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Author name code: cameron
ADS astronomy entries on 2022-09-14
author:"Cameron, Robert H."
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Title: Erratum: "Faculae Cancel out on the Surfaces of Active Suns"
(2022, ApJL, 934, L23)
Authors: Nèmec, N. -E.; Shapiro, A. I.; Işık, E.; Sowmya, K.;
Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Gizon, L.
2022ApJ...936L..17N Altcode:
No abstract at ADS
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Title: Faculae Cancel out on the Surfaces of Active Suns
Authors: Nèmec, N. -E.; Shapiro, A. I.; Işık, E.; Sowmya, K.;
Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Gizon, L.
2022ApJ...934L..23N Altcode: 2022arXiv220706816N
Surfaces of the Sun and other cool stars are filled with magnetic
fields, which are either seen as dark compact spots or more
diffuse bright structures like faculae. Both hamper detection and
characterization of exoplanets, affecting stellar brightness and
spectra, as well as transmission spectra. However, the expected facular
and spot signals in stellar data are quite different, for instance,
they have distinct temporal and spectral profiles. Consequently,
corrections of stellar data for magnetic activity can greatly benefit
from the insight on whether the stellar signal is dominated by spots or
faculae. Here, we utilize a surface flux transport model to show that
more effective cancellation of diffuse magnetic flux associated with
faculae leads to spot area coverages increasing faster with stellar
magnetic activity than that by faculae. Our calculations explain the
observed dependence between solar spot and facular area coverages and
allow its extension to stars that are more active than the Sun. This
extension enables anticipating the properties of stellar signal and its
more reliable mitigation, leading to a more accurate characterization
of exoplanets and their atmospheres.
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Title: Chromospheric extension of the MURaM code
Authors: Przybylski, D.; Cameron, R.; Solanki, S. K.; Rempel, M.;
Leenaarts, J.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.
2022A&A...664A..91P Altcode: 2022arXiv220403126P
Context. Detailed numerical models of the chromosphere and corona are
required to understand the heating of the solar atmosphere. An accurate
treatment of the solar chromosphere is complicated by the effects
arising from non-local thermodynamic equilibrium (NLTE) radiative
transfer. A small number of strong, highly scattering lines dominate the
cooling and heating in the chromosphere. Additionally, the recombination
times of ionised hydrogen are longer than the dynamical timescales,
requiring a non-equilibrium (NE) treatment of hydrogen ionisation. <BR
/> Aims: We describe a set of necessary additions to the MURaM code that
allow it to handle some of the important NLTE effects. We investigate
the impact on solar chromosphere models caused by NLTE and NE effects in
radiation magnetohydrodynamic simulations of the solar atmosphere. <BR
/> Methods: The MURaM code was extended to include the physical
process required for an accurate simulation of the solar chromosphere,
as implemented in the Bifrost code. This includes a time-dependent
treatment of hydrogen ionisation, a scattering multi-group radiation
transfer scheme, and approximations for NLTE radiative cooling. <BR />
Results: The inclusion of NE and NLTE physics has a large impact on the
structure of the chromosphere; the NE treatment of hydrogen ionisation
leads to a higher ionisation fraction and enhanced populations in
the first excited state throughout cold inter-shock regions of the
chromosphere. Additionally, this prevents hydrogen ionisation from
buffering energy fluctuations, leading to hotter shocks and cooler
inter-shock regions. The hydrogen populations in the ground and first
excited state are enhanced by 10<SUP>2</SUP>-10<SUP>3</SUP> in the
upper chromosphere and by up to 10<SUP>9</SUP> near the transition
region. <BR /> Conclusions: Including the necessary NLTE physics
leads to significant differences in chromospheric structure and
dynamics. The thermodynamics and hydrogen populations calculated using
the extended version of the MURaM code are consistent with previous
non-equilibrium simulations. The electron number and temperature
calculated using the non-equilibrium treatment of the chromosphere
are required to accurately synthesise chromospheric spectral
lines. <P />Movies associated to Fig. 2 are only available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141230/olm">https://www.aanda.org</A>
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Title: Impact of spatially correlated fluctuations in sunspots on
metrics related to magnetic twist
Authors: Baumgartner, C.; Birch, A. C.; Schunker, H.; Cameron, R. H.;
Gizon, L.
2022A&A...664A.183B Altcode: 2022arXiv220702135B
Context. The twist of the magnetic field above a sunspot is an
important quantity in solar physics. For example, magnetic twist
plays a role in the initiation of flares and coronal mass ejections
(CMEs). Various proxies for the twist above the photosphere have been
found using models of uniformly twisted flux tubes, and are routinely
computed from single photospheric vector magnetograms. One class of
proxies is based on α<SUB>z</SUB>, the ratio of the vertical current
to the vertical magnetic field. Another class of proxies is based on the
so-called twist density, q, which depends on the ratio of the azimuthal
field to the vertical field. However, the sensitivity of these proxies
to temporal fluctuations of the magnetic field has not yet been well
characterized. <BR /> Aims: We aim to determine the sensitivity of twist
proxies to temporal fluctuations in the magnetic field as estimated
from time-series of SDO/HMI vector magnetic field maps. <BR /> Methods:
To this end, we introduce a model of a sunspot with a peak vertical
field of 2370 Gauss at the photosphere and a uniform twist density
q = −0.024 Mm<SUP>−1</SUP>. We add realizations of the temporal
fluctuations of the magnetic field that are consistent with SDO/HMI
observations, including the spatial correlations. Using a Monte-Carlo
approach, we determine the robustness of the different proxies to the
temporal fluctuations. <BR /> Results: The temporal fluctuations of
the three components of the magnetic field are correlated for spatial
separations up to 1.4 Mm (more than expected from the point spread
function alone). The Monte-Carlo approach enables us to demonstrate that
several proxies for the twist of the magnetic field are not biased in
each of the individual magnetograms. The associated random errors on
the proxies have standard deviations in the range between 0.002 and
0.006 Mm<SUP>−1</SUP>, which is smaller by approximately one order
of magnitude than the mean value of q.
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Title: Theory of solar oscillations in the inertial frequency range:
Amplitudes of equatorial modes from a nonlinear rotating convection
simulation
Authors: Bekki, Yuto; Cameron, Robert H.; Gizon, Laurent
2022arXiv220811081B Altcode:
Several types of inertial modes have been detected on the
Sun. Properties of these inertial modes have been studied in the
linear regime but have not been studied in nonlinear simulations
of solar rotating convection. Comparing the nonlinear simulations,
the linear theory, and the solar observations is important to better
understand the differences between the models and the real Sun. We
wish to detect and characterize the modes present in a nonlinear
numerical simulation of solar convection, in particular to understand
the amplitudes and lifetimes of the modes. We developed a code with
a Yin-Yang grid to carry out fully-nonlinear numerical simulations
of rotating convection in a spherical shell. The stratification is
solar-like up to 0.96R. The simulations cover a duration of about
15 solar years. Various large-scale modes at low frequencies are
extracted from the simulation. Their characteristics are compared to
those from the linear model and to the observations. Among other modes,
both the equatorial Rossby modes and the columnar convective modes
are seen in the simulation. The columnar convective modes contain
most of the large-scale velocity power outside the tangential
cylinder and substantially contribute to the heat and angular
momentum transport. Equatorial Rossby modes with no radial node (n=0)
are also found: They have the same spatial structures as the linear
eigenfunctions. They are stochastically excited by convection and have
the amplitudes of a few m/s and mode linewidths of about 20-30 nHz,
which are comparable to those observed on the Sun. We also confirm the
existence of the mixed modes between the equatorial Rossby modes and
the columnar convective modes in our nonlinear simulation, as predicted
by the linear eigenmode analysis. We also see the high-latitude mode
with m=1 in our nonlinear simulation but its amplitude is much weaker
than that observed on the Sun.
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Title: Small-scale dynamo in cool stars. I. Changes in stratification
and near-surface convection for main-sequence spectral types
Authors: Bhatia, Tanayveer S.; Cameron, Robert H.; Solanki, Sami K.;
Peter, Hardi; Przybylski, Damien; Witzke, Veronika; Shapiro, Alexander
2022A&A...663A.166B Altcode: 2022arXiv220600064B
Context. Some of the small-scale solar magnetic flux can
be attributed to a small-scale dynamo (SSD) operating in the
near-surface convection. The SSD fields have consequences for
solar granular convection, basal flux, and chromospheric heating. A
similar SSD mechanism is expected to be active in the near-surface
convection of other cool main-sequence stars, but this has not been
investigated thus far. <BR /> Aims: We aim to investigate changes in
stratification and convection due to inclusion of SSD fields for F3V,
G2V, K0V, and M0V spectral types in the near-surface convection. <BR
/> Methods: We studied 3D magnetohydrodynamic (MHD) models of the four
stellar boxes, covering the subsurface convection zone up to the lower
photosphere in a small Cartesian box, based on the MURaM radiative-MHD
simulation code. We compared the SSD runs against reference hydrodynamic
runs. <BR /> Results: The SSD is found to efficiently produce magnetic
field with energies ranging between 5% to 80% of the plasma kinetic
energy at different depths. This ratio tends to be larger for larger
T<SUB>eff</SUB>. The relative change in density and gas pressure
stratification for the deeper convective layers due to SSD magnetic
fields is negligible, except for the F-star. For the F-star, there is
a substantial reduction in convective velocities due to Lorentz force
feedback from magnetic fields, which, in turn, reduces the turbulent
pressure. <BR /> Conclusions: The SSD in near-surface convection for
cool main-sequence stars introduces small but significant changes
in thermodynamic stratification (especially for the F-star) due to a
reduction in the convective velocities.
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Title: Theory of solar oscillations in the inertial frequency range:
Linear modes of the convection zone
Authors: Bekki, Yuto; Cameron, Robert H.; Gizon, Laurent
2022A&A...662A..16B Altcode: 2022arXiv220304442B
Context. Several types of global-scale inertial modes of oscillation
have been observed on the Sun. These include the equatorial Rossby
modes, critical-latitude modes, and high-latitude modes. However,
the columnar convective modes (predicted by simulations and also
known as banana cells or thermal Rossby waves) remain elusive. <BR />
Aims: We aim to investigate the influence of turbulent diffusivities,
non-adiabatic stratification, differential rotation, and a latitudinal
entropy gradient on the linear global modes of the rotating solar
convection zone. <BR /> Methods: We numerically solved for the
eigenmodes of a rotating compressible fluid inside a spherical
shell. The model takes into account the solar stratification, turbulent
diffusivities, differential rotation (determined by helioseismology),
and the latitudinal entropy gradient. As a starting point, we restricted
ourselves to a superadiabaticity and turbulent diffusivities that
are uniform in space. We identified modes in the inertial frequency
range, including the columnar convective modes as well as modes of
a mixed character. The corresponding mode dispersion relations and
eigenfunctions are computed for azimuthal orders of m ≤ 16. <BR />
Results: The three main results are as follows. Firstly, we find
that, for m ≳ 5, the radial dependence of the equatorial Rossby
modes with no radial node (n = 0) is radically changed from the
traditional expectation (r<SUP>m</SUP>) for turbulent diffusivities
≳10<SUP>12</SUP> cm<SUP>2</SUP> s<SUP>−1</SUP>. Secondly,
we find mixed modes, namely, modes that share properties of the
equatorial Rossby modes with one radial node (n = 1) and the columnar
convective modes, which are not substantially affected by turbulent
diffusion. Thirdly, we show that the m = 1 high-latitude mode in the
model is consistent with the solar observations when the latitudinal
entropy gradient corresponding to a thermal wind balance is included
(baroclinically unstable mode). <BR /> Conclusions: To our knowledge,
this work is the first realistic eigenvalue calculation of the global
modes of the rotating solar convection zone. This calculation reveals
a rich spectrum of modes in the inertial frequency range, which can
be directly compared to the observations. In turn, the observed modes
can inform us about the solar convection zone.
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Title: The crucial role of surface magnetic fields for stellar
dynamos: ϵ Eridani, 61 Cygni A, and the Sun
Authors: Jeffers, S. V.; Cameron, R. H.; Marsden, S. C.; Boro Saikia,
S.; Folsom, C. P.; Jardine, M. M.; Morin, J.; Petit, P.; See, V.;
Vidotto, A. A.; Wolter, U.; Mittag, M.
2022A&A...661A.152J Altcode: 2022arXiv220107530J
Cool main-sequence stars, such as the Sun, have magnetic fields which
are generated by an internal dynamo mechanism. In the Sun, the dynamo
mechanism produces a balance between the amounts of magnetic flux
generated and lost over the Sun's 11-year activity cycle and it is
visible in the Sun's different atmospheric layers using multi-wavelength
observations. We used the same observational diagnostics, spanning
several decades, to probe the emergence of magnetic flux on the two
close by, active- and low-mass K dwarfs: 61 Cygni A and ϵ Eridani. Our
results show that 61 Cygni A follows the Solar dynamo with a regular
cycle at all wavelengths, while ϵ Eridani represents a more extreme
level of the Solar dynamo, while also showing strong Solar-like
characteristics. For the first time we show magnetic butterfly diagrams
for stars other than the Sun. For the two K stars and the Sun, the rate
at which the toroidal field is generated from surface poloidal field
is similar to the rate at which toroidal flux is lost through flux
emergence. This suggests that the surface field plays a crucial role in
the dynamos of all three stars. Finally, for ϵ Eridani, we show that
the two chromospheric cycle periods, of ∼3 and ∼13 years, correspond
to two superimposed magnetic cycles. <P />The spectropolarimetic
data are available from the Polarbase data archive: <A
href="http://polarbase.irap.omp.eu/">http://polarbase.irap.omp.eu/</A>.
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Title: Testing solar surface flux transport models in the first days
after active region emergence
Authors: Gottschling, N.; Schunker, H.; Birch, A. C.; Cameron, R.;
Gizon, L.
2022A&A...660A...6G Altcode: 2021arXiv211101896G
Context. Active regions (ARs) play an important role in the magnetic
dynamics of the Sun. Solar surface flux transport models (SFTMs) are
used to describe the evolution of the radial magnetic field at the solar
surface. The models are kinematic in the sense that the radial component
of the magnetic field behaves as passively advected corks. There is,
however, uncertainty about using these models in the early stage of
AR evolution, where dynamic effects might be important. <BR /> Aims:
We aim to test the applicability of SFTMs in the first days after the
emergence of ARs by comparing them with observations. The models we
employ range from passive evolution to models where the inflows around
ARs are included. <BR /> Methods: We simulated the evolution of the
surface magnetic field of 17 emerging ARs using a local surface flux
transport simulation. The regions were selected such that they did not
form fully fledged sunspots that exhibit moat flows. The simulation
included diffusion and advection by a velocity field, for which we
tested different models. For the flow fields, we used observed flows
from local correlation tracking of solar granulation, as well as
parametrizations of the inflows around ARs based on the gradient of
the magnetic field. To evaluate our simulations, we measured the cross
correlation between the observed and the simulated magnetic field, as
well as the total unsigned flux of the ARs, over time. We also tested
the validity of our simulations by varying the starting time relative
to the emergence of flux. <BR /> Results: We find that the simulations
using observed surface flows can reproduce the evolution of the observed
magnetic flux. The effect of buffeting the field by supergranulation can
be described as a diffusion process. The SFTM is applicable after 90%
of the peak total unsigned flux of the AR has emerged. Diffusivities
in the range between D = 250-720 km<SUP>2</SUP> s<SUP>−1</SUP> are
consistent with the evolution of the AR flux in the first five days
after this time. We find that the converging flows around emerging
ARs are not important for the evolution of the total flux of the AR
in these first five days; their effect of increasing flux cancellation
is balanced by the decrease in flux transport away from the AR.
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Title: A solar coronal loop in a box: Energy generation and heating
Authors: Breu, C.; Peter, H.; Cameron, R.; Solanki, S. K.; Przybylski,
D.; Rempel, M.; Chitta, L. P.
2022A&A...658A..45B Altcode: 2021arXiv211211549B
Context. Coronal loops are the basic building block of the upper solar
atmosphere as seen in the extreme UV and X-rays. Comprehending how
these are energized, structured, and evolve is key to understanding
stellar coronae. <BR /> Aims: Here we investigate how the energy
to heat the loop is generated by photospheric magneto-convection,
transported into the upper atmosphere, and how the internal
structure of a coronal magnetic loop forms. <BR /> Methods: In a 3D
magnetohydrodynamics model, we study an isolated coronal loop rooted
with both footpoints in a shallow layer within the convection zone
using the MURaM code. To resolve its internal structure, we limited
the computational domain to a rectangular box containing a single
coronal loop as a straightened magnetic flux tube. Field-aligned heat
conduction, gray radiative transfer in the photosphere and chromosphere,
and optically thin radiative losses in the corona were taken into
account. The footpoints were allowed to interact self-consistently
with the granulation surrounding them. <BR /> Results: The loop is
heated by a Poynting flux that is self-consistently generated through
small-scale motions within individual magnetic concentrations in
the photosphere. Turbulence develops in the upper layers of the
atmosphere as a response to the footpoint motions. We see little
sign of heating by large-scale braiding of magnetic flux tubes
from different photospheric concentrations at a given footpoint. The
synthesized emission, as it would be observed by the Atmospheric Imaging
Assembly or the X-Ray Telescope, reveals transient bright strands that
form in response to the heating events. Overall, our model roughly
reproduces the properties and evolution of the plasma as observed
within (the substructures of) coronal loops. <BR /> Conclusions:
With this model we can build a coherent picture of how the energy
flux to heat the upper atmosphere is generated near the solar surface
and how this process drives and governs the heating and dynamics of
a coronal loop. <P />Movie associated to Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141451/olm">https://www.aanda.org</A>
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Title: On the size distribution of spots within sunspot groups
Authors: Mandal, Sudip; Krivova, Natalie A.; Cameron, Robert; Solanki,
Sami K.
2021A&A...652A...9M Altcode: 2021arXiv210403534M
The size distribution of sunspots provides key information about
the generation and emergence processes of the solar magnetic
field. Previous studies of size distribution have primarily focused
on either the whole group or individual spot areas. In this paper we
investigate the organisation of spot areas within sunspot groups. In
particular, we analysed the ratio (R) of the area of the biggest spot
(A<SUB>big_spot</SUB>) inside a group, to the total area of that group
(A<SUB>group</SUB>). We used sunspot observations from Kislovodsk,
Pulkovo, and Debrecen observatories, together covering solar cycles
17-24. We find that at the time when the group area reaches its maximum,
the single biggest spot in a group typically occupies about 60% of the
group area. For half of all groups, R lies in the range between roughly
50% and 70%. We also find R to change with A<SUB>group</SUB>, such that
R reaches a maximum of about 0.65 for groups with A<SUB>group</SUB>
≈ 200 μHem and then remains at about 0.6 for larger groups. Our
findings imply a scale-invariant emergence pattern, providing an
observational constraint on the emergence process. Furthermore,
extrapolation of our results to larger sunspot groups may have a
bearing on the giant unresolved starspot features found in Doppler
images of highly active Sun-like stars. Our results suggest that such
giant features are composed of multiple spots, with the largest spot
occupying roughly 55-75% of the total group area (i.e., the area of
the giant starspots seen in Doppler images).
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Title: Slow magneto-acoustic waves in simulations of a solar plage
region carry enough energy to heat the chromosphere
Authors: Yadav, N.; Cameron, R. H.; Solanki, S. K.
2021A&A...652A..43Y Altcode: 2021arXiv210502932Y
<BR /> Aims: We study the properties of slow magneto-acoustic waves
that are naturally excited as a result of turbulent convection and we
investigate their role in the energy balance of a plage region using
three dimensional radiation magnetohydrodynamic simulations. <BR />
Methods: To follow slow magneto-acoustic waves traveling along the
magnetic field lines, we selected 25 seed locations inside a strong
magnetic element and tracked the associated magnetic field lines both
in space and time. We calculate the longitudinal component (i.e.,
parallel to the field) of velocity at each grid point along the field
line and compute the temporal power spectra at various heights above
the mean solar surface. Additionally, the horizontally-averaged (over
the whole domain) frequency power spectra for both longitudinal and
vertical (i.e., the component perpendicular to the surface) components
of velocity are calculated using time series at fixed locations. To
compare our results with the observations, we degrade the simulation
data with Gaussian kernels having a full width at half maxium of 100
km and 200 km and calculate the horizontally-averaged power spectra
for the vertical component of velocity using time series at fixed
locations. <BR /> Results: The power spectra of the longitudinal
component of velocity, averaged over 25 field lines in the core of
a kG magnetic flux concentration reveal that the dominant period
of oscillations shifts from ∼6.5 min in the photosphere to ∼4
min in the chromosphere. This behavior is consistent with earlier
studies that were restricted to vertically propagating waves. At the
same time, the velocity power spectra, averaged horizontally over
the whole domain, show that low frequency waves (∼6.5 min period)
may reach well into the chromosphere. In addition, the power spectra
at high frequencies follow a power law with an exponent close to
−5/3, suggestive of turbulent excitation. Moreover, waves with
frequencies above 5 mHz propagating along different field lines
are found to be out of phase with each other, even within a single
magnetic concentration. The horizontally-averaged power spectra of
the vertical component of velocity at various effective resolutions
show that the observed acoustic wave energy fluxes are underestimated
by a factor of three, even if determined from observations carried
out at a high spatial resolution of 200 km. Since the waves propagate
along the non-vertical field lines, measuring the velocity component
along the line-of-sight, rather than along the field, contributes
significantly to this underestimation. Moreover, this underestimation of
the energy flux indirectly indicates the importance of high-frequency
waves that are shown to have a smaller spatial coherence and are thus
more strongly influenced by the spatial averaging effect compared to
low-frequency waves. <BR /> Conclusions: Inside a plage region, there
is on average a significant fraction of low frequency waves leaking
into the chromosphere due to inclined magnetic field lines. Our results
show that longitudinal waves carry (just) enough energy to heat the
chromosphere in the solar plage. However, phase differences between
waves traveling along different field lines within a single magnetic
concentration can lead to underestimations of the wave energy flux
due to averaging effects in degraded simulation data and, similarly,
in observations with lower spatial resolution. We find that current
observations (with spatial resolution around 200 km) underestimate the
energy flux by roughly a factor of three - or more if the observations
are carried out at a lower spatial resolution. We expect that even
at a very high resolution, which is expected with the next generation
of telescopes such as DKIST and the EST, less than half, on average,
of the energy flux carried by such waves will be detected if only the
line-of-sight component of the velocity is measured.
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Title: Solar inertial modes: Observations, identification, and
diagnostic promise
Authors: Gizon, Laurent; Cameron, Robert H.; Bekki, Yuto; Birch,
Aaron C.; Bogart, Richard S.; Brun, Allan Sacha; Damiani, Cilia;
Fournier, Damien; Hyest, Laura; Jain, Kiran; Lekshmi, B.; Liang,
Zhi-Chao; Proxauf, Bastian
2021A&A...652L...6G Altcode: 2021arXiv210709499G
The oscillations of a slowly rotating star have long been classified
into spheroidal and toroidal modes. The spheroidal modes include
the well-known 5-min acoustic modes used in helioseismology. Here
we report observations of the Sun's toroidal modes, for which the
restoring force is the Coriolis force and whose periods are on the
order of the solar rotation period. By comparing the observations
with the normal modes of a differentially rotating spherical shell,
we are able to identify many of the observed modes. These are the
high-latitude inertial modes, the critical-latitude inertial modes,
and the equatorial Rossby modes. In the model, the high-latitude
and critical-latitude modes have maximum kinetic energy density at
the base of the convection zone, and the high-latitude modes are
baroclinically unstable due to the latitudinal entropy gradient. As
a first application of inertial-mode helioseismology, we constrain
the superadiabaticity and the turbulent viscosity in the deep
convection zone. <P />Movie associated to Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141462/olm">https://www.aanda.org
</A>
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Title: A journey of exploration to the polar regions of a star:
probing the solar poles and the heliosphere from high helio-latitude
Authors: Harra, Louise; Andretta, Vincenzo; Appourchaux, Thierry;
Baudin, Frédéric; Bellot-Rubio, Luis; Birch, Aaron C.; Boumier,
Patrick; Cameron, Robert H.; Carlsson, Matts; Corbard, Thierry;
Davies, Jackie; Fazakerley, Andrew; Fineschi, Silvano; Finsterle,
Wolfgang; Gizon, Laurent; Harrison, Richard; Hassler, Donald M.;
Leibacher, John; Liewer, Paulett; Macdonald, Malcolm; Maksimovic,
Milan; Murphy, Neil; Naletto, Giampiero; Nigro, Giuseppina; Owen,
Christopher; Martínez-Pillet, Valentín; Rochus, Pierre; Romoli,
Marco; Sekii, Takashi; Spadaro, Daniele; Veronig, Astrid; Schmutz, W.
2021ExA...tmp...93H Altcode: 2021arXiv210410876H
A mission to view the solar poles from high helio-latitudes (above 60°)
will build on the experience of Solar Orbiter as well as a long heritage
of successful solar missions and instrumentation (e.g. SOHO Domingo et
al. (Solar Phys. 162(1-2), 1-37 1995), STEREO Howard et al. (Space
Sci. Rev. 136(1-4), 67-115 2008), Hinode Kosugi et al. (Solar
Phys. 243(1), 3-17 2007), Pesnell et al. Solar Phys. 275(1-2),
3-15 2012), but will focus for the first time on the solar poles,
enabling scientific investigations that cannot be done by any other
mission. One of the major mysteries of the Sun is the solar cycle. The
activity cycle of the Sun drives the structure and behaviour of the
heliosphere and of course, the driver of space weather. In addition,
solar activity and variability provides fluctuating input into the
Earth climate models, and these same physical processes are applicable
to stellar systems hosting exoplanets. One of the main obstructions
to understanding the solar cycle, and hence all solar activity,
is our current lack of understanding of the polar regions. In this
White Paper, submitted to the European Space Agency in response to the
Voyage 2050 call, we describe a mission concept that aims to address
this fundamental issue. In parallel, we recognise that viewing the Sun
from above the polar regions enables further scientific advantages,
beyond those related to the solar cycle, such as unique and powerful
studies of coronal mass ejection processes, from a global perspective,
and studies of coronal structure and activity in polar regions. Not
only will these provide important scientific advances for fundamental
stellar physics research, they will feed into our understanding of
impacts on the Earth and other planets' space environment.
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Title: Coronal loops in a box: 3D models of their internal structure,
dynamics and heating
Authors: Breu, C. A.; Peter, H.; Cameron, R.; Solanki, S.; Przybylski,
D.; Chitta, L.
2021AAS...23810606B Altcode:
The corona of the Sun, and probably also of other stars, is built
up by loops defined through the magnetic field. They vividly appear
in solar observations in the extreme UV and X-rays. High-resolution
observations show individual strands with diameters down to a few 100
km, and so far it remains open what defines these strands, in particular
their width, and where the energy to heat them is generated. <P />The
aim of our study is to understand how the magnetic field couples the
different layers of the solar atmosphere, how the energy generated
by magnetoconvection is transported into the upper atmosphere and
dissipated, and how this process determines the scales of observed
bright strands in the loop. <P />To this end, we conduct 3D resistive
MHD simulations with the MURaM code. We include the effects of heat
conduction, radiative transfer and optically thin radiative losses.We
study an isolated coronal loop that is rooted with both footpoints
in a shallow convection zone layer. To properly resolve the internal
structure of the loop while limiting the size of the computational box,
the coronal loop is modelled as a straightened magnetic flux tube. By
including part of the convection zone, we drive the evolution of
the corona self-consistently by magnetoconvection. <P />We find that
the energy injected into the loop is generated by internal coherent
motions within strong magnetic elements. The resulting Poynting
flux is channelled into the loop in vortex tubes forming a magnetic
connection between the photosphere and corona, where it is dissipated
and heats the upper atmosphere. <P />The coronal emission as it would
be observed in solar extreme UV or X-ray observations, e.g. with AIA
or XRT, shows transient bright strands.The widths of these strands are
consistent with observations. From our model we find that the width
of the strands is governed by the size of the individual photospheric
magnetic field concentrations where the field line through these strands
are rooted. Essentially, each coronal strand is rooted in a single
magnetic patch in the photosphere, and the energy to heat the strand is
generated by internal motions within this magnetic concentration. <P
/>With this model we can build a coherent picture of how energy and
matter are transported into the upper solar atmosphere and how these
processes structure the interior of coronal loops.
---------------------------------------------------------
Title: Small-scale Dynamo in Cool Main-Sequence Stars: Effect on
Stratification, Convection and Bolometric Intensity
Authors: Bhatia, T.; Cameron, R.; Solanki, S.; Peter, H.; Przybylski,
D.; Witzke, V.; Shapiro, A.
2021AAS...23830404B Altcode:
In cool main-sequence stars, the near-surface convection has an
impact on the center-to-limb variation of photospheric emission, with
implications for stellar lightcurves during planetary transits. In
the Sun, there is strong evidence for a small-scale dynamo (SSD)
maintaining the small-scale magnetic flux. This field could affect the
near-surface convection in other cool main-sequence stars. <P />An SSD
could conceivably generate equipartition magnetic fields, which could
lead to non-negligible changes not only in convection and intensity
characteristics, but also in stratification. We aim to investigate these
changes for F, G, K and M stars. 3D MHD models of the four stellar types
covering the subsurface region to lower atmosphere in a small cartesian
box are studied using the MURaM rMHD simulation code. The MHD runs are
compared against a reference hydrodynamic (HD) run. <P />The deviations
in stratification for the deeper convective layers is negligible,
except for the F-star, where reduction in turbulent pressure due to
magnetic fields is substantial. Convective velocities are reduced
by a similar percentage for all the cases due to inhibitory effect
of strong magnetic fields near the bottom boundary. All four cases
show small-scale brightenings in intergranular lanes, corresponding
to magnetic field concentrations, but overall effects on the r.m.s
contrast and spatial powerspectra are varied.
---------------------------------------------------------
Title: First Results of the Chromospheric MURaM code
Authors: Przybylski, D. F.; Cameron, R.; Solanki, S.; Rempel, M.
2021AAS...23810605P Altcode:
The solar chromosphere, spanning the region between the photosphere
and the transition to the corona, remains one of the least understood
parts of the Sun. This is partly because observing the chromosphere
and interpreting these observations is full of pitfalls. Also, the
simulation of the chromosphere is complex, as the particle densities
and collisional rates are too low to maintain local thermodynamic
equilibrium (LTE). Additionally, the recombination rates of hydrogen are
larger than the dynamical timescales and the populations must be solved
in non-equilibrium (NE). Realistic simulations of the chromosphere
must treat the magneto-hydrodynamics, time-dependant atomic and
molecular chemistry, and radiation transfer simultaneously. <P />The
MURaM radiation-MHD code has previously been used for investigation
of the connection between the solar photosphere and corona, ranging
from small-scale dynamo generated 'quiet' sun fields to sunspots and
complex active regions. Until now these simulations have been performed
in LTE, greatly limiting their realism in the solar chromosphere. We
have extended MURaM to include NLTE effects following the prescriptions
used in the Bifrost code. The low viscocity and resistivity of the MURaM
code leads to turbulent convection in the photosphere with kilo-Gauss
mixed-polarity magnetic fields. This results in a dynamic chromosphere
with strong shocks and a finely structured magnetic field. We discuss
the implications of this new model towards observations of chromospheric
spectral lines.
---------------------------------------------------------
Title: Modelling the evolution of the Sun's open and total magnetic
flux
Authors: Krivova, N. A.; Solanki, S. K.; Hofer, B.; Wu, C. -J.;
Usoskin, I. G.; Cameron, R.
2021A&A...650A..70K Altcode: 2021arXiv210315603K
Solar activity in all its varied manifestations is driven by the
magnetic field. Two global quantities are particularly important for
many purposes, the Sun's total and open magnetic flux, which can be
computed from sunspot number records using models. Such sunspot-driven
models, however, do not take into account the presence of magnetic
flux during grand minima, such as the Maunder minimum. Here we
present a major update of a widely used simple model, which now takes
into account the observation that the distribution of all magnetic
features on the Sun follows a single power law. The exponent of the
power law changes over the solar cycle. This allows for the emergence
of small-scale magnetic flux even when no sunspots have been present
for multiple decades and leads to non-zero total and open magnetic
flux also in the deepest grand minima, such as the Maunder minimum,
thus overcoming a major shortcoming of the earlier models. The results
of the updated model compare well with the available observations and
reconstructions of the solar total and open magnetic flux. This opens
up the possibility of improved reconstructions of the sunspot number
from time series of the cosmogenic isotope production rate.
---------------------------------------------------------
Title: Nonequilibrium Equation of State in Stellar Atmospheres
Authors: Anusha, L. S.; van Noort, M.; Cameron, R. H.
2021ApJ...911...71A Altcode: 2021arXiv210413650A
In the stellar chromospheres, radiative energy transport is dominated by
only the strongest spectral lines. For these lines, the approximation of
local thermodynamic equilibrium (LTE) is known to be very inaccurate,
and a state of equilibrium cannot be assumed in general. To calculate
the radiative energy transport under these conditions, the population
evolution equation must be evaluated explicitly, including all
time-dependent terms. We develop a numerical method to solve the
evolution equation for the atomic-level populations in a time-implicit
way, keeping all time-dependent terms to first order. We show that
the linear approximation of the time dependence of the populations
can handle very large time steps without losing accuracy. We
reproduce the benchmark solutions from earlier, well-established
works in terms of non-LTE kinetic equilibrium solutions and typical
ionization/recombination timescales in the solar chromosphere.
---------------------------------------------------------
Title: Small-scale dynamo in an F-star: effects on near-surface
stratification, convection and intensity
Authors: Bhatia, Tanayveer; Cameron, Robert; Solanki, Sami; Peter,
Hardi; Przybylski, Damien; Witzke, Veronika; Shapiro, Alexander
2021csss.confE..75B Altcode:
The emission from the photosphere of stars shows a systematic
center-to-limb variation. In cool main-sequence stars, the near-surface
convection has an impact on this variation, with implications for
lightcurves of stars during planetary transits. In the Sun, there
is strong evidence for a small-scale dynamo (SSD) maintaining the
small-scale magnetic flux. We aim to investigate what additional
effects such a field would play for other cool main-sequence
stars. In our work we first concentrate on F-stars. This is because
they have sonic velocities near the surface, implying a rough
equipartition between internal and kinetic energies. In addition,
an SSD might create a significant magnetic energy density to impact
the results. We investigate the interplay between internal, kinetic
and magnetic energies in 3D cartesian box MHD models of a F3V-star in
the near-surface convection, using the MURaM radiative-MHD simulation
code. Along with a reference hydrodynamic run, two MHD models with
self-consistently generated magnetic fields with two different lower
boundary conditions are considered. We find that the SSD process
creates a magnetic field with energy within an order of magnitude of the
internal and the kinetic energy. Compared to the hydrodynamic run, we
find slight (~1-3%) but significant deviations in density, gas pressure
and temperature stratification. At the surface, this corresponds to a
temperature difference of ~130 K. As expected, there is a significant
reduction in kinetic energy flux once the SSD is operational. The
changes in intensity are more subtle, both in total intensity and
granulation pattern. From this we conclude that the presence of an
SSD will have a significant impact on the atmospheric structure and
intensity characteristics seen at the surface. This makes it clear
that it would be important to consider the spatially and temporally
averaged effects of the SSD also for global stellar models.
---------------------------------------------------------
Title: Sunspot Simulations: Penumbra Formation and the Fluting
Instability
Authors: Panja, Mayukh; Cameron, Robert H.; Solanki, Sami K.
2021ApJ...907..102P Altcode: 2020arXiv201111447P
The fluting instability has been suggested as the driver of the
subsurface structure of sunspot flux tubes. We conducted a series
of numerical experiments where we used flux tubes with different
initial curvatures to study the effect of the fluting instability on
the subsurface structure of spots. We used the MURaM code, which has
previously been used to simulate complete sunspots, to first compute
four sunspots in the slab geometry and then two complete circular
spots of opposite polarities. We find that the curvature of a flux tube
indeed determines the degree of fluting the flux tube will undergo—the
more curved a flux tube is, the more fluted it becomes. In addition,
sunspots with strong curvature have strong horizontal fields at the
surface and therefore readily form penumbral filaments. The fluted
sunspots eventually break up from below, with lightbridges appearing
at the surface several hours after fluting commences.
---------------------------------------------------------
Title: Sensitivity of the Cherenkov Telescope Array for probing
cosmology and fundamental physics with gamma-ray propagation
Authors: Abdalla, H.; Abe, H.; Acero, F.; Acharyya, A.; Adam, R.;
Agudo, I.; Aguirre-Santaella, A.; Alfaro, R.; Alfaro, J.; Alispach,
C.; Aloisio, R.; Alves Batista, R.; Amati, L.; Amato, E.; Ambrosi, G.;
Angüner, E. O.; Araudo, A.; Armstrong, T.; Arqueros, F.; Arrabito,
L.; Asano, K.; Ascasíbar, Y.; Ashley, M.; Backes, M.; Balazs, C.;
Balbo, M.; Balmaverde, B.; Baquero Larriva, A.; Barbosa Martins, V.;
Barkov, M.; Baroncelli, L.; Barres de Almeida, U.; Barrio, J. A.;
Batista, P. -I.; Becerra González, J.; Becherini, Y.; Beck, G.;
Becker Tjus, J.; Belmont, R.; Benbow, W.; Bernardini, E.; Berti, A.;
Berton, M.; Bertucci, B.; Beshley, V.; Bi, B.; Biasuzzi, B.; Biland,
A.; Bissaldi, E.; Biteau, J.; Blanch, O.; Bocchino, F.; Boisson,
C.; Bolmont, J.; Bonanno, G.; Bonneau Arbeletche, L.; Bonnoli, G.;
Bordas, P.; Bottacini, E.; Böttcher, M.; Bozhilov, V.; Bregeon,
J.; Brill, A.; Brown, A. M.; Bruno, P.; Bruno, A.; Bulgarelli, A.;
Burton, M.; Buscemi, M.; Caccianiga, A.; Cameron, R.; Capasso, M.;
Caprai, M.; Caproni, A.; Capuzzo-Dolcetta, R.; Caraveo, P.; Carosi, R.;
Carosi, A.; Casanova, S.; Cascone, E.; Cauz, D.; Cerny, K.; Cerruti,
M.; Chadwick, P.; Chaty, S.; Chen, A.; Chernyakova, M.; Chiaro, G.;
Chiavassa, A.; Chytka, L.; Conforti, V.; Conte, F.; Contreras, J. L.;
Coronado-Blazquez, J.; Cortina, J.; Costa, A.; Costantini, H.; Covino,
S.; Cristofari, P.; Cuevas, O.; D'Ammando, F.; Daniel, M. K.; Davies,
J.; Dazzi, F.; De Angelis, A.; de Bony de Lavergne, M.; De Caprio, V.;
de Cássia dos Anjos, R.; de Gouveia Dal Pino, E. M.; De Lotto, B.;
De Martino, D.; de Naurois, M.; de Oña Wilhelmi, E.; De Palma, F.;
de Souza, V.; Delgado, C.; Della Ceca, R.; della Volpe, D.; Depaoli,
D.; Di Girolamo, T.; Di Pierro, F.; Díaz, C.; Díaz-Bahamondes,
C.; Diebold, S.; Djannati-Ataï, A.; Dmytriiev, A.; Domínguez, A.;
Donini, A.; Dorner, D.; Doro, M.; Dournaux, J.; Dwarkadas, V. V.;
Ebr, J.; Eckner, C.; Einecke, S.; Ekoume, T. R. N.; Elsässer, D.;
Emery, G.; Evoli, C.; Fairbairn, M.; Falceta-Goncalves, D.; Fegan,
S.; Feng, Q.; Ferrand, G.; Fiandrini, E.; Fiasson, A.; Fioretti, V.;
Foffano, L.; Fonseca, M. V.; Font, L.; Fontaine, G.; Franco, F. J.;
Freixas Coromina, L.; Fukami, S.; Fukazawa, Y.; Fukui, Y.; Gaggero,
D.; Galanti, G.; Gammaldi, V.; Garcia, E.; Garczarczyk, M.; Gascon,
D.; Gaug, M.; Gent, A.; Ghalumyan, A.; Ghirlanda, G.; Gianotti, F.;
Giarrusso, M.; Giavitto, G.; Giglietto, N.; Giordano, F.; Glicenstein,
J.; Goldoni, P.; González, J. M.; Gourgouliatos, K.; Grabarczyk, T.;
Grandi, P.; Granot, J.; Grasso, D.; Green, J.; Grube, J.; Gueta, O.;
Gunji, S.; Halim, A.; Harvey, M.; Hassan Collado, T.; Hayashi, K.;
Heller, M.; Hernández Cadena, S.; Hervet, O.; Hinton, J.; Hiroshima,
N.; Hnatyk, B.; Hnatyk, R.; Hoffmann, D.; Hofmann, W.; Holder, J.;
Horan, D.; Hörandel, J.; Horvath, P.; Hovatta, T.; Hrabovsky, M.;
Hrupec, D.; Hughes, G.; Hütten, M.; Iarlori, M.; Inada, T.; Inoue,
S.; Insolia, A.; Ionica, M.; Iori, M.; Jacquemont, M.; Jamrozy,
M.; Janecek, P.; Jiménez Martínez, I.; Jin, W.; Jung-Richardt,
I.; Jurysek, J.; Kaaret, P.; Karas, V.; Karkar, S.; Kawanaka, N.;
Kerszberg, D.; Khélifi, B.; Kissmann, R.; Knödlseder, J.; Kobayashi,
Y.; Kohri, K.; Komin, N.; Kong, A.; Kosack, K.; Kubo, H.; La Palombara,
N.; Lamanna, G.; Lang, R. G.; Lapington, J.; Laporte, P.; Lefaucheur,
J.; Lemoine-Goumard, M.; Lenain, J.; Leone, F.; Leto, G.; Leuschner,
F.; Lindfors, E.; Lloyd, S.; Lohse, T.; Lombardi, S.; Longo, F.;
Lopez, A.; López, M.; López-Coto, R.; Loporchio, S.; Lucarelli, F.;
Luque-Escamilla, P. L.; Lyard, E.; Maggio, C.; Majczyna, A.; Makariev,
M.; Mallamaci, M.; Mandat, D.; Maneva, G.; Manganaro, M.; Manicò,
G.; Marcowith, A.; Marculewicz, M.; Markoff, S.; Marquez, P.; Martí,
J.; Martinez, O.; Martínez, M.; Martínez, G.; Martínez-Huerta, H.;
Maurin, G.; Mazin, D.; Mbarubucyeye, J. D.; Medina Miranda, D.; Meyer,
M.; Micanovic, S.; Miener, T.; Minev, M.; Miranda, J. M.; Mitchell,
A.; Mizuno, T.; Mode, B.; Moderski, R.; Mohrmann, L.; Molina, E.;
Montaruli, T.; Moralejo, A.; Morales Merino, J.; Morcuende-Parrilla,
D.; Morselli, A.; Mukherjee, R.; Mundell, C.; Murach, T.; Muraishi, H.;
Nagai, A.; Nakamori, T.; Nemmen, R.; Niemiec, J.; Nieto, D.; Nievas,
M.; Nikolajuk, M.; Nishijima, K.; Noda, K.; Nosek, D.; Nozaki, S.;
O'Brien, P.; Ohira, Y.; Ohishi, M.; Oka, T.; Ong, R. A.; Orienti,
M.; Orito, R.; Orlandini, M.; Orlando, E.; Osborne, J. P.; Ostrowski,
M.; Oya, I.; Pagliaro, A.; Palatka, M.; Paneque, D.; Pantaleo, F. R.;
Paredes, J. M.; Parmiggiani, N.; Patricelli, B.; Pavletić, L.; Pe'er,
A.; Pech, M.; Pecimotika, M.; Peresano, M.; Persic, M.; Petruk, O.;
Pfrang, K.; Piatteli, P.; Pietropaolo, E.; Pillera, R.; Pilszyk, B.;
Pimentel, D.; Pintore, F.; Pita, S.; Pohl, M.; Poireau, V.; Polo,
M.; Prado, R. R.; Prast, J.; Principe, G.; Produit, N.; Prokoph,
H.; Prouza, M.; Przybilski, H.; Pueschel, E.; Pühlhofer, G.; Pumo,
M. L.; Punch, M.; Queiroz, F.; Quirrenbach, A.; Rando, R.; Razzaque,
S.; Rebert, E.; Recchia, S.; Reichherzer, P.; Reimer, O.; Reimer,
A.; Renier, Y.; Reposeur, T.; Rhode, W.; Ribeiro, D.; Ribó, M.;
Richtler, T.; Rico, J.; Rieger, F.; Rizi, V.; Rodriguez, J.; Rodriguez
Fernandez, G.; Rodriguez Ramirez, J. C.; Rodríguez Vázquez, J. J.;
Romano, P.; Romeo, G.; Roncadelli, M.; Rosado, J.; Rosales de Leon,
A.; Rowell, G.; Rudak, B.; Rujopakarn, W.; Russo, F.; Sadeh, I.;
Saha, L.; Saito, T.; Salesa Greus, F.; Sanchez, D.; Sánchez-Conde,
M.; Sangiorgi, P.; Sano, H.; Santander, M.; Santos, E. M.; Sanuy, A.;
Sarkar, S.; Saturni, F. G.; Sawangwit, U.; Scherer, A.; Schleicher,
B.; Schovanek, P.; Schussler, F.; Schwanke, U.; Sciacca, E.; Scuderi,
S.; Seglar Arroyo, M.; Sergijenko, O.; Servillat, M.; Seweryn, K.;
Shalchi, A.; Sharma, P.; Shellard, R. C.; Siejkowski, H.; Sinha, A.;
Sliusar, V.; Slowikowska, A.; Sokolenko, A.; Sol, H.; Specovius, A.;
Spencer, S.; Spiga, D.; Stamerra, A.; Stanič, S.; Starling, R.;
Stolarczyk, T.; Straumann, U.; Strišković, J.; Suda, Y.; Świerk,
P.; Tagliaferri, G.; Takahashi, H.; Takahashi, M.; Tavecchio, F.;
Taylor, L.; Tejedor, L. A.; Temnikov, P.; Terrier, R.; Terzic, T.;
Testa, V.; Tian, W.; Tibaldo, L.; Tonev, D.; Torres, D. F.; Torresi,
E.; Tosti, L.; Tothill, N.; Tovmassian, G.; Travnicek, P.; Truzzi,
S.; Tuossenel, F.; Umana, G.; Vacula, M.; Vagelli, V.; Valentino, M.;
Vallage, B.; Vallania, P.; van Eldik, C.; Varner, G. S.; Vassiliev, V.;
Vázquez Acosta, M.; Vecchi, M.; Veh, J.; Vercellone, S.; Vergani, S.;
Verguilov, V.; Vettolani, G. P.; Viana, A.; Vigorito, C. F.; Vitale,
V.; Vorobiov, S.; Vovk, I.; Vuillaume, T.; Wagner, S. J.; Walter,
R.; Watson, J.; White, M.; White, R.; Wiemann, R.; Wierzcholska, A.;
Will, M.; Williams, D. A.; Wischnewski, R.; Wolter, A.; Yamazaki, R.;
Yanagita, S.; Yang, L.; Yoshikoshi, T.; Zacharias, M.; Zaharijas, G.;
Zaric, D.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A. A.; Zech, A.;
Zechlin, H.; Zhdanov, V. I.; Živec, M.
2021JCAP...02..048A Altcode: 2020arXiv201001349C
The Cherenkov Telescope Array (CTA), the new-generation ground-based
observatory for γ astronomy, provides unique capabilities to address
significant open questions in astrophysics, cosmology, and fundamental
physics. We study some of the salient areas of γ cosmology that can be
explored as part of the Key Science Projects of CTA, through simulated
observations of active galactic nuclei (AGN) and of their relativistic
jets. Observations of AGN with CTA will enable a measurement of γ
absorption on the extragalactic background light with a statistical
uncertainty below 15% up to a redshift z=2 and to constrain or detect
γ halos up to intergalactic-magnetic-field strengths of at least 0.3
pG . Extragalactic observations with CTA also show promising potential
to probe physics beyond the Standard Model. The best limits on Lorentz
invariance violation from γ astronomy will be improved by a factor
of at least two to three. CTA will also probe the parameter space in
which axion-like particles could constitute a significant fraction, if
not all, of dark matter. We conclude on the synergies between CTA and
other upcoming facilities that will foster the growth of γ cosmology.
---------------------------------------------------------
Title: The solar dynamo and flux emergence
Authors: Cameron, Robert
2021cosp...43E1728C Altcode:
Magnetic flux generated by dynamo action in the solar convection
zone is carried by flows from the solar convection zone, through the
photosphere, into the chromosphere and corona. During the emergence
process a rising magnetic flux loop is given both a random and
systematic tilt with respect to the east-west direction. This rise
through the photosphere is called flux emergence, and it plays an
essential role in the Babcock-Leighton model of the solar dynamo. In
this talke we will consider the flows which are responsible for
flux emergence. We will then show how the emerged field reverses
the polar fields and creates new flux to emerge during the next
cycle. Quantitative estimates will be made for the different terms
involved in the subsurface magnetic flux budget.
---------------------------------------------------------
Title: Vortex flow properties in simulations of solar plage region:
Evidence for their role in chromospheric heating
Authors: Yadav, N.; Cameron, R. H.; Solanki, S. K.
2021A&A...645A...3Y Altcode: 2020arXiv201014971Y
Context. Vortex flows exist across a broad range of spatial and
temporal scales in the solar atmosphere. Small-scale vortices are
thought to play an important role in energy transport in the solar
atmosphere. However, their physical properties remain poorly understood
due to the limited spatial resolution of the observations. <BR />
Aims: We explore and analyze the physical properties of small-scale
vortices inside magnetic flux tubes using numerical simulations, and
investigate whether they contribute to heating the chromosphere in a
plage region. <BR /> Methods: Using the three-dimensional radiative
magnetohydrodynamic simulation code MURaM, we perform numerical
simulations of a unipolar solar plage region. To detect and isolate
vortices we use the swirling strength criterion and select the locations
where the fluid is rotating with an angular velocity greater than
a certain threshold. We concentrate on small-scale vortices as they
are the strongest and carry most of the energy. We explore the spatial
profiles of physical quantities such as density and horizontal velocity
inside these vortices. Moreover, to learn their general characteristics,
a statistical investigation is performed. <BR /> Results: Magnetic
flux tubes have a complex filamentary substructure harboring an
abundance of small-scale vortices. At the interfaces between vortices
strong current sheets are formed that may dissipate and heat the solar
chromosphere. Statistically, vortices have higher densities and higher
temperatures than the average values at the same geometrical height
in the chromosphere. <BR /> Conclusions: We conclude that small-scale
vortices are ubiquitous in solar plage regions; they are denser and
hotter structures that contribute to chromospheric heating, possibly
by dissipation of the current sheets formed at their interfaces.
---------------------------------------------------------
Title: Non-equilibrium equation-of-state in stellar atmospheres
Authors: Lokanathapura Seetharamabhasari, Anusha; Cameron, Robert;
Van Noort, Michiel
2021cosp...43E.985L Altcode:
In the stellar atmospheres, radiative energy transport is dominated by
only the strongest spectral lines. For these lines, the approximation of
local thermo-dynamic equilibrium (LTE) is known to be very inaccurate,
and a state of equilibrium cannot be assumed in general. Therefore to
understand the structure and dynamics of stellar atmospheres through
evolving magneto-hydro-dynamic equations, one needs a non-equilibrium
equation of state. To calculate the radiative energy transport under
these conditions, the population evolution equation must be evaluated
including all time dependent terms. To this end, we have developed a new
numerical method to solve the non-LTE non-equilibrium radiative transfer
problem. We solve evolution equation for the atomic level populations
in a time-implicit way, keeping all time dependent terms to first
order. We have tested our method by reproducing earlier works, namely,
a) determining chromosperic time-scales of ionization/recombination,
b) showing that our non-equilibrium solver evolves to the statistical
equilibrium solution obtained from an independent non-LTE spectral
synthesis code. In this presentation, I will describe the method,
and discuss equilibrium solutions.
---------------------------------------------------------
Title: Sensitivity of the Cherenkov Telescope Array to a dark matter
signal from the Galactic centre
Authors: Acharyya, A.; Adam, R.; Adams, C.; Agudo, I.;
Aguirre-Santaella, A.; Alfaro, R.; Alfaro, J.; Alispach, C.; Aloisio,
R.; Alves Batista, R.; Amati, L.; Ambrosi, G.; Angüner, E. O.;
Antonelli, L. A.; Aramo, C.; Araudo, A.; Armstrong, T.; Arqueros,
F.; Asano, K.; Ascasíbar, Y.; Ashley, M.; Balazs, C.; Ballester,
O.; Baquero Larriva, A.; Barbosa Martins, V.; Barkov, M.; Barres
de Almeida, U.; Barrio, J. A.; Bastieri, D.; Becerra, J.; Beck, G.;
Becker Tjus, J.; Benbow, W.; Benito, M.; Berge, D.; Bernardini, E.;
Bernlöhr, K.; Berti, A.; Bertucci, B.; Beshley, V.; Biasuzzi, B.;
Biland, A.; Bissaldi, E.; Biteau, J.; Blanch, O.; Blazek, J.; Bocchino,
F.; Boisson, C.; Bonneau Arbeletche, L.; Bordas, P.; Bosnjak, Z.;
Bottacini, E.; Bozhilov, V.; Bregeon, J.; Brill, A.; Bringmann, T.;
Brown, A. M.; Brun, P.; Brun, F.; Bruno, P.; Bulgarelli, A.; Burton,
M.; Burtovoi, A.; Buscemi, M.; Cameron, R.; Capasso, M.; Caproni, A.;
Capuzzo-Dolcetta, R.; Caraveo, P.; Carosi, R.; Carosi, A.; Casanova,
S.; Cascone, E.; Cassol, F.; Catalani, F.; Cauz, D.; Cerruti, M.;
Chadwick, P.; Chaty, S.; Chen, A.; Chernyakova, M.; Chiaro, G.;
Chiavassa, A.; Chikawa, M.; Chudoba, J.; Çolak, M.; Conforti, V.;
Coniglione, R.; Conte, F.; Contreras, J. L.; Coronado-Blazquez, J.;
Costa, A.; Costantini, H.; Cotter, G.; Cristofari, P.; D'Aimath, A.;
D'Ammando, F.; Damone, L. A.; Daniel, M. K.; Dazzi, F.; De Angelis,
A.; De Caprio, V.; de Cássia dos Anjos, R.; de Gouveia Dal Pino,
E. M.; De Lotto, B.; De Martino, D.; de Oña Wilhelmi, E.; De Palma,
F.; de Souza, V.; Delgado, C.; Delgado Giler, A. G.; della Volpe,
D.; Depaoli, D.; Di Girolamo, T.; Di Pierro, F.; Di Venere, L.;
Diebold, S.; Dmytriiev, A.; Domínguez, A.; Donini, A.; Doro, M.;
Ebr, J.; Eckner, C.; Edwards, T. D. P.; Ekoume, T. R. N.; Elsässer,
D.; Evoli, C.; Falceta-Goncalves, D.; Fedorova, E.; Fegan, S.;
Feng, Q.; Ferrand, G.; Ferrara, G.; Fiandrini, E.; Fiasson, A.;
Filipovic, M.; Fioretti, V.; Fiori, M.; Foffano, L.; Fontaine, G.;
Fornieri, O.; Franco, F. J.; Fukami, S.; Fukui, Y.; Gaggero, D.;
Galaz, G.; Gammaldi, V.; Garcia, E.; Garczarczyk, M.; Gascon, D.;
Gent, A.; Ghalumyan, A.; Gianotti, F.; Giarrusso, M.; Giavitto, G.;
Giglietto, N.; Giordano, F.; Giuliani, A.; Glicenstein, J.; Gnatyk,
R.; Goldoni, P.; González, M. M.; Gourgouliatos, K.; Granot, J.;
Grasso, D.; Green, J.; Grillo, A.; Gueta, O.; Gunji, S.; Halim, A.;
Hassan, T.; Heller, M.; Hernández Cadena, S.; Hiroshima, N.; Hnatyk,
B.; Hofmann, W.; Holder, J.; Horan, D.; Hörandel, J.; Horvath, P.;
Hovatta, T.; Hrabovsky, M.; Hrupec, D.; Hughes, G.; Humensky, T. B.;
Hütten, M.; Iarlori, M.; Inada, T.; Inoue, S.; Iocco, F.; Iori, M.;
Jamrozy, M.; Janecek, P.; Jin, W.; Jouvin, L.; Jurysek, J.; Karukes,
E.; Katarzyński, K.; Kazanas, D.; Kerszberg, D.; Kherlakian, M. C.;
Kissmann, R.; Knödlseder, J.; Kobayashi, Y.; Kohri, K.; Komin,
N.; Kubo, H.; Kushida, J.; Lamanna, G.; Lapington, J.; Laporte,
P.; Leigui de Oliveira, M. A.; Lenain, J.; Leone, F.; Leto, G.;
Lindfors, E.; Lohse, T.; Lombardi, S.; Longo, F.; Lopez, A.; López,
M.; López-Coto, R.; Loporchio, S.; Luque-Escamilla, P. L.; Mach,
E.; Maggio, C.; Maier, G.; Mallamaci, M.; Malta Nunes de Almeida,
R.; Mandat, D.; Manganaro, M.; Mangano, S.; Manicò, G.; Marculewicz,
M.; Mariotti, M.; Markoff, S.; Marquez, P.; Martí, J.; Martinez, O.;
Martínez, M.; Martínez, G.; Martínez-Huerta, H.; Maurin, G.; Mazin,
D.; Mbarubucyeye, J. D.; Medina Miranda, D.; Meyer, M.; Miceli, M.;
Miener, T.; Minev, M.; Miranda, J. M.; Mirzoyan, R.; Mizuno, T.;
Mode, B.; Moderski, R.; Mohrmann, L.; Molina, E.; Montaruli, T.;
Moralejo, A.; Morcuende-Parrilla, D.; Morselli, A.; Mukherjee, R.;
Mundell, C.; Nagai, A.; Nakamori, T.; Nemmen, R.; Niemiec, J.; Nieto,
D.; Nikołajuk, M.; Ninci, D.; Noda, K.; Nosek, D.; Nozaki, S.; Ohira,
Y.; Ohishi, M.; Ohtani, Y.; Oka, T.; Okumura, A.; Ong, R. A.; Orienti,
M.; Orito, R.; Orlandini, M.; Orlando, S.; Orlando, E.; Ostrowski,
M.; Oya, I.; Pagano, I.; Pagliaro, A.; Palatiello, M.; Pantaleo,
F. R.; Paredes, J. M.; Pareschi, G.; Parmiggiani, N.; Patricelli, B.;
Pavletić, L.; Pe'er, A.; Pecimotika, M.; Pérez-Romero, J.; Persic,
M.; Petruk, O.; Pfrang, K.; Piano, G.; Piatteli, P.; Pietropaolo,
E.; Pillera, R.; Pilszyk, B.; Pintore, F.; Pohl, M.; Poireau, V.;
Prado, R. R.; Prandini, E.; Prast, J.; Principe, G.; Prokoph, H.;
Prouza, M.; Przybilski, H.; Pühlhofer, G.; Pumo, M. L.; Queiroz,
F.; Quirrenbach, A.; Rainò, S.; Rando, R.; Razzaque, S.; Recchia,
S.; Reimer, O.; Reisenegger, A.; Renier, Y.; Rhode, W.; Ribeiro, D.;
Ribó, M.; Richtler, T.; Rico, J.; Rieger, F.; Rinchiuso, L.; Rizi,
V.; Rodriguez, J.; Rodriguez Fernandez, G.; Rodriguez Ramirez, J. C.;
Rojas, G.; Romano, P.; Romeo, G.; Rosado, J.; Rowell, G.; Rudak,
B.; Russo, F.; Sadeh, I.; Sæther Hatlen, E.; Safi-Harb, S.; Salesa
Greus, F.; Salina, G.; Sanchez, D.; Sánchez-Conde, M.; Sangiorgi, P.;
Sano, H.; Santander, M.; Santos, E. M.; Santos-Lima, R.; Sanuy, A.;
Sarkar, S.; Saturni, F. G.; Sawangwit, U.; Schussler, F.; Schwanke,
U.; Sciacca, E.; Scuderi, S.; Seglar-Arroyo, M.; Sergijenko, O.;
Servillat, M.; Seweryn, K.; Shalchi, A.; Sharma, P.; Shellard, R. C.;
Siejkowski, H.; Silk, J.; Siqueira, C.; Sliusar, V.; Słowikowska,
A.; Sokolenko, A.; Sol, H.; Spencer, S.; Stamerra, A.; Stanič, S.;
Starling, R.; Stolarczyk, T.; Straumann, U.; Strišković, J.; Suda,
Y.; Suomijarvi, T.; Świerk, P.; Tavecchio, F.; Taylor, L.; Tejedor,
L. A.; Teshima, M.; Testa, V.; Tibaldo, L.; Todero Peixoto, C. J.;
Tokanai, F.; Tonev, D.; Tosti, G.; Tosti, L.; Tothill, N.; Truzzi,
S.; Travnicek, P.; Vagelli, V.; Vallage, B.; Vallania, P.; van Eldik,
C.; Vandenbroucke, J.; Varner, G. S.; Vassiliev, V.; Vázquez Acosta,
M.; Vecchi, M.; Ventura, S.; Vercellone, S.; Vergani, S.; Verna, G.;
Viana, A.; Vigorito, C. F.; Vink, J.; Vitale, V.; Vorobiov, S.; Vovk,
I.; Vuillaume, T.; Wagner, S. J.; Walter, R.; Watson, J.; Weniger,
C.; White, R.; White, M.; Wiemann, R.; Wierzcholska, A.; Will, M.;
Williams, D. A.; Wischnewski, R.; Yanagita, S.; Yang, L.; Yoshikoshi,
T.; Zacharias, M.; Zaharijas, G.; Zakaria, A. A.; Zampieri, L.; Zanin,
R.; Zaric, D.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A. A.; Zech,
A.; Zechlin, H.; Zhdanov, V. I.; Živec, M.
