The MOONS (Multi-Object Optical and Near-infrared Spectrograph) is a twin, fibre-fed spectrograph for the VLT. Each spectrograph is fed with 512 fibres, the light from which is dispersed into three arms covering the RI, YJ and H bands. A separate camera is provided for each band, requiring six cameras to be produced and individually aligned. All six cameras have been assembled, aligned and cryogenically tested. The RI and YJ cameras, have been successfully integrated into the MOONS instrument cryostat and two more, including at least one of the H-band cameras are expected to be fitted for the next cool-down. Following an overview of the optical design of the camera, this paper presents the mechanical design together with stray light analysis and the inclusion of baffling. Six sets of optics have been provided by Bertin Winlight and an overview of their metrology data is presented. After assembly and pre-alignment of the first set of optics into the camera housing, a series of static and dynamic tests were carried out to ensure that the optics would remain in alignment following handling, transportation and ESO specified earthquake conditions. The pre-alignment stage and subsequent mechanical tests are described together with results from displacement and impulse testing. Because of the steep aspheric surfaces of the camera optics each set must be aligned in tilt and de-space at cryogenic temperatures. The facility specifically designed to accommodate the cryogenic alignment and stability testing of the MOONS cameras is presented and the fine alignment process under both warm and cryogenic conditions is described. Results from the final alignment stage and the stability of alignment under cryogenic cooling are presented and discussed.
The Multi Object Optical and Near-infrared Spectrograph (MOONS) instrument is the next generation multi-object spectrograph for the VLT. This powerful instrument will combine for the first time: the large collecting power of the VLT with a high multipexing capability offered by 1000 optical fibres moved with individual robotic positioners and a novel, very fast spectrograph able to provide both low- and high-resolution spectroscopy simultaneously across the wavelength range 0.64μm - 1.8μm. Such a facility will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic, Extragalactic and Cosmological studies. Th final assembly, integration and verification phase of the instrument is now about to start performance testing.
After completion of its final-design review last year, it is full steam ahead for the construction of the MOONS instrument - the next generation multi-object spectrograph for the VLT. This remarkable instrument will combine for the first time: the 8 m collecting power of the VLT, 1000 optical fibres with individual robotic positioners and both medium- and high-resolution spectral coverage acreoss the wavelength range 0.65μm - 1.8 μm. Such a facility will allow a veritable host of Galactic, Extragalactic and Cosmological questions to be addressed. In this paper we will report on the current status of the instrument, details of the early testing of key components and the major milestones towards its delivery to the telescope.
The first generation of E-ELT instruments will include an optic-infrared High Resolution Spectrograph, conventionally indicated as EELT-HIRES, which will be capable of providing unique breakthroughs in the fields of exoplanets, star and planet formation, physics and evolution of stars and galaxies, cosmology and fundamental physics. A 2-year long phase A study for EELT-HIRES has just started and will be performed by a consortium composed of institutes and organisations from Brazil, Chile, Denmark, France, Germany, Italy, Poland, Portugal, Spain, Sweden, Switzerland and United Kingdom. In this paper we describe the science goals and the preliminary technical concept for EELT-HIRES which will be developed during the phase A, as well as its planned development and consortium organisation during the study.
MOONS (Multi-Object Optical and Near-infrared Spectrograph for the VLT) is entering into the final design phase. This paper presents and discusses the latest proposed version of the optical design of the cryogenic spectrograph. The main developments and modifications were aimed at minimizing the overall size and mass of the cryogenic spectrograph. The most remarkable new feature is the design of an extremely fast (F/0.95), light and compact (40 kg in less than 80 dm3) camera with superb image quality over a very large field of view (9 degrees on a collimated beam of 265 mm). The camera consists of only three optical elements: two lenses and one mirror. All elements are made of fused-silica. The optical performances are independent on the temperature, i.e. the camera can be fully characterized at room temperatures.
The current instrumentation plan for the E-ELT foresees a High Resolution Spectrograph conventionally indicated as
HIRES. Shaped on the study of extra-solar planet atmospheres, Pop-III stars and fundamental physical constants, HIRES
is intended to embed observing modes at high-resolution (up to R=150000) and large spectral range (from the blue limit to the K band) useful for a large suite of science cases that can exclusively be tackled by the E-ELT. We present in this
paper the solution for HIRES envisaged by the "HIRES initiative", the international collaboration established in 2013 to
pursue a HIRES on E-ELT.
