MEGARA: THE NEW MULTI-OBJECT AND INTEGRAL FIELD … · 2017-06-29 · the microlens arrays were...
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XV Latin American Regional IAU Meeting (Cartagena de Indias, Colombia, 3-7 October 2016) Editors: Mario Armando Higuera Garzón & Santiago Vargas Domínguez RevMexAA (Serie de Conferencias), 49, 39–40 (2017) MEGARA: THE NEW MULTI-OBJECT AND INTEGRAL FIELD SPECTROGRAPH FOR GTC E. Carrasco 1 , G. P´ aez 2 , R. Izazaga-P´ erez 1 , A. Gil de Paz 3 , J. Gallego 3 , and J. Iglesias-P´ aramo 4 for the MEGARA team RESUMEN MEGARA es un espectr´ografo de campo integral y multi-objeto para el Gran Telescopio Canarias de 10.4m. En ambos modos de observaci´ on se tendr´ an resoluciones espectrales id´ enticas R fwhm ∼6,000, 12,000 y 18,700. El espectr´ografo es un sistema basado en un colimador y una c´amara. La caracter´ ısticas ´ unicas de MEGARA en t´ erminos de sensibilidad y versatilidad lo hacen el instrumento m´as eficiente hasta hora para analizar objetos a resoluciones espectrales intermedias. El instrumento se encuentra instalado en el telescopio para las pruebas de funcionamiento en el cielo. Se describen las caracter´ ısticas principales del instrumento. ABSTRACT MEGARA is an optical integral-field unit and multi-object spectrograph for the 10.4m Gran Telescopio Ca- narias. Both observational modes will provide identical spectral resolutions R fwhm ∼6,000, 12,000 and 18,700. The spectrograph is a collimator-camera system. The unique characteristics of MEGARA in terms of through- put and versatility make this instrument the most efficient tool to date to analyze astrophysical objects at intermediate spectral resolutions. The instrument is currently at the telescope for on-sky commissioning. Here we describe the as-built main characteristics the instrument. Key Words: instrumentation: spectrographs 1. INTRODUCTION MEGARA (Multi-Espectr´ografo en GTC de Alta Resoluci´on para Astronom´ ıa) is an optical spectro- graph built for the Gran Telescopio Canarias (GTC) by a consortium led by UCM (Spain), that includes INAOE (Mexico) as its main partner and IAA-CSIC (Spain). 2. MEGARA: THE INSTRUMENT Gil de Paz et al. (2016) provides a very detailed description of all the subsystems, here a brief sum- mary follows. MEGARA has two well differentiated units, one located at the 10.4m GTC folded-Cass focus, where the integral field unit (LCB) and the multi-object spectroscopy (MOS) robotic positioners are placed and another one at the Nasmyth platform, where the spectrograph is located. The two units are connected by two 40m-long fiber links. The LCB has 567 hexagonally-shaped spaxels of 0.62 arcsec in size that fully covers a contiguous region of 12.5x11.3 1 Instituto Nacional de Astrof´ ısica, ´ Optica y Electr´onica Luis Enrique Erro No.1, C.P. 72840, Tonantzintla, Puebla, Mexico ([email protected]). 2 Centro de Investigaciones en ´ Optica, Loma del Bosque 115, C.P. 37150, Le´ on, Guanajuato, Mexico ([email protected]). 3 Universidad Complutense de Madrid, Avenida Com- plutense s/n, E-28040, Madrid, Spain (agil@fis.ucm.es). 4 Instituto de Astrof´ ısica de Andaluc´ ıa-CSIC, Glorieta de la Astronom´ ıa s/n, 18008, Granada, Spain, ([email protected]). arcsec 2 on the sky. A microlens array reimages the telescope pupil coming from each of these spaxels on an identical number of 100μm core fibers. The MOS mode with a total of 100 robotic positioners can patrol a region of 3.5x3.5 arcmin 2 around the LCB. Each positioner built by AVS (Spain) has a seven-spaxel microlens array attached to it that, as in the case of the LCB, reimages the pupil on seven 100μm-core optical fibers. Eight of these bundles are devoted to the determination