Focal Plane Instruments Research Articles

Planck cryogenic testing in CSL premises, helium partial pressure management

Both satellite Planck and Herschel are cryogenic ones [1,2], the first one having a cold point around 0.1 K, the second one around 0.3 K. Not only are the detectors cooled, but also major subsystems and systems of the spacecrafts. The Centre Spatial de Liège (CSL) is involved in testing several parts of these spacecrafts [3], starting form optical tests on the mirrors or on the telescope, via cryogenic vibration testing of scientific focal plane instruments, ending with the full Planck spacecraft testing. Each test requires temperature lower than 20 K, in volumes ranging from 1 m 3 to 60 m 3, cooling several kilograms to more than one ton, and withstanding heat load up to 150 W in stabilisation. The overall Planck spacecraft test challenge is very high, as it is the only way to measure the end-to-end cooling chain of the spacecraft. The space conditions reproduction must be as perfect as possible to avoid the test set-up influence on the spacecraft performances, especially linked to radiative cooling, mechanical perturbations and Helium residual pressure. Different challenges are presented, and the related CSL solutions are described, highlighting the Helium partial pressure problem, the related computations and trapping system by large sorption panel.

AKARI—Infrared Satellite Mission—Present Status and Early Results

AKARI, formerly known as ASTRO-F, is a satellite mission dedicated to infrared astronomy for the first time in Japan. It has a 685-mm aperture telescope with two focal-plane instruments cooled by liquid helium (LHe) and mechanical coolers on board for observations in the 2–180 μm infrared spectral range. AKARI was launched on 2006 February 21 (UT) into a sun-synchronous polar orbit and started observations in May, 2006. It carried 179 liter LHe that lasted for 550 days and observations with LHe were carried out for more than 15 months. During the LHe holding period, AKARI made all-sky survey observations with six bands from 9 to 160 μm, which surpass the IRAS all-sky survey data in the sensitivity, spatial resolution, and spectral coverage. Together with the all-sky observation, AKARI also made pointing observations for about 10 min at a given position of the sky to execute deep imaging and spectroscopy from near- to far-infrared. Both focal-plane instruments work successfully on orbit and more than 90% of the sky was observed in the all-sky survey. After LHe exhaustion, near-infrared observations are planned to continue. This paper reports the in-orbit performance of AKARI and its early observational results so far obtained.

Evolution strategies optimization of the multiple Fabry-Perót imaging interferometer for the advanced technology solar telescope

We describe an evolutionary algorithm for the design of an imaging triple-étalon Fabry-Perót interferometer (MFPI), which gives a solution to the multidimensional minimization process through a stochastic search method. The interactions between design variables (the étalon reflectances, interétalon ghost attenuator transmittances, and spacing ratios) are complex, resulting in a fitness landscape that is pitted with local optima. Traditional least-squares and gradient descent algorithms are not useful in such a situation. Instead, we employ a method called evolution strategies in which several preliminary designs are randomly generated subject to constraints. These designs are combined in pairs to produce offspring designs. The offspring population is mutated randomly, and only the fittest designs of the combined population are passed to the next iteration of the evolutionary process. We discuss the evolution strategies method itself, as well as its application to the specific problem of the design of an incoherently coupled triple-étalon interferometer intended for use as a focal plane instrument in the planned National Solar Observatory's Advanced Technology Solar Telescope (NSO's ATST). The algorithm converges quickly to a reasonable design that is well within the constraints imposed on the design variables, and which fulfills all resolution, signal-to-noise, throughput, and parasitic band suppression requirements.

Proposed national large solar telescope

Sun’s atmosphere is an ideal place to study and test many magnetohydrodynamic (MHD) processes controlling turbulent plasma. We wish to resolve some of the finest solar features (which remain unresolved presently) and study their dynamics. Indian Institute of Astrophysics has proposed to design, fabricate and install a 2-meter class solar telescope at a suitable site in India to resolve features on the Sun of the size of about 0.1 arcsec. The focal plane instruments will include a high resolution polarimeteric package to measure polarization with an accuracy of 0.01 per cent; a high spectral resolution spectrograph to obtain spectra in 5 widely separated absorption lines simultaneously and high spatial resolution narrow band imagers in various lines. The Himalayan region appears to be a good choice keeping in view the prevailing dry and clear weather conditions. We have started detailed analysis of the weather conditions in the area and at some other locations in India. The site characterization will be done using the Sun-photometer, S-DIMM and SHABAR techniques to determine the seeing conditions.