This paper presents the latest optical design for the MOONS triple-arm spectrographs. MOONS will be a Multi-Object
Optical and Near-infrared Spectrograph and will be installed on one of the European Southern Observatory (ESO) Very
Large Telescopes (VLT). Included in this paper is a trade-off analysis of different types of collimators, cameras,
dichroics and filters.
We present a new type of R-θ fiber actuator named PotsPos for multi-object astronomical spectroscopy. It was initially intended to use as an alternative positioner design for the 4-meter Multi-Object Spectroscopic Telescope (4MOST). Although another tilting spine technology developed by the Australian Astronomical Observatory (AAO) is currently chosen for the 4MOST, PotsPos design has some technical advantages over other positioning technologies and might therefore be an attractive choice for future spectrographs. The design would be similar in positioning capabilities to the tilting spine design but would not suffer from telecentricity and defocus errors. The mechanical design, suitable motors, computational results from dynamic simulations and finite element analyses are presented.
The 4MOST[1] instrument is a concept for a wide-field, fibre-fed high multiplex spectroscopic instrument facility on the
ESO VISTA telescope designed to perform a massive (initially >25x106 spectra in 5 years) combined all-sky public
survey. The main science drivers are: Gaia follow up of chemo-dynamical structure of the Milky Way, stellar radial
velocities, parameters and abundances, chemical tagging; eROSITA follow up of cosmology with x-ray clusters of
galaxies, X-ray AGN/galaxy evolution to z~5, Galactic X-ray sources and resolving the Galactic edge;
Euclid/LSST/SKA and other survey follow up of Dark Energy, Galaxy evolution and transients. The surveys will be
undertaken simultaneously requiring: highly advanced targeting and scheduling software, also comprehensive data
reduction and analysis tools to produce high-level data products. The instrument will allow simultaneous observations of
~1600 targets at R~5,000 from 390-900nm and ~800 targets at R<18,000 in three channels between ~395-675nm
(channel bandwidth: 45nm blue, 57nm green and 69nm red) over a hexagonal field of view of ~ 4.1 degrees. The initial
5-year 4MOST survey is currently expect to start in 2020. We provide and overview of the 4MOST systems: optomechanical,
control, data management and operations concepts; and initial performance estimates.
4MOST is a wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of the European Southern Observatory (ESO). Its main science drivers are in the fields of galactic archeology, high-energy physics, galaxy evolution and cosmology. 4MOST will in particular provide the spectroscopic complements to the large
area surveys coming from space missions like Gaia, eROSITA, Euclid, and PLATO and from ground-based facilities like VISTA, VST, DES, LSST and SKA. The 4MOST baseline concept features a 2.5 degree diameter field-of-view with ~2400 fibres in the focal surface that are configured by a fibre positioner based on the tilting spine principle. The fibres feed two types of spectrographs; ~1600 fibres go to two spectrographs with resolution R<5000 (λ~390-930 nm) and
~800 fibres to a spectrograph with R>18,000 (λ~392-437 nm and 515-572 nm and 605-675 nm). Both types of spectrographs are fixed-configuration, three-channel spectrographs. 4MOST will have an unique operations concept in which 5 year public surveys from both the consortium and the ESO community will be combined and observed in parallel during each exposure, resulting in more than 25 million spectra of targets spread over a large fraction of the
southern sky. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing
concept. 4MOST has been accepted for implementation by ESO with operations expected to start by the end of 2020.
This paper provides a top-level overview of the 4MOST facility, while other papers in these proceedings provide more
detailed descriptions of the instrument concept[1], the instrument requirements development[2], the systems engineering implementation[3], the instrument model[4], the fibre positioner concepts[5], the fibre feed[6], and the spectrographs[7].
