Our colloquium takes place, unless otherwise specified, on Mondays at 16:00CET. Currently, the colloquium is online-only (via Zoom).
Monday 10.10.2022 at 16:00CET
- Prof. Dr. Manuel Collados Vera, Instituto de Astrofísica de Canarias (Spain)
- Title: The European Solar Telescope: status and perspectives
- Abstract: With first light expected at the end of the present decade, the European Solar Telescope (EST) represents the most important technological joint effort made by the European ground-based Solar Physics community. EST will improve considerably the present observational capabilities thanks to its 4-metre diameter. Its optical design is especially designed to study magnetic phenomena taking place in the solar atmosphere, optimising two crucial aspects. On the one hand, its polarimetrically-compensated design is conceived to cancel out the instrumental polarisation induced by the individual elements of the telescope optical train. This property is crucial to make feasible the detection of very small, spatial and temporal, fluctuations of the magnetic field. Secondly, its design includes a powerful multi-conjugate adaptive optics system (MCAO) to optimally correct the wave-front distortions introduced by the Earth's atmosphere. With its MCAO system, EST is intended to measure the Sun at diffraction limit, with a spatial resolution of 20-30 km and a cadence of few seconds. The design is complemented with the most advanced suite of instruments that will operate simultaneously, to extract the maximum information about the dynamics, thermodynamics and magnetism of the solar plasma at different layers. In this talk, the status of the project will be presented, putting emphasis on the most recent technical developments, on the instrumentation and scientific goals that will be addressable with this facility and the most recent and upcoming milestones.
Monday 17.10.2022 at 16:00CET
- Robert Tawa, DKIST Data Center (National Solar Observatory, Boulder/US)
Monday 26.09.2022 at 16:00CET -- POSTPONED (Date: tbd)
- Dr. Harry Enke, Leibniz-Institut für Astrophysik (AIP, Potsdam/Germany)
- Title: Working environments for astronomical data
Abstract: With the size of astronomical data grows the necessity for efficient and easy access to advanced infrastructure facilities. This includes: careful curated and published astronomical data collections, assorted tools for data analysis and co-location of data and execution environments. The Virtual Observatory has developed valuable methods/standards/protocols for using the distributed data archives, where the data providers (archives) have to implement their data publication processes accordingly. And -- for growing data sizes -- even the workflow with data selection and retrieval across the internet is only partially feasible. Offering public accessible data collection along with (limited) facilities to work with the selected data proves to be much more efficient. PUNCH4NFDI and other infrastructure projects aim to develop means to overcome the limitations of the individual data providers by pooling and sharing such resources across borders of institutions
- Q4 2022
- Dr. Antoine Strugarek. CEA Paris-Saclay, Département d’Astrophysique (Paris, France)
- October / November 2022
- Dr. Oliver J. Hall. ESTEC (Noordwijk, The Netherlands)
- August / September 2022
- Dr. Dirk Schmidt. NSO (Boulder, USA)
- Monday 12.09.2022 at 16:00CET
- Dr. Andrés Asensio Ramos, Instituto de Astrofísica de Canarias (Spain)
- Title: Methods in Machine Learning for solar spectroscopy
- Abstract: Solar spectropolarimetry is entering the realm of big data. Current and future telescopes will produce data at a rate that will make it hard to store in a single machine and even harder to operate on the data. Thankfully, in the last decade, machine learning has experienced an enormous advance, thanks to the open possibility of training very deep and complex neural networks. In this contribution I show options to explore to deal with the big data problem and also how deep learning can be used to efficiently solve difficult problems in Solar Physics. I will focus on how differentiable programming (aka deep learning) is helping us to have access to velocity fields in the solar atmosphere, correct for the atmospheric degradation of spectropolarimetric data and carry out fast 3D inversions of the Stokes parameters to get physical information of the solar atmosphere.
