In this paper we describe the recent advances in the development of new technologies applied in the
construction of Integral Field Units (IFUs) at Laboratório Nacional de Astrofísica (LNA). Our prototype is the
Eucalyptus lenslet IFU constructed for the 1.6m telescope at Pico dos Dias Observatory (OPD), Brazil. This first
concept was the basis to build two other IFUs with significantly improved concepts: the SOAR Integral Field Unit
Spectrograph (SIFS) and FRODOSPEC. All the new technologies used in the construction of these IFUs are described
in detail in this paper and can be replicated in similar instruments with optical fibers, with considerable advantages over
the traditional technologies.
Extremely low temperatures may damage the optical components assembled inside of an astronomical instrument due to the crack in the resin or glue used to attach lenses and mirrors. The environment, very cold and dry, in most of the astronomical observatories contributes to this problem.
This paper describes the solution implemented at SOAR for remotely monitoring and controlling temperatures inside of a spectrograph, in order to prevent a possible damage of the optical parts. The system automatically switches on and off some heat dissipation elements, located near the optics, as the measured temperature reaches a trigger value. This value is set to a temperature at which the instrument is not operational to prevent malfunction and only to protect the optics. The software was developed with LabVIEWTM and based on an object-oriented design that offers flexibility and ease of maintenance.
As result, the system is able to keep the internal temperature of the instrument above a chosen limit, except perhaps during the response time, due to inertia of the temperature. This inertia can be controlled and even avoided by choosing the correct amount of heat dissipation and location of the thermal elements. A log file records the measured temperature values by the system for operation analysis.
Focal Ration Degradation (FRD) is a change in light’s angular distribution caused by fiber optics. FRD is important to
fiber-fed, spectroscopic astronomical systems because it can cause loss of signal, degradation in spectral resolution, or
increased complexity in spectrograph design. Laboratório Nacional de Astrofísica (LNA) has developed a system that
can accurately and precisely measures FRD, using an absolute method that can also measure fiber throughput. This
paper describes the metrology system and shows measurements of Polymicro’s fiber FBP129168190, FBP127165190
and Fujikura fiber 128170190. Although the FRD of the two fibers are low and similar to one another, it is very
important to know the exact characteristics of these fibers since both will be used in the construction of FOCCoS (Fiber
Optical Cable and Connectors System) for PFS (Prime Focus Spectrograph) to be installed at the Subaru telescope.
FOCCoS, "Fiber Optical Cable and Connector System" has the main function of capturing the direct light from the focal plane of Subaru Telescope using optical fibers, each one with a microlens in its tip, and conducting this light through a route containing connectors to a set of four spectrographs. The optical fiber cable is divided in 3 different segments called Cable A, Cable B and Cable C. Multi-fibers connectors assure precise connection among all optical fibers of the segments, providing flexibility for instrument changes. To assure strong and accurate connection, these sets are arranged inside two types of assemblies: the Tower Connector, for connection between Cable C and Cable B; and the Gang Connector, for connection between Cable B and Cable A. Throughput tests were made to evaluate the efficiency of the connections. A lifetime test connection is in progress. Cable C is installed inside the PFI, Prime Focus Instrument, where each fiber tip with a microlens is bonded to the end of the shaft of a 2-stage piezo-electric rotatory motor positioner; this assembly allows each fiber to be placed anywhere within its patrol region, which is 9.5mm diameter.. Each positioner uses a fiber arm to support the ferrule, the microlens, and the optical fiber. 2400 of these assemblies are arranged on a motor bench plate in a hexagonal-closed-packed disposition. All optical fibers from Cable C, protected by tubes, pass through the motors’ bench plate, three modular plates and a strain relief box, terminating at the Tower Connector. Cable B is permanently installed at Subaru Telescope structure, as a link between Cable C and Cable A. This cable B starts at the Tower Connector device, placed on a lateral structure of the telescope, and terminates at the Gang Connector device. Cable B will be routed to minimize the compression, torsion and bending caused by the cable weight and telescope motion. In the spectrograph room, Cable A starts at the Gang Connector, crosses a distribution box and terminates in a slit device. Each slit device receives approximately 600 optical fibers, linearly arrayed in a curve for better orientation of the light to the spectrograph collimator mirror. Four sets of Gang Connectors, distribution boxes and Slit devices complete one Cable A. This paper will review the general design of the FOCCoS subsystem, methods used to manufacture the involved devices, and the needed tests results to evaluate the total efficiency of the set.