2021JCAP...01..057A Altcode: 2020arXiv200716129C
We provide an updated assessment of the power of the Cherenkov Telescope
Array (CTA) to search for thermally produced dark matter at the TeV
scale, via the associated gamma-ray signal from pair-annihilating dark
matter particles in the region around the Galactic centre. We find
that CTA will open a new window of discovery potential, significantly
extending the range of robustly testable models given a standard cuspy
profile of the dark matter density distribution. Importantly, even for
a cored profile, the projected sensitivity of CTA will be sufficient to
probe various well-motivated models of thermally produced dark matter
at the TeV scale. This is due to CTA's unprecedented sensitivity,
angular and energy resolutions, and the planned observational
strategy. The survey of the inner Galaxy will cover a much larger
region than corresponding previous observational campaigns with imaging
atmospheric Cherenkov telescopes. CTA will map with unprecedented
precision the large-scale diffuse emission in high-energy gamma rays,
constituting a background for dark matter searches for which we adopt
state-of-the-art models based on current data. Throughout our analysis,
we use up-to-date event reconstruction Monte Carlo tools developed
by the CTA consortium, and pay special attention to quantifying the
level of instrumental systematic uncertainties, as well as background
template systematic errors, required to probe thermally produced dark
matter at these energies.
---------------------------------------------------------
Title: A Journey of Exploration to the Polar Regions of a Star:
Probing the Solar Poles and the Heliosphere from High Helio-Latitude
Authors: Finsterle, W.; Harra, L.; Andretta, V.; Appourchaux, T.;
Baudin, F.; Bellot Rubio, L.; Birch, A.; Boumier, P.; Cameron, R. H.;
Carlsson, M.; Corbard, T.; Davies, J. A.; Fazakerley, A. N.; Fineschi,
S.; Gizon, L. C.; Harrison, R. A.; Hassler, D.; Leibacher, J. W.;
Liewer, P. C.; Macdonald, M.; Maksimovic, M.; Murphy, N.; Naletto, G.;
Nigro, G.; Owen, C. J.; Martinez-Pillet, V.; Rochus, P. L.; Romoli,
M.; Sekii, T.; Spadaro, D.; Veronig, A.
2020AGUFMSH0110005F Altcode:
A mission to view the solar poles from high helio-latitudes (above
60°) will build on the experience of Solar Orbiter as well as a long
heritage of successful solar missions and instrumentation (e.g. SOHO,
STEREO, Hinode, SDO), but will focus for the first time on the solar
poles, enabling scientific investigations that cannot be done by
any other mission. One of the major mysteries of the Sun is the solar
cycle. The activity cycle of the Sun drives the structure and behaviour
of the heliosphere and is, of course, the driver of space weather. In
addition, solar activity and variability provides fluctuating input
into the Earth climate models, and these same physical processes
are applicable to stellar systems hosting exoplanets. One of the
main obstructions to understanding the solar cycle, and hence all
solar activity, is our current lack of understanding of the polar
regions. We describe a mission concept that aims to address this
fundamental issue. In parallel, we recognise that viewing the Sun
from above the polar regions enables further scientific advantages,
beyond those related to the solar cycle, such as unique and powerful
studies of coronal mass ejection processes, from a global perspective,
and studies of coronal structure and activity in polar regions. Not
only will these provide important scientific advances for fundamental
stellar physics research, they will feed into our understanding of
impacts on the Earth and other planets' space environment.
---------------------------------------------------------
Title: Power spectrum of turbulent convection in the solar photosphere
Authors: Yelles Chaouche, L.; Cameron, R. H.; Solanki, S. K.;
Riethmüller, T. L.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.;
Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort,
M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2020A&A...644A..44Y Altcode: 2020arXiv201009037Y
The solar photosphere provides us with a laboratory for understanding
turbulence in a layer where the fundamental processes of transport
vary rapidly and a strongly superadiabatic region lies very closely
to a subadiabatic layer. Our tools for probing the turbulence are
high-resolution spectropolarimetric observations such as have recently
been obtained with the two balloon-borne SUNRISE missions, and numerical
simulations. Our aim is to study photospheric turbulence with the
help of Fourier power spectra that we compute from observations
and simulations. We also attempt to explain some properties of the
photospheric overshooting flow with the help of its governing equations
and simulations. We find that quiet-Sun observations and smeared
simulations are consistent with each other and exhibit a power-law
behavior in the subgranular range of their Doppler velocity power
spectra with a power-law index of ≈ - 2. The unsmeared simulations
exhibit a power law that extends over the full range between the
integral and Taylor scales with a power-law index of ≈ - 2.25. The
smearing, reminiscent of observational conditions, considerably reduces
the extent of the power-law-like portion of the power spectra. This
suggests that the limited spatial resolution in some observations
might eventually result in larger uncertainties in the estimation of
the power-law indices. The simulated vertical velocity power spectra
as a function of height show a rapid change in the power-law index
(at the subgranular range) from roughly the optical depth unity layer,
that is, the solar surface, to 300 km above it. We propose that the
cause of the steepening of the power-law index is the transition from
a super- to a subadiabatic region, in which the dominant source of
motions is overshooting convection. A scale-dependent transport of
the vertical momentum occurs. At smaller scales, the vertical momentum
is more efficiently transported sideways than at larger scales. This
results in less vertical velocity power transported upward at small
scales than at larger scales and produces a progressively steeper
vertical velocity power law below 180 km. Above this height, the
gravity work progressively gains importance at all relevant scales,
making the atmosphere progressively more hydrostatic and resulting
in a gradually less steep power law. Radiative heating and cooling of
the plasma is shown to play a dominant role in the plasma energetics
in this region, which is important in terms of nonadiabatic damping
of the convective motions.
---------------------------------------------------------
Title: Simulations Show that Vortex Flows Could Heat the Chromosphere
in Solar Plage
Authors: Yadav, N.; Cameron, R.; Solanki, S.
2020SPD....5120107Y Altcode:
Recent advances in both, observational techniques and numerical
simulations have enabled us to detect small-scale vortices in the solar
atmosphere. Vortices are ubiquitous throughout the solar surface and
at all layers of the solar atmosphere existing over a wide range of
spatial and temporal scales. Small-scale vortices are suggested to play
an important role in the energy transport of the solar atmosphere,
however, their physical properties remain poorly understood due
to limited resolution. We explored the relationship between vortex
flows at different spatial scales, analyze their physical properties,
and investigate their contribution to Poynting flux transport. Using
three-dimensional (3D) radiative magnetohydrodynamic (MHD)simulation
code 'MURaM', we perform numerical simulations of a unipolar solar
plage region. For detecting and isolating vortices, we use the
'Swirling Strength' criterion. We explore the spatial profiles of
physical quantities viz. density, horizontal velocity, etc. inside
these vortices. Moreover, to apprehend their general characteristics,
a statistical investigation is performed. We found that magnetic flux
tubes have a complex filamentary substructure abundant of small-scale
vortices. On their interfaces strong current sheets are formed that
may dissipate and heat the solar chromosphere. Statistically, vortices
have higher densities and higher temperatures than the average values
at the same geometrical height. We also degrade our simulation data to
get an effective spatial resolution of 50 km, 100 km, 250 km, and 500
km, respectively. Analyzing simulation data at different effective
resolutions, we found vortex flows existing over various spatial
scales. In high-resolution simulation data, we detect a large number
of small-scale vortices. Whereas, in the degraded data with relatively
poor resolutions, smaller vortices are averaged-out and larger vortices
are detected. The Poynting flux over vortex locations is more than
adequate to compensate for the radiative losses in the chromosphere
indicating their possible role in the chromospheric heating.
---------------------------------------------------------
Title: A Coronal Loop in a Box: Energy Generation, Heating and
Dynamics
Authors: Breu, C.; Peter, H.; Cameron, R.; Solanki, S.; Chitta, P.;
Przybylski, D.
2020SPD....5121008B Altcode:
In our study we aim at an understanding how the energy to heat the
upper atmosphere is generated by the photospheric magneto-convection,
transported into the upper atmosphere, and how its dissipation governs
the formation of the internal structure of a coronal magnetic loop. In
a 3D MHD model we study a coronal loop that is rooted with both
footpoints in a shallow convection zone layer. Therefore the driving
at the coronal base arises self-consistently from magneto-convection
in plage-type areas. To fit into a cartesian box, we straighten the
coronal loop. This allows a high spatial resolution within the loop
that cannot be achieved in a model of a whole active region. To
conduct the numerical experiments we employ the MURaM code that
includes heat conduction, radiative transfer and optically thin
radiative losses. We find that the Poynting flux into the loop is
generated by small-scale photospheric motions within strong magnetic
flux concentrations. Turbulent behaviour develops in the upper layers
of the atmosphere as a response to the footpoint motions. Vortex flows
are found at various heights within the loop. These are organised in
swirls that form coherent structures with a magnetic connection from
the intergranular lanes in the photosphere through the chromosphere
up to several megameters into the corona. In the coronal part of
the loop plasma motions perpendicular to the magnetic axis of the
swirl are associated with an increased heating rate and thus enhanced
temperatures. At any given time, only part of the loop is filled with
swirls which leads to a substructure of the loop in terms of temperature
and density. Consequently the emission as it would be observed by AIA
or XRT reveals transient bright strands that form in response to the
heating events related to the swirls. With this model we can build a
coherent picture of how the energy flux to heat the upper atmosphere
is generated near the solar surface and how this process drives and
governs the heating and dynamics of a coronal loop
---------------------------------------------------------
Title: Effects of inclusion of small-scale dynamo in near-surface
structure of F-stars
Authors: Bhatia, T. S.; Cameron, R.; Solanki, S.; Peter, H.; Przbylski,
D.; Witzke, V.
2020SPD....5120704B Altcode:
The presence of (unresolved) small-scale mixed polarity regions in
the quiet Sun photosphere plays an important role in determining
the basal magnetic flux. Observationally, the magnitude of the
vertical component of this field is estimated to be ~50-100 G on the
Sun. This field is important for determining the energy balance in
the chromosphere and may also subtly affect the radiative properties
of the photosphere. These fields are believed to be the result of a
small-scale dynamo (SSD) operating near the surface. While significant
progress has been made in investigating the role of the SSD in the Sun,
it is unclear what effects SSDs have on other stars. In particular,
for F-stars, the photosheric kinetic and internal energies seem to be
of the same order of magnitude. Since there is a rough equipartition
in energies for a saturated SSD, deviations from a pure hydrodynamic
(HD) stratification are expected. We aim to characterize these
deviations. Box simulations of the upper convection zone and the
photosphere are carried out using the radiative MHD code MURaM. To
obtain SSD simulations, we use initial HD simulations and seed a
magnetic field of negligible strength and zero net flux, which we
then run till the magnetic field reaches saturation. We consider two
different lower boundary conditions (BCs) for the magnetic field to
characterize BC-effects: a) only vertical magnetic field is allowed, b)
both vertical and horizontal magnetic field is allowed. Both boundary
conditions exhibit SSD action. We observe slight increase (fraction
of a percent) in the horizontally-averaged temperature profile for
both the cases. Other thermodynamic quantities exhibit deviations (~
a percent) depending on the boundary condition considered. In addition,
the spatial power spectra of the bolometric intensity shows deviations
from the corresponding HD (without magnetic field) run, implying
larger power at smaller spatial scales for SSD case. The presence of
a SSD results in a significant amount of "quiet"-star magnetic flux
with associated changes in the stratification of the atmosphere and
spatial distribution of the bolometric intensity.
---------------------------------------------------------
Title: Average motion of emerging solar active region
polarities. II. Joy's law
Authors: Schunker, H.; Baumgartner, C.; Birch, A. C.; Cameron, R. H.;
Braun, D. C.; Gizon, L.
2020A&A...640A.116S Altcode: 2020arXiv200605565S
Context. The tilt of solar active regions described by Joy's law
is essential for converting a toroidal field to a poloidal field in
Babcock-Leighton dynamo models. In thin flux tube models the Coriolis
force causes what we observe as Joy's law, acting on east-west flows
as they rise towards the surface. <BR /> Aims: Our goal is to measure
the evolution of the average tilt angle of hundreds of active regions
as they emerge, so that we can constrain the origins of Joy's law. <BR
/> Methods: We measured the tilt angle of the primary bipoles in 153
emerging active regions (EARs) in the Solar Dynamics Observatory
Helioseismic Emerging Active Region survey. We used line-of-sight
magnetic field measurements averaged over 6 h to define the polarities
and measure the tilt angle up to four days after emergence. <BR />
Results: We find that at the time of emergence the polarities are on
average aligned east-west, and that neither the separation nor the
tilt depends on latitude. We do find, however, that EARs at higher
latitudes have a faster north-south separation speed than those closer
to the equator at the emergence time. After emergence, the tilt
angle increases and Joy's law is evident about two days later. The
scatter in the tilt angle is independent of flux until about one day
after emergence, when we find that higher-flux regions have a smaller
scatter in tilt angle than lower-flux regions. <BR /> Conclusions:
Our finding that active regions emerge with an east-west alignment
is consistent with earlier observations, but is still surprising
since thin flux tube models predict that tilt angles of rising flux
tubes are generated below the surface. Previously reported tilt angle
relaxation of deeply anchored flux tubes can be largely explained
by the change in east-west separation. We conclude that Joy's law is
caused by an inherent north-south separation speed present when the
flux first reaches the surface, and that the scatter in the tilt angle
is consistent with buffeting of the polarities by supergranulation.
---------------------------------------------------------
Title: Radiative MHD Simulations of Starspots
Authors: Panja, M.; Cameron, R.; Solanki, S.
2020SPD....5121117P Altcode:
We have performed the first-ever, realistic 3D simulations of the
photospheric structure of complete starspots, including their penumbrae,
for a range of cool main-sequence stars, namely the spectral types M0V,
K0V, and G2V. We used the MHD code MURaM which includes radiative energy
transfer and the effects of partial ionization. We explore several
fundamental properties like umbral intensity contrast, temperature, and
magnetic field strength as functions of spectral type. Our simulations
show that there is an increase in spot contrast with the increase in
stellar surface temperature, which is consistent with observations. The
umbral field strength is determined by the depth at which the optical
surface forms and the surface pressures of the host stars. We will
present our results and discuss the physics behind them.
---------------------------------------------------------
Title: Reply to the comment of T. Metcalfe and J. van Saders on the
Science report "The Sun is less active than other solar-like stars"
Authors: Reinhold, T.; Shapiro, A. I.; Solanki, S. K.; Montet, B. T.;
Krivova, N. A.; Cameron, R. H.; Amazo-Gómez, E. M.
2020arXiv200704817R Altcode:
This is our reply to the comment of T. Metcalfe and J. van Saders
on the Science report "The Sun is less active than other solar-like
stars" by T. Reinhold, A. I. Shapiro, S. K. Solanki, B. T. Montet,
N. A. Krivova, R. H. Cameron, E. M. Amazo-Gomez. We hope that both
the comment and our reply lead to fruitful discussions which of the
two presented scenarios is more likely.
---------------------------------------------------------
Title: Meridional flow in the Sun’s convection zone is a single
cell in each hemisphere
Authors: Gizon, Laurent; Cameron, Robert H.; Pourabdian, Majid; Liang,
Zhi-Chao; Fournier, Damien; Birch, Aaron C.; Hanson, Chris S.
2020Sci...368.1469G Altcode:
The Sun’s magnetic field is generated by subsurface motions of the
convecting plasma. The latitude at which the magnetic field emerges
through the solar surface (as sunspots) drifts toward the equator
over the course of the 11-year solar cycle. We use helioseismology to
infer the meridional flow (in the latitudinal and radial directions)
over two solar cycles covering 1996-2019. Two data sources are used,
which agree during their overlap period of 2001-2011. The time-averaged
meridional flow is shown to be a single cell in each hemisphere,
carrying plasma toward the equator at the base of the convection zone
with a speed of ~4 meters per second at 45° latitude. Our results
support the flux-transport dynamo model, which explains the drift of
sunspot-emergence latitudes through the meridional flow.
---------------------------------------------------------
Title: Simulations Show that Vortex Flows Could Heat the Chromosphere
in Solar Plage
Authors: Yadav, Nitin; Cameron, R. H.; Solanki, S. K.
2020ApJ...894L..17Y Altcode: 2020arXiv200413996Y
The relationship between vortex flows at different spatial scales
and their contribution to the energy balance in the chromosphere
is not yet fully understood. We perform three-dimensional (3D)
radiation-magnetohydrodynamic simulations of a unipolar solar plage
region at a spatial resolution of 10 km using the MURaM code. We
use the swirling-strength criterion that mainly detects the smallest
vortices present in the simulation data. We additionally degrade our
simulation data to smooth out the smaller vortices, so that also the
vortices at larger spatial scales can be detected. Vortex flows at
various spatial scales are found in our simulation data for different
effective spatial resolutions. We conclude that the observed large
vortices are likely clusters of much smaller ones that are not yet
resolved by observations. We show that the vertical Poynting flux
decreases rapidly with reduced effective spatial resolutions and
is predominantly carried by the horizontal plasma motions rather
than vertical flows. Since the small-scale horizontal motions or the
smaller vortices carry most of the energy, the energy transported by
vortices deduced from low-resolution data is grossly underestimated. In
full-resolution simulation data, the Poynting flux contribution due to
vortices is more than adequate to compensate for the radiative losses
in plage, indicating their importance for chromospheric heating.
---------------------------------------------------------
Title: Rossby modes in slowly rotating stars: depth dependence in
distorted polytropes with uniform rotation
Authors: Damiani, C.; Cameron, R. H.; Birch, A. C.; Gizon, L.
2020A&A...637A..65D Altcode: 2020arXiv200305276D
Context. Large-scale Rossby waves have recently been discovered based on
measurements of horizontal surface and near-surface solar flows. <BR />
Aims: We are interested in understanding why it is only equatorial modes
that are observed and in modelling the radial structure of the observed
modes. To this aim, we have characterised the radial eigenfunctions
of r modes for slowly rotating polytropes in uniform rotation. <BR
/> Methods: We followed Provost et al. (1981, A&A, 94, 126) and
considered a linear perturbation theory to describe quasi-toroidal
stellar adiabatic oscillations in the inviscid case. We used
perturbation theory to write the solutions to the fourth order in the
rotational frequency of the star. We numerically solved the eigenvalue
problem, concentrating on the type of behaviour exhibited where the
stratification is nearly adiabatic. <BR /> Results: We find that for
free-surface boundary conditions on a spheroid of non-vanishing surface
density, r modes can only exist for ℓ = m spherical harmonics in the
inviscid case and we compute their depth dependence and frequencies to
leading order. For quasi-adiabatic stratification, the sectoral modes
with no radial nodes are the only modes which are almost toroidal and
the depth dependence of the corresponding horizontal motion scales as
r<SUP>m</SUP>. For all r modes, except the zero radial order sectoral
ones, non-adiabatic stratification plays a crucial role in the radial
force balance. <BR /> Conclusions: The lack of quasi-toroidal solutions
when stratification is close to neutral, except for the sectoral modes
without nodes in radius, follows from the need for both horizontal
and radial force balance. In the absence of super- or sub-adiabatic
stratification and viscosity, both the horizontal and radial parts of
the force balance independently determine the pressure perturbation. The
only quasi-toroidal cases in which these constraints on the pressure
perturbation are consistent are the special cases where ℓ = m and
the horizontal displacement scales with r<SUP>m</SUP>.
---------------------------------------------------------
Title: Towards a more reliable reconstruction of the historical
solar variability: a more realistic description of solar ephemeral
magnetic regions
Authors: Hofer, Bernhard; Krivova, Natalie A.; Wu, Chi-Ju; Usoskin,
Ilya A.; Cameron, Robert
2020EGUGA..2217086H Altcode:
Solar irradiance is a crucial input to climate models, but its
measurements are only available since 1978. The variability of
solar irradiance on climate-relevant time-scales is caused by
the competition between bright and dark features formed by the
magnetic fields emerging on the solar surface. Thus, models have
been developed that reconstruct past irradiance variability from
proxies of the solar magnetic activity. The longest direct proxy is
the sunspot number. The common problem of such reconstructions is,
however, that while sunspots adequately describe the evolution of
the active regions (ARs) (large bipolar regions hosting sunspots),
the evolution of their smaller counterparts, the ephemeral regions
(ERs), is not directly featured by sunspots. At the same time, these
small regions are much more numerous and are believed to be the main
source of the long-term irradiance changes, which are of special
interest to climate models. We develop an improved description of
the ephemeral region emergence taking different solar observational
constraints into account. The model builds on the SATIRE-T model, in
which the emergence of ARs is described by the sunspot number and the
emergence of the ERs is linearly linked to that of ARs. The latter,
however, implies that whenever the sunspot number drops to zero, no
magnetic field emerges in the model. In the new model, the emergence
of the ERs is no longer linked to sunspots linearly. Instead, ARs and
ERs are considered to be parts of a single power-law size distribution
of the emerging magnetic regions. This ensures that even in the absence
of ARs (e.g., during the grand minima of solar activity), the emergence
rate of ERs remains non-zero. In particular, the solar open magnetic
flux reconstructed using this approach does not drop to zero during
the Maunder minimum, in agreement with independent reconstructions
from the cosmogenic isotope data. Such an improved description of the
ERs will allow a better constraint on the maximum solar irradiance
drop during grand minima events. This, in turn, will allow a better
constraint on the potential solar forcing in the future.
---------------------------------------------------------
Title: The Sun is less active than other solar-like stars
Authors: Reinhold, Timo; Shapiro, Alexander I.; Solanki, Sami K.;
Montet, Benjamin T.; Krivova, Natalie A.; Cameron, Robert H.;
Amazo-Gómez, Eliana M.
2020Sci...368..518R Altcode: 2020arXiv200501401R
The magnetic activity of the Sun and other stars causes their brightness
to vary. We investigated how typical the Sun’s variability is
compared with other solar-like stars, i.e., those with near-solar
effective temperatures and rotation periods. By combining 4 years
of photometric observations from the Kepler space telescope with
astrometric data from the Gaia spacecraft, we were able to measure
photometric variabilities of 369 solar-like stars. Most of those with
well-determined rotation periods showed higher variability than the Sun
and are therefore considerably more active. These stars appear nearly
identical to the Sun except for their higher variability. Therefore,
we speculate that the Sun could potentially also go through epochs of
such high variability.
---------------------------------------------------------
Title: Power spectra of solar brightness variations at various
inclinations
Authors: Nèmec, N. -E.; Shapiro, A. I.; Krivova, N. A.; Solanki,
S. K.; Tagirov, R. V.; Cameron, R. H.; Dreizler, S.
2020A&A...636A..43N Altcode: 2020arXiv200210895N
Context. Magnetic features on the surfaces of cool stars lead to
variations in their brightness. Such variations on the surface of
the Sun have been studied extensively. Recent planet-hunting space
telescopes have made it possible to measure brightness variations
in hundred thousands of other stars. The new data may undermine
the validity of setting the sun as a typical example of a variable
star. Putting solar variability into the stellar context suffers,
however, from a bias resulting from solar observations being carried
out from its near-equatorial plane, whereas stars are generally
observed at all possible inclinations. <BR /> Aims: We model solar
brightness variations at timescales from days to years as they would
be observed at different inclinations. In particular, we consider the
effect of the inclination on the power spectrum of solar brightness
variations. The variations are calculated in several passbands that are
routinely used for stellar measurements. <BR /> Methods: We employ the
surface flux transport model to simulate the time-dependent spatial
distribution of magnetic features on both the near and far sides of
the Sun. This distribution is then used to calculate solar brightness
variations following the Spectral And Total Irradiance REconstruction
approach. <BR /> Results: We have quantified the effect of the
inclination on solar brightness variability at timescales down to a
single day. Thus, our results allow for solar brightness records to
be made directly comparable to those obtained by planet-hunting space
telescopes. Furthermore, we decompose solar brightness variations into
components originating from the solar rotation and from the evolution
of magnetic features.
---------------------------------------------------------
Title: 3D Radiative MHD Simulations of Starspots
Authors: Panja, Mayukh; Cameron, Robert; Solanki, Sami K.
2020ApJ...893..113P Altcode: 2020arXiv200309656P
There are no direct spatially resolved observations of spots on stars
other than the Sun, and starspot properties are inferred indirectly
through lightcurves and spectropolarimetric data. We present the first
self-consistent 3D radiative MHD computations of starspots on G2V, K0V,
and M0V stars, which will help us to better understand observations of
activity, variability, and magnetic fields in late-type main-sequence
stars. We used the MURaM code, which has been extensively used to
compute "realistic" sunspots, for our simulations. We aim to study
how fundamental starspot properties such as intensity contrast,
temperature, and magnetic field strength vary with spectral type. We
first simulated in 2D multiple spots of each spectral type to find
out appropriate initial conditions for our 3D runs. We find that
with increasing stellar effective temperature, there is an increase
in the temperature difference between the umbra of the spot and its
surrounding photosphere, from 350 K on the M0V star to 1400 K on the
G2V star. This trend in our simulated starspots is consistent with
observations. The magnetic field strengths of all the starspot umbrae
are in the 3-4.5 kG range. The G2V and K0V umbrae have comparable
magnetic field strengths around 3.5 kG, while the M0V umbra has a
relatively higher field strength around 4 kG. We discuss the physical
reasons behind both these trends. All of the three starspots develop
penumbral filament-like structures with Evershed flows. The average
Evershed flow speed drops from 1.32 km s<SUP>-1</SUP> in the G2V
penumbra to 0.6 km s<SUP>-1</SUP> in the M0V penumbra.
---------------------------------------------------------
Title: Loss of toroidal magnetic flux by emergence of bipolar
magnetic regions
Authors: Cameron, R. H.; Schüssler, M.
2020A&A...636A...7C Altcode: 2020arXiv200205436C
The polarity of the toroidal magnetic field in the solar convection
zone periodically reverses in the course of the 11/22-year solar
cycle. Among the various processes that contribute to the removal of
"old-polarity" toroidal magnetic flux is the emergence of flux loops
forming bipolar regions at the solar surface. We quantify the loss of
subsurface net toroidal flux by this process. To this end, we determine
the contribution of an individual emerging bipolar loop and show that
it is unaffected by surface flux transport after emergence. Together
with the linearity of the diffusion process this means that the
total flux loss can be obtained by adding the contributions of all
emerging bipolar magnetic regions. The resulting total loss rate of
net toroidal flux amounts to 1.3 × 10<SUP>15</SUP> Mx s<SUP>-1</SUP>
during activity maxima and 6.1 × 10<SUP>14</SUP> Mx s<SUP>-1</SUP>
during activity minima, to which ephemeral regions contribute about 90
and 97%, respectively. This rate is consistent with the observationally
inferred loss rate of toroidal flux into interplanetary space and
corresponds to a decay time of the subsurface toroidal flux of about
12 years, also consistent with a simple estimate based on turbulent
diffusivity. Consequently, toroidal flux loss by flux emergence is a
relevant contribution to the budget of net toroidal flux in the solar
convection zone. The consistency between the toroidal flux loss rate
due to flux emergence and what is expected from turbulent diffusion,
and the similarity between the corresponding decay time and the length
of the solar cycle are important constraints for understanding the
solar cycle and the Sun's internal dynamics.
---------------------------------------------------------
Title: The relationship between flux emergence and subsurface toroidal
magnetic flux
Authors: Cameron, R. H.; Jiang, J.
2019A&A...631A..27C Altcode: 2019arXiv190906828C
<BR /> Aims: The 1D mean-field equation describing the evolution of
the subsurface toroidal field can be used with the observed surface
radial field to model the subsurface toroidal flux density. Our aim
is to test this model and determine the relationship between the
observationally inferred surface toroidal field (as a proxy for flux
emergence), and the modelled subsurface toroidal flux density. <BR />
Methods: We used a combination of sunspot area observations and the
surface toroidal field inferred from Wilcox Solar Observatory (WSO)
line-of-sight magnetic field observations. We then compared them with
the results of a 1D mean-field evolution equation for the subsurface
toroidal field, driven by the observed radial field from the National
Solar Observatory/Kitt Peak and SOLIS observations. <BR /> Results:
We derive calibration curves relating the subsurface toroidal flux
density to the observed surface toroidal field strengths and sunspot
areas. The calibration curves are for two regimes, one corresponding to
ephemeral region emergence outside of the butterfly wings, the other
to active region emergence in the butterfly wings. We discuss this in
terms of the size and vertical velocity associated with the two types
of flux emergence.
---------------------------------------------------------
Title: Monte Carlo studies for the optimisation of the Cherenkov
Telescope Array layout
Authors: Acharyya, A.; Agudo, I.; Angüner, E. O.; Alfaro, R.;
Alfaro, J.; Alispach, C.; Aloisio, R.; Alves Batista, R.; Amans,
J. -P.; Amati, L.; Amato, E.; Ambrosi, G.; Antonelli, L. A.; Aramo,
C.; Armstrong, T.; Arqueros, F.; Arrabito, L.; Asano, K.; Ashkar,
H.; Balazs, C.; Balbo, M.; Balmaverde, B.; Barai, P.; Barbano, A.;
Barkov, M.; Barres de Almeida, U.; Barrio, J. A.; Bastieri, D.;
Becerra González, J.; Becker Tjus, J.; Bellizzi, L.; Benbow, W.;
Bernardini, E.; Bernardos, M. I.; Bernlöhr, K.; Berti, A.; Berton,
M.; Bertucci, B.; Beshley, V.; Biasuzzi, B.; Bigongiari, C.; Bird,
R.; Bissaldi, E.; Biteau, J.; Blanch, O.; Blazek, J.; Boisson, C.;
Bonanno, G.; Bonardi, A.; Bonavolontá, C.; Bonnoli, G.; Bordas,
P.; Böttcher, M.; Bregeon, J.; Brill, A.; Brown, A. M.; Brügge,
K.; Brun, P.; Bruno, P.; Bulgarelli, A.; Bulik, T.; Burton, M.;
Burtovoi, A.; Busetto, G.; Cameron, R.; Canestrari, R.; Capalbi, M.;
Caproni, A.; Capuzzo-Dolcetta, R.; Caraveo, P.; Caroff, S.; Carosi,
R.; Casanova, S.; Cascone, E.; Cassol, F.; Catalani, F.; Catalano,
O.; Cauz, D.; Cerruti, M.; Chaty, S.; Chen, A.; Chernyakova, M.;
Chiaro, G.; Cieślar, M.; Colak, S. M.; Conforti, V.; Congiu, E.;
Contreras, J. L.; Cortina, J.; Costa, A.; Costantini, H.; Cotter, G.;
Cristofari, P.; Cumani, P.; Cusumano, G.; D'Aí, A.; D'Ammando, F.;
Dangeon, L.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caprio, V.;
de Cássia dos Anjos, R.; De Frondat, F.; de Gouveia Dal Pino, E. M.;
De Lotto, B.; De Martino, D.; de Naurois, M.; de Oña Wilhelmi, E.;
de Palma, F.; de Souza, V.; Del Santo, M.; Delgado, C.; della Volpe,
D.; Di Girolamo, T.; Di Pierro, F.; Di Venere, L.; Díaz, C.; Diebold,
S.; Djannati-Ataï, A.; Dmytriiev, A.; Dominis Prester, D.; Donini,
A.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Ebr, J.; Ekoume, T. R. N.;
Elsässer, D.; Emery, G.; Falceta-Goncalves, D.; Fedorova, E.; Fegan,
S.; Feng, Q.; Ferrand, G.; Fiandrini, E.; Fiasson, A.; Filipovic,
M.; Fioretti, V.; Fiori, M.; Flis, S.; Fonseca, M. V.; Fontaine, G.;
Freixas Coromina, L.; Fukami, S.; Fukui, Y.; Funk, S.; Füßling,
M.; Gaggero, D.; Galanti, G.; Garcia López, R. J.; Garczarczyk, M.;
Gascon, D.; Gasparetto, T.; Gaug, M.; Ghalumyan, A.; Gianotti, F.;
Giavitto, G.; Giglietto, N.; Giordano, F.; Giroletti, M.; Gironnet,
J.; Glicenstein, J. -F.; Gnatyk, R.; Goldoni, P.; González, J. M.;
González, M. M.; Gourgouliatos, K. N.; Grabarczyk, T.; Granot,
J.; Green, D.; Greenshaw, T.; Grondin, M. -H.; Gueta, O.; Hadasch,
D.; Hassan, T.; Hayashida, M.; Heller, M.; Hervet, O.; Hinton, J.;
Hiroshima, N.; Hnatyk, B.; Hofmann, W.; Horvath, P.; Hrabovsky, M.;
Hrupec, D.; Humensky, T. B.; Hütten, M.; Inada, T.; Iocco, F.; Ionica,
M.; Iori, M.; Iwamura, Y.; Jamrozy, M.; Janecek, P.; Jankowsky, D.;
Jean, P.; Jouvin, L.; Jurysek, J.; Kaaret, P.; Kadowaki, L. H. S.;
Karkar, S.; Kerszberg, D.; Khélifi, B.; Kieda, D.; Kimeswenger,
S.; Kluźniak, W.; Knapp, J.; Knödlseder, J.; Kobayashi, Y.; Koch,
B.; Kocot, J.; Komin, N.; Kong, A.; Kowal, G.; Krause, M.; Kubo,
H.; Kushida, J.; Kushwaha, P.; La Parola, V.; La Rosa, G.; Lallena
Arquillo, M.; Lang, R. G.; Lapington, J.; Le Blanc, O.; Lefaucheur, J.;
Leigui de Oliveira, M. A.; Lemoine-Goumard, M.; Lenain, J. -P.; Leto,
G.; Lico, R.; Lindfors, E.; Lohse, T.; Lombardi, S.; Longo, F.; Lopez,
A.; López, M.; Lopez-Oramas, A.; López-Coto, R.; Loporchio, S.;
Luque-Escamilla, P. L.; Lyard, E.; Maccarone, M. C.; Mach, E.; Maggio,
C.; Majumdar, P.; Malaguti, G.; Mallamaci, M.; Mandat, D.; Maneva, G.;
Manganaro, M.; Mangano, S.; Marculewicz, M.; Mariotti, M.; Martí, J.;
Martínez, M.; Martínez, G.; Martínez-Huerta, H.; Masuda, S.; Maxted,
N.; Mazin, D.; Meunier, J. -L.; Meyer, M.; Micanovic, S.; Millul, R.;
Minaya, I. A.; Mitchell, A.; Mizuno, T.; Moderski, R.; Mohrmann, L.;
Montaruli, T.; Moralejo, A.; Morcuende, D.; Morlino, G.; Morselli, A.;
Moulin, E.; Mukherjee, R.; Munar, P.; Mundell, C.; Murach, T.; Nagai,
A.; Nagayoshi, T.; Naito, T.; Nakamori, T.; Nemmen, R.; Niemiec, J.;
Nieto, D.; Nievas Rosillo, M.; Nikołajuk, M.; Ninci, D.; Nishijima,
K.; Noda, K.; Nosek, D.; Nöthe, M.; Nozaki, S.; Ohishi, M.; Ohtani,
Y.; Okumura, A.; Ong, R. A.; Orienti, M.; Orito, R.; Ostrowski, M.;
Otte, N.; Ou, Z.; Oya, I.; Pagliaro, A.; Palatiello, M.; Palatka, M.;
Paoletti, R.; Paredes, J. M.; Pareschi, G.; Parmiggiani, N.; Parsons,
R. D.; Patricelli, B.; Pe'er, A.; Pech, M.; Peñil Del Campo, P.;
Pérez-Romero, J.; Perri, M.; Persic, M.; Petrucci, P. -O.; Petruk,
O.; Pfrang, K.; Piel, Q.; Pietropaolo, E.; Pohl, M.; Polo, M.;
Poutanen, J.; Prandini, E.; Produit, N.; Prokoph, H.; Prouza, M.;
Przybilski, H.; Pühlhofer, G.; Punch, M.; Queiroz, F.; Quirrenbach,
A.; Rainò, S.; Rando, R.; Razzaque, S.; Reimer, O.; Renault-Tinacci,
N.; Renier, Y.; Ribeiro, D.; Ribó, M.; Rico, J.; Rieger, F.; Rizi,
V.; Rodriguez Fernandez, G.; Rodriguez-Ramirez, J. C.; Rodrí-guez
Vázquez, J. J.; Romano, P.; Romeo, G.; Roncadelli, M.; Rosado,
J.; Rowell, G.; Rudak, B.; Rugliancich, A.; Rulten, C.; Sadeh, I.;
Saha, L.; Saito, T.; Sakurai, S.; Salesa Greus, F.; Sangiorgi, P.;
Sano, H.; Santander, M.; Santangelo, A.; Santos-Lima, R.; Sanuy,
A.; Satalecka, K.; Saturni, F. G.; Sawangwit, U.; Schlenstedt, S.;
Schovanek, P.; Schussler, F.; Schwanke, U.; Sciacca, E.; Scuderi,
S.; Sedlaczek, K.; Seglar-Arroyo, M.; Sergijenko, O.; Seweryn, K.;
Shalchi, A.; Shellard, R. C.; Siejkowski, H.; Sillanpää, A.; Sinha,
A.; Sironi, G.; Sliusar, V.; Slowikowska, A.; Sol, H.; Specovius, A.;
Spencer, S.; Spengler, G.; Stamerra, A.; Stanič, S.; Stawarz, Ł.;
Stefanik, S.; Stolarczyk, T.; Straumann, U.; Suomijarvi, T.; Świerk,
P.; Szepieniec, T.; Tagliaferri, G.; Tajima, H.; Tam, T.; Tavecchio,
F.; Taylor, L.; Tejedor, L. A.; Temnikov, P.; Terzic, T.; Testa, V.;
Tibaldo, L.; Todero Peixoto, C. J.; Tokanai, F.; Tomankova, L.; Tonev,
D.; Torres, D. F.; Tosti, G.; Tosti, L.; Tothill, N.; Toussenel, F.;
Tovmassian, G.; Travnicek, P.; Trichard, C.; Umana, G.; Vagelli, V.;
Valentino, M.; Vallage, B.; Vallania, P.; Valore, L.; Vandenbroucke,
J.; Varner, G. S.; Vasileiadis, G.; Vassiliev, V.; Vázquez Acosta,
M.; Vecchi, M.; Vercellone, S.; Vergani, S.; Vettolani, G. P.; Viana,
A.; Vigorito, C. F.; Vink, J.; Vitale, V.; Voelk, H.; Vollhardt,
A.; Vorobiov, S.; Wagner, S. J.; Walter, R.; Werner, F.; White,
R.; Wierzcholska, A.; Will, M.; Williams, D. A.; Wischnewski, R.;
Yang, L.; Yoshida, T.; Yoshikoshi, T.; Zacharias, M.; Zampieri, L.;
Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A. A.; Zech, A.; Zechlin,
H.; Zenin, A.; Zhdanov, V. I.; Zimmer, S.; Zorn, J.
2019APh...111...35A Altcode: 2019arXiv190401426A
The Cherenkov Telescope Array (CTA) is the major next-generation
observatory for ground-based very-high-energy gamma-ray astronomy. It
will improve the sensitivity of current ground-based instruments by a
factor of five to twenty, depending on the energy, greatly improving
both their angular and energy resolutions over four decades in energy
(from 20 GeV to 300 TeV). This achievement will be possible by using
tens of imaging Cherenkov telescopes of three successive sizes. They
will be arranged into two arrays, one per hemisphere, located on
the La Palma island (Spain) and in Paranal (Chile). We present here
the optimised and final telescope arrays for both CTA sites, as well
as their foreseen performance, resulting from the analysis of three
different large-scale Monte Carlo productions.
---------------------------------------------------------
Title: Solar activity: periodicities beyond 11 years are consistent
with random forcing
Authors: Cameron, R. H.; Schüssler, M.
2019A&A...625A..28C Altcode:
Power spectra of solar activity based on historical records of sunspot
numbers and on cosmogenic isotopes show peaks with enhanced power
apart from the dominant 11-year solar cycle, such as the 90-year
Gleissberg cycle or the 210-year de Vries cycle. In a previous paper
we have shown that the overall shape of the power spectrum is well
represented by the results of the generic normal form model for a
noisy and weakly nonlinear limit cycle, with parameters all determined
by observations. Using this model as a null case, we show here that
all local peaks with enhanced power, apart from the 11-year band,
are consistent with realization noise. Even a 3σ peak is expected
to occur with a probability of about 0.25 at least once among the 216
period bins resolved by the cosmogenic isotope data. This casts doubt
upon interpretations of such peaks in terms of intrinsic periodicities
of the solar dynamo process.
---------------------------------------------------------
Title: Average motion of emerging solar active region
polarities. I. Two phases of emergence
Authors: Schunker, H.; Birch, A. C.; Cameron, R. H.; Braun, D. C.;
Gizon, L.; Burston, R. B.
2019A&A...625A..53S Altcode: 2019arXiv190311839S
<BR /> Aims: Our goal is to constrain models of active region
formation by tracking the average motion of active region polarity
pairs as they emerge onto the surface. <BR /> Methods: We measured
the motion of the two main opposite polarities in 153 emerging active
regions using line-of-sight magnetic field observations from the Solar
Dynamics Observatory Helioseismic Emerging Active Region (SDO/HEAR)
survey. We first measured the position of each of the polarities
eight hours after emergence, when they could be clearly identified,
using a feature recognition method. We then tracked their location
forwards and backwards in time. <BR /> Results: We find that, on
average, the polarities emerge with an east-west orientation and the
separation speed between the polarities increases. At about 0.1 days
after emergence, the average separation speed reaches a peak value
of 229 ± 11 ms<SUP>-1</SUP>, and then starts to decrease. About
2.5 days after emergence the polarities stop separating. We also
find that the separation and the separation speed in the east-west
direction are systematically larger for active regions that have
higher flux. The scatter in the location of the polarities increases
from about 5 Mm at the time of emergence to about 15 Mm at two days
after emergence. <BR /> Conclusions: Our results reveal two phases of
the emergence process defined by the rate of change of the separation
speed as the polarities move apart. Phase 1 begins when the opposite
polarity pairs first appear at the surface, with an east-west alignment
and an increasing separation speed. We define Phase 2 to begin when
the separation speed starts to decrease, and ends when the polarities
have stopped separating. This is consistent with a previous study: the
peak of a flux tube breaks through the surface during Phase 1. During
Phase 2 the magnetic field lines are straightened by magnetic tension,
so that the polarities continue to move apart, until they eventually
lie directly above their anchored subsurface footpoints. The scatter
in the location of the polarities is consistent with the length and
timescales of supergranulation, supporting the idea that convection
buffets the polarities as they separate.
---------------------------------------------------------
Title: Solar activity: intrinsic periodicities beyond 11 years
Authors: Cameron, Robert; Schuessler, Manfred
2019arXiv190305398C Altcode:
Power spectra of solar activity based on historical records of sunspot
numbers and on cosmogenic isotopes show peaks with enhanced power
apart from the dominant 11-year solar cycle, such as the 90-year
Gleissberg cycle or the 210-year de Vries cycle. In a previous paper
we have shown that the overall shape of the power spectrum is well
represented by the results of the generic normal form model for a
noisy and weakly nonlinear limit cycle, with parameters all determined
by observations. Using this model as a null case, we show here that
all local peaks with enhanced power, apart from the 11-year band, are
consistent with realisation noise. Even a $3\sigma$ peak is expected
to occur with a probability of about 0.25 at least once among the 216
period bins resolved by the cosmogenic isotope data. This casts doubt
upon interpretations of such peaks in terms of intrinsic periodicities
of the solar dynamo process.
---------------------------------------------------------
Title: Starspot rotation rates versus activity cycle phase: Butterfly
diagrams of Kepler stars are unlike that of the Sun
Authors: Nielsen, M. B.; Gizon, L.; Cameron, R. H.; Miesch, M.
2019A&A...622A..85N Altcode: 2018arXiv181206414N
Context. During the solar magnetic activity cycle the emergence
latitudes of sunspots change, leading to the well-known butterfly
diagram. This phenomenon is poorly understood for other stars since
starspot latitudes are generally unknown. The related changes in
starspot rotation rates caused by latitudinal differential rotation can,
however, be measured. <BR /> Aims: Using the set of 3093 Kepler stars
with measured activity cycles, we aim to study the temporal change in
starspot rotation rates over magnetic activity cycles, and how this
relates to the activity level, the mean rotation rate of the star, and
its effective temperature. <BR /> Methods: We measured the photometric
variability as a proxy for the magnetic activity and the spot rotation
rate in each quarter over the duration of the Kepler mission. We
phase-folded these measurements with the cycle period. To reduce random
errors, we performed averages over stars with comparable mean rotation
rates and effective temperature at fixed activity-cycle phases. <BR />
Results: We detect a clear correlation between the variation of activity
level and the variation of the starspot rotation rate. The sign and
amplitude of this correlation depends on the mean stellar rotation and -
to a lesser extent - on the effective temperature. For slowly rotating
stars (rotation periods between 15 - 28 days), the starspot rotation
rates are clearly anti-correlated with the level of activity during
the activity cycles. A transition is observed around rotation periods
of 10 - 15 days, where stars with an effective temperature above 4200 K
instead show positive correlation. <BR /> Conclusions: Our measurements
can be interpreted in terms of a stellar "butterfly diagram",
but these appear different from that of the Sun since the starspot
rotation rates are either in phase or anti-phase with the activity
level. Alternatively, the activity cycle periods observed by Kepler are
short (around 2.5 years) and may therefore be secondary cycles, perhaps
analogous to the solar quasi-biennial oscillations. <P />Rotation and
activity tables are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A85">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A85</A>
---------------------------------------------------------
Title: The solar dynamo: Inferences from observations
Authors: Cameron, Robert
2018csc..confE...4C Altcode:
We will show that the observed large-scale structure of the poloidal and
toroidal magnetic fields, together with the differential rotation and
surface meridional flow argue strongly in favour of a Babcock-Leighton
dynamo. The cycle-to-cycle variability is consistent with the idea
that flux emergence takes place in a turbulent environment, and we will
discuss some of the implications of this in the context of the model.
---------------------------------------------------------
Title: Statistical constraints on active region emergence from the
surface motion of the polarities
Authors: Schunker, Hannah; Birch, Aaron; Cameron, Robert; Braun,
Doug; Gizon, Laurent
2018csc..confE..45S Altcode:
We measured the motion of the two main opposite polarities in
154 emerging active regions using line-of-sight magnetograms from
SDO/HMI. Our results reveal two phases of the emergence process defined
by the rate of change of the separation speed as the polarities move
apart. Phase one begins when the opposite polarity pairs first appear at
the surface, with an east-west alignment and an increasing separation
speed of 1.6 +/- 0.4 km/s. Phase two begins when the separation speed
starts to decrease, about 0.1 days after emergence, and ends about 2.5
days after emergence when the polarities have stopped separating. This
is consistent with the picture of Chen, Rempel, & Fan (2017):
during phase one, the peak of a flux tube breaks through the surface
and then, during phase two, the magnetic field lines are straightened
by magnetic tension to eventually lie directly above their subsurface
footpoints. The scatter in the location of the polarities is consistent
with the length and time scales of supergranulation, supporting the idea
that convection buffets the polarities as they separate. On average,
the polarities emerge with an east-west orientation with the tilt angle
developing over time independent of flux, in contrast to predictions
from thin flux tube theory.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Starspot rotation rates
vs. activity cycle phase (Nielsen+, 2019)
Authors: Nielsen, M. B.; Gizon, L.; Cameron, R. H.; Miesch, M.
2018yCat..36220085N Altcode:
Activity cycle parameters for 3093 stars observed by Kepler, with
measured cycle periods from Reinhold et al. (2017A&A...603A..52R,
Cat. J/A+A/603/A52). The integral, A, of the power density
spectrum around the mean rotation rate (nurot, from McQuillan et
al. (2014ApJS..211...24M, Cat. J/ApJS/211/24)) is used as proxy for
magnetic activity. This and the rotation rate, nu, are traced from
quarters Q1 to Q17 of Kepler observations. <P />(1 data file).
---------------------------------------------------------
Title: Origin of the hemispheric asymmetry of solar activity
Authors: Schüssler, M.; Cameron, R. H.
2018A&A...618A..89S Altcode: 2018arXiv180710061S
The frequency spectrum of the hemispheric asymmetry of solar activity
shows enhanced power for the period ranges around 8.5 years and
between 30 and 50 years. This can be understood as the sum and beat
periods of the superposition of two dynamo modes: a dipolar mode with
a (magnetic) period of about 22 years and a quadrupolar mode with a
period between 13 and 15 years. An updated Babcock-Leighton-type dynamo
model with weak driving as indicated by stellar observations shows
an excited dipole mode and a damped quadrupole mode in the correct
range of periods. Random excitation of the quadrupole by stochastic
fluctuations of the source term for the poloidal field leads to a
time evolution of activity and asymmetry that is consistent with the
observational results.
---------------------------------------------------------
Title: Chromospheric activity catalogue of 4454 cool
stars. Questioning the active branch of stellar activity cycles
Authors: Boro Saikia, S.; Marvin, C. J.; Jeffers, S. V.; Reiners,
A.; Cameron, R.; Marsden, S. C.; Petit, P.; Warnecke, J.; Yadav, A. P.
2018A&A...616A.108B Altcode: 2018A&A...616A.108S; 2018arXiv180311123B
Context. Chromospheric activity monitoring of a wide range of cool
stars can provide valuable information on stellar magnetic activity
and its dependence on fundamental stellar parameters such as effective
temperature and rotation. <BR /> Aims: We compile a chromospheric
activity catalogue of 4454 cool stars from a combination of archival
HARPS spectra and multiple other surveys, including the Mount Wilson
data that have recently been released by the NSO. We explore the
variation in chromospheric activity of cool stars along the main
sequence for stars with different effective temperatures. Additionally,
we also perform an activity-cycle period search and investigate its
relation with rotation. <BR /> Methods: The chromospheric activity
index, S-index, was measured for 304 main-sequence stars from
archived high-resolution HARPS spectra. Additionally, the measured
and archived S-indices were converted into the chromospheric flux
ratio log R<SUB>HK</SUB><SUP>'</SUP>. The activity-cycle periods were
determined using the generalised Lomb-Scargle periodogram to study
the active and inactive branches on the rotation - activity-cycle
period plane. <BR /> Results: The global sample shows that the
bimodality of chromospheric activity, known as the Vaughan-Preston
gap, is not prominent, with a significant percentage of the stars at
an intermediate-activity level around R<SUP>'</SUP><SUB>HK</SUB> =
-4.75. Independently, the cycle period search shows that stars can lie
in the region intermediate between the active and inactive branch, which
means that the active branch is not as clearly distinct as previously
thought. <BR /> Conclusions: The weakening of the Vaughan-Preston
gap indicates that cool stars spin down from a higher activity
level and settle at a lower activity level without a sudden break
at intermediate activity. Some cycle periods are close to the solar
value between the active and inactive branch, which suggests that the
solar dynamo is most likely a common case of the stellar dynamo. <P
/>Full Table A.1 is only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A
href="http://cdsarc.u-strasbg.fr">http://130.79.128.5</A>) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/616/A108">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/616/A108</A>
---------------------------------------------------------
Title: VizieR Online Data Catalog: Cool stars chromospheric activity
catalog (Boro Saikia+, 2018)
Authors: Boro Saikia, S.; Marvin, C. J.; Jeffers, S. V.; Reiners,
A.; Cameron, R.; Marsden, S. C.; Petit, P.; Warnecke, J.; Yadav, A. P.
2018yCat..36160108B Altcode:
We tabulate chromospheric activity of cool stars determined from
CaII H and K lines. The catalogue is created by combining archival
HARPS spectra (Lovis et al. 2011, Cat. J/A+A/528/112, Bonfils et
al. 2013A&A...549A.109B) and multiple other surveys (Baliunas
et al. 1995ApJ...438..269B, Duncan et al. 1991ApJS...76..383D,
Cat. III/159, Arriagada et al. 2012, Cat. J/ApJS/200/15, Henry et
al. 1996, Cat. J/AJ/111/439, Gray et al. 2006, Cat. J/AJ/132/161, Hall
et al. 2009, Cat. J/AJ/138/312, Wright et al. 2004, Cat. J/ApJS/152/261,
Issacson & Fischer 2010, Cat. J/ApJ/725/875). The stellar properties
are taken from HIPPARCOS (Cat. I/239). <P />(1 data file).
---------------------------------------------------------
Title: Observing and modeling the poloidal and toroidal fields of
the solar dynamo
Authors: Cameron, R. H.; Duvall, T. L.; Schüssler, M.; Schunker, H.
2018A&A...609A..56C Altcode: 2017arXiv171007126C
Context. The solar dynamo consists of a process that converts poloidal
magnetic field to toroidal magnetic field followed by a process that
creates new poloidal field from the toroidal field. <BR /> Aims:
Our aim is to observe the poloidal and toroidal fields relevant to
the global solar dynamo and to see if their evolution is captured by
a Babcock-Leighton dynamo. <BR /> Methods: We used synoptic maps of
the surface radial field from the KPNSO/VT and SOLIS observatories,
to construct the poloidal field as a function of time and latitude; we
also used full disk images from Wilcox Solar Observatory and SOHO/MDI
to infer the longitudinally averaged surface azimuthal field. We show
that the latter is consistent with an estimate of the longitudinally
averaged surface azimuthal field due to flux emergence and therefore
is closely related to the subsurface toroidal field. <BR /> Results: We
present maps of the poloidal and toroidal magnetic fields of the global
solar dynamo. The longitude-averaged azimuthal field observed at the
surface results from flux emergence. At high latitudes this component
follows the radial component of the polar fields with a short time
lag of between 1-3 years. The lag increases at lower latitudes. The
observed evolution of the poloidal and toroidal magnetic fields is
described by the (updated) Babcock-Leighton dynamo model.
---------------------------------------------------------
Title: The Global Solar Dynamo
Authors: Cameron, R. H.; Dikpati, M.; Brandenburg, A.
2018smf..book..367C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Fermi Large Area Telescope: 9 years of on-orbit performance
Authors: Cameron, R.; Fermi Large Area Telescope Collaboration
2017ifs..confE.128C Altcode: 2017PoS...312E.128C
No abstract at ADS
---------------------------------------------------------
Title: The Global Solar Dynamo
Authors: Cameron, R. H.; Dikpati, M.; Brandenburg, A.
2017SSRv..210..367C Altcode: 2016arXiv160201754C; 2016SSRv..tmp....5C
A brief summary of the various observations and constraints
that underlie solar dynamo research are presented. The arguments
that indicate that the solar dynamo is an alpha-omega dynamo of
the Babcock-Leighton type are then shortly reviewed. The main open
questions that remain are concerned with the subsurface dynamics,
including why sunspots emerge at preferred latitudes as seen in
the familiar butterfly wings, why the cycle is about 11 years long,
and why the sunspot groups emerge tilted with respect to the equator
(Joy's law). Next, we turn to magnetic helicity, whose conservation
property has been identified with the decline of large-scale magnetic
fields found in direct numerical simulations at large magnetic Reynolds
numbers. However, magnetic helicity fluxes through the solar surface
can alleviate this problem and connect theory with observations,
as will be discussed.
