asensio-ramos

explanation blue bibcodes open ADS page with paths to full text

Author name code: asensio-ramos
ADS astronomy entries on 2022-09-14
author:"Asensio Ramos, Andres"

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Title: Towards the Identification and Classification of Solar
Granulation Structures Using Semantic Segmentation
Authors: Díaz Castillo, S. M.; Asensio Ramos, A.; Fischer, C. E.;
Berdyugina, S. V.
2022FrASS...9.6632D Altcode:
Solar granulation is the visible signature of convective cells at
the solar surface. The granulation cellular pattern observed in the
continuum intensity images is characterised by diverse structures e.g.,
bright individual granules of hot rising gas or dark intergranular
lanes. Recently, the access to new instrumentation capabilities has
given us the possibility to obtain high-resolution images, which have
revealed the overwhelming complexity of granulation (e.g., exploding
granules and granular lanes). In that sense, any research focused
on understanding solar small-scale phenomena on the solar surface
is sustained on the effective identification and localization of the
different resolved structures. In this work, we present the initial
results of a proposed classification model of solar granulation
structures based on neural semantic segmentation. We inspect the
ability of the U-net architecture, a convolutional neural network
initially proposed for biomedical image segmentation, to be applied to
the dense segmentation of solar granulation. We use continuum intensity
maps of the IMaX instrument onboard the Sunrise I balloon-borne solar
observatory and their corresponding segmented maps as a training
set. The training data have been labeled using the multiple-level
technique (MLT) and also by hand. We performed several tests of the
performance and precision of this approach in order to evaluate
the versatility of the U-net architecture. We found an appealing
potential of the U-net architecture to identify cellular patterns
in solar granulation images reaching an average accuracy above 80%
in the initial training experiments.

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Title: Polarimetric characterization of segmented mirrors
Authors: Pastor Yabar, A.; Asensio Ramos, A.; Manso Sainz, R.;
Collados, M.
2022ApOpt..61.4908P Altcode: 2022arXiv220514640P
We study the impact of the loss of axial symmetry around the optical
axis on the polarimetric properties of a telescope with segmented
primary mirror when each segment is present in a different aging
stage. The different oxidation stage of each segment as they are
substituted in time leads to non-negligible crosstalk terms. This
effect is wavelength dependent and it is mainly determined by the
properties of the reflecting material. For an aluminum coating, the
worst polarimetric behavior due to oxidation is found for the blue
part of the visible. Contrarily, dust -- as modeled in this work --
does not significantly change the polarimetric behavior of the optical
system . Depending on the telescope, there might be segment substitution
sequences that strongly attenuate this instrumental polarization.

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Title: joshspeagle/dynesty: v1.2.2
Authors: Koposov, Sergey; Speagle, Josh; Barbary, Kyle; Ashton,
Gregory; Buchner, Johannes; Scheffler, Carl; Cook, Ben; Talbot,
Colm; Guillochon, James; Cubillos, Patricio; Asensio Ramos, Andrés;
Johnson, Ben; Lang, Dustin; Ilya; Dartiailh, Matthieu; Nitz, Alex;
McCluskey, Andrew; Archibald, Anne; Deil, Christoph; Foreman-Mackey,
Dan; Goldstein, Danny; Tollerud, Erik; Leja, Joel; Kirk, Matthew;
Pitkin, Matt; Sheehan, Patrick; Cargile, Phillip; Ruskin23; Angus,
Ruth; Daylan, Tansu
2022zndo...6456387K Altcode:
Bug fix release which addresses quite a serious bug which can lead to
biased posteriors. The problem with biased posteriors was fixed when
using multi-ellipsoid bounds and rslice and rwalk samplers. Previously
the chains did not satisfy detailed balance. (issue #364). Original
discovery of the problem and help by Colm Talbot. In the case of
complex posteriors, somewhat slower performance may be seen. Fix the
issue introduced in 1.2.1 when the prior_transform returns a tuple or
or a list (rather than numpy array). Now that should be accepted.

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Title: Accelerating Non-LTE Synthesis and Inversions with Graph
Networks
Authors: Vicente Arévalo, A.; Asensio Ramos, A.; Esteban Pozuelo, S.
2022ApJ...928..101V Altcode:
The computational cost of fast non-LTE synthesis is one of the
challenges that limits the development of 2D and 3D inversion codes. It
also makes the interpretation of observations of lines formed in the
chromosphere and transition region a slow and computationally costly
process, which limits the inference of the physical properties on
rather small fields of view. Having access to a fast way of computing
the deviation from the LTE regime through the departure coefficients
could largely alleviate this problem. We propose to build and train a
graph network that quickly predicts the atomic level populations without
solving the non-LTE problem. We find an optimal architecture for the
graph network for predicting the departure coefficients of the levels of
an atom from the physical conditions of a model atmosphere. A suitable
data set with a representative sample of potential model atmospheres
is used for training. This data set has been computed using existing
non-LTE synthesis codes. The graph network has been integrated into
existing synthesis and inversion codes for the particular case of Ca
II. We demonstrate orders-of-magnitude gain in computing speed. We
analyze the generalization capabilities of the graph network and
demonstrate that it produces good predicted departure coefficients for
unseen models. We implement this approach in Hazel2 and show how the
inversions nicely compare with those obtained with standard non-LTE
inversion codes. Our approximate method opens up the possibility of
extracting physical information from the chromosphere on large fields
of view with time evolution.

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Title: CASPER: A mission to study the time-dependent evolution of
the magnetic solar chromosphere and transition regions
Authors: Orozco Suárez, D.; del Toro Iniesta, J. C.; Bailén, F. J.;
López Jiménez, A.; Balaguez Jiménez, M.; Bellot Rubio, L. R.;
Ishikawa, R.; Katsukawa, Y.; Kano, R.; Shimizu, T.; Trujillo Bueno,
J.; Asensio Ramos, A.; del Pino Alemán, T.
2022ExA...tmp...26O Altcode:
Our knowledge about the solar chromosphere and transition region (TR)
has increased in the last decade thanks to the huge scientific return
of space-borne observatories like SDO, IRIS, and Hinode, and suborbital
rocket experiments like CLASP1, CLASP2, and Hi-C. However, the magnetic
nature of those solar regions remain barely explored. The chromosphere
and TR of the Sun harbor weak fields and are in a low ionization stage
both having critical effects on their thermodynamic behavior. Relatively
cold gas structures, such as spicules and prominences, are located in
these two regions and display a dynamic evolution in high-resolution
observations that static and instantaneous 3D-magnetohydrodynamic (MHD)
models are not able to reproduce. The role of the chromosphere and TR
as the necessary path to a (largely unexplained) very hot corona calls
for the generation of observationally based, time-dependent models
of these two layers that include essential, up to now disregarded,
ingredients in the modeling such as the vector magnetic field. We
believe that the community is convinced that the origin of both the
heat and kinetic energy observed in the upper layers of the solar
atmosphere is of magnetic origin, but reliable magnetic field
measurements are missing. The access to sensitive polarimetric
measurements in the ultraviolet wavelengths has been elusive until
recently due to limitations in the available technology. We propose a
low-risk and high-Technology Readiness Level (TRL) mission to explore
the magnetism and dynamics of the solar chromosphere and TR. The mission
baseline is a low-Earth, Sun-synchronous orbit at an altitude between
600 and 800 km. The proposed scientific payload consists of a 30 cm
aperture telescope with a spectropolarimeter covering the hydrogen
Ly-alpha and the Mg II h&amp;k ultraviolet lines. The instrument shall
record high-cadence, full spectropolarimetric observations of the
solar upper atmosphere. Besides the answers to a fundamental solar
problem the mission has a broader scientific return. For example,
the time-dependent modeling of the chromospheres of stars harboring
exoplanets is fundamental for estimating the planetary radiation
environment. The mission is based on technologies that are mature
enough for space and will provide scientific measurements that are
not available by other means.

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Title: Bayesian Stokes inversion with normalizing flows
Authors: Díaz Baso, C. J.; Asensio Ramos, A.; de la Cruz Rodríguez,
J.
2022A&A...659A.165D Altcode: 2021arXiv210807089D
Stokes inversion techniques are very powerful methods for obtaining
information on the thermodynamic and magnetic properties of solar
and stellar atmospheres. In recent years, highly sophisticated
inversion codes have been developed that are now routinely applied
to spectro-polarimetric observations. Most of these inversion codes
are designed to find an optimum solution to the nonlinear inverse
problem. However, to obtain the location of potentially multimodal
cases (ambiguities), the degeneracies and the uncertainties of each
parameter inferred from the inversions algorithms - such as Markov chain
Monte Carlo (MCMC) - require evaluation of the likelihood of the model
thousand of times and are computationally costly. Variational methods
are a quick alternative to Monte Carlo methods, and approximate the
posterior distribution by a parametrized distribution. In this study,
we introduce a highly flexible variational inference method to perform
fast Bayesian inference, known as normalizing flows. Normalizing flows
are a set of invertible, differentiable, and parametric transformations
that convert a simple distribution into an approximation of any
other complex distribution. If the transformations are conditioned on
observations, the normalizing flows can be trained to return Bayesian
posterior probability estimates for any observation. We illustrate
the ability of the method using a simple Milne-Eddington model and
a complex non-local thermodynamic equilibrium (NLTE) inversion. The
method is extremely general and other more complex forward models
can be applied. The training procedure need only be performed once
for a given prior parameter space and the resulting network can then
generate samples describing the posterior distribution several orders
of magnitude faster than existing techniques.

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Title: Goobley/Lightweaver: Compile Fixes
Authors: cmo; Asensio Ramos, Andrés
2022zndo...4066860C Altcode: 2021zndo...4066860C Fixed macOS compile of ExtraParams Added
return value to iterate_ctx_se as suggested by Jack.

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Title: Approximate Bayesian neural Doppler imaging
Authors: Asensio Ramos, A.; Díaz Baso, C. J.; Kochukhov, O.
2022A&A...658A.162A Altcode: 2021arXiv210809266A
 Aims: The non-uniform surface temperature distribution of
rotating active stars is routinely mapped with the Doppler imaging
technique. Inhomogeneities in the surface produce features in
high-resolution spectroscopic observations that shift in wavelength
because of the Doppler effect, depending on their position on the
visible hemisphere. The inversion problem has been systematically
solved using maximum a posteriori regularized methods assuming
smoothness or maximum entropy. Our aim in this work is to solve the
full Bayesian inference problem by providing access to the posterior
distribution of the surface temperature in the star compatible with
the observations. Methods: We use amortized neural posterior
estimation to produce a model that approximates the high-dimensional
posterior distribution for spectroscopic observations of selected
spectral ranges sampled at arbitrary rotation phases. The posterior
distribution is approximated with conditional normalizing flows, which
are flexible, tractable, and easy-to-sample approximations to arbitrary
distributions. When conditioned on the spectroscopic observations, these
normalizing flows provide a very efficient way of obtaining samples
from the posterior distribution. The conditioning on observations is
achieved through the use of Transformer encoders, which can deal with
arbitrary wavelength sampling and rotation phases. Results: Our
model can produce thousands of posterior samples per second, each one
accompanied by an estimation of the log-probability. Our exhaustive
validation of the model for very high-signal-to-noise observations
shows that it correctly approximates the posterior, albeit with some
overestimation of the broadening. We apply the model to the moderately
fast rotator II Peg, producing the first Bayesian map of its temperature
inhomogenities. We conclude that conditional normalizing flows are a
very promising tool for carrying out approximate Bayesian inference
in more complex problems in stellar physics, such as constraining the
magnetic properties using polarimetry.

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Title: Using Machine Learning Tools To Estimate Photospheric Velocity
Fields Prior To The Formation Of Active Regions.
Authors: Lennard, Matthew; Tremblay, Benoit; Asensio Ramos, Andres;
Hotta, Hideyuki; Iijima, Haruhisa; Park, Sung-Hong; Silva, Suzana;
Verth, Gary; Fedun, Viktor
2021AGUFMSH45B2371L Altcode:
In recent years a number of major advances have been made using
numerical modelling to better our understanding of magnetic structures
and the evolution of active regions (AR, see e.g. Hotta &amp;
Iijima, 2020; Chen et al, 2021). In particular, these high resolution
simulations provide us with the means to study the photospheric flows
associated with the aforementioned magnetic structures. In practice,
plasma flows at the solar surface cannot be directly recovered;
the component transverse to the line-of-sight must be inferred from
observational data. Inferences depend on the method, the observational
data used as input, the spatial resolution of the data and its
cadence. Tracking methods such as local correlation tracking (LCT)
are promising, but the flows they measure are optical and cannot be
used to estimate the flow patterns of an AR until shortly before the
emergence of flux. Another issue with applying LCT to estimate AR
flows is that the recovered velocity field is usually not smooth,
which precludes advanced flow analysis. Besides, depending on the
data, there is a considerable chance of having 'holes' in the velocity
field. Therefore, although LCT methodology can help give a hint on
general flow properties, a more sophisticated technique is necessary
to perform proper analysis on the flow topology. There are also
limitations in the region of the Sun in which we can accurately track
flows as well as problems with accurately extracting longitudinal and
latitudinal velocities. Recently, deep learning has shown promise in
capturing subtleties in Quiet Sun flows at spatial and temporal scales
that typically cannot be recovered by tracking methods (Asensio Ramos
et al, 2017). The DeepVel neural network is trained to infer plasma
flows from surface data using examples from detailed numerical models
(i.e., supervised learning). Using a version of DeepVel that was
trained using a high-resolution numerical simulation of the evolution
of an AR (e.g. Hotta &amp; Iijima, 2020) we developed the algorithm
for predicting flow trajectories from high resolution observational
data. This method was directly compared with previous contenders for
tracking flows and shows more realistic plasma flow field estimation
as well as an increase of reconstruction efficiency.

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Title: Accelerating non-LTE synthesis and inversions with graph
networks
Authors: Arévalo, A. Vicente; Asensio Ramos, A.; Esteban Pozuelo, S.
2021arXiv211110552A Altcode: 2021arXiv211110552V
The computational cost of fast non-LTE synthesis is one of the
challenges that limits the development of 2D and 3D inversion codes. It
also makes the interpretation of observations of lines formed in the
chromosphere and transition region a slow and computationally costly
process, which limits the inference of the physical properties on
rather small fields of view. Having access to a fast way of computing
the deviation from the LTE regime through the departure coefficients
could largely alleviate this problem. We propose to build and train a
graph network that quickly predicts the atomic level populations without
solving the non-LTE problem. We find an optimal architecture for the
graph network for predicting the departure coefficients of the levels of
an atom from the physical conditions of a model atmosphere. A suitable
dataset with a representative sample of potential model atmospheres
is used for training. This dataset has been computed using existing
non-LTE synthesis codes. The graph network has been integrated into
existing synthesis and inversion codes for the particular case of
\caii. We demonstrate orders of magnitude gain in computing speed. We
analyze the generalization capabilities of the graph network and
demonstrate that it produces good predicted departure coefficients for
unseen models. We implement this approach in \hazel\ and show how the
inversions nicely compare with those obtained with standard non-LTE
inversion codes. Our approximate method opens up the possibility
of extracting physical information from the chromosphere on large
fields-of-view with time evolution.

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Title: Temporal evolution of small-scale internetwork magnetic fields
in the solar photosphere (Corrigendum)
Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.;
Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A.
2021A&A...652C...2C Altcode:
No abstract at ADS

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Title: Exploring the Sun's upper atmosphere with neural networks:
Reversed patterns and the hot wall effect
Authors: Socas-Navarro, H.; Asensio Ramos, A.
2021A&A...652A..78S Altcode:
We have developed an inversion procedure designed for high-resolution
solar spectro-polarimeters, such as those of Hinode and the
DKIST. The procedure is based on artificial neural networks trained
with profiles generated from random atmospheric stratifications
for a high generalization capability. When applied to Hinode data,
we find a hot fine-scale network structure whose morphology changes
with height. In the middle layers, this network resembles what is
observed in G-band filtergrams, but it is not identical. Surprisingly,
the temperature enhancements in the middle and upper photosphere have
a reversed pattern. Hot pixels in the middle photosphere, possibly
associated with small-scale magnetic elements, appear cool at the
log τ500 = −3 and −4 level, and vice versa. Finally,
we find hot arcs on the limb side of magnetic pores. We interpret them
as the first piece of direct observational evidence of the "hot wall"
effect, which is a prediction of theoretical models from the 1970's.

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Title: Performance of solar far-side active region neural detection
Authors: Broock, E. G.; Felipe, T.; Asensio Ramos, A.
2021A&A...652A.132B Altcode: 2021arXiv210609365B
Context. Far-side helioseismology is a technique used to infer the
presence of active regions in the far hemisphere of the Sun based on
the interpretation of oscillations measured in the near hemisphere. A
neural network has recently been developed to improve the sensitivity
of the seismic maps to the presence of far-side active regions. Aims: Our aim is to evaluate the performance of the new neural
network approach and to thoroughly compare it with the standard
method commonly applied to predict far-side active regions from seismic
measurements. Methods: We have computed the predictions of active
regions using the neural network and the standard approach from five
years of far-side seismic maps as a function of the selected threshold
in the signatures of the detections. The results have been compared
with direct extreme ultraviolet observations of the far hemisphere
acquired with the Solar Terrestrial Relations Observatory. 
Results: We have confirmed the improved sensitivity of the neural
network to the presence of far-side active regions. Approximately 96%
of the active regions identified by the standard method with a strength
above the threshold commonly employed by previous analyses are related
to locations with enhanced extreme ultraviolet emission. For this
threshold, the false positive ratio is 3.75%. For an equivalent
false positive ratio, the neural network produces 47% more true
detections. Weaker active regions can be detected by relaxing the
threshold in their seismic signature. For almost the entire range
of thresholds, the performance of the neural network is superior
to that of the standard approach, delivering a higher number of
confirmed detections and a lower rate of false positives. 
Conclusions: The neural network is a promising approach for improving
the interpretation of the seismic maps provided by local helioseismic
techniques. Additionally, refined predictions of magnetic activity in
the non-visible solar hemisphere can play a significant role in space
weather forecasting.

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Title: Using artificial neural networks to improve photometric
modeling in airless bodies
Authors: Rizos, J. L.; Asensio-Ramos, A.; Golish, D. R.; DellaGiustina,
D. N.; Licandro, J.; de León, J.; Campins, H.; Tatsumi, E.;
Popescu, M.
2021arXiv210601363R Altcode:
Relevant information about physical properties of the surface of
airless bodies such as porosity, particle size, or roughness can be
inferred knowing the dependence of the brightness with illumination
and observing geometry. Additionally, this knowledge is necessary to
standardize or photometrically correct data acquired under different
illumination conditions. In this work we develop a robust, automatic,
and efficient photometric modeling methodology which is tested and
validated using Bennu images acquired by the camera MapCam from the
OSIRIS-REx spacecraft. It consists of a supervised machine learning
algorithm through an artificial neural network. Our system provides a
more precise modeling for all color filters than the previous procedures
which are already published, offering an improvement over this classic
approach of up to 14.30%, as well as a considerable reduction in
computing time.

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Title: Mapping of Solar Magnetic Fields from the Photosphere to the
Top of the Chromosphere with CLASP2
Authors: McKenzie, D.; Ishikawa, R.; Trujillo Bueno, J.; Auchere, F.;
del Pino Aleman, T.; Okamoto, T.; Kano, R.; Song, D.; Yoshida, M.;
Rachmeler, L.; Kobayashi, K.; Narukage, N.; Kubo, M.; Ishikawa, S.;
Hara, H.; Suematsu, Y.; Sakao, T.; Bethge, C.; De Pontieu, B.; Vigil,
G.; Winebarger, A.; Alsina Ballester, E.; Belluzzi, L.; Stepan, J.;
Asensio Ramos, A.; Carlsson, M.; Leenaarts, J.
2021AAS...23810603M Altcode:
Coronal heating, chromospheric heating, and the heating &amp;
acceleration of the solar wind, are well-known problems in solar
physics. Additionally, knowledge of the magnetic energy that
powers solar flares and coronal mass ejections, important drivers
of space weather, is handicapped by imperfect determination of the
magnetic field in the sun's atmosphere. Extrapolation of photospheric
magnetic measurements into the corona is fraught with difficulties and
uncertainties, partly due to the vastly different plasma beta between
the photosphere and the corona. Better results in understanding
the coronal magnetic field should be derived from measurements of
the magnetic field in the chromosphere. To that end, we are pursuing
quantitative determination of the magnetic field in the chromosphere,
where plasma beta transitions from greater than unity to less than
unity, via ultraviolet spectropolarimetry. The CLASP2 mission, flown
on a sounding rocket in April 2019, succeeded in measuring all four
Stokes polarization parameters in UV spectral lines formed by singly
ionized Magnesium and neutral Manganese. Because these ions produce
spectral lines under different conditions, CLASP2 thus was able to
quantify the magnetic field properties at multiple heights in the
chromosphere simultaneously, as shown in the recent paper by Ishikawa
et al. In this presentation we will report the findings of CLASP2,
demonstrating the variation of magnetic fields along a track on
the solar surface and as a function of height in the chromosphere;
and we will illustrate what is next for the CLASP missions and the
demonstration of UV spectropolarimetry in the solar chromosphere.

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Title: Inferring Plasma Flows In The Solar Photosphere &amp;
Chromosphere Using Deep Learning And Surface Observations
Authors: Tremblay, B.; Reardon, K.; Attie, R.; Kazachenko, M.;
Tilipman, D.; Asensio Ramos, A.
2021AAS...23812301T Altcode:
Direct measurements of plasma motions are limited to the line-of-sight
component at the Sun's surface. Multiple tracking and inversion methods
were developed to infer the transverse motions from observational
data. Recently, the fully convolutional DeepVel &amp; DeepVelU neural
networks were trained in conjunction with detailed magnetohydrodynamics
(MHD) simulations of the Quiet Sun and sunspots to recover the
instantaneous depth/height-dependent transverse velocity vector from a
combination of intensitygrams, magnetograms and/or Dopplergrams of the
solar surface. Through this supervised learning approach, the neural
network attempts to emulate the synthetic flows, and by extension the
physics, from the numerical simulation it was presented during its
training, i.e. its outputs are model-dependent and may be subjected
to biases. Although simulations have become increasingly realistic,
the validity of flows inferred by DeepVel or DeepVelU is subject to
debate when using real observational data as input. As a test, we use
white light images of the Quiet Sun photosphere (optical depth tau=1)
produced by the Interferometric BIdimensional Spectropolarimeter
(IBIS) installed at the Dunn Solar Telescope to infer plasma motions
approx. 150-200 km above the surface (i.e., near the transition between
the photosphere and the chromosphere) using DeepVel. We discuss work
in progress comparing the neural network estimates to the optical
flows determined from a time series of observational data formed near
150-200 km above the surface. Optical flows do not directly track
actual transverse plasma motions, but are correlated with physical
flows over certain spatial and temporal scales.

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Title: Probing Uncertainties in Diagnostics of a Synthetic
Chromosphere
Authors: Schmit, Don; Martinez-Sykora, Juan; Pereira, Tiago; Asensio
Ramos, Andrés
2021ApJ...913...71S Altcode:
Effective spectroscopic diagnostics rely on the ability to convert a
particular flux measurement into a physical interpretation. Knowledge
of uncertainty is a central component of diagnostics. We present data
from a simulated solar-like chromosphere, where we have addressed the
question of whether degeneracy is a problem in mapping from a non-LTE
chromospheric line profile to a particular vertical stratification
of atmospheric properties along the line of sight. Our results
indicate that stratification degeneracies do exist, at least in our
simulated atmosphere. We quantify this effect through the creation
of posterior densities for atmospheric properties based on the Mg
II h line profile using the approximate Bayesian computation (ABC)
technique. We find that the predictive power of the ABC temperature
posterior systematically varies as a function of atmospheric column
mass and ground-truth temperature. The ABC posteriors more effectively
reproduce the spectral intensity in the Ca II 8542 Å line than they do
temperature stratification, although residual error in the Ca II line
core is common. Our results illustrate that some degeneracies should
be alleviated through simultaneous analysis of multiple chromospheric
lines.

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Title: Rubidium abundances in solar metallicity stars
Authors: Abia, C.; de Laverny, P.; Korotin, S.; Asensio Ramos, A.;
Recio-Blanco, A.; Prantzos, N.
2021A&A...648A.107A Altcode: 2021arXiv210202498A
Context. Rubidium is one of the few elements produced by the neutron
capture s- and r-processes in almost equal proportions. Recently,
a Rb deficiency ([Rb/Fe] &lt; 0.0), amounting to a factor of
about two with respect to the Sun, has been found in M dwarfs of
near-solar metallicity. This stands in contrast to the close-to-solar
[Sr, Zr/Fe] ratios derived in the same stars. This deficiency is
difficult to understand from the point of view of observations and
of nucleosynthesis. Aims: To test the reliability of this Rb
deficiency, we study the Rb and Zr abundances in a sample of KM-type
giant stars across a similar metallicity range, extracted from
the AMBRE Project. Methods: We used high-resolution and high
signal-to-noise spectra to derive Rb and Zr abundances in a sample of
54 bright giant stars with metallicities in the range of −0.6 ≲
[Fe/H] ≲ +0.4 dex, via spectral synthesis in both local and non-local
thermodynamic equilibrium (LTE and NLTE, respectively). We also studied
the impact of the Zeeman broadening in the profile of the Rb I at
λ7800 Å line. Results: The LTE analysis also results in a Rb
deficiency in giant stars, however, it is considerably lower than that
obtained in M dwarfs. However, once NLTE corrections are performed, the
[Rb/Fe] ratios are very close to solar (average −0.01 ± 0.09 dex)
in the full metallicity range studied here. This stands in contrast
to the value found for M dwarfs. The [Zr/Fe] ratios derived are in
excellent agreement with those obtained in previous studies in FGK
dwarf stars with a similar metallicity. We investigate the effect of
gravitational settling and magnetic activity as possible causes of
the Rb deficiency found in M dwarfs. Although the former phenomenon
has a negligible impact on the surface Rb abundance, the presence
of an average magnetic field with an intensity that is typical of
that observed in M dwarfs may result in systematic Rb abundance
underestimations if the Zeeman broadening is not considered in the
spectral synthesis. This may explain the Rb deficiency in M dwarfs,
but not fully. On the other hand, the new [Rb/Fe] and [Rb/Zr] versus
[Fe/H] relationships can be explained when the Rb production by rotating
massive stars and low-to-intermediate mass stars (these latter also
producing Zr) are considered, without the need to deviate from the
standard s-process nucleosynthesis in asymptotic giant branch stars,
as suggested previously.

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Title: Inferring Plasma Flows in the Solar Photosphere &amp;
Chromosphere using Deep Learning and Surface Observations
Authors: Tremblay, Benoit; Reardon, Kevin; Attié, Raphaël;
Kazachenko, Maria; Asensio Ramos, Andrés; Tilipman, Dennis
2021csss.confE.204T Altcode:
Direct measurements of plasma motions are limited to the line-of-sight
component at the Sun's surface. Multiple tracking and inversion methods
were developed to infer the transverse motions from observational
data. Recently, the fully convolutional DeepVel &amp; DeepVelU neural
networks were trained in conjunction with detailed magnetohydrodynamics
(MHD) simulations of the Quiet Sun and sunspots to recover the
instantaneous depth/height-dependent transverse velocity vector from a
combination of intensitygrams, magnetograms and/or Dopplergrams of the
solar surface. Through this supervised learning approach, the neural
network attempts to emulate the synthetic flows, and by extension the
physics, from the numerical simulation it was presented during its
training, i.e. its outputs are model-dependent and may be subjected
to biases. Although simulations have become increasingly realistic,
the validity of flows inferred by DeepVel or DeepVelU is subject to
debate when using real observational data as input. As a test, we use
white light images of the Quiet Sun photosphere (optical depth tau=1)
produced by the Interferometric BIdimensional Spectropolarimeter
(IBIS) installed at the Dunn Solar Telescope to infer plasma motions
approx. 150-200 km above the surface (i.e., near the transition between
the photosphere and the chromosphere) using DeepVel. We discuss work
in progress comparing the neural network estimates to the optical
flows determined from a time series of observational data formed near
150-200 km above the surface. Optical flows do not directly track
actual transverse plasma motions, but are correlated with physical
flows over certain spatial and temporal scales.

---------------------------------------------------------
Title: Temporal evolution of small-scale internetwork magnetic fields
in the solar photosphere
Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.;
Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A.
2021A&A...647A.182C Altcode: 2021arXiv210200942C
Context. While the longitudinal field that dominates in photospheric
network regions has been studied extensively, small-scale transverse
fields have recently been found to be ubiquitous in the quiet
internetwork photosphere and this merits further study. Furthermore,
few observations have been able to capture how this field evolves. Aims: We aim to statistically characterize the magnetic vector in
a quiet Sun internetwork region and observe the temporal evolution of
specific small-scale magnetic features. Methods: We present
two high spatio-temporal resolution observations that reveal the
dynamics of two disk-centre internetwork regions taken by the new GREGOR
Infrared Spectrograph Integral Field Unit with the highly magnetically
sensitive photospheric Fe I line pair at 15648.52 Å and 15652.87
Å. We record the full Stokes vector and apply inversions with the
Stokes inversions based on response functions code to retrieve the
parameters characterizing the atmosphere. We consider two inversion
schemes: scheme 1 (S1), where a magnetic atmosphere is embedded in
a field free medium, and scheme 2 (S2), with two magnetic models
and a fixed 30% stray light component. Results: The magnetic
properties produced from S1 inversions returned a median magnetic
field strength of 200 and 240 G for the two datasets, respectively. We
consider the median transverse (horizontal) component, among pixels
with Stokes Q or U, and the median unsigned longitudinal (vertical)
component, among pixels with Stokes V, above a noise threshold. We
determined the former to be 263 G and 267 G, and the latter to be 131
G and 145 G, for the two datasets, respectively. Finally, we present
three regions of interest, tracking the dynamics of small-scale magnetic
features. We apply S1 and S2 inversions to specific profiles of interest
and find that the latter produces better approximations when there is
evidence of mixed polarities. We find patches of linear polarization
with magnetic flux density of the order of 130−150 G and find that
linear polarization appears preferentially at granule-intergranular
lane boundaries. The weak magnetic field appears to be organized in
terms of complex `loop-like' structures, with transverse fields often
flanked by opposite polarity longitudinal fields.

---------------------------------------------------------
Title: Planet cartography with neural learned regularization
Authors: Asensio Ramos, A.; Pallé, E.
2021A&A...646A...4A Altcode: 2020arXiv201204460A
 Aims: Finding potential life harboring exo-Earths with future
telescopes is one of the aims of exoplanetary science. Detecting
signatures of life in exoplanets will likely first be accomplished
by determining the bulk composition of the planetary atmosphere
via reflected or transmitted spectroscopy. However, a complete
understanding of the habitability conditions will surely require mapping
the presence of liquid water, continents, and/or clouds. Spin-orbit
tomography is a technique that allows us to obtain maps of the surface
of exoplanets around other stars using the light scattered by the
planetary surface. Methods: We leverage the enormous potential
of deep learning, and propose a mapping technique for exo-Earths in
which the regularization is learned from mock surfaces. The solution
of the inverse mapping problem is posed as a deep neural network that
can be trained end-to-end with suitable training data. Since we still
lack observational data of the surface albedo of exoplanets, in this
work we propose methods based on the procedural generation of planets,
inspired by what we have found on Earth. We also consider mapping the
recovery of surfaces and the presence of persistent clouds in cloudy
planets, a much more challenging problem. Results: We show that
reliable mapping can be carried out with our approach, producing very
compact continents, even when using single-passband observations. More
importantly, if exoplanets are partially cloudy like the Earth is, we
show that it is possible to map the distribution of persistent clouds
that always occur in the same position on the surface (associated with
orography and sea surface temperatures) together with nonpersistent
clouds that move across the surface. This will become the first test
to perform on an exoplanet for the detection of an active climate
system. For small rocky planets in the habitable zone of their stars,
this weather system will be driven by water, and the detection can be
considered a strong proxy for truly habitable conditions.

---------------------------------------------------------
Title: VizieR Online Data Catalog: 3D shapes of extremely metal-poor
galaxies (Putko+, 2019)
Authors: Putko, J.; Sanchez Almeida, J.; Munoz-Tunon, C.; Asensio
Ramos, A.; Elmegreen, B. G.; Elmegreen, D. M.
2021yCat..18830010P Altcode:
The galaxies used in our inference of 3D shape are from Sanchez Almeida+
(2016, J/ApJ/819/110), who mined the spectroscopic catalog of the Sloan
Digital Sky Survey (SDSS) in producing the largest published sample
(195) of extremely metal-poor galaxies (XMPs) from a single survey. (1 data file).

---------------------------------------------------------
Title: Learning to do multiframe wavefront sensing unsupervised:
Applications to blind deconvolution
Authors: Asensio Ramos, A.; Olspert, N.
2021A&A...646A.100A Altcode: 2020arXiv200601438A
Context. Observations from ground-based telescopes are severely
perturbed by the presence of the Earth's atmosphere. The use of
adaptive optics techniques has allowed us to partly overcome this
limitation. However, image-selection or post-facto image-reconstruction
methods applied to bursts of short-exposure images are routinely
needed to reach the diffraction limit. Deep learning has recently
been proposed as an efficient way to accelerate these image
reconstructions. Currently, these deep neural networks are trained with
supervision, meaning that either standard deconvolution algorithms
need to be applied a priori or complex simulations of the solar
magneto-convection need to be carried out to generate the training
sets. Aims: Our aim here is to propose a general unsupervised
training scheme that allows multiframe blind deconvolution deep
learning systems to be trained with observations only. The approach
can be applied for the correction of point-like as well as extended
objects. Methods: Leveraging the linear image formation theory
and a probabilistic approach to the blind deconvolution problem
produces a physically motivated loss function. Optimization of this
loss function allows end-to-end training of a machine learning model
composed of three neural networks. Results: As examples, we
apply this procedure to the deconvolution of stellar data from the
FastCam instrument and to solar extended data from the Swedish Solar
Telescope. The analysis demonstrates that the proposed neural model
can be successfully trained without supervision using observations
only. It provides estimations of the instantaneous wavefronts, from
which a corrected image can be found using standard deconvolution
techniques. The network model is roughly three orders of magnitude
faster than applying standard deconvolution based on optimization and
shows potential to be used on real-time at the telescope.

---------------------------------------------------------
Title: Mapping the Sun's upper photosphere with artificial neural
networks
Authors: Socas-Navarro, Hector; Asensio Ramos, Andres
2021arXiv210111445S Altcode:
We have developed an inversion procedure designed for high-resolution
solar spectro-polarimeters, such as Hinode/SP or DKIST/ViSP. The
procedure is based on artificial neural networks trained with
profiles generated from random atmospheric stratifications for a high
generalization capability. When applied to Hinode data we find a hot
fine-scale network structure whose morphology changes with height. In
the middle layers this network resembles what is observed in G-band
filtergrams but it is not identical. Surprisingly, the temperature
enhancements in the middle and upper photosphere have a reversed
pattern. Hot pixels in the middle photosphere, possibly associated to
small-scale magnetic elements, appear cool at the log(tau_500)=-3 and
-4 level, and viceversa. Finally, we find hot arcs on the limb side of
magnetic pores, which we interpret as the first direct observational
evidence of the "hot wall" effect in temperature.

---------------------------------------------------------
Title: Inferring Plasma Flows in the Solar Photosphere &amp;
Chromosphere using Deep Learning and Surface Observations
Authors: Tremblay, B.; Reardon, K.; Attié, R.; Asensio Ramos, A.;
Kazachenko, M.; Tilipman, D.
2020AGUFMSH007..08T Altcode:
Direct measurements of plasma motions are limited to the line-of-sight
component at the Sun's surface. Multiple tracking and inversion methods
were developed to infer the transverse motions from observational
data. Optical flows do not directly track actual transverse plasma
motions, but our most recent results show that unsupervised flow
tracking performed on simulation data of the solar surface with the
Ball-tracking method accurately reconstructs the true transverse
plasma velocity over certain spatial and temporal scales. Recently,
the fully convolutional DeepVel &amp; DeepVelU neural networks
were trained in conjunction with detailed magnetohydrodynamics (MHD)
simulations of the Quiet Sun and sunspots to recover the instantaneous
depth/height-dependent transverse velocity vector from a combination
of intensitygrams, magnetograms and/or Dopplergrams of the solar
surface. Through this supervised learning approach, the neural
network attempts to emulate the synthetic flows, and by extension the
physics, from the numerical simulation it was presented during its
training, i.e. its outputs are model-dependent and may be subjected
to biases. Although simulations have become increasingly realistic,
the validity of flows inferred by DeepVel or DeepVelU is subject to
debate when using real observational data as input. As a test, we use
white light images of the Quiet Sun photosphere (optical depth τ=1)
produced by the Interferometric BIdimensional Spectropolarimeter (IBIS)
installed at the Dunn Solar Telescope to infer plasma motions at optical
depth τ=0.1 (i.e., near the transition between the photosphere and
the chromosphere) using DeepVelU. We then compare the results to
the optical flows determined from a time series of observational
data formed near τ=0.1, which may not be subjected to the biases
present in DeepVelU . Finally, we discuss work in progress to infer
photospheric and chromospheric (optical) flows through unsupervised
learning, i.e. learning strictly from observational data and thus
without simulations.

---------------------------------------------------------
Title: Spatially resolved measurements of the solar photospheric
oxygen abundance
Authors: Cubas Armas, M.; Asensio Ramos, A.; Socas-Navarro, H.
2020A&A...643A.142C Altcode: 2020arXiv201002151C
 Aims: We report the results of a novel determination of
the solar oxygen abundance using spatially resolved observations
and inversions. We seek to derive the photospheric solar oxygen
abundance with a method that is robust against uncertainties in the
model atmosphere. Methods: We use observations with spatial
resolution obtained at the Vacuum Tower Telescope to derive the
oxygen abundance at 40 different spatial positions in granules and
intergranular lanes. We first obtain a model for each location by
inverting the Fe I lines with the NICOLE inversion code. These models
are then integrated into a hierarchical Bayesian model that is used
to infer the most probable value for the oxygen abundance that is
compatible with all the observations. The abundance is derived from the
[O I] forbidden line at 6300 Å taking into consideration all possible
nuisance parameters that can affect the abundance. Results: Our
results show good agreement in the inferred oxygen abundance for all the
pixels analyzed, demonstrating the robustness of the analysis against
possible systematic errors in the model. We find a slightly higher
oxygen abundance in granules than in intergranular lanes when treated
separately (log(ɛO) = 8.83 ± 0.02 vs. log(ɛO) =
8.76 ± 0.02), which is a difference of approximately 2-σ. This tension
suggests that some systematic errors in the model or the radiative
transfer still exist but are small. When taking all pixels together,
we obtain an oxygen abundance of log(ɛO) = 8.80 ± 0.03,
which is compatible with both granules and lanes within 1-σ. The
spread of results is due to both systematic and random errors.

---------------------------------------------------------
Title: Ubiquitous hundred-Gauss magnetic fields in solar spicules
Authors: Kriginsky, M.; Oliver, R.; Freij, N.; Kuridze, D.; Asensio
Ramos, A.; Antolin, P.
2020A&A...642A..61K Altcode: 2020arXiv200601809K
 Aims: We aim to study the magnetic field in solar spicules
using high-resolution spectropolarimetric observations in the Ca II
8542 Å line obtained with the Swedish 1-m Solar Telescope. 
Methods: The equations that result from the application of the weak
field approximation (WFA) to the radiative transfer equations were
used to infer the line-of-sight (LOS) component of the magnetic
field (BLOS). Two restrictive conditions were imposed
on the Stokes I and V profiles at each pixel before they could be
used in a Bayesian inversion to compute its BLOS. 
Results: The LOS magnetic field component was inferred in six data sets
totalling 448 spectral scans in the Ca II 8542 Å line and containing
both active region and quiet Sun areas, with values of hundreds of
Gauss being abundantly inferred. There seems to be no difference,
from a statistical point of view, between the magnetic field strength
of spicules in the quiet Sun or near an active region. On the other
hand, the BLOS distributions present smaller values on
the disc than off-limb, a fact that can be explained by the effect of
superposition on the chromosphere of on-disc structures. We show that
on-disc pixels in which the BLOS is determined are possibly
associated with spicular structures because these pixels are co-spatial
with the magnetic field concentrations at the network boundaries and
the sign of their BLOS agrees with that of the underlying
photosphere. We find that spicules in the vicinity of a sunspot have
a magnetic field polarity (i.e. north or south) equal to that of the
sunspot. This paper also contains an analysis of the effect of off-limb
overlapping structures on the observed Stokes I and V parameters and
the BLOS obtained from the WFA. It is found that this value
is equal to or smaller than the largest LOS magnetic field components
of the two structures. In addition, using random BLOS,
Doppler velocities, and line intensities of these two structures
leads in ≃50% of the cases to Stokes I and V parameters that are
unsuitable to be used with the WFA. Conclusions: Our results
present a scarcity of LOS magnetic field components smaller than some
50 G, which must not be taken as evidence against the existence of
these magnetic field strengths in spicules. This fact possibly arises
as the consequence of signal superposition and noise in the data. We
also suggest that the failure of previous works to infer the strong
magnetic fields in spicules detected here is their coarser spatial
and/or temporal resolution.

