CATEGORIES
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EST2018
Affiliation UNIVERSITA' DEGLI STUDI DI CATANIA
Giardini Naxos (Me), Italy
11.06.2018 - 15.06.2018

Organizing institutions
Università degli Studi di Catania
Main category Natural Sciences (Astrophysics and Astrononmy)
Conference/Workshop objectives
The European Solar Telescope (EST), is a 4-metre class aperture telescope designed to investigate our active Sun at very high spatial and temporal resolution and unprecedented polarimetric sensitivity. Equipped with state-of-the-art instrumentation, it will help scientists understand magnetic coupling throughout the solar atmosphere. EST will be installed in the Canary Islands (Spain) to benefit from unique observing conditions. First light is planned for 2027. The project is promoted by the European Association for Solar Telescopes (EAST) whose aim is to ensure access of European solar astronomers to world-class high-resolution ground-based observing facilities and keep Europe at the forefront of solar physics. Thanks to EU FP7 and H2020 funding, joint research activities have been carried out to determine the most advanced technological solutions that would allow the realization of this state-of-the-art 4-metre telescope. In March 2016, EST was included in the European Strategic Forum on Research Infrastructure (ESFRI) Roadmap and it is now in its Preparatory Phase. During this phase, the Science Requirements are being reviewed by the Science Advisory Group (SAG), taking into account both the advancement in our knowledge of the physics of the Sun and the progress in technology. This upcoming EST Science Meeting aims at gathering scientists who wish to present their most recent theoretical and observational research in the field. The meeting will highlight the key science cases that will be addressed by the 4-metre class solar telescopes, and the synergies with both current and future ground-based and space-borne facilities. During the EST Science Meeting the main characteristics and science goals of the EST project will be presented to the scientific community to maximize the sharing of knowledge about the project and provide awareness of the potential telescope capabilities. It will also provide an opportunity to contribute to the definition of the telescope Science Requirements. A Science Requirements Document, describing how and why the unique capabilities of EST will provide answers to several key science questions, will be presented at the meeting. EST will be the heritage of the entire solar physics community, and for this reason it is expected that the scientific community and in particular the EST Science Meeting participants, will contribute with science cases that will then be reflected in the Science Requirement Document.
Local organizing committee
• Clelia Anastasi (Università di Catania, Italy)
• Giancarlo Bellassai (INAF - Osservatorio Astrofisico di Catania, Italy)
• Mariachiara Falco (INAF - Osservatorio Astrofisico di Catania, Italy)
• Manuel González (IAA - CSIC, Spain)
• Salvo Guglielmino (Università di Catania, Italy)
• Alejandra Martin Gálvez (IAC, Spain)
• Eugenio Martinetti (INAF - Osservatorio Astrofisico di Catania, Italy)
• Paolo Romano (Co-Chair, INAF - Osservatorio Astrofisico di Catania, Italy)
• Gina Santagati (INAF - Osservatorio Astrofisico di Catania, Italy)
• Francesca Zuccarello (Chair, Università di Catania, Italy)
Scientific organizing committee (SOC)
• Luca Belluzzi (IRSOL, Switzerland)
• Mats Carlsson (Universitet i Oslo, Norway)
• Manuel Collados Vera (IAC, Spain)
• Jan Jurcak (CAS, Czech Republic)
• Mihalis Mathioudakis (QUB, United Kingdom)
• Sarah Matthews (MSSL, United Kingdom)
• Robertus Erdelyi (U. of Sheffield, United Kingdom)
• Rolf Schlichenmaier (Co-Chair, KIS, Germany)
• Dominik Utz (IGAM, Austria)
• Francesca Zuccarello (Chair, Università di Catania, Italy)
Sessions
• 1. The State-of-the-Art of the EST Project
• 2. Structure and Evolution of Magnetic Flux
• 3. Wave Coupling throughout the Solar Atmosphere
• 4. Chromospheric Dynamics and Heating
• 5. Large Scale Dynamic Structures: Sunspots, Prominences and Filaments
• 6. The Solar Corona
• 7. Solar Flares and Eruptive Filaments
• 8. Scattering Physics and Hanle - Zeeman Diagnostics
Programme
Invited speakers
• Nazaret Bellot Gonzales,
• Roberto Casini,
• Mark Cheung,
• Manolis Georgoulis,
• Viggo Hansten,
• Valery Nagariakov,
Important dates
•     15 February: First announcement
•     22 February: Early Registration begins
•     22 February: Abstract submission begins
•     13 April: Abstract submission ends
•     20 April: Preliminary program
•     30 April: Early Registration Deadline
•     11 May: Final programme
•     11 June: Meeting begins
•     15 June: Meeting ends
Registration and payment information

Registration  is open.

Fees

• Early bird registration fee until April 30, 2018:     € 400,- per person
• Registration fee PhD students                             € 250,- per person
• Late registration after April 30, 2018:                  € 500,- per person

The registration fee covers:

•     welcome reception on Monday evening,
•     coffee breaks
•     lunches from Monday through Friday at the conference venue,
•     conference dinner on Thursday evening

To register, please fill the registration form.

Information on how to do the payment can be found here.

Limited funds are available to support the attendance of PhD students and post-docs (see the registration form).

Conference venue

AtaHotel Naxos Beach Resort - Giardini Naxos (Me), Italy

Hotel information
Travel information

Session: 4. Chromospheric Dynamics and Heating

241 views
24.06.2018
Co-author:
Caption:
1st movie for EST 2018 conference's presentation ("High Cadence Observations of the Solar Flares in the H-alpha Line" by Krzysztof Radziszewski and Pawel Rudawy)

Session: 4. Chromospheric Dynamics and Heating

237 views
24.06.2018
Co-author:
Caption:
2nd movie for EST 2018 conference's presentation ("High Cadence Observations of the Solar Flares in the H-alpha Line" by Krzysztof Radziszewski and Pawel Rudawy)

Session: 4. Chromospheric Dynamics and Heating

243 views
24.06.2018
Co-author:
Caption:
3th movie for EST 2018 conference's presentation ("High Cadence Observations of the Solar Flares in the H-alpha Line" by Krzysztof Radziszewski and Pawel Rudawy)

Session: 4. Chromospheric Dynamics and Heating

299 views
24.06.2018
Co-author:
Caption:
4th movie for EST 2018 conference's presentation ("High Cadence Observations of the Solar Flares in the H-alpha Line" by Krzysztof Radziszewski and Pawel Rudawy)

Session: 4. Chromospheric Dynamics and Heating

302 views
24.06.2018
Co-author:
Caption:
5th movie for EST 2018 conference's presentation ("High Cadence Observations of the Solar Flares in the H-alpha Line" by Krzysztof Radziszewski and Pawel Rudawy)

Session: 1. The State-of-the-Art of the EST Project

157 views
05.07.2018
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Caption:
The first EST Science Meeting took place last month in Sicily thanks to the great coordination of the Università degli Studi di Catania. Solar Physicists from different parts of the world met to discuss the top science cases defined for EST and the state of the art of current instrumentation and the future desired perspectives to understand our active Sun.

Session: 1. The State-of-the-Art of the EST Project

506 views
28.03.2018
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Caption:
Promotional video for the European Solar Telescope (EST-IAC). EST is a revolutionary 4-metre aperture telescope designed to investigate our active Sun at unprecedented resolution. EST will be installed in the Canary Islands (Spain) to benefit from unique observing conditions. First light is planned for 2027.

Session: 7. Solar Flares and Eruptive Filaments

148 views
14.06.2018
Co-author:
Aaron Reid, Ryan Milligan, Paulo Simões, Joel Allred, Mihalis Mathioudakis
Abstract:
Observations of an X1 white-light solar flare on 11 July 2014 showed an extraordinarily weak emission in hydrogen lines, extremely hard X-ray spectrum and indications for proton beams. We have used the radiative hydrodynamic code RADYN to model the response of the solar atmosphere with a grid of models that was based on electron and proton beam parameters that may be most appropriate for this type of event. We then use the radiative transfer code RH to synthesise line profiles from these atmospheres to compare to observations. We selected those models that agree best with the RHESSI/Fermi, ground-based spectra (350 – 440 nm) and HMI white-light continuum data. Our analysis shows that the observed atmospheric response could be reproduced with a relatively weak particle beam with a high low energy cut-off. We found that both electron and proton beams can generate the observed flare emission but it is easier for the protons to penetrate deeper into the atmosphere and deliver their energy in the lower chromosphere where the excess white-light continuum emission originates. Observations of such events with higher spatial resolution at shorter wavelengths would allow more accurately determine the flaring area and the nature of WL emission.

