wedemeyer

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Author name code: wedemeyer
ADS astronomy entries on 2022-09-14
author:"Wedemeyer-Boehm, Sven" OR author:"Wedemeyer, Sven"

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Title: Propagation of transverse waves in the solar chromosphere
probed at different heights with ALMA sub-bands
Authors: Guevara Gómez, Juan Camilo; Jafarzadeh, Shahin; Wedemeyer,
Sven; Szydlarski, Mikolaj
2022arXiv220812070G Altcode:
The Atacama Large Millimeter/sub-millimeter Array (ALMA) has provided
us with an excellent diagnostic tool for studies of the dynamics of
the Solar chromosphere, albeit through a single receiver band at one
time presently. Each ALMA band consists of four sub-bands that are
comprised of several spectral channels. To date, however, the spectral
domain has been neglected in favour of ensuring optimal imaging, so
that time-series observations have been mostly limited to full-band
data products, thereby limiting studies to a single chromospheric
layer. Here, we report the first observations of a dynamical event
(i.e. wave propagation) for which the ALMA Band 3 data (centred at
3\,mm; 100\,GHz) is split into a lower and an upper sideband. In
principle, this approach is aimed at mapping slightly different
layers in the Solar atmosphere. The side-band data were reduced
together with the Solar ALMA Pipeline (SoAP), resulting in time
series of brightness-temperature maps for each side-band. Through a
phase analysis of a magnetically quiet region, where purely acoustic
waves are expected to dominate, the average height difference between
the two side-bands is estimated as $73\pm16$~km. Furthermore, we
examined the propagation of transverse waves in small-scale bright
structures by means of wavelet phase analysis between oscillations at
the two atmospheric heights. We find 6\% of the waves to be standing,
while 54\% and 46\% of the remaining waves are propagating upwards and
downwards, respectively, with absolute propagating speeds on the order
of $\approx96$~km/s, resulting in a mean energy flux of $3800$\,W/m$^2$.

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Title: EMISSA (Exploring millimetre indicators of solar-stellar
activity). II. Towards a robust indicator of stellar activity
Authors: Mohan, A.; Wedemeyer, S.; Hauschildt, P. H.; Pandit, S.;
Saberi, M.
2022A&A...664L...9M Altcode: 2022arXiv220804217M
Context. An activity indicator, which can provide a robust quantitative
mapping between the stellar activity and the physical properties of its
atmosphere, is important in exploring the evolution of the observed
active phenomena across main-sequence stars of different spectral
types. Common activity indicators do provide qualitative correlations
with physical properties such as Teff and the rotation
period, among others. However, due to the large variability in their
values, even for a single star, defining robust quantitative mappings
between activity and physical properties is difficult. Millimetre
(mm) wavelengths probe the different atmospheric layers within the
stellar chromosphere, providing a tomographic view of the atmospheric
dynamics. Aims: The project aims to define a robust activity
indicator by characterising mm brightness temperature spectra
(TB(ν)) of the cool main-sequence stars (Teff
∼ 5000-7000 K) compiled by Paper I in this series. The sample
contains 13 stars, including the Sun. Methods: We derived
the mm TB(ν) spectral indices (αmm) for
cool stars, including the Sun, based on observations in the 30-1000
GHz range. The derived values for αmm are explored as
a function of various physical parameters and empirical power-law
functions were derived. We also compared αmm estimates
with other activity indicators. Results: Despite the estimation
errors, αmm values could distinguish the cool stars well,
unlike common activity indicators. The low estimation errors on the
derived trends of αmm vs. physical parameters suggest
that αmm could be a robust activity indicator. Conclusions: We note that αmm, which is linked to
chromospheric thermal stratification and activity in cool stars,
can well distinguish and physically characterise the stars more
robustly than common activity indicators. We emphasise the need for
multi-frequency data across the mm band for stars, with a range of
physical parameters and gathered at multiple epochs during their
activity cycles. This will help to explore αmm in a
statistically robust manner and to study the emergence of chromospheric
heating on the main sequence.

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Title: Characterisation of bright chromospheric and oscillating
small-scale features observed with ALMA
Authors: Guevara Gómez, Juan Camilo; Jafarzadeh, Shahin; Wedemeyer,
Sven
2022cosp...44.2549G Altcode:
Small-scale chromospheric bright features exhibiting oscillations in
brightness temperature, size and horizontal velocity were identified
and traced in both solar ALMA observations in Bands 3 ($\sim$3
mm) and 6 ($\sim$1.2 mm) and in a Bifrost simulation resembling
the ALMA observation. In total, 492 and 175 features were present
in the observations and simulation respectively. Particularly, an
anti-correlation between brightness temperature and size is present in
the oscillations which might imply that these features are associated
with fast-sausage MHD modes. We have performed a wavelet analysis to
quantify the periods of oscillation for these three quantities as
well as the phase angles between temperature and size. The outcome
of a statistical analysis shows that the found periods correspond
to high frequency oscillations in photosphere and chromosphere by
diagnostics at other wavelengths. We have also estimated the energy
carried by these waves and discussed the results from a statistical
point of view. Specifically, we compared the outcomes between the
the two ALMA frequency bands as they are considered to be formed at
distinct heights and used the simulation to discuss the context of
the observational results.

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Title: Formation of activity indicators in a 3D model atmosphere
Authors: Pandit, Sneha; Wedemeyer, Sven
2022cosp...44.2555P Altcode:
The Sun, being the nearest star, can be used as a reference case for
solar-like stars due to the availability of many spatiotemporally
resolved solar spectra. Amongst several spectral lines, some of
the strongest chromospheric diagnostics are the Ca II H &amp; K
lines which can be used to gauge the temperature stratification of
the atmosphere as the line core and wings are formed in different
regions of the solar atmosphere. Furthermore, the H$\alpha$ line
is a tracer for the magnetic structures and its line core gives an
estimate of the mass density. These two diagnostics together can
provide insights into the stellar structure. The 1.5D radiation
transfer codes RH and Multi3D are used to obtain synthetic spectra
for the Ca II lines and the H$\alpha$ line from an enhanced network
atmosphere model simulated with the state-of-the-art Bifrost code. The
activity indices generated from these lines could further be used to
compare the spectra of sun-like stars with the solar spectrum. These
indices can shed light on the physical properties like temperature
stratification, magnetic structures, mass density distribution in the
stellar atmospheres. Meanwhile, brightness temperatures from ALMA
observations provide a new complementary view on the activity and
the thermal structure of stellar atmospheres. The synthetic Ca II and
H$\alpha$ spectra are therefore compared to corresponding millimetre
continuum maps. The overall aim of the presented study is to establish
more robust solar/stellar activity indicators using ALMA observations
in comparison with classical diagnostics.

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Title: Solar/Stellar atmospheric tomography with mm - cm data:
Initial catalogue of main sequence stars and results
Authors: Mohan, Atul; Wedemeyer, Sven; Pandit, Sneha; Saberi, Maryam;
Hauschildt, Peter
2022cosp...44.2495M Altcode:
Millimeter - Centimeter (10 - 1000 GHz) bands are particularly
sensitive to emission from various outer atmospheric layers of main
sequence stars, with shorter wavelengths probing deeper layers. This
makes the study of mm - cm spectra (S$_{obs}$) a unique tool to study
the vertical atmospheric stratification of these stars as a function
of various physical parameters. A major challenge in the field of mm
astronomy had been the lack of a sensitive interferometer which can not
only detect the faint $\sim$ 10 - 100 $\mu$Jy level atmospheric fluxes
robustly from these stars, but also provide enough spatial resolution
needed to distinguish any emission from companion stars and stellar
disks. With the advent of the Atacama Large Millimeter/Sub-millimeter
array, the aforementioned hurdles have been overcome to a great extent
for at least the stars within a distance of 10\,pc.\\ In this work, we
gathered the archival data of main sequence stars robustly detected with
ALMA, and additionally reported 10 - 80 GHz fluxes if any, from other
modern interferometric arrays like ATCA, JVLA etc. The data for the Sun
were also gathered and the disk-averaged fluxes were recorded to get
the sun-as-a-star spectrum. The resulting sample comprises of 12 main
sequence stars plus the sun-as-a-star covering an effective temperature
(T$_{eff}$) range of 3000 - 10000 K. We compared their observed fluxes
against respective purely photospheric model fluxes obtained using the
PHOENIX code (S$_{model}$) and obtained the upper atmospheric excess
energy spectrum ($\Delta$S/S$_{model}$ = S$_{obs}$/S$_{model}$ - 1
). We find evidence for a stratified atmosphere which gets progressively
hotter with height in cool stars (T$_{eff}$ &lt; 7000 K). The spectral
index of the observed mm-cm brightness spectrum, was characterised
for every star in the sample with sufficient data. The steepness was
found to decrease with T$_{eff}$, possibly hinting at steeper thermal
gradients in cooler stars. This study demonstrates the potential of mm
- cm band diagnostics to perform atmospheric tomography in cool stars
and that long duration light curves for these stars can be powerful
tools for studying the dynamics across different layers. This calls
for the need to have dedicated long duration surveys of nearby cool
stars in mm - cm bands assisted by state of the art modelling to better
understand the nature of atmospheric stratification and dynamics in
cool stars as a function of stellar type.

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Title: First detection of AlF line emission towards M-type AGB stars
Authors: Saberi, M.; Khouri, T.; Velilla-Prieto, L.; Fonfría, J. P.;
Vlemmings, W. H. T.; Wedemeyer, S.
2022A&A...663A..54S Altcode: 2022arXiv220403284S
The nucleosynthesis production of fluorine (F) is still a matter
of debate. Asymptotic giant branch (AGB) stars are one of the main
candidates for F production. However, their contribution to the total
F budget is not fully known due to the lack of observations. In this
paper, we report the detection of aluminium monofluoride (AlF) line
emission, one of the two main carriers of F in the gas-phase in the
outflow of evolved stars, towards five nearby oxygen-rich (M-type)
AGB stars. We studied the Atacama large millimetre/sub-millimetre
array (ALMA) observations of AlF (v = 0, J = 4—3, 9-8, 10-9,
and 15-14) and (v = 1, J = 7-6) line emission towards o Ceti, and
(v = 0, J = 7-6 and 15-14) lines towards R Leo. We also report a
tentative detection of AlF (v = 0, J = 7-6) line in IK Tau, (v = 0,
J = 15-14) line towards R Dor, and (v = 0, J = 7-6 and J = 15-14)
lines in W Hya. From spatially resolved observations, we estimated
the AlF emitting region with a radius ~11R⋆ for o Ceti
and ~9R⋆ for R Leo. From population diagram analysis,
we report the AlF column densities of ~5.8 × 1015
cm−2 and ~3 × 1015 cm−2
for o Ceti and R Leo, respectively, within these regions. For o
Ceti, we used the C18O (v = 0, J = 3-2) observations to
estimate the H2 column density of the emitting region. We
found a fractional abundance of fAIF/H2 ~ (2.5 ± 1.7)
× 10−8. This gives a lower limit on the F budget in
o Ceti and is compatible with the solar F budget fF/H2
= (5 ± 2) × 10−8. For R Leo, a fractional abundance
fAIF/H2 = (1.2 ± 0.5) × 10−8 is estimated. For
other sources, we cannot precisely determine the emitting region
based on the available data. Assuming an emitting region with a
radius of ~11R⋆ and the rotational temperatures derived
for o Ceti and R Leo, we crudely approximated the AlF column density
to be ~(1.2−1.5) × 1015 cm−2 in W Hya,
~(2.5−3.0) × 1014 cm−2 in R Dor, and
~(0.6−1.0) × 1016 cm−2 in IK Tau. These
result in fractional abundances within a range of fAIF/H2 ~
(0.1 − 4) × 10−8 in W Hya, R Dor, and IK Tau.

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Title: The Atacama Large Aperture Submillimeter Telescope: Key
science drivers
Authors: Ramasawmy, Joanna; Klaassen, Pamela D.; Cicone, Claudia;
Mroczkowski, Tony K.; Chen, Chian-Chou; Cornish, Thomas; Lima da Cunha,
Elisabete; Hatziminaoglou, Evanthia; Johnstone, Doug; Liu, Daizhong;
Perrott, Yvette; Schimek, Alice; Stanke, Thomas; Wedemeyer, Sven
2022arXiv220703914R Altcode:
The Atacama Large Aperture Submillimeter Telescope (AtLAST) is
a concept for a 50m class single-dish telescope that will provide
high sensitivity, fast mapping of the (sub-)millimeter sky. Expected
to be powered by renewable energy sources, and to be constructed
in the Atacama desert in the 2030s, AtLAST's suite of up to six
state-of-the-art instruments will take advantage of its large field
of view and high throughput to deliver efficient continuum and
spectroscopic observations of the faint, large-scale emission that
eludes current facilities. Here we present the key science drivers
for the telescope characteristics, and discuss constraints that the
transformational science goals place on future instrumentation.

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Title: A Genetic Algorithm to Model Solar Radio Active Regions From
3D Magnetic Field Extrapolations
Authors: de Oliveira e Silva, Alexandre José; Selhorst, Caius Lucius;
Costa, Joaquim E. R.; Simões, Paulo J. A.; Giménez de Castro,
Carlos Guillermo; Wedemeyer, Sven; White, Stephen M.; Brajša, Roman;
Valio, Adriana
2022FrASS...9.1118D Altcode: 2022arXiv220503385S; 2022arXiv220503385J
In recent decades our understanding of solar active regions (ARs)
has improved substantially due to observations made with better
angular resolution and wider spectral coverage. While prior AR
observations have shown that these structures were always brighter
than the quiet Sun at centimeter wavelengths, recent observations
at millimeter and submillimeter wavelengths have shown ARs with well
defined dark umbrae. Given this new information, it is now necessary to
update our understanding and models of the solar atmosphere in active
regions. In this work, we present a data-constrained model of the AR
solar atmosphere, in which we use brightness temperature measurements
of NOAA 12470 at three radio frequencies: 17, 100 and 230 GHz. The
observations at 17 GHz were made by the Nobeyama Radioheliograph (NoRH),
while the observations at 100 and 230 GHz were obtained by the Atacama
Large Millimeter/submillimeter Array (ALMA). Based on our model, which
assumes that the radio emission originates from thermal free-free and
gyroresonance processes, we calculate radio brightness temperature
maps that can be compared with the observations. The magnetic field at
distinct atmospheric heights was determined in our modelling process by
force-free field extrapolation using photospheric magnetograms taken by
the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory (SDO). In order to determine the best plasma temperature
and density height profiles necessary to match the observations,
the model uses a genetic algorithm that modifies a standard quiet Sun
atmospheric model. Our results show that the height of the transition
region (TR) of the modelled atmosphere varies with the type of region
being modelled: for umbrae the TR is located at 1080 ± 20 km above
the solar surface; for penumbrae, the TR is located at 1800 ± 50 km;
and for bright regions outside sunspots, the TR is located at 2000 ±
100 km. With these results, we find good agreement with the observed
AR brightness temperature maps. Our modelled AR can be used to estimate
the emission at frequencies without observational coverage.

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Title: Power distribution of oscillations in the atmosphere of a
plage region. Joint observations with ALMA, IRIS, and SDO
Authors: Narang, Nancy; Chandrashekhar, Kalugodu; Jafarzadeh, Shahin;
Fleck, Bernhard; Szydlarski, Mikołaj; Wedemeyer, Sven
2022A&A...661A..95N Altcode: 2022arXiv220211547N
Context. Joint observations of the Atacama Large
Millimeter/Submillimeter Array (ALMA) with other solar observatories
can provide a wealth of opportunities for understanding the coupling
between different layers of the solar atmosphere. Aims: We
present a statistical analysis of the power distribution of oscillations
in a plage region in active region NOAA AR12651, which was observed
jointly with ALMA, the Interface Region Imaging Spectrograph (IRIS),
and the Solar Dynamics Observatory (SDO). Methods: We employ
coordinated ALMA Band 6 (1.25 mm) brightness temperature maps,
IRIS slit-jaw images in the 2796 Å passband, and observations in
six passbands (1600 Å, 304 Å, 131 Å, 171 Å, 193 Å, and 211 Å)
from the Atmospheric Imaging Assembly (AIA) on board SDO. We perform
Lomb-Scargle transforms to study the distribution of oscillation power
by means of dominant period maps and power maps. We study the spatial
association of oscillations through the atmosphere, with a focus on
the correlation of the power distribution of ALMA oscillations with
others. Results: We do not observe any significant association
of ALMA oscillations with IRIS and AIA oscillations. While the global
behavior of the dominant ALMA oscillations shows a similarity with
that of the transition region and coronal passbands of AIA, the ALMA
dominant period maps and power maps do not show any correlation with
those from the other passbands. The spatial distribution of dominant
periods and power in different period intervals of ALMA oscillations
is uncorrelated with those of any other passbands. Conclusions:
We speculate that the non-association of ALMA oscillations with those
of IRIS and AIA is due to significant variations in the height of
formation of the millimeter continuum observed by ALMA. Additionally,
the fact that ALMA directly maps the brightness temperature, in contrast
to the intensity observations by IRIS and AIA, can result in the very
different intrinsic nature of the ALMA oscillations compared to the
IRIS and AIA oscillations.

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Title: The Solar ALMA Science Archive (SALSA). First release, SALAT,
and FITS header standard
Authors: Henriques, Vasco M. J.; Jafarzadeh, Shahin; Guevara Gómez,
Juan Camilo; Eklund, Henrik; Wedemeyer, Sven; Szydlarski, Mikołaj;
Haugan, Stein Vidar H.; Mohan, Atul
2022A&A...659A..31H Altcode: 2021arXiv210902374H
In December 2016, the Atacama Large Millimeter/submillimeter Array
(ALMA) carried out the first regular observations of the Sun. These
early observations and the reduction of the respective data posed a
challenge due to the novelty and complexity of observing the Sun with
ALMA. The difficulties with producing science-ready, time-resolved
imaging products in a format familiar to and usable by solar physicists
based on the measurement sets delivered by ALMA had limited the
availability of such data to this point. With the development of the
Solar ALMA Pipeline, it has now become possible to routinely reduce
such data sets. As a result, a growing number of science-ready solar
ALMA data sets are now offered in the form of the Solar ALMA Science
Archive (SALSA). So far, SALSA contains primarily time series of
single-pointing interferometric images at cadences of one or two
seconds, accompanied by the respective single-dish full-disc solar
images. The data arrays are provided in FITS format. We also present
the first version of a standardised header format that accommodates
future expansions and fits within the scope of other standards
including the ALMA Science Archive itself and SOLARNET. The headers
include information designed to aid the reproduction of the imaging
products from the raw data. Links to co-observations, if available,
with a focus on those of the Interface Region Imaging Spectrograph,
are also provided. SALSA is accompanied by the Solar ALMA Library of
Auxiliary Tools (SALAT), which contains Interactive Data Language and
Python routines for convenient loading and a quick-look analysis of
SALSA data. Movies associated to Figs. 3 and 4 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202142291/olm">https://www.aanda.org</A>

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Title: Final Report for SAG 21: The Effect of Stellar Contamination
on Space-based Transmission Spectroscopy
Authors: Rackham, Benjamin V.; Espinoza, Néstor; Berdyugina, Svetlana
V.; Korhonen, Heidi; MacDonald, Ryan J.; Montet, Benjamin T.; Morris,
Brett M.; Oshagh, Mahmoudreza; Shapiro, Alexander I.; Unruh, Yvonne C.;
Quintana, Elisa V.; Zellem, Robert T.; Apai, Dániel; Barclay, Thomas;
Barstow, Joanna K.; Bruno, Giovanni; Carone, Ludmila; Casewell, Sarah
L.; Cegla, Heather M.; Criscuoli, Serena; Fischer, Catherine; Fournier,
Damien; Giampapa, Mark S.; Giles, Helen; Iyer, Aishwarya; Kopp, Greg;
Kostogryz, Nadiia M.; Krivova, Natalie; Mallonn, Matthias; McGruder,
Chima; Molaverdikhani, Karan; Newton, Elisabeth R.; Panja, Mayukh;
Peacock, Sarah; Reardon, Kevin; Roettenbacher, Rachael M.; Scandariato,
Gaetano; Solanki, Sami; Stassun, Keivan G.; Steiner, Oskar; Stevenson,
Kevin B.; Tregloan-Reed, Jeremy; Valio, Adriana; Wedemeyer, Sven;
Welbanks, Luis; Yu, Jie; Alam, Munazza K.; Davenport, James R. A.;
Deming, Drake; Dong, Chuanfei; Ducrot, Elsa; Fisher, Chloe; Gilbert,
Emily; Kostov, Veselin; López-Morales, Mercedes; Line, Mike; Močnik,
Teo; Mullally, Susan; Paudel, Rishi R.; Ribas, Ignasi; Valenti, Jeff A.
2022arXiv220109905R Altcode:
Study Analysis Group 21 (SAG21) of the Exoplanet Exploration Program
Analysis Group (ExoPAG) was organized to study the effect of stellar
contamination on space-based transmission spectroscopy, a method for
studying exoplanetary atmospheres by measuring the wavelength-dependent
radius of a planet as it transits its star. Transmission spectroscopy
relies on a precise understanding of the spectrum of the star being
occulted. However, stars are not homogeneous, constant light sources
but have temporally evolving photospheres and chromospheres with
inhomogeneities like spots, faculae, and plages. This SAG has brought
together an interdisciplinary team of more than 100 scientists, with
observers and theorists from the heliophysics, stellar astrophysics,
planetary science, and exoplanetary atmosphere research communities,
to study the current needs that can be addressed in this context to
make the most of transit studies from current NASA facilities like
HST and JWST. The analysis produced 14 findings, which fall into
three Science Themes encompassing (1) how the Sun is used as our best
laboratory to calibrate our understanding of stellar heterogeneities
("The Sun as the Stellar Benchmark"), (2) how stars other than the Sun
extend our knowledge of heterogeneities ("Surface Heterogeneities of
Other Stars") and (3) how to incorporate information gathered for the
Sun and other stars into transit studies ("Mapping Stellar Knowledge
to Transit Studies").

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Title: The Sun at millimeter wavelengths. III. Impact of the spatial
resolution on solar ALMA observations
Authors: Eklund, Henrik; Wedemeyer, Sven; Szydlarski, Mikołaj;
Jafarzadeh, Shahin
2021A&A...656A..68E Altcode: 2021arXiv210913826E
Context. Interferometric observations of the Sun with the Atacama
Large Millimeter/sub-millimeter Array (ALMA) provide valuable
diagnostic tools for studying the small-scale dynamics of the solar
atmosphere. Aims: The aims are to perform estimations of the
observability of the small-scale dynamics as a function of spatial
resolution for regions with different characteristic magnetic field
topology facilitate a more robust analysis of ALMA observations
of the Sun. Methods: A three-dimensional model of the solar
atmosphere from the radiation-magnetohydrodynamic code Bifrost was used
to produce high-cadence observables at millimeter and submillimeter
wavelengths. The synthetic observables for receiver bands 3-10 were
degraded to the angular resolution corresponding to ALMA observations
with different configurations of the interferometric array from the
most compact, C1, to the more extended, C7. The observability of
the small-scale dynamics was analyzed in each case. The analysis
was thus also performed for receiver bands and resolutions that
are not commissioned so far for solar observations as a means for
predicting the potential of future capabilities. Results:
The minimum resolution required to study the typical small spatial
scales in the solar chromosphere depends on the characteristic
properties of the target region. Here, a range from quiet Sun to
enhanced network loops is considered. Limited spatial resolution
affects the observable signatures of dynamic small-scale brightening
events in the form of reduced brightness temperature amplitudes,
potentially leaving them undetectable, and even shifts in the times
at which the peaks occur of up to tens of seconds. Conversion factors
between the observable brightness amplitude and the original amplitude
in the fully resolved simulation are provided that can be applied to
observational data in principle, but are subject to wavelength-dependent
uncertainties. Predictions of the typical appearance at the different
combinations of receiver band, array configuration, and properties of
the target region are conducted. Conclusions: The simulation
results demonstrate the high scientific potential that ALMA already has
with the currently offered capabilities for solar observations. For the
study of small-scale dynamic events, however, the spatial resolution
is still crucial, and wide array configurations are preferable. In
any case, it is essential to take the effects due to limited spatial
resolution into account in the analysis of observational data. Finally,
the further development of observing capabilities including wider
array configurations and advanced imaging procedures yields a high
potential for future ALMA observations of the Sun.

