The High Efficiency and Resolution Multi Element Spectrograph, HERMES is an optical spectrograph designed
primarily for the GALAH, Galactic Archeology Survey, the first major attempt to create a detailed understanding of
galaxy formation and evolution by studying the history of our own galaxy, the Milky Way<sup>1</sup>. The goal of the GALAH
survey is to reconstruct the mass assembly history of the of the Milky way, through a detailed spatially tagged
abundance study of one million stars in the Milky Way. The spectrograph will be based at the Anglo Australian
Telescope (AAT) and be fed with the existing 2dF robotic fibre positioning system. The spectrograph uses VPH-gratings
to achieve a spectral resolving power of 28,000 in standard mode and also provides a high resolution mode ranging
between 40,000 to 50,000 using a slit mask. The GALAH survey requires a SNR greater than 100 aiming for a star
brightness of V=14. The total spectral coverage of the four channels is about 100nm between 370 and 1000nm for up to
392 simultaneous targets within the 2 degree field of view.
Current efforts are focused on manufacturing and integration. The delivery date of spectrograph at the telescope is
scheduled for 2013. A performance prediction is presented and a complete overview of the status of the HERMES
spectrograph is given. This paper details the following specific topics:
The approach to AIT, the manufacturing and integration of the large mechanical frame, the opto-mechanical slit
assembly, collimator optics and cameras, VPH gratings, cryostats, fibre cable assembly, instrument control hardware and
software, data reduction.
The Australian Astronomical Observatory (AAO) has recently completed a feasibility study for a fiber-positioner facility proposed for the Giant Magellan Telescope (GMT), called MANIFEST (the Many Instrument Fiber System). The MANIFEST instrument takes full advantage of the wide-field focal plane to efficiently feed other instruments. About 2000 individually deployable fiber units are envisaged, with a wide variety of aperture types (single-aperture, image- or pupil-slicing, IFU). MANIFEST allows (a) full use of the GMT's 20' field-of-view, (b) a multiplexed IFU capability, (c) greatly increased spectral resolution via image-slicing, (d) the possibility of OH-suppression in the near-infrared.
The next generation of large ground-based optical and infrared telescopes will provide new challenges for designers of
astronomical instrumentation. The varied science cases for these extremely large telescopes (ELTs) require a large
range of angular resolutions, from near diffraction-limited performance via correction of atmospheric turbulence using
adaptive optics (AO), to seeing-limited observations. Moreover, the scientific output of the telescopes must also be
optimized with the consideration that, with current technology, AO is relatively ineffective at visible wavelengths, and
that atmospheric conditions will often preclude high-performance AO. This paper explores some of the issues that arise
when designing ELT instrumentation that operates across a range of angular-resolutions and wavelengths. We show
that instruments designed for seeing-limited or seeing-enhanced observations have particular challenges in terms of size
and mass, while diffraction-limited instruments are not as straightforward as might be imagined.
The Very Large Telescope Interferometer (VLTI) on Cerro Paranal (2635 m) in Northern Chile reached a major milestone in September 2003 when the mid infrared instrument MIDI was offered for scientific observations to the community. This was only nine months after MIDI had recorded first fringes. In the meantime, the near infrared instrument AMBER saw first fringes in March 2004, and it is planned to offer AMBER in September 2004.
The large number of subsystems that have been installed in the last two years - amongst them adaptive optics for the 8-m Unit Telescopes (UT), the first 1.8-m Auxiliary Telescope (AT), the fringe tracker FINITO and three more Delay Lines for a total of six, only to name the major ones - will be described in this article. We will also discuss the next steps of the VLTI mainly concerned with the dual feed system PRIMA and we will give an outlook to possible future extensions.
Designs for Extremely Large Telescopes (ELTs) are quite well advanced, but the requirements of instruments have had limited impact. Since provision of a suitable environment for instruments is a critical aspect of all telescopes, we outline some well-known and some less-appreciated challenges of designing instruments for ELTs. A wide-field spectrometer (WFSPEC) with ~10 arcmin field-of-view, probably with AO correction of ground-layer seeing, illustrates the well-known difficulty of matching modern detector pixels to large (~0."3) images. The challenges of exploiting wide-field (1'-2' FOV) high-performance AO systems on ELTs are illustrated by a Multi-Object Multi-field Spectrometer and Imager (MOMSI), which provides imaging and integral-field spectroscopy, at near-diffraction-limited pixel scales, of targets in approximately 300 subfields each. This instrument, roughly equivalent to all the astronomical spectrometers yet built, extracts ~200 times less of the available information from the ELT's FOV than near-future instruments on 8-m class telescopes will do for their hosts. We emphasise the great size of such instruments (40-100 tonnes, 100-200 m3) and the need to accommodate this size in telescope plans. A third area of challenge is the exploitation of the potential capabilities of ELTs in the mid-IR, where they would offer powerful complements to JWST and ALMA; low-emissivity telescope designs and, possibly, cryogenic AO, may be needed. Finally, we outline the potential challenges of correcting atmospheric dispersion effects.
