S. Vives

Prime focus spectrograph: Subaru's future

The Prime Focus Spectrograph (PFS) is a new multi-fiber spectrograph on Subaru telescope. PFS will cover around 1.4 degree diameter field with ~2400 fibers. To ensure precise positioning of the fibers, a metrology camera is designed to provide the fiber position information within 5 {\mu}m error. The final positioning accuracy of PFS is targeted to be better than 10 {\mu}m. The metrology camera will locate at the Cassegrain focus of Subaru telescope to cover the whole focal plane. The PFS metrology camera will also serve for the existing multi-fiber infrared spectrograph FMOS.The Prime Focus Spectrograph (PFS) of the Subaru Measurement of Images and Redshifts (SuMIRe) project has been endorsed by Japanese community as one of the main future instruments of the Subaru 8.2-meter telescope at Mauna Kea, Hawaii. This optical/near-infrared multi-fiber spectrograph targets cosmology with galaxy surveys, Galactic archaeology, and studies of galaxy/AGN evolution. Taking advantage of Subaru’s wide field of view, which is further extended with the recently completed Wide Field Corrector, PFS will enable us to carry out multi-fiber spectroscopy of 2400 targets within 1.3 degree diameter. A microlens is attached at each fiber entrance for F-ratio transformation into a larger one so that difficulties of spectrograph design are eased. Fibers are accurately placed onto target positions by positioners, each of which consists of two stages of piezo-electric rotary motors, through iterations by using back-illuminated fiber position measurements with a widefield metrology camera. Fibers then carry light to a set of four identical fast-Schmidt spectrographs with three color arms each: the wavelength ranges from 0.38 μm to 1.3 μm will be simultaneously observed with an average resolving power of 3000. Before and during the era of extremely large telescopes, PFS will provide the unique capability of obtaining spectra of 2400 cosmological/astrophysical targets simultaneously with an 8-10 meter class telescope. The PFS collaboration, led by IPMU, consists of USP/LNA in Brazil, Caltech/JPL, Princeton, and JHU in USA, LAM in France, ASIAA in Taiwan, and NAOJ/Subaru.

Prime Focus Spectrograph for the Subaru telescope: massively multiplexed optical and near-infrared fiber spectrograph

Abstract. The Prime Focus Spectrograph (PFS) is an optical/near-infrared multifiber spectrograph with 2394 science fibers distributed across a 1.3-deg diameter field of view at the Subaru 8.2-m telescope. The wide wavelength coverage from 0.38  μm to 1.26  μm, with a resolving power of 3000, simultaneously strengthens its ability to target three main survey programs: cosmology, galactic archaeology and galaxy/AGN evolution. A medium resolution mode with a resolving power of 5000 for 0.71  μm to 0.89  μm will also be available by simply exchanging dispersers. We highlight some of the technological aspects of the design. To transform the telescope focal ratio, a broad-band coated microlens is glued to each fiber tip. A higher transmission fiber is selected for the longest part of the cable system, optimizing overall throughput; a fiber with low focal ratio degradation is selected for the fiber-positioner and fiber-slit components, minimizing the effects of fiber movements and fiber bending. Fiber positioning will be performed by a positioner consisting of two stages of piezo-electric rotary motors. The positions of these motors are measured by taking an image of artificially back-illuminated fibers with the metrology camera located in the Cassegrain container; the fibers are placed in the proper location by iteratively measuring and then adjusting the positions of the motors. Target light reaches one of the four identical fast-Schmidt spectrograph modules, each with three arms. The PFS project has passed several project-wide design reviews and is now in the construction phase.