---------------------------------------------------------
Title: Cherenkov Telescope Array Contributions to the 35th
International Cosmic Ray Conference (ICRC2017)
Authors: Acero, F.; Acharya, B. S.; Acín Portella, V.; Adams, C.;
Agudo, I.; Aharonian, F.; Samarai, I. Al; Alberdi, A.; Alcubierre,
M.; Alfaro, R.; Alfaro, J.; Alispach, C.; Aloisio, R.; Alves Batista,
R.; Amans, J. -P.; Amato, E.; Ambrogi, L.; Ambrosi, G.; Ambrosio, M.;
Anderson, J.; Anduze, M.; Angüner, E. O.; Antolini, E.; Antonelli,
L. A.; Antonuccio, V.; Antoranz, P.; Aramo, C.; Araya, M.; Arcaro, C.;
Armstrong, T.; Arqueros, F.; Arrabito, L.; Arrieta, M.; Asano, K.;
Asano, A.; Ashley, M.; Aubert, P.; Singh, C. B.; Babic, A.; Backes,
M.; Bajtlik, S.; Balazs, C.; Balbo, M.; Ballester, O.; Ballet, J.;
Ballo, L.; Balzer, A.; Bamba, A.; Bandiera, R.; Barai, P.; Barbier,
C.; Barcelo, M.; Barkov, M.; Barres de Almeida, U.; Barrio, J. A.;
Bastieri, D.; Bauer, C.; Becciani, U.; Becherini, Y.; Becker Tjus,
J.; Bednarek, W.; Belfiore, A.; Benbow, W.; Benito, M.; Berge, D.;
Bernardini, E.; Bernardini, M. G.; Bernardos, M.; Bernhard, S.;
Bernlöhr, K.; Bertinelli Salucci, C.; Bertucci, B.; Besel, M. -A.;
Beshley, V.; Bettane, J.; Bhatt, N.; Bhattacharyya, W.; Bhattachryya,
S.; Biasuzzi, B.; Bicknell, G.; Bigongiari, C.; Biland, A.; Bilinsky,
A.; Bird, R.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blanch, O.;
Blasi, P.; Blazek, J.; Boccato, C.; Bockermann, C.; Boehm, C.;
Bohacova, M.; Boisson, C.; Bolmont, J.; Bonanno, G.; Bonardi, A.;
Bonavolontà, C.; Bonnoli, G.; Borkowski, J.; Bose, R.; Bosnjak,
Z.; Böttcher, M.; Boutonnet, C.; Bouyjou, F.; Bowman, L.; Bozhilov,
V.; Braiding, C.; Brau-Nogué, S.; Bregeon, J.; Briggs, M.; Brill,
A.; Brisken, W.; Bristow, D.; Britto, R.; Brocato, E.; Brown, A. M.;
Brown, S.; Brügge, K.; Brun, P.; Brun, P.; Brun, F.; Brunetti, L.;
Brunetti, G.; Bruno, P.; Bryan, M.; Buckley, J.; Bugaev, V.; Bühler,
R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto, G.;
Buson, S.; Buss, J.; Byrum, K.; Caccianiga, A.; Cameron, R.; Canelli,
F.; Canestrari, R.; Capalbi, M.; Capasso, M.; Capitanio, F.; Caproni,
A.; Capuzzo-Dolcetta, R.; Caraveo, P.; Cárdenas, V.; Cardenzana,
J.; Cardillo, M.; Carlile, C.; Caroff, S.; Carosi, R.; Carosi, A.;
Carquín, E.; Carr, J.; Casandjian, J. -M.; Casanova, S.; Cascone, E.;
Castro-Tirado, A. J.; Castroviejo Mora, J.; Catalani, F.; Catalano, O.;
Cauz, D.; Celestino Silva, C.; Celli, S.; Cerruti, M.; Chabanne, E.;
Chadwick, P.; Chakraborty, N.; Champion, C.; Chatterjee, A.; Chaty, S.;
Chaves, R.; Chen, A.; Chen, X.; Cheng, K.; Chernyakova, M.; Chikawa,
M.; Chitnis, V. R.; Christov, A.; Chudoba, J.; Cieślar, M.; Clark,
P.; Coco, V.; Colafrancesco, S.; Colin, P.; Colombo, E.; Colome, J.;
Colonges, S.; Conforti, V.; Connaughton, V.; Conrad, J.; Contreras,
J. L.; Cornat, R.; Cortina, J.; Costa, A.; Costantini, H.; Cotter, G.;
Courty, B.; Covino, S.; Covone, G.; Cristofari, P.; Criswell, S. J.;
Crocker, R.; Croston, J.; Crovari, C.; Cuadra, J.; Cuevas, O.; Cui,
X.; Cumani, P.; Cusumano, G.; D'Aì, A.; D'Ammando, F.; D'Avanzo,
P.; D'Urso, D.; Da Vela, P.; Dale, Ø.; Dang, V. T.; Dangeon, L.;
Daniel, M.; Davids, I.; Dawson, B.; Dazzi, F.; De Angelis, A.; De
Caprio, V.; de Cássia dos Anjos, R.; De Cesare, G.; De Franco, A.;
De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De Lisio,
C.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; De Lucia, M.;
de Mello Neto, J. R. T.; de Naurois, M.; de Oña Wilhelmi, E.; De
Palma, F.; De Persio, F.; de Souza, V.; Decock, J.; Deil, C.; Deiml,
P.; Del Santo, M.; Delagnes, E.; Deleglise, G.; Delfino Reznicek, M.;
Delgado, C.; Delgado Mengual, J.; Della Ceca, R.; della Volpe, D.;
Detournay, M.; Devin, J.; Di Girolamo, T.; Di Giulio, C.; Di Pierro,
F.; Di Venere, L.; Diaz, L.; Díaz, C.; Dib, C.; Dickinson, H.;
Diebold, S.; Digel, S.; Djannati-Ataï, A.; Doert, M.; Domínguez,
A.; Dominis Prester, D.; Donnarumma, I.; Dorner, D.; Doro, M.;
Dournaux, J. -L.; Downes, T.; Drake, G.; Drappeau, S.; Drass, H.;
Dravins, D.; Drury, L.; Dubus, G.; Dundas Morå, K.; Durkalec, A.;
Dwarkadas, V.; Ebr, J.; Eckner, C.; Edy, E.; Egberts, K.; Einecke,
S.; Eisch, J.; Eisenkolb, F.; Ekoume, T. R. N.; Eleftheriadis, C.;
Elsässer, D.; Emmanoulopoulos, D.; Ernenwein, J. -P.; Escarate,
P.; Eschbach, S.; Espinoza, C.; Evans, P.; Evoli, C.; Fairbairn, M.;
Falceta-Goncalves, D.; Falcone, A.; Fallah Ramazani, V.; Farakos, K.;
Farrell, E.; Fasola, G.; Favre, Y.; Fede, E.; Fedora, R.; Fedorova,
E.; Fegan, S.; Fernandez-Alonso, M.; Fernández-Barral, A.; Ferrand,
G.; Ferreira, O.; Fesquet, M.; Fiandrini, E.; Fiasson, A.; Filipovic,
M.; Fink, D.; Finley, J. P.; Finley, C.; Finoguenov, A.; Fioretti,
V.; Fiorini, M.; Flores, H.; Foffano, L.; Föhr, C.; Fonseca, M. V.;
Font, L.; Fontaine, G.; Fornasa, M.; Fortin, P.; Fortson, L.; Fouque,
N.; Fraga, B.; Franco, F. J.; Freixas Coromina, L.; Fruck, C.; Fugazza,
D.; Fujita, Y.; Fukami, S.; Fukazawa, Y.; Fukui, Y.; Funk, S.; Furniss,
A.; Füßling, M.; Gabici, S.; Gadola, A.; Gallant, Y.; Galloway, D.;
Gallozzi, S.; Garcia, B.; Garcia, A.; García Gil, R.; Garcia López,
R.; Garczarczyk, M.; Gardiol, D.; Gargano, F.; Gargano, C.; Garozzo,
S.; Garrido-Ruiz, M.; Gascon, D.; Gasparetto, T.; Gaté, F.; Gaug,
M.; Gebhardt, B.; Gebyehu, M.; Geffroy, N.; Genolini, B.; Ghalumyan,
A.; Ghedina, A.; Ghirlanda, G.; Giammaria, P.; Gianotti, F.; Giebels,
B.; Giglietto, N.; Gika, V.; Gimenes, R.; Giommi, P.; Giordano, F.;
Giovannini, G.; Giro, E.; Giroletti, M.; Gironnet, J.; Giuliani, A.;
Glicenstein, J. -F.; Gnatyk, R.; Godinovic, N.; Goldoni, P.; Gómez,
J. L.; Gómez-Vargas, G.; González, M. M.; González, J. M.; Gothe,
K. S.; Gotz, D.; Goullon, J.; Grabarczyk, T.; Graciani, R.; Graham,
J.; Grandi, P.; Granot, J.; Grasseau, G.; Gredig, R.; Green, A. J.;
Greenshaw, T.; Grenier, I.; Griffiths, S.; Grillo, A.; Grondin, M. -H.;
Grube, J.; Guarino, V.; Guest, B.; Gueta, O.; Gunji, S.; Gyuk, G.;
Hadasch, D.; Hagge, L.; Hahn, J.; Hahn, A.; Hakobyan, H.; Hara, S.;
Hardcastle, M. J.; Hassan, T.; Haubold, T.; Haupt, A.; Hayashi, K.;
Hayashida, M.; He, H.; Heller, M.; Helo, J. C.; Henault, F.; Henri, G.;
Hermann, G.; Hermel, R.; Herrera Llorente, J.; Herrero, A.; Hervet, O.;
Hidaka, N.; Hinton, J.; Hiroshima, N.; Hirotani, K.; Hnatyk, B.; Hoang,
J. K.; Hoffmann, D.; Hofmann, W.; Holder, J.; Horan, D.; Hörandel,
J.; Hörbe, M.; Horns, D.; Horvath, P.; Houles, J.; Hovatta, T.;
Hrabovsky, M.; Hrupec, D.; Huet, J. -M.; Hughes, G.; Hui, D.; Hull,
G.; Humensky, T. B.; Hussein, M.; Hütten, M.; Iarlori, M.; Ikeno,
Y.; Illa, J. M.; Impiombato, D.; Inada, T.; Ingallinera, A.; Inome,
Y.; Inoue, S.; Inoue, T.; Inoue, Y.; Iocco, F.; Ioka, K.; Ionica,
M.; Iori, M.; Iriarte, A.; Ishio, K.; Israel, G. L.; Iwamura, Y.;
Jablonski, C.; Jacholkowska, A.; Jacquemier, J.; Jamrozy, M.; Janecek,
P.; Jankowsky, F.; Jankowsky, D.; Jansweijer, P.; Jarnot, C.; Jean, P.;
Johnson, C. A.; Josselin, M.; Jung-Richardt, I.; Jurysek, J.; Kaaret,
P.; Kachru, P.; Kagaya, M.; Kakuwa, J.; Kalekin, O.; Kankanyan, R.;
Karastergiou, A.; Karczewski, M.; Karkar, S.; Katagiri, H.; Kataoka,
J.; Katarzyński, K.; Katz, U.; Kawanaka, N.; Kaye, L.; Kazanas, D.;
Kelley-Hoskins, N.; Khélifi, B.; Kieda, D. B.; Kihm, T.; Kimeswenger,
S.; Kimura, S.; Kisaka, S.; Kishida, S.; Kissmann, R.; Kluźniak, W.;
Knapen, J.; Knapp, J.; Knödlseder, J.; Koch, B.; Kocot, J.; Kohri,
K.; Komin, N.; Kong, A.; Konno, Y.; Kosack, K.; Kowal, G.; Koyama,
S.; Kraus, M.; Krause, M.; Krauß, F.; Krennrich, F.; Kruger, P.;
Kubo, H.; Kudryavtsev, V.; Kukec Mezek, G.; Kumar, S.; Kuroda, H.;
Kushida, J.; Kushwaha, P.; La Palombara, N.; La Parola, V.; La Rosa,
G.; Lahmann, R.; Lalik, K.; Lamanna, G.; Landoni, M.; Landriu, D.;
Landt, H.; Lang, R. G.; Lapington, J.; Laporte, P.; Le Blanc, O.;
Le Flour, T.; Le Sidaner, P.; Leach, S.; Leckngam, A.; Lee, S. -H.;
Lee, W. H.; Lees, J. -P.; Lefaucheur, J.; Leigui de Oliveira, M. A.;
Lemoine-Goumard, M.; Lenain, J. -P.; Leto, G.; Lico, R.; Limon, M.;
Lindemann, R.; Lindfors, E.; Linhoff, L.; Lipniacka, A.; Lloyd, S.;
Lohse, T.; Lombardi, S.; Longo, F.; Lopez, M.; Lopez-Coto, R.; Louge,
T.; Louis, F.; Louys, M.; Lucarelli, F.; Lucchesi, D.; Luque-Escamilla,
P. L.; Lyard, E.; Maccarone, M. C.; Maccarone, T.; Mach, E.; Madejski,
G. M.; Maier, G.; Majczyna, A.; Majumdar, P.; Makariev, M.; Malaguti,
G.; Malouf, A.; Maltezos, S.; Malyshev, D.; Malyshev, D.; Mandat,
D.; Maneva, G.; Manganaro, M.; Mangano, S.; Manigot, P.; Mannheim,
K.; Maragos, N.; Marano, D.; Marcowith, A.; Marín, J.; Mariotti,
M.; Marisaldi, M.; Markoff, S.; Martí, J.; Martin, J. -M.; Martin,
P.; Martin, L.; Martínez, M.; Martínez, G.; Martínez, O.; Marx,
R.; Masetti, N.; Massimino, P.; Mastichiadis, A.; Mastropietro, M.;
Masuda, S.; Matsumoto, H.; Matthews, N.; Mattiazzo, S.; Maurin, G.;
Maxted, N.; Mayer, M.; Mazin, D.; Mazziotta, M. N.; Mc Comb, L.;
McHardy, I.; Medina, C.; Melandri, A.; Melioli, C.; Melkumyan, D.;
Mereghetti, S.; Meunier, J. -L.; Meures, T.; Meyer, M.; Micanovic, S.;
Michael, T.; Michałowski, J.; Mievre, I.; Miller, J.; Minaya, I. A.;
Mineo, T.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mitchell, A.;
Mizuno, T.; Moderski, R.; Mohammed, M.; Mohrmann, L.; Molijn, C.;
Molinari, E.; Moncada, R.; Montaruli, T.; Monteiro, I.; Mooney, D.;
Moore, P.; Moralejo, A.; Morcuende-Parrilla, D.; Moretti, E.; Mori,
K.; Morlino, G.; Morris, P.; Morselli, A.; Moscato, F.; Motohashi,
D.; Moulin, E.; Mueller, S.; Mukherjee, R.; Munar, P.; Mundell, C.;
Mundet, J.; Murach, T.; Muraishi, H.; Murase, K.; Murphy, A.; Nagai,
A.; Nagar, N.; Nagataki, S.; Nagayoshi, T.; Nagesh, B. K.; Naito,
T.; Nakajima, D.; Nakamori, T.; Nakamura, Y.; Nakayama, K.; Naumann,
D.; Nayman, P.; Neise, D.; Nellen, L.; Nemmen, R.; Neronov, A.;
Neyroud, N.; Nguyen, T.; Nguyen, T. T.; Nguyen Trung, T.; Nicastro,
L.; Nicolau-Kukliński, J.; Niemiec, J.; Nieto, D.; Nievas-Rosillo,
M.; Nikołajuk, M.; Nishijima, K.; Nishikawa, K. -I.; Nishiyama, G.;
Noda, K.; Nogues, L.; Nolan, S.; Nosek, D.; Nöthe, M.; Novosyadlyj,
B.; Nozaki, S.; Nunio, F.; O'Brien, P.; Oakes, L.; Ocampo, C.; Ochoa,
J. P.; Oger, R.; Ohira, Y.; Ohishi, M.; Ohm, S.; Okazaki, N.; Okumura,
A.; Olive, J. -F.; Ong, R. A.; Orienti, M.; Orito, R.; Orlati, A.;
Osborne, J. P.; Ostrowski, M.; Otte, N.; Ou, Z.; Ovcharov, E.; Oya,
I.; Ozieblo, A.; Padovani, M.; Paiano, S.; Paizis, A.; Palacio, J.;
Palatiello, M.; Palatka, M.; Pallotta, J.; Panazol, J. -L.; Paneque,
D.; Panter, M.; Paoletti, R.; Paolillo, M.; Papitto, A.; Paravac, A.;
Paredes, J. M.; Pareschi, G.; Parsons, R. D.; Paśko, P.; Pavy, S.;
Pe'er, A.; Pech, M.; Pedaletti, G.; Peñil Del Campo, P.; Perez, A.;
Pérez-Torres, M. A.; Perri, L.; Perri, M.; Persic, M.; Petrashyk,
A.; Petrera, S.; Petrucci, P. -O.; Petruk, O.; Peyaud, B.; Pfeifer,
M.; Piano, G.; Piel, Q.; Pieloth, D.; Pintore, F.; García, C. Pio;
Pisarski, A.; Pita, S.; Pizarro, L.; Platos, Ł.; Pohl, M.; Poireau,
V.; Pollo, A.; Porthault, J.; Poutanen, J.; Pozo, D.; Prandini, E.;
Prasit, P.; Prast, J.; Pressard, K.; Principe, G.; Prokhorov, D.;
Prokoph, H.; Prouza, M.; Pruteanu, G.; Pueschel, E.; Pühlhofer,
G.; Puljak, I.; Punch, M.; Pürckhauer, S.; Queiroz, F.; Quinn, J.;
Quirrenbach, A.; Rafighi, I.; Rainò, S.; Rajda, P. J.; Rando, R.;
Rannot, R. C.; Razzaque, S.; Reichardt, I.; Reimer, O.; Reimer, A.;
Reisenegger, A.; Renaud, M.; Reposeur, T.; Reville, B.; Rezaeian,
A. H.; Rhode, W.; Ribeiro, D.; Ribó, M.; Richer, M. G.; Richtler,
T.; Rico, J.; Rieger, F.; Riquelme, M.; Ristori, P. R.; Rivoire, S.;
Rizi, V.; Rodriguez, J.; Rodriguez Fernandez, G.; Rodríguez Vázquez,
J. J.; Rojas, G.; Romano, P.; Romeo, G.; Roncadelli, M.; Rosado, J.;
Rosen, S.; Rosier Lees, S.; Rousselle, J.; Rovero, A. C.; Rowell, G.;
Rudak, B.; Rugliancich, A.; Ruíz del Mazo, J. E.; Rujopakarn, W.;
Rulten, C.; Russo, F.; Saavedra, O.; Sabatini, S.; Sacco, B.; Sadeh,
I.; Sæther Hatlen, E.; Safi-Harb, S.; Sahakian, V.; Sailer, S.; Saito,
T.; Sakaki, N.; Sakurai, S.; Salek, D.; Salesa Greus, F.; Salina, G.;
Sanchez, D.; Sánchez-Conde, M.; Sandaker, H.; Sandoval, A.; Sangiorgi,
P.; Sanguillon, M.; Sano, H.; Santander, M.; Santangelo, A.; Santos,
E. M.; Sanuy, A.; Sapozhnikov, L.; Sarkar, S.; Satalecka, K.; Sato,
Y.; Saturni, F. G.; Savalle, R.; Sawada, M.; Schanne, S.; Schioppa,
E. J.; Schlenstedt, S.; Schmidt, T.; Schmoll, J.; Schneider, M.;
Schoorlemmer, H.; Schovanek, P.; Schulz, A.; Schussler, F.; Schwanke,
U.; Schwarz, J.; Schweizer, T.; Schwemmer, S.; Sciacca, E.; Scuderi,
S.; Seglar-Arroyo, M.; Segreto, A.; Seitenzahl, I.; Semikoz, D.;
Sergijenko, O.; Serre, N.; Servillat, M.; Seweryn, K.; Shah, K.;
Shalchi, A.; Sharma, M.; Shellard, R. C.; Shilon, I.; Sidoli, L.;
Sidz, M.; Siejkowski, H.; Silk, J.; Sillanpää, A.; Simone, D.; Singh,
B. B.; Sironi, G.; Sitarek, J.; Sizun, P.; Sliusar, V.; Slowikowska,
A.; Smith, A.; Sobczyńska, D.; Sokolenko, A.; Sol, H.; Sottile, G.;
Springer, W.; Stahl, O.; Stamerra, A.; Stanič, S.; Starling, R.;
Staszak, D.; Stawarz, Ł.; Steenkamp, R.; Stefanik, S.; Stegmann,
C.; Steiner, S.; Stella, C.; Stephan, M.; Sternberger, R.; Sterzel,
M.; Stevenson, B.; Stodulska, M.; Stodulski, M.; Stolarczyk, T.;
Stratta, G.; Straumann, U.; Stuik, R.; Suchenek, M.; Suomijarvi, T.;
Supanitsky, A. D.; Suric, T.; Sushch, I.; Sutcliffe, P.; Sykes, J.;
Szanecki, M.; Szepieniec, T.; Tagliaferri, G.; Tajima, H.; Takahashi,
K.; Takahashi, H.; Takahashi, M.; Takalo, L.; Takami, S.; Takata, J.;
Takeda, J.; Tam, T.; Tanaka, M.; Tanaka, T.; Tanaka, Y.; Tanaka, S.;
Tanci, C.; Tavani, M.; Tavecchio, F.; Tavernet, J. -P.; Tayabaly,
K.; Tejedor, L. A.; Temme, F.; Temnikov, P.; Terada, Y.; Terrazas,
J. C.; Terrier, R.; Terront, D.; Terzic, T.; Tescaro, D.; Teshima, M.;
Testa, V.; Thoudam, S.; Tian, W.; Tibaldo, L.; Tiengo, A.; Tiziani, D.;
Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.; Toma,
K.; Tomastik, J.; Tonachini, A.; Tonev, D.; Tornikoski, M.; Torres,
D. F.; Torresi, E.; Tosti, G.; Totani, T.; Tothill, N.; Toussenel,
F.; Tovmassian, G.; Trakarnsirinont, N.; Travnicek, P.; Trichard,
C.; Trifoglio, M.; Troyano Pujadas, I.; Tsirou, M.; Tsujimoto,
S.; Tsuru, T.; Uchiyama, Y.; Umana, G.; Uslenghi, M.; Vagelli, V.;
Vagnetti, F.; Valentino, M.; Vallania, P.; Valore, L.; Van den Berg,
A. M.; van Driel, W.; van Eldik, C.; van Soelen, B.; Vandenbroucke,
J.; Vanderwalt, J.; Varner, G. S.; Vasileiadis, G.; Vassiliev, V.;
Vázquez, J. R.; Vázquez Acosta, M.; Vecchi, M.; Vega, A.; Veitch,
P.; Venault, P.; Venter, C.; Vercellone, S.; Veres, P.; Vergani,
S.; Verzi, V.; Vettolani, G. P.; Veyssiere, C.; Viana, A.; Vicha,
J.; Vigorito, C.; Villanueva, J.; Vincent, P.; Vink, J.; Visconti,
F.; Vittorini, V.; Voelk, H.; Voisin, V.; Vollhardt, A.; Vorobiov,
S.; Vovk, I.; Vrastil, M.; Vuillaume, T.; Wagner, S. J.; Wagner, R.;
Wagner, P.; Wakely, S. P.; Walstra, T.; Walter, R.; Ward, M.; Ward,
J. E.; Warren, D.; Watson, J. J.; Webb, N.; Wegner, P.; Weiner, O.;
Weinstein, A.; Weniger, C.; Werner, F.; Wetteskind, H.; White, M.;
White, R.; Wierzcholska, A.; Wiesand, S.; Wijers, R.; Wilcox, P.;
Wilhelm, A.; Wilkinson, M.; Will, M.; Williams, D. A.; Winter, M.;
Wojcik, P.; Wolf, D.; Wood, M.; Wörnlein, A.; Wu, T.; Yadav, K. K.;
Yaguna, C.; Yamamoto, T.; Yamamoto, H.; Yamane, N.; Yamazaki, R.;
Yanagita, S.; Yang, L.; Yelos, D.; Yoshida, T.; Yoshida, M.; Yoshiike,
S.; Yoshikoshi, T.; Yu, P.; Zaborov, D.; Zacharias, M.; Zaharijas, G.;
Zajczyk, A.; Zampieri, L.; Zandanel, F.; Zanin, R.; Zanmar Sanchez,
R.; Zaric, D.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A. A.; Zech,
A.; Zechlin, H.; Zhdanov, V. I.; Ziegler, A.; Ziemann, J.; Ziętara,
K.; Zink, A.; Ziółkowski, J.; Zitelli, V.; Zoli, A.; Zorn, J.
2017arXiv170903483A Altcode: 2017arXiv170903483C
List of contributions from the Cherenkov Telescope Array Consortium
presented at the 35th International Cosmic Ray Conference, July 12-20
2017, Busan, Korea.
---------------------------------------------------------
Title: Observing and modelling the poloidal and toroidal magnetic
fields of the global dynamo
Authors: Cameron, Robert; Duvall, Thomas; Schüssler, Manfred;
Schunker, Hannah
2017SPD....4830601C Altcode:
The large scale solar dynamo is a cycle where poloidal flux is
generated from toroidal flux, and toroidal flux is generated from
poloidal flux. The toroidal and poloidal fields can be inferred from
observations, and the Babcock-Leighton model shows how differential
rotation and flux emergence explain the observed evolution of the
fields.
---------------------------------------------------------
Title: The nature of solar brightness variations
Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Cameron,
R. H.; Yeo, K. L.; Schmutz, W. K.
2017NatAs...1..612S Altcode: 2017arXiv171104156S
Determining the sources of solar brightness variations<SUP>1,2</SUP>,
often referred to as solar noise<SUP>3</SUP>, is important because
solar noise limits the detection of solar oscillations<SUP>3</SUP>,
is one of the drivers of the Earth's climate system<SUP>4,5</SUP> and
is a prototype of stellar variability<SUP>6,7</SUP>—an important
limiting factor for the detection of extrasolar planets. Here,
we model the magnetic contribution to solar brightness variability
using high-cadence<SUP>8,9</SUP> observations from the Solar Dynamics
Observatory (SDO) and the Spectral And Total Irradiance REconstruction
(SATIRE)<SUP>10,11</SUP> model. The brightness variations caused by
the constantly evolving cellular granulation pattern on the solar
surface were computed with the Max Planck Institute for Solar System
Research (MPS)/University of Chicago Radiative Magnetohydrodynamics
(MURaM)<SUP>12</SUP> code. We found that the surface magnetic field
and granulation can together precisely explain solar noise (that
is, solar variability excluding oscillations) on timescales from
minutes to decades, accounting for all timescales that have so far
been resolved or covered by irradiance measurements. We demonstrate
that no other sources of variability are required to explain the
data. Recent measurements of Sun-like stars by the COnvection ROtation
and planetary Transits (CoRoT)<SUP>13</SUP> and Kepler<SUP>14</SUP>
missions uncovered brightness variations similar to that of the Sun,
but with a much wider variety of patterns<SUP>15</SUP>. Our finding
that solar brightness variations can be replicated in detail with
just two well-known sources will greatly simplify future modelling of
existing CoRoT and Kepler as well as anticipated Transiting Exoplanet
Survey Satellite<SUP>16</SUP> and PLAnetary Transits and Oscillations
of stars (PLATO)<SUP>17</SUP> data.
---------------------------------------------------------
Title: Evidence for photometric activity cycles in 3203 Kepler stars
Authors: Reinhold, Timo; Cameron, Robert H.; Gizon, Laurent
2017A&A...603A..52R Altcode: 2017arXiv170503312R
Context. In recent years it has been claimed that the length of stellar
activity cycles is determined by the stellar rotation rate. It has been
observed that the cycle period increases with rotation period along
two distinct sequences, known as the active and inactive sequences. In
this picture the Sun occupies a solitary position between the two
sequences. Whether the Sun might undergo a transitional evolutionary
stage is currently under debate. <BR /> Aims: Our goal is to measure
cyclic variations of the stellar light curve amplitude and the rotation
period using four years of Kepler data. Periodic changes in the light
curve amplitude or the stellar rotation period are associated with
an underlying activity cycle. <BR /> Methods: Using a recent sample
of active stars we compute the rotation period and the variability
amplitude for each individual Kepler quarter and search for periodic
variations of both time series. To test for periodicity in each
stellar time series we consider Lomb-Scargle periodograms and use a
selection based on a false alarm probability (FAP). <BR /> Results:
We detect amplitude periodicities in 3203 stars between 0.5 <
P<SUB>cyc</SUB> < 6 yr covering rotation periods between 1 <
P<SUB>rot</SUB> < 40 days. Given our sample size of 23 601 stars
and our selection criteria that the FAP is less than 5%, this number
is almost three times higher than that expected from pure noise. We do
not detect periodicities in the rotation period beyond those expected
from noise. Our measurements reveal that the cycle period shows a weak
dependence on rotation rate, slightly increasing for longer rotation
periods. We further show that the shape of the variability deviates from
a pure sine curve, consistent with observations of the solar cycle. The
cycle shape does not show a statistically significant dependence on
effective temperature. <BR /> Conclusions: We detect activity cycles
in more than 13% of our final sample with a FAP of 5% (calculated by
randomly shuffling the measured 90-day variability measurements for
each star). Our measurements do not support the existence of distinct
sequences in the P<SUB>rot</SUB>-P<SUB>cyc</SUB> plane, although there
is some evidence for the inactive sequence for rotation periods between
5-25 days. Unfortunately, the total observing time is too short to draw
sound conclusions on activity cycles with similar lengths to that of the
solar cycle. <P />A table containing all cycle periods and time series
is only available in electronic form at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(130.79.128.5) or via <A
href="http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/603/A52">http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/603/A52</A>
---------------------------------------------------------
Title: Understanding Solar Cycle Variability
Authors: Cameron, R. H.; Schüssler, M.
2017ApJ...843..111C Altcode: 2017arXiv170510746C
The level of solar magnetic activity, as exemplified by the number
of sunspots and by energetic events in the corona, varies on a wide
range of timescales. Most prominent is the 11-year solar cycle,
which is significantly modulated on longer timescales. Drawing from
dynamo theory, together with the empirical results of past solar
activity and similar phenomena for solar-like stars, we show that
the variability of the solar cycle can be essentially understood in
terms of a weakly nonlinear limit cycle affected by random noise. In
contrast to ad hoc “toy models” for the solar cycle, this leads
to a generic normal-form model, whose parameters are all constrained
by observations. The model reproduces the characteristics of the
variable solar activity on timescales between decades and millennia,
including the occurrence and statistics of extended periods of very
low activity (grand minima). Comparison with results obtained with
a Babcock-Leighton-type dynamo model confirm the validity of the
normal-mode approach.
---------------------------------------------------------
Title: Effects of pH and Redox Gradients on Prebiotic Organic
Synthesis and the Generation of Free Energy in Simulated Hydrothermal
Systems
Authors: Barge, L. M.; Flores, E.; Abedian, Y.; Maltais, T.; Cameron,
R.; Hermis, N.; Chin, K.; Russell, M. J.; Baum, M. M.
2017LPICo1967.4179B Altcode:
Hydrothermal minerals in alkaline vents can promote phosphorus and
organic concentration, redox reactions driven by catalytic metal
sulfides, and the ambient pH and redox gradients can affect the
synthesis of organics.
---------------------------------------------------------
Title: Evolution of the Sun's non-axisymmetric toroidal field
Authors: Martin-Belda, D.; Cameron, R. H.
2017A&A...603A..53M Altcode: 2017arXiv170310075M
<BR /> Aims: We aim to infer the sub-surface distribution of the Sun's
non-axisymmetric azimuthal magnetic flux from observable quantities,
such as the surface magnetic field and the large scale plasma flows. <BR
/> Methods: We have built a kinematic flux transport model of the
solar dynamo based on the Babcock-Leighton framework. We constructed
the source term for the poloidal field using SOLIS magnetograms
spanning three solar cycles. Based on this source we calculated the
azimuthal flux below the surface. The flux transport model has two
free parameters which we constrained using sunspot observations from
cycle 22. We compared the model results with observations from cycle
23. <BR /> Results: The structure of the azimuthal field is mainly
axisymmetric. The departures from axisymmetry represent, on average,
3% of the total azimuthal flux. Owing to its relative weakness, the
non-axisymmetric structure of the azimuthal field does not have a
significant impact on the location in which the emergences appear or
on the amount of flux contained in them. We find that the probability
of emergence is a function of the ratio between the flux content of
an active region and the underlying azimuthal flux.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Activity cycles in 3203 Kepler
stars (Reinhold+, 2017)
Authors: Reinhold, T.; Cameron, R. H.; Gizon, L.
2017yCat..36030052R Altcode:
Rvar time series, sine fit parameters, mean rotation periods, and
false alarm probabilities of all 3203 Kepler stars are presented. For
simplicity, the KIC number and the fit parameters of a certain star
are repeated in each line. The fit function to the Rvar(t) time
series equals y_fit=Acyc*sin(2*pi/(Pcyc*365)*(t-t0))+Offset. <P />(2
data files).
---------------------------------------------------------
Title: Prospects for Cherenkov Telescope Array Observations of the
Young Supernova Remnant RX J1713.7-3946
Authors: Acero, F.; Aloisio, R.; Amans, J.; Amato, E.; Antonelli,
L. A.; Aramo, C.; Armstrong, T.; Arqueros, F.; Asano, K.; Ashley, M.;
Backes, M.; Balazs, C.; Balzer, A.; Bamba, A.; Barkov, M.; Barrio,
J. A.; Benbow, W.; Bernlöhr, K.; Beshley, V.; Bigongiari, C.; Biland,
A.; Bilinsky, A.; Bissaldi, E.; Biteau, J.; Blanch, O.; Blasi, P.;
Blazek, J.; Boisson, C.; Bonanno, G.; Bonardi, A.; Bonavolontà,
C.; Bonnoli, G.; Braiding, C.; Brau-Nogué, S.; Bregeon, J.; Brown,
A. M.; Bugaev, V.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi,
A.; Busetto, G.; Böttcher, M.; Cameron, R.; Capalbi, M.; Caproni, A.;
Caraveo, P.; Carosi, R.; Cascone, E.; Cerruti, M.; Chaty, S.; Chen, A.;
Chen, X.; Chernyakova, M.; Chikawa, M.; Chudoba, J.; Cohen-Tanugi, J.;
Colafrancesco, S.; Conforti, V.; Contreras, J. L.; Costa, A.; Cotter,
G.; Covino, S.; Covone, G.; Cumani, P.; Cusumano, G.; D'Ammando, F.;
D'Urso, D.; Daniel, M.; Dazzi, F.; De Angelis, A.; De Cesare, G.;
De Franco, A.; De Frondat, F.; de Gouveia Dal Pino, E. M.; De Lisio,
C.; de los Reyes Lopez, R.; De Lotto, B.; de Naurois, M.; De Palma,
F.; Del Santo, M.; Delgado, C.; della Volpe, D.; Di Girolamo, T.;
Di Giulio, C.; Di Pierro, F.; Di Venere, L.; Doro, M.; Dournaux, J.;
Dumas, D.; Dwarkadas, V.; Díaz, C.; Ebr, J.; Egberts, K.; Einecke,
S.; Elsässer, D.; Eschbach, S.; Falceta-Goncalves, D.; Fasola,
G.; Fedorova, E.; Fernández-Barral, A.; Ferrand, G.; Fesquet, M.;
Fiandrini, E.; Fiasson, A.; Filipović, M. D.; Fioretti, V.; Font, L.;
Fontaine, G.; Franco, F. J.; Freixas Coromina, L.; Fujita, Y.; Fukui,
Y.; Funk, S.; Förster, A.; Gadola, A.; Garcia López, R.; Garczarczyk,
M.; Giglietto, N.; Giordano, F.; Giuliani, A.; Glicenstein, J.; Gnatyk,
R.; Goldoni, P.; Grabarczyk, T.; Graciani, R.; Graham, J.; Grandi,
P.; Granot, J.; Green, A. J.; Griffiths, S.; Gunji, S.; Hakobyan, H.;
Hara, S.; Hassan, T.; Hayashida, M.; Heller, M.; Helo, J. C.; Hinton,
J.; Hnatyk, B.; Huet, J.; Huetten, M.; Humensky, T. B.; Hussein, M.;
Hörandel, J.; Ikeno, Y.; Inada, T.; Inome, Y.; Inoue, S.; Inoue, T.;
Inoue, Y.; Ioka, K.; Iori, M.; Jacquemier, J.; Janecek, P.; Jankowsky,
D.; Jung, I.; Kaaret, P.; Katagiri, H.; Kimeswenger, S.; Kimura, S.;
Knödlseder, J.; Koch, B.; Kocot, J.; Kohri, K.; Komin, N.; Konno, Y.;
Kosack, K.; Koyama, S.; Kraus, M.; Kubo, H.; Kukec Mezek, G.; Kushida,
J.; La Palombara, N.; Lalik, K.; Lamanna, G.; Landt, H.; Lapington,
J.; Laporte, P.; Lee, S.; Lees, J.; Lefaucheur, J.; Lenain, J. -P.;
Leto, G.; Lindfors, E.; Lohse, T.; Lombardi, S.; Longo, F.; Lopez,
M.; Lucarelli, F.; Luque-Escamilla, P. L.; López-Coto, R.; Maccarone,
M. C.; Maier, G.; Malaguti, G.; Mandat, D.; Maneva, G.; Mangano, S.;
Marcowith, A.; Martí, J.; Martínez, M.; Martínez, G.; Masuda, S.;
Maurin, G.; Maxted, N.; Melioli, C.; Mineo, T.; Mirabal, N.; Mizuno,
T.; Moderski, R.; Mohammed, M.; Montaruli, T.; Moralejo, A.; Mori,
K.; Morlino, G.; Morselli, A.; Moulin, E.; Mukherjee, R.; Mundell,
C.; Muraishi, H.; Murase, K.; Nagataki, S.; Nagayoshi, T.; Naito,
T.; Nakajima, D.; Nakamori, T.; Nemmen, R.; Niemiec, J.; Nieto, D.;
Nievas-Rosillo, M.; Nikołajuk, M.; Nishijima, K.; Noda, K.; Nogues,
L.; Nosek, D.; Novosyadlyj, B.; Nozaki, S.; Ohira, Y.; Ohishi, M.;
Ohm, S.; Okumura, A.; Ong, R. A.; Orito, R.; Orlati, A.; Ostrowski,
M.; Oya, I.; Padovani, M.; Palacio, J.; Palatka, M.; Paredes, J. M.;
Pavy, S.; Pe'er, A.; Persic, M.; Petrucci, P.; Petruk, O.; Pisarski,
A.; Pohl, M.; Porcelli, A.; Prandini, E.; Prast, J.; Principe, G.;
Prouza, M.; Pueschel, E.; Pühlhofer, G.; Quirrenbach, A.; Rameez,
M.; Reimer, O.; Renaud, M.; Ribó, M.; Rico, J.; Rizi, V.; Rodriguez,
J.; Rodriguez Fernandez, G.; Rodríguez Vázquez, J. J.; Romano, P.;
Romeo, G.; Rosado, J.; Rousselle, J.; Rowell, G.; Rudak, B.; Sadeh,
I.; Safi-Harb, S.; Saito, T.; Sakaki, N.; Sanchez, D.; Sangiorgi,
P.; Sano, H.; Santander, M.; Sarkar, S.; Sawada, M.; Schioppa,
E. J.; Schoorlemmer, H.; Schovanek, P.; Schussler, F.; Sergijenko,
O.; Servillat, M.; Shalchi, A.; Shellard, R. C.; Siejkowski, H.;
Sillanpää, A.; Simone, D.; Sliusar, V.; Sol, H.; Stanič, S.;
Starling, R.; Stawarz, Ł.; Stefanik, S.; Stephan, M.; Stolarczyk, T.;
Szanecki, M.; Szepieniec, T.; Tagliaferri, G.; Tajima, H.; Takahashi,
M.; Takeda, J.; Tanaka, M.; Tanaka, S.; Tejedor, L. A.; Telezhinsky,
I.; Temnikov, P.; Terada, Y.; Tescaro, D.; Teshima, M.; Testa, V.;
Thoudam, S.; Tokanai, F.; Torres, D. F.; Torresi, E.; Tosti, G.;
Townsley, C.; Travnicek, P.; Trichard, C.; Trifoglio, M.; Tsujimoto,
S.; Vagelli, V.; Vallania, P.; Valore, L.; van Driel, W.; van Eldik,
C.; Vandenbroucke, J.; Vassiliev, V.; Vecchi, M.; Vercellone, S.;
Vergani, S.; Vigorito, C.; Vorobiov, S.; Vrastil, M.; Vázquez
Acosta, M. L.; Wagner, S. J.; Wagner, R.; Wakely, S. P.; Walter,
R.; Ward, J. E.; Watson, J. J.; Weinstein, A.; White, M.; White, R.;
Wierzcholska, A.; Wilcox, P.; Williams, D. A.; Wischnewski, R.; Wojcik,
P.; Yamamoto, T.; Yamamoto, H.; Yamazaki, R.; Yanagita, S.; Yang, L.;
Yoshida, T.; Yoshida, M.; Yoshiike, S.; Yoshikoshi, T.; Zacharias,
M.; Zampieri, L.; Zanin, R.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski,
A.; Zech, A.; Zechlin, H.; Zhdanov, V.; Ziegler, A.; Zorn, J.
2017ApJ...840...74A Altcode: 2017arXiv170404136C
We perform simulations for future Cherenkov Telescope Array (CTA)
observations of RX J1713.7-3946, a young supernova remnant (SNR)
and one of the brightest sources ever discovered in very high energy
(VHE) gamma rays. Special attention is paid to exploring possible
spatial (anti)correlations of gamma rays with emission at other
wavelengths, in particular X-rays and CO/H I emission. We present a
series of simulated images of RX J1713.7-3946 for CTA based on a set of
observationally motivated models for the gamma-ray emission. In these
models, VHE gamma rays produced by high-energy electrons are assumed
to trace the nonthermal X-ray emission observed by XMM-Newton, whereas
those originating from relativistic protons delineate the local gas
distributions. The local atomic and molecular gas distributions are
deduced by the NANTEN team from CO and H I observations. Our primary
goal is to show how one can distinguish the emission mechanism(s) of the
gamma rays (I.e., hadronic versus leptonic, or a mixture of the two)
through information provided by their spatial distribution, spectra,
and time variation. This work is the first attempt to quantitatively
evaluate the capabilities of CTA to achieve various proposed scientific
goals by observing this important cosmic particle accelerator.
---------------------------------------------------------
Title: High-frequency Oscillations in Small Magnetic Elements Observed
with Sunrise/SuFI
Authors: Jafarzadeh, S.; Solanki, S. K.; Stangalini, M.; Steiner,
O.; Cameron, R. H.; Danilovic, S.
2017ApJS..229...10J Altcode: 2016arXiv161109302J
We characterize waves in small magnetic elements and investigate
their propagation in the lower solar atmosphere from observations at
high spatial and temporal resolution. We use the wavelet transform to
analyze oscillations of both horizontal displacement and intensity
in magnetic bright points found in the 300 nm and the Ca II H 396.8
nm passbands of the filter imager on board the Sunrise balloon-borne
solar observatory. Phase differences between the oscillations at the
two atmospheric layers corresponding to the two passbands reveal
upward propagating waves at high frequencies (up to 30 mHz). Weak
signatures of standing as well as downward propagating waves are also
obtained. Both compressible and incompressible (kink) waves are found
in the small-scale magnetic features. The two types of waves have
different, though overlapping, period distributions. Two independent
estimates give a height difference of approximately 450 ± 100 km
between the two atmospheric layers sampled by the employed spectral
bands. This value, together with the determined short travel times of
the transverse and longitudinal waves provide us with phase speeds of 29
± 2 km s<SUP>-1</SUP> and 31 ± 2 km s<SUP>-1</SUP>, respectively. We
speculate that these phase speeds may not reflect the true propagation
speeds of the waves. Thus, effects such as the refraction of fast
longitudinal waves may contribute to an overestimate of the phase speed.
---------------------------------------------------------
Title: Kinematics of Magnetic Bright Features in the Solar Photosphere
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Barthol, P.;
Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon,
L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Riethmüller, T. L.; Schmidt, W.; van Noort, M.
2017ApJS..229....8J Altcode: 2016arXiv161007634J
Convective flows are known as the prime means of transporting magnetic
fields on the solar surface. Thus, small magnetic structures are good
tracers of turbulent flows. We study the migration and dispersal
of magnetic bright features (MBFs) in intergranular areas observed
at high spatial resolution with Sunrise/IMaX. We describe the flux
dispersal of individual MBFs as a diffusion process whose parameters are
computed for various areas in the quiet-Sun and the vicinity of active
regions from seeing-free data. We find that magnetic concentrations
are best described as random walkers close to network areas (diffusion
index, γ =1.0), travelers with constant speeds over a supergranule
(γ =1.9{--}2.0), and decelerating movers in the vicinity of flux
emergence and/or within active regions (γ =1.4{--}1.5). The three
types of regions host MBFs with mean diffusion coefficients of 130
km<SUP>2</SUP> s<SUP>-1</SUP>, 80-90 km<SUP>2</SUP> s<SUP>-1</SUP>,
and 25-70 km<SUP>2</SUP> s<SUP>-1</SUP>, respectively. The MBFs in
these three types of regions are found to display a distinct kinematic
behavior at a confidence level in excess of 95%.
---------------------------------------------------------
Title: An update of Leighton's solar dynamo model
Authors: Cameron, R. H.; Schüssler, M.
2017A&A...599A..52C Altcode: 2016arXiv161109111C
In 1969, Leighton developed a quasi-1D mathematical model of the solar
dynamo, building upon the phenomenological scenario of Babcock published
in 1961. Here we present a modification and extension of Leighton's
model. Using the axisymmetric component (longitudinal average) of
the magnetic field, we consider the radial field component at the
solar surface and the radially integrated toroidal magnetic flux in
the convection zone, both as functions of latitude. No assumptions
are made with regard to the radial location of the toroidal flux. The
model includes the effects of (I) turbulent diffusion at the surface
and in the convection zone; (II) poleward meridional flow at the
surface and an equatorward return flow affecting the toroidal flux;
(III) latitudinal differential rotation and the near-surface layer of
radial rotational shear; (iv) downward convective pumping of magnetic
flux in the shear layer; and (v) flux emergence in the form of tilted
bipolar magnetic regions treated as a source term for the radial surface
field. While the parameters relevant for the transport of the surface
field are taken from observations, the model condenses the unknown
properties of magnetic field and flow in the convection zone into a
few free parameters (turbulent diffusivity, effective return flow,
amplitude of the source term, and a parameter describing the effective
radial shear). Comparison with the results of 2D flux transport
dynamo codes shows that the model captures the essential features of
these simulations. We make use of the computational efficiency of the
model to carry out an extended parameter study. We cover an extended
domain of the 4D parameter space and identify the parameter ranges
that provide solar-like solutions. Dipole parity is always preferred
and solutions with periods around 22 yr and a correct phase difference
between flux emergence in low latitudes and the strength of the polar
fields are found for a return flow speed around 2 m s<SUP>-1</SUP>,
turbulent diffusivity below about 80 km<SUP>2</SUP>s<SUP>-1</SUP>,
and dynamo excitation not too far above the threshold (linear growth
rate less than 0.1 yr<SUP>-1</SUP>).
---------------------------------------------------------
Title: Inflows towards active regions and the modulation of the
solar cycle: A parameter study
Authors: Martin-Belda, D.; Cameron, R. H.
2017A&A...597A..21M Altcode: 2016A&A...597A..21M; 2016arXiv160901199M
<BR /> Aims: We aim to investigate how converging flows towards active
regions affect the surface transport of magnetic flux, as well as
their impact on the generation of the Sun's poloidal field. The inflows
constitute a potential non-linear mechanism for the saturation of the
global dynamo and may contribute to the modulation of the solar cycle in
the Babcock-Leighton framework. <BR /> Methods: We build a surface flux
transport code incorporating a parametrized model of the inflows and run
simulations spanning several cycles. We carry out a parameter study to
assess how the strength and extension of the inflows affect the build-up
of the global dipole field. We also perform simulations with different
levels of activity to investigate the potential role of the inflows in
the saturation of the global dynamo. <BR /> Results: We find that the
interaction of neighbouring active regions can lead to the occasional
formation of single-polarity magnetic flux clumps that are inconsistent
with observations. We propose the darkening caused by pores in areas
of high magnetic field strength as a possible mechanism preventing
this flux-clumping. We find that inflows decrease the amplitude of the
axial dipole moment by 30%, relative to a no-inflows scenario. Stronger
(weaker) inflows lead to larger (smaller) reductions of the axial dipole
moment. The relative amplitude of the generated axial dipole is about
9% larger after very weak cycles than after very strong cycles. This
supports the idea that the inflows are a non-linear mechanism that
is capable of saturating the global dynamo and contributing to the
modulation of the solar cycle within the Babcock-Leighton framework.
---------------------------------------------------------
Title: Babcock-Leighton Solar Dynamo: The Role of Downward Pumping
and the Equatorward Propagation of Activity
Authors: Karak, Bidya Binay; Cameron, Robert
2016ApJ...832...94K Altcode: 2016arXiv160506224K
The key elements of the Babcock-Leighton dynamos are the generation of
poloidal field through decay and the dispersal of tilted bipolar active
regions and the generation of toroidal field through the observed
differential rotation. These models are traditionally known as flux
transport dynamo models as the equatorward propagations of the butterfly
wings in these models are produced due to an equatorward flow at the
bottom of the convection zone. Here we investigate the role of downward
magnetic pumping near the surface using a kinematic Babcock-Leighton
model. We find that the pumping causes the poloidal field to become
predominately radial in the near-surface shear layer, which allows
the negative radial shear to effectively act on the radial field to
produce a toroidal field. We observe a clear equatorward migration of
the toroidal field at low latitudes as a consequence of the dynamo wave
even when there is no meridional flow in the deep convection zone. Both
the dynamo wave and the flux transport type solutions are thus able to
reproduce some of the observed features of the solar cycle including
the 11-year periodicity. The main difference between the two types of
solutions is the strength of the Babcock-Leighton source required to
produce the dynamo action. A second consequence of the magnetic pumping
is that it suppresses the diffusion of fields through the surface,
which helps to allow an 11-year cycle at (moderately) larger values
of magnetic diffusivity than have previously been used.
---------------------------------------------------------
Title: Comparing Time-Distance Results within a Coronal Hole to the
Quiet Sun
Authors: Hess Webber, Shea A.; Pesnell, W. Dean; Duvall, Thomas, Jr.;
Birch, Aaron; Cameron, Robert
2016usc..confE...1H Altcode:
Time-distance helioseismology studies perturbations in solar
wave modes. We use these techniques with SDO/HMI time-distance
velocity-tracked dopplergram data to investigate differences between f
-mode wave propagation within a coronal hole feature and without. We
use symmetry arguments to enhance the signal-to-noise ratio of the
cross-correlation results. We then look for phase and amplitude
discrepancies between the coronal hole and quiet sun by comparing
statistically significant differences between the regions.
---------------------------------------------------------
Title: A solar-like magnetic cycle on the mature K-dwarf 61 Cygni A
(HD 201091)
Authors: Boro Saikia, S.; Jeffers, S. V.; Morin, J.; Petit, P.;
Folsom, C. P.; Marsden, S. C.; Donati, J. -F.; Cameron, R.; Hall,
J. C.; Perdelwitz, V.; Reiners, A.; Vidotto, A. A.
2016A&A...594A..29B Altcode: 2016arXiv160601032B
Context. The long-term monitoring of magnetic cycles in cool stars is a
key diagnostic in understanding how dynamo generation and amplification
of magnetic fields occur in stars similar in structure to the Sun. <BR
/> Aims: We investigated the temporal evolution of a possible magnetic
cycle of 61 Cyg A. The magnetic cycle is determined from 61 Cyg A's
large-scale field over its activity cycle using spectropolarimetric
observations and compared to the solar large-scale magnetic field. <BR
/> Methods: We used the tomographic technique of Zeeman Doppler imaging
(ZDI) to reconstruct the large-scale magnetic geometry of 61 Cyg A
over multiple observational epochs spread over a time span of nine
years. We investigated the time evolution of the different components
of the large-scale field and compared it with the evolution of the
star's chromospheric activity by measuring the flux in three different
chromospheric indicators: Ca II H&K, Hα and Ca II infrared triplet
lines. We also compared our results with the star's coronal activity
using XMM-Newton observations. <BR /> Results: The large-scale magnetic
geometry of 61 Cyg A exhibits polarity reversals in both poloidal and
toroidal field components, in phase with its chromospheric activity
cycle. We also detect weak solar-like differential rotation with
a shear level similar to that of the Sun. During our observational
time span of nine years, 61 Cyg A exhibits solar- like variations in
its large-scale field geometry as it evolves from minimum activity
to maximum activity and vice versa. During its activity minimum in
epoch 2007.59, ZDI reconstructs a simple dipolar geometry which becomes
more complex when it approaches activity maximum in epoch 2010.55. The
radial field flips polarity and reverts back to a simple geometry in
epoch 2013.61. The field is strongly dipolar and the evolution of the
dipole component of the field is reminiscent of solar behaviour. The
polarity reversal of the large-scale field indicates a magnetic cycle
that is in phase with the chromospheric and coronal cycle.
---------------------------------------------------------
Title: Observed and simulated power spectra of kinetic and magnetic
energy retrieved with 2D inversions
Authors: Danilovic, S.; Rempel, M.; van Noort, M.; Cameron, R.
2016A&A...594A.103D Altcode: 2016arXiv160706242D
Context. Information on the origin of internetwork magnetic field is
hidden at the smallest spatial scales. <BR /> Aims: We try to retrieve
the power spectra with certainty to the highest spatial frequencies
allowed by current instrumentation. <BR /> Methods: To accomplish this,
we use a 2D inversion code that is able to recover information up to
the instrumental diffraction limit. <BR /> Results: The retrieved power
spectra have shallow slopes that extend further down to much smaller
scales than has been found before. They do not seem to show any power
law. The observed slopes at subgranular scales agree with those obtained
from recent local dynamo simulations. Small differences are found for
the vertical component of kinetic energy that suggest that observations
suffer from an instrumental effect that is not taken into account. <BR
/> Conclusions: Local dynamo simulations quantitatively reproduce the
observed magnetic energy power spectra on the scales of granulation
down to the resolution limit of Hinode/SP, within the error bars
inflicted by the method used and the instrumental effects replicated.
