ESPRESSO sees the sky for the first time at the UT1/VLT (ESO)
The first light of the coudè train of the ESPRESSO spectrograph at the UT1/VLT/ESO telescope took place during the first half of the night of December 13, 2016. As already noticed during the day-time tests, astronomical observations have confirmed the superb alignment, optimal image quality and very high stability that are fundamental prerequisites to fulfill the ambitious scientific cases for ESPRESSO.
After very encouraging results obtained during the installation of the first coudé train on the ESO/VLT telescope UT4 at the first light on September 2016 ( e ), the ESPRESSO team started the installation and alignment of the second coudé train, this time on UT1. We could call this event “second light of ESPRESSO”. Despite its complexity, the experience gained during the first commissioning allowed to proceed with opto-mechanical installation very rapidly. Tests performed during day-light before the actual on-sky observations already demonstrated the very good image quality achieved by the system and its super alignment.
Figure 1 shows the very high optical quality achieved both on the field as well as on the pupil detector. The measured FWHM of the star is of the order, or better, than the seeing and amounts to 0.5 arcsec. Figure 2 shows a binary star separated by 3.2 arcsec which confirmed the theoretical plate scale of 0.042 arcsec/pixel (binned, 2x2). The slightly elongated images are due to atmospheric dispersion not fully corrected yet.