08/04/2013, 10:00
08/04/2013, 10:30
08/04/2013, 15:00
08/04/2013, 16:00
09/04/2013, 10:00
09/04/2013, 10:40
09/04/2013, 15:30
09/04/2013, 17:30
10/04/2013, 10:30
10/04/2013, 12:00
11/04/2013, 10:00
11/04/2013, 10:30
11/04/2013, 15:00
11/04/2013, 15:30
11/04/2013, 16:00
11/04/2013, 17:30
12/04/2013, 09:30
12/04/2013, 10:30
12/04/2013, 11:30
12/04/2013, 12:00
Dmitry Sokoloff
12/04/2013, 12:30
Mikkel Lund
(Stellar Astrophysics Centre, Aarhus University)
15/04/2013, 14:00
Prof.
Kandaswamy Subramanian
16/04/2013, 11:00
The talk discusses the possibility that cosmic magnetic fields can
originate in the early universe. Primordial fields could be
generated during one of the early universe phase transitions like,
inflation or the elctroweak/QCD phase transitions. We discuss
these possibilities, their subsequent evolution, and the possible
signals they leave on the Cosmic microwave background and on...
Leonid Kitchatinov
(Institute for Solar-Terrestrial Physics)
16/04/2013, 16:00
Dr
Nobumitsu Yokoi
(Institute of Industrial Science, University of Tokyo)
17/04/2013, 11:00
Effect of cross helicity (velocity--magnetic-field correlation) in the
mean momentum equation is investigated. Turbulent cross helicity
enters the expression for the mean-field Lorentz force. Combined
with the contributions through the Reynolds and turbulent Maxwell
stresses, it gives a possibility to induce a flow. Mean momentum
equation is examined from this viewpoint. As for some...
Ana Borisova
(Institute of Astronomy and NAO-Rozhen, Bulgarian Academy of Sciences)
18/04/2013, 11:00
Mr
Rainer Arlt
(Leibniz Institute for Astrophysics Potsdam)
23/04/2013, 11:00
Levente Kriskovics
(Konkoly Observatory of the Hungarian Academy of Sciences, Budapest)
23/04/2013, 15:30
Seminar
Fast rotating red giant branch stars in the first dredge-up phase
provide a unique opportunity to study connections between
enhanced Li abundance and activity. DI Psc is (HD 217352) a Li-
rich, active single K giant, a new candidate for the rather small
group of giants currently in this state. We reconstructed the
surface temperature distribution by the means of Doppler
Imaging on...
Matteo Cantiello
(Kavli Institute for Theoretical Physics, University of California)
24/04/2013, 11:00
Seminar
Recent observations have revealed the presence of both pulsations and magnetic fields
in massive stars.
As these phenomena can directly affect the mass-loss and the rotation rate, their
impact on stellar evolution is potentially huge, with consequences for the final fate
of massive stars. I will review some of the latest observational and theoretical
developments in the field, focusing in...
Alexander F. Kholtygin
(Astronomical Institute, Saint-Petersburg State University)
24/04/2013, 15:30
Seminar
The standard method of the magnetic field measurement, based on an analysis of
the relation between the Stokes V-parameter and the first derivative of the total
line profile intensity, has been modified by applying a linear integral operator L to
the both sides of this relation. The
wavelet transform with DOG-wavelets as the operator L is used. The advantage of the
method is an effective...
Nathan J. Kleeorin
(Ben-Gurion University of the Negev, Beer-Sheva)
25/04/2013, 11:00
We discuss a new theory of differential rotation in anisotropic
density stratified
inhomogeneous turbulent convection. A key point of this theory is
an effect of the
turbulent heat flux on the Reynolds stresses in a rotating
turbulent convection. We
solved a coupled system of dynamical equations which includes
the equations for the
Reynolds stresses, the entropy fluctuations and...
