Abstracts-Talks - Dynamics of the Sun & Stars: Honoring the Life & Work of Michael Thompson

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William Chaplin, University of Birmingham

Title: Michael Thompson's legacy in solar and stellar physics

Abstract: In this overview talk I will review Michael's crucial contributions to solar and stellar physics, through his research in helio- and asteroseismology.

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Rekha Jain, University of Sheffield

Title: Michael Thompson in Sheffield

Abstract: Michael Thompson contributed greatly to the field of Helioseismology and inspired many young researchers in this discipline with his insight and new ideas. He was a committed academic and a very efficient manager. His hard work and sincere approach was infectious for many colleagues who worked with him. This tribute is an opportunity to share a little part of his work and life during his time in Sheffield.

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Jim Hurrell, Colorado State University & former director NCAR

Title: Michael Thompson at HAO and NCAR

Abstract: TBD

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Robin Thompson, University of Oxford

Title: Using modelling for forecasting and control of infectious disease outbreaks

Abstract: Everyone at this workshop knows more than I do about my father’s seminal work in helio- and asteroseismology, but he also had a significant impact on my own research career in a different field - mathematical epidemiology. For example, he suggested I compile a special issue of a journal to coincide with the centenary of the 1918 “Spanish Flu” pandemic, which led to the publication of two theme issues of Philosophical Transactions of the Royal Society B. In this talk, I will provide an introduction to the field of mathematical epidemiology and will discuss how mathematical models can provide useful tools for policy-makers at different stages of an infectious disease outbreak. The field of mathematical epidemiology may not be as removed as it first seems from the work that my father oversaw at NCAR. Climate change is a key driver of disease emergence, and epidemics are predicted to be more frequent and more severe in future. As a result, there are increasing opportunities for collaboration between climate scientists and mathematical epidemiologists; integrating climate science methods with the modelling techniques discussed in this talk will lead to improved forecasting of future infectious disease epidemics.

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Sarbani Basu, Yale University

Title: Uncovering the hidden layers of the Sun

Abstract: Helioseismic analyses have allowed us to determine the structure of the inner layers of the Sun. This in turn has led to tests of solar models, and perhaps more importantly, tests of the properties of stellar material. Helioseismic results of the structure of the solar core was the first clue that the erstwhile “solar neutrino problem” was not a result of incorrect solar models, and that a particle physics solution was required to solve it. In this talk I shall review some of the interesting results that helioseismic structure inversions have revealed and how today we are still using structure inversions to reveal subtle features of solar structure.

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Rachel Howe, University of Birmingham

Title: Solar rotation

Abstract: The study of the solar interior rotation has a long history, in which helioseismology has played a vital role and produced some unexpected results that challenged modellers -- such as the nearly-radial profile of the lines of constant rotation in the convection zone, the thin shear layer or tachocline at its base, and the nearly-rigid rotation in the radiative interior. This review will highlight Michael Thompson's important contributions to techniques for helioseismic rotation inversions, and the results that those contributions have enabled. These include the study of the near-surface shear layer and the evolution of zonal flows in the convection zone over the solar cycle -- the so-called torsional oscillation, which can be seen in surface observations but which helioseismology reveals to penetrate deep into the convection zone. Finally, I will present some preliminary results from the collaborative effort that was initiated by Michael in 2017 with the aim of taking advantage of more than twenty years of high-quality helioseismic observations to refine our picture of the interior rotation profile.

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Sacha Brun, CEA-AIM, Saclay

Title: Dynamo action in Sun-like stars

Abstract: We will present our current understanding of dynamo action in Sun-like stars and how the research of Mike Thompson contributed to that field by providing constraint on both the internal fields and flows.

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Scott McIntosh, NCAR/HAO

Title: On the remarkably abrupt transition between solar cycles

Abstract: We observe the abrupt end of solar activity cycles at the Sun's equator by combining almost 140 years of observations from ground and space. These "terminator" events appear to be very closely related to the onset of magnetic activity belonging to the next sunspot cycle at mid-latitudes and the polar-reversal process at high-latitudes. Using multi-scale tracers of solar activity we examine the timing of these events in relation to the excitation of new activity and find that the time taken for the solar plasma to communicate this transition is of the order of one solar rotation, but could be shorter. Utilizing uniquely comprehensive solar observations from the Solar Terrestrial Relations Observatory (STEREO), and Solar Dynamics Observatory (SDO) we see that this transitional event is strongly longitudinal in nature. Combined, these characteristics imply that magnetic information is communicated through the solar interior rapidly. A range of possibilities exist to explain such behavior: the presence of magnetic reconnection in the deep interior, internal gravity waves on the solar tachocline, or that the magnetic fields present in the Sun's convection zone could be very large, with a poloidal field strengths reaching 50kG - considerably larger than conventional explorations of solar and stellar dynamos estimate. Regardless of mechanism responsible, the rapid timescales demonstrated by the Sun's global magnetic field reconfiguration present strong constraints on first-principles numerical simulations of the solar interior and, by extension, other stars.

