Darwin is one of the most challenging space projects ever considered by the European Space Agency (ESA). Its principal objectives are to detect Earth-like planets around nearby stars and to characterise their atmospheres. Darwin is conceived as a space "nulling interferometer" which makes use of on-axis destructive interferences to extinguish the stellar light while keeping the off-axis signal of the orbiting planet. Within the frame of the Darwin program, the European Space Agency (ESA) and the European Southern
Observatory (ESO) intend to build a ground-based technology demonstrator called GENIE (Ground based European Nulling Interferometry Experiment). Such a ground-based demonstrator built
around the Very Large Telescope Interferometer (VLTI) in Paranal will
test some of the key technologies required for the Darwin Infrared Space Interferometer. It will demonstrate that nulling interferometry can be achieved in a broad mid-IR band as a precursor to the next phase of the Darwin program. The instrument will operate in the L' band around 3.8 μm, where the thermal emission from the telescopes and the atmosphere is reduced. GENIE will be able to operate in two different configurations, i.e. either as a single Bracewell nulling interferometer or as a double-Bracewell nulling interferometer with an internal modulation scheme.
The Very Large Telescope Interferometer (VLTI) on Cerro Paranal (2635 m) in Northern Chile reached a major milestone in September 2003 when the mid infrared instrument MIDI was offered for scientific observations to the community. This was only nine months after MIDI had recorded first fringes. In the meantime, the near infrared instrument AMBER saw first fringes in March 2004, and it is planned to offer AMBER in September 2004.
The large number of subsystems that have been installed in the last two years - amongst them adaptive optics for the 8-m Unit Telescopes (UT), the first 1.8-m Auxiliary Telescope (AT), the fringe tracker FINITO and three more Delay Lines for a total of six, only to name the major ones - will be described in this article. We will also discuss the next steps of the VLTI mainly concerned with the dual feed system PRIMA and we will give an outlook to possible future extensions.
The VLT interferometer has been operating since the time of first fringes in March 2001 with a pair of 40 cm diameter siderostats at baselines of 16 and 66 m and a pair of 8 m diameter telescopes (UT1 and UT3) with a baseline of 102 m using the test camera VINCI operating in the K band. A fair fraction of its commissioning time has been devoted to observing a number of objects of scientific interest around the southern sky bright enough to allow high precision visibilities to be obtained on a routine basis. A large number of stellar sources with correlated magnitudes brighter than K approximately 6 and K approximately 3 with the 8 m and 40 cm telescopes respectively have been observed over this time period with limited, u,v plane coverage. In this paper, the most interesting results on sources never observed before at these spatial resolutions and on known sources for which the VLTI data allow the establishment of tighter constraints on theoretical models will be reviewed.
The Very Large Telescope (VLT) Observatory on Cerro Paranal (2635 m) in Northern Chile is approaching completion. After the four 8-m Unit Telescopes (UT) individually saw first light in the last years, two of them were combined for the first time on October 30, 2001 to form a stellar interferometer, the VLT Interferometer. The remaining two UTs will be integrated into the interferometric array later this year. In this article, we will describe the subsystems of the VLTI and the planning for the following years.
ESO is embarking on the construction of a complex and high performance dual feed system that will allow Phase Referenced Imaging and Microarcsecond Astrometry (PRIMA) on the VLT Interferometer on Cerro Paranal in Chile. In this paper, I will describe in some detail the scientific objectives of this facility that drive the technical specifications and justify the chosen priorities. Of particular importance because of its uniqueness and rich variety of scientific applications will be the early development of the components allowing very high precision astrometry on sources such as extrasolar planets, binaries in nearby clusters, microlenses in the halo, and stars in the circumnuclear cluster in the galactic center.
On March 17, 2001, the VLT interferometer saw for the first time interferometric fringes on sky with its two test siderostats on a 16m baseline. Seven months later, on October 29, 2001, fringes were found with two of the four 8.2m Unit Telescopes (UTs), named Antu and Melipal, spanning a baseline of 102m. First shared risk science operations with VLTI will start in October 2002. The time between these milestones is used for further integration as well as for commissioning of the interferometer with the goal to understand all its characteristics and to optimize performance and observing procedures. In this article we will describe the various commissioning tasks carried out and present some results of our work.
In June 1997, NASA made the decision to extend the end of the Hubble Space Telescope (HST) mission from 2005 until 2010. As a result, the age of the instruments on board the HST became a consideration. After careful study, NASA decided to ensure the imaging capabilities of the HST by replacing the Wide Field Planetary Camera 2 with a low-cost facility instrument, the Wide Field Camera 3. This paper provides an overview of the scientific goals and capabilities of the instrument.