IRAIT (Science to be done with...)

The International Robotic Antarctic Infrared Telescope (IRAIT) will be the first European infrared telescope to operate on the Antarctic Plateau: IRAIT is scheduled to arrive at Dome C during the 2007–2008 Antarctic campaign. The main IRAIT Focal Plane Instrument is AMICA (Antarctic Multiband Infrared CAmera) an instrument designed to observe in the Near- and Mid-infrared (2–28 μ m). Here we give a brief description of the telescope and discuss which kind of science could be performed from Dome C.

Main tasks for IRAIT installation at Dome C

IRAIT (International Robotic Antarctic Infrared Telescope) is a telescope with an 80 cm aperture, ready for installation at Dome C. Equipped with AMICA (Antarctic Multiband Infrared CAmera), the main focal plane instrument, it will observe in near (1–5 μ ) and mid infrared regions (5–28 μ ), benefiting from the exceptional site characteristics. The installation will start in December 2007. An overview of interfacing devices and the integration of various IRAIT subsystems are here presented.

Designing high-performance spectrographs for extremely large telescopes

To answer the increasingly challenging questions of modern astronomy, larger and larger optical telescopes have been built in the last few decades, equipped with a sizable suite of focal-plane instruments devoted to observations at all wavelengths, and spatial and spectral resolutions. As a general rule, for a given spectral resolution and under seeing-limited conditions, larger telescopes require larger instruments because spectrograph dimensions scale with the slit width, which scales with telescope diameter. For example, the High Resolution Echelle Spectrometer at the Keck telescope1 has a 1.2 × 0.3m2 mosaic grating consisting of three segments, and collimator and camera mirrors of the same order of magnitude. Some attempts to reduce the dimensions of the optics have been made, for instance for the Ultraviolet and Visual Echelle Spectrograph2 at the Very Large Telescope (VLT), where a smaller 0.8 × 0.2m2 grating has been used. If we were to linearly scale such instruments to 30–40mclass telescopes, such as the 42m European Extremely Large Telescope3 (E-ELT, illustrated in Figure 1), this would result in three to five times larger components and thus very large, heavy, and expensive instruments. Moreover, manufacturing constraints have been reached in many areas. For example, the ruling engines that are used to make diffraction gratings—the main dispersing component of a spectrograph—are limited to ruled areas of around 40 × 30cm2. We have investigated a new design approach4 that uses slicing techniques (at image or pupil planes) and ‘anamorphic’ magnification at different levels to keep instrument size and cost affordable. We can use these methods because the resolving Figure 1. Model of the E-ELT within its enclosure. The main mirror has a diameter of 42m. The COsmic Dynamics EXperiment (CODEX) instrument will be situated at a stationary location below the telescope and receive its light via an optical train of mirrors and fibers. (Courtesy: European Southern Observatory.)

The Infrared Astronomical Mission AKARI

Abstract AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from mid–to far-infrared. The instruments also have a capability for imaging and spectroscopy in the wavelength range 2-180$\mu$m in the pointed observation mode, occasionally inserted into a continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90% of the whole sky with a higher spatial resolution and a wider wavelength coverage than that of the previous IRAS all-sky survey. Point-source catalogues of the All-Sky Survey will be released to the astronomical community. Pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission.

Flight Performance of the AKARI Cryogenic System

Abstract We describe the flight performance of the cryogenic system of the infrared astronomical satellite AKARI, which was successfully launched on 2006 February 21 (UT). AKARI carries a 68.5 cm telescope together with two focal-plane instruments, Infrared Cameras and Far Infrared Surveyor, all of which are cooled down to cryogenic temperature to achieve superior sensitivity. AKARI has a unique cryogenic system, which consists of cryogen (liquid helium) and mechanical coolers (2-stage Stirling coolers). With the help of mechanical coolers, 179 L (26.0 kg) of super-fluid liquid helium can keep the instruments cryogenically cooled for more than 500 days. The on-orbit performance of the AKARI cryogenics is consistent with the design and a pre-flight test, and the boil-off gas flow rate is as small as 0.32 mg s$^{-1}$. We observed an increase in the major axis of the AKARI orbit, which can be explained by thrust due to the thermal pressure of vented helium gas.