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Title: EMISSA (Exploring Millimeter Indicators of Solar-Stellar
Activity). I. The initial millimeter-centimeter main-sequence
star sample
Authors: Mohan, A.; Wedemeyer, S.; Pandit, S.; Saberi, M.; Hauschildt,
P. H.
2021A&A...655A.113M Altcode: 2021arXiv211013339M
Context. Due to their wide wavelength coverage across the millimeter
to centimeter (mm-cm) range and their increased sensitivity, modern
interferometric arrays facilitate observations of the thermal and
non-thermal radiation that is emitted from different layers in the
outer atmospheres of stars. Aims: We study the spectral energy
distribution (Sobs(ν)) of main-sequence stars based on
archival observations in the mm-cm range with the aim to study their
atmospheric stratification as a function of stellar type. 
Methods: The main-sequence stars with significant detection in mm
bands were identified in the ALMA Science Archive. These data were
then complemented with spectral flux data in the extreme ultraviolet
to cm range as compiled from various catalogues and observatory
archives. We compared the resultant Sobs(ν) of each star
with a photospheric emission model (Smod(ν)) calculated
with the PHOENIX code. The departures of Sobs(ν) from
Smod(ν) were quantified in terms of a spectral flux
excess parameter (ΔS∕Smod) and studied as a function
of stellar type. Results: The initial sample consists of 12
main-sequence stars across a broad range of spectral types from
A1 to M3.5 and the Sun-as-a-star as reference. The stars with
Teff = 3000-7000 K (F-M type) showed a systematically
higher Sobs(ν) than Smod(ν) in the mm-cm
range. Their ΔS∕Smod exhibits a monotonic rise with
decreasing frequency. The steepness of this rise is higher for cooler
stars in the Teff = 3000-7000 K range, although the single
fully convective star (Teff ~ 3000 K) in the sample deviates
from this trend. Meanwhile, Sobs(ν) of the A-type stars
agrees with Smod(ν) within errors. Conclusions:
The systematically high ΔS∕Smod in F-M stars indicates
hotter upper atmospheric layers, that is, a chromosphere and corona in
these stars, like for the Sun. The mm-cm ΔS∕Smod spectrum
offers a way to estimate the efficiency of the heating mechanisms
across various outer atmospheric layers in main-sequence stars, and
thereby to understand their structure and activity. We emphasise the
need for dedicated surveys of main-sequence stars in the mm-cm range.

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Title: Dynamics of small-scale dark features observed by the Atacama
Large Millimeter/Submillimeter Array (ALMA)
Authors: Guevara Gómez, Juan Camilo; Wedemeyer, Sven
2021csss.confE.227G Altcode:
Observations of the Sun with the Atacama Large Millimeter/submillimeter
Array (ALMA) now allow for more quantitative determination of
temperatures in the chromosphere. ALMA observations of Quiet Sun regions
in receiver Band 3 (3 mm; 100 GHz) exhibit small-scale features that
resemble a mesh-like chromospheric pattern, similar to what was earlier
detected with other chromospheric diagnostics. Tracking the features
in time results in lifetimes, velocities and sizes, which are analysed
within the context given by co-aligned images of the Solar Dynamics
Observatory (SDO). Here we present a statistical analysis and compare
the results with a 3D MHD simulation with Bifrost of an enhanced
network which has been degraded to the ALMA spatial resolution. The
match between observations and simulations suggests that the dark
features are post-shock regions. The thermodynamics and kinetic
properties derived from the ALMA observations will therefore enhance
our understanding of the small-scale dynamics and heating of the solar
chromosphere and its potential implications for other solar-like stars.

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Title: An overall view of temperature oscillations in the solar
chromosphere with ALMA
Authors: Jafarzadeh, S.; Wedemeyer, S.; Fleck, B.; Stangalini, M.;
Jess, D. B.; Morton, R. J.; Szydlarski, M.; Henriques, V. M. J.; Zhu,
X.; Wiegelmann, T.; Guevara Gómez, J. C.; Grant, S. D. T.; Chen,
B.; Reardon, K.; White, S. M.
2021RSPTA.37900174J Altcode: 2021RSTPA.379..174J; 2020arXiv201001918J
By direct measurements of the gas temperature, the Atacama Large
Millimeter/submillimeter Array (ALMA) has yielded a new diagnostic
tool to study the solar chromosphere. Here, we present an overview
of the brightness-temperature fluctuations from several high-quality
and high-temporal-resolution (i.e. 1 and 2 s cadence) time series
of images obtained during the first 2 years of solar observations
with ALMA, in Band 3 and Band 6, centred at around 3 mm (100 GHz)
and 1.25 mm (239 GHz), respectively. The various datasets represent
solar regions with different levels of magnetic flux. We perform
fast Fourier and Lomb-Scargle transforms to measure both the spatial
structuring of dominant frequencies and the average global frequency
distributions of the oscillations (i.e. averaged over the entire field
of view). We find that the observed frequencies significantly vary from
one dataset to another, which is discussed in terms of the solar regions
captured by the observations (i.e. linked to their underlying magnetic
topology). While the presence of enhanced power within the frequency
range 3-5 mHz is found for the most magnetically quiescent datasets,
lower frequencies dominate when there is significant influence from
strong underlying magnetic field concentrations (present inside and/or
in the immediate vicinity of the observed field of view). We discuss
here a number of reasons which could possibly contribute to the power
suppression at around 5.5 mHz in the ALMA observations. However,
it remains unclear how other chromospheric diagnostics (with an
exception of Hα line-core intensity) are unaffected by similar
effects, i.e. they show very pronounced 3-min oscillations dominating
the dynamics of the chromosphere, whereas only a very small fraction
of all the pixels in the 10 ALMA datasets analysed here show peak power
near 5.5 mHz. This article is part of the Theo Murphy meeting issue
`High-resolution wave dynamics in the lower solar atmosphere'.

---------------------------------------------------------
Title: High-frequency oscillations in small chromospheric bright
features observed with Atacama Large Millimetre/Submillimetre Array
Authors: Guevara Gómez, J. C.; Jafarzadeh, S.; Wedemeyer, S.;
Szydlarski, M.; Stangalini, M.; Fleck, B.; Keys, P. H.
2021RSPTA.37900184G Altcode: 2020arXiv200804179G
We report detection of oscillations in brightness temperature,
size and horizontal velocity of three small bright features in the
chromosphere of a plage/enhanced-network region. The observations,
which were taken with high temporal resolution (i.e. 2 s cadence)
with the Atacama large millimetre/ submillimetre array (ALMA) in Band
3 (centred at 3 mm; 100 GHz), exhibit three small-scale features with
oscillatory behaviour with different, but overlapping, distributions of
period on the order of, on average, 90 ± 22 s, 110 ± 12 s and 66 ±
23 s, respectively. We find anti-correlations between perturbations in
brightness, temperature and size of the three features, which suggest
the presence of fast sausage-mode waves in these small structures. In
addition, the detection of transverse oscillations (although with
a larger uncertainty) may also suggest the presence of Alfvénic
oscillations which are likely representative of kink waves. This work
demonstrates the diagnostic potential of high-cadence observations with
ALMA for detecting high-frequency magnetohydrodynamic waves in the
solar chromosphere. Such waves can potentially channel a vast amount
of energy into the outer atmosphere of the Sun. This article is
part of the Theo Murphy meeting issue `High-resolution wave dynamics
in the lower solar atmosphere'.

---------------------------------------------------------
Title: Characterization of shock wave signatures at millimetre
wavelengths from Bifrost simulations
Authors: Eklund, Henrik; Wedemeyer, Sven; Snow, Ben; Jess, David B.;
Jafarzadeh, Shahin; Grant, Samuel D. T.; Carlsson, Mats; Szydlarski,
Mikołaj
2021RSPTA.37900185E Altcode: 2020arXiv200805324E
Observations at millimetre wavelengths provide a valuable tool to study
the small-scale dynamics in the solar chromosphere. We evaluate the
physical conditions of the atmosphere in the presence of a propagating
shock wave and link that to the observable signatures in mm-wavelength
radiation, providing valuable insights into the underlying physics
of mm-wavelength observations. A realistic numerical simulation from
the three-dimensional radiative magnetohydrodynamic code Bifrost
is used to interpret changes in the atmosphere caused by shock wave
propagation. High-cadence (1 s) time series of brightness temperature
(Tb) maps are calculated with the Advanced Radiative Transfer
code at the wavelengths 1.309 mm and 1.204 mm, which represents opposite
sides of spectral band 6 of the Atacama Large Millimeter/submillimeter
Array (ALMA). An example of shock wave propagation is presented. The
brightness temperatures show a strong shock wave signature with large
variation in formation height between approximately 0.7 and 1.4 Mm. The
results demonstrate that millimetre brightness temperatures efficiently
track upwardly propagating shock waves in the middle chromosphere. In
addition, we show that the gradient of the brightness temperature
between wavelengths within ALMA band 6 can potentially be used as
a diagnostics tool in understanding the small-scale dynamics at the
sampled layers. This article is part of the Theo Murphy meeting
issue `High-resolution wave dynamics in the lower solar atmosphere'.

---------------------------------------------------------
Title: Dynamics of small-scale dark features observed by the Atacama
Large Millimeter/submillimeter Array (ALMA)
Authors: Guevara Gómez, Juan Camilo; Wedemeyer, Sven
2021cosp...43E.974G Altcode:
Solar ALMA observations exhibit small-scale features resembling the
mesh-like chromospheric pattern that was earlier detected with other
chromospheric diagnostics. In this work, we present a first statistical
study of the dynamics of dark features observed using ALMA Band 3
receivers (~3 mm; 100 GHz). By tracing the features in time, we estimate
their lifetimes, velocities and sizes, which are analysed within the
context given by co-aligned images of the Solar Dynamics Observatory
(SDO). Furthermore, the results are compared with those obtained from
applying the same method to a 3D MHD simulation with Bifrost of an
enhanced network which has been degraded to the ALMA spatial resolution.

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Title: ALMA and IRIS Observations of the Solar
Chromosphere. II. Structure and Dynamics of Chromospheric Plages
Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora,
Juan; Hansteen, Viggo; de la Cruz Rodríguez, Jaime; Szydlarski,
Mikolaj; Jafarzadeh, Shahin; Wedemeyer, Sven; Bastian, Timothy S.;
Sainz Dalda, Alberto
2021ApJ...906...83C Altcode: 2020arXiv201205970C
We propose and employ a novel empirical method for determining
chromospheric plage regions, which seems to better isolate a plage from
its surrounding regions than other methods commonly used. We caution
that isolating a plage from its immediate surroundings must be done
with care in order to successfully mitigate statistical biases that,
for instance, can impact quantitative comparisons between different
chromospheric observables. Using this methodology, our analysis suggests
that λ = 1.25 mm free-free emission in plage regions observed with
the Atacama Large Millimeter/submillimeter Array (ALMA)/Band6 may
not form in the low chromosphere as previously thought, but rather
in the upper chromospheric parts of dynamic plage features (such as
spicules and other bright structures), i.e., near geometric heights
of transition-region temperatures. We investigate the high degree of
similarity between chromospheric plage features observed in ALMA/Band6
(at 1.25 mm wavelengths) and the Interface Region Imaging Spectrograph
(IRIS)/Si IV at 1393 Å. We also show that IRIS/Mg II h and k are
not as well correlated with ALMA/Band6 as was previously thought,
and we discuss discrepancies with previous works. Lastly, we report
indications of chromospheric heating due to propagating shocks supported
by the ALMA/Band6 observations.

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Title: ALMA and IRIS Observations of the Solar Chromosphere. I. An
On-disk Type II Spicule
Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora,
Juan; Hansteen, Viggo; de la Cruz Rodríguez, Jaime; Szydlarski,
Mikolaj; Jafarzadeh, Shahin; Wedemeyer, Sven; Bastian, Timothy S.;
Sainz Dalda, Alberto
2021ApJ...906...82C Altcode: 2020arXiv200512717C
We present observations of the solar chromosphere obtained
simultaneously with the Atacama Large Millimeter/submillimeter Array
(ALMA) and the Interface Region Imaging Spectrograph. The observatories
targeted a chromospheric plage region of which the spatial distribution
(split between strongly and weakly magnetized regions) allowed the
study of linear-like structures in isolation, free of contamination
from background emission. Using these observations in conjunction with
a radiative magnetohydrodynamic 2.5D model covering the upper convection
zone all the way to the corona that considers nonequilibrium ionization
effects, we report the detection of an on-disk chromospheric spicule
with ALMA and confirm its multithermal nature.

---------------------------------------------------------
Title: ALMA and IRIS Observations Highlighting the Dynamics and
Structure of Chromospheric Plage
Authors: Chintzoglou, G.; De Pontieu, B.; Martinez-Sykora, J.;
Hansteen, V. H.; de la Cruz Rodriguez, J.; Szydlarski, M.; Jafarzadeh,
S.; Wedemeyer, S.; Bastian, T.; Sainz Dalda, A.
2020AGUFMSH0010009C Altcode:
We present observations of the solar chromosphere obtained
simultaneously with the Atacama Large Millimeter/submillimeter Array
(ALMA) and the Interface Region Imaging Spectrograph (IRIS). The
observatories targeted a chromospheric plage region of which the spatial
distribution (split between strongly and weakly magnetized regions)
allowed the study of linear-like structures in isolation, free of
contamination from background emission. Using these observations
in conjunction with a radiative magnetohydrodynamic 2.5D model
covering the upper convection zone all the way to the corona
that considers non-equilibrium ionization effects, we report the
detection of an on-disk chromospheric spicule with ALMA and confirm
its multithermal nature. In addition, we discuss the strikingly high
degree of similarity between chromospheric plage features observed
in ALMA/Band6 and IRIS/\ion{Si}{4} (also reproduced in our model)
suggesting that ALMA/Band6 does not observe in the low chromosphere as
previously thought but rather observes the upper chromospheric parts
of structures such as spicules and other bright structures above plage
at geometric heights near transition region temperatures. We also show
that IRIS/\ion{Mg}{2} is not as well correlated with ALMA/Band6 as was
previously thought. For these comparisons, we propose and employ a novel
empirical method for the determination of plage regions, which seems
to better isolate plage from its surrounding regions as compared to
other methods commonly used. We caution that isolating plage from its
immediate surroundings must be done with care to mitigate statistical
bias in quantitative comparisons between different chromospheric
observables. Lastly, we report indications for chromospheric heating
due to traveling shocks supported by the ALMA/Band6 observations.

---------------------------------------------------------
Title: The Sun at millimeter wavelengths. II. Small-scale dynamic
events in ALMA Band 3
Authors: Eklund, Henrik; Wedemeyer, Sven; Szydlarski, Mikolaj;
Jafarzadeh, Shahin; Guevara Gómez, Juan Camilo
2020A&A...644A.152E Altcode: 2020arXiv201006400E
Context. Solar observations with the Atacama Large
Millimeter/sub-millimeter Array (ALMA) facilitate studies of the
atmosphere of the Sun at chromospheric heights at high spatial and
temporal resolution at millimeter wavelengths. Aims: ALMA
intensity data at millimeter(mm)-wavelengths are used for a first
detailed systematic assessment of the occurrence and properties of
small-scale dynamical features in the quiet Sun. Methods: We
analyzed ALMA Band 3 data (∼3 mm/100 GHz) with a spatial resolution
of ∼1.4-2.1 arcsec and a duration of ∼40 min together with SDO/HMI
magnetograms. The temporal evolution of the mm maps is studied to
detect pronounced dynamical features, which then are connected to
dynamical events via a k-means clustering algorithm. We studied the
physical properties of the resulting events and explored whether or
not they show properties consistent with propagating shock waves. For
this purpose, we calculated observable shock wave signatures at mm
wavelengths from one- and three-dimensional model atmospheres. 
Results: We detect 552 dynamical events with an excess in brightness
temperature (ΔTb) of at least ≥400 K. The events show a
large variety in size up to ∼9″, amplitude ΔTb up to
∼1200 K with typical values in the range ∼450-750 K, and lifetime
at full width at half maximum of ΔTb of between ∼43 and
360 s, with typical values between ∼55 and 125 s. Furthermore, many
of the events show signature properties suggesting that they are likely
produced by propagating shock waves. Conclusions: There are a
lot of small-scale dynamic structures detected in the Band 3 data,
even though the spatial resolution sets limitations on the size of
events that can be detected. The number of dynamic signatures in the
ALMA mm data is very low in areas with photospheric footpoints with
stronger magnetic fields, which is consistent with the expectation
for propagating shock waves.

---------------------------------------------------------
Title: The Sun at millimeter wavelengths. I. Introduction to ALMA
Band 3 observations
Authors: Wedemeyer, Sven; Szydlarski, Mikolaj; Jafarzadeh, Shahin;
Eklund, Henrik; Guevara Gomez, Juan Camilo; Bastian, Tim; Fleck,
Bernhard; de la Cruz Rodriguez, Jaime; Rodger, Andrew; Carlsson, Mats
2020A&A...635A..71W Altcode: 2020arXiv200102185W
Context. The Atacama Large Millimeter/submillimeter Array (ALMA) started
regular observations of the Sun in 2016, first offering receiver Band
3 at wavelengths near 3 mm (100 GHz) and Band 6 at wavelengths around
1.25 mm (239 GHz). Aims: Here we present an initial study
of one of the first ALMA Band 3 observations of the Sun. Our aim is
to characterise the diagnostic potential of brightness temperatures
measured with ALMA on the Sun. Methods: The observation covers
a duration of 48 min at a cadence of 2 s targeting a quiet Sun region
at disc-centre. Corresponding time series of brightness temperature
maps are constructed with the first version of the Solar ALMA Pipeline
and compared to simultaneous observations with the Solar Dynamics
Observatory (SDO). Results: The angular resolution of the
observations is set by the synthesised beam, an elliptical Gaussian
that is approximately 1.4″ × 2.1″ in size. The ALMA maps exhibit
network patches, internetwork regions, and elongated thin features
that are connected to large-scale magnetic loops, as confirmed by a
comparison with SDO maps. The ALMA Band 3 maps correlate best with
the SDO/AIA 171 Å, 131 Å, and 304 Å channels in that they exhibit
network features and, although very weak in the ALMA maps, imprints
of large-scale loops. A group of compact magnetic loops is very
clearly visible in ALMA Band 3. The brightness temperatures in the
loop tops reach values of about 8000-9000 K and in extreme moments
up to 10 000 K. Conclusions: ALMA Band 3 interferometric
observations from early observing cycles already reveal temperature
differences in the solar chromosphere. The weak imprint of magnetic
loops and the correlation with the 171, 131, and 304 SDO channels
suggests, however, that the radiation mapped in ALMA Band 3 might
have contributions from a wider range of atmospheric heights than
previously assumed, but the exact formation height of Band 3 needs to
be investigated in more detail. The absolute brightness temperature
scale as set by total power measurements remains less certain and
must be improved in the future. Despite these complications and the
limited angular resolution, ALMA Band 3 observations have a large
potential for quantitative studies of the small-scale structure and
dynamics of the solar chromosphere. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201937122/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: The multi-thermal chromosphere. Inversions of ALMA and
IRIS data
Authors: da Silva Santos, J. M.; de la Cruz Rodríguez, J.; Leenaarts,
J.; Chintzoglou, G.; De Pontieu, B.; Wedemeyer, S.; Szydlarski, M.
2020A&A...634A..56D Altcode: 2019arXiv191209886D
Context. Numerical simulations of the solar chromosphere predict a
diverse thermal structure with both hot and cool regions. Observations
of plage regions in particular typically feature broader and brighter
chromospheric lines, which suggests that they are formed in hotter
and denser conditions than in the quiet Sun, but also implies a
nonthermal component whose source is unclear. Aims: We revisit
the problem of the stratification of temperature and microturbulence
in plage and the quiet Sun, now adding millimeter (mm) continuum
observations provided by the Atacama Large Millimiter Array (ALMA) to
inversions of near-ultraviolet Interface Region Imaging Spectrograph
(IRIS) spectra as a powerful new diagnostic to disentangle the
two parameters. We fit cool chromospheric holes and track the fast
evolution of compact mm brightenings in the plage region. 
Methods: We use the STiC nonlocal thermodynamic equilibrium (NLTE)
inversion code to simultaneously fit real ultraviolet and mm spectra
in order to infer the thermodynamic parameters of the plasma. 
Results: We confirm the anticipated constraining potential of ALMA
in NLTE inversions of the solar chromosphere. We find significant
differences between the inversion results of IRIS data alone compared to
the results of a combination with the mm data: the IRIS+ALMA inversions
have increased contrast and temperature range, and tend to favor lower
values of microturbulence (∼3-6 km s-1 in plage compared
to ∼4-7 km s-1 from IRIS alone) in the chromosphere. The
average brightness temperature of the plage region at 1.25 mm is 8500
K, but the ALMA maps also show much cooler (∼3000 K) and hotter
(∼11 000 K) evolving features partially seen in other diagnostics. To
explain the former, the inversions require the existence of localized
low-temperature regions in the chromosphere where molecules such as CO
could form. The hot features could sustain such high temperatures due to
non-equilibrium hydrogen ionization effects in a shocked chromosphere
- a scenario that is supported by low-frequency shock wave patterns
found in the Mg II lines probed by IRIS.

---------------------------------------------------------
Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array - from continuum to magnetic fields
Authors: Wedemeyer, Sven; Szydlarski, Mikolaj; Rodriguez, Jaime de
la Cruz; Jafarzadeh, Shahin
2020IAUS..354...24W Altcode:
The Atacama Large Millimeter/submillimeter Array offers regular
observations of our Sun since 2016. After an extended period of
further developing and optimizing the post-processing procedures,
first scientific results are now produced. While the first observing
cycles mostly provided mosaics and time series of continuum brightness
temperature maps with a cadence of 1-2s, additional receiver bands and
polarization capabilities will be offered in the future. Currently,
polarization capabilities are offered for selected receiver bands but
not yet for solar observing. An overview of the recent development,
first scientific results and potential of solar magnetic field
measurements with ALMA will be presented.

---------------------------------------------------------
Title: Solar Astronomy with ALMA
Authors: Wedemeyer, Sven
2019asrc.confE..12W Altcode:
Solar observing with ALMA is offered as a non-standard mode since Cycle
4. The requirements for such observations are different from many other
observations with ALMA in the sense that the mapped atmospheric layers
of the Sun evolve on very short timescales and the primary beam being
filled with complex emission. High-cadence (snapshot) imaging is needed
for such a dynamic target but is very challenging. The effort and time
that went into developing the observing mode seems well justified given
that ALMA provides a new complementary view at a part of the solar
atmosphere that is still elusive in many aspects. The solar observing
campaigns with ALMA are co-ordinated with a number of space-borne and
ground-based telescopes covering the UV to IR range. Co-ordinating
such strictly simultaneous multi-telescope observations adds another
layer of complexity but results in rich data sets covering all layers
of the solar atmosphere while probing different properties of the
atmospheric gas. Since Cycle 4, the imaging procedures for solar
ALMA observations have been significantly improved and science-ready
data are being produced. I will give a brief overview over ALMA's
diagnostic potential for the Sun and challenges with carrying out
solar observations and post-processing the data. First examples for
Band 3 and Band 6 data are presented and illustrate the dynamic nature
of the solar atmosphere, featuring, among other things, the imprint
of magnetic fields and propagating shock waves.

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Title: Extreme Precision Radial Velocity Working Group
Authors: Gaudi, Scott; Blackwood, Gary; Howard, Andrew; Latham,
David; Fischer, Debra; Ford, Eric; Cegla, Heather; Plavchan, Peter;
Quirrenbach, Andreas; Burt, Jennifer; Mamajek, Eric; Beichman, Chas;
Bender, Chad; Crass, Jonathan; Diddams, Scott; Dumusque, Xavier;
Eastman, Jason; Fulton, BJ; Halverson, Sam; Haywood, Raphaelle;
Hearty, Fred; Leifer, Stephanie; Loehner-Boettcher, Johannes;
Mortier, Annelies; Reiners, Ansgar; Robertson, Paul; Roy, Arpita;
Schwab, Christian; Seifahrt, Andreas; Szentgyorgyi, Andrew; Terrien,
Ryan; Teske, Johanna; Thompson, Samantha; Vasisht, Gautam; Aigrain,
Suzanne; Bedell, Megan; Bernstein, Rebecca; Blackman, Ryan; Blake,
Cullen; Buchhave, Lars; Callas, John; Ciardi, David; Chaplain, William;
Cisewski-Kehe, Jessi; Collier-Cameron, Andrew; Cornachione, Matthew;
Meunier, Nadege; Ninan, Joe; O'Meara, John; Ong, Joel; Wang, Sharon;
Wedemeyer-Boehm, Sven; Zhao, Lily; Boss, Alan; Oppenheimer, Rebecca;
Pitman, Joe; Poyneer, Lisa; Ridgeway, Stephen
2019BAAS...51g.232G Altcode: 2019astro2020U.232G
NASA and NSF are jointly commissioning a community-based “Extreme
Precision Radial Velocity (EPRV) working Group” to develop a blueprint
for a strategy for an EPRV initiative. The purpose of this white paper
is to describe the (EPRV) Working Group, whose primary responsibility
is to lay out the blueprint mentioned above.

