explanation blue bibcodes open ADS page with paths to full text
Author name code: orozco-suarez
ADS astronomy entries on 2022-09-14
author:"Orozco Suarez, David"
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Title: The on-ground data reduction and calibration pipeline for
SO/PHI-HRT
Authors: Sinjan, J.; Calchetti, D.; Hirzberger, J.; Orozco Suárez,
D.; Albert, K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero,
A.; Blanco Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero,
L.; Gutierrez Marquez, P.; Kahil, F.; Kolleck, M.; Solanki, S. K.; del
Toro Iniesta, J. C.; Volkmer, R.; Woch, J.; Fiethe, B.; Gómez Cama,
J. M.; Pérez-Grande, I.; Sanchis Kilders, E.; Balaguer Jiménez,
M.; Bellot Rubio, L. R.; Carmona, M.; Deutsch, W.; Fernandez-Rico,
G.; Fernández-Medina, A.; García Parejo, P.; Gasent Blesa, J. L.;
Gizon, L.; Grauf, B.; Heerlein, K.; Korpi-Lagg, A.; Lange, T.; López
Jiménez, A.; Maue, T.; Meller, R.; Michalik, H.; Moreno Vacas, A.;
Müller, R.; Nakai, E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub,
J.; Strecker, H.; Torralbo, I.; Valori, G.
2022arXiv220814904S Altcode:
The ESA/NASA Solar Orbiter space mission has been successfully launched
in February 2020. Onboard is the Polarimetric and Helioseismic Imager
(SO/PHI), which has two telescopes, a High Resolution Telescope
(HRT) and the Full Disc Telescope (FDT). The instrument is designed
to infer the photospheric magnetic field and line-of-sight velocity
through differential imaging of the polarised light emitted by the
Sun. It calculates the full Stokes vector at 6 wavelength positions
at the Fe I 617.3 nm absorption line. Due to telemetry constraints,
the instrument nominally processes these Stokes profiles onboard,
however when telemetry is available, the raw images are downlinked and
reduced on ground. Here the architecture of the on-ground pipeline
for HRT is presented, which also offers additional corrections not
currently available on board the instrument. The pipeline can reduce
raw images to the full Stokes vector with a polarimetric sensitivity
of $10^{-3}\cdot I_{c}$ or better.
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Title: Unipolar versus Bipolar Internetwork Flux Appearance
Authors: Gosic, Milan; Katsukawa, Yukio; Bellot Rubio, L. R.; Del
Toro Iniesta, Jose Carlos; Cheung, Mark; Orozco Suárez, David
2022cosp...44.2513G Altcode:
Small-scale internetwork (IN) magnetic fields are considered to be
the main building blocks of the quiet Sun magnetism. It is therefore
of paramount importance to understand how these fields are generated
on the solar surface. To shed new light on this open question,
we studied the appearance modes and spatio-temporal evolution of
individual IN magnetic elements inside one supergranular cell. For
that purpose, we employed a high-resolution, high-sensitivity,
long-duration Hinode/NFI magnetogram sequence. From identification
of flux patches and magnetofrictional simulations, we show that there
are two distinct populations of IN flux concentrations: unipolar and
bipolar features. Bipolar features tend to be bigger, live longer
and carry more flux than unipolar features. About $70$% of the total
instantaneous IN flux detected inside the supergranule is in the form
of bipoles. Both types of flux concentrations are uniformly distributed
over the solar surface. However, bipolar features appear (randomly
oriented) at a faster rate than unipolar features (68 as opposed to
55~Mx~cm$^{-2}$~day$^{-1}$). Our results lend support to the idea that
bipolar features may be the signature of local dynamo action, while
unipolar features seem to be formed by coalescence of background flux.
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Title: Magnetic properties of short-lived penumbral microjets
Authors: Tapia, Azaymi Siu; Bellot Rubio, L. R.; Gafeira, Ricardo;
Orozco Suárez, David
2022cosp...44.2520T Altcode:
Penumbral microjets (PMJs) are fast elongated brightenings above
sunspots penumbrae. They are presumed to be related to photospheric
magnetic reconnection processes and contribute to the heating of the
plasma in the higher atmospheric layers. Studying the spectral and
polarization properties of the shortest-living microjets requires
the fastest temporal cadence possible and is currently a challenging
task. In this work, we use fast spectropolarimetric measurements of
the Ca II 8542 A line made with the CRISP instrument at the Swedish
1 m Solar Telescope, and exploit the diagnostic capabilities of this
line to retrieve the magnetic field configuration and its evolution
at different atmospheric heights during PMJs. Our findings show that
short-lived PMJs are associated with a transient perturbation in
the photospheric magnetic field and sometimes they show clear but
weaker changes in the chromospheric field as well. We will describe
the different types of evolution that were identified. These results
support the idea that PMJs may be the result of magnetic reconnection
at low altitudes in sunspot penumbra.
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Title: The magnetic drivers of campfires seen by the Polarimetric
and Helioseismic Imager (PHI) on Solar Orbiter
Authors: Kahil, F.; Hirzberger, J.; Solanki, S. K.; Chitta, L. P.;
Peter, H.; Auchère, F.; Sinjan, J.; Orozco Suárez, D.; Albert,
K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero, A.; Blanco
Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero, L.; Gutiérrez
Márquez, P.; Kolleck, M.; del Toro Iniesta, J. C.; Volkmer, R.;
Woch, J.; Fiethe, B.; Gómez Cama, J. M.; Pérez-Grande, I.; Sanchis
Kilders, E.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Calchetti,
D.; Carmona, M.; Deutsch, W.; Fernández-Rico, G.; Fernández-Medina,
A.; García Parejo, P.; Gasent-Blesa, J. L.; Gizon, L.; Grauf, B.;
Heerlein, K.; Lagg, A.; Lange, T.; López Jiménez, A.; Maue, T.;
Meller, R.; Michalik, H.; Moreno Vacas, A.; Müller, R.; Nakai,
E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub, J.; Strecker, H.;
Torralbo, I.; Valori, G.; Aznar Cuadrado, R.; Teriaca, L.; Berghmans,
D.; Verbeeck, C.; Kraaikamp, E.; Gissot, S.
