Space Infrared Telescope For Cosmology And Astrophysics Research Articles

Maintenance of Halo Orbits Under the Thrusting Constraints

This paper investigates the preliminary orbit maintenance for the next-generation infrared astronomical mission, Space InfraredTelescope forCosmology andAstrophysics, which is to be launched into the sun–Earth L2 halo orbit. Particularly, the impact of the reaction wheel unloading V on the spacecraft trajectory from the viewpoint of orbit maintenance is analyzed. In addition, the nondivergent and suppressive methods using the characteristics of the dynamical theory for unloading V are proposed and validated.

Optimal pupil apodizations of arbitrary apertures for high-contrast imaging

In the context of exoplanet direct detection and characterization, where high-contrast imaging is mandatory, we present fully optimized two-dimensional pupil apodizations for which no specific geometric constraints are put on the pupil plane apodization, apart from the shape of the aperture itself. Masks for circular and segmented apertures are displayed, with and without a central obstruction and spiders. We can now optimize apodizers for any aperture shape, and examples of optimal masks are shown for the Subaru telescope, the Space Infrared telescope for Cosmology and Astrophysics (SPICA) and the James Webb Space Telescope (JWST). Several high-contrast regions are considered with different sizes, positions, shapes and contrasts. It is interesting to note that all the masks that result from these optimizations tend to have a binary transmission profile.

Demonstrating the feasibility of line intensity mapping using mock data of galaxy clustering from simulations

Visbal & Loeb (2010) have shown that it is possible to measure theclustering of galaxies by cross correlating the cumulative emissionfrom two different spectral lines which originate at the sameredshift. Through this cross correlation, one can study galaxieswhich are too faint to be individually resolved. This technique, knownas intensity mapping, is a promising probe of the global properties ofhigh redshift galaxies. Here, we test the feasibility of suchmeasurements with synthetic data generated from cosmological darkmatter simulations. We use a simple prescription for associatinggalaxies with dark matter halos and create a realization of emittedradiation as a function of angular position and wavelength over apatch of the sky. This is then used to create synthetic data forthree different hypothetical instruments, one aboard the SpaceInfrared Telescope for Cosmology and Astrophysics (SPICA), anotherconsisting of a pair of ground based radio telescopes designed tomeasure the CO(1-0) and CO(2-1) emission lines, and one on the CornellCaltech Atacama Telescope (CCAT). We find that the line cross powerspectrum can be measured accurately from the synthetic data witherrors consistent with the analytical prediction of Visbal & Loeb(2010). Removal of astronomical backgrounds and masking bright lineemission from foreground contaminating galaxies do not preventaccurate cross power spectrum measurements.

A software simulator for the SPICA Safari instrument

A software simulator that has been developed for the Safari instrument proposed for the SPace Infrared telescope for Cosmology and Astrophysics (SPICA) mission is presented. The simulator can ingest a range of realistic input spectra and, following a thorough radiative transfer analysis, calculates the power reaching the detector as a function of the optical path difference within the interferometer. The simulator is modular in design so that it can be easily modified to ingest test data as they become available. The simulator will not only find use during the design phase of the Safari instrument, but also during ground performance verification campaigns of the flight model. Through validation of the simulator on ground test data, it will be possible to predict accurately the in-orbit performance of the Safari instrument.

Measuring the 3D clustering of undetected galaxies through cross correlation of their cumulative flux fluctuations from multiple spectral lines