---------------------------------------------------------
Title: Contributions of the Cherenkov Telescope Array (CTA) to
the 6th International Symposium on High-Energy Gamma-Ray Astronomy
(Gamma 2016)
Authors: CTA Consortium, The; :; Abchiche, A.; Abeysekara, U.; Abril,
Ó.; Acero, F.; Acharya, B. S.; Adams, C.; Agnetta, G.; Aharonian,
F.; Akhperjanian, A.; Albert, A.; Alcubierre, M.; Alfaro, J.; Alfaro,
R.; Allafort, A. J.; Aloisio, R.; Amans, J. -P.; Amato, E.; Ambrogi,
L.; Ambrosi, G.; Ambrosio, M.; Anderson, J.; Anduze, M.; Angüner,
E. O.; Antolini, E.; Antonelli, L. A.; Antonucci, M.; Antonuccio,
V.; Antoranz, P.; Aramo, C.; Aravantinos, A.; Araya, M.; Arcaro, C.;
Arezki, B.; Argan, A.; Armstrong, T.; Arqueros, F.; Arrabito, L.;
Arrieta, M.; Asano, K.; Ashley, M.; Aubert, P.; Singh, C. B.; Babic,
A.; Backes, M.; Bais, A.; Bajtlik, S.; Balazs, C.; Balbo, M.; Balis,
D.; Balkowski, C.; Ballester, O.; Ballet, J.; Balzer, A.; Bamba,
A.; Bandiera, R.; Barber, A.; Barbier, C.; Barcelo, M.; Barkov,
M.; Barnacka, A.; Barres de Almeida, U.; Barrio, J. A.; Basso, S.;
Bastieri, D.; Bauer, C.; Becciani, U.; Becherini, Y.; Becker Tjus,
J.; Beckmann, V.; Bednarek, W.; Benbow, W.; Benedico Ventura, D.;
Berdugo, J.; Berge, D.; Bernardini, E.; Bernardini, M. G.; Bernhard,
S.; Bernlöhr, K.; Bertucci, B.; Besel, M. -A.; Beshley, V.; Bhatt,
N.; Bhattacharjee, P.; Bhattacharyya, W.; Bhattachryya, S.; Biasuzzi,
B.; Bicknell, G.; Bigongiari, C.; Biland, A.; Bilinsky, A.; Bilnik,
W.; Biondo, B.; Bird, R.; Bird, T.; Bissaldi, E.; Bitossi, M.;
Blanch, O.; Blasi, P.; Blazek, J.; Bockermann, C.; Boehm, C.; Bogacz,
L.; Bogdan, M.; Bohacova, M.; Boisson, C.; Boix, J.; Bolmont, J.;
Bonanno, G.; Bonardi, A.; Bonavolontà, C.; Bonifacio, P.; Bonnarel,
F.; Bonnoli, G.; Borkowski, J.; Bose, R.; Bosnjak, Z.; Böttcher, M.;
Bousquet, J. -J.; Boutonnet, C.; Bouyjou, F.; Bowman, L.; Braiding,
C.; Brantseg, T.; Brau-Nogué, S.; Bregeon, J.; Briggs, M.; Brigida,
M.; Bringmann, T.; Brisken, W.; Bristow, D.; Britto, R.; Brocato, E.;
Bron, S.; Brook, P.; Brooks, W.; Brown, A. M.; Brügge, K.; Brun, F.;
Brun, P.; Brun, P.; Brunetti, G.; Brunetti, L.; Bruno, P.; Buanes,
T.; Bucciantini, N.; Buchholtz, G.; Buckley, J.; Bugaev, V.; Bühler,
R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto,
G.; Buson, S.; Buss, J.; Byrum, K.; Cadoux, F.; Calvo Tovar, J.;
Cameron, R.; Canelli, F.; Canestrari, R.; Capalbi, M.; Capasso, M.;
Capobianco, G.; Caproni, A.; Caraveo, P.; Cardenzana, J.; Cardillo,
M.; Carius, S.; Carlile, C.; Carosi, A.; Carosi, R.; Carquín, E.;
Carr, J.; Carroll, M.; Carter, J.; Carton, P. -H.; Casandjian, J. -M.;
Casanova, S.; Casanova, S.; Cascone, E.; Casiraghi, M.; Castellina,
A.; Castroviejo Mora, J.; Catalani, F.; Catalano, O.; Catalanotti,
S.; Cauz, D.; Cavazzani, S.; Cerchiara, P.; Chabanne, E.; Chadwick,
P.; Chaleil, T.; Champion, C.; Chatterjee, A.; Chaty, S.; Chaves, R.;
Chen, A.; Chen, X.; Chen, X.; Cheng, K.; Chernyakova, M.; Chiappetti,
L.; Chikawa, M.; Chinn, D.; Chitnis, V. R.; Cho, N.; Christov, A.;
Chudoba, J.; Cieślar, M.; Ciocci, M. A.; Clay, R.; Colafrancesco,
S.; Colin, P.; Colley, J. -M.; Colombo, E.; Colome, J.; Colonges, S.;
Conforti, V.; Connaughton, V.; Connell, S.; Conrad, J.; Contreras,
J. L.; Coppi, P.; Corbel, S.; Coridian, J.; Cornat, R.; Corona,
P.; Corti, D.; Cortina, J.; Cossio, L.; Costa, A.; Costantini, H.;
Cotter, G.; Courty, B.; Covino, S.; Covone, G.; Crimi, G.; Criswell,
S. J.; Crocker, R.; Croston, J.; Cuadra, J.; Cumani, P.; Cusumano,
G.; Da Vela, P.; Dale, Ø.; D'Ammando, F.; Dang, D.; Dang, V. T.;
Dangeon, L.; Daniel, M.; Davids, I.; Davids, I.; Dawson, B.; Dazzi,
F.; de Aguiar Costa, B.; De Angelis, A.; de Araujo Cardoso, R. F.;
De Caprio, V.; de Cássia dos Anjos, R.; De Cesare, G.; De Franco,
A.; De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.;
De Lisio, C.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; de
Mello Neto, J. R. T.; de Naurois, M.; de Oña Wilhelmi, E.; De Palma,
F.; De Persio, F.; de Souza, V.; Decock, G.; Decock, J.; Deil, C.;
Del Santo, M.; Delagnes, E.; Deleglise, G.; Delgado, C.; Delgado, J.;
della Volpe, D.; Deloye, P.; Detournay, M.; Dettlaff, A.; Devin, J.;
Di Girolamo, T.; Di Giulio, C.; Di Paola, A.; Di Pierro, F.; Diaz,
M. A.; Díaz, C.; Dib, C.; Dick, J.; Dickinson, H.; Diebold, S.;
Digel, S.; Dipold, J.; Disset, G.; Distefano, A.; Djannati-Ataï, A.;
Doert, M.; Dohmke, M.; Domínguez, A.; Dominik, N.; Dominique, J. -L.;
Dominis Prester, D.; Donat, A.; Donnarumma, I.; Dorner, D.; Doro,
M.; Dournaux, J. -L.; Downes, T.; Doyle, K.; Drake, G.; Drappeau,
S.; Drass, H.; Dravins, D.; Drury, L.; Dubus, G.; Ducci, L.; Dumas,
D.; Dundas Morå, K.; Durand, D.; D'Urso, D.; Dwarkadas, V.; Dyks,
J.; Dyrda, M.; Ebr, J.; Edy, E.; Egberts, K.; Eger, P.; Egorov, A.;
Einecke, S.; Eisch, J.; Eisenkolb, F.; Eleftheriadis, C.; Elsaesser,
D.; Elsässer, D.; Emmanoulopoulos, D.; Engelbrecht, C.; Engelhaupt,
D.; Ernenwein, J. -P.; Escarate, P.; Eschbach, S.; Espinoza, C.;
Evans, P.; Fairbairn, M.; Falceta-Goncalves, D.; Falcone, A.; Fallah
Ramazani, V.; Fantinel, D.; Farakos, K.; Farnier, C.; Farrell, E.;
Fasola, G.; Favre, Y.; Fede, E.; Fedora, R.; Fedorova, E.; Fegan, S.;
Ferenc, D.; Fernandez-Alonso, M.; Fernández-Barral, A.; Ferrand, G.;
Ferreira, O.; Fesquet, M.; Fetfatzis, P.; Fiandrini, E.; Fiasson, A.;
Filipčič, A.; Filipovic, M.; Fink, D.; Finley, C.; Finley, J. P.;
Finoguenov, A.; Fioretti, V.; Fiorini, M.; Fleischhack, H.; Flores,
H.; Florin, D.; Föhr, C.; Fokitis, E.; Fonseca, M. V.; Font, L.;
Fontaine, G.; Fontes, B.; Fornasa, M.; Fornasa, M.; Förster, A.;
Fortin, P.; Fortson, L.; Fouque, N.; Franckowiak, A.; Franckowiak,
A.; Franco, F. J.; Freire Mota Albuquerque, I.; Freixas Coromina,
L.; Fresnillo, L.; Fruck, C.; Fuessling, M.; Fugazza, D.; Fujita, Y.;
Fukami, S.; Fukazawa, Y.; Fukuda, T.; Fukui, Y.; Funk, S.; Furniss, A.;
Gäbele, W.; Gabici, S.; Gadola, A.; Galindo, D.; Gall, D. D.; Gallant,
Y.; Galloway, D.; Gallozzi, S.; Galvez, J. A.; Gao, S.; Garcia, A.;
Garcia, B.; García Gil, R.; Garcia López, R.; Garczarczyk, M.;
Gardiol, D.; Gargano, C.; Gargano, F.; Garozzo, S.; Garrecht, F.;
Garrido, L.; Garrido-Ruiz, M.; Gascon, D.; Gaskins, J.; Gaudemard,
J.; Gaug, M.; Gaweda, J.; Gebhardt, B.; Gebyehu, M.; Geffroy, N.;
Genolini, B.; Gerard, L.; Ghalumyan, A.; Ghedina, A.; Ghislain, P.;
Giammaria, P.; Giannakaki, E.; Gianotti, F.; Giarrusso, S.; Giavitto,
G.; Giebels, B.; Gieras, T.; Giglietto, N.; Gika, V.; Gimenes, R.;
Giomi, M.; Giommi, P.; Giordano, F.; Giovannini, G.; Girardot, P.;
Giro, E.; Giroletti, M.; Gironnet, J.; Giuliani, A.; Glicenstein,
J. -F.; Gnatyk, R.; Godinovic, N.; Goldoni, P.; Gomez, G.; Gonzalez,
M. M.; González, A.; Gora, D.; Gothe, K. S.; Gotz, D.; Goullon, J.;
Grabarczyk, T.; Graciani, R.; Graham, J.; Grandi, P.; Granot, J.;
Grasseau, G.; Gredig, R.; Green, A. J.; Green, A. M.; Greenshaw, T.;
Grenier, I.; Griffiths, S.; Grillo, A.; Grondin, M. -H.; Grube, J.;
Grudzinska, M.; Grygorczuk, J.; Guarino, V.; Guberman, D.; Gunji, S.;
Gyuk, G.; Hadasch, D.; Hagedorn, A.; Hagge, L.; Hahn, J.; Hakobyan,
H.; Hara, S.; Hardcastle, M. J.; Hassan, T.; Hatanaka, K.; Haubold,
T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, M.; Heller,
R.; Helo, J. C.; Henault, F.; Henri, G.; Hermann, G.; Hermel, R.;
Herrera Llorente, J.; Herrera Llorente, J.; Herrero, A.; Hervet,
O.; Hidaka, N.; Hinton, J.; Hirai, W.; Hirotani, K.; Hnatyk, B.;
Hoang, J.; Hoffmann, D.; Hofmann, W.; Holch, T.; Holder, J.; Hooper,
S.; Horan, D.; Hörandel, J.; Hörbe, M.; Horns, D.; Horvath, P.;
Hose, J.; Houles, J.; Hovatta, T.; Hrabovsky, M.; Hrupec, D.; Huet,
J. -M.; Huetten, M.; Hughes, G.; Hui, D.; Humensky, T. B.; Hussein,
M.; Iacovacci, M.; Ibarra, A.; Ikeno, Y.; Illa, J. M.; Impiombato,
D.; Inada, T.; Incorvaia, S.; Infante, L.; Inome, Y.; Inoue, S.;
Inoue, T.; Inoue, Y.; Iocco, F.; Ioka, K.; Iori, M.; Ishio, K.;
Ishio, K.; Israel, G. L.; Iwamura, Y.; Jablonski, C.; Jacholkowska,
A.; Jacquemier, J.; Jamrozy, M.; Janecek, P.; Janiak, M.; Jankowsky,
D.; Jankowsky, F.; Jean, P.; Jegouzo, I.; Jenke, P.; Jimenez, J. J.;
Jingo, M.; Jingo, M.; Jocou, L.; Jogler, T.; Johnson, C. A.; Jones,
M.; Josselin, M.; Journet, L.; Jung, I.; Kaaret, P.; Kagaya, M.;
Kakuwa, J.; Kalekin, O.; Kalkuhl, C.; Kamon, H.; Kankanyan, R.;
Karastergiou, A.; Kärcher, K.; Karczewski, M.; Karkar, S.; Karn, P.;
Kasperek, J.; Katagiri, H.; Kataoka, J.; Katarzyński, K.; Kato, S.;
Katz, U.; Kawanaka, N.; Kaye, L.; Kazanas, D.; Kelley-Hoskins, N.;
Kersten, J.; Khélifi, B.; Kieda, D. B.; Kihm, T.; Kimeswenger, S.;
Kisaka, S.; Kishida, S.; Kissmann, R.; Klepser, S.; Kluźniak, W.;
Knapen, J.; Knapp, J.; Knödlseder, J.; Koch, B.; Köck, F.; Kocot,
J.; Kohri, K.; Kokkotas, K.; Kokkotas, K.; Kolitzus, D.; Komin, N.;
Kominis, I.; Kong, A.; Konno, Y.; Kosack, K.; Koss, G.; Kossatz, M.;
Kowal, G.; Koyama, S.; Kozioł, J.; Kraus, M.; Krause, J.; Krause, M.;
Krawzcynski, H.; Krennrich, F.; Kretzschmann, A.; Kruger, P.; Kubo, H.;
Kudryavtsev, V.; Kukec Mezek, G.; Kuklis, M.; Kuroda, H.; Kushida, J.;
La Barbera, A.; La Palombara, N.; La Parola, V.; La Rosa, G.; Laffon,
H.; Lahmann, R.; Lakicevic, M.; Lalik, K.; Lamanna, G.; Landriu,
D.; Landt, H.; Lang, R. G.; Lapington, J.; Laporte, P.; Le Fèvre,
J. -P.; Le Flour, T.; Le Sidaner, P.; Lee, S. -H.; Lee, W. H.; Lees,
J. -P.; Lefaucheur, J.; Leffhalm, K.; Leich, H.; Leigui de Oliveira,
M. A.; Lelas, D.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J. -P.;
Leonard, R.; Leoni, R.; Lessio, L.; Leto, G.; Leveque, A.; Lieunard,
B.; Limon, M.; Lindemann, R.; Lindfors, E.; Linhoff, L.; Liolios,
A.; Lipniacka, A.; Lockart, H.; Lohse, T.; Łokas, E.; Lombardi, S.;
Longo, F.; Lopatin, A.; Lopez, M.; Loreggia, D.; Louge, T.; Louis,
F.; Louys, M.; Lucarelli, F.; Lucchesi, D.; Lüdecke, H.; Luigi, T.;
Luque-Escamilla, P. L.; Lyard, E.; Maccarone, M. C.; Maccarone, T.;
Maccarone, T. J.; Mach, E.; Madejski, G. M.; Madonna, A.; Magniette,
F.; Magniez, A.; Mahabir, M.; Maier, G.; Majumdar, P.; Majumdar, P.;
Makariev, M.; Malaguti, G.; Malaspina, G.; Mallot, A. K.; Malouf,
A.; Maltezos, S.; Malyshev, D.; Mancilla, A.; Mandat, D.; Maneva, G.;
Manganaro, M.; Mangano, S.; Manigot, P.; Mankushiyil, N.; Mannheim, K.;
Maragos, N.; Marano, D.; Marchegiani, P.; Marcomini, J. A.; Marcowith,
A.; Mariotti, M.; Marisaldi, M.; Markoff, S.; Martens, C.; Martí,
J.; Martin, J. -M.; Martin, L.; Martin, P.; Martínez, G.; Martínez,
M.; Martínez, O.; Martynyuk-Lototskyy, K.; Marx, R.; Masetti, N.;
Massimino, P.; Mastichiadis, A.; Mastroianni, S.; Mastropietro, M.;
Masuda, S.; Matsumoto, H.; Matsuoka, S.; Matthews, N.; Mattiazzo, S.;
Maurin, G.; Maxted, N.; Maxted, N.; Maya, J.; Mayer, M.; Mazin, D.;
Mazziotta, M. N.; Mc Comb, L.; McCubbin, N.; McHardy, I.; Medina,
C.; Mehrez, F.; Melioli, C.; Melkumyan, D.; Melse, T.; Mereghetti,
S.; Merk, M.; Mertsch, P.; Meunier, J. -L.; Meures, T.; Meyer, M.;
Meyrelles, J. L., jr; Miccichè, A.; Michael, T.; Michałowski, J.;
Mientjes, P.; Mievre, I.; Mihailidis, A.; Miller, J.; Mineo, T.;
Minuti, M.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.;
Mitchell, A.; Mizuno, T.; Moderski, R.; Mognet, I.; Mohammed, M.;
Moharana, R.; Mohrmann, L.; Molinari, E.; Molyneux, P.; Monmarthe,
E.; Monnier, G.; Montaruli, T.; Monte, C.; Monteiro, I.; Mooney, D.;
Moore, P.; Moralejo, A.; Morello, C.; Moretti, E.; Mori, K.; Morris,
P.; Morselli, A.; Moscato, F.; Motohashi, D.; Mottez, F.; Moudden,
Y.; Moulin, E.; Mueller, S.; Mukherjee, R.; Munar, P.; Munari, M.;
Mundell, C.; Mundet, J.; Muraishi, H.; Murase, K.; Muronga, A.; Murphy,
A.; Nagar, N.; Nagataki, S.; Nagayoshi, T.; Nagesh, B. K.; Naito,
T.; Nakajima, D.; Nakajima, D.; Nakamori, T.; Nakayama, K.; Nanni,
J.; Naumann, D.; Nayman, P.; Nellen, L.; Nemmen, R.; Neronov, A.;
Neyroud, N.; Nguyen, T.; Nguyen, T. T.; Nguyen Trung, T.; Nicastro, L.;
Nicolau-Kukliński, J.; Niederwanger, F.; Niedźwiecki, A.; Niemiec,
J.; Nieto, D.; Nievas-Rosillo, M.; Nikolaidis, A.; Nikołajuk, M.;
Nishijima, K.; Nishikawa, K. -I.; Nishiyama, G.; Noda, K.; Noda,
K.; Nogues, L.; Nolan, S.; Northrop, R.; Nosek, D.; Nöthe, M.;
Novosyadlyj, B.; Nozka, L.; Nunio, F.; Oakes, L.; O'Brien, P.; Ocampo,
C.; Occhipinti, G.; Ochoa, J. P.; OFaolain de Bhroithe, A.; Oger, R.;
Ohira, Y.; Ohishi, M.; Ohm, S.; Ohoka, H.; Okazaki, N.; Okumura, A.;
Olive, J. -F.; Olszowski, D.; Ong, R. A.; Ono, S.; Orienti, M.; Orito,
R.; Orlati, A.; Osborne, J.; Ostrowski, M.; Ottaway, D.; Otte, N.;
Öttl, S.; Ovcharov, E.; Oya, I.; Ozieblo, A.; Padovani, M.; Pagano,
I.; Paiano, S.; Paizis, A.; Palacio, J.; Palatka, M.; Pallotta, J.;
Panagiotidis, K.; Panazol, J. -L.; Paneque, D.; Panter, M.; Panzera,
M. R.; Paoletti, R.; Paolillo, M.; Papayannis, A.; Papyan, G.; Paravac,
A.; Paredes, J. M.; Pareschi, G.; Park, N.; Parsons, D.; Paśko, P.;
Pavy, S.; Pech, M.; Peck, A.; Pedaletti, G.; Pe'er, A.; Peet, S.;
Pelat, D.; Pepato, A.; Perez, M. d. C.; Perri, L.; Perri, M.; Persic,
M.; Persic, M.; Petrashyk, A.; Petrucci, P. -O.; Petruk, O.; Peyaud,
B.; Pfeifer, M.; Pfeiffer, G.; Piano, G.; Pieloth, D.; Pierre, E.;
Pinto de Pinho, F.; García, C. Pio; Piret, Y.; Pisarski, A.; Pita,
S.; Platos, Ł.; Platzer, R.; Podkladkin, S.; Pogosyan, L.; Pohl,
M.; Poinsignon, P.; Pollo, A.; Porcelli, A.; Porthault, J.; Potter,
W.; Poulios, S.; Poutanen, J.; Prandini, E.; Prandini, E.; Prast, J.;
Pressard, K.; Principe, G.; Profeti, F.; Prokhorov, D.; Prokoph, H.;
Prouza, M.; Pruchniewicz, R.; Pruteanu, G.; Pueschel, E.; Pühlhofer,
G.; Puljak, I.; Punch, M.; Pürckhauer, S.; Pyzioł, R.; Queiroz,
F.; Quel, E. J.; Quinn, J.; Quirrenbach, A.; Rafighi, I.; Rainò, S.;
Rajda, P. J.; Rameez, M.; Rando, R.; Rannot, R. C.; Rataj, M.; Ravel,
T.; Razzaque, S.; Reardon, P.; Reichardt, I.; Reimann, O.; Reimer,
A.; Reimer, O.; Reisenegger, A.; Renaud, M.; Renner, S.; Reposeur,
T.; Reville, B.; Rezaeian, A.; Rhode, W.; Ribeiro, D.; Ribeiro Prado,
R.; Ribó, M.; Richards, G.; Richer, M. G.; Richtler, T.; Rico, J.;
Ridky, J.; Rieger, F.; Riquelme, M.; Ristori, P. R.; Rivoire, S.; Rizi,
V.; Roache, E.; Rodriguez, J.; Rodriguez Fernandez, G.; Rodríguez
Vázquez, J. J.; Rojas, G.; Romano, P.; Romeo, G.; Roncadelli, M.;
Rosado, J.; Rose, J.; Rosen, S.; Rosier Lees, S.; Ross, D.; Rouaix,
G.; Rousselle, J.; Rovero, A. C.; Rowell, G.; Roy, F.; Royer, S.;
Rubini, A.; Rudak, B.; Rugliancich, A.; Rujopakarn, W.; Rulten,
C.; Rupiński, M.; Russo, F.; Russo, F.; Rutkowski, K.; Saavedra,
O.; Sabatini, S.; Sacco, B.; Sadeh, I.; Saemann, E. O.; Safi-Harb,
S.; Saggion, A.; Sahakian, V.; Saito, T.; Sakaki, N.; Sakurai, S.;
Salamon, A.; Salega, M.; Salek, D.; Salesa Greus, F.; Salgado, J.;
Salina, G.; Salinas, L.; Salini, A.; Sanchez, D.; Sanchez-Conde, M.;
Sandaker, H.; Sandoval, A.; Sangiorgi, P.; Sanguillon, M.; Sano, H.;
Santander, M.; Santangelo, A.; Santos, E. M.; Santos-Lima, R.; Sanuy,
A.; Sapozhnikov, L.; Sarkar, S.; Satalecka, K.; Satalecka, K.; Sato,
Y.; Savalle, R.; Sawada, M.; Sayède, F.; Schanne, S.; Schanz, T.;
Schioppa, E. J.; Schlenstedt, S.; Schmid, J.; Schmidt, T.; Schmoll,
J.; Schneider, M.; Schoorlemmer, H.; Schovanek, P.; Schubert, A.;
Schullian, E. -M.; Schultze, J.; Schulz, A.; Schulz, S.; Schure, K.;
Schussler, F.; Schwab, T.; Schwanke, U.; Schwarz, J.; Schweizer, T.;
Schwemmer, S.; Schwendicke, U.; Schwerdt, C.; Sciacca, E.; Scuderi,
S.; Segreto, A.; Seiradakis, J. -H.; Sembroski, G. H.; Semikoz, D.;
Sergijenko, O.; Serre, N.; Servillat, M.; Seweryn, K.; Shafi, N.;
Shalchi, A.; Sharma, M.; Shayduk, M.; Shellard, R. C.; Shibata, T.;
Shigenaka, A.; Shilon, I.; Shum, E.; Sidoli, L.; Sidz, M.; Sieiro, J.;
Siejkowski, H.; Silk, J.; Sillanpää, A.; Simone, D.; Simpson, H.;
Singh, B. B.; Sinha, A.; Sironi, G.; Sitarek, J.; Sizun, P.; Sliusar,
V.; Sliusar, V.; Smith, A.; Sobczyńska, D.; Sol, H.; Sottile, G.;
Sowiński, M.; Spanier, F.; Spengler, G.; Spiga, R.; Stadler, R.;
Stahl, O.; Stamerra, A.; Stanič, S.; Starling, R.; Staszak, D.;
Stawarz, Ł.; Steenkamp, R.; Stefanik, S.; Stegmann, C.; Steiner, S.;
Stella, C.; Stephan, M.; Stergioulas, N.; Sternberger, R.; Sterzel, M.;
Stevenson, B.; Stinzing, F.; Stodulska, M.; Stodulski, M.; Stolarczyk,
T.; Stratta, G.; Straumann, U.; Stringhetti, L.; Strzys, M.; Stuik,
R.; Sulanke, K. -H.; Suomijärvi, T.; Supanitsky, A. D.; Suric, T.;
Sushch, I.; Sutcliffe, P.; Sykes, J.; Szanecki, M.; Szepieniec, T.;
Szwarnog, P.; Tacchini, A.; Tachihara, K.; Tagliaferri, G.; Tajima,
H.; Takahashi, H.; Takahashi, K.; Takahashi, M.; Takalo, L.; Takami,
S.; Takata, J.; Takeda, J.; Talbot, G.; Tam, T.; Tanaka, M.; Tanaka,
S.; Tanaka, T.; Tanaka, Y.; Tanci, C.; Tanigawa, S.; Tavani, M.;
Tavecchio, F.; Tavernet, J. -P.; Tayabaly, K.; Taylor, A.; Tejedor,
L. A.; Telezhinsky, I.; Temme, F.; Temnikov, P.; Tenzer, C.; Terada,
Y.; Terrazas, J. C.; Terrier, R.; Terront, D.; Terzic, T.; Tescaro,
D.; Teshima, M.; Teshima, M.; Testa, V.; Tezier, D.; Thayer, J.;
Thornhill, J.; Thoudam, S.; Thuermann, D.; Tibaldo, L.; Tiengo,
A.; Timpanaro, M. C.; Tiziani, D.; Tluczykont, M.; Todero Peixoto,
C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Tomastik, J.; Tomono, Y.;
Tonachini, A.; Tonev, D.; Torii, K.; Tornikoski, M.; Torres, D. F.;
Torres, M.; Torresi, E.; Toso, G.; Tosti, G.; Totani, T.; Tothill, N.;
Toussenel, F.; Tovmassian, G.; Toyama, T.; Travnicek, P.; Trichard,
C.; Trifoglio, M.; Troyano Pujadas, I.; Trzeciak, M.; Tsinganos, K.;
Tsujimoto, S.; Tsuru, T.; Uchiyama, Y.; Umana, G.; Umetsu, Y.; Upadhya,
S. S.; Uslenghi, M.; Vagelli, V.; Vagnetti, F.; Valdes-Galicia, J.;
Valentino, M.; Vallania, P.; Valore, L.; van Driel, W.; van Eldik,
C.; van Soelen, B.; Vandenbroucke, J.; Vanderwalt, J.; Vasileiadis,
G.; Vassiliev, V.; Vázquez, J. R.; Vázquez Acosta, M. L.; Vecchi,
M.; Vega, A.; Vegas, I.; Veitch, P.; Venault, P.; Venema, L.; Venter,
C.; Vercellone, S.; Vergani, S.; Verma, K.; Verzi, V.; Vettolani,
G. P.; Veyssiere, C.; Viana, A.; Viaux, N.; Vicha, J.; Vigorito,
C.; Vincent, P.; Vincent, S.; Vink, J.; Vittorini, V.; Vlahakis, N.;
Vlahos, L.; Voelk, H.; Voisin, V.; Vollhardt, A.; Volpicelli, A.; von
Brand, H.; Vorobiov, S.; Vovk, I.; Vrastil, M.; Vu, L. V.; Vuillaume,
T.; Wagner, R.; Wagner, R.; Wagner, S. J.; Wakely, S. P.; Walstra, T.;
Walter, R.; Walther, T.; Ward, J. E.; Ward, M.; Warda, K.; Warren,
D.; Wassberg, S.; Watson, J. J.; Wawer, P.; Wawrzaszek, R.; Webb,
N.; Wegner, P.; Weiner, O.; Weinstein, A.; Wells, R.; Werner, F.;
Wetteskind, H.; White, M.; White, R.; Więcek, M.; Wierzcholska, A.;
Wiesand, S.; Wijers, R.; Wilcox, P.; Wild, N.; Wilhelm, A.; Wilkinson,
M.; Will, M.; Will, M.; Williams, D. A.; Williams, J. T.; Willingale,
R.; Wilson, N.; Winde, M.; Winiarski, K.; Winkler, H.; Winter, M.;
Wischnewski, R.; Witt, E.; Wojcik, P.; Wolf, D.; Wood, M.; Wörnlein,
A.; Wu, E.; Wu, T.; Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamane,
N.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yelos, D.; Yoshida, A.;
Yoshida, M.; Yoshida, T.; Yoshiike, S.; Yoshikoshi, T.; Yu, P.;
Zabalza, V.; Zaborov, D.; Zacharias, M.; Zaharijas, G.; Zajczyk,
A.; Zampieri, L.; Zandanel, F.; Zanmar Sanchez, R.; Zaric, D.;
Zavrtanik, D.; Zavrtanik, M.; Zdziarski, A.; Zech, A.; Zechlin, H.;
Zhao, A.; Zhdanov, V.; Ziegler, A.; Ziemann, J.; Ziętara, K.; Zink,
A.; Ziółkowski, J.; Zitelli, V.; Zoli, A.; Zorn, J.; Żychowski, P.
2016arXiv161005151C Altcode:
List of contributions from the Cherenkov Telescope Array (CTA)
Consortium presented at the 6th International Symposium on High-Energy
Gamma-Ray Astronomy (Gamma 2016), July 11-15, 2016, in Heidelberg,
Germany.
---------------------------------------------------------
Title: MESA meets MURaM. Surface effects in main-sequence solar-like
oscillators computed using three-dimensional radiation hydrodynamics
simulations
Authors: Ball, W. H.; Beeck, B.; Cameron, R. H.; Gizon, L.
2016A&A...592A.159B Altcode: 2016arXiv160602713B
Context. Space-based observations of solar-like oscillators have
identified large numbers of stars in which many individual mode
frequencies can be precisely measured. However, current stellar models
predict oscillation frequencies that are systematically affected by
simplified modelling of the near-surface layers. <BR /> Aims: We use
three-dimensional radiation hydrodynamics simulations to better model
the near-surface equilibrium structure of dwarfs with spectral types F3,
G2, K0 and K5, and examine the differences between oscillation mode
frequencies computed in stellar models with and without the improved
near-surface equilibrium structure. <BR /> Methods: We precisely match
stellar models to the simulations' gravities and effective temperatures
at the surface, and to the temporally- and horizontally-averaged
densities and pressures at their deepest points. We then replace
the near-surface structure with that of the averaged simulation and
compute the change in the oscillation mode frequencies. We also fit
the differences using several parametric models currently available
in the literature. <BR /> Results: The surface effect in the stars of
solar-type and later is qualitatively similar and changes steadily
with decreasing effective temperature. In particular, the point of
greatest frequency difference decreases slightly as a fraction of
the acoustic cut-off frequency and the overall scale of the surface
effect decreases. The surface effect in the hot, F3-type star follows
the same trend in scale (I.e. it is larger in magnitude) but shows
a different overall variation with mode frequency. We find that a
two-term fit using the cube and inverse of the frequency divided by
the mode inertia is best able to reproduce the surface terms across
all four spectral types, although the scaled solar term and a modified
Lorentzian function also match the three cooler simulations reasonably
well. <BR /> Conclusions: Three-dimensional radiation hydrodynamics
simulations of near-surface convection can be averaged and combined with
stellar structure models to better predict oscillation mode frequencies
in solar-like oscillators. Our simplified results suggest that the
surface effect is generally larger in hotter stars (and correspondingly
smaller in cooler stars) and of similar shape in stars of solar type
and cooler. However, we cannot presently predict whether this will
remain so when other components of the surface effect are included.
---------------------------------------------------------
Title: The global solar dynamo
Authors: Cameron, Robert
2016cosp...41E.286C Altcode:
I will review our understanding of the solar dynamo, concentrating on
how observations constrain the theoretical possibilities. Possibilities
for future progress, including understanding the Sun in the
solar-stellar context will be outlined.
---------------------------------------------------------
Title: Solar activity in the coming decades
Authors: Cameron, Robert
2016cosp...41E.287C Altcode:
I will discuss the current state of our understanding of the solar
dynamo with an emphasis on the extent to which we can predict solar
activity on timescales from years to decades. Possible paths which
might lead to progress will be outlined and assessed.
---------------------------------------------------------
Title: A low upper limit on the subsurface rise speed of solar
active regions
Authors: Birch, A. C.; Schunker, H.; Braun, D. C.; Cameron, R.; Gizon,
L.; Lo ptien, B.; Rempel, M.
2016SciA....2E0557B Altcode: 2016arXiv160705250B
Magnetic field emerges at the surface of the Sun as sunspots and active
regions. This process generates a poloidal magnetic field from a rising
toroidal flux tube, it is a crucial but poorly understood aspect of
the solar dynamo. The emergence of magnetic field is also important
because it is a key driver of solar activity. We show that measurements
of horizontal flows at the solar surface around emerging active regions,
in combination with numerical simulations of solar magnetoconvection,
can constrain the subsurface rise speed of emerging magnetic flux. The
observed flows imply that the rise speed of the magnetic field is
no larger than 150 m/s at a depth of 20 Mm, that is, well below the
prediction of the (standard) thin flux tube model but in the range
expected for convective velocities at this depth. We conclude that
convective flows control the dynamics of rising flux tubes in the upper
layers of the Sun and cannot be neglected in models of flux emergence.
---------------------------------------------------------
Title: Surface flux transport simulations. Inflows towards active
regions and the modulation of the solar cycle.
Authors: Martin-Belda, David; Cameron, Robert
2016cosp...41E1255M Altcode:
Aims. We investigate the way near-surface converging flows
towards active regions affect the build-up of magnetic field at
the Sun's polar caps. In the Babcock-Leighton dynamo framework,
this modulation of the polar fields could explain the variability of
the solar cycle. Methods. We develop a surface flux transport code
incorporating a parametrized model of the inflows and run simulations
spanning several cycles. We carry out a parameter study to test how
the strength and extension of the inflows affect the amplitude of the
polar fields. Results. Inflows are seen to play an important role in
the build-up of the polar fields, and can act as the non-linearity
feedback mechanism required to limit the strength of the solar cycles
in the Babcock-Leighton dynamo framework.
---------------------------------------------------------
Title: The origin of Total Solar Irradiance variability on timescales
less than a day
Authors: Shapiro, Alexander; Krivova, Natalie; Schmutz, Werner;
Solanki, Sami K.; Leng Yeo, Kok; Cameron, Robert; Beeck, Benjamin
2016cosp...41E1774S Altcode:
Total Solar Irradiance (TSI) varies on timescales from minutes to
decades. It is generally accepted that variability on timescales of
a day and longer is dominated by solar surface magnetic fields. For
shorter time scales, several additional sources of variability have
been proposed, including convection and oscillation. However, available
simplified and highly parameterised models could not accurately explain
the observed variability in high-cadence TSI records. We employed the
high-cadence solar imagery from the Helioseismic and Magnetic Imager
onboard the Solar Dynamics Observatory and the SATIRE (Spectral And
Total Irradiance Reconstruction) model of solar irradiance variability
to recreate the magnetic component of TSI variability. The recent 3D
simulations of solar near-surface convection with MURAM code have been
used to calculate the TSI variability caused by convection. This allowed
us to determine the threshold timescale between TSI variability caused
by the magnetic field and convection. Our model successfully replicates
the TSI measurements by the PICARD/PREMOS radiometer which span the
period of July 2010 to February 2014 at 2-minute cadence. Hence,
we demonstrate that solar magnetism and convection can account for
TSI variability at all timescale it has ever been measured (sans the
5-minute component from p-modes).
---------------------------------------------------------
Title: Solar Cycle 25: Another Moderate Cycle?
Authors: Cameron, R. H.; Jiang, J.; Schüssler, M.
2016ApJ...823L..22C Altcode: 2016arXiv160405405C
Surface flux transport simulations for the descending phase of
Cycle 24 using random sources (emerging bipolar magnetic regions)
with empirically determined scatter of their properties provide a
prediction of the axial dipole moment during the upcoming activity
minimum together with a realistic uncertainty range. The expectation
value for the dipole moment around 2020 (2.5 ± 1.1 G) is comparable
to that observed at the end of Cycle 23 (about 2 G). The empirical
correlation between the dipole moment during solar minimum and the
strength of the subsequent cycle thus suggests that Cycle 25 will
be of moderate amplitude, not much higher than that of the current
cycle. However, the intrinsic uncertainty of such predictions resulting
from the random scatter of the source properties is considerable and
fundamentally limits the reliability with which such predictions can
be made before activity minimum is reached.
---------------------------------------------------------
Title: The turbulent diffusion of toroidal magnetic flux as inferred
from properties of the sunspot butterfly diagram
Authors: Cameron, R. H.; Schüssler, M.
2016A&A...591A..46C Altcode: 2016arXiv160407340C
Context. In order to match observed properties of the solar cycle,
flux-transport dynamo models require the toroidal magnetic flux to be
stored in a region of low magnetic diffusivity, typically located at
or below the bottom of the convection zone. <BR /> Aims: We infer the
turbulent magnetic diffusivity affecting the toroidal field on the basis
of empirical data. <BR /> Methods: We considered the time evolution of
mean latitude and width of the activity belts of solar cycles 12-23 and
their dependence on cycle strength. We interpreted the decline phase
of the cycles as a diffusion process. <BR /> Results: The activity
level of a given cycle begins to decline when the centers of its
equatorward propagating activity belts come within their (full) width
(at half maximum) from the equator. This happens earlier for stronger
cycles because their activity belts are wider. From that moment on, the
activity and the belt width decrease in the same manner for all cycles,
independent of their maximum activity level. In terms of diffusive
cancellation of opposite-polarity toroidal flux across the equator,
we infer the turbulent diffusivity experienced by the toroidal field,
wherever it is located, to be in the range 150-450 km<SUP>2</SUP>
s<SUP>-1</SUP>. Strong diffusive latitudinal spreading of the toroidal
flux underneath the activity belts can be inhibited by an inflow toward
the toroidal field bands in the convection zone with a magnitude of
several meters per second. <BR /> Conclusions: The inferred value of
the turbulent magnetic diffusivity affecting the toroidal field agrees,
to order of magnitude, with estimates based on mixing-length models for
the solar convection zone. This is at variance with the requirement of
flux-transport dynamo models. The inflows required to keep the toroidal
field bands together before they approach the equator are similar to the
inflows toward the activity belts observed with local helioseismology.
---------------------------------------------------------
Title: Statistical Differences in Time-Distance Helioseismology
Results
Authors: Hess Webber, Shea A.; Pesnell, William D.; Duvall, Thomas;
Cameron, Robert; Birch, A. C.
2016SPD....4720301H Altcode:
Time-distance helioseismology studies phase correlations in solar wave
modes. We use these techniques to investigate the phase differences in
f-mode wave propagation within a coronal hole feature and without. We
isolate the coronal hole boundary location using edge detection
techniques on SDO AIA data. We then use this location information to
inform the analysis of the corresponding HMI time-distance velocity
tracked data product, provided by Stanford's JSOC archive. We look
at time-distance results inside the coronal hole, outside the coronal
hole, the coronal hole data as a whole, and an independent quiet sun
region. We use Student's t-Test to evaluate the significance of the
differences between the various regions.
---------------------------------------------------------
Title: Babcock-Leighton solar dynamo: the role of downward pumping
and the equatorward propagation of activity
Authors: Karak, Bidya Binay; Cameron, Robert
2016SPD....47.0717K Altcode:
We investigate the role of downward magnetic pumping near the surface
using a kinematic Babcock-Leighton model. We find that the pumping
causes the poloidal field to become predominately radial in the
near-surface shear layer. This allows the negative radial shear in the
near-surface layer to effectively act on the radial field to produce a
toroidal field. Consequently, we observe a clear equatorward migration
of the toroidal field at low latitudes even when there is no meridional
flow in the deep CZ. We show a case where the period of a dynamo wave
solution is approximately 11 years. Flux transport models are also shown
with periods close to 11 years. Both the dynamo wave and flux transport
dynamo are thus able to reproduce some of the observed features of solar
cycle. The main difference between the two types of dynamo is the value
of $\alpha$ required to produce dynamo action. In both types of dynamo,
the surface meridional flow helps to advect and build the polar field
in high latitudes, while in flux transport dynamo the equatorward flow
near the bottom of CZ advects toroidal field to cause the equatorward
migration in butterfly wings and this advection makes the dynamo easier
by transporting strong toroidal field to low latitudes where $\alpha$
effect works. Another conclusion of our study is that the magnetic
pumping suppresses the diffusion of fields through the photospheric
surface which helps to achieve the 11-year dynamo cycle at a moderately
larger value of magnetic diffusivity than has previously been used.
---------------------------------------------------------
Title: Semi-empirical Long-term Reconstruction of the Heliospheric
Parameters: Validation by Cosmogenic Radionuclide Records
Authors: Asvestari, E.; Usoskin, I. G.; Cameron, R. H.; Krivova, N. A.
2016ASPC..504..269A Altcode:
We have developed a semi-empirical model that describes the heliospheric
modulation of galactic cosmic rays considering different heliospheric
parameters. This model is an improvement of a previous model. The
parameters of the model are fitted using the observations and
reconstructions of the heliospheric parameters for the period 1976 -
2013, which includes the latest very weak solar minimum. The modulation
potential is computed since 1610 using different reconstructions of the
open solar magnetic flux and it is then used to compute the production
and distribution of cosmogenic isotope <SUP>14</SUP>C, which was
subsequently compared with terrestrial archives in tree rings. It is
shown that the group sunspot number series by Svalgaard & Schatten
(2015) is inconsistent with the data, while other series agree well.
---------------------------------------------------------
Title: Surface flux transport simulations: Effect of inflows toward
active regions and random velocities on the evolution of the Sun's
large-scale magnetic field
Authors: Martin-Belda, D.; Cameron, R. H.
2016A&A...586A..73M Altcode: 2015arXiv151202541M
<BR /> Aims: We aim to determine the effect of converging flows on
the evolution of a bipolar magnetic region (BMR), and to investigate
the role of these inflows in the generation of poloidal flux. We
also discuss whether the flux dispersal due to turbulent flows can
be described as a diffusion process. <BR /> Methods: We developed
a simple surface flux transport model based on point-like magnetic
concentrations. We tracked the tilt angle, the magnetic flux and the
axial dipole moment of a BMR in simulations with and without inflows and
compared the results. To test the diffusion approximation, simulations
of random walk dispersal of magnetic features were compared against the
predictions of the diffusion treatment. <BR /> Results: We confirm the
validity of the diffusion approximation to describe flux dispersal on
large scales. We find that the inflows enhance flux cancellation, but
at the same time affect the latitudinal separation of the polarities
of the bipolar region. In most cases the latitudinal separation is
limited by the inflows, resulting in a reduction of the axial dipole
moment of the BMR. However, when the initial tilt angle of the BMR
is small, the inflows produce an increase in latitudinal separation
that leads to an increase in the axial dipole moment in spite of the
enhanced flux destruction. This can give rise to a tilt of the BMR
even when the BMR was originally aligned parallel to the equator.
---------------------------------------------------------
Title: Limitations of force-free magnetic field extrapolations:
Revisiting basic assumptions
Authors: Peter, H.; Warnecke, J.; Chitta, L. P.; Cameron, R. H.
2015A&A...584A..68P Altcode: 2015arXiv151004642P
Context. Force-free extrapolations are widely used to study the magnetic
field in the solar corona based on surface measurements. <BR /> Aims:
The extrapolations assume that the ratio of internal energy of the
plasma to magnetic energy, the plasma β, is negligible. Despite the
widespread use of this assumption observations, models, and theoretical
considerations show that β is of the order of a few percent to more
than 10%, and thus not small. We investigate what consequences this
has for the reliability of extrapolation results. <BR /> Methods: We
use basic concepts starting with force and energy balance to infer
relations between plasma β and free magnetic energy to study the
direction of currents in the corona with respect to the magnetic
field, and to estimate the errors in the free magnetic energy by
neglecting effects of the plasma (β ≪ 1). A comparison with a 3D
magneto-hydrodynamics (MHD) model supports our basic considerations. <BR
/> Results: If plasma β is of the order of the relative free energy
(the ratio of the free magnetic energy to the total magnetic energy)
then the pressure gradient can balance the Lorentz force. This is the
case in solar corona, and therefore the currents are not properly
described. In particular, the error in terms of magnetic energy by
neglecting the plasma is of the order of the free magnetic energy, so
that the latter cannot be reliably determined by an extrapolation. <BR
/> Conclusions: While a force-free extrapolation might capture the
magnetic structure and connectivity of the coronal magnetic field,
the derived currents and free magnetic energy are not reliable. Thus
quantitative results of extrapolations on the location and amount of
heating in the corona (through current dissipation) and on the energy
storage of the magnetic field (e.g. for eruptive events) are limited.
---------------------------------------------------------
Title: Toward the construction of a medium size prototype
Schwarzschild-Couder telescope for CTA
Authors: Rousselle, J.; Byrum, K.; Cameron, R.; Connaughton, V.;
Errando, M.; Griffiths, S.; Guarino, V.; Humensky, T. B.; Jenke, P.;
Kaaret, P.; Kieda, D.; Limon, M.; Mognet, I.; Mukherjee, R.; Nieto,
D.; Okumura, A.; Peck, A.; Petrashyk, A.; Ribeiro, D.; Stevenson,
B.; Vassiliev, V.; Yu, P.
2015SPIE.9603E..05R Altcode:
The construction of a prototype Schwarzschild-Couder telescope (pSCT)
started in early June 2015 at the Fred Lawrence Whipple Observatory
in Southern Arizona, as a candidate medium-sized telescope for the
Cherenkov Telescope Array (CTA). Compared to current Davies-Cotton
telescopes, this novel instrument with an aplanatic two-mirror
optical system will offer a wider field-of-view and improved angular
resolution. In addition, the reduced plate scale of the camera
allows the use of highly-integrated photon detectors such as silicon
photo multipliers. As part of CTA, this design has the potential to
greatly improve the performance of the next generation ground-based
observatory for very high-energy (E>60 GeV) gamma-ray astronomy. In
this contribution we present the design and performance of both optical
and alignment systems of the pSCT.
---------------------------------------------------------
Title: Three-dimensional simulations of near-surface convection
in main-sequence stars. III. The structure of small-scale magnetic
flux concentrations
Authors: Beeck, B.; Schüssler, M.; Cameron, R. H.; Reiners, A.
2015A&A...581A..42B Altcode: 2015arXiv150504739B
Context. The convective envelopes of cool main-sequence stars harbour
magnetic fields with a complex global and local structure. These fields
affect the near-surface convection and the outer stellar atmospheres
in many ways and are responsible for the observable magnetic activity
of stars. <BR /> Aims: Our aim is to understand the local structure in
unipolar regions with moderate average magnetic flux density. These
correspond to plage regions covering a substantial fraction of the
surface of the Sun (and likely also the surface of other Sun-like stars)
during periods of high magnetic activity. <BR /> Methods: We analyse
the results of 18 local-box magnetohydrodynamics simulations covering
the upper layers of the convection zones and the photospheres of cool
main-sequence stars of spectral types F to early M. The average vertical
field in these simulations ranges from 20 to 500 G. <BR /> Results:
We find a substantial variation of the properties of the surface
magnetoconvection between main-sequence stars of different spectral
types. As a consequence of a reduced efficiency of the convective
collapse of flux tubes, M dwarfs lack bright magnetic structures in
unipolar regions of moderate field strength. The spatial correlation
between velocity and the magnetic field as well as the lifetime
of magnetic structures and their sizes relative to the granules
vary significantly along the model sequence of stellar types. <P
/>Movies associated to Fig. A.1 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201525788/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Three-dimensional simulations of near-surface convection
in main-sequence stars. IV. Effect of small-scale magnetic flux
concentrations on centre-to-limb variation and spectral lines
Authors: Beeck, B.; Schüssler, M.; Cameron, R. H.; Reiners, A.
2015A&A...581A..43B Altcode: 2015arXiv150504744B
Context. Magnetic fields affect the local structure of the photosphere
of stars. They can considerably influence the radiative properties near
the optical surface, flow velocities, and the temperature and pressure
profiles. This has an impact on observables such as limb darkening
and spectral line profiles. <BR /> Aims: We aim at understanding
qualitatively the influence of small magnetic flux concentrations
in unipolar plage regions on the centre-to-limb variation of
the intensity and its contrast and on the shape of spectral line
profiles in cool main-sequence stars. <BR /> Methods: We analyse
the bolometric and continuum intensity and its angular dependence
of 24 radiative magnetohydrodynamic simulations of the near-surface
layers of main-sequence stars with six different sets of stellar
parameters (spectral types F to early M) and four different average
magnetic field strengths (including the non-magnetic case). We also
calculated disc-integrated profiles of three spectral lines. <BR />
Results: The small magnetic flux concentrations formed in the magnetic
runs of simulations have a considerable impact on the intensity and
its centre-to-limb variation. In some cases, the difference in limb
darkening between magnetic and non-magnetic runs is larger than the
difference between the spectral types. Spectral lines are not only
broadened owing to the Zeeman effect, but are also strongly affected by
the modified thermodynamical structure and flow patterns. This indirect
magnetic impact on the line profiles is often bigger than that of the
Zeeman effect. <BR /> Conclusions: The effects of the magnetic field on
the radiation leaving the star can be considerable and is not restricted
to spectral line broadening and polarisation by the Zeeman effect. The
inhomogeneous structure of the magnetic field on small length scales and
its impact on (and spatial correlation with) the local thermodynamical
structure and the flow field near the surface influence the measurement
of the global field properties and stellar parameters. These
effects need to be taken into account in the interpretation of
observations. <P />Appendix A is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201525874/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: A Medium Sized Schwarzschild-Couder Cherenkov Telescope
Mechanical Design Proposed for the Cherenkov Telescope Array
Authors: Byrum, K.; Humensky, T. B.; Benbow, W.; Cameron, R.; Criswell,
S.; Errando, M.; Guarino, V.; Kaaret, P.; Kieda, D.; Mukherjee,
R.; Naumann, D.; Nieto, D.; Northrop, R.; Okumura, A.; Roache, E.;
Rousselle, J.; Schlenstedt, S.; Sternberger, R.; Vassiliev, V.;
Wakely, S.; Zhao, H.
2015arXiv150903074B Altcode:
The Cherenkov Telescope Array (CTA) is an international next-generation
ground-based gamma-ray observatory. CTA will be implemented as southern
and northern hemisphere arrays of tens of small, medium and large-sized
imaging Cherenkov telescopes with the goal of improving the sensitivity
over the current-generation experiments by an order of magnitude. CTA
will provide energy coverage from ~20 GeV to more than 300 TeV. The
Schwarzschild-Couder (SC) medium size (9.5m) telescopes will feature
a novel aplanatic two-mirror optical design capable of accommodating
a wide field-of-view with significantly improved angular resolution as
compared to the traditional Davies-Cotton optical design. A full-scale
prototype SC medium size telescope structure has been designed and will
be constructed at the Fred Lawrence Whipple Observatory in southern
Arizona during the fall of 2015. concentrate on the novel features of
the design.