2022A&A...660A.143K Altcode: 2022arXiv220213859K
Context. The Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter
(SO) spacecraft observed small extreme ultraviolet (EUV) bursts,
termed campfires, that have been proposed to be brightenings near the
apexes of low-lying loops in the quiet-Sun atmosphere. The underlying
magnetic processes driving these campfires are not understood. <BR
/> Aims: During the cruise phase of SO and at a distance of 0.523
AU from the Sun, the Polarimetric and Helioseismic Imager on Solar
Orbiter (SO/PHI) observed a quiet-Sun region jointly with SO/EUI,
offering the possibility to investigate the surface magnetic field
dynamics underlying campfires at a spatial resolution of about 380
km. <BR /> Methods: We used co-spatial and co-temporal data of the
quiet-Sun network at disc centre acquired with the High Resolution
Imager of SO/EUI at 17.4 nm (HRI<SUB>EUV</SUB>, cadence 2 s) and the
High Resolution Telescope of SO/PHI at 617.3 nm (HRT, cadence 2.5
min). Campfires that are within the SO/PHI−SO/EUI common field
of view were isolated and categorised according to the underlying
magnetic activity. <BR /> Results: In 71% of the 38 isolated events,
campfires are confined between bipolar magnetic features, which seem to
exhibit signatures of magnetic flux cancellation. The flux cancellation
occurs either between the two main footpoints, or between one of the
footpoints of the loop housing the campfire and a nearby opposite
polarity patch. In one particularly clear-cut case, we detected the
emergence of a small-scale magnetic loop in the internetwork followed
soon afterwards by a campfire brightening adjacent to the location
of the linear polarisation signal in the photosphere, that is to
say near where the apex of the emerging loop lays. The rest of the
events were observed over small scattered magnetic features, which
could not be identified as magnetic footpoints of the campfire hosting
loops. <BR /> Conclusions: The majority of campfires could be driven
by magnetic reconnection triggered at the footpoints, similar to the
physical processes occurring in the burst-like EUV events discussed
in the literature. About a quarter of all analysed campfires, however,
are not associated to such magnetic activity in the photosphere, which
implies that other heating mechanisms are energising these small-scale
EUV brightenings.
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Title: DeSIRe: Departure coefficient aided Stokes Inversion based
on Response functions
Authors: Ruiz Cobo, B.; Quintero Noda, C.; Gafeira, R.; Uitenbroek,
H.; Orozco Suárez, D.; Páez Mañá, E.
2022A&A...660A..37R Altcode: 2022arXiv220202226R
Future ground-based telescopes, such as the 4-metre class facilities
DKIST and EST, will dramatically improve on current capabilities for
simultaneous multi-line polarimetric observations in a wide range of
wavelength bands, from the near-ultraviolet to the near-infrared. As a
result, there will be an increasing demand for fast diagnostic tools,
i.e., inversion codes, that can infer the physical properties of the
solar atmosphere from the vast amount of data these observatories
will produce. The advent of substantially larger apertures,
with the concomitant increase in polarimetric sensitivity, will
drive an increased interest in observing chromospheric spectral
lines. Accordingly, pertinent inversion codes will need to take
account of line formation under general non-local thermodynamic
equilibrium (NLTE) conditions. Several currently available codes can
already accomplish this, but they have a common practical limitation
that impairs the speed at which they can invert polarised spectra,
namely that they employ numerical evaluation of the so-called response
functions to changes in the atmospheric parameters, which makes them
less suitable for the analysis of very large data volumes. Here we
present DeSIRe (Departure coefficient aided Stokes Inversion based on
Response functions), an inversion code that integrates the well-known
inversion code SIR with the NLTE radiative transfer solver RH. The
DeSIRe runtime benefits from employing analytical response functions
computed in local thermodynamic equilibrium (through SIR), modified
with fixed departure coefficients to incorporate NLTE effects in
chromospheric spectral lines. This publication describes the operating
fundamentals of DeSIRe and describes its behaviour, robustness,
stability, and speed. The code is ready to be used by the solar
community and is being made publicly available.
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Title: A modified Milne-Eddington approximation for a qualitative
interpretation of chromospheric spectral lines
Authors: Dorantes-Monteagudo, A. J.; Siu-Tapia, A. L.; Quintero-Noda,
C.; Orozco Suárez, D.
2022A&A...659A.156D Altcode: 2021arXiv211214536D
Context. The Milne-Eddington approximation provides an analytic and
simple solution to the radiative transfer equation. It can be easily
implemented in inversion codes used to fit spectro-polarimetric
observations and infer average values of the magnetic field vector
and the line-of-sight velocity of the solar plasma. However, in
principle, it is restricted to spectral lines that are formed under
local thermodynamic conditions, namely, photospheric and optically
thin lines. <BR /> Aims: We show that a simple modification to
the Milne-Eddington approximation is sufficient to infer relevant
physical parameters from spectral lines that deviate from local
thermodynamic equilibrium, such as those typically observed in the
solar chromosphere. <BR /> Methods: We modified the Milne-Eddington
approximation by including several exponential terms in the source
function to reproduce the prototypical shape of chromospheric spectral
lines. To check the validity of such an approximation, we first studied
the influence of these new terms on the profile shape by means of the
response functions. Then we tested the performance of an inversion
code including the modification against the presence of noise. The
approximation was also tested with realistic spectral lines generated
with the RH numerical radiative transfer code. Finally, we confronted
the code with synthetic profiles generated from magneto-hydrodynamic
simulations carried out with the Bifrost code. For the various tests, we
focused on the vector magnetic field and the line-of-sight velocity. We
compared our results with the weak-field approximation and center
of gravity technique as well. <BR /> Results: The response function
corresponding to the new terms in the source function have no trade-offs
with the response to the different components of the magnetic field
vector and line-of-sight velocity. This allows us to perform a robust
inference of the physical parameters from the interpretation of spectral
line shapes. The strategy has been successfully applied to synthetic
chromospheric Stokes profiles generated with both standard models and
realistic magnetohydrodynamic (MHD) simulations. The magnetic field
vector and velocity can be successfully recovered with the modified
Milne-Eddington approximation. <BR /> Conclusions: Milne-Eddington
model atmospheres that include exponential terms are not new to the
solar community but have been overlooked for quite some time. We show
that our modification to the Milne-Eddington approximation succeeds
in reproducing the profile shape of two chromospheric spectral lines,
namely, the Mg I b2 line and the Ca II at 854.2 nm. The results obtained
with this approach are in good agreement with the results obtained
from the weak field approximation (for magnetic field) and the center
of gravity (for velocity). However, the Milne-Eddington approximation
possesses a great advantage over classical methods since it is not
limited to weak magnetic fields or to a restricted range of velocities.