We discuss a method for detecting the emission from high redshiftgalaxies by cross correlating flux fluctuations from multiple spectrallines. If one can fit and subtract away the continuum emission with asmooth function of frequency, the remaining signal containsfluctuations of flux with frequency and angle from line emittinggalaxies. Over a particular small range of observed frequencies,these fluctuations will originate from sources corresponding to aseries of different redshifts, one for each emission line. It ispossible to statistically isolate the fluctuations at a particularredshift by cross correlating emission originating from the sameredshift, but in different emission lines. This technique will allowdetection of clustering fluctuations from the faintest galaxies whichindividually cannot be detected, but which contribute substantially tothe total signal due to their large numbers. We describe thesefluctuations quantitatively through the line cross power spectrum. Asan example of a particular application of this technique, we calculatethe signal-to-noise ratio for a measurement of the cross powerspectrum of the OI(63 μm) and OIII(52 μm) fine structure lineswith the proposed Space Infrared Telescope for Cosmology andAstrophysics (SPICA). We find that the cross power spectrum can bemeasured beyond a redshift of z = 8. Such observations couldconstrain the evolution of the metallicity, bias, and duty cycle offaint galaxies at high redshifts and may also be sensitive to thereionization history through its effect on the minimum mass ofgalaxies. As another example of this technique, we calculate thesignal-to-noise ratio for the cross power spectrum of CO line emissionmeasured with a large ground based telescope like the Cornell CaltechAtacama Telescope (CCAT) and 21-cm radiation originating from hydrogenin galaxies after reionization with an interferometer similar in scaleto the Murchison Widefield Array (MWA), but optimized forpost-reionization redshifts.

Studies of expolanets and solar systems with SPICA

The SPace Infrared telescope for Cosmology and Astrophysics (SPICA) is a proposed mid-to-far infrared (4-200 um) astronomy mission, scheduled for launch in 2017. A single, 3.5m aperture telescope would provide superior image quality at 5-200 um, and its very cold (~5 K) instrumentation would provide superior sensitivity in the 25-200 um wavelength regimes. This would provide a breakthrough opportunity for studies of exoplanets, protoplanetary and debris disk, and small solar system bodies. This paper summarizes the potential scientific impacts for the proposed instrumentation.

SPICA infrared coronagraph for the direct observation of exo-planets

We present a mid-infrared coronagraph to target the direct observation of extrasolar planets, for Space Infrared telescope for Cosmology and Astrophysics (SPICA). SPICA is a proposed JAXA–ESA mission, which will carry a telescope cooled to 5 K with a 3.5 m diameter aperture, and is planned to be launched in 2018 by an H II family rocket. The SPICA mission gives us a unique opportunity for high-contrast observations because of the large telescope aperture, the simple pupil shape, and the capability for infrared observations from space. We have commenced studies for a coronagraph for SPICA, in which this coronagraph is currently regarded as an option of the focal plane instruments. The primary target of the SPICA coronagraph is the direct observation of Jovian exo-planets. A strategy of the baseline survey and the specifications for the coronagraph instrument for the survey are introduced together. The main wavelengths and the contrast required for the observations are 3.5–27 μm, and 10 −6 , respectively. Laboratory experiments were performed with a visible laser to demonstrate the principles of the coronagraphs. In an experiment using binary-shaped pupil coronagraphs, a contrast of 6.7 × 10 −8 was achieved, as derived from the linear average in the dark region and the core of the point spread function (PSF). A coronagraph by a binary-shaped pupil mask is a baseline solution for SPICA because of its feasibility and robustness. On the other hand, a laboratory experiment of the phase induced amplitude apodization/binary-mask hybrid coronagraph has been executed to obtain an option of higher performance (i.e., smaller inner working angle and higher throughput), and a contrast of 6.5 × 10 −7 was achieved with active wavefront control. Potentially important by-product of the instrument, transit monitoring for characterization of exo-planets, is also described. We also present recent progress of technology on a design of a binary-shaped pupil mask for the actual pupil of SPICA, PSF subtraction, the development of free-standing binary masks, a vacuum chamber, and a cryogenic deformable mirror. Considering SPICA to be an essential platform for coronagraphs and the progress of key technologies, we propose to develop a mid-infrared coronagraph instrument for SPICA and to perform the direct observation of exo-planets with it.