of the sky dur- ing the observation with the LCB, so 92 of these positioners (644 fibers) are available for MOS ob- servations. The two optical-fiber bundles reach the spectrograph with a two identical curved telecentric pseudo-slits. These pseudo-slits are placed on top of an x-y mechanism that is used to exchange between the two instrument modes and to focus the instru- ment as a function of the disperser element being used and of temperature. The fiber bundles were built by SEDIATI Fibres-Optiques (France) while the microlens arrays were manufactured by [aμs] ad- vanced microoptic systems gmbh (Germany). The design of the pre-optics has been carried out by Frac- tal S.L.N.E. (Spain). The spectrograph is a fully- refractive optical system composed by a f/3 collima- tor with 5 lenses and a f/1.5 camera with 7 lenses that both form an angle of 68 ◦ . The spectrograph and the field lens designs were carried out by Fractal 39
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RevMexAA (Serie de Conferencias), 49, 39–40 (2017)
MEGARA: THE NEW MULTI-OBJECT AND INTEGRAL FIELD
SPECTROGRAPH FOR GTC
E. Carrasco1, G. Paez2, R. Izazaga-Perez1, A. Gil de Paz3, J. Gallego3, and J. Iglesias-Paramo4 for theMEGARA team
RESUMEN
MEGARA es un espectrografo de campo integral y multi-objeto para el Gran Telescopio Canarias de 10.4m.En ambos modos de observacion se tendran resoluciones espectrales identicas Rfwhm∼6,000, 12,000 y 18,700.El espectrografo es un sistema basado en un colimador y una camara. La caracterısticas unicas de MEGARAen terminos de sensibilidad y versatilidad lo hacen el instrumento mas eficiente hasta hora para analizar objetosa resoluciones espectrales intermedias. El instrumento se encuentra instalado en el telescopio para las pruebasde funcionamiento en el cielo. Se describen las caracterısticas principales del instrumento.
ABSTRACT
MEGARA is an optical integral-field unit and multi-object spectrograph for the 10.4m Gran Telescopio Ca-narias. Both observational modes will provide identical spectral resolutions Rfwhm∼6,000, 12,000 and 18,700.The spectrograph is a collimator-camera system. The unique characteristics of MEGARA in terms of through-put and versatility make this instrument the most efficient tool to date to analyze astrophysical objects atintermediate spectral resolutions. The instrument is currently at the telescope for on-sky commissioning. Herewe describe the as-built main characteristics the instrument.
Key Words: instrumentation: spectrographs
1. INTRODUCTION
MEGARA (Multi-Espectrografo en GTC de AltaResolucion para Astronomıa) is an optical spectro-graph built for the Gran Telescopio Canarias (GTC)by a consortium led by UCM (Spain), that includesINAOE (Mexico) as its main partner and IAA-CSIC(Spain).
2. MEGARA: THE INSTRUMENT
Gil de Paz et al. (2016) provides a very detaileddescription of all the subsystems, here a brief sum-mary follows. MEGARA has two well differentiatedunits, one located at the 10.4m GTC folded-Cassfocus, where the integral field unit (LCB) and themulti-object spectroscopy (MOS) robotic positionersare placed and another one at the Nasmyth platform,where the spectrograph is located. The two units areconnected by two 40m-long fiber links. The LCBhas 567 hexagonally-shaped spaxels of 0.62 arcsec insize that fully covers a contiguous region of 12.5x11.3
1Instituto Nacional de Astrofısica, Optica y ElectronicaLuis Enrique Erro No.1, C.P. 72840, Tonantzintla, Puebla,Mexico ([email protected]).
2Centro de Investigaciones en Optica, Loma del Bosque115, C.P. 37150, Leon, Guanajuato, Mexico ([email protected]).
3Universidad Complutense de Madrid, Avenida Com-plutense s/n, E-28040, Madrid, Spain ([email protected]).