Based on expected Science Drivers for a 60 to 100-m diameter OWL-class telescope, we derive the basic instrumental capabilities that are needed to address them effectively. They come in three flavors -viz. an extremely high-contrast fully diffraction-limited spectro-imager, a cryogenic AO-assisted imager and multi-integral field spectrometer. Their highest priority wavelength range lies in the near-IR. In terms of size and technical requirements, these instruments belong to a quite similar class than instruments currently being developed for the 8-10 m telescopes. This places them hopefully in the feasible category, even if already rather challenging. A big caveat however is that enlarging the imaging field or the spectrometer multiplex would require large clusters of these basic “bricks”. The requirements on the adaptive optics correction are stringent and call for a close and careful integration between the telescope adaptive optics systems and the instruments. We also introduce here, as a relevant example of a new observational strategy, an instrument focused on a specific scientific program - the direct measurement of the acceleration of the Universe at different epochs via the Lyα forest in QSO spectra. Being able to host dedicated facilities of this type, used for a specific observing programs in a CERN experiment-like fashion, is deemed essential to ensure that the giant telescopes of the future get and stay at the cutting edge of research in the next decade and beyond. Finally, we comment briefly on the articulation between the development of generic instrument concepts for ELTs in the frame of the European ELT Design Study and their adaptation to the OWL case.
Progress in the conceptual design phase of ESO's OWL 100-m optical and near-infrared telescope is reported, with emphasis on the development of the science case. The Phase A opto-mechanical design is now basically completed, and provides a clean, symmetrical geometry of the pupil, with a near-circular outer edge. We also report about the latest outcome of industrial studies, introduce the essential definition of the wavefront control systems, and outline operational concepts and instruments priorities. Finally, we elaborate on the favorable cost factors associated to the telescope design, its compatibility with low industrial risks, and argue that progressive implementation allows for competitive timescales. In particular, we show that suitable fabrication and integration schemes should accommodate for a start of science operation at unequalled potential and within a time frame comparable to that of smaller designs, while at the same time maximizing R&D time for critical subsystems.
SINFONI is an adaptive optics assisted near-infrared integral field spectrometer for the ESO VLT. The Adaptive OPtics Module (built by the ESO Adaptive Optics Group) is a 60-elements curvature-sensor based system, designed for operations with natural or sodium laser guide stars. The near-infrared integral field spectrometer SPIFFI (built by the Infrared Group of MPE) provides simultaneous spectroscopy of 32 x 32 spatial pixels, and a spectral resolving power of up to 3300. The adaptive optics module is in the phase of integration; the spectrometer is presented tested in the laboratory. We provide an overview of the project, with particular emphasis on the problems encountered in designing and building an adaptive optics assisted spectrometer.
Multi-Conjugate Adaptive Optics (MCAO) is working on the principle to perform wide field of view atmospheric turbulence correction using many Guide Stars located in and/or surrounding the observed target. The vertical distribution of the atmospheric turbulence is reconstructed by observing several guide stars and the correction is applied by some deformable mirrors optically conjugated at different altitudes above the telescope.
The European Southern Observatory together with external research institutions is going to build a Multi-Conjugate Adaptive Optics Demonstrator (MAD) to perform wide field of view adaptive optics correction. The aim of MAD is to demonstrate on the sky the feasibility of the MCAO technique and to evaluate all the critical aspects in building such kind of instrument in the framework of both the 2nd generation VLT instrumentation and the 100-m telescope OWL.
In this paper we present the conceptual design of the MAD module that will be installed at one of the VLT unit telescope in Paranal to perform on-sky observations. MAD is based on a two deformable mirrors correction system and on two multi-reference wavefront sensors capable to observe simultaneously some pre-selected configurations of Natural Guide Stars. MAD is expected to correct up to 2 arcmin field of view in K band.
