Luca Giovannelli

The Fabry-Pérot interferometer prototype for the ADAHELI solar small mission

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 space application.

ADAHELI+: exploring the fast, dynamic Sun in the x-ray, optical, and near-infrared

Abstract. 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 effects of AO systems on polarized light

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.

Hyperspectral camera based on a Fabry-Pérot with varying beam incidence

Fabry-Perot interferometers are commonly used as tunable filters in a variety of scientific fields. We here consider the use of a single Fabry-Perot as a universal tunable filter in hyperspectral imaging applications, when it is necessary to recover image information of the scientific target at different wavelengths. Fabry-Perot are commonly used to scan small portions of the spectrum, defined by suitable prefilters. This is necessary due to the multi-peak response of a single interferometer. In order to overcome this issue we propose a novel triple-pass configuration, able to provide a fast and continuous sampling of the electromagnetic spectrum in the visible-infrared range without the need for a collection of dedicated prefilters.

JP3D compression of solar data-cubes: Photospheric imaging and spectropolarimetry

Hyperspectral imaging is an ubiquitous technique in solar physics observations and the recent advances in solar instrumentation enabled us to acquire and record data at an unprecedented rate. The huge amount of data which will be archived in the upcoming solar observatories press us to compress the data in order to reduce the storage space and transfer times. The correlation present over all dimensions, spatial, temporal and spectral, of solar data-sets suggests the use of a 3D base wavelet decomposition, to achieve higher compression rates. In this work, we evaluate the performance of the recent JPEG2000 Part 10 standard, known as JP3D, for the lossless compression of several types of solar data-cubes. We explore the differences in: a) The compressibility of broad-band or narrow-band time-sequence; I or V Stokes profiles in spectropolarimetric data-sets; b) Compressing data in [x,y, λ] packages at different times or data in [x,y,t] packages of different wavelength; c) Compressing a single large data-cube or several smaller data-cubes; d) Compressing data which is under-sampled or super-sampled with respect to the diffraction cut-off.

N-body model of magnetic flux tubes reconnecting in the solar atmosphere

The investigation of dynamics of the small scale magnetic field on the Sun photosphere is necessary to understand the physical processes occurring in the higher layers of solar atmosphere due to the magnetic coupling between the photosphere and the corona. We present a simulation able to address these phenomena investigating the statistics of magnetic loops reconnections. The simulation is based on N-body model approach and is divided in two computational layers. We simplify the convection problem, interpreting the larger convective scale, mesogranulation, as the result of the collective interaction of convective downflow of granular scale. The N-body advection model is the base to generate a synthetic time series of nanoflares produced by interacting magnetic loops. The reconnection of magnetic field lines is the result of the advection of the magnetic footpoints following the velocity field generated by the interacting downflows. The model gives a quantitative idea of how much energy is expected to be released by the reconfiguration of magnetic loops in the quiet Sun.

Optical cavity characterization of the Tor Vergata Fabry-Pérot interferometer

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.

Optical tests of the LUTIN Fabry-Pérot prototype

The soLar group University of Tor vergata fabry-perot INterferometer (LUTIN) is a narrow band filter based on an optical cavity resonator with Capacitance-Stabilised Etalon (CSE) control. The prototype, developed at the University of Rome Tor Vergata, is part of the study for the narrow band channel of the ADvanced Astronomy for HELIophysics (ADAHELI) mission designed to investigate the dynamics of solar atmosphere as part of the Italian Space Agency (ASI) Small Missions program. We developed the electro-mechanical control for the optical cavity, necessary for the tuning and the gap control of the instrument. We present the measures of the microroughness of the optical plates, performed with a Zygo interferometer, and the instrument spectral stability behaviour in on-optical-bench open-air mode. The measures refer to the upgraded version of the LUTIN prototype, which mounts the new λ/60 optical plates.

Improvements on adaptive optics control approaches: experimental tests of wavefront correction forecasting

Abstract. 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.

The birth of Tor Vergata Fabry-Pérot interferometer

Fabry-Perot tunable niters are of great interest in high spectral resolution imaging for both ground-based and space astronomical observations. Major advantages include imaging capabilities and the study of extended astronomical sources, such as the solar photosphere. The high transparency of the instrument allows the high time-resolution necessary for the observation of fast dynamic processes. The prototype here presented has been developed as part of the study for the narrow band channel of the ADAHELI mission. The ADvanced Astronomy for HELIophysics (ADAHELI) is a solar satellite designed to investigate the dynamics of solar atmosphere as part of the Italian Space Agency (ASI) program.