The European contribution to the SPICA mission

The Japanese led Space Infrared telescope for Cosmology and Astrophysics (SPICA) will observe the universe over the 5 to 210 micron band with unprecedented sensitivity owing to its cold (~5 K) 3.5m telescope. The scientific case for a European involvement in the SPICA mission has been accepted by the ESA advisory structure and a European contribution to SPICA is undergoing an assessment study as a Mission of Opportunity within the ESA Cosmic Vision 1015-2015 science mission programme. In this paper we describe the elements that are being studied for provision by Europe for the SPICA mission. These entail ESA directly providing the cryogenic telescope and ground segment support and a consortium of European insitutes providing a Far Infrared focal plane instrument. In this paper we describe the status of the ESA study and the design status of the FIR focal plane instrument.

Original image slicer designed for integral field spectroscopy with the near-infrared spectrograph for the James Webb Space Telescope

Integral field spectroscopy (IFS) provides a spectrum simultaneously for each spatial sample of an extended 2-D field. It consists of an integral field unit (IFU), which slices and rearranges the initial field along the entrance slit of a spectrograph. We present an original design of IFU based on the advanced image slicer concept. To reduce optical aberrations, pupil and slit mirrors are disposed in a fan-shaped configuration, which means that angles between incident and reflected beams on each element are minimized. The fan-shaped image slicer improves image quality in terms of wavefront error by a factor of 2 compared with a classical image slicer, and furthermore, it guaranties a negligible level of differential aberration in the field. As an example, we present the design LAM used for its proposal at the near-infrared spectrograph (NIRSpec/IFU) invitation of tender for the James Webb Space Telescope (JWST).

Improved stray light suppression performance for the solar orbiter/METIS inverted external occulter

The Solar Orbiter/METIS visible and UV coronagraph introduces the concept of occulter inversion in solar coronagraphy. Classical externally occulted coronagraphs usually have a disk in front of the telescope entrance pupil. According to the mission requirements, in order to reduce the amount of power entering the instrument and to limit the instrument dimensions, METIS is equipped with an inverted external occulter (IEO). The IEO consists of a circular aperture on the Solar Orbiter thermal shield that acts as coronagraph entrance pupil. A spherical mirror (M0), located ~800 mm behind the IEO, rejects back the disk-light through the IEO itself. A light-tight boom connects the IEO to the M0 through the thermal shield. In order to achieve high performance in stray light suppression, the IEO design needs optimization. Due to the novelty of the concept we can only use the heritage of past space-borne coronagraph occulters as a starting point to design a dedicated occulter optimization shape. A 1.5 years long, accurate test campaign has been carried out to evaluate the best optimization configuration for the IEO. Two prototypes were manufactured to take into account the impact of the boom geometry on the stray light suppression performance. Two optimization concepts were compared: the inverted cone (that derives from the conic optimization of classical occulting disks) and the serrated edge, of which several samples were manufactured, with different geometrical parameters, surface roughnesses and coatings. This work summarizes the activity we have been carrying on to define the flight specifications for the METIS occulter.

Progress in the critical assessment for a far-infrared space interferometer with double fourier modulation (FP7-FISICA)

The progress and results of the ongoing FP7-FISICA programme to re-asses the scientific goals of a Far-Infrared Space Interfereometer and push the development of some of its key technology elements are reported.

EAGLE: an MOAO fed multi-IFU working in the NIR on the E-ELT

EAGLE is an instrument for the European Extremely Large Telescope (E-ELT). EAGLE will be installed at the Gravity Invariant Focal Station of the E-ELT, covering a field of view of 50 square arcminutes. Its main scientific drivers are the physics and evolution of high-redshift galaxies, the detection and characterization of first-light objects and the physics of galaxy evolution from stellar archaeology. These key science programs, generic to all ELT projects and highly complementary to JWST, require 3D spectroscopy on a limited (~20) number of targets, full near IR coverage up to 2.4 micron and an image quality significantly sharper than the atmospheric seeing. The EAGLE design achieves these requirements with innovative, yet simple, solutions and technologies already available or under the final stages of development. EAGLE relies on Multi-Object Adaptive Optics (MOAO) which is being demonstrated in the laboratory and on sky. This paper provides a summary of the phase A study instrument design.

