MOSAIC in a nutshellMOSAIC is a multi-object and multi-integral field spectrograph that will use the widest possible field of view provided by the ELT. The MOSAIC top-level requirements have been based on a comprehensive White Paper summarizing the very numerous scientific cases for a multi-object spectrograph on the ELT. MOSAIC is conceived as a multi-purpose MOS for the ELT, covering the Visible and Near Infrared bandwidth (0.45 – 1.8 μm) with two modes: multi-object spectroscopy (MOS) and spatially resolved spectroscopy (mIFU). MOSAIC will be located at the Nasmyth B port of the ELT. The instrument will work with Ground Layer Adaptive Optics image quality over the full field of view of the ELT ~40 arcmin2 and over a nearly full sky coverage. GLAO combines 4 laser guide stars with fainter natural guide to achieve 40% ensquared energy within 0.4 arcsec in H-band.
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MOS and IFU modes
Even with the unbeatable collecting power of the ELT, the observed astronomical sources are so faint, that it will require several hours to obtain spectra. The multi-object spectroscopy mode enables us to observe hundreds of targets simultaneoulsy in a single exposure of a few hours (1h at ELT). Without multiplex capability, i.e. possibility to observe several objects at the same time, the same observations would require several hundreds of hours (100h).
The IFU mode combines spectrographic and imaging capabilities. The integral field unit slices the astronomical object into several regions, each of them being spectrographied. This leads to spatially resolved observations of the object, by providing a spectrum for each region
Each mode offers a number of instrument configurations with different spectral resolution and aperture on sky summarized in the table below:
Spectral configurations
Nine spectral resolution settings of 4000, 9000 and 18000 are provided in all instrumental modes, covering the wavelength range of 0.45–1.80 micrometres. In the visible channel, the operating wavelength will be covered by the 2 LR bands but not simultaneously.
The full near-IR band spanning from 0.77 to 1.8μm is covered simultaneously at low spectral resolution. The two HR bands in the near-IR can also be observed simultaneously.