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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&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: The Solar Internetwork. III. Unipolar versus Bipolar Flux
Appearance
Authors: Gošić, M.; Bellot Rubio, L. R.; Cheung, M. C. M.; Orozco
Suárez, D.; Katsukawa, Y.; del Toro Iniesta, J. C.
2022ApJ...925..188G Altcode: 2021arXiv211103208G
Small-scale internetwork (IN) magnetic fields are considered to be the
main building blocks of quiet Sun magnetism. For this reason, it is
crucial to understand how they appear on the solar surface. Here,
we employ a high-resolution, high-sensitivity, long-duration
Hinode/NFI magnetogram sequence to analyze the appearance modes and
spatiotemporal evolution of individual IN magnetic elements inside a
supergranular cell at the disk center. From identification of flux
patches and magnetofrictional simulations, we show that there are
two distinct populations of IN flux concentrations: unipolar and
bipolar features. Bipolar features tend to be bigger and stronger
than unipolar features. They also live longer and carry more flux
per feature. Both types of flux concentrations appear uniformly over
the solar surface. However, we argue that bipolar features truly
represent the emergence of new flux on the solar surface, while
unipolar features seem to be formed by the coalescence of background
flux. Magnetic bipoles appear at a faster rate than unipolar features
(68 as opposed to 55 Mx cm<SUP>-2</SUP> day<SUP>-1</SUP>), and provide
about 70% of the total instantaneous IN flux detected in the interior
of the supergranule.
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Title: Probing Upflowing Regions in the Quiet Sun and Coronal Holes
Authors: Schwanitz, Conrad; Harra, Louise; Raouafi, Nour E.; Sterling,
Alphonse C.; Moreno Vacas, Alejandro; del Toro Iniesta, Jose Carlos;
Orozco Suárez, David; Hara, Hirohisa
2021SoPh..296..175S Altcode: 2021arXiv211012753S
Recent observations from Parker Solar Probe have revealed that the
solar wind has a highly variable structure. How this complex behaviour
is formed in the solar corona is not yet known, since it requires
omnipresent fluctuations, which constantly emit material to feed
the wind. In this article we analyse 14 upflow regions in the solar
corona to find potential sources for plasma flow. The upflow regions
are derived from spectroscopic data from the EUV Imaging Spectrometer
(EIS) on board Hinode determining their Doppler velocity and defining
regions which have blueshifts stronger than −6 kms−<SUP>1</SUP>. To
identify the sources of these blueshift data from the Atmospheric
Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI),
on board the Solar Dynamics Observatory (SDO), and the X-ray Telescope
(XRT), on board Hinode, are used. The analysis reveals that only 5 out
of 14 upflows are associated with frequent transients, like obvious
jets or bright points. In contrast to that, seven events are associated
with small-scale features, which show a large variety of dynamics. Some
resemble small bright points, while others show an eruptive nature, all
of which are faint and only live for a few minutes; we cannot rule out
that several of these sources may be fainter and, hence, less obvious
jets. Since the complex structure of the solar wind is known, this
suggests that new sources have to be considered or better methods used
to analyse the known sources. This work shows that small and frequent
features, which were previously neglected, can cause strong upflows in
the solar corona. These results emphasise the importance of the first
observations from the Extreme-Ultraviolet Imager (EUI) on board Solar
Orbiter, which revealed complex small-scale coronal structures.
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Title: Diagnostic capabilities of spectropolarimetric observations for
understanding solar phenomena. I. Zeeman-sensitive photospheric lines
Authors: Quintero Noda, C.; Barklem, P. S.; Gafeira, R.; Ruiz Cobo,
B.; Collados, M.; Carlsson, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Uitenbroek, H.; Katsukawa, Y.
2021A&A...652A.161Q Altcode: 2021arXiv210605084Q
Future ground-based telescopes will expand our capabilities for
simultaneous multi-line polarimetric observations in a wide range of
wavelengths, from the near-ultraviolet to the near-infrared. This
creates a strong demand to compare candidate spectral lines to
establish a guideline of the lines that are most appropriate for each
observation target. We focused in this first work on Zeeman-sensitive
photospheric lines in the visible and infrared. We first examined their
polarisation signals and response functions using a 1D semi-empirical
atmosphere. Then we studied the spatial distribution of the line core
intensity and linear and circular polarisation signals using a realistic
3D numerical simulation. We ran inversions of synthetic profiles, and
we compared the heights at which we obtain a high correlation between
the input and the inferred atmosphere. We also used this opportunity
to revisit the atomic information we have on these lines and computed
the broadening cross-sections due to collisions with neutral hydrogen
atoms for all the studied spectral lines. The results reveal that
four spectral lines stand out from the rest for quiet-Sun and network
conditions: Fe I 5250.2, 6302, 8468, and 15 648 Å. The first three
form higher in the atmosphere, and the last line is mainly sensitive to
the atmospheric parameters at the bottom of the photosphere. However,
as they reach different heights, we strongly recommend using at least
one of the first three candidates together with the Fe I 15 648 Å line
to optimise our capabilities for inferring the thermal and magnetic
properties of the lower atmosphere.
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Title: Machine learning initialization to accelerate Stokes profile
inversions
Authors: Gafeira, R.; Orozco Suárez, D.; Milić, I.; Quintero Noda,
C.; Ruiz Cobo, B.; Uitenbroek, H.