---------------------------------------------------------
Title: CTA Contributions to the 34th International Cosmic Ray
Conference (ICRC2015)
Authors: CTA Consortium, The; :; Abchiche, A.; Abeysekara, U.; Abril,
Ó.; Acero, F.; Acharya, B. S.; Actis, M.; Agnetta, G.; Aguilar,
J. A.; Aharonian, F.; Akhperjanian, A.; Albert, A.; Alcubierre,
M.; Alfaro, R.; Aliu, E.; Allafort, A. J.; Allan, D.; Allekotte,
I.; Aloisio, R.; Amans, J. -P.; Amato, E.; Ambrogi, L.; Ambrosi, G.;
Ambrosio, M.; Anderson, J.; Anduze, M.; Angüner, E. O.; Antolini, E.;
Antonelli, L. A.; Antonucci, M.; Antonuccio, V.; Antoranz, P.; Aramo,
C.; Aravantinos, A.; Argan, A.; Armstrong, T.; Arnaldi, H.; Arnold, L.;
Arrabito, L.; Arrieta, M.; Arrieta, M.; Asano, K.; Asorey, H. G.; Aune,
T.; Singh, C. B.; Babic, A.; Backes, M.; Bais, A.; Bajtlik, S.; Balazs,
C.; Balbo, M.; Balis, D.; Balkowski, C.; Ballester, O.; Ballet, J.;
Balzer, A.; Bamba, A.; Bandiera, R.; Barber, A.; Barbier, C.; Barceló,
M.; Barnacka, A.; Barres de Almeida, U.; Barrio, J. A.; Basso, S.;
Bastieri, D.; Bauer, C.; Baushev, A.; Becciani, U.; Becherini, Y.;
Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Benbow, W.; Benedico
Ventura, D.; Berdugo, J.; Berge, D.; Bernardini, E.; Bernhard, S.;
Bernlöhr, K.; Bertucci, B.; Besel, M. -A.; Bhatt, N.; Bhattacharjee,
P.; Bhattachryya, S.; Biasuzzi, B.; Bicknell, G.; Bigongiari, C.;
Biland, A.; Billotta, S.; Bilnik, W.; Biondo, B.; Bird, T.; Birsin,
E.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blanch Bigas, O.; Blasi,
P.; Boehm, C.; Bogacz, L.; Bogdan, M.; Bohacova, M.; Boisson, C.;
Boix Gargallo, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonifacio,
P.; Bonnoli, G.; Borkowski, J.; Bose, R.; Bosnjak, Z.; Bottani, A.;
Böttcher, M.; Bousquet, J. -J.; Boutonnet, C.; Bouyjou, F.; Braiding,
C.; Brandt, L.; Brau-Nogué, S.; Bregeon, J.; Bretz, T.; Briggs,
M.; Brigida, M.; Bringmann, T.; Brisken, W.; Brocato, E.; Brook, P.;
Brown, A. M.; Brun, P.; Brunetti, G.; Brunetti, L.; Bruno, P.; Bryan,
M.; Buanes, T.; Bucciantini, N.; Buchholtz, G.; Buckley, J.; Bugaev,
V.; Bühler, R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.;
Busetto, G.; Buson, S.; Buss, J.; Byrum, K.; Cameron, R.; Camprecios,
J.; Canelli, F.; Canestrari, R.; Cantu, S.; Capalbi, M.; Capasso, M.;
Capobianco, G.; Caraveo, P.; Cardenzana, J.; Carius, S.; Carlile, C.;
Carmona, E.; Carosi, A.; Carosi, R.; Carr, J.; Carroll, M.; Carter,
J.; Carton, P. -H.; Caruso, R.; Casandjian, J. -M.; Casanova, S.;
Cascone, E.; Casiraghi, M.; Castellina, A.; Catalano, O.; Catalanotti,
S.; Cavazzani, S.; Cazaux, S.; Cefalà, M.; Cerchiara, P.; Cereda,
M.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chaty,
S.; Chaves, R.; Cheimets, P.; Chen, A.; Chen, X.; Chernyakova, M.;
Chiappetti, L.; Chikawa, M.; Chinn, D.; Chitnis, V. R.; Cho, N.;
Christov, A.; Chudoba, J.; Cieślar, M.; Cillis, A.; Ciocci, M. A.;
Clay, R.; Cohen-Tanugi, J.; Colafrancesco, S.; Colin, P.; Colombo,
E.; Colome, J.; Colonges, S.; Compin, M.; Conforti, V.; Connaughton,
V.; Connell, S.; Conrad, J.; Contreras, J. L.; Coppi, P.; Corbel, S.;
Coridian, J.; Corona, P.; Corti, D.; Cortina, J.; Cossio, L.; Costa,
A.; Costantini, H.; Cotter, G.; Courty, B.; Covino, S.; Covone, G.;
Crimi, G.; Criswell, S. J.; Crocker, R.; Croston, J.; Cusumano, G.;
Da Vela, P.; Dale, Ø.; D'Ammando, F.; Dang, D.; Daniel, M.; Davids,
I.; Dawson, B.; Dazzi, F.; de Aguiar Costa, B.; De Angelis, A.; de
Araujo Cardoso, R. F.; De Caprio, V.; De Cesare, G.; De Franco, A.;
De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De La
Vega, G. A.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; de
Mello Neto, J. R. T.; de Naurois, M.; de Oña Wilhelmi, E.; De Palma,
F.; de Souza, V.; Decock, G.; Deil, C.; Del Santo, M.; Delagnes, E.;
Deleglise, G.; Delgado, C.; della Volpe, D.; Deloye, P.; Depaola, G.;
Detournay, M.; Dettlaff, A.; Di Girolamo, T.; Di Giulio, C.; Di Paola,
A.; Di Pierro, F.; Di Sciascio, G.; Díaz, C.; Dick, J.; Dickinson, H.;
Diebold, S.; Diez, V.; Digel, S.; Dipold, J.; Disset, G.; Distefano,
A.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko, W.; Dominik,
N.; Dominis Prester, D.; Donat, A.; Donnarumma, I.; Dorner, D.; Doro,
M.; Dournaux, J. -L.; Doyle, K.; Drake, G.; Dravins, D.; Drury, L.;
Dubus, G.; Dumas, D.; Dumm, J.; Durand, D.; D'Urso, D.; Dwarkadas,
V.; Dyks, J.; Dyrda, M.; Ebr, J.; Echaniz, J. C.; Edy, E.; Egberts,
K.; Egberts, K.; Eger, P.; Einecke, S.; Eisch, J.; Eisenkolb, F.;
Eleftheriadis, C.; Elsässer, D.; Emmanoulopoulos, D.; Engelbrecht,
C.; Engelhaupt, D.; Ernenwein, J. -P.; Errando, M.; Eschbach, S.;
Etchegoyen, A.; Evans, P.; Fairbairn, M.; Falcone, A.; Fantinel, D.;
Farakos, K.; Farnier, C.; Farrell, E.; Farrell, S.; Fasola, G.; Fegan,
S.; Feinstein, F.; Ferenc, D.; Fernandez, A.; Fernandez-Alonso, M.;
Ferreira, O.; Fesquet, M.; Fetfatzis, P.; Fiasson, A.; Filipčič, A.;
Filipovic, M.; Fink, D.; Finley, C.; Finley, J. P.; Finoguenov, A.;
Fioretti, V.; Fiorini, M.; Firpo Curcoll, R.; Fleischhack, H.; Flores,
H.; Florin, D.; Föhr, C.; Fokitis, E.; Font, L.; Fontaine, G.; Fontes,
B.; Forest, F.; Fornasa, M.; Förster, A.; Fortin, P.; Fortson, L.;
Fouque, N.; Franckowiak, A.; Franco, F. J.; Frankowski, A.; Frega,
N.; Freire Mota Albuquerque, I.; Freixas Coromina, L.; Fresnillo,
L.; Fruck, C.; Fuessling, M.; Fugazza, D.; Fujita, Y.; Fukami, S.;
Fukazawa, Y.; Fukuda, T.; Fukui, Y.; Funk, S.; Gäbele, W.; Gabici,
S.; Gadola, A.; Galante, N.; Gall, D. D.; Gallant, Y.; Galloway, D.;
Gallozzi, S.; Gao, S.; Garcia, B.; García Gil, R.; Garcia López,
R.; Garczarczyk, M.; Gardiol, D.; Gargano, C.; Gargano, F.; Garozzo,
S.; Garrecht, F.; Garrido, D.; Garrido, L.; Gascon, D.; Gaskins,
J.; Gaudemard, J.; Gaug, M.; Gaweda, J.; Geffroy, N.; Gérard, L.;
Ghalumyan, A.; Ghedina, A.; Ghigo, M.; Ghislain, P.; Giannakaki, E.;
Gianotti, F.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Giglietto,
N.; Gika, V.; Gimenes, R.; Giomi, M.; Giommi, P.; Giordano, F.;
Giovannini, G.; Giro, E.; Giroletti, M.; Giuliani, A.; Glicenstein,
J. -F.; Godinovic, N.; Goldoni, P.; Gomez Berisso, M.; Gomez Vargas,
G. A.; Gonzalez, M. M.; González, A.; González, F.; González
Muñoz, A.; Gothe, K. S.; Gotz, D.; Grabarczyk, T.; Graciani, R.;
Grandi, P.; Grañena, F.; Granot, J.; Grasseau, G.; Gredig, R.;
Green, A. J.; Green, A. M.; Greenshaw, T.; Grenier, I.; Grillo, A.;
Grondin, M. -H.; Grube, J.; Grudzinska, M.; Grygorczuk, J.; Guarino,
V.; Guberman, D.; Gunji, S.; Gyuk, G.; Hadasch, D.; Hagedorn, A.;
Hahn, J.; Hakansson, N.; Hamer Heras, N.; Hanabata, Y.; Hara, S.;
Hardcastle, M. J.; Harris, J.; Hassan, T.; Hatanaka, K.; Haubold,
T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, M.; Heller, R.;
Henault, F.; Henri, G.; Hermann, G.; Hermel, R.; Herrera Llorente, J.;
Herrero, A.; Hervet, O.; Hidaka, N.; Hinton, J.; Hirai, W.; Hirotani,
K.; Hoard, D.; Hoffmann, D.; Hofmann, W.; Hofverberg, P.; Holch, T.;
Holder, J.; Hooper, S.; Horan, D.; Hörandel, J. R.; Hormigos, S.;
Horns, D.; Hose, J.; Houles, J.; Hovatta, T.; Hrabovsky, M.; Hrupec,
D.; Huet, J. -M.; Hütten, M.; Humensky, T. B.; Huovelin, J.; Huppert,
J. -F.; Iacovacci, M.; Ibarra, A.; Idźkowski, B.; Ikawa, D.; Illa,
J. M.; Impiombato, D.; Incorvaia, S.; Inome, Y.; Inoue, S.; Inoue,
T.; Inoue, Y.; Iocco, F.; Ioka, K.; Iori, M.; Ishio, K.; Israel,
G. L.; Jablonski, C.; Jacholkowska, A.; Jacquemier, J.; Jamrozy,
M.; Janecek, P.; Janiak, M.; Jankowsky, F.; Jean, P.; Jeanney, C.;
Jegouzo, I.; Jenke, P.; Jimenez, J. J.; Jingo, M.; Jingo, M.; Jocou,
L.; Jogler, T.; Johnson, C. A.; Journet, L.; Juffroy, C.; Jung,
I.; Kaaret, P. E.; Kagaya, M.; Kakuwa, J.; Kalekin, O.; Kalkuhl, C.;
Kankanyan, R.; Karastergiou, A.; Kärcher, K.; Karczewski, M.; Karkar,
S.; Karn, P.; Kasperek, J.; Katagiri, H.; Kataoka, J.; Katarzyński,
K.; Katz, U.; Kaufmann, S.; Kawanaka, N.; Kawashima, T.; Kazanas,
D.; Kelley-Hoskins, N.; Kellner-Leidel, B.; Kendziorra, E.; Kersten,
J.; Khélifi, B.; Kieda, D. B.; Kihm, T.; Kisaka, S.; Kissmann, R.;
Klepser, S.; Kluźniak, W.; Knapen, J.; Knapp, J.; Knödlseder, J.;
Köck, F.; Kocot, J.; Kodakkadan, A.; Kodani, K.; Kohri, K.; Kojima,
T.; Kokkotas, K.; Kolitzus, D.; Komin, N.; Kominis, I.; Konno, Y.;
Kosack, K.; Koss, G.; Koul, R.; Kowal, G.; Koyama, S.; Kozioł,
J.; Kraus, M.; Krause, J.; Krause, M.; Krawzcynski, H.; Krennrich,
F.; Kretzschmann, A.; Kruger, P.; Kubo, H.; Kudryavtsev, V.; Kukec
Mezek, G.; Kushida, J.; Kuznetsov, A.; La Barbera, A.; La Palombara,
N.; La Parola, V.; La Rosa, G.; Laffon, H.; Lagadec, T.; Lahmann,
R.; Lalik, K.; Lamanna, G.; Landriu, D.; Landt, H.; Lang, R. G.;
Languignon, D.; Lapington, J.; Laporte, P.; Latovski, N.; Law-Green,
D.; Le Fèvre, J. -P.; Le Flour, T.; Le Sidaner, P.; Lee, S. -H.; Lee,
W. H.; Leffhalm, K.; Leich, H.; Leigui de Oliveira, M. A.; Lelas,
D.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J. -P.; Leonard, R.;
Leoni, R.; Lessio, L.; Leto, G.; Leveque, A.; Lieunard, B.; Limon,
M.; Lindemann, R.; Lindfors, E.; Liolios, A.; Lipniacka, A.; Lockart,
H.; Lohse, T.; Loiseau, D.; Łokas, E.; Lombardi, S.; Longo, F.;
Longo, G.; Lopatin, A.; Lopez, M.; López-Coto, R.; López-Oramas,
A.; Loreggia, D.; Louge, T.; Louis, F.; Lu, C. -C.; Lucarelli, F.;
Lucchesi, D.; Lüdecke, H.; Luque-Escamilla, P. L.; Luz, O.; Lyard,
E.; Maccarone, M. C.; Maccarone, T. J.; Mach, E.; Madejski, G. M.;
Madonna, A.; Mahabir, M.; Maier, G.; Majumdar, P.; Makariev, M.;
Malaguti, G.; Malaspina, G.; Mallot, A. K.; Maltezos, S.; Mancilla,
A.; Mandat, D.; Maneva, G.; Manigot, P.; Mankushiyil, N.; Mannheim,
K.; Maragos, N.; Marano, D.; Marchegiani, P.; Marcomini, J. A.;
Marcowith, A.; Mariotti, M.; Marisaldi, M.; Markoff, S.; Marszałek,
A.; Martens, C.; Martí, J.; Martin, J. -M.; Martin, P.; Martínez, G.;
Martínez, M.; Martínez, O.; Marx, R.; Massimino, P.; Mastichiadis,
A.; Mastroianni, S.; Mastropietro, M.; Masuda, S.; Matsumoto, H.;
Matsuoka, S.; Mattiazzo, S.; Maurin, G.; Maxted, N.; Maya, J.; Mayer,
M.; Mazin, D.; Mazureau, E.; Mazziotta, M. N.; Mc Comb, L.; McCann,
A.; McCubbin, N.; McHardy, I.; McKay, R.; McKinney, K.; Meagher, K.;
Medina, C.; Mehrez, F.; Melioli, C.; Melkumyan, D.; Melo, D.; Melse,
T.; Mereghetti, S.; Mertsch, P.; Meyer, M.; Meyrelles, J. L., jr;
Miccichè, A.; Michałowski, J.; Micolon, P.; Mientjes, P.; Mignot,
S.; Mihailidis, A.; Mineo, T.; Minuti, M.; Mirabal, N.; Mirabel, F.;
Miranda, J. M.; Mirzoyan, R.; Mistò, A.; Mitchell, A.; Mizuno, T.;
Moderski, R.; Mognet, I.; Mohammed, M.; Moharana, R.; Molinari, E.;
Monmarthe, E.; Monnier, G.; Montaruli, T.; Monte, C.; Monteiro, I.;
Moore, P.; Moralejo Olaizola, A.; Morello, C.; Moretti, E.; Mori,
K.; Morlino, G.; Morselli, A.; Mottez, F.; Moudden, Y.; Moulin, E.;
Mrusek, I.; Mueller, S.; Mukherjee, R.; Munar-Adrover, P.; Mundell,
C.; Muraishi, H.; Murase, K.; Muronga, A.; Murphy, A.; Nagataki,
S.; Nagayoshi, T.; Nagesh, B. K.; Naito, T.; Nakajima, D.; Nakamori,
T.; Nakayama, K.; Naumann, D.; Nayman, P.; Nellen, L.; Nemmen, R.;
Neronov, A.; Neustroev, V.; Neyroud, N.; Nguyen, T.; Nicastro,
L.; Nicolau-Kukliński, J.; Niederwanger, F.; Niedźwiecki, A.;
Niemiec, J.; Nieto, D.; Nievas, M.; Nikolaidis, A.; Nishijima, K.;
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G.; O'Faolain de Bhroithe, A.; Ogino, M.; Ohira, Y.; Ohishi, M.; Ohm,
S.; Ohoka, H.; Okumura, A.; Olive, J. -F.; Olszowski, D.; Ong, R. A.;
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A.; Padovani, M.; Pagano, I.; Paiano, S.; Paizis, A.; Palacio, J.;
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D.; Panter, M.; Panzera, M. R.; Paoletti, R.; Paolillo, M.; Papayannis,
A.; Papyan, G.; Paravac, A.; Paredes, J. M.; Pareschi, G.; Park, N.;
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A.; Pedaletti, G.; Peet, S.; Pelassa, V.; Pelat, D.; Peres, C.;
Perez, M. d. C.; Perri, L.; Persic, M.; Petrashyk, A.; Petrucci,
P. -O.; Peyaud, B.; Pfeifer, M.; Pfeiffer, G.; Piano, G.; Pichel,
A.; Pieloth, D.; Pierbattista, M.; Pierre, E.; Pinto de Pinho, F.;
García, C. Pio; Piret, Y.; Pita, S.; Planes, A.; Platino, M.; Platos,
Ł.; Platzer, R.; Podkladkin, S.; Pogosyan, L.; Pohl, M.; Poinsignon,
P.; Ponz, J. D.; Porcelli, A.; Potter, W.; Poulios, S.; Poutanen,
J.; Prandini, E.; Prast, J.; Preece, R.; Profeti, F.; Prokhorov, D.;
Prokoph, H.; Prouza, M.; Proyetti, M.; Pruchniewicz, R.; Pueschel,
E.; Pühlhofer, G.; Puljak, I.; Punch, M.; Pyzioł, R.; Queiroz,
F.; Quel, E. J.; Quinn, J.; Quirrenbach, A.; Racero, E.; Räck,
T.; Rafalski, J.; Rafighi, I.; Rainò, S.; Rajda, P. J.; Rameez, M.;
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D.; Razzaque, S.; Reardon, P.; Reimann, O.; Reimer, A.; Reimer, O.;
Reitberger, K.; Renaud, M.; Renner, S.; Reposeur, T.; Rettig, R.;
Reville, B.; Rhode, W.; Ribeiro, D.; Ribó, M.; Richards, G.; Richer,
M. G.; Rico, J.; Ridky, J.; Rieger, F.; Ringegni, P.; Ristori, P. R.;
Rivière, A.; Rivoire, S.; Roache, E.; Rodeghiero, G.; Rodriguez,
J.; Rodriguez Fernandez, G.; Rodríguez Vázquez, J. J.; Rogers, T.;
Rojas, G.; Romano, P.; Romay Rodriguez, M. P.; Romeo, G.; Romero,
G. E.; Roncadelli, M.; Rose, J.; Rosen, S.; Rosier Lees, S.; Ross,
D.; Rossiter, P.; Rouaix, G.; Rousselle, J.; Rovero, A. C.; Rowell,
G.; Roy, F.; Royer, S.; Różańska, A.; Rudak, B.; Rugliancich,
A.; Rulten, C.; Rupiński, M.; Russo, F.; Rutkowski, K.; Saavedra,
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Sahakian, V.; Saito, K.; Saito, T.; Sakaki, N.; Salega, M.; Salek, D.;
Salgado, J.; Salini, A.; Sanchez, D.; Sanchez, F.; Sanchez-Conde, M.;
Sandaker, H.; Sandoval, A.; Sangiorgi, P.; Sanguillon, M.; Sano, H.;
Santander, M.; Santangelo, A.; Santos, E. M.; Santos-Lima, R.; Sanuy,
A.; Sapozhnikov, L.; Sarkar, S.; Satalecka, K.; Savalle, R.; Sawada,
M.; Sayède, F.; Schafer, J.; Schanne, S.; Schanz, T.; Schioppa, E. J.;
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M.; Schovanek, P.; Schubert, A.; Schultz, C.; Schultze, J.; Schulz,
A.; Schulz, S.; Schure, K.; Schussler, F.; Schwab, T.; Schwanke, U.;
Schwarz, J.; Schweizer, T.; Schwemmer, S.; Schwendicke, U.; Schwerdt,
C.; Segreto, A.; Seiradakis, J. -H.; Sembroski, G. H.; Semikoz, D.;
Serre, N.; Servillat, M.; Seweryn, K.; Shafi, N.; Sharma, M.; Shayduk,
M.; Shellard, R. C.; Shibata, T.; Shiningayamwe Pandeni, K.; Shukla,
A.; Shum, E.; Sidoli, L.; Sidz, M.; Sieiro, J.; Siejkowski, H.; Silk,
J.; Sillanpää, A.; Simone, D.; Singh, B. B.; Sinha, A.; Sironi, G.;
Sitarek, J.; Sizun, P.; Slyusar, V.; Smith, A.; Smith, J.; Sobczyńska,
D.; Sol, H.; Sottile, G.; Sowiński, M.; Spanier, F.; Spengler, G.;
Spiga, D.; Stadler, R.; Stahl, O.; Stamatescu, V.; Stamerra, A.;
Stanič, S.; Starling, R.; Stawarz, Ł.; Steenkamp, R.; Stefanik, S.;
Stegmann, C.; Steiner, S.; Stella, C.; Stergioulas, N.; Sternberger,
R.; Sterzel, M.; Stevenson, B.; Stinzing, F.; Stodulska, M.; Stodulski,
M.; Stolarczyk, T.; Straumann, U.; Strazzeri, E.; Stringhetti, L.;
Strzys, M.; Stuik, R.; Sulanke, K. -H.; Supanitsky, A. D.; Suric, T.;
Sushch, I.; Sutcliffe, P.; Sykes, J.; Szanecki, M.; Szepieniec, T.;
Szwarnog, P.; Tacchini, A.; Tachihara, K.; Tagliaferri, G.; Tajima, H.;
Takahashi, H.; Takahashi, K.; Takahashi, M.; Takalo, L.; Takami, H.;
Talbot, G.; Tammi, J.; Tanaka, M.; Tanaka, S.; Tanaka, T.; Tanaka, Y.;
Tanci, C.; Tarantino, E.; Tavani, M.; Tavecchio, F.; Tavernet, J. -P.;
Tayabaly, K.; Tejedor, L. A.; Telezhinsky, I.; Temme, F.; Temnikov, P.;
Tenzer, C.; Terada, Y.; Terrier, R.; Tescaro, D.; Teshima, M.; Testa,
V.; Tezier, D.; Thayer, J.; Thomas, V.; Thornhill, J.; Thuermann,
D.; Tibaldo, L.; Tibolla, O.; Tiengo, A.; Tijsseling, G.; Timpanaro,
M. C.; Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.;
Toma, K.; Toma, K.; Tomastik, J.; Tomono, Y.; Tonachini, A.; Tonev,
D.; Torii, K.; Tornikoski, M.; Torres, D. F.; Torres, M.; Torresi, E.;
Toscano, S.; Toso, G.; Tosti, G.; Totani, T.; Tothill, N.; Toussenel,
F.; Tovmassian, G.; Townsley, C.; Toyama, T.; Travnicek, P.; Trifoglio,
M.; Troyano Pujadas, I.; Troyano Pujadas, I.; Trzeciak, M.; Tsinganos,
K.; Tsubone, Y.; Tsuchiya, Y.; Tsujimoto, S.; Tsuru, T.; Uchiyama, Y.;
Umana, G.; Umetsu, Y.; Underwood, C.; Upadhya, S. S.; Uslenghi, M.;
Vagnetti, F.; Valdes-Galicia, J.; Vallania, P.; Vallejo, G.; Valore,
L.; van Driel, W.; van Eldik, C.; van Soelen, B.; Vandenbroucke, J.;
Vanderwalt, J.; Vasileiadis, G.; Vassiliev, V.; Vázquez Acosta,
M. L.; Vecchi, M.; Vegas, I.; Veitch, P.; Venema, L.; Venter, C.;
Vercellone, S.; Vergani, S.; Verma, K.; Verzi, V.; Vettolani, G. P.;
Viana, A.; Vicha, J.; Videla, M.; Vigorito, C.; Vincent, P.; Vincent,
S.; Vink, J.; Vittorini, V.; Vlahakis, N.; Vlahos, L.; Voelk, H.;
Vogler, P.; Voisin, V.; Vollhardt, A.; Volpicelli, A.; Vorobiov,
S.; Vovk, I.; Vu, L. V.; Wagner, R.; Wagner, R. M.; Wagner, R. G.;
Wagner, S. J.; Wakely, S. P.; Walter, R.; Walther, T.; Ward, J. E.;
Ward, M.; Warda, K.; Warwick, R.; Wassberg, S.; Watson, J.; Wawer,
P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weinstein, A.; Weitzel, Q.;
Wells, R.; Werner, F.; Werner, M.; Wetteskind, H.; White, M.; White,
R.; Więcek, M.; Wierzcholska, A.; Wiesand, S.; Wijers, R.; Wild, N.;
Wilhelm, A.; Wilkinson, M.; Will, M.; Williams, D. A.; Williams, J. T.;
Willingale, R.; Winde, M.; Winiarski, K.; Winkler, H.; Wischnewski,
R.; Wojcik, P.; Wolf, D.; Wood, M.; Wörnlein, A.; Wu, E.; Wu, T.;
Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamazaki, R.; Yanagita, S.;
Yang, L.; Yebras, J. M.; Yelos, D.; Yeung, W.; Yoshida, A.; Yoshida,
T.; Yoshiike, S.; Yoshikoshi, T.; Yu, P.; Zabalza, V.; Zabalza, V.;
Zacharias, M.; Zaharijas, G.; Zajczyk, A.; Zampieri, L.; Zandanel,
F.; Zanin, R.; Zanmar Sanchez, R.; Zavrtanik, D.; Zavrtanik, M.;
Zdziarski, A.; Zech, A.; Zechlin, H.; Zhao, A.; Ziegler, A.; Ziemann,
J.; Ziętara, K.; Ziółkowski, J.; Zitelli, V.; Zoli, A.; Zurbach,
C.; Żychowski, P.
2015arXiv150805894C Altcode:
List of contributions from the CTA Consortium presented at the 34th
International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague,
The Netherlands.
---------------------------------------------------------
Title: The Cause of the Weak Solar Cycle 24
Authors: Jiang, J.; Cameron, R. H.; Schüssler, M.
2015ApJ...808L..28J Altcode: 2015arXiv150701764J
The ongoing 11 year cycle of solar activity is considerably less
vigorous than the three cycles before. It was preceded by a very deep
activity minimum with a low polar magnetic flux, the source of the
toroidal field responsible for solar magnetic activity in the subsequent
cycle. Simulation of the evolution of the solar surface field shows
that the weak polar fields and thus the weakness of the present cycle
24 are mainly caused by a number of bigger bipolar regions emerging at
low latitudes with a “wrong” (i.e., opposite to the majority for
this cycle) orientation of their magnetic polarities in the north-south
direction, which impaired the growth of the polar field. These regions
had a particularly strong effect since they emerged within +/- 10^\circ
latitude from the solar equator.
---------------------------------------------------------
Title: Construction of a Schwarzschild-Couder telescope as a candidate
for the Cherenkov Telescope Array: Implementation of the opti
Authors: Rousselle, J.; Byrum, K.; Cameron, R.; Connaughton, V.;
Errando, M.; Guarino, V.; Humensky, B.; Jenke, P.; Kieda, D.;
Mukherjee, R.; Nieto Castano, D.; Okumura, A.; Petrashyk, A.;
Vassiliev, V.
2015ICRC...34..938R Altcode: 2015PoS...236..938R; 2015arXiv150901143R
We present the design and the status of procurement of the optical
system of the prototype Schwarzschild-Couder telescope (pSCT), for
which construction is scheduled to begin in fall at the Fred Lawrence
Whipple Observatory in southern Arizona, USA. The Schwarzschild-Couder
telescope is a candidate for the medium-sized telescopes of the
Cherenkov Telescope Array, which utilizes imaging atmospheric
Cherenkov techniques to observe gamma rays in the energy range of
60Gev-60TeV. The pSCT novel aplanatic optical system is made of two
segmented aspheric mirrors. The primary mirror has 48 mirror panels
with an aperture of 9.6 m, while the secondary, made of 24 panels,
has an diameter of 5.4 m. The resulting point spread function (PSF)
is required to be better than 4 arcmin within a field of view of 6.4
degrees (80% of the field of view), which corresponds to a physical
size of 6.4 mm on the focal plane. This goal represents a challenge
for the inexpensive fabrication of aspheric mirror panels and for the
precise alignment of the optical system as well as for the rigidity
of the optical support structure. In this submission we introduce
the design of the Schwarzschild-Couder optical system and describe
the solutions adopted for the manufacturing of the mirror panels and
their integration with the optical support structure.
---------------------------------------------------------
Title: A Medium Sized Schwarzschild-Couder Cherenkov Telescope Design
Proposed for the Cherenkov Telescope Array
Authors: Benbow, W.; Byrum, K.; Cameron, R.; Criswell, S.; Errando,
M.; Guarino, V.; Humensky, B.; Kaaret, P.; Kieda, D.; Mukherjee,
R.; Naumann, D.; Nieto, D.; Northrop, R.; Okumura, A.; Roache, E.;
Rousselle, J.; Schlenstedt, S.; Sternberger, R.; Vassiliev, V.;
Wakely, S.; Zhao, H. A.
2015ICRC...34.1029B Altcode: 2015PoS...236.1029B
No abstract at ADS
---------------------------------------------------------
Title: Characterising exoplanets and their environment with UV
transmission spectroscopy
Authors: Fossati, L.; Bourrier, V.; Ehrenreich, D.; Haswell, C. A.;
Kislyakova, K. G.; Lammer, H.; Lecavelier des Etangs, A.; Alibert,
Y.; Ayres, T. R.; Ballester, G. E.; Barnes, J.; Bisikalo, D. V.;
Collier, A.; Cameron; Czesla, S.; Desert, J. -M.; France, K.; Guedel,
M.; Guenther, E.; Helling, Ch.; Heng, K.; Homstrom, M.; Kaltenegger,
L.; Koskinen, T.; Lanza, A. F.; Linsky, J. L.; Mordasini, C.; Pagano,
I.; Pollacco, D.; Rauer, H.; Reiners, A.; Salz, M.; Schneider, P. C.;
Shematovich, V. I.; Staab, D.; Vidotto, A. A.; Wheatley, P. J.; Wood,
B. E.; Yelle, R. V.
2015arXiv150301278F Altcode:
Exoplanet science is now in its full expansion, particularly after
the CoRoT and Kepler space missions that led us to the discovery of
thousands of extra-solar planets. The last decade has taught us that
UV observations play a major role in advancing our understanding of
planets and of their host stars, but the necessary UV observations can
be carried out only by HST, and this is going to be the case for many
years to come. It is therefore crucial to build a treasury data archive
of UV exoplanet observations formed by a dozen "golden systems" for
which observations will be available from the UV to the infrared. Only
in this way we will be able to fully exploit JWST observations for
exoplanet science, one of the key JWST science case.
---------------------------------------------------------
Title: The Solar cycle: looking forward
Authors: Cameron, Robert H.
2015HiA....16..111C Altcode:
We discuss predictions for cycle 24 and the way forward if progress
is to be made for cycle 25 and beyond.
---------------------------------------------------------
Title: The crucial role of surface magnetic fields for the solar
dynamo
Authors: Cameron, Robert; Schüssler, Manfred
2015Sci...347.1333C Altcode: 2015arXiv150308469C
Sunspots and the plethora of other phenomena occurring in the course of
the 11-year cycle of solar activity are a consequence of the emergence
of magnetic flux at the solar surface. The observed orientations
of bipolar sunspot groups imply that they originate from toroidal
(azimuthally orientated) magnetic flux in the convective envelope
of the Sun. We show that the net toroidal magnetic flux generated by
differential rotation within a hemisphere of the convection zone is
determined by the emerged magnetic flux at the solar surface and thus
can be calculated from the observed magnetic field distribution. The
main source of the toroidal flux is the roughly dipolar surface
magnetic field at the polar caps, which peaks around the minima of
the activity cycle.
---------------------------------------------------------
Title: Simulated magnetic flows in the solar photosphere
Authors: Danilovic, S.; Cameron, R. H.; Solanki, S. K.
2015A&A...574A..28D Altcode: 2014arXiv1408.6159D
Context. Recent Sunrise/IMaX observations have revealed supersonic
magnetic flows. <BR /> Aims: Our aim is to determine the origin of
these flows by using realistic magnetohydrodynamics simulations. <BR
/> Methods: We simulated cancellation and emergence of magnetic
flux through the solar photosphere. Our first numerical experiment
started with a magnetic field of both polarities. To simulate
emergence into a region with pre-existing field, we introduced a
large-scale horizontally uniform sheet of a horizontal field. We
followed the subsequent evolution and created synthetic polarimetric
observations, including known instrumental effects of the Sunrise/IMaX
and Hinode/SP instruments. We compared the simulated and observed
spectropolarimetric signals. <BR /> Results: Strongly blue- and
redshifted Stokes V signals are produced in locations where strong
line-of-sight velocities coincide with the strong line-of-sight
component of the magnetic field. The size and strength of simulated
events is smaller than observed, and they are mostly associated with
downflows, contrary to observations. In a few cases where they appear
above a granule, single blue-lobed Stokes V are produced by strong
gradients in magnetic field and velocity. No change of magnetic field
sign is detected along the line of sight in these instances. More
high-speed magnetised flows occurred when an emergence was simulated
than when no horizontal field was added. <BR /> Conclusions: The
simulations indicate that the observed events result from magnetic flux
emergences in which reconnection may take place, but does not seem to
be necessary. <P />The movies are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201423779/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Magnetic Flux Transport at the Solar Surface
Authors: Jiang, J.; Hathaway, D. H.; Cameron, R. H.; Solanki, S. K.;
Gizon, L.; Upton, L.
2015sac..book..491J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Flux Transport at the Solar Surface
Authors: Jiang, J.; Hathaway, D. H.; Cameron, R. H.; Solanki, S. K.;
Gizon, L.; Upton, L.
2014SSRv..186..491J Altcode: 2014SSRv..tmp...43J; 2014arXiv1408.3186J
After emerging to the solar surface, the Sun's magnetic field displays a
complex and intricate evolution. The evolution of the surface field is
important for several reasons. One is that the surface field, and its
dynamics, sets the boundary condition for the coronal and heliospheric
magnetic fields. Another is that the surface evolution gives us insight
into the dynamo process. In particular, it plays an essential role
in the Babcock-Leighton model of the solar dynamo. Describing this
evolution is the aim of the surface flux transport model. The model
starts from the emergence of magnetic bipoles. Thereafter, the model is
based on the induction equation and the fact that after emergence the
magnetic field is observed to evolve as if it were purely radial. The
induction equation then describes how the surface flows—differential
rotation, meridional circulation, granular, supergranular flows,
and active region inflows—determine the evolution of the field (now
taken to be purely radial). In this paper, we review the modeling of
the various processes that determine the evolution of the surface
field. We restrict our attention to their role in the surface flux
transport model. We also discuss the success of the model and some of
the results that have been obtained using this model.
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Ojha,
Roopesh; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Cheung,
Teddy; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus,
Guillaume; Cameron, Robert; Abraham, Falcone; Schinzel, Frank
2014atnf.prop.6430C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Interpreting the Helioseismic and Magnetic Imager (HMI)
Multi-Height Velocity Measurements
Authors: Nagashima, Kaori; Löptien, Björn; Gizon, Laurent; Birch,
Aaron C.; Cameron, Robert; Couvidat, Sebastien; Danilovic, Sanja;
Fleck, Bernhard; Stein, Robert
2014SoPh..289.3457N Altcode: 2014arXiv1404.3569N; 2014SoPh..tmp...84N
The Solar Dynamics Observatory/Helioseismic and Magnetic Imager
(SDO/HMI) filtergrams, taken at six wavelengths around the Fe I 6173.3
Å line, contain information about the line-of-sight velocity over
a range of heights in the solar atmosphere. Multi-height velocity
inferences from these observations can be exploited to study wave
motions and energy transport in the atmosphere. Using realistic
convection-simulation datasets provided by the STAGGER and MURaM
codes, we generate synthetic filtergrams and explore several methods
for estimating Dopplergrams. We investigate at which height each
synthetic Dopplergram correlates most strongly with the vertical
velocity in the model atmospheres. On the basis of the investigation,
we propose two Dopplergrams other than the standard HMI-algorithm
Dopplergram produced from HMI filtergrams: a line-center Dopplergram
and an average-wing Dopplergram. These two Dopplergrams correlate most
strongly with vertical velocities at the heights of 30 - 40 km above
(line center) and 30 - 40 km below (average wing) the effective height
of the HMI-algorithm Dopplergram. Therefore, we can obtain velocity
information from two layers separated by about a half of a scale height
in the atmosphere, at best. The phase shifts between these multi-height
Dopplergrams from observational data as well as those from the simulated
data are also consistent with the height-difference estimates in the
frequency range above the photospheric acoustic-cutoff frequency.
---------------------------------------------------------
Title: The Role of Subsurface Flows in Solar Surface Convection:
Modeling the Spectrum of Supergranular and Larger Scale Flows
Authors: Lord, J. W.; Cameron, R. H.; Rast, M. P.; Rempel, M.;
Roudier, T.
2014ApJ...793...24L Altcode: 2014arXiv1407.2209L
We model the solar horizontal velocity power spectrum at scales
larger than granulation using a two-component approximation to the
mass continuity equation. The model takes four times the density
scale height as the integral (driving) scale of the vertical motions
at each depth. Scales larger than this decay with height from the
deeper layers. Those smaller are assumed to follow a Kolmogorov
turbulent cascade, with the total power in the vertical convective
motions matching that required to transport the solar luminosity in a
mixing length formulation. These model components are validated using
large-scale radiative hydrodynamic simulations. We reach two primary
conclusions. (1) The model predicts significantly more power at low
wavenumbers than is observed in the solar photospheric horizontal
velocity spectrum. (2) Ionization plays a minor role in shaping the
observed solar velocity spectrum by reducing convective amplitudes in
the regions of partial helium ionization. The excess low wavenumber
power is also seen in the fully nonlinear three-dimensional radiative
hydrodynamic simulations employing a realistic equation of state. This
adds to other recent evidence suggesting that the amplitudes of
large-scale convective motions in the Sun are significantly lower
than expected. Employing the same feature tracking algorithm used
with observational data on the simulation output, we show that the
observed low wavenumber power can be reproduced in hydrodynamic
models if the amplitudes of large-scale modes in the deep layers
are artificially reduced. Since the large-scale modes have reduced
amplitudes, modes on the scale of supergranulation and smaller remain
important to convective heat flux even in the deep layers, suggesting
that small-scale convective correlations are maintained through the
bulk of the solar convection zone.
---------------------------------------------------------
Title: Effects of the Scatter in Sunspot Group Tilt Angles on the
Large-scale Magnetic Field at the Solar Surface
Authors: Jiang, J.; Cameron, R. H.; Schüssler, M.
2014ApJ...791....5J Altcode: 2014arXiv1406.5564J
The tilt angles of sunspot groups represent the poloidal field source
in Babcock-Leighton-type models of the solar dynamo and are crucial for
the build-up and reversals of the polar fields in surface flux transport
(SFT) simulations. The evolution of the polar field is a consequence
of Hale's polarity rules, together with the tilt angle distribution
which has a systematic component (Joy's law) and a random component
(tilt-angle scatter). We determine the scatter using the observed tilt
angle data and study the effects of this scatter on the evolution of
the solar surface field using SFT simulations with flux input based
upon the recorded sunspot groups. The tilt angle scatter is described
in our simulations by a random component according to the observed
distributions for different ranges of sunspot group size (total
umbral area). By performing simulations with a number of different
realizations of the scatter we study the effect of the tilt angle
scatter on the global magnetic field, especially on the evolution of
the axial dipole moment. The average axial dipole moment at the end
of cycle 17 (a medium-amplitude cycle) from our simulations was 2.73
G. The tilt angle scatter leads to an uncertainty of 0.78 G (standard
deviation). We also considered cycle 14 (a weak cycle) and cycle 19
(a strong cycle) and show that the standard deviation of the axial
dipole moment is similar for all three cycles. The uncertainty mainly
results from the big sunspot groups which emerge near the equator. In
the framework of Babcock-Leighton dynamo models, the tilt angle scatter
therefore constitutes a significant random factor in the cycle-to-cycle
amplitude variability, which strongly limits the predictability of
solar activity.
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Ojha,
Roopesh; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Cheung,
Teddy; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus,
Guillaume; Cameron, Robert; Abraham, Falcone; Schinzel, Frank
2014atnf.prop.6049C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Migration of Ca II H bright points in the internetwork
Authors: Jafarzadeh, S.; Cameron, R. H.; Solanki, S. K.; Pietarila,
A.; Feller, A.; Lagg, A.; Gandorfer, A.
2014A&A...563A.101J Altcode: 2014arXiv1401.7522J
Context. The migration of magnetic bright point-like features (MBP)
in the lower solar atmosphere reflects the dispersal of magnetic
flux as well as the horizontal flows of the atmospheric layer they
are embedded in. <BR /> Aims: We analyse trajectories of the proper
motion of intrinsically magnetic, isolated internetwork Ca ii H MBPs
(mean lifetime 461 ± 9 s) to obtain their diffusivity behaviour. <BR
/> Methods: We use seeing-free high spatial and temporal resolution
image sequences of quiet-Sun, disc-centre observations obtained in
the Ca ii H 3968 Å passband of the Sunrise Filter Imager (SuFI)
onboard the Sunrise balloon-borne solar observatory. Small MBPs in
the internetwork are automatically tracked. The trajectory of each
MBP is then calculated and described by a diffusion index (γ) and
a diffusion coefficient (D). We also explore the distribution of the
diffusion indices with the help of a Monte Carlo simulation. <BR />
Results: We find γ = 1.69 ± 0.08 and D = 257 ± 32 km<SUP>2</SUP>
s<SUP>-1</SUP> averaged over all MBPs. Trajectories of most MBPs are
classified as super-diffusive, i.e. γ > 1, with the determined γ
being the largest obtained so far to our knowledge. A direct correlation
between D and timescale (τ) determined from trajectories of all MBPs is
also obtained. We discuss a simple scenario to explain the diffusivity
of the observed, relatively short-lived MBPs while they migrate within
a small area in a supergranule (i.e. an internetwork area). We show
that the scatter in the γ values obtained for individual MBPs is due
to their limited lifetimes. <BR /> Conclusions: The super-diffusive
MBPs can be described as random walkers (due to granular evolution and
intergranular turbulence) superposed on a large systematic (background)
velocity, caused by granular, mesogranular, and supergranular flows.
---------------------------------------------------------
Title: Physical causes of solar cycle amplitude variability
Authors: Cameron, R. H.; Jiang, J.; Schüssler, M.; Gizon, L.
2014JGRA..119..680C Altcode:
The level of solar activity varies from cycle to cycle. This
variability is probably caused by a combination of nonlinear and
random effects. Based on surface flux transport simulations, we
show that the observed inflows into active regions and toward the
activity belts provide an important nonlinearity in the framework of
Babcock-Leighton model for the solar dynamo. Inclusion of these inflows
also leads to a reproduction of the observed proportionality between
the open heliospheric flux during activity minima and the maximum
sunspot number of the following cycle. A substantial component of
the random variability of the cycle strength is associated with the
cross-equatorial flux plumes that occur when large, highly tilted
sunspot groups emerge close to the equator. We show that the flux
transported by these events is important for the amplitude of the polar
fields and open flux during activity minima. The combined action of
inflows and cross-equatorial flux plumes provides an explanation for
the weakness of the polar fields at the end of solar cycle 23 (and
hence for the relative weakness of solar cycle 24).
---------------------------------------------------------
Title: Can Surface Flux Transport Account for the Weak Polar Field
in Cycle 23?
Authors: Jiang, Jie; Cameron, Robert H.; Schmitt, Dieter; Schüssler,
Manfred
2014crh..book..289J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Snowmass Cosmic Frontiers 6 (CF6) Working Group Summary --The
Bright Side of the Cosmic Frontier: Cosmic Probes of Fundamental
Physics
Authors: Beatty, J. J.; Nelson, A. E.; Olinto, A.; Sinnis, G.;
Abeysekara, A. U.; Anchordoqui, L. A.; Aramaki, T.; Belz, J.; Buckley,
J. H.; Byrum, K.; Cameron, R.; Chen, M-C.; Clark, K.; Connolly, A.;
Cowen, D.; DeYoung, T.; Dumm, P. von Doetinchem J.; Errando, M.;
Farrar, G.; Ferrer, F.; Fortson, L.; Funk, S.; Grant, D.; Griffiths,
S.; Groß, A.; Hailey, C.; Hogan, C.; Holder, J.; Humensky, B.;
Kaaret, P.; Klein, S. R.; Krawczynski, H.; Krennrich, F.; Krings,
K.; Krizmanic, J.; Kusenko, A.; Linnemann, J. T.; MacGibbon, J. H.;
Matthews, J.; McCann, A.; Mitchell, J.; Mukherjee, R.; Nitz, D.;
Ong, R. A.; Orr, M.; Otte, N.; Paul, T.; Resconi, E.; Sanchez-Conde,
M. A.; Sokolsky, P.; Stecker, F.; Stump, D.; Taboada, I.; Thomson,
G. B.; Tollefson, K.; von Doetinchem, P.; Ukwatta, T.; Vandenbroucke,
J.; Vasileiou, V.; Vassileiv, V. V.; Weiler, T. J.; Williams, D. A.;
Weinstein, A.; Wood, M.; Zitzer, B.
2013arXiv1310.5662B Altcode:
Report of the CF6 Working Group at Snowmass 2013. Topics addressed
include ultra-high energy cosmic rays, neutrinos, gamma rays,
baryogenesis, and experiments probing the fundamental nature of
spacetime.
---------------------------------------------------------
Title: Three-dimensional simulations of near-surface convection in
main-sequence stars. II. Properties of granulation and spectral lines
Authors: Beeck, B.; Cameron, R. H.; Reiners, A.; Schüssler, M.
2013A&A...558A..49B Altcode: 2013arXiv1308.4873B
Context. The atmospheres of cool main-sequence stars are structured
by convective flows from the convective envelope that penetrate the
optically thin layers and lead to structuring of the stellar atmospheres
analogous to solar granulation. The flows have considerable influence on
the 3D structure of temperature and pressure and affect the profiles
of spectral lines formed in the photosphere. <BR /> Aims: For the
set of six 3D radiative (M)HD simulations of cool main-sequence
stars described in the first paper of this series, we analyse the
near-surface layers. We aim at describing the properties of granulation
of different stars and at quantifying the effects on spectral lines of
the thermodynamic structure and flows of 3D convective atmospheres. <BR
/> Methods: We detected and tracked granules in brightness images
from the simulations to analyse their statistical properties, as well
as their evolution and lifetime. We calculated spatially resolved
spectral line profiles using the line synthesis code SPINOR. To enable
a comparison to stellar observations, we implemented a numerical
disc-integration, which includes (differential) rotation. <BR />
Results: Although the stellar parameters change considerably along the
model sequence, the properties of the granules are very similar. The
impact of the 3D structure of the atmospheres on line profiles is
measurable in disc-integrated spectra. Line asymmetries caused by
convection are modulated by stellar rotation. <BR /> Conclusions:
The 3D structure of cool stellar atmospheres as shaped by convective
flows has to be taken into account when using photospheric lines to
determine stellar parameters.
---------------------------------------------------------
Title: Polar plumes' orientation and the Sun's global magnetic field
Authors: de Patoul, Judith; Inhester, Bernd; Cameron, Robert
2013A&A...558L...4D Altcode: 2013arXiv1309.5916D
<BR /> Aims: We characterize the orientation of polar plumes as a
tracer of the large-scale coronal magnetic field configuration. We
monitor in particular the north and south magnetic pole locations and
the magnetic opening during 2007-2008 and provide some understanding
of the variations in these quantities. <BR /> Methods: The polar plume
orientation is determined by applying the Hough-wavelet transform to
a series of EUV images and extracting the key Hough space parameters
of the resulting maps. The same procedure is applied to the polar cap
field inclination derived from extrapolating magnetograms generated
by a surface flux transport model. <BR /> Results: We observe that
the position where the magnetic field is radial (the Sun's magnetic
poles) reflects the global organization of magnetic field on the
solar surface, and we suggest that this opens the possibility of both
detecting flux emergence anywhere on the solar surface (including the
far side) and better constraining the reorganization of the corona
after flux emergence.
---------------------------------------------------------
Title: Three-dimensional simulations of near-surface convection in
main-sequence stars. I. Overall structure
Authors: Beeck, B.; Cameron, R. H.; Reiners, A.; Schüssler, M.
2013A&A...558A..48B Altcode: 2013arXiv1308.4874B
Context. The near-surface layers of cool main-sequence stars are
structured by convective flows, which are overshooting into the
atmosphere. The flows and the associated spatio-temporal variations of
density and temperature affect spectral line profiles and thus have an
impact on estimates of stellar properties such as effective temperature,
gravitational acceleration, and abundances. <BR /> Aims: We aim at
identifying distinctive properties of the thermodynamic structure of
the atmospheres of different stars and understand their causes. <BR />
Methods: We ran comprehensive 3D radiation hydrodynamics simulations
of the near-surface layers of six simulated stars of spectral type
F3V to M2V with the MURaM code. We carry out a systematic parameter
study of the mean stratifications, flow structures, and the energy
flux in these stars. <BR /> Results: We find monotonic trends along
the lower main sequence in granule size, flow velocity, and intensity
contrast. The convection in the M-star models differs substantially
from that of the hotter stars, mainly owing to the more gradual
transition from convective to radiative energy transport. <BR />
Conclusions: While the basic mechanisms driving surface convection
in cool stars are the same, the properties of the convection vary
along the main sequence. Apart from monotonic trends in rms velocity,
intensity contrast, granule size, etc., there is a transition between
"naked" and "hidden" granulation around spectral type K5V caused by
the (highly non-linear) temperature dependence of the opacity. These
variations have to be taken into account when stellar parameters are
derived from spectra. <P />Appendix A is available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Helioseismology of sunspots: how sensitive are travel times
to the Wilson depression and to the subsurface magnetic field?
Authors: Schunker, H.; Gizon, L.; Cameron, R. H.; Birch, A. C.
2013A&A...558A.130S Altcode: 2013arXiv1303.6307S
To assess the ability of helioseismology to probe the subsurface
structure and magnetic field of sunspots, we need to determine
how helioseismic travel times depend on perturbations to
sunspot models. Here we numerically simulate the propagation of f,
p<SUB>1</SUB>, and p<SUB>2</SUB> wave packets through magnetic sunspot
models. Among the models we considered, a ±50 km change in the height
of the Wilson depression and a change in the subsurface magnetic
field geometry can both be detected above the observational noise
level. We also find that the travel-time shifts due to changes in a
sunspot model must be modeled by computing the effects of changing the
reference sunspot model, and not by computing the effects of changing
the subsurface structure in the quiet-Sun model. For p<SUB>1</SUB>
modes, the latter is wrong by a factor of four. In conclusion, numerical
modeling of MHD wave propagation is an essential tool for interpreting
the effects of sunspots on seismic waveforms.
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Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Ojha,
Roopesh; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Cheung,
Teddy; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus,
Guillaume; Cameron, Robert; Abraham, Falcone; Schinzel, Frank
2013atnf.prop.5777C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
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Title: Limits to solar cycle predictability: Cross-equatorial
flux plumes
Authors: Cameron, R. H.; Dasi-Espuig, M.; Jiang, J.; Işık, E.;
Schmitt, D.; Schüssler, M.
2013A&A...557A.141C Altcode: 2013arXiv1308.2827C
Context. Within the Babcock-Leighton framework for the solar dynamo, the
strength of a cycle is expected to depend on the strength of the dipole
moment or net hemispheric flux during the preceding minimum, which
depends on how much flux was present in each hemisphere at the start of
the previous cycle and how much net magnetic flux was transported across
the equator during the cycle. Some of this transport is associated
with the random walk of magnetic flux tubes subject to granular and
supergranular buffeting, some of it is due to the advection caused by
systematic cross-equatorial flows such as those associated with the
inflows into active regions, and some crosses the equator during the
emergence process. <BR /> Aims: We aim to determine how much of the
cross-equatorial transport is due to small-scale disorganized motions
(treated as diffusion) compared with other processes such as emergence
flux across the equator. <BR /> Methods: We measure the cross-equatorial
flux transport using Kitt Peak synoptic magnetograms, estimating both
the total and diffusive fluxes. <BR /> Results: Occasionally a large
sunspot group, with a large tilt angle emerges crossing the equator,
with flux from the two polarities in opposite hemispheres. The largest
of these events carry a substantial amount of flux across the equator
(compared to the magnetic flux near the poles). We call such events
cross-equatorial flux plumes. There are very few such large events
during a cycle, which introduces an uncertainty into the determination
of the amount of magnetic flux transported across the equator in any
particular cycle. As the amount of flux which crosses the equator
determines the amount of net flux in each hemisphere, it follows that
the cross-equatorial plumes introduce an uncertainty in the prediction
of the net flux in each hemisphere. This leads to an uncertainty in
predictions of the strength of the following cycle.
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Title: No evidence for planetary influence on solar activity
Authors: Cameron, R. H.; Schüssler, M.
2013A&A...557A..83C Altcode: 2013arXiv1307.5988C
Context. Recently, Abreu et al. (2012, A&A. 548, A88) proposed
a long-term modulation of solar activity through tidal effects
exerted by the planets. This claim is based upon a comparison of
(pseudo-)periodicities derived from records of cosmogenic isotopes
with those arising from planetary torques on an ellipsoidally deformed
Sun. <BR /> Aims: We examined the statistical significance of the
reported similarity of the periods. <BR /> Methods: The tests carried
out by Abreu et al. were repeated with artificial records of solar
activity in the form of white or red noise. The tests were corrected
for errors in the noise definition as well as in the apodisation and
filtering of the random series. <BR /> Results: The corrected tests
provide probabilities for chance coincidence that are higher than
those claimed by Abreu et al. by about 3 and 8 orders of magnitude
for white and red noise, respectively. For an unbiased choice of the
width of the frequency bins used for the test (a constant multiple of
the frequency resolution) the probabilities increase by another two
orders of magnitude to 7.5% for red noise and 22% for white noise. <BR
/> Conclusions: The apparent agreement between the periodicities
in records of cosmogenic isotopes as proxies for solar activity and
planetary torques is statistically insignificant. There is no evidence
for a planetary influence on solar activity.
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Title: Sunspot group tilt angles and the strength of the solar cycle
(Corrigendum)
Authors: Dasi-Espuig, M.; Solanki, S. K.; Krivova, N. A.; Cameron,
R.; Peñuela, T.
2013A&A...556C...3D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: CTA contributions to the 33rd International Cosmic Ray
Conference (ICRC2013)
Authors: CTA Consortium, The; :; Abril, O.; Acharya, B. S.; Actis, M.;
Agnetta, G.; Aguilar, J. A.; Aharonian, F.; Ajello, M.; Akhperjanian,
A.; Alcubierre, M.; Aleksic, J.; Alfaro, R.; Aliu, E.; Allafort,
A. J.; Allan, D.; Allekotte, I.; Aloisio, R.; Amato, E.; Ambrosi,
G.; Ambrosio, M.; Anderson, J.; Angüner, E. O.; Antonelli, L. A.;
Antonuccio, V.; Antonucci, M.; Antoranz, P.; Aravantinos, A.; Argan,
A.; Arlen, T.; Aramo, C.; Armstrong, T.; Arnaldi, H.; Arrabito, L.;
Asano, K.; Ashton, T.; Asorey, H. G.; Aune, T.; Awane, Y.; Baba, H.;
Babic, A.; Baby, N.; Bähr, J.; Bais, A.; Baixeras, C.; Bajtlik, S.;
Balbo, M.; Balis, D.; Balkowski, C.; Ballet, J.; Bamba, A.; Bandiera,
R.; Barber, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barnstedt,
J.; Barres de Almeida, U.; Barrio, J. A.; Basili, A.; Basso, S.;
Bastieri, D.; Bauer, C.; Baushev, A.; Becciani, U.; Becerra, J.;
Becerra, J.; Becherini, Y.; Bechtol, K. C.; Becker Tjus, J.; Beckmann,
V.; Bednarek, W.; Behera, B.; Belluso, M.; Benbow, W.; Berdugo, J.;
Berge, D.; Berger, K.; Bernard, F.; Bernardino, T.; Bernlöhr, K.;
Bertucci, B.; Bhat, N.; Bhattacharyya, S.; Biasuzzi, B.; Bigongiari,
C.; Biland, A.; Billotta, S.; Bird, T.; Birsin, E.; Bissaldi, E.;
Biteau, J.; Bitossi, M.; Blake, S.; Blanch Bigas, O.; Blasi, P.;
Bobkov, A.; Boccone, V.; Böttcher, M.; Bogacz, L.; Bogart, J.;
Bogdan, M.; Boisson, C.; Boix Gargallo, J.; Bolmont, J.; Bonanno,
G.; Bonardi, A.; Bonev, T.; Bonifacio, P.; Bonnoli, G.; Bordas,
P.; Borgland, A.; Borkowski, J.; Bose, R.; Botner, O.; Bottani, A.;
Bouchet, L.; Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.;
Braun, I.; Bretz, T.; Briggs, M.; Brigida, M.; Bringmann, T.; Britto,
R.; Brook, P.; Brun, P.; Brunetti, L.; Bruno, P.; Bucciantini, N.;
Buanes, T.; Buckley, J.; Bühler, R.; Bugaev, V.; Bulgarelli, A.;
Bulik, T.; Busetto, G.; Buson, S.; Byrum, K.; Cailles, M.; Cameron,
R.; Camprecios, J.; Canestrari, R.; Cantu, S.; Capalbi, M.; Caraveo,
P.; Carmona, E.; Carosi, A.; Carosi, R.; Carr, J.; Carter, J.;
Carton, P. -H.; Caruso, R.; Casanova, S.; Cascone, E.; Casiraghi, M.;
Castellina, A.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerchiara,
P.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chaves,
R.; Cheimets, P.; Chen, A.; Chiang, J.; Chiappetti, L.; Chikawa, M.;
Chitnis, V. R.; Chollet, F.; Christof, A.; Chudoba, J.; Cieślar, M.;
Cillis, A.; Cilmo, M.; Codino, A.; Cohen-Tanugi, J.; Colafrancesco,
S.; Colin, P.; Colome, J.; Colonges, S.; Compin, M.; Conconi, P.;
Conforti, V.; Connaughton, V.; Conrad, J.; Contreras, J. L.; Coppi,
P.; Coridian, J.; Corona, P.; Corti, D.; Cortina, J.; Cossio, L.;
Costa, A.; Costantini, H.; Cotter, G.; Courty, B.; Couturier, S.;
Covino, S.; Crimi, G.; Criswell, S. J.; Croston, J.; Cusumano, G.;
Dafonseca, M.; Dale, O.; Daniel, M.; Darling, J.; Davids, I.; Dazzi,
F.; de Angelis, A.; De Caprio, V.; De Frondat, F.; de Gouveia Dal Pino,
E. M.; de la Calle, I.; De La Vega, G. A.; de los Reyes Lopez, R.;
de Lotto, B.; De Luca, A.; de Naurois, M.; de Oliveira, Y.; de Oña
Wilhelmi, E.; de Palma, F.; de Souza, V.; Decerprit, G.; Decock, G.;
Deil, C.; Delagnes, E.; Deleglise, G.; Delgado, C.; della Volpe, D.;
Demange, P.; Depaola, G.; Dettlaff, A.; Di Girolamo, T.; Di Giulio,
C.; Di Paola, A.; Di Pierro, F.; di Sciascio, G.; Díaz, C.; Dick, J.;
Dickherber, R.; Dickinson, H.; Diez-Blanco, V.; Digel, S.; Dimitrov,
D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko,
W.; Dominis Prester, D.; Donat, A.; Dorner, D.; Doro, M.; Dournaux,
J. -L.; Drake, G.; Dravins, D.; Drury, L.; Dubois, F.; Dubois, R.;
Dubus, G.; Dufour, C.; Dumas, D.; Dumm, J.; Durand, D.; Dwarkadas, V.;
Dyks, J.; Dyrda, M.; Ebr, J.; Edy, E.; Egberts, K.; Eger, P.; Einecke,
S.; Eleftheriadis, C.; Elles, S.; Emmanoulopoulos, D.; Engelhaupt,
D.; Enomoto, R.; Ernenwein, J. -P.; Errando, M.; Etchegoyen, A.;
Evans, P. A.; Falcone, A.; Faltenbacher, A.; Fantinel, D.; Farakos,
K.; Farnier, C.; Farrell, E.; Fasola, G.; Favill, B. W.; Fede,
E.; Federici, S.; Fegan, S.; Feinstein, F.; Ferenc, D.; Ferrando,
P.; Fesquet, M.; Fetfatzis, P.; Fiasson, A.; Fillin-Martino, E.;
Fink, D.; Finley, C.; Finley, J. P.; Fiorini, M.; Firpo Curcoll,
R.; Flandrini, E.; Fleischhack, H.; Flores, H.; Florin, D.; Focke,
W.; Föhr, C.; Fokitis, E.; Font, L.; Fontaine, G.; Fornasa, M.;
Förster, A.; Fortson, L.; Fouque, N.; Franckowiak, A.; Franco, F. J.;
Frankowski, A.; Fransson, C.; Fraser, G. W.; Frei, R.; Fresnillo, L.;
Fruck, C.; Fugazza, D.; Fujita, Y.; Fukazawa, Y.; Fukui, Y.; Funk,
S.; Gäbele, W.; Gabici, S.; Gabriele, R.; Gadola, A.; Galante, N.;
Gall, D.; Gallant, Y.; Gámez-García, J.; Garczarczyk, M.; García,
B.; Garcia López, R.; Gardiol, D.; Gargano, F.; Garrido, D.; Garrido,
L.; Gascon, D.; Gaug, M.; Gaweda, J.; Gebremedhin, L.; Geffroy, N.;
Gerard, L.; Ghedina, A.; Ghigo, M.; Ghislain, P.; Giannakaki, E.;
Gianotti, F.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Giglietto,
N.; Gika, V.; Giomi, M.; Giommi, P.; Giordano, F.; Girard, N.; Giro,
E.; Giuliani, A.; Glanzman, T.; Glicenstein, J. -F.; Godinovic, N.;
Golev, V.; Gomez Berisso, M.; Gómez-Ortega, J.; Gonzalez, M. M.;
González, A.; González, F.; González Muñoz, A.; Gothe, K. S.;
Grabarczyk, T.; Gougerot, M.; Graciani, R.; Grandi, P.; Grañena,
F.; Granot, J.; Grasseau, G.; Gredig, R.; Green, A.; Greenshaw, T.;
Grégoire, T.; Grillo, A.; Grimm, O.; Grondin, M. -H.; Grube, J.;
Grudzinska, M.; Gruev, V.; Grünewald, S.; Grygorczuk, J.; Guarino,
V.; Gunji, S.; Gyuk, G.; Hadasch, D.; Hagedorn, A.; Hagiwara, R.;
Hahn, J.; Hakansson, N.; Hallgren, A.; Hamer Heras, N.; Hara, S.;
Hardcastle, M. J.; Harezlak, D.; Harris, J.; Hassan, T.; Hatanaka,
K.; Haubold, T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, R.;
Henault, F.; Henri, G.; Hermann, G.; Hermel, R.; Herrero, A.; Hervet,
O.; Hidaka, N.; Hinton, J. A.; Hirotani, K.; Hoffmann, D.; Hofmann,
W.; Hofverberg, P.; Holder, J.; Hörandel, J. R.; Horns, D.; Horville,
D.; Houles, J.; Hrabovsky, M.; Hrupec, D.; Huan, H.; Huber, B.; Huet,
J. -M.; Hughes, G.; Humensky, T. B.; Huovelin, J.; Huppert, J. -F.;
Ibarra, A.; Ikawa, D.; Illa, J. M.; Impiombato, D.; Incorvaia, S.;
Inoue, S.; Inoue, Y.; Iocco, F.; Ioka, K.; Israel, G. L.; Jablonski,
C.; Jacholkowska, A.; Jacquemier, J.; Jamrozy, M.; Janiak, M.; Jean,
P.; Jeanney, C.; Jimenez, J. J.; Jogler, T.; Johnson, C.; Johnson,
T.; Journet, L.; Juffroy, C.; Jung, I.; Kaaret, P.; Kabuki, S.;
Kagaya, M.; Kakuwa, J.; Kalkuhl, C.; Kankanyan, R.; Karastergiou,
A.; Kärcher, K.; Karczewski, M.; Karkar, S.; Kasperek, J.; Kastana,
D.; Katagiri, H.; Kataoka, J.; Katarzyński, K.; Katz, U.; Kawanaka,
N.; Kazanas, D.; Kelley-Hoskins, N.; Kellner-Leidel, B.; Kelly, H.;
Kendziorra, E.; Khélifi, B.; Kieda, D. B.; Kifune, T.; Kihm, T.;
Kishimoto, T.; Kitamoto, K.; Kluźniak, W.; Knapic, C.; Knapp, J.;
Knödlseder, J.; Köck, F.; Kocot, J.; Kodani, K.; Köhne, J. -H.;
Kohri, K.; Kokkotas, K.; Kolitzus, D.; Komin, N.; Kominis, I.; Konno,
Y.; Köppel, H.; Korohoda, P.; Kosack, K.; Koss, G.; Kossakowski,
R.; Koul, R.; Kowal, G.; Koyama, S.; Kozioł, J.; Krähenbühl, T.;
Krause, J.; Krawzcynski, H.; Krennrich, F.; Krepps, A.; Kretzschmann,
A.; Krobot, R.; Krueger, P.; Kubo, H.; Kudryavtsev, V. A.; Kushida,
J.; Kuznetsov, A.; La Barbera, A.; La Palombara, N.; La Parola, V.;
La Rosa, G.; Lacombe, K.; Lamanna, G.; Lande, J.; Languignon, D.;
Lapington, J. S.; Laporte, P.; Laurent, B.; Lavalley, C.; Le Flour,
T.; Le Padellec, A.; Lee, S. -H.; Lee, W. H.; Lefèvre, J. -P.; Leich,
H.; Leigui de Oliveira, M. A.; Lelas, D.; Lenain, J. -P.; Leoni,
R.; Leopold, D. J.; Lerch, T.; Lessio, L.; Leto, G.; Lieunard, B.;
Lieunard, S.; Lindemann, R.; Lindfors, E.; Liolios, A.; Lipniacka,
A.; Lockart, H.; Lohse, T.; Lombardi, S.; Longo, F.; Lopatin, A.;
Lopez, M.; López-Coto, R.; López-Oramas, A.; Lorca, A.; Lorenz,
E.; Louis, F.; Lubinski, P.; Lucarelli, F.; Lüdecke, H.; Ludwin, J.;
Luque-Escamilla, P. L.; Lustermann, W.; Luz, O.; Lyard, E.; Maccarone,
M. C.; Maccarone, T. J.; Madejski, G. M.; Madhavan, A.; Mahabir, M.;
Maier, G.; Majumdar, P.; Malaguti, G.; Malaspina, G.; Maltezos, S.;
Manalaysay, A.; Mancilla, A.; Mandat, D.; Maneva, G.; Mangano, A.;
Manigot, P.; Mannheim, K.; Manthos, I.; Maragos, N.; Marcowith, A.;
Mariotti, M.; Marisaldi, M.; Markoff, S.; Marszałek, A.; Martens,
C.; Martí, J.; Martin, J. -M.; Martin, P.; Martínez, G.; Martínez,
F.; Martínez, M.; Massaro, F.; Masserot, A.; Mastichiadis, A.;
Mathieu, A.; Matsumoto, H.; Mattana, F.; Mattiazzo, S.; Maurer, A.;
Maurin, G.; Maxfield, S.; Maya, J.; Mazin, D.; Mc Comb, L.; McCann,
A.; McCubbin, N.; McHardy, I.; McKay, R.; Meagher, K.; Medina, C.;
Melioli, C.; Melkumyan, D.; Melo, D.; Mereghetti, S.; Mertsch, P.;
Meucci, M.; Meyer, M.; Michałowski, J.; Micolon, P.; Mihailidis,
A.; Mineo, T.; Minuti, M.; Mirabal, N.; Mirabel, F.; Miranda, J. M.;
Mirzoyan, R.; Mistò, A.; Mizuno, T.; Moal, B.; Moderski, R.; Mognet,
I.; Molinari, E.; Molinaro, M.; Montaruli, T.; Monte, C.; Monteiro, I.;
Moore, P.; Moralejo Olaizola, A.; Mordalska, M.; Morello, C.; Mori,
K.; Morlino, G.; Morselli, A.; Mottez, F.; Moudden, Y.; Moulin, E.;
Mrusek, I.; Mukherjee, R.; Munar-Adrover, P.; Muraishi, H.; Murase, K.;
StJ. Murphy, A.; Nagataki, S.; Naito, T.; Nakajima, D.; Nakamori, T.;
Nakayama, K.; Naumann, C.; Naumann, D.; Naumann-Godo, M.; Nayman, P.;
Nedbal, D.; Neise, D.; Nellen, L.; Neronov, A.; Neustroev, V.; Neyroud,
N.; Nicastro, L.; Nicolau-Kukliński, J.; Niedźwiecki, A.; Niemiec,
J.; Nieto, D.; Nikolaidis, A.; Nishijima, K.; Nishikawa, K. -I.;
Noda, K.; Nolan, S.; Northrop, R.; Nosek, D.; Nowak, N.; Nozato, A.;
Oakes, L.; O'Brien, P. T.; Ohira, Y.; Ohishi, M.; Ohm, S.; Ohoka, H.;
Okuda, T.; Okumura, A.; Olive, J. -F.; Ong, R. A.; Orito, R.; Orr, M.;
Osborne, J. P.; Ostrowski, M.; Otero, L. A.; Otte, N.; Ovcharov, E.;
Oya, I.; Ozieblo, A.; Padilla, L.; Pagano, I.; Paiano, S.; Paillot, D.;
Paizis, A.; Palanque, S.; Palatka, M.; Pallota, J.; Palatiello, M.;
Panagiotidis, K.; Panazol, J. -L.; Paneque, D.; Panter, M.; Panzera,
M. R.; Paoletti, R.; Papayannis, A.; Papyan, G.; Paredes, J. M.;
Pareschi, G.; Parraud, J. -M.; Parsons, D.; Pauletta, G.; Paz Arribas,
M.; Pech, M.; Pedaletti, G.; Pelassa, V.; Pelat, D.; Perez, M. d. C.;
Persic, M.; Petrucci, P. -O.; Peyaud, B.; Pichel, A.; Pieloth, D.;
Pierre, E.; Pita, S.; Pivato, G.; Pizzolato, F.; Platino, M.; Platos,
Ł.; Platzer, R.; Podkladkin, S.; Pogosyan, L.; Pohl, M.; Pojmanski,
G.; Ponz, J. D.; Potter, W.; Poutanen, J.; Prandini, E.; Prast,
J.; Preece, R.; Profeti, F.; Prokoph, H.; Prouza, M.; Proyetti, M.;
Puerto-Giménez, I.; Pühlhofer, G.; Puljak, I.; Punch, M.; Pyzioł,
R.; Quel, E. J.; Quesada, J.; Quinn, J.; Quirrenbach, A.; Racero, E.;
Rainò, S.; Rajda, P. J.; Rameez, M.; Ramon, P.; Rando, R.; Rannot,
R. C.; Rataj, M.; Raue, M.; Ravignani, D.; Reardon, P.; Reimann,
O.; Reimer, A.; Reimer, O.; Reitberger, K.; Renaud, M.; Renner,
S.; Reville, B.; Rhode, W.; Ribó, M.; Ribordy, M.; Richards, G.;
Richer, M. G.; Rico, J.; Ridky, J.; Rieger, F.; Ringegni, P.; Ripken,
J.; Ristori, P. R.; Rivière, A.; Rivoire, S.; Rob, L.; Rodeghiero,
G.; Roeser, U.; Rohlfs, R.; Rojas, G.; Romano, P.; Romaszkan, W.;
Romero, G. E.; Rosen, S. R.; Rosier Lees, S.; Ross, D.; Rouaix, G.;
Rousselle, J.; Rousselle, S.; Rovero, A. C.; Roy, F.; Royer, S.;
Rudak, B.; Rulten, C.; Rupiński, M.; Russo, F.; Ryde, F.; Saavedra,
O.; Sacco, B.; Saemann, E. O.; Saggion, A.; Sahakian, V.; Saito, K.;
Saito, T.; Saito, Y.; Sakaki, N.; Sakonaka, R.; Salini, A.; Sanchez,
F.; Sanchez-Conde, M.; Sandoval, A.; Sandaker, H.; Sant'Ambrogio, E.;
Santangelo, A.; Santos, E. M.; Sanuy, A.; Sapozhnikov, L.; Sarkar,
S.; Sartore, N.; Sasaki, H.; Satalecka, K.; Sawada, M.; Scalzotto, V.;
Scapin, V.; Scarcioffolo, M.; Schafer, J.; Schanz, T.; Schlenstedt,
S.; Schlickeiser, R.; Schmidt, T.; Schmoll, J.; Schovanek, P.;
Schroedter, M.; Schubert, A.; Schultz, C.; Schultze, J.; Schulz,
A.; Schure, K.; Schussler, F.; Schwab, T.; Schwanke, U.; Schwarz,
J.; Schwarzburg, S.; Schweizer, T.; Schwemmer, S.; Schwendicke, U.;
Schwerdt, C.; Segreto, A.; Seiradakis, J. -H.; Sembroski, G. H.;
Servillat, M.; Seweryn, K.; Sharma, M.; Shayduk, M.; Shellard,
R. C.; Shi, J.; Shibata, T.; Shibuya, A.; Shore, S.; Shum, E.;
Sideras-Haddad, E.; Sidoli, L.; Sidz, M.; Sieiro, J.; Sikora, M.;
Silk, J.; Sillanpää, A.; Singh, B. B.; Sironi, G.; Sitarek, J.;
Skole, C.; Smareglia, R.; Smith, A.; Smith, D.; Smith, J.; Smith,
N.; Sobczyńska, D.; Sol, H.; Sottile, G.; Sowiński, M.; Spanier,
F.; Spiga, D.; Spyrou, S.; Stamatescu, V.; Stamerra, A.; Starling,
R. L. C.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steiner, S.;
Stella, C.; Stergioulas, N.; Sternberger, R.; Sterzel, M.; Stinzing,
F.; Stodulski, M.; Stolarczyk, Th.; Straumann, U.; Strazzeri, E.;
Stringhetti, L.; Suarez, A.; Suchenek, M.; Sugawara, R.; Sulanke,
K. -H.; Sun, S.; Supanitsky, A. D.; Suric, T.; Sutcliffe, P.; Sykes,
J. M.; Szanecki, M.; Szepieniec, T.; Szostek, A.; Tagliaferri, G.;
Tajima, H.; Takahashi, H.; Takahashi, K.; Takalo, L.; Takami, H.;
Talbot, G.; Tammi, J.; Tanaka, M.; Tanaka, S.; Tasan, J.; Tavani,
M.; Tavernet, J. -P.; Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.;
Tenzer, C.; Terada, Y.; Terrier, R.; Teshima, M.; Testa, V.; Tezier,
D.; Thayer, J.; Thuermann, D.; Tibaldo, L.; Tibaldo, L.; Tibolla,
O.; Tiengo, A.; Timpanaro, M. C.; Tluczykont, M.; Todero Peixoto,
C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Tonachini, A.; Torii, K.;
Tornikoski, M.; Torres, D. F.; Torres, M.; Toscano, S.; Toso, G.;
Tosti, G.; Totani, T.; Toussenel, F.; Tovmassian, G.; Travnicek, P.;
Treves, A.; Trifoglio, M.; Troyano, I.; Tsinganos, K.; Ueno, H.; Umana,
G.; Umehara, K.; Upadhya, S. S.; Usher, T.; Uslenghi, M.; Vagnetti, F.;
Valdes-Galicia, J. F.; Vallania, P.; Vallejo, G.; van Driel, W.; van
Eldik, C.; Vandenbrouke, J.; Vanderwalt, J.; Vankov, H.; Vasileiadis,
G.; Vassiliev, V.; Veberic, D.; Vegas, I.; Vercellone, S.; Vergani,
S.; Verzi, V.; Vettolani, G. P.; Veyssière, C.; Vialle, J. P.;
Viana, A.; Videla, M.; Vigorito, C.; Vincent, P.; Vincent, S.; Vink,
J.; Vlahakis, N.; Vlahos, L.; Vogler, P.; Voisin, V.; Vollhardt, A.;
von Gunten, H. -P.; Vorobiov, S.; Vuerli, C.; Waegebaert, V.; Wagner,
R.; Wagner, R. G.; Wagner, S.; Wakely, S. P.; Walter, R.; Walther,
T.; Warda, K.; Warwick, R. S.; Wawer, P.; Wawrzaszek, R.; Webb, N.;
Wegner, P.; Weinstein, A.; Weitzel, Q.; Welsing, R.; Werner, M.;
Wetteskind, H.; White, R. J.; Wierzcholska, A.; Wiesand, S.; Wilhelm,
A.; Wilkinson, M. I.; Williams, D. A.; Willingale, R.; Winde, M.;
Winiarski, K.; Wischnewski, R.; Wiśniewski, Ł.; Wojcik, P.; Wood,
M.; Wörnlein, A.; Xiong, Q.; Yadav, K. K.; Yamamoto, H.; Yamamoto,
T.; Yamazaki, R.; Yanagita, S.; Yebras, J. M.; Yelos, D.; Yoshida,
A.; Yoshida, T.; Yoshikoshi, T.; Yu, P.; Zabalza, V.; Zacharias, M.;
Zajczyk, A.; Zampieri, L.; Zanin, R.; Zdziarski, A.; Zech, A.; Zhao,
A.; Zhou, X.; Zietara, K.; Ziolkowski, J.; Ziółkowski, P.; Zitelli,
V.; Zurbach, C.; Zychowski, P.
