The European Solar Telescope is a project for a 4-meter class telescope to be located in the Canary Islands. EST is
promoted by the European Association for Solar Telescopes (EAST). This is a consortium formed by a number of
research organizations from fifteen European countries (Austria, Croatia, Czech Republic, France, Germany, Hungary,
Italy, the Netherlands, Norway, Poland, Slovak Republic, Spain, Sweden, Switzerland, and United Kingdom). EST will
specialize in high spatial and temporal resolution using diverse instruments that can efficiently produce two-dimensional
spectropolarimetric information of the thermal, dynamic and magnetic properties of the plasma over many scale heights
in the solar atmosphere. In this contribution, the status of the development of the Design Study of EST is presented,
emphasizing the most important aspects of the optical design, mechanical structure, AO and MCAO systems for
wavefront correction, instruments and polarization analysis.
EST (European Solar Telescope) is a 4-m class solar telescope, which is currently in the conceptual design phase. EST
will be located at the Canary Islands and aims at observations with the best possible spectral, spatial and temporal
resolution and best polarimetric performance, of the solar photosphere and chromosphere, using a suite of instruments
that can efficiently produce two-dimensional spectropolarimetric information of the thermal, dynamic and magnetic
properties of the plasma over many scale heights, and ranging from λ=350 until 2300 nm.
In order to be able to fulfill the stringent requirements for polarimetric sensitivity and accuracy, from the very beginning
the polarimetry has been included in the design work. The overall philosophy has been to use a combination of
techniques, which includes a telescope with low (and stable) instrumental polarization, optimal full Stokes polarimeters,
differential measurement schemes, fast modulation and demodulation, and accurate calibration.
The current baseline optical layout consists of a 14-mirror layout, which is polarimetrically compensated and nonvarying
in time. In the polarization free F2 focus ample space is reserved for calibration and modulators and a
polarimetric switch. At instrument level the s-, and p-planes of individual components are aligned, resulting in a system
in which eigenvectors can travel undisturbed through the system.
Spectro-polarimetry plays an important role in the study of solar magnetism and strongly influences the design of the
new generation of solar telescopes. Calibration of the polarization properties of the telescope is a critical requirement
needed to use these observations to infer solar magnetic fields. However, the large apertures of these new telescopes
make direct calibration with polarization calibration optics placed before all the telescope optical elements impractical.
It is therefore desirable to be able to infer the polarization properties of the telescope optical elements utilizing solar
observations themselves. Taking advantage of the fact that the un-polarized, linearly, and circularly polarized spectra
originating from the Sun are uncorrelated, we have developed techniques to utilize observations of solar spectra with
redundant combination of the polarization states measured at several different telescope configurations to infer the
polarization properties of the telescope as a whole and of its optical elements. We show results of these techniques
applied to spectro-plarimetric data obtained at the Dunn Solar Telescope.
This communication reviews the participation of the Instituto de Astrofísica de Canarias (IAC) in the design of the
European Solar Telescope. Apart of being the coordinator institution of the whole project, and, as such, responsible for
the project managing, the IAC leads several tasks like overall instrument definition or characterization of the
atmospheric turbulence profile with height or the definition of adequate detectors. More in particular, the IAC will
design and build two long-base SHABAR (SHAdow BAnd Ranger), instruments to measure medium-altitude seeing.
The IAC is also responsible for the design, together with other institutions, of the design of grating spectropolarimeters
suitable for multiwavelength high spatial and spectral resolution.
The Advanced Solar Technology Telescope (ATST) is a 4-m solar telescope being designed for high spatial, spectral and temporal resolution, as well as IR and low-scattered light observations. The overall limit of performance of the telescope is strongly influenced by the qualities of the site at which it is located. Six sites were tested with a seeing monitor and a sky brightness instrument for 1.5 to 2 years. The sites were Big Bear (California), Haleakala (Hawaii), La Palma (Canary Islands, Spain), Panguitch Lake (Utah), Sacramento Peak (New Mexico), and San Pedro Martir (Baja California, Mexico). In this paper we will describe the methods and results of the site survey, which chose Haleakala as the location of the ATST.