2021A&A...651A..31G Altcode: 2021arXiv210309651G
Context. At present, an exponential growth in scientific data
from current and upcoming solar observatories is expected. Most of
the data consist of high spatial and temporal resolution cubes of
Stokes profiles taken in both local thermodynamic equilibrium (LTE)
and non-LTE spectral lines. The analysis of such solar observations
requires complex inversion codes. Hence, it is necessary to develop
new tools to boost the speed and efficiency of inversions and reduce
computation times and costs. <BR /> Aims: In this work we discuss
the application of convolutional neural networks (CNNs) as a tool to
advantageously initialize Stokes profile inversions. <BR /> Methods:
To demonstrate the usefulness of CNNs, we concentrate in this paper on
the inversion of LTE Stokes profiles. We use observations taken with
the spectropolarimeter on board the Hinode spacecraft as a test bench
mark. First, we carefully analyse the data with the SIR inversion code
using a given initial atmospheric model. The code provides a set of
atmospheric models that reproduce the observations well. These models
are then used to train a CNN. Afterwards, the same data are again
inverted with SIR but using the trained CNN to provide the initial
guess atmospheric models for SIR. <BR /> Results: The CNNs allow us
to significantly reduce the number of inversion cycles when used to
compute initial guess model atmospheres (`assisted inversions'),
therefore decreasing the computational time for LTE inversions by
a factor of two to four. CNNs alone are much faster than assisted
inversions, but the latter are more robust and accurate. CNNs also
help to automatically cluster pixels with similar physical properties,
allowing the association with different solar features on the solar
surface, which is useful when inverting huge datasets where completely
different regimes are present. The advantages and limitations of machine
learning techniques for estimating optimum initial atmospheric models
for spectral line inversions are discussed. Finally, we describe a
python wrapper for the SIR and DeSIRe codes that allows for the easy
setup of parallel inversions. The tool implements the assisted inversion
method described in this paper. The parallel wrapper can also be used
to synthesize Stokes profiles with the RH code. <BR /> Conclusions:
The assisted inversions can speed up the inversion process, but the
efficiency and accuracy of the inversion results depend strongly on
the solar scene and the data used for the CNN training. This method
(assisted inversions) will not obviate the need for analysing individual
events with the utmost care but will provide solar scientists with
a much better opportunity to sample large amounts of inverted data,
which will undoubtedly broaden the physical discovery space.
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Title: On Fabry-Pérot Etalon-based Instruments. IV. Analytical
Formulation of Telecentric Etalons
Authors: Bailén, F. J.; Orozco Suárez, D.; del Toro Iniesta, J. C.
2021ApJS..254...18B Altcode: 2022arXiv220506026B
Fabry-Pérot etalons illuminated with collimated beams have been
analytically characterized in detail since their invention. Meanwhile,
most of the features of etalons located in telecentric planes have been
studied only numerically, despite the wide use of this configuration
in astrophysical instrumentation for decades. In this work we present
analytical expressions for the transmitted electric field and its
derivatives that are valid for etalons placed in slow telecentric
beams, like the ones commonly employed in solar instruments. We use
the derivatives to infer the sensitivity of the electric field to
variations in the optical thickness for different reflectivities and
apertures of the incident beam, and we compare them to the collimated
case. This allows us to estimate the wavefront degradation produced by
roughness errors on the surfaces of the Fabry-Pérot etalons and to
establish the maximum allowed rms value of the cavity irregularities
across the footprint of the incident beam on the etalons that ensures
diffraction-limited performance. We also evaluate the wavefront
degradation intrinsic to these mounts, which is produced only by the
finite aperture of the beam and that must be added to the one produced
by defects. Finally, we discuss the differences in performance of
telecentric and collimated etalon-based instruments and we generalize
our formulation to anisotropic etalons.
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Title: First results from SO/PHI's on-board data reduction
Authors: Albert, K.; Hirzberger, J.; Kolleck, M.; Albelo Jorge,
N.; Busse, D.; Blanco Rodriguez, J.; Cobos Carrascosa, J. P.;
Fiethe, B.; Gandorfer, A.; Germerott, D.; Guan, Y.; Guerrero, L.;
Gutierrez-Marques, P.; Hernández Expósito, D.; Lange, T.; Michalik,
H.; Orozco Suárez, D.; Schou, J.; Solanki, S. K.; Woch, J. G.
2020AGUFMSH038..05A Altcode:
The Polarimetric and Helioseismic Imager (PHI), on-board Solar
Orbiter (SO), is a spectropolarimeter imaging the solar photosphere
at the wavelengths of the Fe I 617.3 nm Zeeman sensitive absorption
line. SO/PHI's aim is to provide data about the magnetic structures and
the line-of-sight (LOS) velocity in the solar atmosphere. For this, it
takes time series of data sets consisting of 2048 x 2048 pixel images of
the Sun at 6 wavelengths, each in 4 different polarisation states. With
the minimum necessary 17 bits pixel depth, one data set amounts to
approx. 0.2 GB. The guaranteed data telemetry for PHI, in contrast,
is only 50 GiB/orbit which would also need to contain any calibration
data obtained on-board, i.e. our flat and dark fields. To cope with
this discrepancy, SO/PHI is performing full data reduction on-board,
including the inversion of the radiative transfer equation. The
downloaded results are science ready data, containing 5 final images: a
total intensity image from nearby the spectral line, the magnetic field
strength, azimuth and inclination (describing the magnetic vector) and
the LOS velocity. This process maximises the science return by reducing
the number of necessary images in a data set, as well as rendering the
download of calibration data unessential. In the commissioning phase
of SO/PHI we used the on-board data reduction system successfully
for the first time. We have calibrated the instrument to its optimal
operational parameters (calculation of exposure time, focus, etc.),
acquired and processed calibration data (dark and flat fields),
removed the most significant instrumental artefacts from the data
(dark field, flat field, polarimetric modulation and polarimetric
cross-talk), and performed the inversion of the radiative transfer
equation. The data have then been compressed to further maximise the
use of our telemetry. This contribution presents and discusses the
final results from this process.