P1640 high contrast imaging system on the Palomar 200 inch Telescope consists of an apodized-pupil Lyot coronagraph, the PALM-3000 adaptive optics (P3K-AO), and P1640 Calibrator (CAL). Science images are recorded by an integral field spectrograph covering J-H bands for detecting and characterizing stellar companions. With aberrations from atmosphere corrected by the P3K-AO, instrument performance is limited mainly by the quasi-static speckles due to noncommon path wavefront aberrations for the light to propagate to the P3K-AO wavefront sensor and to the coronagraph mask. The non-common path wavefront aberrations are sensed by CAL, which measures the post-coronagraph E-field using interferometry, and can be effectively corrected by offsetting the P3K-AO deformable mirror target position accordingly. Previously, we have demonstrated using CAL measurements to correct high order wavefront aberrations, which is directly connected to the static speckles in the image plane. Low order wavefront, on the other hand, usually of larger amplitudes, causes light to leak through the coronagraph making the whole image plane brighter. Knowledge error in low order wavefront aberrations can also affect the estimation of the high order wavefront. Even though, CAL is designed to sense efficiently high order wavefront aberrations, the low order wavefront front can be inferred with less sensitivity. Here, we describe our method for estimating both low and high order wavefront aberrations using CAL measurements by propagating the post-coronagraph E-field to a pupil before the coronagraph. We present the results from applying this method to both simulated and experiment data.
The Project 1640 instrument on the 200-inch Hale telescope at Palomar Observatory is a coronagraphic instru- ment with an integral eld spectrograph at the back end, designed to nd young, self-luminous planets around nearby stars. To reach the necessary contrast for this, the PALM-3000 adaptive optics system corrects for fast atmospheric speckles, while CAL, a phase-shifting interferometer in a Mach-Zehnder con guration, measures the quasistatic components of the complex electric eld in the pupil plane following the coronagraphic stop. Two additional sensors measure and control low-order modes. These eld measurements may then be combined with a system model and data taken separately using a white-light source internal to the AO system to correct for both phase and amplitude aberrations. Here, we discuss and demonstrate the procedure to maintain a half-plane dark hole in the image plane while the spectrograph is taking data, including initial on-sky performance.
The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim to develop a wide-field ( < 3 square degree, goal < 5 square degree), high-multiplex ( < 1500 fibres, goal 3000 fibres) spectroscopic survey facility for an ESO 4m-class telescope (VISTA). 4MOST will run permanently on the telescope to perform a 5 year public survey yielding more than 20 million spectra at resolution R∼5000 (λ=390–1000 nm) and more than 2 million spectra at R~20,000 (395–456.5 nm and 587–673 nm). The 4MOST design is especially intended to complement three key all-sky, space-based observatories of prime European interest: Gaia, eROSITA and Euclid. Initial design and performance estimates for the wide-field corrector concepts are presented. Two fibre positioner concepts are being considered for 4MOST. The first one is a Phi-Theta system similar to ones used on existing and planned facilities. The second one is a new R-Theta concept with large patrol area. Both positioner concepts effectively address the issues of fibre focus and pupil pointing. The 4MOST spectrographs are fixed configuration two-arm spectrographs, with dedicated spectrographs for the high- and low-resolution fibres. A full facility simulator is being developed to guide trade-off decisions regarding the optimal field-of-view, number of fibres needed, and the relative fraction of high-to-low resolution fibres. The simulator takes mock catalogues with template spectra from Design Reference Surveys as starting point, calculates the output spectra based on a throughput simulator, assigns targets to fibres based on the capabilities of the fibre positioner designs, and calculates the required survey time by tiling the fields on the sky. The 4MOST consortium aims to deliver the full 4MOST facility by the end of 2018 and start delivering high-level data products for both consortium and ESO community targets a year later with yearly increments.
P1640 calibrator is a wavefront sensor working with the P1640 coronagraph and the Palomar 3000 actuator
adaptive optics system (P3K) at the Palomar 200 inch Hale telescope. It measures the wavefront by interfering
post-coronagraph light with a reference beam formed by low-pass filtering the blocked light from the coronagraph
focal plane mask. The P1640 instrument has a similar architecture to the Gemini Planet Imager (GPI) and its
performance is currently limited by the quasi-static speckles due to non-common path wavefront errors, which
comes from the non-common path for the light to arrive at the AO wavefront sensor and the coronagraph mask.