Session: 6. The Solar Corona

155 views
14.06.2018
Co-author:
D. H. Mackay, L. M. Green
Abstract:
To gain a better understanding of the formation and evolution of the pre-eruptive structure of CMEs requires the direct measurement of the coronal magnetic field, which is currently very difficult. An alternative approach, such as using the photospheric magnetic field as a boundary condition to simulate a time series of the coronal field must be used to infer the pre-eruptive magnetic structure and coronal evolution prior to eruption. The evolution of the coronal magnetic field of a small sub-set of bipolar active regions is simulated by applying the magnetofrictonal relaxation technique of Mackay et al. (2011). A sequence of photospheric line-of-sight magnetograms produced by SDO/HMI are used to drive the simulation and continuously evolve the coronal magnetic field of the active regions through a series of non-linear force-free equilibria. The simulation is started during the first stages of active region emergence so that the full evolution from emergence to decay can be simulated. A comparison of the simulation results with SDO/AIA observations show that many aspects of the observed coronal evolution of the active regions can be reproduced, including the majority of eruptions associated with the regions. To better constrain these models requires the use of accurate vector magnetic field measurements with high polarimetric precision as the initial condition such as those that will be produced by EST.

Session: 3. Wave Coupling throughout the Solar Atmosphere

142 views
14.06.2018
Co-author:
Thomas Williams
Abstract:
The ubiquity of magnetic twists and plasma flows, as well as their importance in generating the dynamic behaviour of the Sun has become apparent only recently due to improvements in spectral, temporal and spatial resolution of instrumentation. We demonstrate how energy is transferred from plasma flows into magnetic twists and vice-versa. The dynamic and energetic consequences of coupling between plasma l ows and magnetic twists in the solar atmosphere will be addressed using time-dependent modelling in 1.5 dimensions. These consequences include the excitation of large amplitude propagating Alfven waves, the subsequent generation of slow and fast shocks due to nonlinear coupling, the formation of globally twisted structures that may become unstable. The implications of the coupling process and the twist amplification will be discussed in the contexts of Evershed flows, intergranular downdrafts, and chromospheric evaporation in coronal loops.

Session: 2. Structure and Evolution of Magnetic Flux

174 views
15.06.2018
Co-author:
Abstract:
This is the second part of my talk at the meeting EST2018.

Session: 7. Solar Flares and Eruptive Filaments

171 views
15.06.2018
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Abstract:
Solar flares and eruptive events are driven by the 3D evolution of current-carrying magnetic fields in the solar atmosphere. While several mechanisms have been identified, we still do not know which ones are really responsible for the trigger of these flaring phenomena. This is because our knowledge of the 3D magnetic field in the solar atmosphere mostly rely on the approximate 3D solution obtained from force-free coronal magnetic field extrapolations of the 2D photospheric measurements. The European Solar Telescope will provide magnetic field measurements of the solar photosphere and chromosphere with unprecedented polarimetric sensitivity and very high spatial and temporal resolution. Such measurements will provide original information for better constraining the 3D magnetic field in the solar atmosphere. In this talk, we discuss how EST measurements may help us identifying the mechanisms triggering solar flares and eruptive events, and the relationships between the local 3D magnetic field properties and the flare signatures.

Session: 2. Structure and Evolution of Magnetic Flux

136 views
15.06.2018
Co-author:
KuanVai Tam & Yanxiao,Liu & CGST team
Abstract:
This is the first part of my talk at the meeting EST2018.

Session: 6. The Solar Corona

129 views
16.06.2018
Co-author:
A. Petralia, P. Testa
Abstract:
IRIS has observed bright spots at the transition region footpoints. These spots showed significant blueshifts in the Si IV line at 1402.77 A (T~ 10^4.9 K). Such blueshifts could not be reproduced by coronal loop models assuming heating by thermal conduction only, but were consistent with electron beam heating, highlighting for the first time the possible importance of non-thermal electrons in the heating of non-flaring active regions (Testa et al. 2014, Science). Here we report on the coronal counterparts of these brightenings observed in the hot channels of the Imaging Atmospheric Assembly on board the Solar Dynamics Observatory. We show that the IRIS bright spots are the footpoints of very hot and transient coronal loops which clearly experience strong magnetic rearrangements, thus confirming the impulsive nature of the heating and providing important constraints for physical interpretation (Petralia et al., this meeting).

Session: 7. Solar Flares and Eruptive Filaments

173 views
16.06.2018
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Abstract:
The Large Angle Spectrometric Coronagraph (LASCO), onboard the Solar and Heliospheric Observatory (SOHO) provided us observations extending for the two Solar Cycles 23 and 24 (31 July 1996 - 31 March 2014) that allow one to compare some properties (speed, acceleration, polar angle, angular width, and mass) of Coronal Mass Ejection (CMEs). The Coordinated Data Analysis Workshops (CDAW) Data Center datasets uses manual identification for the detection of the CMEs, while the Computer Aided CME Tracking software (CACTus) datasets uses an automatic detection algorithm. Some important results found in this analysis, for both dataset, are that there are more CMEs during the maximum of Solar Cycle 24 than during the maximum of Solar Cycle 23, although the photospheric level and magnetic activity of the Sun during Cycle 24 was weaker than during Cycle 23. Peaks of CMEs observed by CACTus are of the same order of magnitude with respect to the two cycles, but the distribution of CMEs observed by CACTus exhibits a long lasting peak during the Solar Cycle 24. The discrepancy between the CACTus and CDAW results may be due to an observer bias giving origin to different definition of CMEs in CDAW catalog. In order to investigate on the correlation between Flares and CMEs, during the Solar Cycles 23 and 24 we used the Geostationary Operational Environmental Satellite (GOES) datasets that contain observations of 19811 flares of C-, M-, and X-class and found 11441 flares temporally correlated with CMEs for CDAW and 9120 for CACTus. We also found some characteristics of the mean CMEs velocity and acceleration of the CMEs associated with flares and the CMEs not associated with flares. The most important results of this statistical analysis is a log-log relationship between the flux of the flares integrated from the start to end in the 0.1 – 0.8 nm range and the CME mass, valid not only when we consider the energy released by the flare during the whole events, but also considering the flux emitted at the peak of the corresponding flares and the mass ejected by the CMEs.

Session: 7. Solar Flares and Eruptive Filaments

477 views
17.06.2018
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Abstract:
Understanding the physics of solar eruptive activity is a key pursuit of solar physics that continues unabated for at least half a century. Over the past two decades, however, solar eruptions are studied from an additional angle, aiming to generate the necessary operational knowledge to predict them. This has been dictated by recent, vivid interest in space weather forecasting. Moving from understanding to forecasting is a paradigm of research-to-operations (R2O), via which one builds comprehensive databases of quantitative parameters of solar active regions at various stages prior to eruptions. Ranking these parameters in terms of forecasting significance enables another, equally meaningful, step, namely that of operations to research (O2R). In this action, one focuses on the best performing parameters to understand the physics of their (absolute or relative) success. The EU FLARECAST project has managed to collect more than a hundred solar flare (and coronal mass ejection) predictors for each of tens of thousands solar photospheric magnetograms acquired by the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). With a number of ranking exercises complete, we single out a few of these parameters, whose physics and ramifications for the active-region photosphere and the photosphere-chromosphere coupling we present and discuss. This physics can be boosted from future, ultra high-resolution observations that EST will obtain at high cadence. Therefore, among its other objectives, EST can use existing knowledge to fine-tune its scientific targets, aiming to break ground on the understanding of solar eruptions, potentially even identifying and observing their actual trigger(s). The question of the existence, or lack thereof, of unambiguous eruption precursors is also one of central importance, which EST could successfully put to rest.

Session: 1. The State-of-the-Art of the EST Project

155 views
18.06.2018
Co-author:
Abstract:
Over the past decades we have discovered that most of the processes on the Sun are coupled across many layers of the atmosphere. For instance, filaments and arch filament systems are best observed in the chromosphere and corona but are rooted in the photosphere. Another example are the changes in the vector magnetic field during flares which are noticeable from the corona down to the photosphere. Furthermore, small magnetic flux emergence has been tracked observationally from the photosphere to the corona. Therefore, it is crucial to have simultaneous observations covering as many atmospheric layers as possible. The next generation of large solar telescopes will focus on the ability to simultaneously observe the Sun in many different wavelengths. Until now, this has been only possible by coordinating different ground and space based telescopes, in order to observe the same area on the Sun with different instruments. In this talk I will present some examples of recent multi-wavelength studies and show how the European Solar Telescope will improve such multi-wavelength observations.

Session: 5. Large Scale Dynamic Structures: Sunspots, Prominences and Filaments

142 views
18.06.2018
Co-author:
Luc Rouppe van der Voort
Abstract:
In recent years, various chromospheric jet-like phenomena have been discovered in sunspots. There are impulsive penumbral and umbral microjets and slower, longer-lived, and more ubiquitous sunspot dynamic fibrils. Furthermore, surges and jest observed above sunspots light bridges. There have been strong indications that magnetic reconnection is the driving mechanism of the impulsive type of these phenomena. The more regular and cyclic occurring type of jets are attributed to magneto-acoustic waves leaking into the higher atmosphere. Comprehensive studies demonstrate the need for further multi-height investigation of the magnetic and dynamic structure through the photosphere and chromosphere, in order to identify heating mechanisms and the height at which energy is deposited. EST will be optimised for this type of analyses as it will provide simultaneously high spatial and temporal resolution observations of multiple spectral lines sampling different layers of the solar photosphere and chromosphere. Combined with high-sensitivity spectro-polarimetry, we will be able to fully characterise the different types of jets in sunspots and address their formation mechanisms.