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Title: Power spectrum of turbulent convection in the solar photosphere
Authors: Yelles Chaouche, L.; Cameron, R. H.; Solanki, S. K.;
Riethmüller, T. L.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.;
Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort,
M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2020A&A...644A..44Y Altcode: 2020arXiv201009037Y
The solar photosphere provides us with a laboratory for understanding
turbulence in a layer where the fundamental processes of transport
vary rapidly and a strongly superadiabatic region lies very closely
to a subadiabatic layer. Our tools for probing the turbulence are
high-resolution spectropolarimetric observations such as have recently
been obtained with the two balloon-borne SUNRISE missions, and numerical
simulations. Our aim is to study photospheric turbulence with the
help of Fourier power spectra that we compute from observations
and simulations. We also attempt to explain some properties of the
photospheric overshooting flow with the help of its governing equations
and simulations. We find that quiet-Sun observations and smeared
simulations are consistent with each other and exhibit a power-law
behavior in the subgranular range of their Doppler velocity power
spectra with a power-law index of ≈ - 2. The unsmeared simulations
exhibit a power law that extends over the full range between the
integral and Taylor scales with a power-law index of ≈ - 2.25. The
smearing, reminiscent of observational conditions, considerably reduces
the extent of the power-law-like portion of the power spectra. This
suggests that the limited spatial resolution in some observations
might eventually result in larger uncertainties in the estimation of
the power-law indices. The simulated vertical velocity power spectra
as a function of height show a rapid change in the power-law index
(at the subgranular range) from roughly the optical depth unity layer,
that is, the solar surface, to 300 km above it. We propose that the
cause of the steepening of the power-law index is the transition from
a super- to a subadiabatic region, in which the dominant source of
motions is overshooting convection. A scale-dependent transport of
the vertical momentum occurs. At smaller scales, the vertical momentum
is more efficiently transported sideways than at larger scales. This
results in less vertical velocity power transported upward at small
scales than at larger scales and produces a progressively steeper
vertical velocity power law below 180 km. Above this height, the
gravity work progressively gains importance at all relevant scales,
making the atmosphere progressively more hydrostatic and resulting
in a gradually less steep power law. Radiative heating and cooling of
the plasma is shown to play a dominant role in the plasma energetics
in this region, which is important in terms of nonadiabatic damping
of the convective motions.
---------------------------------------------------------
Title: Sunrise Chromospheric Infrared SpectroPolarimeter (SCIP)
for sunrise III: system design and capability
Authors: Katsukawa, Y.; del Toro Iniesta, J. C.; Solanki, S. K.;
Kubo, M.; Hara, H.; Shimizu, T.; Oba, T.; Kawabata, Y.; Tsuzuki,
T.; Uraguchi, F.; Nodomi, Y.; Shinoda, K.; Tamura, T.; Suematsu,
Y.; Ishikawa, R.; Kano, R.; Matsumoto, T.; Ichimoto, K.; Nagata, S.;
Quintero Noda, C.; Anan, T.; Orozco Suárez, D.; Balaguer Jiménez,
M.; López Jiménez, A. C.; Cobos Carrascosa, J. P.; Feller, A.;
Riethmueller, T.; Gandorfer, A.; Lagg, A.
2020SPIE11447E..0YK Altcode:
The Sunrise balloon-borne solar observatory carries a 1 m aperture
optical telescope and provides us a unique platform to conduct
continuous seeing-free observations at UV-visible-IR wavelengths from
an altitude of higher than 35 km. For the next flight planned for
2022, the post-focus instrumentation is upgraded with new spectro-
polarimeters for the near UV (SUSI) and the near-IR (SCIP), whereas
the imaging spectro-polarimeter Tunable Magnetograph (TuMag) is capable
of observing multiple spectral lines within the visible wavelength. A
new spectro-polarimeter called the Sunrise Chromospheric Infrared
spectroPolarimeter (SCIP) is under development for observing near-IR
wavelength ranges of around 770 nm and 850 nm. These wavelength ranges
contain many spectral lines sensitive to solar magnetic fields and
SCIP will be able to obtain magnetic and velocity structures in the
solar atmosphere with a sufficient height resolution by combining
spectro-polarimetric data of these lines. Polarimetric measurements are
conducted using a rotating waveplate as a modulator and polarizing beam
splitters in front of the cameras. The spatial and spectral resolutions
are 0.2" and 2 105, respectively, and a polarimetric sensitivity of
0.03 % (1σ) is achieved within a 10 s integration time. To detect
minute polarization signals with good precision, we carefully designed
the opto-mechanical system, polarization optics and modulation, and
onboard data processing.
---------------------------------------------------------
Title: Coordination within the remote sensing payload on the Solar
Orbiter mission
Authors: Auchère, F.; Andretta, V.; Antonucci, E.; Bach, N.;
Battaglia, M.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Caminade,
S.; Carlsson, M.; Carlyle, J.; Cerullo, J. J.; Chamberlin, P. C.;
Colaninno, R. C.; Davila, J. M.; De Groof, A.; Etesi, L.; Fahmy,
S.; Fineschi, S.; Fludra, A.; Gilbert, H. R.; Giunta, A.; Grundy,
T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.;
Howard, R. A.; Hurford, G.; Kleint, L.; Kolleck, M.; Krucker, S.;
Lagg, A.; Landini, F.; Long, D. M.; Lefort, J.; Lodiot, S.; Mampaey,
B.; Maloney, S.; Marliani, F.; Martinez-Pillet, V.; McMullin, D. R.;
Müller, D.; Nicolini, G.; Orozco Suarez, D.; Pacros, A.; Pancrazzi,
M.; Parenti, S.; Peter, H.; Philippon, A.; Plunkett, S.; Rich, N.;
Rochus, P.; Rouillard, A.; Romoli, M.; Sanchez, L.; Schühle, U.;
Sidher, S.; Solanki, S. K.; Spadaro, D.; St Cyr, O. C.; Straus, T.;
Tanco, I.; Teriaca, L.; Thompson, W. T.; del Toro Iniesta, J. C.;
Verbeeck, C.; Vourlidas, A.; Watson, C.; Wiegelmann, T.; Williams,
D.; Woch, J.; Zhukov, A. N.; Zouganelis, I.
