Heat rejecter (HR) is a critical component of large aperture solar telescopes. It has the double task of acting as a Field Stop, to select the solar region to be studied, and as a heat rejecter to reduce the thermal load in the subsequent optics and keep the temperature of all internal surfaces within a few degrees of the ambient temperature. This last request is necessary to avoid the onset of internal convective air plumes and the subsequent generation of internal seeing. Since the thermal flux at the primary focus of a 4-m class telescope, as the European Solar Telescope (EST), is expected to be of the order of several MW=m2, even considering high HR reflectivity, the residual thermal load is conceivably high and a suitable Cooling Systems must be considered. Among the available cooling techniques, the most promising, and already applied in critical conditions such as for nuclear fusion reactor divertor, is the Multiple Jet Impingement (MJI) techniques. To fulfill the technological challenge of the HR for the next generation 4-m class European Solar Telescope (EST), a new prototype for the 1.5 meters GREGOR solar telescope has been developed as technological proof of concept. With the aim of testing this technique, a prototype of HR was realized to be mounted at the 1.5 meters GREGOR solar telescope at the at the Teide Observatory (Canary Islands, Spain). We present the HR thermal-hydraulic design based on the expected thermal load on the GREGOR primary focal plane (⋍ 1500W) and the constraints on the HR temperature. The MJI technology consists in a series of nozzles impinging the liquid coolant on the backside of the field stop hot wall. The high cooling capabilities of MJI relies on the high Reynolds numbers achievable, even with modest velocity flow. In this work we describe our efforts to design, fabricate and test the prototype of an HR to characterize the MJI technology. More in detail, we show the results of the hydraulic and thermal tests carried out in the opto-electronics laboratory of the Physics Department of the University of Rome Tor Vergata.
Synoptic telescopes are fundamental tools in Solar Physics and Space Weather. Their typical high cadence full-disk observations are pivotal to assess the physical conditions on the Sun and to forecast the evolution in time of those conditions. The TSST (Tor vergata Synoptic Solar Telescope) is a synoptic telescope composed of two main full-disk instruments: an H-alpha Daystar SR-127 telescope and a Magneto Optical Filter (MOF)-based telescope in the Potassium KI at 769.90 nm. The MOF consists in a glass cell containing a Potassium vapor where a longitudinal magnetic field is applied. The MOF-based channel produces full disk Line-of-Sight magnetic field and velocity maps of the solar photosphere at 300 km above the solar surface. In this work, we present the optical setup, the spectral characterization of the MOF-based telescope, and details on the spectral characterization of the MOFs cells which is a required test to obtain calibrated magnetograms and dopplergrams.
We present the IBIS2.0 project, which aims to upgrade and to install the Interferometric BIdimensional Spectrometer at the solar Vacuum Tower Telescope (Tenerife, Spain) after its disassembling from the Dunn Solar Telescope (New Mexico, USA). The instrument is undergoing a hardware and software revision that will allow it to perform new spectropolarimetric measurements of the solar atmosphere at high spatial, spectral and temporal resolution in coordination with other ground- and space-based instruments. Here we present the new opto-mechanical layout and control system designed for the instrument, and describe future steps.
Residual speckles in adaptive optics (AO) images represent a well-known limitation on the achievement of the contrast needed for faint source detection. Speckles in AO imagery can be the result of either residual atmospheric aberrations, not corrected by the AO, or slowly evolving aberrations induced by the optical system. We take advantage of the high temporal cadence (1 ms) of the data acquired by the System for Coronagraphy with High-order Adaptive Optics from R to K bands-VIS forerunner experiment at the Large Binocular Telescope to characterize the AO residual speckles at visible wavelengths. An accurate knowledge of the speckle pattern and its dynamics is of paramount importance for the application of methods aimed at their mitigation. By means of both an automatic identification software and information theory, we study the main statistical properties of AO residuals and their dynamics. We therefore provide a speckle characterization that can be incorporated into numerical simulations to increase their realism and to optimize the performances of both real-time and postprocessing techniques aimed at the reduction of the speckle noise.
The European Solar Telescope (EST) will be best suited for very high accuracy polarization measurements. Indeed, its optical design is such that the telescope as a whole does not modify the polarization state of the incoming light. For this reason, a mutually compensating configuration with non-standard 45 degrees tilted deformable mirrors (DMs) is proposed for its multi-conjugated adaptive optics (MCAO) system. We studied such non-standard configuration and the impact of DMs with large incidence angles on the overall performances of the EST MCAO system. In this work we present some preliminary results derived from our study.
Residual speckles in adaptive optics (AO) images represent a well known limitation to the achievement of the contrast needed for faint stellar companions detection. Speckles in AO imagery can be the result of either residual atmospheric aberrations, not corrected by the AO, or slowly evolving aberrations induced by the optical system. In this work we take advantage of new high temporal cadence (1 ms) data acquired by the SHARK forerunner experiment at the Large Binocular Telescope (LBT), to characterize the AO residual speckles at visible waveleghts. By means of an automatic identification of speckles, we study the main statistical properties of AO residuals. In addition, we also study the memory of the process, and thus the clearance time of the atmospheric aberrations, by using information Theory. These information are useful for increasing the realism of numerical simulations aimed at assessing the instrumental performances, and for the application of post-processing techniques on AO imagery.