CUBES is a high-efficiency, medium-resolution (R ≃ 20, 000) spectrograph dedicated to the “ground based UV”
(approximately the wavelength range from 300 to 400nm) destined for the Cassegrain focus of one of ESO’s VLT
unit telescopes in 2018/19. The CUBES project is a joint venture between ESO and Instituto de Astronomia,
Geof´ısica e Ciˆencias Atmosf´ericas (IAG) at the Universidade de S˜ao Paulo and the Brazilian Laborat´orio Nacional
de Astrofs´ıca (LNA). CUBES will provide access to a wealth of new and relevant information for stellar as well as
extra-galactic sources. Principle science cases include the study of heavy elements in metal-poor stars, the direct
determination of carbon, nitrogen and oxygen abundances by study of molecular bands in the UV range and the
determination of the Beryllium abundance as well as the study of active galactic nuclei and the inter-galactic
medium. With a streamlined modern instrument design, high efficiency dispersing elements and UV-sensitive
detectors, it will enable a significant gain in sensitivity over existing ground based medium-high resolution
spectrographs enabling vastly increased sample sizes accessible to the astronomical community. We present here
a brief overview of the project, introducing the science cases that drive the design and discussing the design
options and technological challenges.
We present a conceptual design for a high-resolution optical spectrograph appropriate for mounting at Cassegrain on a large aperture telescope. The design is based on our work for the Gemini High Resolution Optical Spectrograph (CUGHOS) project. Our design places the spectrograph at Cassegrain focus to maximize throughput and blue wavelength coverage, delivering R=40,000 resolving power over a continuous 320–1050 nm waveband with throughputs twice those of current instruments. The optical design uses a two-arm, cross-dispersed echelle format with each arm optimized to maximize efficiency. A fixed image slicer is used to minimize optics sizes. The principal challenge for the instrument design is to minimize flexure and degradation of the optical image. To ensure image stability, our opto-mechanical design combines a cost-effective, passively stable bench employing a honeycomb aluminum structure with active flexure control. The active flexure compensation consists of hexapod mounts for each focal plane with full 6-axis range of motion capability to correct for focus and beam displacement. We verified instrument performance using an integrated model that couples the optical and mechanical design to image performance. The full end-to-end modeling of the system under gravitational, thermal, and vibrational perturbations shows that deflections of the optical beam at the focal plane are <29 μm per exposure under the worst case scenario (<10 μm for most orientations), with final correction to 5 μm or better using open-loop active control to meet the stability requirement. The design elements and high fidelity modeling process are generally applicable to instruments requiring high stability under a varying gravity vector.
The SOAR Telescope Echelle Spectrograph - STELES - is part of the Brazilian participation on the 4.1m SOAR
telescope second-generation instrumentation. In view of SOAR´s high image quality and moderately large collecting
area and the near UV capability, it will be able to yield high quality spectroscopic data for a large variety of objects of
astrophysical interests. The spectrograph is a R4 cross-dispersed echelle fed by the SOAR Nasmyth focus, operating in a
quasi-Littrow white pupil configuration, and a resolving power of R ≈ 50,000, covering the 300-900nm spectral range in
STELES is a bench spectrograph which will be mounted vertically on one side of the SOAR Telescope fork. The ninetydegree
inversion of the mechanical components, due to the vertical position of the instrument, plus the close proximity of
most components, due to the spectrograph compactness, were requirements carefully observed during the mechanical
design process. This paper describes the mechanical characteristics of the individual assemblies that make up the
STELES mechanical design. The STELES instrument can be separated into two sections, the fore optics, and the
spectrograph. The fore optics has the mechanisms from the SOAR telescope down to the STELES bench spectrograph,
and the bench spectrograph has the mechanisms for the spectrograph covering the red and blue spectrum.