4Instituto de Astrofısica de Andalucıa-CSIC, Glorieta dela Astronomıa s/n, 18008, Granada, Spain, ([email protected]).
arcsec2 on the sky. A microlens array reimages thetelescope pupil coming from each of these spaxelson an identical number of 100µm core fibers. TheMOS mode with a total of 100 robotic positionerscan patrol a region of 3.5x3.5 arcmin2 around theLCB. Each positioner built by AVS (Spain) has aseven-spaxel microlens array attached to it that, asin the case of the LCB, reimages the pupil on seven100µm-core optical fibers. Eight of these bundlesare devoted to the determination of the sky dur-ing the observation with the LCB, so 92 of thesepositioners (644 fibers) are available for MOS ob-servations. The two optical-fiber bundles reach thespectrograph with a two identical curved telecentricpseudo-slits. These pseudo-slits are placed on top ofan x-y mechanism that is used to exchange betweenthe two instrument modes and to focus the instru-ment as a function of the disperser element beingused and of temperature. The fiber bundles werebuilt by SEDIATI Fibres-Optiques (France) whilethe microlens arrays were manufactured by [aµs] ad-vanced microoptic systems gmbh (Germany). Thedesign of the pre-optics has been carried out by Frac-tal S.L.N.E. (Spain). The spectrograph is a fully-refractive optical system composed by a f/3 collima-tor with 5 lenses and a f/1.5 camera with 7 lensesthat both form an angle of 68◦. The spectrographand the field lens designs were carried out by Fractal
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40 CARRASCO ET AL.
S.L.N.E. while its construction was done by INAOEand CIO (Mexico).
The disperser elements are Volume Phase Holo-graphic (VPH) gratings built by Wasatch Photon-ics (USA). When sandwiched between flat win-dows alone the VPHs yield a spectral resolutionsRfwhm∼6,000 (LR, low-resolution). By means ofprisms that are coupled to the flat windows theVPHs reach spectral resolutions ranging between12,000 (MR, mid-resolution) and 18,700 (HR, high-resolution). The VPHs are inserted in the pupil byan insertion mechanism that extracts the VPH froma wheel where up to a total of 11 VPHs can be placed.To provide 18 spectroscopic configurations 36 FusedSilica windows and 24 prisms were manufactured atINAOE. The antireflection coatings depositions ofthe main optics and the pupil elements were carriedout by CIO (Mexico). The camera focuses the lightonto an E2V 231-84 deep-depleted 4k x 4k 15-µmpixels CCD located in a cryostat designed and builtby INAOE.
MEGARA control system controls the differentinstrument mechanisms: the focal-plane cover, fiber-MOS robotic positioners, pseudo-slit exchange, fo-cus, shutter, and VPH wheel, insertion mechanism,data acquisition and monitors.
The science team scientific interests includes thestudy of Galactic and extragalactic extended nebu-lae such as the study of planetary nebulae, nearbygalaxies, and the high-redshift IGM and the study ofnumerous compact sources clustered in the sky withintermediate-to-high surface densities such as Galac-tic open stellar clusters, resolved stellar popula-tions in Local Group galaxies, intermediate-redshiftdwarf and starburst galaxies, and high-redshift clus-ter galaxies. The MEGARA science team includesresearchers with broad range of interests that belongto the GTC community.
3. RESULTS
As part of the laboratory acceptance tests ofMEGARA, the resolving power (Rfwhm) of the LCBand MOS modes for the 18 spectral configurationswas measured. The results are summarized in fig-ures 1 and 2. The design resolutions are shown incolors. The spectral resolution changes across thedetector due to the use of VPHs. For each spec-tral configuration, the grey lines are the resolutionmeasured for each fiber, the thick black curve is theaverage resolution and the thin black curves are theaverage ±σ.
Fig. 1. Coverage of the MEGARA VPHs in resolvingpower (Rfwhm) and wavelength for the LCB mode. Ex-planation in the text.
Fig. 2. Coverage of the MEGARA VPHs in resolvingpower (Rfwhm) and wavelength for the MOS mode. Ex-planation in the text.
4. CONCLUSIONS
MEGARA is a case of sucess as it has fulfilled thespecifications and has been finished within scheduleand budget. The instrument is at GTC for integra-tion and on-sky commissioning. It will be offered tothe community for the second semester of 2017.
REFERENCES
Gil de Paz, A. et al. 2016 Proc. of SPIE Vol. 990899081K-1