Advanced Astronomy for Heliophysics Plus (ADAHELI+) is a project concept for a small solar and space weather mission with a budget compatible with an European Space Agency (ESA) S-class mission, including launch, and a fast development cycle. ADAHELI+ was submitted to the European Space Agency by a European-wide consortium of solar physics research institutes in response to the “Call for a small mission opportunity for a launch in 2017,” of March 9, 2012. The ADAHELI+ project builds on the heritage of the former ADAHELI mission, which had successfully completed its phase-A study under the Italian Space Agency 2007 Small Mission Programme, thus proving the soundness and feasibility of its innovative low-budget design. ADAHELI+ is a solar space mission with two main instruments: ISODY+: an imager, based on Fabry–Pérot interferometers, whose design is optimized to the acquisition of highest cadence, long-duration, multiline spectropolarimetric images in the visible/near-infrared region of the solar spectrum. XSPO: an x-ray polarimeter for solar flares in x-rays with energies in the 15 to 35 keV range. ADAHELI+ is capable of performing observations that cannot be addressed by other currently planned solar space missions, due to their limited telemetry, or by ground-based facilities, due to the problematic effect of the terrestrial atmosphere.
The FORS (closed loop forecasting system) control algorithm has been already successfully applied to improve the efficiency of a simulated adaptive optics (AO) system. To test its performance in real conditions, we implemented this algorithm in a hardware AO demonstrator, introducing controlled aberrations into the system. We present here the results of introducing into the system both a simple periodic defocus aberration and a real open loop defocus time sequence acquired at the vacuum tower telescope solar telescope. In both cases, FORS yields a significant performance increase, improving the stability of the system in closed-loop conditions and decreasing the amplitude of the residual uncorrected wavefront aberrations.
Spectropolarimetry is nowadays one of the most used tool to investigate small scale (100 km) magnetic fields in the Sun’s atmosphere. In addition, the forthcoming 4-meter class solar telescopes will provide an unprecedented view of the solar magnetism with an accuracy (10-4) never reached before, and on spatial scales which are at least twice as smaller. For this reason MCAO systems providing high Strehl ratios on a large field of view are being developed. Thus, the study of any possible effect of such AO systems on the polarization accuracy has to be carefully assessed. In this contribution we present preliminary results of laboratory tests conducted with the aim of evaluating possible drawbacks of the use of deformable mirrors on the spectropolarimetric accuracy.
We report the first optical and control performances of the Tor Vergata Fabry-P´erot interferometer prototype designed and realized in the framework of the ADvanced Astronomy for HELIophysics (ADAHELI) solar mission project. The characterization of the the coated surfaces of the two plates defining the optical cavity has been carried out with a Zygo interferometer able to measure the microroughness and global curvature of the cavity. The peak-to-valley errors are compliant with the manufacturer specifications and correspond to λ/70 and λ/80
@632.8 nm respectively. In addition, we present a first estimate of the interferometer spectral stability in stable open-air condition. A spectral uncertainty equal to 0.95 pm is found as the typical RMS over one hour of the passband central wavelength position.
In this contribution we present preliminary mechanical and optical tests of the Fabry-P´erot interferometer pro-
totype developed at the "Tor Vergata" University Solar Physics Laboratory. Fabry-P´erot narrow filters are of
great interest for the study of extended astronomical sources, such as the solar photosphere and chromosphere.
The high transparency of the instrument allows for the necessary high time-resolution for fast dynamic processes
observations. A dedicated software has been developed to control both coarse and fine piezo-actuated move-
ments, allowing for fast (1ms) tuning capabilities. General mechanical behaviour has been tested for use at the
focal plane of ground based telescopes and in the perspective of a new space-qualified prototype.
A forecasting algorithm (FORS) based on Auto Regressive Moving Average (ARMA) processes was developed
to correctly model stationary processes and was applied in simulations to the problem of improving the efficiency
of an adaptive optics (AO) system. We present here a hardware demonstrator developed at the Solar Physics
Laboratory of the University of Rome Tor Vergata where this algorithm has been implemented. An AO system
has been deployed to test the efficiency of the algorithm, in which controlled aberrations are introduced in the
system and the efficiency of the correction is measured. The demonstrator has proved that there is a significant
performance gain by using the FORS algorithm.
We present an overview of the conceptual design of the data handling unit of the ECS, the Control System for the
European Solar Telescope (EST). We will focus on describing the critical requirements for this unit resulting from the
overall design of the telescope, together with its architecture and the results of the feasibility analysis carried out to date.
