MEGARA is an integral-field and multi-object medium-resolution spectrograph for the GTC 10.4m telescope, which was commissioned on June - August 2017. MEGARA offers two observing modes, the LCB mode, a large central IFU; and a Multi-Object Spectrograph (MOS) mode, composed by 92 robotic positioners carrying 7-fiber minibundles each. This paper presents the models and measurements developed for the alignment between the image of the telescope pupil and the 100-μm fiber cores during the integration and verification at the laboratory. On the one hand, the error in the positioner-minibundles assembly was optimized with the aim of achieving a fiber-to-fiber flux homogeneity better than 10%. On the other hand, the positioner pointing was characterized in order to achieve a pointing precision of 1/5 of the spaxel size (which has been designed to be 0.62 arcsec). The on-sky measurements obtained during the commissioning to verify our laboratory results are also presented.
MEGARA is an IFU & MOS medium-resolution spectrograph that finished its commissioning at the GTC 10m telescope on August 2017. MEGARA is a fiber-fed high-resolution spectrograph with two major units, Fiber-MOS & Spectrograph, that are now located at the Folded-Cass F and Nasmyth-A foci of GTC respectively. These are linked by more than 1200 fibers 44.5m-length split between two observing modes, the LCB (Integral Field Unit, IFU) and a Multi- Object (MOS) capability with 92 robotic positioners each one provided with a mini-bundle of 7 fibers. The spectrograph can accommodate 18 VPHs (11 of them can be simultaneously mounted) covering the visible wavelength range at Resolving Powers between R=6000-20000. This paper presents the sequence of tasks carried out after Laboratory Acceptance at the Universidad Complutense de Madrid to move the whole instrument to the GTC. A detailed day-to-day plan was followed to disassemble, pack, transport, reintegrate the full instrument at the GTC and to verify performance to ensure the instrument was ready for commissioning. The lessons learnt are relevant to other double-focus instruments being developed such as WEAVE@WHT or PFS@Subaru.
On June 25th 2017, the new intermediate-resolution optical IFU and MOS of the 10.4-m GTC had its first light. As part of the tests carried out to verify the performance of the instrument in its two modes (IFU and MOS) and 18 spectral setups (identical number of VPHs with resolutions R=6000-20000 from 0.36 to 1 micron) a number of astronomical objects were observed. These observations show that MEGARA@GTC is called to fill a niche of high-throughput, intermediateresolution IFU and MOS observations of extremely-faint narrow-lined objects. Lyman-α absorbers, star-forming dwarfs or even weak absorptions in stellar spectra in our Galaxy or in the Local Group can now be explored to a new level. Thus, the versatility of MEGARA in terms of observing modes and spectral resolution and coverage will allow GTC to go beyond current observational limits in either depth or precision for all these objects. The results to be presented in this talk clearly demonstrate the potential of MEGARA in this regard.
MEGARA is the new generation IFU and MOS optical spectrograph built for the 10.4m Gran Telescopio CANARIAS (GTC). The project was developed by a consortium led by UCM (Spain) that also includes INAOE (Mexico), IAA-CSIC (Spain) and UPM (Spain). The instrument arrived to GTC on March 28th 2017 and was successfully integrated and commissioned at the telescope from May to August 2017. During the on-sky commissioning we demonstrated that MEGARA is a powerful and robust instrument that provides on-sky intermediate-to-high spectral resolutions RFWHM ~ 6,000, 12,000 and 20,000 at an unprecedented efficiency for these resolving powers in both its IFU and MOS modes. The IFU covers 12.5 x 11.3 arcsec<sup>2</sup> while the MOS mode allows observing up to 92 objects in a region of 3.5 x 3.5 arcmin<sup>2</sup>. In this paper we describe the instrument main subsystems, including the Folded-Cassegrain unit, the fiber link, the spectrograph, the cryostat, the detector and the control subsystems, and its performance numbers obtained during commissioning where the fulfillment of the instrument requirements is demonstrated.
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 arcmin<sup>2</sup> 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 (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 (<i>Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía</i>) 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<sup>2</sup> with a spaxel size of 0.62 arcsec (Large Compact Bundle; LCB) and
another one covering 8.5x6.7 arcsec<sup>2</sup> 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<sup>2</sup> around the two IFU bundles.
Both the LCB IFU and MOS capabilities of MEGARA will provide intermediate-to-high spectral resolutions
(R<sub>FWHM</sub>~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 R<sub>FWHM</sub>~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 arcsec<sup>2</sup> 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 arcsec<sup>2</sup> 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 arcmin<sup>2</sup>. 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 future optical Integral-Field Unit
(IFU) and Multi-Object Spectrograph (MOS) for GTC. The Fiber Units are placed at one Folded Cassegrain focus and
feed the spectrograph located on a Nasmyth-type platform.
This paper summarizes the status of the design of the MEGARA Folded Cassegrain Subsystems after the PDR (held on
March 2012), as well as the prototyping that has been carried out during this phase.
The MEGARA Fiber Unit has two IFUs: a Large Compact Bundle covering 12.5 arcsec x 11.3 arcsec on sky (100
microns fiber-core), and a Small Compact Bundle, of 8.5 arcsec x 6.7 arcsec (70 microns fiber-core), plus a Fiber MOS
positioner, able to place up to 100 mini-bundles 7 fibers each (100 microns fiber-core) in MOS configuration within a
3.5arcmin x 3.5arcmin FOV. A field lens provides a telecentric focal plane where the fibers are located. Microlens arrays
couple the telescope beam to the collimator focal ratio at the entrance of the fibers (providing the f/17 to f/3 focal ratio
reduction to enter into the fibers). Finally, the fibers, organized in bundles, end in the pseudo-slit plate, which will be
placed at the entrance focal plane of the MEGARA spectrographs.
Fiber-fed spectrographs dedicated to observing massive portions of the sky are increasingly being more demanded
within the astronomical community. For all the fiber-fed instruments, the primordial and common problem is the
positioning of the fiber ends, which must match the position of the objects of a target field on the sky. Amongst
the different approaches found in the state of the art, actuator arrays are one of the best. Indeed, an actuator
array is able to position all the fiber heads simultaneously, thus making the reconfiguration time extremely short
and the instrument efficiency high. The SIDE group* at the Instituto de Astrofisica de Andalucia, together with
the industrial company AVS and the University of Barcelona, has been developing an actuator suitable for a large
and scalable array. A real-scale prototype has been built and tested in order to validate its innovative design
concept, as well as to verify the fulfillment of the mechanical requirements. The present article describes both
the concept design and the test procedures and conditions. The main results are shown and a full justification
of the validity of the proposed concept is provided.