Session: 7. Solar Flares and Eruptive Filaments

173 views
18.06.2018
Co-author:
Salvo Luigi Guglielmino, Mariachiara Falco, Mariarita Murabito
Abstract:
We describe high-resolution observations of a GOES B-class flare observed at the Dunn Solar Telescope with IBIS and ROSA instruments. The flare was characterized by a circular ribbon at chromospheric level and was interpreted as a consequence of a magnetic reconnection event that occurred at a three-dimensional (3D) coronal null point located above a supergranular cell. We highlight some interesting observational aspects that need to be explained by models. We observe a bundle of loops corresponding to the outer spine that becomes brighter a few minutes before the onset of the flare. The circular ribbon was formed by several adjacent compact kernels with a size of 1″–2″ and brightening sequentially in clockwise direction. We note that the kernels with a stronger intensity emission were located at the outer footpoint of the darker filaments, departing radially from the center of the supergranular cell. The site of the 3D null point and the shape of the outer spine were also detected by RHESSI in the low-energy channel between 6.0 and 12.0 keV. We ascribe the low intensity of the flare to the low amount of the involved magnetic flux and to its symmetric magnetic configuration.

Session: 4. Chromospheric Dynamics and Heating

154 views
18.06.2018
Co-author:
Jorrit Leenaarts, Mats Carlsson, Peter Gomory, Christoph Kuckein
Abstract:
The chromosphere is the interface between the photosphere and the corona. In the chromosphere the dynamics change from gas-pressure driving to magnetic-force driving, radiation transport changes from optically thick to optically thin, the gas state changes from neutral to ionized, and from local thermodynamic equilibrium to non-equilibrium conditions. The magnetic field is the key quantity in the physics of the chromosphere. Understanding its physics thus requires determination of the magnetic field at all locations of the chromosphere. The chromosphere is relatively dificult to study compared to the photosphere: evolution timescales are shorter, chromospheric lines are broad and deep, and thus have a relatively small photon flux, magnetic flux densities and polarization signals are weaker and fundamental spatial scales are expected to be very small. In this talk I will introduce the science that SG3 has planned for EST, some selected examples of observing plans and the requirements that we think EST should deliver in order to be able to carry out the mentioned science.

Session: 3. Wave Coupling throughout the Solar Atmosphere

277 views
18.06.2018
Co-author:
Abstract:
The SRD Working Group 2 has worked within the theme “Wave Coupling Throughout the Solar Atmosphere”. This report will cover the sample science cases the WG2 has worked on, including observing programs and a discussion of trade-offs needed and possible instrument configurations to optimize the science return.

Session: 4. Chromospheric Dynamics and Heating

142 views
19.06.2018
Co-author:
Michal Švanda, Petr Heinzel
Abstract:
An EST science case concerning the possible heating of solar chromosphere by magneto-acoustic waves is elaborated. The case is based on observations of intensity, polarisation, and Doppler velocity of selected spectral lines with high temporal resolution to detect fluctuations with frequencies up to 40 mHz. The required observing parameters, including the list of proposed spectral lines, together with the tools for velocity and magnetic-field measurements are described. An important point is the determination of time-dependent and time-averaged model atmospheres under the non-LTE conditions in quiet and magnetic regions. These models are used to calculate the energy flux transported by magneto-acoustic waves and net radiative cooling rates at different heights in the atmosphere. Finally, an example of a comparison between acoustic energy fluxes and radiative losses in quiet and magnetised chromosphere is given.

Session: 5. Large Scale Dynamic Structures: Sunspots, Prominences and Filaments

132 views
19.06.2018
Co-author:
P. Romano, F. Zuccarello, B. Ruiz Cobo, M. Murabito
Abstract:
Recent observations have shown the presence of bright filamentary structures that intrude sunspot umbrae, different in morphology, evolution, and magnetic configuration from light bridges that are usually observed in sunspots. Such structures have been called umbral filaments (UFs). In this context, we characterise an UF inside the umbra of the big sunspot in active region NOAA 12529. We analysed high-resolution observations taken in the photosphere with the spectropolarimeter aboard the Hinode satellite and in the upper chromosphere and transition region with the IRIS telescope. These observations were complemented with data from the Solar Dynamic Observatory satellite and from the INAF-OACT equatorial spar to study the evolution of this structure. The maps of the vertical component of the photospheric magnetic field indicate that a portion of the feature has a polarity opposite to that of the hosting sunspot. Furthermore, in the entire UF the horizontal component of the magnetic field is about 2500 G, substantially stronger than in the surrounding penumbral filaments. In the upper atmospheric layers, the UF is co-spatial to one of the footpoints of a small filament, which appears to be rooted in the sunspot umbra. Therefore, we have interpreted the UF as the photospheric counterpart of a flux rope touching the sunspot and giving rise to penumbral-like filaments in the umbra. New observations from the photosphere to the corona with higher spatial resolution, like those which will be provided by EST, are required to shed light on the nature of these structures.

Session: 3. Wave Coupling throughout the Solar Atmosphere

141 views
19.06.2018
Co-author:
D. Jess et al.
Abstract:
The elusive Alfvén wave has been at the centre of atmospheric heating studies for decades, due to its unique incompressible nature making it an ideal energy transporter. However, the viability of Alfvén waves as a heating mechanism in the chromosphere, and beyond, depends on efficient thermalisation of the wave energy, which has previously been undetectable. We combine high resolution spectral imaging with advanced inversion techniques to uncover the first evidence of Alfvén wave energy conversion, in the form of non-linear shock fronts in a sunspot umbra. Observed local temperature enhancements of 5% are observed in regions where conventional umbral flash formation is inhibited, providing a unique and unprecedented insight into Alfvén wave behaviour in the solar atmosphere. Importantly, this work also provides avenues for future research with next generation telescopes and observations.

Session: 5. Large Scale Dynamic Structures: Sunspots, Prominences and Filaments

131 views
19.06.2018
Co-author:
Marco Stangalini, Fabrizio Giorgi, Ilaria Ermolli
Abstract:
We analyzed spectropolarimetric data in the Fe I 617.3 nm and Ca II K 854.2 nm lines of the sunspot in AR 12546 observed with the IBIS at the Dunn Solar Telescope on 20th May 2016 and co-temporal filtergrams by IRIS and SDO/AIA. The observed sunspot is one among the largest such features occurred over the last solar cycle. The IBIS data, taken under excellent seeing conditions that lasted more than three hours, were restored for seeing-induced degradations not accounted for during observations, and inverted with the NICOLE code, in order to retrieve the temperature, magnetic field, and plasma velocity of the studied sunspot as a function of optical depth and time. The umbral and penumbral regions are for the most part stable in the photosphere, while co-spatial chromospheric areas show waves in the umbra-penumbra boundary and intense brightening along penumbral filaments. We explored the origin of these chromospheric processes and their relation to changes in the 3D magnetic structure of the observed sunspot.

Session: 3. Wave Coupling throughout the Solar Atmosphere

131 views
19.06.2018
Co-author:
S.J. Houston, A. Asensio Ramos, S.D.T. Grant, C. Beck, A.A. Norton, S. Krishna Prasad
Abstract:
Previous research has documented the ubiquitous presence of non-linear shocks that are introduced by upwardly propagating magneto-acoustic waves in sunspot umbral atmospheres. In recent years, extensive analyses have been undertaken to examine the effect of these shocks on the surrounding magnetically-dominated plasma, with previous work identifying line-of-sight modulations of the magnetic field strengths and temperature enhancements on the order of several hundred degrees Kelvin. We employ simultaneous slit-based spectro-polarimetry and spectral imaging observations of the chromospheric He I 10830Å and Ca II 8542Å lines to examine full vector fluctuations in the umbral magnetic field caused by the steepening of magneto-acoustic waves into umbral flashes. Following the application of the HAZEL inversion routine, we find evidence to support the scenario that umbral shock events cause expansion of the embedded magnetic field lines due to the increased adiabatic pressure, hence providing increased transversal magnetic field fluctuations up to ~200 Gauss. Through comparisons with non-linear force-free field extrapolations, we demonstrate how the development of umbral flashes can deflect the quiescent magnetic field geometry by up to 8 degrees in both inclination and azimuthal directions.

Session: 2. Structure and Evolution of Magnetic Flux

161 views
19.06.2018
Co-author:
Fabio Giannattasio Istituto Nazionale di Geofisica e Vulcanologia fabio.giannattasio@ingv.it Adalia Caroli Università di Roma “Tor Vergata” adalia.caroli@roma2.infn.it Luca Giovannelli Università di Roma “Tor Vergata” luca.giovannelli@roma2.infn.it Francesco Berrilli Università di Roma “Tor Vergata” berrilli@roma2.infn.it
Abstract:
The study of the dynamics of the photosphere allow us to investigate the physical processes occurring in both the interior of the Sun and in the higher layers of the solar atmosphere due the magnetic coupling between the photosphere and the corona. This field concerns many basic stellar processes such as: global dynamo, turbulent convection and super-hot corona. We report on the recent results on the transport of small scale magnetic field by advection/diffusion as seen on different data-sets from ground-based and space telescopes. We compare those results with simplified advective models that mimic the motion scales observed on the solar surface. We will digress on how the advection of the smallest magnetic elements on the solar surface can affects the toroidal-to-poloidal conversion in the solar cycle, orr how it can be used to estimate the possible nano-flare contribution to the coronal heating.

