IBIS-TRE-01: Conceptual design of the IBIS 2.0 polarimetric unit

This document describes the polarimetric and optical design of the IBIS 2.0 polarimetric unit. Designed for the German Vacuum Tower Telescope, it will allow to acquire high resolution spectro-polarimetric data of the solar photosphere and chromosphere

Testing the steady-state fluctuation relation in the solar photospheric convection

The turbulent thermal convection on the Sun is an example of an irreversible non-equilibrium phenomenon in a quasi-steady state characterized by a continuous entropy production rate. Here, the statistical features of a proxy of the local entropy production rate, in solar quiet regions at different timescales, are investigated and compared with the symmetry conjecture of the steady-state fluctuation theorem by Gallavotti and Cohen. Our results show that solar turbulent convection satisfies the symmetries predicted by the fluctuation relation of the Gallavotti and Cohen theorem at a local level

IBIS2.0: The new Interferometric BIdimensional Spectrometer

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...

Observation and characterization of the solar turbulent convection

The turbulent solar magneto-convection is one of the most intriguing phenomena observed in our star. The convection zone regulates the energy transport from the radiative zone to the photosphere (where the photons are free to escape) by means of the bulk displacement of the solar plasma. The motions of convective cells is established by the gravitational field and the vertical temperature gradient and it basically consists in the upflow of the hotter and brighter plasma elements (the so-called granules) and the downflow of the colder and darker plasma elements (the intergranular lanes). The latter are turbulent due to the high stratification in density of the solar convective plasma and they are considered the drivers of the solar convection. This mere scenario is considerably complicated by the presence of the photospheric magnetic fields, which interact with the convection pattern and alter it, originating a large variety of phenomena, such as the appearance of magnetic bright points in the intergranular lanes or the onset of micropores. These phenomena are rather well explained by radiative magnetohydrodynamical (MHD) numerical simulations, which combine the properties of the solar plasma with the presence of the interacting magnetic fields and with the radiative transfer of the light. Despite the good agreement between radiative MHD simulations and high resolution observations, there are still several scientific open questions to be addressed and several processes that are not completely clear. High resolution spectro-polarimetry is the more suitable methodological tool that can be used to infer the physical conditions of the solar convective plasma. In fact, the polarization states at different wavelengths of the incoming solar light own the imprinting of the physical parameters of the solar atmosphere, which can be extracted using inversion techniques. To do this, we need high spatial (< 100 km on the solar surface), spectral (R > 200.000) and temporal (few tenth of seconds) resolution spectro-polarimetric data acquired with top level technology instruments and telescopes. In this PhD thesis, of the PhD program in Astronomy, Astrophysics and Space Science" of the jointly collaboration between University of Rome La Sapienza, University of Rome Tor Vergata and Istituto Nazionale di Astrofisica, I am interested in the study of the physical properties of the solar turbulent magneto-convection using two complementary approaches: data analysis of high-resolution spectro-polarimetric dataset, and design, development and realization of instrumentation for Solar Physics applications. In the Introduction, I present the current knowledge on turbulent solar magneto-convection, the parameters used to describe the convective plasma and the observation evidences compared to the theoretical approach of radiative MHD simulations. Then, I discuss on the open scientific questions on solar convection the instruments and methods needed and the organization of the manuscript. The Second Chapter is devoted to the theory of solar spectro-polarimetry, the radiative transfer and the analysis methods used in this thesis, the Center of Gravity Method (CoG) and the Inversion Techniques. After describing the dataset, I introduce my contribution to the data analysis part of this manuscript. I present a comparison analysis between the CoG method and the inversion techniques, showing evidences that the inversion techniques tend to overestimate weak magnetic fields in Quiet Sun regions. After that, I use the same dataset to evaluate the vertical heat flux maps, a proxy of the entropy production rate, which can be used as a clue to study the solar convection. With this analysis, I obtain strong evidenced that the solar turbulent convection satisfies the simmetry conjecture predicted by the Gallavotti-Cohen Fluctuation Theorem, analyzing the solar convection as a non-equilibrium stationary-state system. The Third Chapter is dedicated to the spectro-polarimetric instrumentation required for the observation of the solar convection. After describing the theory behind the operation of a Fabry-Perot Interferometer (FPI), I present three instrumental activities. I partecipated in the design, assembly and test phases of a FPI prototype controlled with one of the first digital controller, featuring its electronical noise and resulting spectral stability. This kind of digital control could substitute the old analog ones and they will be of fundamental importance for the next generation spectro polarimetric imaging instruments based on FPIs. After that, I realized a feasibility study of a narrow band imager based on large diameter FPIs and off-axis parabolic mirrors, starting from the conceptual design of Greco and Cavallini, using Zemax software. I implemented a new 3D version of the optical scheme, pointing out the improvements and the tolerance problem, and suggesting possible solutions to overcome these instrumental issues. At the end of this Chapter, I present the optical scheme of a full-disk solar synoptic telescope based on the Magneto-Optical Filters (MOF) technology that I entirely designed with Zemax. The new Tor vergata Solar Synoptic Telescope (TSST) will consist in this MOF-based telescope coupled with an Halpha solar telescope, and it will be used for large scale patterns studies, Space Weather applications and are forecasting. The last Chapter summarizes the results that I obtained during my PhD, discussing the achieved scientific impact and instrumental improvements. The thesis is concluded by discussions on future developments of the work done