Hans-Erich Fröhlich, Mr
Rainer Arlt
(Leibniz Institute for Astrophysics Potsdam)
25/04/2013, 15:30
Kate Rubin
26/04/2013, 10:30
Bidya Binay Karak
(Department of Physics, Indian Institute of Science, Bangalore)
26/04/2013, 14:00
Seminar
The irregular nature of the solar cycle makes the prediction of
future cycles
challenging. However, the prediction of the solar activity is
important for several
reasons. In the Babcock-Leighton dynamo models,
the poloidal field is generated near the solar surface whereas the
toroidal field is
generated near the base of the convection zone. Therefore a
finite time necessary...
Mr
Rainer Arlt
(Leibniz Institute for Astrophysics Potsdam)
29/04/2013, 14:30
Nadezhda V. Zolotova
(Earth's Physics Department, St.Petersburg State University)
29/04/2013, 15:30
Seminar
Using Greenwich catalogue of sunspots and magnetic field
observations
it was shown that impulses of sunspot activity during a course of
solar cycle are responsible for residual magnetic flux transported
by
meridional circulation toward the poles. This, in turn, is related to
the polarity reversal of the axisymmetric magnetic fields. Single
and
compound magnetic field reversals at...
Kirill Kuzanyan
(IZMIRAN, Russia)
30/04/2013, 11:00
Seminar
We study observational proxies of magnetic helicity (and the
alpha effect) in the Sun
by analysis of photospheric vector magnetograms. The newest
finding is determination
of anisotropy of helicity near the solar surface. We can
demonstrate that assumptions
of local homogeneity and isotropy require serious revision
in the light of these
findings. Furthermore, we can show that rotation...
Lúcia D. V. Duarte
(Max-Planck-Institut für Sonnensystemforschung, Lindau)
30/04/2013, 11:30
Seminar
Observations of the gas giants show that both planets have
dipolar magnetic fields:
Jupiter's is very similar to the Earth's magnetic field and Saturn's
is very
axisymmetric. In addition, both gas giants present a very
dynamical behaviour of the
atmospheric flow, organized in banded structures of east-west
flow. Our main goal is
to approach more realistic numerical models that...
Rakesh Yadav
(Max-Planck-Institut für Sonnensystemforschung, Lindau)
30/04/2013, 14:00
Seminar
Numerical dynamo models always operate at parameters which
are many orders of
magnitude smaller or larger than the values expected in natural
objects. However,
numerical modelling has been very successful in reproducing
many interesting
properties of dynamos existing in nature. This qualitative
agreement fuels the idea
that both numerical and natural systems are in an asymptotic...
Dr
Gustavo Guerrero
(NORDITA)
01/05/2013, 11:00
Raynaud Raphael
01/05/2013, 11:30
We will present a summary of different versions of the convective
approximations of the fully compressible version of the Navier-Stokes
equation, and question their numerical implementation.
Prof.
Alexander Kholtygin
(Astronomical Institute of Saint-Petersburg University, Russia)
02/05/2013, 11:00
Sarah Jabbari
(KTH Royal Institute of Technology, Stockholm)
02/05/2013, 15:30
Seminar
In the presence of strong density stratification, turbulence can
lead to a
large-scale instability of a horizontal magnetic field if its strength
is in a
suitable range (within a few percent of the turbulent equipartition
value). This
instability is related to a suppression of the turbulent pressure so
that the
turbulence contribution to the mean magnetic pressure becomes...
Mr
Jörn Warnecke
(Nordita)
03/05/2013, 10:30
Mark Miesch
(High Altitude Observatory, National Center for Atmospheric Research, Boulder)
Seminar
One of the leading paradigms to account for the 11-year solar activity cycle is the
Babcock-Leighton (BL) dynamo model, whereby the principle source of mean poloidal
field is attributed to the destabilization, rise, emergence, and dispersal of buoyant
magnetic flux structures. Though the existence of sunspots and bipolar active
regions is central to the operation of a BL dynamo, their...