---------------------------------------------------------
Title: VizieR Online Data Catalog: HAT-P-26 differential transit
photometry (von Essen+, 2019)
Authors: von Essen, C.; Wedemeyer, S.; Sosa, M. S.; Hjorth, M.;
Parkash, V.; Freudenthal, J.; Mallonn, M.; Miculan, R. G.; Zibecchi,
L.; Cellone, S.; Torres, A. F.
2019yCat..36280116V Altcode:
11 differential photometry time series of primary transit events of
HAT-P-26b in the R band. (1 data file).

---------------------------------------------------------
Title: Multiwavelength High-resolution Observations of Chromospheric
Swirls in the Quiet Sun
Authors: Shetye, Juie; Verwichte, Erwin; Stangalini, Marco; Judge,
Philip G.; Doyle, J. G.; Arber, Tony; Scullion, Eamon; Wedemeyer, Sven
2019ApJ...881...83S Altcode:
We report observations of small-scale swirls seen in the solar
chromosphere. They are typically 2 Mm in diameter and last around
10 minutes. Using spectropolarimetric observations obtained by the
CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope,
we identify and study a set of swirls in chromospheric Ca II 8542 Å
and Hα lines as well as in the photospheric Fe I line. We have three
main areas of focus. First, we compare the appearance, morphology,
dynamics, and associated plasma parameters between the Ca II and Hα
channels. Rotation and expansion of the chromospheric swirl pattern
are explored using polar plots. Second, we explore the connection to
underlying photospheric magnetic concentration (MC) dynamics. MCs are
tracked using the SWAMIS tracking code. The swirl center and MC remain
cospatial and share similar periods of rotation. Third, we elucidate
the role swirls play in modifying chromospheric acoustic oscillations
and found a temporary reduction in wave period during swirls. We use
cross-correlation wavelets to examine the change in period and phase
relations between different wavelengths. The physical picture that
emerges is that a swirl is a flux tube that extends above an MC in a
downdraft region in an intergranular lane. The rotational motion of
the MC matches the chromospheric signatures. We could not determine
whether a swirl is a gradual response to the photospheric motion or
an actual propagating Alfvénic wave.

---------------------------------------------------------
Title: Indications for transit-timing variations in the exo-Neptune
HAT-P-26b
Authors: von Essen, C.; Wedemeyer, S.; Sosa, M. S.; Hjorth, M.;
Parkash, V.; Freudenthal, J.; Mallonn, M.; Miculán, R. G.; Zibecchi,
L.; Cellone, S.; Torres, A. F.
2019A&A...628A.116V Altcode: 2019arXiv190406360V
Upon its discovery, the low-density transiting Neptune HAT-P-26b showed
a 2.1σ detection drift in its spectroscopic data, while photometric
data showed a weak curvature in the timing residuals, the confirmation
of which required further follow-up observations. To investigate this
suspected variability, we observed 11 primary transits of HAT-P-26b
between March, 2015, and July, 2018. For this, we used the 2.15 m Jorge
Sahade Telescope placed in San Juan, Argentina, and the 1.2 m STELLA
and the 2.5 m Nordic Optical Telescope, both located in the Canary
Islands, Spain. To add to valuable information on the transmission
spectrum of HAT-P-26b, we focused our observations in the R-band
only. To contrast the observed timing variability with possible stellar
activity, we carried out a photometric follow-up of the host star over
three years. We carried out a global fit to the data and determined
the individual mid-transit times focusing specifically on the light
curves that showed complete transit coverage. Using bibliographic data
corresponding to both ground and space-based facilities, plus our new
characterized mid-transit times derived from parts-per-thousand precise
photometry, we observed indications of transit timing variations
in the system, with an amplitude of 4 min and a periodicity of 270
epochs. The photometric and spectroscopic follow-up observations
of this system will be continued in order to rule out any aliasing
effects caused by poor sampling and the long-term periodicity. The
transit photometry (time, flux, error) and the long term monitoring
in three bands 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/628/A116">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A116</A>

---------------------------------------------------------
Title: Kepler Object of Interest Network. III. Kepler-82f: a new
non-transiting 21 M⊕ planet from photodynamical modelling
Authors: Freudenthal, J.; von Essen, C.; Ofir, A.; Dreizler, S.; Agol,
E.; Wedemeyer, S.; Morris, B. M.; Becker, A. C.; Deeg, H. J.; Hoyer,
S.; Mallonn, M.; Poppenhaeger, K.; Herrero, E.; Ribas, I.; Boumis,
P.; Liakos, A.
2019A&A...628A.108F Altcode: 2019arXiv190706534F
Context. The Kepler Object of Interest Network (KOINet) is a
multi-site network of telescopes around the globe organised for
follow-up observations of transiting planet candidate Kepler objects of
interest with large transit timing variations (TTVs). The main goal of
KOINet is the completion of their TTV curves as the Kepler telescope
stopped observing the original Kepler field in 2013. Aims: We
ensure a comprehensive characterisation of the investigated systems
by analysing Kepler data combined with new ground-based transit data
using a photodynamical model. This method is applied to the Kepler-82
system leading to its first dynamic analysis. Methods: In order
to provide a coherent description of all observations simultaneously,
we combine the numerical integration of the gravitational dynamics of
a system over the time span of observations with a transit light curve
model. To explore the model parameter space, this photodynamical model
is coupled with a Markov chain Monte Carlo algorithm. Results:
The Kepler-82b/c system shows sinusoidal TTVs due to their near 2:1
resonance dynamical interaction. An additional chopping effect in
the TTVs of Kepler-82c hints to a further planet near the 3:2 or 3:1
resonance. We photodynamically analysed Kepler long- and short-cadence
data and three new transit observations obtained by KOINet between 2014
and 2018. Our result reveals a non-transiting outer planet with a mass
of mf = 20.9 ± 1.0 M⊕ near the 3:2 resonance to
the outermost known planet, Kepler-82c. Furthermore, we determined the
densities of planets b and c to the significantly more precise values
ρb = 0.98-0.14+0.10 g cm-3
and ρc = 0.494-0.077+0.066
g cm-3. Ground-based photometry
is 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/628/A108">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A108</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: Photometry of Kepler-82b and c
transits (Freudenthal+, 2019)
Authors: Freudenthal, J.; von Essen, C.; Ofir, A.; Dreizler, S.; Agol,
E.; Wedemeyer, S.; Morris, B. M.; Becker, A. C.; Deeg, H. J.; Hoyer,
S.; Mallonn, M.; Poppenhaeger, K.; Herrero, E.; Ribas, I.; Boumis,
P.; Liakos, A.
2019yCat..36280108F Altcode:
All our observations were carried out using R-band filter. We provide
the differential photometry with varying reference stars for each
observation together with the used detrending components. We measured
one Kepler-82b and two Kepler-82c transits in three observations
between 2014 and 2018. (4 data files).

---------------------------------------------------------
Title: High-cadence imaging of the Sun
Authors: Wedemeyer, Sven
2019adw..confE..47W Altcode:
A challenge of observing the Sun with ALMA is that the primary beam
covers only a small region on the Sun and is therefore filled with a
complex radiation pattern, which evolves on extremely short time scales
of only seconds and below. Fully exploiting ALMA's possibilities
therefore requires imaging at very high cadence. Accordingly,
there is much potential for improving the solar observing modes
and post-processing of data. The development study "High-cadence
imaging of the Sun", which started in 2018, aims at developing a
high-cadence imaging capability by employing realistic test cases based
on state-of-the-art numerical simulations, the Solar ALMA Simulator
tool, and a solar simulation pipeline. Comparisons between the input
and output of the simulation pipeline will reveal how well imaging at
high cadence performs and how to optimize it. We present an overview
of the study and its current state.

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Title: First Spectral Analysis of a Solar Plasma Eruption Using ALMA
Authors: Rodger, Andrew S.; Labrosse, Nicolas; Wedemeyer, Sven;
Szydlarski, Mikolaj; Simões, Paulo J. A.; Fletcher, Lyndsay
2019ApJ...875..163R Altcode: 2019arXiv190201319R
The aim of this study is to demonstrate how the logarithmic
millimeter continuum gradient observed using the Atacama Large
Millimeter/submillimeter Array (ALMA) may be used to estimate optical
thickness in the solar atmosphere. We discuss how using multiwavelength
millimeter measurements can refine plasma analysis through knowledge
of the absorption mechanisms. Here we use subband observations from
the publicly available science verification (SV) data, while our
methodology will also be applicable to regular ALMA data. The spectral
resolving capacity of ALMA SV data is tested using the enhancement
coincident with an X-ray bright point and from a plasmoid ejection
event near active region NOAA12470 observed in Band 3 (84-116 GHz) on
2015 December 17. We compute the interferometric brightness temperature
light curve for both features at each of the four constituent subbands
to find the logarithmic millimeter spectrum. We compared the observed
logarithmic spectral gradient with the derived relationship with optical
thickness for an isothermal plasma to estimate the structures’
optical thicknesses. We conclude, within 90% confidence, that the
stationary enhancement has an optical thickness between 0.02 ≤ τ
≤ 2.78, and that the moving enhancement has 0.11 ≤ τ ≤ 2.78,
thus both lie near to the transition between optically thin and thick
plasma at 100 GHz. From these estimates, isothermal plasmas with
typical Band 3 background brightness temperatures would be expected
to have electron temperatures of ∼7370-15300 K for the stationary
enhancement and between ∼7440 and 9560 K for the moving enhancement,
thus demonstrating the benefit of subband ALMA spectral analysis.

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Title: The solar chromosphere at millimetre and ultraviolet
wavelengths. I. Radiation temperatures and a detailed comparison
Authors: Jafarzadeh, S.; Wedemeyer, S.; Szydlarski, M.; De Pontieu,
B.; Rezaei, R.; Carlsson, M.
2019A&A...622A.150J Altcode: 2019arXiv190105763J
Solar observations with the Atacama Large Millimeter/submillimeter
Array (ALMA) provide us with direct measurements of the brightness
temperature in the solar chromosphere. We study the temperature
distributions obtained with ALMA Band 6 (in four sub-bands at 1.21,
1.22, 1.29, and 1.3 mm) for various areas at, and in the vicinity of,
a sunspot, comprising quasi-quiet and active regions with different
amounts of underlying magnetic fields. We compare these temperatures
with those obtained at near- and far-ultraviolet (UV) wavelengths
(and with the line-core intensities of the optically-thin far-UV
spectra), co-observed with the Interface Region Imaging Spectrograph
(IRIS) explorer. These include the emission peaks and cores of the Mg
II k 279.6 nm and Mg II h 280.4 nm lines as well as the line cores
of C II 133.4 nm, O I 135.6 nm, and Si IV 139.4 nm, sampling the
mid-to-high chromosphere and the low transition region. Splitting the
ALMA sub-bands resulted in an slight increase of spatial resolution in
individual temperature maps, thus, resolving smaller-scale structures
compared to those produced with the standard averaging routines. We
find that the radiation temperatures have different, though somewhat
overlapping, distributions in different wavelengths and in the various
magnetic regions. Comparison of the ALMA temperatures with those of
the UV diagnostics should, however, be interpreted with great caution,
the former is formed under the local thermodynamic equilibrium (LTE)
conditions, the latter under non-LTE. The mean radiation temperature
of the ALMA Band 6 is similar to that extracted from the IRIS C II
line in all areas with exception of the sunspot and pores where the C
II poses higher radiation temperatures. In all magnetic regions, the
Mg II lines associate with the lowest mean radiation temperatures in
our sample. These will provide constraints for future numerical models.

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Title: First high-resolution look at the quiet Sun with ALMA at 3mm
Authors: Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos,
S.; De Pontieu, B.; Warren, H.; Ayres, T.; Hudson, H. S.; Shimizu,
T.; Vial, J. -C.; Wedemeyer, S.; Yurchyshyn, V.
2018A&A...619L...6N Altcode: 2018arXiv181005223N
We present an overview of high-resolution quiet Sun observations,
from disk center to the limb, obtained with the Atacama Large
millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun
regions were observed at a resolution of up to 2.5″ by 4.5″. We
produced both average and snapshot images by self-calibrating the ALMA
visibilities and combining the interferometric images with full-disk
solar images. The images show well the chromospheric network, which,
based on the unique segregation method we used, is brighter than the
average over the fields of view of the observed regions by ∼305
K while the intranetwork is less bright by ∼280 K, with a slight
decrease of the network/intranetwork contrast toward the limb. At 3
mm the network is very similar to the 1600 Å images, with somewhat
larger size. We detect, for the first time, spicular structures,
rising up to 15″ above the limb with a width down to the image
resolution and brightness temperature of ∼1800 K above the local
background. No trace of spicules, either in emission or absorption,
is found on the disk. Our results highlight the potential of ALMA for
the study of the quiet chromosphere.

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Title: Kepler Object of Interest Network. II. Photodynamical modelling
of Kepler-9 over 8 years of transit observations
Authors: Freudenthal, J.; von Essen, C.; Dreizler, S.; Wedemeyer, S.;
Agol, E.; Morris, B. M.; Becker, A. C.; Mallonn, M.; Hoyer, S.; Ofir,
A.; Tal-Or, L.; Deeg, H. J.; Herrero, E.; Ribas, I.; Khalafinejad,
S.; Hernández, J.; Rodríguez S., M. M.
2018A&A...618A..41F Altcode: 2018arXiv180700007F
Context. The Kepler Object of Interest Network (KOINet) is a multi-site
network of telescopes around the globe organised to follow up transiting
planet-candidate Kepler objects of interest (KOIs) with large transit
timing variations (TTVs). Its main goal is to complete their TTV
curves, as the Kepler telescope no longer observes the original
Kepler field. Aims: Combining Kepler and new ground-based
transit data we improve the modelling of these systems. To this end,
we have developed a photodynamical model, and we demonstrate its
performance using the Kepler-9 system as an example. Methods:
Our comprehensive analysis combines the numerical integration of the
system's dynamics over the time span of the observations along with
the transit light curve model. This provides a coherent description of
all observations simultaneously. This model is coupled with a Markov
chain Monte Carlo algorithm, allowing for the exploration of the
model parameter space. Results: Applied to the Kepler-9 long
cadence data, short cadence data, and 13 new transit observations
collected by KOINet between the years 2014 and 2017, our modelling
provides well constrained predictions for the next transits and the
system's parameters. We have determined the densities of the planets
Kepler-9b and 9c to the very precise values of ρb =
0.439 ± 0.023 g cm-3 and ρc = 0.322 ±
0.017 g cm-3. Our analysis reveals that Kepler-9c will
stop transiting in about 30 yr due to strong dynamical interactions
between Kepler-9b and 9c, near 2:1 resonance, leading to a periodic
change in inclination. Conclusions: Over the next 30 years, the
inclination of Kepler-9c (-9b) will decrease (increase) slowly. This
should be measurable by a substantial decrease (increase) in the transit
duration, in as soon as a few years' time. Observations that contradict
this prediction might indicate the presence of additional objects
in this system. If this prediction turns out to be accurate, this
behaviour opens up a unique chance to scan the different latitudes of a
star: high latitudes with planet c and low latitudes with planet b. Ground-based photometry 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/618/A41">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/618/A41</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: KOINet. Study of exoplanet systems
via TTVs (von Essen+, 2018)
Authors: von Essen, C.; Ofir, A.; Dreizler, S.; Agol, E.; Freudenthal,
J.; Hernandez, J.; Wedemeyer, S.; Parkash, V.; Deeg, H. J.; Hoyer,
S.; Morris, B. M.; Becker, A. C.; Sun, L.; Gu, S. H.; Herrero, E.;
Tal-Or, L.; Poppenhaeger, K.; Mallonn, M.; Albrecht, S.; Khalafinejad,
S.; Boumis, P.; Delgado-Correal, C.; Fabrycky, D. C.; Janulis, R.;
Lalitha, S.; Liakos, A.; Mikolaitis, S.; Moyano D'Angelo, M. L.; Sokov,
E.; Pakstiene, E.; Popov, A.; Krushinsky, V.; Ribas, I.; Rodriguez,
M. M. S.; Rusov, S.; Sokova, I.; Tautvaisiene, G.; Wang, X.
2018yCat..36150079V Altcode:
All our observations were carried out using R-band filter. We
provide the differential photometry with varying reference stars for
each observation together with the used detrending components. We
provide four transits of KOI-0410.01, and one transit of KOI-0902.01,
KOI-0525.01, and KOI-0760.01, respectively. The telescope nomenclature,
in agreement with the names of the files, is the following: IAC0.8: IAC80 telescope (0.8m), Instituto de Astrofisica de Canarias,
Spain. ARC3.5: Apache Point Observatory (3.5 m), USA. NOT2.5: Nordic
Optical Telescope (2.5 m), Spain. YO2.4: Yunnan Observatories (2.4 m),
PR China. (8 data files).

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Title: VizieR Online Data Catalog: Photometry of Kepler-9b and c
transits (Freudenthal+, 2018)
Authors: Freudenthal, J.; von Essen, C.; Dreizler, S.; Wedemeyer, S.;
Agol, E.; Morris, B. M.; Becker, A. C.; Mallonn, M.; Hoyer, S.; Ofir,
A.; Tal-Or, L.; Deeg, H. J.; Herrero, E.; Ribas, I.; Khalafinejad,
S.; Hernandez, J.; Rodriguez, S. M. M.
2018yCat..36180041F Altcode:
All our observations were carried out using R-band filter. We provide
the differential photometry with varying reference stars for each
observation together with the used detrending components. We measured
five Kepler-9b and four Kepler-9c transits in thirteen observations
between 2014 and 2017. (14 data files).

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Title: Kepler Object of Interest Network. I. First results combining
ground- and space-based observations of Kepler systems with transit
timing variations
Authors: von Essen, C.; Ofir, A.; Dreizler, S.; Agol, E.; Freudenthal,
J.; Hernández, J.; Wedemeyer, S.; Parkash, V.; Deeg, H. J.; Hoyer, S.;
Morris, B. M.; Becker, A. C.; Sun, L.; Gu, S. H.; Herrero, E.; Tal-Or,
L.; Poppenhaeger, K.; Mallonn, M.; Albrecht, S.; Khalafinejad, S.;
Boumis, P.; Delgado-Correal, C.; Fabrycky, D. C.; Janulis, R.; Lalitha,
S.; Liakos, A.; Mikolaitis, Š.; Moyano D'Angelo, M. L.; Sokov, E.;
Pakštienė, E.; Popov, A.; Krushinsky, V.; Ribas, I.; Rodríguez S.,
M. M.; Rusov, S.; Sokova, I.; Tautvaišienė, G.; Wang, X.
2018A&A...615A..79V Altcode: 2018arXiv180106191V
During its four years of photometric observations, the Kepler
space telescope detected thousands of exoplanets and exoplanet
candidates. One of Kepler's greatest heritages has been the confirmation
and characterization of hundreds of multi-planet systems via transit
timing variations (TTVs). However, there are many interesting candidate
systems displaying TTVs on such long timescales that the existing Kepler
observations are of insufficient length to confirm and characterize
them by means of this technique. To continue with Kepler's unique work,
we have organized the "Kepler Object of Interest Network" (KOINet),
a multi-site network formed of several telescopes located throughout
America, Europe, and Asia. The goals of KOINet are to complete the TTV
curves of systems where Kepler did not cover the interaction timescales
well, to dynamically prove that some candidates are true planets (or
not), to dynamically measure the masses and bulk densities of some
planets, to find evidence for non-transiting planets in some of the
systems, to extend Kepler's baseline adding new data with the main
purpose of improving current models of TTVs, and to build a platform
that can observe almost anywhere on the northern hemisphere, at almost
any time. KOINet has been operational since March 2014. Here we show
some promising first results obtained from analyzing seven primary
transits of KOI-0410.01, KOI-0525.01, KOI-0760.01, and KOI-0902.01,
in addition to the Kepler data acquired during the first and second
observing seasons of KOINet. While carefully choosing the targets
we set demanding constraints on timing precision (at least 1 min)
and photometric precision (as good as one part per thousand) that
were achieved by means of our observing strategies and data analysis
techniques. For KOI-0410.01, new transit data revealed a turnover
of its TTVs. We carried out an in-depth study of the system, which is
identified in the NASA Data Validation Report as a false positive. Among
others, we investigated a gravitationally bound hierarchical triple
star system and a planet-star system. While the simultaneous transit
fitting of ground- andspace-based data allowed for a planet solution,
we could not fully reject the three-star scenario. New data,
already scheduled in the upcoming 2018 observing season, will set
tighter constraints on the nature of the system. Ground-based
photometry is 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/615/A79">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/615/A79</A>

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Title: Observations of the solar chromosphere with ALMA and comparison
with theoretical models
Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold O.;
Kuhar, Matej; Kobelski, Adam; Wedemeyer, Sven; White, Stephen M.;
Ludwig, Hans-G.; Temmer, Manuela; Saar, Steven H.; Selhorst, Caius L.
2018csss.confE..37B Altcode: 2018arXiv181207293B
In this work we use solar observations with the ALMA radio telescope
at the wavelength of 1.21 mm. The aim of the analysisis to improve
understanding of the solar chromosphere, a dynamic layer in the
solar atmosphere between the photosphere andcorona. The study has
an observational and a modeling part. In the observational part
full-disc solar images are analyzed.Based on a modied FAL atmospheric
model, radiation models for various observed solar structures are
developed. Finally, theobservational and modeling results are compared
and discussed.

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Title: First analysis of solar structures in 1.21 mm full-disc ALMA
image of the Sun
Authors: Brajša, R.; Sudar, D.; Benz, A. O.; Skokić, I.; Bárta,
M.; De Pontieu, B.; Kim, S.; Kobelski, A.; Kuhar, M.; Shimojo, M.;
Wedemeyer, S.; White, S.; Yagoubov, P.; Yan, Y.
2018A&A...613A..17B Altcode: 2017arXiv171106130B
Context. Various solar features can be seen in emission or absorption
on maps of the Sun in the millimetre and submillimetre wavelength
range. The recently installed Atacama Large Millimetre/submillimetre
Array (ALMA) is capable of observing the Sun in that wavelength range
with an unprecedented spatial, temporal and spectral resolution. To
interpret solar observations with ALMA, the first important step is to
compare solar ALMA maps with simultaneous images of the Sun recorded in
other spectral ranges. Aims: The first aim of the present work
is to identify different structures in the solar atmosphere seen in the
optical, infrared, and EUV parts of the spectrum (quiet Sun, active
regions, prominences on the disc, magnetic inversion lines, coronal
holes and coronal bright points) in a full-disc solar ALMA image. The
second aim is to measure the intensities (brightness temperatures) of
those structures and to compare them with the corresponding quiet Sun
level. Methods: A full-disc solar image at 1.21 mm obtained on
December 18, 2015, during a CSV-EOC campaign with ALMA is calibrated and
compared with full-disc solar images from the same day in Hα line, in
He I 1083 nm line core, and with various SDO images (AIA at 170 nm, 30.4
nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness
temperatures of various structures are determined by averaging over
corresponding regions of interest in the calibrated ALMA image. 
Results: Positions of the quiet Sun, active regions, prominences on
the disc, magnetic inversion lines, coronal holes and coronal bright
points are identified in the ALMA image. At the wavelength of 1.21
mm, active regions appear as bright areas (but sunspots are dark),
while prominences on the disc and coronal holes are not discernible
from the quiet Sun background, despite having slightly less intensity
than surrounding quiet Sun regions. Magnetic inversion lines appear as
large, elongated dark structures and coronal bright points correspond
to ALMA bright points. Conclusions: These observational results
are in general agreement with sparse earlier measurements at similar
wavelengths. The identification of coronal bright points represents
the most important new result. By comparing ALMA and other maps,
it was found that the ALMA image was oriented properly and that the
procedure of overlaying the ALMA image with other images is accurate
at the 5 arcsec level. The potential of ALMA for physics of the solar
chromosphere is emphasised.

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Title: Solar Observations with ALMA
Authors: Wedemeyer, Sven
2018iss..confE..38W Altcode:
The continuum intensity at millimeter wavelengths can serve as an
essentially linear thermometer of the plasma in a thin layer in
the atmosphere of the Sun, whereas the polarisation of the received
radiation is a measure for the longitudinal magnetic field component in
the same layer. The enormous leap in terms of spatial resolution with
the Atacama Large Millimeter/submillimeter Array (ALMA) now makes it
possible to observe the intricate fine-structure of the solar atmosphere
at sufficiently high spatial, temporal, and spectral resolution, thus
enabling studies of a wide range of scientific topics in solar physics
that had been inaccessible at millimeter wavelengths before. The
radiation observed by ALMA originates mostly from the chromosphere
- a complex and dynamic layer between the photosphere and corona,
which plays a crucial role in the transport of energy and matter
and, ultimately, the heating of the outer solar atmosphere. ALMA
observations of the solar chromosphere, which are offered as a
regular capability since 2016, therefore have the potential to make
important contributions towards the solution of fundamental questions
in solar physics with implications for our understanding of stars
in general. In this presentation, I will give a short description
of ALMA's solar observing mode, it challenges and opportunities,
and selected science cases in combination with numerical simulations
and coordinated observations at other wavelengths. ALMA's scientific
potential for studying the dynamic small-scale pattern of the solar
chromosphere is illustrated with first results from Cycle 4.