Spectro-polarimetric analysis of a short lived solar active region

The physical processes related to the formation, evolution and disappearance of solar active regions are not completely clear. High-resolution solar spectro-polarimetric data are needed to investigate these processes with unprecedented details. Here we present the analysis of the short-lived NOAA 12549 active region using high-resolution spectro-polarimetric data acquired with the GREGOR solar telescope and the GRIS instrument, inverted using the SIR code

Analysis of Pseudo-Lyapunov Exponents of Solar Convection Using State-of-the-Art Observations

The solar photosphere and the outer layer of the Sun’s interior are characterized by convective motions, which display a chaotic and turbulent character. In this work, we evaluated the pseudo-Lyapunov exponents of the overshooting convective motions observed on the Sun’s surface by using a method employed in the literature to estimate those exponents, as well as another technique deduced from their definition. We analyzed observations taken with state-of-the-art instruments at ground- and space-based telescopes, and we particularly benefited from the spectro-polarimetric data acquired with the Interferometric Bidimensional Spectrometer, the Crisp Imaging SpectroPolarimeter, and the Helioseismic and Magnetic Imager. Following previous studies in the literature, we computed maps of four quantities which were representative of the physical properties of solar plasma in each observation, and estimated the pseudo-Lyapunov exponents from the residuals between the values of the quantities computed at any point in the map and the mean of values over the whole map. In contrast to previous results reported in the literature, we found that the computed exponents hold negative values, which are typical of a dissipative regime, for all the quantities derived from our observations. The values of the estimated exponents increase with the spatial resolution of the data and are almost unaffected by small concentrations of magnetic field. Finally, we showed that similar results were also achieved by estimating the exponents from residuals between the values at each point in maps derived from observations taken at different times. The latter estimation technique better accounts for the definition of these exponents than the method employed in previous studies

IBIS-04 System Design Description

The IBIS-04 "System Design Description" document presents the proposed opto-mechanical, electronical, automation and software design of the instrument for the preliminary Phase A of the project IBIS 2.0

The Tor Vergata Synoptic Solar Telescope (TSST): A robotic, compact facility for solar full disk imaging

By the continuous multi-line observation of the solar atmosphere, it is possible to infer the magnetic and dynamical status of the Sun. This activity is essential to identify the possible precursors of space weather events, such as flare or coronal mass ejections. We describe the design and assembly of TSST (Tor Vergata Synoptic Solar Telescope), a robotic synoptic telescope currently composed of two main full-disk instruments, a Hα telescope and a Potassium (KI D1) magneto-optical filter (MOF)-based telescope operating at 769.9 nm. TSST is designed to be later upgraded with a second MOF channel. This paper describes the TSST concepts and presents the first light observation carried out in February 2020. We show that TSST is a low-cost robotic facility able to achieve the necessary data for the study of precursors of space weather events (using the magnetic and velocity maps by the MOF telescope) and fast flare detection (by the Hα telescope) to support Space Weather investigation and services