An AO-free coronagraph experiment in vacuum with a binary-shaped pupil mask

We present our first results from laboratory experiments on a binary-shaped checkerboard mask coronagraph that was fitted inside a vacuum chamber for the development of skills to the direct observation of extra-solar planets. The aim of this work was to utilize a vacuum chamber for our coronagraph experiments in order to achieve an environment with higher thermal stability and which is free from air turbulence. We also aimed to evaluate and improve the performance of such a system consisting of a vacuum chamber with a coronagraph set inside the chamber. Both the raw contrast and the contrast after point spread function (PSF) subtraction are evaluated. We sited the vacuum chamber in a clean room, and we installed an optical fiber coupled to a visible He–Ne laser, appropriate coronagraph optics, a temperature sensor and heaters in the chamber. This provided a vacuum environment and a temperature-controlled environment with a visible light source, and was shown to improve the stability of the coronagraph. A contrast of 1.7 × 10 - 7 was achieved for the raw coronagraphic images by analyzing the areal mean of all of the observed dark regions. A contrast of 7.3 × 10 - 9 was achieved for the PSF subtraction by areal variance (1 σ) of all of the observed dark regions. Speckles were a major limiting factor throughout the dark regions of both the raw images and the PSF subtracted images. The application of PSF subtraction for the Space Infrared telescope for Cosmology and Astrophysics (SPICA) and for other platforms is discussed.

The space infrared telescope for cosmology and astrophysics: SPICA A joint mission between JAXA and ESA

The Space Infrared telescope for Cosmology and Astrophysics (SPICA) is planned to be the next space astronomy mission observing in the infrared. The mission is planned to be launched in 2017 and will feature a 3.5 m telescope cooled to 30 microns wavelength). We describe the scientific advances that will be made possible by this large increase in sensitivity and give details of the mission, spacecraft and focal plane conceptual design.

High contrast experiment of an AO-free coronagraph with a checkerboard pupil mask

A high contrast coronagraph is expected to provide one of the promising ways to directly observe extra-solar planets. We present the newest results of our laboratory experiment investigating "rigid" coronagraph with a binary shaped checkerboard pupil mask, which should offer a highly stable solution for telescopes without adaptive optics (AO) for wavefront correction in space missions. The primary aim of this work was to study the stability of the coronagraph, and to demonstrate its performance without adaptive wavefront correction. Estimation of both the raw contrast and the gain of the point spread function (PSF) subtraction were needed. The limiting factor of the contrast was also important. A binary shaped pupil mask of a checkerboard type has been designed. The mask, consisting of an aluminum film on a glass substrate, was manufactured using nano-fabrication techniques with electron beam lithography. Careful evaluation of coronagraphic performance, including PSF subtraction, was carried out in air using the developed mask. A contrast of $6.7 \times 10^{-8}$ was achieved for the raw coronagraphic image by areal averaging of all of the observed dark regions. Following PSF subtraction, the contrast reached $6.8 \times 10^{-9}$. Speckles were a major limiting factor throughout the dark regions of both the raw image and the PSF subtracted image. A rigid coronagraph with PSF subtraction without AO is a useful method to achieve high contrast observations. Applications of a rigid coronagraph to a Space Infrared telescope for Cosmology and Astrophysics (SPICA) and other platforms are discussed.

DLAs AND GALAXY FORMATION

Damped Lyman-α systems (DLAs) are useful probes of star formation and galaxy formation at high-redshift (hereafter high-z). We study the physical properties of DLAs and their relationship to Lyman break galaxies (LBGs) using cosmological hydrodynamic simulations based on the concordance Λ cold dark matter model. Fundamental statistics such as global neutral hydrogen (H I) mass density, H I column density distribution function, DLA rate-of-incidence and mean halo mass of DLAs are reproduced reasonably well by the simulations, but with some deviations that need to be understood better in the future. We discuss the feedback effects by supernovae and galactic winds on the DLA distribution. We also compute the [C II] emission from neutral gas in high-z galaxies, and make predictions for the future observations by the Atacama Large Millimeter Array (ALMA) and Space Infrared Telescope for Cosmology and Astrophysics (SPICA). Agreement and disagreement between simulations and observations are discussed, as well as the future directions of our DLA research.