2013arXiv1307.2232C Altcode:
Compilation of CTA contributions to the proceedings of the 33rd
International Cosmic Ray Conference (ICRC2013), which took place in
2-9 July, 2013, in Rio de Janeiro, Brazil
---------------------------------------------------------
Title: Can Surface Flux Transport Account for the Weak Polar Field
in Cycle 23?
Authors: Jiang, Jie; Cameron, Robert H.; Schmitt, Dieter; Schüssler,
Manfred
2013SSRv..176..289J Altcode: 2011SSRv..tmp..212J; 2011SSRv..tmp...69J; 2011arXiv1104.4183J;
2011SSRv..tmp..136J; 2011SSRv..tmp..368J
To reproduce the weak magnetic field on the polar caps of the Sun
observed during the declining phase of cycle 23 poses a challenge to
surface flux transport models since this cycle has not been particularly
weak. We use a well-calibrated model to evaluate the parameter changes
required to obtain simulated polar fields and open flux that are
consistent with the observations. We find that the low polar field
of cycle 23 could be reproduced by an increase of the meridional flow
by 55% in the last cycle. Alternatively, a decrease of the mean tilt
angle of sunspot groups by 28% would also lead to a similarly low polar
field, but cause a delay of the polar field reversals by 1.5 years in
comparison to the observations.
---------------------------------------------------------
Title: First evidence of interaction between longitudinal and
transverse waves in solar magnetic elements
Authors: Stangalini, M.; Solanki, S. K.; Cameron, R.; Martínez
Pillet, V.
2013A&A...554A.115S Altcode: 2013arXiv1304.7088S
Small-scale magnetic fields are thought to play an important role in
the heating of the outer solar atmosphere. By taking advantage of
the unprecedented high-spatial and temporal cadence of the Imaging
Magnetograph eXperiment (IMaX), the filter vector polarimeter on board
the Sunrise balloon-borne observatory, we study the transversal and
longitudinal velocity oscillations in small magnetic elements. The
results of this analysis are then compared to magnetohydrodynamic (MHD)
simulations, showing excellent agreement. We found buffeting-induced
transverse oscillations with velocity amplitudes of the order of 1-2
km s<SUP>-1</SUP> to be common along with longitudinal oscillations
with amplitudes ~0.4 km s<SUP>-1</SUP>. Moreover, we also found an
interaction between transverse oscillations and longitudinal velocity
oscillations, showing a ± 90° phase lag at the frequency at which
they exhibit the maximum coherence in the power spectrum. Our results
are consistent with the theoretical picture in which MHD longitudinal
waves are excited inside small magnetic elements as a response of the
flux tube to the forcing action of the granular flows.
---------------------------------------------------------
Title: Modeling solar cycles 15 to 21 using a flux transport dynamo
Authors: Jiang, J.; Cameron, R. H.; Schmitt, D.; Işık, E.
2013A&A...553A.128J Altcode: 2013arXiv1304.5730J
Context. The Sun's polar fields and open flux around the time of
activity minima have been considered to be strongly correlated with
the strength of the subsequent maximum of solar activity. <BR /> Aims:
We aim to investigate the behavior of a Babcock-Leighton dynamo with
a source poloidal term that is based on the observed sunspot areas
and tilts. In particular, we investigate whether the toroidal fields
at the base of convection zone from the model are correlated with the
observed solar cycle activity maxima. <BR /> Methods: We used a flux
transport dynamo model that includes convective pumping and a poloidal
source term based on the historical record of sunspot group areas,
locations, and tilt angles to simulate solar cycles 15 to 21. <BR />
Results: We find that the polar fields near minima and the toroidal
flux at the base of the convection zone are both highly correlated
with the subsequent maxima of solar activity levels (r = 0.85 and r =
0.93, respectively). <BR /> Conclusions: The Babcock-Leighton dynamo
is consistent with the observationally inferred correlations.
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Ojha,
Roopesh; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Cheung,
Teddy; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus,
Guillaume; Cameron, Robert; Abraham, Falcone; Schinzel, Frank
2013atnf.prop.5452C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Introducing the CTA concept
Authors: Acharya, B. S.; Actis, M.; Aghajani, T.; Agnetta, G.;
Aguilar, J.; Aharonian, F.; Ajello, M.; Akhperjanian, A.; Alcubierre,
M.; Aleksić, J.; Alfaro, R.; Aliu, E.; Allafort, A. J.; Allan, D.;
Allekotte, I.; Amato, E.; Anderson, J.; Angüner, E. O.; Antonelli,
L. A.; Antoranz, P.; Aravantinos, A.; Arlen, T.; Armstrong, T.;
Arnaldi, H.; Arrabito, L.; Asano, K.; Ashton, T.; Asorey, H. G.; Awane,
Y.; Baba, H.; Babic, A.; Baby, N.; Bähr, J.; Bais, A.; Baixeras, C.;
Bajtlik, S.; Balbo, M.; Balis, D.; Balkowski, C.; Bamba, A.; Bandiera,
R.; Barber, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barnstedt, J.;
Barres de Almeida, U.; Barrio, J. A.; Basili, A.; Basso, S.; Bastieri,
D.; Bauer, C.; Baushev, A.; Becerra, J.; Becherini, Y.; Bechtol, K. C.;
Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Behera, B.; Belluso,
M.; Benbow, W.; Berdugo, J.; Berger, K.; Bernard, F.; Bernardino, T.;
Bernlöhr, K.; Bhat, N.; Bhattacharyya, S.; Bigongiari, C.; Biland,
A.; Billotta, S.; Bird, T.; Birsin, E.; Bissaldi, E.; Biteau, J.;
Bitossi, M.; Blake, S.; Blanch Bigas, O.; Blasi, P.; Bobkov, A.;
Boccone, V.; Boettcher, M.; Bogacz, L.; Bogart, J.; Bogdan, M.;
Boisson, C.; Boix Gargallo, J.; Bolmont, J.; Bonanno, G.; Bonardi,
A.; Bonev, T.; Bonifacio, P.; Bonnoli, G.; Bordas, P.; Borgland,
A.; Borkowski, J.; Bose, R.; Botner, O.; Bottani, A.; Bouchet, L.;
Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.; Braun, I.;
Bretz, T.; Briggs, M.; Bringmann, T.; Brook, P.; Brun, P.; Brunetti,
L.; Buanes, T.; Buckley, J.; Buehler, R.; Bugaev, V.; Bulgarelli, A.;
Bulik, T.; Busetto, G.; Buson, S.; Byrum, K.; Cailles, M.; Cameron,
R.; Camprecios, J.; Canestrari, R.; Cantu, S.; Capalbi, M.; Caraveo,
P.; Carmona, E.; Carosi, A.; Carr, J.; Carton, P. -H.; Casanova,
S.; Casiraghi, M.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerruti,
M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chen, A.; Chiang, J.;
Chiappetti, L.; Chikawa, M.; Chitnis, V. R.; Chollet, F.; Chudoba, J.;
Cieślar, M.; Cillis, A.; Cohen-Tanugi, J.; Colafrancesco, S.; Colin,
P.; Colome, J.; Colonges, S.; Compin, M.; Conconi, P.; Conforti, V.;
Connaughton, V.; Conrad, J.; Contreras, J. L.; Coppi, P.; Corona, P.;
Corti, D.; Cortina, J.; Cossio, L.; Costantini, H.; Cotter, G.; Courty,
B.; Couturier, S.; Covino, S.; Crimi, G.; Criswell, S. J.; Croston,
J.; Cusumano, G.; Dafonseca, M.; Dale, O.; Daniel, M.; Darling, J.;
Davids, I.; Dazzi, F.; De Angelis, A.; De Caprio, V.; De Frondat,
F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De La Vega, G. A.;
de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; de Mello Neto,
J. R. T.; de Naurois, M.; de Oliveira, Y.; de Oña Wilhelmi, E.;
de Souza, V.; Decerprit, G.; Decock, G.; Deil, C.; Delagnes, E.;
Deleglise, G.; Delgado, C.; Della Volpe, D.; Demange, P.; Depaola,
G.; Dettlaff, A.; Di Paola, A.; Di Pierro, F.; Díaz, C.; Dick, J.;
Dickherber, R.; Dickinson, H.; Diez-Blanco, V.; Digel, S.; Dimitrov,
D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko,
W.; Dominis Prester, D.; Donat, A.; Dorner, D.; Doro, M.; Dournaux,
J. -L.; Drake, G.; Dravins, D.; Drury, L.; Dubois, F.; Dubois, R.;
Dubus, G.; Dufour, C.; Dumas, D.; Dumm, J.; Durand, D.; Dyks, J.;
Dyrda, M.; Ebr, J.; Edy, E.; Egberts, K.; Eger, P.; Einecke, S.;
Eleftheriadis, C.; Elles, S.; Emmanoulopoulos, D.; Engelhaupt, D.;
Enomoto, R.; Ernenwein, J. -P.; Errando, M.; Etchegoyen, A.; Evans,
P.; Falcone, A.; Fantinel, D.; Farakos, K.; Farnier, C.; Fasola,
G.; Favill, B.; Fede, E.; Federici, S.; Fegan, S.; Feinstein, F.;
Ferenc, D.; Ferrando, P.; Fesquet, M.; Fiasson, A.; Fillin-Martino,
E.; Fink, D.; Finley, C.; Finley, J. P.; Fiorini, M.; Firpo Curcoll,
R.; Flores, H.; Florin, D.; Focke, W.; Föhr, C.; Fokitis, E.; Font,
L.; Fontaine, G.; Fornasa, M.; Förster, A.; Fortson, L.; Fouque,
N.; Franckowiak, A.; Fransson, C.; Fraser, G.; Frei, R.; Albuquerque,
I. F. M.; Fresnillo, L.; Fruck, C.; Fujita, Y.; Fukazawa, Y.; Fukui,
Y.; Funk, S.; Gäbele, W.; Gabici, S.; Gabriele, R.; Gadola, A.;
Galante, N.; Gall, D.; Gallant, Y.; Gámez-García, J.; García, B.;
Garcia López, R.; Gardiol, D.; Garrido, D.; Garrido, L.; Gascon,
D.; Gaug, M.; Gaweda, J.; Gebremedhin, L.; Geffroy, N.; Gerard, L.;
Ghedina, A.; Ghigo, M.; Giannakaki, E.; Gianotti, F.; Giarrusso, S.;
Giavitto, G.; Giebels, B.; Gika, V.; Giommi, P.; Girard, N.; Giro,
E.; Giuliani, A.; Glanzman, T.; Glicenstein, J. -F.; Godinovic, N.;
Golev, V.; Gomez Berisso, M.; Gómez-Ortega, J.; Gonzalez, M. M.;
González, A.; González, F.; González Muñoz, A.; Gothe, K. S.;
Gougerot, M.; Graciani, R.; Grandi, P.; Grañena, F.; Granot, J.;
Grasseau, G.; Gredig, R.; Green, A.; Greenshaw, T.; Grégoire,
T.; Grimm, O.; Grube, J.; Grudzinska, M.; Gruev, V.; Grünewald,
S.; Grygorczuk, J.; Guarino, V.; Gunji, S.; Gyuk, G.; Hadasch, D.;
Hagiwara, R.; Hahn, J.; Hakansson, N.; Hallgren, A.; Hamer Heras,
N.; Hara, S.; Hardcastle, M. J.; Harris, J.; Hassan, T.; Hatanaka,
K.; Haubold, T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, R.;
Henault, F.; Henri, G.; Hermann, G.; Hermel, R.; Herrero, A.; Hidaka,
N.; Hinton, J.; Hoffmann, D.; Hofmann, W.; Hofverberg, P.; Holder, J.;
Horns, D.; Horville, D.; Houles, J.; Hrabovsky, M.; Hrupec, D.; Huan,
H.; Huber, B.; Huet, J. -M.; Hughes, G.; Humensky, T. B.; Huovelin,
J.; Ibarra, A.; Illa, J. M.; Impiombato, D.; Incorvaia, S.; Inoue,
S.; Inoue, Y.; Ioka, K.; Ismailova, E.; Jablonski, C.; Jacholkowska,
A.; Jamrozy, M.; Janiak, M.; Jean, P.; Jeanney, C.; Jimenez, J. J.;
Jogler, T.; Johnson, T.; Journet, L.; Juffroy, C.; Jung, I.; Kaaret,
P.; Kabuki, S.; Kagaya, M.; Kakuwa, J.; Kalkuhl, C.; Kankanyan, R.;
Karastergiou, A.; Kärcher, K.; Karczewski, M.; Karkar, S.; Kasperek,
J.; Kastana, D.; Katagiri, H.; Kataoka, J.; Katarzyński, K.; Katz,
U.; Kawanaka, N.; Kellner-Leidel, B.; Kelly, H.; Kendziorra, E.;
Khélifi, B.; Kieda, D. B.; Kifune, T.; Kihm, T.; Kishimoto, T.;
Kitamoto, K.; Kluźniak, W.; Knapic, C.; Knapp, J.; Knödlseder, J.;
Köck, F.; Kocot, J.; Kodani, K.; Köhne, J. -H.; Kohri, K.; Kokkotas,
K.; Kolitzus, D.; Komin, N.; Kominis, I.; Konno, Y.; Köppel, H.;
Korohoda, P.; Kosack, K.; Koss, G.; Kossakowski, R.; Kostka, P.;
Koul, R.; Kowal, G.; Koyama, S.; Kozioł, J.; Krähenbühl, T.;
Krause, J.; Krawzcynski, H.; Krennrich, F.; Krepps, A.; Kretzschmann,
A.; Krobot, R.; Krueger, P.; Kubo, H.; Kudryavtsev, V. A.; Kushida,
J.; Kuznetsov, A.; La Barbera, A.; La Palombara, N.; La Parola, V.;
La Rosa, G.; Lacombe, K.; Lamanna, G.; Lande, J.; Languignon, D.;
Lapington, J.; Laporte, P.; Lavalley, C.; Le Flour, T.; Le Padellec,
A.; Lee, S. -H.; Lee, W. H.; Leigui de Oliveira, M. A.; Lelas, D.;
Lenain, J. -P.; Leopold, D. J.; Lerch, T.; Lessio, L.; Lieunard, B.;
Lindfors, E.; Liolios, A.; Lipniacka, A.; Lockart, H.; Lohse, T.;
Lombardi, S.; Lopatin, A.; Lopez, M.; López-Coto, R.; López-Oramas,
A.; Lorca, A.; Lorenz, E.; Lubinski, P.; Lucarelli, F.; Lüdecke, H.;
Ludwin, J.; Luque-Escamilla, P. L.; Lustermann, W.; Luz, O.; Lyard,
E.; Maccarone, M. C.; Maccarone, T. J.; Madejski, G. M.; Madhavan,
A.; Mahabir, M.; Maier, G.; Majumdar, P.; Malaguti, G.; Maltezos, S.;
Manalaysay, A.; Mancilla, A.; Mandat, D.; Maneva, G.; Mangano, A.;
Manigot, P.; Mannheim, K.; Manthos, I.; Maragos, N.; Marcowith, A.;
Mariotti, M.; Marisaldi, M.; Markoff, S.; Marszałek, A.; Martens, C.;
Martí, J.; Martin, J. -M.; Martin, P.; Martínez, G.; Martínez, F.;
Martínez, M.; Masserot, A.; Mastichiadis, A.; Mathieu, A.; Matsumoto,
H.; Mattana, F.; Mattiazzo, S.; Maurin, G.; Maxfield, S.; Maya, J.;
Mazin, D.; Mc Comb, L.; McCubbin, N.; McHardy, I.; McKay, R.; Medina,
C.; Melioli, C.; Melkumyan, D.; Mereghetti, S.; Mertsch, P.; Meucci,
M.; Michałowski, J.; Micolon, P.; Mihailidis, A.; Mineo, T.; Minuti,
M.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mizuno,
T.; Moal, B.; Moderski, R.; Mognet, I.; Molinari, E.; Molinaro,
M.; Montaruli, T.; Monteiro, I.; Moore, P.; Moralejo Olaizola,
A.; Mordalska, M.; Morello, C.; Mori, K.; Mottez, F.; Moudden, Y.;
Moulin, E.; Mrusek, I.; Mukherjee, R.; Munar-Adrover, P.; Muraishi,
H.; Murase, K.; Murphy, A.; Nagataki, S.; Naito, T.; Nakajima, D.;
Nakamori, T.; Nakayama, K.; Naumann, C.; Naumann, D.; Naumann-Godo,
M.; Nayman, P.; Nedbal, D.; Neise, D.; Nellen, L.; Neustroev, V.;
Neyroud, N.; Nicastro, L.; Nicolau-Kukliński, J.; Niedźwiecki, A.;
Niemiec, J.; Nieto, D.; Nikolaidis, A.; Nishijima, K.; Nolan, S.;
Northrop, R.; Nosek, D.; Nowak, N.; Nozato, A.; O'Brien, P.; Ohira,
Y.; Ohishi, M.; Ohm, S.; Ohoka, H.; Okuda, T.; Okumura, A.; Olive,
J. -F.; Ong, R. A.; Orito, R.; Orr, M.; Osborne, J.; Ostrowski, M.;
Otero, L. A.; Otte, N.; Ovcharov, E.; Oya, I.; Ozieblo, A.; Padilla,
L.; Paiano, S.; Paillot, D.; Paizis, A.; Palanque, S.; Palatka, M.;
Pallota, J.; Panagiotidis, K.; Panazol, J. -L.; Paneque, D.; Panter,
M.; Paoletti, R.; Papayannis, A.; Papyan, G.; Paredes, J. M.; Pareschi,
G.; Parks, G.; Parraud, J. -M.; Parsons, D.; Paz Arribas, M.; Pech,
M.; Pedaletti, G.; Pelassa, V.; Pelat, D.; Perez, M. d. C.; Persic,
M.; Petrucci, P. -O.; Peyaud, B.; Pichel, A.; Pita, S.; Pizzolato, F.;
Platos, Ł.; Platzer, R.; Pogosyan, L.; Pohl, M.; Pojmanski, G.; Ponz,
J. D.; Potter, W.; Poutanen, J.; Prandini, E.; Prast, J.; Preece, R.;
Profeti, F.; Prokoph, H.; Prouza, M.; Proyetti, M.; Puerto-Gimenez, I.;
Pühlhofer, G.; Puljak, I.; Punch, M.; Pyzioł, R.; Quel, E. J.; Quinn,
J.; Quirrenbach, A.; Racero, E.; Rajda, P. J.; Ramon, P.; Rando, R.;
Rannot, R. C.; Rataj, M.; Raue, M.; Reardon, P.; Reimann, O.; Reimer,
A.; Reimer, O.; Reitberger, K.; Renaud, M.; Renner, S.; Reville, B.;
Rhode, W.; Ribó, M.; Ribordy, M.; Richer, M. G.; Rico, J.; Ridky,
J.; Rieger, F.; Ringegni, P.; Ripken, J.; Ristori, P. R.; Riviére,
A.; Rivoire, S.; Rob, L.; Roeser, U.; Rohlfs, R.; Rojas, G.; Romano,
P.; Romaszkan, W.; Romero, G. E.; Rosen, S.; Rosier Lees, S.; Ross,
D.; Rouaix, G.; Rousselle, J.; Rousselle, S.; Rovero, A. C.; Roy,
F.; Royer, S.; Rudak, B.; Rulten, C.; Rupiński, M.; Russo, F.; Ryde,
F.; Sacco, B.; Saemann, E. O.; Saggion, A.; Sahakian, V.; Saito, K.;
Saito, T.; Saito, Y.; Sakaki, N.; Sakonaka, R.; Salini, A.; Sanchez,
F.; Sanchez-Conde, M.; Sandoval, A.; Sandaker, H.; Sant'Ambrogio,
E.; Santangelo, A.; Santos, E. M.; Sanuy, A.; Sapozhnikov, L.;
Sarkar, S.; Sartore, N.; Sasaki, H.; Satalecka, K.; Sawada, M.;
Scalzotto, V.; Scapin, V.; Scarcioffolo, M.; Schafer, J.; Schanz,
T.; Schlenstedt, S.; Schlickeiser, R.; Schmidt, T.; Schmoll, J.;
Schovanek, P.; Schroedter, M.; Schultz, C.; Schultze, J.; Schulz,
A.; Schure, K.; Schwab, T.; Schwanke, U.; Schwarz, J.; Schwarzburg,
S.; Schweizer, T.; Schwemmer, S.; Segreto, A.; Seiradakis, J. -H.;
Sembroski, G. H.; Seweryn, K.; Sharma, M.; Shayduk, M.; Shellard,
R. C.; Shi, J.; Shibata, T.; Shibuya, A.; Shum, E.; Sidoli, L.; Sidz,
M.; Sieiro, J.; Sikora, M.; Silk, J.; Sillanpää, A.; Singh, B. B.;
Sitarek, J.; Skole, C.; Smareglia, R.; Smith, A.; Smith, D.; Smith,
J.; Smith, N.; Sobczyńska, D.; Sol, H.; Sottile, G.; Sowiński, M.;
Spanier, F.; Spiga, D.; Spyrou, S.; Stamatescu, V.; Stamerra, A.;
Starling, R.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steiner,
S.; Stergioulas, N.; Sternberger, R.; Sterzel, M.; Stinzing, F.;
Stodulski, M.; Straumann, U.; Strazzeri, E.; Stringhetti, L.;
Suarez, A.; Suchenek, M.; Sugawara, R.; Sulanke, K. -H.; Sun, S.;
Supanitsky, A. D.; Suric, T.; Sutcliffe, P.; Sykes, J.; Szanecki, M.;
Szepieniec, T.; Szostek, A.; Tagliaferri, G.; Tajima, H.; Takahashi,
H.; Takahashi, K.; Takalo, L.; Takami, H.; Talbot, G.; Tammi, J.;
Tanaka, M.; Tanaka, S.; Tasan, J.; Tavani, M.; Tavernet, J. -P.;
Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.; Tenzer, C.; Terada,
Y.; Terrier, R.; Teshima, M.; Testa, V.; Tezier, D.; Thuermann, D.;
Tibaldo, L.; Tibolla, O.; Tiengo, A.; Tluczykont, M.; Todero Peixoto,
C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Torii, K.; Tornikoski,
M.; Torres, D. F.; Torres, M.; Tosti, G.; Totani, T.; Toussenel, F.;
Tovmassian, G.; Travnicek, P.; Trifoglio, M.; Troyano, I.; Tsinganos,
K.; Ueno, H.; Umehara, K.; Upadhya, S. S.; Usher, T.; Uslenghi, M.;
Valdes-Galicia, J. F.; Vallania, P.; Vallejo, G.; van Driel, W.; van
Eldik, C.; Vandenbrouke, J.; Vanderwalt, J.; Vankov, H.; Vasileiadis,
G.; Vassiliev, V.; Veberic, D.; Vegas, I.; Vercellone, S.; Vergani,
S.; Veyssiére, C.; Vialle, J. P.; Viana, A.; Videla, M.; Vincent, P.;
Vincent, S.; Vink, J.; Vlahakis, N.; Vlahos, L.; Vogler, P.; Vollhardt,
A.; von Gunten, H. -P.; Vorobiov, S.; Vuerli, C.; Waegebaert, V.;
Wagner, R.; Wagner, R. G.; Wagner, S.; Wakely, S. P.; Walter, R.;
Walther, T.; Warda, K.; Warwick, R.; Wawer, P.; Wawrzaszek, R.; Webb,
N.; Wegner, P.; Weinstein, A.; Weitzel, Q.; Welsing, R.; Werner, M.;
Wetteskind, H.; White, R.; Wierzcholska, A.; Wiesand, S.; Wilkinson,
M.; Williams, D. A.; Willingale, R.; Winiarski, K.; Wischnewski, R.;
Wiśniewski, Ł.; Wood, M.; Wörnlein, A.; Xiong, Q.; Yadav, K. K.;
Yamamoto, H.; Yamamoto, T.; Yamazaki, R.; Yanagita, S.; Yebras,
J. M.; Yelos, D.; Yoshida, A.; Yoshida, T.; Yoshikoshi, T.; Zabalza,
V.; Zacharias, M.; Zajczyk, A.; Zanin, R.; Zdziarski, A.; Zech, A.;
Zhao, A.; Zhou, X.; Ziętara, K.; Ziolkowski, J.; Ziółkowski, P.;
Zitelli, V.; Zurbach, C.; Żychowski, P.; CTA Consortium
2013APh....43....3A Altcode: 2013APh....43....3C
The Cherenkov Telescope Array (CTA) is a new observatory for very
high-energy (VHE) gamma rays. CTA has ambitions science goals, for which
it is necessary to achieve full-sky coverage, to improve the sensitivity
by about an order of magnitude, to span about four decades of energy,
from a few tens of GeV to above 100 TeV with enhanced angular and energy
resolutions over existing VHE gamma-ray observatories. An international
collaboration has formed with more than 1000 members from 27 countries
in Europe, Asia, Africa and North and South America. In 2010 the CTA
Consortium completed a Design Study and started a three-year Preparatory
Phase which leads to production readiness of CTA in 2014. In this paper
we introduce the science goals and the concept of CTA, and provide an
overview of the project.
---------------------------------------------------------
Title: Coupled model for the formation of an active region corona
Authors: Chen, Feng; Bingert, Sven; Peter, Hardi; Cameron, Robert;
Schüssler; , Manfred; Cheung, Mark C. M.
2013enss.confE..21C Altcode:
We will present the first model that couples the formation of an active
region corona to a model of the emergence. This allows us to study
when, where, and why active region loops form, and how they evolve. For
this we use an existing 3D radiation MHD model of the emergence of an
active region through the upper convection zone and the photosphere
as a lower boundary for a coronal model. Our 3D MHD coronal model
accounts for the braiding of the magnetic field lines that induces
currents in the corona that is getting filled with the emerging magnetic
field. Starting with a basically field-free atmosphere we follow the
flux emergence until numerous individually identifiable hot coronal
loops have been formed. The temperatures in the coronal loops of well
above 1 MK are reached at densities corresponding to actually observed
active region loops. The loops develop over a very short time period
of the order of several minutes through the evaporation of material
from the chromosphere. Because we have full access to the heating
rate as a function of time and space in our computational domain we
can determine the conditions under which these loops form.
---------------------------------------------------------
Title: On the relation between continuum brightness and magnetic
field in solar active regions
Authors: Danilovic, S.; Röhrbein, D.; Cameron, R. H.; Schüssler, M.
2013A&A...550A.118D Altcode:
Context. Variations of solar irradiance are mainly determined
by the changing coverage of the visible solar disk with magnetic
flux concentrations. The relationship between brightness and field
strength is an important ingredient for models and reconstructions of
irradiance variations. <BR /> Aims: We assess the effect of limited
observational resolution on the relationship between brightness
and magnetic field by comparing comprehensive MHD simulations with
observational results. <BR /> Methods: Simulations of magnetoconvection
representing the near-surface layers of a plage region were used to
determine maps of the continuum brightness and Stokes profiles for the
Fe i line at 630.22 nm. After convolving with instrumental profiles,
synthetic observations of the magnetic field were generated by applying
a Stokes inversion code. We compare the resulting relation between
brightness and apparent vertical magnetic field to the corresponding
outcome derived from real observations of a plage region with the
Hinode satellite. <BR /> Results: Consideration of the image smearing
effects due to the limited resolution of the observations transform the
largely monotonic relation between brightness and field strength at the
original resolution of the simulations into a profile with a maximum
at intermediate field strength, which is in good agreement with the
observations. <BR /> Conclusions: Considering the effect of limited
observational resolution renders the relation between brightness and
magnetic field from comprehensive MHD simulations consistent with
observational results. This is a necessary prerequisite for the
utilization of simulations for models and reconstruction of solar
irradiance variations.
---------------------------------------------------------
Title: MHD waves in small magnetic elements: comparing IMaX
observations to simulations.
Authors: Stangalini, M.; Solanki, S. K.; Cameron, R.
2013MmSAI..84..444S Altcode:
Small-scale magnetic fields are thought to play an important role in the
heating of the outer solar atmosphere. By exploiting the high-spatial
and temporal resolution of IMaX, the bidimensional spectropolarimeter on
board the Sunrise balloon-borne observatory, we study the excitation of
MHD waves in small magnetic elements, providing clues on the interaction
of the magnetic structures with the photospheric forcing and the ambient
acoustic field. The large fraction of magnetic features observed by
IMaX made it possible to study the interaction between the photospheric
granulation and the flux tubes from a statistical point-of-view. In
particular we find a 90 degree phase lag with an high confidence level
between the horizontal displacements of the flux tubes and the velocity
perturbations measured inside them. We also find that the observational
results are in excellent agreement with MHD simulations. This result
suggests that the horizontal displacement of small-scale magnetic
features by the surrounding granulation excites longitudinal waves
within the magnetic elements.
---------------------------------------------------------
Title: MHD simulation of the inner-heliospheric magnetic field
Authors: Wiengarten, T.; Kleimann, J.; Fichtner, H.; Cameron, R.;
Jiang, J.; Kissmann, R.; Scherer, K.
2013JGRA..118...29W Altcode: 2013arXiv1303.4260W
Maps of the radial magnetic field at a heliocentric distance of 10
solar radii are used as boundary conditions in the MHD code CRONOS to
simulate a three-dimensional inner-heliospheric solar wind emanating
from the rotating Sun out to 1 AU. The input data for the magnetic
field are the result of solar surface flux transport modeling using
observational data of sunspot groups coupled with a current-sheet
source surface model. Among several advancements, this allows for
higher angular resolution than that of comparable observational data
from synoptic magnetograms. The required initial conditions for the
other MHD quantities are obtained following an empirical approach using
an inverse relation between flux tube expansion and radial solar wind
speed. The computations are performed for representative solar minimum
and maximum conditions, and the corresponding state of the solar wind
up to the Earth's orbit is obtained. After a successful comparison
of the latter with observational data, they can be used to drive
outer-heliospheric models.
---------------------------------------------------------
Title: Are the strengths of solar cycles determined by converging
flows towards the activity belts?
Authors: Cameron, R. H.; Schüssler, M.
2012A&A...548A..57C Altcode: 2012arXiv1210.7644C
It is proposed that the observed near-surface inflows towards the
active regions and sunspot zones provide a nonlinear feedback mechanism
that limits the amplitude of a Babcock-Leighton-type solar dynamo and
determines the variation of the cycle strength. This hypothesis is
tested with surface flux transport simulations including converging
latitudinal flows that depend on the surface distribution of magnetic
flux. The inflows modulate the build-up of polar fields (represented
by the axial dipole) by reducing the tilt angles of bipolar magnetic
regions and by affecting the cross-equator transport of leading-polarity
magnetic flux. With flux input derived from the observed record of
sunspot groups, the simulations cover the period between 1874 and 1980
(corresponding to solar cycles 11 to 20). The inclusion of the inflows
leads to a strong correlation of the simulated axial dipole strength
during activity minimum with the observed amplitude of the subsequent
cycle. This in agreement with empirical correlations and in line with
what is expected from a Babcock-Leighton-type dynamo. The results
provide evidence that the latitudinal inflows are a key ingredient in
determining the amplitude of solar cycles.
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Thompson,
David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier,
Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham,
Falcone
2012atnf.prop.5094C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Surface flux evolution constraints for flux transport dynamos
Authors: Cameron, R. H.; Schmitt, D.; Jiang, J.; Işık, E.
2012A&A...542A.127C Altcode: 2012arXiv1205.1136C
The surface flux transport (SFT) model of solar magnetic fields involves
empirically well-constrained velocity and magnetic fields. The basic
evolution of the Sun's large-scale surface magnetic field is well
described by this model. The azimuthally averaged evolution of the SFT
model can be compared to the surface evolution of the flux transport
dynamo (FTD), and the evolution of the SFT model can be used to
constrain several near-surface properties of the FTD model. We compared
the results of the FTD model with different upper boundary conditions
and diffusivity profiles against the results of the SFT model. Among
the ingredients of the FTD model, downward pumping of magnetic flux,
related to a positive diffusivity gradient, has a significant effect
in slowing down the diffusive radial transport of magnetic flux through
the solar surface. Provided the pumping was strong enough to give rise
to a downflow of a magnetic Reynolds number of 5 in the near-surface
boundary layer, the FTD using a vertical boundary condition matches the
SFT model based on the average velocities above the boundary layer. The
FTD model with a potential field was unable to match the SFT results.
---------------------------------------------------------
Title: Waves as the Source of Apparent Twisting Motions in Sunspot
Penumbrae
Authors: Bharti, L.; Cameron, R. H.; Rempel, M.; Hirzberger, J.;
Solanki, S. K.
2012ApJ...752..128B Altcode: 2012arXiv1204.2221B
The motion of dark striations across bright filaments in a sunspot
penumbra has become an important new diagnostic of convective gas
flows in penumbral filaments. The nature of these striations has,
however, remained unclear. Here, we present an analysis of small-scale
motions in penumbral filaments in both simulations and observations. The
simulations, when viewed from above, show fine structure with dark lanes
running outward from the dark core of the penumbral filaments. The
dark lanes either occur preferentially on one side or alternate
between both sides of the filament. We identify this fine structure
with transverse (kink) oscillations of the filament, corresponding to
a sideways swaying of the filament. These oscillations have periods in
the range of 5-7 minutes and propagate outward and downward along the
filament. Similar features are found in observed G-band intensity time
series of penumbral filaments in a sunspot located near disk center
obtained by the Broadband Filter Imager on board the Hinode. We also
find that some filaments show dark striations moving to both sides
of the filaments. Based on the agreement between simulations and
observations we conclude that the motions of these striations are
caused by transverse oscillations of the underlying bright filaments.
---------------------------------------------------------
Title: Vortices, shocks, and heating in the solar photosphere:
effect of a magnetic field
Authors: Moll, R.; Cameron, R. H.; Schüssler, M.
2012A&A...541A..68M Altcode: 2012arXiv1201.5981M
<BR /> Aims: We study the differences between non-magnetic and
magnetic regions in the flow and thermal structure of the upper solar
photosphere. <BR /> Methods: Radiative MHD simulations representing
a quiet region and a plage region, respectively, which extend into
the layers around the temperature minimum, are analyzed. <BR />
Results: The flow structure in the upper photospheric layers of the
two simulations is considerably different: the non-magnetic simulation
is dominated by a pattern of moving shock fronts while the magnetic
simulation shows vertically extended vortices associated with magnetic
flux concentrations. Both kinds of structures induce substantial local
heating. The resulting average temperature profiles are characterized by
a steep rise above the temperature minimum due to shock heating in the
non-magnetic case and by a flat photospheric temperature gradient mainly
caused by Ohmic dissipation in the magnetic run. <BR /> Conclusions:
Shocks in the quiet Sun and vortices in the strongly magnetized
regions represent the dominant flow structures in the layers around
the temperature minimum. They are closely connected with dissipation
processes providing localized heating.
---------------------------------------------------------
Title: Magnetohydrodynamics of the Weakly Ionized Solar Photosphere
Authors: Cheung, Mark C. M.; Cameron, Robert H.
2012ApJ...750....6C Altcode: 2012arXiv1202.1937C
We investigate the importance of ambipolar diffusion and Hall
currents for high-resolution comprehensive ("realistic") photospheric
simulations. To do so, we extended the radiative magnetohydrodynamics
code MURaM to use the generalized Ohm's law under the assumption
of local thermodynamic equilibrium. We present test cases comparing
analytical solutions with numerical simulations for validation of the
code. Furthermore, we carried out a number of numerical experiments
to investigate the impact of these neutral-ion effects in the
photosphere. We find that, at the spatial resolutions currently used
(5-20 km per grid point), the Hall currents and ambipolar diffusion
begin to become significant—with flows of 100 m s<SUP>-1</SUP> in
sunspot light bridges, and changes of a few percent in the thermodynamic
structure of quiet-Sun magnetic features. The magnitude of the effects
is expected to increase rapidly as smaller-scale variations are resolved
by the simulations.
---------------------------------------------------------
Title: Break up of returning plasma after the 7 June 2011 filament
eruption by Rayleigh-Taylor instabilities
Authors: Innes, D. E.; Cameron, R. H.; Fletcher, L.; Inhester, B.;
Solanki, S. K.
2012A&A...540L..10I Altcode: 2012arXiv1202.4981I
Context. A prominence eruption on 7 June 2011 produced spectacular
curtains of plasma falling through the lower corona. At the solar
surface they created an incredible display of extreme ultraviolet
brightenings. <BR /> Aims: To identify and analyze some of the local
instabilities which produce structure in the falling plasma. <BR />
Methods: The structures were investigated using SDO/AIA 171 Å and
193 Å images in which the falling plasma appeared dark against
the bright coronal emission. <BR /> Results: Several instances of
the Rayleigh-Taylor instability were investigated. In two cases the
Alfvén velocity associated with the dense plasma could be estimated
from the separation of the Rayleigh-Taylor fingers. A second type of
feature, which has the appearance of self-similar branching horns was
discussed. <P />Appendix A and two movies are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Thompson,
David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier,
Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham,
Falcone
2012atnf.prop.4533C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Diffusivity of Isolated Internetwork Ca II H Bright Points
Observed by SuFI/SUNRISE
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Feller, A.;
Pietarila, A.; Lagg, A.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knoelker, M.; Martinez Pillet, V.; Schmidt, W.; Title, A.
2012decs.confE..99J Altcode:
We analyze trajectories of the proper motion of intrinsically magnetic,
isolated internetwork Ca II H BPs (with mean lifetime of 461 sec) to
obtain their diffusivity behaviors. We use high spatial and temporal
resolution image sequences of quiet-Sun, disc-centre observations
obtained in the Ca II H 397 nm passband of the Sunrise Filter Imager
(SuFI) on board the SUNRISE balloon-borne solar observatory. In
order to avoid misidentification, the BPs are semi-manually selected
and then automatically tracked. The trajectory of each BP is then
calculated and its diffusion index is described by a power law
exponent, using which we classify the BPs' trajectories into sub-,
normal and super- diffusive. In addition, the corresponding diffusion
coefficients (D) based on the observed displacements are consequently
computed. We find a strong super-diffusivity at a height sampled by the
SuFI/SUNRISE Ca II H passband (i.e. a height corresponding roughly to
the temperature minimum). We find that 74% of the identified tiny BPs
are super-diffusive, 18% move randomly (i.e. their motion corresponds
to normal diffusion) and only 8% belong to the sub-diffusion regime. In
addition, we find that 53% of the super-diffusion regime (i.e. 39% of
all BPs) have the diffusivity index of 2 which are termed as "Ballistic
BPs". Finally, we explore the distribution of diffusion index with the
help of a simple simulation. The results suggest that the BPs are random
walkers superposed by a systematic (background) velocity in which the
magnitude of each component (and hence their ratio) depends on the time
and spatial scales. We further discuss a simple sketch to explain the
diffusivity of observed BPs while they migrate within a supergranule
(i.e. internetwork areas) or close to the network regions.
---------------------------------------------------------
Title: To the top of the photosphere
Authors: Cameron, Robert
2012decs.confE..17C Altcode:
We will discuss the interaction of convection and magnetic fields in
the solar photosphere. In particular we will concentrate on the broad
range of time and spatial scales over which structures are generated
and evolve. The importance of waves, vortices and braiding of the
magnetic footpoints will be mentioned, as well as future problems
which need to be tackled.
---------------------------------------------------------
Title: Simulations of the solar near-surface layers with the CO5BOLD,
MURaM, and Stagger codes
Authors: Beeck, B.; Collet, R.; Steffen, M.; Asplund, M.; Cameron,
R. H.; Freytag, B.; Hayek, W.; Ludwig, H. -G.; Schüssler, M.
2012A&A...539A.121B Altcode: 2012arXiv1201.1103B
Context. Radiative hydrodynamic simulations of solar and stellar surface
convection have become an important tool for exploring the structure and
gas dynamics in the envelopes and atmospheres of late-type stars and for
improving our understanding of the formation of stellar spectra. <BR
/> Aims: We quantitatively compare results from three-dimensional,
radiative hydrodynamic simulations of convection near the solar surface
generated with three numerical codes (CO<SUP>5</SUP>BOLD, MURaM,
and Stagger) and different simulation setups in order to investigate
the level of similarity and to cross-validate the simulations. <BR
/> Methods: For all three simulations, we considered the average
stratifications of various quantities (temperature, pressure, flow
velocity, etc.) on surfaces of constant geometrical or optical depth,
as well as their temporal and spatial fluctuations. We also compared
observables, such as the spatially resolved patterns of the emerging
intensity and of the vertical velocity at the solar optical surface
as well as the center-to-limb variation of the continuum intensity
at various wavelengths. <BR /> Results: The depth profiles of the
thermodynamical quantities and of the convective velocities as well as
their spatial fluctuations agree quite well. Slight deviations can be
understood in terms of differences in box size, spatial resolution
and in the treatment of non-gray radiative transfer between the
simulations. <BR /> Conclusions: The results give confidence in the
reliability of the results from comprehensive radiative hydrodynamic
simulations.
---------------------------------------------------------
Title: Design concepts for the Cherenkov Telescope Array CTA: an
advanced facility for ground-based high-energy gamma-ray astronomy
Authors: Actis, M.; Agnetta, G.; Aharonian, F.; Akhperjanian,
A.; Aleksić, J.; Aliu, E.; Allan, D.; Allekotte, I.; Antico, F.;
Antonelli, L. A.; Antoranz, P.; Aravantinos, A.; Arlen, T.; Arnaldi,
H.; Artmann, S.; Asano, K.; Asorey, H.; Bähr, J.; Bais, A.; Baixeras,
C.; Bajtlik, S.; Balis, D.; Bamba, A.; Barbier, C.; Barceló, M.;
Barnacka, A.; Barnstedt, J.; Barres de Almeida, U.; Barrio, J. A.;
Basso, S.; Bastieri, D.; Bauer, C.; Becerra, J.; Becherini, Y.;
Bechtol, K.; Becker, J.; Beckmann, V.; Bednarek, W.; Behera, B.;
Beilicke, M.; Belluso, M.; Benallou, M.; Benbow, W.; Berdugo, J.;
Berger, K.; Bernardino, T.; Bernlöhr, K.; Biland, A.; Billotta, S.;
Bird, T.; Birsin, E.; Bissaldi, E.; Blake, S.; Blanch, O.; Bobkov,
A. A.; Bogacz, L.; Bogdan, M.; Boisson, C.; Boix, J.; Bolmont,
J.; Bonanno, G.; Bonardi, A.; Bonev, T.; Borkowski, J.; Botner, O.;
Bottani, A.; Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.;
Braun, I.; Bretz, T.; Briggs, M. S.; Brun, P.; Brunetti, L.; Buckley,
J. H.; Bugaev, V.; Bühler, R.; Bulik, T.; Busetto, G.; Buson, S.;
Byrum, K.; Cailles, M.; Cameron, R.; Canestrari, R.; Cantu, S.;
Carmona, E.; Carosi, A.; Carr, J.; Carton, P. H.; Casiraghi, M.;
Castarede, H.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerruti,
B.; Cerruti, M.; Chadwick, P. M.; Chiang, J.; Chikawa, M.; Cieślar,
M.; Ciesielska, M.; Cillis, A.; Clerc, C.; Colin, P.; Colomé, J.;
Compin, M.; Conconi, P.; Connaughton, V.; Conrad, J.; Contreras, J. L.;
Coppi, P.; Corlier, M.; Corona, P.; Corpace, O.; Corti, D.; Cortina,
J.; Costantini, H.; Cotter, G.; Courty, B.; Couturier, S.; Covino,
S.; Croston, J.; Cusumano, G.; Daniel, M. K.; Dazzi, F.; de Angelis,
A.; de Cea Del Pozo, E.; de Gouveia Dal Pino, E. M.; de Jager, O.;
de La Calle Pérez, I.; de La Vega, G.; de Lotto, B.; de Naurois,
M.; de Oña Wilhelmi, E.; de Souza, V.; Decerprit, B.; Deil, C.;
Delagnes, E.; Deleglise, G.; Delgado, C.; Dettlaff, T.; di Paolo,
A.; di Pierro, F.; Díaz, C.; Dick, J.; Dickinson, H.; Digel, S. W.;
Dimitrov, D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Domainko,
W.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Dravins, D.; Drury, L.;
Dubois, F.; Dubois, R.; Dubus, G.; Dufour, C.; Durand, D.; Dyks,
J.; Dyrda, M.; Edy, E.; Egberts, K.; Eleftheriadis, C.; Elles, S.;
Emmanoulopoulos, D.; Enomoto, R.; Ernenwein, J. -P.; Errando, M.;
Etchegoyen, A.; Falcone, A. D.; Farakos, K.; Farnier, C.; Federici,
S.; Feinstein, F.; Ferenc, D.; Fillin-Martino, E.; Fink, D.; Finley,
C.; Finley, J. P.; Firpo, R.; Florin, D.; Föhr, C.; Fokitis, E.;
Font, Ll.; Fontaine, G.; Fontana, A.; Förster, A.; Fortson, L.;
Fouque, N.; Fransson, C.; Fraser, G. W.; Fresnillo, L.; Fruck, C.;
Fujita, Y.; Fukazawa, Y.; Funk, S.; Gäbele, W.; Gabici, S.; Gadola,
A.; Galante, N.; Gallant, Y.; García, B.; García López, R. J.;
Garrido, D.; Garrido, L.; Gascón, D.; Gasq, C.; Gaug, M.; Gaweda,
J.; Geffroy, N.; Ghag, C.; Ghedina, A.; Ghigo, M.; Gianakaki, E.;
Giarrusso, S.; Giavitto, G.; Giebels, B.; Giro, E.; Giubilato, P.;
Glanzman, T.; Glicenstein, J. -F.; Gochna, M.; Golev, V.; Gómez
Berisso, M.; González, A.; González, F.; Grañena, F.; Graciani,
R.; Granot, J.; Gredig, R.; Green, A.; Greenshaw, T.; Grimm, O.;
Grube, J.; Grudzińska, M.; Grygorczuk, J.; Guarino, V.; Guglielmi,
L.; Guilloux, F.; Gunji, S.; Gyuk, G.; Hadasch, D.; Haefner, D.;
Hagiwara, R.; Hahn, J.; Hallgren, A.; Hara, S.; Hardcastle, M. J.;
Hassan, T.; Haubold, T.; Hauser, M.; Hayashida, M.; Heller, R.; Henri,
G.; Hermann, G.; Herrero, A.; Hinton, J. A.; Hoffmann, D.; Hofmann,
W.; Hofverberg, P.; Horns, D.; Hrupec, D.; Huan, H.; Huber, B.; Huet,
J. -M.; Hughes, G.; Hultquist, K.; Humensky, T. B.; Huppert, J. -F.;
Ibarra, A.; Illa, J. M.; Ingjald, J.; Inoue, Y.; Inoue, S.; Ioka, K.;
Jablonski, C.; Jacholkowska, A.; Janiak, M.; Jean, P.; Jensen, H.;
Jogler, T.; Jung, I.; Kaaret, P.; Kabuki, S.; Kakuwa, J.; Kalkuhl,
C.; Kankanyan, R.; Kapala, M.; Karastergiou, A.; Karczewski, M.;
Karkar, S.; Karlsson, N.; Kasperek, J.; Katagiri, H.; Katarzyński, K.;
Kawanaka, N.; Kȩdziora, B.; Kendziorra, E.; Khélifi, B.; Kieda, D.;
Kifune, T.; Kihm, T.; Klepser, S.; Kluźniak, W.; Knapp, J.; Knappy,
A. R.; Kneiske, T.; Knödlseder, J.; Köck, F.; Kodani, K.; Kohri,
K.; Kokkotas, K.; Komin, N.; Konopelko, A.; Kosack, K.; Kossakowski,
R.; Kostka, P.; Kotuła, J.; Kowal, G.; Kozioł, J.; Krähenbühl,
T.; Krause, J.; Krawczynski, H.; Krennrich, F.; Kretzschmann, A.;
Kubo, H.; Kudryavtsev, V. A.; Kushida, J.; La Barbera, N.; La Parola,
V.; La Rosa, G.; López, A.; Lamanna, G.; Laporte, P.; Lavalley, C.;
Le Flour, T.; Le Padellec, A.; Lenain, J. -P.; Lessio, L.; Lieunard,
B.; Lindfors, E.; Liolios, A.; Lohse, T.; Lombardi, S.; Lopatin,
A.; Lorenz, E.; Lubiński, P.; Luz, O.; Lyard, E.; Maccarone, M. C.;
Maccarone, T.; Maier, G.; Majumdar, P.; Maltezos, S.; Małkiewicz,
P.; Mañá, C.; Manalaysay, A.; Maneva, G.; Mangano, A.; Manigot,
P.; Marín, J.; Mariotti, M.; Markoff, S.; Martínez, G.; Martínez,
M.; Mastichiadis, A.; Matsumoto, H.; Mattiazzo, S.; Mazin, D.; McComb,
T. J. L.; McCubbin, N.; McHardy, I.; Medina, C.; Melkumyan, D.; Mendes,
A.; Mertsch, P.; Meucci, M.; Michałowski, J.; Micolon, P.; Mineo,
T.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mizuno,
T.; Moal, B.; Moderski, R.; Molinari, E.; Monteiro, I.; Moralejo, A.;
Morello, C.; Mori, K.; Motta, G.; Mottez, F.; Moulin, E.; Mukherjee,
R.; Munar, P.; Muraishi, H.; Murase, K.; Murphy, A. Stj.; Nagataki,
S.; Naito, T.; Nakamori, T.; Nakayama, K.; Naumann, C.; Naumann, D.;
Nayman, P.; Nedbal, D.; Niedźwiecki, A.; Niemiec, J.; Nikolaidis,
A.; Nishijima, K.; Nolan, S. J.; Nowak, N.; O'Brien, P. T.; Ochoa,
I.; Ohira, Y.; Ohishi, M.; Ohka, H.; Okumura, A.; Olivetto, C.; Ong,
R. A.; Orito, R.; Orr, M.; Osborne, J. P.; Ostrowski, M.; Otero, L.;
Otte, A. N.; Ovcharov, E.; Oya, I.; Oziȩbło, A.; Paiano, S.; Pallota,
J.; Panazol, J. L.; Paneque, D.; Panter, M.; Paoletti, R.; Papyan,
G.; Paredes, J. M.; Pareschi, G.; Parsons, R. D.; Paz Arribas, M.;
Pedaletti, G.; Pepato, A.; Persic, M.; Petrucci, P. O.; Peyaud,
B.; Piechocki, W.; Pita, S.; Pivato, G.; Płatos, Ł.; Platzer,
R.; Pogosyan, L.; Pohl, M.; Pojmański, G.; Ponz, J. D.; Potter,
W.; Prandini, E.; Preece, R.; Prokoph, H.; Pühlhofer, G.; Punch,
M.; Quel, E.; Quirrenbach, A.; Rajda, P.; Rando, R.; Rataj, M.;
Raue, M.; Reimann, C.; Reimann, O.; Reimer, A.; Reimer, O.; Renaud,
M.; Renner, S.; Reymond, J. -M.; Rhode, W.; Ribó, M.; Ribordy,
M.; Rico, J.; Rieger, F.; Ringegni, P.; Ripken, J.; Ristori, P.;
Rivoire, S.; Rob, L.; Rodriguez, S.; Roeser, U.; Romano, P.; Romero,
G. E.; Rosier-Lees, S.; Rovero, A. C.; Roy, F.; Royer, S.; Rudak, B.;
Rulten, C. B.; Ruppel, J.; Russo, F.; Ryde, F.; Sacco, B.; Saggion, A.;
Sahakian, V.; Saito, K.; Saito, T.; Sakaki, N.; Salazar, E.; Salini,
A.; Sánchez, F.; Sánchez Conde, M. Á.; Santangelo, A.; Santos,
E. M.; Sanuy, A.; Sapozhnikov, L.; Sarkar, S.; Scalzotto, V.; Scapin,
V.; Scarcioffolo, M.; Schanz, T.; Schlenstedt, S.; Schlickeiser, R.;
Schmidt, T.; Schmoll, J.; Schroedter, M.; Schultz, C.; Schultze, J.;
Schulz, A.; Schwanke, U.; Schwarzburg, S.; Schweizer, T.; Seiradakis,
J.; Selmane, S.; Seweryn, K.; Shayduk, M.; Shellard, R. C.; Shibata,
T.; Sikora, M.; Silk, J.; Sillanpää, A.; Sitarek, J.; Skole, C.;
Smith, N.; Sobczyńska, D.; Sofo Haro, M.; Sol, H.; Spanier, F.; Spiga,
D.; Spyrou, S.; Stamatescu, V.; Stamerra, A.; Starling, R. L. C.;
Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steiner, S.; Stergioulas,
N.; Sternberger, R.; Stinzing, F.; Stodulski, M.; Straumann, U.;
Suárez, A.; Suchenek, M.; Sugawara, R.; Sulanke, K. H.; Sun, S.;
Supanitsky, A. D.; Sutcliffe, P.; Szanecki, M.; Szepieniec, T.;
Szostek, A.; Szymkowiak, A.; Tagliaferri, G.; Tajima, H.; Takahashi,
H.; Takahashi, K.; Takalo, L.; Takami, H.; Talbot, R. G.; Tam, P. H.;
Tanaka, M.; Tanimori, T.; Tavani, M.; Tavernet, J. -P.; Tchernin, C.;
Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.; Tenzer, C.; Terada,
Y.; Terrier, R.; Teshima, M.; Testa, V.; Tibaldo, L.; Tibolla, O.;
Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.; Toma,
K.; Torres, D. F.; Tosti, G.; Totani, T.; Toussenel, F.; Vallania,
P.; Vallejo, G.; van der Walt, J.; van Eldik, C.; Vandenbroucke, J.;
Vankov, H.; Vasileiadis, G.; Vassiliev, V. V.; Vegas, I.; Venter, L.;
Vercellone, S.; Veyssiere, C.; Vialle, J. P.; Videla, M.; Vincent,
P.; Vink, J.; Vlahakis, N.; Vlahos, L.; Vogler, P.; Vollhardt, A.;
Volpe, F.; von Gunten, H. P.; Vorobiov, S.; Wagner, S.; Wagner,
R. M.; Wagner, B.; Wakely, S. P.; Walter, P.; Walter, R.; Warwick,
R.; Wawer, P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weinstein, A.;
Weitzel, Q.; Welsing, R.; Wetteskind, H.; White, R.; Wierzcholska,
A.; Wilkinson, M. I.; Williams, D. A.; Winde, M.; Wischnewski, R.;
Wiśniewski, Ł.; Wolczko, A.; Wood, M.; Xiong, Q.; Yamamoto, T.;
Yamaoka, K.; Yamazaki, R.; Yanagita, S.; Yoffo, B.; Yonetani, M.;
Yoshida, A.; Yoshida, T.; Yoshikoshi, T.; Zabalza, V.; Zagdański,
A.; Zajczyk, A.; Zdziarski, A.; Zech, A.; Ziȩtara, K.; Ziółkowski,
P.; Zitelli, V.; Zychowski, P.