2020A&A...642A...6A Altcode:
Context. To meet the scientific objectives of the mission, the Solar
Orbiter spacecraft carries a suite of in-situ (IS) and remote sensing
(RS) instruments designed for joint operations with inter-instrument
communication capabilities. Indeed, previous missions have shown that
the Sun (imaged by the RS instruments) and the heliosphere (mainly
sampled by the IS instruments) should be considered as an integrated
system rather than separate entities. Many of the advances expected
from Solar Orbiter rely on this synergistic approach between IS and
RS measurements. <BR /> Aims: Many aspects of hardware development,
integration, testing, and operations are common to two or more
RS instruments. In this paper, we describe the coordination effort
initiated from the early mission phases by the Remote Sensing Working
Group. We review the scientific goals and challenges, and give an
overview of the technical solutions devised to successfully operate
these instruments together. <BR /> Methods: A major constraint for the
RS instruments is the limited telemetry (TM) bandwidth of the Solar
Orbiter deep-space mission compared to missions in Earth orbit. Hence,
many of the strategies developed to maximise the scientific return from
these instruments revolve around the optimisation of TM usage, relying
for example on onboard autonomy for data processing, compression,
and selection for downlink. The planning process itself has been
optimised to alleviate the dynamic nature of the targets, and an
inter-instrument communication scheme has been implemented which can
be used to autonomously alter the observing modes. We also outline the
plans for in-flight cross-calibration, which will be essential to the
joint data reduction and analysis. <BR /> Results: The RS instrument
package on Solar Orbiter will carry out comprehensive measurements
from the solar interior to the inner heliosphere. Thanks to the close
coordination between the instrument teams and the European Space
Agency, several challenges specific to the RS suite were identified
and addressed in a timely manner.
---------------------------------------------------------
Title: Models and data analysis tools for the Solar Orbiter mission
Authors: Rouillard, A. P.; Pinto, R. F.; Vourlidas, A.; De Groof, A.;
Thompson, W. T.; Bemporad, A.; Dolei, S.; Indurain, M.; Buchlin, E.;
Sasso, C.; Spadaro, D.; Dalmasse, K.; Hirzberger, J.; Zouganelis, I.;
Strugarek, A.; Brun, A. S.; Alexandre, M.; Berghmans, D.; Raouafi,
N. E.; Wiegelmann, T.; Pagano, P.; Arge, C. N.; Nieves-Chinchilla,
T.; Lavarra, M.; Poirier, N.; Amari, T.; Aran, A.; Andretta, V.;
Antonucci, E.; Anastasiadis, A.; Auchère, F.; Bellot Rubio, L.;
Nicula, B.; Bonnin, X.; Bouchemit, M.; Budnik, E.; Caminade, S.;
Cecconi, B.; Carlyle, J.; Cernuda, I.; Davila, J. M.; Etesi, L.;
Espinosa Lara, F.; Fedorov, A.; Fineschi, S.; Fludra, A.; Génot,
V.; Georgoulis, M. K.; Gilbert, H. R.; Giunta, A.; Gomez-Herrero, R.;
Guest, S.; Haberreiter, M.; Hassler, D.; Henney, C. J.; Howard, R. A.;
Horbury, T. S.; Janvier, M.; Jones, S. I.; Kozarev, K.; Kraaikamp,
E.; Kouloumvakos, A.; Krucker, S.; Lagg, A.; Linker, J.; Lavraud,
B.; Louarn, P.; Maksimovic, M.; Maloney, S.; Mann, G.; Masson, A.;
Müller, D.; Önel, H.; Osuna, P.; Orozco Suarez, D.; Owen, C. J.;
Papaioannou, A.; Pérez-Suárez, D.; Rodriguez-Pacheco, J.; Parenti,
S.; Pariat, E.; Peter, H.; Plunkett, S.; Pomoell, J.; Raines, J. M.;
Riethmüller, T. L.; Rich, N.; Rodriguez, L.; Romoli, M.; Sanchez,
L.; Solanki, S. K.; St Cyr, O. C.; Straus, T.; Susino, R.; Teriaca,
L.; del Toro Iniesta, J. C.; Ventura, R.; Verbeeck, C.; Vilmer, N.;
Warmuth, A.; Walsh, A. P.; Watson, C.; Williams, D.; Wu, Y.; Zhukov,
A. N.
2020A&A...642A...2R Altcode:
Context. The Solar Orbiter spacecraft will be equipped with a wide
range of remote-sensing (RS) and in situ (IS) instruments to record
novel and unprecedented measurements of the solar atmosphere and
the inner heliosphere. To take full advantage of these new datasets,
tools and techniques must be developed to ease multi-instrument and
multi-spacecraft studies. In particular the currently inaccessible
low solar corona below two solar radii can only be observed
remotely. Furthermore techniques must be used to retrieve coronal
plasma properties in time and in three dimensional (3D) space. Solar
Orbiter will run complex observation campaigns that provide interesting
opportunities to maximise the likelihood of linking IS data to their
source region near the Sun. Several RS instruments can be directed
to specific targets situated on the solar disk just days before
data acquisition. To compare IS and RS, data we must improve our
understanding of how heliospheric probes magnetically connect to the
solar disk. <BR /> Aims: The aim of the present paper is to briefly
review how the current modelling of the Sun and its atmosphere
can support Solar Orbiter science. We describe the results of a
community-led effort by European Space Agency's Modelling and Data
Analysis Working Group (MADAWG) to develop different models, tools,
and techniques deemed necessary to test different theories for the
physical processes that may occur in the solar plasma. The focus here
is on the large scales and little is described with regards to kinetic
processes. To exploit future IS and RS data fully, many techniques have
been adapted to model the evolving 3D solar magneto-plasma from the
solar interior to the solar wind. A particular focus in the paper is
placed on techniques that can estimate how Solar Orbiter will connect
magnetically through the complex coronal magnetic fields to various
photospheric and coronal features in support of spacecraft operations
and future scientific studies. <BR /> Methods: Recent missions such as
STEREO, provided great opportunities for RS, IS, and multi-spacecraft
studies. We summarise the achievements and highlight the challenges
faced during these investigations, many of which motivated the Solar
Orbiter mission. We present the new tools and techniques developed
by the MADAWG to support the science operations and the analysis of
the data from the many instruments on Solar Orbiter. <BR /> Results:
This article reviews current modelling and tool developments that ease
the comparison of model results with RS and IS data made available
by current and upcoming missions. It also describes the modelling
strategy to support the science operations and subsequent exploitation
of Solar Orbiter data in order to maximise the scientific output
of the mission. <BR /> Conclusions: The on-going community effort
presented in this paper has provided new models and tools necessary
to support mission operations as well as the science exploitation of
the Solar Orbiter data. The tools and techniques will no doubt evolve
significantly as we refine our procedure and methodology during the
first year of operations of this highly promising mission.
---------------------------------------------------------
Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
2020A&A...642A...3Z Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.