---------------------------------------------------------
Title: Determining the dynamics and magnetic fields in He I 10830
Å during a solar filament eruption
Authors: Kuckein, C.; González Manrique, S. J.; Kleint, L.; Asensio
Ramos, A.
2020A&A...640A..71K Altcode: 2020arXiv200610473K
 Aims: We investigate the dynamics and magnetic properties of
the plasma, including the line-of-sight velocity (LOS) and optical
depth, as well as the vertical and horizontal magnetic fields,
belonging to an erupted solar filament. Methods: The filament
eruption was observed with the GREGOR Infrared Spectrograph at
the 1.5-meter GREGOR telescope on July 3, 2016. We acquired three
consecutive full-Stokes slit-spectropolarimetric scans in the He
I 10830 Å spectral range. The Stokes I profiles were classified
using the machine learning k-means algorithm and then inverted with
different initial conditions using the HAZEL code. Results: The
erupting-filament material presents the following physical conditions:
(1) ubiquitous upward motions with peak LOS velocities of ∼73 km
s-1; (2) predominant large horizontal components of the
magnetic field, on average, in the range of 173-254 G, whereas the
vertical components of the fields are much lower, on average between
39 and 58 G; (3) optical depths in the range of 0.7-1.1. The average
azimuth orientation of the field lines between two consecutive
raster scans (&lt;2.5 min) remained constant. Conclusions:
The analyzed filament eruption belongs to the fast rising phase, with
total velocities of about 124 km s-1. The orientation of the
magnetic field lines does not change from one raster scan to the other,
indicating that the untwisting phase has not yet started. The untwisting
appears to start about 15 min after the beginning of the filament
eruption. Movies attached to Figs. 1 and 3 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202038408/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Chromospheric Magnetic Field: A Comparison of He I 10830 Å
Observations with Nonlinear Force-free Field Extrapolation
Authors: Kawabata, Yusuke; Asensio Ramos, Andrés; Inoue, Satoshi;
Shimizu, Toshifumi
2020ApJ...898...32K Altcode: 2020arXiv200600179K
The nonlinear force-free field (NLFFF) modeling has been extensively
used to infer the three-dimensional magnetic field in the solar
corona. One of the assumptions in the NLFFF extrapolation is that the
plasma beta is low, but this condition is considered to be incorrect in
the photosphere. We examine direct measurements of the chromospheric
magnetic field in two active regions through spectropolarimetric
observations at He I 10830 Å, which are compared with the potential
fields and NLFFFs extrapolated from the photosphere. The comparisons
allow quantitative estimation of the uncertainty in the NLFFF
extrapolation from the photosphere. Our analysis shows that observed
chromospheric magnetic field may have larger nonpotentiality compared to
the photospheric magnetic field. Moreover, the large nonpotentiality
in the chromospheric height may not be reproduced by the NLFFF
extrapolation from the photospheric magnetic field. The magnitude of
the underestimation of the nonpotentiality at chromospheric heights may
reach 30°-40° in shear signed angle in some locations. This deviation
may be caused by the non-force-freeness in the photosphere. Our study
suggests the importance of the inclusion of measured chromospheric
magnetic fields in the NLFFF modeling for the improvement of the
coronal extrapolation.

---------------------------------------------------------
Title: Magnetic field inference in the chromosphere and lower corona
Authors: Kriginsky, M.; Oliver, R.; Freij, N.; Kuridze, D.; Asensio
Ramos, A.; Antolin, P.
2020sea..confE.201K Altcode:
The Weak Field Approximation (WFA) is used to infer the line-of-sight
magnetic field of the solar chromosphere and lower corona. Using near
limb spectropolarimetric observations in the Ca II 8542 Å line taken
with the CRISP instrument at the Swedish 1-metre telescope in La Palma,
the presence of an active region near/in the field of view allows
for the presence of chromospheric spicules and coronal rain blobs
to be detected. This work focuses mostly in the inference of magnetic
fields of off-limb spicules, but a successful attempt to obtain Stokes V
signal from the coronal rain blobs allowed for the inference of coronal
magnetic fields. A careful treatment of the data pixels is undertaken in
order to guarantee the correct application of the WFA, and the results
show the presence of ubiquitous hundred-Gauss magnetic fields in the
spicular material and in the coronal rain blobs. A Bayesian approach
is used to infer the results.

---------------------------------------------------------
Title: Determining the dynamics and magnetic fields in the
chromospheric He I 10830 Å triplet during a solar filament eruption
Authors: Kuckein, C.; González Manrique, S. J.; Kleint, L.; Asensio
Ramos, A.
2020sea..confE.202K Altcode:
We investigate the dynamics and magnetic properties of the plasma, such
as line-of-sight velocity (LOS), optical depth, vertical and horizontal
magnetic fields, belonging to an erupted solar filament. The filament
eruption was observed with the GREGOR Infrared Spectrograph (GRIS)
at the 1.5-meter GREGOR telescope on 2016 July 3. Three consecutive
full-Stokes slit-spectropolarimetric scans in the He I 10830 Å
spectral range were acquired. The Stokes I profiles were classified
using the machine learning k-means algorithm and then inverted with
different initial conditions using the inversion code HAZEL. The
erupting-filament material presents the following physical conditions:
(i) ubiquitous upward motions with peak LOS velocities of ∼73 km/s;
(ii) predominant large horizontal components of the magnetic field, on
average, in the range of 173-254 G, whereas the vertical components of
the fields are much lower, on average between 39-58 G; (iii) optical
depths in the range of 0.7-1.1. The average azimuth orientation of
the field lines between two consecutive raster scans (&lt;2.5 minutes)
remained constant. The analyzed filament eruption belonged to the fast
rising phase, with total velocities of about 124 km/s.

---------------------------------------------------------
Title: A chromospheric resonance cavity in a sunspot mapped with
seismology
Authors: Jess, David B.; Snow, Ben; Houston, Scott J.; Botha, Gert
J. J.; Fleck, Bernhard; Krishna Prasad, S.; Asensio Ramos, Andrés;
Morton, Richard J.; Keys, Peter H.; Jafarzadeh, Shahin; Stangalini,
Marco; Grant, Samuel D. T.; Christian, Damian J.
2020NatAs...4..220J Altcode: 2019NatAs...4..220J; 2019NatAs.tmp..502J
Sunspots are intense collections of magnetic fields that pierce through
the Sun's photosphere, with their signatures extending upwards into the
outermost extremities of the solar corona1. Cutting-edge
observations and simulations are providing insights into the
underlying wave generation2, configuration3,4 and
damping5 mechanisms found in sunspot atmospheres. However,
the in situ amplification of magnetohydrodynamic waves6,
rising from a few hundreds of metres per second in the photosphere to
several kilometres per second in the chromosphere7, has,
until now, proved difficult to explain. Theory predicts that the
enhanced umbral wave power found at chromospheric heights may come
from the existence of an acoustic resonator8-10, which
is created due to the substantial temperature gradients experienced
at photospheric and transition region heights11. Here,
we provide strong observational evidence of a resonance cavity
existing above a highly magnetic sunspot. Through a combination of
spectropolarimetric inversions and comparisons with high-resolution
numerical simulations, we provide a new seismological approach to
mapping the geometry of the inherent temperature stratifications across
the diameter of the underlying sunspot, with the upper boundaries of the
chromosphere ranging between 1,300 ± 200 km and 2,300 ± 250 km. Our
findings will allow the three-dimensional structure of solar active
regions to be conclusively determined from relatively commonplace
two-dimensional Fourier power spectra. The techniques presented are
also readily suitable for investigating temperature-dependent resonance
effects in other areas of astrophysics, including the examination of
Earth-ionosphere wave cavities12.

---------------------------------------------------------
Title: Three-dimensional magnetic field structure of a flux-emerging
region in the solar atmosphere
Authors: Yadav, Rahul; de la Cruz Rodríguez, Jaime; Díaz Baso,
Carlos José; Prasad, Avijeet; Libbrecht, Tine; Robustini, Carolina;
Asensio Ramos, Andrés
2019A&A...632A.112Y Altcode: 2019arXiv191013279Y
We analyze high-resolution spectropolarimetric observations of a
flux-emerging region (FER) in order to understand its magnetic and
kinematic structure. Our spectropolarimetric observations in the He
I 10830 Å spectral region of a FER were recorded with GRIS at the
1.5 m aperture GREGOR telescope. A Milne-Eddington-based inversion
code was employed to extract the photospheric information of the Si I
spectral line, whereas the He I triplet line was analyzed with the Hazel
inversion code, which takes into account the joint action of the Hanle
and the Zeeman effects. The spectropolarimetric analysis of the Si I
line reveals a complex magnetic structure near the vicinity of the FER,
where a weak (350-600 G) and horizontal magnetic field was observed. In
contrast to the photosphere, the analysis of the He I triplet presents
a smooth variation of the magnetic field vector (ranging from 100 to
400 G) and velocities across the FER. Moreover, we find supersonic
downflows of ∼40 km s-1 appearing near the foot points
of loops connecting two pores of opposite polarity, whereas strong
upflows of 22 km s-1 appear near the apex of the loops. At
the location of supersonic downflows in the chromosphere, we observed
downflows of 3 km s-1 in the photosphere. Furthermore,
nonforce-free field extrapolations were performed separately at
two layers in order to understand the magnetic field topology of
the FER. We determine, using extrapolations from the photosphere and
the observed chromospheric magnetic field, that the average formation
height of the He I triplet line is ∼2 Mm from the solar surface. The
reconstructed loops using photospheric extrapolations along an arch
filament system have a maximum height of ∼10.5 Mm from the solar
surface with a foot-point separation of ∼19 Mm, whereas the loops
reconstructed using chromospheric extrapolations reach around ∼8.4
Mm above the solar surface with a foot-point separation of ∼16 Mm at
the chromospheric height. The magnetic topology in the FER suggests
the presence of small-scale loops beneath the large loops. Under
suitable conditions, due to magnetic reconnection, these loops can
trigger various heating events in the vicinity of the FER.

---------------------------------------------------------
Title: Improved detection of far-side solar active regions using
deep learning
Authors: Felipe, T.; Asensio Ramos, A.
2019A&A...632A..82F Altcode: 2019arXiv191101099F
Context. The analysis of waves on the visible side of the Sun
allows the detection of active regions on the far side through local
helioseismology techniques. Knowing the magnetism in the whole Sun,
including the non-visible hemisphere, is fundamental for several space
weather forecasting applications. Aims: Seismic identification of
far-side active regions is challenged by the reduced signal-to-noise
ratio, and only large and strong active regions can be reliable
detected. Here we develop a new method to improve the identification
of active region signatures in far-side seismic maps. Methods:
We constructed a deep neural network that associates the far-side
seismic maps obtained from helioseismic holography with the probability
that active regions lie on the far side. The network was trained with
pairs of helioseismic phase-shift maps and Helioseismic and Magnetic
Imager (HMI) magnetograms acquired half a solar rotation later, which
were used as a proxy for the presence of active regions on the far
side. The method was validated using a set of artificial data, and
it was also applied to actual solar observations during the period of
minimum activity of solar cycle 24. Results: Our approach shows
a higher sensitivity to the presence of far-side active regions than
standard methods that have been applied up to date. The neural network
can significantly increase the number of detected far-side active
regions, and will potentially improve the application of far-side
seismology to space weather forecasting.

---------------------------------------------------------
Title: Inferring the 3D Shapes of Extremely Metal-poor Galaxies from
Sets of Projected Shapes
Authors: Putko, J.; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Asensio
Ramos, A.; Elmegreen, B. G.; Elmegreen, D. M.
2019ApJ...883...10P Altcode: 2019arXiv190710496P
The three-dimensional (3D) shape of a galaxy inevitably is tied to how
it has formed and evolved and to its dark matter halo. Local extremely
metal-poor galaxies (XMPs; defined as having an average gas-phase
metallicity &lt;0.1 solar) are important objects for understanding
galaxy evolution largely because they appear to be caught in the act
of accreting gas from the cosmic web, and their 3D shape may reflect
this. Here, we report on the 3D shape of XMPs as inferred from their
observed projected minor-to-major axial ratios using a hierarchical
Bayesian inference model, which determines the likely shape and
orientation of each galaxy, while simultaneously inferring the average
shape and dispersion. We selected a sample of 149 XMPs and divided
it into three subsamples according to physical size and found that
(1) the stellar component of XMPs of all sizes tends to be triaxial,
with an intermediate axis ≈0.7 times the longest axis and that (2)
smaller XMPs tend to be relatively thicker, with the shortest axis going
from ≈0.15 times the longest axis for the large galaxies to ≈0.4 for
the small galaxies. We provide the inferred 3D shape and inclination of
the individual XMPs in electronic format. We show that our results for
the intermediate axis are not clouded by a selection effect against
face-on XMPs. We discuss how an intermediate axis significantly
smaller than the longest axis may be produced by several mechanisms,
including lopsided gas accretion, non-axisymmetric star formation, or
coupling with an elongated dark matter halo. Large relative thickness
may reflect slow rotation, stellar feedback, or recent gas accretion.

---------------------------------------------------------
Title: Torus model properties of an ultra-hard X-ray selected sample
of Seyfert galaxies
Authors: García-Bernete, I.; Ramos Almeida, C.; Alonso-Herrero,
A.; Ward, M. J.; Acosta-Pulido, J. A.; Pereira-Santaella, M.;
Hernán-Caballero, A.; Asensio Ramos, A.; González-Martín, O.;
Levenson, N. A.; Mateos, S.; Carrera, F. J.; Ricci, C.; Roche, P.;
Marquez, I.; Packham, C.; Masegosa, J.; Fuller, L.
2019MNRAS.486.4917G Altcode: 2019arXiv190403694G; 2019MNRAS.tmp..920G
We characterize for the first time the torus properties of an ultra-hard
X-ray (14-195 keV) volume-limited (DL &lt; 40 Mpc) sample
of 24 Seyfert (Sy) galaxies (BCS40 sample). The sample was
selected from the Swift/BAT nine-month catalogue. We use high angular
resolution nuclear infrared (IR) photometry and N-band spectroscopy,
the CLUMPY torus models and a Bayesian tool to characterize the
properties of the nuclear dust. In the case of the Sy1s, we estimate
the accretion disc contribution to the subarcsecond resolution nuclear
IR SEDs (∼0.4 arcsec) which is, on average, 46 ± 28, 23 ± 13,
and 11 ± 5 per cent in the J, H, and K bands, respectively. This
indicates that the accretion disc templates that assume a steep fall
for longer wavelengths than 1 μm might underestimate its contribution
to the near-IR emission. Using both optical (broad versus narrow lines)
and X-ray (unabsorbed versus absorbed) classifications, we compare the
global posterior distribution of the torus model parameters. We confirm
that Sy2s have larger values of the torus covering factor (CT
∼ 0.95) than Sy1s (CT ∼ 0.65) in our volume-limited
Seyfert sample. These findings are independent of whether we use an
optical or X-ray classification. We find that the torus covering factor
remains essentially constant within the errors in our luminosity range
and there is no clear dependence with the Eddington ratio. Finally,
we find tentative evidence that even an ultra-hard X-ray selection is
missing a significant fraction of highly absorbed type 2 sources with
very high covering factor tori.

---------------------------------------------------------
Title: High-resolution spectroscopy of Boyajian's star during optical
dimming events
Authors: Martínez González, M. J.; González-Fernández, C.; Asensio
Ramos, A.; Socas-Navarro, H.; Westendorp Plaza, C.; Boyajian, T. S.;
Wright, J. T.; Collier Cameron, A.; González Hernández, J. I.;
Holgado, G.; Kennedy, G. M.; Masseron, T.; Molinari, E.; Saario, J.;
Simón-Díaz, S.; Toledo-Padrón, B.
2019MNRAS.486..236M Altcode: 2019MNRAS.tmp..828M; 2018arXiv181206837M
Boyajian's star is an apparently normal main-sequence F-type star
with a very unusual light curve. The dipping activity of the star,
discovered during the Kepler mission, presents deep, asymmetric,
and aperiodic events. Here we present high-resolution spectroscopic
follow-up during some dimming events recorded post-Kepler observations,
from ground-based telescopes. We analyse data from the HERMES, HARPS-N,
and FIES spectrographs to characterize the stellar atmosphere and
to put some constraints on the hypotheses that have appeared in the
literature concerning the occulting elements. The star's magnetism,
if existing, is not extreme. The spots on the surface, if present,
would occupy 0.02 per cent of the area, at most. The chromosphere,
irrespective of the epoch of observation, is hotter than the values
expected from radiative equilibrium, meaning that the star has some
degree of activity. We find no clear evidence of the interstellar
medium or exocoments being responsible for the dimmings of the light
curve. However, we detect at 1-2σ level, a decrease of the radial
velocity of the star during the first dip recorded after the Kepler
observations. We claim the presence of an optically thick object with
likely inclined and high impact parameter orbits that produces the
observed Rossiter-McLaughlin effect.

---------------------------------------------------------
Title: Stokes inversion based on convolutional neural networks
Authors: Asensio Ramos, A.; Díaz Baso, C. J.
2019A&A...626A.102A Altcode: 2019arXiv190403714A
Context. Spectropolarimetric inversions are routinely used in the
field of solar physics for the extraction of physical information
from observations. The application to two-dimensional fields of view
often requires the use of supercomputers with parallelized inversion
codes. Even in this case, the computing time spent on the process is
still very large. Aims: Our aim is to develop a new inversion
code based on the application of convolutional neural networks that can
quickly provide a three-dimensional cube of thermodynamical and magnetic
properties from the interpreation of two-dimensional maps of Stokes
profiles. Methods: We trained two different architectures of
fully convolutional neural networks. To this end, we used the synthetic
Stokes profiles obtained from two snapshots of three-dimensional
magneto-hydrodynamic numerical simulations of different structures
of the solar atmosphere. Results: We provide an extensive
analysis of the new inversion technique, showing that it infers the
thermodynamical and magnetic properties with a precision comparable to
that of standard inversion techniques. However, it provides several key
improvements: our method is around one million times faster, it returns
a three-dimensional view of the physical properties of the region of
interest in geometrical height, it provides quantities that cannot be
obtained otherwise (pressure and Wilson depression) and the inferred
properties are decontaminated from the blurring effect of instrumental
point spread functions for free. The code, models, and data are all open
source and available for free, to allow both evaluation and training.

---------------------------------------------------------
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: McKenzie, D. E.; Ishikawa, R.; Trujillo Bueno, J.; Auchére,
F.; Rachmeler, L. A.; Kubo, M.; Kobayashi, K.; Winebarger, A. R.;
Bethge, C. W.; Narukage, N.; Kano, R.; Ishikawa, S.; de Pontieu,
B.; Carlsson, M.; Yoshida, M.; Belluzzi, L.; Štěpán, J.; del Pino
Alemán, T.; Alsina Ballester, E.; Asensio Ramos, A.
2019ASPC..526..361M Altcode:
The hydrogen Lyman-α line at 121.6 nm and the Mg k line at 279.5
nm are especially relevant for deciphering the magnetic structure
of the chromosphere since their line-center signals are formed in
the chromosphere and transition region, with unique sensitivities to
magnetic fields. We propose the Chromospheric LAyer Spectro-Polarimeter
(CLASP2), to build upon the success of the first CLASP flight, which
measured the linear polarization in H I Lyman-α. The existing CLASP
instrument will be refitted to measure all four Stokes parameters in
the 280 nm range, including variations due to the anisotropic radiation
pumping, the Hanle effect, and the Zeeman effect.

---------------------------------------------------------
Title: Spectropolarimetric analysis of an active region
filament. II. Evidence of the limitations of a single-component model
Authors: Díaz Baso, C. J.; Martínez González, M. J.; Asensio
Ramos, A.
2019A&A...625A.129D Altcode: 2019arXiv190410688D
 Aims: Our aim is to demonstrate the limitations of using a
single-component model to study the magnetic field of an active region
filament. To do this, we analyzed the polarimetric signals of the He I
10830 Å multiplet, which were acquired with the infrared spectrograph
GRIS of the GREGOR telescope (Tenerife, Spain). Methods: After
a first analysis of the general properties of the filament using HAZEL
under the assumption of a single-component model atmosphere, in this
second part we focus our attention on the observed Stokes profiles
and the signatures that cannot be explained with this model. 
Results: We have found an optically thick filament whose blue and
red components have the same sign in the linear polarization as an
indication of radiative transfer effects. Moreover, the circular
polarization signals inside the filament show strong magnetic field
gradients. We also show that even a filament with such high absorption
still shows signatures of the circular polarization that is generated
by the magnetic field below the filament. The reason is that the
absorption of the spectral line decays very quickly toward the wings,
just where the circular polarization has a larger amplitude. In order
to separate the two contributions, we explore the possibility of a
two-component model, but the inference becomes impossible to overcome
because very many solutions are compatible with the observations.

---------------------------------------------------------
Title: Comparison of Scattering Polarization Signals Observed by
CLASP: Possible Indication of the Hanle Effect
Authors: Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.;
Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa,
Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Shimizu, T.;
Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.;
Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso
Sainz, R.; De Pomtieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.
2019ASPC..526..305I Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP; Kano et
al. 2012; Kobayashi et al. 2012; Kubo et al. 2014) observed, for the
first time, the linear polarization produced by scattering processes
in the hydrogen Lyman-α (121.57 nm) and Si III (120.56 nm) lines of
the solar disk radiation. The complexity of the observed scattering
polarization (i.e., conspicuous spatial variations in Q/I and U/I
at spatial scales of 10″-20″ and the absence of center-to- limb
variation at the Lyman-α center; see Kano et al. 2017) motivated us
to search for possible hints of the operation of the Hanle effect by
comparing: (a) the Lyman-α line center signal, for which the critical
field strength (BH) for the onset of the Hanle effect is
53 G, (b) the Lyman-α wing, which is insensitive to the Hanle effect,
and (c) the Si III line, whose BH = 290 G. We focus on four
regions with different total unsigned photospheric magnetic fluxes
(estimated from SDO/HMI observations), and compare the corresponding
U/I spatial variations in the Lyman-α wing, Lyman-α center, and Si III
line. The U/I signal in the Lyman-α wing shows an antisymmetric spatial
distribution, which is caused by the presence of a bright structure in
all the selected regions, regardless of the total unsigned photospheric
magnetic flux. In an internetwork region, the Lyman-α center shows an
antisymmetric spatial variation across the selected bright structure,
but it does not show it in other more magnetized regions. In the Si III
line, the spatial variation of U/I deviates from the above-mentioned
antisymmetric shape as the total unsigned photospheric magnetic flux
increases. We argue that a plausible explanation of this differential
behavior is the operation of the Hanle effect. This work, presented
in an oral contribution at this Workshop, has been published on The
Astrophysical Journal (Ishikawa et al. 2017).

---------------------------------------------------------
Title: Spectropolarimetric analysis of an active region
filament. I. Magnetic and dynamical properties from single component
inversions
Authors: Díaz Baso, C. J.; Martínez González, M. J.; Asensio
Ramos, A.
2019A&A...625A.128D Altcode: 2019arXiv190409593D
 Aims: The determination of the magnetic filed vector in solar
filaments is made possible by interpreting the Hanle and Zeeman
effects in suitable chromospheric spectral lines like those of the
He I multiplet at 10 830 Å. We study the vector magnetic field of an
active region filament (NOAA 12087). Methods: Spectropolarimetric
data of this active region was acquired with the GRIS instrument at
the GREGOR telescope and studied simultaneously in the chromosphere
with the He I 10 830 Å multiplet and in the photosphere Si I 10 827
Å line. As has been done in previous studies, only a single-component
model was used to infer the magnetic properties of the filament. The
results are put into a solar context with the help of the Solar Dynamic
Observatory images. Results: Some results clearly point out
that a more complex inversion had to be performed. First, the Stokes
V map of He I does not show a clear signature of the presence of the
filament. Second, the local azimuth map follows the same pattern as
Stokes V; it appears that polarity of Stokes V is conditioning the
inference to very different magnetic fields even with similar linear
polarization signals. This indication suggests that the Stokes V could
be dominated from below by the magnetic field coming from the active
region, and not from the filament itself. This evidence, and others,
will be analyzed in depth and a more complex inversion will be attempted
in the second part of this series.

---------------------------------------------------------
Title: Inference of magnetic field strength and density from damped
transverse coronal waves
Authors: Arregui, I.; Montes-Solís, M.; Asensio Ramos, A.
2019A&A...625A..35A Altcode: 2019arXiv190305437A
A classic application of coronal seismology uses transverse oscillations
of waveguides to obtain estimates of the magnetic field strength. The
procedure requires information on the density of the structures. Often
it ignores the damping of the oscillations. We computed marginal
posteriors for parameters such as the waveguide density, the density
contrast, the transverse inhomogeneity length scale, and the magnetic
field strength under the assumption that the oscillations can be
modelled as standing magnetohydrodynamic (MHD) kink modes damped by
resonant absorption. Our results show that the magnetic field strength
can be properly inferred, even if the densities inside and outside the
structure are largely unknown. Incorporating observational estimates of
plasma density further constrains the obtained posteriors. The amount of
information that is included a priori for the density and the density
contrast influences their corresponding posteriors, but very little
the inferred magnetic field strength. The decision to include or leave
out the information on the damping and the damping timescales has a
minimal impact on the obtained magnetic field strength. In contrast
to the classic method, which provides numerical estimates with error
bars or possible ranges of variation for the magnetic field strength,
Bayesian methods offer the full distribution of plausibility over the
considered range of possible values. The methods applied to available
datasets of observed transverse loop oscillations can be extended to
prominence fine structures or chromospheric spicules, and implemented
to propagating waves in addition to standing oscillations.

---------------------------------------------------------
Title: SICON: Stokes Inversion based on COnvolutional Neural networks
Authors: Asensio Ramos, A.; Diaz Baso, C.
2019ascl.soft05024A Altcode:
SICON (Stokes Inversion based on COnvolutional Neural networks) provides
a three-dimensional cube of thermodynamical and magnetic properties
from the interpretation of two-dimensional maps of Stokes profiles by
use of a convolutional neural network. In addition to being much faster
than parallelized inversion codes, SICON, when trained on synthetic
Stokes profiles from two numerical simulations of different structures
of the solar atmosphere, also provided a three-dimensional view of the
physical properties of the region of interest in geometrical height,
and pressure and Wilson depression properties that are decontaminated
from the blurring effect of instrumental point spread functions.

---------------------------------------------------------
Title: Diagnostic potential of the Ca II 8542 Å line for solar
filaments
Authors: Díaz Baso, C. J.; Martínez González, M. J.; Asensio Ramos,
A.; de la Cruz Rodríguez, J.
2019A&A...623A.178D Altcode: 2019arXiv190206574D
 Aims: In this study we explore the diagnostic potential of
the chromospheric Ca II line at 8542 Å for studying the magnetic and
dynamic properties of solar filaments. We have acquired high spatial
resolution spectropolarimetric observations in the Ca II 8542 Å line
using the CRISP instrument at the Swedish 1 m Solar Telescope. 
Methods: We used the NICOLE inversion code to infer physical properties
from observations of a solar filament. We discuss the validity of
the results due to the assumption of hydrostatic equilibrium. We have
used observations from other telescopes such as CHROTEL and SDO, in
order to study large scale dynamics and the long term evolution of the
filament. Results: We show that the Ca II 8542 Å line encodes
information of the temperature, line-of-sight velocity and magnetic
field vector from the region where the filament is located. The current
noise levels only allow us to estimate an upper limit of 260 G for the
total magnetic field of the filament. Our study also reveals that if we
consider information from the aforementioned spectral line alone, the
geometric height, the temperature and the density could be degenerated
parameters outside the hydrostatic equilibrium approach.

---------------------------------------------------------
Title: Highlights on Spanish Astrophysics X
Authors: Montesinos, B.; Asensio Ramos, A.; Buitrago, F.; Schödel,
R.; Villaver, E.; Pérez-Hoyos, S.; Ordóñez-Etxeberria, I.
2019hsax.conf.....M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Real-time, multiframe, blind deconvolution of solar images
Authors: Asensio Ramos, A.; de la Cruz Rodríguez, J.; Pastor Yabar, A.
2018A&A...620A..73A Altcode: 2018arXiv180607150A
The quality of images of the Sun obtained from the ground are
severely limited by the perturbing effect of the Earth's turbulent
atmosphere. The post-facto correction of the images to compensate
for the presence of the atmosphere require the combination of
high-order adaptive optics techniques, fast measurements to freeze
the turbulent atmosphere, and very time-consuming blind deconvolution
algorithms. Under mild seeing conditions, blind deconvolution algorithms
can produce images of astonishing quality. They can be very competitive
with those obtained from space, with the huge advantage of the
flexibility of the instrumentation thanks to the direct access to the
telescope. In this contribution we make use of deep learning techniques
to significantly accelerate the blind deconvolution process and produce
corrected images at a peak rate of ∼100 images per second. We present
two different architectures that produce excellent image corrections
with noise suppression while maintaining the photometric properties of
the images. As a consequence, polarimetric signals can be obtained with
standard polarimetric modulation without any significant artifact. With
the expected improvements in computer hardware and algorithms, we
anticipate that on-site real-time correction of solar images will be
possible in the near future.

---------------------------------------------------------
Title: CLASP Constraints on the Magnetization and Geometrical
Complexity of the Chromosphere-Corona Transition Region
Authors: Trujillo Bueno, J.; Štěpán, J.; Belluzzi, L.; Asensio
Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Ishikawa,
R.; Kano, R.; Winebarger, A.; Auchère, F.; Narukage, N.; Kobayashi,
K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara,
H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.;
Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M.
2018ApJ...866L..15T Altcode: 2018arXiv180908865T
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a
suborbital rocket experiment that on 2015 September 3 measured
the linear polarization produced by scattering processes in the
hydrogen Lyα line of the solar disk radiation. The line-center
photons of this spectral line radiation mostly stem from the
chromosphere-corona transition region (TR). These unprecedented
spectropolarimetric observations revealed an interesting surprise,
namely that there is practically no center-to-limb variation (CLV) in
the Q/I line-center signals. Using an analytical model, we first show
that the geometric complexity of the corrugated surface that delineates
the TR has a crucial impact on the CLV of the Q/I and U/I line-center
signals. Second, we introduce a statistical description of the solar
atmosphere based on a 3D model derived from a state-of-the-art radiation
magnetohydrodynamic simulation. Each realization of the statistical
ensemble is a 3D model characterized by a given degree of magnetization
and corrugation of the TR, and for each such realization we solve the
full 3D radiative transfer problem taking into account the impact
of the CLASP instrument degradation on the calculated polarization
signals. Finally, we apply the statistical inference method presented
in a previous paper to show that the TR of the 3D model that produces
the best agreement with the CLASP observations has a relatively weak
magnetic field and a relatively high degree of corrugation. We emphasize
that a suitable way to validate or refute numerical models of the upper
solar chromosphere is by confronting calculations and observations
of the scattering polarization in ultraviolet lines sensitive to the
Hanle effect.

---------------------------------------------------------
Title: A Statistical Inference Method for Interpreting the CLASP
Observations
Authors: Štěpán, J.; Trujillo Bueno, J.; Belluzzi, L.; Asensio
Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Kano, R.;
Winebarger, A.; Auchère, F.; Ishikawa, R.; Narukage, N.; Kobayashi,
K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara,
H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.;
Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M.
2018ApJ...865...48S Altcode: 2018arXiv180802725S
On 2015 September 3, the Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP) successfully measured the linear polarization produced by
scattering processes in the hydrogen Lyα line of the solar disk
radiation, revealing conspicuous spatial variations in the Q/I and U/I
signals. Via the Hanle effect, the line-center Q/I and U/I amplitudes
encode information on the magnetic field of the chromosphere-corona
transition region, but they are also sensitive to the three-dimensional
structure of this corrugated interface region. With the help of a simple
line-formation model, here we propose a statistical inference method
for interpreting the Lyα line-center polarization observed by CLASP.

---------------------------------------------------------
Title: MOLPOP-CEP: an exact, fast code for multi-level systems
Authors: Asensio Ramos, Andrés; Elitzur, Moshe
2018A&A...616A.131A Altcode: 2018arXiv180602611A
We present MOLPOP-CEP, a universal line transfer code that allows the
exact calculation of multi-level line emission from a slab with variable
physical conditions for any arbitrary atom or molecule for which atomic
data exist. The code includes error control to achieve any desired
level of accuracy, providing full confidence in its results. Publicly
available, MOLPOP-CEP employs our recently developed coupled escape
probability (CEP) technique, whose performance exceeds other exact
methods by orders of magnitude. The program also offers the option of
an approximate solution with different variants of the familiar escape
probability method. As an illustration of the MOLPOP-CEP capabilities we
present an exact calculation of the Spectral Line Energy Distribution
(SLED) of the CO molecule and compare it with escape probability
results. We find that the popular large-velocity gradient (LVG)
approximation is unreliable at large CO column densities. Providing
a solution of the multi-level line transfer problem at any prescribed
level of accuracy, MOLPOP-CEP is removing any doubts about the validity
of its final results.

---------------------------------------------------------
Title: Current State of UV Spectro-Polarimetry and its Future
Direction
Authors: Ishikawa, Ryohko; Sakao, Taro; Katsukawa, Yukio; Hara,
Hirohisa; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Kubo, Masahito;
Auchere, Frederic; De Pontieu, Bart; Winebarger, Amy; Kobayashi,
. Ken; Kano, Ryouhei; Narukage, Noriyuki; Trujillo Bueno, Javier;
Song, Dong-uk; Manso Sainz, Rafael; Asensio Ramos, Andres; Leenaarts,
Jorritt; Carlsson, Mats; Bando, Takamasa; Ishikawa, Shin-nosuke;
Tsuneta, Saku; Belluzzi, Luca; Suematsu, Yoshinori; Giono, Gabriel;
Yoshida, Masaki; Goto, Motoshi; Del Pino Aleman, Tanausu; Stepan,
Jiri; Okamoto, Joten; Tsuzuki, Toshihiro; Uraguchi, Fumihiro; Champey,
Patrick; Alsina Ballester, Ernest; Casini, Roberto; McKenzie, David;
Rachmeler, Laurel; Bethge, Christian
2018cosp...42E1564I Altcode:
To obtain quantitative information on the magnetic field in low beta
regions (i.e., upper chromosphere and above) has been increasingly
important to understand the energetic phenomena of the outer
solar atmosphere such as flare, coronal heating, and the solar wind
acceleration. In the UV range, there are abundant spectral lines that
originate in the upper chromosphere and transition region. However,
the Zeeman effect in these spectral lines does not give rise to easily
measurable polarization signals because of the weak magnetic field
strength and the larger Doppler broadening compared with the Zeeman
effect. Instead, the Hanle effect in UV lines is expected to be a
suitable diagnostic tool of the magnetic field in the upper atmospheric
layers. To investigate the validity of UV spectro-polarimetry and
the Hanle effect, the Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP), which is a NASA sounding- rocket experiment, was launched at
White Sands in US on September 3, 2015. During its 5 minutes ballistic
flight, it successfully performed spectro-polarimetric observations
of the hydrogen Lyman-alpha line (121.57 nm) with an unprecedentedly
high polarization sensitivity of 0.1% in this wavelength range. CLASP
observed the linear polarization produced by scattering process in VUV
lines for the first time and detected the polarization signals which
indicate the operation of the Hanle effect. Following the success
of CLASP, we are confident that UV spectro-polarimetry is the way
to proceed, and we are planning the second flight of CLASP (CLASP2:
Chromospheric LAyer SpectroPolarimeter 2). For this second flight we
will carry out spectro-polarimetry in the Mg II h and k lines around
280 nm, with minimum modifications of the CLASP1 instrument. The linear
polarization in the Mg II k line is induced by scattering processes and
the Hanle effect, being sensitive to magnetic field strengths of 5 to 50
G. In addition, the circular polarizations in the Mg II h and k lines
induced by the Zeeman effect can be measurable in at least plage and
active regions. The combination of the Hanle and Zeeman effects could
help us to more reliably infer the magnetic fields of the upper solar
chromosphere. CLASP2 was selected for flight and is being developed for
launch in the spring of 2019.Based on these sounding rocket experiments
(CLASP1 and 2), we aim at establishing the strategy and refining the
instrument concept for future space missions to explore the enigmatic
atmospheric layers via UV spectro-polarimetry.

---------------------------------------------------------
Title: The real time MCAO solar prototype for the EST
Authors: Montoya, Luzma M.; Velasco, Sergio; Sánchez Capuchino, Jorge;
Collados Vera, Manuel; Rodríguez Ramos, Luis Fernando; De Cos Juez,
Francisco J.; Asensio Ramos, Andrés.
2018SPIE10703E..48M Altcode:
The European Solar Telescope (EST) will be equipped with a MCAO
system to provide an excellent correction within one arcminute field
of view (FOV). A prototype of this system will be built with the same
requirements except for the frame rate. This prototype will allow to
test and verify new concepts for Solar MCAO, as, e.g., the integration
of neuronal networks in the reconstruction process. This prototype will
work as follows: a high-resolution image of the sun will be created and
perturbed by a turbulence simulator with different phase screens placed
at different heights. MCAO correction will be performed by one pupil DM
and four altitude DMs. Two wide field wavefront sensors will be used
to perform the tomography. The calibration and control strategies are
still to be defined in the lab for the future implementation on the
EST MCAO system. A scientific camera will evaluate the performance on
a 60" field. The prototype is currently under construction and it is
expected to be finished by 2019.

---------------------------------------------------------
Title: Enhancing SDO/HMI images using deep learning
Authors: Díaz Baso, C. J.; Asensio Ramos, A.
2018A&A...614A...5D Altcode: 2018A&A...614A...5B; 2017arXiv170602933D
Context. The Helioseismic and Magnetic Imager (HMI) provides continuum
images and magnetograms with a cadence better than one per minute. It
has been continuously observing the Sun 24 h a day for the past 7
yr. The trade-off between full disk observations and spatial resolution
means that HMI is not adequate for analyzing the smallest-scale
events in the solar atmosphere. Aims: Our aim is to develop
a new method to enhance HMI data, simultaneously deconvolving and
super-resolving images and magnetograms. The resulting images will
mimic observations with a diffraction-limited telescope twice the
diameter of HMI. Methods: Our method, which we call Enhance,
is based on two deep, fully convolutional neural networks that input
patches of HMI observations and output deconvolved and super-resolved
data. The neural networks are trained on synthetic data obtained from
simulations of the emergence of solar active regions. Results:
We have obtained deconvolved and super-resolved HMI images. To solve
this ill-defined problem with infinite solutions we have used a neural
network approach to add prior information from the simulations. We test
Enhance against Hinode data that has been degraded to a 28 cm diameter
telescope showing very good consistency. The code is open source.

---------------------------------------------------------
Title: The Magnetic Response of the Solar Atmosphere to Umbral Flashes
Authors: Houston, S. J.; Jess, D. B.; Asensio Ramos, A.; Grant,
S. D. T.; Beck, C.; Norton, A. A.; Krishna Prasad, S.
2018ApJ...860...28H Altcode: 2018arXiv180300018H
Chromospheric observations of sunspot umbrae offer an exceptional
view of magnetoacoustic shock phenomena and the impact they have on
the surrounding magnetically dominated plasma. We employ simultaneous
slit-based spectro-polarimetry and spectral imaging observations of
the chromospheric He I 10830 Å and Ca II 8542 Å lines to examine
fluctuations in the umbral magnetic field caused by the steepening of
magnetoacoustic waves into umbral flashes. Following the application
of modern inversion routines, we find evidence to support the scenario
that umbral shock events cause expansion of the embedded magnetic
field lines due to the increased adiabatic pressure. The large number
statistics employed allow us to calculate the adiabatic index, γ =
1.12 ± 0.01, for chromospheric umbral locations. Examination of
the vector magnetic field fluctuations perpendicular to the solar
normal revealed changes up to ∼200 G at the locations of umbral
flashes. Such transversal magnetic field fluctuations have not been
described before. Through comparisons with nonlinear force-free field
extrapolations, we find that the perturbations of the transverse field
components are oriented in the same direction as the quiescent field
geometries. This implies that magnetic field enhancements produced by
umbral flashes are directed along the motion path of the developing
shock, hence producing relatively small changes, up to a maximum
of ∼8°, in the inclination and/or azimuthal directions of the
magnetic field. Importantly, this work highlights that umbral flashes
are able to modify the full vector magnetic field, with the detection
of the weaker transverse magnetic field components made possible by
high-resolution data combined with modern inversion routines.