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Title: Exploring the Sun with ALMA
Authors: Bastian, T. S.; Bárta, M.; Brajša, R.; Chen, B.; Pontieu,
B. D.; Gary, D. E.; Fleishman, G. D.; Hales, A. S.; Iwai, K.; Hudson,
H.; Kim, S.; Kobelski, A.; Loukitcheva, M.; Shimojo, M.; Skokić,
I.; Wedemeyer, S.; White, S. M.; Yan, Y.
2018Msngr.171...25B Altcode:
The Atacama Large Millimeter/submillimeter Array (ALMA) Observatory
opens a new window onto the Universe. The ability to perform continuum
imaging and spectroscopy of astrophysical phenomena at millimetre and
submillimetre wavelengths with unprecedented sensitivity opens up new
avenues for the study of cosmology and the evolution of galaxies, the
formation of stars and planets, and astrochemistry. ALMA also allows
fundamentally new observations to be made of objects much closer
to home, including the Sun. The Sun has long served as a touchstone
for our understanding of astrophysical processes, from the nature of
stellar interiors, to magnetic dynamos, non-radiative heating, stellar
mass loss, and energetic phenomena such as solar flares. ALMA offers
new insights into all of these processes.

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Title: Impact of magnetic fields on the structure of convective
atmospheres of red giant stars
Authors: Klevas, J.; Kučinskas, A.; Wedemeyer, S.; Ludwig, H. -G.
2018CoSka..48..280K Altcode:
We use 3D magnetohydrodynamic CO5BOLD model atmospheres
to study the interplay between magnetic fields and convection in the
atmospheres of red giant stars. We find that vortex-like structures
occur prominently in stars with stronger magnetic fields and lead to
alterations of their thermal structures.

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Title: A comparison of solar ALMA observations and model based
predictions of the brightness temperature
Authors: Brajša, R.; Kuhar, M.; Benz, A. O.; Skokić, I.; Sudar,
D.; Wedemeyer, S.; Báarta, M.; De Pontieu, B.; Kim, S.; Kobelski,
A.; Shimojo, M.; White, S.; Yagoubov, P.; Yan, Y.; Ludwig, H. G.;
Temmer, M.; Saar, S. H.; Selhorst, C. L.; Beuc, R.
2018CEAB...42....1B Altcode:
The new facility Atacama Large Millimeter/submillimeter Array (ALMA) is
capable of observing the Sun in the wavelength range from 0.3 mm to 10
mm with an unprecedented spatial, temporal and spectral resolution. The
first aim of the present work is to identify different structures
in the solar atmosphere (quiet Sun, active regions, filaments on the
disc, and coronal holes) in a full disc solar ALMA image at 1.21 mm
obtained on December 18, 2015 during a CSV-EOC campaign. It is compared
with full disc solar images from the same day in the Hα line (Cerro
Tololo Observatory, NISP), and at three EUV wavelengths (30.4 nm,
21.1 nm, 17.1 nm; a composite SDO image). Positions of the quiet Sun
areas, active regions, filaments on the disc, and coronal holes are
identified in the ALMA image. To interpret solar observations with ALMA
it is important to compare the measured and calculated intensities
of various solar structures. So, the second aim of this work is to
calculate the intensity (brightness temperature) for those structures
(quiet Sun, active regions, filaments on the disc, and coronal holes)
for a broad wavelength range (from 0.3 mm to 10 mm), closely related
to that of the ALMA, and to compare the results with available
ALMA observations. Thermal bremsstrahlung is the dominant radiation
mechanism for explanation of the observed phenomena. A procedure for
calculating the brightness temperature for a given wavelength and
model atmosphere, which integrates the radiative transfer equation
for thermal bremsstrahlung, is used. At the wavelength of 1.21 mm
active regions appear as bright areas, while filaments on the disc and
coronal holes are not discernible from the quiet Sun background. The
models generally agree with the observed results: Active regions are
bright primarily due to higher densities, filaments can appear bright,
dark or not at all and coronal holes cannot be easily identified.

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Title: Three-dimensional hydrodynamical CO5BOLD model
atmospheres of red giant stars. VI. First chromosphere model of a
late-type giant
Authors: Wedemeyer, Sven; Kučinskas, Arūnas; Klevas, Jonas; Ludwig,
Hans-Günter
2017A&A...606A..26W Altcode: 2017arXiv170509641W
 Aims: Although observational data unequivocally point to
the presence of chromospheres in red giant stars, no attempts
have been made so far to model them using 3D hydrodynamical model
atmospheres. We therefore compute an exploratory 3D hydrodynamical model
atmosphere for a cool red giant in order to study the dynamical and
thermodynamic properties of its chromosphere, as well as the influence
of the chromosphere on its observable properties. Methods:
Three-dimensional radiation hydrodynamics simulations are carried out
with the CO5BOLD model atmosphere code for a star with the
atmospheric parameters (Teff ≈ 4010 K, log g = 1.5, [ M / H
] = 0.0), which are similar to those of the K-type giant star Aldebaran
(α Tau). The computational domain extends from the upper convection
zone into the chromosphere (7.4 ≥ log τRoss ≥ - 12.8)
and covers several granules in each horizontal direction. Using this
model atmosphere, we compute the emergent continuum intensity maps at
different wavelengths, spectral line profiles of Ca II K, the Ca II
infrared triplet line at 854.2 nm, and Hα, as well as the spectral
energy distribution (SED) of the emergent radiative flux. 
Results: The initial model quickly develops a dynamical chromosphere
that is characterised by propagating and interacting shock waves. The
peak temperatures in the chromospheric shock fronts reach values of
up to 5000 K, although the shock fronts remain quite narrow. Similar
to the Sun, the gas temperature distribution in the upper layers
of red giant stars is composed of a cool component due to adiabatic
cooling in the expanding post-shock regions and a hot component due
to shock waves. For this red giant model, the hot component is a
rather flat high-temperature tail, which nevertheless affects the
resulting average temperatures significantly. Conclusions:
The simulations show that the atmospheres of red giant stars are
dynamic and intermittent. Consequently, many observable properties
cannot be reproduced with static 1D models, but require advanced 3D
hydrodynamical modelling. Furthermore, including a chromosphere in the
models might produce significant contributions to the emergent UV flux.

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Title: Solar Commissioning Observations of the Sun with ALMA
Authors: White, Stephen M.; Shimojo, Masumi; Bastian, Timothy S.;
Iwai, Kazumasa; Hales, Antonio; Brajsa, Roman; Skokic, Ivica; Kim,
Sujin; Hudson, Hugh S.; Loukitcheva, Maria; Wedemeyer, Sven
2017SPD....4820402W Altcode:
PI-led science observations have commenced with the Atacama
Large Millimeter-submillimeter Array (ALMA) following an extensive
commissioning effort. This talk will summarize that effort and discuss
some of the scientific results derived from the commissioning data. As
the solar cycle declines, ALMA observations will mainly address
chromospheric science topics. Examples of data obtained during
commissioning, both from the interferometer and from single-dish
observations, will be presented. The temperatures of the layers that
ALMA is most sensitive to have been determined for the two frequency
bands currently used for solar observations. Curious behavior in a
sunspot umbra and an observations of a small chromospheric ejection
will be discussed.

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Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA): High-Resolution Interferometric
Imaging
Authors: Shimojo, M.; Bastian, T. S.; Hales, A. S.; White, S. M.;
Iwai, K.; Hills, R. E.; Hirota, A.; Phillips, N. M.; Sawada, T.;
Yagoubov, P.; Siringo, G.; Asayama, S.; Sugimoto, M.; Brajša, R.;
Skokić, I.; Bárta, M.; Kim, S.; de Gregorio-Monsalvo, I.; Corder,
S. A.; Hudson, H. S.; Wedemeyer, S.; Gary, D. E.; De Pontieu, B.;
Loukitcheva, M.; Fleishman, G. D.; Chen, B.; Kobelski, A.; Yan, Y.
2017SoPh..292...87S Altcode: 2017arXiv170403236S
Observations of the Sun at millimeter and submillimeter wavelengths
offer a unique probe into the structure, dynamics, and heating of the
chromosphere; the structure of sunspots; the formation and eruption
of prominences and filaments; and energetic phenomena such as jets
and flares. High-resolution observations of the Sun at millimeter and
submillimeter wavelengths are challenging due to the intense, extended,
low-contrast, and dynamic nature of emission from the quiet Sun,
and the extremely intense and variable nature of emissions associated
with energetic phenomena. The Atacama Large Millimeter/submillimeter
Array (ALMA) was designed with solar observations in mind. The
requirements for solar observations are significantly different from
observations of sidereal sources and special measures are necessary
to successfully carry out this type of observations. We describe the
commissioning efforts that enable the use of two frequency bands,
the 3-mm band (Band 3) and the 1.25-mm band (Band 6), for continuum
interferometric-imaging observations of the Sun with ALMA. Examples of
high-resolution synthesized images obtained using the newly commissioned
modes during the solar-commissioning campaign held in December 2015
are presented. Although only 30 of the eventual 66 ALMA antennas
were used for the campaign, the solar images synthesized from the
ALMA commissioning data reveal new features of the solar atmosphere
that demonstrate the potential power of ALMA solar observations. The
ongoing expansion of ALMA and solar-commissioning efforts will continue
to enable new and unique solar observing capabilities.

---------------------------------------------------------
Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping
Authors: White, S. M.; Iwai, K.; Phillips, N. M.; Hills, R. E.; Hirota,
A.; Yagoubov, P.; Siringo, G.; Shimojo, M.; Bastian, T. S.; Hales,
A. S.; Sawada, T.; Asayama, S.; Sugimoto, M.; Marson, R. G.; Kawasaki,
W.; Muller, E.; Nakazato, T.; Sugimoto, K.; Brajša, R.; Skokić, I.;
Bárta, M.; Kim, S.; Remijan, A. J.; de Gregorio, I.; Corder, S. A.;
Hudson, H. S.; Loukitcheva, M.; Chen, B.; De Pontieu, B.; Fleishmann,
G. D.; Gary, D. E.; Kobelski, A.; Wedemeyer, S.; Yan, Y.
2017SoPh..292...88W Altcode: 2017arXiv170504766W
The Atacama Large Millimeter/submillimeter Array (ALMA) radio
telescope has commenced science observations of the Sun starting
in late 2016. Since the Sun is much larger than the field of view
of individual ALMA dishes, the ALMA interferometer is unable to
measure the background level of solar emission when observing the
solar disk. The absolute temperature scale is a critical measurement
for much of ALMA solar science, including the understanding of energy
transfer through the solar atmosphere, the properties of prominences,
and the study of shock heating in the chromosphere. In order to provide
an absolute temperature scale, ALMA solar observing will take advantage
of the remarkable fast-scanning capabilities of the ALMA 12 m dishes
to make single-dish maps of the full Sun. This article reports on the
results of an extensive commissioning effort to optimize the mapping
procedure, and it describes the nature of the resulting data. Amplitude
calibration is discussed in detail: a path that uses the two loads in
the ALMA calibration system as well as sky measurements is described
and applied to commissioning data. Inspection of a large number of
single-dish datasets shows significant variation in the resulting
temperatures, and based on the temperature distributions, we derive
quiet-Sun values at disk center of 7300 K at λ =3 mm and 5900 K at
λ =1.3 mm. These values have statistical uncertainties of about 100
K, but systematic uncertainties in the temperature scale that may be
significantly larger. Example images are presented from two periods
with very different levels of solar activity. At a resolution of about
25″, the 1.3 mm wavelength images show temperatures on
the disk that vary over about a 2000 K range. Active regions and plages
are among the hotter features, while a large sunspot umbra shows up as
a depression, and filament channels are relatively cool. Prominences
above the solar limb are a common feature of the single-dish images.

---------------------------------------------------------
Title: Vortex flows in the solar chromosphere. I. Automatic detection
method
Authors: Kato, Y.; Wedemeyer, S.
2017A&A...601A.135K Altcode: 2017arXiv170206032K
Solar "magnetic tornadoes" are produced by rotating magnetic
field structures that extend from the upper convection zone and
the photosphere to the corona of the Sun. Recent studies show that
these kinds of rotating features are an integral part of atmospheric
dynamics and occur on a large range of spatial scales. A systematic
statistical study of magnetic tornadoes is a necessary next step
towards understanding their formation and their role in mass and energy
transport in the solar atmosphere. For this purpose, we develop a
new automatic detection method for chromospheric swirls, meaning
the observable signature of solar tornadoes or, more generally,
chromospheric vortex flows and rotating motions. Unlike existing
studies that rely on visual inspections, our new method combines a line
integral convolution (LIC) imaging technique and a scalar quantity that
represents a vortex flow on a two-dimensional plane. We have tested two
detection algorithms, based on the enhanced vorticity and vorticity
strength quantities, by applying them to three-dimensional numerical
simulations of the solar atmosphere with CO5BOLD. We conclude that
the vorticity strength method is superior compared to the enhanced
vorticity method in all aspects. Applying the method to a numerical
simulation of the solar atmosphere reveals very abundant small-scale,
short-lived chromospheric vortex flows that have not been found
previously by visual inspection.

---------------------------------------------------------
Title: 3D hydrodynamical COBOLD simulations of a chromosphere of a
red giant
Authors: Klevas, J.; Wedemeyer, S.; Kučinskas, A.; Ludwig, H. -G.
2017MmSAI..88..100K Altcode:
We present the results of a 3D hydrodynamical simulation of a cool red
giant star with a chromosphere. The simulation was performed using
a 3D hydrodynamic COBOLD model atmosphere (Teff=4000 K,
{log g}=1.5 cgs, [M/H]=0.0 [dex]), which was extended outwards to
include chromospheric layers. We synthesized the spectral energy
distribution of a model atmosphere including chromosphere and compare
it to the spectral energy distribution of a model atmosphere without
the chromosphere. We find that adding a model chromosphere leads to a
significant increase of the radiative flux at wavelengths smaller than
300 nm. The increase in the UV flux is attributed to the presence of
shock waves, which provide additional heating in the chromosphere.

---------------------------------------------------------
Title: Observing the Formation of Flare-driven Coronal Rain
Authors: Scullion, E.; Rouppe van der Voort, L.; Antolin, P.;
Wedemeyer, S.; Vissers, G.; Kontar, E. P.; Gallagher, P. T.
2016ApJ...833..184S Altcode: 2016arXiv161009255S
Flare-driven coronal rain can manifest from rapidly cooled plasma
condensations near coronal loop tops in thermally unstable postflare
arcades. We detect five phases that characterize the postflare decay:
heating, evaporation, conductive cooling dominance for ∼120 s,
radiative/enthalpy cooling dominance for ∼4700 s, and finally
catastrophic cooling occurring within 35-124 s, leading to rain
strands with a periodicity of 55-70 s. We find an excellent agreement
between the observations and model predictions of the dominant
cooling timescales and the onset of catastrophic cooling. At the
rain-formation site, we detect comoving, multithermal rain clumps
that undergo catastrophic cooling from ∼1 MK to ∼22,000 K. During
catastrophic cooling, the plasma cools at a maximum rate of 22,700
K s-1 in multiple loop-top sources. We calculated the
density of the extreme-ultraviolet (EUV) plasma from the differential
emission measure of the multithermal source employing regularized
inversion. Assuming a pressure balance, we estimate the density of
the chromospheric component of rain to be 9.21 × 1011
± 1.76 × 1011 cm-3, which is comparable with
quiescent coronal rain densities. With up to eight parallel strands
in the EUV loop cross section, we calculate the mass loss rate from
the postflare arcade to be as much as 1.98 × 1012 ±
4.95 × 1011 g s-1. Finally, we reveal a close
proximity between the model predictions of {10}5.8 K and the
observed properties between {10}5.9 and {10}6.2
K, which defines the temperature onset of catastrophic cooling. The
close correspondence between the observations and numerical models
suggests that indeed acoustic waves (with a sound travel time of 68 s)
could play an important role in redistributing energy and sustaining
the enthalpy-based radiative cooling.

---------------------------------------------------------
Title: Lower solar atmosphere and magnetism at ultra-high spatial
resolution
Authors: Collet, Remo; Criscuoli, Serena; Ermolli, Ilaria; Fabbian,
Damian; Guerreiro, Nuno; Haberreiter, Margit; Peck, Courtney; Pereira,
Tiago M. D.; Rempel, Matthias; Solanki, Sami K.; Wedemeyer-Boehm, Sven
2016arXiv161202348C Altcode:
We present the scientific case for a future space-based telescope
aimed at very high spatial and temporal resolution imaging of the
solar photosphere and chromosphere. Previous missions (e.g., HINODE,
SUNRISE) have demonstrated the power of observing the solar photosphere
and chromosphere at high spatial resolution without contamination from
Earth's atmosphere. We argue here that increased spatial resolution
(from currently 70 km to 25 km in the future) and high temporal cadence
of the observations will vastly improve our understanding of the
physical processes controlling solar magnetism and its characteristic
scales. This is particularly important as the Sun's magnetic field
drives solar activity and can significantly influence the Sun-Earth
system. At the same time a better knowledge of solar magnetism can
greatly improve our understanding of other astrophysical objects.

---------------------------------------------------------
Title: Phoenix Meets CO5BOLD: 3D NLTE Radiative Transfer Calculations
For M-Dwarf Chromospheres
Authors: De Gennaro Aquino, Ivan; Hauschildt, Peter H.; Wedemeyer, Sven
2016csss.confE.149D Altcode:
M-dwarf atmospheres are phenomenologically so rich that is currently
impossible to include all the physical processes in one astrophysical
simulation code. 1D models have greatly improved our understanding
of the radiative properties of M-dwarf photospheres and important
achievements have been obtained in 1D and 3D magneto-hydrodynamic
simulations. Using a snapshot from a CO5BOLD M-dwarf simulation as
input model, we use the 3D atmosphere code PHOENIX/3D to compute the
radiative properties of a M-dwarf photosphere-chromosphere atmosphere
with NLTE treatment for several atomic species and background atomic
and molecular opacities.

---------------------------------------------------------
Title: Chromospheric and Coronal Wave Generation in a Magnetic
Flux Sheath
Authors: Kato, Yoshiaki; Steiner, Oskar; Hansteen, Viggo; Gudiksen,
Boris; Wedemeyer, Sven; Carlsson, Mats
2016ApJ...827....7K Altcode: 2016arXiv160608826K
Using radiation magnetohydrodynamic simulations of the solar
atmospheric layers from the upper convection zone to the lower corona,
we investigate the self-consistent excitation of slow magneto-acoustic
body waves (slow modes) in a magnetic flux concentration. We
find that the convective downdrafts in the close surroundings of
a two-dimensional flux slab “pump” the plasma inside it in
the downward direction. This action produces a downflow inside the
flux slab, which encompasses ever higher layers, causing an upwardly
propagating rarefaction wave. The slow mode, excited by the adiabatic
compression of the downflow near the optical surface, travels along the
magnetic field in the upward direction at the tube speed. It develops
into a shock wave at chromospheric heights, where it dissipates,
lifts the transition region, and produces an offspring in the form
of a compressive wave that propagates further into the corona. In the
wake of downflows and propagating shock waves, the atmosphere inside
the flux slab in the chromosphere and higher tends to oscillate with a
period of ν ≈ 4 mHz. We conclude that this process of “magnetic
pumping” is a most plausible mechanism for the direct generation
of longitudinal chromospheric and coronal compressive waves within
magnetic flux concentrations, and it may provide an important heat
source in the chromosphere. It may also be responsible for certain
types of dynamic fibrils.

---------------------------------------------------------
Title: Ssalmon - The Solar Simulations For The Atacama Large
Millimeter Observatory Network
Authors: Wedemeyer, Sven; Ssalmon Group
2016csss.confE..84W Altcode:
The Atacama Large Millimeter/submillimeter Array (ALMA) provides a new
powerful tool for observing the solar chromosphere at high spatial,
temporal, and spectral resolution, which will allow for addressing a
wide range of scientific topics in solar physics. Numerical simulations
of the solar atmosphere and modeling of instrumental effects are
valuable tools for constraining, preparing and optimizing future
observations with ALMA and for interpreting the results. In order
to co-ordinate related activities, the Solar Simulations for the
Atacama Large Millimeter Observatory Network (SSALMON) was initiated
on September 1st, 2014, in connection with the NA- and EU-led solar
ALMA development studies. As of April, 2015, SSALMON has grown to 83
members from 18 countries (plus ESO and ESA). Another important goal
of SSALMON is to promote the scientific potential of solar science
with ALMA, which has resulted in two major publications so far. During
2015, the SSALMON Expert Teams produced a White Paper with potential
science cases for Cycle 4, which will be the first time regular solar
observations will be carried out. Registration and more information
at http://www.ssalmon.uio.no.

---------------------------------------------------------
Title: Testing Wave Propagation Properties in the Solar Chromosphere
with ALMA and IRIS
Authors: Fleck, Bernard; Straus, Thomas; Wedemeyer, Sven
2016SPD....47.0102F Altcode:
Waves and oscillations are interesting not only from the point of view
that they can propagate energy into the chromosphere and dissipate that
energy to produce non-radiative heating, they also carry information
about the structure of the atmosphere in which they propagate. Since
the late 80s there is substantial evidence that the chromospheric
wave field is dominated by a non-propagating component, presumably
resulting from wave reflection at the transition region. Observations
of Doppler oscillations measured in the Ca II infrared tripet lines,
Ca II K, and He 10830 all show vanishing phase lags (i.e. vanishing
travel time differences) between the various lines, in particular also
for frequencies above the cut-off frequency. Why is the apparent phase
speed of high frequency acoustic waves in the chromosphere so high? Are
these results misleading because of complex radiation transfer effects
in these optically thick lines? ALMA, which acts as a linear thermometer
of the solar chromosphere, will provide measurements of the local
plasma conditions that should be, at least in principle, much easier
to interpret. Multi-wavelength time series of ALMA observations of the
temperature fluctuations of inter-network oscillations should allow
travel time measurements between different heights as these disturbances
propagate through the chromosphere and thus should finally settle the
long-standing question about the propagation characteristics of high
frequency acoustic waves in the chromosphere. We plan to combine ALMA
mm-observations with high resolution IRIS observations in the Mg II
h and k lines, and until ALMA observations are available, will study
the expected signals using time series of mm-maps from 3D radiation
hydrodynamics simulations that are being prepared within the framework
of the Solar Simulations for the Atacama Large Millimeter Observatory
Network (SSALMON).

---------------------------------------------------------
Title: Solar Observations with the Atacama Large
Millimeter/submillimeter Array (ALMA)
Authors: Kobelski, A.; Bastian, T. S.; Bárta, M.; Brajša, R.; Chen,
B.; De Pontieu, B.; Fleishman, G.; Gary, D.; Hales, A.; Hills, R.;
Hudson, H.; Hurford, G.; Loukitcheva, M.; Iwai, K.; Krucker, S.;
Shimojo, M.; Skokić, I.; Wedemeyer, S.; White, S.; Yan, Y.; ALMA
Solar Development Team
2016ASPC..504..327K Altcode:
The Atacama Large Millimeter/Submillimeter Array (ALMA) is a
joint North American, European, and East Asian project that opens
the mm-sub mm wavelength part of the electromagnetic spectrum for
general astrophysical exploration, providing high-resolution imaging
in frequency bands currently ranging from 84 GHz to 950 GHz (300
microns to 3 mm). It is located in the Atacama desert in northern
Chile at an elevation of 5000 m. Despite being a general purpose
instrument, provisions have been made to enable solar observations
with ALMA. Radiation emitted at ALMA wavelengths originates mostly
from the chromosphere, which plays an important role in the transport
of matter and energy, and the in heating the outer layers of the solar
atmosphere. Despite decades of research, the solar chromosphere remains
a significant challenge: both to observe, owing to the complicated
formation mechanisms of currently available diagnostics; and to
understand, as a result of the complex nature of the structure and
dynamics of the chromosphere. ALMA has the potential to change the
scene substantially as it serves as a nearly linear thermometer at
high spatial and temporal resolution, enabling us to study the complex
interaction of magnetic fields and shock waves and yet-to-be-discovered
dynamical processes. Moreover, ALMA will play an important role in
the study of energetic emissions associated with solar flares at
sub-THz frequencies.

---------------------------------------------------------
Title: Solar Science with the Atacama Large Millimeter/Submillimeter
Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
Selhorst, C. L.; Barta, M.
2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
powerful tool for observing the Sun at high spatial, temporal, and
spectral resolution. These capabilities can address a broad range
of fundamental scientific questions in solar physics. The radiation
observed by ALMA originates mostly from the chromosphere—a complex
and dynamic region between the photosphere and corona, which plays a
crucial role in the transport of energy and matter and, ultimately,
the heating of the outer layers of the solar atmosphere. Based on
first solar test observations, strategies for regular solar campaigns
are currently being developed. State-of-the-art numerical simulations
of the solar atmosphere and modeling of instrumental effects can help
constrain and optimize future observing modes for ALMA. Here we present
a short technical description of ALMA and an overview of past efforts
and future possibilities for solar observations at submillimeter and
millimeter wavelengths. In addition, selected numerical simulations
and observations at other wavelengths demonstrate ALMA's scientific
potential for studying the Sun for a large range of science cases.