- Tuesday 05.04.2022 at 16:00
- Dr. David Orozco Suarez. Instituto de Astrofisica de Andalucia, IAA (Granada, Spain)
- Title: CMAG: A Coronal MAGnetograph mission for studying the inner corona magnetic fields
- Abstract: The detailed study of the Sun's inner coronal magnetic fields is one of the technological challenges of solar physics today since it requires measuring the four Stokes components in forbidden coronal emission lines whose polarization signals can differ orders of magnitude in their amplitude. In this talk I will present an overview of the main challenges for determining the inner corona magnetic fields and how they can be addressed from space. In particular, I will present preliminary concept of the CMAG (Coronal MAGnetograph), a space mission designed to obtain maps of the coronal magnetic fields with unprecedented spatial and temporal resolutions by means of a dedicated imaging spectropolarimeter whose external occulter is placed about 400 meters away. CMAG baseline consists of two different spacecraft in formation flight. The first one is meant to act as an external occulter by carrying a dedicated disk. The second one would be a small satellite with a refracting telescope and an internal occulter to image the solar inner corona measuring all four Stokes parameters at given wavelength samples of selected emission spectral lines from the corona.
- Monday 11.04.2022 at 16:00
- Dr. Mariarita Murabito. INAF Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Roma (Italy)
- Title: On the origin of magnetic perturbations associated to the FIP effect
- Abstract: Observations of the photosphere, chromosphere, and corona combined with magnetic field modeling of one of the biggest sunspots of the 24 solar cycle, revealed that regions of high FIP bias plasma in the corona were magnetically linked to the locations of the intrinsic magnetic oscillations in the solar chromosphere. In order to characterize the driver of the oscillations, we analyzed the relation between the spatial distribution of the magnetic wave power and the overall field geometry and plasma parameters obtained from the multi-height spectropolarimetric non-local thermodynamic equilibrium (NLTE) inversions. In correspondence with the locations where the magnetic wave energy is observed at chromospheric heights, we found evidence in support of locally excited acoustic waves that, after crossing the equipartition layer located close to the umbra-penumbra boundary at photospheric heights, are converted into magnetic-like waves. These results indicate a direct connection between sunspot chromospheric activity and observable changes in coronal plasma composition, demonstrating the power of high resolution, multi-height studies of the solar atmosphere that will become the gold standard in the era of DKIST.
- Monday 25.04.2022
- Dr. Jaime de la Cruz Rodriguez. Stockholm University (Stockholm, Sweden)
- Title: Setting observational constraints to the chromospheric heating problem.
- Abstract: The solar atmosphere is hotter than predicted by assuming radiative equilibrium. This is most obviously evidenced by the high temperature of the solar corona, but the bulk of the energy deposition happens already down in the much cooler chromosphere. While in recent years we have gain detailed understanding of many important processes that must be at work in the chromosphere, also from numerical simulations, their exact contribution to the total energy budget remains unclear. Chromospheric heating or cooling can be estimated by calculating the radiative losses whenever a model atmosphere is available. Most comparisons between simulations and observations have used canonical values of radiative losses that have been derived from 1D models of spatio-temporal averages of solar spectra (e.g., FAL / VAL models). Such approach cannot capture the high complexity and fine structures that is observed in high resolution observations. In this talk, I will discuss the accuracy and challenges associated with the methods that we use to infer radiative losses from observations. I will also present our first spatially resolved maps of the radiative losses derived from very high spatial resolutions observations acquired with the Swedish 1-m Solar Telescope in the Ca II K, Ca II 8542 and Fe I 6301/6302 lines.
- Monday 02.05.2022
- Dr. Arturo López Ariste. IRAP, Université de Toulouse, (Toulouse, France)
- Title: Spectropolarimetric Imaging of Red SuperGiants. Doing solar physics in other stars.
- Abstract: The unexpected recent discovery of linear polarisation in the spectra of Betelgeuse led us to a new imaging technique of the photosphere of this and other red supergiant stars. At present, we are able to periodically produce 3-dimensional images of the convection patterns of these stars. We have been able to measure typical scales and lifetimes of granulation. We also measured supersonic radial velocities, confirming the results from 3D simulations. In the last work, we have been able to measure the radial velocity profile of granulation and found some interesting cases in which this velocity is constant up to large heights. This points to an unknown force, compensating gravity, and potentially responsible for the high rates of mass loss that characterise the last stage of the lives of these stars. Through these techniques we are abandoning the exploration of stars as unresolved objects, and enter the era where we examine them with spatial resolution, as for the Sun. We do solar physics in other stars.