The Doppler-Intensity-Magnetograms with a Magneto-optical filter Instrument at two heights (DIMMI-2h) is a
double channel imager using Magneto Optical Filters (MOF) in the potassium 770 nm and sodium 589 nm lines.
The instrument will provide simultaneous dopplergrams (velocity fields), continuum intensity and longitudinal
magnetic flux images at two heights in the solar atmosphere corresponding to low and high photosphere. Dimmi-
2h is the possible piggy-back payload on ADAHELI satellite. The spatial resolution (approximately 4 arcsec) and
the high temporal cadence (15 s) will permit to investigate low and medium oscillating modes (from 0 to below
1000) up to approximately 32 mHz in the frequency spectrum. The acquisition of long-term simultaneous velocity,
intensity and magnetic information up to these high frequencies will permit also the study of the propagation
and excitation of the waves with a frequency resolution never obtained before.
ADAHELI ADvanced Astronomy for HELIophysics is a solar satellite designed to investigate the fast dynamics of
the solar photosphere and chromosphere performing visible and NIR broad-band and monochromatic observations
of selected atomic lines. ADAHELI is an Italian Space Agency (ASI) project, approved for a feasibility study
within the ASI Small Missions call. ISODY Interferometer for SOlar DYnamics is a Gregorian telescope and
its focal plane suite (FPS). The FPS is composed of a high-resolution fast acquisition system, based upon a
tandem of Fabry-Pérot interferometers operating in the visible and NIR regions on selected solar atmospheric
lines, a broad band channel, and a correlation tracker used as image stabilization system. In this contribution we
describe the Fabry-Pérot étalon prototype, based on the capacitance-stabilised concept, realized in our laboratory
to perform preliminary mechanical and optical tests with a view to a future Fabry-Pérot étalon prototype for
In this work we conduct a comparative study on different data compression methods applied to high resolution
images of the solar surface acquired at the Solar Dunn Telescope in Sacramento Peak with the IBIS (Interferometric
Bidimensional Spectrometer) instrument. Our aim is to perform an estimation of the quality, efficiency
and workload of the considered computing techniques both in the so-called lossless modality, where in the reconstruction
phase there is no loss of information, and in lossy mode, where it should be possible to reach a
high compression ratio at the expense of image information. In the latter case we quantify the quality with image
analysis conventional methods and more specifically with the reconstruction of physical parameters through
standard procedures used in this kind of observations. The considered methods constitute the most frequently
adopted image compression procedures in a variety of fields of application; they exploit in different ways the
properties of the Discrete Wavelet Transforms often coupled with standard entropy coders or similar coding
procedures applied to the different bit planes in order to allow a progressive handling of the original image. In
the lossless approach we found that all methods give a compression ratio around 2. For a lossy compression
we reached a compression ratio of 8 (equivalent to a 2 bit per pixel) without any perceptual difference between
original and reconstructed images, but with effects on the photometric accuracy. We also tested the performance
of 3-D lossy methods for the compression of data-cubes. Maintaining the same data degradation level, those
methods allows us to gain a 2x in the compression ratio over the 2-D methods.
A study is presented for the realization of the heat stop for the 4-m European Solar Telescope EST, whose
feasibility study will be completed in 2011. EST is an on-axis Gregorian telescope, equipped with a four-meter
diameter primary mirror and primary focal length of about six meters. The heat stop, positioned at the primary
focus, must be able to remove a heat load of 13 kW, while maintaining its surfaces very close to room temperature,
to avoid the onset of seeing. In order to remove the heat, three configurations have been taken into consideration:
1) a flat 45° inclined heat rejecter, 2) a 45° conical heat rejecter and 3) a heat trap (made of a conical heat
rejecter and a cylindrical heat absorber). All devices include an air removal system to avoid the formation of
In the framework of a 4m class Solar Telescope we studied the performance of the MCAO using the LOST
simulation package. In particular, in this work we focus on two different methods to reduce the time delay
error which is particularly critical in solar adaptive optics: a) the optimization of the wavefront reconstruction
by reordering the modal base on the basis of the Mutual Information and b) the possibility of forecasting the
wavefront correction through different approaches. We evaluate these techniques underlining pros and cons of
their usage in different control conditions by analyzing the results of the simulations and make some preliminary
tests on real data.
We give an overview of the Adaptive Optics (AO) and Multi-conjugate Adaptive Optics (MCAO) system of the
planned 4m European Solar Telescope (EST). The parameter space and the problems of solar MCAO working
in the visible are explained. The wavefront reconstruction schemes presently being considered are explained.
First estimates of the expected MCAO performance for varying parameter sets are given.
A consortium of more than 20 European solar physics institution from 15 different countries is conducting a design
study for a 4 m class solar telescope which shall be situated at the Canary Islands. In this paper we introduce the AO and
MCAO design concept for EST. A ground layer deformable mirror is combined with an arrangement of four deformable
layer mirrors. A combination of Shack-Hartmann wave front sensors with wide and narrow fields of view is used to
control the system and to achieve a corrected field of view of one arcmin.