Egor Illarionov
(Moscow State University)
Talk
We obtain the latitude-time distribution of the averaged tilt angle
of solar bipoles. For large bipoles, which are mainly bipolar
sunspot groups, the spatially averaged tilt angle is positive in the
Northern solar hemisphere and negative in the Southern, with
modest variations during course of the solar cycle. We consider
the averaged tilt angle to be a tracer for a crucial element...
Delphine Hypolite
(Research Institute in Astrophysics and Planetology (IRAP), Toulouse)
Talk
Aims: We investigate the shape of the rotation profile of radiative stellar envelopes
undergoing gravitational contraction to obtain a better understanding of the dynamics
of such objects.
Methods: We construct a model of a rotating core absorbing a baroclinic envelope
enclosed in an undeformable spherical shell and solve the hydrodynamic equations
using the Boussinesq...
Ana Borisova
(Institute of Astronomy and NAO Rozhen, BAS)
Seminar
We present analysis of the long-term photometric data of the active giant OP And. Our
research is based on previously published photometric data, Hyparcos photometric
series and observations obtained at Belogradchik observatory, Bulgaria.
We provide Bayesian estimate photometric period of the star in the time interval
1983-1999 and compare it with the previous published ones. We have...
Thomas Hackman
(Finnish Centre for Astronomy with ESO)
Talk
A basic method to measure the surface differential rotation on both the Sun and stars
is to trace the movement of spots. The general notion is that spots on late-type
stars are equivalents of sunspots. However, results from Doppler imaging and
photometric time series analysis as well as numerical modelling have cast shadows of
doubts on this assumption. It has been hard to observationally...
Leonid L. Kitchatinov
(Institute for Solar-Terrestrial Physics, Irkutsk)
Seminar
Instabilities in stellar radiation zones are important for angular momentum
transport, mixing of chemical species and, possibly, for dynamos. It is shown that
even a very small radial differential rotation can lead to instability. Surfaces of
constant density and constant pressure do not coincide in differentially rotating
stars. The baroclinicity of stratification results in a...
Scott G. Gregory
(School of Physics & Astronomy University of St Andrews)
Talk
A number of maps of the surface magnetic fields of newborn Sun-like stars have now
been obtained using the technique of Zeeman-Doppler imaging. Their magnetic fields
can be significantly more complex than a simple dipole, the usual assumption of
models, and can vary markedly between sources. I will summarize the magnetic field
topology information obtained to date and present...
Reinhard Schlickeiser
(Inst. f. Theoretische Physik, Ruhr-Universitaet Bochum)
Talk
Magnets have practically become everyday objects. Permanent
ferromagnetism is a property of only a few densely packed
materials, such as iron, in which the spin exchange interactions of
individual atoms naturally line up in the same direction and
create a residual persistent magnetic field. In the early universe,
before iron and other magnetic materials had been created inside...
Alfio Bonanno
(INAF, Osservatorio Astrofisico di Catania)
Talk
The stability of a toroidal field in stellar radiation zone will be discussed by
considering the combined effect of rotation, stable stratification and thermal
conductivity. It will be shown that the influence of rotation depends on the magnetic
configuration of the basic state. If the toroidal field increases sufficiently
rapidly with the spherical radius, the instability cannot be...
Elena Benevolenskaya
(Pulkovo Astronomical Observatory, Saint Petersburg)
Talk
In this presentation I discuss the results of the detailed evolution of the solar
active regions: NOAA 11101 during 10 days from 26 August 2010 to 4 September 2010 and
NOAA 11106 from 12 September 2010 to 20 September 2010 using magnetic data of the
line-of-sight component of the magnetic field and intensitygrams in continuum with
720 sec cadence. This period permits us to investigate...