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Aaron Birch, Max Planck Institute for Solar System Research

Title: Local helioseismology: methods and results

Abstract: Local helioseismology is a set of methods for inferring three dimensional dynamics and structure in the solar interior from observations of acoustic and surface-gravity waves at the surface. The main methods of local helioseismology are time-distance helioseismology, ring-diagram analysis, and helioseismology holography. In all of these methods, linear inverse problems are solved to determine models of the flows in the solar interior from bi-linear combinations of the oscillation data. Mike Thompson contributed significantly to the development of inversion methods for local helioseismology. A few important current topics in local helioseismology are the strength of convection, Rossby waves, flows associated with active regions, and the subsurface meridional flow. These results build on earlier observational work from Mike.

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Paul Rajaguru, Indian Institute of Astrophysics, Bangalore, India

Title: Time-distance helioseismology of deep meridional circulation

Abstract: A key component of solar interior dynamics is the meridional circulation (MC), which has been well observed on the surface and near-surface layers. Time-distance helioseismic observation of the deep structure of MC, however, has been plagued by a large center-to-limb systematics (CLS) and conflicting inferences from different groups/researchers. Here, using seven years of data from the Helioseismic and Doppler Imager (HMI) onboard Solar Dynamics Observatory (SDO), we present an analysis of (p mode) frequency dependences in systematics, inverted MC, and in their temporal variations. We derive signatures that point to the residual systematics in travel times as a major source of differing inferences especially for the deep structure of MC. We confirm additional N-S asymmetric temporal variations, which correlate with surface magnetic activity (and hence the phase of the solar cycle). We discuss implications of our results for models that relate the differential rotation, MC and magnetic fields. Authors: S.P. Rajaguru, Indian Institute of Astrophysics and H.M. Antia, Tata Institute of Fundamental Research.

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Shravan Hanasoge, Tata Institute of Fundamental Research

Title: Inferences of solar internal dynamics using normal-mode coupling

Abstract: Normal mode coupling presents a powerful means of imaging time-varying and spatially inhomogeneous features in the Sun. I will describe general aspects of the method and outline the potential for applying it to infer a variety of important features of solar dynamics. I will present inferences of the spectrum of toroidal convective flows as a function of spatial wavenumber, temporal frequency up to some depth in the solar interior, obtained from analyses of 8 years of HMI observations. In contrast to simulations, observed velocity power weakens with decreasing spatial wavenumber and temporal frequency, indicating that large scales of solar convection are suppressed.

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Ricky Egeland, NCAR/HAO

Title: Is the Sun in a transitory state of its dynamical evolution?

Abstract: In January of 2017 Michael Thompson, Deputy Director of NCAR, contacted me, a lowly graduate student, to collaborate in developing a SHINE session proposal titled "Is the Sun in a transitory state of its dynamical evolution?" The impetus was Van Saders et al. 2016 Nature paper that, using precise ages from asteroseismology, reported stars older than the Sun are rotating more rapidly than expected given Skumanich Law angular momentum loss due to a magnetized stellar winds. The Sun is very near the critical Rossby number during which stellar spin-down suddenly stops, and later work gave additional stellar and model-based evidence that the Sun is presently in a transition phase of its dynamo evolution. In this presentation, I will recount the story of my collaboration with Michael to develop and execute the fruitful SHINE 2017 session in Quebec, review the evidence and implications of a solar magnetic transitory phase, and present the most recent observations that give additional support to the theory of a finite magnetic braking period and eventual death of the large-scale dynamo.

