KIS Astrophysical Colloquium 2018

The colloquium usually takes place on Thursdays at 11:30 if not stated otherwise.

Upcoming Talks:
July 5, 2018 Eberhard Wiehr, Institut für Astrophysik, Göttingen: The different behavior of ions and neutrals in solar prominences
Time varying Doppler shifts of NaD and SrII in a quiescent prominence are coherent in phase but show 15% larger amplitude of the ions. This is equally found for He5015 and FeII5018 and suggests a drag effect between neutrals and ions, when moved by the magnetic field. The non-thermal velocities, responsible for the SrII broadening are not related to its Doppler shifts.
September 20, 2018 Stefan Poedts, CmPA, Department of Mathematics, KU Leuven, Belgium: Physics-based models for forecasting space weather
Solar Coronal Mass Ejections (CMEs) are large-scale eruptive events in which large amounts of plasma (up to 10^13-10^16 g) and magnetic field are expelled into interplanetary space at very high velocities (typ. 450 km/s, but up to 3000 km/s). When sampled in situ by a spacecraft in the interplanetary medium, they are termed Interplanetary CMEs (ICMEs). They are nowadays considered to be the major drivers of “space weather” and the associated geomagnetic activity. The detectable space weather effects on Earth appear in a broad spectrum of time and length scales and have various harmful effects for human health and for our technologies on which we are ever more dependent. Severe conditions in space can hinder or damage satellite operations as well as communication and navigation systems and can even cause power grid outages leading to a variety of socio-economic losses.
September 27, 2018 Edgar Carlin, IRSOL – Istituto Ricerche Solari Locarno, Switzerland:
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October 11, 2018 Ariane Lancon, Observatoire Astronomique de Strasbourg, France:
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October 15, 2018 (Monday), 11:30 Nour-Eddine Raouafi, Johns Hopkins University Applied Physics Lab, USA:
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Past Talks:
January 15, 2018 17:15 Physics High Tower Conny Aerts, University Leuven, Belgium: The Interior Rotation and Chemical Mixing of Stars from Gravity-Mode Asteroseismology
The 4-year long uninterrupted high-precision data from the NASA Kepler space mission led to a revolution in stellar physics. This is particularly the case for gravity-mode asteroseismology of young stars, which requires years of continuous monitoring. In this seminar, we first explain how asteroseismology allows to deduce the interior physics of stars at a level that is impossible to reach in any other way. We focus on the capability of the Kepler data to derive the interior rotation properties of stars born with a convective core. We also highlight the most recent findings on chemical mixing in the deep interior of stars and discuss its implications for stellar evolution theory. Finally, we provide an outlook for future projects in asteroseismology to illustrate the bright future of this research domain.
January 25, 2018 Kostas Kokkotas, Universität Tübingen: Neutron Stars in the Era of Gravitational Waves
Neutron stars are the densest objects in the present Universe. These unique and irreproducible laboratories allow us to study physics in some of its most extreme regimes. The multifaceted nature of neutron stars involves a delicate interplay among astrophysics, gravitational physics, and nuclear physics. The recent direct detection of gravitational waves from beak-hole and neutron star binaries turned gravitational physics into an observational science. Gravitational waves by tight binary neutron star systems, supernovae explosions, non-axisymmetric or unstable spinning neutron stars will provide us with a unique opportunity to make major breakthroughs in gravitational physics, in particle and high-energy astrophysics. The focus of the talk will be on neutron star as sources of gravitational waves and their impact on astrophysics and nuclear physics.
January 30, 2018 Gioele Janett , Istituto Ricerche Solari Locarno: Numerical integration of the polarized radiative transfer equation
The numerical evaluation of reliable and accurate Stokes profiles is of great relevance in solar physics. Efficient numerical approximation of polarized radiative transfer is challenging because many actors play a role in the problem: among them the numerical scheme, the discrete atmospheric model, and the spectral lines. Aiming at the optimal numerical solution, we analyze the advantages and drawbacks of different numerical schemes in terms of order of accuracy, numerical stability, and computational cost. We test the performances of different numerical schemes for the synthesis of polarization spectra for different atmospheric models and spectral lines, identifying instability issues, and suggesting practical remedies.
February 1, 2018 Jürg Beer, EAWAG, Zürich, Schweiz:
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February 8, 2018 Sebastian Wolf, Universität Kiel: Can we observe the formation of planets?
Planets are expected to form in circumstellar disks around young stellar objects - a common by-product of the star-formation process. Consequently, these disks provide the key to evaluate and to refine existing hypotheses for the various phases of the planet formation process. Currently, various instruments / observatories which provide the required angular resolution and sensitivity over a broad wavelength range and which are ideal for investigating the potential planet-forming region in circumstellar disks became available. I will discuss the feasibility to study the various stages of the planet formation process observationally - from the growth of submicron-sized dust grains in young, gas-rich circumstellar disks to the stage of long-term stable planetary systems embedded in debris disks. In this context, a special focus will be on protoplanets which represent the major missing link on the way from dust to planets.