- Monday 09.05.2022
- Dr. Ivan Milic. University of Colorado (Boulder, USA)
- Title: How to train your inversion
- Abstract: Spectropolarimetric inversions are the method of choice for quantitative diagnostics of the solar atmosphere. They allow us to go from three-dimensional cubes of Stokes parameters (x,y, wavelength), to pseudo-three-dimensional cubes of physical parameters (x,y, optical depth). The process involves non-linear least-squares fitting of very complicated forward models and is subject to many pitfalls, limitations, and systematic errors. The first part of the talk will present the inversion process, focusing on the limitations and computational assumptions that lead to different systematic errors and biases. We will review state-of-the-art approaches that aim to rectify some of these problems. We will then discuss a few examples where we use MHD simulations as a testbed for the inversions. Finally, we will present some simple but robust applications of neural networks to spectropolarimetric inversions.
- Monday 16.05.2022
- Dr. Ioannis Kontogiannis. Leibniz Institute for Astrophysics Potsdam, AIP (Potsdam, Germany)
- Title: Magnetic properties of active regions and eruptive activity: recent results and future directions
- Abstract: The active regions that produce major flares and coronal mass ejections (CMEs) exhibit common morphological characteristics, such as δ-spots, filaments, sigmoids, and strongly sheared magnetic PILs. These are indicative of complex magnetic configurations, associated with strong electric currents and storing huge amounts of free magnetic energy and helicity. Using this empirical knowledge and appropriate observations we calculate parameters/predictors that can help us distinguish between quiet, flare-, and CME-productive (eruptive) active regions. In the era of near real time, uninterrupted, high-quality observations from space, and large, statistically significant samples, machine learning methods accommodate the processing of data of increasing volume and complexity. These comprise not only photospheric magnetograms, but also EUV images, spectra, and time series and, thus, our inventory of data sources and feature extraction methods expands. Additionally, exploratory research has focused on the study of active regions in terms of these magnetic parameters shedding more light on the mechanisms that produce flares and CMEs and leading to new magnetic predictors and prediction models. In this talk, I will review these efforts to parameterize the characteristics of eruptive active regions and I will discuss some recently introduced and promising magnetic parameters, as well as future prospects.
- Monday 23.05.2022
- Dr. Lena Khomenko. Instituto de Astrofisica de Canarias, IAC (La Laguna, Spain)
- Title: Towards multi-fluid simulations of the solar chromosphere
- Abstract: Solar chromosphere has been at the focus of solar physics studies for decades. Chromosphere is a transition layer between the interior and exterior of the Sun where the temperature starts to increase further from the surface, but the heating mechanisms responsible for this increase are still unknown. The chromospheric dynamics is defined by magnetic fields. Chromospheric plasma is strongly stratified, weakly ionised and not completely collisionally coupled. The latter circumstances need to be taken into account in theoretical models of the chromosphere. In this talk I will overview our recent results of the modeling of the solar chromosphere, comparing a more standard single-fluid approach and a more novel multi-fluid approach. I will describe the challenges posted by the multi-fluid modeling that still need to be overcome. Finally, I will talk about the observational effort in detecting the dynamical decoupling of the neutral and ionized species in the solar chromosphere.
- Monday 20.06.2022
- Dr. Ryan Campbell. Queen's University (Belfast, UK)
- Title: Exploring pervasive small-scale internetwork magnetism with the GRIS-IFU
- Abstract: Synthetic observations produced from MURaM outputs have predicted that higher polarization fractions in the quiet solar photosphere would be revealed by increasing the total integration time or increasing the spatial resolution of GREGOR Infrared Spectrograph Integral Field Unit (GRIS-IFU)/GREGOR observations. We take advantage of improvements to GREGOR to reveal an unprecedented abundance of weak, small-scale internetwork (IN) magnetism. We present several new GRIS-IFU datasets of the Fe I 1564.9 nm line, with two datasets in particular taken during exceptional seeing conditions showing very high polarization fractions. We uncover evidence that could suggest GREGOR's overhaul has helped achieve a higher effective spatial resolution, and modelling with degraded synthetic profiles suggests that these datasets, compared to previous observations, are closer to the diffraction limit in the near infrared. By observing with high signal-to-noise (S/N), high spatial resolution, one of the most magnetically sensitive spectral line available to solar observations, and exceptional seeing conditions, we reveal one of the highest fraction of polarization ever recorded in the (not-so) quiet Sun. We present several case studies of the zoo of magnetic features present in these data, including small-scale magnetic loops and serpentine fields, focusing on regions where the full Stokes vector has been recorded. The open-source Python 3 Inversion Explorer application will also be showcased, which has been developed to help the community to interrogate spectropolarimetric inversions with ease.