This paper addresses the issue of calibrating the Advanced Technology Solar Telescope for high-precision polarimetry, in particular of the optical train above the Gregorian station (where suitable calibration optics will be placed). Conventional techniques would not be adequate for this telescope given its large aperture. Here we explore two different methods that are currently being considered by the design team. The first one is the "sub-aperture" method, which uses small calibration optics above the primary mirror to calibrate a small sub-aperture of the system. This calibration is then extended to the full aperture by means of actual observations. The second method is based on analyzing the polarization observed in a spectral line with a peculiar Zeeman pattern, such as the FeII 614.9 nm line, which does not produce any intrinsic linear polarization. Numerical simulations are presented that show the robustness of both techniques and their respective advantages and disadvantages are discussed.
The mission of the ATST visible spectro-polarimeter (ViSP) is to provide precision measurements of the full state of polarization (Stokes parameters) simultaneously at diverse wavelengths in the visible spectrum and fully resolve (or nearly so) the profiles of spectrum lines originating in the solar atmosphere. We present the instrument science requirements, their flow down to instrument specifications, and a preliminary ViSP design. The ViSP spectrograph allows for reconfiguration while maintaining an immediately selectable configuration. We describe how the ViSP will utilize the ATST polarimetry facility.
The 4-m aperture Advanced Technology Solar Telescope (ATST) is the next generation ground based solar telescope. In this paper we provide an overview of the ATST post-focus instrumentation. The majority of ATST instrumentation is located in an instrument Coude lab facility, where a rotating platform provides image de-rotation. A high order adaptive optics system delivers a corrected beam to the Coude lab facility. Alternatively, instruments can be mounted at Nasmyth or a small Gregorian area. For example, instruments for observing the faint corona preferably will be mounted at Nasmyth focus where maximum throughput is achieved. In addition, the Nasmyth focus has minimum telescope polarization and minimum stray light. We describe the set of first generation instruments, which include a Visible-Light Broadband Imager (VLBI), Visible and Near-Infrared (NIR) Spectropolarimeters, Visible and NIR Tunable Filters, a Thermal-Infrared Polarimeter & Spectrometer and a UV-Polarimeter. We also discuss unique and efficient approaches to the ATST instrumentation, which builds on the use of common components such as detector systems, polarimetry packages and various opto-mechanical components.
The location of the Advanced Technology Solar Telescope (ATST) is a critical factor in the overall performance of the telescope. We have developed a set of instrumentation to measure daytime seeing, sky brightness, cloud cover, water vapor, dust levels, and weather. The instruments have been located at six sites for periods of one to two years. Here we describe the sites and instrumentation, discuss the data reduction, and present some preliminary results. We demonstrate that it is possible to estimate seeing as a function of height near the ground with an array of scintillometers, and that there is a distinct qualitative difference in daytime seeing between sites with or without a nearby lake.
Measuring vector magnetic fields in the solar atmosphere using the profiles of the Stokes parameters of polarized spectral lines split by the Zeeman effect is known as Stokes Inversion. This inverse problem is usually solved by least-squares fitting of the Stokes profiles. However least-squares inversion is too slow for the new generation of solar instruments (THEMIS, SOLIS, Solar-B, ...) which will produce an ever-growing flood of spectral data. The solar community urgently requires a new approach capable of handling this information explosion, preferably in real-time. We have successfully applied pattern recognition and machine learning techniques to tackle this problem. For example, we have developed PCA-inversion, a database search technique based on Principal Component Analysis of the Stokes profiles. Search is fast because it is carried out in low dimensional PCA feature space, rather than the high dimensional space of the spectral signals. Such a data compression approach has been widely used for search and retrieval in many areas of data mining. PCA-inversion is the basis of a new inversion code called FATIMA (Fast Analysis Technique for the Inversion of Magnetic Atmospheres). Tests on data from HAO's Advanced Stokes Polarimeter show that FATIMA isover two orders of magnitude faster than least squares inversion. Initial tests on an alternative code (DIANNE - Direct Inversion based on Artificial Neural NEtworks) show great promise of achieving real-time performance. In this paper we present the latest achievements of FATIMA and DIANNE, two powerful examples of how pattern recognition techniques can revolutionize data analysis in astronomy.