April 26, 2018 Manfred Schüssler, Max Planck Institut für Sonnensystemforschung, Göttigen: The simplicity and complexity of the solar dynamos
Observations reveal a stunning complexity of the magnetic field due to its interaction with turbulent convection. Numerical simulations and observations strongly suggest that most of the small-scale field is generated by small-scale dynamo action. The fundamental nature of this process makes it potentially relevant in a broad variety of astrophysical settings. On the other hand, the global nature of the 11-year cycle reveals a surprising simplicity. This suggests a description of the global dynamo process in terms of relatively simple concepts. During the last decades, studies of magnetic flux transport at the solar surface confirmed the visionary approach proposed Babcock and Leighton. A recent update of their dynamo model permits a full study of the space spanned by the few remaining parameters in order to identify the regions with solar-like solutions. Observations of other cool stars suggest that the relatively slow rotation of the Sun puts it near to the threshold for which global dynamo action ceases. This suggests a further simplification of the dynamo model in terms of a generic normal form for a weakly nonlinear system. Including the inherent randomness brought about by the flux emergence process leads to a stochastic model whose parameters are fixed by observations. The model results explain the variability of the solar cycle amplitudes from decadal to millennial time scales. However, the true complexity of the processes cannot be ignored. The connection between the toroidal field in the convection zone and the magnetic flux emerging at the surface is highly complex and non-trivial. This is an important "loose end" of Babcock-Leighton-type dynamo models. Furthermore, internal differential rotation, convective flows, meridional flows, and tilt angles are largely unknown in stars other the Sun. Consequently, models for the solar dynamo cannot be simply transferred to stars with different rotation rate, structure, or evolutionary state.
May 15, 2018 (Tuesday 14:30) Manolis Georgoulis, Science Academy of Athens, Greece: Physics and Prediction of Solar Flare Triggering
Solar flares, along with coronal mass ejections (CMEs) and solar energetic particles (SEPs), are the main agents of adverse space weather at Earth and geospace. Over the past two solar cycles, at least, interest exists in predicting flares *prior* to their triggering in the solar atmosphere. Predicting solar flares implies an assessment of the level of complexity and the proximity to instability of flare hosts, namely solar active regions. In this line, the EU FLARECAST project has adopted a "brute-force" approach gathering and evaluating on common grounds every viable flare predictor proposed over the last 25 years. To navigate through the immense parameter space formed, FLARECAST has been relying on diverse machine learning prediction algorithms, evaluating and validating the performance of each of them. A key benefit of machine learning, among others, is the ranking of parameters with respect to their importance in flare prediction, which can then feed back into an improved physical picture with why best / worst performing parameters behave this way. We aim to draw some (preliminary) conclusions in this respect, that may further shed light in certain aspects of flare triggering, the ambivalent flare - CME connection and an overall improved assessment of the pre-eruption situation in solar active regions. Part of this work has been supported by the EU Horizon 2020 Research and Innovation Action under grant agreement No.640216 for the “Flare Likelihood And Region Eruption foreCASTing” (FLARECAST) project.
May 17, 2018 Thomas Dent, Institute for Gravitational Physics (Albert-Einstein-Institut), Hannover: Gravitational Waves in an Expanding Universe - Kolloquium zu Ehren von Herrn Prof. Dr. Mattigs 90. Geburtstag
Since the discovery in the early 20th century that astronomical objects far outside our Galaxy are inexorably receding, a picture has emerged in which space itself is expanding, affecting all the matter and energy in the Universe. Fast forwarding to the early 21st century, many puzzles remain in this picture: how exactly fast is the Universe actually expanding at present? What is causing this expansion to accelerate? And what powered the ultra-fast inflationary expansion in the very early Universe that left its marks on the cosmic microwave background? Is General Relativity, which first suggested the idea of expanding space, still a valid description? I will look at a number of ways these questions can be connected to another of GR's predictions on extragalactic scales : the emission of gravitational waves, as confirmed in the spectacular first direct detections by the LIGO and Virgo interferometers
May 24, 2018 Henrik Hargita, NASA Aimes, USA: How and why do we map planets where nobody lives?
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June 25, 2018 (Monday), 14:30 Michael J. Thompson, National Center for Atmospheric Research, Boulder, USA: Future directions for helioseismology
Helioseismology has been spectacularly successful at revealing many aspects of the Sun's internal structure and dynamics. What then are the new challenges and opportunities for the field? In this talk I will briefly review the current state of helioseismology, and will then discuss science opportunities and future directions for observations from the ground and space.