The Far-Infrared Surveyor (FIS) for AKARI

Abstract The Far-Infrared Surveyor (FIS) is one of two focal-plane instruments on the AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 $\mu \rm m$, and uses two kinds of array detectors. The FIS arrays and optics are designed to sweep the sky with high spatial resolution and redundancy. The actual scan width is more than eight arcminutes, and the pixel pitch matches the diffraction limit of the telescope. Derived point-spread functions (PSFs) from observations of asteroids are similar to those given by the optical model. Significant excesses, however, are clearly seen around tails of the PSFs, whose contributions are about 30% of the total power. All FIS functions are operating well in orbit, and the performance meets the laboratory characterizations, except for the two longer wavelength bands, which are not performing as well as characterized. Furthermore, the FIS has a spectroscopic capability using a Fourier transform spectrometer (FTS). Because the FTS takes advantage of the optics and detectors of the photometer, it can simultaneously make a spectral map. This paper summarizes the in-flight technical and operational performance of the FIS.

The Infrared Camera (IRC) for AKARI–Design and Imaging Performance

Abstract The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI satellite. It is designed for wide-field deep imaging and low-resolution spectroscopy in the near–to mid-infrared (1.8–26.5$\mu$m) in the pointed observation mode of AKARI. The IRC is also operated in the survey mode to make an All-Sky Survey at 9 and 18$\mu$m. It comprises three channels. The NIR channel (1.8–5.5$\mu$m) employs a 512 $\times$ 412 InSb array, whereas both the MIR-S (4.6–13.4$\mu$m) and MIR-L (12.6–26.5$\mu$m) channels use 256 $\times$ 256 Si:As impurity band conduction arrays. Each of the three channels has a field-of-view of about $10^\prime \times 10^\prime$, and they are operated simultaneously. The NIR and MIR-S share the same field-of-view by virtue of a beam splitter. The MIR-L observes the sky about 25$^\prime$ away from the NIR/MIR-S field-of-view. The IRC gives us deep insights into the formation and evolution of galaxies, the evolution of planetary disks, the process of star-formation, the properties of interstellar matter under various physical conditions, and the nature and evolution of solar system objects. The in-flight performance of the IRC has been confirmed to be in agreement with the pre-flight expectation. This paper summarizes the design and the in-flight operation and imaging performance of the IRC.

SUNRISE: High resolution UV/VIS observations of the sun from the stratosphere

SUNRISE is an international project for the development, construction and operation of a balloon-borne solar telescope with an aperture of 1 m, working in the UV/VIS spectral domain. The main scientific goal of SUNRISE is to understand the structure and dynamics of the magnetic field in the atmosphere of the Sun. SUNRISE will provide near diffraction-limited images of the photosphere and chromosphere with an unprecedented resolution down to 35 km on the solar surface at wavelengths around 220 nm. Active in-flight alignment and image stabilization techniques are used. The focal-plane instrumentation consists of a polarization sensitive spectrograph, a Fabry–Perot filter magnetograph and a phase-diverse filter imager working in the near UV. The first stratospheric long-duration balloon flight of SUNRISE is planned in summer 2009 from the Swedish ESRANGE station. SUNRISE is a joint project of the German Max-Planck-Institut für Sonnensystemforschung (MPS), Katlenburg-Lindau, with the Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder, USA, the Lockheed-Martin Solar and Astrophysics Laboratory (LMSAL), Palo Alto, USA, and the Spanish IMaX consortium. This paper will give an overview about the mission and a description of its scientific and technological aspects.

No wavefront sensor adaptive optics system for compensation of primary aberrations by software analysis of a point source image 2 Tests

The description of an adaptive optics (AO) system with no wavefront sensor to correct primary aberrations is presented. This system is based on closed loop software that iteratively analyzes a point source target image on the instrument focal plane and suitably modifies the AO device. The performed tests with a pull-only deformable mirror (DM) have shown that the system works very well, reaching an optimal focusing condition in a few seconds using standard components. Such a system can be conveniently applied in all the fields in which a not very fast optical adaptation is acceptable.