---------------------------------------------------------
Title: The Polarimetric and Helioseismic Imager on Solar Orbiter
Authors: Solanki, S. K.; del Toro Iniesta, J. C.; Woch, J.; Gandorfer,
A.; Hirzberger, J.; Alvarez-Herrero, A.; Appourchaux, T.; Martínez
Pillet, V.; Pérez-Grande, I.; Sanchis Kilders, E.; Schmidt, W.;
Gómez Cama, J. M.; Michalik, H.; Deutsch, W.; Fernandez-Rico, G.;
Grauf, B.; Gizon, L.; Heerlein, K.; Kolleck, M.; Lagg, A.; Meller, R.;
Müller, R.; Schühle, U.; Staub, J.; Albert, K.; Alvarez Copano, M.;
Beckmann, U.; Bischoff, J.; Busse, D.; Enge, R.; Frahm, S.; Germerott,
D.; Guerrero, L.; Löptien, B.; Meierdierks, T.; Oberdorfer, D.;
Papagiannaki, I.; Ramanath, S.; Schou, J.; Werner, S.; Yang, D.;
Zerr, A.; Bergmann, M.; Bochmann, J.; Heinrichs, J.; Meyer, S.;
Monecke, M.; Müller, M. -F.; Sperling, M.; Álvarez García, D.;
Aparicio, B.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Cobos
Carracosa, J. P.; Girela, F.; Hernández Expósito, D.; Herranz, M.;
Labrousse, P.; López Jiménez, A.; Orozco Suárez, D.; Ramos, J. L.;
Barandiarán, J.; Bastide, L.; Campuzano, C.; Cebollero, M.; Dávila,
B.; Fernández-Medina, A.; García Parejo, P.; Garranzo-García, D.;
Laguna, H.; Martín, J. A.; Navarro, R.; Núñez Peral, A.; Royo, M.;
Sánchez, A.; Silva-López, M.; Vera, I.; Villanueva, J.; Fourmond,
J. -J.; de Galarreta, C. Ruiz; Bouzit, M.; Hervier, V.; Le Clec'h,
J. C.; Szwec, N.; Chaigneau, M.; Buttice, V.; Dominguez-Tagle, C.;
Philippon, A.; Boumier, P.; Le Cocguen, R.; Baranjuk, G.; Bell,
A.; Berkefeld, Th.; Baumgartner, J.; Heidecke, F.; Maue, T.; Nakai,
E.; Scheiffelen, T.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Blanco
Rodríguez, J.; Domingo, V.; Ferreres Sabater, A.; Gasent Blesa,
J. L.; Rodríguez Martínez, P.; Osorno Caudel, D.; Bosch, J.; Casas,
A.; Carmona, M.; Herms, A.; Roma, D.; Alonso, G.; Gómez-Sanjuan, A.;
Piqueras, J.; Torralbo, I.; Fiethe, B.; Guan, Y.; Lange, T.; Michel,
H.; Bonet, J. A.; Fahmy, S.; Müller, D.; Zouganelis, I.
2020A&A...642A..11S Altcode: 2019arXiv190311061S
<BR /> Aims: This paper describes the Polarimetric and Helioseismic
Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and
helioseismology instrument to observe the Sun from outside the Sun-Earth
line. It is the key instrument meant to address the top-level science
question: How does the solar dynamo work and drive connections between
the Sun and the heliosphere? SO/PHI will also play an important role
in answering the other top-level science questions of Solar Orbiter,
while hosting the potential of a rich return in further science. <BR
/> Methods: SO/PHI measures the Zeeman effect and the Doppler shift
in the Fe I 617.3 nm spectral line. To this end, the instrument
carries out narrow-band imaging spectro-polarimetry using a tunable
LiNbO<SUB>3</SUB> Fabry-Perot etalon, while the polarisation modulation
is done with liquid crystal variable retarders. The line and the nearby
continuum are sampled at six wavelength points and the data are recorded
by a 2k × 2k CMOS detector. To save valuable telemetry, the raw data
are reduced on board, including being inverted under the assumption of
a Milne-Eddington atmosphere, although simpler reduction methods are
also available on board. SO/PHI is composed of two telescopes; one,
the Full Disc Telescope, covers the full solar disc at all phases of
the orbit, while the other, the High Resolution Telescope, can resolve
structures as small as 200 km on the Sun at closest perihelion. The high
heat load generated through proximity to the Sun is greatly reduced by
the multilayer-coated entrance windows to the two telescopes that allow
less than 4% of the total sunlight to enter the instrument, most of
it in a narrow wavelength band around the chosen spectral line. <BR />
Results: SO/PHI was designed and built by a consortium having partners
in Germany, Spain, and France. The flight model was delivered to
Airbus Defence and Space, Stevenage, and successfully integrated into
the Solar Orbiter spacecraft. A number of innovations were introduced
compared with earlier space-based spectropolarimeters, thus allowing
SO/PHI to fit into the tight mass, volume, power and telemetry budgets
provided by the Solar Orbiter spacecraft and to meet the (e.g. thermal)
challenges posed by the mission's highly elliptical orbit.
---------------------------------------------------------
Title: Temporal evolution of short-lived penumbral microjets
Authors: Siu-Tapia, A. L.; Bellot Rubio, L. R.; Orozco Suárez, D.;
Gafeira, R.
2020A&A...642A.128S Altcode: 2020arXiv200715926S
Context. Penumbral microjets (PMJs) is the name given to elongated
jet-like brightenings observed in the chromosphere above sunspot
penumbrae. They are transient events that last from a few seconds
to several minutes, and their origin is presumed to be related to
magnetic reconnection processes. Previous studies have mainly focused
on their morphological and spectral characteristics, and more recently
on their spectropolarimetric signals during the maximum brightness
stage. Studies addressing the temporal evolution of PMJs have also
been carried out, but they are based on spatial and spectral time
variations only. <BR /> Aims: Here we investigate, for the first
time, the temporal evolution of the polarization signals produced by
short-lived PMJs (lifetimes < 2 min) to infer how the magnetic field
vector evolves in the upper photosphere and mid-chromosphere. <BR />
Methods: We use fast-cadence spectropolarimetric observations of the
Ca II 854.2 nm line taken with the CRisp Imaging Spectropolarimeter
at the Swedish 1 m Solar Telescope. The weak-field approximation (WFA)
is used to estimate the strength and inclination of the magnetic field
vector. By separating the Ca II 854.2 nm line into two different
wavelength domains to account for the chromospheric origin of the
line core and the photospheric contribution to the wings, we infer
the height variation of the magnetic field vector. <BR /> Results:
The WFA reveals larger magnetic field changes in the upper photosphere
than in the chromosphere during the PMJ maximum brightness stage. In
the photosphere, the magnetic field inclination and strength undergo
a transient increase for most PMJs, but in 25% of the cases the field
strength decreases during the brightening. In the chromosphere, the
magnetic field tends to be slightly stronger during the PMJs. <BR
/> Conclusions: The propagation of compressive perturbation fronts
followed by a rarefaction phase in the aftershock region may explain
the observed behavior of the magnetic field vector. The fact that such
behavior varies among the analyzed PMJs could be a consequence of the
limited temporal resolution of the observations and the fast-evolving
nature of the PMJs.
