The Cherenkov Telescope Array (CTA) is the next generation ground-based observatory for gamma-ray astronomy at very high energies. With more than 100 telescopes at two sites, CTA will be the world’s largest and most sensitive highenergy gamma-ray observatory covering the full sky with a northern array located at the Roque de los Muchachos astronomical observatory on the island of La Palma (Spain) and a southern array near the European Southern Observatory site at Paranal (Chile). Three classes of telescope types with imaging Cherenkov cameras, calibration, clock and timing systems, site infrastructure as well as control and data handling/processing software, developed in a large international collaboration, are required to build the CTA observatory system.
As a large and international collaboration, with almost all hardware and software elements to be delivered as in-kind contributions by participating institutes to build a complex observatory system on two sites, CTA faces quite a few challenges in the areas of systems engineering and project management.
The Cherenkov Telescope Array (CTA) is the next generation ground-based observatory for gamma-ray astronomy at very high energies. With more than 100 telescopes at two sites, CTA will be the world’s largest and most sensitive high-energy gamma-ray observatory covering the full sky with a northern array located at the Roque de los Muchachos astronomical observatory on the island of La Palma (Spain) and a southern array near the European Southern Observatory site at Paranal (Chile). Three classes of telescope types spread over a large area are required to cover the full CTA very-high energy range from 20 GeV to 300 TeV.
Building on the technology of current generation ground-based gamma-ray detectors (H.E.S.S., VERITAS and MAGIC), CTA will be 5 to 20 times more sensitive, depending on gamma-ray energy, and have unprecedented accuracy in its detection of high-energy gamma rays. Current gamma-ray telescope arrays host up to five individual telescopes, but CTA is designed to detect gamma rays over a larger area and a wider field of view.
Prototypes for the major CTA subsystems including the various size telescopes and cameras have been developed and built at different places. CTA is currently preparing for the full construction phase, both technically and organizationally, with the goal to achieve first light by the year 2022 and completion by 2024/25.
CTA will be the first ground-based gamma-ray observatory open to the worldwide astronomical and particle physics communities as a resource for data from unique, high-energy astronomical observations.
The Heterodyne Instrument for the Far-Infrared (HIFI) of the ESA cornerstone mission Herschel is required to operate at wavelengths between 157 and 625 μm. Because of the long-wavelength character, and the complexity and modularity of the optical design, there is a clear need for accurate electromagnetic simulations supported by experimental verification. The need for a compact layout in order to reduce mass and volume as far as possible has important optical consequences. Several mirrors are illuminated in the propagating near-field rather than in the far-field. Consequently the classical geometrical design and analysis approach is inadequate. The long-wavelength character of the system can not be ignored and the associated diffraction effects inevitably become important. In this paper we describe the results of electromagnetic simulations of the optical system for band 1 of HIFI at a wavelength of 625 μm. In order to verify the results of the front-to-end coherent propagation of the detector beams, near-field facilities capable of measuring both amplitude and phase of the electromagnetic field have been developed. A unique feature of these facilities is that the absolute coordinates of the measured field components are known within a fraction of a wavelength. Therefore a true comparison with theoretical predictions can be made. We compare measurement data taken at 625 μm with simulations and discuss to what extent measured and simulated results may be expected to agree. We conclude by presenting the consequences of our observations in terms of system performance.
The highest sky quality demands for astronomical research impose to locate observatories often in areas not easily reached by the existing power infrastructures. At the same time, availability and cost of power is a primary factor for sustainable operations. Power may also be a potential source for CO2 pollution. As part of its green initiatives, ESO is in the process of replacing the power sources for its own, La Silla and Paranal-Armazones, and shared, ALMA, installations in Chile in order to provide them with more reliable, affordable, and smaller CO2 footprint power solutions. The connectivity to the Chilean interconnected power systems (grid) which is to extensively use Non-Conventional Renewable Energy (NCRE) as well as the use of less polluting fuels wherever self-generation cannot be avoided are key building blocks for the solutions selected for every site. In addition, considerations such as the environmental impact and - if required - the partnership with other entities have also to be taken into account. After years of preparatory work to which the Chilean Authorities provided great help and support, ESO has now launched an articulated program to upgrade the existing agreements/facilities in i) the La Silla Observatory, from free to regulated grid client status due to an agreement with a Solar Farm private initiative, in ii) the Paranal-Armazones Observatory, from local generation using liquefied petroleum gas (LPG) to connection to the grid which is to extensively use NCRE, and last but not least, in iii) the ALMA Observatory where ESO participates together with North American and East Asian partners, from replacing the LPG as fuel for the turbine local generation system with the use of less polluting natural gas (NG) supplied by a pipe connection to eliminate the pollution caused by the LPG trucks (currently 1 LPG truck from the VIII region, Bio Bio, to the II region, ALMA and back every day, for a total of 3000km). The technologies used and the status of completion of the different projects, as well as the expected benefits are discussed in this paper.