---------------------------------------------------------
Title: The First Post-Kepler Brightness Dips of KIC 8462852
Authors: Boyajian, Tabetha. S.; Alonso, Roi; Ammerman, Alex; Armstrong,
David; Asensio Ramos, A.; Barkaoui, K.; Beatty, Thomas G.; Benkhaldoun,
Z.; Benni, Paul; Bentley, Rory O.; Berdyugin, Andrei; Berdyugina,
Svetlana; Bergeron, Serge; Bieryla, Allyson; Blain, Michaela G.;
Capetillo Blanco, Alicia; Bodman, Eva H. L.; Boucher, Anne; Bradley,
Mark; Brincat, Stephen M.; Brink, Thomas G.; Briol, John; Brown,
David J. A.; Budaj, J.; Burdanov, A.; Cale, B.; Aznar Carbo, Miguel;
Castillo García, R.; Clark, Wendy J.; Clayton, Geoffrey C.; Clem,
James L.; Coker, Phillip H.; Cook, Evan M.; Copperwheat, Chris M.;
Curtis, J. L.; Cutri, R. M.; Cseh, B.; Cynamon, C. H.; Daniels, Alex
J.; Davenport, James R. A.; Deeg, Hans J.; De Lorenzo, Roberto; de
Jaeger, Thomas; Desrosiers, Jean-Bruno; Dolan, John; Dowhos, D. J.;
Dubois, Franky; Durkee, R.; Dvorak, Shawn; Easley, Lynn; Edwards, N.;
Ellis, Tyler G.; Erdelyi, Emery; Ertel, Steve; Farfán, Rafael. G.;
Farihi, J.; Filippenko, Alexei V.; Foxell, Emma; Gandolfi, Davide;
Garcia, Faustino; Giddens, F.; Gillon, M.; González-Carballo,
Juan-Luis; González-Fernández, C.; González Hernández, J. I.;
Graham, Keith A.; Greene, Kenton A.; Gregorio, J.; Hallakoun, Na'ama;
Hanyecz, Ottó; Harp, G. R.; Henry, Gregory W.; Herrero, E.; Hildbold,
Caleb F.; Hinzel, D.; Holgado, G.; Ignácz, Bernadett; Ilyin, Ilya;
Ivanov, Valentin D.; Jehin, E.; Jermak, Helen E.; Johnston, Steve;
Kafka, S.; Kalup, Csilla; Kardasis, Emmanuel; Kaspi, Shai; Kennedy,
Grant M.; Kiefer, F.; Kielty, C. L.; Kessler, Dennis; Kiiskinen,
H.; Killestein, T. L.; King, Ronald A.; Kollar, V.; Korhonen, H.;
Kotnik, C.; Könyves-Tóth, Réka; Kriskovics, Levente; Krumm, Nathan;
Krushinsky, Vadim; Kundra, E.; Lachapelle, Francois-Rene; LaCourse,
D.; Lake, P.; Lam, Kristine; Lamb, Gavin P.; Lane, Dave; Lau, Marie
Wingyee; Lewin, Pablo; Lintott, Chris; Lisse, Carey; Logie, Ludwig;
Longeard, Nicolas; Lopez Villanueva, M.; Whit Ludington, E.; Mainzer,
A.; Malo, Lison; Maloney, Chris; Mann, A.; Mantero, A.; Marengo,
Massimo; Marchant, Jon; Martínez González, M. J.; Masiero, Joseph R.;
Mauerhan, Jon C.; McCormac, James; McNeely, Aaron; Meng, Huan Y. A.;
Miller, Mike; Molnar, Lawrence A.; Morales, J. C.; Morris, Brett M.;
Muterspaugh, Matthew W.; Nespral, David; Nugent, C. R.; Nugent,
Katherine M.; Odasso, A.; O'Keeffe, Derek; Oksanen, A.; O'Meara,
John M.; Ordasi, András; Osborn, Hugh; Ott, John J.; Parks, J. R.;
Rodriguez Perez, Diego; Petriew, Vance; Pickard, R.; Pál, András;
Plavchan, P.; Pollacco, Don; Pozo Nuñez, F.; Pozuelos, F. J.; Rau,
Steve; Redfield, Seth; Relles, Howard; Ribas, Ignasi; Richards, Jon;
Saario, Joonas L. O.; Safron, Emily J.; Sallai, J. Martin; Sárneczky,
Krisztián; Schaefer, Bradley E.; Schumer, Clea F.; Schwartzendruber,
Madison; Siegel, Michael H.; Siemion, Andrew P. V.; Simmons, Brooke D.;
Simon, Joshua D.; Simón-Díaz, S.; Sitko, Michael L.; Socas-Navarro,
Hector; Sódor, Á.; Starkey, Donn; Steele, Iain A.; Stone, Geoff;
Strassmeier, Klaus G.; Street, R. A.; Sullivan, Tricia; Suomela, J.;
Swift, J. J.; Szabó, Gyula M.; Szabó, Róbert; Szakáts, Róbert;
Szalai, Tamás; Tanner, Angelle M.; Toledo-Padrón, B.; Tordai, Tamás;
Triaud, Amaury H. M. J.; Turner, Jake D.; Ulowetz, Joseph H.; Urbanik,
Marian; Vanaverbeke, Siegfried; Vanderburg, Andrew; Vida, Krisztián;
Vietje, Brad P.; Vinkó, József; von Braun, K.; Waagen, Elizabeth
O.; Walsh, Dan; Watson, Christopher A.; Weir, R. C.; Wenzel, Klaus;
Westendorp Plaza, C.; Williamson, Michael W.; Wright, Jason T.; Wyatt,
M. C.; Zheng, WeiKang; Zsidi, Gabriella
2018ApJ...853L...8B Altcode: 2018arXiv180100732B
We present a photometric detection of the first brightness dips of
the unique variable star KIC 8462852 since the end of the Kepler space
mission in 2013 May. Our regular photometric surveillance started in
2015 October, and a sequence of dipping began in 2017 May continuing
on through the end of 2017, when the star was no longer visible from
Earth. We distinguish four main 1%-2.5% dips, named “Elsie,”
“Celeste,” “Skara Brae,” and “Angkor,” which persist
on timescales from several days to weeks. Our main results so far
are as follows: (i) there are no apparent changes of the stellar
spectrum or polarization during the dips and (ii) the multiband
photometry of the dips shows differential reddening favoring non-gray
extinction. Therefore, our data are inconsistent with dip models that
invoke optically thick material, but rather they are in-line with
predictions for an occulter consisting primarily of ordinary dust,
where much of the material must be optically thin with a size scale
≪1 μm, and may also be consistent with models invoking variations
intrinsic to the stellar photosphere. Notably, our data do not place
constraints on the color of the longer-term “secular” dimming,
which may be caused by independent processes, or probe different
regimes of a single process.

---------------------------------------------------------
Title: Signatures of the impact of flare-ejected plasma on the
photosphere of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Rajaguru, S. P.;
Franz, M.; Kuckein, C.; Asensio Ramos, A.
2017A&A...608A..97F Altcode: 2017arXiv170806133F
 Aims: We investigate the properties of a sunspot light bridge,
focusing on the changes produced by the impact of a plasma blob ejected
from a C-class flare. Methods: We observed a sunspot in active
region NOAA 12544 using spectropolarimetric raster maps of the four
Fe I lines around 15 655 Å with the GREGOR Infrared Spectrograph,
narrow-band intensity images sampling the Fe I 6173 Å line with
the GREGOR Fabry-Pérot Interferometer, and intensity broad-band
images in G-band and Ca II H-band with the High-resolution Fast
Imager. All these instruments are located at the GREGOR telescope at
the Observatorio del Teide, Tenerife, Spain. The data cover the time
before, during, and after the flare event. The analysis is complemented
with Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager
data from the Solar Dynamics Observatory. The physical parameters of
the atmosphere at differents heights were inferred using spectral-line
inversion techniques. Results: We identify photospheric and
chromospheric brightenings, heating events, and changes in the Stokes
profiles associated with the flare eruption and the subsequent arrival
of the plasma blob to the light bridge, after traveling along an
active region loop. Conclusions: The measurements suggest that
these phenomena are the result of reconnection events driven by the
interaction of the plasma blob with the magnetic field topology of the
light bridge. Movies attached to Figs. 1 and 3 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201731374/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: Rachmeler, Laurel; E McKenzie, David; Ishikawa, Ryohko;
Trujillo Bueno, Javier; Auchère, Frédéric; Kobayashi, Ken;
Winebarger, Amy; Bethge, Christian; Kano, Ryouhei; Kubo, Masahito;
Song, Donguk; Narukage, Noriyuki; Ishikawa, Shin-nosuke; De Pontieu,
Bart; Carlsson, Mats; Yoshida, Masaki; Belluzzi, Luca; Stepan, Jiri;
del Pino Alemná, Tanausú; Ballester, Ernest Alsina; Asensio Ramos,
Andres
2017SPD....4811010R Altcode:
We present the instrument, science case, and timeline of the CLASP2
sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha
Spectro-Polarimeter) sounding rocket flight in 2015 resulted in
the first-ever linear polarization measurements of solar hydrogen
Lyman-alpha line, which is sensitive to the Hanle effect and can be used
to constrain the magnetic field and geometric complexity of the upper
chromosphere. Ly-alpha is one of several upper chromospheric lines that
contain magnetic information. In the spring of 2019, we will re-fly
the modified CLASP telescope to measure the full Stokes profile of Mg
II h &amp; k near 280 nm. This set of lines is sensitive to the upper
chromospheric magnetic field via both the Hanle and the Zeeman effects.

---------------------------------------------------------
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: Rachmeler, Laurel A.; McKenzie, D. E.; Ishikawa, R.;
Trujillo-Bueno, J.; Auchere, F.; Kobayashi, K.; Winebarger, A.;
Bethge, C.; Kano, R.; Kubo, M.; Song, D.; Narukage, N.; Ishikawa, S.;
De Pontieu, B.; Carlsson, M.; Yoshida, M.; Belluzzi, L.; Stepan, J.;
del Pino Alemán, T.; Alsina Ballester, E.; Asensio Ramos, A.
2017shin.confE..79R Altcode:
We present the instrument, science case, and timeline of the CLASP2
sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha
Spectro-Polarimeter) sounding rocket flight in 2015 resulted in
the first-ever linear polarization measurements of solar hydrogen
Lyman-alpha line, which is sensitive to the Hanle effect and can be used
to constrain the magnetic field and geometric complexity of the upper
chromosphere. Ly-alpha is one of several upper chromospheric lines that
contain magnetic information. In the spring of 2019, we will re-fly
the modified CLASP telescope to measure the full Stokes profile of Mg
II h &amp; k near 280 nm. This set of lines is sensitive to the upper
chromospheric magnetic field via both the Hanle and the Zeeman effects.

---------------------------------------------------------
Title: DeepVel: Deep learning for the estimation of horizontal
velocities at the solar surface
Authors: Asensio Ramos, A.; Requerey, I. S.; Vitas, N.
2017A&A...604A..11A Altcode: 2017arXiv170305128A
Many phenomena taking place in the solar photosphere are controlled
by plasma motions. Although the line-of-sight component of the
velocity can be estimated using the Doppler effect, we do not have
direct spectroscopic access to the components that are perpendicular
to the line of sight. These components are typically estimated using
methods based on local correlation tracking. We have designed DeepVel,
an end-to-end deep neural network that produces an estimation of the
velocity at every single pixel, every time step, and at three different
heights in the atmosphere from just two consecutive continuum images. We
confront DeepVel with local correlation tracking, pointing out that they
give very similar results in the time and spatially averaged cases. We
use the network to study the evolution in height of the horizontal
velocity field in fragmenting granules, supporting the buoyancy-braking
mechanism for the formation of integranular lanes in these granules. We
also show that DeepVel can capture very small vortices, so that we can
potentially expand the scaling cascade of vortices to very small sizes
and durations. The movie attached to Fig. 3 is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201730783/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: The dusty tori of nearby QSOs as constrained by high-resolution
mid-IR observations
Authors: Martínez-Paredes, M.; Aretxaga, I.; Alonso-Herrero,
A.; González-Martín, O.; Lopéz-Rodríguez, E.; Ramos Almeida,
C.; Asensio Ramos, A.; Diaz Santos, T.; Elitzur, M.; Esquej, P.;
Hernán-Caballero, A.; Ichikawa, K.; Nikutta, R.; Packham, C.;
Pereira-Santaella, M.; Telesco, C.
2017MNRAS.468....2M Altcode: 2017arXiv170202960M
We present mid-infrared (MIR; 7.5-13.5 μm) imaging and spectroscopy
observations obtained with the CanariCam (CC) instrument on the 10.4-m
Gran Telescopio CANARIAS for a sample of 20 nearby, MIR bright and
X-ray luminous quasi-stellar objects (QSOs). We find that for the
majority of QSOs the MIR emission is unresolved at angular scales
∼0.3 arcsec, corresponding to physical scales ≲600 pc. We find
that the higher-spatial resolution CC spectra have similar shapes
to those obtained with Spitzer/IRS, and hence we can assume that the
spectra are not heavily contaminated by extended emission in the host
galaxy. We thus take advantage of the higher signal-to-noise ratio
Spitzer/IRS spectra, as a fair representation of the nuclear emission,
to decompose it into a combination of active galactic nuclei (AGN),
polycyclic aromatic hydrocarbon (PAH) and stellar components. In most
cases, the AGN is the dominant component, with a median contribution
of 85 per cent of the continuum light at MIR (5-15 μm) within the
IRS slit. This IR AGN emission is well reproduced by clumpy torus
models. We find evidence for significant differences in the parameters
that describe the dusty tori of QSOs when compared with the same
parameters of Seyfert 1 and 2 nuclei. In particular, we find a lower
number of clouds (N0 ≲ 12), steeper radial distribution
of clouds (q ∼ 1.5-3.0) and clouds that are less optically thick
(τV ≲ 100) than in Seyfert 1, which could be attributed
to dusty structures that have been partially evaporated and piled up
by the higher radiation field in QSOs. We find that the combination of
the angular width σtorus, viewing angle I, and number of
clouds along the equatorial line, N0, produces large escape
probabilities (Pesc &gt; 2 per cent) and low geometrical
covering factors (f2 ≲ 0.6), as expected for AGN with
broad lines in their optical spectra.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Zeeman effect in sulfur monoxide
(SO) (Cazzoli+, 2017)
Authors: Cazzoli, G.; Lattanzi, V.; Coriani, S.; Gauss, J.; Codella,
C.; Asensio Ramos, A.; Cernicharo, J.; Puzzarini, C.
2017yCat..36050020C Altcode:
The complete list of measured Zeeman components of sulfur monoxide
(SO). (1 data file).

---------------------------------------------------------
Title: Penumbral thermal structure below the visible surface
Authors: Borrero, J. M.; Franz, M.; Schlichenmaier, R.; Collados,
M.; Asensio Ramos, A.
2017A&A...601L...8B Altcode: 2017arXiv170502832B
Context. The thermal structure of the penumbra below its visible
surface (I.e., τ5 ≥ 1) has important implications for
our present understanding of sunspots and their penumbrae: their
brightness and energy transport, mode conversion of magneto-acoustic
waves, sunspot seismology, and so forth. Aims: We aim at
determining the thermal stratification in the layers immediately
beneath the visible surface of the penumbra: τ5 ∈ [1,3]
(≈70-80 km below the visible continuum-forming layer) Methods:
We analyzed spectropolarimetric data (I.e., Stokes profiles) in three Fe
I lines located at 1565 nm observed with the GRIS instrument attached
to the 1.5-m solar telescope GREGOR. The data are corrected for the
smearing effects of wide-angle scattered light and then subjected
to an inversion code for the radiative transfer equation in order
to retrieve, among others, the temperature as a function of optical
depth T(τ5). Results: We find that the temperature
gradient below the visible surface of the penumbra is smaller than
in the quiet Sun. This implies that in the region τ5 ≥
1 the penumbral temperature diverges from that of the quiet Sun. The
same result is obtained when focusing only on the thermal structure
below the surface of bright penumbral filaments. Conclusions:
We interpret these results as evidence of a thick penumbra, whereby
the magnetopause is not located near its visible surface. In addition,
we find that the temperature gradient in bright penumbral filaments is
lower than in granules. This can be explained in terms of the limited
expansion of a hot upflow inside a penumbral filament relative to
a granular upflow, as magnetic pressure and tension forces from the
surrounding penumbral magnetic field hinder an expansion like this.

---------------------------------------------------------
Title: Indication of the Hanle Effect by Comparing the Scattering
Polarization Observed by CLASP in the Lyα and Si III 120.65 nm Lines
Authors: Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.;
Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa,
Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Shimizu, T.;
Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.;
Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso
Sainz, R.; De Pontieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.
2017ApJ...841...31I Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding
rocket experiment that has provided the first successful measurement
of the linear polarization produced by scattering processes in
the hydrogen Lyα line (121.57 nm) radiation of the solar disk. In
this paper, we report that the Si III line at 120.65 nm also shows
scattering polarization and we compare the scattering polarization
signals observed in the Lyα and Si III lines in order to search for
observational signatures of the Hanle effect. We focus on four selected
bright structures and investigate how the U/I spatial variations vary
between the Lyα wing, the Lyα core, and the Si III line as a function
of the total unsigned photospheric magnetic flux estimated from Solar
Dynamics Observatory/Helioseismic and Magnetic Imager observations. In
an internetwork region, the Lyα core shows an antisymmetric spatial
variation across the selected bright structure, but it does not show
it in other more magnetized regions. In the Si III line, the spatial
variation of U/I deviates from the above-mentioned antisymmetric
shape as the total unsigned photospheric magnetic flux increases. A
plausible explanation of this difference is the operation of the Hanle
effect. We argue that diagnostic techniques based on the scattering
polarization observed simultaneously in two spectral lines with very
different sensitivities to the Hanle effect, like Lyα and Si III,
are of great potential interest for exploring the magnetism of the
upper solar chromosphere and transition region.

---------------------------------------------------------
Title: Polarization Calibration of the Chromospheric Lyman-Alpha
SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV
Range. Part II: In-Flight Calibration
Authors: Giono, G.; Ishikawa, R.; Narukage, N.; Kano, R.; Katsukawa,
Y.; Kubo, M.; Ishikawa, S.; Bando, T.; Hara, H.; Suematsu, Y.;
Winebarger, A.; Kobayashi, K.; Auchère, F.; Trujillo Bueno, J.;
Tsuneta, S.; Shimizu, T.; Sakao, T.; Cirtain, J.; Champey, P.; Asensio
Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu,
B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M.
2017SoPh..292...57G Altcode:
The Chromospheric Lyman-Alpha SpectroPolarimeter is a sounding
rocket instrument designed to measure for the first time the linear
polarization of the hydrogen Lyman-α line (121.6 nm). The instrument
was successfully launched on 3 September 2015 and observations were
conducted at the solar disc center and close to the limb during the
five-minutes flight. In this article, the disc center observations are
used to provide an in-flight calibration of the instrument spurious
polarization. The derived in-flight spurious polarization is consistent
with the spurious polarization levels determined during the pre-flight
calibration and a statistical analysis of the polarization fluctuations
from solar origin is conducted to ensure a 0.014% precision on the
spurious polarization. The combination of the pre-flight and the
in-flight polarization calibrations provides a complete picture of
the instrument response matrix, and a proper error transfer method
is used to confirm the achieved polarization accuracy. As a result,
the unprecedented 0.1% polarization accuracy of the instrument in the
vacuum ultraviolet is ensured by the polarization calibration.

---------------------------------------------------------
Title: Uncertainties in the solar photospheric oxygen abundance
Authors: Cubas Armas, M.; Asensio Ramos, A.; Socas-Navarro, H.
2017A&A...600A..45C Altcode: 2017arXiv170106809C
 Aims: The purpose of this work is to better understand the
confidence limits of the photospheric solar oxygen abundance derived
from three-dimensional models using the forbidden [OI] line at 6300
Å, including correlations with other parameters involved. 
Methods: We worked with a three-dimensional empirical model and two
solar intensity atlases. Bayesian inference was employed as a tool
to determine the most probable value for the solar oxygen abundance
given the model chosen. We considered a number of error sources,
such as uncertainties in the continuum derivation, in the wavelength
calibration and in the abundance/strength of Ni. Results: Our
results show correlations between the effects of several parameters
employed in the derivation. The Bayesian analysis provides robust
confidence limits taking into account all of these factors in a rigorous
manner. We obtain that, given the empirical three-dimensional model and
the atlas observations employed here, the most probable value for the
solar oxygen abundance is log (ɛO) = 8.86 ± 0.04. However,
we note that this uncertainty does not consider possible sources of
systematic errors due to the model choice.

---------------------------------------------------------
Title: Discovery of Scattering Polarization in the Hydrogen Lyα
Line of the Solar Disk Radiation
Authors: Kano, R.; Trujillo Bueno, J.; Winebarger, A.; Auchère, F.;
Narukage, N.; Ishikawa, R.; Kobayashi, K.; Bando, T.; Katsukawa, Y.;
Kubo, M.; Ishikawa, S.; Giono, G.; Hara, H.; Suematsu, Y.; Shimizu,
T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.; Goto, M.; Belluzzi, L.;
Štěpán, J.; Asensio Ramos, A.; Manso Sainz, R.; Champey, P.;
Cirtain, J.; De Pontieu, B.; Casini, R.; Carlsson, M.
2017ApJ...839L..10K Altcode: 2017arXiv170403228K
There is a thin transition region (TR) in the solar atmosphere where
the temperature rises from 10,000 K in the chromosphere to millions
of degrees in the corona. Little is known about the mechanisms that
dominate this enigmatic region other than the magnetic field plays a
key role. The magnetism of the TR can only be detected by polarimetric
measurements of a few ultraviolet (UV) spectral lines, the Lyα line
of neutral hydrogen at 121.6 nm (the strongest line of the solar UV
spectrum) being of particular interest given its sensitivity to the
Hanle effect (the magnetic-field-induced modification of the scattering
line polarization). We report the discovery of linear polarization
produced by scattering processes in the Lyα line, obtained with
the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) rocket
experiment. The Stokes profiles observed by CLASP in quiet regions of
the solar disk show that the Q/I and U/I linear polarization signals are
of the order of 0.1% in the line core and up to a few percent in the
nearby wings, and that both have conspicuous spatial variations with
scales of ∼10 arcsec. These observations help constrain theoretical
models of the chromosphere-corona TR and extrapolations of the
magnetic field from photospheric magnetograms. In fact, the observed
spatial variation from disk to limb of polarization at the line core
and wings already challenge the predictions from three-dimensional
magnetohydrodynamical models of the upper solar chromosphere.

---------------------------------------------------------
Title: Magnetic field strength in solar coronal waveguides
Authors: Arregui, I.; Asensio Ramos, A.
2017hsa9.conf..587A Altcode:
We applied Bayesian techniques to the problem of inferring the magnetic
field strength in transversely oscillating solar coronal loops from
observed periods and damping times. This was done by computing the
marginal posterior probability density for parameters such as the
waveguide density, the density contrast, the transverse inhomogeneity
length scale, and the magnetic field strength under the assumption
that the observed waves can be modelled as standing or propagating
magnetohydrodynamic (MHD) kink modes of magnetic flux tubes. Our
results indicate that the magnetic field strength can be inferred,
even if the densities inside and outside the structure are largely
unknown. When information on plasma density is available, the method
enables to self-consistently include this knowledge to further constrain
the inferred magnetic field strength. The inclusion of the observed
oscillation damping enables to obtain information on the transverse
density structuring and considerably alters the obtained posterior
for the magnetic field strength.

---------------------------------------------------------
Title: Inference of the chromospheric magnetic field orientation in
the Ca II 8542 Å line fibrils
Authors: Asensio Ramos, A.; de la Cruz Rodríguez, J.; Martínez
González, M. J.; Socas-Navarro, H.
2017A&A...599A.133A Altcode: 2016arXiv161206088A
Context. Solar chromospheric fibrils, as observed in the core of
strong chromospheric spectral lines, extend from photospheric field
concentrations suggesting that they trace magnetic field lines. These
images have been historically used as proxies of magnetic fields
for many purposes. Aims: Use statistical analysis to test
whether the association between fibrils and magnetic field lines is
justified. Methods: We use a Bayesian hierarchical model to
analyze several tens of thousands of pixels in spectro-polarimetric
chromospheric images of penumbrae and chromospheric fibrils. We
compare the alignment between the field azimuth inferred from the
linear polarization signals through the transverse Zeeman effect and
the direction of the fibrils in the image. Results: We conclude
that, in the analyzed fields of view, fibrils are often well aligned
with the magnetic field azimuth. Despite this alignment, the analysis
also shows that there is a non-negligible dispersion. In penumbral
filaments, we find a dispersion with a standard deviation of 16°,
while this dispersion goes up to 34° in less magnetized regions.

---------------------------------------------------------
Title: How to infer the Sun's global magnetic field using the
Hanle effect
Authors: Vieu, T.; Martínez González, M. J.; Pastor Yabar, A.;
Asensio Ramos, A.
2017MNRAS.465.4414V Altcode:
We present a different approach to determine the characteristics
of the global magnetic field of the Sun based on the study of the
Hanle signals. The Hanle effect of a stellar dipole produces a surface
asymmetric pattern of linear polarization that depends on the strength
and geometry of this global field. Moreover, if the dipole is misaligned
with respect to the rotation, the Hanle signals are modulated following
the rotational period. We explore the possibility to retrieve those
characteristics by comparing the computed theoretical signatures with
actual observations. We show that this is possible, in the case of the
Sr I line of the Sun, provided that the polarimetric sensitivity is of
the order or below 10-5-10-6. The inference can
be done either using the maps of resolved signals, in particular the
spread of values obtained along different directions on the stellar
disc, or using the disc-integrated signals.

---------------------------------------------------------
Title: Synthetic polarimetric spectra from stellar prominences
Authors: Felipe, T.; Martínez González, M. J.; Asensio Ramos, A.
2017MNRAS.465.1654F Altcode: 2016arXiv161009282F
Stellar prominences detected in rapidly rotating stars serve as probes
of the magnetism in the corona of cool stars. We have synthesized the
temporal evolution of the Stokes profiles generated in the He I 10
830 and 5876 Å triplets during the rotation of a prominence around
a star. The synthesis was performed with the HAZEL code using a cloud
model in which the prominence is characterized by a slab located at a
fixed latitude and height. It accounts for the scattering polarization
and Zeeman and Hanle effects. Several cases with different prominence
magnetic field strengths and orientations have been analysed. The
results show an emission feature that drifts across the profile while
the prominence is out of the stellar disc. When the prominence eclipses
the star, the intensity profile shows an absorption. The scattering
induced by the prominence generates linear polarization signals
in Stokes Q and U profiles, which are modified by the Hanle effect
when a magnetic field is present. Due to the Zeeman effect, Stokes V
profiles show a signal with very low amplitude when the magnetic field
along the line of sight is different from zero. The estimated linear
polarization signals could potentially be detected with the future
spectropolarimeter Mid-resolution InfRAreD Astronomical Spectrograph,
to be attached to Gran Telescopio Canarias telescope.

---------------------------------------------------------
Title: First tests on the Integral Field Unit for GRIS at GREGOR
Authors: Dominguez-Tagle, C.; Collados, M.; Lopez, R. L.; Vaz Cedillo,
J. J.; Esteves, M. A.; Paez, E.; Asensio Ramos, A.
2017sone.meetE..89D Altcode:
The observation of the highly dynamic events in the chromosphere with
current slit or filter spectropolarimeters is not adequate. With the
sake of incresing the time, spectral and spatial coherence of the
data, an integral field unit prototype has been developed for the
GRIS spectrograph on the GREGOR telescope. In this talk, we present
the first tests of the prototype.

---------------------------------------------------------
Title: Discovery of Ubiquitous Fast-Propagating Intensity Disturbances
by the Chromospheric Lyman Alpha Spectropolarimeter (CLASP)
Authors: Kubo, M.; Katsukawa, Y.; Suematsu, Y.; Kano, R.; Bando,
T.; Narukage, N.; Ishikawa, R.; Hara, H.; Giono, G.; Tsuneta, S.;
Ishikawa, S.; Shimizu, T.; Sakao, T.; Winebarger, A.; Kobayashi, K.;
Cirtain, J.; Champey, P.; Auchère, F.; Trujillo Bueno, J.; Asensio
Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu,
B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M.
2016ApJ...832..141K Altcode:
High-cadence observations by the slit-jaw (SJ) optics system of the
sounding rocket experiment known as the Chromospheric Lyman Alpha
Spectropolarimeter (CLASP) reveal ubiquitous intensity disturbances
that recurrently propagate in either the chromosphere or the transition
region or both at a speed much higher than the speed of sound. The
CLASP/SJ instrument provides a time series of two-dimensional images
taken with broadband filters centered on the Lyα line at a 0.6 s
cadence. The multiple fast-propagating intensity disturbances appear in
the quiet Sun and in an active region, and they are clearly detected in
at least 20 areas in a field of view of 527″ × 527″ during the 5
minute observing time. The apparent speeds of the intensity disturbances
range from 150 to 350 km s-1, and they are comparable
to the local Alfvén speed in the transition region. The intensity
disturbances tend to propagate along bright elongated structures away
from areas with strong photospheric magnetic fields. This suggests
that the observed fast-propagating intensity disturbances are related
to the magnetic canopy structures. The maximum distance traveled by
the intensity disturbances is about 10″, and the widths are a few
arcseconds, which are almost determined by a pixel size of 1.″03. The
timescale of each intensity pulse is shorter than 30 s. One possible
explanation for the fast-propagating intensity disturbances observed
by CLASP is magnetohydrodynamic fast-mode waves.

---------------------------------------------------------
Title: Deep probing of the photospheric sunspot penumbra: no evidence
of field-free gaps
Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.;
Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.;
Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe,
O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.;
Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.;
Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H.
2016A&A...596A...2B Altcode: 2016arXiv160708165B
Context. Some models for the topology of the magnetic field in
sunspot penumbrae predict regions free of magnetic fields or with
only dynamically weak fields in the deep photosphere. Aims:
We aim to confirm or refute the existence of weak-field regions in
the deepest photospheric layers of the penumbra. Methods:
We investigated the magnetic field at log τ5 = 0 is
by inverting spectropolarimetric data of two different sunspots
located very close to disk center with a spatial resolution of
approximately 0.4-0.45”. The data have been recorded using the GRIS
instrument attached to the 1.5-m solar telescope GREGOR at the El
Teide observatory. The data include three Fe I lines around 1565 nm,
whose sensitivity to the magnetic field peaks half a pressure scale
height deeper than the sensitivity of the widely used Fe I spectral
line pair at 630 nm. Before the inversion, the data were corrected
for the effects of scattered light using a deconvolution method with
several point spread functions. Results: At log τ5
= 0 we find no evidence of regions with dynamically weak (B&lt;
500 Gauss) magnetic fields in sunspot penumbrae. This result is much
more reliable than previous investigations made on Fe I lines at 630
nm. Moreover, the result is independent of the number of nodes employed
in the inversion, is independent of the point spread function used to
deconvolve the data, and does not depend on the amount of stray light
(I.e., wide-angle scattered light) considered.

---------------------------------------------------------
Title: Three-dimensional structure of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio
Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.;
Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier,
R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki,
S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.;
von der Lühe, O.; Waldmann, T.
2016A&A...596A..59F Altcode: 2016arXiv161104803F
Context. Active regions are the most prominent manifestations of solar
magnetic fields; their generation and dissipation are fundamental
problems in solar physics. Light bridges are commonly present during
sunspot decay, but a comprehensive picture of their role in the
removal of the photospheric magnetic field is still lacking. 
Aims: We study the three-dimensional configuration of a sunspot,
and in particular, its light bridge, during one of the last stages of
its decay. Methods: We present the magnetic and thermodynamical
stratification inferred from full Stokes inversions of the photospheric
Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
Infrared Spectrograph of the GREGOR telescope at the Observatorio del
Teide, Tenerife, Spain. The analysis is complemented by a study of
continuum images covering the disk passage of the active region, which
are provided by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory. Results: The sunspot shows a light bridge
with penumbral continuum intensity that separates the central umbra from
a smaller umbra. We find that in this region the magnetic field lines
form a canopy with lower magnetic field strength in the inner part. The
photospheric light bridge is dominated by gas pressure (high-β),
as opposed to the surrounding umbra, where the magnetic pressure
is higher. A convective flow is observed in the light bridge. This
flow is able to bend the magnetic field lines and to produce field
reversals. The field lines merge above the light bridge and become
as vertical and strong as in the surrounding umbra. We conclude that
this occurs because two highly magnetized regions approach each other
during the sunspot evolution. Movies associated to Figs. 2 and 13
are available at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Inference of magnetic fields in the very quiet Sun
Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.;
Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.;
Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.;
González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.;
Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.;
Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman,
T.; Volkmer, R.
2016A&A...596A...5M Altcode: 2018arXiv180410089M
Context. Over the past 20 yr, the quietest areas of the solar surface
have revealed a weak but extremely dynamic magnetism occurring
at small scales (&lt;500 km), which may provide an important
contribution to the dynamics and energetics of the outer layers of
the atmosphere. Understanding this magnetism requires the inference
of physical quantities from high-sensitivity spectro-polarimetric
data with high spatio-temporal resolution. Aims: We present
high-precision spectro-polarimetric data with high spatial resolution
(0.4”) of the very quiet Sun at 1.56 μm obtained with the GREGOR
telescope to shed some light on this complex magnetism. Methods:
We used inversion techniques in two main approaches. First, we assumed
that the observed profiles can be reproduced with a constant magnetic
field atmosphere embedded in a field-free medium. Second, we assumed
that the resolution element has a substructure with either two constant
magnetic atmospheres or a single magnetic atmosphere with gradients of
the physical quantities along the optical depth, both coexisting with
a global stray-light component. Results: Half of our observed
quiet-Sun region is better explained by magnetic substructure within
the resolution element. However, we cannot distinguish whether this
substructure comes from gradients of the physical parameters along the
line of sight or from horizontal gradients (across the surface). In
these pixels, a model with two magnetic components is preferred, and
we find two distinct magnetic field populations. The population with
the larger filling factor has very weak ( 150 G) horizontal fields
similar to those obtained in previous works. We demonstrate that the
field vector of this population is not constrained by the observations,
given the spatial resolution and polarimetric accuracy of our data. The
topology of the other component with the smaller filling factor is
constrained by the observations for field strengths above 250 G:
we infer hG fields with inclinations and azimuth values compatible
with an isotropic distribution. The filling factors are typically
below 30%. We also find that the flux of the two polarities is not
balanced. From the other half of the observed quiet-Sun area 50% are
two-lobed Stokes V profiles, meaning that 23% of the field of view
can be adequately explained with a single constant magnetic field
embedded in a non-magnetic atmosphere. The magnetic field vector and
filling factor are reliable inferred in only 50% based on the regular
profiles. Therefore, 12% of the field of view harbour hG fields with
filling factors typically below 30%. At our present spatial resolution,
70% of the pixels apparently are non-magnetised.

---------------------------------------------------------
Title: Probing deep photospheric layers of the quiet Sun with high
magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
Schmidt, D.; Kiess, C.; Nicklas, H.
2016A&A...596A...6L Altcode: 2016arXiv160506324L
Context. Investigations of the magnetism of the quiet Sun are hindered
by extremely weak polarization signals in Fraunhofer spectral
lines. Photon noise, straylight, and the systematically different
sensitivity of the Zeeman effect to longitudinal and transversal
magnetic fields result in controversial results in terms of the strength
and angular distribution of the magnetic field vector. Aims:
The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
spatial straylight and photon noise into account. Methods: Highly
sensitive full Stokes measurements of a quiet-Sun region at disk center
in the deep photospheric Fe I lines in the 1.56 μm region were obtained
with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
diagnostics based directly on the shape and strength of the profiles
were applied to the GRIS data. We made use of the magnetic line ratio
technique, which was tested against realistic magneto-hydrodynamic
simulations (MURaM). Results: About 80% of the GRIS spectra
of a very quiet solar region show polarimetric signals above a 3σ
level. Area and amplitude asymmetries agree well with small-scale
surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields. Conclusions:
The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
are so far unique in the combination of high spatial resolution scans
and high magnetic field sensitivity. Nevertheless, the unavoidable
effect of spatial straylight and the resulting dilution of the weak
Stokes profiles means that inversion techniques still bear a high risk
of misinterpretating the data.

---------------------------------------------------------
Title: Non-LTE Inversions of the Mg II h &amp; k and UV Triplet Lines
Authors: de la Cruz Rodríguez, Jaime; Leenaarts, Jorrit; Asensio
Ramos, Andrés
2016ApJ...830L..30D Altcode: 2016arXiv160909527D
The Mg II h &amp; k lines are powerful diagnostics for studying the
solar chromosphere. They have become particularly popular with the
launch of the Interface Region Imaging Spectrograph (IRIS) satellite,
and a number of studies that include these lines have lead to great
progress in understanding chromospheric heating, in many cases thanks
to the support from 3D MHD simulations. In this study, we utilize
another approach to analyze observations: non-LTE inversions of
the Mg II h &amp; k and UV triplet lines including the effects of
partial redistribution. Our inversion code attempts to construct a
model atmosphere that is compatible with the observed spectra. We have
assessed the capabilities and limitations of the inversions using the
FALC atmosphere and a snapshot from a 3D radiation-MHD simulation. We
find that Mg II h &amp; k allow reconstructing a model atmosphere from
the middle photosphere to the transition region. We have also explored
the capabilities of a multi-line/multi-atom setup, including the Mg
II h &amp; k, the Ca II 854.2 nm, and the Fe I 630.25 lines to recover
the full stratification of physical parameters, including the magnetic
field vector, from the photosphere to the chromosphere. Finally, we
present the first inversions of observed IRIS spectra from quiet-Sun,
plage, and sunspot, with very promising results.

---------------------------------------------------------
Title: Upholding the unified model for active galactic nuclei:
VLT/FORS2 spectropolarimetry of Seyfert 2 galaxies
Authors: Ramos Almeida, C.; Martínez González, M. J.; Asensio Ramos,
A.; Acosta-Pulido, J. A.; Hönig, S. F.; Alonso-Herrero, A.; Tadhunter,
C. N.; González-Martín, O.
2016MNRAS.461.1387R Altcode: 2016arXiv160602204R
The origin of the unification model for active galactic nuclei (AGN)
was the detection of broad hydrogen recombination lines in the optical
polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since
then, a search for the hidden broad-line region (HBLR) of nearby
Sy2s started, but polarized broad lines have only been detected
in ∼30-40 per cent of the nearby Sy2s observed to date. Here we
present new VLT/FORS2 optical spectropolarimetry of a sample of 15
Sy2s, including Compton-thin and Compton-thick sources. The sample
includes six galaxies without previously published spectropolarimetry,
some of them normally treated as non-hidden BLR (NHBLR) objects in
the literature, four classified as NHBLR, and five as HBLR based on
previous data. We report ≥4σ detections of a HBLR in 11 of these
galaxies (73 per cent of the sample) and a tentative detection in NGC
5793, which is Compton-thick according to the analysis of X-ray data
performed here. Our results confirm that at least some NHBLRs are
misclassified, bringing previous publications reporting differences
between HBLR and NHBLR objects into question. We detect broad Hα and
Hβ components in polarized light for 10 targets, and just broad Hα
for NGC 5793 and NGC 6300, with line widths ranging between 2100 and
9600 km s-1. High bolometric luminosities and low column
densities are associated with higher polarization degrees, but not
necessarily with the detection of the scattered broad components.

---------------------------------------------------------
Title: Upholding the unified model for AGN: VLT/FORS2
spectropolarimetry of Seyfert 2 galaxies
Authors: Ramos Almeida, Cristina; Martínez González, M.; Asensio
Ramos, A.; Acosta Pulido, J.; Hönig, S.; Alonso-Herrero, A.;
Tadhunter, C.; González-Martín, O.
2016agnw.confE..52R Altcode:
The origin of the unification model for AGN was the detection of broad
hydrogen recombination lines in the optical polarized spectrum of the
Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden
broad-line region (HBLR) of nearby Sy2s started, but polarized broad
lines have only been detected in ~30-40% of the nearby Sy2s observed
to date. Here we present new VLT/FORS2 optical spectropolarimetry
of a sample of 15 Sy2s, including Compton-thin and Compton-thick
sources. The sample includes six galaxies without previously published
spectropolarimetry, some of them normally treated as non-hidden BLR
(NHBLR) objects in the literature, and four Sy2s classified as NHBLR
based on previous data. We report &gt;4sigma detections of a HBLR in
11 of these galaxies (73% of the sample). Our results confirm that at
least some NHBLRs were misclassified, bringing previous publications
reporting differences between HBLR and NHBLR objects into question. We
detect broad Ha and Hb components in polarized light for 9 targets,
and just broad Ha for the other two. We do not find any correlation
between the properties of the polarized spectra and the column densities
measured from the X-rays or torus inclination, but a larger sample is
required to confirm this.

---------------------------------------------------------
Title: On the Magnetism and Dynamics of Prominence Legs Hosting
Tornadoes
Authors: Martínez González, M. J.; Asensio Ramos, A.; Arregui, I.;
Collados, M.; Beck, C.; de la Cruz Rodríguez, J.
2016ApJ...825..119M Altcode: 2016arXiv160501183M
Solar tornadoes are dark vertical filamentary structures observed
in the extreme ultraviolet associated with prominence legs and
filament barbs. Their true nature and relationship to prominences
requires an understanding of their magnetic structure and dynamic
properties. Recently, a controversy has arisen: is the magnetic field
organized forming vertical, helical structures or is it dominantly
horizontal? And concerning their dynamics, are tornadoes really rotating
or is it just a visual illusion? Here we analyze four consecutive
spectro-polarimetric scans of a prominence hosting tornadoes on its
legs, which helps us shed some light on their magnetic and dynamical
properties. We show that the magnetic field is very smooth in all the
prominence, which is probably an intrinsic property of the coronal
field. The prominence legs have vertical helical fields that show
slow temporal variation that is probably related to the motion of
the fibrils. Concerning the dynamics, we argue that (1) if rotation
exists, it is intermittent, lasting no more than one hour, and (2)
the observed velocity pattern is also consistent with an oscillatory
velocity pattern (waves).