Optical solutions for the multi-IFU instrument EAGLE for the European ELT

This paper summarizes the different optical concepts developed for the EAGLE Phase A design. EAGLE will be an MOAO (Multi-object AO) IFU spectrometer operating between 0.8 and 2.5μm. The EAGLE consortium have developed different concepts for the challenging problem of acquiring more than twenty objects in the patrol field of view (FOV), correcting the wavefront along the line of sight to each of the objects and analyzing each object spatially and spectrally with an Integral Field Spectrograph. The target selection FOV will be ≥20 square arcmin and the individual target FOV can be selected to be either 1.65×1.65arcsec or 1.65×3.3arcsec. They will be sampled spatially at 75mas and with spectral resolutions of 4000 and 10000. Optical designs for target acquisition systems, integral-field unit, and spectrographs have been developed. These will be compared and the expected performance will be described in terms of the number of targets, overall patrol field of view, individual field of view, throughput, spectral resolving power and image quality.

The near infrared camera for the Subaru Prime Focus Spectrograph

We present the detailed design of the near infrared camera for the SuMIRe (Subaru Measurement of Images and Redshifts) Prime Focus Spectrograph (PFS) being developed for the Subaru Telescope. The PFS spectrograph is designed to collect spectra from 2394 objects simultaneously, covering wavelengths that extend from 380 nm - 1.26 μm. The spectrograph is comprised of four identical spectrograph modules, with each module collecting roughly 600 spectra from a robotic fiber positioner at the telescope prime focus. Each spectrograph module will have two visible channels covering wavelength ranges 380 nm - 640 nm and 640 nm - 955 nm, and one near infrared (NIR) channel with a wavelength range 955 nm - 1.26 μm. Dispersed light in each channel is imaged by a 300 mm focal length, f/1.07, vacuum Schmidt camera onto a 4k x 4k, 15 µm pixel, detector format. For the NIR channel a HgCdTe substrate-removed Teledyne 1.7 μm cutoff device is used. In the visible channels, CCDs from Hamamatsu are used. These cameras are large, having a clear aperture of 300 mm at the entrance window, and a mass of ~ 250 kg. Like the two visible channel cameras, the NIR camera contains just four optical elements: a two-element refractive corrector, a Mangin mirror, and a field flattening lens. This simple design produces very good imaging performance considering the wide field and wavelength range, and it does so in large part due to the use of a Mangin mirror (a lens with a reflecting rear surface) for the Schmidt primary. In the case of the NIR camera, the rear reflecting surface is a dichroic, which reflects in-band wavelengths and transmits wavelengths beyond 1.26 μm. This, combined with a thermal rejection filter coating on the rear surface of the second corrector element, greatly reduces the out-of-band thermal radiation that reaches the detector. The camera optics and detector are packaged in a cryostat and cooled by two Stirling cycle cryocoolers. The first corrector element serves as the vacuum window, while the second element is thermally isolated and floats cold. An assembly constructed primarily of silicon carbide is used to mount the Mangin mirror, and to support the detector and field flattener. Thermal isolation between the cold optics and warm ambient surroundings is provided by G10 supports, multi-layer insulation, and the vacuum space within the cryostat. In this paper we describe the detailed design of the PFS NIR camera and discuss its predicted optical, thermal, and mechanical performance.

An integral field spectrograph for SNAP

A well-adapted spectrograph concept has been developed for the SNAP (SuperNova/Acceleration Probe) experiment. The goal is to ensure proper identification of Type Iz supernovae and to standardize the magnitude of each candidate by determining explosion parameters. The spectrograph is also a key element for the calibration of the science mission. An instrument based on an integral field method with the powerful concept of imager slicing has been designed and is presented in this paper. The spectrograph concept is optimized to have high efficiency and low spectral resolution (R~100), constant through the wavelength range (0.35-1.7μm), adapted to the scientific goals of the mission.