2011ExA....32..193A Altcode: 2011ExA...tmp..121A; 2010arXiv1008.3703C
Ground-based gamma-ray astronomy has had a major breakthrough with
the impressive results obtained using systems of imaging atmospheric
Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge
potential in astrophysics, particle physics and cosmology. CTA is
an international initiative to build the next generation instrument,
with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV
range and the extension to energies well below 100 GeV and above 100
TeV. CTA will consist of two arrays (one in the north, one in the south)
for full sky coverage and will be operated as open observatory. The
design of CTA is based on currently available technology. This document
reports on the status and presents the major design concepts of CTA.
---------------------------------------------------------
Title: Fermi Detection of a Luminous γ-Ray Pulsar in a Globular
Cluster
Authors: Freire, P. C. C.; Abdo, A. A.; Ajello, M.; Allafort, A.;
Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini,
R.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.;
Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G.;
Cameron, R.; Camilo, F.; Caraveo, P. A.; Cecchi, C.; Çelik, Ö.;
Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Ciprini, S.;
Claus, R.; Cognard, I.; Cohen-Tanugi, J.; Cominsky, L. R.; de Palma,
F.; Dermer, C. D.; do Couto e Silva, E.; Dormody, M.; Drell, P. S.;
Dubois, R.; Dumora, D.; Espinoza, C. M.; Favuzzi, C.; Fegan, S. J.;
Ferrara, E. C.; Focke, W. B.; Fortin, P.; Fukazawa, Y.; Fusco, P.;
Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto,
N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier,
I. A.; Grondin, M. -H.; Grove, J. E.; Guillemot, L.; Guiriec, S.;
Hadasch, D.; Harding, A. K.; Jóhannesson, G.; Johnson, A. S.; Johnson,
T. J.; Johnston, S.; Katagiri, H.; Kataoka, J.; Keith, M.; Kerr, M.;
Knödlseder, J.; Kramer, M.; Kuss, M.; Lande, J.; Latronico, L.; Lee,
S. -H.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lovellette, M. N.;
Lubrano, P.; Lyne, A. G.; Manchester, R. N.; Marelli, M.; Mazziotta,
M. N.; McEnery, J. E.; Michelson, P. F.; Mizuno, T.; Moiseev, A. A.;
Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia,
S.; Nakamori, T.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohsugi,
T.; Okumura, A.; Omodei, N.; Orlando, E.; Ozaki, M.; Paneque, D.;
Parent, D.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Porter,
T. A.; Rainò, S.; Ransom, S. M.; Ray, P. S.; Reimer, A.; Reimer,
O.; Reposeur, T.; Ritz, S.; Romani, R. W.; Roth, M.; Sadrozinski,
H. F. -W.; Saz Parkinson, P. M. Sgrò, C.; Shannon, R.; Siskind,
E. J. Smith, D. A.; Smith, P. D.; Spinelli, P.; Stappers, B. W.;
Suson, D. J.; Takahashi, H.; Tanaka, T.; Tauris, T. M.; Thayer,
J. B.; Theureau, G.; Thompson, D. J.; Thorsett, S. E.; Tibaldo, L.;
Torres, D. F.; Tosti, G.; Troja, E.; Vandenbroucke, J.; Van Etten,
A.; Vasileiou, V.; Venter, C.; Vianello, G.; Vilchez, N.; Vitale, V.;
Waite, A. P.; Wang, P.; Wood, K. S.; Yang, Z.; Ziegler, M.; Zimmer, S.
2011Sci...334.1107F Altcode: 2011Sci...334.1107.; 2011arXiv1111.3754T
We report on the Fermi Large Area Telescope’s detection of γ-ray
(>100 mega-electron volts) pulsations from pulsar J1823-3021A in
the globular cluster NGC 6624 with high significance (∼7 σ). Its
γ-ray luminosity, L<SUB>γ</SUB> = (8.4 ± 1.6) × 10<SUP>34</SUP>
ergs per second, is the highest observed for any millisecond pulsar
(MSP) to date, and it accounts for most of the cluster emission. The
nondetection of the cluster in the off-pulse phase implies that it
contains <32 γ-ray MSPs, not ∼100 as previously estimated. The
γ-ray luminosity indicates that the unusually large rate of change
of its period is caused by its intrinsic spin-down. This implies that
J1823-3021A has the largest magnetic field and is the youngest MSP
ever detected and that such anomalous objects might be forming at
rates comparable to those of the more normal MSPs.
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Thompson,
David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier,
Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham,
Falcone
2011atnf.prop.4337C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Vortices in simulations of solar surface convection
Authors: Moll, R.; Cameron, R. H.; Schüssler, M.
2011A&A...533A.126M Altcode: 2011arXiv1108.0800M
We report on the occurrence of small-scale vortices in simulations of
the convective solar surface. Using an eigenanalysis of the velocity
gradient tensor, we find the subset of high-vorticity regions in which
the plasma is swirling. The swirling regions form an unsteady, tangled
network of filaments in the turbulent downflow lanes. Near-surface
vertical vortices are underdense and cause a local depression of the
optical surface. They are potentially observable as bright points in
the dark intergranular lanes. Vortex features typically exist for a
few minutes, during which they are moved and twisted by the motion
of the ambient plasma. The bigger vortices found in the simulations
are possibly, but not necessarily, related to observations of
granular-scale spiraling pathlines in "cork animations" or feature
tracking. <P />Three movies are available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Decay of a simulated mixed-polarity magnetic field in the
solar surface layers
Authors: Cameron, R.; Vögler, A.; Schüssler, M.
2011A&A...533A..86C Altcode: 2011arXiv1108.1155C
Magnetic flux is continuously being removed and replenished on the
solar surface. To understand the removal process we carried out 3D
radiative MHD simulations of the evolution of patches of photospheric
magnetic field with equal amounts of positive and negative flux. We
find that the flux is removed at a rate corresponding to an effective
turbulent diffusivity, η<SUB>eff</SUB>, of 100-340 km<SUP>2</SUP>
s<SUP>-1</SUP>, depending on the boundary conditions. For average
unsigned flux densities above about 70 Gauss, the percentage of surface
magnetic energy coming from different field strengths is almost
invariant. The overall process is then one where magnetic elements
are advected by the horizontal granular motions and occasionally come
into contact with opposite-polarity elements. These reconnect above
the photosphere on a comparatively short time scale after which the
U loops produced rapidly escape through the upper surface while the
downward retraction of inverse-U loops is significantly slower, because
of the higher inertia and lower plasma beta in the deeper layers.
---------------------------------------------------------
Title: Is there a non-monotonic relation between photospheric
brightness and magnetic field strength in solar plage regions?
Authors: Röhrbein, D.; Cameron, R.; Schüssler, M.
2011A&A...532A.140R Altcode:
Context. The relationship between the brightness and field strength
of small-scale solar magnetic features is an important factor for
solar irradiance variations and a constraint for simulations of solar
magneto-convection. <BR /> Aims: We wish to clarify the origin of
the apparent discrepancy between observational results and radiative
MHD simulations. <BR /> Methods: Maps of (bolometric) brightness and
magnetic field strength from the simulation of a plage region were
convolved and rebinned to mimic observations obtained with telescopes
with finite aperture. <BR /> Results: Image smearing changes the
monotonic relation between brightness and field strength obtained at
the original resolution of the simulation into a profile with a maximum
at intermediate field strength, which is in qualitative agreement with
the observations. This result is mainly due to the smearing of strong
magnetic fields at the bright edges of magnetic structures into the
weakly magnetized adjacent areas. <BR /> Conclusions: Observational
and simulation results are qualitatively consistent with each other if
the finite spatial resolution of the observations is taken into account.
---------------------------------------------------------
Title: Constructing and Characterising Solar Structure Models for
Computational Helioseismology
Authors: Schunker, H.; Cameron, R. H.; Gizon, L.; Moradi, H.
2011SoPh..271....1S Altcode: 2011SoPh..tmp..124S; 2011arXiv1105.0219S; 2011SoPh..tmp..179S;
2011SoPh..tmp..248S
In local helioseismology, numerical simulations of wave propagation
are useful to model the interaction of solar waves with perturbations
to a background solar model. However, the solution to the linearised
equations of motion include convective modes that can swamp the
helioseismic waves that we are interested in. In this article,
we construct background solar models that are stable against
convection, by modifying the vertical pressure gradient of Model S
(Christensen-Dalsgaard et al., 1996, Science272, 1286) relinquishing
hydrostatic equilibrium. However, the stabilisation affects the
eigenmodes that we wish to remain as close to Model S as possible. In
a bid to recover the Model S eigenmodes, we choose to make additional
corrections to the sound speed of Model S before stabilisation. No
stabilised model can be perfectly solar-like, so we present three
stabilised models with slightly different eigenmodes. The models are
appropriate to study the f and p<SUB>1</SUB> to p<SUB>4</SUB> modes with
spherical harmonic degrees in the range from 400 to 900. Background
model CSM has a modified pressure gradient for stabilisation and has
eigenfrequencies within 2% of Model S. Model CSM_A has an additional 10%
increase in sound speed in the top 1 Mm resulting in eigenfrequencies
within 2% of Model S and eigenfunctions that are, in comparison with
CSM, closest to those of Model S. Model CSM_B has a 3% decrease in
sound speed in the top 5 Mm resulting in eigenfrequencies within 1%
of Model S and eigenfunctions that are only marginally adversely
affected. These models are useful to study the interaction of
solar waves with embedded three-dimensional heterogeneities, such
as convective flows and model sunspots. We have also calculated the
response of the stabilised models to excitation by random near-surface
sources, using simulations of the propagation of linear waves. We find
that the simulated power spectra of wave motion are in good agreement
with an observed SOHO/MDI power spectrum. Overall, our convectively
stabilised background models provide a good basis for quantitative
numerical local helioseismology. The models are available for download
from http://www.mps.mpg.de/projects/seismo/NA4/.
---------------------------------------------------------
Title: EUV jets, type III radio bursts and sunspot waves investigated
using SDO/AIA observations
Authors: Innes, D. E.; Cameron, R. H.; Solanki, S. K.
2011A&A...531L..13I Altcode: 2011arXiv1106.3417I
Context. Quasi-periodic plasma jets are often ejected from the Sun
into interplanetary space. The commonly observed signatures are
day-long sequences of type III radio bursts. <BR /> Aims: The aim is
to identify the source of quasi-periodic jets observed on 3 Aug. 2010
in the Sun's corona and in interplanetary space. <BR /> Methods:
Images from the Solar Dynamics Observatory (SDO) at 211 Å are used
to identify the solar source of the type III radio bursts seen in
WIND/WAVES dynamic spectra. We analyse a 2.5 h period during which six
strong bursts are seen. The radio signals are cross-correlated with
emission from extreme ultraviolet (EUV) jets coming from the western
side of a sunspot in AR 11092. The jets are further cross-correlated
with brightening at a small site on the edge of the sunspot umbra,
and the brightening with 3-min sunspot intensity oscillations. <BR />
Results: The radio bursts correlate very well with the EUV jets. The
EUV jet emission also correlates well with brightening at what looks
like their footpoint at the edge of the umbra. The jet emission lags
the radio signals and the footpoint brightening by about 30 s because
the EUV jets take time to develop. For 10-15 min after strong EUV jets
are ejected, the footpoint brightens at roughly 3 min intervals. In
both the EUV images and the extracted light curves, it looks as though
the brightening is related to the 3-min sunspot oscillations, although
the correlation coefficient is rather low. The only open field near
the jets is rooted in the sunspot. <BR /> Conclusions: Active region
EUV/X-ray jets and interplanetary electron streams originate on the
edge of the sunspot umbra. They form along a current sheet between
the sunspot open field and closed field connecting to underlying
satellite flux. Sunspot running penumbral waves cause roughly 3-min
jet footpoint brightening. The relationship between the waves and
jets is less clear. <P />Movie is available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Universality of the Small-scale Dynamo Mechanism
Authors: Moll, R.; Pietarila Graham, J.; Pratt, J.; Cameron, R. H.;
Müller, W. -C.; Schüssler, M.
2011ApJ...736...36M Altcode: 2011arXiv1105.0546M
We quantify possible differences between turbulent dynamo action in
the Sun and the dynamo action studied in idealized simulations. For
this purpose, we compare Fourier-space shell-to-shell energy transfer
rates of three incrementally more complex dynamo simulations: an
incompressible, periodic simulation driven by random flow, a simulation
of Boussinesq convection, and a simulation of fully compressible
convection that includes physics relevant to the near-surface layers
of the Sun. For each of the simulations studied, we find that the
dynamo mechanism is universal in the kinematic regime because energy
is transferred from the turbulent flow to the magnetic field from
wavenumbers in the inertial range of the energy spectrum. The addition
of physical effects relevant to the solar near-surface layers, including
stratification, compressibility, partial ionization, and radiative
energy transport, does not appear to affect the nature of the dynamo
mechanism. The role of inertial-range shear stresses in magnetic
field amplification is independent from outer-scale circumstances,
including forcing and stratification. Although the shell-to-shell energy
transfer functions have similar properties to those seen in mean-flow
driven dynamos in each simulation studied, the saturated states of
these simulations are not universal because the flow at the driving
wavenumbers is a significant source of energy for the magnetic field.
---------------------------------------------------------
Title: Universality of the Small-Scale Dynamo Mechanism
Authors: Pietarila Graham, Jonathan; Moll, R.; Pratt, J.; Cameron,
R.; Mueller, W.; Schuessler, M.
2011SPD....42.1621P Altcode: 2011BAAS..43S.1621P
We quantify possible differences between turbulent dynamo action in
the Sun and the dynamo action studied in idealized simulation. For this
purpose we compare Fourier-space shell-to-shell energy transfer rates of
three incrementally more complex dynamo simulations: an incompressible,
periodic simulation driven by random flow, a simulation of Boussinesq
convection, and a simulation of fully compressible convection that
includes physics relevant to the near-surface layers of the Sun. For
each of the simulations studied, we find that energy is transferred
from the turbulent flow to the magnetic field from length-scales in the
inertial range of the energy spectrum. The addition of physical effects
relevant to the solar near-surface layers, including stratification,
compressibility, partial ionization, and radiative energy transport,
does not appear to affect the nature of the dynamo mechanism. The role
of inertial-range shear stresses in magnetic field amplification is
independent from outer-scale circumstances, including forcing and
stratification. Although shell-to-shell energy transfer functions
have similar properties in each simulation studied, the saturated
states of these simulations are not universal; the flow at the driving
scales is a significant source of energy for the magnetic field. The
mechanism of energy-transfer in kinematic small-scale dynamo simulations
exhibits universal properties. <P />This work has been supported by
the Max-Planck Society in the framework of the Interinstitutional
Research Initiative Turbulent transport and ion heating, reconnection
and electron acceleration in solar and fusion plasmas</u> of the
MPI for Solar System Research, Katlenburg-Lindau, and the Institute
for Plasma Physics, Garching (project MIF-IF-A-AERO8047).
---------------------------------------------------------
Title: SLiM: A Code for the Simulation of Wave Propagation through
an Inhomogeneous, Magnetised Solar Atmosphere
Authors: Cameron, R.; Gizon, L.; Daiffallah, K.
2011ascl.soft05004C Altcode:
The semi-spectral linear MHD (SLiM) code follows the interaction
of linear waves through an inhomogeneous three-dimensional solar
atmosphere. The background model allows almost arbitrary perturbations
of density, temperature, sound speed as well as magnetic and velocity
fields. The code is useful in understanding the helioseismic signatures
of various solar features, including sunspots.
---------------------------------------------------------
Title: The solar magnetic field since 1700. II. Physical
reconstruction of total, polar and open flux
Authors: Jiang, J.; Cameron, R. H.; Schmitt, D.; Schüssler, M.
2011A&A...528A..83J Altcode: 2011arXiv1102.1270J
We have used semi-synthetic records of emerging sunspot groups based
on sunspot number data as input for a surface flux transport model to
reconstruct the evolution of the large-scale solar magnetic field and
the open heliospheric flux from the year 1700 onward. The statistical
properties of the semi-synthetic sunspot group records reflect
those of the observed Royal Greenwich Observatory photoheliographic
results. These include correlations between the sunspot numbers
and sunspot group latitudes, longitudes, areas and tilt angles. The
reconstruction results for the total surface flux, the polar field,
and the heliospheric open flux (determined by a current sheet source
surface extrapolation) agree well with the available observational or
empirically derived data and reconstructions. We confirm a significant
positive correlation between the polar field during activity minimum
periods and the strength of the subsequent sunspot cycle, which has
implications for flux transport dynamo models for the solar cycle. Just
prior to the Dalton minimum, at the end of the 18th century, a long
cycle was followed by a weak cycle. We find that introducing a possibly
"lost" cycle between 1793 and 1800 leads to a shift of the minimum of
the open flux by 15 years which is inconsistent with the cosmogenic
isotope record.
---------------------------------------------------------
Title: The solar magnetic field since 1700. I. Characteristics of
sunspot group emergence and reconstruction of the butterfly diagram
Authors: Jiang, J.; Cameron, R. H.; Schmitt, D.; Schüssler, M.
2011A&A...528A..82J Altcode: 2011arXiv1102.1266J
We use the historic record of sunspot groups compiled by the Royal
Greenwich Observatory together with the sunspot number to derive
the dependence of the statistical properties of sunspot emergence on
the cycle phase and strength. In particular we discuss the latitude,
longitude, area and tilt angle of sunspot groups as functions of the
cycle strength and of time during the solar cycle. Using these empirical
characteristics the time-latitude diagram of sunspot group emergence
(butterfly diagram) is reconstructed from 1700 onward on the basis of
the Wolf and group sunspot numbers. This reconstruction will be useful
in studies of the long-term evolution of the Sun's magnetic field.
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Thompson,
David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier,
Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham,
Falcone
2011atnf.prop.3824C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Transport of Magnetic Flux from the Canopy to the Internetwork
Authors: Pietarila, A.; Cameron, R. H.; Danilovic, S.; Solanki, S. K.
2011ApJ...729..136P Altcode: 2011arXiv1102.1397P
Recent observations have revealed that 8% of linear polarization
patches in the internetwork (INW) quiet Sun are fully embedded in
downflows. These are not easily explained with the typical scenarios for
the source of INW fields which rely on flux emergence from below. Using
radiative MHD simulations, we explore a scenario where magnetic flux
is transported from the magnetic canopy overlying the INW into the
photosphere by means of downward plumes associated with convective
overshoot. We find that if a canopy-like magnetic field is present in
the simulation, the transport of flux from the canopy is an important
process for seeding the photospheric layers of the INW with magnetic
field. We propose that this mechanism is relevant for the Sun as well,
and it could naturally explain the observed INW linear polarization
patches entirely embedded in downflows.
---------------------------------------------------------
Title: 3D Numerical Simulations of f-Mode Propagation Through Magnetic
Flux Tubes
Authors: Daiffallah, K.; Abdelatif, T.; Bendib, A.; Cameron, R.;
Gizon, L.
2011SoPh..268..309D Altcode: 2010SoPh..tmp..204D; 2010SoPh..tmp..228D; 2010arXiv1008.2531D
Three-dimensional numerical simulations have been used to study the
scattering of a surface-gravity wave packet by vertical magnetic-flux
tubes, with radii from 200 km to 3 Mm, embedded in stratified polytropic
atmosphere. The scattered wave has been found to consist primarily of
m=0 (axisymmetric) and m=1 modes. The ratio of the amplitude of these
two modes was found to be strongly dependent on the radius of the flux
tube. The kink mode is the dominant mode excited in tubes with a small
radius, while the sausage mode is dominant for large tubes. Simulations
of this type provide a simple, efficient, and robust way to start to
understand the seismic signature of flux tubes, which have recently
begun to be observed.
---------------------------------------------------------
Title: Constructing Semi-Empirical Sunspot Models for Helioseismology
Authors: Cameron, R. H.; Gizon, L.; Schunker, H.; Pietarila, A.
2011SoPh..268..293C Altcode: 2010arXiv1003.0528C; 2010SoPh..tmp..167C
One goal of helioseismology is to determine the subsurface structure
of sunspots. In order to do so, it is important to understand
first the near-surface effects of sunspots on solar waves, which are
dominant. Here we construct simplified, cylindrically-symmetric sunspot
models that are designed to capture the magnetic and thermodynamics
effects coming from about 500 km below the quiet-Sun τ<SUB>5000</SUB>=1
level to the lower chromosphere. We use a combination of existing
semi-empirical models of sunspot thermodynamic structure (density,
temperature, pressure): the umbral model of Maltby et al. (1986,
Astrophys. J. 306, 284) and the penumbral model of Ding and Fang (1989,
Astron. Astrophys. 225, 204). The OPAL equation-of-state tables are used
to derive the sound-speed profile. We smoothly merge the near-surface
properties to the quiet-Sun values about 1 Mm below the surface. The
umbral and penumbral radii are free parameters. The magnetic field is
added to the thermodynamic structure, without requiring magnetostatic
equilibrium. The vertical component of the magnetic field is assumed
to have a Gaussian horizontal profile, with a maximum surface field
strength fixed by surface observations. The full magnetic-field vector
is solenoidal and determined by the on-axis vertical field, which,
at the surface, is chosen such that the field inclination is 45° at
the umbral - penumbral boundary. We construct a particular sunspot
model based on SOHO/MDI observations of the sunspot in active region
NOAA 9787. The helioseismic signature of the model sunspot is studied
using numerical simulations of the propagation of f, p<SUB>1</SUB>,
and p<SUB>2</SUB> wave packets. These simulations are compared
against cross-covariances of the observed wave field. We find that
the sunspot model gives a helioseismic signature that is similar to
the observations.
---------------------------------------------------------
Title: Quenching of the alpha effect in the Sun -- what observations
are telling us
Authors: Cameron, R. H.
2011ASInC...2..143C Altcode: 2011arXiv1108.1308C
The Babcock-Leighton type of dynamo has received recent support in
terms of the discovery in the observational records of systematic
cycle-to-cycle variations in the tilt angle of sunspot groups. It has
been proposed that these variations might be the consequence of the
observed inflow into the active region belt. Furthermore simulations
have shown that such inflows restrict the creation of net poloidal
flux, in effect acting to quench the alpha effect associated with the
Coriolis force acting on rising flux tubes. In this paper we expand
on these ideas.
---------------------------------------------------------
Title: Small-scale dynamo in solar surface simulations
Authors: Graham, J. P.; Moll, R.; Cameron, R.; Schüssler, M.
2010AGUFMNG51C..01G Altcode:
A magneto-convection simulation incorporating essential physical
processes governing solar surface convection exhibits turbulent
small-scale dynamo action. By presenting a derivation of the
energy balance equation and transfer functions for compressible
magnetohydrodynamics (MHD), we quantify the source of magnetic energy
on a scale-by-scale basis. We rule out the two alternative mechanisms
for the generation of small-scale magnetic field in the simulations:
tangling of magnetic field lines associated with the turbulent cascade
and Alfvenization of small-scale velocity fluctuations ("turbulent
induction"). Instead, we find the dominant source of small-scale
magnetic energy is stretching by inertial-range fluid motions of
small-scale magnetic field lines against the magnetic tension force to
produce (against Ohmic dissipation) more small-scale magnetic field. The
scales involved become smaller with increasing Reynolds number, which
identifies the dynamo as a small-scale turbulent dynamo. Comparisons
are made between the details of the dynamo mechanism in compressible
magneto-convection, Boussinesq convection, and randomly-forced
incompressible turbulence. Net energy transfers (kinematic phase):
work against magnetic tension (stretching) is 95% of magnetic energy
generated; work against magnetic pressure (compression) is 5%. The
latter is involved in the breaking down larger-scale field (25%) into
smaller-scale field (30%) as part of the cascade. The dominant producer
of magnetic energy is the stretching of magnetic field lines against the
magnetic tension force (turbulent dynamo action). <P />Fluid motions
at a scale of ~140km create magnetic energy predominately at a scale
of ~65km. As the three wave-vectors must form a triad, the scale of
the magnetic field being stretched must is 80+/-40km. All 3 scales
are in the inertial range: this is turbulent small-scale dynamo.
---------------------------------------------------------
Title: Modeling the Subsurface Structure of Sunspots
Authors: Moradi, H.; Baldner, C.; Birch, A. C.; Braun, D. C.; Cameron,
R. H.; Duvall, T. L.; Gizon, L.; Haber, D.; Hanasoge, S. M.; Hindman,
B. W.; Jackiewicz, J.; Khomenko, E.; Komm, R.; Rajaguru, P.; Rempel,
M.; Roth, M.; Schlichenmaier, R.; Schunker, H.; Spruit, H. C.;
Strassmeier, K. G.; Thompson, M. J.; Zharkov, S.
2010SoPh..267....1M Altcode: 2009arXiv0912.4982M; 2010SoPh..tmp..171M
While sunspots are easily observed at the solar surface, determining
their subsurface structure is not trivial. There are two main
hypotheses for the subsurface structure of sunspots: the monolithic
model and the cluster model. Local helioseismology is the only means
by which we can investigate subphotospheric structure. However, as
current linear inversion techniques do not yet allow helioseismology to
probe the internal structure with sufficient confidence to distinguish
between the monolith and cluster models, the development of physically
realistic sunspot models are a priority for helioseismologists. This
is because they are not only important indicators of the variety of
physical effects that may influence helioseismic inferences in active
regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In
this article, we provide a critical review of the existing sunspot
models and an overview of numerical methods employed to model wave
propagation through model sunspots. We then carry out a helioseismic
analysis of the sunspot in Active Region 9787 and address the serious
inconsistencies uncovered by Gizon et al. (2009a, 2009b). We find that
this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model)
and that travel-time measurements are consistent with a horizontal
outflow in the surrounding moat.
---------------------------------------------------------
Title: Erratum: Erratum to: Helioseismology of Sunspots: A Case
Study of NOAA Region 9787
Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch,
A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.;
Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.;
Zharkov, S.
2010SSRv..156..257G Altcode: 2010SSRv..tmp...99G
No abstract at ADS
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Thompson,
David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier,
Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham,
Falcone
2010atnf.prop.3546C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Mesogranular structure in a hydrodynamical simulation
Authors: Matloch, Ł.; Cameron, R.; Shelyag, S.; Schmitt, D.;
Schüssler, M.
2010A&A...519A..52M Altcode: 2010arXiv1007.0387M
<BR /> Aims: We analyse mesogranular flow patterns in
a three-dimensional hydrodynamical simulation of solar surface
convection in order to determine its characteristics. <BR /> Methods:
We calculate divergence maps from horizontal velocities obtained with
the local correlation tracking (LCT) method. Mesogranules are identified
as patches of positive velocity divergence. We track the mesogranules
to obtain their size and lifetime distributions. We vary the analysis
parameters to verify if the pattern has characteristic scales. <BR />
Results: The characteristics of the resulting flow patterns depend on
the averaging time and length used in the analysis. <BR /> Conclusions:
We conclude that the mesogranular patterns do not exhibit intrinsic
length and time scales.
---------------------------------------------------------
Title: Changes of the Solar Meridional Velocity Profile During Cycle
23 Explained by Flows Toward the Activity Belts
Authors: Cameron, R. H.; Schüssler, M.
2010ApJ...720.1030C Altcode: 2010arXiv1007.2548C
The solar meridional flow is an important ingredient in Babcock-Leighton
type models of the solar dynamo. Global variations of this flow
have been suggested to explain the variations in the amplitudes and
lengths of the activity cycles. Recently, cycle-related variations in
the amplitude of the P <SUP>1</SUP> <SUB>2</SUB> term in the Legendre
decomposition of the observed meridional flow have been reported. The
result is often interpreted in terms of an overall variation in the
flow amplitude during the activity cycle. Using a semi-empirical model
based upon the observed distribution of magnetic flux on the solar
surface, we show that the reported variations of the P <SUP>1</SUP>
<SUB>2</SUB> term can be explained by the observed localized inflows
into the active region belts. No variation of the overall meridional
flow amplitude is required.
---------------------------------------------------------
Title: Surface Flux Transport Modeling for Solar Cycles 15-21:
Effects of Cycle-Dependent Tilt Angles of Sunspot Groups
Authors: Cameron, R. H.; Jiang, J.; Schmitt, D.; Schüssler, M.
2010ApJ...719..264C Altcode: 2010arXiv1006.3061C
We model the surface magnetic field and open flux of the Sun from
1913 to 1986 using a surface flux transport model, which includes the
observed cycle-to-cycle variation of sunspot group tilts. The model
reproduces the empirically derived time evolution of the solar open
magnetic flux and the reversal times of the polar fields. We find
that both the polar field and the axial dipole moment resulting from
this model around cycle minimum correlate with the strength of the
following cycle.
---------------------------------------------------------
Title: Saturation and time dependence of geodynamo models
Authors: Schrinner, M.; Schmitt, D.; Cameron, R.; Hoyng, P.
2010GeoJI.182..675S Altcode: 2009arXiv0909.2181S
In this study we address the question under which conditions a
saturated velocity field stemming from geodynamo simulations leads
to an exponential growth of the magnetic field in a corresponding
kinematic calculation. We perform global self-consistent geodynamo
simulations and calculate the evolution of a kinematically advanced
tracer field. The self-consistent velocity field enters the induction
equation in each time step, but the tracer field does not contribute to
the Lorentz force. This experiment has been performed by Cattaneo and
Tobias and is closely related to the test field method by Schrinner
et al. We find two dynamo regimes in which the tracer field either
grows exponentially or approaches a state aligned with the actual
self-consistent magnetic field after an initial transition period. Both
regimes can be distinguished by the Rossby number and coincide with
the dipolar and multipolar dynamo regimes identified by Christensen and
Aubert. Dipolar dynamos with low Rossby number are kinematically stable
whereas the tracer field grows exponentially in the multipolar dynamo
regime. This difference in the saturation process for dynamos in both
regimes comes along with differences in their time variability. Within
our sample of 20 models, solely kinematically unstable dynamos show
dipole reversals and large excursions. The complicated time behaviour
of these dynamos presumably relates to the alternating growth of
several competing dynamo modes. On the other hand, dynamos in the low
Rossby number regime exhibit a rather simple time dependence and their
saturation merely results in a fluctuation of the fundamental dynamo
mode about its critical state.
---------------------------------------------------------
Title: Sunspot group tilt angles and the strength of the solar cycle
Authors: Dasi-Espuig, M.; Solanki, S. K.; Krivova, N. A.; Cameron,
R.; Peñuela, T.
2010A&A...518A...7D Altcode: 2010arXiv1005.1774D
Context. It is well known that the tilt angles of active regions
increase with their latitude (Joy's law). It has never been checked
before, however, whether the average tilt angles change from one cycle
to the next. Flux transport models show the importance of tilt angles
for the reversal and build up of magnetic flux at the poles, which is in
turn correlated to the strength of the next cycle. <BR /> Aims: Here we
analyse time series of tilt angle measurements and look for a possible
relationship of the tilt angles with other solar cycle parameters,
in order to glean information on the solar dynamo and to estimate
their potential for predicting solar activity. <BR /> Methods: We
employed tilt angle data from Mount Wilson and Kodaikanal observatories
covering solar cycles 15 to 21. We analyse the latitudinal distribution
of the tilt angles (Joy's law), their variation from cycle to cycle,
and their relationship to other solar cycle parameters, such as the
strength (or total area covered by sunspots in a cycle), amplitude,
and length. <BR /> Results: The two main results of our analysis
follow. 1. We find an anti-correlation between the mean normalised
tilt angle of a given cycle and the strength (or amplitude) of that
cycle, with a correlation coefficient of r<SUB>c</SUB> = -0.95 (99.9%
confidence level) and r<SUB>c</SUB> = -0.93 (99.76% confidence level)
for Mount Wilson and Kodaikanal data, respectively. 2. The product
of the cycle's averaged tilt angle and the strength of the same cycle
displays a significant correlation with the strength of the next cycle
(r<SUB>c</SUB> = 0.65 at 89% confidence level and r<SUB>c</SUB> =
0.70 at 92% confidence level for Mount Wilson and Kodaikanal data,
respectively). An even better correlation is obtained between the
source term of the poloidal flux in Babcock-Leighton-type dynamos (which
contains the tilt angle) and the amplitude of the next cycle. Further we
confirm the linear relationship (Joy's law) between the tilt angle and
latitude with slopes of 0.26 and 0.28 for Mount Wilson and Kodaikanal
data, respectively. In addition, we obtain good positive correlations
between the normalised-area-weighted tilt angle and the length of the
following cycle, whereas the strength or the amplitude of the next cycle
does not appear to be correlated to the tilt angles of the current cycle
alone. <BR /> Conclusions: The results of this study indicate that,
in combination with the cycle strength, the active region tilt angles
play an important role in building up the polar fields at cycle minimum.
---------------------------------------------------------
Title: Expansion of magnetic flux concentrations: a comparison of
Hinode SOT data and models
Authors: Pietarila, A.; Cameron, R.; Solanki, S. K.
2010A&A...518A..50P Altcode: 2010arXiv1005.3405P
Context. The expansion of network magnetic fields with height is a
fundamental property of flux tube models. A rapid expansion is required
to form a magnetic canopy. <BR /> Aims: We characterize the observed
expansion properties of magnetic network elements and compare them
with the thin flux tube and sheet approximations, as well as with
magnetoconvection simulations. <BR /> Methods: We used data from
the Hinode SOT NFI NaD<SUB>1</SUB> channel and spectropolarimeter to
study the appearance of magnetic flux concentrations seen in circular
polarization as a function of position on the solar disk. We compared
the observations with synthetic observables from models based on the
thin flux tube approximation and magnetoconvection simulations with two
different upper boundary conditions for the magnetic field (potential
and vertical). <BR /> Results: The observed circular polarization signal
of magnetic flux concentrations changes from unipolar at disk center to
bipolar near the limb, which implies an expanding magnetic field. The
observed expansion agrees with expansion properties derived from the
thin flux sheet and tube approximations. Magnetoconvection simulations
with a potential field as the upper boundary condition for the magnetic
field also produce bipolar features near the limb while a simulation
with a vertical field boundary condition does not. <BR /> Conclusions:
The near-limb apparent bipolar magnetic features seen in high-resolution
Hinode observations can be interpreted using a simple flux sheet
or tube model. This lends further support to the idea that magnetic
features with vastly varying sizes have similar relative expansion
rates. The numerical simulations presented here are less useful in
interpreting the expansion since the diagnostics we are interested in
are strongly influenced by the choice of the upper boundary condition
for the magnetic field in the purely photospheric simulations.
---------------------------------------------------------
Title: The Effect of Activity-related Meridional Flow Modulation on
the Strength of the Solar Polar Magnetic Field
Authors: Jiang, J.; Işik, E.; Cameron, R. H.; Schmitt, D.;
Schüssler, M.
2010ApJ...717..597J Altcode: 2010arXiv1005.5317J
We studied the effect of the perturbation of the meridional flow in the
activity belts detected by local helioseismology on the development and
strength of the surface magnetic field at the polar caps. We carried
out simulations of synthetic solar cycles with a flux transport model,
which follows the cyclic evolution of the surface field determined
by flux emergence and advective transport by near-surface flows. In
each hemisphere, an axisymmetric band of latitudinal flows converging
toward the central latitude of the activity belt was superposed
onto the background poleward meridional flow. The overall effect of
the flow perturbation is to reduce the latitudinal separation of the
magnetic polarities of a bipolar magnetic region and thus diminish its
contribution to the polar field. As a result, the polar field maximum
reached around cycle activity minimum is weakened by the presence of
the meridional flow perturbation. For a flow perturbation consistent
with helioseismic observations, the polar field is reduced by about 18%
compared to the case without inflows. If the amplitude of the flow
perturbation depends on the cycle strength, its effect on the polar
field provides a nonlinearity that could contribute to limiting the
amplitude of a Babcock-Leighton type dynamo.
---------------------------------------------------------
Title: Developing Physics-Based Procedures for Local Helioseismic
Probing of Sunspots and Magnetic Regions
Authors: Birch, Aaron; Braun, D. C.; Crouch, A.; Rempel, M.; Fan,
Y.; Centeno, R.; Toomre, J.; Haber, D.; Hindman, B.; Featherstone,
N.; Duvall, T., Jr.; Jackiewicz, J.; Thompson, M.; Stein, R.; Gizon,
L.; Cameron, R.; Saidi, Y.; Hanasoge, S.; Burston, R.; Schunker, H.;
Moradi, H.
2010AAS...21630805B Altcode:
We have initiated a project to test and improve the local helioseismic
techniques of time-distance and ring-diagram analysis. Our goals are
to develop and implement physics-based methods that will (1) enable the
reliable determinations of subsurface flow, magnetic field, and thermal
structure in regions of strong magnetic fields and (2) be quantitatively
tested with realistic solar magnetoconvection simulations in the
presence of sunspot-like magnetic fields. We are proceeding through a
combination of improvements in local helioseismic measurements, forward
modeling of the helioseismic wavefield, kernel computations, inversions,
and validation through numerical simulations. As improvements over
existing techniques are made they will be applied to the SDO/HMI
observations. This work is funded through the the NASA Heliophysics
Science Division through the Solar Dynamics Observatory (SDO) Science
Center program.
---------------------------------------------------------
Title: The solar cycle and the current solar minimum
Authors: Cameron, R.; Jiang, J.; Schmitt, D.; Schuessler, M.
2010EGUGA..1215494C Altcode:
In this talk we discuss the evolution of the Sun's large-scale magnetic
field, on timescales relevant to the solar cycle. This evolution can
be modeled using the surface flux transport equations, and we will
outline the ingredients which go into the model. Special attention
will be paid to the term describing the emergence of new flux onto
the solar surface. The results of the model will be compared against
observations covering most of the twentieth century, and in particular
we will discuss what determines the surface field during solar minima.
---------------------------------------------------------
Title: Turbulent Small-Scale Dynamo Action in Solar Surface
Simulations
Authors: Pietarila Graham, Jonathan; Cameron, Robert; Schüssler,
Manfred
2010ApJ...714.1606P Altcode: 2010ApJ...714.1606G; 2010arXiv1002.2750P
We demonstrate that a magneto-convection simulation incorporating
essential physical processes governing solar surface convection exhibits
turbulent small-scale dynamo action. By presenting a derivation of
the energy balance equation and transfer functions for compressible
magnetohydrodynamics, we quantify the source of magnetic energy on a
scale-by-scale basis. We rule out the two alternative mechanisms for
the generation of the small-scale magnetic field in the simulations:
the tangling of magnetic field lines associated with the turbulent
cascade and Alfvénization of small-scale velocity fluctuations
("turbulent induction"). Instead, we find that the dominant source
of small-scale magnetic energy is stretching by inertial-range fluid
motions of small-scale magnetic field lines against the magnetic tension
force to produce (against Ohmic dissipation) more small-scale magnetic
field. The scales involved become smaller with increasing Reynolds
number, which identifies the dynamo as a small-scale turbulent dynamo.
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Burrows,
David; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Wieringa,
Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron,
Robert
2010atnf.prop.3161C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Convectively stabilised background solar models for local
helioseismology
Authors: Schunker, H.; Cameron, R.; Gizon, L.
2010arXiv1002.1969S Altcode:
In local helioseismology numerical simulations of wave propagation
are useful to model the interaction of solar waves with perturbations
to a background solar model. However, the solution to the equations
of motions include convective modes that can swamp the waves we are
interested in. For this reason, we choose to first stabilise the
background solar model against convection by altering the vertical
pressure gradient. Here we compare the eigenmodes of our convectively
stabilised model with a standard solar model (Model S) and find a
good agreement.
---------------------------------------------------------
Title: Modeling the Sun's Open Magnetic Flux and the Heliospheric
Current Sheet
Authors: Jiang, J.; Cameron, R.; Schmitt, D.; Schüssler, M.
2010ApJ...709..301J Altcode: 2009arXiv0912.0108J
By coupling a solar surface flux transport model with an extrapolation
of the heliospheric field, we simulate the evolution of the Sun's
open magnetic flux and the heliospheric current sheet (HCS) based
on observational data of sunspot groups since 1976. The results are
consistent with measurements of the interplanetary magnetic field near
Earth and with the tilt angle of the HCS as derived from extrapolation
of the observed solar surface field. This opens the possibility for
an improved reconstruction of the Sun's open flux and the HCS into
the past on the basis of empirical sunspot data.
---------------------------------------------------------
Title: Numerical Simulations of Quiet Sun Oscillations
Authors: Schunker, H.; Cameron, R.; Gizon, L.
2009ASPC..416...49S Altcode:
We develop a quiet Sun background model to be used for the numerical
simulation of solar oscillations and explore the properties of this
model using the three-dimensional Semi-spectral Linear MHD (SLiM)
code. We first suggest criteria for defining a convectively stable,
but solar-like, background model. A first step in the development
of such a solar-like model is presented and we demonstrate that it
meets the first of the criteria by comparing the power spectrum of
the simulation with SoHO/MDI observations.
---------------------------------------------------------
Title: Expansion of Magnetic Flux Concentrations with Height:
A Comparison of Hinode SOT Data and MHD Simulations
Authors: Pietarila, A.; Cameron, R.; Solanki, S.
2009ASPC..415...91P Altcode:
The Hinode SOT (Tsuneta et al. 2008) NFI Na I D<SUB>1</SUB> and SP Fe I
data sampled at different positions on the solar disk provide a unique
diagnostic for studying the expansion of magnetic flux concentrations
with height. We make a comparative study of SOT observations and
2-dimensional (2D) radiative MHD-simulations to see how well the
simulations capture the expansion properties. The expansion of flux
concentrations is clearly seen in the SOT Na I D<SUB>1</SUB> data,
where most of the magnetic features appear unipolar at disk center while
close to the limb bipolar appearance strongly dominates. This trend,
albeit not as strong, is seen in the SP data as well. Some aspects of
the observations are qualitatively reproduced by simulations with a
potential (as opposed to vertical) upper boundary condition for the
magnetic field.
---------------------------------------------------------
Title: Radiative MHD simulations of sunspot structure
Authors: Rempel, M.; Schuessler, M.; Cameron, R.; Knoelker, M.
2009AGUFMSH53B..07R Altcode:
For a long time radiative MHD simulations of entire sunspots from
first principles were out of reach due to insufficient computing
resources. Over the past 4 years simulations have evolved from
6x6x2 Mm size domains focusing on the details of umbral dots to
simulations covering a pair of opposite polarity sunspots in a
100x50x6 Mm domain. Numerical simulations point toward a common magneto
convective origin of umbral dots and filaments in the inner and outer
penumbra. Most recent simulations also capture the processes involved
in the formation of an extended outer penumbra with strong horizontal
outflows averaging around 5 km/s in the photosphere. In this talk I
will briefly review the progress made in this field over the past 4
years and discuss in detail the magneto convective origin of penumbral
fine structure as well as the Evershed flow.
---------------------------------------------------------
Title: Solar surface magnetoconvection simulations: A brief review
of solar dermatology
Authors: Cameron, Robert
2009ScChG..52.1665C Altcode:
Rapid improvement in the speed of computers has enabled realistic
simulations of magnetoconvective processes in the surface layers of
the Sun. The simulations now cover a wide range of features found in
observations. In many cases a direct comparison with the observations
is justified, and in all cases our understanding and interpretation of
the observations is being improved. Current and future opportunities
and difficulties will be discussed.
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Burrows,
David; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Wieringa,
Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron,
Robert
2009atnf.prop.2654C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Radiative MHD simulations of sunspot structure
Authors: Rempel, M.; Schüssler, M.; Cameron, R.; Knölker, M.
2009iac..talk..192R Altcode: 2009iac..talk..106R
No abstract at ADS
---------------------------------------------------------
Title: Modelling of solar mesogranulation
Authors: Matloch, L.; Cameron, R.; Schmitt, D.; Schüssler, M.
2009A&A...504.1041M Altcode:
We study whether mesogranulation flow patterns at the solar surface
can arise solely from the statistical properties of granules and
intergranular lanes. We have developed one- and two-dimensional models
with local interaction rules between the artificial “granules”
mimicking the actual physical processes on the solar surface. Defining
mesogranulation according to the age of intergranular (downflow) lanes
corresponding to the often applied “cork method”, as well as the
areas of divergence of the horizontal velocity (two-dimensional model),
we find that mesogranular patterns are present in our models. Our study
of the dependence of the properties of the mesogranular patterns on
the model parameter and interaction rules reveals that the patterns
do not possess intrinsic length and time scales. <P />Appendix is only
available in electronic from at http://www.aanda.org
---------------------------------------------------------
Title: Penumbral Structure and Outflows in Simulated Sunspots
Authors: Rempel, M.; Schüssler, M.; Cameron, R. H.; Knölker, M.
2009Sci...325..171R Altcode: 2009arXiv0907.2259R
Sunspots are concentrations of magnetic field on the visible solar
surface that strongly affect the convective energy transport in their
interior and surroundings. The filamentary outer regions (penumbrae)
of sunspots show systematic radial outward flows along channels of
nearly horizontal magnetic field. These flows were discovered 100
years ago and are present in all fully developed sunspots. By using
a comprehensive numerical simulation of a sunspot pair, we show
that penumbral structures with such outflows form when the average
magnetic field inclination to the vertical exceeds about 45 degrees. The
systematic outflows are a component of the convective flows that provide
the upward energy transport and result from anisotropy introduced by
the presence of the inclined magnetic field.
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Burrows,
David; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Wieringa,
Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron,
Robert
2009atnf.prop.2459C Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Radiative MHD Simulations of Sunspot Structure
Authors: Rempel, Matthias D.; Schuessler, M.; Cameron, R.; Knoelker, M.
2009SPD....40.0604R Altcode:
We summarize the recent progress made in magneto convection simulations
of sunspot structure. Over the past 4 years simulations have evolved
from local 6x6x2 Mm size domains focusing on the details of umbral
dots to simulations covering a pair of opposite polarity spots in
a 100x50x6 Mm domain. The simulations point out the common magneto
convective origin of umbral dots and filaments in the inner penumbra
and most recently also reveal the processes involved in the formation
of an extended outer penumbra with strong horizontal outflows averaging
around 5 km/s in the photosphere.
---------------------------------------------------------
Title: Helioseismology of Sunspots: A Case Study of NOAA Region 9787
Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch,
A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.;
Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.;
Zharkov, S.
2009SSRv..144..249G Altcode: 2008SSRv..tmp..188G; 2010arXiv1002.2369G
Various methods of helioseismology are used to study the subsurface
properties of the sunspot in NOAA Active Region 9787. This sunspot
was chosen because it is axisymmetric, shows little evolution during
20-28 January 2002, and was observed continuously by the MDI/SOHO
instrument. AR 9787 is visible on helioseismic maps of the farside
of the Sun from 15 January, i.e. days before it crossed the East
limb. Oscillations have reduced amplitudes in the sunspot at all
frequencies, whereas a region of enhanced acoustic power above 5.5 mHz
(above the quiet-Sun acoustic cutoff) is seen outside the sunspot and
the plage region. This enhanced acoustic power has been suggested to
be caused by the conversion of acoustic waves into magneto-acoustic
waves that are refracted back into the interior and re-emerge as
acoustic waves in the quiet Sun. Observations show that the sunspot
absorbs a significant fraction of the incoming p and f modes around 3
mHz. A numerical simulation of MHD wave propagation through a simple
model of AR 9787 confirmed that wave absorption is likely to be due
to the partial conversion of incoming waves into magneto-acoustic
waves that propagate down the sunspot. Wave travel times and mode
frequencies are affected by the sunspot. In most cases, wave packets
that propagate through the sunspot have reduced travel times. At
short travel distances, however, the sign of the travel-time shifts
appears to depend sensitively on how the data are processed and,
in particular, on filtering in frequency-wavenumber space. We carry
out two linear inversions for wave speed: one using travel-times
and phase-speed filters and the other one using mode frequencies
from ring analysis. These two inversions give subsurface wave-speed
profiles with opposite signs and different amplitudes. The travel-time
measurements also imply different subsurface flow patterns in the
surface layer depending on the filtering procedure that is used. Current
sensitivity kernels are unable to reconcile these measurements, perhaps
because they rely on imperfect models of the power spectrum of solar
oscillations. We present a linear inversion for flows of ridge-filtered
travel times. This inversion shows a horizontal outflow in the upper
4 Mm that is consistent with the moat flow deduced from the surface
motion of moving magnetic features. From this study of AR 9787, we
conclude that we are currently unable to provide a unified description
of the subsurface structure and dynamics of the sunspot.
---------------------------------------------------------
Title: ATCA monitoring of gamma-ray loud AGN in support of the
Fermi mission
Authors: Tingay, Steven; Macquart, Jean-Pierre; Lovell, Jim; Edwards,
Philip; Sadler, Elaine; Ojha, Roopesh; Romani, Roger W.; Kadler,
Matthias; Murphy, David; Gehrels, Neil; Michelson, Peter; Cameron,
Robert
2009atnf.prop.1995T Altcode:
Following a successful pilot investigation to determine the feasibility
of monitoring bright gamma-ray AGN at 7 mm throughout the year (C1730),
we propose a continuation of the project into a one year phase of
observations that will support the Fermi mission following its June 2008
launch. The goal of this project is to monitor Fermi-identified AGN
at 4.8, 8.6, 17, 19, 38, and 40 GHz at monthly intervals, tracking
variability in the AGN (in particular flaring activity) that can
be related to gamma-ray variability observed by Fermi and pc-scale
structural variability observed by our concurrent Southern Hemipshere
VLBI monitoring program in support of Fermi. The ATCA, VLBI, and Fermi
data will contribute to a multi-wavelength AGN database that will help
us understand the origins of high energy emission in AGN.
---------------------------------------------------------
Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources
Authors: Edwards, Philip; Sadler, Elaine; Romani, Roger W.; Tingay,
Steven; Wieringa, Mark; Michelson, Peter; Cameron, Robert
2009atnf.prop.2222E Altcode:
This NAPA proposal will be triggered by the detection of a
gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray
satellite. The Fermi team will identify bright sources flaring on
day-timescales to trigger ATCA observations for southern sources for
which no counterpart is known, which we expect to occur predominantly
for sources with |b|<1.5degrees. As Fermi source localizations
are often better than 10arcmin, we will initially make simultaneous
5GHz/9GHz observation, for which the primary beam is matched to the
Fermi error region. If a radio counterpart can be identified, we will
make follow-up observations at higher frequencies to help characterise
the Spectral Energy Distribution of the source, and to monitor the
evolution of the outburst at radio frequencies. History indicates
this rapid localization and follow-up of flaring sources may well be
critical in identifying a new class (or classes) of high energy object.
---------------------------------------------------------
Title: Countercell Meridional Flow and Latitudinal Distribution of
the Solar Polar Magnetic Field
Authors: Jiang, J.; Cameron, R.; Schmitt, D.; Schüssler, M.
2009ApJ...693L..96J Altcode:
Recent observations indicate that the latitudinal profile of the
magnetic flux shows a pronounced decrease close to the solar north
pole during the minimum phase of solar cycle 23. Using a surface flux
transport model, we have performed numerical experiments to study the
conditions that could lead to such a latitudinal distribution. We find
that a strong decrease of the magnetic field near the poles results
if a weak countercell of the meridional flow at high latitudes with
an equatorward speed of a few m s<SUP>-1</SUP> is present.
---------------------------------------------------------
Title: Surface-Focused Seismic Holography of Sunspots:
II. Expectations from Numerical Simulations Using Sound-Speed
Perturbations
Authors: Birch, A. C.; Braun, D. C.; Hanasoge, S. M.; Cameron, R.
2009SoPh..254...17B Altcode: 2008SoPh..tmp..186B
Helioseismic observations of sunspots show that wave travel times, at
fixed horizontal phase speed, depend on the temporal frequency of the
waves employed in the data analysis. This frequency variation has been
suggested to be consistent with near-surface (vertical length scales
of order one Mm or smaller) changes in wave propagation properties
relative to the quiet Sun. We investigate this suggestion by employing
numerical simulations of acoustic-wave propagation through models
with horizontally and vertically inhomogeneous structure. Standard
methods of surface-focused helioseismic holography are applied to the
resulting simulated wave fields. We find that the travel-time shifts
measured using holography from the simulations with deep sound-speed
perturbations (relative to a plane-parallel quiet-Sun model) do not
show a systematic frequency dependence at phase speeds above about
20 km s<SUP>−1</SUP>. However, shallow sound-speed perturbations,
similar to those proposed to model the acoustic scattering properties
of sunspots observed with Hankel analysis, produce systematic frequency
dependence at these phase speeds. In both cases, positive travel-time
shifts can be caused by positive sound-speed perturbations. The details
of the travel-time shifts are, however, model dependent.
---------------------------------------------------------
Title: Helioseismology of Sunspots: A Case Study of NOAA Region 9787
Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch,
A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.;
Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.;
Zharkov, S.
2009odsm.book..249G Altcode:
Various methods of helioseismology are used to study the subsurface
properties of the sunspot in NOAA Active Region 9787. This sunspot
was chosen because it is axisymmetric, shows little evolution during
20-28 January 2002, and was observed continuously by the MDI/SOHO
instrument. AR 9787 is visible on helioseismic maps of the farside of
the Sun from 15 January, i.e. days before it crossed the East limb.
---------------------------------------------------------
Title: A Robust Correlation between Growth Rate and Amplitude of
Solar Cycles: Consequences for Prediction Methods
Authors: Cameron, R.; Schüssler, M.
2008ApJ...685.1291C Altcode:
We consider the statistical relationship between the growth rate
of activity in the early phase of a solar cycle with its subsequent
amplitude on the basis of four data sets of global activity indices
(Wolf sunspot number, group sunspot number, sunspot area, and 10.7 cm
radio flux). In all cases, a significant correlation is found: stronger
cycles tend to rise faster. Owing to the overlapping of sunspot cycles,
this correlation leads to an amplitude-dependent shift of the solar
minimum epoch. We show that this effect explains the correlations
underlying various so-called precursor methods for the prediction
of solar cycle amplitudes and also affects the prediction tool of
Dikpati et al. based on a dynamo model. Inferences as to the nature
of the solar dynamo mechanism resulting from predictive schemes which
(directly or indirectly) use the timing of solar minima should therefore
be treated with caution.