---------------------------------------------------------
Title: Solar adaptive optics: specificities, lessons learned, and
open alternatives
Authors: Montilla, I.; Marino, J.; Asensio Ramos, A.; Collados, M.;
Montoya, L.; Tallon, M.
2016SPIE.9909E..1HM Altcode:
First on sky adaptive optics experiments were performed on the
Dunn Solar Telescope on 1979, with a shearing interferometer and
limited success. Those early solar adaptive optics efforts forced
to custom-develop many components, such as Deformable Mirrors and
WaveFront Sensors, which were not available at that time. Later on, the
development of the correlation Shack-Hartmann marked a breakthrough in
solar adaptive optics. Since then, successful Single Conjugate Adaptive
Optics instruments have been developed for many solar telescopes,
i.e. the National Solar Observatory, the Vacuum Tower Telescope and
the Swedish Solar Telescope. Success with the Multi Conjugate Adaptive
Optics systems for GREGOR and the New Solar Telescope has proved
to be more difficult to attain. Such systems have a complexity not
only related to the number of degrees of freedom, but also related
to the specificities of the Sun, used as reference, and the sensing
method. The wavefront sensing is performed using correlations on
images with a field of view of 10", averaging wavefront information
from different sky directions, affecting the sensing and sampling of
high altitude turbulence. Also due to the low elevation at which solar
observations are performed we have to include generalized fitting
error and anisoplanatism, as described by Ragazzoni and Rigaut, as
non-negligible error sources in the Multi Conjugate Adaptive Optics
error budget. For the development of the next generation Multi Conjugate
Adaptive Optics systems for the Daniel K. Inouye Solar Telescope and
the European Solar Telescope we still need to study and understand
these issues, to predict realistically the quality of the achievable
reconstruction. To improve their designs other open issues have to
be assessed, i.e. possible alternative sensing methods to avoid the
intrinsic anisoplanatism of the wide field correlation Shack-Hartmann,
new parameters to estimate the performance of an adaptive optics solar
system, alternatives to the Strehl and the Point Spread Function used
in night time adaptive optics but not really suitable to the solar
systems, and new control strategies more complex than the ones used in
nowadays solar Multi Conjugate Adaptive Optics systems. In this paper
we summarize the lessons learned with past and current solar adaptive
optics systems and focus on the discussion on the new alternatives to
solve present open issues limiting their performance.

---------------------------------------------------------
Title: Chromospheric LAyer SpectroPolarimeter (CLASP2)
Authors: Narukage, Noriyuki; McKenzie, David E.; Ishikawa, Ryoko;
Trujillo-Bueno, Javier; De Pontieu, Bart; Kubo, Masahito; Ishikawa,
Shin-nosuke; Kano, Ryouhei; Suematsu, Yoshinori; Yoshida, Masaki;
Rachmeler, Laurel A.; Kobayashi, Ken; Cirtain, Jonathan W.; Winebarger,
Amy R.; Asensio Ramos, Andres; del Pino Aleman, Tanausu; Štępán,
Jiri; Belluzzi, Luca; Larruquert, Juan Ignacio; Auchère, Frédéric;
Leenaarts, Jorrit; Carlsson, Mattias J. L.
2016SPIE.9905E..08N Altcode:
The sounding rocket Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP) was launched on September 3rd, 2015, and successfully detected
(with a polarization accuracy of 0.1 %) the linear polarization signals
(Stokes Q and U) that scattering processes were predicted to produce
in the hydrogen Lyman-alpha line (Lyα 121.567 nm). Via the Hanle
effect, this unique data set may provide novel information about the
magnetic structure and energetics in the upper solar chromosphere. The
CLASP instrument was safely recovered without any damage and we have
recently proposed to dedicate its second flight to observe the four
Stokes profiles in the spectral region of the Mg II h and k lines
around 280 nm; in these lines the polarization signals result from
scattering processes and the Hanle and Zeeman effects. Here we describe
the modifications needed to develop this new instrument called the
"Chromospheric LAyer SpectroPolarimeter" (CLASP2).

---------------------------------------------------------
Title: Analysis of spatially deconvolved polar faculae
Authors: Quintero Noda, C.; Suematsu, Y.; Ruiz Cobo, B.; Shimizu,
T.; Asensio Ramos, A.
2016MNRAS.460..956Q Altcode: 2016MNRAS.tmp..838Q; 2016arXiv160500330Q
Polar faculae are bright features that can be detected in
solar limb observations and they are related to magnetic field
concentrations. Although there are a large number of works studying
them, some questions about their nature as their magnetic properties
at different heights are still open. Thus, we aim to improve the
understanding of solar polar faculae. In that sense, we infer
the vertical stratification of the temperature, gas pressure,
line-of-sight velocity and magnetic field vector of polar faculae
regions. We performed inversions of the Stokes profiles observed
with Hinode/Spectropolarimeter after removing the stray light
contamination produced by the spatial point spread function of the
telescope. Moreover, after solving the azimuth ambiguity, we transform
the magnetic field vector to local solar coordinates. The obtained
results reveal that the polar faculae are constituted by hot plasma with
low line-of-sight velocities and single polarity magnetic fields in the
kilogauss range that are nearly perpendicular to the solar surface. We
also found that the spatial location of these magnetic fields is
slightly shifted respect to the continuum observations towards the
disc centre. We believe that this is due to the hot wall effect that
allows detecting photons that come from deeper layers located closer
to the solar limb.

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Title: Active Region Filaments Might Harbor Weak Magnetic Fields
Authors: Díaz Baso, C. J.; Martínez González, M. J.; Asensio
Ramos, A.
2016ApJ...822...50D Altcode: 2016arXiv160304645D
Recent spectropolarimetric observations of active region filaments have
revealed polarization profiles with signatures typical of the strong
field Zeeman regime. The conspicuous absence in those observations of
scattering polarization and Hanle effect signatures was then pointed
out by some authors. This was interpreted as either a signature of
mixed “turbulent” field components or as a result of optical
thickness. In this article, we present a natural scenario to explain
these Zeeman-only spectropolarimetric observations of active region
(AR) filaments. We propose a two-component model, one on top of
the other. Both components have horizontal fields, with the azimuth
difference between them being close to 90°. The component that lies
lower in the atmosphere is permeated by a strong field of the order of
600 G, while the upper component has much weaker fields, of the order of
10 G. The ensuing scattering polarization signatures of the individual
components have opposite signs, so its combination along the line of
sight reduces—and even can cancel out—the Hanle signatures, giving
rise to an apparent Zeeman-only profile. This model is also applicable
to other chromospheric structures seen in absorption above ARs.

---------------------------------------------------------
Title: Spectro-polarimetric observation in UV with CLASP to probe
the chromosphere and transition region
Authors: Kano, Ryouhei; Ishikawa, Ryohko; Winebarger, Amy R.; Auchère,
Frédéric; Trujillo Bueno, Javier; Narukage, Noriyuki; Kobayashi,
Ken; Bando, Takamasa; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-Nosuke; Giono, Gabriel; Hara, Hirohisa; Suematsu, Yoshinori;
Shimizu, Toshifumi; Sakao, Taro; Tsuneta, Saku; Ichimoto, Kiyoshi;
Goto, Motoshi; Cirtain, Jonathan W.; De Pontieu, Bart; Casini, Roberto;
Manso Sainz, Rafael; Asensio Ramos, Andres; Stepan, Jiri; Belluzzi,
Luca; Carlsson, Mats
2016SPD....4710107K Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a NASA
sounding-rocket experiment that was performed in White Sands in
the US on September 3, 2015. During its 5-minute ballistic flight,
CLASP successfully made the first spectro-polarimetric observation in
the Lyman-alpha line (121.57 nm) originating in the chromosphere and
transition region. Since the Lyman-alpha polarization is sensitive
to magnetic field of 10-100 G by the Hanle effect, we aim to infer
the magnetic field information in such upper solar atmosphere with
this experiment.The obtained CLASP data showed that the Lyman-alpha
scattering polarization is about a few percent in the wings and
the order of 0.1% in the core near the solar limb, as it had been
theoretically predicted, and that both polarization signals have a
conspicuous spatio-temporal variability. CLASP also observed another
upper-chromospheric line, Si III (120.65 nm), whose critical field
strength for the Hanle effect is 290 G, and showed a measurable
scattering polarization of a few % in this line. The polarization
properties of the Si III line could facilitate the interpretation of
the scattering polarization observed in the Lyman-alpha line.In this
presentation, we would like to show how the upper chromosphere and
transition region are seen in the polarization of these UV lines and
discuss the possible source of these complicated polarization signals.

---------------------------------------------------------
Title: Inversion of Stokes profiles with systematic effects
Authors: Asensio Ramos, A.; de la Cruz Rodríguez, J.; Martínez
González, M. J.; Pastor Yabar, A.
2016A&A...590A..87A Altcode: 2016arXiv160405470A
Quantitative thermodynamical, dynamical and magnetic properties of the
solar and stellar plasmas are obtained by interpreting their emergent
non-polarized and polarized spectrum. This inference requires the
selection of a set of spectral lines that are particularly sensitive to
the physical conditions in the plasma and a suitable parametric model
of the solar/stellar atmosphere. Nonlinear inversion codes are then
used to fit the model to the observations. However, the presence of
systematic effects, like nearby or blended spectral lines, telluric
absorption, or incorrect correction of the continuum, among others,
can strongly affect the results. We present an extension to current
inversion codes that can deal with these effects in a transparent
way. The resulting algorithm is very simple and can be applied to any
existing inversion code with the addition of a few lines of code as
an extra step in each iteration.

---------------------------------------------------------
Title: X-Ray Absorption, Nuclear Infrared Emission, and Dust Covering
Factors of AGNs: Testing Unification Schemes
Authors: Mateos, S.; Carrera, F. J.; Alonso-Herrero, A.;
Hernán-Caballero, A.; Barcons, X.; Asensio Ramos, A.; Watson, M. G.;
Blain, A.; Caccianiga, A.; Ballo, L.; Braito, V.; Ramos Almeida, C.
2016ApJ...819..166M Altcode: 2016arXiv160104439M
We present the distributions of the geometrical covering factors
of the dusty tori (f2) of active galactic nuclei (AGNs)
using an X-ray selected complete sample of 227 AGNs drawn from the
Bright Ultra-hard XMM-Newton Survey. The AGNs have z from 0.05 to 1.7,
2-10 keV luminosities between 1042 and 1046
erg s-1, and Compton-thin X-ray absorption. Employing
data from UKIDSS, 2MASS, and the Wide-field Infrared Survey Explorer
in a previous work, we determined the rest-frame 1-20 μm continuum
emission from the torus, which we model here with the clumpy torus
models of Nenkova et al. Optically classified type 1 and type 2 AGNs
are intrinsically different, with type 2 AGNs having, on average,
tori with higher f2 than type 1 AGNs. Nevertheless,
∼20% of type 1 AGNs have tori with large covering factors, while
∼23%-28% of type 2 AGNs have tori with small covering factors. Low
f2 are preferred at high AGN luminosities, as postulated by
simple receding torus models, although for type 2 AGNs the effect is
certainly small. f2 increases with the X-ray column density,
which implies that dust extinction and X-ray absorption take place in
material that share an overall geometry and most likely belong to the
same structure, the putative torus. Based on our results, the viewing
angle, AGN luminosity, and also f2 determine the optical
appearance of an AGN and control the shape of the rest-frame ∼1-20
μm nuclear continuum emission. Thus, the torus geometrical covering
factor is a key ingredient of unification schemes.

---------------------------------------------------------
Title: Random sub-Nyquist polarimetric modulator
Authors: Asensio Ramos, A.
2016ApOpt..55.1324A Altcode: 2016arXiv160105211A
We show that it is possible to measure polarization with a polarimeter
that gets rid of the seeing while still measuring at a frequency
well below that of the seeing. We study a standard polarimeter made
of two retarders and a beamsplitter. The retarders are modulated at
$\sim 500$ Hz, a frequency comparable to that of the variations of
the refraction index in the Earth atmosphere, what is usually termed
as seeing in astronomical observations. However, we assume that the
camera is slow, so that our measurements are time integrations of
these modulated signals. In order to recover the time variation of the
seeing and obtain the Stokes parameters, we use the theory of compressed
sensing to solve the demodulation by impose a sparsity constraint on the
Fourier coefficients of the seeing. We demonstrate the feasibility of
this sub-Nyquist polarimeter using numerical simulations, both in the
case without noise and with noise. We show that a sensible modulation
scheme is obtained by randomly changing the fast axis of the modulators
or their retardances in specific ways. We finally demonstrate that the
value of the Stokes parameters can be recovered with great precision
at almost maximum efficiency, although it slightly degrades when the
signal-to-noise ratio of the observations increase, a consequence of
the multiplexing under the presence of photon noise.

---------------------------------------------------------
Title: A deep look at the nuclear region of UGC 5101 through high
angular resolution mid-IR data with GTC/CanariCam
Authors: Martínez-Paredes, M.; Alonso-Herrero, A.; Aretxaga, I.;
Ramos Almeida, C.; Hernán-Caballero, A.; González-Martín, O.;
Pereira-Santaella, M.; Packham, C.; Asensio Ramos, A.; Díaz-Santos,
T.; Elitzur, M.; Esquej, P.; García-Bernete, I.; Imanishi, M.;
Levenson, N. A.; Rodríguez Espinosa, J. M.
2015MNRAS.454.3577M Altcode: 2015arXiv150904396M
We present an analysis of the nuclear infrared (IR, 1.6-18 μm)
emission of the ultraluminous IR galaxy UGC 5101 to derive the
properties of its active galactic nucleus (AGN) and its obscuring
material. We use new mid-IR high angular resolution (0.3-0.5 arcsec)
imaging using the Si-2 filter (λC = 8.7 μm) and 7.5-13 μm
spectroscopy taken with CanariCam (CC) on the 10.4 m Gran Telescopio
CANARIAS. We also use archival Hubble Space Telescope/NICMOS and
Subaru/COMICS imaging and Spitzer/IRS spectroscopy. We estimate the
near- and mid-IR unresolved nuclear emission by modelling the imaging
data with GALFIT. We decompose the Spitzer/IRS and CC spectra using a
power-law component, which represents the emission due to dust heated
by the AGN, and a starburst component, both affected by foreground
extinction. We model the resulting unresolved near- and mid-IR, and
the starburst subtracted CC spectrum with the CLUMPY torus models
of Nenkova et al. The derived geometrical properties of the torus,
including the large covering factor and the high foreground extinction
needed to reproduce the deep 9.7 μm silicate feature, are consistent
with the lack of strong AGN signatures in the optical. We derive an
AGN bolometric luminosity Lbol ∼ 1.9 × 1045
erg s-1 that is in good agreement with other estimates in
the literature.

---------------------------------------------------------
Title: Bayesian least squares deconvolution
Authors: Asensio Ramos, A.; Petit, P.
2015A&A...583A..51A Altcode: 2015arXiv150904220A
 Aims: We develop a fully Bayesian least squares deconvolution
(LSD) that can be applied to the reliable detection of magnetic
signals in noise-limited stellar spectropolarimetric observations using
multiline techniques. Methods: We consider LSD under the Bayesian
framework and we introduce a flexible Gaussian process (GP) prior for
the LSD profile. This prior allows the result to automatically adapt to
the presence of signal. We exploit several linear algebra identities to
accelerate the calculations. The final algorithm can deal with thousands
of spectral lines in a few seconds. Results: We demonstrate
the reliability of the method with synthetic experiments and we apply
it to real spectropolarimetric observations of magnetic stars. We are
able to recover the magnetic signals using a small number of spectral
lines, together with the uncertainty at each velocity bin. This allows
the user to consider if the detected signal is reliable. The code to
compute the Bayesian LSD profile is freely available.

---------------------------------------------------------
Title: New generation Stokes inversion codes
Authors: Asensio Ramos, A.; de la Cruz Rodríguez, J.
2015IAUS..305..225A Altcode: 2015IAUS..305..225R
We utilize the concept of sparsity or compressibility to develop
an new generation of inversion codes for the Stokes parameters. The
inversion code uses numerical optimization techniques based on the idea
of proximal algorithms to impose sparsity. In so doing, we allow to
exploit the presence of spatial correlation on the maps of physical
parameters. Sparsity also regularizes the solution by reducing the
number of unknowns. The solution has an increased robustness.

---------------------------------------------------------
Title: Model Comparison for the Density Structure across Solar
Coronal Waveguides
Authors: Arregui, I.; Soler, R.; Asensio Ramos, A.
2015ApJ...811..104A Altcode: 2015arXiv150902340A
The spatial variation of physical quantities, such as the mass density,
across solar atmospheric waveguides governs the timescales and spatial
scales for wave damping and energy dissipation. The direct measurement
of the spatial distribution of density, however, is difficult,
and indirect seismology inversion methods have been suggested as
an alternative. We applied Bayesian inference, model comparison,
and model-averaging techniques to the inference of the cross-field
density structuring in solar magnetic waveguides using information on
periods and damping times for resonantly damped magnetohydrodynamic
transverse kink oscillations. Three commonly employed alternative
profiles were used to model the variation of the mass density across
the waveguide boundary. Parameter inference enabled us to obtain
information on physical quantities such as the Alfvén travel time, the
density contrast, and the transverse inhomogeneity length scale. The
inference results from alternative density models were compared and
their differences quantified. Then, the relative plausibility of the
considered models was assessed by performing model comparison. Our
results indicate that the evidence in favor of any of the three
models is minimal, unless the oscillations are strongly damped. In
such a circumstance, the application of model-averaging techniques
enables the computation of an evidence-weighted inference that takes
into account the plausibility of each model in the calculation of a
combined inversion for the unknown physical parameters.

---------------------------------------------------------
Title: CLASP: A UV Spectropolarimeter on a Sounding Rocket for
Probing theChromosphere-Corona Transition Regio
Authors: Ishikawa, Ryohko; Kano, Ryouhei; Winebarger, Amy; Auchere,
Frederic; Trujillo Bueno, Javier; Bando, Takamasa; Narukage,
Noriyuki; Kobayashi, Ken; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-nosuke; Giono, Gabriel; Tsuneta, Saku; Hara, Hirohisa; Suematsu,
Yoshinori; Shimizu, Toshifumi; Sakao, Taro; Ichimoto, Kiyoshi;
Cirtain, Jonathan; De Pontieu, Bart; Casini, Roberto; Manso Sainz,
Rafael; Asensio Ramos, Andres; Stepan, Jiri; Belluzzi, Luca
2015IAUGA..2254536I Altcode:
The wish to understand the energetic phenomena of the outer solar
atmosphere makes it increasingly important to achieve quantitative
information on the magnetic field in the chromosphere-corona
transition region. To this end, we need to measure and model the
linear polarization produced by scattering processes and the Hanle
effect in strong UV resonance lines, such as the hydrogen Lyman-alpha
line. A team consisting of Japan, USA, Spain, France, and Norway has
been developing a sounding rocket experiment called the Chromospheric
Lyman-alpha Spectro-Polarimeter (CLASP). The aim is to detect the
scattering polarization produced by anisotropic radiation pumping in
the hydrogen Lyman-alpha line (121.6 nm), and via the Hanle effect to
try to constrain the magnetic field vector in the upper chromosphere
and transition region. In this talk, we will present an overview
of our CLASP mission, its scientific objectives, ground tests made,
and the latest information on the launch planned for the Summer of 2015.

---------------------------------------------------------
Title: Spatial deconvolution of spectropolarimetric data: an
application to quiet Sun magnetic elements
Authors: Quintero Noda, C.; Asensio Ramos, A.; Orozco Suárez, D.;
Ruiz Cobo, B.
2015A&A...579A...3Q Altcode: 2015arXiv150503219Q
Context. One of the difficulties in extracting reliable information
about the thermodynamical and magnetic properties of solar plasmas from
spectropolarimetric observations is the presence of light dispersed
inside the instruments, known as stray light. Aims: We aim
to analyze quiet Sun observations after the spatial deconvolution
of the data. We examine the validity of the deconvolution process
with noisy data as we analyze the physical properties of quiet Sun
magnetic elements. Methods: We used a regularization method
that decouples the Stokes inversion from the deconvolution process,
so that large maps can be quickly inverted without much additional
computational burden. We applied the method on Hinode quiet Sun
spectropolarimetric data. We examined the spatial and polarimetric
properties of the deconvolved profiles, comparing them with the
original data. After that, we inverted the Stokes profiles using the
Stokes Inversion based on Response functions (SIR) code, which allow
us to obtain the optical depth dependence of the atmospheric physical
parameters. Results: The deconvolution process increases
the contrast of continuum images and makes the magnetic structures
sharper. The deconvolved Stokes I profiles reveal the presence of
the Zeeman splitting while the Stokes V profiles significantly change
their amplitude. The area and amplitude asymmetries of these profiles
increase in absolute value after the deconvolution process. We inverted
the original Stokes profiles from a magnetic element and found that
the magnetic field intensity reproduces the overall behavior of
theoretical magnetic flux tubes, that is, the magnetic field lines
are vertical in the center of the structure and start to fan when we
move far away from the center of the magnetic element. The magnetic
field vector inferred from the deconvolved Stokes profiles also mimic a
magnetic flux tube but in this case we found stronger field strengths
and the gradients along the line-of-sight are larger for the magnetic
field intensity and for its inclination. Moreover, the discontinuity
between the magnetic and non magnetic environment in the flux tube
gets sharper. Conclusions: The deconvolution process used
in this paper reveals information that the smearing induced by the
point spread function (PSF) of the telescope hides. Additionally,
the deconvolution is done with a low computational load, making it
appealing for its use on the analysis of large data sets. A
copy of the IDL code is 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/579/A3">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/579/A3</A>

---------------------------------------------------------
Title: An open-source, massively parallel code for non-LTE synthesis
and inversion of spectral lines and Zeeman-induced Stokes profiles
Authors: Socas-Navarro, H.; de la Cruz Rodríguez, J.; Asensio Ramos,
A.; Trujillo Bueno, J.; Ruiz Cobo, B.
2015A&A...577A...7S Altcode: 2014arXiv1408.6101S
With the advent of a new generation of solar telescopes and
instrumentation, interpreting chromospheric observations (in
particular, spectropolarimetry) requires new, suitable diagnostic
tools. This paper describes a new code, NICOLE, that has been
designed for Stokes non-LTE radiative transfer, for synthesis and
inversion of spectral lines and Zeeman-induced polarization profiles,
spanning a wide range of atmospheric heights from the photosphere
to the chromosphere. The code features a number of unique features
and capabilities and has been built from scratch with a powerful
parallelization scheme that makes it suitable for application on
massive datasets using large supercomputers. The source code is
written entirely in Fortran 90/2003 and complies strictly with the
ANSI standards to ensure maximum compatibility and portability. It
is being publicly released, with the idea of facilitating future
branching by other groups to augment its capabilities. The
source code is currently hosted at the following repository: <A
href="http://github.com/hsocasnavarro/NICOLE">https://github.com/hsocasnavarro/NICOLE</A>

---------------------------------------------------------
Title: Estimating the magnetic field strength from magnetograms
Authors: Asensio Ramos, A.; Martínez González, M. J.; Manso Sainz, R.
2015A&A...577A.125A Altcode: 2015arXiv150307670A
A properly calibrated longitudinal magnetograph is an instrument
that measures circular polarization and gives an estimation of the
magnetic flux density in each observed resolution element. This usually
constitutes a lower bound of the field strength in the resolution
element, given that it can be made arbitrarily large as long as it
occupies a proportionally smaller area of the resolution element
and/or becomes more transversal to the observer while still produce
the same magnetic signal. However, we know that arbitrarily stronger
fields are less likely - hG fields are more probable than kG fields,
with fields above several kG virtually absent - and we may even have
partial information about their angular distribution. Based on a set of
sensible considerations, we derive simple formulae based on a Bayesian
analysis to give an improved estimation of the magnetic field strength
for magnetographs.

---------------------------------------------------------
Title: Sparse inversion of Stokes profiles. I. Two-dimensional
Milne-Eddington inversions
Authors: Asensio Ramos, A.; de la Cruz Rodríguez, J.
2015A&A...577A.140A Altcode: 2015arXiv150307666A
Context. Inversion codes are numerical tools used to infer physical
properties from observations. Despite their success, the quality of
current spectropolarimetric observations and those expected in the
near future presents a challenge to current inversion codes. 
Aims: The pixel-by-pixel strategy of inverting spectropolarimetric
data that we currently use needs to be surpassed and improved. The
inverted physical parameters have to take into account the spatial
correlation that is present in the data and that contains valuable
physical information. Methods: We used the concept of
sparsity or compressibility to develop a new generation of inversion
codes for the Stokes parameters. The inversion code uses numerical
optimization techniques based on the idea of proximal algorithms to
impose sparsity. In so doing, we allow for the first time exploiting
the spatial correlation on the maps of physical parameters. Sparsity
also regularizes the solution by reducing the number of unknowns. Results: We compare the results of the new inversion code with
pixel-by-pixel inversions to demonstrate the increased robustness of
the solution. We also show how the method can easily compensate for
the effect of the telescope point spread function, producing solutions
with an enhanced contrast.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Spatial deconvolution code
(Quintero Noda+, 2015)
Authors: Quintero Noda, C.; Asensio Ramos, A.; Orozco Suarez, D.;
Ruiz Cobo, B.
2015yCat..35790003Q Altcode:
This deconvolution method follows the scheme presented in Ruiz Cobo
&amp; Asensio Ramos (2013A&amp;A...549L...4R) The Stokes parameters
are projected onto a few spectral eigenvectors and the ensuing maps
of coefficients are deconvolved using a standard Lucy-Richardson
algorithm. This introduces a stabilization because the PCA filtering
reduces the amount of noise. (1 data file).

---------------------------------------------------------
Title: The Differences in the Torus Geometry between Hidden and
Non-hidden Broad Line Active Galactic Nuclei
Authors: Ichikawa, Kohei; Packham, Christopher; Ramos Almeida,
Cristina; Asensio Ramos, Andrés; Alonso-Herrero, Almudena;
González-Martín, Omaira; Lopez-Rodriguez, Enrique; Ueda, Yoshihiro;
Díaz-Santos, Tanio; Elitzur, Moshe; Hönig, Sebastian F.; Imanishi,
Masatoshi; Levenson, Nancy A.; Mason, Rachel E.; Perlman, Eric S.;
Alsip, Crystal D.
2015ApJ...803...57I Altcode: 2015arXiv150106584I
We present results from the fitting of infrared (IR) spectral energy
distributions of 21 active galactic nuclei (AGNs) with clumpy torus
models. We compiled high spatial resolution (∼0.3-0.7 arcsec) mid-IR
(MIR) N-band spectroscopy, Q-band imaging, and nuclear near- and MIR
photometry from the literature. Combining these nuclear near- and MIR
observations, far-IR photometry, and clumpy torus models enables us
to put constraints on the torus properties and geometry. We divide
the sample into three types according to the broad line region (BLR)
properties: type-1s, type-2s with scattered or hidden broad line
region (HBLR) previously observed, and type-2s without any published
HBLR signature (NHBLR). Comparing the torus model parameters gives us
the first quantitative torus geometrical view for each subgroup. We
find that NHBLR AGNs have smaller torus opening angles and larger
covering factors than HBLR AGNs. This suggests that the chance to
observe scattered (polarized) flux from the BLR in NHBLR could be
reduced by the dual effects of (a) less scattering medium due to the
reduced scattering volume given the small torus opening angle and (b)
the increased torus obscuration between the observer and the scattering
region. These effects give a reasonable explanation for the lack of
observed HBLR in some type-2 AGNs.

---------------------------------------------------------
Title: Height Variation of the Vector Magnetic Field in Solar Spicules
Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.
2015ApJ...803L..18O Altcode: 2015arXiv150404637O
Proving the magnetic configuration of solar spicules has hitherto been
difficult due to the lack of spatial resolution and image stability
during off-limb ground-based observations. We report spectropolarimetric
observations of spicules taken in the He i 1083 nm spectral region
with the Tenerife Infrared Polarimeter II at the German Vacuum Tower
Telescope of the Observatorio del Teide (Tenerife, Canary Islands,
Spain). The data provide the variation with geometrical height of
the Stokes I, Q, U, and V profiles, whose encoded information allows
the determination of the magnetic field vector by means of the HAZEL
inversion code. The inferred results show that the average magnetic
field strength at the base of solar spicules is about 80 gauss, and
then it decreases rapidly with height to about 30 gauss at a height of
3000 km above the visible solar surface. Moreover, the magnetic field
vector is close to vertical at the base of the chromosphere and has
mid-inclinations (about 50°) above 2 Mm height.

---------------------------------------------------------
Title: Chromospheric Diagnosis with Ca II Lines: Forward Modeling
in Forward Scattering. I
Authors: Carlin, E. S.; Asensio Ramos, A.
2015ApJ...801...16C Altcode: 2014arXiv1412.5386C
This paper presents a synthetic tomography of the quiet solar
chromosphere formed by spatial maps of scattering polarization. It
has been calculated for the Ca II 8498, 8542, and 3934 Å lines by
solving the non-LTE radiative transfer problem of the second kind
in a three-dimensional atmosphere model obtained from realistic
magneto-hydrodynamical simulations. Our investigation focuses on the
linear polarization signals induced by kinematics, radiation field
anisotropy, and the Hanle effect in forward-scattering geometry. Thus,
instead of considering slit profiles at the limb as normally done in
the study of the second solar spectrum, we synthesize and analyze
spatial maps of polarization at the disk center. This allows us to
understand the spatial signatures of dynamics and magnetic field in the
linear polarization in order to discriminate them observationally. Our
results suggest some ideas for chromospheric diagnosis that will be
developed throughout a series of papers. In particular, Hanle polarity
inversion lines and dynamic Hanle diagrams are two concepts introduced
in the present work. We find that chromospheric dynamics and magnetic
field topology create spatial polarization fingerprints that trace the
dynamic situation of the plasma and the magnetic field. This allows us
to reconstruct the magnetic field intensity in the middle chromosphere
using Stokes V along grooves of null linear polarization. We finally
address the problems of diagnosing Hanle saturation and kinematic
amplification of scattering signals using Hanle diagrams.

---------------------------------------------------------
Title: Spectro-Polarimetric Imaging Reveals Helical Magnetic Fields
in Solar Prominence Feet
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
A.; Beck, C.; de la Cruz Rodríguez, J.; Díaz, A. J.
2015ApJ...802....3M Altcode: 2015arXiv150103295M
Solar prominences are clouds of cool plasma levitating above
the solar surface and insulated from the million-degree corona by
magnetic fields. They form in regions of complex magnetic topology,
characterized by non-potential fields, which can evolve abruptly,
disintegrating the prominence and ejecting magnetized material
into the heliosphere. However, their physics is not yet fully
understood because mapping such complex magnetic configurations
and their evolution is extremely challenging, and must often be
guessed by proxy from photometric observations. Using state-of-the-art
spectro-polarimetric data, we reconstruct the structure of the magnetic
field in a prominence. We find that prominence feet harbor helical
magnetic fields connecting the prominence to the solar surface below.

---------------------------------------------------------
Title: Constraining the shaping mechanism of the Red Rectangle
through the spectro-polarimetry of its central star
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
R.; Corradi, R. L. M.; Leone, F.
2015A&A...574A..16M Altcode: 2014arXiv1410.6365M
We carried out high-sensitivity spectro-polarimetric observations of
the central star of the Red Rectangle protoplanetary nebula with the
aim of constraining the mechanism that gives its biconical shape. The
stellar light of the central binary system is linearly polarised since
it is scattered on the dust particles of the nebula. Surprisingly,
the linear polarisation in the continuum is aligned with one of the
spikes of the biconical outflow. Also, the observed Balmer lines,
as well as the Ca ii K lines, are polarised. These observational
constraints are used to confirm or reject current theoretical models
for the shaping mechanism of the Red Rectangle. We propose that the
observed polarisation is not very likely to be generated by a uniform
biconical stellar wind. Also, the hypothesis of a precessing jet does
not completely match observations since it requires a larger aperture
jet than for the nebula.

---------------------------------------------------------
Title: Hierarchical analysis of the quiet-Sun magnetism
Authors: Asensio Ramos, A.; Martínez González, M. J.
2014A&A...572A..98A Altcode: 2014arXiv1410.5953A
Standard statistical analysis of the magnetic properties of the
quiet Sun rely on simple histograms of quantities inferred from
maximum-likelihood estimations. Because of the inherent degeneracies,
either intrinsic or induced by the noise, this approach is not optimal
and can lead to highly biased results. We carried out a meta-analysis
of the magnetism of the quiet Sun from Hinode observations using a
hierarchical probabilistic method. This method allowed us to infer the
statistical properties of the magnetic field vector over the observed
field-of-view, consistently taking into account the uncertainties
in each pixel that are due to noise and degeneracies. Our results
imply that the magnetic fields are very weak, below 275 G with 95%
probability, with a slight preference for horizontal fields, although
the distribution is not far from a quasi-isotropic distribution.

---------------------------------------------------------
Title: A Sounding Rocket Experiment for the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP)
Authors: Kubo, M.; Kano, R.; Kobayashi, K.; Bando, T.; Narukage, N.;
Ishikawa, R.; Tsuneta, S.; Katsukawa, Y.; Ishikawa, S.; Suematsu, Y.;
Hara, H.; Shimizu, T.; Sakao, T.; Ichimoto, K.; Goto, M.; Holloway,
T.; Winebarger, A.; Cirtain, J.; De Pontieu, B.; Casini, R.; Auchère,
F.; Trujillo Bueno, J.; Manso Sainz, R.; Belluzzi, L.; Asensio Ramos,
A.; Štěpán, J.; Carlsson, M.
2014ASPC..489..307K Altcode:
A sounding-rocket experiment called the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP) is presently under development to measure
the linear polarization profiles in the hydrogen Lyman-alpha (Lyα)
line at 121.567 nm. CLASP is a vacuum-UV (VUV) spectropolarimeter to aim
for first detection of the linear polarizations caused by scattering
processes and the Hanle effect in the Lyα line with high accuracy
(0.1%). This is a fist step for exploration of magnetic fields in
the upper chromosphere and transition region of the Sun. Accurate
measurements of the linear polarization signals caused by scattering
processes and the Hanle effect in strong UV lines like Lyα are
essential to explore with future solar telescopes the strength
and structures of the magnetic field in the upper chromosphere and
transition region of the Sun. The CLASP proposal has been accepted by
NASA in 2012, and the flight is planned in 2015.

---------------------------------------------------------
Title: The magnetic field configuration of a solar prominence inferred
from spectropolarimetric observations in the He i 10 830 Å triplet
Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.
2014A&A...566A..46O Altcode: 2014arXiv1403.7976O
Context. Determining the magnetic field vector in quiescent solar
prominences is possible by interpreting the Hanle and Zeeman effects
in spectral lines. However, observational measurements are scarce and
lack high spatial resolution. Aims: We determine the magnetic
field vector configuration along a quiescent solar prominence by
interpreting spectropolarimetric measurements in the He i 1083.0 nm
triplet obtained with the Tenerife Infrared Polarimeter installed at
the German Vacuum Tower Telescope of the Observatorio del Teide. Methods: The He i 1083.0 nm triplet Stokes profiles were analyzed
with an inversion code that takes the physics responsible for the
polarization signals in this triplet into account. The results are put
into a solar context with the help of extreme ultraviolet observations
taken with the Solar Dynamic Observatory and the Solar Terrestrial
Relations Observatory satellites. Results: For the most probable
magnetic field vector configuration, the analysis depicts a mean field
strength of 7 gauss. We do not find local variations in the field
strength except that the field is, on average, lower in the prominence
body than in the prominence feet, where the field strength reaches ~25
gauss. The averaged magnetic field inclination with respect to the local
vertical is ~77°. The acute angle of the magnetic field vector with the
prominence main axis is 24° for the sinistral chirality case and 58°
for the dextral chirality. These inferences are in rough agreement with
previous results obtained from the analysis of data acquired with lower
spatial resolutions. A movie is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322903/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: On the Inversion of the Scattering Polarization and the Hanle
Effect Signals in the Hydrogen Lyα Line
Authors: Ishikawa, R.; Asensio Ramos, A.; Belluzzi, L.; Manso Sainz,
R.; Štěpán, J.; Trujillo Bueno, J.; Goto, M.; Tsuneta, S.
2014ApJ...787..159I Altcode: 2014arXiv1404.0786I
Magnetic field measurements in the upper chromosphere and above,
where the gas-to-magnetic pressure ratio β is lower than unity,
are essential for understanding the thermal structure and dynamical
activity of the solar atmosphere. Recent developments in the theory and
numerical modeling of polarization in spectral lines have suggested
that information on the magnetic field of the chromosphere-corona
transition region could be obtained by measuring the linear polarization
of the solar disk radiation at the core of the hydrogen Lyα line at
121.6 nm, which is produced by scattering processes and the Hanle
effect. The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP)
sounding rocket experiment aims to measure the intensity (Stokes I)
and the linear polarization profiles (Q/I and U/I) of the hydrogen
Lyα line. In this paper, we clarify the information that the Hanle
effect can provide by applying a Stokes inversion technique based on
a database search. The database contains all theoretical Q/I and U/I
profiles calculated in a one-dimensional semi-empirical model of the
solar atmosphere for all possible values of the strength, inclination,
and azimuth of the magnetic field vector, though this atmospheric
region is highly inhomogeneous and dynamic. We focus on understanding
the sensitivity of the inversion results to the noise and spectral
resolution of the synthetic observations as well as the ambiguities and
limitation inherent to the Hanle effect when only the hydrogen Lyα is
used. We conclude that spectropolarimetric observations with CLASP can
indeed be a suitable diagnostic tool for probing the magnetism of the
transition region, especially when complemented with information on
the magnetic field azimuth that can be obtained from other instruments.

---------------------------------------------------------
Title: Upper Limits to the Magnetic Field in Central Stars of
Planetary Nebulae
Authors: Asensio Ramos, A.; Martínez González, M. J.; Manso Sainz,
R.; Corradi, R. L. M.; Leone, F.
2014ApJ...787..111A Altcode: 2014arXiv1404.2718A
More than about 20 central stars of planetary nebulae (CSPNs) have
been observed spectropolarimetrically, yet no clear, unambiguous
signal of the presence of a magnetic field in these objects has
been found. We perform a statistical (Bayesian) analysis of all the
available spectropolarimetric observations of CSPN to constrain the
magnetic fields in these objects. Assuming that the stellar field is
dipolar and that the dipole axis of the objects is oriented randomly
(isotropically), we find that the dipole magnetic field strength
is smaller than 400 G with 95% probability using all available
observations. The analysis introduced allows integration of future
observations to further constrain the parameters of the distribution,
and it is general, so that it can be easily applied to other classes of
magnetic objects. We propose several ways to improve the upper limits
found here.

---------------------------------------------------------
Title: Depolarizing Collisions with Hydrogen: Neutral and Singly
Ionized Alkaline Earths
Authors: Manso Sainz, Rafael; Roncero, Octavio; Sanz-Sanz, Cristina;
Aguado, Alfredo; Asensio Ramos, Andrés; Trujillo Bueno, Javier
2014ApJ...788..118M Altcode: 2014arXiv1404.6339M
Depolarizing collisions are elastic or quasielastic collisions
that equalize the populations and destroy the coherence between
the magnetic sublevels of atomic levels. In astrophysical plasmas,
the main depolarizing collider is neutral hydrogen. We consider
depolarizing rates on the lowest levels of neutral and singly
ionized alkali earths Mg I, Sr I, Ba I, Mg II, Ca II, and Ba II,
due to collisions with H°. We compute ab initio potential curves of
the atom-H° system and solve the quantum mechanical dynamics. From
the scattering amplitudes, we calculate the depolarizing rates for
Maxwellian distributions of colliders at temperatures T &lt;= 10,000
K. A comparative analysis of our results and previous calculations in
the literature is completed. We discuss the effect of these rates on
the formation of scattering polarization patterns of resonant lines
of alkali earths in the solar atmosphere, and their effect on Hanle
effect diagnostics of solar magnetic fields.

---------------------------------------------------------
Title: Determination of the cross-field density structuring in
coronal waveguides using the damping of transverse waves
Authors: Arregui, I.; Asensio Ramos, A.
2014A&A...565A..78A Altcode: 2014arXiv1404.0584A
Context. Time and spatial damping of transverse magnetohydrodynamic
(MHD) kink oscillations is a source of information on the cross-field
variation of the plasma density in coronal waveguides. Aims:
We show that a probabilistic approach to the problem of determining
the density structuring from the observed damping of transverse
oscillations enables us to obtain information on the two parameters
that characterise the cross-field density profile. Methods: The
inference is performed by computing the marginal posterior distributions
for density contrast and transverse inhomogeneity length-scale using
Bayesian analysis and damping ratios for transverse oscillations under
the assumption that damping is produced by resonant absorption. 
Results: The obtained distributions show that, for damping times of a
few oscillatory periods, low density-contrasts and short inhomogeneity
length scales are more plausible to explain observations. 
Conclusions: This means that valuable information on the cross-field
density profile can be obtained even if the inversion problem, with
two unknowns and one observable, is a mathematically ill-posed problem.