By measuring the wavefront after the coronagraph mask, the non-common path wavefront error can be estimated
and corrected by feeding back the error signal to the deformable mirror (DM) of the P3K AO system. Here, we
present a first order wavefront estimation algorithm and an instrument calibration scheme used in experiments
done recently at Palomar observatory. We calibrate the P1640 calibrator by measuring its responses to poking
DM actuators with a sparse checkerboard pattern at different amplitudes. The calibration yields a complex
normalization factor for wavefront estimation and establishes the registration of the DM actuators at the pupil
camera of the P1640 calibrator, necessary for wavefront correction. Improvement of imaging quality after feeding
back the wavefront correction to the AO system demonstrated the efficacy of the algorithm.
Project 1640, a high-contrast spectral-imaging effort involving a coordinated set of instrumentation and software, built at
AMNH, JPL, Cambridge and Caltech, has been commissioned and is fully operational. This novel suite of
instrumentation includes a 3388+241-actuator adaptive optics system, an optimized apodized pupil Lyot coronagraph, an
integral field spectrograph, and an interferometric calibration wave front sensor. Project 1640 is the first of its kind of
instrumentation, designed to image and characterize planetary systems around nearby stars, employing a variety of
techniques to break the speckle-noise barrier. It is operational roughly one year before any similar project, with the goal
of reaching a contrast of 10-7 at 1 arcsecond separation. We describe the instrument, highlight recent results, and
document on-sky performance at the start of a 3-year, 99-night survey at the Palomar 5-m Hale telescope.
A non-redundant pupil mask placed in front of a low-resolution integral field spectrograph (IFS) adds a spectral dimension to high angular resolution imaging behind adaptive optics systems. We demonstrate the first application of this technique, using the spectroscopic binary star system β CrB as our target. The mask and IFS combination enabled us to measure the first low-resolution spectrum of the F3-F5 dwarf secondary component of β CrB, at an angular separation 141 mas from its A5-A7Vp primary star. To record multi-wavelength closure phases, we collected interferograms simultaneously in 23 spectral channels spanning the J and H bands (1.1 μm-1.8 μm), using the Project 1640 IFS behind the 249-channel PalAO adaptive optics system on the Hale telescope at Palomar Observatory. In addition to providing physical information about the source, spectrally resolved mask fringes have the potential to enhance detection limits over single filter observations. While the overall dynamic range of our observation suffers from large systematic calibration errors, the information gleaned from the full channel range improves the dynamic range by a factor of 3 to 4 over the best single channel.
In July 2008, a new integral field spectrograph and a diffraction limited, apodized-pupil Lyot coronagraph was installed behind the adaptive optics system at the Hale 200-inch telescope at Palomar. This instrument serves as the basis of a long-term observational program in high-contrast imaging. The technical goal is to utilize the spectral nature of speckle noise to overcome it. The coronagraph alone will achieve an initial dynamic range of 10-5 at 1", with first light in mid-2008, without speckle noise suppression. Initial work indicates that spectral speckle suppression will provide a factor of 10 to 100 improvement over this. Such sensitivity provides detection and low resolution spectra of young planets of several Jupiter masses around young stars within 25 pc. The spectrograph obtains 32 images across the J and H bands (1.05 - 1.75 &mgr;m), with a spectral resolution of 30-100. The image plane is subdivided by a 200 x 200 element micro-lenslet array with a plate scale of 21 mas per lenslet, diffraction-limited at 1.0 &mgr;m. Data is collected with a 2048 x 2048 pixel Rockwell Hawaii-II HgCdTe infrared detector cooled with liquid Nitrogen. This system is the first of a new generation of apodized pupil coronagraphs combined with high-order adaptive optics and integral field spectrographs.
A key instrument for an Extremely Large Telescope (ELT) is likely to be multi-object spectrometer which observes at least 100 discrete sources with diffraction limited spatial resolution and moderate spectral resolution in the wavelength region from 1.0 to 2.5 μm. Such an instrument has been chosen as the principal driver for the Smart Focal Planes technology development project which has brought together 14 companies and institutes in Europe and Australia. An overview of a new ELT instrument concept based upon beam manipulators (including novel 'starbug' miniature robots) is presented; supported by a summary of scientific goals and systems requirements. Progress made on specific support technology studies is also presented, including work on image slicer replication and cryogenic reconfigurable slits.