The Very Large Telescope (VLT) Observatory on Cerro Paranal (2635 m) in Northern Chile is approaching completion in this year when the fourth of the 8-m Unit Telescopes will see first light. At the same time, the preparation for first fringes of the VLT Interferometer (VLTI) is advancing rapidly with the goal of having the first fringes with two siderostats within this year. In this article we describe the status of the VLTI and its subsystems, we discuss the planning for first fringes with the different telescopes and instruments. Eventually, we present an outlook for the future of interferometry with Very Large Telescopes.
We describe the design of the ESO Adaptive Optics (AO) systems for the very large telescope interferometer (VLTI). We consider hereafter both the tip-tilt only corrections and the high order systems. The high order AO systems are designed for K-band operation on the Unit Telescopes (UT). The K-band UT beams will be combined with the 1.8m Auxiliary Telescopes (AT) operating with tip-tilt correction only, via ESO's Strap system. The UT-AO system will be hosted in the Coude' laboratory, with the deformable mirror inserted at the M8 location of the optical train. The wavefront sensor retains the option to be either in the Coude' lab, before the delay lines, or at the end of the beam combining path in the Interferometry laboratory, depending on the instrument attached and its use.
The VLTI (Very Large Telescope Interferometer) is one of the operating modes of the VLT, presently being built on Cerro Paranal, Chile. It aims at providing access to an observing mode at very high angular resolution and very high sensitivity (with respect to the currently operating astronomical interferometers). After a long period of conceptual, then detailed, studies, ESO is starting to build and to procure the main components of the interferometer in order to open this unpaired observing facility by the turn of the century.
The interferometric mode of the ESO very large telescope (VLT) permits coherent combination of stellar light beams collected by four telescopes with 8 m diameter and by several auxiliary telescopes of the 2 m class. While the position of the 8 m telescopes is fixed, auxiliary telescopes can be moved on rails, and can operate from 30 stations distributed on the top of the observatory site for efficient UV coverage. Coherent beam combination can be achieved with the 8 m telescopes alone, with the auxiliary telescopes alone, or with any combination, up to eight telescopes in total. A distinct feature of the interferometric mode is the high sensitivity due to the 8 m pupil of the main telescopes, with the potential for adaptive optics compensation in the near- infrared spectral regime. The VLT interferometer is conceived as an evolutionary program where a significant fraction of the interferometer's functionality is initially funded, and more capability may be added later while experience is gained and further funding becomes available. The scientific program is now defined by a team which consists of a VLTI scientist at ESO and fifteen astronomers from the VLT community. ESO has recently decided to resume the construction of the VLTI which was delayed in December 1993, in order to achieve first interferometric fringes with two of the 8 m telescopes around the year 2000, and routine operation with 2 m auxiliary telescopes from 2003 onwards. This paper presents an overview of the recent evolution of the project and its future development.
The interferometric mode of the ESO very large telescope (VLT) permits coherent combination of stellar light beams collected by four telescopes with 8m diameter and by several auxiliary telescopes of the 2m class. While the position of the 8m telescopes is fixed, auxiliary telescopes can be moved on rails, and can operate from 30 stations distributed on the top of the observatory site for efficient UV coverage. Coherent beam combination can be achieved with the 8m telescopes alone, with the auxiliary telescopes alone, or with any combination, up to eight telescopes in total. A distinct feature of the interferrometric mode is the high sensitivity due to the 8m pupil of the main telescopes which will be compensated by adaptive optics in the near-infrared spectral regime. The VLT interferometer (VLTI) part of the VLT program is conceived as an evolutionary program where a significant fraction of the interferometer's functionality is initially funded, and more capability may be added later while experience is gained and further funding becomes available. Major subsystems of the present baseline VLTI include: three auxiliary telescopes, three delay lines which permit combining the light from up to four telescopes, and a laboratory which contains an imaging beam combiner telescope, and enough space to accomodate a number of experimental setups. This paper presents a general overview of the recent evolution of the project and its future development.
This paper gives an update on the performance of the faint object camera following the highly successful installation of the corrective optics in COSTAR during the servicing mission. We review the effect that COSTAR has had on the point spread function and detector quantum efficiency, and discuss the improvements in our knowledge of sensitivity, PSF variations, camera distortion, and nonlinearity. The status of the f/48 relay, which has been successfully turned on a number of times, is reviewed.
The stellar coronograph built by STScl and the OATO operating at the SUSI focus of ESO's New Technology Telescope (NTT), described with particular emphasis on its optical and mechanical characteristics, is one of the most powerful coronographs in operation. Observations with angular resolutions of 0.6 arcsec over field of view of 45 arcsec diameter have been routinely achieved in the observing runs carried out so far. We describe the results from the application of the coronograph to the problem of observing the inner regions in the (beta) Pictoris dust disk.
