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 arcsec2 while the MOS mode allows observing up to 92 objects in a region of 3.5 x 3.5 arcmin2. 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 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 (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.
The Gran Telescopio Canarias (GTC) primary mirror control system is responsible for making the 36 segments behave
like a monolithic mirror. It deals with 108 positioners giving 3 degrees of freedom to each segment, 168 position sensors
installed between adjacent segments measuring nanometrical displacements, 216 actuators controling the figure of each
segment creating torques, 216 load cells quantifying the applied deforming forces and 216 PT100 monitoring the
primary mirror temperature gradient to predict structural dilatations. It provides simple engineering access to all
functionalities of each device as well as real time capabilities required to work in closed-loop. All the critical parameters
can be monitored from any observatory's workstation thanks to the fully embedded distributed environment included in
the control system framework. Hardware interfaces as VME, CAN field buses are fully transparent for the user thanks to
the Java front-end (Inspector) that allows to start, control and
turn-off each part of the system with a simple mouse click.
Only a very few examples of near-infrared wavefront sensors can be found in the litterature. However, none of these sensors provide routine observation yet. Our sensor is the only one to be operated routinely on a large AO system. Entirely cryogenized, this sensor is built around a so-called HAWAII array from Rockwell (HgCdTe, 1024×1024). It is working in the huge spectral band ranging from 0.8 to 2.55 microns, and may use -when required- all the flux from this very whole band. It allows to switch between several optical configurations in order to match all atmospheric and observing conditions, while its original mechanical design allows to keep, even at cryogenic temperatures, a mechanical stability lower than 4 microns in any position. It also has some particular read-out schemes, allowing to obtain frame rates as high as 1200 Hz while keeping a read-out noise performance of 10 electrons rms/pixel. The analysis of the design parameters (pixel size, field of view) is exposed in this article. Some results, obtained during the comissioning runs at ESO, will also be presented.
Adaptive Optics as a new tool for astronomical observation has proved a powerful means of investigation in high angular resolution programs. However, in spite of the complexity of the components involved (wavefront sensor, real-time computer), its use must be made as simple as possible in order to make it accessible to the largest audience of observers, and to answer the more demanding needs of modern observatories such as queue scheduling, service observing or remote observing. The Computer Aided Control developed for the Nasmyth Adaptive Optics System of the Very Large Telescope, will provide the astronomer with an extensive support, from the preparation of optimized observations to the automated operation of the instrument at the telescope either for hardware control, real time computing, or even preventive maintenance.