---------------------------------------------------------
Title: New Eyes on the Sun — Solar Science with ALMA
Authors: Wedemeyer, S.
2016Msngr.163...15W Altcode:
In Cycle 4, which starts in October 2016, the Atacama Large
Millimeter/submillimeter Array (ALMA) will be open for regular
observations of the Sun for the first time. ALMA’s impressive
capabilities have the potential to revolutionise our understanding
of our host star, with far-reaching implications for our knowledge
about stars in general. The radiation emitted at ALMA wavelengths
originates mostly from the chromosphere — a complex and dynamic layer
between the photosphere and the corona that is prominent during solar
eclipses. Despite decades of intensive research, the chromosphere is
still elusive due to its complex nature and the resulting challenges to
its observation. ALMA will change the scene substantially by opening up
a new window on the Sun, promising answers to long-standing questions.

---------------------------------------------------------
Title: Synthetic activity indicators for M-type dwarf stars
Authors: Wedemeyer, Sven; Ludwig, Hans-Günter
2016IAUS..320..303W Altcode: 2015arXiv151106153W
Here, we present a set of time-dependent 3D RMHD simulations of a
M-dwarf star representative of AD Leo, which extend from the upper
convection zone into the chromosphere. The 3D model atmospheres are
characterized by a very dynamic and intermittent structure on small
spatial and temporal scales and a wealth of physical processes,
which by nature cannot be described by means of 1D static model
atmospheres. Artificial observations of these models imply that a
combination of complementary diagnostics such as Ca II lines and the
continuum intensity from UV to millimeter wavelengths, probe various
properties of the dynamics, thermal and magnetic structure of the
photosphere and the chromosphere and thus provide measures of stellar
activity, which can be compared to observations. The complicated
magnetic field structure and its imprint in synthetic diagnostics may
have important implications for the understanding and characterization
of stellar activity and with it possibly for the evaluation of planetary
habitability around active M-dwarf stars.

---------------------------------------------------------
Title: ALMA Observations of the Sun in Cycle 4 and Beyond
Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.;
Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.;
Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson,
M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.;
Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov,
V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões,
P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig,
A.; White, S.; Yagoubov, P.; Zaqarashvili, T.
2016arXiv160100587W Altcode:
This document was created by the Solar Simulations for the Atacama
Large Millimeter Observatory Network (SSALMON) in preparation of
the first regular observations of the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA), which are anticipated to start
in ALMA Cycle 4 in October 2016. The science cases presented here
demonstrate that a large number of scientifically highly interesting
observations could be made already with the still limited solar
observing modes foreseen for Cycle 4 and that ALMA has the potential
to make important contributions to answering long-standing scientific
questions in solar physics. With the proposal deadline for ALMA Cycle
4 in April 2016 and the Commissioning and Science Verification campaign
in December 2015 in sight, several of the SSALMON Expert Teams composed
strategic documents in which they outlined potential solar observations
that could be feasible given the anticipated technical capabilities
in Cycle 4. These documents have been combined and supplemented
with an analysis, resulting in recommendations for solar observing
with ALMA in Cycle 4. In addition, the detailed science cases also
demonstrate the scientific priorities of the solar physics community
and which capabilities are wanted for the next observing cycles. The
work on this White Paper effort was coordinated in close cooperation
with the two international solar ALMA development studies led by
T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be
further updated until the beginning of Cycle 4 in October 2016. In
particular, we plan to adjust the technical capabilities of the solar
observing modes once finally decided and to further demonstrate the
feasibility and scientific potential of the included science cases by
means of numerical simulations of the solar atmosphere and corresponding
simulated ALMA observations.

---------------------------------------------------------
Title: Solar Simulations for the Atacama Large Millimeter Observatory
Network
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.;
Shimojo, M.
2015ASPC..499..341W Altcode: 2015arXiv150206379W
The Atacama Large Millimeter/submillimeter Array (ALMA) will
be a valuable tool for observing the chromosphere of our Sun at
(sub-)millimeter wavelengths at high spatial, temporal and spectral
resolution and as such has great potential to address long-standing
scientific questions in solar physics. In order to make the best use
of this scientific opportunity, the Solar Simulations for the Atacama
Large Millimeter Observatory Network has been initiated. A key goal
of this international collaboration is to support the preparation and
interpretation of future observations of the Sun with ALMA.

---------------------------------------------------------
Title: ALMA's High-Cadence Imaging Capabilities for Solar Observations
Authors: Wedemeyer, S.; Parmer, A.
2015ASPC..499..343W Altcode: 2015arXiv150203580W
The Atacama Large Millimeter/submillimeter Array offers an unprecedented
view of our Sun at sub-/millimeter wavelengths. The high spatial,
temporal, and spectral resolution facilitates the measurement of gas
temperatures and magnetic fields in the solar chromosphere with high
precision. The anticipated results will revolutionize our understanding
of the solar atmosphere and may in particular result in major steps
towards solving the coronal heating problem. Based on state-of-the-art
3D radiation magnetohydrodynamic simulations, we calculate the emergent
continuum intensity (and thus brightness temperature maps) in the
wavelength range accessed by ALMA and simulate instrumental effects
for different array configurations. First results show that the local
gas temperature can be closely mapped with ALMA and that much of the
complex small-scale chromospheric pattern can be resolved.

---------------------------------------------------------
Title: SSALMON - The Solar Simulations for the Atacama Large
Millimeter Observatory Network
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson,
H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu,
B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.;
Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.;
Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier,
A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M.
2015AdSpR..56.2679W Altcode: 2015arXiv150205601W
The Solar Simulations for the Atacama Large Millimeter Observatory
Network (SSALMON) was initiated in 2014 in connection with two ALMA
development studies. The Atacama Large Millimeter/submillimeter Array
(ALMA) is a powerful new tool, which can also observe the Sun at
high spatial, temporal, and spectral resolution. The international
SSALMONetwork aims at co-ordinating the further development of solar
observing modes for ALMA and at promoting scientific opportunities
for solar physics with particular focus on numerical simulations,
which can provide important constraints for the observing modes and
can aid the interpretation of future observations. The radiation
detected by ALMA originates mostly in the solar chromosphere - a
complex and dynamic layer between the photosphere and corona, which
plays an important role in the transport of energy and matter and the
heating of the outer layers of the solar atmosphere. Potential targets
include active regions, prominences, quiet Sun regions, flares. Here,
we give a brief overview over the network and potential science cases
for future solar observations with ALMA.

---------------------------------------------------------
Title: Fast Single-Dish Scans of the Sun Using ALMA
Authors: Phillips, N.; Hills, R.; Bastian, T.; Hudson, H.; Marson,
R.; Wedemeyer, S.
2015ASPC..499..347P Altcode: 2015arXiv150206122P
We have implemented control and data-taking software that makes it
possible to scan the beams of individual ALMA antennas to perform
quite complex patterns while recording the signals at high rates. We
conducted test observations of the Sun in September and December,
2014. The data returned have excellent quality; in particular they
allow us to characterize the noise and signal fluctuations present
in this kind of observation. The fast-scan experiments included both
Lissajous patterns covering rectangular areas, and “double-circle”
patterns of the whole disk of the Sun and smaller repeated maps of
specific disk-shaped targets. With the latter we find that we can
achieve roughly Nyquist sampling of the Band 6 (230 GHz) beam in 60
s over a region 300” in diameter. These maps show a peak-to-peak
brightness-temperature range of up to 1000 K, while the time-series
variability at any given point appears to be of order 0.5% RMS over
times of a few minutes. We thus expect to be able to separate the
noise contributions due to transparency fluctuations from variations in
the Sun itself. Such timeseries have many advantages, in spite of the
non-interferometric observations. In particular such data should make
it possible to observe microflares in active regions and nanoflares
in any part of the solar disk and low corona.

---------------------------------------------------------
Title: Solar ALMA Observations - A New View of Our Host Star
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Shimojo,
M.; Hales, A.; Yagoubov, P.; Hudson, H.
2015ASPC..499..345W Altcode: 2015arXiv150206397W
ALMA provides the necessary spatial, temporal and spectral resolution to
explore central questions in contemporary solar physics with potentially
far-reaching implications for stellar atmospheres and plasma physics. It
can uniquely constraint the thermal and magnetic field structure in
the solar chromosphere with measurements that are highly complementary
to simultaneous observations with other ground-based and space-borne
instruments. Here, we highlight selected science cases.

---------------------------------------------------------
Title: On the Evolution of Magnetic White Dwarfs
Authors: Tremblay, P. -E.; Fontaine, G.; Freytag, B.; Steiner, O.;
Ludwig, H. -G.; Steffen, M.; Wedemeyer, S.; Brassard, P.
2015ApJ...812...19T Altcode: 2015arXiv150905398T
We present the first radiation magnetohydrodynamic simulations of the
atmosphere of white dwarf stars. We demonstrate that convective energy
transfer is seriously impeded by magnetic fields when the plasma-β
parameter, the thermal-to-magnetic-pressure ratio, becomes smaller
than unity. The critical field strength that inhibits convection
in the photosphere of white dwarfs is in the range B = 1-50 kG,
which is much smaller than the typical 1-1000 MG field strengths
observed in magnetic white dwarfs, implying that these objects have
radiative atmospheres. We have employed evolutionary models to study the
cooling process of high-field magnetic white dwarfs, where convection
is entirely suppressed during the full evolution (B ≳ 10 MG). We
find that the inhibition of convection has no effect on cooling rates
until the effective temperature (Teff) reaches a value of
around 5500 K. In this regime, the standard convective sequences start
to deviate from the ones without convection due to the convective
coupling between the outer layers and the degenerate reservoir of
thermal energy. Since no magnetic white dwarfs are currently known
at the low temperatures where this coupling significantly changes the
evolution, the effects of magnetism on cooling rates are not expected
to be observed. This result contrasts with a recent suggestion
that magnetic white dwarfs with Teff ≲ 10,000 K cool
significantly slower than non-magnetic degenerates.

---------------------------------------------------------
Title: The statistical properties of vortex flows in the solar
atmosphere
Authors: Wedemeyer, Sven; Kato, Yoshiaki; Steiner, Oskar
2015IAUGA..2256852W Altcode:
Rotating magnetic field structures associated with vortex flows
on the Sun, also known as “magnetic tornadoes”, may serve
as waveguides for MHD waves and transport mass and energy upwards
through the atmosphere. Magnetic tornadoes may therefore potentially
contribute to the heating of the upper atmospheric layers in quiet
Sun regions.Magnetic tornadoes are observed over a large range
of spatial and temporal scales in different layers in quiet Sun
regions. However, their statistical properties such as size, lifetime,
and rotation speed are not well understood yet because observations
of these small-scale events are technically challenging and limited
by the spatial and temporal resolution of current instruments. Better
statistics based on a combination of high-resolution observations and
state-of-the-art numerical simulations is the key to a reliable estimate
of the energy input in the lower layers and of the energy deposition
in the upper layers. For this purpose, we have developed a fast and
reliable tool for the determination and visualization of the flow
field in (observed) image sequences. This technique, which combines
local correlation tracking (LCT) and line integral convolution (LIC),
facilitates the detection and study of dynamic events on small scales,
such as propagating waves. Here, we present statistical properties
of vortex flows in different layers of the solar atmosphere and try
to give realistic estimates of the energy flux which is potentially
available for heating of the upper solar atmosphere

---------------------------------------------------------
Title: The Atacama Large Millimeter/Submillimeter Array: a New Asset
for Solar and Heliospheric Physics
Authors: Bastian, Timothy S.; Barta, Miroslav; Brajsa, Roman; Chen,
Bin; De Pontieu, Bart; Fleishman, Gregory; Gary, Dale; Hales, Antonio;
Hills, Richard; Hudson, Hugh; Iwai, Kazamasu; Shimojo, Masumi; White,
Stephen; Wedemeyer, Sven; Yan, Yihua
2015IAUGA..2257295B Altcode:
The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint
North American, European, and East Asian interferometric array that
opens the mm-submm wavelength part of the electromagnetic spectrum
for general astrophysical exploration, providing high-resolution
imaging in frequency bands ranging from 86 to 950 GHz. Despite being
a general purpose instrument, provisions have been made to enable
solar observations with ALMA. Radiation emitted at ALMA wavelengths
originates mostly from the chromosphere, which plays an important
role in the transport of energy and matter and the heating of the
outer layers of the solar atmosphere. In this paper we describe
recent efforts to ensure that ALMA can be usefully exploited by
the scientific community to address outstanding questions in solar
physics. We summarize activities under North American and European
ALMA development studies, including instrument testing, calibration
and imaging strategies, a science simulations. With the support of
solar observations, ALMA joins next-generation groundbased instruments
that can be used alone or in combination with other ground-based and
space-based instruments to address outstanding questions in solar
and heliospheric physics. Opportunities for the wider community to
contribute to these efforts will be highlighted.

---------------------------------------------------------
Title: Synthetic activity indicators for M-type dwarf stars
Authors: Wedemeyer, Sven; Ludwig, Hans-Günter; Hauschildt, Peter;
De Gennaro Aquino, Ivan
2015IAUGA..2255174W Altcode:
Our understanding of the Sun has been substantially progressed
owing to the advances in high-resolution observations during the
last decades. These observations guided the development of numerical
simulation codes for stellar atmospheres towards unprecedented levels
of realism and complexity. Such 3D radiation magnetohydrodynamic (RMHD)
codes can be applied and adapted to cooler stars. Here, we present a
set of time-dependent 3D RMHD simulations for dwarf stars of spectral
type M (representative of AD Leo). "M-dwarfs" are the most abundant
stars in our galaxy and known to exhibit mega-flares. Comparisons
of M-dwarf models with the Sun as fundamental reference case reveal
differences and similarities, which lead to important insights into
the structure and dynamics of quiescent "background" atmospheres. The
models, which extend from the upper convection zone into the
chromosphere, have different initial magnetic field strengths (up to
500G) and topologies, representing regions with different activity
levels. The 3D model atmospheres are characterized by a very dynamic
and intermittent structure on small spatial and temporal scales,
final field strengths reaching a few kG and a wealth of physical
processes, which by nature cannot be described by means of 1D static
model atmospheres.Synthetic observables, i.e. spectra and intensity
images, are calculated by using these models as input for detailed
radiative transfer calculations and can be combined into synthetic full
stellar disks, thus simulating spatially unresolved observations of
M-dwarfs. The considered diagnostics, like, e.g., Halpha, Ca II lines,
or the continuum intensity from UV to millimeter wavelengths, sample
various properties of the dynamics, thermal and magnetic structure
of the photosphere and the chromosphere and thus provide measures of
stellar activity, which can be compared to observations. The complicated
magnetic field structure and its imprint in synthetic diagnostics may
have important implications for the understanding and characterization
of stellar activity and with it possibly for the evaluation of planetary
habitability around active M-dwarf stars.

---------------------------------------------------------
Title: SSALMON - The Solar Simulations for the Atacama Large
Millimeter Observatory Network
Authors: Wedemeyer, Sven; Bastian, Timothy S.; Brajsa, Roman; Barta,
Miroslav
2015IAUGA..2257466W Altcode:
The Atacama Large Millimeter/submillimeter Array (ALMA) provides
a new powerful tool for observing the solar chromosphere at high
spatial, temporal, and spectral resolution, which will allow for
addressing fundamental scientific questions. Based on first solar test
observations, observing strategies for regular solar campaigns are
currently under development. State-of-the-art numerical simulations of
the solar atmosphere and modeling of instrumental effects can help in
this respect, constraining and optimizing future observing modes for
ALMA. On September 1st, 2014, the Solar Simulations for the Atacama
Large Millimeter Observatory Network (SSALMON) has been initiated
with the aim to co-ordinate related activities and to promote the
scientific potential of ALMA observations of the Sun. The network
is connected to two currently ongoing ALMA development studies. As
of March 18th, 57 scientists from 15 countries have joined the
international SSALMONetwork. Among the affiliations are NRAO, ESO,
NAOJ, the Czech ALMA ARC node at Ondrejov, ESA and many more. Since
March 2015, we are building up expert teams, which work on specific
tasks in preparation of future regular ALMA observations (expected to
start in late 2016) and their interpretation. Registration and more
information at http://www.ssalmon.uio.no.

---------------------------------------------------------
Title: Solar ALMA observations - A revolutionizing new view at our
host star
Authors: Wedemeyer, Sven; Brajsa, Roman; Bastian, Timothy S.; Barta,
Miroslav; Hales, Antonio; Yagoubov, Pavel; Hudson, Hugh; Loukitcheva,
Maria; Fleishman, Gregory
2015IAUGA..2256732W Altcode:
Observations of the Sun with the Atacama Large Millimeter/submillimeter
Array (ALMA) have a large potential for revolutionizing our
understanding of our host star with far reaching implications
for stars in general. The radiation emitted at ALMA wavelengths
originates mostly from the chromosphere - a complex and dynamic layer
between the photosphere and the corona, which plays an important
role in the transport of energy and matter and the heating of the
outer layers of the solar atmosphere.Despite decades of intensive
research, the chromosphere is still elusive and challenging to
observe owing to the complicated formation mechanisms of currently
available diagnostics. ALMA will change the scene substantially as
it serves as a nearly linear thermometer at high spatial, temporal,
and spectral resolution, enabling us to study the complex interaction
of magnetic fields and shock waves and yet-to-be-discovered dynamical
processes. Furthermore, radio recombination and molecular lines
may have great diagnostic potential but need to be investigated
first. These unprecedented capabilities promise important new findings
for a large range of topics in solar physics including the structure,
dynamics and energy balance of quiet Sun regions, active regions and
sunspots, flares and prominences. As a part of ongoing development
studies, an international network has been initiated, which aims at
defining and preparing key solar science with ALMA through simulation
studies: SSALMON -- Solar Simulations for the Atacama Large Millimeter
Observatory Network (http://ssalmon.uio.no). Here, we give an overview
of potential science cases.

---------------------------------------------------------
Title: Solar Observations with the Atacama Large
Millimeter/submillimeter Array
Authors: Wedemeyer, Sven
2015IAUGA..2252221W Altcode:
The interferometric Atacama Large Millimeter/submillimeter Array (ALMA)
has already demonstrated its impressive capabilities by observing a
large variety of targets ranging from protoplanetary disks to galactic
nuclei. ALMA is also capable of observing the Sun and has been used
for five solar test campaigns so far. The technically challenging solar
observing modes are currently under development and regular observations
are expected to begin in late 2016.ALMA consists of 66 antennas located
in the Chilean Andes at an altitude of 5000 m and is a true leap forward
in terms of spatial resolution at millimeter wavelengths. The resolution
of reconstructed interferometric images of the Sun is anticipated to
be close to what current optical solar telescopes can achieve. In
combination with the high temporal and spectral resolution, these
new capabilities open up new parameter spaces for solar millimeter
observations.The solar radiation at wavelengths observed by ALMA
originates from the chromosphere, where the height of the sampled
layer increases with selected wavelength. The continuum intensity is
linearly correlated to the local gas temperature in the probed layer,
which makes ALMA essentially a linear thermometer. During flares, ALMA
can detect additional non-thermal emission contributions. Measurements
of the polarization state facilitate the valuable determination of
the chromospheric magnetic field. In addition, spectrally resolved
observations of radio recombination and molecular lines may yield
great diagnostic potential, which has yet to be investigated
and developed.Many different scientific applications for a large
range of targets from quiet Sun to active regions and prominences
are possible, ranging from ultra-high cadence wave studies to flare
observations. ALMA, in particular in combination with other ground-based
and space-borne instruments, will certainly lead to fascinating new
findings, which will advance our understanding of the atmosphere of
our Sun. Here we give an overview of ALMA's capabilities and potential
science cases.

---------------------------------------------------------
Title: Observing the Sun with ALMA: A New Window into Solar Physics
Authors: Bastian, Timothy S.; Shimojo, Masumi; Wedemeyer-Bohm, Sven;
ALMA North American Solar Development Team
2015AAS...22541301B Altcode:
The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint
North American, European, and East Asian interferometric array that
opens the mm-submm wavelength part of the electromagnetic spectrum for
general astrophysical exploration, providing high resolution imaging
in frequency bands. Despite being a general purpose instrument,
provisions have been made to enable solar observations with ALMA,
thereby offering a new window into solar physics. Radiation emitted
at ALMA wavelengths originates mostly from the chromosphere, which
plays an important role in the transport of energy and matter and the
heating of the outer layers of the solar atmosphere. Despite decades
of intensive research, an understanding of the chromosphere is still
elusive, and challenging to observe owing to the complicated formation
mechanisms of currently available diagnostics. ALMA will change
the scene substantially as it serves as a nearly linear thermometer
at high spatial, temporal, and spectral resolution, enabling us to
study the complex interaction of magnetic fields and shock waves and
yet-to-be-discovered dynamical processes.Moreover, ALMA will play an
important role in the study of energetic emissions associated with
solar flares at sub-THz frequencies.This presentations introduces
ALMA to the solar physcis community and motivates the science that
can be addressed by ALMA using a number of examples based on 3D MHD
simulations. In addition, the means by which ALMA is used to acquire and
calibrate solar observations will be discussed. Finally, we encourage
potential users to join us in further defining and articulating the
exciting science to be explored with this fundamentally new instrument.

---------------------------------------------------------
Title: Unresolved Fine-scale Structure in Solar Coronal Loop-tops
Authors: Scullion, E.; Rouppe van der Voort, L.; Wedemeyer, S.;
Antolin, P.
2014ApJ...797...36S Altcode: 2014arXiv1409.1920S
New and advanced space-based observing facilities continue to lower
the resolution limit and detect solar coronal loops in greater
detail. We continue to discover even finer substructures within
coronal loop cross-sections, in order to understand the nature of
the solar corona. Here, we push this lower limit further to search
for the finest coronal loop substructures, through taking advantage
of the resolving power of the Swedish 1 m Solar Telescope/CRisp
Imaging Spectro-Polarimeter (CRISP), together with co-observations
from the Solar Dynamics Observatory/Atmospheric Image Assembly
(AIA). High-resolution imaging of the chromospheric Hα 656.28 nm
spectral line core and wings can, under certain circumstances, allow
one to deduce the topology of the local magnetic environment of the
solar atmosphere where its observed. Here, we study post-flare coronal
loops, which become filled with evaporated chromosphere that rapidly
condenses into chromospheric clumps of plasma (detectable in Hα)
known as a coronal rain, to investigate their fine-scale structure. We
identify, through analysis of three data sets, large-scale catastrophic
cooling in coronal loop-tops and the existence of multi-thermal,
multi-stranded substructures. Many cool strands even extend fully
intact from loop-top to footpoint. We discover that coronal loop
fine-scale strands can appear bunched with as many as eight parallel
strands within an AIA coronal loop cross-section. The strand number
density versus cross-sectional width distribution, as detected by CRISP
within AIA-defined coronal loops, most likely peaks at well below 100
km, and currently, 69% of the substructure strands are statistically
unresolved in AIA coronal loops.

---------------------------------------------------------
Title: On the plasma flow inside magnetic tornadoes on the Sun
Authors: Wedemeyer, Sven; Steiner, Oskar
2014PASJ...66S..10W Altcode: 2014PASJ..tmp...98W; 2014arXiv1406.7270W
High-resolution observations with the Swedish 1-m Solar Telescope (SST)
and the Solar Dynamics Observatory (SDO) reveal rotating magnetic field
structures that extend from the solar surface into the chromosphere
and the corona. These so-called magnetic tornadoes are primarily
detected as rings or spirals of rotating plasma in the Ca II 854.2 nm
line core (also known as chromospheric swirls). Detailed numerical
simulations show that the observed chromospheric plasma motion is
caused by the rotation of magnetic field structures, which again
are driven by photospheric vortex flows at their footpoints. Under
the right conditions, two vortex flow systems are stacked on top of
each other. We refer to the lower vortex, which extends from the low
photosphere into the convection zone, as intergranular vortex flow
(IVF). Once a magnetic field structure is co-located with an IVF,
the rotation is mediated into the upper atmospheric layers and an
atmospheric vortex flow (AVF, or magnetic tornado) is generated. In
contrast to the recent work by Shelyag et al. (2013, ApJ, 776, L4),
we demonstrate that particle trajectories in a simulated magnetic
tornado indeed follow spirals and argue that the properties of the
trajectories decisively depend on the location in the atmosphere and
the strength of the magnetic field.