Session: 6. The Solar Corona

132 views
19.06.2018
Co-author:
Abstract:
Observations of the solar corona during the past decades have clearly shown that this region of the solar atmosphere is bound to follow the structure and evolution of the solar magnetic fields. They form in the sub-photospheric convection zone and subsequently emerge in the photosphere, chromosphere and corona, so characterizing the entire atmosphere as a highly coupled system. The physical properties of various coronal structures (loop systems, coronal holes, streamers, prominences, etc.) indeed depend on the intensity and configuration of the magnetic fields filling the corona. The topology of such fields, in turn, is bound to follow the driving provided by photospheric flows. Significant and rapid changes of the magnetic topology, on the other hand, can cause high energy explosive events occurring in the solar corona, such as flares and eruptive prominences, that in turn may give rise to coronal mass ejections, phenomena with high impact on the space weather. This presentation will concentrate on some typical coronal structures whose physical understanding and modeling is crucially related to a detailed knowledge of the flow fields and magnetic fields, and of their interaction, at the bottom boundary. It will also attempt to put into evidence the role that a 4-m class aperture solar telescope can have in addressing these science topics, thanks to its optical design capable of investigating the active Sun at very high spatial and temporal resolution, and unprecedented polarimetric sensitivity.

Session: 4. Chromospheric Dynamics and Heating

205 views
20.06.2018
Co-author:
Christoph Kuckein, Manuel Collados, Carsten Denker, Sami K. Solanki, Peter Gömöry, Meetu Verma, Horst Balthasar, and Andrea Diercke
Abstract:
We aim to study the evolution of an arch filament system (AFS) and of its individual arch filaments to learn about the processes occurring in them. We observed the AFS at the GREGOR solar telescope on Tenerife at high cadence with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) in the He I 10830 Å spectral range. The He I triplet line profiles were fit with analytical functions to infer line-of-sight (LOS) velocities to follow the plasma motions within the AFS. We tracked the temporal evolution of an individual arch filament over its entire lifetime as seen with the He I 10830 Å triplet. The studied individual arch filament expands in height and extends in length (from 13” to 21”). The lifetime of this arch filament is about 30 min. About 11~min after the arch filament is seen in He I, the loop top starts to rise with an average LOS velocity of 6 kms-1. Only two minutes later, plasma drains down with supersonic velocities towards the footpoints reaching peaks up to 40 kms-1 in the chromosphere. The temporal evolution of He I 10830 Å profiles near the leading pore showed almost ubiquitous dual red components of the He I triplet, indicating strong downflows, along with material nearly at rest within the same resolution element during the whole observing time. We follow the arch filament as it carries plasma during its rise from the photosphere to the corona. The material then drains toward the photosphere, reaching supersonic velocities, along the legs of the arch filament. Our observational results support theoretical AFS models and will serve to improve future models. The consequences of observations such as AFS for EST will be deduced. Also recommendations about EST performance and its instrumentation will be presented.

Session: 3. Wave Coupling throughout the Solar Atmosphere

181 views
20.06.2018
Co-author:
Ineke De Moortel
Abstract:
Observations of coronal loops have long revealed ubiquitous, transverse velocity perturbations, that undergo strong damping as they propagate. Observational estimates show that these perturbations contain significant amounts of energy and a clear power spectrum for these transverse oscillations has been identified, composed of three distinct distributions: one for long periods, one for near 5 minutes oscillations and one for short periods. We have previously demonstrated that the damping of transverse waves can be understood in terms of coupling of the transversal modes (kink) with azimuthal modes (Alfveìn) in the inhomogeneous boundaries of the loops. Moreoever this process strongly depends on the wavelength of the kink modes, where short wavelength oscillations are more efficiently damped, but carry less energy. However observed wave damping does not automatically imply dissipation and hence heating. To investigate under which circumstances this process can contribute to coronal heating and to what extent the heating rate is sustainable, we perform 3D numerical experiments modelling the observed power spectrum of transverse oscillations including the effects of resistivity and thermal conduction. By means of this simulation, we can address to what extent the observed power spectrum of transverse oscillations can contribute to coronal heating and how the simultaneous propagation of long and short period wavelengths affects the heat deposition distribution. In addition, we will address what high resolution instruments can reveal about this mechanism if the structure of the heating deposition is resolved and how to extend the modelling of this mechanism from isolated loops to complex loop systems as observed in active regions.

Session: 4. Chromospheric Dynamics and Heating

173 views
21.06.2018
Co-author:
G. Tsiropoula, I. Kontogiannis, E. Scullion
Abstract:
Vortex flows have been extensively observed over a large range of spatial and temporal scales in different lines and hence layers of the solar atmosphere and widely found in numerical simulations. However, they have never been reported so far in observations in the Hα line centre. High spatial and temporal resolution observations obtained with the CRISP instrument at the Swedish 1-m Solar Telescope in several wavelengths along the Ηα and Ca II 8542 Å line profiles reveal the existence of a persistent 1.7-hours small-scale vortex flow in contrast to short-lived such structures reported so far in literature. We discuss the appearance, characteristics, structure and dynamics of this vortex flow in these two lines as well as in simultaneous UV and EUV SDO/AIA channels and HMI magnetograms. Our analysis includes visual inspection and comparison of simultaneous or near-simultaneous observations in the different spectral lines and channels, study of Doppler velocities derived from the Ηα line profiles and detailed investigation of the vortex appearance, characteristics and dynamics using time slices along linear and circular slits. It reveals the existence of a funnel-like expanding structure with height that is possibly rotating rigidly or quasi-rigidly and exhibits significant substructure within it, manifested as several individual intermittent chromospheric swirls with typical sizes and durations. We further investigate oscillations within the vortex area using a wavelet analysis, phase differences using a cross-wavelet analysis and search for signatures of waves. We also discuss the possible generating physical mechanisms behind this unusual persistent vortex flow and try to understand its relation to previously reported short-duration small-scale magnetic swirls.

Session: 6. The Solar Corona

151 views
21.06.2018
Co-author:
F.Reale, P.Testa
Abstract:
IRIS has observed bright spots at the transition region footpoints. These spots showed significant blueshifts in the Si IV line at 1402.77 A (T∼104.9K). Such blueshifts could not be reproduced by coronal loop models assuming heating by thermal conduction only, but were consistent with electron beam heating, highlighting for the first time the possible importance of non-thermal electrons in the heating of non-flaring active regions (Testa et al. 2014, Science). The coronal counterparts of these brightenings ob-served in the hot channels of the Imaging Atmospheric Assembly on board the Solar Dynamics Observatory show that the IRIS bright spots are the footpoints of very hot and transient coronal loops which clearly experience strong magnetic rearrangements (Reale et al., this meeting). Here we explore in detail how these hot loops might be produced through numerical 3D MHD modeling of interacting magnetic structures including the full plasma chromospheric and coronal response.

Session: 8. Scattering Physics and Hanle - Zeeman Diagnostics

141 views
22.06.2018
Co-author:
Javier Trujillo Bueno
Abstract:
Scientific interest for the spectral region around 1083 nm is growing over the last years following advances in theory as well as in IR instrumentation. Such facilities require further development of diagnostic tools.The aim of our study is to analyze the validity of the weak field approximation for the photospheric Si I 1082.7 nm line. We solve the NLTE formation problem of this line by means of multilevel radiative transfer calculations in a 3D snapshot model taken from the magneto-convection simulations with small-scale dynamo action. The spectral images of the snapshot are degraded because of the seeing and light diffraction by the telescope aperture. We apply the weak field approximation both to the original and smeared Stokes I, Q, U, V profiles supposing that they represent real Sun'' observations. We compare the longitudinal and transverse components of the magnetic field that one would expect from observations of the Si I 1082.7 nm line under perfect spatial resolution and under different seeing conditions of the observations done with the VTT, GREGOR and EST (DKIST) telescopes. We show that crucial condition for observation of polarization in the quiet photosphere using the Si i 1082.7 nm line is the best possible spatial resolution, clearly better than 0.5 arc sec. We find that with the spatial resolution close to the diffraction limit of the EST telescope the surface maps of the magnetic field inferred from this line using the weak field approximation are close to the maps of the real field derived on a surface with the single optical depth. The correlation between them is rather high, except that the inferred longitudinal component of the magnetic field strength turn out to be lower than the vertical component of the real Sun''. At the same time, the transverse component is rather close to the horizontal one.