The Cambridge Infra-red Panoramic Survey Spectrograph (CIRPASS) is described. This near-infrared (NIR) spectrograph has been used on the 8m Gemini-South Telescope, the 3.9m Anglo-Australian Telescope (AAT) and the 4.2m William Herschel Telescope (WHT). Its performance in both integral field mode and multi-object mode is discussed and some scientific highlights are presented. A multi-IFU system, which is currently under construction, is also described.
DAzLE is a near infrared narrowband differential imager being built by the Institute of Astronomy, Cambridge, in collaboration with the Anglo-Australian observatory. It is a special purpose instrument designed with a sole aim; the detection of redshifted Lyman-α emission from star forming galaxies at z>7. DAzLE will use pairs of high resolution (R=1000) narrowband filters to exploit low background 'windows' in the near infrared sky emission spectrum. This will enable it to reach sensitivities of ~2 x 10-21Wm-2, thereby allowing the detection of z>7 galaxies with star formation rates as low as a few solar masses per year. The design of the instrument, and in particular the crucial narrowband filters, are presented. The predicted performance of DAzLE, including the sensitivity, volume coverage and expected number counts, is discussed. The current status of the DAzLE project, and its projected timeline, are also presented.
Smart Focal Planes are devices that enable the efficient sampling of a telescope's focal plane to feed spectroscopic and imaging instruments. Examples are integral field units (fiber and image slicers), cryogenic beam manipulators, and MOEMS (micro-opto-electromechanical systems) such as miniature slit shutters. These technologies are critical in making best use of the current 8m class telescopes for key science goals such as spectroscopic surveys of high redshift galaxies, and will be even more important for Extremely Large Telescope (ELT) instruments. In fact, the density of pixels in an ELT focal plane with several milliarcsecond resolution will mean that sub-sampling of the field will be needed even for imaging. We have proposed a joint European project to develop these technologies, building on expertise from partners in the UK, France, the Netherlands, Spain, Germany and others, and led by the UK. We describe the current status of these technologies, showing how they will contribute to the feasibility and performance of proposed instruments for ELTs, and concentrating on capabilities within Europe. We then outline the proposed future developments, highlighting the technical challenges, such as the difficulties of manufacturing and verifying complex image slicers with thousands of optical surfaces, and building highly reliable cryogenic mechanisms such as pick-off arms, beam steering mirrors and reconfigurble slit mechanisms.
Design concept of the fiber multi-object spectrograph (FMOS) for Subaru Telescope together with innovative ideas of optical and structural components is presented. Main features are; i) wide field coverage of 30 arcmin in diameter, ii) 400 target multiplicity, iii) 0.9 to 1.8 micrometers near-IR wavelengths, and iv) OH-airglow suppression capability. The instrument is proposed to be built under the Japan-UK-Australia international collaboration scheme.
Gemini have funded a design study to investigate the technologies needed in a versatile multi-object spectrograph for IR astronomy. We report on our investigations into wide- field spectroscopy using multiple integral-field units (MIFUs) to match particular areas of interest to the available detector(s). Such technologies enable integral field spectroscopy of several targets over a much wider field than can be covered with a single IFU. A brief overview of the scientific rationale for a multipel0IFU capability matched to multi-conjugate adaptive optics, and with its wider uncorrected field, on Gemini is given. A proposed method of deploying MIFUs is then described along with the optical consequences of the method.
Craig Mackay, Richard McMahon, Martin Beckett, Meghan Gray, Richard Ellis, Andrew Firth, M. Hoenig, James Lewis, Steve Medlen, Ian Parry, Jim Pritchard, Chris Sabbey
The search for galaxies at redshifts > becomes increasingly difficult in the visible since most of the light emitted by these objects is redshifted into the near IR. The recent development of high-performance near IR arrays has made it practical to built a wide field survey instrument for operation in the near IR part of the spectrum. CIRSI, the Cambridge IR Survey Instrument, uses four of the Hawaii-1 MCT arrays each of which has 1024 by 1024 pixels. This paper describes a number of the novel feature of CIRSI and summarizes the present performance achieved by CIRSI and the scientific programs it is principally engaged in.