---------------------------------------------------------
Title: Investigating the sensitivity of observed spectral energy
distributions to clumpy torus properties in Seyfert galaxies
Authors: Ramos Almeida, C.; Alonso-Herrero, A.; Levenson, N. A.;
Asensio Ramos, A.; Rodríguez Espinosa, J. M.; González-Martín,
O.; Packham, C.; Martínez, M.
2014MNRAS.439.3847R Altcode: 2014arXiv1402.0345R; 2014MNRAS.tmp..444R
We present nuclear spectral energy distributions (SEDs) from 1 to
18 μm of a small sample of nearby, nearly face-on and undisturbed
Seyfert galaxies without prominent nuclear dust lanes. These nuclear
SEDs probe the central ∼35 pc of the galaxies, on average, and include
photometric and spectroscopic infrared (IR) data. We use these SEDs, the
clumpy torus models of Nenkova et al. and a Bayesian approach to study
the sensitivity of different IR wavelengths to the torus parameters. We
find that high angular resolution 8-13 μm spectroscopy alone reliably
constrains the number of clumps and their optical depth (N0
and τV). On the other hand, we need a combination of mid-
and near-IR subarcsecond resolution photometry to constrain torus width
and inclination, as well as the radial distribution of the clouds
(σ, i and q). For flat radial profiles (q = 0, 1), it is possible
to constrain the extent of the mid-IR-emitting dust within the torus
(Y) when N-band spectroscopy is available, in addition to near-IR
photometry. Finally, by fitting different combinations of average and
individual Seyfert 1 and Seyfert 2 data, we find that, in general,
for undisturbed, nearly face-on Seyferts without prominent nuclear dust
lanes, the minimum combination of data necessary to reliably constrain
all the torus parameters is J+K+M-band photometry + N-band spectroscopy.

---------------------------------------------------------
Title: Time Evolution of Plasma Parameters during the Rise of a
Solar Prominence Instability
Authors: Orozco Suárez, D.; Díaz, A. J.; Asensio Ramos, A.; Trujillo
Bueno, J.
2014ApJ...785L..10O Altcode: 2014arXiv1403.5640O
We present high-spatial resolution spectropolarimetric observations
of a quiescent hedgerow prominence taken in the He I 1083.0 nm
triplet. The observation consisted of a time series in sit-and-stare
mode of ~36 minutes duration. The spectrograph's slit crossed the
prominence body and we recorded the time evolution of individual
vertical threads. Eventually, we observed the development of a dark
Rayleigh-Taylor plume that propagated upward with a velocity, projected
onto the plane of the sky, of 17 km s-1. Interestingly, the
plume apex collided with the prominence threads pushing them aside. We
inferred Doppler shifts, Doppler widths, and magnetic field strength
variations by interpreting the He I Stokes profiles with the HAZEL
code. The Doppler shifts show that clusters of threads move coherently
while individual threads have oscillatory patterns. Regarding the
plume we found strong redshifts (~9-12 km s-1) and large
Doppler widths (~10 km s-1) at the plume apex when it passed
through the prominence body and before it disintegrated. We associate
the redshifts with perspective effects while the Doppler widths are
more likely due to an increase in the local temperature. No local
variations of the magnetic field strength associated with the passage
of the plume were found; this leads us to conclude that the plumes are
no more magnetized than the surroundings. Finally, we found that some
of the threads' oscillations are locally damped, what allowed us to
apply prominence seismology techniques to infer additional prominence
physical parameters.

---------------------------------------------------------
Title: A search for magnetic fields on central stars in planetary
nebulae
Authors: Leone, F.; Corradi, R. L. M.; Martínez González, M. J.;
Asensio Ramos, A.; Manso Sainz, R.
2014A&A...563A..43L Altcode: 2014arXiv1401.6282L
Context. One of the possible mechanisms responsible for the panoply
of shapes in planetary nebulae is the presence of magnetic fields
that drive the ejection of ionized material during the proto-planetary
nebula phase. Aims: Therefore, detecting magnetic fields in such
objects is of key importance for understanding their dynamics. Still,
magnetic fields have not been detected using polarimetry in the central
stars of planetary nebulae. Methods: Circularly polarized light
spectra have been obtained with the Focal Reducer and Low Dispersion
Spectrograph at the Very Large Telescope of the European Southern
Observatory and the Intermediate dispersion Spectrograph and Imaging
System at the William Herschel Telescope. Twentythree planetary nebulae
that span very different morphology and evolutionary stages have been
selected. Most of central stars have been observed at different rotation
phases to point out evidence of magnetic variability. Results:
In this paper, we present the result of two observational campaigns
aimed to detect and measure the magnetic field in the central stars of
planetary nebulae on the basis of low resolution spectropolarimetry. In
the limit of the adopted method, we can state that large scale fields
of kG order are not hosted on the central star of planetary nebulae.

---------------------------------------------------------
Title: A meta-analysis of the magnetic line broadening in the solar
atmosphere
Authors: Asensio Ramos, A.
2014A&A...563A.114A Altcode: 2014arXiv1401.8111A
A multiline Bayesian analysis of the Zeeman broadening in the solar
atmosphere is presented. A hierarchical probabilistic model, based
on the simple but realistic Milne-Eddington approximation to the
solution of the radiative transfer equation is used to explain the
data in the optical and near infrared. Our method makes use of the
full line profiles of more than 500 spectral lines from 4000 Å to
1.8 μm. Although the problem suffers from a strong degeneracy between
the magnetic broadening and any other remaining broadening mechanism,
the hierarchical model allows the magnetic contribution to be isolated
with reliability. We obtain the cumulative distribution function for
the field strength and use it to put reliable upper limits on the
unresolved magnetic field strength in the solar atmosphere. The field
is below 160-180 G with a 90% probability.

---------------------------------------------------------
Title: Infrared Extinction in the Inner Milky Way through Red
Clump Giants
Authors: González-Fernández, C.; Asensio Ramos, A.; Garzón, F.;
Cabrera-Lavers, A.; Hammersley, P. L.
2014ApJ...782...86G Altcode: 2014arXiv1402.0083G
While the shape of the extinction curve in the infrared is considered
to be set and the extinction ratios between infrared bands are usually
taken to be approximately constant, a number of recent studies point to
either a spatially variable behavior of the exponent of the power law
or a different extinction law altogether. In this paper, we propose a
method to analyze the overall behavior of the interstellar extinction
by means of the red-clump population, and we apply it to those areas
of the Milky Way where the presence of interstellar matter is heavily
felt: areas located in 5° &lt; l &lt; 30° and b = 0°. We show that
the extinction ratios traditionally used for the near infrared could
be inappropriate for the inner Galaxy and we analyze the behavior of
the extinction law from 1 μm to 8 μm.

---------------------------------------------------------
Title: Magnetic, Thermal and Dynamical Evolution of AN M3.2 Two-Ribbon
Flare
Authors: Collados, Manuel; Kuckein, Christoph; Manso Sainz, Rafael;
Asensio Ramos, Andres
2014cosp...40E.568C Altcode:
On 2013, 17th May, a two-ribbon M3.2 flare took place in the solar
atmosphere on the active region AR 11748. The flare evolution was
observed at the German VTT of the Observatorio del Teide using the
instrument TIP-II, with spectropolarimetric measurements of the
photosphere (Si I at 1082.7 nm) and the chromosphere (Helium triplet
at 1083 nm). Simultaneous spectroscopic data of the chromospheric
spectral line of Ca II at 854.2 nm and filtergrams at Halpha were
also obtained. The flare evolution as observed from the ground can be
compared with the changes observed by AIA@SDO at different ultraviolet
wavelengths. The ground observations covered several hours, including
the pre-flare, impulsive, gradual and post-flare phases. We present
maps of the magnetic field, thermal and dynamical properties of the
region during its evolution from pre- to post-flare phase.

---------------------------------------------------------
Title: A first look into the magnetic field configuration of
prominence threads using spectropolarimetric data
Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.
2014IAUS..300..112O Altcode: 2014IAUS..300..112S; 2013arXiv1310.0257O
We show preliminary results of an ongoing investigation aimed at
determining the configuration of the magnetic field vector in the
threads of a quiescent hedgerow solar prominence using high-spatial
resolution spectropolarimetric observations taken in the He I 1083.0
nm multiplet. The data consist of a two-dimensional map of a quiescent
hedgerow prominence showing vertical threads. The observations were
obtained with the Tenerife Infrared Polarimeter attached to the German
Vacuum Tower Telescope at the Observatorio del Teide (Spain). The He
I 1083.0 nm Stokes signals are interpreted with an inversion code,
which takes into account the key physical processes that generate
and/or modify circular and linear polarization signals in the He I
1083.0 nm triplet: the Zeeman effect, anisotropic radiation pumping,
and the Hanle effect. We present initial results of the inversions,
i.e, the strength and orientation of the magnetic field vector along
the prominence and in prominence threads.

---------------------------------------------------------
Title: Uncovering the Deeply Embedded Active Galactic Nucleus Activity
in the Nuclear Regions of the Interacting Galaxy Arp 299
Authors: Alonso-Herrero, A.; Roche, P. F.; Esquej, P.;
González-Martín, O.; Pereira-Santaella, M.; Ramos Almeida, C.;
Levenson, N. A.; Packham, C.; Asensio Ramos, A.; Mason, R. E.;
Rodríguez Espinosa, J. M.; Alvarez, C.; Colina, L.; Aretxaga, I.;
Díaz-Santos, T.; Perlman, E.; Telesco, C. M.
2013ApJ...779L..14A Altcode: 2013arXiv1311.3446A
We present mid-infrared (MIR) 8-13 μm spectroscopy of the nuclear
regions of the interacting galaxy Arp 299 (IC 694+NGC 3690) obtained
with CanariCam (CC) on the 10.4 m Gran Telescopio Canarias (GTC). The
high angular resolution (~0.”3-0.”6) of the data allows us to probe
nuclear physical scales between 60 and 120 pc, which is a factor of
10 improvement over previous MIR spectroscopic observations of this
system. The GTC/CC spectroscopy displays evidence of deeply embedded
active galactic nucleus (AGN) activity in both nuclei. The GTC/CC
nuclear spectrum of NGC 3690/Arp 299-B1 can be explained as emission
from AGN-heated dust in a clumpy torus with both a high covering factor
and high extinction along the line of sight. The estimated bolometric
luminosity of the AGN in NGC 3690 is 3.2 ± 0.6 × 1044
erg s-1. The nuclear GTC/CC spectrum of IC 694/Arp 299-A
shows 11.3 μm polycyclic aromatic hydrocarbon emission stemming
from a deeply embedded (AV ~ 24 mag) region of less than
120 pc in size. There is also a continuum-emitting dust component. If
associated with the putative AGN in IC 694, we estimate that it would
be approximately five times less luminous than the AGN in NGC 3690. The
presence of dual AGN activity makes Arp 299 a good example to study
such phenomena in the early coalescence phase of interacting galaxies.

---------------------------------------------------------
Title: Improved Search of Principal Component Analysis Databases
for Spectro-polarimetric Inversion
Authors: Casini, R.; Asensio Ramos, A.; Lites, B. W.; López Ariste, A.
2013ApJ...773..180C Altcode: 2013arXiv1307.0061C
We describe a simple technique for the acceleration of
spectro-polarimetric inversions based on principal component analysis
(PCA) of Stokes profiles. This technique involves the indexing of the
database models based on the sign of the projections (PCA coefficients)
of the first few relevant orders of principal components of the
four Stokes parameters. In this way, each model in the database can
be attributed a distinctive binary number of 24n bits,
where n is the number of PCA orders used for the indexing. Each of
these binary numbers (indices) identifies a group of "compatible"
models for the inversion of a given set of observed Stokes profiles
sharing the same index. The complete set of the binary numbers so
constructed evidently determines a partition of the database. The
search of the database for the PCA inversion of spectro-polarimetric
data can profit greatly from this indexing. In practical cases it
becomes possible to approach the ideal acceleration factor of 24n
 as compared to the systematic search of a non-indexed database
for a traditional PCA inversion. This indexing method relies on the
existence of a physical meaning in the sign of the PCA coefficients
of a model. For this reason, the presence of model ambiguities and of
spectro-polarimetric noise in the observations limits in practice the
number n of relevant PCA orders that can be used for the indexing.

---------------------------------------------------------
Title: Chromospheric Lyman Alpha SpectroPolarimeter: CLASP
Authors: Kobayashi, Ken; Kano, R.; Trujillo Bueno, J.; Winebarger,
A. R.; Cirtain, J. W.; Bando, T.; De Pontieu, B.; Ishikawa, R.;
Katsukawa, Y.; Kubo, M.; Narukage, N.; Sakao, T.; Tsuneta, S.;
Auchère, F.; Asensio Ramos, A.; Belluzzi, L.; Carlsson, M.; Casini,
R.; Hara, H.; Ichimoto, K.; Manso Sainz, R.; Shimizu, T.; Stepan,
J.; Suematsu, Y.; Holloway, T.
2013SPD....44..142K Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a VUV
spectropolarimeter optimized for measuring the linear polarization of
the Lyman-alpha line (121.6 nm). The Lyman-alpha line is predicted to
show linear polarization caused by atomic scattering in the chromosphere
and modified by the magnetic field through the Hanle effect. The
Hanle effect is sensitive to weaker magnetic fields than Zeeman
effect, and is not canceled by opposing fields, making it sensitive
to tangled or unresolved magnetic field structures. These factors make
the Hanle effect a valuable tool for probing the magnetic field in the
chromosphere above the quiet sun. To meet this goal, CLASP is designed
to measure linear polarization with 0.1% polarization sensitivity
at 0.01 nm spectral resolution and 10" spatial resolution. CLASP is
scheduled to be launched in 2015.

---------------------------------------------------------
Title: Coronal loop physical parameters from the analysis of multiple
observed transverse oscillations
Authors: Asensio Ramos, A.; Arregui, I.
2013A&A...554A...7A Altcode: 2013arXiv1304.1921A
The analysis of quickly damped transverse oscillations of solar coronal
loops using magneto-hydrodynamic seismology allows us to infer physical
parameters that are difficult to measure otherwise. Under the assumption
that such damped oscillations are due to the resonant conversion
of global modes into Alfvén oscillations of the tube surface, we
carry out a global seismological analysis of a large set of coronal
loops. A Bayesian hierarchical method is used to obtain distributions
for coronal loop physical parameters by means of a global analysis of
a large number of observations. The resulting distributions summarize
global information and constitute data-favoured information that can
be used for the inversion of individual events. The results strongly
suggest that internal Alfvén travel times along the loop are longer
than 100 s and shorter than 540 s with 95% probability. Likewise,
the density contrast between the loop interior and the surrounding is
larger than 2.3 and below 6.9 with 95% probability.

---------------------------------------------------------
Title: Determination of Transverse Density Structuring from
Propagating Magnetohydrodynamic Waves in the Solar Atmosphere
Authors: Arregui, I.; Asensio Ramos, A.; Pascoe, D. J.
2013ApJ...769L..34A Altcode: 2013arXiv1304.6869A
We present a Bayesian seismology inversion technique for propagating
magnetohydrodynamic transverse waves observed in coronal waveguides. The
technique uses theoretical predictions for the spatial damping
of propagating kink waves in transversely inhomogeneous coronal
waveguides. It combines wave amplitude damping length scales
along the waveguide with theoretical results for resonantly damped
propagating kink waves to infer the plasma density variation across
the oscillating structures. Provided that the spatial dependence of
the velocity amplitude along the propagation direction is measured
and the existence of two different damping regimes is identified, the
technique would enable us to fully constrain the transverse density
structuring, providing estimates for the density contrast and its
transverse inhomogeneity length scale.

---------------------------------------------------------
Title: A PCA approach to stellar effective temperatures
Authors: Muñoz Bermejo, J.; Asensio Ramos, A.; Allende Prieto, C.
2013A&A...553A..95M Altcode: 2013arXiv1303.7218M
Context. The derivation of the effective temperature of
a star is a critical first step in a detailed spectroscopic
analysis. Spectroscopic methods suffer from systematic errors related
to model simplifications. Photometric methods may be more robust, but
are exposed to the distortions caused by interstellar reddening. Direct
methods are difficult to apply, since fundamental data of high accuracy
are hard to obtain. Aims: We explore a new approach in which the
spectrum is used to characterize a star's effective temperature based
on a calibration established by a small set of standard stars. Methods: We perform principal component analysis on homogeneous
libraries of stellar spectra, then calibrate a relationship between
the principal components and the effective temperature using a set of
stars with reliable effective temperatures. Results: We find
that our procedure gives excellent consistency when spectra from a
homogenous set of observations are used. Systematic offsets may appear
when combining observations from different sources. Using as reference
the spectra of stars with high-quality spectroscopic temperatures
in the Elodie library, we define a temperature scale for FG-type
disk dwarfs with an internal consistency of about 50 K, in excellent
agreement with temperatures from direct determinations and widely used
scales based on the infrared flux method. Tables 2, 4, 5, and
reduced spectra are only available at the CDS via anonymous ftp to
<A href="http://cdsarc.u-strasbg.fr>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/553/A95</A>

---------------------------------------------------------
Title: Measuring vector magnetic fields in solar prominences
Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.
2013hsa7.conf..786O Altcode: 2012arXiv1211.2119O
We present spectropolarimetric observations in the He I 1083.0 nm
multiplet of a quiescent, hedgerow solar prominence. The data were taken
with the Tenerife Infrared Polarimeter attached to the German Vacuum
Tower Telescope at the Observatorio del Teide (Tenerife; Canary Islands;
Spain). The observed He I circular and linear polarization signals
are dominated by the Zeeman effect and by atomic level polarization
and the Hanle effect, respectively. These observables are sensitive
to the strength and orientation of the magnetic field vector at each
spatial point of the field of view. We determine the magnetic field
vector of the prominence by applying the HAZEL inversion code to the
observed Stokes profiles. We briefly discuss the retrieved magnetic
field vector configuration.

---------------------------------------------------------
Title: Signal detection for spectroscopy and polarimetry
Authors: Asensio Ramos, A.; Manso Sainz, R.
2013hsa7.conf..771A Altcode:
Spectroscopic and spectropolarimetric observations with high
spectral resolution provide extremely rich information on the
physical conditions of distant celestial objects; sometimes, even the
mere presence of a spectroscopic or polarimetric pattern may offer
fundamental insights. But these are photon-starving techniques. Signals
are often at the noise level or buried in it and, many times, just
detection proves difficult. Here we present a Bayesian technique for
the detection of spectropolarimetric signals based on the application
of the non-parametric relevance vector machine to the observations,
which allows computing the evidence for the presence of a signal and
its most probable value.

---------------------------------------------------------
Title: VizieR Online Data Catalog: PCA approach to stellar effective
temperatures (Bermejo+, 2013)
Authors: Bermejo, J. M.; Asensio Ramos, A.; Allende Prieto, C.
2013yCat..35530095B Altcode: 2013yCat..35539095B
Effective temperatures, derived for stars with observations in the
Elodie library or the Elodie archive, from a PCA-based spectroscopic
calibration. (3 data files).

---------------------------------------------------------
Title: Bayesian Analysis of Multiple Harmonic Oscillations in the
Solar Corona
Authors: Arregui, I.; Asensio Ramos, A.; Díaz, A. J.
2013ApJ...765L..23A Altcode: 2013arXiv1302.3393A
The detection of multiple mode harmonic kink oscillations in coronal
loops enables us to obtain information on coronal density stratification
and magnetic field expansion using seismology inversion techniques. The
inference is based on the measurement of the period ratio between the
fundamental mode and the first overtone and theoretical results for
the period ratio under the hypotheses of coronal density stratification
and magnetic field expansion of the wave guide. We present a Bayesian
analysis of multiple mode harmonic oscillations for the inversion of
the density scale height and magnetic flux tube expansion under each
of the hypotheses. The two models are then compared using a Bayesian
model comparison scheme to assess how plausible each one is given our
current state of knowledge.

---------------------------------------------------------
Title: The Filling Factor-Radius Relation for 58 H II Regions across
the Disk of NGC 6946
Authors: Cedrés, Bernabé; Beckman, John E.; Bongiovanni,
Ángel; Cepa, Jordi; Asensio Ramos, Andrés; Giammanco, Corrado;
Cabrera-Lavers, Antonio; Alfaro, Emilio J.
2013ApJ...765L..24C Altcode: 2013arXiv1302.1009C
Using the OSIRIS tunable narrowband imager on the 10.4 m GTC (La
Palma), we have mapped the SAB(rs)cd galaxy NGC 6946 over a ~7.3
× 7.5 arcmin2 field in the emission lines of the [S II]
λλ6717, 6731 doublet, and in Hα. From these maps we have produced
catalogs of the Hα luminosities and effective radii of 557 H II
regions across the disk, and derived the [S II] emission line ratios
of 370 of these. The Hα observations were used to derive the mean
luminosity-weighted electron densities for the regions of the sample,
while the [S II] line ratios allowed us to derive values of the in situ
electron densities in the denser zones from which the major fraction
of the radiation in these lines is emitted for 58 of the regions. This
is by far the largest data set of its kind for a single galaxy. A
classical two-phase model is used to derive the filling factors of
the regions. We find that although the mean electron density decreases
with the square root of the radius of the regions, the in situ density
is essentially independent of this radius. Thus the filling factor
falls systematically, as the radius and the luminosity of the regions
increases, with a power law of exponent -2.23 between filling factor
and radius. These measurements should enhance the perspectives for
more refined physical models of H II regions.

---------------------------------------------------------
Title: VizieR Online Data Catalog: PCA approach to stellar effective
temperatures (Bermejo+, 2013)
Authors: Munoz Bermejo, J.; Asensio Ramos, A.; Allende Prieto, C.
2013yCat..35530095M Altcode: 2013yCat..35539095M
Effective temperatures, derived for stars with observations in the
Elodie library or the Elodie archive, from a PCA-based spectroscopic
calibration. (3 data files).

---------------------------------------------------------
Title: Application of Bayesian Inference and Model Comparison
Techniques to Solar Atmospheric Seismology
Authors: Arregui, I.; Asensio Ramos, A.; Pascoe, D. J.; Diaz, A. J.
2013enss.confE.131A Altcode:
Wave activity is ubiquitous in the solar atmosphere. The detection and
analysis of waves and oscillations is important for our understanding
of solar atmospheric physics. Seismology deals with the determination
of difficult to measure physical parameters by a comparison between
observed and theoretical wave properties. We present recent results form
the application of Bayesian inference and model comparison techniques
to seismology. In the first example, quickly damped transverse coronal
loop oscillation data are inverted to obtain estimates for the density
contrast, the transverse inhomogeneity length scale, and the Alfvén
speed in the oscillating loops. In the second example, we use the
detection of multiple mode harmonic kink oscillations in coronal
loops to obtain information on coronal density stratification and
magnetic field expansion. The inference is based on the measurement
of period ratios and their deviation due to the hypotheses of either
coronal density stratification or magnetic field expansion of the wave
guide. The two models are compared using a Bayesian model comparison
scheme to assess how plausible each one is, given our current state
of knowledge. In the last example, the spatial damping of propagating
waves and the characteristic damping length scales are used to obtain
estimates for the plasma density variation across the oscillating
structures. This method could be applied to extended regions in
the corona for obtaining information about the cross-field density
structuring of the medium where these waves propagate.

---------------------------------------------------------
Title: Temporal Evolution of the Scattering Polarization of the Ca
II IR Triplet in Hydrodynamical Models of the Solar Chromosphere
Authors: Carlin, E. S.; Asensio Ramos, A.; Trujillo Bueno, J.
2013ApJ...764...40C Altcode: 2012arXiv1210.1525C
Velocity gradients in a stellar atmospheric plasma have an effect
on the anisotropy of the radiation field that illuminates each
point within the medium, and this may in principle influence the
scattering line polarization that results from the induced atomic level
polarization. Here, we analyze the emergent linear polarization profiles
of the Ca II infrared triplet after solving the radiative transfer
problem of scattering polarization in time-dependent hydrodynamical
models of the solar chromosphere, taking into account the effect of the
plasma macroscopic velocity on the atomic level polarization. We discuss
the influence that the velocity and temperature shocks in the considered
chromospheric models have on the temporal evolution of the scattering
polarization signals of the Ca II infrared lines as well as on the
temporally averaged profiles. Our results indicate that the increase
of the linear polarization amplitudes caused by macroscopic velocity
gradients may be significant in realistic situations. We also study
the effect of the integration time, the microturbulent velocity, and
the photospheric dynamical conditions, and discuss the feasibility of
observing with large-aperture telescopes the temporal variation of the
scattering polarization profiles. Finally, we explore the possibility
of using a Hanle effect line-ratio technique in the IR triplet of Ca
II to facilitate magnetic field diagnostics in dynamic situations.

---------------------------------------------------------
Title: Returning magnetic flux in sunspot penumbrae
Authors: Ruiz Cobo, B.; Asensio Ramos, A.
2013A&A...549L...4R Altcode: 2012arXiv1211.6335R
 Aims: We study the presence of reversed polarity magnetic flux in
sunspot penumbra. Methods: We applied a new regularized method to
deconvolve spectropolarimetric data observed with the spectropolarimeter
SP onboard Hinode. The new regularization is based on a principal
component decomposition of the Stokes profiles. The resulting Stokes
profiles were inverted to infer the magnetic field vector using SIR. Results: We find, for the first time, reversed polarity fields at
the border of many bright penumbral filaments in the whole penumbra.

---------------------------------------------------------
Title: Constraining clumpy dusty torus models using optimized
filter sets
Authors: Asensio Ramos, A.; Ramos Almeida, C.
2013MNRAS.428..195A Altcode: 2012MNRAS.tmp...39R; 2012arXiv1209.3870A
Recent success in explaining several properties of the dusty torus
around the central engine of active galactic nuclei has been gathered
with the assumption of clumpiness. The properties of such clumpy dusty
tori can be inferred by analysing spectral energy distributions (SEDs),
sometimes with scarce sampling given that large aperture telescopes and
long integration times are needed to get good spatial resolution and
signal. We aim at using the information already present in the data
and the assumption of clumpy dusty torus, in particular, the CLUMPY
models of Nenkova et al., to evaluate the optimum next observation
such that we maximize the constraining power of the new observed
photometric point. To this end, we use the existing and barely applied
idea of Bayesian adaptive exploration, a mixture of Bayesian inference,
prediction and decision theories. The result is that the new photometric
filter we use is the one that maximizes the expected utility, which
we approximate with the entropy of the predictive distribution. In
other words, we have to sample where there is larger variability
in the SEDs compatible with the data with what we know of the model
parameters. We show that Bayesian adaptive exploration can be used to
suggest new observations, and ultimately optimal filter sets, to better
constrain the parameters of the clumpy dusty torus models. In general,
we find that the region between 10 and 200 μm produces the largest
increase in the expected utility, although sub-mm data from Atacama
Large Millimeter Array also prove to be useful. It is important to
note that here we are not considering the angular resolution of the
data, which is key when constraining torus parameters. Therefore,
the expected utilities derived from this methodology must be weighted
with the spatial resolution of the data.

---------------------------------------------------------
Title: Evidence for Rotational Motions in the Feet of a Quiescent
Solar Prominence
Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.
2012ApJ...761L..25O Altcode: 2012arXiv1211.6980O
We present observational evidence of apparent plasma rotational motions
in the feet of a solar prominence. Our study is based on spectroscopic
observations taken in the He I 1083.0 nm multiplet with the Tenerife
Infrared Polarimeter attached to the German Vacuum Tower Telescope. We
recorded a time sequence of spectra with 34 s cadence placing the slit
of the spectrograph almost parallel to the solar limb and crossing two
feet of an intermediate size, quiescent hedgerow prominence. The data
show opposite Doppler shifts, ±6 km s-1, at the edges of
the prominence feet. We argue that these shifts may be interpreted as
prominence plasma rotating counterclockwise around the vertical axis to
the solar surface as viewed from above. The evolution of the prominence
seen in EUV images taken with the Solar Dynamics Observatory provided
us with clues to interpret the results as swirling motions. Moreover,
time-distance images taken far from the central wavelength show
plasma structures moving parallel to the solar limb with velocities
of about 10-15 km s-1. Finally, the shapes of the observed
intensity profiles suggest the presence of, at least, two components
at some locations at the edges of the prominence feet. One of them is
typically Doppler shifted (up to ~20 km s-1) with respect to
the other, thus suggesting the existence of supersonic counter-streaming
flows along the line of sight.

---------------------------------------------------------
Title: Constraining clumpy dusty torus models using optimized
filter sets
Authors: Asensio Ramos, A.; Ramos Almeida, C.
2012toru.work..215A Altcode:
Recent success in explaining several properties of the dusty torus
around the central engine of active galactic nuclei has been gathered
with the assumption of clumpiness. The properties of such clumpy dusty
tori can be inferred by analyzing spectral energy distributions (SEDs),
sometimes with scarce sampling given that large aperture telescopes
and long integration times are needed to get good spatial resolution
and signal. We apply the formalism of Bayesian adaptive exploration
to evaluate the optimum next observation such that we maximize the
constraining power of the new observed photometric point. In general, we
find that the region between 10 and 200 um produces the largest increase
in the expected utility, although sub-mm data from ALMA also prove to
be useful. It is important to note that here we are not considering
the angular resolution of the data, which is key when con- straining
torus parameters. Therefore, the expected utilities derived from this
methodology must be weighted with the spatial resolution of the data.

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Title: Extracting Information from the Data Flood of New Solar
Telescopes: Brainstorming
Authors: Asensio Ramos, A.
2012ASPC..463..215A Altcode: 2012arXiv1210.2682A
Extracting magnetic and thermodynamic information from
spectropolarimetric observations is a difficult and time consuming
task. The amount of science-ready data that will be generated by the
new family of large solar telescopes is so large that we will be forced
to modify the present approach to inference. In this contribution,
I propose several possible ways that might be useful for extracting
the thermodynamic and magnetic properties of solar plasmas from such
observations quickly.

---------------------------------------------------------
Title: Anomalous Circular Polarization Profiles in the He I 1083.0
nm Multiplet from Solar Spicules
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
R.; Beck, C.; Belluzzi, L.
2012ApJ...759...16M Altcode: 2012arXiv1209.2589M
We report Stokes vector observations of solar spicules and a prominence
in the He I 1083 nm multiplet carried out with the Tenerife Infrared
Polarimeter. The observations show linear polarization profiles that
are produced by scattering processes in the presence of a magnetic
field. After a careful data reduction, we demonstrate the existence of
extremely asymmetric Stokes V profiles in the spicular material that
we are able to model with two magnetic components along the line of
sight, and under the presence of atomic orientation in the energy
levels that give rise to the multiplet. We discuss some possible
scenarios that can generate the atomic orientation in spicules. We
stress the importance of spectropolarimetric observations across the
limb to distinguish such signals from observational artifacts.

---------------------------------------------------------
Title: Signal detection for spectroscopy and polarimetry
Authors: Asensio Ramos, A.; Manso Sainz, R.
2012A&A...547A.113A Altcode: 2012arXiv1209.6455A
The analysis of high spectral resolution spectroscopic and
spectropolarimetric observations constitutes a very powerful way of
inferring the dynamical, thermodynamical, and magnetic properties of
distant objects. However, these techniques starve photons, making
it difficult to use them for all purposes. A common problem is not
being able to detect a signal because it is buried on the noise at
the wavelength of some interesting spectral feature. This problem is
especially relevant for spectropolarimetric observations, because only a
small fraction of the received light is typically polarized. We present
in this paper a Bayesian technique for detecting spectropolarimetric
signals. The technique is based on applying the nonparametric relevance
vector machine to the observations, which allows us to compute the
evidence for the presence of the signal and compute the more probable
signal. The method is suited for analyzing data from experimental
instruments onboard space missions and rockets aiming at detecting
spectropolarimetric signals in unexplored regions of the spectrum,
such as the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP)
sounding rocket experiment.

---------------------------------------------------------
Title: Chromospheric Lyman-alpha spectro-polarimeter (CLASP)
Authors: Kano, Ryouhei; Bando, Takamasa; Narukage, Noriyuki; Ishikawa,
Ryoko; Tsuneta, Saku; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-nosuke; Hara, Hirohisa; Shimizu, Toshifumi; Suematsu, Yoshinori;
Ichimoto, Kiyoshi; Sakao, Taro; Goto, Motoshi; Kato, Yoshiaki; Imada,
Shinsuke; Kobayashi, Ken; Holloway, Todd; Winebarger, Amy; Cirtain,
Jonathan; De Pontieu, Bart; Casini, Roberto; Trujillo Bueno, Javier;
Štepán, Jiří; Manso Sainz, Rafael; Belluzzi, Luca; Asensio Ramos,
Andres; Auchère, Frédéric; Carlsson, Mats
2012SPIE.8443E..4FK Altcode:
One of the biggest challenges in heliophysics is to decipher the
magnetic structure of the solar chromosphere. The importance of
measuring the chromospheric magnetic field is due to both the key role
the chromosphere plays in energizing and structuring the outer solar
atmosphere and the inability of extrapolation of photospheric fields to
adequately describe this key boundary region. Over the last few years,
significant progress has been made in the spectral line formation
of UV lines as well as the MHD modeling of the solar atmosphere. It
is found that the Hanle effect in the Lyman-alpha line (121.567 nm)
is a most promising diagnostic tool for weaker magnetic fields in
the chromosphere and transition region. Based on this groundbreaking
research, we propose the Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP) to NASA as a sounding rocket experiment, for making the first
measurement of the linear polarization produced by scattering processes
and the Hanle effect in the Lyman-alpha line (121.567 nm), and making
the first exploration of the magnetic field in the upper chromosphere
and transition region of the Sun. The CLASP instrument consists
of a Cassegrain telescope, a rotating 1/2-wave plate, a dual-beam
spectrograph assembly with a grating working as a beam splitter, and
an identical pair of reflective polarization analyzers each equipped
with a CCD camera. We propose to launch CLASP in December 2014.

---------------------------------------------------------
Title: Analytical Calculation of Stokes Profiles of Rotating Stellar
Magnetic Dipole
Authors: Martínez González, M. J.; Asensio Ramos, A.
2012ApJ...755...96M Altcode: 2012arXiv1206.2502M
The observation of the polarization emerging from a rotating star
at different phases opens up the possibility to map the magnetic
field in the stellar surface thanks to the well-known Zeeman-Doppler
imaging. When the magnetic field is sufficiently weak, the circular
and linear polarization profiles locally in each point of the star are
proportional to the first and second derivatives of the unperturbed
intensity profile, respectively. We show that the weak-field
approximation (for weak lines in the case of linear polarization)
can be generalized to the case of a rotating star including the
Doppler effect and taking into account the integration on the stellar
surface. The Stokes profiles are written as a linear combination of
wavelength-dependent terms expressed as series expansions in terms of
Hermite polynomials. These terms contain the surface-integrated magnetic
field and velocity components. The direct numerical evaluation of these
quantities is limited to rotation velocities not larger than eight
times the Doppler width of the local absorption profiles. Additionally,
we demonstrate that in a rotating star, the circular polarization
flux depends on the derivative of the intensity flux with respect to
the wavelength and also on the profile itself. Likewise, the linear
polarization depends on the profile and on its first and second
derivatives with respect to the wavelength. We particularize the
general expressions to a rotating dipole.

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Title: Dead Calm Areas in the Very Quiet Sun
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
A.; Hijano, E.
2012ApJ...755..175M Altcode: 2012arXiv1206.4545M
We analyze two regions of the quiet Sun (35.6 × 35.6 Mm2)
observed at high spatial resolution (lsim100 km) in polarized light by
the IMaX spectropolarimeter on board the SUNRISE balloon. We identify
497 small-scale (~400 km) magnetic loops, appearing at an effective
rate of 0.25 loop h -1 arcsec-2 further, we
argue that this number and rate are underestimated by ~30%. However,
we find that these small dipoles do not appear uniformly on the solar
surface: their spatial distribution is rather filamentary and clumpy,
creating dead calm areas, characterized by a very low magnetic signal
and a lack of organized loop-like structures at the detection level
of our instruments, which cannot be explained as just statistical
fluctuations of a Poisson spatial process. We argue that this is an
intrinsic characteristic of the mechanism that generates the magnetic
fields in the very quiet Sun. The spatio-temporal coherences and the
clumpy structure of the phenomenon suggest a recurrent, intermittent
mechanism for the generation of magnetic fields in the quietest areas
of the Sun.

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Title: Testing the AGN Unification Model in the Infrared
Authors: Ramos Almeida, C.; Levenson, N. A.; Alonso-Herrero, A.;
Asensio Ramos, A.; Rodríguez Espinosa, J. M.; Pérez García, A. M.;
Packham, C.; Mason, R.; Radomski, J. T.; Díaz-Santos, T.
2012JPhCS.372a2004R Altcode: 2012arXiv1201.4240R
We present near-to-mid-infrared spectral energy distributions (SEDs) for
21 Seyfert galaxies, using subarcsecond resolution imaging data. Our aim
is to compare the properties Seyfert 1 (Sy1) and Seyfert 2 (Sy2) tori
using clumpy torus models and a Bayesian approach to fit the infrared
(IR) nuclear SEDs. These dusty tori have physical sizes smaller than
6 pc radius, as derived from our fits. Active galactic nuclei (AGN)
unification schemes account for a variety of observational differences
in terms of viewing geometry. However, we find evidence that strong
unification may not hold, and that the immediate dusty surroundings of
Sy1 and Sy2 nuclei are intrinsically different. The Type 2 tori studied
here are broader, have more clumps, and these clumps have lower optical
depths than those of Type 1 tori. The larger the covering factor of the
torus, the smaller the probability of having direct view of the AGN,
and vice-versa. In our sample, Sy2 tori have larger covering factors
(CT = 0.95±0.02) and smaller escape probabilities than
those of Sy1 (CT = 0.5±0.1). Thus, on the basis of the
results presented here, the classification of a Seyfert galaxy may
depend more on the intrinsic properties of the torus rather than on its
mere inclination, in contradiction with the simplest unification model.

---------------------------------------------------------
Title: Scattering Polarization in the Ca II Infrared Triplet with
Velocity Gradients
Authors: Carlin, E. S.; Manso Sainz, R.; Asensio Ramos, A.; Trujillo
Bueno, J.
2012ApJ...751....5C Altcode: 2012arXiv1203.4438C
Magnetic field topology, thermal structure, and plasma motions are the
three main factors affecting the polarization signals used to understand
our star. In this theoretical investigation, we focus on the effect
that gradients in the macroscopic vertical velocity field have on the
non-magnetic scattering polarization signals, establishing the basis for
general cases. We demonstrate that the solar plasma velocity gradients
may have a significant effect on the linear polarization produced by
scattering in chromospheric spectral lines. In particular, we show the
impact of velocity gradients on the anisotropy of the radiation field
and on the ensuing fractional alignment of the Ca II levels, and how
they can lead to an enhancement of the zero-field linear polarization
signals. This investigation remarks on the importance of knowing
the dynamical state of the solar atmosphere in order to correctly
interpret spectropolarimetric measurements, which is important, among
other things, for establishing a suitable zero-field reference case
to infer magnetic fields via the Hanle effect.

---------------------------------------------------------
Title: The Chromospheric Lyman-Alpha SpectroPolarimeter: CLASP
Authors: Kobayashi, K.; Kano, R.; Trujillo-Bueno, J.; Asensio Ramos,
A.; Bando, T.; Belluzzi, L.; Carlsson, M.; De Pontieu, R. C. B.; Hara,
H.; Ichimoto, K.; Ishikawa, R.; Katsukawa, Y.; Kubo, M.; Manso Sainz,
R.; Narukage, N.; Sakao, T.; Stepan, J.; Suematsu, Y.; Tsuneta, S.;
Watanabe, H.; Winebarger, A.
2012ASPC..456..233K Altcode:
The magnetic field plays a crucial role in the chromosphere and the
transition region, and our poor empirical knowledge of the magnetic
field in the upper chromosphere and transition region is a major
impediment to advancing the understanding of the solar atmosphere. The
Hanle effect promises to be a valuable alternative to Zeeman effect
as a method of measuring the magnetic field in the chromosphere and
transition region; it is sensitive to weaker magnetic fields, and
also sensitive to tangled, unresolved field structures. CLASP
is a sounding rocket experiment that aims to observe the Hanle effect
polarization of the Lyman α (1215.67Å) line in the solar chromosphere
and transition region, and prove the usefulness of this technique in
placing constraints on the magnetic field strength and orientation
in the low plasma-β region of the solar atmosphere. The Ly-α line
has been chosen because it is a chromospheric/transition-region line,
and because the Hanle effect polarization of this line is predicted to
be sensitive to 10-250 Gauss, encompassing the range of interest. The
CLASP instrument is designed to measure linear polarization in the
Ly-α line with a polarization sensitivity of 0.1%. The instrument is
currently funded for development. The optical design of the instrument
has been finalized, and an extensive series of component-level tests
are underway to validate the design.

---------------------------------------------------------
Title: Rotating discs and non-kinematic double peaks
Authors: Elitzur, Moshe; Asensio Ramos, Andrés.; Ceccarelli, Cecilia
2012MNRAS.422.1394E Altcode: 2012arXiv1202.1450E
Double-peaked line profiles are commonly considered a hallmark of
rotating discs, with the distance between the peaks a measure of the
rotation velocity. However, double-peaks can arise also from radiative
transfer effects in optically thick non-rotating sources. Utilizing
exact solutions of the line transfer problem we present a detailed study
of line emission from geometrically thin Keplerian discs. We derive
the conditions for emergence of kinematic double peaks in optically
thin and thick discs, and find that it is generally impossible to
disentangle the effects of kinematics and line opacity in observed
double-peaked profiles. Unless supplemented by additional information,
a double-peaked profile alone is not a reliable indicator of a rotating
disc. In certain circumstances, triple and quadruple profiles might
be better indicators of rotation in optically thick discs.