---------------------------------------------------------
Title: Helioseismology of Sunspots: Confronting Observations with
Three-Dimensional MHD Simulations of Wave Propagation
Authors: Cameron, R.; Gizon, L.; Duvall, T. L., Jr.
2008SoPh..251..291C Altcode: 2008arXiv0802.1603C; 2008SoPh..tmp...51C
The propagation of solar waves through the sunspot of AR 9787
is observed by using temporal cross-correlations of SOHO/MDI
Dopplergrams. We then use three-dimensional MHD numerical simulations
to compute the propagation of wave packets through self-similar
magnetohydrostatic sunspot models. The simulations are set up in
such a way as to allow a comparison with observed cross-covariances
(except in the immediate vicinity of the sunspot). We find that the
simulation and the f-mode observations are in good agreement when the
model sunspot has a peak field strength of 3 kG at the photosphere
and less so for lower field strengths. Constraining the sunspot model
with helioseismology is only possible because the direct effect of
the magnetic field on the waves has been fully taken into account. Our
work shows that the full-waveform modeling of sunspots is feasible.
---------------------------------------------------------
Title: The seismic effects of a sunspot
Authors: Schunker, H.; Cameron, R.; Gizon, L.
2008ESPM...12..3.5S Altcode:
We simulate the helioseismic wave field by using the three-dimensional
Semi-spectral Linear MHD (SLiM) code and exciting small-amplitude waves
by sources distributed in the near-surface layers of a model solar
atmosphere.Our model atmosphere is realistic in the sense that it has
a standard sound-speed profile. Our source function is a realization
drawn from a random process specified by a statistical description of
solar convection. We obtain a quiet-Sun power spectrum of wave motions,
which is consistent with Doppler observations. In order to study wave
propagation through sunspots, we derive a simplified monolithic model
sunspot embedded in the quiet-Sun model atmosphere. The corresponding
wave field computed with SLiM is then compared with MDI observations
of f- and p-mode scattering by magnetic region AR9787. The comparison
is encouraging as the numerical simulation is able to reproduce wave
absorption and scattering phase shifts. As part of our analysis, we
show the advantage of computing a reference quiet-Sun wave field using
the same realization of the sources for the purpose of comparisons
and noise reduction.
---------------------------------------------------------
Title: Radiative magnetohydrodynamic simulations of solar pores
Authors: Cameron, R.; Schüssler, M.; Vögler, A.; Zakharov, V.
2007A&A...474..261C Altcode:
Context: Solar pores represent a class of magnetic structures
intermediate between small-scale magnetic flux concentrations in
intergranular lanes and fully developed sunspots with penumbrae. <BR
/>Aims: We study the structure, energetics, and internal dynamics
of pore-like magnetic structures by means of exploratory numerical
simulations. <BR />Methods: The MURaM code has been used to carry
out several 3D radiative MHD simulations for pores of various sizes
and with different boundary conditions. <BR />Results: The general
properties of the simulated pores (morphology, continuum intensity,
magnetic field geometry, surrounding flow pattern, mean height
profiles of temperature, pressure, and density) are consistent with
observational results. No indications for the formation of penumbral
structure are found. The simulated pores decay by gradually shedding
magnetic flux into the surrounding pattern of intergranular downflows
(“turbulent erosion”). When viewed under an angle (corresponding
to observations outside solar disc center), granules behind the pore
appear brightened. <BR />Conclusions: Radiative MHD simulations capture
many observed properties of solar pores.
---------------------------------------------------------
Title: Photospheric magnetoconvection
Authors: Cameron, Robert; Vögler, Alexander; Schüssler, Manfred
2007IAUS..239..475C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Cycle Prediction Using Precursors and Flux Transport
Models
Authors: Cameron, R.; Schüssler, M.
2007ApJ...659..801C Altcode: 2006astro.ph.12693C
We study the origin of the predictive skill of some methods to
forecast the strength of solar activity cycles. A simple flux
transport model for the azimuthally averaged radial magnetic field at
the solar surface is used, which contains a source term describing
the emergence of new flux based on observational sunspot data. We
consider the magnetic flux diffusing over the equator as a predictor,
since this quantity is directly related to the global dipole field from
which a Babcock-Leighton dynamo generates the toroidal field for the
next activity cycle. If the source is represented schematically by a
narrow activity belt drifting with constant speed over a fixed range
of latitudes between activity minima, our predictor shows considerable
predictive skill, with correlation coefficients up to 0.95 for past
cycles. However, the predictive skill is completely lost when the
actually observed emergence latitudes are used. This result originates
from the fact that the precursor amplitude is determined by the sunspot
activity a few years before solar minimum. Since stronger cycles tend to
rise faster to their maximum activity (known as the Waldmeier effect),
the temporal overlapping of cycles leads to a shift of the minimum
epochs that depends on the strength of the following cycle. This
information is picked up by precursor methods and also by our flux
transport model with a schematic source. Therefore, their predictive
skill does not require a memory, i.e., a physical connection between
the surface manifestations of subsequent activity cycles.
---------------------------------------------------------
Title: SLiM: a code for the simulation of wave propagation through
an inhomogeneous, magnetised solar atmosphere
Authors: Cameron, R.; Gizon, L.; Daiffallah, K.
2007AN....328..313C Altcode: 2010arXiv1002.2344C
In this paper we describe the semi-spectral linear MHD (SLiM) code
which we have written to follow the interaction of linear waves through
an inhomogeneous three-dimensional solar atmosphere. The background
model allows almost arbitrary perturbations of density, temperature,
sound speed as well as magnetic and velocity fields. We give details of
several of the tests we have used to check the code. The code will be
useful in understanding the helioseismic signatures of various solar
features, including sunspots.
---------------------------------------------------------
Title: Solar mesogranulation as a cellular automaton effect
Authors: Matloch, L.; Cameron, R.; Schmitt, D.; Schüssler, M.
2007msfa.conf..339M Altcode:
We present a simple cellular automaton model of solar granulation
that captures the granular cell characteristics in terms of lifetime
and size distributions. We show that mesogranulation, as defined in
observational data, is an intrinsic feature of such a cell system.
---------------------------------------------------------
Title: Helioseismology at MPS
Authors: Gizon, L.; Cameron, R.; Jackiewicz, J.; Roth, M.; Schunker,
H.; Stahn, T.
2007msfa.conf...89G Altcode:
Research in solar and stellar seismology at the Max Planck Institute
for Solar System Research (MPS) is supported by the Junior Research
Group "Helio- and Asteroseismology" of the Max Planck Society since
September 2005. A presentation of the current topics of research is
given, with particular emphasis on local helioseismology.
---------------------------------------------------------
Title: Three-dimensional numerical simulation of wave propagation
through a model sunspot
Authors: Cameron, R.; Gizon, L.
2006ESASP.624E..63C Altcode: 2006soho...18E..63C
No abstract at ADS
---------------------------------------------------------
Title: ChaMP Serendipitous Galaxy Cluster Survey
Authors: Barkhouse, W. A.; Green, P. J.; Vikhlinin, A.; Kim, D. -W.;
Perley, D.; Cameron, R.; Silverman, J.; Mossman, A.; Burenin, R.;
Jannuzi, B. T.; Kim, M.; Smith, M. G.; Smith, R. C.; Tananbaum, H.;
Wilkes, B. J.
2006ApJ...645..955B Altcode: 2006astro.ph..3521B
We present a survey of serendipitous extended X-ray sources and optical
cluster candidates from the Chandra Multiwavelength Project (ChaMP). Our
main goal is to make an unbiased comparison of X-ray and optical
cluster detection methods. In 130 archival Chandra pointings covering
13 deg<SUP>2</SUP>, we use a wavelet decomposition technique to detect
55 extended sources, of which 6 are nearby single galaxies. Our X-ray
cluster catalog reaches a typical flux limit of about ~10<SUP>-14</SUP>
ergs cm<SUP>-2</SUP> s<SUP>-1</SUP>, with a median cluster core radius
of 21<SUP>”</SUP>. For 56 of the 130 X-ray fields, we use the ChaMP's
deep NOAO 4 m MOSAIC g<SUP>'</SUP>, r<SUP>'</SUP>, and i<SUP>'</SUP>
imaging to independently detect cluster candidates using a Voronoi
tessellation and percolation (VTP) method. Red-sequence filtering
decreases the galaxy fore- and background contamination and provides
photometric redshifts to z~0.7. From the overlapping 6.1 deg<SUP>2</SUP>
X-ray/optical imaging, we find 115 optical clusters (of which 11%
are in the X-ray catalog) and 28 X-ray clusters (of which 46% are in
the optical VTP catalog). The median redshift of the 13 X-ray/optical
clusters is 0.41, and their median X-ray luminosity (0.5-2 keV) is
L<SUB>X</SUB>=(2.65+/-0.19)×10<SUP>43</SUP> ergs s<SUP>-1</SUP>. The
clusters in our sample that are only detected in our optical data are
poorer on average (~4 σ) than the X-ray/optically matched clusters,
which may partially explain the difference in the detection fractions.
---------------------------------------------------------
Title: High field strength modified ABC and rotor dynamos
Authors: Cameron, Robert; Galloway, David
2006MNRAS.367.1163C Altcode: 2006MNRAS.tmp..233C
The Archontis dynamo was the first stationary dynamo discovered
which saturates with almost equal magnetic and kinetic energies in
the limit of large Reynolds numbers. In this paper we present two
further examples, one based on a series of numerical calculations and
the other on the analytic rotor dynamos of Herzenberg. The forcing and
flow in these new examples lack some of the symmetries of the Archontis
dynamo are therefore more generic. The saturation mechanism is thus
not a unique property of the Archontis dynamo. <P />For the numerical
solutions, we also have investigated the structure and stability of
the flow and field near the stagnation points and those streamlines
which enter and leave them. These structures play an important part
in the operation of the dynamo mechanism, and the way they interact
with one another is mirrored in the analytic example based on the
Herzenberg rotors.
---------------------------------------------------------
Title: Extending the X-ray Luminosity Function of AGN to High Redshift
Authors: Silverman, J.; Green, P.; Barkhouse, W.; Cameron, R.; Kim,
M.; Kim, D. -W.; Wilkes, B.; Hasinger, G.; Full Champ Project, The
2006ESASP.604..795S Altcode: 2005astro.ph.11552S; 2006xru..conf..795S
X-ray surveys of the extragalactic universe are now able to detect
significant numbers of AGN out to high redshift (z~5). We highlight some
results from the Chandra Multiwavelength Project (ChaMP) to measure
the X-ray luminosity function out to these early epochs. At z > 3,
we show that the comoving space density of luminous (log Lx > 44.5)
AGN has a behavior similar to the optical QSO luminosity function. With
a newly compiled sample of AGN from ChaMP supplemented with those from
additional surveys including the Chandra Deep fields, we present a
preliminary measure of the luminosity function in the hard (2-8 keV)
band. With 37 AGN at z > 3, we continue to see a decline in the
space density at high redshift over a wider range in luminosity. We
discuss the need to identify a larger sample of obscured AGN at high
redshift to determine if an early epoch of hidden supermassive black
hole growth occurred.
---------------------------------------------------------
Title: Saturation properties of the Archontis dynamo
Authors: Cameron, Robert; Galloway, David
2006MNRAS.365..735C Altcode: 2005MNRAS.tmp.1100C
This paper discusses the generation and subsequent non-linear limiting
of magnetic fields by motions in a periodic flow driven by a force
whose components are proportional to (sinz, sinx, siny). This problem
was originally studied by Archontis; the purpose of the present work
is to remove certain complications present in the original model in
order to understand better the underlying physical mechanism which
limits the total magnetic energy growth. At high Reynolds numbers the
resulting dynamos end up with almost equal total magnetic and kinetic
energies, and thus yield fields strong enough to be astrophysically
relevant. Until now, the existence of such dynamos has been doubted,
so this demonstration of an example appears very important. At
least up to Reynolds numbers of 800, these solutions are laminar
and attracting. <P />We then present an argument showing that any
stationary, incompressible dynamo can be used to create a family of
solutions with an arbitrary ratio of magnetic to kinetic energies in
the limit of large Reynolds numbers. The stability of such solutions
is also discussed.
---------------------------------------------------------
Title: Simulations of Solar Pores
Authors: Cameron, R.; Vögler, A.; Schüssler, M.; Zakharov, V.
2005ESASP.600E..11C Altcode: 2005ESPM...11...11C; 2005dysu.confE..11C
No abstract at ADS
---------------------------------------------------------
Title: The structure of small-scale magnetic flux tubes
Authors: Cameron, Robert; Galloway, David
2005MNRAS.358.1025C Altcode: 2005MNRAS.tmp..199C
Three main mechanisms have been described to determine the maximum
field strength and structure of a solar or stellar magnetic flux
tube. This paper attempts to relate them to one another through a
series of magnetoconvective calculations. The first process is the
balancing of the Lorentz force by radial gradients in the buoyancy
force. It was first found in the Boussinesq regime, where it was
studied in the late 1970s by Galloway, Proctor & Weiss. A similar
balance can occur in the fully compressible case, where we refer to it
as quasi-Boussinesq (QB). The second process involves a balance between
an outward-directed radial pressure gradient and radial gradients in the
buoyancy force outside the tube. This is the mechanism proposed in the
early 1990s by Kerswell & Childress (the KC mechanism). The third
mechanism, convective collapse (CC), is a process whereby a flux tube
can evolve to a high field strength because of an instability due to
the superadiabaticity of the material within the tube. Until now, it
has been studied using the so-called `thin flux tube' approximation in
which convective motions are ignored even though there is a background
superadiabatic density stratification. Here we place these three
mechanisms in a unified framework and explore the transitions between
the solutions as various parameters are varied. In particular, we show
that the QB solutions are preferred for a wide range of parameters,
whereas CC solutions occur only in very specific circumstances. In
particular, on the Sun, the latter are probably limited to flux tubes
with radii less than approximately 10 km, the turbulent magnetic
diffusivity length-scale.
---------------------------------------------------------
Title: The Decay of a Simulated Pore
Authors: Cameron, R.; Vögler, A.; Shelyag, S.; Schüssler, M.
2004ASPC..325...57C Altcode:
Using MURaM -- Max-Planck Institut für Aeronomie University of
Chicago Radiative Magnetohydrodynamics -- an MHD code which includes
radiative transfer and partial ionization, we have studied the decay
phase of a solar pore. The simulations are sufficiently realistic
in their treatment of the photosphere to allow a direct comparison
with observations, both current and those of upcoming missions such
as SolarB. As well as discussing the structure and decay of pores,
we show the formation of shallow, field aligned, convective rolls
which are an important feature of our solutions.
---------------------------------------------------------
Title: Finding the Obscured AGN with ChAMP
Authors: Aldcroft, T.; Green, P.; Silverman, J.; Cameron, R.; Kim,
D.; Wilkes, B.; ChaMP Collaboration
2004HEAD....8.3506A Altcode: 2004BAAS...36..973A
X-ray surveys with \textit{Chandra} and \textit{XMM} provide the most
complete census of accretion powered luminosity in the universe. Coupled
with recent advances suggesting an intimate connection between galaxy
and supermassive black hole evolution, X-ray AGN surveys have emerged as
a powerful tool for investigating topics from galaxies to large scale
cosmology. One empirical input which plays a key role in modeling is
the distribution of obscuration in AGN. Obscuration changes the AGN
spectral contribution to the hard Cosmic X-ray Background (CXRB), the
apparent luminosity of AGN, and can even make them entirely "disappear",
so understanding this phenomenon is important. Using X-ray and optical
imaging and spectroscopic data from the \textit{Chandra} Multiwavelength
Project (ChaMP), we have assembled a sample of ∼ 900 AGN, covering
3.8 square degrees to a uniform flux limit of 2.7× 10<SUP>-15</SUP>
ergs cm<SUP>-2</SUP> sec<SUP>-1</SUP>. Using direct spectral fitting
with \textit{CIAO/Sherpa} we estimate the intrinsic absorbing column
N<SUB>H</SUB> in each source. Because of the large sample size,
we are able to determine the N<SUB>H</SUB> distribution within each
of six flux bins, confirming the trend of increasing obscuration at
lower fluxes and providing the strongest constraints to date on the
obscured fraction. We discuss the implications for modeling of the
CXRB and AGN luminosity function.
---------------------------------------------------------
Title: Distribution of Faraday Rotation Measure in Jets from Active
Galactic Nuclei. II. Prediction from Our Sweeping Magnetic Twist
Model for the Wiggled Parts of Active Galactic Nucleus Jets and Tails
Authors: Kigure, Hiromitsu; Uchida, Yutaka; Nakamura, Masanori;
Hirose, Shigenobu; Cameron, Robert
2004ApJ...608..119K Altcode: 2004astro.ph..2545K
Distributions of Faraday rotation measure (FRM) and the projected
magnetic field derived by a three-dimensional simulation of MHD
jets are investigated based on our “sweeping magnetic twist
model.” FRM and Stokes parameters were calculated to be compared
with radio observations of large-scale wiggled AGN jets on kiloparsec
scales. We propose that the FRM distribution can be used to discuss
the three-dimensional structure of the magnetic field around jets
and the validity of existing theoretical models, together with the
projected magnetic field derived from Stokes parameters. In a previous
paper we investigated the basic straight part of AGN jets by using
the result of a two-dimensional axisymmetric simulation. The derived
FRM distribution has a general tendency to have a gradient across
the jet axis, which is due to the toroidal component of the magnetic
field generated by the rotation of the accretion disk. In this paper
we consider the wiggled structure of the AGN jets by using the result
of a three-dimensional simulation. Our numerical results show that
the distributions of FRM and the projected magnetic field have a clear
correlation with the large-scale structure of the jet itself, namely,
three-dimensional helix. Distributions, seeing the jet from a certain
direction, show a good matching with those in a part of the 3C 449
jet. This suggests that the jet has a helical structure and that the
magnetic field (especially the toroidal component) plays an important
role in the dynamics of the wiggle formation because it is due to a
current-driven helical kink instability in our model.
---------------------------------------------------------
Title: X-ray Emitting AGN Unveiled by the Chandra Multiwavelength
Project
Authors: Silverman, J.; Green, P.; Aldcroft, T.; Kim, D.; Barkhouse,
W.; Cameron, R.; Wilkes, B.
2004ASPC..311..321S Altcode: 2004apsd.conf..321S; 2003astro.ph.10907S
We present an X-ray and optical analysis of a flux limited
(f<SUB>2.0-8.0 keV</SUB> > 10<SUP>-14</SUP> erg s<SUP>-1</SUP>
cm<SUP>-2</SUP>) sample of 126 AGN detected in 16 Chandra fields. This
work represents a small though significant subset of the Chandra
Multiwavelength Project (ChaMP). We have chosen this limiting flux
to have a reasonable degree of completeness (50%) in our optical
spectroscopic identifications. The optical counterparts of these AGN
are characterized as either broad emission line AGN (BLAGN; 59%),
narrow emission line galaxies (NELG; 20%) or absorption line galaxies
(ALG; 12%) without any evidence of an AGN signature. Based on their
X-ray luminosity and spectral properties, we show that NELG and ALG are
primarily the hosts of obscured AGN with an intrinsic absorbing column
in the range of 10<SUP>21.5</SUP>< N<SUB>H</SUB><10<SUP>23.3</SUP>
cm<SUP>-2</SUP>. While most of the BLAGN are unobscured, there are a
few with substantial absorption. X-ray surveys such as the ChaMP nicely
complement optical surveys such as the SDSS to completely determine
the demographics of the AGN population.
---------------------------------------------------------
Title: Distribution of Faraday Rotation Measure in Jets from Active
Galactic Nuclei. I. Predictions from our Sweeping Magnetic Twist Model
Authors: Uchida, Yutaka; Kigure, Hiromitsu; Hirose, Shigenobu;
Nakamura, Masanori; Cameron, Robert
2004ApJ...600...88U Altcode: 2003astro.ph..9605U
Using the numerical data of MHD simulation for active galactic nucleus
(AGN) jets based on our “sweeping magnetic twist model,” we calculated
the Faraday rotation measure (FRM) and the Stokes parameters to compare
with observations. We propose that the FRM distribution can be used to
discuss the three-dimensional structure of magnetic field around jets,
together with the projected magnetic field derived from the Stokes
parameters. In the present paper, we assumed the basic straight part
of the AGN jet and used the data of axisymmetric simulation. The FRM
distribution that we derived has a general tendency to have gradient
across the jet axis, which is due to the toroidal component of the
helical magnetic field generated by the rotation of the accretion
disk. This kind of gradient in the FRM distribution is actually observed
in some AGN jets, which suggests a helical magnetic field around the
jets and thus supports our MHD model. Following this success, we are now
extending our numerical observation to the wiggled part of the jets,
using the data of three-dimensional simulation based on our model,
in an upcoming paper.
---------------------------------------------------------
Title: Stormy Weather
Authors: Cameron, Robert
2004ChNew..11...22C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Investigation of Loop-Type CMEs with a 3D MHD Simulation
Authors: Kuwabara, J.; Uchida, Y.; Cameron, R.
2003ASPC..289..389K Altcode: 2003aprm.conf..389K
CMEs have erupted filaments (core) and flux loops that lie over the
filament (leading edge) and a cavity between the core and leading
edge. In one model “Flux loops are pushed up by erupted filaments and
expand upwards" which roughly explains much about CMEs. But there are
some CMEs with characteristics that are inexplicable with this model,
which have a twisted structure along the loop and the structure
of a convex lens at the loop top (Illing and Hundhausen 2000). We
consider Torsional Alfven Wave (TAW) propagation as the cause of these
characteristics for some CMEs, and have studied this with a 3D MHD
simulation. As a result, we found that TAW propagation most likely
explains these characteristics for some CMEs and that a TAW can carry
out plasma from the chromosphere to coronal space along the loop. We
propose a new scenario about the occurrence of CMEs based on results
of our simulation and observations.
---------------------------------------------------------
Title: Optical spectroscopic followup of serendipitous Chandra
sources: the Chandra Multiwavelength Project (ChaMP)
Authors: Silverman, J.; Green, P.; Wilkes, B.; Foltz, C.; Smith,
P.; Smith, C.; Kim, Dong-Woo; Morris, D.; Mossman, A.; Cameron, R.;
Adelberger, K.; ChaMP Collaboration
2003AN....324...97S Altcode:
A primary goal of the Chandra Multiwavelength Project (ChaMP) is
to investigate the evolution of Active Galactic Nuclei (AGN) and
quasars by measuring the luminosity function out to z>=4 including
obscured AGN that have been missed by previous surveys. To do so,
we are acquiring spectra of optical counterparts to serendipitious
X-ray sources detected by Chandra for classification and redshift
determination. We have amassed about 200 spectra using the FLWO 1.5m,
WIYN 3.5m, CTIO/4m, Magellan and the MMT 6.5m. We have classified
the majority of optical counterparts as 65 AGN, 14 galaxies. The
remaining counterparts are either stars (8 clusters (1 fields. With
a limiting magnitude of r<SUP>'</SUP>=22 for spectroscopic followup,
we are able to detect quasars out to z ~ 5 and galaxies out to z ~
0.7. This preliminary sample forms the foundation for our measurement
of the X-ray luminosity function of AGNs out to z ~ 4.
---------------------------------------------------------
Title: Quantitative measure of quiet photospheric magnetic fields
Authors: Zirin, H.; Cameron, R.
2002AAS...200.3903Z Altcode: 2002BAAS...34..701Z
We have analyzed a set of 110 Stokes V spectra of the quiet Sun taken
with the spectrovideomagnetograph at BBSO June 23, 2000. The 480x512
pixel spectrograms are bundled into 3 pixel (1 arc sec) spectra, giving
160 distinct spectra on each frame, or 16400 spectra overall. An element
of magnetic network was included in each spectrogram, so that actual
splitting measurements could be used to check absolute calibration
of the field measures. In each case we measured the V signal in both
5250 and 5247 and compared the values. If the ratio was 3:2 as given by
the g-factors, the data must represent true measured magnetic fields,
since random noise does not understand g-factors. We find the mean
field on each spectrum to range from 3 to 49 gauss in the different
frames, and the median absolute field, from 13 to 30 G. In all cases the
difference between V(5250) and 1.5xV( 5247) is zero within 1.2 standard
errors. To check the popular “emperor's new clothes" model in which
the fields measured are due to invisible spots with kilogauss fields,
we calculate the mean value of 1.5xV(5247)/0.78- V(5250), expected to
be zero for that model. Rather than zero, that result is typically 3
standard errors from zero, and invariably negative. That result means
that the V(5250) is not saturated, as would be expected in the kilogauss
model. Thus the emperor, in fact, has no clothes. The fields measured in
network elements run from 250 to 700 gauss, and are typically confirmed
within 20% by the measured splitting. The existence of fields of mixed
polarity and strength >10 gauss everywhere in the photosphere gives
an explanation for the support of the chromosphere, which has a scale
height of 1000 Km instead of the expected hydrostatic scale height
<200 Km, as well as the filtering out of unionized high-FIP elements,
which cannot be supported by the magnetic fields, from the solar wind.
---------------------------------------------------------
Title: The true structure of weak solar magnetic fields
Authors: Zirin, H.; Cameron, R.
2002ocnd.confE..30Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Loop-Type CME Produced by Magnetic Reconnection of Two Large
Loops at the Associated Arcade Flare
Authors: Uchida, Y.; Kuwabara, J.; Cameron, R.; Suzuki, I.; Tanaka,
T.; Kouduma, K.
2002mwoc.conf..199U Altcode:
We claim from observational analyses that there are, at least, two
distinctly different types among CME's: One with a bubble shape
expanding roughly isotropically with constant velocity caused by
explosive flares (Bubble-type), and the other with a large loop shape
whose anchor point in the middle is released by the occurrence of an
arcade flare between the footpoints of CME's, rising with acceleration
and deformation (Loop-type). The characteristic difference between these
types is that the footpoints stay fixed on the solar surface in the
Loop-type, whereas the structure does not have such fixed footpoints
for the Bubble-type since the skirts of the bubble (Moreton wave
and EIT wave separately propagating) sweep on the solar surface. We
investigate MHD models for these two types of CME's, fulfilling the
observed characteristics described above, with our 3D MHD simulations,
and show dynamic behaviors of those with movies. We believe that these
are examples of new generation approach with time-dependent 3D MHD
modelling, allowing actual comparison of dynamic models with dynamic
results from advanced observations.
---------------------------------------------------------
Title: The Chandra Multi-wavelength Project (ChaMP): Preliminary
results of X-ray Analysis
Authors: Kim, D. -W.; Cameron, R.; Drake, J.; Freeman, P.; Fruscione,
A.; Gaetz, T. J.; Green, P. J.; Grimes, J.; Ghosh, H.; Kashyap, V.;
Schlegel, E.; Vikhlinin, A.; Wilkes, B.; Tananbaum, H.
2001tysc.confE.222K Altcode:
We present preliminary results of X-ray data analysis as part of the
Chandra Multi-wavelength Project. We describe basic data corrections,
screening and source analysis procedures. About 1/4 of 160 fields
selected in AO1 and AO2 have been processed through the ChaMP
X-pipeline. About 2000 sources are detected (this number may not be
prorated). Average X-ray source properties in terms of LogN-LogS,
X-ray color, optical color and X-ray to optical luminosity ratio
are discussed.
---------------------------------------------------------
Title: Optical Classification of Chandra Serendipitous Sources by
the ChaMP
Authors: Green, Paul J.; Cameron, Robert
2001tysc.confE..53G Altcode:
We describe our ongoing optical imaging and spectroscopy of a deep,
wide-area sample of serendipitous X-ray sources detected in Chandra
archival images. The Chandra Multiwavelength Project (ChaMP) thus
enables studies of the nature, evolution, and clustering of X-ray
selected AGN and galaxies. Chandra's subarcsecond astrometry enables
unambiguous identification of optical counterparts, and the broadband
X-ray sensitivity (0.3-8keV) means that our sample is less affected
by absorption than previous optical, UV, or soft X-ray surveys. Unlike
radio surveys , the ChaMP will allow the first complete census of the
intrinsic population of AGN (not just the radio bright fraction). We
present initial results that will eventually encompass a sample of
thousands of serendipitous sources detected in 150 Chandra archival
images, to constrain the X-ray luminosity function and its evolution.
---------------------------------------------------------
Title: The Field Strength of the Quiet Sun Magnetic Elements
Authors: Zirin, H.; Cameron, R.
2001AAS...198.7105Z Altcode: 2001BAAS...33..893Z
By attaching the videomagnetograph to the Coude spectrograph at BBSO,
we can measure weak fields down to 10-20 gauss, and splittings down
to 200 gauss. Using Stenflo's technique of comparing 5250 and 5247,
we find no saturation; the lines (corrected for g-factor) give equal
results within a few per cent and are truly weak. The V measurements
are calibrated by comparison to Zeeman splitting measures above 200
gauss. The filling factor is unity and there are no hidden strong
fields. We find noevidence for kilogauss fileds in the quiet Sun. While
noise limits the agreement of the two lines below 20 gauss, there is
a detectable V signal almost everywhere on the Sun, both unipolar
and mixed, of the order of 5 gauss. We call the new instrument the
spectrovideo-magnetograph (SPVMG). This work supported by the NSF.
---------------------------------------------------------
Title: Blast Waves in the Magnetized Solar Atmosphere
Authors: Cameron, R.; Uchida, Y.
2001AGUSM..SH42A09C Altcode:
Solar flares convert large amounts of magnetic energy into thermal
and bulk plasma motions. Such large changes in the magnetic field and
plasma properties excite the available wave modes. Not all modes are
equally excited of course and, in principle, this can be used to probe
the flare mechanism. In practice however we are still at the stage of
identifying the different modes we see. The initial breakthrough in this
regard occurred in the early 1970s when Uchida (Uchida 1968) identified
the previously observed Moreton waves (Moreton and Ramsey 1960) as the
skirt of a fast mode shock propagating in the Corona. This picture
has remained essentially unchanged since. In the 1990s the regular
observation of the sun in EUV wavelengths revealed the existence of a
new blast related wave: the EIT wave. The most distinctive difference
between the behavior of the two types of waves is their different
velocities, with the Moreton wave being about twice as fast as the EIT
wave. Where the two waves are similar however is in the fact that they
can both propagate almost isotropically. For the Moreton wave this is
expected as the Moreton wave is a fast mode disturbance. For the EIT
wave the isotropic behavior suggests that the information is also being
carried by the fast mode. We suggest that the difference between the
two types of modes is not in the way the information is being carried,
but rather in the information content of the two different types of
waves. The Moreton wave conveys the information of the sharp, rapid
energy release associated with the impulsive phase of the flare. The EIT
wave conveys information as to the ejection of excess mass and energy
from the system via the slow mode. Unlike the simple spiked structure
which characterizes the impulsive phase, the time-scale associated with
the energy release is determined by the bulk mass motion along the
magnetic field lines - typically the slow mode velocity.. It will be
shown that this variation in the `source term' of the EIT disturbance
gives rise to an apparent velocity consistent with the EIT observations.
---------------------------------------------------------
Title: Spectovideomagnetograph results and the Stokes V assymmetry
Authors: Cameron, R.; Zirin, H.
2001AAS...198.7104C Altcode: 2001BAAS...33R.893C
The Spectrovideomagnetograph at Big Bear Solar Observatory was used
to obtain several thousand individual spectra of small elements
on the solar surface. These measurements display the well known
Stokes V assymmetry, however because the BBSO SPVMG has a significant
different spatial and temporal resolution than previous measurements,
the assymmetry has different properties. In this poster we present our
measurements of the assymmetry and use them to place constraints on the
mechanism producing the assymmetry. We then discuss how the assymmetry
contaminates other quantities derived from the SPVMG measurements, and
how this contamination can be minimized and controlled in our data set.
---------------------------------------------------------
Title: Rotational Signature of Disk Spicules in H-alpha
Authors: Lee, C.; Cameron, R.; Wang, H.
2001AGUSM..SP41B09L Altcode:
The Littrow spectrograph at Big Bear Solar Observatory (BBSO) can
produce a 4-dimensional data array, the intensity as a function of
position, wavelength and time. A week long observation at BBSO was
carried out on August 25-30, 1997. The spectral scan data is unique in
the sense that Doppler maps can be constructed free from mis-alignment
problems. We selected the best data set obtained on August 26 for the
present study. A number of disk spicules were identified and analysed
by considering their Doppler map and time evolution at different
wavelengths. It is estimated that 1/3 of the chosen disk spicules
are found to display rotational signature. The result is the first
clearest demonstration of spicule rotation. The cloud model of Beckers'
was used to determine a lower bound for the angular velocity.
---------------------------------------------------------
Title: The Spectrovideomagnetograph Reveals the True Strength of
Photospheric Magnetic Fields
Authors: Zirin, H.; Cameron, R.
2001AGUSM..SH32C04Z Altcode:
We present new observations of weak solar magnetic fields from an
instrument which we term the spectrovideomagnetograph (SPVMG). The
sensing system of the videomagnetograph is attached to the Coude
spectrograph at Big Bear and yields a high sensitivity. Using the
criteria introduced by Stenflo, we measure the Stokes V and I components
for the lines FeI 5250 and 5247 in hundreds of spectra. We find that
from 20 to 350 gauss derived field strengths are strictly proportional
to the g-factor and show no saturation. Hence the widely accepted strong
invisible magnetic elements postulated by Stenflo do not exist. The
filling factor is near unity. We measure the Zeeman splitting directly
down to 200 gauss and find good correspondence with our V measure. We
find that the area (outside of sunspots) of the solar surface occupied
by magnetic field of different strengths follows a power law in the
inverse square of the field strength. This applies to fields down to
200G. This has obvious relevance for turbulent surface dynamo models. We
find that at least 90% of the solar surface is covered by weak fields
above 5 gauss, sometimes unipolar and sometimes mixed.
---------------------------------------------------------
Title: Investigation of Coronal Mass Ejections I. Loop-type with
Arcade Flare between the Fixed Legs, and Bubble-type Due to Flare
Blast Waves
Authors: Uchida, Y.; Tanaka, T.; Hata, M.; Cameron, R.
2001PASA...18..345U Altcode:
In this paper, we give arguments that there are two types of
coronal mass ejection (CME). The first type of CME discussed here
is the `loop-type', whose occurrence is related to an arcade flare
somewhere between the footpoints. It was found that there were pre-event
magnetic connections between the flare location and the locations of the
footpoints of a CME of this type, and that these connections disappeared
after the event. This suggests that the footpoints of loop-type CMEs
are special prescribed points, and this was verified by the observation
that the footpoints do not move in this type of CME. The other type
of CME is the `bubble-type', which is associated with the flare blast
from explosive flares. We confirmed the association of this type of
CME with the so-called EIT (Extreme Ultra-violet Imaging Telescope)
waves, but the velocity of expansion of the bubble is twice or more
greater than that of the EIT waves depending on events. Although EIT
waves were widely considered to be Moreton waves viewed by SoHO/EIT in
the solar activity minimum period, recent simultaneous observations
of both have revealed that the EIT wave is something different from
the Moreton wave, and propagates separately with a velocity less
than half that of a Moreton wave. We therefore propose a new overall
picture: the bubble-type CMEs are the flare-produced MHD blast waves
themselves, whose skirt is identified as a Moreton wave. EIT waves may
be interpreted as follows: the slow-mode gas motions from the source
cause secondary long wavelength fast-mode waves which are trapped
in the 'waveguide' in the low corona. The secondary long-wavelength
wave in the fast-mode, which is trapped in the low corona, has a
slower propagation velocity due to the nature of the waves trapped
in a 'waveguide'. This trapped wave induces slow-mode motions of
the gas through a mode-coupling process in the high chromosphere,
where the propagation velocities of the fast-and slow-mode waves
match. Three-dimensional MHD simulations for these two types of CME
are in progress, and are previewed in this paper.
---------------------------------------------------------
Title: The Chandra Multi-wavelength Project (ChaMP): a Serendipitous
Survey with Chandra Archival Data.
Authors: Wilkes, B. J.; Green, P.; Brissenden, R.; Cameron, R.;
Dobrzycki, A.; Drake, J.; Evans, N.; Fruscione, A.; Gaetz, T.; Garcia,
M.; Ghosh, H.; Grimes, J.; Grindlay, J.; Hooper, E.; Karovska, M.;
Kashyap, V.; Kim, D. -W.; Kowal, K.; Marshall, H.; Mossman, A.; Morris,
D.; Nichols, J.; Szentgyorgyi, A.; Tananbaum, H.; van Speybroeck,
L.; Vikhlinin, A.; Virani, S.; Zhao, P.
2001ASPC..232...47W Altcode: 2000astro.ph.11377W; 2001newf.conf...47W
The launch of the Chandra X-ray Observatory in July 1999 opened a new
era in X-ray astronomy. Its unprecedented, <0.5" spatial resolution
and low background are providing views of the X-ray sky 10-100 times
fainter than previously possible. We have initiated a serendipitous
survey (ChaMP) using Chandra archival data to flux limits covering
the range between those reached by current satellites and those of the
small area Chandra deep surveys. We estimate the survey will cover ~5
sq.deg./year to X-ray fluxes (2-10 keV) in the range 1E(-13)-6E(-16)
erg/cm^2/s discovering ~2000 new X-ray sources, ~80% of which are
expected to be AGN. The ChaMP has two parts, the extragalactic survey
(ChaMP) and the galactic plane survey (ChaMPlane). ChaMP promises
profoundly new science return on a number of key questions at the
current frontier of many areas of astronomy including (1) locating
and studying high redshift clusters and so constraining cosmological
parameters (2) defining the true population of AGN, including those
that are absorbed, and so constraining the accretion history of the
universe, (3) filling in the gap in the luminosity/redshift plane
between Chandra deep and previous surveys in studying the CXRB, (4)
studying coronal emission from late-type stars and (5) search for
CVs and quiescent Low-Mass X-ray Binaries (qLXMBs) to measure their
luminosity functions. In this paper we summarize the status, predictions
and initial results from the X-ray analysis and optical imaging.
---------------------------------------------------------
Title: The Spectrovideomagnetograph Reveals the True Strength of
Quiet Sun Magnetic Fields
Authors: Zirin, H.; Cameron, R.
2000AAS...197.5107Z Altcode: 2000BAAS...32.1489Z
We present new observations of weak solar magnetic fields with a
technique, which we term the spectro-videomagnetograph (SPVMG) which
permits direct measurement of splittings as small as 200 gauss. Using
the technique of Stenflo we compared the Stokes V-component for the
5250 and 5247 lines. Contrary to Stenflo's results, we find no evidence
for strong fields with small filling factor; i. e., the field strengths
measured as 200 gaussare really 200 gauss and not some stronger field
partly filling the sample. For the weakest measured fields this cannot
be absolutely established, but the evidence supports the existence
of field elements at least as weak as 200 gauss. Observations of
active regions also yield new results. In many cases of fields near
inversion lines, we find doubled sets of Zeeman components, as well as
`flags,' broad components, usually confined to one side of the line,
extending to displacements corresponding to thousands of gauss, with
no corresponding component on the opposite side of the line. We show
examples of these spectra, along with slit jaw images, but have only
a limited understanding of the field structures they represent. We
also have examples of the V-splitting increasing as we approach the
inversion line. We are struggling to understand these and will at
least show them, with or without explanation. Finally, the regions
involving these anomalous Zeeman patterns seem to flare more frequently,
although statistics are limited. This work has been supported by the
NSF under ATM-9726147.
---------------------------------------------------------
Title: The Chandra Multi-wavelength Project (ChaMP): X-ray Data
Analysis
Authors: Kim, D. -W.; Cameron, R.; Drake, J.; Fruscione, A.; Gaetz,
T. J.; Garcia, M.; Green, P. J.; Grimes, J.; Kashyap, V.; Prestwich,
A.; Schlegel, E.; Vikhlinin, A.; Virani, S. N.; Wilkes, B.; Tananbaum,
H.; Freedman, D.; ChaMP Collaboration
2000HEAD....5.2604K Altcode: 2000BAAS...32.1223K
We present step-by-step X-ray data analysis procedures as part of
the Chandra Multi-wavelength Project. They consist of additional data
corrections and data screening post CXC Standard Data Processing Rev
1 and the determination of sources and their X-ray properties. Using 3
deep ACIS imaging fields (MS 1137.5+6625, CL0848.6+4453 and A0620-00)
with exposure times ranging from 50 ks to 190 ks, we discuss in
particular gain correction, aspect correction, removing bad pixels and
node boundaries, removing ACIS flaring pixels, streak correction for
the S4 chip and excluding high background intervals. Optimal parameters
for source detection and X-ray source properties such as X-ray colors
are also discussed.
---------------------------------------------------------
Title: The ChaMP: Keck Spectroscopy of Serendipitous Chandra Sources
Authors: Green, P. J.; Chaffee, F. H.; Cameron, R.; Virani, S. N.;
Dey, A.; Jannuzi, B.; Kindt, A.; van Speybroeck, L.; Tananbaum, H.;
Wilkes, B.; ChaMP Collaboration
2000HEAD....5.2618G Altcode: 2000BAAS...32.1226G
We describe the X-ray and optical characteristics of faint serendipitous
X-ray sources detected during a deep (120ksec) Chandra exposure with
ACIS. While the target is MS 1137.5+6625, the second most distant
cluster of galaxies in the Einstein Extended Medium Sensitivity Survey
(EMSS) at redshift 0.78, as part of the Chandra Multiwavelength Project
(ChaMP), we obtained Keck spectroscopy of a dozen optical counterparts
in an adjacent field (7 arcmin off-axis) that reveals an intriguing
variety of objects, dominated by AGN and galaxies between redshifts
of 0.5 to 2.
---------------------------------------------------------
Title: The Chandra Multi-wavelength Project (ChaMP): a serendipitous
X-ray Survey using Chandra Archival Data
Authors: Wilkes, B.; Green, P.; Cameron, R.; Evans, N.; Ghosh, H.;
Kim, D. W.; Tananbaum, H.; ChaMP Collaboration
2000HEAD....5.2105W Altcode: 2000BAAS...32.1212W
The Chandra X-ray Observatory, launched in July 1999, has begun a new
era in X-ray astronomy. Its unprecedented, ~ 0.5" spatial resolution and
low background provide views of the X-ray sky 10-100 times fainter than
previously possible. We have begun a serendipitous X-ray survey using
Chandra archival data to flux limits in between those reached by earlier
satellites and those of the small area, Chandra deep surveys. The survey
will cover ~ 5 sq.deg. per year to X-ray fluxes (2-10 keV) in the range
10<SUP>-13}-6<SUP>{-16</SUP></SUP> erg cm<SUP>2</SUP> s<SUP>-1</SUP>
and include ~3000 sources per year, ~ 70% of which are expected to be
active galactic nuclei (AGN). Optical imaging of the ChaMP fields is
underway at NOAO and SAO telescopes using SDSS g',r',z' colors with
which we will be able to classify the X-ray sources into object types
and, in some cases, estimate their redshifts. We are also planning to
obtain optical spectroscopy of a well-defined subset of fields to allow
confirmation of classification and redshift determination. All X-ray
and optical results and supporting optical data will be placed in the
ChaMP archive within a year of the completion of our data analysis. Over
the five years of Chandra operations, ChaMP will provide both a major
resource for Chandra observers and a key research tool for the study
of the cosmic X-ray background and the individual source populations
which comprise it. ChaMP promises profoundly new science return on
a number of key questions at the current frontier of many areas of
astronomy including the Cosmic X-ray Background, locating and studying
high redshift clusters and so constraining cosmological parameters,
defining the true population of quasars and studying coronal emission
from late-type stars that are almost fully convective. An overview of
the ChaMP will be presented including an introduction to our methods
and early results many of which will be presented in more detail in
accompanying papers at this meeting.
---------------------------------------------------------
Title: Tangential Field Changes in the Great Flare of 1990 May 24
Authors: Cameron, Robert; Sammis, Ian
1999ApJ...525L..61C Altcode:
We examine the great (solar) flare of 1990 May 24 that occurred
in active region NOAA 6063. The Big Bear Solar Observatory
videomagnetograph Stokes V and I images show a change in the
longitudinal field before and after the flare. Since the flare occurred
near the limb, the change reflects a rearrangement of the tangential
components of the magnetic field. These observations lack the 180°
ambiguity that characterizes vector magnetograms.
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Title: Chromospheric Sources of Coronal Rays
Authors: Zirin, H.; Cameron, R.
1999AAS...194.7808Z Altcode: 1999BAAS...31..962Z
TRACE images in the 171A FeIX line show coronal rays or small streamers
from network elements. We obtained chromospheric images in center and
wing of Hα at BBSO to investigate the relation of these to spicule
activity at the base, as well as to brightenings and other changes in
the underlying chromosphere. There is a close match of the brightest
Hα centerline elements to coronal rays; other network elements
are seen. Spicule activity does not appear to play a big role. The
coronal changes are fairly slow. We shall also present new data on
spicule lifetimes.
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Title: Axisymmetric Magnetoconvection in a Twisted Field: the effect
of Compressibility
Authors: Cameron, R.
1999AAS...194.5615C Altcode: 1999BAAS...31..914C
The magnetic flux threading the solar surface is believed to be
concentrated by convective motions into kilogauss strength flux
tubes. What is less well known is the extent to which convective motions
also concentrates the vertical current threading the solar surface. This
question can be addressed using the non-ideal MHD approximation. As
is the case with most such nonlinear problems a numerical treatment
is called for. This issue is perhaps best treated in an axisymmetric
geometry, where the computational cost of the calculations remains
modest (2 (1)/(2) dimensional) compared with a full 3 dimensional
simulation, and where flux tubes rather than flux sheets (which form in
2 (1)/(2) dimensional planar simulations) are produced. The problem
then equates to that of twisted, axisymmetric magnetoconvection,
which has been treated in the Boussinesq problem by Jones and Galloway
(1993). The results obtained in the Boussinesq problem indicate that
the problem is sensitive to the way in which the azimuthal components
are generated by the boundary conditions. This paper extends that work
by including the effect of compressibility. Compressible axisymmetric
magnetoconvection has two non-dimensional parameters in addition
to those describing the Boussinesq problem. To isolate the effect
of compressibility, we treat the same cases as Jones and Galloway,
and vary the two additional parameters.
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Title: Variability of Solar UV Irradiance Related to Bright Magnetic
Features Observed in Call K-Line: Relationship between Lyman alpha
and K-line Report for UARS funding agency
Authors: Zirin, Harold; Cameron, Robert
1999STIN...9910690Z Altcode:
In this report we comment on the relationship between the Lyman alpha
and Calcium K-line emission from the Sun. We firstly examine resolved
Lyman alpha images (from TRACE) and resolved K-line images. We find
that the Lyman alpha emission is consistent with a linear dependence
on the K-line emission. As this is in conflict with the analysis
of Johannesson et al.(1995, 1998) we proceed by comparing the disk
integrated Lyman alpha flux as a function of ratio between the disk
integrated Mg II core and wing fluxes (Johannesson et al (1998) having
previously found a linear dependence between this index and the BBSO
K-line index). We find that a reasonably good fit can be obtained,
however note the discrepancies which lead Johannesson et al to consider
the square root relationship. We suggest an alternative interpretation
of the discrepancy.
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Title: A new estimate of the solar meridional flow
Authors: Cameron, R.; Hopkins, A.
1998SoPh..183..263C Altcode:
We present a new method for measuring the solar magnetic meridional
flow, and provide a comparison with other recent work. We have
performed a least-squares fit to azimuthally averaged Mount Wilson
Observatory synoptic data encompassing Carrington rotations 1722 to
1929 to produce an estimate of the solar meridional flow. A parametric
fit to our results expresses the solar meridional flow as v(φ) =
28.5 sin2.5 φ cos φ.
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Title: New Studies of Polar Spicules
Authors: Zirin, H.; Cameron, R.
1998AAS...192.1506Z Altcode: 1998BAAS...30..840Z
We have studied several hundred images of solar spicules obtained
on June 18 and 19 and July 15 of 1997. The observations were made at
BBSO with the 65cm telescope feeding a Zeiss 1/4 Angstroms filter and
a 1536x1024 Kodak CCD. Overexposed observations were made above the
limb as well as normal exposures on the limb. The filter was tuned
to Hα -0.65A and a 30sec interval was used. We were limited to a
single wavelength because new software was being installed in a new
control computer. The images obtained were processed by high-pass
digital filtering of the original FITS images and reregistered by an
FFT technique. The image scale is 0.17 arcsec per pixel. The disk was
observed on June 18, 1997 to detect the sources of macrospicules and
the limb was observed by overexposure on June 19 to determine the height
trajectory of the faintest Hα We found that: Many more spicules go up
than come down. There are numerous double and multiple spicules. The
macrospicules come from normal network elements and start with an
"Eiffel tower" shape. There is evidence of magnetic changes underlying
these features. Both long macrospicules and complex eruptions are
important at the pole. There is some evidence for rotation in spicules.
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Title: A Combined X-Ray and Gamma Ray Study of the Seyfert Galaxies
NGC 7469 and NGC 3227
Authors: Cameron, Robert
1996rxte.prop10293C Altcode:
We propose XTE observations of the Seyfert 1 galaxies NGC 7469 and
NGC 3227, to be combined with gamma ray spectra of these AGN obtained
with the Compton OSSE instrument. The combined XTE and OSSE data,
providing continuous energy coverage from 2 keV to >1 MeV, will
be used to test and refine the increasingly complex Seyfert spectral
models in this energy range. The known variability of these Seyferts
may also give information on the separate emission components in the
broadband X-ray spectra, since we expect correlated variability between
the intrinsic source X-ray flux and reflected emission. Finally,
improved models for Seyfert AGN will provide better constraints on
the contribution of Seyferts to the diffuse X-ray background.
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Title: The Hard X-Ray Telescope Mission
Authors: Gorenstein, P.; Joensen, K.; Romaine, S.; Worrall, D.;
Cameron, R.; Weisskopf, M.; Ramsey, B.; Bilbro, J.; Kroeger, R.;
Gehrels, N.; Parsons, A.; Smither, R.; Christensen, F.; Citterio,
O.; von Ballmoos, P.
1995AAS...187.7203G Altcode: 1995BAAS...27Q1388G
The Hard X-Ray Telescope (HXT) mission concept contains focusing
telescopes that collectively, observe simultaneously from the
ultraviolet to 100 keV and in several narrow bands extending to 1
MeV. In pointed observations HXT is expected to have an order of
magnitude more sensitivity and much finer angular resolution in the
10 to 100 keV band than all current and currently planned future
missions, and considerably more sensitivity for detecting narrow
lines in the 100 keV to 1 MeV regime. The detectors are small, cooled
arrays of relatively low mass with very good energy resolution and
some polarization sensitivity. HXT contains two types of hard X-ray
telescopes. One type, called the modular modular telescope (MMT)
utilizes a novel type of multilayer coating and small graze angles to
extend the regime of focusing to 100keV. There is a two stage imaging
detector at each focus, a CCD for X-rays < 10 keV followed down
stream by either a germanium strip array or cadmium zinc telluride array
for 10-100 keV X-rays. The other type of telescope, called the Laue
Crystal Telescope (LCT) is a single adjustable array of several hundred
Ge crystals that focus by Laue scattering. Individual picomotors adjust
the angle of each crystal to diffract photons of a fixed energy to
the same point along the optic axis where they converge upon a movable
array of cooled germanium detectors. The LCT will have high sensitivity
for detecting narrow X-ray lines of known energy such as those expected
from Type 1 supernova. The UV monitor is a three telescope system that
provides coverage in the ultraviolet band for study of time correlated
changes across the broad electromagnetic spectrum of an AGN such as
are expected in “reverberation” models. A WWW page will be created as
a public bulletin board. This work is supported by NASA grant NAG8-1194
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Title: New Observations of the Optical Spectrum of SiO + and the
Prediction of Its Rotational Spectrum
Authors: Zhang, L.; Cameron, R.; Holt, R. A.; Scholl, T. J.; Rosner,
S. D.
1993ApJ...418..307Z Altcode:
The (0, 0) and (1, 0) bands of the
B<SUP>2</SUP>Σ<SUP>+</SUP>-Χ<SUP>2</SUP>Σ<SUP>+</SUP> system of
<SUP>28</SUP>Si<SUP>16</SUP>O<SUP>+</SUP> have been observed with
very high resolution using the technique of laser-induced fluorescence
from a mass-selected fast ion beam. The data yield values of the υ"
= 0 rotational and fine-structure constants with an improvement in
precision by about an order of magnitude over earlier work. This makes
it possible to predict the frequencies of pure rotational transitions
within this vibrational level at a level of precision that allows
unambiguous comparison with molecular lines observed in interstellar
clouds. In particular, the transition (J = 5/2, N = 2) → (J = 3/2,
N = 1), which has been considered as the source of the observed U86.2
line at 86,243.45(40) MHz, is predicted to occur at 86,037(6) MHz.
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Title: Search for solar axions
Authors: Lazarus, D. M.; Smith, G. C.; Cameron, R.; Melissinos, A. C.;
Ruoso, G.; Semertzidis, Y. K.; Nezrick, F. A.
1992PhRvL..69.2333L Altcode:
We have searched for a flux of axions produced in the Sun by exploiting
their conversion to x rays in a static magnetic field. The signature of
a solar axion flux would be an increase in the rate of x rays detected
in a magnetic telescope when the Sun passes within its acceptance. From
the absence of such a signal we set a 3σ limit on the axion coupling
to two photons g<SUB>aγγ</SUB>≡1/M<3.6×10<SUP>-9</SUP>
GeV<SUP>-1</SUP>, provided the axion mass m<SUB>a</SUB><0.03
eV and <7.7×10<SUP>-9</SUP> GeV<SUP>-1</SUP> for 0.03
<m<SUB>a</SUB><0.11 eV.
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Title: GRO J0422+32
Authors: Harmon, B. A.; Wilson, R. B.; Fishman, G. J.; Meegan, C. A.;
Paciesas, W. S.; Briggs, M. S.; Finger, M. H.; Cameron, R.; Kroeger,
R.; Grove, E.
1992IAUC.5584....2H Altcode: 1992IAUC.5584....1H
B. A. Harmon, R. B. Wilson, G. J. Fishman, and C. A. Meegan, Marshall
Space Flight Center, NASA; W. S. Paciesas and M. S. Briggs, University
of Alabama, Huntsville; M. H. Finger, Computer Sciences Corporation;
R. Cameron, Universities Space Research Association; and R. Kroeger,
and E. Grove, Naval Research Laboratory, report for BATSE and OSSE:
"The hard x-ray/gamma-ray transient discovered by the BATSE experiment
on the Compton Observatory (IAUC 5580) continued to emit at high
intensity, about 3 Crab (40-230 keV), over the past three days. The
Observatory was re-pointed on Aug. 11.07 UT, so that the source is
observable by all four Compton instruments. An improved location based
on combined BATSE and OSSE data is R.A. = 4h22m.1, Decl. = +32 49'
(equinox J2000.0; uncertainty radius of 0.2 deg). A significant flux
is seen to at least 500 keV, with a hard spectrum. The source continues
to show strong variability on all timescales."
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Title: GRO/OSSE Observations of Nuclear Line Emission from the
Intense Flares of June 1991
Authors: Murphy, R. J.; Share, G. H.; Johnson, W. N.; Kinzer, R. L.;
Kroeger, R.; Kurfess, J. D.; Strickman, M. S.; Grove, J. E.; Cameron,
R.; Jung, G.; Grabelsky, D.; Matz, S. M.; Purcell, W.; Ulmer, M. P.;
Frye, G.; Jenkins, T.; Jensen, C.
1992AAS...180.3407M Altcode: 1992BAAS...24Q.784M
The Oriented Scintillation Spectroscopy Experiment (OSSE) on the
Compton Gamma Ray Observatory is comprised of 4 independently-oriented
large-area ( ~ 500 cm(2) /detector at 511 keV) NaI detectors
covering the energy range from 0.050 to 10 MeV. Solar observations
are typically performed with two of the detectors staring at the Sun
and two alternating between viewing the Sun and viewing background
regions on two-minute timescales. In June of 1991, OSSE observed 4
of the X10+ flares from Active Region 6659. Intense gamma-ray line
emission at 0.511 MeV (positron annihilation) and 2.223 MeV (neutron
capture), and from several deexcitation lines of carbon and oxygen
were recorded. Using a combination of data from sunward-pointing
and off-pointing detectors to avoid saturation effects during the
intense portions of the flares, background-subtracted spectra have
been obtained. These spectra were fit to derive photon fluxes for
the above-mentioned gamma-ray lines. Preliminary lower limits to the
integrated fluxes in the 2.223 MeV line (not accounting for saturation
effects and based on data collected only during the OSSE observation
times) are about 300, 200, 30 and 100 photons/cm(2) for the June 4, 6,
9 and 11 flares, respectively. This is to be compared to a fluence of
about 300 photons/cm(2) for the 1982 June 3 flare observed by the SMM
Gamma-Ray Spectrometer. Integrated fluxes for the other lines will be
presented and compared to line flux measurements of flares obtained
with the SMM/GRS. This work is supported under NASA contract S10987C.
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Title: GRO/OSSE Observations of the Intense June 1991 Flares from
AR 6659
Authors: Share, G. H.; Murphy, R. J.; Johnson, W. N.; Kinzer, R. L.;
Kroeger, R.; Kurfess, J. D.; Strickman, M. S.; Cameron, R.; Jung,
G.; Grabelsky, D.; Matz, S. M.; Purcell, W.; Ulmer, M. P.; Frye, G.;
Jenkins, T.; Jensen, C.
1991BAAS...23.1388S Altcode:
No abstract at ADS
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Title: A search for the coherent production of axions in the milli
eV range
Authors: Cameron, R.; Melissinos, A. C.; Semertzidis, Y.; Cantatore,
G.; Rizzo, C.; Ruoso, P.; Zavattini, E.; Halama, H.; Lazarus, D.
1991pafi.rept...18C Altcode:
Axions provide a natural explanation for the absence of CP violation
in the strong interaction. As weakly interacting light particles they
are also candidates for the much sought after dark matter allegedly
responsible for our lack of understanding of galactic dynamics. Beam
dump, particle decay and astrophysical measurements carried out over the
past decade have failed to provide positive evidence for their existence
over a wide range of masses and coupling strengths. This experiment
attempts to produce and detect scalar and pseudoscalar particles
coherently produced through the interaction of laser photons with the
virtual photons of the magnetic fields of superconducting dipole magnets
as manifested by small changes in the polarization state of the laser
light. A limit on the coupling of the axion to 2 photons of g(sub a
gamma gamma) less than 6.67 x 10(exp -7) GeV(exp -1) was achieved.
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Title: An Experiment to Produce Light Pseudoscalars and QED Vacuum
Polarization
Authors: Semertzidis, Y.; Cameron, R.; Cantatore, G.; Melissions,
A. C.; Rogers, J. T.; Halama, H. J.; Moskowitz, B. E.; Prodell, A. G.;
Nezrick, F. A.; Zavattini, E.
1990coax.conf..137S Altcode:
No abstract at ADS
