Clemens D. Gneiding

A new concept for echelle spectrographs: the SOAR Telescope Echelle 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.

Studying focal ratio degradation of optical fibers for Subaru's Prime Focus Spectrograph

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.

The SOAR integral field unit spectrograph optical design and IFU implementation

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 lenslet/fiber IFU.

ECHARPE mechanical design

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.

Astrometric and photometric study of Dias 4, Dias 6, and other five open clusters using ground-based and Gaia DR2 data

We present a study of 7 southern open clusters based on UBVRI CCD photomety (Johnsons-Cousins system) and Gaia DR2 data. Dias 4, Dias 6 and four other clusters had UBVRI photometric observations determined for the first time. From the observational UBVRI data we obtained photometric membership probability estimates and, using the proper motions from the UCAC5 catalog, we also determined the kinematic membership. From Gaia DR2 astrometric data we determine the stellar membership using proper motions and parallaxes, taking into account the full covariance matrix. For both independent sets of data and membership we apply our non subjective multidimensional global optimization tool to fit theoretical isochrones to determine the distance, age, reddening, metallicity and binary fraction of the clusters. The results of the mean proper motions, distances and ages are in agreement, but the ones obtained from Gaia DR2 data are more precise in both membership selection and estimated parameters. In the case of NGC 6087, the Cepheid S Nor, member of the open cluster, was used to obtain an independent distance estimate, confirming the one determined by our fitting method. We also report a serendipitous discovery of two new clusters in the extended field near what was originally Dias 4.

Developing a new technology in the construction of fiber lenslet IFUs

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.

Temperature control system for optical elements in astronomical instrumentation

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.

Introducing CUBES: the Cassegrain U-band Brazil-ESO spectrograph

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.

A conceptual design for a Cassegrain-mounted high-resolution optical spectrograph for large-aperture telescopes

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.

STELES mechanical design

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 one shot. 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.