AMON-RA 광학계를 활용한 통합적 광선 추적 기법의 지구 반사율 측정 성능 검증

Earth-Sun-Heliosphere Interactions Experiments(EARTHSHINE) 미션의 주 탑재체인 Albedo Monitor and Radiometer(Amon-Ra) 광학계는 최초로 제1 라그랑제 지점(Lagrange point 1) 주위의 혜일로(Halo) 궤도에 위치하여 태양 복사 활동 및 지구 반사율 변화를 1% 정확도 이내로 측정함으로서 현존하는 지구 반사율 추이의 모순을 해결할 수 있는 과학적 측정 자료를 제시하는데 그 목적을 가지고 있다. 이에 이미 개발된 광학 성능 검증용 Amon-Ra 광학계의 가시광채널 시험 모델 및 광선 추적 기법을 이용한 통합적 광선 추적 end-to-end 과학 임무 성능 평가 수치 모사 기법을 확립하였으며, 개발된 기법을 이용하여 실제 제작된 Amon-Ra 광학계를 제1라그랑제 지점에 위치시키고 태양과 지구 밝기를 다양하게 변화시킨 후 광학계에 입사되는 에너지 복사량을 수치 모사로 측정하였다. 관측된 지구 및 태양 밝기로부터 지구 반사율 변환을 위하여 각 분포 모델(GLobal Angular Distribution Model, ADM)을 이용하였으며 수치 모사에 의한 지구 반사율 측정 결과를 Amon-Ra 광학계의 측정 오차 범위인 <TEX>${\pm}0.28%$</TEX>와 비교함으로서 개발된 end-to-end 성능 검증 기법의 계산 정밀도를 확인하였다. 이는 기존의 광학계 성능 검증법의 한계를 뛰어넘어 광학계 성능 평가를 실시간으로 검증할 수 있다는 점에서 큰 의의를 지닌다. The international EARTHSHINE mission is to measure 1% anomaly of the Earth global albedo and total solar irradiance using Amon-Ra instrument around Lagrange point 1. We developed a new ray truing based integrated end-to-end simulation tool that overcomes the shortcomings of the existing end-to-end performance simulation techniques. We then studied the in-orbit radiometric performance of the breadboard Anon-Ra visible channel optical system. The TSI variation and the Earth albedo anomaly, reported elsewhere, were used as the key input variables in the simulation. The output flux at the instrument focal plane confirms that the integrated ray tracing based end-to-end science simulation delivers the correct level of incident power to the Amon-Ra instrument well within the required measurement error budget of better than <TEX>${\pm}0.28%$</TEX>. Using the global angular distribution model (ADM), the incident flux is then used to estimate the Earth global albedo and the TSI variation, confirming the validity of the primary science cases at the L1 halo orbit. These results imply that the integrated end-to-end ray tracing technique, reported here, can serve as an effective and powerful building block of the on-line science analysis tool in support of the international EARTHSHINE mission currently being developed.

Astronomical applications of quantum optics for extremely large telescopes

A programme has been started to investigate photon properties that are not currently exploited in astronomical instruments, namely second- and higher-order coherence functions encoded in their arrival time, and the orbital angular momentum. This paper expounds the first results achieved in the study of a novel astronomical photometer capable of pushing time tagging towards the picosecond region. This conceptual device has been developed as a possible focal plane instrument for the future OverWhelmingly Large Telescope (OWL) of the European Southern Observatory. This instrument has been named QuantEYE, that is, the Quantum Eye of OWL.

IRAIT: A Facility for IR Astronomy at Dome C

The IRAIT (International Robotic Antarctic Infrared Telescope) telescope will be the first European infrared telescope operated on the Antarctic Plateau. The main IRAIT Focal Plane Instrument is AMICA (Antarctic Multiband Infrared CAmera), a two-detector instrument designed to operate in the Near- and Mid-infrared (2-28 µm) regions. IRAIT will start operation during the 2007–2008 Antarctic campaign, though the instrumentation will reach Antarctica one year before, at the end of 2006. It will offer a unique opportunity to test the science that can be done from Dome C (in this sense it is a precursor for larger facilities as PILOT ). We briefly describe the telescope and its auxiliary equipment, and we present example of the kind of science that will be feasible with this infrared observatory of moderate size.