Observational Characteristics of the First Protostellar Cores

Abstract First protostellar cores are young stellar objects in the earliest evolutionary stage. They are hydrostatic objects formed soon after the central portions of star-forming cores become optically thick to dust emission. We consider their characteristics in the emitted radiation, and discuss their evolution with increasing mass of the cores. Particular attention is paid to detailed radiative and chemical processes in the postshock relaxation layer located at the surface of the core, where the majority of radiation is emitted. Most of the radiation is originally emitted in the dust continuum in mid-infrared wavelength ($\sim$ 10–30 $\mu$m), which reprocessed to far-infrared with $\sim$ 100–200 $\mu$m. Although some fraction ($\sim$ 0.1) of the radiation energy is emitted in the H$_2$O lines at the accretion shock, most is absorbed and reemitted in the dust continuum in the envelope. The H$_2$O lines account for at most $\sim 1/100$ of the observed luminosity. If a cavity is present in the envelope due to outflow or rotation, the dust and H$_2$O line emission in the mid-infrared wavelength from the shock can be observed directly, or as a reflection nebula. Among forthcoming observational facillities, SPace Infrared telescope for Cosmology and Astrophysics (SPICA) is the most suitable for detecting either direct or processed radiation from first-core objects.

High‐Precision CTE Measurement of SiC‐100 for Cryogenic Space Telescopes

ABSTRACTWe present the results of high‐precision measurements of the thermal expansion of sintered SiC, SiC‐100, intended for use in cryogenic space telescopes, in which minimization of thermal deformation of the mirror is critical, and precise information of the thermal expansion is needed for the telescope design. The temperature range of the measurements extends from room temperature down to ∼10 K. Three samples, Nos. 1, 2, and 3, were manufactured from blocks of SiC produced in different lots. The thermal expansion of the samples was measured with a cryogenic dilatometer, consisting of a laser interferometer, a cryostat, and a mechanical cooler. The typical thermal expansion curve is presented using an eighth‐order polynomial of the temperature. For the three samples, the coefficients of thermal expansion (CTE), α 1, α 2, and α 3, were derived for temperatures between 293 and 10 K. The average and the dispersion (1 σ rms) of these three CTEs are 0.816 × 10−6 and 0.002 × 10−6 K−1, respectively. No significant difference was detected in the CTE of the three samples from the different lots. Neither inhomogeneity nor anisotropy of the CTE was observed. Based on the CTE dispersion obtained, we performed a finite‐element method (FEM) analysis of the thermal deformation of a 3.5 m diameter cryogenic mirror made of six SiC‐100 segments. It was shown that the present CTE measurement has an accuracy that is sufficient for the design of the 3.5 m cryogenic infrared telescope mission SPICA (Space Infrared Telescope for Cosmology and Astrophysics).

Detecting extra-solar planets with the Japanese 3.5 m SPICA space telescope

We present the 3.5 m SPace Infrared telescope for Cosmology and Astrophysics (SPICA) space telescope, the launch of which is schedule around year 2015 by the Japanese HII-A rocket, and specifically discuss its use in the context of direct observation of extra-solar planets. This actively cooled (4.5 K), single aperture telescope will operate in the mid and far infrared spectral regions, and up to submillimetric wavelengths (200 μm). The lowest spectral region (5 to 20 μm), where the spatial resolution is the most favorable, will be dedicated to high contrast imaging with coronagraphy. This article describes the SPICA coronagraph project in terms of science, as well as our efforts to study a suitable instrumental concept, compatible with the constraints of the telescope architecture. To cite this article: L. Abe et al., C. R. Physique 8 (2007).

Microscopic surface structure of C/SiC composite mirrors for space cryogenic telescopes

We report on the microscopic surface structure of carbon-fiber-reinforced silicon carbide (C/SiC) composite mirrors that have been improved for the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and other cooled telescopes. The C/SiC composite consists of carbon fiber, silicon carbide, and residual silicon. Specific microscopic structures are found on the surface of the bare C/SiC mirrors after polishing. These structures are considered to be caused by the different hardness of those materials. The roughness obtained for the bare mirrors is 20 nm rms for flat surfaces and 100 nm rms for curved surfaces. It was confirmed that a SiSiC slurry coating is effective in reducing the roughness to 2 nm rms. The scattering properties of the mirrors were measured at room temperature and also at 95 K. No significant change was found in the scattering properties through cooling, which suggests that the microscopic surface structure is stable with changes in temperature down to cryogenic values. The C/SiC mirror with the SiSiC slurry coating is a promising candidate for the SPICA telescope.

