped and re-integrated at the Very Large Telescope (VLT) site in Cerro Paranal (Chile). The instrument control software, designed and developed at INAF-Osservatorio Astronomico di Trieste, had to face several challenges since ESPRESSO is the first instrument placed at the VLT Coude Combined Laboratory able to be fed by up to 4 Telescope Units simultaneously (through an incoherent focus), and whose electronics is based on Beckhoff PLCs. Moreover, ESPRESSO requires a careful stabilization of the field image in order to maximize the light flux through the fiber hole, and reach the instrumental radial-velocity precision level of 10 cm/s. These circumstances lead to the development of a few solutions specifically dedicated to ESPRESSO. In this paper we will summarize the features of the ESPRESSO control software, the tests performed during the integration phase in Europe, and discuss the main performances obtained during the commissioning phase and "first light" observations in Chile.