We discuss the present implementation of the data acquisition electronics and the planned upgraded version, together with the related algorithms, of the new Torino IR camera: TC-MIRC. A detailed description of the camera is available in M. Robberto et al., 1994, presented in this SPIE meeting. The electronic structure of TC-MIRC is based on a PC-compatible host computer, using IDL/Windows, and a transputer network for detectors management and data processing; the engineering advantages of an intrinsically distributed environment and the computational scalability are discussed. The data acquisition procedures (standard algorithms for coadding and nondestructive readout, and their use in normal operations) are evaluated, with respect to their present performance and to the upgrade needed to fulfill the design requirements.
Following the availability on the market of IR arrays able to perform ground-based astronomical observations in the atmospheric windows longward of 2.5 micrometers , we started at the Torino Astronomical Observatory a new project aimed at the construction of a thermal IR camera to be installed at the TIRGO telescope. Located in the Swiss alps at 3100 m a.s.l., this Italian facility (1.5 m f/20 IR optimized) provides during the winter months a relatively high number of nights (20%) with first-rate conditions (low temperature and emissivity) for medium-IR observations. In order to fully exploit this potential, we designed an instrument, named Two-Channel Medium IR Camera (TC-MIRC) operating over the entire 1 to 14 micrometers region and optimized for the 2.5 to 14 micrometers thermal bands. TC-MIRC covers such a broad range of wavelengths using two IR array detectors: an InSb device for the 1 to 5 micrometers region and a Si:Ga device for the 8 to 14 micrometers band. The main characteristic of the camera is that both arrays can simultaneously observe the same region. In this way, we can not only approach an almost double observing efficiency (time really spent `on target'), but also use both detectors for correlated observations and testing of unconventional acquisition techniques. It follows that TC-MIRC is a complex instrument presenting several interesting features. Thanks to the presence of two independent optical channels, the user can change the filters, adjust the focus and vary the optical scale on a channel without affecting the acquisition running on the other array. In particular, the possibility of adjusting the optical scale on each detector during the observations allows the user to select the most convenient sampling and field of view on the basis of the actual seeing or diffraction conditions, background level and scientific needs. Moreover, the adopted cryogenic system is entirely based on a mechanical closed-cycle cooler and allows very low-cost operations and easy maintenance on the mountain for long periods of time. In this paper we present the opto/mechanical design and construction, the general structure of the control system and the software architecture. We report the performances reached by the most critical parts of the instrument during the test carried out in the laboratory and at the telescope during the first engineering run in January 1994.
The installation of COSTAR will improve the imaging performance of the Hubble Space Telescope such that the Faint Object Camera performance will approach that predicted before the discovery of the spherical aberration. However, this is not achieved without some undesirable side-effects. Despite these, it will be possible to achieve scientific goals with the COSTAR-corrected Faint Object Camera that are not currently feasible.
We present a discussion of the various sources of FOC Point Spread Functions (PSFs), and the problems associated with their use. In particular, we highlight the time variability of the PSF halo structure and indicate some of the causes. We examine the usefulness of the PSF modelling software, TinyTim, and show that although this software creates visually similar images, these similarities are to a large extent superficial. We conclude by showing that the theoretical PSFs produced by TinyTim are inadequate for the restoration of high S/N FOC point source images. We also conclude that, because of 'breathing', there is a strong likelihood that empirical PSFs, whether pre-existing or specifically obtained, may not be sufficient either.
This paper gives an update on the performance of the Faint Object Camera--launched with the Hubble Space Telescope--since the last report two years ago. The primary camera, the f/96 relay, continues to work well, but the f/48 relay has recently developed serious problems. The stability of the f/96 relay has been very good with the only change being a small apparent decrease in UV sensitivity. Preliminary results for the f/48 DQE are presented. In-orbit UV flat fields have been obtained and the f/96 objective prisms and polarizers have been calibrated.
An overview of the Faint Object Camera and its performance to date is presented. In particular, the detector's efficiency, the spatial uniformity of response, distortion characteristics, detector and sky background, detector linearity, spectrography, and operation are discussed. The effect of the severe spherical aberration of the telescope's primary mirror on the camera's point spread function is reviewed, as well as the impact it has on the camera's general performance. The scientific implications of the performance and the spherical aberration are outlined, with emphasis on possible remedies for spherical aberration, hardware remedies, and stellar population studies.
Results are presented of an evaluation of the first RANICON detector with a Negative Electron Affinity (NEA) photocathode, known as the Red-RANICON. The Red-RANICON offers a photocathode responsive quantum efficiency of about 22 percent from 0.6 - 0.9 micron, yielding a significant improvement in photon counting performance when compared with multialkali (S20) photocathode detectors. The operating characteristics of the Red-RANICON are similar to standard 25-mm active-area RANICONS, with imaging formats of 512 x 512 or 1024 x 1024 pixels. Spatial resolution is currently about 80 microns FWHM and could be improved to 40 microns FWHM with a modest decrease in the photocathode to microchannel-plate gap. The application of the Red-RANICON to high-resolution imaging and other applications requiring excellent temporal resolution is discussed. Future prospects for improving the long-wavelength response and quantum yield are also explored.