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Savita Mathur, Instituto de Astrofisica de Canarias

Title: Surface rotation and magnetic activity of solar-like stars: impact on seismic detections

Abstract: Stars with an external convective envelope have rotation periods evolving with time, roughly as the square root of their ages during an important part of their lives. Thus, by measuring the surface rotation period of a solar-like star, we can have an estimate of its age using these empirical gyrochronology relations. While it was recently shown using Kepler data that these relations seem to be valid only up to a given Rossby number (ratio of the rotation period and the convective turnover time of about 2), they still hold for K and M dwarfs. This is great news as measuring rotation is somewhat easier by studying the modulation in the light curves due to the passage of spots/active regions on the stellar discs. Moreover, as these measurements depend on the presence of spots, we can also derive a proxy of the magnetic activity based on the photometric observations that we call Sph. In this work, we present the analysis of the rotation periods of more than 26,000 M and K dwarfs observed in long cadence for ~4 years with the Kepler mission. First, we removed all kind of pollutions (e.g. classical pulsators, known binaries, etc). For this analysis we used our improved rotation pipeline where we combine three different methods (time-frequency analysis, auto-correlation function and composite spectrum) with different ways of calibrating the photometric signal. We obtained reliable rotation periods for more than 15,000 stars, including ~4,000 stars without rotation periods reported up to now. We also derived the Sph values for those stars. We will also show preliminary results of the extension of this work towards F and G dwarfs where we are incorporating a machine learning algorithm to reduce the visual checks of the results. Finally, as we know for the Sun and many solar-like stars now, magnetic activity has an impact on the amplitude of the acoustic modes by suppressing them. We will present the analysis of a sample of ~1,000 solar-like stars observed in short-cadence during the survey phase of the mission and for which no modes where detected. We investigated the reason for the non-detection. Surprisingly the conclusion of our analysis is that magnetic activity is not the main reason for not detecting acoustic modes in those stars.

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Juri Toomre, University of Colorado

Title: Touching the interior and dynamics of our nearest star

Abstract: The inside of the Sun is throbbing with a vast number of sound waves that are excited by the turbulent convection just below its surface. This results in about ten million acoustic modes of the solar interior that can be observed at its surface, permitting study of the Sun’s interior structure and dynamics. Michael Thompson played key roles in the development of this breakthrough subject called helioseismology, devising and applying so-called inversion methods to the observed modes. We have thus learned how the Sun rotates differentially in its deep interior, that it has a surprising tachocline of shear at the base of the convection zone, along with complex jet streams and fast flows. All such dynamics influence and control the cycles of intense magnetic activity that the Sun possesses. We will show how Michael’s passions with helioseismology have guided the efforts to understand how the Sun, like many other stars, may be operating in its deep interior. There is clearly both beauty and mystery within our nearest star.

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Yvonne Elsworth, University of Birmingham

Title: How do stars work and why is knowledge of the Sun's interior a key?

Abstract: Study of the Sun was very prominent in Michael’s impressive portfolio of science achievements. However, we should not forget his contribution to the studies of stars beyond the Sun. I will present some key ideas that focus around how we can use modern measurements of stellar oscillation frequencies to probe a range of stellar interiors. The great advantage that the Sun presents is its proximity. For distant stars the input information is much more limited and hence there are considerable challenges in mapping their interiors. The additional aspect that I will consider relates to solar and stellar activity levels and cycles. Understanding the drivers for stellar activity is not only important for exploring (and perhaps constraining) the near-surface physical conditions in stars but also for viability of life in any surrounding planetary systems.

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Mark Rast, CU Boulder

Title: Deciphering solar convection

Abstract: While the properties of solar granulation are well captured by radiative magnetohydrodynamic simulations, the spectrum of motions at larger scales remains enigmatic. The amplitudes of large scale motions in all numerical simulations of stratified solar convection are higher than those observed on the Sun. In global spherical shell models this results in weak rotational constraint on the motions and consequent non solar-like differential rotation profiles. In local area radiative magnetohydrodynamic models it yields strong horizontal flows in the photosphere on scales much larger than the observed supergranulation. These difficulties are not confined to the Sun, and the mismatch between the observed oscillation frequencies and those implied by mixing length based models motivates a more comprehensive understanding of the upper superadiabatic region of convective stellar envelopes.