---------------------------------------------------------
Title: The Detection of Upwardly Propagating Waves Channeling Energy
from the Chromosphere to the Low Corona
Authors: Freij, N.; Scullion, E. M.; Nelson, C. J.; Mumford, S.;
Wedemeyer, S.; Erdélyi, R.
2014ApJ...791...61F Altcode: 2014arXiv1408.4621F
There have been ubiquitous observations of wave-like motions in
the solar atmosphere for decades. Recent improvements to space- and
ground-based observatories have allowed the focus to shift to smaller
magnetic structures on the solar surface. In this paper, high-resolution
ground-based data taken using the Swedish 1 m Solar Telescope is
combined with co-spatial and co-temporal data from the Atmospheric
Imaging Assembly (AIA) on board the Solar Dynamics Observatory
(SDO) satellite to analyze running penumbral waves (RPWs). RPWs
have always been thought to be radial wave propagation that occurs
within sunspots. Recent research has suggested that they are in fact
upwardly propagating field-aligned waves (UPWs). Here, RPWs within a
solar pore are observed for the first time and are interpreted as UPWs
due to the lack of a penumbra that is required to support RPWs. These
UPWs are also observed co-spatially and co-temporally within several
SDO/AIA elemental lines that sample the transition region and low
corona. The observed UPWs are traveling at a horizontal velocity of
around 17 ± 0.5 km s-1 and a minimum vertical velocity
of 42 ± 21 km s-1. The estimated energy of the waves is
around 150 W m-2, which is on the lower bound required to
heat the quiet-Sun corona. This is a new, yet unconsidered source of
wave energy within the solar chromosphere and low corona.

---------------------------------------------------------
Title: Are Giant Tornadoes the Legs of Solar Prominences?
Authors: Wedemeyer, Sven; Scullion, Eamon; Rouppe van der Voort, Luc;
Bosnjak, Antonija; Antolin, Patrick
2013ApJ...774..123W Altcode: 2013arXiv1306.2661W
Observations in the 171 Å channel of the Atmospheric Imaging Assembly
of the space-borne Solar Dynamics Observatory show tornado-like
features in the atmosphere of the Sun. These giant tornadoes appear
as dark, elongated, and apparently rotating structures in front of
a brighter background. This phenomenon is thought to be produced
by rotating magnetic field structures that extend throughout the
atmosphere. We characterize giant tornadoes through a statistical
analysis of properties such as spatial distribution, lifetimes,
and sizes. A total number of 201 giant tornadoes are detected in a
period of 25 days, suggesting that, on average, about 30 events are
present across the whole Sun at a time close to solar maximum. Most
tornadoes appear in groups and seem to form the legs of prominences,
thus serving as plasma sources/sinks. Additional Hα observations with
the Swedish 1 m Solar Telescope imply that giant tornadoes rotate as
a structure, although they clearly exhibit a thread-like structure. We
observe tornado groups that grow prior to the eruption of the connected
prominence. The rotation of the tornadoes may progressively twist
the magnetic structure of the prominence until it becomes unstable
and erupts. Finally, we investigate the potential relation of giant
tornadoes to other phenomena, which may also be produced by rotating
magnetic field structures. A comparison to cyclones, magnetic tornadoes,
and spicules implies that such events are more abundant and short-lived
the smaller they are. This comparison might help to construct a power
law for the effective atmospheric heating contribution as a function
of spatial scale.

---------------------------------------------------------
Title: Magnetic tornadoes and chromospheric swirls - Definition
and classification
Authors: Wedemeyer, Sven; Scullion, Eamon; Steiner, Oskar; de la Cruz
Rodriguez, Jaime; Rouppe van der Voort, L. H. M.
2013JPhCS.440a2005W Altcode: 2013arXiv1303.0179W
Chromospheric swirls are the observational signatures of rotating
magnetic field structures in the solar atmosphere, also known as
magnetic tornadoes. Swirls appear as dark rotating features in the core
of the spectral line of singly ionized calcium at a wavelength of 854.2
nm. This signature can be very subtle and difficult to detect given
the dynamic changes in the solar chromosphere. Important steps towards
a systematic and objective detection method are the compilation and
characterization of a statistically significant sample of observed
and simulated chromospheric swirls. Here, we provide a more exact
definition of the chromospheric swirl phenomenon and also present a
first morphological classification of swirls with three types: (I) Ring,
(II) Split, (III) Spiral. We also discuss the nature of the magnetic
field structures connected to tornadoes and the influence of limited
spatial resolution on the appearance of their photospheric footpoints.

---------------------------------------------------------
Title: Is the Sun Lighter than the Earth? Isotopic CO in the
Photosphere, Viewed through the Lens of Three-dimensional Spectrum
Synthesis
Authors: Ayres, Thomas R.; Lyons, J. R.; Ludwig, H. -G.; Caffau, E.;
Wedemeyer-Böhm, S.
2013ApJ...765...46A Altcode: 2013arXiv1301.5281A
We consider the formation of solar infrared (2-6 μm) rovibrational
bands of carbon monoxide (CO) in CO5BOLD 3D convection models,
with the aim of refining abundances of the heavy isotopes of carbon
(13C) and oxygen (18O, 17O), to
compare with direct capture measurements of solar wind light ions
by the Genesis Discovery Mission. We find that previous, mainly 1D,
analyses were systematically biased toward lower isotopic ratios (e.g.,
R 23 ≡ 12C/13C), suggesting an
isotopically "heavy" Sun contrary to accepted fractionation processes
that were thought to have operated in the primitive solar nebula. The
new 3D ratios for 13C and 18O are R 23
= 91.4 ± 1.3 (R ⊕ = 89.2) and R 68 =
511 ± 10 (R ⊕ = 499), where the uncertainties are
1σ and "optimistic." We also obtained R 67 = 2738 ±
118 (R ⊕ = 2632), but we caution that the observed
12C17O features are extremely weak. The new solar
ratios for the oxygen isotopes fall between the terrestrial values and
those reported by Genesis (R 68 = 530, R 67 =
2798), although including both within 2σ error flags, and go in the
direction favoring recent theories for the oxygen isotope composition
of Ca-Al inclusions in primitive meteorites. While not a major focus
of this work, we derive an oxygen abundance, epsilonO ~
603 ± 9 ppm (relative to hydrogen; log epsilon ~ 8.78 on the H =
12 scale). The fact that the Sun is likely lighter than the Earth,
isotopically speaking, removes the necessity of invoking exotic
fractionation processes during the early construction of the inner
solar system.

---------------------------------------------------------
Title: Isotopic CO in the Solar Photosphere, Viewed Through the Lens
of 3D Spectrum Synthesis
Authors: Ayres, T. R.; Lyons, J. R.; Ludwig, H. -G.; Caffau, E.;
Wedemeyer-Bohm, S.
2013LPI....44.3038A Altcode: 2013LPICo1719.3038A
New analyses of CO isotopologue abundances in the solar photosphere
are now consistent with Genesis solar wind results, although ^17O
error bars are still large.

---------------------------------------------------------
Title: Three-dimensional magnetohydrodynamic simulations of M-dwarf
chromospheres
Authors: Wedemeyer, S.; Ludwig, H. -G.; Steiner, O.
2013AN....334..137W Altcode: 2013csss...17..137W; 2012arXiv1207.2342W
We present first results from three-dimensional radiation
magnetohydrodynamic simulations of M-type dwarf stars with
CO5BOLD. The local models include the top of the convection
zone, the photosphere, and the chromosphere. The results are illustrated
for models with an effective temperature of 3240 K and a gravitational
acceleration of {log g = 4.5}, which represent analogues of AD Leo. The
models have different initial magnetic field strengths and field
topologies. This first generation of models demonstrates that the
atmospheres of M dwarfs are highly dynamic and intermittent. Magnetic
fields and propagating shock waves produce a complicated fine-structure,
which is clearly visible in synthetic intensity maps in the core of the
Ca II K spectral line and also at millimeter wavelengths. The dynamic
small-scale pattern cannot be described by means of one-dimensional
models, which has important implications for the construction of
semi-empirical model atmospheres and thus for the interpretation
of observations in general. Detailed three-dimensional numerical
simulations are valuable in this respect. Furthermore, such models
facilitate the analysis of small-scale processes, which cannot be
observed on stars but nevertheless might be essential for understanding
M-dwarf atmospheres and their activity. An example are so-called
“magnetic tornadoes”, which have recently been found on the Sun and
are presented here in M-dwarf models for the first time.

---------------------------------------------------------
Title: The CO5BOLD analysis tool.
Authors: Wedemeyer, S.
2013MSAIS..24...96W Altcode: 2013arXiv1301.1497W
The interactive IDL-based CO5BOLD Analysis Tool (CAT) was developed
to facilitate an easy and quick analysis of numerical simulation data
produced with the 2D/3D radiation magnetohydrodynamics code CO5BOLD. The
basic mode of operation is the display and analysis of cross-sections
through a model either as 2D slices or 1D graphs. A wide range of
physical quantities can be selected. Further features include the export
of models into VAPOR format or the output of images and animations. A
short overview including scientific analysis examples is given.

---------------------------------------------------------
Title: Solar carbon monoxide: poster child for 3D effects .
Authors: Ayres, T. R.; Lyons, J. R.; Ludwig, H. -G.; Caffau, E.;
Wedemeyer-Böhm, S.
2013MSAIS..24...85A Altcode:
Photospheric infrared (2-6 mu m) rovibrational bands of carbon
monoxide (CO) provide a tough test for 3D convection models such as
those calculated using CO5BOLD. The molecular formation is highly
temperature-sensitive, and thus responds in an exaggerated way to
thermal fluctuations in the dynamic atmosphere. CO, itself, is an
important tracer of the oxygen abundance, a still controversial
issue in solar physics; as well as the heavy isotopes of carbon
(13C) and oxygen (18O, 17O), which,
relative to terrestrial values, are fingerprints of fractionation
processes that operated in the primitive solar nebula. We show how 3D
models impact the CO line formation, and add in a second constraint
involving the near-UV Ca RIPTSIZE II line wings, which also are highly
temperature sensitive, but in the opposite sense to the molecules. We
find that our reference CO5BOLD snapshots appear to be slightly too
cool on average in the outer layers of the photosphere where the CO
absorptions and Ca RIPTSIZE II wing emissions arise. We show, further,
that previous 1D modeling was systematically biased toward higher
oxygen abundances and lower isotopic ratios (e.g., R23equiv
12C/13C), suggesting an isotopically “heavy”
Sun contrary to direct capture measurements of solar wind light ions
by the Genesis Discovery Mission. New 3D ratios for the oxygen isotopes
are much closer to those reported by Genesis, and the associated oxygen
abundance from CO now is consistent with the recent Caffau et al. study
of atomic oxygen. Some lingering discrepancies perhaps can be explained
by magnetic bright points. Solar CO demonstrates graphically the wide
gulf that can occur between a 3D analysis and 1D.

---------------------------------------------------------
Title: Magnetic tornadoes as energy channels into the solar corona
Authors: Wedemeyer-Böhm, Sven; Scullion, Eamon; Steiner, Oskar;
Rouppe van der Voort, Luc; de La Cruz Rodriguez, Jaime; Fedun, Viktor;
Erdélyi, Robert
2012Natur.486..505W Altcode:
Heating the outer layers of the magnetically quiet solar atmosphere to
more than one million kelvin and accelerating the solar wind requires
an energy flux of approximately 100 to 300 watts per square metre,
but how this energy is transferred and dissipated there is a puzzle and
several alternative solutions have been proposed. Braiding and twisting
of magnetic field structures, which is caused by the convective flows
at the solar surface, was suggested as an efficient mechanism for
atmospheric heating. Convectively driven vortex flows that harbour
magnetic fields are observed to be abundant in the photosphere
(the visible surface of the Sun). Recently, corresponding swirling
motions have been discovered in the chromosphere, the atmospheric
layer sandwiched between the photosphere and the corona. Here we
report the imprints of these chromospheric swirls in the transition
region and low corona, and identify them as observational signatures
of rapidly rotating magnetic structures. These ubiquitous structures,
which resemble super-tornadoes under solar conditions, reach from
the convection zone into the upper solar atmosphere and provide an
alternative mechanism for channelling energy from the lower into the
upper solar atmosphere.

---------------------------------------------------------
Title: Small-scale rotating magnetic flux structures as alternative
energy channels into the low corona
Authors: Wedemeyer-Böhm; , Sven; Scullion; , Eamon; Steiner; , Oskar;
Rouppe van der Voort, Luc; de la Cruz Rodriguez, Jaime; Erdelyi,
Robertus; Fedun, Viktor
2012decs.confE..67W Altcode:
Vortex flows are frequently observed in the downflow areas in the lanes
between granules. The magnetic field is advected and trapped by these
flows in the low photosphere. Consequently, the rotation of a vortex
flow is transferred to the atmospheric layers above by means of the
magnetic flux structure. This effect results in so-called swirls, which
are observed in the chromosphere. New simultaneous observations with
the Swedish Solar Telescope and the Solar Dynamics Observatory reveal
that chromospheric swirls can have a coronal counterpart. This finding
implies that the rotating flux structure couples the layers of the solar
atmosphere from the photosphere to the (low) corona. Three-dimensional
numerical simulations confirm this picture and reproduce the swirl
signature. A combined analysis of the simulations and observations
implies that such small-scale rotating flux structures could provide
an alternative mechanism for channeling substantial energy from the
photosphere into the upper solar atmosphere.

---------------------------------------------------------
Title: Simulations of stellar convection with CO5BOLD
Authors: Freytag, B.; Steffen, M.; Ludwig, H. -G.; Wedemeyer-Böhm,
S.; Schaffenberger, W.; Steiner, O.
2012JCoPh.231..919F Altcode: 2011arXiv1110.6844F
High-resolution images of the solar surface show a granulation
pattern of hot rising and cooler downward-sinking material - the
top of the deep-reaching solar convection zone. Convection plays a
role for the thermal structure of the solar interior and the dynamo
acting there, for the stratification of the photosphere, where most
of the visible light is emitted, as well as for the energy budget of
the spectacular processes in the chromosphere and corona. Convective
stellar atmospheres can be modeled by numerically solving the coupled
equations of (magneto)hydrodynamics and non-local radiation transport
in the presence of a gravity field. The CO5BOLD code described in this
article is designed for so-called "realistic" simulations that take
into account the detailed microphysics under the conditions in solar
or stellar surface layers (equation-of-state and optical properties of
the matter). These simulations indeed deserve the label "realistic"
because they reproduce the various observables very well - with only
minor differences between different implementations. The agreement
with observations has improved over time and the simulations are now
well-established and have been performed for a number of stars. Still,
severe challenges are encountered when it comes to extending these
simulations to include ideally the entire star or substellar object:
the strong stratification leads to completely different conditions in
the interior, the photosphere, and the corona. Simulations have to cover
spatial scales from the sub-granular level to the stellar diameter and
time scales from photospheric wave travel times to stellar rotation
or dynamo cycle periods. Various non-equilibrium processes have to be
taken into account. Last but not least, realistic simulations are based
on detailed microphysics and depend on the quality of the input data,
which can be the actual accuracy limiter. This article provides an
overview of the physical problem and the numerical solution and the
capabilities of CO5BOLD, illustrated with a number of applications.

---------------------------------------------------------
Title: Non-equilibrium calcium ionisation in the solar atmosphere
Authors: Wedemeyer-Böhm, S.; Carlsson, M.
2011A&A...528A...1W Altcode: 2011arXiv1101.2211W
Context. The chromosphere of the Sun is a temporally and spatially
very varying medium for which the assumption of ionisation equilibrium
is questionable. Aims: Our aim is to determine the dominant
processes and timescales for the ionisation equilibrium of calcium under
solar chromospheric conditions. Methods: The study is based on
numerical simulations with the RADYN code, which combines hydrodynamics
with a detailed solution of the radiative transfer equation. The
calculations include a detailed non-equilibrium treatment of hydrogen,
calcium, and helium. Next to an hour long simulation sequence,
additional simulations are produced, for which the stratification is
slightly perturbed so that a ionisation relaxation timescale can be
determined. The simulations are characterised by upwards propagating
shock waves, which cause strong temperature fluctuations and variations
of the (non-equilibrium) ionisation degree of calcium. Results:
The passage of a hot shock front leads to a strong net ionisation
of Ca II, rapidly followed by net recombination. The relaxation
timescale of the calcium ionisation state is found to be of the
order of a few seconds at the top of the photosphere and 10 to 30 s
in the upper chromosphere. At heights around 1 Mm, we find typical
values around 60 s and in extreme cases up to ~150 s. Generally,
the timescales are significantly reduced in the wakes of ubiquitous
hot shock fronts. The timescales can be reliably determined from a
simple analysis of the eigenvalues of the transition rate matrix. The
timescales are dominated by the radiative recombination from Ca III
into the metastable Ca II energy levels of the 4d 2D
term. These transitions depend strongly on the density of free
electrons and therefore on the (non-equilibrium) ionisation degree of
hydrogen, which is the main electron donor. Conclusions: The
ionisation/recombination timescales derived here are too long for the
assumption of an instantaneous ionisation equilibrium to be valid and,
on the other hand, are not long enough to warrant an assumption of a
constant ionisation fraction. Fortunately, the ionisation degree of Ca
ii remains small in the height range, where the cores of the H, K, and
the infrared triplet lines are formed. We conclude that the difference
due to a detailed treatment of Ca ionisation has only negligible impact
on the modelling of spectral lines of Ca ii and the plasma properties
under the conditions in the quiet solar chromosphere.

---------------------------------------------------------
Title: CO5BOLD: COnservative COde for the COmputation of COmpressible
COnvection in a BOx of L Dimensions with l=2,3
Authors: Freytag, Bernd; Steffen, Matthias; Wedemeyer-Böhm, Sven;
Ludwig, Hans-Günter; Leenaarts, Jorrit; Schaffenberger, Werner;
Allard, France; Chiavassa, Andrea; Höfner, Susanne; Kamp, Inga;
Steiner, Oskar
2010ascl.soft11014F Altcode:
CO5BOLD - nickname COBOLD - is the short form of "COnservative
COde for the COmputation of COmpressible COnvection in a BOx of L
Dimensions with l=2,3". It is used to model solar and stellar
surface convection. For solar-type stars only a small fraction of the
stellar surface layers are included in the computational domain. In
the case of red supergiants the computational box contains the entire
star. Recently, the model range has been extended to sub-stellar objects
(brown dwarfs). CO5BOLD solves the coupled non-linear equations
of compressible hydrodynamics in an external gravity field together
with non-local frequency-dependent radiation transport. Operator
splitting is applied to solve the equations of hydrodynamics (including
gravity), the radiative energy transfer (with a long-characteristics
or a short-characteristics ray scheme), and possibly additional 3D
(turbulent) diffusion in individual sub steps. The 3D hydrodynamics
step is further simplified with directional splitting (usually). The 1D
sub steps are performed with a Roe solver, accounting for an external
gravity field and an arbitrary equation of state from a table. The radiation transport is computed with either one of three
modules: MSrad module: It uses long characteristics. The lateral
boundaries have to be periodic. Top and bottom can be closed or open
("solar module"). LHDrad module: It uses long characteristics
and is restricted to an equidistant grid and open boundaries at all
surfaces (old "supergiant module"). SHORTrad module: It uses
short characteristics and is restricted to an equidistant grid and
open boundaries at all surfaces (new "supergiant module"). The
code was supplemented with an (optional) MHD version [Schaffenberger
et al. (2005)] that can treat magnetic fields. There are also modules
for the formation and advection of dust available. The current version
now contains the treatment of chemical reaction networks, mostly used
for the formation of molecules [Wedemeyer-Böhm et al. (2005)], and
hydrogen ionization [Leenaarts &amp; Wedemeyer-Böhm (2005)], too. CO5BOLD is written in Fortran90. The parallelization is done with
OpenMP directives.

---------------------------------------------------------
Title: Are there variations in Earth's global mean temperature
related to the solar activity?
Authors: Kjeldseth-Moe, Olav; Wedemeyer-Böhm, Sven
2010IAUS..264..320K Altcode:
We have analyzed the record of Earth's global temperature variations
between 1850 and 2007 looking for signals of periodic variations and
compared our results with solar activity variations in the same time
period. Significant periods are found at 9.4, 10.6 and 20.9 years. These
periodic variations may be caused by solar activity. However, and
amazingly enough, we also find at least 17 other significant periodic
variations in addition to expected variations with periods of 1 year
and of half a year. The result is considered in terms of solar related
forcing mechanisms. These may be variable solar heating associated
with the small changes in solar irradiance over the solar cycle,
or direct effects of interactions between variable magnetic fields
carried by the solar wind and particles and fields in interplanetary
space or in the Earth's ionosphere.

---------------------------------------------------------
Title: Small-scale structure and dynamics of the chromospheric
magnetic field
Authors: Wedemeyer-Böhm, S.
2010MmSAI..81..693W Altcode: 2009arXiv0911.5639W
Recent advances in observational performance and numerical simulations
have revolutionised our understanding of the solar chromosphere. This
concerns in particular the structure and dynamics on small spatial and
temporal scales. As a result, the picture of the solar chromosphere
changed from an idealised static and plane-parallel stratification to a
complex compound of intermittent domains, which are dynamically coupled
to the layers below and above. In this picture, the chromosphere in
a stricter sense is associated with the typical fibrilar structure
shaped by magnetic fields like it is known from images taken in
the Halpha line core. In internetwork regions below this layer,
there exists a domain with propagating shock waves and weak magnetic
fields, which both probably interact with the overlying large scale
field. The existence of such a sub-canopy domain certainly depends on
the properties of the overlying field. Details of the structure of the
lower atmosphere can therefore be expected to vary significantly from
location to location. Here, high-resolution observations, which were
obtained with the CRISP filter at the Swedish Solar Telescope, are
used to derive qualitative constraints for the atmospheric structure
of quiet-Sun regions.

---------------------------------------------------------
Title: NLTE spectral synthesis based on 3D MHD convection simulations
-understanding the role of the magnetic field in intensity variations
Authors: Haberreiter, Margit; Wedemeyer-Boehm, Sven; Rast, Mark
2010cosp...38..132H Altcode: 2010cosp.meet..132H
While the magnetic field is considered to be the main driver for Solar
Spectral Irradiance (SSI) variations, the detailed physical mechanisms
that explain this relation are not yet fully understood. In this paper
we analyze the effect of small scale magnetic field on the intensity in
Ca II 393.4 nm and various continuum wavelengths calculated with the
NLTE radiative tranfer code SolMod3D. The code calculates NLTE level
populations and line spectra based on 3D MHD simulations carried out
with CO5BOLD. This enables us to study in great detail the effect of
the varying small scale magnetic field on intensity variations. The
results are important for a better understanding of the role of
small-scale magnetic field in irradiance variations.

---------------------------------------------------------
Title: Toward the analysis of waves in the solar atmosphere based
on NLTE spectral synthesis from 3D MHD simulations.
Authors: Haberreiter, M.; Finsterle, W.; McIntosh, S.; Wedemeyer-Böhm,
S.
2010MmSAI..81..782H Altcode: 2010arXiv1001.5086H
From the analysis of Dopplergrams in the K I 7699 Å and Na I 5890
Å spectral lines observed with the Magneto-Optical filter at Two
Heights (MOTH) experiment during the austral summer in 2002-03 we find
upward traveling waves in magnetic regions. Our analysis shows that
the dispersion relation of these waves strongly depends on whether
the wave is detected in the low-beta or high-beta regime. Moreover,
the observed dispersion relation does not show the expected decrease
of the acoustic cut-off frequency for the field guided slow magnetic
wave. Instead, we detected an increase of the travel times below the
acoustic cut-off frequency and at the same time a decrease of the travel
time above it. To study the formation height of the spectral lines
employed by MOTH in greater detail we are currently in the process of
employing 3D MHD simulations carried out with CO5BOLD to
perform NLTE spectral synthesis.

---------------------------------------------------------
Title: Recovering the line-of-sight magnetic field in the chromosphere
from Ca II IR spectra
Authors: Wöger, F.; Wedemeyer-Böhm, S.; Uitenbroek, H.; Rimmele, T.
2010MmSAI..81..598W Altcode: 2009arXiv0912.3467W
We propose a method to derive the line-of-sight magnetic flux density
from measurements in the chromospheric Ca II IR line at 854.2 nm. The
method combines two well-understood techniques, the center-of-gravity
and bisector method, in a single hybrid technique. The technique
is tested with magneto-static simulations of a flux tube. We apply
the method to observations with the Interferometric Bidimensional
Spectrometer (IBIS) installed at the Dunn Solar Telescope of the NSO/SP
to investigate the morphology of the lower chromosphere, with focus on
the chromospheric counterparts to the underlying photospheric magnetic
flux elements.

