MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is the future optical Integral-Field Unit (IFU) and Multi-Object Spectrograph (MOS) for the GTC 10.4m telescope. The spectrograph is currently being integrated in the laboratory for a pre-shipping review in September 2016. This paper presents the current status and final performance of the spectrograph mechanics and opto-mechanics, composed of the mechanisms and the large optomechanical elements mounts.
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 that is being built by a Consortium led by UCM (Spain) that also includes INAOE (Mexico), IAA-CSIC (Spain), and UPM (Spain). The instrument is currently finishing AIV and will be sent to GTC on November 2016 for its on-sky commissioning on April 2017. The MEGARA IFU fiber bundle (LCB) covers 12.5x11.3 arcsec2 with a spaxel size of 0.62 arcsec while the MEGARA MOS mode allows observing up to 92 objects in a region of 3.5x3.5 arcmin2 around the IFU. The IFU and MOS modes of MEGARA will provide identical intermediate-to-high spectral resolutions (RFWHM~6,000, 12,000 and 18,700, respectively for the low-, mid- and high-resolution Volume Phase Holographic gratings) in the range 3700-9800ÅÅ. An x-y mechanism placed at the pseudo-slit position allows (1) exchanging between the two observing modes and (2) focusing the spectrograph for each VPH setup. 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 a 4kx4k 15-μm CCD. The unique characteristics of MEGARA in terms of throughput and versatility and the unsurpassed collecting are of GTC make of this instrument the most efficient tool to date to analyze astrophysical objects at intermediate spectral resolutions. In these proceedings we present a summary of the instrument characteristics and the results from the AIV phase. All subsystems have been successfully integrated and the system-level AIV phase is progressing as expected.
MEGARA is the multi-object medium-resolution spectrograph for the GTC 10m telescope. MEGARA offers two observing modes, the LCB mode, a large central IFU; and a MOS mode composed by 92 robotic positioners carrying 7 fibers minibundles. Microlens are required to fit the GTC f/17 to the f/3 at the fiber entrance, where pupil image is oversized to have a fiber-to-fiber flux variation better than 10%. This tight requirement imposed manufacturing tolerances for the different components and required the development of a gluing station to provide a centering precision better than 5μm. We present the overview of the optical bundles, the gluing station and the final performance obtained during the integration and tests.
MEGARA is a third generation spectrograph for the Spanish 10.4m telescope (GTC) providing two observing modes: a large central Integral Field Unit (IFU), called the Large Compact Bundle (LCB), covering a FOV of 12.5 × 11.3 arcsec2, and a Multi-Object Spectrograph (MOS) with a FOV of 3.5 × 3.5 arcmin2. MEGARA will observe the whole visible range from 3650A to 10000A allowing different spectral resolutions (low, medium and high) with R = 6000, 11000 and 18000 respectively. The dispersive elements are placed at the spectrograph pupil position in the path of the collimated beam and they are composed of a set of volume phase hologram gratings (VPHs) sandwiched between two flat windows and coupled in addition to two prisms in the case of the medium- and high-resolution units. We will describe the tests and setups developed to check the requirements of all units, as well as the obtained performance at laboratory
MEGARA (Multi Espectrógrafo en GTC de Alta Resolución para Astronomía) is the future optical Integral-Field Unit
(IFU) and Multi-Object Spectrograph (MOS) for the 10.4-m Gran Telescopio CANARIAS (GTC). MEGARA has three
different fiber bundles, the Large Central Bundle covering 12.5 arcsec x 11.3 arcsec on sky, the Small Compact Bundle,
of 8.5 arcsec x 6.7 arcsec, and a Fiber MOS positioner system that is able to place up to 100 mini-bundles with 7 fibers
each in MOS configuration within a 3.5 arcmin x 3.5 arcmin FOV. The MEGARA focal plane subsystems are located at
one of the GTC Folded Cassegrain focal stations. A field lens provides a telecentric focal plane, where the fibers are
located. Micro-lenses arrays couple the telescope beam to the collimator focal ratio at the entrance of the fibers. Finally,
the fibers, organized in bundles conducted the light from the focal plane to the pseudo-slit plates at the entrance of the
MEGARA spectrograph, which shall be located at one of the Nasmyth platforms. This article also summarizes the
prototypes already done and describes the set-up that shall be used to integrate fibers and micro-lens and characterize the
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 arcsec2 with a spaxel size of 0.62 arcsec (Large Compact Bundle; LCB) and
another one covering 8.5x6.7 arcsec2 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 arcmin2 around the two IFU bundles.
Both the LCB IFU and MOS capabilities of MEGARA will provide intermediate-to-high spectral resolutions
(RFWHM~6,000, 12,000 and 18,700, respectively for the low-, mid- and high-resolution Volume Phase Holographic
gratings) in the range 3650-9700ÅÅ. These values become RFWHM~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.
In these proceedings we give a summary of the characteristics and current status of the MEGARA instrument,
the future optical IFU and MOS for the 10.4-m Gran Telescopio Canarias (GTC). MEGARA is being built
by a Consortium of public research institutions led by the Universidad Complutense de Madrid (UCM, Spain)
that also includes INAOE (Mexico), IAA-CSIC (Spain) and UPM (Spain). The MEGARA IFU includes two
different fiber bundles, one called LCB (Large Compact Bundle) with a field-of-view of 12.5×11.3 arcsec2 and
a spaxel size of 0.62 arcsec yielding spectral resolutions between R=6,800-17,000 and another one called SCB
(Small Compact Bundle) covering 8.5×6.7 arcsec2 with hexagonally-shaped and packed 0.42-arcsec spaxels and
resolutions R=8,000-20,000. The MOS component allows observing up to 100 targets in 3.5×3.5 arcmin2. Both
the IFU bundles and the set of 100 robotic positioners of the MOS will be placed at one of the GTC Folded-Cass
foci while the spectrographs (one in the case of the MEGARA-Basic concept) will be placed at the Nasmyth
platform. On March 2012 MEGARA passed the Preliminary Design Review and its first light is expected to
take place at the end of 2015.
The goal of VIENTOS project is to analyze pupil innovative systems that could be used in the new generation of
instruments for the large telescopes. This study tries to identify the current scientific needs, to understand why some of
them have not been fulfilled yet (due to pre-conceived technical ideas or to managerial reasons) and to propose optomechanical
solutions for these pupil elements that could produce a qualitative leap in the performance of the instruments
to operate in the large telescopes. VIENTOS is currently on-going as a collaborative project between FRACTAL and the
University Complutense of Madrid (UCM) and is being partially funded by a CDTI grant under the program Industry for
Science. CDTI is the Development and Industrial Transfer Center from the Minister of Science and Innovation (Spain).
Among the different innovative systems that we have carried out, our team has explored potential solutions for narrow
band Imaging with tunable filters in the near-IR and a novel pupil system called sliced-pupil grating, a device designed
for increasing the spectral resolution in astronomical spectrographs, without changing the geometry of the main optics.
Nanotechnology customized filters to be applicable to astronomical systems are under study.
This paper presents the opto-mechanical design of a novel spectroscopic element - sliced pupil grating - that allows
increasing the spectral resolution while keeping the instrument geometry. The concept is based on "cutting" the pupil
into different slices by placing a number of prisms at the two sites of a VPH grating. The independent beams are guided
through a precise opto-mechanical assembly to assure the recombination of the individual images on the detector within
the available error budget, producing a single spectrum. To probe the feasibility of the concept, we have designed and
manufactured a 3-slice prototype for an already-built spectrograph (Elmer, for the GTC 10-m telescope).