We suggest that convection in stellar envelopes is even more nonlocal than numerical simulations suggest. Small scale photospherically driven downflows dominate convective transport even at great depth, descending through a very nearly adiabatically stratified (even more nearly adiabatically stratified in the mean than current numerical models can achieve) or slightly subadiabatic interior. We show that a simple model based on the superposition of downflowing plumes and adiabatic upflows can closely recover the mean thermodynamic stratification of three-dimensional numerical stellar envelope convection models. The mean stratification depends only on the filling factor and entropy fluctuations of the granular downflows in the stars' photospheres. Extrapolating this strictly adiabatic behavior to greater depths yields an estimate for the supergranular scale of motion likely found on those stars. As additional support for this idea, we show that the observed change of the supergranular scale with solar magnetic activity is consistent with variation in the mean stratification of the upper superadiabatic boundary due to the presence of magnetic fields. Finally, we point to some early efforts to use SOLA methods (Pijpers and Thompson 1994) in high resolution spectropolarimetric inversions to further constrain the vertical structure of the solar photosphere.

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Yvonne Elsworth, University of Birmingham

Title: Solar g modes (and MS stellar)

Abstract: Determining the interior structure of the Sun to high precision is one of the driving motivators of helioseismology. Michael Thompson was a key person in the development of the process to turn observations into maps. The modes that are easiest to observe are p-modes with pressure as the restoring force. These have allowed beautiful maps to be made and inferences drawn. However, to really constrain the inner core we would like to observe very low order, low degree p-modes and certainly g modes. These g modes have buoyancy as their restoring force. However, observing neither of these modes is easy. This talk will explore the reasons why these classes of modes are so important, why they are difficult to observe, and the observations that have been made to date together with the conclusions to be drawn from them.

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Othman Benomar, NAOJ, Mitaka, Japan

Title: Bridging the gap from the Sun to stars: solar analogue and twins

Abstract: Due to the space-based instrument Kepler, lightcurves obtained from integrated photometry for the brightest distant stars are now of comparable quality than the solar data 25 years ago. This allows to study low-degree pulsation modes using the knowledge acquired from decades of solar studies. This significantly improved our understanding of solar-like pulsators. In particular, inversion-based approaches applied to red giants and subgiants have revealed the radial internal rotation profile of aging stars (Deheuvels+2012, Deheuvels+2014). Weak radial differential rotation was also found for main sequence stars (Benomar+2015, Nielsen+2017), consistent with helioseismic inferences (Thompson M.J, 2003). Kepler data also enabled us to evaluate the latitudinal differential rotation for main-sequence Sun-like stars. This has shown that a vast majority of them are likely to have a slow pole and a faster equator, as it is observed for the Sun (Benomar+2018, Bazot+2019). The inference of the latitudinal differential rotation is important for tracking the latitudinal migration of stellar spots on solar analogues (see Bazot+2018). This could also be decisive to understand the links between magnetism, activity and dynamo in Sun-like stars. Due to the similarities between the Sun and solar-analogues, the pioneering work from M. J. Thompson regarding solar rotation was greatly beneficial for understanding the rotation of distant stars. This talk will review the advances made on the study of the stellar rotation of solar analogues and twins, pointing out the contributions from M.J. Thompson.

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Earl Bellinger, Stellar Astrophysics Centre, Aarhus University

Title: Inverse analyses of helioseismic data

Abstract: Inverse analyses of helioseismic data have provided a trove of insights into the solar interior. With the success of the Kepler mission, we now face the opportunity to extract similar information from other stars. However, the present quality of stellar data comes with some unique challenges. Unlike with the Sun, where thousands of modes of high spherical degree can be observed, currently only at most dozens of low-degree modes can be detected in stars. This restricts inferences to the deepest layers of the star, and rules out the use of some inversion techniques. Even more severely, unlike the Sun, the fundamental parameters (mass, radius, age) of the stars under investigation lack precise and accurate independent constraints, and usually must be estimated from the same data with which one wishes to perform the inversion. In this talk, I will review the various approaches that are being taken to overcome these challenges to invert asteroseismic data, and discuss the progress that is being made toward revealing the internal structures of stars.

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Margarida Cunha, Institute of Astrophysics and Space Sciences, Porto, Portugal

Title: Diagnostics from solar and stellar glitches

Abstract: Sudden changes in the internal structure of stars, placed at the interface between convective and radiative regions, regions of partial ionisation, or between layers that have acquired different chemical composition as a result of nuclear burning, often produce specific signatures in the stars’ oscillation spectra. Through the study of these signatures one may gain information on the physical processes that shape the regions that produce them, including diffusion and chemical mixing beyond the convectively unstable regions, as well as information about the helium content of stars. In this talk, I will review important theoretical and observational efforts conducted over the years towards this goal. I will emphasise the potential offered by the study of acoustic, gravity, and mixed modes observed in stars of different masses and evolutionary stages, at a time when space-based data is allowing us to build on the knowledge gained from the study of the sun and white dwarfs, where these efforts have long been undertaken, extending the methods developed to stars across the HR diagramme.