---------------------------------------------------------
Title: Morphology and Dynamics of Photospheric and Chromospheric
Magnetic Fields
Authors: Wöger, F.; Wedemeyer-Böhm, S.; Rimmele, T.
2009ASPC..415..319W Altcode: 2009arXiv0912.3285W
We use joint observations obtained with the Hinode space observatory
and the Interferometric Bidimensional Spectrometer (IBIS) installed
at the DST of the NSO/SP to investigate the morphology and dynamics
of (a) non-magnetic and (b) magnetic regions in the fluctosphere. In
inter-network regions with no significant magnetic flux contributions
above the detection limit of IBIS, we find intensity structures with
similar characteristics as those seen in numerical simulations by
Wedemeyer-Böhm et al. (2008) The magnetic flux elements in the network
are stable and seem to resemble the spatially extended counterparts
to the underlying photospheric magnetic elements. We will explain
some of the difficulties in deriving the magnetic field vector from
observations of the fluctosphere.

---------------------------------------------------------
Title: The Horizontal Magnetic Field of the Quiet Sun: Numerical
Simulations in Comparison to Observations with Hinode
Authors: Steiner, O.; Rezaei, R.; Schlichenmaier, R.; Schaffenberger,
W.; Wedemeyer-Böhm, S.
2009ASPC..415...67S Altcode: 2009arXiv0904.2030S
Three-dimensional magnetohydrodynamic simulations of the surface layers
of the Sun intrinsically produce a predominantly horizontal magnetic
field in the photosphere. This is a robust result in the sense that it
arises from simulations with largely different initial and boundary
conditions for the magnetic field. While the disk-center synthetic
circular and linear polarization signals agree with measurements from
Hinode, their center-to-limb variation sensitively depends on the
height variation of the horizontal and the vertical field component
and they seem to be at variance with the observed behavior.

---------------------------------------------------------
Title: Morphology and Dynamics of the Low Solar Chromosphere
Authors: Wöger, F.; Wedemeyer-Böhm, S.; Uitenbroek, H.; Rimmele,
T. R.
2009ApJ...706..148W Altcode: 2009arXiv0910.1381W
The Interferometric Bidimensional Spectrometer (IBIS) installed at
the Dunn Solar Telescope of the NSO/SP is used to investigate the
morphology and dynamics of the lower chromosphere and the virtually
non-magnetic fluctosphere below. The study addresses in particular the
structure of magnetic elements that extend into these layers. We choose
different quiet-Sun regions inside and outside the coronal holes. In
inter-network regions with no significant magnetic flux contributions
above the detection limit of IBIS, we find intensity structures with the
characteristics of a shock wave pattern. The magnetic flux elements in
the network are long lived and seem to resemble the spatially extended
counterparts to the underlying photospheric magnetic elements. We
suggest a modification to common methods to derive the line-of-sight
magnetic field strength and explain some of the difficulties in deriving
the magnetic field vector from observations of the fluctosphere.

---------------------------------------------------------
Title: Small-scale swirl events in the quiet Sun chromosphere
Authors: Wedemeyer-Böhm, S.; Rouppe van der Voort, L.
2009A&A...507L...9W Altcode: 2009arXiv0910.2226W
Context: Recent progress in instrumentation enables solar observations
with high resolution simultaneously in the spatial, temporal, and
spectral domains. Aims: We use such high-resolution observations
to study small-scale structures and dynamics in the chromosphere
of the quiet Sun. Methods: We analyse time series of spectral
scans through the Ca ii 854.2 nm spectral line obtained with the CRISP
instrument at the Swedish 1-m Solar Telescope. The targets are quiet
Sun regions inside coronal holes close to disc-centre. Results:
The line core maps exhibit relatively few fibrils compared to what
is normally observed in quiet Sun regions outside coronal holes. The
time series show a chaotic and dynamic scene that includes spatially
confined “swirl” events. These events feature dark and bright
rotating patches, which can consist of arcs, spiral arms, rings or
ring fragments. The width of the fragments typically appears to be of
the order of only 0.2 arcsec, which is close to the effective spatial
resolution. They exhibit Doppler shifts of -2 to -4 km s-1
but sometimes up to -7 km s-1, indicating fast upflows. The
diameter of a swirl is usually of the order of 2´´. At the location
of these swirls, the line wing and wide-band maps show close groups of
photospheric bright points that move with respect to each other. Conclusions: A likely explanation is that the relative motion of the
bright points twists the associated magnetic field in the chromosphere
above. Plasma or propagating waves may then spiral upwards guided by
the magnetic flux structure, thereby producing the observed intensity
signature of Doppler-shifted ring fragments. The movie is only
available in electronic form at http://www.aanda.org Marie Curie
Intra-European Fellow of the European Commission.

---------------------------------------------------------
Title: On the continuum intensity distribution of the solar
photosphere
Authors: Wedemeyer-Böhm, S.; Rouppe van der Voort, L.
2009A&A...503..225W Altcode: 2009arXiv0905.0705W
Context: For many years, there seemed to be significant differences
between the continuum intensity distributions derived from observations
and simulations of the solar photosphere. Aims: In order to
settle the discussion on these apparent discrepancies, we present a
detailed comparison between simulations and seeing-free observations
that takes into account the crucial influence of instrumental image
degradation. Methods: We use a set of images of quiet Sun
granulation taken in the blue, green and red continuum bands of the
Broadband Filter Imager of the Solar Optical Telescope (SOT) onboard
Hinode. The images are deconvolved with point spread functions (PSF)
that account for non-ideal contributions due to instrumental stray-light
and imperfections. In addition, synthetic intensity images are degraded
with the corresponding PSFs. The results are compared with respect to
spatial power spectra, intensity histograms, and the centre-to-limb
variation of the intensity contrast. Results: The intensity
distribution of SOT granulation images is broadest for the blue
continuum at disc-centre and narrows towards the limb and for longer
wavelengths. The distributions are relatively symmetric close to the
limb but exhibit a growing asymmetry towards disc-centre. The intensity
contrast, which is connected to the width of the distribution, is found
to be (12.8 ± 0.5)%, (8.3 ± 0.4)%, and (6.2 ± 0.2)% at disc-centre
for blue, green, and red continuum, respectively. Removing the influence
of the PSF unveils much broader intensity distributions with a secondary
component that is otherwise only visible as an asymmetry between
the darker and brighter than average part of the distribution. The
contrast values increase to (26.7 ± 1.3)%, (19.4 ± 1.4)%, and
(16.6 ± 0.7)% for blue, green, and red continuum, respectively. The
power spectral density of the images exhibits a pronounced peak at
spatial scales characteristic for the granulation pattern and a steep
decrease towards smaller scales. The observational findings like the
absolute values and centre-to-limb variation of the intensity contrast,
intensity histograms, and power spectral density are well matched with
corresponding synthetic observables from three-dimensional radiation
(magneto-)hydrodynamic simulations. Conclusions: We conclude that
the intensity contrast of the solar continuum intensity is higher than
usually derived from ground-based observations and is well reproduced
by modern radiation (magneto-)hydrodynamic models. Properly accounting
for image degradation effects is of crucial importance for comparisons
between observations and numerical models.

---------------------------------------------------------
Title: Coupling from the Photosphere to the Chromosphere and the
Corona
Authors: Wedemeyer-Böhm, S.; Lagg, A.; Nordlund, Å.
2009SSRv..144..317W Altcode: 2008SSRv..tmp..171W; 2008arXiv0809.0987W
The atmosphere of the Sun is characterized by a complex interplay of
competing physical processes: convection, radiation, conduction, and
magnetic fields. The most obvious imprint of the solar convection
and its overshooting in the low atmosphere is the granulation
pattern. Beside this dominating scale there is a more or less smooth
distribution of spatial scales, both towards smaller and larger
scales, making the Sun essentially a multi-scale object. Convection and
overshooting give the photosphere its face but also act as drivers for
the layers above, namely the chromosphere and corona. The magnetic field
configuration effectively couples the atmospheric layers on a multitude
of spatial scales, for instance in the form of loops that are anchored
in the convection zone and continue through the atmosphere up into
the chromosphere and corona. The magnetic field is also an important
structuring agent for the small, granulation-size scales, although
(hydrodynamic) shock waves also play an important role—especially in
the internetwork atmosphere where mostly weak fields prevail. Based on
recent results from observations and numerical simulations, we attempt
to present a comprehensive picture of the atmosphere of the quiet Sun
as a highly intermittent and dynamic system.

---------------------------------------------------------
Title: The solar continuum intensity distribution. Settling the
conflict between observations and simulations
Authors: Wedemeyer-Böhm, S.; Rouppe van der Voort, L.
2009MmSAI..80..635W Altcode: 2009arXiv0908.3758W
For many years, there seemed to be significant differences between
the continuum intensity distributions derived from observations and
simulations of the solar photosphere. In order to settle the discussion
on these apparent discrepancies, we present a detailed comparison
between simulations and seeing-free observations that takes into
account the crucial influence of instrumental image degradation. We
use a set of images of quiet Sun granulation taken in the blue, green
and red continuum bands of the Broadband Filter Imager of the Solar
Optical Telescope (SOT) onboard Hinode. The images are deconvolved with
Point Spread Functions (PSF) that account for non-ideal contributions
due to instrumental stray-light and imperfections. In addition,
synthetic intensity images are degraded with the corresponding
PSFs. The results are compared with respect to spatial power spectra,
intensity histograms, and the centre-to-limb variation of the
intensity contrast. The observational findings are well matched with
corresponding synthetic observables from three-dimensional radiation
(magneto-)hydrodynamic simulations. We conclude that the intensity
contrast of the solar continuum intensity is higher than usually
derived from ground-based observations and is well reproduced by
modern numerical simulations. Properly accounting for image degradation
effects is of crucial importance for comparisons between observations
and numerical models. It finally settles the traditionally perceived
conflict between observations and simulations.

---------------------------------------------------------
Title: Coupling from the Photosphere to the Chromosphere and the
Corona
Authors: Wedemeyer-Böhm, S.; Lagg, A.; Nordlund, Å.
2009odsm.book..317W Altcode:
The atmosphere of the Sun is characterized by a complex interplay of
competing physical processes: convection, radiation, conduction, and
magnetic fields. The most obvious imprint of the solar convection
and its overshooting in the low atmosphere is the granulation
pattern. Beside this dominating scale there is a more or less smooth
distribution of spatial scales, both towards smaller and larger
scales, making the Sun essentially a multi-scale object. Convection and
overshooting give the photosphere its face but also act as drivers for
the layers above, namely the chromosphere and corona. The magnetic field
configuration effectively couples the atmospheric layers on a multitude
of spatial scales, for instance in the form of loops that are anchored
in the convection zone and continue through the atmosphere up into
the chromosphere and corona. The magnetic field is also an important
structuring agent for the small, granulation-size scales, although
(hydrodynamic) shock waves also play an important role—especially in
the internetwork atmosphere where mostly weak fields prevail. Based on
recent results from observations and numerical simulations, we attempt
to present a comprehensive picture of the atmosphere of the quiet Sun
as a highly intermittent and dynamic system.

---------------------------------------------------------
Title: Observational Evidence for Shocks in the Solar Photosphere -
New TESOS/VTT Results
Authors: Rybak, J.; Kucera, A.; Hanslmeier, A.; Woehl, H.;
Wedemeyer-Boehm, S.; Steiner, O.
2008ESPM...12.2.36R Altcode:
High-resolution spectroscopic observations recently acquired with the
TESOS spectrometer at the Vacuum Tower Telescope (VTT, Observatorio
del Teide, Tenerife) are used to test predictions regarding strongly
dynamic events in the photosphere as obtained from three-dimensional
numerical simulations with the CO5BOLD-code. Time series of
two-dimensional maps of the Fe I 543.4 nm spectral line profile at
different centre-to-limb positions are investigated in a statistical
sense by comparing the distributions of individual spectral parameters
derived from observations with the corresponding distributions
from synthesized spectra calculated with the LINFOR3D code from
the simulations. Appropriate degradation of the synthesized spectra
was applied in order to take the limited spatial resolution of the
telescope, seeing effects, and the scattered instrumental light into
account. At the actual spatial resolution of 0.5 arc sec, the
statistics show that signatures of the photospheric dynamics, including
the most dynamical events like occasional supersonic flows of plasma in
the nearly horizontal direction, are very similar in both observations
and simulations. Discrepancies are found only for those spectral
parameters (residual line intensity, Doppler line core shifts), which
are affected by non-LTE effects, since non-LTE effects are not taken
into account in the synthesis of the Fe I 543.4nm spectral line.

---------------------------------------------------------
Title: The Horizontal Internetwork Magnetic Field: Numerical
Simulations in Comparison to Observations with Hinode
Authors: Steiner, O.; Rezaei, R.; Schaffenberger, W.; Wedemeyer-Böhm,
S.
2008ESPM...12.3.22S Altcode:
Observations with the Hinode space observatory led to the discovery
of predominantly horizontal magnetic fields in the photosphere of the
quiet internetwork region. Here we investigate realistic numerical
simulations of the surface layers of the Sun with respect to horizontal
magnetic fields and compute the corresponding polarimetric response
in the Fe I 630 nm line pair. We find a local maximum in the mean
strength of the horizontal field component at a height of around 500
km in the photosphere, where, depending on the initial state or the
boundary condition, it surpasses the vertical component by a factor
of 2.0 or 5.6. From the synthesized Stokes profiles, we derive a mean
horizontal field component that is 1.6 or 4.3 times stronger than
the vertical component, depending on the initial state or the boundary
condition. This is a consequence of both the intrinsically stronger flux
density of and the larger area occupied by the horizontal fields. We
find that convective overshooting expels horizontal fields to the upper
photosphere, making the Poynting flux positive in the photosphere,
whereas it is negative in the convectively unstable layer below it.

---------------------------------------------------------
Title: Radiation hydrodynamics simulations of stellar surface
convection
Authors: Freytag, Bernd; Steffen, Matthias; Ludwig, Hans-Guenter;
Wedemeyer-Boehm, Sven
2008asd..soft...36F Altcode:
The code is used to perform radiation hydrodynamics simulations of
the convective surface layers and the photosphere of cool stars.

---------------------------------------------------------
Title: Point spread functions for the Solar optical telescope
onboard Hinode
Authors: Wedemeyer-Böhm, S.
2008A&A...487..399W Altcode: 2008arXiv0804.4536W
Aims: We investigate the combined point spread function (PSF) of the
Broadband Filter Imager (BFI) and the Solar Optical Telescope (SOT)
onboard the Hinode spacecraft. Methods: Observations of the
Mercury transit from November 2006 and the solar eclipse(s) from 2007
are used to determine the PSFs of SOT for the blue, green, and red
continuum channels of the BFI. For each channel, we calculate large
grids of theoretical point spread functions by convolution of the ideal
diffraction-limited PSF and Voigt profiles. These PSFs are applied to
artificial images of an eclipse and a Mercury transit. The comparison
of the resulting artificial intensity profiles across the terminator
and the corresponding observed profiles yields a quality measure for
each case. The optimum PSF for each observed image is indicated by the
best fit. Results: The observed images of the Mercury transit and
the eclipses exhibit a clear proportional relation between the residual
intensity and the overall light level in the telescope. In addition,
there is an anisotropic stray-light contribution. These two factors
make it very difficult to pin down a single unique PSF that can account
for all observational conditions. Nevertheless, the range of possible
PSF models can be limited by using additional constraints like the
pre-flight measurements of the Strehl ratio. Conclusions: The
BFI/SOT operate close to the diffraction limit and have only a rather
small stray-light contribution. The FWHM of the PSF is broadened by only
~1% with respect to the diffraction-limited case, while the overall
Strehl ratio is ~0.8. In view of the large variations - best seen in
the residual intensities of eclipse images - and the dependence on the
overall light level and position in the FOV, a range of PSFs should
be considered instead of a single PSF per wavelength. The individual
PSFs of that range allow then the determination of error margins
for the quantity under investigation. Nevertheless, the stray-light
contributions are found to be best matched with Voigt functions with
the parameters σ = 0.008 arcsec and γ = 0.004 arcsec, 0.005 arcsec,
and 0.006 arcsec for the blue, green, and red continuum channels,
respectively.

---------------------------------------------------------
Title: The Horizontal Internetwork Magnetic Field: Numerical
Simulations in Comparison to Observations with Hinode
Authors: Steiner, O.; Rezaei, R.; Schaffenberger, W.; Wedemeyer-Böhm,
S.
2008ApJ...680L..85S Altcode: 2008arXiv0801.4915S
Observations with the Hinode space observatory led to the discovery
of predominantly horizontal magnetic fields in the photosphere of the
quiet internetwork region. Here we investigate realistic numerical
simulations of the surface layers of the Sun with respect to horizontal
magnetic fields and compute the corresponding polarimetric response
in the Fe I 630 nm line pair. We find a local maximum in the mean
strength of the horizontal field component at a height of around 500
km in the photosphere, where, depending on the initial state or the
boundary condition, it surpasses the vertical component by a factor
of 2.0 or 5.6. From the synthesized Stokes profiles, we derive a mean
horizontal field component that is 1.6 or 4.3 times stronger than
the vertical component, depending on the initial state or the boundary
condition. This is a consequence of both the intrinsically stronger flux
density of and the larger area occupied by the horizontal fields. We
find that convective overshooting expels horizontal fields to the upper
photosphere, making the Poynting flux positive in the photosphere,
whereas the Poynting flux is negative in the convectively unstable
layer below it.

---------------------------------------------------------
Title: Small-scale structure and dynamics of the lower solar
atmosphere
Authors: Wedemeyer-Böhm, Sven; Wöger, Friedrich
2008IAUS..247...66W Altcode: 2007IAUS..247...66W; 2007arXiv0710.4776W
The chromosphere of the quiet Sun is a highly intermittent and dynamic
phenomenon. Three-dimensional radiation (magneto-)hydrodynamic
simulations exhibit a mesh-like pattern of hot shock fronts and
cool expanding post-shock regions in the sub-canopy part of the
inter-network. This domain might be called “fluctosphere”. The
pattern is produced by propagating shock waves, which are excited
at the top of the convection zone and in the photospheric overshoot
layer. New high-resolution observations reveal a ubiquitous small-scale
pattern of bright structures and dark regions in-between. Although it
qualitatively resembles the picture seen in models, more observations
e.g. with the future ALMA are needed for thorough comparisons
with present and future models. Quantitative comparisons demand
for synthetic intensity maps and spectra for the three-dimensional
(magneto-)hydrodynamic simulations. The necessary radiative transfer
calculations, which have to take into account deviations from local
thermodynamic equilibrium, are computationally very involved so
that no reliable results have been produced so far. Until this task
becomes feasible, we have to rely on careful qualitative comparisons
of simulations and observations. Here we discuss what effects have to
be considered for such a comparison. Nevertheless we are now on the
verge of assembling a comprehensive picture of the solar chromosphere
in inter-network regions as dynamic interplay of shock waves and
structuring and guiding magnetic fields.

---------------------------------------------------------
Title: Hinode observations reveal boundary layers of magnetic elements
in the solar photosphere
Authors: Rezaei, R.; Steiner, O.; Wedemeyer-Böhm, S.; Schlichenmaier,
R.; Schmidt, W.; Lites, B. W.
2007A&A...476L..33R Altcode: 2007arXiv0711.0408R
Aims:We study the structure of the magnetic elements in network-cell
interiors. Methods: A quiet Sun area close to the disc centre was
observed with the spectro-polarimeter of the Solar Optical Telescope
on board the Hinode space mission, which yielded the best spatial
resolution ever achieved in polarimetric data of the Fe I 630 nm line
pair. For comparison and interpretation, we synthesize a similar data
set from a three-dimensional magneto-hydrodynamic simulation. Results: We find several examples of magnetic elements, either
roundish (tube) or elongated (sheet), which show a central area of
negative Stokes-V area asymmetry framed or surrounded by a peripheral
area with larger positive asymmetry. This pattern was predicted
some eight years ago on the basis of numerical simulations. Here,
we observationally confirm its existence for the first time. Conclusions: We gather convincing evidence that this pattern of
Stokes-V area asymmetry is caused by the funnel-shaped boundary of
magnetic elements that separates the flux concentration from the
weak-field environment. On this basis, we conclude that electric
current sheets induced by such magnetic boundary layers are common in
the photosphere.

---------------------------------------------------------
Title: Variation of the Stokes-V area asymmetry across magnetic
elements
Authors: Rezaei, R.; Steiner, O.; Wedemeyer-Böhm, S.; Schlichenmaier,
R.; Lites, B. W.
2007AN....328..706R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Inter-network regions of the Sun at millimetre wavelengths
Authors: Wedemeyer-Böhm, S.; Ludwig, H. G.; Steffen, M.; Leenaarts,
J.; Freytag, B.
2007A&A...471..977W Altcode: 2007arXiv0705.2304W
Aims:The continuum intensity at wavelengths around 1 mm provides an
excellent way to probe the solar chromosphere and thus valuable input
for the ongoing controversy on the thermal structure and the dynamics of
this layer. The synthetic continuum intensity maps for near-millimetre
wavelengths presented here demonstrate the potential of future
observations of the small-scale structure and dynamics of internetwork
regions on the Sun. Methods: The synthetic intensity/brightness
temperature maps are calculated on basis of three-dimensional
radiation (magneto-)hydrodynamic (MHD) simulations. The assumption
of local thermodynamic equilibrium (LTE) is valid for the source
function. The electron densities are also treated in LTE for most maps
but also in non-LTE for a representative model snapshot. Quantities
like intensity contrast, intensity contribution functions, spatial
and temporal scales are analysed in dependence on wavelength and
heliocentric angle. Results: While the millimetre continuum
at 0.3 mm originates mainly from the upper photosphere, the longer
wavelengths considered here map the low and middle chromosphere. The
effective formation height increases generally with wavelength and
also from disk-centre towards the solar limb. The average intensity
contribution functions are usually rather broad and in some cases they
are even double-peaked as there are contributions from hot shock waves
and cool post-shock regions in the model chromosphere. The resulting
shock-induced thermal structure translates to filamentary brightenings
and fainter regions in between. Taking into account the deviations from
ionisation equilibrium for hydrogen gives a less strong variation of
the electron density and with it of the optical depth. The result is
a narrower formation height range although the intensity maps still
are characterised by a highly complex pattern. The average brightness
temperature increases with wavelength and towards the limb although
the wavelength-dependence is reversed for the MHD model and the NLTE
brightness temperature maps. The relative contrast depends on wavelength
in the same way as the average intensity but decreases towards the
limb. The dependence of the brightness temperature distribution on
wavelength and disk-position can be explained with the differences in
formation height and the variation of temperature fluctuations with
height in the model atmospheres. The related spatial and temporal
scales of the chromospheric pattern should be accessible by future
instruments. Conclusions: Future high-resolution millimetre
arrays, such as the Atacama Large Millimeter Array (ALMA), will
be capable of directly mapping the thermal structure of the solar
chromosphere. Simultaneous observations at different wavelengths
could be exploited for a tomography of the chromosphere, mapping its
three-dimensional structure, and also for tracking shock waves. The
new generation of millimetre arrays will be thus of great value for
understanding the dynamics and structure of the solar atmosphere.

---------------------------------------------------------
Title: Non-equilibrium Hydrogen Ionization in the Solar Atmosphere
Authors: Leenaarts, J.; Wedemeyer-Böhm, S.; Carlsson, M.; Hansteen,
V. H.
2007ASPC..368..103L Altcode:
The assumption of statistical equilibrium for atomic level populations
of hydrogen does not hold under the conditions of the chromosphere
due to the low density and the short dynamic timescale. In order to
calculate the hydrogen ionization balance and the electron density one
has to solve the time-dependent rate equations. We present results
from 2D and 3D radiation-magneto-hydrodynamics simulations of the
solar atmosphere incorporating the time-dependent rate equations
for hydrogen. Both the hydrogen ionization degree and the electron
density in our models are much more constant than LTE and statistical
equilibrium theory predict. These simulations provide multi-dimensional
model atmospheres with realistic electron densities and hydrogen level
populations that can be used in detailed radiative transfer modeling.

---------------------------------------------------------
Title: Dynamic models of the sun from the convection zone to the
chromosphere
Authors: Wedemeyer-Böhm, Sven
2007IAUS..239...52W Altcode: 2006astro.ph.10327W
The chromosphere in internetwork regions of the quiet Sun was regarded
as a static and homogeneous layer for a long time. Thanks to advances
in observations and numerical modelling, the wave nature of these
atmospheric regions received increasing attention during the last
decade. Recent three-dimensional radiation magnetohydrodynamic
simulations with CO5BOLD feature the chromosphere of internetwork
regions as a dynamic and intermittent phenomenon. It is a direct product
of interacting waves that form a mesh-like pattern of hot shock fronts
and cool post-shock regions. The waves are excited self-consistently
at the top of the convection zone. In the middle chromosphere above
an average height of 1000 km, plasma beta gets larger than one and
magnetic fields become more important. The model chromosphere exhibits
a magnetic field that is much more homogeneous than in the layers
below and evolves much faster. That includes fast propagating (MHD)
waves. Further improvements of the simulations like time-dependent
hydrogen ionisation are currently in progress. This class of models
is capable of explaining apparently contradicting diagnostics such as
carbon monoxide and UV emission at the same time.