Mid- and far-infrared astronomy mission SPICA

We present an overview and the current status of SPICA (Space Infrared Telescope for Cosmology and Astrophysics), which is an astronomical mission with a cryogenically cooled 3.5 m telescope optimized for mid- and far-infrared astronomy. Because of its high spatial resolution and unprecedented sensitivity in the mid- to far-infrared, SPICA can address a number of key problems in current astrophysics, ranging from the star-formation history of the universe to the formation of planets. To reduce the mass of the whole mission, SPICA carries no cryogen. SPICA will be launched at ambient temperature and cooled down on orbit by mechanical coolers on board with an efficient radiative cooling system. This combination enables a 3.5-m class cooled (4.5 K) telescope in space. We also describe recent activities of the technology development programs for SPICA. The target year of the launch of SPICA is mid 2010s.

Detectability of [Cii] 158 μm Emission from High‐Redshift Galaxies: Predictions for ALMA andSPICA

We discuss the detectability of high-redshift galaxies via [C II] 158 μm line emission by coupling an analytic model with cosmological smoothed particle hydrodynamics (SPH) simulations that are based on the concordance Λ cold dark matter (CDM) model. Our analytic model describes a multiphase interstellar medium (ISM) irradiated by the far-ultraviolet (FUV) radiation from local star-forming regions, and it calculates thermal and ionization equilibrium between cooling and heating. The model allows us to predict the mass fraction of a cold neutral medium (CNM) embedded in a warm neutral medium (WNM). Our cosmological SPH simulations include a treatment of radiative cooling/heating, star formation, and feedback effects from supernovae and galactic winds. Using our method, we make predictions for the [C II] luminosity from high-redshift galaxies that can be directly compared with upcoming observations by the Atacama Large Millimeter Array (ALMA) and the Space Infrared Telescope for Cosmology and Astrophysics (SPICA). We find that the number density of high-redshift galaxies detectable by ALMA and SPICA via [C II] emission depends significantly on the amount of neutral gas, which is highly uncertain. Our calculations suggest that, in a CDM universe, most [C II] sources at z = 3 are faint objects with Sν < 0.01 mJy. Lyman break galaxies (LBGs) brighter than RAB = 23.5 mag are expected to have flux densities Sν = 1-3 mJy depending on the strength of galactic wind feedback. The recommended observing strategy for ALMA and SPICA is to aim at very bright LBGs or star-forming DRG/BzK galaxies.

Mechanical coolers operating below 4.5 K for space application

This paper reports the 4 K- and 1 K-class mechanical coolers developed for space use. The 4 K-class cooler has been developed for Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES), which is to be operated onboard the International Space Station (ISS). The cooling capacity is 20 mW at 4.5 K, with the total input power of approximately 120 W. The 1 K-class cooler has been developed for cooling far-infrared detectors to 1.7 K in the Space Infrared Telescope for Cosmology and Astrophysics (SPICA). The cooling capacity is 10 mW at 1.7 K and the total input power to the cooler is about 180 W. A future possible cryogen-free cooling system for temperature below 0.1 K is also presented, which uses these coolers as a pre-cooler.

Shaped pupil coronagraphs for high-contrast imaging with SPICA

We present configurations of shaped pupil coronagraphs optimized for a realistic telescope to directly detect extrasolar giant planets in the mid-IR wavelengths. This study is linked to the development of the coronagraphic instrument aboard SPICA (SPace Infrared telescope for Cosmology and Astrophysics). We made a systematic assessment of the performance of the “checkerboard” and “concentric ring” masks, introducing a large central obstruction (C.O.) due to a secondary mirror and its related support spiders. With a small secondary mirror, we also propose a modification to the original symmetrical checkerboard apodization, which enables us to achieve a . The transmission through the optimal binary masks exhibits abrupt increases and plateaus as the inner working angle (IWA) is increased. We attribute these properties of binary apodization function to the existence of threshold IWAs that allow large openings in the pupil.

FUTURE SPACE INFRARED TELESCOPE MISSION, SPICA

SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is an infrared astronomical satellite with a 3.5 m cooled telescope which is very powerful in mid- and far- infrared observations and makes complementary role to JWST and Herschel. SPICA will be launched at ambient temperature without any cryogen into the Sun-Earth L2 orbit and cooled down in space to 4.5 K with use of efficient radiative cooling and mechanical coolers. The present status of SPICA and the developments of the satellite system are reported.