Small IRAIT Telescope: photometry and asteroseismology at Dome C

Inhalt (u.a.): M. BREGER: Delta Scuti stars: Observational aspects; M.S. Cunha: Theory of rapidly oscillating Ap stars; M. SACHKOV et al.: Vertical structure of pulsations in roAp stars; G. HOUDEK: Theoretical asteroseismology of solar-like oscillations; B.L. POPIELSKI: Core modes as a seismic probe of mixing beyond the convective core; M. GODART: Temperature gradients in the core overshooting region; W.A. DZIEMBOWSKI – J. DASZYŃSKA-DASZKIEWICZ – A.A. PAMYATNYKH: Interpretation of the Be star HD 163868 oscillation spectrum based on the MOST observations; D. KILKENNY: Pulsating Hot Subdwarfs – An Observational Review; M.H. MONTGOMERY: Mapping Convection using Pulsating White Dwarf Stars; M. ROTH: The Network Activities in HELAS; I. KUDZEJ et al.: A New Slovak Observatory 500 km from Vienna; W.W. WEISS: Microsatellites; G. KOPACKI – S. FRANDSEN: RR Lyrae stars in M4

Detection of CFIRB with AKARI/FIS deep observations

The Cosmic Far-Infrared Background (CFIRB) contains information about the number and distribution of contributing sources and thus gives us an important key to understand the evolution of galaxies. Using a confusion study to set a fundamental limit to the observations, we investigate the potential to explore the CFIRB with AKARI/FIS deep observations. The Far-Infrared Surveyor (FIS) is one of the focal-plane instruments on the AKARI (formerly known as ASTRO-F) satellite, which was launched in early 2006. Based upon source distribution models assuming three different cosmological evolutionary scenarios (no evolution, weak evolution, and strong evolution), an extensive model for diffuse emission from infrared cirrus, and instrumental noise estimates, we present a comprehensive analysis for the determination of the confusion levels for deep far-infrared observations. We use our derived sensitivities to suggest the best observational strategy for the AKARI/FIS mission to detect the CFIRB fluctuations. If the source distribution follows the evolutionary models, observations will be mostly limited by source confusion. We find that we will be able to detect the CFIRB fluctuations and that these will in turn provide information to discriminate between the evolutionary scenarios of galaxies in most low-to-medium cirrus regions.

Galaxy colours in the AKARI deep SEP survey

We investigate the segregation of the extragalactic population via colour criteria to produce an efficient and inexpensive methodology to select specific source populations as a function of far-infrared flux. Combining galaxy evolution scenarios and a detailed spectral library of galaxies, we produce simulated catalogues incorporating segregation of the extragalactic population into component types (normal, star-forming, AGN) via colour cuts. As a practical application we apply our criteria to the deepest survey to be undertaken in the far-infrared with the AKARI (formerly ASTRO-F) satellite. Using the far-infrared wavebands of the Far-Infrared Surveyor (FIS, one of the focal-plane instruments on AKARI) we successfully segregate the normal, starburst and ULIRG populations. We also show that with additional MIR imaging from AKARI’s Infrared Camera (IRC), significant contamination and/or degeneracy can be further decreased and show a particular example of the separation of cool normal galaxies and cold ULIRG sources. We conclude that our criteria provide an efficient means of selecting source populations (including rare luminous objects) and produce colour-segregated source counts without the requirement of time intensive ground-based follow up to differentiate between the general galaxy population.

Simulated performance of dedicated Ge-strip Compton telescopes as γ-lens focal plane instrumentation

With focusing of gamma rays in the nuclear-line energy regime starting to establish itself as a feasible and very promising approach for high-sensitivity γ-ray (line) studies of individual sources, optimizing the focal plane instrumentation for γ-ray lens telescopes is a prime concern. Germanium detectors offer the best energy resolution available at ∼2 keV FWHM at 1MeV and thus constitute the detector of choice for a spectroscopy mission in the MeV energy range. Using a Compton detector focal plane has three advantages over monolithic detectors: additional knowledge about (Compton) events enhances background rejection capabilities, the inherently finely pixellated detector naturally allows the selection of events according to the focal spot size and position, and Compton detectors are inherently sensitive to γ-ray polarization. We use the extensive simulation and analysis package assembled for the ACT vision mission study to explore achievable sensitivities for different Ge Compton focal plane configurations as a first step towards determining an optimum configuration.