Ian Parry, Craig Mackay, Rachel Johnson, Richard McMahon, Andrew Dean, Anamparambu Ramaprakash, David King, Jim Pritchard, Steve Medlen, Chris Sabbey, Richard Ellis, Alfonso Aragon-Salamanca
We describe CIRPASS which is currently being completed at the Institute of Astronomy in Cambridge. The optical design is presented and contrasted with more conventional software- suppression designs. The limiting magnitudes on Gemini are expected to be J 22.6 and H 21.7 in a 3 hour exposure.
We describe the current status of the technical aspects of the GOHSS project. It consists of a fiber-fed NIR spectrograph for faint objects. It will be a second-light instrument for the Nasmyth focus of the 3.5m Galileo telescope located on La Palma. GOHSS is an innovative instrument which accomplishes OH night-sky subtraction, differently from the hardware solution used by other devices; it provides a multiechelle design with software OH subtraction capable of yielding about 25 spectra in the z,J and H bands at an effective spectral resolution of about 4000, which is necessary to strongly reduce the impact of atmospheric OH lines. The GOHSS design is completed and the operative phase is already started through the procurement of the most important components. We have also started to develop the data reduction package for the instrument and the first result of the 1D approach as presented.
We have built a panoramic wide field near infrared imaging camera based on 4 Rockwell HAWAII 1024 X 1024 detectors. The baseline survey instrument operates in the region 0.8 to 1.8 micrometers on non-IR optimized telescopes with an upgrade at K band in 1999. The instrument was commission on the 2.5m INT and 4.2m WHT telescopes in December 1997 and January 1998. The main design goals in this project were to produce a highly productive astronomical instrument in a very short space of time and for low cost. Survey instruments are by their nature very versatile and CIRSI will support the wide range of astronomical interests at the Institute of Astronomy. Furthermore, since CIRSI is a traveling instrument and we are able to operate at a number of different telescopes to take opportunity of a range of image sizes and scales.
COHSI was successfully commissioned at the United Kingdom IR Telescope on Mauna Kea during a seven night observing run which coincided with this conference. Here we briefly describe the instrument and give a preliminary report on its performance at this time. The suppression optics and masks worked extremely well and the instrument background was found to be very low.
This paper describes the results of a test program to evaluate four Rockwell HAWAII and two PICNIC near IR array detectors with a view to their application in imaging, spectroscopy and in fast telescope tracking and interferometer fringe detection. Results of the laboratory test of the arrays are presented, together with a guide for their general operation.
We discuss the design and construction techniques of the Integral Field Units (IFU's) for SPIRAL and COHSI (Cambridge OH Suppression Instrument). The design for both is similar and we explain our reasons for adopting our particular approach. Both IFU's have been used on telescopes and found to perform very well. Finally, our plans for future instruments which will use the same techniques are briefly discussed.
We are currently building a panoramic wide field near infrared imaging camera based on 4 Rockwell Hawaii HgCdTe 10242 detectors. The survey instrument will operate in the J and H bands and will be as scientifically versatile and as easy to use as a large format CCD camera. It is expected to be ready for astronomical use by late 1997. It will be particularly well-suited for surveys of star-forming regions, low mass stars, distant galaxies, clusters and QSOs. The camera will be commissioned at the prime focus of the 2.5 m Isaac Newton telescope, where the image scale is 0.45'/pixel, giving an effective field of view of 14.6 by 14.6 arc minutes. The field of view of this camera with 0.15' pixels is 5.1 by 5.1 arc minutes and is thus approximately 60 times larger than the current near-infrared imager on Keck (NIRC). When combined with a 4.0 m class telescope, the combination is approximately 10 times as powerful as the Keck 10.0 m, when the apertures are taken into account. The options for upgrading the camera into a wide field spectroscopic survey instrument are currently being investigated.
One of the main limitations to the study of faint objects in the near-infrared (1 to 2 micrometer) is the luminous, varying sky background from very narrow OH emission lines originating in the Earth's upper atmosphere. This source of background contributes 95% to 98% of the total sky counts in the J & H atmospheric windows. We present the optical layout of the Cambridge OH suppression instrument. COHSI is designed to deliver OH suppressed, R equals 500, spectroscopy for both J & H spectral bands simultaneously providing an integral field mode and a multi-object mode. COHSI also has an OH suppression imaging mode. A modular approach has been selected for COHSI with the instrument consisting of three components. The first section consists of simple re-imaging lenses and a lens array interfacing the telescope to a set of optical fibers. This decouples the design of COHSI's main components from the telescope allowing COHSI to be easily used with different telescopes and making it free from flexure problems. The second section of COHSI is the OH suppression 'filter' itself. The size of this section is significantly smaller than in other similarly planned instruments. The third and final module of COHSI is the cryogenic low-resolution imaging spectrograph.