---------------------------------------------------------
Title: What is Heating the Quiet-Sun Chromosphere?
Authors: Wedemeyer-Böhm, S.; Steiner, O.; Bruls, J.; Rammacher, W.
2007ASPC..368...93W Altcode: 2006astro.ph.12627W
It is widely believed that the heating of the chromosphere in quiet-Sun
internetwork regions is provided by dissipation of acoustic waves
that are excited by the convective motions close to the top of
the convection zone and in the photospheric overshoot layer. This
view lately became challenged by observations suggesting that the
acoustic energy flux into the chromosphere is too low, by a factor
of at least ten. Based on a comparison of TRACE data with synthetic
image sequences for a three-dimensional simulation extending from
the top layers of the convection zone to the middle chromosphere,
we come to the contradicting conclusion that the acoustic flux in the
model provides sufficient energy for heating the solar chromosphere of
internetwork regions. The role of a weak magnetic field and associated
electric current sheets is also discussed.

---------------------------------------------------------
Title: First local helioseismic experiments with CO5BOLD
Authors: Steiner, O.; Vigeesh, G.; Krieger, L.; Wedemeyer-Böhm, S.;
Schaffenberger, W.; Freytag, B.
2007AN....328..323S Altcode: 2007astro.ph..1029S
With numerical experiments we explore the feasibility of using high
frequency waves for probing the magnetic fields in the photosphere and
the chromosphere of the Sun. We track a plane-parallel, monochromatic
wave that propagates through a non-stationary, realistic atmosphere,
from the convection-zone through the photosphere into the magnetically
dominated chromosphere, where it gets refracted and reflected. We
compare the wave travel time between two fixed geometrical height levels
in the atmosphere (representing the formation height of two spectral
lines) with the topography of the surface of equal magnetic and thermal
energy density (the magnetic canopy or β=1 contour) and find good
correspondence between the two. We conclude that high frequency waves
indeed bear information on the topography of the `magnetic canopy'.

---------------------------------------------------------
Title: Carbon monoxide in the solar atmosphere. II. Radiative cooling
by CO lines
Authors: Wedemeyer-Böhm, S.; Steffen, M.
2007A&A...462L..31W Altcode: 2006astro.ph.12197W
Aims: The role of carbon monoxide as a cooling agent for the thermal
structure of the mid-photospheric to low-chromospheric layers of the
solar atmosphere in internetwork regions is investigated. Methods:
The treatment of radiative cooling via spectral lines of carbon
monoxide (CO) has been added to the radiation chemo-hydrodynamics code
CO5BOLD. The radiation transport has now been solved in a continuum band
with Rosseland mean opacity and an additional band with CO opacity. The
latter is calculated as a Planck mean over the CO band between 4.4
and 6.2 μm. The time-dependent CO number density is derived from
the solution of a chemical reaction network. Results: The CO
opacity indeed causes additional cooling at the fronts of propagating
shock waves in the chromosphere. There, the time-dependent approach
results in a higher CO number density compared to the equilibrium
case and hence in a larger net radiative cooling rate. The average
gas temperature stratification of the model atmosphere, however, is
only reduced by roughly 100 K. Also the temperature fluctuations and
the CO number density are only affected to small extent. A numerical
experiment without dynamics shows that the CO cooling process works in
principle and drives the atmosphere to a cool radiative equilibrium
state. At chromospheric heights, the radiative relaxation of the
atmosphere to a cool state takes several 1000 s. The CO cooling process
thus would seem to be too slow compared to atmospheric dynamics to be
responsible for the very cool temperature regions observed in the solar
atmosphere. Conclusions: . The hydrodynamical timescales in our
solar atmosphere model are much too short to allow for the radiative
relaxation to a cool state, thus suppressing the potential thermal
instability due to carbon monoxide as a cooling agent. Apparently,
the thermal structure and dynamics of the outer model atmosphere are
instead determined primarily by shock waves.

---------------------------------------------------------
Title: On the fine structure of the quiet solar Ca II K atmosphere
Authors: Tritschler, A.; Schmidt, W.; Uitenbroek, H.; Wedemeyer-Böhm,
S.
2007A&A...462..303T Altcode: 2006astro.ph.11402T
Aims:We investigate the morphological, dynamical, and evolutionary
properties of the internetwork and network fine structure of the quiet
sun at disk centre. Methods: The analysis is based on a ~6 h
time sequence of narrow-band filtergrams centred on the inner-wing
Ca II K2v reversal at 393.3 nm. To examine the temporal evolution of
network and internetwork areas separately we employ a double-Gaussian
decomposition of the mean intensity distribution. An autocorrelation
analysis is performed to determine the respective characteristic
time scales. In order to analyse statistical properties of the fine
structure we apply image segmentation techniques. Results: The
results for the internetwork are related to predictions derived from
numerical simulations of the quiet sun. The average evolutionary time
scale of the internetwork in our observations is 52 s. Internetwork
grains show a tendency to appear on a mesh-like pattern with a
mean cell size of ~4-5 arcsec. Based on this size and the spatial
organisation of the mesh we speculate that this pattern is related to
the existence of photospheric downdrafts as predicted by convection
simulations. The image segmentation shows that typical sizes of both
network and internetwork grains are in the order of 1.6 arcsec.

---------------------------------------------------------
Title: Dynamic Hydrogen Ionization in Simulations of the Solar
Chromosphere
Authors: Leenaarts, J.; Wedemeyer-Böhm, S.
2006ASPC..354..306L Altcode:
Since the assumption of statistical equilibrium does not hold under the
conditions of the dynamical solar chromosphere, the time dependence
of the rate equations has to be taken into account when calculating
ionization stages of elements. We present a method based on the
work by Sollum (1999) to calculate the dynamic hydrogen ionization
degree and electron density in the 3-D radiation-hydrodynamics code
CO^5BOLD. In our model chromosphere, both quantities are more constant
over time and horizontal position than LTE theory predicts. We compare
synthetic brightness temperature images at λ=1~mm calculated with LTE
and time-dependent NLTE electron densities. Both formation height and
average brightness temperature change significantly compared to LTE
when using time-dependent electron densities.

---------------------------------------------------------
Title: A First Three-Dimensional Model for the Carbon Monoxide
Concentration in the Solar Atmosphere
Authors: Wedemeyer-Böhm, S.; Kamp, I.; Freytag, B.; Bruls, J.;
Steffen, M.
2006ASPC..354..301W Altcode:
The time-dependent and self-consistent treatment of carbon monoxide
(CO) has been added to the radiation chemo-hydrodynamics code
CO5BOLD. It includes the solution of a chemical reaction network and
the advection of the resulting particle densities with the hydrodynamic
flow field. Here we present a first 3D simulation of the non-magnetic
solar photosphere and low chromosphere, calculated with the upgraded
code. In the resulting model, the highest amount of CO is located in
the cool regions of the reversed granulation pattern in the middle
photosphere. A large fraction of carbon is bound by CO throughout
the chromosphere with exception of hot shock waves where the CO
concentration is strongly reduced. The distribution of carbon monoxide
is very inhomogeneous due to co-existing regions of hot and cool gas
caused by the hydrodynamic flow. High-resolution observations of CO
could thus provide important constraints for the thermal structure of
the solar photosphere and chromosphere.

---------------------------------------------------------
Title: Time-dependent hydrogen ionisation in 3D simulations of the
solar chromosphere. Methods and first results
Authors: Leenaarts, J.; Wedemeyer-Böhm, S.
2006A&A...460..301L Altcode: 2006astro.ph..8620L
Context: .The hydrogen ionisation degree deviates substantially
from statistical equilibrium under the conditions of the solar
chromosphere. A realistic description of this atmospheric layer
thus must account for time-dependent non-equilibrium effects. 
Aims: .Advancing the realism of numerical simulations of the solar
chromosphere by improved numerical treatment of the relevant physics
will provide more realistic models that are essential for interpretation
of existing and future observations. Methods: .An approximate
method for solving the rate equations for the hydrogen populations
was extended and implemented in the three-dimensional radiation
(magneto-)hydrodynamics code CO^5BOLD. The method is based on a
model atom with six energy levels and fixed radiative rates. It has
been tested extensively in one-dimensional simulations. The extended
method has been used to create a three-dimensional model that extends
from the upper convection zone to the chromosphere. Results:
.The ionisation degree of hydrogen in our time-dependent simulation is
comparable to the corresponding equilibrium value up to 500 km above
optical depth unity. Above this height, the non-equilibrium ionisation
degree is fairly constant over time and space, and tends to be at a
value set by hot propagating shock waves. The hydrogen level populations
and electron density are much more constant than the corresponding
values for statistical equilibrium, too. In contrast, the equilibrium
ionisation degree varies by more than 20 orders of magnitude between
hot, shocked regions and cool, non-shocked regions. Conclusions:
.The simulation shows for the first time in 3D that the chromospheric
hydrogen ionisation degree and electron density cannot be calculated
in equilibrium. Our simulation can provide realistic values of those
quantities for detailed radiative transfer computations.

---------------------------------------------------------
Title: A New Method for Comparing Numerical Simulations with
Spectroscopic Observations of the Solar Photosphere
Authors: Rybák, J.; Kučera, A.; Wöhl, H.; Wedemeyer-Böhm, S.;
Steiner, O.
2006ASPC..354...77R Altcode:
A method for comparing high-resolution spectroscopic observations of
the solar photosphere with numerical simulations of convection in the
solar photosphere is presented. It is based on the comparison of
the granular continuum contrast obtained from both the observations and
the synthetic spectra, when the latter are calculated from numerical
simulations using a particular type of data degradation. This method
can be used post facto when a minimum of auxiliary information on
characteristics of the telescope/spectrograph and on seeing conditions
is available. Here, the method is applied to results of numerical
simulations computed with the CO5BOLD code and high-resolution
spectroscopic observations obtained with the VTT on Tenerife.

---------------------------------------------------------
Title: Holistic MHD-Simulation from the Convection Zone to the
Chromosphere
Authors: Schaffenberger, W.; Wedemeyer-Böhm, S.; Steiner, O.;
Freytag, B.
2006ASPC..354..345S Altcode:
A three-dimensional magnetohydrodynamic simulation of the integral
layers from the convection zone to the chromosphere has been
carried out. The simulation represents magnetoconvection in a quiet
network-cell interior. The following preliminary new results are
obtained: The chromospheric magnetic field is very dynamic with a
continuous rearrangement of magnetic flux on a time scale of less than
one~minute. Rapidly moving magnetic filaments (rarely exceeding 40~G)
form in the compression zone downstream and along propagating shock
fronts that are present throughout the chromosphere. The magnetic
filaments rapidly move, form, and dissolve with the shock waves. Flux
concentrations strongly expand through the photosphere into a more
homogeneous, space filling chromospheric field. “Canopy fields”
form on a granular scale above largely field-free granule centers
leading to a mesh-work of current sheets in a height range between
approximately 400 and 900~km.

---------------------------------------------------------
Title: High Resolution Time Series of Narrowband Ca IIK Images in
the Chromosphere
Authors: Wöger, F.; Wedemeyer-Böhm, S.; Schmidt, W.; von der
Lühe, O.
2006ASPC..354..284W Altcode:
We have observed a region of quiet Sun near disk center with the Vacuum
Tower Telescope (VTT) of the Kiepenheuer-Institut für Sonnenphysik at
the Observatorio del Teide, Tenerife, Spain in April 2005 in several
wavelengths. Observations were made at the Ca II K line at 393.3 nm,
using a Lyot filter with a bandwidth of 30 ± FWHM, centered at the
K_{2v} emission peak; at the Hα line at 656.3 nm, using a Lyot filter
(25 ± FWHM) centered at line core, and in the G-band (430.5 nm),
using an interference filter (1 nm FWHM). We acquired a two-hour long
sequence of images at a cadence of ten seconds and a spatial resolution
of about 0.3 arcsec. We present our Ca observations of excellent spatial
resolution which show morphological structures in internetwork regions
similar in form, size and lifetime to those present in recent numerical
models of the solar chromosphere.

---------------------------------------------------------
Title: Observation of a short-lived pattern in the solar chromosphere
Authors: Wöger, F.; Wedemeyer-Böhm, S.; Schmidt, W.; von der
Lühe, O.
2006A&A...459L...9W Altcode: 2006astro.ph..9382W
Aims.In this work we investigate the dynamic behavior of inter-network
regions of the solar chromosphere. Methods: .We observed the
chromosphere of the quiet Sun using a narrow-band Lyot filter centered
at the Ca II K2v emission peak with a bandpass of 0.3 Å. We achieved
a spatial resolution of on average 0.7 arcsec at a cadence of 10 s. Results: .In the inter-network we find a mesh-like pattern that
features bright grains at the vertices. The pattern has a typical
spatial scale of 1.95 arcsec and a mean evolution time scale of 53 s
with a standard deviation of 10 s. A comparison of our results with a
recent three-dimensional radiation hydrodynamical model implies that
the observed pattern is of chromospheric origin. The measured time
scales are not compatible with those of reversed granulation in the
photosphere although the appearance is similar. A direct comparison
between network and inter-network structure shows that their typical
time scales differ by at least a factor of two. Conclusions:
.The existence of a rapidly evolving small-scale pattern in the
inter-network regions supports the picture of the lower chromosphere
as a highly dynamical and intermittent phenomenon.

---------------------------------------------------------
Title: Simulations of Magnetohydrodynamics and CO Formation from
the Convection Zone to the Chromosphere
Authors: Wedemeyer-Böhm, S.; Schaffenberger, W.; Steiner, O.; Steffen,
M.; Freytag, B.; Kamp, I.
2005ESASP.596E..16W Altcode: 2005ccmf.confE..16W
No abstract at ADS

---------------------------------------------------------
Title: Magnetohydrodynamic Simulation from the Convection Zone to
the Chromosphere
Authors: Schaffenberger, W.; Wedemeyer-Böhm, S.; Steiner, O.;
Freytag, B.
2005ESASP.596E..65S Altcode: 2005ccmf.confE..65S
No abstract at ADS

---------------------------------------------------------
Title: Carbon monoxide in the solar atmosphere. I. Numerical method
and two-dimensional models
Authors: Wedemeyer-Böhm, S.; Kamp, I.; Bruls, J.; Freytag, B.
2005A&A...438.1043W Altcode: 2005astro.ph..3496W
The radiation hydrodynamic code CO5BOLD has been supplemented with
the time-dependent treatment of chemical reaction networks. Advection
of particle densities due to the hydrodynamic flow field is also
included. The radiative transfer is treated frequency-independently,
i.e. grey, so far. The upgraded code has been applied to two-dimensional
simulations of carbon monoxide (CO) in the non-magnetic solar
photosphere and low chromosphere. For this purpose a reaction network
has been constructed, taking into account the reactions that are most
important for the formation and dissociation of CO under the physical
conditions of the solar atmosphere. The network has been strongly
reduced to 27 reactions, involving the chemical species H, H2, C, O,
CO, CH, OH and a representative metal. The resulting CO number density
is highest in the cool regions of the reversed granulation pattern
at mid-photospheric heights and decreases strongly above. There, the
CO abundance stays close to a value of 8.3 on the usual logarithmic
abundance scale with [H] = 12 but is reduced in hot shock waves which
are a ubiquitous phenomenon of the model atmosphere. For comparison, the
corresponding equilibrium densities have been calculated, based on the
reaction network but also under the assumption of instantaneous chemical
equilibrium by applying the Rybicki &amp; Hummer (RH) code. Owing to the
short chemical timescales, the assumption holds for a large fraction
of the atmosphere, in particular the photosphere. In contrast, the CO
number density deviates strongly from the corresponding equilibrium
value in the vicinity of chromospheric shock waves. Simulations with
altered reaction networks clearly show that the formation channel via
hydroxide (OH) is the most important one under the conditions of the
solar atmosphere.

---------------------------------------------------------
Title: The shock-patterned solar chromosphere in the light of ALMA
Authors: Wedemeyer-Böhm, S.; Ludwig, H. -G.; Steffen, M.; Freytag,
B.; Holweger, H.
2005ESASP.560.1035W Altcode: 2005csss...13.1035W; 2005astro.ph..9747W
Recent three-dimensional radiation hydrodynamic simulations by Wedemeyer
et al. (2004) suggest that the solar chromosphere is highly structured
in space and time on scales of only 1000 km and 20-25 sec, resp.. The
resulting pattern consists of a network of hot gas and enclosed cool
regions which are due to the propagation and interaction of shock
fronts. In contrast to many other diagnostics, the radio continuum at
millimeter wavelengths is formed in LTE, and provides a rather direct
measure of the thermal structure. It thus facilitates the comparison
between numerical model and observation. While the involved time
and length scales are not accessible with todays equipment for that
wavelength range, the next generation of instruments, such as the
Atacama Large Millimeter Array (ALMA), will provide a big step towards
the required resolution. Here we present results of radiative transfer
calculations at mm and sub-mm wavelengths with emphasis on spatial
and temporal resolution which are crucial for the ongoing discussion
about the chromospheric temperature structure.

---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. III. Observations
and simulations of reversed granulation
Authors: Leenaarts, J.; Wedemeyer-Böhm, S.
2005A&A...431..687L Altcode:
We compare high-quality image sequences from the Dutch Open
Telescope (DOT) with synthetic image sequences obtained from 3D
radiation-hydrodynamics simulations of the solar granulation. In
particular, we study the subsonic brightness pattern observed in the
wings of Ca II HK. The simulations reproduce the observed intensity
contrast, time scales, and Fourier behaviour rather well. Most
differences can be attributed to the resolution difference between the
observations and the simulation and the small geometrical extent of
the simulation. We conclude that magnetic fields play no major role
in the formation of reversed granulation.

---------------------------------------------------------
Title: Numerical simulation of the three-dimensional structure and
dynamics of the non-magnetic solar chromosphere
Authors: Wedemeyer, S.; Freytag, B.; Steffen, M.; Ludwig, H. -G.;
Holweger, H.
2004A&A...414.1121W Altcode: 2003astro.ph.11273W
Three-dimensional numerical simulations with CO5, a
new radiation hydrodynamics code, result in a dynamic, thermally
bifurcated model of the non-magnetic chromosphere of the quiet Sun. The
3D model includes the middle and low chromosphere, the photosphere,
and the top of the convection zone, where acoustic waves are excited
by convective motions. While the waves propagate upwards, they steepen
into shocks, dissipate, and deposit their mechanienergy as heat in
the chromosphere. Our numerical simulations show for the first time
a complex 3D structure of the chromospheric layers, formed by the
interaction of shock waves. Horizontal temperature cross-sections of
the model chromosphere exhibit a network of hot filaments and enclosed
cool regions. The horizontal pattern evolves on short time-scales of
the order of typically 20-25 s, and has spatial scales comparable to
those of the underlying granulation. The resulting thermal bifurcation,
i.e., the co-existence of cold and hot regions, provides temperatures
high enough to produce the observed chromospheric UV emission and -
at the same time - temperatures cold enough to allow the formation
of molecules (e.g., carbon monoxide). Our 3D model corroborates the
finding by \citet{carlsson94} that the chromospheric temperature rise
of semi-empirical models does not necessarily imply an increase in
the average gas temperature but can be explained by the presence of
substantial spatial and temporal temperature inhomogeneities.

---------------------------------------------------------
Title: Modelling the Chromospheric Background Pattern of the
Non-magnetic Sun
Authors: Wedemeyer, Sven; Freytag, Bernd; Steffen, Matthias; Ludwig,
Hans-Günter; Holweger, Hartmut
2003ANS...324R..66W Altcode: 2003ANS...324..I07W
No abstract at ADS

---------------------------------------------------------
Title: Multi-dimensional radiation hydrodynamic simulations of the
non-magnetic solar atmosphere
Authors: Wedemeyer, Sven
2003PhDT.......190W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Acoustic Waves in the Solar Chromosphere - Numerical
Simulations with COBOLD
Authors: Wedemeyer, S.; Freytag, B.; Steffen, M.; Ludwig, H. -G.;
Holweger, H.
2003IAUS..210P..C1W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 3-D hydrodynamic simulations of the solar chromosphere
Authors: Wedemeyer, S.; Freytag, B.; Steffen, M.; Ludwig, H. -G.;
Holweger, H.
2003AN....324..410W Altcode:
We present first results of three-dimensional numerical simulations
of the non-magnetic solar chromosphere, computed with the radiation
hydrodynamics code CO5BOLD. Acoustic waves which are
excited at the top of the convection zone propagate upwards into the
chromosphere where the waves steepen into shocks. The interaction of
the waves leads to the formation of complex structures which evolve
on short time scales. Consequently, the model chromosphere is highly
dynamical, inhomogeneous, and thermally bifurcated.

---------------------------------------------------------
Title: Statistical equilibrium and photospheric abundance of silicon
in the Sun and in Vega
Authors: Wedemeyer, S.
2001A&A...373..998W Altcode:
Based on detailed non-LTE calculations, an updated determination of
the abundance of silicon in the Sun and Vega is presented. The model
atom includes neutral and singly ionized stages of silicon with 115
energy levels and 84 line transitions. Non-LTE effects are found to
be quite small in the Sun. The mean non-LTE abundance correction is
-0.010 dex with respect to standard LTE calculations, leading to a
solar abundance of log ɛNLTE = 7.550 ± 0.056. For the
prototype A0 V star Vega the non-LTE effects are small, too. With a
non-LTE abundance correction of Δ log ɛ = -0.054, a silicon abundance
of -0.599 dex with respect to the Sun. This confirms the classification
of Vega as a mild λ Boo star

---------------------------------------------------------
Title: Acoustic Energy Generated by Convection: 3-D Numerical
Simulations for the Sun
Authors: Wedemeyer, Sven; Freytag, Bernd; Holweger, Hartmut; Ludwig,
Hans-Günter; Steffen, Matthias
2001AGM....18..P01W Altcode:
Dissipation of acoustic waves may be an efficient heating mechanism for
the lower and middle chromosphere of the quiet Sun. The basic idea is
that turbulent motions at the top of the solar convection zone generate
acoustic waves which propagate upwards and dissipate in the lower and
middle chromosphere, transporting energy into the higher layers. But
still the question remains if this amount of energy is sufficient to
explain the observed temperature increase without invoking magnetic
fields. With a new version of the COBOLD radiation hydrodynamics code
we are able to compute 3-D models extending all the way from the upper
convection zone to the middle chromosphere. First 3-D simulations reveal
a complex, inhomogenous and highly dynamical structure of the lower and
middle chromosphere which evolves on rather short timescales. On small
spatial dimensions very cool regions are present next to a "network"
of hotter matter. The code is being developed further to provide a
more detailed analysis and comparison with observations.

---------------------------------------------------------
Title: Radiation Hydrodynamics Simulations of the Solar Chromosphere
Authors: Wedemeyer, Sven; Freytag, Bernd; Steffen, Matthias; Holweger,
Hartmut
2000AGM....17..P01W Altcode:
While heating of the solar corona is commonly attributed to
reconnection of magnetic field lines, the mechanism responsible for
heating the chromosphere of the quiet Sun, away from active regions,
is still under debate1,2. The basic question which we will
address in this contribution i s: Can generation of acoustic waves by
turbulent convection in photospheric and subphotospheric layers explain
the chromospheric emission of the quiet Sun? With a new 3D radiation
hydrodynamics code3 we are able to compute models ex tending
from the upper convection zone to the middle chromosphere. The code
can handle shocks with a minimum of numerical dissipation. Therefore
generation and propagation of acoustic waves can be investigated,
permitting the evaluation of wave dissipation in the chromosphere in
a physically consistent manner. We present first results and discuss
the principal problems and future prospects.

---------------------------------------------------------
Title: Silicon as a cosmic reference element: a reassessment of the
solar SI abundance
Authors: Wedemeyer, Sven; Holweger, Hartmut; Steffen, Matthias
1999AGAb...15..113V Altcode: 1999AGM....15..P53V; 1999AGM....15..P54W
Silicon is an important reference elements for comparing various
types of cosmic matter with the Sun. The most widely used sources
of solar (photospheric) abundances, the compilation by Anders &amp;
Grevesse (1989) and its updates (e.g. Grevesse &amp; Sauval 1998), are
based on standard abundance analyses employing 1D solar models and,
in most cases, assuming LTE. We report NLTE calculations for Si and
a first attempt to determine the effect of horizontal temperature
inhomogeneities associated with convection on the photospheric
abundance of Si. We combine the result with that obtained previously
for O and Fe (Aellig et al. 1999; Schnabel et al. 1999) and compare
the photospheric Si/Fe, Si/O and Si/H abundance ratios with literature
data for meteorites, the corona and solar wind, energetic particles and
galactic B stars and H ii regions. References: Aellig M.R., Holweger H.,
Bochsler P., et al., 1999, Solar Wind Nine, AIP Conf. Proc. Vol. 471,
255 Anders E., Grevesse N., 1989, Geochim. Comochim. Acta 53, 197
Grevesse N., Sauval A.J., 1998, Space Sci. Rev. 85, 161 Schnabel R.,
Kock M., Holweger H., 1999, A&amp;A 342, 610