At least during the last ten years, the Brazilian astronomical community has been asking for an echelle spectrograph for
the 1.6 m telescope installed at Pico dos Dias Observatory (Brazópolis, MG, Brazil, OPD/MCTI/LNA). Among the
scientific cases are topics related to the chemical evolution of the Galaxy, asteroseismology, chemical composition and
chromospheric activities of solar type stars and the relations between solar analogues and terrestrial planets. During 2009
the project finally got started. The called ECHARPE spectrograph (Espectrógrafo ECHelle de Alta Resolução para o
telescópio Perkin-Elmer) is being projected to offer a spectral resolution of R ~ 50000, in the range 390-900 nm and with
a single exposition. It will be a bench spectrograph with two channels: blue and red, fed by two optical fibers (object, sky
or calibration) with aperture of 1.5 or 2.0 arcseconds. The instrument will be placed in one of the telescope pillar
ramification, in the originals installations of a Coudé spectrograph and in a specially created environment controlled
room. In this work we will present the scientific motivations, the conceptual optical design, the expected performance of
the spectrograph, and the status of its development. ECHARPE is expected to be delivered to the astronomical
community in 2014, fully prepared and optimized for remote operations.
ECHARPE spectrograph - Espectrógrafo ECHelle de Alta Resolução para o telescópio Perkin-Elmer - is being
designed at LNA - Laboratório Nacional de Astrofísica, Brazil - to be mounted on 1.60 meter telescope at Pico dos
Dias Observatory, Brazil. It will offer a spectral resolution of R ~ 50000, in the interval 390-900 nm and in a single
exposition. It will be a fiber fed, bench spectrograph with two channels: blue and red, fed by two optical fibers (object,
sky or calibration) with aperture of 1.5 or 2.0 arcseconds. This paper reports on technical characteristics of the
spectrograph mechanical design and presents a new developed mounting system for echelle grating and collimator and
relay mirrors, which allows linear and rotational adjustments in all degrees of freedom without using springs.
The SOAR Integral Field Unit Spectrograph (SIFS) is fed by an integral field unit composed of a bi-dimensional
arrangement of 1300 optical fibers. It has been developed in Brazil by a team of scientists and engineers led by the
National Laboratory of Astrophysics (MCT/LNA) and the Department of Astronomy of the Institute of Astronomy,
Geophysics and Atmospheric Sciences of the University of São Paulo (IAG/USP). It comprises three major subsystems;
a fore-optics installed on the Nasmyth port of the telescope or the SOAR Adaptive Optics Module, a 14-m optical fiber
IFU, and a bench-mounted spectrograph installed on the telescope fork. SIFS is successfully assembled and tested on the
SOAR Telescope in Chile and has now moved to the commissioning phase. This paper reports on technical
characteristics of the mechanical design and the assembly, integration and technical activities.
SIFS is a lenslet/fiber Integral Field Unit Spectrograph which has just been delivered to the SOAR 4.1m telescope in
Chile. The instrument was designed and constructed by the National Laboratory of Astrophysics (MCT/LNA) in
collaboration with the Department of Astronomy of the Institute of Astronomy, Geophysics and Atmospheric Sciences of
the University of Sao Paulo (IAG/USP). It is designed to operate at both the raw Nasmyth and the SAM (the SOAR
Adaptive Optics Module) which delivers GLAO-corrected images in optical wave-bands longward of 500nm. The
lenslets have a 1mm pitch feeding a set of 1,300 fibres in a 26-by-50 format. Sets of deployable fore-optics convert the
f/16.5 input beam to give samplings between ~0.1 and 0.3 arcsec. The fiber output is in the form of a curved, pupil-centric,
long-slit which is fed into a bench-mounted spectrograph. An off-axis Maksutov collimates the beam onto a set
of VPH gratings and thence imaged by an f/3 refractive camera onto a 2-by-1 mosaic of 2k-by-4k E2V CCDs. The
camera is articulated over a >90 deg. angle to allow the grating/camera combination to operate in a transmission Littrow
configuration. The wavelength range is limited by the CCDs to the 350 to 1000nm range with spectral resolution
maxima of ~20,000. The paper will review the optical design of the spectrograph and the methods used to fabricate the
The use of Volume Phase Holographic (VPH) gratings in astronomy is increasing worldwide due to its high efficiency,
flexibility in manufacturing and lower costs. For example 3 of 4 SOAR Telescope spectrographs are based on VPH