Autofib-2 is a robotic fiber system for the prime focus of the William Herschel telescope capable of placing up to 150 fibers in the 1 degree focal plane of the telescope. The fibers are fed to a purpose built spectrograph (WYFFOS) mounted on one of the Nasmyth platforms. Autofib-2 and WYFFOS are now entering a common user phase as fully commissioned instruments. We describe the novel techniques used to achieve the high precision in fiber placement delivered by this instrument and the quality control procedures devised to measure and monitor instrument stability. The characterization of the distortions of focal plane delivered by the prime focus corrector of the telescope was a vital procedure during the commissioning. We describe the methods of measuring these distortions and discuss the limitations of the instrument, telescope and astrometry.
As telescope apertures increase, fundamental limits for doing efficient slit-based spectroscopy are being reached. We propose that lens arrays feeding fiber bundles be used in the focal plane of large telescopes to counteract these problems and in the process add the capability of integral field spectroscopy. A description of the first phase of the SPIRAL (segmented pupil/image reformatting array lenses) project is presented. This system will provide spatially mapped spectroscopy with high spectral resolution and high throughput. An alternative mode in which the lens array is used to segment the pupil rather than the sky is also described. Finally, we briefly discuss our future instrument development plans.
We are currently testing an automated fibre positioner for the 4.2 m William Herschel Telescope (WHT). This instrument, known as Autofib-2, operates at the prime focus where it is able to utilize the full 1 degree field provided by the prime focus corrector (PFC). The robotic positioner is able to place 160 optical fibres in the focal plane of the WHT which feeds the light to a dedicated spectrograph (WYFFOS) located on the Nasmyth platform. This paper contains a description of the instrument which highlights the new techniques demanded by the prime focus plate scale and the scale distortions due to the PFC and its atmospheric dispersion compensator. These include robot vision to help achieve the high positioning accuracy and the use of two sky viewing probes to accurately determine the time dependent transformation from celestial coordinates to instrumental Cartesian coordinates. Also presented are the initial technical results on the performance of the instrument and the operational results of particular interest to the astronomical observer.
We present details of an instrumental configuration dedicated to the detection of large gas-giant planets orbiting main sequence stars via the small drop in stellar brightness that occurs when the planet transits the stellar disk. Our proposed scheme involves the long-term monitoring of the light-curves of tens of thousands of stars using a Schmidt telescope coupled to a CCD via a bundle of 10,000 optical fibres. Using an existing theoretical model of planetary system formation, we calculate a detection rate of 14 transits per year for our proposed system. Some fibre- optic laboratory results and some tests of a 10 fibre multi- object photometer prototype used on the UK Schmidt telescope (UKST) are also presented to support the feasibility of this idea.
The first part of this paper describes the microcomputer software that controls the individual mechanisms of the Autofib-2 instrument. All previous microprocessor systems built for the William Herschel Telescope used a variant of the Forth language to implement the control system; however, Autofib-2 is the first instrument to be controlled using a UNIX-style real-time operating system. Facets of the implementation will be discussed, including the reengineering of the interfaces in OS/9 C to allow connection to the existing interinstrument communications systems (Utility Network). The algorithms needed to successfully configure 160 fibers taking into account prime focus corrector (PFC) distortions are also discussed. The second part of this paper describes the astronomer-level control system running on the VAX System Computer. Details will be given of the way in which the astronomer's target field is defined and converted into the configuration data to be sent to the microprocessor system, including the mapping of the PFC distortions and the acquisition of new target fields.
We describe an IR multi-fibre system we are currently building for UKIRT. SMIRFS (Spectroscopic multiple infrared fibre system) will feed the CGS4 spectrograph, providing it with a multi-object capability in the J, H and K bands. For efficient coupling the inputs and outputs of the fibres are microlensed. Because the telescope is normally focused inside CGS4 for conventional spectroscopy the SMIRFS fibre slit is projected in to CGS4 by a spherical mirror. IR optimised Silica fibres are used for the J and H bands and Zirconium Fluoride fibres are used for the K band.