Session: 1. The State-of-the-Art of the EST Project

210 views
22.06.2018
Co-author:
Abstract:
In the solar atmosphere, the perpendicular spatial scale of Alfvén waves is typically much shorter than the parallel scale, and hence the waves appear in the torsional form. Similar to the linearly polarised plane Alfvén waves, torsional waves nonlinearly induce compressive perturbations by the ponderomotive force. The modification of the local plasma density and magnetic field strengths, and hence the Alfvén speed, leads to the nonlinear self-interaction of Alfvén waves, accompanied by the nonlinear cascade and enhanced damping. In the case of torsional waves, the ponderomotive effect is much richer than in the case of plane Alfvén waves, as torsional waves are essentially oblique due to their intrinsic dependence on the radial coordinate. The ponderomotive force leads to the induction of compressive flows in the perpendicular direction. Also, the radial non-uniformity of the torsional wave amplitude makes the wave speed dependent on the radial coordinate too, which causes phase mixing. In waveguiding magnetic flux tubes, nonlinearly induced compressive perturbations are found to be of three types: the longitudinal flows propagating at the Alfvén and tube speeds, respectively, and transverse flows propagating at the Alfvén speed outside the flux tube. The efficiency of the nonlinear cascade in torsional wave could be significantly weaker than in plane Alfvén waves. We also discuss the typical observational signatures of torsional waves that are important for their identification in the EST data, with implications for the coronal heating problem and MHD seismology.

Session: 8. Scattering Physics and Hanle - Zeeman Diagnostics

166 views
22.06.2018
Co-author:
Alex Feller and Javier Trujillo Bueno
Abstract:
The chapter "Scattering physics and Hanle-Zeeman diagnostics" of the EST Scientific Requirement Document (SRD) collects a series of observing programs (OPs) focused on spectral lines that we consider of highest priority because they produce scattering polarization signals of particular interest either because of their diagnostic potential for the investigation of the magnetism of the solar atmosphere (especially in domains that are not accessible through the Zeeman effect), or because their theoretical interpretation is still unclear. The OPs are specifically designed so as to exploit the specific advantages of the EST, in particular the combination of high polarimetric sensitivity and high spatio-temporal resolution. In this talk, we review the status of this chapter of the SRD, and we present in detail some of the observing programs that have been proposed so far.

Session: 4. Chromospheric Dynamics and Heating

141 views
24.06.2018
Co-author:
Abstract:
The H-alpha emission of chromospheric plasma in solar flares is powered mostly by high energy particle beams and conduction. Particles (mostly electrons) transfer energy from the reconnection region in a fraction of second, while conduction front is much slower, and its contribution reached maximum some tens of seconds after energy release in the solar corona. Energy deposed in the chromosphere causes immediately variations of the hard X-ray emission and after 1-2 seconds correlated variations of the emission of the flaring kernels in the H-alpha line. Basic properties of the emissions in the Hα line induced by particles and frons, geometrical properties of the magnetic loops in the chromosphere and basic properties of the energy deposition layers were already investigated by us using - inter alia - Multi-Channel Subtractive Double Pass (MSDP) observations having spatial, spectral and high time resolutions. More detailed observations, collected with high cadence in broad spectral ranges and with sub-arcsec spatial resolution, as offered by EST telescope, are necessary for detailed studies of interactions of the non-thermal electrons accelerated during impulsive phases of flares with chromosphere. On the basis of our fast-cadence (20 images per second) observations of the flaring kernels collected with MSDP imaging spectrograph we discuss new opportunities offered by the EST telescope in investigations of the feet of the flaring loops, with a special interest in stratification of the energy deposit in the different depths into the chromosphere and its emission in thick chromospheric lines during the impulsive phase of the solar flares.

Session: 5. Large Scale Dynamic Structures: Sunspots, Prominences and Filaments

220 views
29.06.2018
Co-author:
Abstract:
The Swedish 1-m Solar Telescope has been operating on La Palma since 2002. Before that, the Swedish solar observatory hosted other solar telescopes for almost 20 years. From this experience we will formulate a number of conclusions that we believe are relevant for the EST. These points will touch upon telescope and instrument design, telescope operations, and the science that could or should be made with EST. Finally we will try to answer the question “When is the seeing good?”

Session: 1. The State-of-the-Art of the EST Project

226 views
01.07.2018
Co-author:
Abstract:
An important discovery achieved with Hinode’s Solar Optical Telescope/Spectro-Polarimeter (SOT/SP) was that in the mean, the magnetic field over wide areas of the quiet Sun photosphere is predominantly horizontal, i.e., parallel to the solar surface. This result, however, remained not undisputed because the transversal Zeeman component is much more affected by photon noise than the longitudinal component. This noise may be the source for a gross overestimate of the horizontal field. The present contribution briefly reviews the status of the debate and proposes a bias-free measurement method. Furthermore, the polarimetric accuracy required for a definitive answer of the quest of the horizontal magnetic field is discussed. A new method for the removal of systematic errors, practiced at IRSOL, is presented.

Session: 1. The State-of-the-Art of the EST Project

190 views
20.06.2018
Co-author:
Abstract:
I will report on the activities of the EST Science Advisory Group (SAG) and give an overview of the SRD for EST. The SAG formed in November 2017 and consists of 23 European scientists. The first top-level goal is to revise the existing SRD that dates back to 2010 and to present the new version at this meeting. Revisiting the design details of EST, the SAG distilled the excellent and unique science that EST can do. I will address the structure and objectives of the SRD. The top-level science goals are split in 7 Sections. Each section forms a session at the meeting. In addition, I will elaborate on the scientific uniqueness of the EST Nasmyth focus.

Session: 6. The Solar Corona

132 views
08.07.2018
Co-author:
S. Matthews and M. Mathioudakis
Abstract:
Here, we report on what EST may offer towards making a leap in coronal sciences. After a brief introduction to the aims and objectives of WG5, we will outline the currently proposed observing programmes. These programmes, by no means, are final and it is highly encouraged that anyone who may feel they have a contribution, should contact the WG Team (R. Erdelyi, S. Matthews and M. Mathioudakis). The currently elaborated and proposed specific observing programmes, in the context of coronal studies, include e.g., sunspot light-bridges/light walls, solar spicules/macrospicules , coronal upflows and outflows, probing the pre-flare triggers, observables on constraining the coronal magnetic field, and exploring the limits of MHD. A particularly interesting aspect are the potential synergies with Solar C EUVST, Solar Orbiter, and other potential missions that overlap with the operation of EST.

Session: 3. Wave Coupling throughout the Solar Atmosphere

172 views
18.07.2018
Co-author:
Ineke De Moortel
Abstract:
Observations of coronal loops have long revealed ubiquitous, transverse velocity perturbations, that undergo strong damping as they propagate. Observational estimates show that these perturbations contain significant amounts of energy and a clear power spectrum for these transverse oscillations has been identified, composed of three distinct distributions: one for long periods, one for near 5 minutes oscillations and one for short periods. We have previously demonstrated that the damping of transverse waves can be understood in terms of coupling of the transversal modes (kink) with azimuthal modes (Alfveìn) in the inhomogeneous boundaries of the loops. Moreoever this process strongly depends on the wavelength of the kink modes, where short wavelength oscillations are more efficiently damped, but carry less energy. However observed wave damping does not automatically imply dissipation and hence heating. To investigate under which circumstances this process can contribute to coronal heating and to what extent the heating rate is sustainable, we perform 3D numerical experiments modelling the observed power spectrum of transverse oscillations including the effects of resistivity and thermal conduction. By means of this simulation, we can address to what extent the observed power spectrum of transverse oscillations can contribute to coronal heating and how the simultaneous propagation of long and short period wavelengths affects the heat deposition distribution. In addition, we will address what high resolution instruments can reveal about this mechanism if the structure of the heating deposition is resolved and how to extend the modelling of this mechanism from isolated loops to complex loop systems as observed in active regions.

Session: 2. Structure and Evolution of Magnetic Flux

127 views
19.07.2018
Co-author:
María Jesús Martínez González, Manuel Collados
Abstract:
The magnetism at the poles is similar to that of the quiet Sun in the sense that no active regions are present there. However, the polar quiet Sun is somewhat different from that at the activity belt as it has a global polarity that is clearly modulated by the solar cycle. We study the polar magnetism near an activity maximum when these regions change their polarity, from which it is expected that its magnetism should be less affected by the global field. To fully characterise the magnetic field vector, we use deep full Stokes polarimetric observations of the 15648.5 ˚A and 15652.8 ˚A Fe I lines. We observe the north pole as well as a quiet region at disc centre to compare their field distributions. In order to calibrate the projection effects, we observe an additional quiet region at the east limb. We find that the two limb datasets share similar magnetic field vector distributions. However, we infer a new population of magnetic field distributions at the limbs that are different from the distribution inferred at disc centre. We propose that this new population at the limbs is due to the observation of unresolved magnetic loops as seen close to the limb. This is the first (indirect) evidence of small-scale magnetic loops outside the disc centre and would imply that these small-scale structures are ubiquitous on the entire solar surface. The proper characterisation of this new population of magnetic fields imposes strong observational constraints. First, quiet Sun magnetism shows very faint polarisation signals. Second, very high spatial resolution is required to resolve them. Finally, since the inferred unresolved loops show a polarity imbalance, bigger fields-of-view are necessary to address whether it is due to a statistical fluctuation or it is related with the solar magnetic cycle. Currently, these goals cannot be achieved by any solar telescope and EST would be an excellent candidate to accomplish them.