The 25 European antennas of ALMA were delivered by ESO to the ALMA project in Chile between April 2011 and September 2013. Their combined time of operation is already significant and allows us to draw conclusions regarding their ability to fulfil the original specification, in terms of both scientific performance and operational availability. In this paper, we will summarize the experience gained during the past five years of operation. We will characterize the performance of the antennas in routine operation and compare with the data obtained during acceptance testing. We will also describe the few technical issues experienced while operating at 5000m and the way in which these were treated during these first years of operation. We will evaluate the effective reliability obtained in service based on field data and draw some conclusions as to the way in which reliability and maintainability aspects were covered during the process which led to the final design of the antenna. We will discuss the smart use of software to handle redundancy in a flexible way and to exclude failed components without affecting overall antenna operability. The use of low-level diagnostics enabled by remote access allows us to shorten the trouble-shooting cycle and to optimise physical interventions on the antennas. Finally, the paper will cover Antenna maintenance manuals edited using an industrial interactive standard. It will be explained why this advanced and innovative concept has not achieved the success that was expected, and why the traditional form is preferred at the ALMA Observatory.
In the far-infrared (FIR) / THz regime the angular (and often spectral) resolution of observing facilities is still very
restricted despite the fact that this frequency range has become of prime importance for modern astrophysics. ALMA
(Atacama Large Millimeter Array) with its superb sensitivity and angular resolution will only cover frequencies up to
about 1 THz, while the HIFI instrument for ESA'a Herschel Space Observatory will provide limited angular resolution
(10 to 30 arcsec) up to 2 THz. Observations of regions with star and planet formation require extremely high angular
resolution as well as frequency resolution in the full THz regime. In order to open these regions for high-resolution
astrophysics we present a study concept for a heterodyne space interferometer, ESPRIT (Exploratory Submm Space
Radio-Interferometric Telescope). This mission will cover the Terahertz regime inaccessible from the ground and outside
the operating range of the James Webb Space Telescope (JWST).
Many studies on the formation of stars and planets require high angular and high spectral resolution in the far-infrared
regime. Even with the upcoming operation of the Herschel Space Observatory, ALMA, and JWST, angular resolutions
of better than 1 arcsec combined with high spectral resolution in the crucial far-infrared domain of 1 THz to ~ 10 THz
(300 μm to 30 μm) are still beyond observational reach. Only a far-infrared heterodyne interferometer can close this gap.
Here we present the general requirements for a FIR heterodyne interferometer in space and address a number of critical
key technologies needed for such an instrument.
The large submillimeter telescope (LST) is a proposed wide-field, 30m-class telescope operating from a ground-based site in the relatively unexplored 0.2 - 1mm waveband. The telescope will be equipped with imaging and spectroscopic instrumentation to allow astronomers to probe the earliest evolutionary stages of galaxies, stars and planets. It is intended to operate the telescope in the 200μm atmospheric window, giving access to unique science; probing the peak emission from the cosmic far-IR/submm background and proto-stellar cores. The wide field-of-view and superb image fidelity will be perfect for large-scale surveys of the sky, such as entire giant molecular clouds and of fields of dusty galaxies at early epochs. It will therefore be an ideal complement to new generation interferometers (such as ALMA). In this paper we present an update on the science case and outline initial designs for both the telescope and instrumentation.
In the far-infrared (FIR) / THz regime the angular (and often spectral) resolution of observing facilities is still very restricted despite the fact that this frequency range has become of prime importance for modern astrophysics. ALMA (Atacama Large Millimeter Array) with its superb sensitivity and angular resolution will only cover frequencies up to about 1 THz, while the HIFI instrument for ESA'a Herschel Space Observatory will provide limited angular resolution (10 to 30 arcsec) up to 2 THz. Observations of regions with star and planet formation require extremely high angular resolution as well as frequency resolution in the full THz regime. In order to open these regions for high-resolution astrophysics we propose a heterodyne space interferometer mission, ESPRIT (Exploratory Submm Space Radio-Interferometric Telescope), for the Terahertz regime inaccessible from ground and outside the operating range of the James Webb Space Telescope (JWST).
The far-infrared (FIR) wavelength regime has become of prime importance for astrophysics. Observations of ionic, atomic and molecular lines, many of them present in the FIR, provide important and unique information on the star and planet formation process occurring in interstellar clouds, and on the lifecycle of gas and dust in general.
As these regions are heavily obscured by dust, FIR observations are the only means of getting insight in the physical and chemical conditions and their evolution. These investigations require, besides high spectral, also high angular resolution in order to match the small angular sizes of star forming cores and circum-stellar disks. We present here a mission concept, ESPRIT, which will provide both, in a wavelength regime not accessible from ground by ALMA (Atacama Large Millimeter Array), nor with JWST (James Webb Space Telescope).
The Atacama Large Millimeter Array (ALMA), a joint project between Europe and the U.S. and at present in its design and development phase, is a major new ground based telescope facility for millimeter and submillimeter astronomy. Its huge collecting area (7000 m2), sensitive receivers and location at one of the driest sites on Earth will make it a unique instrument. We present preliminary design concepts for the overall receiver configuration. Optics and cryostat design concepts from OSO, OVRO, RAL, IRAM, NRAO and SRON and their main features are described.
The IRAM 30 m telescope is located in the Sierra Nevada mountain range, 50 km to the south of the city of Granada/Spain, at an altitude of 2900 m. More than 100 scientific projects are executed every year by about 200 visiting observers. Since 1990, observations can be made from the Granada office in a way very much like on the telescope. Since 1998, such remote observing is also possible from the IRAM headquarters in Grenoble, France. About 5 percent of the time the telescope is controlled from these remote stations. We plan to install additional remote observing stations in order to facilitate a more flexible telescope scheduling.