KEYWORDS: Telescopes, Spectrographs, Calibration, Fabry Perot interferometers, Observatories, Control systems, Sensors, Control software, Equipment, Domes
MARVEL is a new facility at the Roque de los Muchachos Observatory (La Palma) which comprises an array of four 0.8m telescopes, each feeding via fibre link into a single high-resolution spectrograph. The facility will provide dedicated target vetting and follow-up capability to support large exoplanet surveys through radial velocity measurements with precision at the metre-per-second level. The observatory site, with four new domes and a standalone stabilised spectrograph building, will soon be complete and ready for hardware installation and commissioning. Here we present an overview of the facility and a status update on several component subsystems: the telescope hardware, control software, and scheduling software; the fibre injection units at each telescope; the optical and mechanical design and tolerances of the spectrograph and vacuum vessel; the calibration system hardware and calibration strategies; and the progress in development of the instrument’s data reduction pipeline.
We describe the Sloan Digital Sky Survey Local Volume Mapper Instrument (LVM-I) construction, testing, and initial performance. The facility is designed to produce the first integral map of thousands of degrees of the Southern sky. The map will cover spectra from bluer than [O II] to 980 nm with a dispersion of over R = Δλ/λ > 4, 000 at Hα wavelength. Each spaxel will have a pitch of ∼35′′, and the survey will be conducted using four integral field units (IFUs) with an instantaneous field of view of 530 arcmin2. The LVM facility is designed to achieve the required sub-Rayleigh spectroscopy over large sky areas with outstanding spectrophotometric accuracy and precision. LVM-I is designed to produce this unique dataset using four siderostats on commercial mounts. The four beams are fed into 16-cm-diameter f/11.4 apochromatic objectives, and the sky is derotated with K mirrors. These telescopes produce an image of the field onto both guider cameras and a lenslet array. The array reimages the field at f/3.7 onto 107-micron-diameter fibers. Blue throughput is maximized with a short 18.5-m fiber run from the IFUs to the spectrographs. The fibers are reconfigured inside a splicing box to distribute the fibers from the four telescopes to three spectrographs. The spectrographs are near-copies of the Dark Energy Survey three-band f/1.7 spectrographs, which deliver sharp images over the entire chromatic range. Nine STA charge-coupled devices (CCDs), cooled with liquid-nitrogen dewars, are used for the survey. The LVM-I is controlled with custom Python software and distributed over various computers using power-over-ethernet networking. The system is housed in a custom enclosure with a roll-off roof to grant access to the sky. The enclosure allows all four telescopes to point all over the sky and measure the transmissivity of the atmosphere and the sky background. Some of the first-light data products are highlighted here.
The Sloan Digital Sky Survey V (SDSS–V) is an all-sky spectroscopic survey of <6 million objects, designed to decode the history of the Milky Way, reveal the inner workings of stars, investigate the origin of solar systems, and track the growth of supermassive black holes across the universe. The Local Volume Mapper (LVM) is a facility designed to provide a contiguous 2500 deg2 integral-field survey over a 3.5 year period from Las Campa˜nas Observatory (LCO) in Chile. The facility comprises four 0.16 m bench-mounted telescopes that feed three multiobject spectrographs with 1801 science fibres, 119 calibration fibres, and 24 sky-background fibres. The fibre cable spans approximately 20 meters from the telescope platform to the spectrograph slits. A sorting hat, located in the spectrograph room, redistributes the 1944 fibres into three 648–element bundles that terminate at the spectrograph slits. In this paper, we briefly summarize the current production progress of the integral-field units, the spectrograph slits, and the sorting hat.
The 4m DAG telescope is under construction at East Anatolia Observatory in Turkey. DIRAC, the “DAG InfraRed Adaptive optics Camera”, is one of the facility instruments. This paper describes the design of the camera to meet the performance specifications. Adaptive and auxiliary optics relay the telescope F/14 input 1:1 into DIRAC. The camera has an all refractive design for the wavelength range 0.9 - 2.4 micron. Lenses reimage the telescope focal plane 33 x 33 as (9 x 9 mm) on a 1k x 1k focal plane array. With magnification of 2x, the plate scale on the detector is 33 mas/pixel. There are 4 standard filters (Y, J, H, K) and 4 narrowband continuum filters. A 12 position filter wheel allows installation of 2 extra customer filters for specific needs; the filter wheel also deploys a pupil viewer lens. Optical tolerancing is carried out to deliver the required image quality at polychromatic Strehl ratio of 90% with focus compensator. This reveals some challenges in the precision assembly of optics for cryogenic environments. We require cells capable of maintaining precision alignment and keeping lenses stress free. The goal is achieved by a combination of flexures with special bonding epoxy matching closely the CTE of the lens cells and crystalline materials. The camera design is very compact with object to image distance <220 mm and lens diameters <25 mm. A standalone cryostat is LN2 cooled for vibration free operation with the bench mounted adaptive optics module (TROIA) and coronagraph (PLACID) at the Nasmyth focus of the DAG telescope.
