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 (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is an optical Integral-Field Unit and
Multi-Object Spectrograph designed for the GTC (Gran Telescopio de Canarias) 10.4m telescope in La Palma.
MEGARA project has already passed preliminary design review and the optics critical design review, first-light it is
expected to take place at the end of 2016. MEGARA is a development under a GRANTECAN contract.
In this paper we summarize the current status of the LN2 open-cycle cryostat which has been designed by the
“Astronomical Instrumentation Lab for Millimeter Wavelengths” at the Instituto Nacional de Astrofísica, Óptica y
Electrónica (INAOE) and emphasize the key parts of the system that have updated since the Preliminary Design, the
main activities related to acceptance, integration, fabrication and maintenance plans which fit into the overall structure of
the management plan of MEGARA are also described. The cryogenic work package of MEGARA has completed all the
design stages and is ready for its Critical Design Review and then proceed to fabrication.
MEGARA is the future integral-field and multi-object spectrograph for the GTC 10.4m telescope located in the
Observatorio del Roque de los Muchachos in La Palma. INAOE is a member of the MEGARA Consortium and it is
in charge of the Optics Manufacturing work package. In addition to the manufacturing of 73 elements, the work
package includes the opto-mechanics i.e. the opto-mechanical design, manufacture, tests and integration of the
complete assembly of the main optics composed by the collimator and camera subsystems. MEGARA passed the
Optics Detailed Design Review in May 2013 and will have the Detailed Design Review of the complete instrument
early 2014. Here we describe the detailed design of the collimator and camera barrels. We also present the finite
elements models developed to simulate the behavior of the barrel, sub-cells and other mechanical elements. These
models verify that the expected stress fields and the gravitational displacements on the lenses are compatible with
the optical quality tolerances. The design is finished and ready for fabrication.
MEGARA is the future visible integral-field and multi-object spectrograph for the GTC 10.4-m telescope
located in La Palma. INAOE is a member of the MEGARA Consortium and it is in charge of the Optics
Manufacturing work package. MEGARA passed the Optics Detailed Design Review in May 2013, and the
blanks of the main optics have been already ordered and their manufacturing is in progress. Except for
the optical fibers and microlenses, the complete MEGARA optical system will be manufactured in
Mexico, shared between the workshops of INAOE and CIO. This includes a field lens, a 5-lenses collimator, a
7-lenses camera and a complete set of volume phase holographic gratings with 36 flat windows and 24 prisms,
being all these elements very large and complex. Additionally, the optical tests and the complete assembly of
the camera and collimator subsystems will be carried out in Mexico. Here we describe the current status of the
optics manufacturing process.
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.
MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is the new integral field unit (IFU) and
multi-object spectrograph (MOS) instrument for the GTC. The spectrograph subsystems include the pseudo-slit, the
shutter, the collimator with a focusing mechanism, pupil elements on a volume phase holographic grating (VPH) wheel
and the camera joined to the cryostat through the last lens, with a CCD detector inside.
In this paper we describe the full preliminary design of the cryostat which will harbor the CCD detector for the
spectrograph. The selected cryogenic device is an LN2 open-cycle cryostat which has been designed by the
"Astronomical Instrumentation Lab for Millimeter Wavelengths" at INAOE. A complete description of the cryostat
main body and CCD head is presented as well as all the vacuum and temperature sub-systems to operate it. The CCD is
surrounded by a radiation shield to improve its performance and is placed in a custom made mechanical mounting which
will allow physical adjustments for alignment with the spectrograph camera. The 4k x 4k pixel CCD231 is our selection
for the cryogenically cooled detector of MEGARA. The characteristics of this CCD, the internal cryostat cabling and
CCD controller hardware are discussed. Finally, static structural finite element modeling and thermal analysis results are
shown to validate the cryostat model.