Klaus G. Strassmeier
(Leibniz-Institut fuer Astrophysik Potsdam (AIP))
Talk
I will discuss Doppler imaging (DI) and Zeeman-Doppler imaging (ZDI)
techniques to map stellar magnetic fields and differential surface
rotation and possibly meridional flows on cool stars. Emphasis will be
on the techniques and their limitations but I will also highlight
previous results and present some of our more recent DI and ZDI maps.
An outlook is given for observing programs with...
Allan Sacha Brun
(Laboratoire AIM Paris-Saclay, CEA/Irfu Université Paris)
Talk
We will present our recent efforts to model G & K stars with the ASH code. We have
designed new model coupling the convective envelope to a deep stable radiative
interior. We have varied both the mass & rotation rates in order to pave a large
parameter space and to derive scaling laws for these type of solar-like stars. We
have also introduced seed magnetic field to study how dynamo action...
Elizabeth Cole
(Department of Physics, University of Helsinki)
Talk
We report the results from turbulent convection simulations in spherical wedges,
keeping the density stratification fixed and varying the rotation rate. An upper
limit to the Coriolis number that resulted in solar-like differential rotation is
reported, above which the simulations exhibit almost-rigid rotation profiles. Adding
a magnetic field into these rapid rotators within this...
Julien Morin
(Institut für Astrophysik, Georg-August-Universität Göttingen)
Talk
M dwarfs are of prime interest for stellar dynamo theories. They indeed span a wide
range of parameters, in terms of relative depth of the convection zone (the
lowest-mass M dwarfs being fully convective) and rotation. The number of magnetic
field measurements on M dwarfs has been rapidly growing in the past few years, trends
are emerging and now need to be understood in the framework of...
Aditi Sood
(School of Mathematics and Statistics, University of Sheffield)
Talk
A dynamic model of dynamo and rotation is investigated to understand the
observational data of the dependence of the magnetic activities and the differential
rotation \Delta \Omega on the rotation rate \Omega. Specifically, we propose a
minimal seventh order non-linear dynamical system for magnetic fields and
differential rotation \Delta \Omega by parameterizing the generation...
Gustavo Guerrero
(Solar Physics, HEPL, Stanford University)
Talk
Solar and stellar activity is thought to be the result of the collective effects of
turbulent-rotating convection. It develops large-scale flow patterns like
differential rotation and meridional flows, induces the generation of magnetic fields
as well as enhances their diffusion. In this work we explore the first part of the
process,
namely, the physic governing the development of the...
Santiago A. Triana
(Institute of Astronomy, KU Leuven)
Talk
A 3-meter diameter liquid-metal spherical-Couette flow, composed of a rotating
spherical container and a differentially rotating internal core, exhibits a sequence
of sharp and strong inertial mode oscillations when the (inner core to outer sphere)
rotation rate ratio is less than one or negative. At larger rotation ratios the flow
exhibit bi-stable fluctuations. These observations are...
Mikkel Lund
(Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark)
Seminar
With the launch of the Kepler spacecraft, long and uninterrupted time series have
become available for a large variety of stars. These data are ideal for asteroseismic
studies of the stars. As my PhD project I am studying how we can hope to use these
data to infer properties on the differential rotation of solar-like star. I will discuss the
current status of this project in addition...
Petri J. Käpylä
(Department of Physics, University of Helsinki)
Talk
We present results from three-dimensional simulations of rotating, magnetised,
turbulent convection in spherical wedge geometry. We concentrate on the parameter
regime where the differential rotation is solar-like, i.e. the equator rotates faster
than the poles. We find that large-scale magnetic fields are generated within the
whole convection zone. Many of the simulations show cyclic...
Yori Fournier
(Leibniz-Institut fuer Astrophysik Potsdam (AIP))
Talk
There is still a missing link in dynamo models between generating strong toroidal
fields at the bottom of the convection zone and the sunspots as measures of activity.
Since rotation is an important factor in the rise of magnetic flux through convection
zones, we study the flux emergence under the influence of different rotation
profiles. It is difficult to simulate realistic convection,...