The Australian Astronomical Observatory’s (AAO’s) AESOP project is part of the Multi-Object Spectrograph Telescope (4MOST) system for the VISTA telescope. It includes the 2436-fibre positioner, space frame and electronics enclosures. The AESOP concept and the role of the AAO in the 4MOST project have been described in previous SPIE proceedings. The project final assembly stage has recently been completed. In this paper, key results in accurate manufacturing and assembly of critical AESOP components are discussed. The major performance requirement for AESOP is that all 2436 science fibre cores and 12 guide fibre bundles are to be re-positioned to an accuracy of 10 micron within 1 minute. With a fast prime-focus focal-ratio, a close tolerance of +/-70 microns on the axial position of the fibre tips must be held so efficiency does not suffer from de-focus losses. Positioning accuracy is controlled with the metrology cameras installed on the telescope, which measures the positions of the fibre tips to an accuracy of a few micrometers and allows iterative positioning until all fibre tips are within tolerance on the ultimate position. Maintaining co-planarity of the fibre tips requires accurate control in the assembly of several components that contribute to such errors. Overall, the AESOP design fully complies with all its requirements and in most cases achieves its goals. A thorough consideration of all the relevant interfaces during the design and assembly phases, has resulted in comprehensive set of ICDs for the mechanical, electrical and software aspects of AESOP.
The Australian Astronomical Observatory’s (AAO’s) AESOP project is part of the Multi-Object Spectrograph Telescope (4MOST) system for the VISTA telescope. It includes the 2436-fibre positioner, space frame and electronics enclosures. The AESOP concept and the role of the AAO in the 4MOST project have been described in previous SPIE proceedings. The project final assembly stage has been completed. In this paper, engineering principles applied during assembly of critical components and testing of the instrument are discussed. The major performance requirement for AESOP is that all 2436 science fiber cores and 12 guide fiber bundles are to be re-positioned to an accuracy of 10 micron within 1 minute. With a fast prime-focus focal-ratio, a close tolerance on the axial position of the fiber tips must be held so efficiency does not suffer from de-focus losses. Positioning accuracy is controlled with the metrology cameras installed on the telescope, which measures the positions of the fiber tips to an accuracy of a few micrometers and allows iterative positioning until all fiber tips are within tolerance on the focal surface plane. Maintaining co-planarity of the fiber tips requires accurate control in the assembly of several components that contribute to such errors. AESOP requires a consistent production of high accuracy components and assemblies in a quantity of above 2500 items. To achieve this, we had to apply the highest engineering standards, including assembly procedures, metrology, and control systems. We designed many jigs and fixtures, which enabled us to produce high quality components and assemblies at reasonable cost. The results – working instrument was vastly achieved with the help of university students after providing a training in engineering practices.
The Sloan Digital Sky Survey V (SDSS-V) is an all-sky spectroscopic survey of >6 million objects, designed to decode the history of the Milky Way, reveal the inner workings of stars, investigate the origin of solar systems, and track the growth of supermassive black holes across the Universe. The Local Volume Mapper (LVM) is a facility designed to provide a contiguous 2500 deg2 integral-field survey over a 3.5 year period from Las Campanas Observatory (LCO) in Chile. The facility comprises four small (16 cm) telescopes that deliver science, calibration, and spectro-photometric light to three bench-mounted multi-object spectrographs, designed and build by Winlight Systems. All four telescopes will be equipped with a microlens array integral-field unit (IFU) to slice the focal plane into 35–arcsec large spatial elements while maintaining near-telecentric coupling at the fiber input. The science IFU comprises 1801 fibers, additional 143 fibers are allocated for sky-background and spectro-photometric calibration, totaling 1944 fibers. Each spectrograph will be fed by 648 fibers, which are reformatted into a linear array, forming the entrance slit. In this paper, we present the opto-mechanical design of the LVM-LCO fiber cable system.
VELOCE is an IFU fibre feed and spectrograph for the AAT that is replacing CYCLOPS2. It is being constructed by the AAO and ANU. In this paper we discuss the design and engineering of the IFU/fibre feed components of the cable. We discuss the mode scrambling gain obtained with octagonal core fibres and how these octagonal core fibres should be spliced to regular circular core fibres to ensure maximum throughput for the cable using specialised splicing techniques. In addition we also describe a new approach to manufacturing a precision 1D/2D array of optical fibres for some applications in IFU manufacture and slit manufacture using 3D printed fused silica substrates, allowing for a cheap substitute to expensive lithographic etching in silicon at the expense of positional accuracy. We also discuss the Menlo Systems laser comb which employs endlessly-singlemode fibre to eliminate modal noise associated with multimode fibre transmission to provide the VELOCE spectrograph with a stable and repeatable source of wavelength calibration lines.
Veloce is an ultra-stable fibre-fed R4 echelle spectrograph for the 3.9 m Anglo-Australian Telescope. The first channel to be commissioned, Veloce ‘Rosso’, utilises multiple low-cost design innovations to obtain Doppler velocities for sun-like and M-dwarf stars at <1 ms -1 precision. The spectrograph has an asymmetric white-pupil format with a 100-mm beam diameter, delivering R>75,000 spectra over a 580-930 nm range for the Rosso channel. Simultaneous calibration is provided by a single-mode pulsed laser frequency comb in tandem with a traditional arc lamp. A bundle of 19 object fibres ensures full sampling of stellar targets from the AAT site. Veloce is housed in dual environmental enclosures that maintain positive air pressure at a stability of ±0.3 mbar, with a thermal stability of ±0.01 K on the optical bench. We present a technical overview and early performance data from Australia's next major spectroscopic machine.
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