---------------------------------------------------------
Title: Model Selection for Spectropolarimetric Inversions
Authors: Asensio Ramos, A.; Manso Sainz, R.; Martínez González,
M. J.; Viticchié, B.; Orozco Suárez, D.; Socas-Navarro, H.
2012ApJ...748...83A Altcode: 2012arXiv1201.5063A
Inferring magnetic and thermodynamic information from
spectropolarimetric observations relies on the assumption of
a parameterized model atmosphere whose parameters are tuned by
comparison with observations. Often, the choice of the underlying
atmospheric model is based on subjective reasons. In other cases,
complex models are chosen based on objective reasons (for instance,
the necessity to explain asymmetries in the Stokes profiles) but it
is not clear what degree of complexity is needed. The lack of an
objective way of comparing models has, sometimes, led to opposing
views of the solar magnetism because the inferred physical scenarios
are essentially different. We present the first quantitative model
comparison based on the computation of the Bayesian evidence ratios for
spectropolarimetric observations. Our results show that there is not
a single model appropriate for all profiles simultaneously. Data with
moderate signal-to-noise ratios (S/Ns) favor models without gradients
along the line of sight. If the observations show clear circular and
linear polarization signals above the noise level, models with gradients
along the line are preferred. As a general rule, observations with large
S/Ns favor more complex models. We demonstrate that the evidence ratios
correlate well with simple proxies. Therefore, we propose to calculate
these proxies when carrying out standard least-squares inversions to
allow for model comparison in the future.

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Title: The Gaia-ESO Public Spectroscopic Survey
Authors: Gilmore, G.; Randich, S.; Asplund, M.; Binney, J.; Bonifacio,
P.; Drew, J.; Feltzing, S.; Ferguson, A.; Jeffries, R.; Micela, G.;
Negueruela, I.; Prusti, T.; Rix, H. -W.; Vallenari, A.; Alfaro, E.;
Allende-Prieto, C.; Babusiaux, C.; Bensby, T.; Blomme, R.; Bragaglia,
A.; Flaccomio, E.; François, P.; Irwin, M.; Koposov, S.; Korn, A.;
Lanzafame, A.; Pancino, E.; Paunzen, E.; Recio-Blanco, A.; Sacco,
G.; Smiljanic, R.; Van Eck, S.; Walton, N.; Aden, D.; Aerts, C.;
Affer, L.; Alcala, J. -M.; Altavilla, G.; Alves, J.; Antoja, T.;
Arenou, F.; Argiroffi, C.; Asensio Ramos, A.; Bailer-Jones, C.;
Balaguer-Nunez, L.; Bayo, A.; Barbuy, B.; Barisevicius, G.; Barrado
y Navascues, D.; Battistini, C.; Bellas Velidis, I.; Bellazzini, M.;
Belokurov, V.; Bergemann, M.; Bertelli, G.; Biazzo, K.; Bienayme, O.;
Bland-Hawthorn, J.; Boeche, C.; Bonito, S.; Boudreault, S.; Bouvier,
J.; Brandao, I.; Brown, A.; de Bruijne, J.; Burleigh, M.; Caballero,
J.; Caffau, E.; Calura, F.; Capuzzo-Dolcetta, R.; Caramazza, M.;
Carraro, G.; Casagrande, L.; Casewell, S.; Chapman, S.; Chiappini,
C.; Chorniy, Y.; Christlieb, N.; Cignoni, M.; Cocozza, G.; Colless,
M.; Collet, R.; Collins, M.; Correnti, M.; Covino, E.; Crnojevic,
D.; Cropper, M.; Cunha, M.; Damiani, F.; David, M.; Delgado, A.;
Duffau, S.; Edvardsson, B.; Eldridge, J.; Enke, H.; Eriksson, K.;
Evans, N. W.; Eyer, L.; Famaey, B.; Fellhauer, M.; Ferreras, I.;
Figueras, F.; Fiorentino, G.; Flynn, C.; Folha, D.; Franciosini,
E.; Frasca, A.; Freeman, K.; Fremat, Y.; Friel, E.; Gaensicke, B.;
Gameiro, J.; Garzon, F.; Geier, S.; Geisler, D.; Gerhard, O.; Gibson,
B.; Gomboc, A.; Gomez, A.; Gonzalez-Fernandez, C.; Gonzalez Hernandez,
J.; Gosset, E.; Grebel, E.; Greimel, R.; Groenewegen, M.; Grundahl,
F.; Guarcello, M.; Gustafsson, B.; Hadrava, P.; Hatzidimitriou, D.;
Hambly, N.; Hammersley, P.; Hansen, C.; Haywood, M.; Heber, U.; Heiter,
U.; Held, E.; Helmi, A.; Hensler, G.; Herrero, A.; Hill, V.; Hodgkin,
S.; Huelamo, N.; Huxor, A.; Ibata, R.; Jackson, R.; de Jong, R.;
Jonker, P.; Jordan, S.; Jordi, C.; Jorissen, A.; Katz, D.; Kawata,
D.; Keller, S.; Kharchenko, N.; Klement, R.; Klutsch, A.; Knude,
J.; Koch, A.; Kochukhov, O.; Kontizas, M.; Koubsky, P.; Lallement,
R.; de Laverny, P.; van Leeuwen, F.; Lemasle, B.; Lewis, G.; Lind,
K.; Lindstrom, H. P. E.; Lobel, A.; Lopez Santiago, J.; Lucas, P.;
Ludwig, H.; Lueftinger, T.; Magrini, L.; Maiz Apellaniz, J.; Maldonado,
J.; Marconi, G.; Marino, A.; Martayan, C.; Martinez-Valpuesta, I.;
Matijevic, G.; McMahon, R.; Messina, S.; Meyer, M.; Miglio, A.;
Mikolaitis, S.; Minchev, I.; Minniti, D.; Moitinho, A.; Momany, Y.;
Monaco, L.; Montalto, M.; Monteiro, M. J.; Monier, R.; Montes, D.;
Mora, A.; Moraux, E.; Morel, T.; Mowlavi, N.; Mucciarelli, A.; Munari,
U.; Napiwotzki, R.; Nardetto, N.; Naylor, T.; Naze, Y.; Nelemans, G.;
Okamoto, S.; Ortolani, S.; Pace, G.; Palla, F.; Palous, J.; Parker, R.;
Penarrubia, J.; Pillitteri, I.; Piotto, G.; Posbic, H.; Prisinzano,
L.; Puzeras, E.; Quirrenbach, A.; Ragaini, S.; Read, J.; Read, M.;
Reyle, C.; De Ridder, J.; Robichon, N.; Robin, A.; Roeser, S.; Romano,
D.; Royer, F.; Ruchti, G.; Ruzicka, A.; Ryan, S.; Ryde, N.; Santos,
N.; Sanz Forcada, J.; Sarro Baro, L. M.; Sbordone, L.; Schilbach, E.;
Schmeja, S.; Schnurr, O.; Schoenrich, R.; Scholz, R. -D.; Seabroke, G.;
Sharma, S.; De Silva, G.; Smith, M.; Solano, E.; Sordo, R.; Soubiran,
C.; Sousa, S.; Spagna, A.; Steffen, M.; Steinmetz, M.; Stelzer, B.;
Stempels, E.; Tabernero, H.; Tautvaisiene, G.; Thevenin, F.; Torra,
J.; Tosi, M.; Tolstoy, E.; Turon, C.; Walker, M.; Wambsganss, J.;
Worley, C.; Venn, K.; Vink, J.; Wyse, R.; Zaggia, S.; Zeilinger, W.;
Zoccali, M.; Zorec, J.; Zucker, D.; Zwitter, T.; Gaia-ESO Survey Team
2012Msngr.147...25G Altcode:
The Gaia-ESO Public Spectroscopic Survey has begun and will obtain high
quality spectroscopy of some 100000 Milky Way stars, in the field and
in open clusters, down to magnitude 19, systematically covering all the
major components of the Milky Way. This survey will provide the first
homogeneous overview of the distributions of kinematics and chemical
element abundances in the Galaxy. The motivation, organisation and
implementation of the Gaia-ESO Survey are described, emphasising the
complementarity with the ESA Gaia mission. Spectra from the very first
observing run of the survey are presented.

---------------------------------------------------------
Title: Influence of phase-diversity image reconstruction techniques
on circular polarization asymmetries
Authors: Asensio Ramos, A.; Martínez González, M. J.; Khomenko,
E.; Martínez Pillet, V.
2012A&A...539A..42A Altcode: 2011arXiv1111.2496A
Context. Full Stokes filter-polarimeters are key instruments for
investigating the rapid evolution of magnetic structures on the solar
surface. To this end, the image quality is routinely improved using
a-posteriori image reconstruction methods. Aims: We analyze
the robustness of circular polarization asymmetries to phase-diversity
image reconstruction techniques. Methods: We used snapshots of
magneto-hydrodynamical simulations carried out with different initial
conditions to synthesize spectra of the magnetically sensitive Fe
i line at 5250.2 Å. We degraded the synthetic profiles spatially
and spectrally to simulate observations with the IMaX full Stokes
filter-polarimeter. We also simulated the focused/defocused pairs of
images used by the phase-diversity algorithm for reconstruction and the
polarimetric modulation scheme. We assume that standard optimization
methods are able to infer the projection of the wavefront on the Zernike
polynomials with 10% precision. We also consider the less favorable case
of 25% precision. We obtain reconstructed monochromatic modulated images
that are later demodulated and compared with the original maps. 
Results: Although asymmetries are often difficult to define in the
quiet Sun due to the complexity of the Stokes V profiles, we show
how asymmetries are degraded with spatial and spectral smearing. The
results indicate that, although image reconstruction techniques reduce
the spatial smearing, they can modify the asymmetries of the profiles,
which are mainly caused by the appearance of spatially-correlated noise.

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Title: Inversion tools for chromospheric lines
Authors: Asensio Ramos, A.
2012decs.confE...1A Altcode:
Chromospheric lines are usually formed in non-local thermodynamical
equilibrium conditions. The radiation that we see with our telescopes
in a point of the solar atmosphere strongly depends on what are the
physical conditions in very distant regions. This highly complicates
the extraction of thermodynamical and magnetic information from the
observations. In this talk I discuss the complexity of the inversion
of chromospheric spectral lines, how to deal with them and the
main differences with the inversion of photospheric spectral lines:
non-locality and the presence of magnetic structures. I present the
tools we have to extract information from the relatively optical thin
lines of He I and from the optically thick Ca II infrared lines. I
will also discuss some extensions to these tools that I consider we
need to develop in the future.

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Title: Analytical maximum likelihood estimation of stellar magnetic
fields
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
A.; Belluzzi, L.
2012MNRAS.419..153M Altcode: 2011MNRAS.tmp.1583M; 2011arXiv1108.4366M
The polarized spectrum of stellar radiation encodes valuable information
on the conditions of stellar atmospheres and the magnetic fields
that permeate them. In this paper, we give explicit expressions to
estimate the magnetic field vector and its associated error from the
observed Stokes parameters. We study the solar case where specific
intensities are observed and then the stellar case, where we receive
the polarized flux. In the second case, we concentrate on the explicit
expression for the case of a slow rotator with a dipolar magnetic
field geometry. Moreover, we also give explicit formulae to retrieve
the magnetic field vector from the least-squares deconvolution (LSD)
profiles without assuming mean values for the LSD artificial spectral
line. The formulae have been obtained assuming that the spectral lines
can be described in the weak-field regime and using a maximum likelihood
approach. The errors are recovered by means of the Hermitian matrix. The
bias of the estimators is analysed in depth.

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Title: The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP)j
Authors: Kobayashi, K.; Tsuneta, S.; Trujillo Bueno, J.; Bando, T.;
Belluzzi, L.; Casini, R.; Carlsson, M.; Cirtain, J. W.; De Pontieu,
B.; Hara, H.; Ichimoto, K.; Ishikawa, R.; Kano, R.; Katsukawa, Y.;
Kim, T.; Kubo, M.; Manso Sainz, R.; Narukage, N.; Asensio Ramos,
A.; Robinson, B.; Sakao, T.; Shimizu, T.; Stepan, J.; Suematsu, Y.;
Watanabe, H.; West, E.; Winebarger, A. R.
2011AGUFM.P14C..05K Altcode:
We present an overview of the Chromospheric Lyman-Alpha
SpectroPolarimeter (CLASP) program. CLASP is a proposed sounding rocket
experiment currently under development as collaboration between Japan,
USA and Spain. The aim is to achieve the first measurement of magnetic
field in the upper chromosphere and transition region of the Sun
through the detection and measurement of Hanle effect polarization
of the Lyman alpha line. The Hanle effect (i.e. the magnetic field
induced modification of the linear polarization due to scattering
processes in spectral lines) is believed to be a powerful tool for
measuring the magnetic field in the upper chromosphere, as it is more
sensitive to weaker magnetic fields than the Zeeman effect, and also
sensitive to magnetic fields tangled at spatial scales too small to be
resolved. The Lyman-alpha (121.567 nm) line has been chosen because
it is a chromospheric/transition-region line, and because the Hanle
effect polarization of the Lyman-alpha line is predicted to be sensitive
to 10-250 Gauss, encompassing the range of interest. Hanle effect is
predicted to be observable as linear polarization or depolarization,
depending on the geometry, with a fractional polarization amplitude
varying between 0.1% and 1% depending on the strength and orientation of
the magnetic field. This quantification of the chromospheric magnetic
field requires a highly sensitive polarization measurement. The
CLASP instrument consists of a large aperture (287 mm) Cassegrain
telescope mated to a polarizing beamsplitter and a matched pair
of grating spectrographs. The polarizing beamsplitter consists
of a continuously rotating waveplate and a linear beamsplitter,
allowing simultaneous measurement of orthogonal polarizations and
in-flight self-calibration. Development of the instrument is underway,
and prototypes of all optical components have been tested using a
synchrotron beamline. The experiment is proposed for flight in 2014.

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Title: Spectrophotometric study of the inner Galaxy
Authors: Gonzalez-Fernandez, C.; Garzon, F.; Asensio-Ramos, A.
2011hsa6.conf..454G Altcode:
The study if the large scale structure and properties of the Milky Way
has always walked hand in hand with the availability of photometric
and spectroscopic large scale surveys. Using the data from programs
as 2MASS or UKIDSS, we show how we can derive large scale properties
of our Galaxy, such as the behavior of the interstellar extinction or
the spatial distribution of the stellar content of the inner Milky Way.

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Title: Bayesian Magnetohydrodynamic Seismology of Coronal Loops
Authors: Arregui, I.; Asensio Ramos, A.
2011ApJ...740...44A Altcode: 2011arXiv1107.3943A
We perform a Bayesian parameter inference in the context of resonantly
damped transverse coronal loop oscillations. The forward problem is
solved in terms of parametric results for kink waves in one-dimensional
flux tubes in the thin tube and thin boundary approximations. For
the inverse problem, we adopt a Bayesian approach to infer the most
probable values of the relevant parameters, for given observed periods
and damping times, and to extract their confidence levels. The posterior
probability distribution functions are obtained by means of Markov
Chain Monte Carlo simulations, incorporating observed uncertainties in
a consistent manner. We find well-localized solutions in the posterior
probability distribution functions for two of the three parameters
of interest, namely the Alfvén travel time and the transverse
inhomogeneity length scale. The obtained estimates for the Alfvén
travel time are consistent with previous inversion results, but the
method enables us to additionally constrain the transverse inhomogeneity
length scale and to estimate real error bars for each parameter. When
observational estimates for the density contrast are used, the method
enables us to fully constrain the three parameters of interest. These
results can serve to improve our current estimates of unknown physical
parameters in coronal loops and to test the assumed theoretical model.

---------------------------------------------------------
Title: Resolving the nuclear dust distribution of the Seyfert 2
galaxy NGC 3081
Authors: Ramos Almeida, C.; Sánchez-Portal, M.; Pérez García,
A. M.; Acosta-Pulido, J. A.; Castillo, M.; Asensio Ramos, A.;
González-Serrano, J. I.; Alonso-Herrero, A.; Rodríguez Espinosa,
J. M.; Hatziminaoglou, E.; Coia, D.; Valtchanov, I.; Pović, M.;
Esquej, P.; Packham, C.; Altieri, B.
2011MNRAS.417L..46R Altcode: 2011arXiv1107.2420R
We report far-infrared (FIR) imaging of the Seyfert 2 galaxy NGC
3081 in the range 70-500 μm, obtained with an unprecedented angular
resolution, using the Herschel Space Observatory instruments PACS and
SPIRE. The 11 kpc (∼70 arcsec) diameter star-forming ring of the
galaxy appears resolved up to 250 μm. We extracted IR (1.6-500 μm)
nuclear fluxes, that is active nucleus-dominated fluxes, and fitted
them with clumpy torus models, which successfully reproduce the FIR
emission with small torus sizes. Adding the FIR data to the near- and
mid-IR spectral energy distribution (SED) results in a torus radial
extent of Ro= 4+2- 1 pc, as well as
in a flat radial distribution of the clouds (i.e. the q parameter). At
wavelengths beyond 200 μm, cold dust emission at T= 28 ± 1 K from the
circumnuclear star-forming ring of 2.3 kpc (∼15 arcsec) in diameter
starts making a contribution to the nuclear emission. The dust in the
outer parts of the galaxy is heated by the interstellar radiation field
(19 ± 3 K).

---------------------------------------------------------
Title: Overview of Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP)
Authors: Narukage, Noriyuki; Tsuneta, Saku; Bando, Takamasa; Kano,
Ryouhei; Kubo, Masahito; Ishikawa, Ryoko; Hara, Hirohisa; Suematsu,
Yoshinori; Katsukawa, Yukio; Watanabe, Hiroko; Ichimoto, Kiyoshi;
Sakao, Taro; Shimizu, Toshifumi; Kobayashi, Ken; Robinson, Brian; Kim,
Tony; Winebarger, Amy; West, Edward; Cirtain, Jonathan; De Pontieu,
Bart; Casini, Roberto; Trujillo Bueno, Javier; Stepan, Jiri; Manso
Sainz, Rafael; Belluzzi, Luca; Asensio Ramos, Andres; Carlsson, Mats
2011SPIE.8148E..0HN Altcode: 2011SPIE.8148E..16N
The solar chromosphere is an important boundary, through which all of
the plasma, magnetic fields and energy in the corona and solar wind
are supplied. Since the Zeeman splitting is typically smaller than
the Doppler line broadening in the chromosphere and transition region,
it is not effective to explore weak magnetic fields. However, this is
not the case for the Hanle effect, when we have an instrument with
high polarization sensitivity (~ 0.1%). "Chromospheric Lyman- Alpha
SpectroPolarimeter (CLASP)" is the sounding rocket experiment to detect
linear polarization produced by the Hanle effect in Lyman-alpha line
(121.567 nm) and to make the first direct measurement of magnetic
fields in the upper chromosphere and lower transition region. To
achieve the high sensitivity of ~ 0.1% within a rocket flight (5
minutes) in Lyman-alpha line, which is easily absorbed by materials,
we design the optical system mainly with reflections. The CLASP
consists of a classical Cassegrain telescope, a polarimeter and a
spectrometer. The polarimeter consists of a rotating 1/2-wave plate
and two reflecting polarization analyzers. One of the analyzer also
works as a polarization beam splitter to give us two orthogonal linear
polarizations simultaneously. The CLASP is planned to be launched in
2014 summer.

---------------------------------------------------------
Title: HAZEL: HAnle and ZEeman Light
Authors: Asensio Ramos, Andrés; Trujillo Bueno, Javier; Landi
Degl'Innocenti, E.
2011ascl.soft09004A Altcode:
A big challenge in solar and stellar physics in the coming years
will be to decipher the magnetism of the solar outer atmosphere
(chromosphere and corona) along with its dynamic coupling with
the magnetic fields of the underlying photosphere. To this end, it
is important to develop rigorous diagnostic tools for the physical
interpretation of spectropolarimetric observations in suitably chosen
spectral lines. HAZEL is a computer program for the synthesis and
inversion of Stokes profiles caused by the joint action of atomic level
polarization and the Hanle and Zeeman effects in some spectral lines
of diagnostic interest, such as those of the He I 1083.0 nm and 587.6
nm (or D3) multiplets. It is based on the quantum theory of spectral
line polarization, which takes into account in a rigorous way all
the relevant physical mechanisms and ingredients (optical pumping,
atomic level polarization, level crossings and repulsions, Zeeman,
Paschen-Back and Hanle effects). The influence of radiative transfer
on the emergent spectral line radiation is taken into account through
a suitable slab model. The user can either calculate the emergent
intensity and polarization for any given magnetic field vector
or infer the dynamical and magnetic properties from the observed
Stokes profiles via an efficient inversion algorithm based on global
optimization methods.

---------------------------------------------------------
Title: Torus and Active Galactic Nucleus Properties of Nearby Seyfert
Galaxies: Results from Fitting Infrared Spectral Energy Distributions
and Spectroscopy
Authors: Alonso-Herrero, Almudena; Ramos Almeida, Cristina; Mason,
Rachel; Asensio Ramos, Andrés; Roche, Patrick F.; Levenson, Nancy
A.; Elitzur, Moshe; Packham, Christopher; Rodríguez Espinosa, José
Miguel; Young, Stuart; Díaz-Santos, Tanio; Pérez-García, Ana M.
2011ApJ...736...82A Altcode: 2011arXiv1105.2368A
We used the CLUMPY torus models and a Bayesian approach to fit the
infrared spectral energy distributions and ground-based high angular
resolution mid-infrared spectroscopy of 13 nearby Seyfert galaxies. This
allowed us to put tight constraints on torus model parameters such as
the viewing angle i, the radial thickness of the torus Y, the angular
size of the cloud distribution σtorus, and the average
number of clouds along radial equatorial rays N 0. We
found that the viewing angle i is not the only parameter controlling
the classification of a galaxy into type 1 or type 2. In principle,
type 2s could be viewed at any viewing angle i as long as there is
one cloud along the line of sight. A more relevant quantity for clumpy
media is the probability for an active galactic nucleus (AGN) photon to
escape unabsorbed. In our sample, type 1s have relatively high escape
probabilities, P esc ~ 12%-44%, while type 2s, as expected,
tend to have very low escape probabilities. Our fits also confirmed that
the tori of Seyfert galaxies are compact with torus model radii in the
range 1-6 pc. The scaling of the models to the data also provided the
AGN bolometric luminosities L bol(AGN), which were found
to be in good agreement with estimates from the literature. When we
combined our sample of Seyfert galaxies with a sample of PG quasars
from the literature to span a range of L bol(AGN) ~
1043-1047 erg s-1, we found plausible
evidence of the receding torus. That is, there is a tendency for the
torus geometrical covering factor to be lower (f 2 ~ 0.1-0.3)
at high AGN luminosities than at low AGN luminosities (f 2
~ 0.9-1 at ~1043-1044 erg s-1). This
is because at low AGN luminosities the tori appear to have wider
angular sizes (larger σtorus) and more clouds along radial
equatorial rays. We cannot, however, rule out the possibility that this
is due to contamination by extended dust structures not associated
with the dusty torus at low AGN luminosities, since most of these in
our sample are hosted in highly inclined galaxies.

---------------------------------------------------------
Title: Characterization of telescope polarization properties across
the visible and near-infrared spectrum. Case study: the Dunn Solar
Telescope
Authors: Socas-Navarro, H.; Elmore, D.; Asensio Ramos, A.; Harrington,
D. M.
2011A&A...531A...2S Altcode: 2010arXiv1009.2866S
Accurate astrophysical polarimetry requires a proper characterization
of the polarization properties of the telescope and instrumentation
employed to obtain the observations. Determining the telescope and
instrument Muller matrix is becoming increasingly difficult with
the increase in aperture size, precision requirements and instrument
complexity of new and upcoming projects. We have carried out a detailed
multi-wavelength characterization of the Dunn Solar Telescope (DST)
at the National Solar Observatory/Sacramento Peak as a case study and
explore various possibilites for the determination of its polarimetric
properties. We show that the telescope model proposed in this paper is
more suitable than that in previous work in that it describes better
the wavelength dependence of aluminum-coated mirrors. We explore the
adequacy of the degrees of freedom allowed by the model using a novel
mathematical formalism. Finally, we investigate the use of polarimeter
calibration data taken at different times of the day to characterize
the telescope and find that very valuable information on the telescope
properties can be obtained in this manner. The results are also
consistent with the entrance window polarizer measurements. This general
method opens interesting possibilities for the calibration of future
large-aperture telescopes and precision polarimetric instrumentation.

---------------------------------------------------------
Title: Advection and dispersal of small magnetic elements in the
very quiet Sun
Authors: Manso Sainz, R.; Martínez González, M. J.; Asensio Ramos, A.
2011A&A...531L...9M Altcode:
We track small magnetic structures on very quiet regions (internetwork)
of the Sun. We follow the footpoints of small-scale magnetic loops that
appear on the photosphere at granular scales using spectropolarimetric
and magnetographic data obtained with Hinode. We find two different
regimes for their wanderings. Within granules (where they appear),
they seem to be passively advected by the plasma - which is
justified by their relatively low magnetic flux (~1016
Mx), and magnetic field strength (~200 G). The plasma flow thus
traced is roughly laminar with a characteristic mean velocity of 2
km s-1 and very low vorticity. Once the magnetic markers
reach intergranular lanes, they remain there and are buffeted by the
random flows of neighbouring granules and turbulent intergranules,
follow random walks, and disperse across the solar surface with a
diffusion constant of 195 km2 s-1. While on
their intergranular random walking, they may fall close to whirlpools
(on scales ≲400 km) associated with convective downdrafts, similar
to the events recently reported in mesogranular and supergranular cell
boundaries tracking magnetic bright points, which provides additional
evidence that these events are ubiquitous on the solar surface.

---------------------------------------------------------
Title: Clear detection of dusty torus signatures in a weak-line
radio galaxy: the case of PKS 0043-42
Authors: Ramos Almeida, C.; Dicken, D.; Tadhunter, C.; Asensio Ramos,
A.; Inskip, K. J.; Hardcastle, M. J.; Mingo, B.
2011MNRAS.413.2358R Altcode: 2011arXiv1101.1868R
We report the clearest detection to date of dusty torus signatures in a
weak-line radio galaxy (WLRG). The deep Spitzer InfraRed Spectrograph
(IRS) rest-frame mid-infrared (MIR) spectrum of the WLRG PKS 0043-42
(z= 0.116) shows a clear spectral turnover at λ≳ 20 μs suggestive
of warm dust, as well as a 9.7-μm silicate absorption feature. In
addition, the hard X-ray results, based on Chandra data, strongly
support a picture in which PKS 0043-42 has a torus and accretion disc
more typical of strong-line radio galaxies (SLRGs). The MIR and X-ray
spectra are markedly different from those of other WLRGs at similar
redshifts, and here we show that the former can be successfully
fitted with clumpy torus models with parameters characteristic of
Type-2 AGN tori: close to edge-on (i= 74°) and relatively broad
(σ= 60°), with an outer radius of 2 pc, NH= 1.6
±0.20.1× 1023 cm-2,
and AGN bolometric luminosity LAGNbol= 1.6
±0.20.1× 1044 erg s-1. The
presence of a compact torus in PKS 0043-42 provides evidence that this
WLRG is fuelled by cold, rather than hot, gas accretion. We suggest that
WLRGs are a diverse population, and PKS 0043-42 may represent a type of
radio galaxy in which the AGN activity has been recently re-triggered
as a consequence of intermittent gas supply, or in which the covering
factor of the narrow-line region (NLR) clouds is relatively low.

---------------------------------------------------------
Title: Exploring the Magnetic Fields of Solar Prominences and Spicules
via He I D3 Spectropolarimetry
Authors: Ramelli, R.; Trujillo Bueno, J.; Bianda, M.; Asensio Ramos, A.
2011ASPC..437..109R Altcode:
Over the last few years a large set of spectropolarimetric observations
of prominences and spicules in the He I D3 multiplet have
been collected at the observatory of the Istituto Ricerche Solari
Locarno (IRSOL), using increasingly improved versions of the ZIMPOL
polarimeter. The novel HAZEL inversion code of Stokes profiles generated
by the joint action of the Hanle and Zeeman effects is being applied
to this set of data, in order to infer the strength and geometry of
the magnetic field present in these structures. This paper presents
a brief overview of the most recent observations and inversions.

---------------------------------------------------------
Title: Bayesian Techniques for Inference
Authors: Asensio Ramos, A.
2011ASPC..437..135A Altcode:
I summarize the tools of Bayesian theory for inference that are recently
being applied to extract information from spectro-polarimetric data
obtained with the most advanced instruments. I present the machinery to
carry out inference, model comparison and model averaging, together
with some illustrative examples, with the hope that the power of
these techniques help us solve some of the problems inherent to the
inference of the physical properties of the solar plasma from noisy
spectro-polarimetric observations.

---------------------------------------------------------
Title: Testing the Unification Model for Active Galactic Nuclei in the
Infrared: Are the Obscuring Tori of Type 1 and 2 Seyferts Different?
Authors: Ramos Almeida, C.; Levenson, N. A.; Alonso-Herrero, A.;
Asensio Ramos, A.; Rodríguez Espinosa, J. M.; Pérez García, A. M.;
Packham, C.; Mason, R.; Radomski, J. T.; Díaz-Santos, T.
2011ApJ...731...92R Altcode: 2011arXiv1101.3335R
We present new mid-infrared imaging data for three Type-1 Seyfert
galaxies obtained with T-ReCS on the Gemini-South Telescope at
subarcsecond resolution. Our aim is to enlarge the sample studied in a
previous work to compare the properties of Type-1 and Type-2 Seyfert
tori using clumpy torus models and a Bayesian approach to fit the
infrared (IR) nuclear spectral energy distributions. Thus, the sample
considered here comprises 7 Type-1, 11 Type-2, and 3 intermediate-type
Seyferts. The unresolved IR emission of the Seyfert 1 galaxies can be
reproduced by a combination of dust heated by the central engine and
direct active galactic nucleus (AGN) emission, while for the Seyfert 2
nuclei only dust emission is considered. These dusty tori have physical
sizes smaller than 6 pc radius, as derived from our fits. Unification
schemes of AGN account for a variety of observational differences
in terms of viewing geometry. However, we find evidence that strong
unification may not hold and that the immediate dusty surroundings of
Type-1 and Type-2 Seyfert nuclei are intrinsically different. The Type-2
tori studied here are broader, have more clumps, and these clumps have
lower optical depths than those of Type-1 tori. The larger the covering
factor of the torus, the smaller the probability of having a direct
view of the AGN, and vice versa. In our sample, Seyfert 2 tori have
larger covering factors (CT = 0.95 ± 0.02) and smaller
escape probabilities (P esc = 0.05% ± 0.08
0.03%) than those of Seyfert 1 (CT = 0.5 ±
0.1; P esc = 18% ± 3%). All the previous differences
are significant according to the Kullback-Leibler divergence. Thus,
on the basis of the results presented here, the classification of a
Seyfert galaxy as a Type-1 or Type-2 depends more on the intrinsic
properties of the torus rather than on its mere inclination toward us,
in contradiction with the simplest unification model.

---------------------------------------------------------
Title: On the Inversion of Stokes Profiles with Local Stray-light
Contamination
Authors: Asensio Ramos, A.; Manso Sainz, R.
2011ApJ...731..125A Altcode: 2011arXiv1102.4703A
Obtaining the magnetic properties of non-resolved structures in the
solar photosphere is always challenging and problems arise because
the inversion is carried out through the numerical minimization of a
merit function that depends on the proposed model. We investigate the
reliability of inversions in which the stray-light contamination is
obtained from the same observations as a local average. In this case,
we show that it is fundamental to include the covariance between
the observed Stokes profiles and the stray-light contamination. The
ensuing modified merit function of the inversion process penalizes
large stray-light contaminations simply because of the presence of
positive correlations between the observables and the stray light,
fundamentally produced by spatially variable systematics. We caution
that if the wrong merit function is used, artificially large stray-light
contaminations might be inferred. Since this effect disappears if the
stray-light contamination is obtained as an average over the full field
of view, we recommend taking into account stray-light contamination
using a global approach.

---------------------------------------------------------
Title: Unnoticed Magnetic Field Oscillations in the Very Quiet Sun
Revealed by SUNRISE/IMaX
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
R.; Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; López Ariste,
A.; Schmidt, W.; Barthol, P.; Gandorfer, A.
2011ApJ...730L..37M Altcode: 2011arXiv1103.0145M
We present observational evidence for oscillations of magnetic flux
density in the quiet areas of the Sun. The majority of magnetic
fields on the solar surface have strengths of the order of or lower
than the equipartition field (300-500 G). This results in a myriad of
magnetic fields whose evolution is largely determined by the turbulent
plasma motions. When granules evolve they squash the magnetic field
lines together or pull them apart. Here, we report on the periodic
deformation of the shapes of features in circular polarization observed
at high resolution with SUNRISE. In particular, we note that the
area of patches with a constant magnetic flux oscillates with time,
which implies that the apparent magnetic field intensity oscillates
in antiphase. The periods associated with this oscillatory pattern
are compatible with the granular lifetime and change abruptly, which
suggests that these oscillations might not correspond to characteristic
oscillatory modes of magnetic structures, but to the forcing by granular
motions. In one particular case, we find three patches around the same
granule oscillating in phase, which means that the spatial coherence
of these oscillations can reach 1600 km. Interestingly, the same kind
of oscillatory phenomenon is also found in the upper photosphere.

---------------------------------------------------------
Title: Bayesian Inference of Solar and Stellar Magnetic Fields in
the Weak-field Approximation
Authors: Asensio Ramos, A.
2011ApJ...731...27A Altcode: 2011arXiv1102.2068A
The weak-field approximation is one of the simplest models that allows
us to relate the observed polarization induced by the Zeeman effect
with the magnetic field vector present on the plasma of interest. It is
usually applied for diagnosing magnetic fields in the solar and stellar
atmospheres. A fully Bayesian approach to the inference of magnetic
properties in unresolved structures is presented. The analytical
expression for the marginal posterior distribution is obtained,
from which we can obtain statistically relevant information about
the model parameters. The role of a priori information is discussed
and a hierarchical procedure is presented that gives robust results
that are almost insensitive to the precise election of the prior. The
strength of the formalism is demonstrated through an application to
IMaX data. Bayesian methods can optimally exploit data from filter
polarimeters given the scarcity of spectral information as compared
with spectro-polarimeters. The effect of noise and how it degrades our
ability to extract information from the Stokes profiles is analyzed
in detail.

---------------------------------------------------------
Title: Photospheric Hanle diagnostic of weak magnetic dipoles in stars
Authors: López Ariste, A.; Asensio Ramos, A.; González Fernández, C.
2011A&A...527A.120L Altcode: 2010arXiv1011.6288L
 Aims: We propose and explore a new diagnostic technique
based upon the linear polarization emitted in Hanle-sensitive lines
in disk-integrated stars where a dipolar magnetic field breaks the
rotational symmetry of the resonance scattering polarization 
Methods: A star with a simple dipolar field and a 1-0 spectral line were
used to compute polarization amplitudes and angles. Results:
Predicted amplitudes are low but within reach of present instruments
 Conclusions: A new application of the Hanle effect is proposed
and analyzed as a tool that allows measuring of some of the weakest
stellar magnetic fields.

---------------------------------------------------------
Title: Detecting photons with orbital angular momentum in extended
astronomical objects: application to solar observations
Authors: Uribe-Patarroyo, N.; Alvarez-Herrero, A.; López Ariste, A.;
Asensio Ramos, A.; Belenguer, T.; Manso Sainz, R.; Lemen, C.; Gelly, B.
2011A&A...526A..56U Altcode:
Context. The orbital angular momentum (OAM) of the photon is a
property of light from astronomical objects that has not yet been
measured. We propose a method of measuring the OAM spectrum of light
from an extended natural source, the Sun. Relating the OAM spectrum of
different solar areas to its structures could lead to a novel remote
sensing technique. Aims: We present a method for measuring the
OAM spectrum of solar photons. Methods: The THEMIS (Télescope
Héliographique pour l'Étude du Magnetisme et les Instabilités
Solaires is a 0.9 m solar telescope property of the French CNRS-INSU
at the Spanish Observatorio del Teide.) telescope is being used with
a novel phase-diversity technique. A spatial light modulator is placed
on one pupil image, and an ad-hoc optical setup allows the measurement
of two simultaneous phase-diverse images in the same CCD, with equal
optical paths. Results: Preliminary results show that very good
seeing is mandatory for this kind of observation. The method works in
the laboratory, and good seeing conditions in the 2010 campaign are
being awaited.

---------------------------------------------------------
Title: Compressed sensing for spectroscopy and polarimetry
Authors: Asensio Ramos, A.
2010ada..confE..15A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Spectroscopy from Photometry Using Sparsity: The SDSS Case
Study
Authors: Asensio Ramos, A.; Allende Prieto, C.
2010ApJ...719.1759A Altcode: 2010arXiv1006.5391A
We explore whether medium-resolution stellar spectra can be
reconstructed from photometric observations, taking advantage of the
highly compressible nature of the spectra. We formulate the spectral
reconstruction as a least-squares problem with a sparsity constraint. In
our test case using data from the Sloan Digital Sky Survey, only three
broadband filters are used as input. We demonstrate that reconstruction
using three principal components is feasible with these filters,
leading to median differences with respect to the original spectrum
smaller than 5%. We analyze the effect of uncertainties in the observed
magnitudes and find that the available high photometric precision
induces very small errors in the reconstruction. This process may
facilitate the extraction of purely spectroscopic quantities, such as
the overall metallicity, for hundreds of millions of stars for which
only photometric information is available, using standard analysis
techniques applied to the reconstructed spectra.

---------------------------------------------------------
Title: Image reconstruction with analytical point spread functions
Authors: Asensio Ramos, A.; López Ariste, A.
2010A&A...518A...6A Altcode: 2010arXiv1004.3278A
Context. The image degradation produced by atmospheric turbulence
and optical aberrations is usually alleviated using post-facto image
reconstruction techniques, even when observing with adaptive optics
systems. Aims: These techniques rely on the development of the
wavefront using Zernike functions and the non-linear optimization of a
certain metric. The resulting optimization procedure is computationally
heavy. Our aim is to alleviate this computational burden. 
Methods: We generalize the extended Zernike-Nijboer theory to carry
out the analytical integration of the Fresnel integral and present a
natural basis set for the development of the point spread function when
the wavefront is described using Zernike functions. Results:
We present a linear expansion of the point spread function in terms
of analytic functions, which, in addition, takes defocusing into
account in a natural way. This expansion is used to develop a very
fast phase-diversity reconstruction technique, which is demonstrated
in terms of some applications. Conclusions: We propose that
the linear expansion of the point spread function can be applied to
accelerate other reconstruction techniques in use that are based on
blind deconvolution.

---------------------------------------------------------
Title: Compressed sensing for next generation instruments
Authors: Asensio Ramos, A.
2010AN....331..652A Altcode:
This document discusses the possibility of using compressed sensing
techniques for measuring 2D spectro-polarimetric information using
only one etalon and a broad prefilter. Instead of using an etalon
and an extremely narrow prefilter (with all the subsequent problems of
alignment), the idea is to use multiplexing techniques to include in the
observations all the secondary peaks of the etalon. The reconstruction
of the signal is done under the assumption that it can be efficiently
reproduced in an orthogonal basis set.

---------------------------------------------------------
Title: Double-pass spectro-imaging: TUNIS
Authors: López Ariste, A.; Le Men, C.; Gelly, B.; Asensio Ramos, A.
2010AN....331..658L Altcode:
We present TUNIS, a double-pass spectro-imager built in THEMIS as a
proof-of-concept for EST. Basic concepts and selected first results
are shown. We introduce the concept of a Hadamard spectral mask as
a proposition to move forward from the present implementation of a
single-wavelength per image pixel to a more general one of multiplexed
spectral information that improves the temporal coherence of the
spectral measurement.

---------------------------------------------------------
Title: Small Magnetic Loops Connecting the Quiet Surface and the
Hot Outer Atmosphere of the Sun
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
A.; Bellot Rubio, L. R.
2010ApJ...714L..94M Altcode: 2010arXiv1003.1255M
Sunspots are the most spectacular manifestation of solar magnetism,
yet 99% of the solar surface remains "quiet" at any time of the solar
cycle. The quiet sun is not void of magnetic fields, though; they
are organized at smaller spatial scales and evolve relatively fast,
which makes them difficult to detect. Thus, although extensive quiet
Sun magnetism would be a natural driver to a uniform, steady heating of
the outer solar atmosphere, it is not clear what the physical processes
involved would be, due to lack of observational evidence. We report on
the topology and dynamics of the magnetic field in very quiet regions of
the Sun from spectropolarimetric observations of the Hinode satellite,
showing a continuous injection of magnetic flux with a well-organized
topology of Ω-loop from below the solar surface into the upper
layers. At first stages, when the loop travels across the photosphere,
it has a flattened (staple-like) geometry and a mean velocity ascent
of ~3 km s-1. When the loop crosses the minimum temperature
region, the magnetic fields at the footpoints become almost vertical and
the loop topology resembles a potential field. The mean ascent velocity
at chromospheric height is ~12 km s-1. The energy input rate
of these small-scale loops in the lower boundary of the chromosphere
is (at least) of 1.4 × 106-2.2 × 107 erg
cm-2 s-1. Our findings provide empirical evidence
for solar magnetism as a multi-scale system, in which small-scale
low-flux magnetism plays a crucial role, at least as important as active
regions, coupling different layers of the solar atmosphere and being
an important ingredient for chromospheric and coronal heating models.

