MOONS: A New Powerful Multi-Object Spectrograph for the VLT

MOONS (the Multi-Object Optical and Near-infrared Spectrograph) is a third-generation instrument for the ESO Very Large Telescope (VLT). The large collecting area offered by the VLT (8.2m diameter), combined with the large multiplex and wavelength coverage (optical to near-LR: 0.64 m- 1.8,um) of MOONS will provide the European astronomical community with a powerful, unique instrument able to pioneer a wide range of Galactic, Extragalactic and Cosmological studies, and the crucial follow-up for major facilities such as Gaia, VISTA, Euclid and LSST. MOONS has the observational power needed to unveil galaxy formation and evolution over the entire history of the Universe, from stars in our Milky Way, through the redshift desert, and up to the epoch of the very first galaxies and reionization of the Universe at redshifts of z > 8-9, just a few million years after the Big Bang. From five years of observations MOONS will provide high-quality spectra for >3 M stars in our Galaxy and the Local Group, and for 1-2 M galaxies at z>1 (for an SDSS-like survey), promising to revolutionize our understanding of the Universe. The baseline design consists of 1024 fibers, deployable over a field-of-view of similar to 500 sq. arcmin, the largest patrol field offered by the Nasmyth focus at the VLT. The total wavelength coverage is 0.64 m- 1.8 m with two spectral resolving power settings: in the medium-resolution mode (R similar to 4,000-6,000) the entire wavelength range is observed simultaneously, while the high-resolution mode will cover simultaneously selected sub-regions: one region with R similar to 9,000 near the Ca II triplet to measure stellar radial velocities, and part of the H-band at R similar to 20,000 for precision measurements of chemical abundances.