Session: 8. Scattering Physics and Hanle - Zeeman Diagnostics

151 views
20.09.2018
Co-author:
Wenxian Li, Steve Tomczyk
Abstract:
We realized a laboratory experiment to study the scattering polarization of the NaI D-doublet at 589.0 and 589.6 nm in the presence of a magnetic field. This work was stimulated by solar observations of that doublet, which have proven particularly challenging to explain through available models of polarized line formation, even to the point of casting doubts on our very understanding of the underlying physics. The purpose of the experiment was to test a quantum theory for the polarized scattering of spectrally flat incident radiation, on which much of the current magnetic diagnostics of stellar atmospheres is based. The experiment has confirmed the predictions of that theory, and its adequacy for the modeling of scattering polarization under flat-spectrum illumination.

Session: 1. The State-of-the-Art of the EST Project

105 views
21.09.2018
Co-author:
Abstract:
The EST Capabilities

Session: 7. Solar Flares and Eruptive Filaments

110 views
21.09.2018
Co-author:
Abstract:
An M3.2 flare was observed in 2013 May 17 with the Vacuum Tower Telescope (VTT, Tenerife, Spain) at a heliocentric angle of 0.8. The observations covered the activation, impulsive, and relaxation phases of the flare. This work is an extension of the already published work from Kuckein et al. (2015, ApJL,799, L25), which was based on photospheric changes during this flare. In this work, we concentrate on the changes in the chromosphere, analyzing the Ca II 8542 line during the M-class flare. Large emission peaks are present during the flare and relaxation phases. Strong asymmetries of the intensity profiles are detected in the red wing during the flare, which indicates strong downflows. Temperatures and velocities were inferred from selected profiles using the inversion code NICOLE. Our results add to the few earlier studies concerning flare observations in the Ca II infrared line. Observing flares from ground-based telescopes is very challenging. Recommendations about instrumentation will be presented including possible strategies for flare observations with the European Solar Telescope (EST) in the chromosphere.

Session: 8. Scattering Physics and Hanle - Zeeman Diagnostics

121 views
25.09.2018
Co-author:
Luca Belluzzi (belluzzi@irsol.ch), IRSOL (Istituto Ricerche Solari Locarno); Javier Trujillo Bueno (jtb@iac.es), IAC (Instituto de Astrofísica de Canarias)
Abstract:
The scattering polarization signal of the Ca I line at 4227 angstrom shows a peculiar triple-peak profile, with a sharp peak in the line core and broader peaks in the wings. This structure is due to frequency coherence in line scattering processes and cannot be modeled under the assumption of CRD. Since the Hanle effect operates in the line core region only, it has generally been thought that the amplitude of the scattering polarization wing lobes is insensitive to the presence of weak magnetic fields. However, recent theoretical investigations have shown that such wing lobes are in fact sensitive to the magnetic field through another physical mechanism, namely the magneto-optical effects that rotate the plane of linear polarization as radiation propagates through the solar atmosphere. Here, the expected signatures of such mechanism are discussed, focusing on the implications for magnetic field diagnostics in quiet or weakly magnetized regions.

Session: 7. Solar Flares and Eruptive Filaments

140 views
01.10.2018
Co-author:
Francesca Zuccarello, Christoph Kuckein, Sanja Danilovic
Abstract:
The European Solar Telescope offers unique and novel opportunities for solving some of the long-standing problems related to solar flares, such as the slow evolution of the stored energy preceding the flare, the rapid deposition in the chromosphere during the flare impulsive phase, and the response of the chromosphere as the atmosphere responds. The focus of EST on the solar chromosphere - where flare radiation is intense and flare-related magnetic changes likely to be significant, will lead to unique insights. This talk will overview the progress and recommendations of Working Group 6 on Solar Flares and Eruptive Events.

Session: 1. The State-of-the-Art of the EST Project

155 views
18.10.2018
Co-author:
Abstract:
We will present a number of activities on curation, dissemination and visualisation of solar data proposed by the European solar physics commu- nity within the framework of the SOLARNET H2020 and ESCAPE H2020 project proposals as a common effort and first steps towards building up a European Solar Data Centre, envisaged for EST.

Session: 5. Large Scale Dynamic Structures: Sunspots, Prominences and Filaments

157 views
18.10.2018
Co-author:
Abstract:
How do sunspots form? How is this large amount of magnetic flux gath- ered? Why do certain pores become sunspots? Why some large pores never develop penumbra? How is penumbra formed? What is the role of light bridges during sunspot formation? What is hidden in the dark umbrae? How do sunspots decay? What is the role of the moat flow? We will review our current understanding on sunspot formation, evolu- tion and decay addressing these and other questions.

Session: 2. Structure and Evolution of Magnetic Flux

925 views
03.12.2018
Co-author:
Abstract:
Magnetic flux emergence from the solar convection zone into the atmosphere drives dynamic phenomena observable over a range of temperatures and spatiotemporal scales. In this talk, we review the fundamental physical processes important for flux emergence and relate these processes to observables accessible to ground-based and space borne observatories. We illustrate how continuous spectropolarimetric observations enabled the recent development of data-driven simulations of emerging flux, and how such simulations will improve our understanding of the solar atmosphere. We give suggestions for coordinated studies involving observations by existing and next generation solar telescopes (European Solar Telescope, Daniel K. Inouye Solar Telescope, ALMA and future space missions) and data-driven models. We also explore how machine learning techniques can be applied to perform physical diagnostics of the solar atmosphere.

Session: 1. The State-of-the-Art of the EST Project

110 views
30.01.2019
Co-author:
The EST Team
Abstract:
EST will be the largest solar telescope ever built in Europe. With a 4-metre primary mirror and state-of-the-art technology, it will furnish astronomers with a unique tool to understand the Sun. The main goal of EST is to investigate the structure, dynamics, and energetics of the lower solar atmosphere, where magnetic fields continually interact with the plasma, and magnetic energy is sometimes released in powerful explosions. Understanding these phenomena requires observing fundamental processes at scales of about 30 kilometres on the solar surface and short time scales. To accomplish this goal, EST will be equipped with the most advanced adaptive optics system and a suite of innovative instruments for high-resolution, high-sensitivity, multi-wavelength spectropolarimetric observations. The EST consortium successfully accomplished in 2011 the EST conceptual design, based on novel approaches thanks to the expertise accumulated by the EST partners in building powerful solar telescopes and instruments during the last decades. The inclusion of EST in the ESFRI roadmap in March 2016 represented a key milestone for the project, since it was recognised as a strategic European infrastructure that is expected to be ready for operations in about ten years from now. All these elements have led to the start of the Preparatory Phase of the project as an intermediate phase to consolidate its science goals, technical definition, legal issues and national budget contributions. In this talk, the most relevant aspects related to the present status of EST will be presented: main innovative technical characteristics, timeline, budget, preparatory phase, location of the facility, future legal entity for its construction and operation, as well as the expected involvement of the different European countries

Session: 1. The State-of-the-Art of the EST Project

104 views
30.01.2019
Co-author:
Abstract:
Integral field units (IFUs) represent the most important instrumental development for solar telescopes in recent times. They aim at obtaining the simultaneous spectral/spectropolarimetric information in all points in a 2D field of view at the best achievable spatial resolution. Present IFU developments are based on three different approaches: image slicers, microlenses, and optical fibres. The first two options have been addressed under the EST framework and very promising results have been obtained up to now. Fibre-based IFUs are being developed for one of the first-light instruments of DKIST. In this talk, the three alternatives will be presented and described, putting especial emphasis on the alternatives developed as prototypes of the future EST instruments. A microlens-based IFU has been developed by MPS and tested at the SST. In parallel, a slicer-based IFU has also been developed by IAC and tested at GREGOR. The latter has been offered to all observers at this telescope to gain experience about its performance, stability and data reduction and analysis. These prototypes are fundamental for the final definition of the EST spectrograph(s) and crucial for the science that will be addressable with EST. IFUs will facilitate, v.g., the study of the fast evolution of small-scale solar structures, high-frequency waves, fast acceleration and heating of the plasma, reconnection events, etc. The present status of these instrument developments will be presented, as well as the future steps for their improvement and their final expected performance if/when installed at EST.