Nicolas BESSOLAZ
(University of Exeter)
Talk
Magnetic fields play an important role in the early evolution of young stars during
the pre-main sequence phase.
We present an investigation into the magnetic fields built by 3D convective dynamo
action in such stars using the ASH code. We have extended our initial attempts to
reproduce the magnetic field observed for BP Tau using spectropolarimetry (Bessolaz &
Brun 2011) by computing a...
Leonid L. Kitchatinov
(Institute for Solar-Terrestrial Physics, Irkutsk)
Talk
Meridional circulation is driven by non-conservative parts of the centrifugal and
buoyancy forces. Each of the forces alone would drive a flow of hundreds meters per
second. The forces, however, almost balance each other in the so-called thermal wind
balance. The meridional flow results from slight deviation from the balance. The flow
attains its largest velocities in the boundary layers...
Mark Miesch
(High Altitude Observatory, National Center for Atmospheric Research, Boulder)
Talk
The mean (axisymmetric) circulation in the meridional plane plays a key role in many
recent solar and stellar dynamo models. This is particularly the case in so-called
"Flux-Transport" dynamo models in which the meridional circulation regulates the
duration of magnetic activity cycles. Many of these models are kinematic in nature
so the meridional circulation must be prescribed. Yet,...
Manfred Kueker
(Leibniz-Institut fuer Astrophysik Potsdam (AIP))
Talk
The meridional flow is a key ingredient in the currently most favored model of the
solar activity cycle, the flux transport dynamo. One major uncertainty in this model
is the subsurface flow pattern, which is not yet sufficiently constrained by
observations. We discuss the flows predicted by the mean field theory of stellar
differential rotation for the Sun, lower main sequence stars, and giants.
Bidya Binay Karak
(Department of Physics, Indian Institute of Science, Bangalore)
Talk
One of the most striking aspects of the sunspot cycle is that there have been times
in the past when sunspots did not appear for several years and a few cycles went
missing. A most well-known example of this is the Maunder minimum during 1645-1715.
Although reliable sunspot data did not exist before 1611, several indirect studies
(C14 data from old tree rings and the Be10 data from...
Federico Spada
(Leibniz-Institut fuer Astrophysik Potsdam (AIP))
Talk
A long-standing issue in the theory of low mass stars is the disagreement between the
theoretical and observed mass-radius-Teff relationships. Stellar models
systematically underpredict stellar radii by ~10% and overpredict effective
temperatures at the ~5% level. Interestingly, the two effects compensate each other
to give approximately the same luminosity, suggesting a surface origin for...
Igor Rogachevskii
(Ben-Gurion University, Beer Sheva, Israel)
Talk
We discuss an analytic theory for a new scaling for the alpha effect in turbulence
with large Reynolds numbers and slow rotation. Using this theory and direct numerical
simulations of slowly rotating stratified turbulence, we show that the alpha effect
responsible for the generation of astrophysical magnetic fields is proportional to
the logarithmic gradient of kinetic energy density...
Igor Rogachevskii
(Ben-Gurion University of the Negev, Beer-Sheva)
Seminar
We discuss a new theory of differential rotation in anisotropic
density stratified
inhomogeneous turbulent convection. A key point of this theory is
an effect of the
turbulent heat flux on the Reynolds stresses in a rotating
turbulent convection. We
solved a coupled system of dynamical equations which includes
the equations for the
Reynolds stresses, the entropy fluctuations and...
Michael Mond
(Ben-Gurion University, Beer Sheva, Israel)
Talk
A new non-dissipative mechanism is proposed for the saturation of the axisymmetric
magneto-rotational (MRI) instability in thin Keplerian disks that are subject to an
axial magnetic field. The proposed mechanism relies on the energy transfer from the
MRI to stable magnetosonic (MS) waves. A second order Duffing-like amplitude equation
for the initially unstable MRI modes is derived. The...