gratings. Following the growth in this technology use, tools are needed to characterize these gratings for their physical
and diffraction efficiency properties. We developed, at Laboratorio Nacional de Astrofisica / MCT (LNA), Brazil, an
assembly for characterization of VPH gratings. The relative efficiency of the gratings can be measured for specific
angles or scanned through the grating operation angles. Furthermore surface flatness and mounting stress effects are
measured using interferometric techniques. We present the experiment design and characteristics, describe the
measurement procedures and show the characterization results for some gratings of the SOAR Telescope spectrograph
We present the design of the SOAR Telescope Echelle Spectrograph (STELES). The instrument is part of the Brazilian participation on the 4.1m SOAR telescope second-generation instrumentation. A multi-institutional team is designing the echelle spectrograph with UV capability. In view of its high image quality and moderately large collecting area, SOAR will be able to yield high quality spectroscopic data for a large variety of objects of astrophysical interests. Another point that should be explored in SOAR is the near UV capability, not available in most of the current available high-resolution spectrographs. The proposed spectrograph is a R4 cross-dispersed echelle fed by the SOAR Nasmyth focus, operating in a quasi-Littrow white pupil configuration, and a resolving power of R ~ 50,000, covering the 300-890nm spectral range in one shot.
The concept developed for this spectrograph is based on VPH grating crossdispersers and all spherical optics (including the collimator mirrors). The transfer collimator is mounted in a position so that the 100mm F/8.5 beam is resized to 50mm, allowing very compact cameras design. These modifications on the standard quasi-Littrow, white pupil configuration design yield a very efficient, compact and cheaper spectrograph.
As part of the Brazilian contribution to the 4.2 m SOAR telescope project we are building the Integral Field Unit spectrograph, "SIFUS." With the aim of testing the performance of optical fibers with 50 microns core size on IFUs, we constructed a prototype of the IFU and a spectrograph that were installed at the 1.6 m telescope of the Observatorio do Pico dos Dias (OPD), managed by Laboratorio Nacional de Astrofisica (LNA) in Brazil. The IFU has 512 fibers coupled to a LIMO microlens array (16 x 32) covering a 15" x 30" field on the sky. The spectrograph is a medium resolution instrument, operating in a quasi-Littrow mode. It was based on the design of the SPIRAL spectrograph built by the Anglo-Australian Observatory. The name Eucalyptus was given following the name of the native Australian tree that adapted very well in Brazil and it was given in recognition to the collaboration with the colleagues of the Anglo-Australian Observatory. The instrument first light occurred in the first semester of 2001. The results confirmed the possibility of using the adopted fibers and construction techniques for the SIFUS. We present the features of the instrument, some examples of the scientific data obtained, and the status of the commissioning, calibration and automation plans. The efficiency of this IFU was determined to be 53% during telescope commissioning tests.
We present the project of an optical spectrograph equipped with a 1300-element Integral Field Unit (IFU), that will be one of the main instruments of the SOAR (4m) telescope. The instrument consists of two separate parts, the fore-optics and the bench spectrograph, that are connected by an 11 m long fiber bundle. The fore optics system is installed at one of the Nasmyth focii of the telescope, and
produces an image of the observed object on a 26x50 array of square microlenses, each 1 mm x 1 mm lens feeding one fiber. The fibers have 50 micron cores, and are aligned at the entrance of bench spectrograph to form a slit that feeds a 100 mm beam collimator.
A set of Volume Phase-Holographic (VPH) transmission gratings can be interchanged by remote control, providing a choice of resolution and wavelength coverage. The spectrograph is tunable over the wavelength range 350 to 1000 nm, with resolution R from about 5000 to 20000. This spectrograph is ideally suited for high spatial resolution studies, with a sampled area of the sky 8" x 15", with 0.30" per microlens, in the mode to be used with the tip-tilt correction of SOAR. The project has been approved at the Project Design Review and the spectrograph is presently being constructed.