Preliminary requirements and possible technological solutions for the next generation of ground-based optical telescopes were laid down at ESO in 1998. Since then, a phase A study has been commissioned, the objective of which is to produce a conceptual design compatible, to the maximum possible extent, with proven technology, and establish realistic plans for detailed design, site selection, construction and operation for a 100-m class optical, diffraction-limited telescope. There was no doubt about how daunting such a challenge would be, but, somewhat surprisingly, it turns out to be firmly confined to adaptive optics concepts and technologies. The telescope itself appears to be feasible within the allocated budget and without reliance on exotic assumptions. Fabrication of key subsystems is fully within the reach of a properly engineered, industrialized process. A consolidated baseline is taking shape, and alternative system and subsystem solutions are being explored, strengthening the confidence that requirements could be met. Extensive development of wavefront measurement techniques enlarges the palette of solutions available for active wavefront control of a segmented, active telescope. At system level, ESO is developing enabling experiments to validate multi-conjugate adaptive optics (MAD for Multi-conjugate Adaptive optics Demonstrator) and telescope wavefront control (APE, for Active Phasing Experiment).
Superb quality small Volume Phase Holographic Gratings are available and in operation at ESO. Compared to Surface Relief Transmission Gratings, they have better efficiencies at high dispersion. Their role at ESO would/will expand with larger sizes, high index modulation (larger bandwidth; access to the near-IR domain), cooled operation (also for the near-IR) and the articulated spectrograph approach (higher dispersion & efficiency than with Grisms).
The VIRMOS consortium of French and Italian Institutes is manufacturing 2 wide field imaging multi-object spectrographs for the European Southern Observatory Very Large Telescope, with emphasis on the ability to carry over spectroscopic surveys of large numbers of sources. The Visible Multi-Object Spectrograph, VIMOS, is covering the 0.37 to 1 micron wavelength domain, with a full field of view of 4 by 7 by 8 arcmin<SUP>2</SUP> in imaging and MOS mode. The Near IR Multi-Object Spectrograph, NIRMOS, is covering the 0.9 to 1.8 microns wavelength range, with afield of view 4 by 6 by 8 arcmin<SUP>2</SUP> in MOS mode. The spectral resolution for both instrument scan reach up to R equals 5000 for a 0.5 arcsec wide slit. Multi-slit masks are produced by a dedicated Mask Manufacturing Machine cutting through thin Invar sheets and capable of producing 4 slit masks approximately 300 by 300 mm each with approximately slits 5.7 mm long in less than one hour. Integral field spectroscopy is made possible in VIMOS by switching in the beam specially build masks fed by 6400 fibers coming form a 54 by 54 arcsec<SUP>2</SUP> integral field head with a 80 by 80 array of silica micro-lenses. NIRMOS has a similar IFS unit with a field of 30 by 30 arcmin<SUP>2</SUP>. These instruments are designed to offer very large multiplexing capabilities. In MOS mode, about 1000 objects can be observed simultaneously with VIMOS, with a S/N equals 10 obtained on galaxies with I equals 24 in one hour, and approximately 200 objects can be observed simultaneously with NIRMOS, with a S/N equals 10 obtained don galaxies with J equals 22, H equals 20.6 in 1h at R<SUB>eq</SUB> equals 200. We present here the status of VIMOS, currently under final integration, with expected first light in the summer 2000, together with the final design of NIRMOS presented at the Final Design Review. The VLT-VIRMOS deep redshift survey of more with the final design of NIRMOS presented at the Final Design Review. The VLT-VIRMOS deep redshift survey of more than 150000 galaxies over the redshift range 0 < z < 5 will be undertaken based on 120 guaranteed nights awarded to the project.
The paper deals with the global approach in place at ESO to optimize observing efficiency at the VLT. It involves not only the telescopes and their associated instrumentation, but as a mater of fact the whole observing process from proposals to data distribution. The ten main avenues pursued to reach that goal are presented, and early experience at Paranal Observatory reported. The need for continuous renewal of instrument complements at large telescope facilities is stressed.
In this paper, we describe a concept of multiple laser guide stars system based on tomographic reconstruction and multi- conjugate correction for 8-m class telescopes. We show that this type of adaptive optics (AO) systems can be considered as the next generation of AO systems for 8-m telescopes and represents a necessary intermediate step toward AO systems for Extremely Large Telescopes. Multiple guide stars allow to correct the cone effect which affects single LGS systems and prevents from going to wavelengths shorter than approximately 1 micrometer. With 4 LGS plus 1 NGS, it is expected that correction with a high Strehl can be obtained at least in the R and I bands, with an extended corrected field of view (FOV). An analytic AO model is used to assess the expected on-axis performance. Using recent results on 3D mapping of turbulence (i.e. tomography), we estimate the sky coverage of such a system. We also discuss the implications of a large corrected field of view on the system design: large wavefront sensor field, constrains on the optics and deformable mirrors, and size of the science detector. With an MCAO system, large telescopes would be able to observe faint extragalactic objects and wide crowded fields (2 arcmin) at the diffraction limit.