Klaus-Peter Schröder
(Universidad de Guanajuato)
Talk
We studied the evolutionary age and mass of the solar-type MS
stars of the sample described by Baliunas et al. 1995, of the
Mt. Wilson CaII monitoring programme. Organized by subsamples
of stars with strong and chaotic, moderate (clyclic or not), and
low or absent activity, the activity strength (mean S-value) and
characteristics show a very clear correlation with relative MS age....
Ansgar Reiners
(Georg-August Universität, Institut für Astrophysik, Göttingen)
Talk
Magnetic dynamos are known to operate in sun-like and fully convective stars. Our
conceptual models of dynamos produce predictions for stellar properties, among them
rotation and angular momentum evolution, the generation of magnetic fields,
non-thermal emission, and stellar activity cycles. I review the observational
evidence for magnetic dynamos in low-mass stars and collect arguments...
Ludovic Petitdemange
(MAG(CNRS/ENS/IPGP), LRA, Ecole Normale Supérieure, Paris)
Talk
Magnetic fields of low-mass stars and planets are thought to
originate from
self-excited dynamo action in their convective interiors.
Observations reveal a huge
variety of stellar and planetary magnetic fields that differ in their
field strength
and topologies. We try to better understand the conditions
responsible for this
diversity by means of numerical dynamo simulations. In a...
Matteo Cantiello
(Kavli Institute for Theoretical Physics, University of California)
Talk
Recent observations have revealed the presence of both pulsations and magnetic fields
in massive stars.
As these phenomena can directly affect the mass-loss and the rotation rate, their
impact on stellar evolution is potentially huge, with consequences for the final fate
of massive stars. I will review some of the latest observational and theoretical
developments in the field, focusing in...
Dmitry Sokoloff
(Moscow State University)
Talk
We study activity waves of the kind that determine cyclic magnetic
activity of various stars, including the Sun, as a more general
physical rather than a purely astronomical problem. We try to
identify
resonances which are expected to occur when a mean-field
dynamo
excites waves of quasi-stationary magnetic field in two distinct
spherical layers. We isolate some features that can be...
Dmitry Sokoloff
(Moscow State University)
Talk
During a solar magnetic field reversal the magnetic dipole
moment does not
vanish, but migrates between poles, in contradiction to the
predictions of mean-
field dynamo theory. We try to explain this as a consequence of
magnetic
fluctuations. We used the statistics of fluctuations to estimate
observable
signatures. Simple statistical estimates, taken with results from...
Timo Reinhold
(Institute for Astrophysics Goettingen)
Talk
The Kepler space telescope monitors more than 160.000 stars with an unprecedented
precision providing the opportunity to study stellar variability of thousands of stars.
We present rotation periods for thousands of active stars in the Kepler field. In
most cases a second period close to the rotation period has been detected which is
considered as hint for surface Differential Rotation...
Kwing L. Chan
(Department of Mathematics, Hong Kong University of Science & Technology)
Talk
Rotation exerts very significant effects on convection zones of stars. The
phenomenology consists of two types: differential rotation and large‐scale long‐lived
vortices. Both types exhibit prominently in outer planets of our solar system; these
planets possess outer convective layers and rotate fast. Differential rotation
appears in the form of multiple wind bands on Jupiter and Saturn,...
Matthew Browning
(University of Exeter)
Talk
Most stars in our galaxy are smaller than the Sun. More than half (by number) are
M-dwarfs, stars less than half as massive as the Sun and ten to a thousand times less
luminous; below about spectral type M3.5, these stars are convective throughout their
interiors. We examine the differential rotation and magnetism that may be realised
in such stars, using 3-D MHD simulations with the...
Joern Warnecke
(NORDITA, KTH Royal Institute of Technology and Stockholm University)
Talk
We report on the results of three convective dynamo simulations with an outer coronal
layer. The magnetic field is self-consistently generated by the convective motions
beneath the surface. Above the convection zone we include a polytropic layer that
extends to 1.6 solar radii. The temperature increases in this region to \approx8
times the value at the surface, corresponding to \approx 1.2...