Session: 5. Large Scale Dynamic Structures: Sunspots, Prominences and Filaments

106 views
30.01.2019
Co-author:
E. Khomenko
Abstract:
The aim of this work is to measure possible differences in the dynamics of the ionized and neutral components of the solar plasma, as a manifestation of partial ionization effects due to an incomplete collisional coupling, causing deviations from ideal MHD. Here we report the detection of differences in ion and neutral velocities in prominences using very high temporal resolution spectral data obtained in 2012 at the German VTT (Observatorio del Teide, Tenerife). A time series of scans of a small portion of a solar prominence was obtained simultaneously with a high cadence using spectral lines of two elements with different ionization states, namely the CaII 8542 A and the HeI 10830 A. Displacements, widths and amplitudes of both lines were carefully compared to extract dynamical information about the plasma. Many dynamical features are detected, such as counterstreaming flows, jets and propagating waves. In all the cases we find a very strong correlation between the parameters extracted from the lines of both elements, confirming that both trace the same plasma. Nevertheless, we also find short-lived transients where this correlation is lost. These transients are associated with ion-neutral drift velocities of the order of several hundred m/s. The patches of non-zero drift velocity show coherence on time-distance diagrams. We continue and expand this initial study with another set of data, also obtained under similar conditions at the VTT in 2016, this time including He I D3 5876 A, Halpha, and Ca II 8542 A, measured simultaneously. The new dataset has an advantage of including two lines of neutral elements with different atomic mass, together with one line of an ionized element. The importance of such kind of simultaneous observations for detecting partial ionization effects will be emphasized. The EST instrumentation should be designed to make possible these type of observations with the highest temporal cadence and spatial resolution.

Session: 2. Structure and Evolution of Magnetic Flux

87 views
23.06.2019
Co-author:
Abstract:
SRD: Report from WG1

Session: 1. The State-of-the-Art of the EST Project

192 views
14.06.2018
Co-author:
Scuderi S., Cecconi M.
Abstract:
The BBI (Broad Band Imager) for EST will be one of the 'first light' instruments of the telescope. The scientific objectives will be the the study of fundamental astrophysical processes at their intrinsic scales in the Sun's atmosphere, and this goal will be reached with an instrument able to obtain diffraction limited images over the full field of view of EST at multiple wavelengths and high frame rate. The BBI will cover the 390 to 900nm wavelength range, using two different arms(390-500nm and 600-900nm), and three different channels. Each subchannel will be further split in thre subchannels, each one served by a different 4kx4k detector; one subchannel will be dedicated to chromospheric observations with narrow band filters, the second one for photospheric obeservations with wide band filters, and the third one with the same filters, used out of focus for phase recostruction. The total number of foreseen filters will be 11, with bandpasses FWHM from 0.05 to 0.5 nm. The instrument will exploit the diffraction limited quality of the telescope, and will operate in two modalities: maximum field (2'x2'), and high resolution (better than 0.04" at 500nm).

Session: 1. The State-of-the-Art of the EST Project

279 views
16.06.2018
Co-author:
Abstract:
The Large Angle Spectrometric Coronagraph (LASCO), onboard the Solar and Heliospheric Observatory (SOHO) provided us observations extending for the two Solar Cycles 23 and 24 (31 July 1996 - 31 March 2014) that allow one to compare some properties (speed, acceleration, polar angle, angular width, and mass) of Coronal Mass Ejection (CMEs). The Coordinated Data Analysis Workshops (CDAW) Data Center datasets uses manual identification for the detection of the CMEs, while the Computer Aided CME Tracking software (CACTus) datasets uses an automatic detection algorithm. Some important results found in this analysis, for both dataset, are that there are more CMEs during the maximum of Solar Cycle 24 than during the maximum of Solar Cycle 23, although the photospheric level and magnetic activity of the Sun during Cycle 24 was weaker than during Cycle 23. Peaks of CMEs observed by CACTus are of the same order of magnitude with respect to the two cycles, but the distribution of CMEs observed by CACTus exhibits a long lasting peak during the Solar Cycle 24. The discrepancy between the CACTus and CDAW results may be due to an observer bias giving origin to different definition of CMEs in CDAW catalog. In order to investigate on the correlation between Flares and CMEs, during the Solar Cycles 23 and 24 we used the Geostationary Operational Environmental Satellite (GOES) datasets that contain observations of 19811 flares of C-, M-, and X-class and found 11441 flares temporally correlated with CMEs for CDAW and 9120 for CACTus. We also found some characteristics of the mean CMEs velocity and acceleration of the CMEs associated with flares and the CMEs not associated with flares. The most important results of this statistical analysis is a log-log relationship between the flux of the flares integrated from the start to end in the 0.1 – 0.8 nm range and the CME mass, valid not only when we consider the energy released by the flare during the whole events, but also considering the flux emitted at the peak of the corresponding flares and the mass ejected by the CMEs.

Session: 7. Solar Flares and Eruptive Filaments

185 views
18.06.2018
Co-author:
Salvo Luigi Guglielmino, Mariachiara Falco, Mariarita Murabito
Abstract:
We describe high-resolution observations of a GOES B-class flare observed at the Dunn Solar Telescope with IBIS and ROSA instruments. The flare was characterized by a circular ribbon at chromospheric level and was interpreted as a consequence of a magnetic reconnection event that occurred at a three-dimensional (3D) coronal null point located above a supergranular cell. We highlight some interesting observational aspects that need to be explained by models. We observe a bundle of loops corresponding to the outer spine that becomes brighter a few minutes before the onset of the flare. The circular ribbon was formed by several adjacent compact kernels with a size of 1″–2″ and brightening sequentially in clockwise direction. We note that the kernels with a stronger intensity emission were located at the outer footpoint of the darker filaments, departing radially from the center of the supergranular cell. The site of the 3D null point and the shape of the outer spine were also detected by RHESSI in the low-energy channel between 6.0 and 12.0 keV. We ascribe the low intensity of the flare to the low amount of the involved magnetic flux and to its symmetric magnetic configuration.

Session: 8. Scattering Physics and Hanle - Zeeman Diagnostics

228 views
18.06.2018
Co-author:
Sergio Javier González Manrique and Christoph Kuckein
Abstract:
We compare two methods to compute the Doppler shifts and infer the line-of-sight (LOS) velocities of the largely used photospheric Si I 10827 Å line. This line yields information about the upper photosphere. The first method consisted of computing the height-depend bisectors of the line. The second method required much longer computational time since an inversion code was used. For this purpose we used the Stokes inversion based on response function (SIR) code, which provided height-dependent information, in an optical depth scale, of the LOS velocities. The used data set of this study was observed on 2015 April 17 with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS). Small pores and large quiet Sun areas were within the field of view. Two different data sets at different times were exploited for this study. The wavelength positions of the bisectors were computed in 10%-steps of the line depth using linear interpolation in both line wings. The output model from the SIR code covered 55 optical depth positions which range between 1.4 ≥ log τ ≥ -4.0. These LOS velocity maps from SIR at different log τ were compared with those originated from the bisector method at different percentages. The comparison between both methods allowed us to associate the bisector percentages to a specific optical depth. We associated nine LOS velocity bisector maps, in 10% steps of the line depth, starting from the lowest value at 10% and ending at the highest value of 80%. The bisector and SIR velocity maps were compared using the Pearson linear correlation coefficient. Each of the LOS velocity bisector maps was compared and correlated with the SIR LOS velocity maps. High linear correlations in the range of 95-98% were found. Bisector velocities obtained deeper in the line correspond to lower optical depths. The best correlation (97.8%) was achieved for the SIR velocity map at log τ = -2.6, which corresponds to a bisector of 20%. The inferred correspondence between bisector percentage and optical depth can be used to quickly obtain information about the LOS velocity stratification versus optical depth.

Session: 2. Structure and Evolution of Magnetic Flux

183 views
19.06.2018
Co-author:
F. Zuccarello, P.R. Young, P. Romano, M. Murabito
Abstract:
We report multi-wavelength ultraviolet observations taken with the IRIS satellite, concerning the emergence phase in the upper chromosphere and transition region of an emerging flux region (EFR) embedded in the unipolar plage of active region NOAA 12529. These data are complemented by full-disk, simultaneous observations of the Solar Dynamics Observatory satellite, relevant to the photosphere and the corona. The photospheric configuration of the EFR is also analyzed by measurements taken with the spectropolarimeter aboard the Hinode satellite, when the EFR was fully developed. Recurrent intense brightenings that resemble UV bursts, with counterparts in all coronal passbands, are identified at the edges of the EFR and in the region of the arch filament system (AFS) cospatial to the EFR. Jet activity is also found at chromospheric and coronal levels, near the AFS and the observed brightness enhancement sites. The analysis of the IRIS line profiles reveals the heating of dense plasma in the low solar atmosphere and the driving of bi-directional high-velocity flows with speeds up to 100 km/s at the same locations. Comparing these signatures with previous observations and numerical models, we suggest evidence of several long-lasting, small-scale magnetic reconnection episodes occurring between the emerging bipole and the ambient field. This process leads to the cancellation of a pre-existing photospheric flux concentration of the plage with the opposite polarity flux patch of the EFR. Moreover, the reconnection appears to take place higher in the atmosphere than usually found in UV bursts, explaining the observed coronal counterparts. These observations provide a case study for the EST science requirements, as higher spatial and temporal resolution are necessary to better understand and characterize the onset and development of such small-scale reconnection events.

