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.
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<sup>-4</sup>) 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.
The possibility to perform polarimetry in the soft X-ray energy band (2-10 keV) with the Gas Pixel Detector, filled with low Z mixtures, has been widely explored so far. The possibility to extend the technique to higher energies, in combination with multilayer optics, has been also hypothesized in the past, on the basis of simulations. Here we present a recent development to perform imaging polarimetry between 6 and 35 keV, employing a new design for the GPD, filled with a Ar-DME gas mixture at high pressure. In order to improve the efficiency by increasing the absorption gap, while preserving a good parallel electric field, we developed a new configuration characterized by a wider gas cell and a wider GEM. The uniform electric field allows to maintain high polarimetric capabilities without any decrease of spectroscopic and imaging properties. We present the first measurements of this prototype showing that it is now possible to perform imaging and spectro-polarimetry of hard X-ray sources.
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.
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
We used a laser system for determining the bandpasses of the two vapour cells, the Magneto-Optical Filter (MOF)
and the Wing Selector (WS), which are the core of solar narrow-band filters based on the MOF technology. A
new result, which we called the Intensity Effect, was found: the MOF and WS bandpasses depend not only on
the temperature at which the cell is heated and the external magnetic field in which the cell is embedded, but
also on the radiation intensity entering the cell. A theoretical interpretation of the Intensity Effect is proposed
in terms of the kinetic equilibrium of the potassium atomic populations inside the vapour cell. We need to take
the Intensity Effect into account for setting-up MOF based instruments for solar and stellar observations as well
as for modelling the MOF and WS spectral transmissions.
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.
ADvanced Astronomy for HELIophysics (ADAHELI) is a Small Mission to study the structure and fast dynamics of
the low solar atmosphere, performing Visible-NIR monochromatic and broad-band observations. The mission will
achieve millimeter full disk observations as well. The ADAHELI Team has succesfully completed, in December
2008, the Phase A study awarded by the Italian Space Agency (ASI).
The Interferometer for SOlar Dynamics (ISODY), on board the ADAHELI satellite, comprises a Gregorian
telescope and its focal plane suite. The advanced design focal plane suite uses fast CMOS cameras for investigating
photospheric and chromospheric fast dynamics and structure. ISODY is equipped with a pioneering focal plane suite
composed of a spectral channel, based upon a tandem of Fabry-Perot interferometers operating in the visible-NIR
spectral region, a broad band channel for high resolution imaging, and a correlation tracker used as an image
stabilization system. ADAHELI's mission profile has been tailored to limit the spacecraft's radial velocity in the
Sunward direction, to not exceed ±4 km/s, during 95% of the yearly orbit, to allow a continuous use of the on-board
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.
The solar telescope EST is currently in the conceptual design phase. It is planned to be build on the Canary Islands until
end of the decade. It is specialized on polarimetric observations and will provide high spatial and spectral observations of
the different solar atmospheric layers.
The diameter of the primary mirror blank is 4.2m. Different types of mirror shapes were investigated with respect to
thermal and mechanical characteristics.
To remove the absorbed heat an air cooling system from the back side will be applied. Additional an air flushing system
will remove remaining warm air from the front side.
A major problem of a large open telescope will be the wind load. Results of the investigations will be shown. To achieve
optimal optical performance an active support system is planned. The primary mirror cell needs to be stiff enough to
support the primary mirror without deformation at strong wind in case of the open telescope option, but sufficient room
for the active support system and cooling system below the backside of the mirror is also required. Preliminary designs
and analysis results will be presented.
We briefly describe the design and the characteristics of the Italian Panoramic Monochromator installed at the focal plane of the THEMIS telescope built in Izana by a joint venture of the French and Italian National Research Councils. The Panoramic Monochromator substantially is a narrow band filter (approximately equals 22 mAngstrom bandwidth) tunable on the visible spectrum for quasi simultaneous bidimensional spectrometry of the solar atmosphere. The narrow bandwidth is obtained by using a non standard birefringent filter and a Fabry Perot interferometer mounted in series. This assembly has the advantage of the spectral purity of one channel of the Fabry Perot interferometer and a very large free spectral range. Moreover the spectral stability depends on the interferometer, the environment of which may be carefully controlled. The design of this instrument is not really new, but, only now it has been possible to build it thanks to the development of servo controlled Fabry Perot interferometers, which are stable in time and may easily be tuned. The system seems to perform well. It is stable in wavelength and the spectral pass band and stray light are within the expected values, as it may be deduced by very preliminary tests performed at the THEMIS Telescope and in Arcetri (Firenze) at the 'G. B. Donati' solar tower.