Christoffer Karoff
(Aarhus University, Department of Physics and Astronomy)
Talk
Since the launch of the Kepler spacecraft in 2009 we have
monitored 20 Sun-like stars
in the Kepler field-of-view for excess flux with the FIES
spectrograph on the Nordic
Optical Telescope. These 20 stars were selected based on
their asteroseismic
properties to sample the parameter space around the Sun and
cover both sides of the
Vaughan-Preston gap. The ultimate goal of this is to be...
Rafael A. Garcia Garcia
(Laboratoire AIM, CEA/DSM-CNRS-Université Paris)
Talk
Continuous photometric coverage of stars provided by asteroseismic space missions,
are a great opportunity to study their surface rotation and stellar variability. In
particular, long and uninterrupted Kepler observations of more than 3.5 years allows
us to study stellar activity cycles of many stars. A surface stellar activity proxy
can be built from the variance of the light curve as the...
Dieter Schmitt
(Max-Planck-Institut für Sonnensystemforschung, Lindau)
Talk
The velocity and magnetic fields are well-known on the solar surface. Surface flux
transport models describe the evolution of the magnetic field after emergence on the
surface under the action of differential rotation, meridional circulation and
turbulent magnetic diffusivity. Especially the polar field and the Sun's open flux
are determined by the surface distribution of the magnetic...
Elena Benevolenskaya
(Pulkovo Astronomical Observatory, Saint Petersburg)
Talk
The current solar cycle 24 attracts an attention of researchers to study the nature
of the solar activity at the different levels of the Sun from the interior to the
solar corona. The Solar Dynamics Observatory (SDO) provides us multi-waves data from
the Extreme Ultraviolet to the visible light and magnetic field measurements. Here,
it is presented the synoptic structure of the solar cycle...
Rainer Arlt
(Leibniz Institute for Astrophysics Potsdam)
Talk
Based on the sunspot drawings of Johann Staudacher made in 1749-1799, we derive the solar
differential rotation for a period shortly after the Maunder minimum. A Bayesian analysis provides
us with the full probability distribution for the unknowns, whence their uncertainties. The study
demonstrates how valuable historical observations can be for today's astrophysics.
Jon Braithwaite
(Argelander Institut für Astronomie, Universität Bonn)
Talk
The Tayler instability appears in stars with predominantly toroidal magnetic fields.
It is thought to be particularly relevant in the case of differentially-rotating
radiative zones where the toroidal component of any seed field will be amplified. I
shall present results from numerical simulations where the effects of magnetic
diffusivity, rotation, and a weak poloidal field are...
Jyri Lehtinen
(University of Helsinki)
Talk
One popular method for detecting and quantifying surface differential rotation of
active stars has been to monitor how the periods of their observed light curves fluctuate
over time. The observed period fluctuations should indicate major spotted areas situated at
different latitudes that have different rotation periods. The period determination of the light
curves becomes, however,...
Gibor Basri
(Astronomy Department, Univ. of California, Berkeley)
Talk
The Kepler Mission has opened a whole new volume of parameter space in the realm of
stellar photometry. It combines unprecedented precision with unprecedented long and
complete time coverage, for well over 100,000 stars throughout the HR diagram. In
particular it is very sensitive to starspots, with complete phase coverage over many
rotation periods. This affords us the opportunity to...
Oleg Kochukhov
(Department of Astronomy and Space Physics, Uppsala University)
Talk
Zeeman Doppler imaging is the only observational method capable of providing
spatially resolved maps of stellar magnetic fields. This technique is routinely used
to reconstruct magnetic field topologies in different types of active stars. Recently
ZDI of cool stars was improved to include a more realistic treatment of the polarised
radiative transfer and a self-consistent modelling of the...