Session: 5. Large Scale Dynamic Structures: Sunspots, Prominences and Filaments

473 views
19.06.2018
Co-author:
P. Romano, S. L. Guglielmino, F. Zuccarello
Abstract:
Using high-resolution spectropolarimetric data acquired by IBIS, as well as SDO/HMI observations, we studied the penumbra formation in AR NOAA 11490 and in a sample of twelve ARs appeared on the solar disk on 2011 and 2012, with the β-type magnetic field configuration. The results concerning the leading polarity of AR NOAA 11490 show that the onset of the classical Evershed flow occurs in a very short time scale, 1-3 hours, while the penumbra is forming to the side away from the opposite polarity of the AR. Conversely, studying the formation of the first penumbral sector around the following proto-spot, we found that a stable penumbra forms in the area facing the opposite polarity, which appears to be located below an AFS, i.e. in a flux emergence region, in contrast with the results of Schlichenmaier et al. (2010). Analyzing the sample of twelve ARs, we noticed that there is not a preferred location for the formation of the first penumbral sector. We also observed before the penumbra formation an inverse Evershed flow, which changes its sign when the penumbra appears. This confirms the observational evidence that the appearance of the penumbral filaments is correlated with the transition from the inverse Evershed to the classical Evershed flow. Furthermore, the analysis suggests that the time needed to form the penumbra may be related to the location where the penumbra first appears. New high-resolution observations, like those provided by the European Solar Telescope, are expected to increase our understanding of the penumbra formation process.

Session: 7. Solar Flares and Eruptive Filaments

196 views
19.06.2018
Co-author:
V. Capparelli, M. Mathioudakis, P. Keys, L. Fletcher, S. Criscuoli, M. Falco, S.L. Guglielmino, and M. Murabito
Abstract:
During solar flares, magnetic energy can be converted into electromagnetic radiation from radio waves to gamma rays. In the most energetic events, enhancements in the continuum at visible wavelengths may be present (white-light [WL] flares). Recently, the WL emission has also been correlated with enhancements in the FUV and NUV passbands. In this context, we describe observations acquired by ground-based (ROSA@DST) and satellite (IRIS) instruments during two consecutive C7.0 and X1.6 flares occurred in active region NOAA 12205 on 2014 November 7. The results of the analysis of these data show the presence of continuum enhancements during the evolution of the events, observed both in ROSA images and in IRIS spectra. Moreover, we analyze the role played by the evolution of the δ sunspots of the active region in the flare triggering, discussing the disappearance of a large portion of penumbra around these sunspots as a further consequence of these energetic flares. We expect that high-resolution observations acquired during the EST operations will enable us to extend our knowledge about the physical process that determines WL emission during solar events like those discussed here.

Session: 1. The State-of-the-Art of the EST Project

1355 views
19.06.2018
Co-author:
F. Berrilli, G. Consolini, D. Del Moro, F. Giannattasio, L. Giovannelli
Abstract:
The understanding of fluctuations in systems far from equilibrium is one of the key issues of non-equilibrium statistical thermodynamics. The Fluctuation Theorem of Gallavotti and Cohen (1995) [GCFT] portrays some symmetry features of entropy production rate and deviations in non-linear and far from equilibrium regime. In this framework, the turbulent solar convection, observed in the photosphere and viewed as a dissipative non-equilibrium system near a steady state, provides an incomparable laboratory where to attempt a test the GCFT. In fact, solar convection flows emerge in the photosphere in terms of a structured pattern: the granulation. High resolutions spectro-polarimetric data acquired with Interferometric BIdimensional Spectropolarimeter (IBIS) instrument installed at the Dunn Solar Telescope (DST) are used to perform this analysis. Here, we present a preliminary analysis of the validity of the GCFT in the solar convection field. The statistical features of entropy production rate, which is at the core of the irreversibility, is estimated through the vertical heat flux. The vertical heat flux along the line of sight (LOS), in its turn, is evaluated using temperature and LOS velocity map obtained with spectro-polarimetric inversion using the NICOLE code and with the simplest center of gravity method.

Session: 5. Large Scale Dynamic Structures: Sunspots, Prominences and Filaments

185 views
22.06.2018
Co-author:
G. Puglisi, S.L. Guglielmino, P. Romano, I. Ermolli, and F. Zuccarello
Abstract:
One of the most visible manifestations of convective motions occurring in the uppermost layers of the solar convection zone is the granulation. Strong magnetic fields hinder the convective motions, but the appearance of bright structures such as umbral dots (UDs) and light bridges (LBs) in sunspots also shows that in strong magnetic field regions, the convection is not completely suppressed. To improve the current knowledge of the mechanism behind the appearance of the different bright structures in sunspots, we investigate the properties of the granules identified by a new segmentation algorithm in regions characterized by different magnetic field strength. We analyzed data relevant to a large sunspot with a LB observed in AR NOAA 11263. The data were acquired by the CRisp Imaging SpectroPo- larimeter at the SST on 6 August 2011. We applied a new segmentation algorithm to the data acquired along the Fe I 630.15 nm line. We found that the granules in the LB have a diameter between 0 . 22 ′′ and 0 . 99 ′′ , being smaller than the granules in a nearby plage region (PL) and similar to those of the UDs. The values of the mean continuum inten- sity, between 0.42 Ic and 0.98 Ic for the LB granules, are similar to those of the UDs. PL granules have higher values of continuum intensity, proba- bly reflecting different conditions of the plasma convection. Mean Doppler velocity and mean magnetic field strength have similar values between LB granules and UDs as well. Different values for the physical properties analyzed have been found between the granules of the PL and LB granules of the three analyzed so- lar regions, suggesting that PL and sunspot granules have different physical properties. This clearly depends on the different physical conditions of the regions where these two types of granular structures are embedded and con- firms the recent findings on the similarity between granules in PL and quiet Sun regions. Finally, a noteworthy result is that the granules observed in the faint LB have physical properties similar to those found for UDs.

Session: 1. The State-of-the-Art of the EST Project

1178 views
22.06.2018
Co-author:
Gömöry, P., Rybák, J., Schwartz, P., Kučera, A., Ambróz, J., Kozák, M., Koza, J., Tomczyk, S., Sewell, S., Aumiller, P., Gallagher, D., Summers, R., Sutherland, L., Watt , A.
Abstract:
We present actual status and observing possibilities of the Coronal Multi-channel Polarimeter (CoMP-S) and Solar Chromospheric Detector (SCD) installed at the Lomnicky Peak Observatory. The CoMP-S is a dual beam spectropolarimeter developed to detect full Stokes parameters of prominent coronal and chromospheric spectral lines in order to estimate magnetic and velocity fields in the solar corona and in prominences. The SCD is a single beam spectropolarimetric instrument designed for on disk measurements of Stokes parameters in the chromosphere. Both instruments were designed and manufactured by HAO/NCAR (Boulder, USA). We present technical parameters of the instruments and the acquired data which can serve as complementary observing material to high resolution measurements taken by the European Solar Telescope (EST).

Session: 6. The Solar Corona

191 views
03.07.2018
Co-author:
Rudawy, P., Radziszewski, K., Berlicki, A., Phillips, K.J.H., Jess, D.B., Keys, P.H., Keenan, F.P.
Abstract:
An instrument using fast-frame cameras has been used during several recent total solar eclipses to search for oscillations in the green-line coronal emission. A much more sophisticated version of the instrument was prepared, tested, and successfully used during the August 21, 2017 total eclipse from a location in the Rocky Mountains, Idaho, USA. A pair of cameras, one observing the corona through a narrow-passband green line filter (wavelength 530.3 nm), and the other the white-light corona, was mounted on a 20 cm f/10 Celestron telescope on a Sky-Watcher EQ8 mounthead. During the 122 s of totality, 428 images in a field-of-view that included approximately two-thirds of the corona were obtained in the 530.3 nm FeXIV line with an Andor iXon3 885 camera working at approximately 3.5 frames per second. The image format was 1004x1002, with a scale of 1.55 arcsec (1200 km) per pixel. The field-of-view included the loop system above the active region AR12672 which was near the Sun's east limb. Emission is recognizable out to a distance of 150,000 km, and the brightest structures in the active region loop have a strong signal (up to 3000 DN) that enables a search to be made for oscillations and other rapid fluctuations. This compares with a maximum signal of about 60 DN with a frame rate of 40 frames per second in a similar (negative) search by a previous version of this instrument during the 2001 total eclipse visible from central Africa. After dark-current subtraction and flat-fielding, a careful analysis of jitter and drifting motion of the images has enabled the solar coronal images to be placed on a frame that is stable to only 0.1 pixel, or 0.15 arcsec. As a preliminary result, we did not detect any statistically significant evidence of local periodic variations of the coronal emission in FeXIV green line in any of the 480 000 investigated points . The result is in accordance with our previous findings based on observations collected during the 1999 and 2001 total solar eclipses and it confirms that the wave phenomena of Alfven-type, reported already by Tomczyk et al. (Nature 2007, ApJ 2009), even if common and always present in the solar corona, do not rise periodic fluctuations of the intensity of the coronal emission. An in-depth wavelet analysis of the collected data is under way.

Session: 2. Structure and Evolution of Magnetic Flux

963 views