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Pascale Garaud, UC Santa Cruz

Title: The tachocline revisited

Abstract: I will review recent theoretical progress on modeling the solar tachocline, and discuss how these findings relate to observations.

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Steve Kawaler, Iowa State University

Title: Evolution of internal rotation of low-mass stars: clues from asteroseismology

Abstract: Studying the time evolution of the internal rotation of the Sun presents a familiar challenge for astronomers: we see the Sun only as a single snapshot in time. So though helioseismology can provide a measure of the rotational velocity as a function of depth (and latitude), we only have today's Sun before us. Inferences about how the Sun reached this state, and how it will rotate in the distant future, require study of stars like our Sun in different stages of evolution and/or computational modeling of the physics relevant to angular momentum transport and evolution. With interiors accessible to asteroseismic study using space-based photometric observations, later states of evolution (the subgiant phase, evolution on the red giant and AGB tracks, and white dwarfs) provide interesting boundary conditions. Here, I'll review some of those observations and inferences, which provide critical tests of our understanding of a variety of processes that govern stellar evolution and provide tight constraints on angular momentum transport models.

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Nicholas Brummell, University of California, Santa Cruz

Title: Towards self-consistent models of the solar tachocline

Abstract: The tachocline plays a central role in solar dynamics and yet is still far from well understood. Theories for the dynamics of this region vary widely from the laminar balanced models (see e.g. Gough & McIntyre, 1998) to ones based on anisotropic turbulence (see e.g. Spiegel & Zahn 1992). Which are more likely, or are all at play? We report on some progress on the understanding of this region, a topic dear to the heart of MJT.

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Yoshiki Hatta, SOKENDAI/National Astronomical Observatory of Japan

Title: Asteroseismic study of KIC 11145123: its structure and rotation

Abstract: KIC 11145123 is one of the Kepler targets which have been actively studied via asteroseismology. Its well-resolved frequency splittings for both g and p modes have enabled us to infer the 1-dimensional surface-to-core rotation of the star (Kurtz et al. 2014) and to measure the asphericity of the star sensed by the modes (Gizon et al. 2016). Each of the researches has been the first attempt for main-sequence stars other than the Sun, showing us the potential of the future asteroseismology. In this talk, we report further detailed asteroseimic analyses of KIC 11145123, focusing on inferring 2-dimensional rotation profile and on fine-tuning the equilibrium model of the star. Our main results are as follows: 1) the convective core might be rotating 6 times faster than the other parts of the star, and 2) adopting diffusion ‘weaker' than usual settings used in standard 1-d stellar evolution calculations leads to a better agreement with the observed g-mode period spacing pattern. These two results imply that the rotational velocity shear might cause some extra mixing around the boundary between convective core and radiative region above, and the extra mixing weakens the diffusion process there, which resembles a mechanism thought to be at work around the solar tachocline.

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Angela Santos, Space Science Institute

Title: Seismic signatures of solar and stellar magnetic activity

Abstract: Acoustic modes are sensitive to the properties of the stellar interior, including magnetic fields. Activity-related variations on the properties of the solar acoustic modes have been observed for more than three decades. Such variations encode information on the magnetic changes that take place in the stellar interiors. In 2010 thanks to CoRoT space mission, it was possible to measure for the first time the signatures of magnetic activity in the seismic data of a star other than the Sun. With the high-precision long-term photometric observations collected by Kepler, we are now able to measure temporal variations in the seismic properties of several tens of solar-type stars. Although, currently, we are not able to establish the source for the variations for each star individually, ensemble studies confirm that the observed variations are consistent with an activity-related origin. Kepler observations are thus a unique opportunity to learn about stellar magnetism through asteroseismology.

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Jim Fuller, Caltech

Title: Magnetic fields in stellar cores

Abstract: Magnetic fields are always present in stellar interiors, yet their impact on stellar evolution is poorly understood. Despite their ubiquity, it is very hard to measure magnetic fields inside stars or determine their effects on stars. Fortunately, Kepler asteroseismic data has revealed gravity modes in thousands of red giant stars, which turn out to be sensitive probes of the core magnetic fields of these stars. I will show how gravity modes (or rather, the lack thereof) can reveal strong magnetic fields in the cores of red giants, and I will demonstrate that strong fields appear to be common within "retired" A stars but are absent in their lower-mass counterparts. Gravity modes in red giants also provide measurements of the core rotation rates, which may be determined by magnetic torques in the stellar interiors. The slow core rotation measured for red giants indicates magnetic torques must be at work, and I will present a revised model of angular momentum transport arising from the Tayler instability of magnetic fields. The model can largely explain the core rotation rates of main sequence and red giant stars, allowing us to predict the natal spin rates of compact objects.