- Monday 27.06.2022
- Dr. Joao da Silva Santos. National Solar Observatory (Boulder, USA)
- Title: Observations and modeling of heating in chromospheric current sheets
- Abstract: The chromosphere is a transition layer between the cool photosphere and the million-degree hot corona. Different heating mechanisms, such as damping of magnetohydrodynamics waves and dissipation of magnetic energy in current sheets or field reconnection, may account for a significant fraction of the energy input required to sustain the observed radiative cooling. The active chromosphere, in particular, appears significantly brighter than the quiet one, suggesting magnetically mediated heating. We present co-temporal SDO ultraviolet imaging, SST spectropolarimetry in the Fe I 6173 Å and Ca II 8542Å lines, and ALMA brightness temperature maps in the continuum at 3 mm of a solar active region. Nonlocal thermodynamic equilibrium inversions of the SST+ALMA dataset constrain the atmospheric stratification and show that enhanced chromospheric temperatures and cooling rates are associated with strong and inclined magnetic fields that connect patches of opposite magnetic polarity in the photosphere. Numerical simulations show that energy dissipation in current sheets during flux emergence leads to enhanced radiative losses and a range of observational signatures in the millimeter continuum from compact, transient brightenings to warm fibril-like structures consistent with the observations. Finally, we will discuss how coordination between different observatories offers a promising albeit challenging way of addressing chromospheric heating.
- Monday 04.07.2022
- Dr. Juie Shetye. New Mexico State University (Las Cruces, NM, USA)
- Title: Using chromospheric jets to connect the solar atmosphere
- Abstract: The solar chromosphere serves as a bridging region between the photosphere, which is the surface of the Sun, and the corona, its outer region. This dynamic region is filled with a plethora of features that vary in time and space. With the advent of high-resolution ground-based observations we can discover new features. We use some of the World’s biggest solar telescopes to zoom into this region and it reveals never seen before dynamics.
Here, I present detailed observations of two science topics that are guided by observations. I show a statistical study of spicules, which are long-thin grass-like features observed on the sun. These events wiggle-jiggle and sway around their axes or along a common centre of mass to create wave-like motions on the Sun. These waves can travel with speeds on 100s of km per second to energise the solar chromosphere. The second example I show are swirling-whirling events, that look like Tornadoes on the Earth. These churn the matter from the Lowe photosphere to the chromosphere. Studying the behaviour of such events is vital in understanding the workings of mass and energy cycles of the solar atmosphere.
In addition, the current work presented already tests the limits of current telescopes in terms of the temporal and spatial resolution. The answer to exploring the depth of chromosphere lies in building next-generation solar physics observatories such as DKIST that have 3 times more spatial resolution than CRISP/SST.
- Monday 18.07.2022
- Dr. Maria Weber. Delta State University (Cleveland, MS, USA)
- Title: How Suns Get Their Spots: What we know and what we don’t
- Abstract: Starspots are manifestations of a star’s internal magnetic processes. However, even for our own Sun, there are still many uncertainties about the complex mechanisms that give the Sun its spots. Within the context of magnetic flux emergence in the Sun, I will discuss what we know and what we don’t about how active region magnetism is generated and rises through the solar interior to produce sunspot observables. I will also discuss our work to establish links between dynamo-generated magnetic fields, shearing and fluid motions, and observations of starspots in solar-like stars down to fully convective M dwarfs.