We describe the current activity at ESO on Curvature Adaptive Optics Systems. The strategy, aimed at implementing several system via a cloning process, will allow faster production time,lower costs and better maintenance. Curvature systems fulfill the performance requirements for NIR spectroscopy and interferometry at the VLT, for which AO is requested. This development and the systems described are complementary to the foreseen ESO high NIR Strehl Ratio Ao system, NAOS in combination with the camera CONICA.
SINFONI, the SINgle Faint Object Near-IR Investigation, is an instrument for the very large telescope, designed to provide spectroscopy at the telescope diffraction limit in the near-IR. This unique capability is achieved by combining two state-of-the-art developments, an integral field spectrometer and a curvature sensor based adaptive optics system. SINFONI is a collaborative effort by the Max-Planck- Institut fuer extraterrsetrische Physik and the European Southern Observatory.
We explore the scientific case and the conceptual feasibility of giant filled aperture telescopes, in the light of science goals needing an order of magnitude increase in aperture size, and investigate the requirements (and challenges) these imply for possible technical options in the case of a 100 m telescope. The 100-m f/6.4 telescope optical concept is of a four mirror design with segmented, spherical primary and secondary mirrors, and 8-m class aspheric tertiary and quaternary mirrors, providing a 3 arc minutes field of view. Building on the experience of the VLT and other large telescope projects, we investigate mirror fabrication issues, a possible mechanical solution, the requirements for the absolutely essential adaptive optics system and for the instrumentation package, and the implications for budget and schedule.
Instrumentation packages for the new generation of 8 m. class Telescopes aim at delivering global observational capabilities in the most effective way: (1) technically, with 'perfect' individual instruments, (2) observationally with extensive covering of the parameter space and most of the instruments tailored to specific classes of astronomical targets, (3) operationally with reliable, automatic, fast systems linked with an 'adapted-observing' scheduler, and finally, (4) scientifically with flexible observing strategies and target finding capabilities. The ESO VLT with four Unit Telescopes and twelve foci, all but one equipped with a (quasi) permanently mounted instrument, offers a good ground for this challenging task.
Since the digital detectors (like CCDs) presently available for astronomical instruments have two dimensions only, there is an obvious problem for obtaining detailed spectroscopic information on extended astronomical objects (e.g. active galaxies, regions of star formation, globular clusters, etc.); the classical long- slit spectrographic techniques are grossly inadequate. Several so-called integral field spectrographs (IFS) have been used at the Canada-France-Hawaii telescope during the past years to improve this situation. They typically provide hundreds of spectra in a small (approximately 10' by 10') field with a subarcsecond spatial resolution capability and hundreds of spectral elements, both simultaneously accessed. We describe these various instruments and their present performances, review a few illustrative results obtained with CFH telescope and discuss the expected developments: use of IFS in combination with adaptive optics systems for the study of individual objects at spatial resolution near the 0.1' level, as well as their potential capabilities on Very Large Telescopes, with or without adaptive optics.
A photon counting wavefront curvature sensor (WFS) with 13 subapertures suitable for adaptive optics in astronomy has been developed at the University of Hawaii. This sensor is capable of using very faint point sources or slightly extended sources to derive the wavefront signal. The sensitivity of this sensor is continuously variable and can be adjusted in real time to match the seeing conditions at the time. The wavefront sampling geometry has been optimized for correcting the standard atmosphere up to 9 orders expressed in terms of Zernike's. Its output is used in conjunction with a newly developed deformable bimorph mirror for high efficiency correction capabilities. This WFS has successfully been used recently at the CFHT and UKIRT facilities on Mauna Kea on a variety of astronomical objects. Point sources, double stars, planetary nebula, galactic nuclei, and some of the moons of Jupiter have all been successfully attempted. Limiting magnitude has not been explored in great detail at the telescope, but we have taken the system down to magnitude R equals 13.7 (V equals 15) with a 3.6 meter aperture with success. This was achieved during bright time or whilst the full moon was present.
The Canada-France-Hawaii Telescope has undertaken the development of an Adaptive Optic bonette for general use at its telescope. There will be separate mirrors for tip-tilt and for higher order corrections. A 19 element curvature wavefront sensor will be used with a bimorph (19 electrodes) deformable mirror. Modal control will be used in order to optimize the number of modes corrected according to the atmospheric turbulence coherence time and brightness of the reference source. The optical design minimizes the number of reflections by using off-axis mirrors. It is planned that various instruments such as CCD cameras, IR cameras and integral field Spectrographs (TIGER type) will be used. At this point phase A design studies have been completed and fabrication has started.