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Lisa Bugnet, CEA Saclay

Title: The impact of fossil magnetic fields on dipolar mixed modes

Abstract: Both the presence of highly magnetized white dwarfs and the recent discovery of low-amplitude dipolar oscillation modes in massive red giants indicate a missing process inside the core of some red giants. Stars more massive than ~1.3 Ms are known to develop a convective core during the main-sequence: the dynamo process due to this convection could be the origin of a strong magnetic field, trapped inside the core of the star for the rest of its evolution. If such field exists, it should affect the mixed modes of red giants as they are sensitive to processes affecting the most intern layers of the stars. The impact of a magnetic field on dipolar oscillation modes was one of the study of Michael J. Thompson during the 90s when preparing the SOHO/MDI mission. The investigation of the solar oscillation modes did not provide any hint of the existence of a magnetic field in the solar core. The idea of generalizing this work to evolved solar-like stars came from great discussions with Michael J. Thompson who was part of this project: today we have access to the core of evolved stars thanks to the observation of mixed modes from the Kepler, K2 and TESS missions. We investigate the theoretical effect of multiple magnetic field configurations on the mixed modes frequencies of a simulated sub-giant. A theoretical perturbative study along with an order-of-magnitude analysis enable us to estimate the magnetic perturbation on the frequencies of mixed dipolar modes, depending on the magnetic field strength and its configuration. This study allows us to quantify which model, the classical mixed modes or the magnetic one, represents the observed low-amplitude dipolar modes the best.

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Benard Nsamba, Institute of Astrophysics and Space Sciences, Porto

Title: Asteroseismic stellar modelling: In-depth exploration of the treatment of the initial helium abundance

Abstract: The initial helium abundance is an essential ingredient in the modelling of solar-type stars. The abundance of helium in these stars remains, however, a poorly constrained observational property. This is because it cannot be directly determined from spectroscopic observations, i.e., helium lines are not detectable in the spectra of solar-type stars. A common solution is then to estimate the initial helium abundance via a semi-empirical helium-to-heavy-element ratio anchored to the standard Big Bang nucleosynthesis values. Depending on the choice of solar composition used in model calibration, the helium-to-heavy-element ratio is found to vary between 1 and 3. In this work, we adopt the Kepler LEGACY stellar sample, for which precise asteroseismology is available, and explore the systematic uncertainties on modelled stellar fundamental parameters (density, radius, mass, and age) arising from different values of the helium-to-heavy-element ratio used. Finally, we compare the initial helium abundance in our optimised models with the values derived observationally by Verma et al. based on a glitch analysis.

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Markus Roth, Leibniz-Institut für Sonnenphysik (KIS), Freiburg

Title: A future path for solar synoptic ground-based observations

Abstract: Since the Sun changes on time scales of seconds to millennia, observations need to be as continuous as possible in order to capture solar phenomena with minimal temporal aliasing and to ensure that rare and fast events are recorded. As a consequence solar observations with a telescope providing a large field-of-view are of advantage for such solar synoptic observations. A ground-based network is a set of geographically distributed telescopes equipped with nearly-identical observing instruments so that gaps from the night time, weather and instrumental problems are minimized. This strategy has been clearly demonstrated to provide such observations, as shown by the success of the UK BiSON (Birmingham Solar Oscillations Network) and US GONG (Global Oscillation Network Group) networks. Telescopes with a small aperture but a large field-of-view provide important and valuable solar data and are now becoming available for complementary programs that require long and contiguous observations. Equipped with modern instrumentation and formed as a network they could provide the data for the highly demanded synoptic observations giving the possibility to integrate a large fraction of scientific topics of solar physics. The Solar Physics Research Integrated Network Group (SPRING) is a concept for such a new network of ground-based telescopes. The scientific objectives are manifold and cover topics like: the physical origins of the solar activity cycle; the interaction of the p-mode oscillations and the solar magnetic field; the formation, growth, decay, and disappearance of active regions; the connections of the solar magnetic field from the interior to the corona; the mechanisms of coronal mass ejections (CMEs), erupting filaments, flares, and other phenomena that can affect terrestrial technology and society; the variations in solar irradiance that may affect terrestrial climate; and solar-stellar connections.