---------------------------------------------------------
Title: Statistical Analysis of the very Quiet Sun Magnetism
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
A.; López Ariste, A.; Bianda, M.
2010ApJ...711L..57M Altcode: 2010arXiv1001.4551M
The behavior of the observed polarization amplitudes with spatial
resolution is a strong constraint on the nature and organization
of solar magnetic fields below the resolution limit. We study the
polarization of the very quiet Sun at different spatial resolutions
using ground- and space-based observations. It is shown that 80% of the
observed polarization signals do not change with spatial resolution,
suggesting that, observationally, the very quiet Sun magnetism
remains the same despite the high spatial resolution of space-based
observations. Our analysis also reveals a cascade of spatial scales
for the magnetic field within the resolution element. It is manifest
that the Zeeman effect is sensitive to the microturbulent field usually
associated with Hanle diagnostics. This demonstrates that Zeeman and
Hanle studies show complementary perspectives of the same magnetism.

---------------------------------------------------------
Title: On the 3D structure of the magnetic field in regions of
emerging flux .
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2010MmSAI..81..625A Altcode: 2010arXiv1001.2108A
We explore the photospheric and chromospheric magnetic field in an
emerging flux region. An image of the equivalent width of the He I
10830 Å red blended component shows the presence of filamentary
structures that might be interpreted as magnetic loops. We point
out that the magnetic field strength in the chromosphere resembles a
smoothed version of that found in the photosphere and that it is not
correlated at all with the above-mentioned equivalent width map. Lacking
other diagnostics, this suggests that one cannot discard the possibility
that the chromospheric field we infer from the observations is tracing
the lower chromosphere of the active region instead of tracing the
magnetic field along loops. If the He I line is formed within magnetic
loops, we point out a potential problem that appears when interpreting
observations using only one component along the line-of-sight.

---------------------------------------------------------
Title: On the Magnetic Field of Off-limb Spicules
Authors: Centeno, Rebecca; Trujillo Bueno, Javier; Asensio Ramos,
Andrés
2010ApJ...708.1579C Altcode: 2009arXiv0911.3149C
Determining the magnetic field related to solar spicules is vital for
developing adequate models of these plasma jets, which are thought to
play a key role in the thermal, dynamic, and magnetic structure of the
chromosphere. Here we report on the magnetic properties of off-limb
spicules in a very quiet region of the solar atmosphere, as inferred
from new spectropolarimetric observations in the He I 10830 Å triplet
obtained with the Tenerife Infrared Polarimeter. We have used a novel
inversion code for Stokes profiles caused by the joint action of atomic
level polarization and the Hanle and Zeeman effects to interpret the
observations (HAZEL, from HAnle and ZEeman Light). Magnetic fields as
strong as ~50 G were detected in a very localized area of the slit,
which could represent a possible lower value of the field strength of
organized network spicules.

---------------------------------------------------------
Title: Compressive sensing for spectroscopy and polarimetry
Authors: Asensio Ramos, A.; López Ariste, A.
2010A&A...509A..49A Altcode: 2009arXiv0909.4439A
We demonstrate, through numerical simulations with real data, the
feasibility of using compressive sensing techniques for the acquisition
of spectro-polarimetric data. This allows us to combine the measurement
and the compression process into one consistent framework. Signals are
recovered using a sparse reconstruction scheme from projections of
the signal of interest onto appropriately chosen vectors, typically
noise-like vectors. The compressibility properties of spectral lines
are analyzed in detail. The results shown in this paper demonstrate
that, thanks to the compressibility properties of spectral lines, it
is feasible to reconstruct the signals using only a small fraction of
the information that is measured nowadays. We investigate in depth
the quality of the reconstruction as a function of the amount of
data measured and the influence of noise. This change of paradigm
also allows us to define new instrumental strategies and to propose
modifications to existing instruments in order to take advantage of
compressive sensing techniques.

---------------------------------------------------------
Title: The Magnetic Field of Solar Spicules
Authors: Centeno, R.; Trujillo Bueno, J.; Asensio Ramos, A.
2010ASSP...19..255C Altcode: 2010mcia.conf..255C; 2009arXiv0903.0002C
Determining the magnetic field of solar spicules is vital for
developing adequate models of these plasma jets, which are thought to
play a key role in the thermal, dynamic, and magnetic structure of the
chromosphere. Here we report on magnetic spicule properties in a very
quiet region of the off-limb solar atmosphere, as inferred from new
spectropolarimetric observations in the He I 10830Å triplet. We have
used a novel inversion code for Stokes profiles caused by the joint
action of atomic level polarization and the Hanle and Zeeman effects
(HAZEL) to interpret the observations. Magnetic fields as strong as
40G were unambiguously detected in a very localized area of the slit,
which may represent a possible lower value of the field strength of
organized network spicules.

---------------------------------------------------------
Title: IR And X-ray Tests Of The Clumpy Torus Models Of AGN
Authors: Packham, Christopher C.; Levenson, N.; Ramos Almeida, C.;
Radomski, J.; Alonso-Herrero, A.; Rodríguez Espinosa, J.; Asensio
Ramos, A.; Mason, R.; Fisher, S.; Telesco, C.; Schaefer, J.
2010AAS...21541117P Altcode: 2010BAAS...42Q.242P
On-going explorations of AGN based at mid-IR wavelengths has tightly
constrained individual torus sizes to a few pc and found that spectral
fitting in the N band window is consistent with toroidal obscuration
at the center of AGN in a non-homogenous or `clumpy’ structure. We
discuss results of two recent papers where we combine our mid-IR data
with data at other wavelengths to further constrain the torus size
and structure. In the first paper, we combine archival high spatial
resolution near-IR data with our mid-IR observations to construct an IR
SED, which is then fit to the clump torus model. In the second paper we
construct at optimal spatial resolution a mid-IR to x-ray correlation,
comparing carefully the AGN types. We discuss the implications to
models of the AGN torus.

---------------------------------------------------------
Title: The quiet Sun magnetic field observed with ZIMPOL on
THEMIS. I. The probability density function
Authors: Bommier, V.; Martínez González, M.; Bianda, M.; Frisch,
H.; Asensio Ramos, A.; Gelly, B.; Landi Degl'Innocenti, E.
2009A&A...506.1415B Altcode:
Context: The quiet Sun magnetic field probability density function (PDF)
remains poorly known. Modeling this field also introduces a magnetic
filling factor that is also poorly known. With these two quantities,
PDF and filling factor, the statistical description of the quiet Sun
magnetic field is complex and needs to be clarified. Aims:
In the present paper, we propose a procedure that combines direct
determinations and inversion results to derive the magnetic field
vector and filling factor, and their PDFs. Methods: We used
spectro-polarimetric observations taken with the ZIMPOL polarimeter
mounted on the THEMIS telescope. The target was a quiet region at disk
center. We analyzed the data by means of the UNNOFIT inversion code,
with which we inferred the distribution of the mean magnetic field α
B, α being the magnetic filling factor. The distribution of α was
derived by an independent method, directly from the spectro-polarimetric
data. The magnetic field PDF p(B) could then be inferred. By introducing
a joint PDF for the filling factor and the magnetic field strength, we
have clarified the definition of the PDF of the quiet Sun magnetic field
when the latter is assumed not to be volume-filling. Results: The
most frequent local average magnetic field strength is found to be 13
G. We find that the magnetic filling factor is related to the magnetic
field strength by the simple law α = B_1/B with B1 = 15
G. This result is compatible with the Hanle weak-field determinations,
as well as with the stronger field determinations from the Zeeman effect
(kGauss field filling 1-2% of space). From linear fits, we obtain the
analytical dependence of the magnetic field PDF. Our analysis has also
revealed that the magnetic field in the quiet Sun is isotropically
distributed in direction. Conclusions: We conclude that the
quiet Sun is a complex medium where magnetic fields having different
field strengths and filling factors coexist. Further observations
with a better polarimetric accuracy are, however, needed to confirm
the results obtained in the present work. Based on observations
made with the French-Italian telescope THEMIS operated by the CNRS
and CNR on the island of Tenerife in the Spanish Observatorio del
Teide of the Instituto de Astrofísica de Canarias. Present address:
Instituto de Astrofísica de Canarias, vía Láctea s/n, 38205 La
Laguna, Tenerife, Spain.

---------------------------------------------------------
Title: Multiline Zeeman signatures through line addition
Authors: Semel, M.; Ramírez Vélez, J. C.; Martínez González,
M. J.; Asensio Ramos, A.; Stift, M. J.; López Ariste, A.; Leone, F.
2009A&A...504.1003S Altcode: 2009arXiv0906.4226S
Context: To obtain a significant Zeeman signature in the polarised
spectra of a magnetic star, we usually “add” the contributions
of numerous spectral lines; the ultimate goal is to recover the
spectropolarimetric prints of the magnetic field in these line
additions. Aims: Here we want to clarify the meaning of these
techniques of line addition; in particular, we try to interpret the
meaning of the “pseudo-line” formed during this process and to
find out why and how its Zeeman signature is still meaningful. Methods: We create a synthetic case of line addition and apply well
tested standard solar methods routinely used in research on magnetism
in the Sun. Results: The results are convincing and the Zeeman
signatures well detected; Solar methods are found to be quite efficient
for stellar observations. We statistically compare line addition
with least-squares deconvolution and demonstrate that they both give
very similar results, as a consequence of the special statistical
properties of the weights. Conclusions: The Zeeman signatures
are unequivocally detected in this multiline approach. We suggest
that magnetic field detection is reliable well beyond the weak-field
approximation. Linear polarisation in the spectra of solar type stars
can be detected when the spectral resolution is sufficiently high.

---------------------------------------------------------
Title: The Infrared Nuclear Emission of Seyfert Galaxies on Parsec
Scales: Testing the Clumpy Torus Models
Authors: Ramos Almeida, C.; Levenson, N. A.; Rodríguez Espinosa,
J. M.; Alonso-Herrero, A.; Asensio Ramos, A.; Radomski, J. T.; Packham,
C.; Fisher, R. S.; Telesco, C. M.
2009ApJ...702.1127R Altcode: 2009arXiv0906.5368R
We present subarcsecond resolution mid-infrared (mid-IR) photometry
in the wavelength range from 8 to 20 μm of 18 Seyfert galaxies,
reporting high spatial resolution nuclear fluxes for the entire
sample. We construct spectral energy distributions (SEDs) that the
active galactic nucleus (AGN) dominates, relatively uncontaminated by
starlight, adding near-IR measurements from the literature at similar
angular resolution. We find that the IR SEDs of intermediate-type
Seyferts are flatter and present higher 10 to 18 μm ratios than
those of Seyfert 2 galaxies. We fit the individual SEDs with clumpy
dusty torus models using the in-house-developed BayesClumpy tool. We
find that the clumpy models reproduce the high spatial resolution
measurements. Regardless of the Seyfert type, even with high spatial
resolution data, near- to mid-IR SED fitting poorly constrains the
radial extent of the torus. For the Seyfert 2 galaxies, we find that
edge-on geometries are more probable than face-on views, with a number
of clouds along equatorial rays of N 0 = 5-15. The 10 μm
silicate feature is generally modeled in shallow absorption. For the
intermediate-type Seyferts, N 0 and the inclination angle
of the torus are lower than those of the Seyfert 2 nuclei, with the
silicate feature appearing in weak emission or absent. The columns
of material responsible for the X-ray absorption are larger than
those inferred from the model fits for most of the galaxies, which
is consistent with X-ray absorbing gas being located within the dust
sublimation radius, whereas the mid-IR flux arises from an area farther
from the accretion disk. The fits yield both the bolometric luminosity
of the intrinsic AGN and the torus-integrated luminosity, from which
we derive the reprocessing efficiency of the torus. In the models,
the outer radial extent of the torus scales with the AGN luminosity,
and we find the tori to be confined to scales less than 5 pc.

---------------------------------------------------------
Title: Evidence for Quasi-Isotropic Magnetic Fields from Hinode
Quiet-Sun Observations
Authors: Asensio Ramos, A.
2009ApJ...701.1032A Altcode: 2009ApJ...701.1032R; 2009arXiv0906.4230A
Some recent investigations of spectropolarimetric observations of the
Zeeman effect in the Fe I lines at 630 nm carried out with the Hinode
solar space telescope have concluded that the strength of the magnetic
field vector in the internetwork regions of the quiet Sun is in the
hG regime and that its inclination is predominantly horizontal. We
critically reconsider the analysis of such observations and carry
out a complete Bayesian analysis with the aim of extracting as much
information as possible from them, including error bars. We apply
the recently developed BAYES-ME code that carries out a complete
Bayesian inference for Milne-Eddington atmospheres. The sampling of
the posterior distribution function is obtained with a Markov Chain
Monte Carlo scheme and the marginal distributions are analyzed in
detail. The Kullback-Leibler divergence is used to study the extent
to which the observations introduce new information in the inference
process resulting in sufficiently constrained parameters. Our
analysis clearly shows that only upper limits to the magnetic field
strength can be inferred, with fields in the kG regime completely
discarded. Furthermore, the noise level present in the analyzed Hinode
observations induces a substantial loss of information for constraining
the azimuth of the magnetic field. Concerning the inclination of the
field, we demonstrate that some information is available to constrain
it for those pixels with the largest polarimetric signal. The results
also point out that the field in pixels with small polarimetric signals
can be nicely reproduced in terms of a quasi-isotropic distribution.

---------------------------------------------------------
Title: Variability of the polarization profiles of the Ba II D{2}
line in the solar atmosphere
Authors: López Ariste, A.; Asensio Ramos, A.; Manso Sainz, R.;
Derouich, M.; Gelly, B.
2009A&A...501..729L Altcode:
Resonance-scattering polarization and the Hanle effect are powerful
but seldom exploited probes into the magnetism of the quiet solar
atmosphere. They are also very interesting checks of the quantum theory
of atomic polarization. The Ba ii D2 line has been known for more than
20 years as presenting a conspicuous signal of resonance scattering
polarization thanks to its atomic configuration and the presence
of five different isotopes of Ba, two of which present a hyperfine
structure.A model that considers most of the known ingredients of the
atomic polarization of Ba ii related to the formation of the D2 line
was presented in 2007. We intend to observe all the variability of the
Stokes profiles of this line in conditions of resonance scattering
to verify the general validity of the model and to ascertain the
use of the model for magnetic field diagnostics in the quiet solar
chromosphere and in spicules. The new CCD cameras at THEMIS and the
recently commissioned tip-tilt tracking system gave us the opportunity
to perform the required observations with unprecedented precision
and reliability, resulting in data ready to confront the present
theory.The Stokes Q profiles, both off-limb and on disk, appear to
verify this theory in qualitative terms. The observed departures in
terms of overall signal amplitude and relative ratios among the three
spectral features point to a refinement of the theory for quantitative
purposes, perhaps including radiative-transfer effects. We observed,
on the other hand, anomalous Stokes V profiles in the absence of Zeeman
effect that remain unexplained.The qualitative agreement between the
theory and the observations encourages an increased effort to also
match the observations from a quantitative point of view, including
the observed anomalous Stokes V profiles.

---------------------------------------------------------
Title: Centre to Limb Variation of the Internetwork Magnetism
Authors: Martínez González, M. J.; Asensio Ramos, A.; López
Ariste, A.
2009ASPC..405..219M Altcode:
We analyse 1.5 μm spectropolarimetric observations of quiet
regions at different positions on the solar surface. Neither the
circular and linear polarization signals nor the area and amplitude
asymmetries present a clear trend with the position on the Sun. This
fact discards a network-like scenario for the internetwork magnetic
fields. An isotropically distributed magnetic field would reproduce the
observations, whatever its organisation (myriads of low-lying loops,
turbulent field, etc.).

---------------------------------------------------------
Title: Bayesian Inversion of Stokes Profiles
Authors: Asensio Ramos, A.; Martínez González, M. J.;
Rubiño-Martín, J. A.
2009ASPC..405..315A Altcode:
Inversion techniques are the most powerful methods to obtain information
about the thermodynamical and magnetic properties of solar and stellar
atmospheres. In the last years, we have witnessed the development of
highly sophisticated inversion codes that are now widely applied to
spectro-polarimetric observations. However, no realistic confidence
intervals are obtained for the inferred parameters. Additionally, it
is fundamental to apply efficient techniques to assess the ability
of models to reproduce the observations and to know to what extent
the models have to be refined or can be simplified. We propose the
application of Bayesian techniques. The posterior distribution, that
takes into account both the a-priori knowledge and the information
given by the data, is efficiently sampled using a Markov Chain Monte
Carlo method. We demonstrate the capabilities of the code with the
aid of an interesting example.

---------------------------------------------------------
Title: Synthesis and Inversion of He I Stokes Profiles Caused by
the Joint Action of the Hanle and Zeeman Effects
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2009ASPC..405..281A Altcode: 2009ASPC..405..281R
We have developed a robust but user-friendly computer program for the
synthesis and inversion of Stokes profiles caused by the joint action
of the Hanle and Zeeman effects in some spectral lines of diagnostic
interest. The influence of radiative transfer on the emergent spectral
line radiation is taken into account through a suitable slab model. The
dynamical and magnetic properties of the observed plasma structure are
inferred from the observed Stokes profiles via an efficient inversion
algorithm based on global optimization methods. Here we introduce
it briefly to the solar and stellar physics community by showing the
first results of an application to the He I 10830 Å multiplet, whose
aim is to obtain empirical information on the strength and orientation
of the magnetic field vector in an internetwork region of the solar
chromosphere.

---------------------------------------------------------
Title: Flux Cancellation in the Solar Photosphere: a near-IR Line
of Mn I as a Diagnostic Tool
Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste,
A.; Trujillo Bueno, J.; Collados, M.
2009ASPC..405..215A Altcode:
Recently, \cite{asensio_2_asensio_mn07} pointed out that the near-IR
line of Mn I at 15262.702 Å provides a new diagnostic window for
exploring the magnetism of the quiet Sun. In contrast with previously
considered Mn I lines located at visible wavelengths this near-IR
line has the advantage that the shape of its intensity profile is very
sensitive to the presence of magnetic fields. This enhanced magnetic
sensitivity is produced by the coincidence of two favorable facts:
the enhanced Zeeman sensitivity of near-IR lines and because this line
is subjected to particularly strong Paschen-Back perturbations due to
the hyperfine structure of manganese. Of great diagnostic interest is
that the intensity profile itself give us information on the unsigned
magnetic flux, while the polarization profiles are sensitive to the
net flux. An application to spectropolarimetric observations with the
Tenerife Infrared Polarimeter has allowed us to obtain the first flux
cancellation map in an enhanced network region.

---------------------------------------------------------
Title: Ciencia con CanariCam
Authors: Ramos-Almeida, C.; Levenson, N.; Rodríguez Espinosa, J. M.;
Alonso-Herrero, A.; Asensio Ramos, A.; Radomski, J.; Packham, C.;
Fisher, S.; Telesco, C.
2009iac..talk...86R Altcode: 2009iac..talk...82R
No abstract at ADS

---------------------------------------------------------
Title: Bayesclumpy: Bayesian Inference with Clumpy Dusty Torus Models
Authors: Asensio Ramos, A.; Ramos Almeida, C.
2009ApJ...696.2075A Altcode: 2009arXiv0903.0622A
Our aim is to present a fast and general Bayesian inference framework
based on the synergy between machine learning techniques and standard
sampling methods and apply it to infer the physical properties
of clumpy dusty torus using infrared photometric high spatial
resolution observations of active galactic nuclei. We make use of the
Metropolis-Hastings Markov Chain Monte Carlo algorithm for sampling
the posterior distribution function. Such distribution results from
combining all a priori knowledge about the parameters of the model and
the information introduced by the observations. The main difficulty
resides in the fact that the model used to explain the observations is
computationally demanding and the sampling is very time consuming. For
this reason, we apply a set of artificial neural networks that are used
to approximate and interpolate a database of models. As a consequence,
models not present in the original database can be computed ensuring
continuity. We focus on the application of this solution scheme to the
recently developed public database of clumpy dusty torus models. The
machine learning scheme used in this paper allows us to generate
any model from the database using only a factor of 10-4
of the original size of the database and a factor of 10-3
in computing time. The posterior distribution obtained for each model
parameter allows us to investigate how the observations constrain the
parameters and which ones remain partially or completely undetermined,
providing statistically relevant confidence intervals. As an example,
the application to the nuclear region of Centaurus A shows that the
optical depth of the clouds, the total number of clouds, and the radial
extent of the cloud distribution zone are well constrained using only
six filters. The code is freely available from the authors.

---------------------------------------------------------
Title: The Magnetic Sensitivity of the Stokes I Profile of the 15260
Å Line of Mn I
Authors: Asensio Ramos, A.
2009ApJ...690..416A Altcode: 2009ApJ...690..416R
The near-IR line of Mn I at 15262.7 Å has recently been proposed as
a new tool for diagnosing the magnetic field strength and magnetic
energy density associated with unresolved magnetic structures, due
to the enhanced sensitivity of the Stokes I profile. In this paper,
the behavior of the line, focusing on the properties of the Stokes
I profile, is analyzed in detail with the aid of state-of-the-art
magneto-hydrodynamical simulations of the solar surface convection. The
line is synthesized taking into account that the splitting and
the strength of the Zeeman components have to be calculated
under the framework of the Paschen-Back theory via the numerical
diagonalization of the total Hamiltonian, including the hyperfine and
Zeeman contributions. The peak ratio and separation of the blue and
red lobes of the emergent Stokes I profile are shown to be correlated
with the magnetic field strength when no smearing is taken into account,
while the correlation slightly degrades when diffraction and stray-light
contamination is accounted for. We also analyze the dependence of the
first two line moments with the magnetic field, showing that the first
and second moments can be used to trace the velocity and the magnetic
field strength, respectively. This correlation is still maintained
for ground-based observations.

---------------------------------------------------------
Title: Markov properties of solar granulation
Authors: Asensio Ramos, A.
2009A&A...494..287A Altcode:
Aims: We estimate the minimum length on which solar granulation can
be considered to be a Markovian process. Methods: We measure
the variation in the bright difference between two pixels in images of
the solar granulation for different distances between the pixels. This
scale-dependent data is empirically analyzed to find the minimum scale
on which the process can be considered Markovian. Results:
The results suggest that the solar granulation can be considered
to be a Markovian process on scales longer than r_M=300-500 km. On
longer length scales, solar images can be considered to be a Markovian
stochastic process that consists of structures of size r_M. Smaller
structures exhibit correlations on many scales simultaneously yet
cannot be described by a hierarchical cascade in scales. An analysis
of the longitudinal magnetic-flux density indicates that it cannot be
a Markov process on any scale. Conclusions: The results presented
in this paper constitute a stringent test for the realism of numerical
magneto-hydrodynamical simulations of solar magneto-convection. In
future exhaustive analyse, the non-Markovian properties of the magnetic
flux density on all analyzed scales might help us to understand the
physical mechanism generating the field that we detect in the solar
surface.

---------------------------------------------------------
Title: PCA detection and denoising of Zeeman signatures in polarised
stellar spectra
Authors: Martínez González, M. J.; Asensio Ramos, A.; Carroll,
T. A.; Kopf, M.; Ramírez Vélez, J. C.; Semel, M.
2008A&A...486..637M Altcode: 2008arXiv0804.4692M
Aims: Our main objective is to develop a denoising strategy to
increase the signal to noise ratio of individual spectral lines
of stellar spectropolarimetric observations. Methods: We
use a multivariate statistics technique called Principal Component
Analysis. The cross-product matrix of the observations is diagonalized
to obtain the eigenvectors in which the original observations can be
developed. This basis is such that the first eigenvectors contain
the greatest variance. Assuming that the noise is uncorrelated a
denoising is possible by reconstructing the data with a truncated
basis. We propose a method to identify the number of eigenvectors for
an efficient noise filtering. Results: Numerical simulations are
used to demonstrate that an important increase of the signal to noise
ratio per spectral line is possible using PCA denoising techniques. It
can be also applied for detection of magnetic fields in stellar
atmospheres. We analyze the relation between PCA and commonly used
techniques like line addition and least-squares deconvolution. Moreover,
PCA is very robust and easy to compute.

---------------------------------------------------------
Title: Advanced Forward Modeling and Inversion of Stokes Profiles
Resulting from the Joint Action of the Hanle and Zeeman Effects
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Landi Degl'Innocenti,
E.
2008ApJ...683..542A Altcode: 2008arXiv0804.2695A
A big challenge in solar and stellar physics in the coming years
will be to decipher the magnetism of the solar outer atmosphere
(chromosphere and corona) along with its dynamic coupling with
the magnetic fields of the underlying photosphere. To this end, it
is important to develop rigorous diagnostic tools for the physical
interpretation of spectropolarimetric observations in suitably chosen
spectral lines. Here we present a computer program for the synthesis and
inversion of Stokes profiles caused by the joint action of atomic level
polarization and the Hanle and Zeeman effects in some spectral lines
of diagnostic interest, such as those of the He I 10830 Å and 5876 Å
(or D3) multiplets. It is based on the quantum theory of
spectral line polarization, which takes into account in a rigorous way
all the relevant physical mechanisms and ingredients (optical pumping,
atomic level polarization, level crossings and repulsions, Zeeman,
Paschen-Back, and Hanle effects). The influence of radiative transfer
on the emergent spectral line radiation is taken into account through
a suitable slab model. The user can either calculate the emergent
intensity and polarization for any given magnetic field vector or infer
the dynamical and magnetic properties from the observed Stokes profiles
via an efficient inversion algorithm based on global optimization
methods. The reliability of the forward modeling and inversion code
presented here is demonstrated through several applications, which range
from the inference of the magnetic field vector in solar active regions
to determining whether or not it is canopy-like in quiet chromospheric
regions. This user-friendly diagnostic tool called "HAZEL" (from HAnle
and ZEeman Light) is offered to the astrophysical community, with the
hope that it will facilitate new advances in solar and stellar physics.

---------------------------------------------------------
Title: Error propagation in polarimetric demodulation
Authors: Asensio Ramos, A.; Collados, M.
2008ApOpt..47.2541A Altcode: 2008arXiv0804.4708A
The polarization analysis of light is typically carried out using
modulation schemes. The light of an unknown polarization state is passed
through a set of known modulation optics, and a detector is used to
measure the total intensity passing the system. The modulation optics is
modified several times, and, with the aid of several such measurements,
the unknown polarization state of the light can be inferred. How to
find the optimal demodulation process has been investigated in the
past. However, since the modulation matrix has to be measured for a
given instrument and the optical elements can present problems of
repeatability, some uncertainty is present in the elements of the
modulation matrix or covariances between these elements. We analyze in
detail this issue, presenting analytical formulas for calculating the
covariance matrix produced by the propagation of such uncertainties on
the demodulation matrix, on the inferred Stokes parameters, and on the
efficiency of the modulation process. We demonstrate that even if the
covariance matrix of the modulation matrix is diagonal, the covariance
matrix of the demodulation matrix is in general nondiagonal because
matrix inversion is a nonlinear operation. This propagates through
the demodulation process and induces correlations on the inferred
Stokes parameters.

---------------------------------------------------------
Title: Multiline Spectropolarimetry of the Quiet Sun at 5250 and
6302 Å
Authors: Socas-Navarro, H.; Borrero, J. M.; Asensio Ramos, A.;
Collados, M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez
González, M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez
Almeida, J.
2008ApJ...674..596S Altcode:
The reliability of quiet-Sun magnetic field diagnostics based on the
Fe I lines at 6302 Å has been questioned by recent work. Here we
present the results of a thorough study of high-resolution multiline
observations taken with the new spectropolarimeter SPINOR, comprising
the 5250 and 6302 Å spectral domains. The observations were analyzed
using several inversion algorithms, including Milne-Eddington,
LTE with 1 and 2 components, and MISMA codes. We find that the
line-ratio technique applied to the 5250 Å lines is not sufficiently
reliable to provide a direct magnetic diagnostic in the presence
of thermal fluctuations and variable line broadening. In general,
one needs to resort to inversion algorithms, ideally with realistic
magnetohydrodynamic constrains. When this is done, the 5250 Å lines
do not seem to provide any significant advantage over those at 6302
Å. In fact, our results point toward a better performance with the
latter (in the presence of turbulent line broadening). In any case,
for very weak flux concentrations, neither spectral region alone
provides sufficient constraints to fully disentangle the intrinsic
field strengths. Instead, we advocate for a combined analysis of both
spectral ranges, which yields a better determination of the quiet-Sun
magnetic properties. Finally, we propose the use of two other Fe I
lines (at 4122 and 9000 Å) with identical line opacities that seem
to work much better than the others.

---------------------------------------------------------
Title: Near-IR internetwork spectro-polarimetry at different
heliocentric angles
Authors: Martínez González, M. J.; Asensio Ramos, A.; López Ariste,
A.; Manso Sainz, R.
2008A&A...479..229M Altcode: 2007arXiv0710.5219M
Aims:The analysis of near infrared spectropolarimetric data at the
internetwork in different regions on the solar surface could offer
constraints that reject current modeling of these quiet areas. Methods: We present spectro-polarimetric observations of very
quiet regions for different values of the heliocentric angle for the
Fe i lines at 1.56 μm, from disc centre to positions close to the
limb. The spatial resolution of the data is 0.7{-}1”. We analyse
direct observable properties of the Stokes profiles as the amplitude
of circular and linear polarisation, as well as the total degree of
polarisation. The area and amplitude asymmetries are also studied. Results: We do not find any significant variation in the properties of
the polarimetric signals with the heliocentric angle. This means that
the magnetism of the solar internetwork remains the same regardless
of the position on the solar disc. This observational fact discards
the possibility of modeling the internetwork as a network-like
scenario. The magnetic elements of internetwork areas seem to be
isotropically distributed when observed at our spatial resolution.

---------------------------------------------------------
Title: Bayesian inversion of Stokes profiles
Authors: Asensio Ramos, A.; Martínez González, M. J.;
Rubiño-Martín, J. A.
2007A&A...476..959A Altcode: 2007arXiv0709.0596A
Context: Inversion techniques are the most powerful methods to obtain
information about the thermodynamical and magnetic properties of
solar and stellar atmospheres. In the recent years, we have witnessed
the development of highly sophisticated inversion codes that are now
widely applied to spectro-polarimetric observations. The majority of
these inversion codes are based on the optimization of a complicated
non-linear merit function. The experience gained has facilitated the
recovery of the model that best fits a given observation. However,
and except for the recently developed inversion codes based
on database search algorithms together with the application
of Principal Component Analysis, no reliable and statistically
well-defined confidence intervals can be obtained for the parameters
inferred from the inversions. Aims: A correct estimation of the
confidence intervals for all the parameters that describe the model is
mandatory. Additionally, it is fundamental to apply efficient techniques
to assess the ability of models to reproduce the observations and
to determine to what extent the models have to be refined or can
be simplified. Methods: Bayesian techniques are applied to
analyze the performance of the model to fit a given observed Stokes
vector. The posterior distribution, that takes into account both the
information about the priors and the likelihood, is efficiently sampled
using a Markov chain Monte Carlo method. For simplicity, we focus on
the Milne-Eddington approximate solution of the radiative transfer
equation and we only take into account the generation of polarization
through the Zeeman effect. However, the method is extremely general
and other more complex forward models can be applied, even allowing
for the presence of atomic polarization. Results: We illustrate
the method with different problems, from academic to more realistic
examples. We show that the information provided by the posterior
distribution is fundamental to understand and determine the amount
of information available in the Stokes profiles in these particular
cases. Appendix A and B are only available in electronic form
at http://www.aanda.org.

---------------------------------------------------------
Title: Multi-Line Quiet Sun Spectro-Polarimetry at 5250 and 6302 Å
Authors: Socas-Navarro, H.; Borrero, J.; Asensio Ramos, A.; Collados,
M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez González,
M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez Almeida, J.
2007arXiv0710.1099S Altcode:
The reliability of quiet Sun magnetic field diagnostics based on the
\ion{Fe}{1} lines at 6302 Åhas been questioned by recent work. We
present here the results of a thorough study of high-resolution
multi-line observations taken with the new spectro-polarimeter SPINOR,
comprising the 5250 and 6302 Åspectral domains. The observations were
analyzed using several inversion algorithms, including Milne-Eddington,
LTE with 1 and 2 components, and MISMA codes. We find that the
line-ratio technique applied to the 5250 Ålines is not sufficiently
reliable to provide a direct magnetic diagnostic in the presence
of thermal fluctuations and variable line broadening. In general,
one needs to resort to inversion algorithms, ideally with realistic
magneto-hydrodynamical constrains. When this is done, the 5250 Ålines
do not seem to provide any significant advantage over those at 6302
Å. In fact, our results point towards a better performance with the
latter (in the presence of turbulent line broadening). In any case,
for very weak flux concentrations, neither spectral region alone
provides sufficient constraints to fully disentangle the intrinsic field
strengths. Instead, we advocate for a combined analysis of both spectral
ranges, which yields a better determination of the quiet Sun magnetic
properties. Finally, we propose the use of two other \ion{Fe}{1} lines
(at 4122 and 9000 Å) with identical line opacities that seem to work
much better than the others.

---------------------------------------------------------
Title: Extreme value theory and the solar cycle
Authors: Asensio Ramos, A.
2007A&A...472..293A Altcode: 2007arXiv0706.2590A
Aims:We investigate the statistical properties of the extreme events
of the solar cycle as measured by the sunspot number. Methods:
The recent advances in the methodology of the theory of extreme values
are applied to the maximal extremes of the time series of sunspots. We
focus on the extreme events that exceed a carefully chosen threshold
and a generalized Pareto distribution is fitted to the tail of the
empirical cumulative distribution. A maximum likelihood method is used
to estimate the parameters of the generalized Pareto distribution and
confidence levels are also given to the parameters. Due to the lack
of an automatic procedure for selecting the threshold, we analyze the
sensitivity of the fitted generalized Pareto distribution to the exact
value of the threshold. Results: According to the available data,
which only span the previous ~250 years, the cumulative distribution
of the time series is bounded, yielding an upper limit of 324 for
the sunspot number. We also estimate that the return value for each
solar cycle is ~188, while the return value for a century increases
to ~228. Finally, the results also indicate that the most probable
return time for a large event such as the maximum at solar cycle 19,
happens once every ~700 years and that the probability of finding such
a large event with a frequency smaller than ~50 years is very small. In
spite of the essentially extrapolative character of these results,
their statistical significance is very large.

---------------------------------------------------------
Title: H{2}D+ line emission in Proto-Planetary Disks
Authors: Asensio Ramos, A.; Ceccarelli, C.; Elitzur, M.
2007A&A...471..187A Altcode: 2007arXiv0706.1040A
Context: Previous studies have indicated that the 372.4 GHz ground
transition of ortho-H2D+ might be a powerful probe of
Proto-Planetary Disks. The line could be especially suited for study
of the disk mid-plane, where the bulk of the mass resides and where
planet formation takes place. Aims: Provide detailed theoretical
predictions for the line intensity, profile and maps expected for
representative disk models. Methods: We determine the physical
and chemical structure of the disks from the model developed by
Ceccarelli &amp; Dominik (2005, A&amp;A, 440, 583). The line emission
is computed with the new radiative transfer method developed recently
by Elitzur &amp; Asensio Ramos (2006, MNRAS, 365, 779). Results:
We present intensity maps convolved with the expected ALMA resolution,
which delineate the origin of the H2D+ 372.4 GHz line. In
the disk inner regions, the line probes the conditions in the mid-plane
out to radial distances of a few tens of AU, where Solar-like planetary
systems might form. In the disk outermost regions, the line originates
from slightly above the mid-plane. When the disk is spatially resolved,
the variation of line profile across the image provides important
information about the velocity field. Spectral profiles of the entire
disk flux show a double peak shape at most inclination angles. Conclusions: Our study confirms that the 372.4 GHz H2D+
line provides powerful diagnostics of the mid-plane of Proto-Planetary
Disks. Current submillimeter telescopes are capable of observing this
line, though with some difficulties. The future ALMA interferometer
will have the sensitivity to observe and even spatially resolve the
H2D+ line emission.

---------------------------------------------------------
Title: Turbulent fields in the quiet sun from Hanle and Zeeman
effects with THEMIS
Authors: López Ariste, A.; Malherbe, J. M.; Manso Sainz, R.; Asensio
Ramos, A.; Ramírez Vélez, J. C.; Martínez González, M.
2007sf2a.conf..596L Altcode:
The measurement of the Sr I line with full polarimetry and spatial
resolution with THEMIS has provided the unexpected result of an apparent
correlation between the Hanle effect signals and the Zeeman effect
signals on this line. Traditionnally, Hanle effect signals in linear
polarisation have been interpreted as the signature of unorganized,
turbulent fields, while Zeeman effect signals -mostly in circular
polarisation- were interpreted as structured fields. The correlation
between both observed by THEMIS requires a change of mind respect to the
picture of the quiet sun, with fewer structured fields and a turbulent
field visible also in deep magnetograms. This picture is supported also
by recent results with Mn lines with strong coupling with its hyperfine
structure and of center-to-limb histograms of Zeeman amplitudes.

---------------------------------------------------------
Title: A User-Friendly Code to Diagnose Chromospheric Plasmas
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2007ASPC..368..163A Altcode: 2007arXiv0704.1723A
The physical interpretation of spectropolarimetric observations of
lines of neutral helium, such as those of the 10830 Å multiplet,
represents an excellent opportunity for investigating the magnetism
of plasma structures in the solar chromosphere. Here we present a
powerful forward modeling and inversion code that permits either to
calculate the emergent intensity and polarization for any given magnetic
field vector or to infer the dynamical and magnetic properties from
the observed Stokes profiles. This diagnostic tool is based on the
quantum theory of spectral line polarization, which self-consistently
accounts for the Hanle and Zeeman effects in the most general case of
the incomplete Paschen-Back effect regime. We also take into account
radiative transfer effects. An efficient numerical scheme based on
global optimization methods has been applied. Our Stokes inversion
code permits a fast and reliable determination of the global minimum.

---------------------------------------------------------
Title: Comparison of spatially and spectrally resolved solar data
with numerical simulations
Authors: Cauzzi, G.; Asensio Ramos, A.; Reardon, K. P.; Janssen, K.
2007IAUS..239..138C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Intrinsic Dimensionality of Spectropolarimetric Data
Authors: Asensio Ramos, A.; Socas-Navarro, H.; López Ariste, A.;
Martínez González, M. J.
2007ApJ...660.1690A Altcode: 2007astro.ph..1604A
The amount of information available in spectropolarimetric data is
estimated. To this end, the intrinsic dimensionality of the data is
inferred with the aid of a recently derived estimator based on nearest
neighbor considerations and obtained applying the principle of maximum
likelihood. We show in detail that the estimator correctly captures the
intrinsic dimension of artificial data sets with known dimension. The
effect of noise in the estimated dimension is analyzed thoroughly,
and we conclude that it introduces a positive bias that needs to be
accounted for. Real simultaneous spectropolarimetric observations
in the visible 630 nm and the near-infrared 1.5 μm spectral regions
are also investigated in detail, showing that the near-infrared data
set provides more information of the physical conditions in the solar
atmosphere than the visible data set. Finally, we demonstrate that the
amount of information present in an observed data set is a monotonically
increasing function of the number of available spectral lines.

---------------------------------------------------------
Title: Molecular Line Survey of CRL 618 from 80 to 276 GHz and
Complete Model
Authors: Pardo, Juan R.; Cernicharo, José; Goicoechea, Javier R.;
Guélin, Michel; Asensio Ramos, Andrés
2007ApJ...661..250P Altcode: 2007astro.ph..3022P
We present the complete data set, model, and line identification of
a survey of the emission from the C-rich proto-planetary nebula CRL
618 performed with the IRAM 30 m telescope in the frequency ranges
80.25-115.75 GHz, 131.25-179.25 GHz, and 204.25-275.250 GHz. A
selection of lines from different species has been used in previous
works to derive the structure of the source, its physical conditions,
and the chemical abundances in the different gas regions. In this
work, we have used this information to run a global simulation of the
spectrum in order to check the consistency of the model and to ease
the task of line identification. The total number of lines that have a
correspondence in both data and model is ~3100, although quite often in
this object many lines blend into complex features, so that the model,
which takes into account line blending, is a key tool at this stage of
the analysis. Of all the lines that we have been able to label, ~55%
of them belong to the different forms of HC3N, and ~18%
to HC5N. The density of remaining unidentified features
above the 3 σ limit is only 1 per ~2.1 GHz (74 features), which is
unprecedented in the analysis of this type of large millimeter-wave
line surveys.

---------------------------------------------------------
Title: A Near-Infrared Line of Mn I as a Diagnostic Tool of the
Average Magnetic Energy in the Solar Photosphere
Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste,
A.; Trujillo Bueno, J.; Collados, M.
2007ApJ...659..829A Altcode: 2006astro.ph.12389A
We report on spectropolarimetric observations of a near-IR line of Mn I
located at 15262.702 Å whose intensity and polarization profiles are
very sensitive to the presence of hyperfine structure. A theoretical
investigation of the magnetic sensitivity of this line uncovers several
interesting properties. The most important one is that the presence
of strong Paschen-Back perturbations due to the hyperfine structure
produces an intensity line profile whose shape changes according to the
absolute value of the magnetic field strength. A line ratio technique is
developed from the intrinsic variations of the line profile. This line
ratio technique is applied to spectropolarimetric observations of the
quiet solar photosphere in order to explore the probability distribution
function of the magnetic field strength. Particular attention is given
to the quietest area of the observed field of view, which was encircled
by an enhanced network region. A detailed theoretical investigation
shows that the inferred distribution yields information on the average
magnetic field strength and on the spatial scale at which the magnetic
field is organized. A first estimation gives ~250 G for the mean field
strength and a tentative value of ~0.4" for the spatial scale at which
the observed magnetic field is horizontally organized.