The design and performance of the FOS-2 faint-object spectrograph for the Herschel Telescope at the Observatorio del Roque de los Muchachos are described and illustrated with diagrams and drawings. The FOS-2 has an image scale of 223 microns/arcsec at the slit and features a cryostat-cooled 385 x 578-pixel CCD detector with 22-micron-sq pixels, operating with resolution 1.5 pixels and dispersion 8.73 A/pixel at 460-970 nm (first order) or 4.32 A/pixel at 350-490 nm (second order). The high-efficiency optical system is of the type described by Wynne (1982) and operates in the diverging f/11 Cassegrain beam without a collimator. Overall system efficiency in first order with a 5-arcsec slit has a peak at 16 percent at 700 nm and remains above 1 percent at all wavelengths imaged by the CCD; in second order the peak efficiency is about 3 percent at 490 nm and remains above 1 percent except below 370 nm. The mechanical system, the control and data acquisition procedures, and the data-reduction software are briefly discussed.
We have built a laboratory prototype to evaluate the performance of an innovative design of robot for optical fibre
placement as part of the design study for the proposed 2° field (2dF)"5 for the Anglo Australian Telescope (AAT).
Based on the Autofib-12'4 system operating at the AAT, it uses a new design of gripper to manipulate, and also
measure the positions of fibre optic probes.
The new design incorporates a CCD TV camera to check on the accuracy of each fibre's position in real time as
the fibres are being placed, with any slight adjustment required being made automatically. This automatic error
correction will eliminate the need for extensive calibration procedures, and provide the improved accuracy required
to work at typical 4m prime focus platescales.
Our laboratory prototype exhibits good accuracy (<10pm rms) and reliability and we now intend to use this
approach at the prime focus of the William Herschel Telescope (WHT)3. In this paper we report on the overall
performance of the new design and assess it's practicality in applications on real telescopes.
The design and operation of the automated optical-fiber positioning system used for spectroscopic observations at the Cassegrain focus of the 4.2-m William Herschel Telescope (WHT) at Observatorio del Roque de los Muchachos are described. The system is a modified version of the Autofib positioner for the AAT and employs 64 spectroscopic fibers and 8 guide fiber bundles arranged to form a 17-arcmin-diameter field. The fibers are 1-m-long polyimide-coated high-OH silica, with core diameter 260 microns and outer diameter 315 microns, and a 1.2-mm side-length microprism is cemented to the end of each fiber or (7-fiber) guide bundle. The fibers are positioned one at a time by a pick-and-place robot assembly, and a viewing head permitting simultaneous observation of the back-illuminated fiber and the object it is trying to acquire is provided. This prototype Cassegrain-focus system is being studied to aid in the development of a more accurate fiber positioner for use at the prime focus of the WHT.
This paper describes the Low Dispersion Survey Sectrograph (LDSS-2) currently under construction for the 4.2-m William Herschel Telescope. The instrument is a versatile highly efficient multiobject spectrograph with an 11.5-arcmin field of view. Around 100 objects can be observed simultaneously using multiaperture masks made at the telescope in real-time at dispersions selectable between 10 and 47 nm/mm. By removing the dispersing element, the instrument can act as a focal reducer with a final focal ratio of f/2. This allows the field to be imaged first in order to derive accurate instrumental coordinates for the manufacture of the aperture mask.
Techniques for improving the subtraction of sky background when performing multiobject spectroscopy with fiber-optic-link instruments are examined analytically and by means of numerical simulations. The sky subtraction problems for multislit, long-slit, and fiber-optic spectroscopy are compared; the detrimental effects of fiber misalignment, poor-quality fiber end preparation, stress-related focal-ratio degradation, absorption losses, and connector losses are described; and consideration is given to improvements based on (1) using higher-quality fibers, (2) allowing for wavelength-dependent differences in fiber response, and (3) mimicking the multislit method by allocating more fibers to each object. The effects of vignetting and parameter shifts on computer-simulated spectra are shown in graphs.
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