MEGARA: a new generation optical spectrograph for GTC

Abstract

MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is an optical Integral-Field Unit (IFU) and Multi-Object Spectrograph (MOS) designed for the GTC 10.4m telescope in La Palma. MEGARA offers two IFU fiber bundles, one covering 12.5x11.3 arcsec^2 with a spaxel size of 0.62 arcsec (Large Compact Bundle; LCB) and another one covering 8.5x6.7 arcsec^2 with a spaxel size of 0.42 arcsec (Small Compact Bundle; SCB). The MEGARA MOS mode will allow observing up to 100 objects in a region of 3.5x3.5 arcmin^2 around the two IFU bundles. Both the LCB IFU and MOS capabilities of MEGARA will provide intermediate-to-high spectral resolutions (R_FWHM∽6,000, 12,000 and 18,700, respectively for the low-, mid-and high-resolution Volume Phase Holographic gratings) in the range 3650-9700 ÅÅ. These values become R_FWHM∽7,000, 13,500, and 21,500 when the SCB is used. A mechanism placed at the pseudo-slit position allows exchanging the three observing modes and also acts as focusing mechanism. The spectrograph is a collimator-camera system that has a total of 11 VPHs simultaneously available (out of the 18 VPHs designed and being built) that are placed in the pupil by means of a wheel and an insertion mechanism. The custom-made cryostat hosts an E2V231-84 4kx4k CCD. The UCM (Spain) leads the MEGARA Consortium that also includes INAOE (Mexico), IAA-CSIC (Spain), and UPM (Spain). MEGARA is being developed under a contract between GRANTECAN and UCM. The detailed design, construction and AIV phases are now funded and the instrument should be delivered to GTC before the end of 2016.