---------------------------------------------------------
Title: A synthetic stellar polarization atlas from 400 to 1000 nm
Authors: Socas-Navarro, H.; Asensio Ramos, A.; Manso Sainz, R.
2007A&A...465..339S Altcode: 2006astro.ph.12388S
Context: With the development of new polarimeters for large telescopes,
the spectro-polarimetric study of astrophysical bodies is becoming
feasible and, indeed, more frequent. In particular, this is permitting
the observational study of stellar magnetic fields. Aims: With
the aim to optimize and interpret this kind of observations, we have
produced a spectral atlas of circular polarization in a grid of stellar
atmospheric models with effective temperatures between 3500 and 10 000
K, surface gravities log(g)=3.5-5, metallicities between 10-2
and 1, and magnetic field strengths of 100, 1000 and 5000 G. Methods: We have computed the emergent Stokes I and V flux spectra
in LTE of more than 105 spectral lines. Results: The
atlas and several numerical tools are available in electronic format
and may be downloaded from http://download.hao.ucar.edu/pub/PSA/. In
this paper we review and discuss some of its most relevant features,
such as which spectral regions and individual lines harbor the
strongest signals, what are interesting lines to observe, how to
disentangle field strength from filling factor, etc. Full
line lists and spectra are only available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/ qcat?J/A+A/465/339

---------------------------------------------------------
Title: VizieR Online Data Catalog: Synthetic stellar polarization
400-1000nm (Socas-Navarro+ 2007)
Authors: Socas-Navarro, H.; Asensio Ramos, A.; Manso Sainz, R.
2007yCat..34650339S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Influence of Atomic Polarization and Horizontal Illumination
on the Stokes Profiles of the He I 10830 Å Multiplet
Authors: Trujillo Bueno, Javier; Asensio Ramos, Andrés
2007ApJ...655..642T Altcode: 2006astro.ph.10128T
The polarization observed in the spectral lines of the He I 10830
Å multiplet carries valuable information on the dynamical and
magnetic properties of plasma structures in the solar chromosphere and
corona. Therefore, it is crucial to have a good physical understanding
of its sensitivity to the various competing physical mechanisms. Here
we focus on investigating the influence of atomic-level polarization
on the emergent Stokes profiles for a broad range of magnetic field
strengths, in both 90° and forward-scattering geometry. We show that,
contrary to a widespread belief, the selective emission and absorption
processes caused by the presence of atomic-level polarization may have
an important influence on the emergent linear polarization, even for
magnetic field strengths as large as 1000 G. Consequently, the modeling
of the Stokes Q- and U-profiles should not be done by taking into
account only the contribution of the transverse Zeeman effect within
the framework of the Paschen-Back effect theory, unless the magnetic
field intensity of the observed plasma structure is sensibly larger
than 1000 G. We also point out that in low-lying optically thick plasma
structures, such as those of active region filaments, the (horizontal)
radiation field generated by the structure itself may substantially
reduce the positive contribution to the anisotropy factor caused by the
(vertical) radiation field coming from the underlying solar photosphere,
so that the amount of atomic-level polarization may turn out to be
negligible. Only under such circumstances can the emergent linear
polarization of the He I 10830 Å multiplet in such structures of the
solar atmospheric plasma be dominated by the contribution caused by
the transverse Zeeman effect.

---------------------------------------------------------
Title: THEMIS observations of the Hanle effect in C_2 lines.
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2007MmSAI..78...42A Altcode:
Analysis of the Hanle effect in solar molecular lines allows us to
obtain empirical information on unresolved, tangled magnetic fields at
subresolution scales in the (granular) upflowing regions of the `quiet'
solar photosphere. Here we show observations of scattering polarization
in selected C_2 lines at increasingly closer distances to the solar
limb, pointing out that the ratio of polarization amplitudes between
suitably chosen line pairs varies in a systematic way. We interpret this
variation in terms of a microturbulent magnetic field of the order of a
few gauss whose strength decreases with height in the solar atmosphere.

---------------------------------------------------------
Title: Radiative Transfer in Molecular Lines. Astrophysical
Applications
Authors: Asensio Ramos, A.
2007hsa..conf..105A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High-resolution IBIS Observations and Comparison with 3D
Simulations
Authors: Cauzzi, G.; Asensio Ramos, A.; Reardon, K.; Janssen, K.
2006ASPC..354...26C Altcode:
We present first comparisons between high resolution observations of
the quiet photosphere, obtained with the Interferometric BIdimensional
Spectrometer (IBIS) in the non-magnetic Fe I 7090.4 Å spectral
line, and the synthetic spectrum calculated for a 3D snapshot of a
radiation-hydrodynamical simulation of the solar atmosphere. Together
with morphological comparisons between the synthetic images and the
observed ones at different wavelengths, we have carried out comparisons
between several observables. The simulations reproduce quite well
many of the observational properties of the high resolution IBIS data,
apart from the velocity distribution, that contains values quite larger
than observed.

---------------------------------------------------------
Title: The Hanle Effect in Atomic and Molecular Lines: A New Look
at the Sun's Hidden Magnetism
Authors: Trujillo Bueno, J.; Asensio Ramos, A.; Shchukina, N.
2006ASPC..358..269T Altcode: 2006astro.ph.12678T
This paper reviews some of the most recent advances in the application
of the Hanle effect to solar physics, and how these developments are
allowing us to explore the magnetism of the photospheric regions that
look “empty” in solar magnetograms--that is, the Sun's “hidden”
magnetism. In particular, we show how a joint analysis of the Hanle
effect in atomic and molecular lines indicates that there is a vast
amount of hidden magnetic energy and unsigned magnetic flux localized in
the (intergranular) downflowing regions of the quiet solar photosphere,
carried mainly by tangled fields at sub-resolution scales with strengths
between the equipartition field values and ∼1 kG. This article
combines in one contribution Trujillo Bueno's invited keynote paper
and the contributed papers by Asensio Ramos &amp; Trujillo Bueno and
by Shchukina &amp; Trujillo Bueno.

---------------------------------------------------------
Title: Three-Dimensional Radiative Transfer Modeling of the Scattering
Polarization in MgH Lines
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2006ASPC..358..318A Altcode:
Analysis of the Hanle effect in solar molecular lines allows us to
obtain empirical information on hidden, mixed-polarity magnetic fields
at subresolution scales in the (granular) upflowing regions of the
`quiet' solar photosphere. Here we report that collisions seem to be
very efficient in depolarizing the rotational levels of MgH lines. This
has the interesting consequence that in the upflowing regions of the
quiet solar photosphere the strength of the hidden magnetic field cannot
be sensibly larger than 10 G, assuming the simplest case of a single
valued microturbulent field that fills the entire upflowing photospheric
volume. Alternatively, an equally good theoretical fit to the observed
scattering polarization amplitudes can be achieved by assuming that the
rate of depolarizing collisions is an order of magnitude smaller than
in the previous collisionally dominated case, but then the required
strength of the hidden field in the upflowing regions turns out to
be unrealistically high. These constraints reinforce our previously
obtained conclusion that there is a vast amount of hidden magnetic
energy and unsigned magnetic flux localized in the (intergranular)
downflowing regions of the quiet solar photosphere. This work has been
presented by tet{a4 AT05}.

---------------------------------------------------------
Title: Theory, Observation, and Modeling of the Zeeman and
Paschen-Back Effects in Molecular Lines
Authors: Asensio Ramos, A.
2006ASPC..358..301A Altcode:
We present a historical review of the theory of the Zeeman effect in
molecular lines, from its discovery at the end of the 19th century
till today. The fast development of the quantum theory owes much to
the impulse given by the experimental investigation of the molecular
Zeeman effect. Laboratory experiments produced fruitful results after
the predictions made by the quantum theory. The introduction by Racah
of the powerful angular momentum algebra gave a second impulse to
the theory and allowed to fully understand the fine structure and
polarization properties of molecular transitions. At present, the
theory of the Zeeman and Paschen-Back effects in molecular lines is
being applied to spectro-(polarimetric) observations to infer the
physical and magnetic properties of cold plasmas in the atmospheres
of the Sun and of other stars.

---------------------------------------------------------
Title: The Minimum Description Length Principle and Model Selection
in Spectropolarimetry
Authors: Asensio Ramos, A.
2006ApJ...646.1445A Altcode: 2006astro.ph..6516A
It is shown that the two-part minimum description length principle
can be used to discriminate among different models that can explain
a given observed data set. The description length is chosen to be the
sum of the lengths of the message needed to encode the model plus the
message needed to encode the data when the model is applied to the
data set. It is verified that the proposed principle can efficiently
distinguish the model that correctly fits the observations while
avoiding overfitting. The capabilities of this criterion are shown in
two simple problems for the analysis of observed spectropolarimetric
signals. The first is the denoising of observations with the aid
of the PCA technique. The second is the selection of the optimal
number of parameters in LTE inversions. We propose this criterion as a
quantitative approach for distinguishing the most plausible model among
a set of proposed models. This quantity is very easy to implement as
an additional output on the existing inversion codes.

---------------------------------------------------------
Title: Warm Water Vapor around Sagittarius B2
Authors: Cernicharo, José; Goicoechea, Javier R.; Pardo, Juan R.;
Asensio-Ramos, Andrés
2006ApJ...642..940C Altcode: 2006astro.ph..1336C
Several condensations heated externally by nearby hot stars are
present in the Sgr B2 region for which H2O far-IR lines are
expected to probe only an external low-density and high temperature
section. Millimeter-wave lines can penetrate deeper into them
(higher densities and lower Tk). We have conducted a study
combining H2O lines in both spectral regions using the ISO
(far-IR lines) and the IRAM 30 m telescope (183 GHz line). The far-IR
H2O lines, seen in absorption, are optically thick. They
form in the outermost gas in front of the far-IR continuum sources,
probing a maximum visual extinction of ~5-10 mag. IR photons from
the dust play a dominant role in their excitation. We conclude, based
on observations of the CO J=7-6 line at 806.65 GHz, and the lack of
emission from the far-IR CO lines, that the gas density has to be below
~104 cm-3. Using the gas kinetic temperature and
density derived from OH, CO, and other molecular species, we derive
a water column density of (9+/-3)×1016 cm-2 in
the absorbing gas, implying an abundance of ~=(1-2)×10-5 in
this region. The resulting relatively low H2O/OH abundance
ratio, ~=2-4, is a signature of UV photon-dominated surface layers
traced by far-IR observations. As a consequence, the temperature of
the absorbing gas is high, Tk~=300-500 K, which allows
very efficient neutral-neutral reactions producing H2O and
OH. Finally, the 183.31 GHz data allow one to trace the inner, denser
(n(H2)&gt;=105-106 cm-3),
and colder (Tk~40 K) gas. The emission is very strong
toward the cores with an estimated water vapor abundance of a few ×
10-7. There is also moderate extended emission around Sgr
B2 main condensations, in agreement with the water vapor abundance
derived from far-IR H2O lines. Based on observations
with ISO, an ESA project with instruments funded by ESA Member States
(especially the PI countries: France, Germany, the Netherlands, and
the United Kingdom) and with participation of ISAS and NASA.

---------------------------------------------------------
Title: Theory and Modeling of the Zeeman and Paschen-Back Effects
in Molecular Lines
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2006ApJ...636..548A Altcode: 2005astro.ph.10262A
This paper describes a very general approach to the calculation of
the Zeeman splitting effect produced by an external magnetic field
on the rotational levels of diatomic molecules. The method is valid
for arbitrary values of the total electronic spin and of the magnetic
field strength-that is, it holds for molecular electronic states of
any multiplicity and for both the Zeeman and incomplete Paschen-Back
regimes. It is based on an efficient numerical diagonalization of
the effective Zeeman Hamiltonian, which can incorporate easily all the
contributions one may eventually be interested in, such as the hyperfine
interaction of the external magnetic field with the spin motions of
the nuclei. The reliability of the method is demonstrated by comparing
our results with previous ones obtained via formulae valid only for
doublet states. We also present results for molecular transitions
arising between nondoublet electronic states, illustrating that their
Zeeman patterns show signatures produced by the Paschen-Back effect.

---------------------------------------------------------
Title: A new exact method for line radiative transfer
Authors: Elitzur, Moshe; Asensio Ramos, Andrés
2006MNRAS.365..779E Altcode: 2005astro.ph.10616E
We present a new method, the coupled escape probability (CEP), for exact
calculation of line emission from multi-level systems, solving only
algebraic equations for the level populations. The CEP formulation
of the classical two-level problem is a set of linear equations,
and we uncover an exact analytic expression for the emission from
two-level optically thick sources that holds as long as they are in
the `effectively thin' regime. In a comparative study of a number of
standard problems, the CEP method outperformed the leading line transfer
methods by substantial margins. The algebraic equations employed
by our new method are already incorporated in numerous codes based on
the escape probability approximation. All that is required for an exact
solution with these existing codes is to augment the expression for the
escape probability with simple zone-coupling terms. As an application,
we find that standard escape probability calculations generally produce
the correct cooling emission by the CII 158-μm line but not by the
3P lines of OI.

---------------------------------------------------------
Title: High-resolution IBIS Observations and Comparison with 3D
Simulations .
Authors: Asensio Ramos, A.; Janssen, K.; Cauzzi, G.; Reardon, K.
2006MSAIS...9...59A Altcode:
High resolution observations of a very quiet region of the solar
surface have been obtained with IBIS (Interferometric BIdimensional
Spectrometer) in the non-magnetic Fe I 7090.4 Å spectral line. We
present a first comparison between the observed, spatially resolved,
spectral data and the simulated spectra in a 3D snapshot of a
radiation-hydrodynamical simulation of the solar atmosphere. Preliminary
results indicate that the simulations reproduce quite well many of
the observational properties of the high resolution IBIS data, even
though the simulations present a velocity distribution that contains
values quite larger than the observed ones.

---------------------------------------------------------
Title: Very Efficient Methods for Multilevel Radiative Transfer in
Atomic and Molecular Lines
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2006EAS....18...25A Altcode: 2005astro.ph.12248A
The development of fast numerical methods for multilevel radiative
transfer (RT) applications often leads to important breakthroughs
in astrophysics, because they allow the investigation of problems
that could not be properly tackled using the methods previously
available. Probably, the most familiar example is the so-called
Multilevel Accelerated Λ-Iteration (MALI) technique of Rybicki &amp;
Hummer for the case of a local approximate operator, which is based
on Jacobi iteration. However, there are superior operator-splitting
methods, based on Gauss-Seidel (GS) and Successive Overrelaxation (SOR)
iteration, which provide a dramatic increase in the speed with which
non-LTE multilevel transfer problems can be solved in one, two and
three-dimensional geometries. Such RT methods, which were introduced
by Trujillo Bueno &amp; Fabiani Bendicho ten years ago, are the main
subject of the first part of this paper. We show in some detail how they
can be applied for solving multilevel RT problems in spherical geometry,
for both atomic and molecular line transitions. The second part of the
article addresses the issue of the calculation of the molecular number
densities when the approximation of instantaneous chemical equilibrium
turns out to be inadequate, which happens to be the case whenever the
dynamical time scales of the astrophysical plasma under consideration
are much shorter than the time needed by the molecules to form.

---------------------------------------------------------
Title: Quiet Solar Photosphere: Comparisons of High Resolution
Observations with 3-D Simulations
Authors: Cauzzi, G.; Asensio Ramos, A.; Reardon, K.; Janssen, K.
2005ESASP.600E..12C Altcode: 2005dysu.confE..12C; 2005ESPM...11...12C
No abstract at ADS

---------------------------------------------------------
Title: Evidence for Collisional Depolarization in the MgH Lines of
the Second Solar Spectrum
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2005ApJ...635L.109A Altcode: 2005astro.ph.10711A
The analysis of the Hanle effect in solar molecular lines allows us to
obtain empirical information on hidden, mixed-polarity magnetic fields
at subresolution scales in the (granular) upflowing regions of the
“quiet” solar photosphere. Here we report that collisions seem to be
very efficient in depolarizing the rotational levels of MgH lines. This
has the interesting consequence that in the upflowing regions of the
quiet solar photosphere the strength of the hidden magnetic field cannot
be much larger than 10 G, assuming the simplest case of a single-valued
microturbulent field that fills the entire upflowing photospheric
volume. Alternatively, an equally good theoretical fit to the observed
scattering polarization amplitudes can be achieved by assuming that the
rate of depolarizing collisions is an order of magnitude smaller than
in the previous collisionally dominated case, but then the required
strength of the hidden field in the upflowing regions turns out to
be unrealistically high. These constraints reinforce our previously
obtained conclusion that there is a vast amount of hidden magnetic
energy and unsigned magnetic flux localized in the (intergranular)
downflowing regions of the quiet solar photosphere.

---------------------------------------------------------
Title: An artificial neural network approach to the solution of
molecular chemical equilibrium
Authors: Asensio Ramos, A.; Socas-Navarro, H.
2005A&A...438.1021A Altcode: 2005astro.ph..5322A
A novel approach is presented for the solution of instantaneous
chemical equilibrium problems. The chemical equilibrium can be
considered, due to its intrinsically local character, as a mapping
of the three-dimensional parameter space spanned by the temperature,
hydrogen density and electron density into many one-dimensional
spaces representing the number density of each species. We take
advantage of the ability of artificial neural networks to approximate
non-linear functions and construct neural networks for the fast and
efficient solution of the chemical equilibrium problem in typical
stellar atmosphere physical conditions. The neural network approach
has the advantage of providing an analytic function, which can be
rapidly evaluated. The networks are trained with a learning set (that
covers the entire parameter space) until a relative error below 1%
is reached. It has been verified that the networks are not overtrained
by using an additional verification set. The networks are then applied
to a snapshot of realistic three-dimensional convection simulations
of the solar atmosphere showing good generalization properties.

---------------------------------------------------------
Title: Dichroic Masers Due to Radiation Anisotropy and the Influence
of the Hanle Effect on the Circumstellar SiO Polarization
Authors: Asensio Ramos, A.; Landi Degl'Innocenti, E.; Trujillo
Bueno, J.
2005ApJ...625..985A Altcode: 2005astro.ph..2405A
The theory of the generation and transfer of polarized radiation, mainly
developed for interpreting solar spectropolarimetric observations,
allows us to reconsider, in a more rigorous and elegant way, a physical
mechanism that has been suggested some years ago to interpret the high
degree of polarization often observed in astronomical masers. This
mechanism, for which the name of “dichroic maser” is proposed,
can operate when a low-density molecular cloud is illuminated by
an anisotropic source of radiation (e.g., a nearby star). Here we
investigate completely unsaturated masers and show that selective
stimulated emission processes are capable of producing highly polarized
maser radiation in a nonmagnetic environment. The polarization of
the maser radiation is linear and is directed tangentially to a ring
equidistant to the central star. We show that the Hanle effect due
to the presence of a magnetic field can produce a rotation (from the
tangential direction) of the polarization by more that 45° for some
selected combinations of the strength, inclination, and azimuth of the
magnetic field vector. However, these very same conditions produce a
drastic inhibition of the maser effect. The rotations of about 90°
observed in SiO masers in the evolved stars TX Cam by Kemball &amp;
Diamond and IRC +10011 by Desmurs and coworkers may then be explained
by a local modification of the anisotropy of the radiation field,
being transformed from mainly radial to mainly tangential.

---------------------------------------------------------
Title: Observation and Modeling of Anomalous CN Polarization Profiles
Produced by the Molecular Paschen-Back Effect in Sunspots
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Collados, M.
2005ApJ...623L..57A Altcode: 2005astro.ph..5076A
We report novel spectropolarimetric observations of sunspots carried
out with the Tenerife Infrared Polarimeter in a near-IR spectral
region around 15410 Å, which is known to contain two groups of
prominent OH lines that show circular polarization signals of
opposite polarity. Surrounding these well-known OH lines, we have
discovered the presence of CN lines of the Δv=1 band that show
anomalous polarization profiles. Although the Stokes V signals of
the OH lines are antisymmetric and of a sizable amplitude, the CN
lines show almost negligible circular polarization. On the contrary,
the linear polarization signals turn out to be much stronger in the
CN lines than in the OH lines. Interestingly, these CN lines present
striking antisymmetric linear polarization profiles, which we are able
to explain and model via the Paschen-Back effect theory for diatomic
molecules. The presence of such peculiar CN lines in the same spectral
region of the OH lines may be useful to improve our empirical knowledge
of solar magnetic fields via the simultaneous observation and modeling
of the transverse and longitudinal Zeeman effects in two different
molecular species.

---------------------------------------------------------
Title: Observation of the Molecular Zeeman Effect in the G Band
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Bianda, M.; Manso
Sainz, R.; Uitenbroek, H.
2004ApJ...611L..61A Altcode: 2004astro.ph..7332A; 2004astro.ph..7332R
Here we report on the first observational investigation of the
Zeeman effect in the G band around 4305 Å. Our spectropolarimetric
observations of sunspots with the Zürich Imaging Polarimeter at the
Istituto Ricerche Solari Locarno confirm our previous theoretical
prediction that the molecular Zeeman effect produces measurable
circular polarization signatures in several CH lines that are not
overlapped with atomic transitions. We also find both circular and
linear polarization signals produced by atomic lines whose wavelengths
lie in the G-band spectral region. Together, such molecular and atomic
lines are potentially important for empirical investigations of solar
and stellar magnetism. For instance, a comparison between observed and
calculated Stokes profiles suggests that the thermodynamical and/or
magnetic properties of the photospheric regions of sunspot umbrae are
horizontally structured with a component that might be associated with
umbral dots.

---------------------------------------------------------
Title: A substantial amount of hidden magnetic energy in the quiet Sun
Authors: Trujillo Bueno, J.; Shchukina, N.; Asensio Ramos, A.
2004Natur.430..326T Altcode: 2004astro.ph..9004T; 2004astro.ph..9004B
Deciphering and understanding the small-scale magnetic activity of the
quiet solar photosphere should help to solve many of the key problems
of solar and stellar physics, such as the magnetic coupling to the
outer atmosphere and the coronal heating. At present, we can see only
~1 per cent of the complex magnetism of the quiet Sun, which highlights
the need to develop a reliable way to investigate the remaining 99 per
cent. Here we report three-dimensional radiative transfer modelling of
scattering polarization in atomic and molecular lines that indicates
the presence of hidden, mixed-polarity fields on subresolution
scales. Combining this modelling with recent observational data, we
find a ubiquitous tangled magnetic field with an average strength of
~130G, which is much stronger in the intergranular regions of solar
surface convection than in the granular regions. So the average magnetic
energy density in the quiet solar photosphere is at least two orders
of magnitude greater than that derived from simplistic one-dimensional
investigations, and sufficient to balance radiative energy losses from
the solar chromosphere.

---------------------------------------------------------
Title: The Zeeman Effect in the G Band
Authors: Uitenbroek, H.; Miller-Ricci, E.; Asensio Ramos, A.; Trujillo
Bueno, J.
2004ApJ...604..960U Altcode: 2004astro.ph..1467U
We investigate the possibility of measuring magnetic field strength in
G-band bright points through the analysis of Zeeman polarization in
molecular CH lines. To this end we solve the equations of polarized
radiative transfer in the G band through a standard plane-parallel
model of the solar atmosphere with an imposed magnetic field
and through a more realistic snapshot from a simulation of solar
magnetoconvection. This region of the spectrum is crowded with many
atomic and molecular lines. Nevertheless, we find several instances of
isolated groups of CH lines that are predicted to produce a measurable
Stokes V signal in the presence of magnetic fields. In part this is
possible because the effective Landé factors of lines in the stronger
main branch of the CH A2Δ-X2Π transition
tend to zero rather quickly for increasing total angular momentum J,
resulting in a Stokes V spectrum of the G band that is less crowded than
the corresponding Stokes I spectrum. We indicate that, by contrast,
the effective Landé factors of the R and P satellite subbranches of
this transition tend to +/-1 for increasing J. However, these lines
are in general considerably weaker and do not contribute significantly
to the polarization signal. In one wavelength location near 430.4 nm,
the overlap of several magnetically sensitive and nonsensitive CH lines
is predicted to result in a single-lobed Stokes V profile, raising
the possibility of high spatial resolution narrowband polarimetric
imaging. In the magnetoconvection snapshot we find circular polarization
signals of the order of 1%, prompting us to conclude that measuring
magnetic field strength in small-scale elements through the Zeeman
effect in CH lines is a realistic prospect.

---------------------------------------------------------
Title: Evidence for a New Elliptical-Galaxy Paradigm: Sérsic and
Core Galaxies
Authors: Trujillo, I.; Erwin, Peter; Asensio Ramos, A.; Graham,
Alister W.
2004AJ....127.1917T Altcode: 2004astro.ph..3659T
We fitted the surface-brightness profiles of 21 elliptical galaxies
using both the Sérsic function and a new empirical model that combines
an inner power law with an outer Sérsic function. The profiles are
combinations of deconvolved Hubble Space Telescope (HST) profiles
from the literature and ellipse fits to the full WFPC2 mosaic images
and thus span a radial range from ~0.02" to about twice the half-light
radius. We are able to accurately fit the entire profiles using either
the Sérsic function or our new model. In doing so, we demonstrate that
most, if not all, so-called “power-law” galaxies are better described
as “Sérsic galaxies”-they are well modeled by the three-parameter
Sérsic profile into the limits of HST resolution-and that “core”
galaxies are best understood as consisting of an outer Sérsic profile
with an inner power-law cusp, which is a downward deviation from
the inward extrapolation of the Sérsic profile. This definition of
cores resolves ambiguities that result when the popular “Nuker law”
is fitted to the profiles of ellipticals and bulges, particularly at
lower luminosities. We also find that using the Nuker law to model
core-galaxy nuclear profiles systematically overestimates the core
radii by factors of 1.5-4.5 and underestimates the inner power-law
slope by ~20%-40% or more.

---------------------------------------------------------
Title: Detection of Polarization from the
E4Π-A4Π System of FeH in Sunspot Spectra
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Collados, M.
2004ApJ...603L.125A Altcode: 2004astro.ph..1597A; 2004astro.ph..1597R
Here we report the first detection of polarization signals
induced by the Zeeman effect in spectral lines of the
E4Π-A4Π system of FeH located around 1.6
μm. Motivated by the tentative detection of this band in the
intensity spectrum of late-type dwarfs, we have investigated the
full Stokes sunspot spectrum and have found circular and linear
polarization signatures that we associate with the FeH lines of the
E4Π-A4Π band system. We investigate the Zeeman
effect in these molecular transitions and point out that in Hund's case
(a) coupling, the effective Landé factors are never negative. For this
reason, the fact that our spectropolarimetric observations indicate that
the Landé factors of pairs of FeH lines have opposite signs prompts
us to conclude that the E4Π-A4Π system must be
in intermediate angular momentum coupling between Hund's cases (a) and
(b). We emphasize that theoretical and/or laboratory investigations of
this molecular system are urgently needed for exploiting its promising
diagnostic capabilities.

---------------------------------------------------------
Title: Inner and Outer Photometric Structure of Elliptical Galaxies
Authors: Graham, Alister W.; Erwin, P.; Trujillo, I.; Asensio Ramos, A.
2004cbhg.sympE..21G Altcode:
The Nuker model, when applied to the inner regions of “core” galaxies,
is shown to produce systematic biases in the determination of the
core “break-radii”. These radii can easily be (and often have been,
see Trujillo et al. 2003) over-estimated by more than 100%. Moreover,
due to curvature in the outer profiles of early-type galaxies (i.e.,
beyond the break-radius), none of the Nuker model parameters are found
to be robust quantities. A new empirical model that simultaneously
describes both the inner and outer light-profiles of elliptical galaxies
(and bulges in general) is presented. It consists of a Sérsic function
with an inner power-law and a variable transition region.

---------------------------------------------------------
Title: Transporte radiativo en líneas moleculares: aplicaciones
en Astrofísica

---------------------------------------------------------
Title: Transporte radiativo en líneas moleculares:
aplicaciones en Astrofísica

---------------------------------------------------------
Title: Radiative transfer in molecular
lines: applications in astrophysics;
Authors: Asensio Ramos, Andrés
2004PhDT.......178A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A New Empirical Model for the Structural Analysis of Early-Type
Galaxies, and A Critical Review of the Nuker Model
Authors: Graham, Alister W.; Erwin, Peter; Trujillo, I.; Asensio
Ramos, A.
2003AJ....125.2951G Altcode: 2003astro.ph..6023G
The Nuker law was designed to match the inner few (~3-10) arcseconds of
predominantly nearby (&lt;~30 Mpc) early-type galaxy light profiles;
it was never intended to describe an entire profile. The Sérsic
model, on the other hand, was developed to fit the entire profile;
however, because of the presence of partially depleted galaxy cores,
the Sérsic model cannot always describe the very inner region. We have
therefore developed a new empirical model consisting of an inner power
law, a transition region, and an outer Sérsic model to connect the
inner and outer structure of elliptical galaxies. We have additionally
explored the stability of the Nuker model parameters. Surprisingly,
none are found to be stable quantities; all are shown to vary
systematically with a profile's fitted radial extent, and often by
more than 100%. Considering elliptical galaxies spanning a range
of 7.5 mag, we reveal that the central stellar densities of the
underlying host galaxies increase with galaxy luminosity until the
onset of core formation, detected only in the brightest elliptical
galaxies. We suggest that the so-called power-law galaxies may actually
be described by the Sérsic model over their entire radial range. Based on observations made with the NASA/ESA Hubble Space Telescope,
obtained at the Space Telescope Science Institute, which is operated
by the Association of Universities for Research in Astronomy, Inc.,
under NASA contract NAS 5-26555.

---------------------------------------------------------
Title: Nonequilibrium CO Chemistry in the Solar Atmosphere
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Carlsson, M.;
Cernicharo, J.
2003ApJ...588L..61A Altcode: 2003astro.ph..3460R; 2003astro.ph..3460A
Investigating the reliability of the assumption of instantaneous
chemical equilibrium (ICE) for calculating the CO number density in
the solar atmosphere is of crucial importance for the resolution of
the long-standing controversy over the existence of “cool clouds”
in the chromosphere and for determining whether the cool gas owes its
existence to CO radiative cooling or to a hydrodynamical process. Here
we report the first results of such an investigation in which we
have carried out time-dependent gas-phase chemistry calculations
in radiation hydrodynamical simulations of solar chromospheric
dynamics. We show that while the ICE approximation turns out to be
suitable for modeling the observed infrared CO lines at the solar disk
center, it may substantially overestimate the “heights of formation”
of strong CO lines synthesized close to the edge of the solar disk,
especially concerning vigorous dynamic cases resulting from relatively
strong photospheric disturbances. This happens because during the
cool phases of the hydrodynamical simulations, the CO number density
in the outer atmospheric regions is smaller than what is stipulated
by the ICE approximation, resulting in decreased CO opacity in the
solar chromosphere. As a result, the cool CO-bearing gas that produces
the observed molecular lines must be located at atmospheric heights
not greater than ~700 km. We conclude that taking into account the
nonequilibrium chemistry improves the agreement with the available
on-disk and off-limb observations but that the hydrodynamical simulation
model has to be even cooler than anticipated by the ICE approximation,
and this has to be the case at the “new” (i.e., deeper) formation
regions of the rovibrational CO lines.

---------------------------------------------------------
Title: Radiative Transfer tools for the GTC
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Cernicharo, J.
2003RMxAC..16..162A Altcode:
We present very fast radiative transfer tools of interest for the
interpretation of future spectroscopic observations taken with the
GTC and its post-focus instrumentation. Our radiative transfer codes
are based on the iterative methods introduced by Trujillo Bueno &amp;
Fabiani Bendicho (1995). Taking into consideration spherical geometry
and macroscopic velocity fields, we present results from the application
of these fast radiative transfer methods. We show why it is of interest
to develop a medium-high resolution spectrograph in order to be able
to resolve the rotational structure of the molecular bands. We show
some spectropolarimetric observations made with the Tenerife Infrared
Polarimeter (TIP), developed at the IAC and the theoretical modeling
done with the theoretical tools we have developed.

---------------------------------------------------------
Title: Non-equilibrium Chemistry and Molecular Spectropolarimetry
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2003ASPC..307..195A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radiative Transfer in Molecular Lines
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2003ASPC..288..335A Altcode: 2003sam..conf..335A
Molecular lines are generally very good tracers of the physical
conditions in cold regions of the Universe (e.g. molecular clouds,
cool stars, etc.), but molecular species are also found in not so
cold environments (e.g. the magnetized solar atmosphere). For a
reliable interpretation of spectroscopic and spectropolarimetric
observations of molecular lines it is often necessary to carry out
detailed radiative transfer simulations in molecular lines, both in
LTE and NLTE. Here we present a multilevel radiative transfer code for
the synthesis of molecular lines in stellar atmospheres, showing some
illustrations of calculations in different astrophysical contexts and
considering molecules like H2O, CO and OH. We will discuss
our implementation of highly convergent iterative methods and formal
solvers with especial emphasis on spherical geometry. We will also
present a chemical evolution code which is currently allowing us to
check the approximation of instantaneous chemical equilibrium in the
calculation of the abundances of a variety of molecular species.

---------------------------------------------------------
Title: Detection of polarization from the
E4Π-A4Π system of FeH in sunspot spectra
Authors: Asensio Ramos, Andrés
2003cnam.conf...44A Altcode:
We report the first detection of polarization signals induced by the
Zeeman Effect in lines of the E4Π-A4Π system
of FeH located at 1.6 μm. Motivated by the tentative detection of
this band in the intensity spectrum of late-type dwarfs, we have
investigated in detail the full Stokes sunspot spectrum in the
near-infrared around 1.6 μm, finding conspicuous signals which we
associate with the FeH lines of the E4Π-A4Π
band. We investigate the Zeeman Effect in these molecular transitions in
order to identify the observed lines and to point out their potential
interest for magnetic field diagnostics. First, we use nearby OH lines
for estimating the magnetic field strength in the sunspot umbra. We
then apply the weak-field approximation to obtain a first estimation
of the effective Landé factor of some spectral lines, which we
identify as FeH lines. Our tentative identification is performed
under the assumption that Hund's case coupling is a sufficiently good
approximation. Theoretical and/or laboratory investigations of this
molecular system are urgently needed for a full exploitation of the
diagnostic capabilities of the band.

---------------------------------------------------------
Title: New Spectropolarimetric Observations of Solar Coronal Filaments
in the He I 10830 Å Multiplet
Authors: Collados, M.; Trujillo Bueno, J.; Asensio Ramos, A.
2003ASPC..307..468C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Connecting the central and global structure of early-type
galaxies
Authors: Graham, A. W.; Erwin, P.; Trujillo, I.; Asensio Ramos, A.
2002AAS...201.6806G Altcode: 2002BAAS...34R1219G
A new empirical model that accurately describes the inner and
outer light-profiles of early-type galaxies is presented. This model
effectively unites the Sérsic and Nuker models, and in so doing allows
one to perform meaningful comparisons between the inner and outer
properties of early-type galaxies. New and fundamental connections
between a galaxies structure and it's central supermassive black hole
will be presented.

---------------------------------------------------------
Title: Triaxial stellar systems following the r1/n
luminosity law: an analytical mass-density expression, gravitational
torques and the bulge/disc interplay
Authors: Trujillo, I.; Asensio Ramos, A.; Rubiño-Martín, J. A.;
Graham, Alister W.; Aguerri, J. A. L.; Cepa, J.; Gutiérrez, C. M.
2002MNRAS.333..510T Altcode: 2002astro.ph..1485T
We have investigated the structural and dynamical properties of
triaxial stellar systems whose surface brightness profiles follow the
r1/n luminosity law - extending the analysis by Ciotti,
who explored the properties of spherical r1/n systems. A
new analytical expression that accurately reproduces the spatial (i.e.,
deprojected) luminosity density profiles (error less than 0.1 per cent)
is presented for detailed modelling of the Sérsic family of luminosity
profiles. We evaluate both the symmetric and the non-axisymmetric
components of the gravitational potential and force, and compute the
torques as a function of position. For a given triaxiality, stellar
systems with smaller values of n have a greater non-axisymmetric
gravitational field component. We also explore the strength of the
non-axisymmetric forces produced by bulges with differing n and
triaxiality on systems having a range of bulge-to-disc ratios. The
increasing disc-to-bulge ratio with increasing galaxy type (decreasing
n) is found to greatly reduce the amplitude of the non-axisymmetric
terms, and therefore reduce the possibility that triaxial bulges in
late-type systems may be the mechanism or perturbation for non-symmetric
structures in the disc. Using seeing-convolved r1/n-bulge
plus exponential-disc fits to the K-band data from a sample of 80 nearby
disc galaxies, we probe the relations between galaxy type, Sérsic index
n and the bulge-to-disc luminosity ratio. These relations are shown
to be primarily a consequence of the relation between n and the total
bulge luminosity. In the K band, the trend of decreasing bulge-to-disc
luminosity ratio along the spiral Hubble sequence is predominantly,
though not entirely, a consequence of the change in the total bulge
luminosity; the trend between the total disc luminosity and Hubble
type is much weaker.

---------------------------------------------------------
Title: Radiative transfer in molecular lines
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Cernicharo, J.
2001ESASP.460..265A Altcode: 2001astro.ph..2270R; 2001astro.ph..2270A; 2001phso.conf..265A
The highly convergent iterative methods developed by Trujillo Bueno
and Fabiani Bendicho (1995) for radiative transfer (RT) applications
are generalized to spherical symmetry with velocity fields. These RT
methods are based on Jacobi, Gauss-Seidel (GS), and SOR iteration
and they form the basis of a new NLTE multilevel transfer code for
atomic and molecular lines. The benchmark tests carried out so far are
presented and discussed. The main aim is to develop a number of powerful
RT tools for the theoretical interpretation of molecular spectra.

---------------------------------------------------------
Title: G-Band Spectral Synthesis in Solar Magnetic Concentrations
Authors: Sánchez Almeida, J.; Asensio Ramos, A.; Trujillo Bueno,
J.; Cernicharo, J.
2001ApJ...555..978S Altcode: 2001astro.ph..3006A; 2001astro.ph..3006S
Narrowband imaging in the G band is commonly used to trace the small
magnetic field concentrations of the Sun, although the mechanism that
makes them bright has remained unclear. We carry out LTE syntheses
of the G band in an assorted set of semiempirical model magnetic
concentrations. The syntheses include all CH lines as well as the main
atomic lines within the bandpass. The model atmospheres produce bright
G-band spectra having many properties in common with the observed G-band
bright points. In particular, the contrast referring to the quiet Sun
is about twice the contrast in continuum wavelengths. The agreement
with observations does not depend on the specificities of the model
atmosphere; rather, it holds from single flux tubes to microstructured
magnetic atmospheres. However, the agreement requires that the real
G-band bright points are not spatially resolved, even in the best
observations. Since the predicted G-band intensities exceed by far
the observed values, we foresee a notable increase of contrast of the
G-band images upon improvement of the angular resolution. According
to the LTE modeling, the G-band spectrum emerges from the deep
photosphere that produces the continuum. Our syntheses also predict
solar magnetic concentrations showing up in continuum images but
not in the G band. Finally, we have examined the importance of the
CH photodissociation in setting the amount of G-band absorption. It
turns out to play a minor role.

---------------------------------------------------------
Title: The effective temperature scale of giant stars
(F0-K5). III. Stellar radii and the calibration of convection
Authors: Alonso, A.; Salaris, M.; Arribas, S.; Martínez-Roger, C.;
Asensio Ramos, A.
2000A&A...355.1060A Altcode:
We present an analysis of radii of giant stars with 6200 K&gt;= T_eff
&gt;= 3800 K based on angular diameters obtained by means of the IRFM
and distances computed from Hipparcos parallaxes. In order to asses the
reliability of IRFM diameters we have considered a selected sample of
stars whose diameters have been directly measured by interferometric
techniques with internal errors below 5%. The intercomparison shows
a fairly good consistency and no systematic differences against
temperature are apparent in the analysis. By averaging the individual
values obtained for a sample of approximately 300 stars, we present mean
values of linear radii of giants of solar metallicity; the results are
tentatively extended to metal-poor giants. We have also devised a method
to derive distance moduli of globular clusters complementary to the
standard Main Sequence (MS) and Horizontal Branch (HB) fitting. This
method is based on the fit of observed linear radii and effective
temperatures of Red Giant Branch stars of a given globular cluster
to the yields of theoretical isochrones. A careful assessment of the
uncertainty on the derived distances is provided. As expected, the
distances are critically dependent on the value of the mixing length
parameter adopted in the stellar models. We have applied the method
to provide a homogeneous distance scale for a representative sample
of Galactic globular clusters. The comparison of these distances
with the distance scale obtained by means of the MS- or HB-fitting
permits a consistent calibration and/or test of the superadiabatic
gradient in stellar envelopes, independent of the use of colour-T_eff
transformations.