In this talk, I will provide an overview of the status of the work on this new ground-based network for future synoptic observations of the Sun, which we started planning together with Michael Thompson. A technical feasibility concept was completed in 2017, on which the next steps of work towards a preliminary design are based.

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Dan Huber, Institute for Astronomy (IfA), University of Hawaii

Title: Observational Asteroseismology in the 2020’s and beyond

Abstract: Building on the foundation in helioseismology and asteroseismology laid out by pioneers such as Michael Thompson, observational progress in asteroseismology has exploded over the past decade thanks to space-based missions such as CoRoT and Kepler/K2. Over the coming decade, this revolution is set to continue through facilities that will provide a several order of magnitude increase of known solar-like oscillators, as well as a dramatic increase in the number and quality of classical pulsator observations, providing unprecedented possibilities to study stellar physics and galactic stellar populations. In this talk, I will discuss the prospects and challenges for observational asteroseismology in the coming decade and beyond using space-based telescopes such as TESS, WFIRST and PLATO, as well as ground-based observations using dedicated networks such as SONG, photometric transient surveys, and 8-m class telescopes.

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Don Kurtz, University of Central Lancashire

Title: Oblique Pulsation: New, challenging observations with TESS data

Abstract: For nonradial pulsation modes it has traditionally been assumed that the pulsation axis coincides with rotation axis of the star, in the belief that rotation provides the major distortion from spherical symmetry. That assumption is not well-tested in many types of pulsating stars. For 40 years the oblique pulsator model has provided information about the geometry of pulsation modes in stars with strong magnetic fields, where the pulsation axis is close to the magnetic axis. Now, new challenges arise in TESS data. 1) The oblique pulsator model in the roAp star, HD6532, gives a strikingly different result in TESS red data and ground-based B data. Has the star changed pulsation axes? Can stars do that? Is the oblique pulsator model flawed? Or is the geometric structure of the pulsation in HD6532 very different at the different atmospheric depths probed by red and blue observations? These will be discussed. 2) After years of searching binary stars for oblique pulsation along the tidal axis, such a star has been found in TESS data, with surprising behaviour. This, too, will be discussed.

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Kyle Augustson, CEA Saclay

Title: Asteroseismology of magnetic fields

Abstract: The improvement of the knowledge of stellar magnetism is one of the major challenges in stellar physics. The modern era of asteroseismology has enabled the probing of stellar interiors through the waves excited there. Indeed, with powerful ground-based instruments and space-based missions, the interaction between stellar oscillations and magnetic fields needs to be illuminated. Specifically, for helioseismology and asteroseismology, the perturbations to the spectrum of stellar oscillations excited within stars due to a general magnetic field should be identified. This leads to a method for also inverting for the internal structure of the magnetic field as well. To accomplish this, the eigenfunctions are constructed with the spin-vector harmonics, yielding relatively compact expressions for the contributions of the Lorentz force and its indirect effects to the eigenfrequency. The spin-vector harmonics arise in quantum mechanical approaches to angular momentum coupling, but also provide a useful basis for asteroseismology.

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Jørgen Christensen-Dalsgaard, Aarhus University

Title: Contemplating the future

Abstract: The prospects for the further development of stellar astrophysics remain golden. Much can still be done based on the Kepler data, the TESS mission is providing data over most of the sky, at a 10 min cadence in the extended phase, PLATO will provide data comparable with those of Kepler for relatively near-by stars, ground-based observations yield data of even higher quality for selected stars, and Gaia is revolutionizing the determination of global stellar properties. On the modelling side ever more realistic simulations are becoming possible of dynamic phenomena in stellar interiors, and new techniques, known as artificial intelligence or deep learning, are helping the analysis of the huge amounts of data that are becoming available. Much of this effort is aimed at applications of stellar physics in other areas of astrophysics, such as exoplanets or Galactic archaeology. Despite the excitement of these developments, in the spirit of Michael we should not forget the basic goal of improving our physical understanding of stars, combining human intelligence and intuition with mathematical analysis and modelling, observations, and data interpretation. This should be kept in mind in our work and, even more importantly, in the education of coming generations of stellar astrophysicists.

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