---------------------------------------------------------
Title: Magnetic properties of short-lived penumbral microjets
Authors: Siu-Tapia, A.; Bellot Rubio, L.; Orozco Suárez, D.;
Gafeira, R.
2020sea..confE.208S Altcode:
We investigate the temporal evolution of the polarization properties
during penumbral microjets (PMJs). Studying the magnetic properties
of these transients requires spectropolarimetric observations with
the fastest temporal cadence possible and is currently a challenging
task. In this work, we used fast temporal cadence spectropolarimetric
measurements of the Ca II 8542 Å line from the CRISP instrument at the
Swedish 1 m Solar Telescope, and exploited the diagnosis capabilities of
this line to retrieve the magnetic field configuration and its evolution
at different atmospheric heights during PMJs. Our findings show that
the short-lived PMJs are associated to a transient perturbation in
the photospheric magnetic field and sometimes they show clear but
weaker changes in the chromospheric field as well. Here we describe
the different types of evolution that were identified.
---------------------------------------------------------
Title: On Fabry-Pérot Etalon-based Instruments. III. Instrument
Applications
Authors: Bailén, F. J.; Orozco Suárez, D.; del Toro Iniesta, J. C.
2020ApJS..246...17B Altcode: 2020arXiv200200599B
The spectral, imaging, and polarimetric behavior of Fabry-Pérot
etalons have an influence on imaging vector magnetograph instruments
based on these devices. The impact depends on the optical configuration
(collimated or telecentric), on the relative position of the etalon
with respect to the polarimeter, on the type of etalon (air-gapped
or crystalline), and even on the polarimetric technique to be used
(single-beam or dual-beam). In this paper, we evaluate the artificial
line-of-sight velocities and magnetic field strengths that arise
in etalon-based instruments, attending to the factors mentioned. We
differentiate between signals that are implicit to telecentric mounts
due to the wavelength dependence of the point-spread function and
those emerging in both collimated and telecentric setups from the
polarimetric response of birefringent etalons. For the anisotropic
case, we consider two possible locations of the etalon—between the
modulator and the analyzer or after it—and we include the effect on
different channels when dual-beam polarimetry is employed. We also
evaluate the impact of the loss of symmetry produced in telecentric
mounts due to imperfections in the illumination and/or to a tilt of
the etalon relative to the incident beam.
---------------------------------------------------------
Title: A flexible and heterogeneous framework for scientific image
data processing on-board the Solar Orbiter PHI instrument
Authors: Lange, Tobias; Fiethe, Björn; Guan, Yejun; Michalik,
Harald; Albert, Kinga; Hirzberger, Johann; Orozco Suárez, David;
Rodríguez-Valido, Manuel
2019SPIE11155E..06L Altcode:
Present scientific space instruments generate a high amount of raw
data while deep-space missions only have a very limited telemetry
rate. Because the computation of the scientific relevant parameters
is usually accompanied with the reduction of the data, the processing
is desired to be carried out already on-board. To accomplish this,
the following paper presents a flexible image processing framework
which makes use of a heterogeneous data processing module consisting
of a space-grade General Purpose Processor (GPP) as well as two
dynamically reconfigurable Field-Programmable Gate Arrays used for
hardware acceleration. The flexibility and capabilities of the presented
framework are proven by means of three exemplary processing tasks of
the Polarimetric and Helioseismic Imager (PHI) on-board Solar Orbiter.
---------------------------------------------------------
Title: Chromospheric polarimetry through multiline observations of
the 850 nm spectral region III: Chromospheric jets driven by twisted
magnetic fields
Authors: Quintero Noda, C.; Iijima, H.; Katsukawa, Y.; Shimizu,
T.; Carlsson, M.; de la Cruz Rodríguez, J.; Ruiz Cobo, B.; Orozco
Suárez, D.; Oba, T.; Anan, T.; Kubo, M.; Kawabata, Y.; Ichimoto,
K.; Suematsu, Y.
2019MNRAS.486.4203Q Altcode: 2019MNRAS.tmp.1081N; 2019arXiv190409151Q
We investigate the diagnostic potential of the spectral lines at 850
nm for understanding the magnetism of the lower atmosphere. For that
purpose, we use a newly developed 3D simulation of a chromospheric
jet to check the sensitivity of the spectral lines to this phenomenon
as well as our ability to infer the atmospheric information through
spectropolarimetric inversions of noisy synthetic data. We start
comparing the benefits of inverting the entire spectrum at 850 nm versus
only the Ca II 8542 Å spectral line. We found a better match of the
input atmosphere for the former case, mainly at lower heights. However,
the results at higher layers were not accurate. After several tests,
we determined that we need to weight more the chromospheric lines
than the photospheric ones in the computation of the goodness of the
fit. The new inversion configuration allows us to obtain better fits and
consequently more accurate physical parameters. Therefore, to extract
the most from multiline inversions, a proper set of weights needs to
be estimated. Besides that, we conclude again that the lines at 850
nm, or a similar arrangement with Ca II 8542 Å plus Zeeman-sensitive
photospheric lines, pose the best-observing configuration for examining
the thermal and magnetic properties of the lower solar atmosphere.
---------------------------------------------------------
Title: On Fabry-Pérot Etalon-based Instruments. II. The Anisotropic
(Birefringent) Case
Authors: Bailén, F. J.; Orozco Suárez, D.; del Toro Iniesta, J. C.
2019ApJS..242...21B Altcode: 2019arXiv190610361B
Crystalline etalons present several advantages with respect to other
types of filtergraphs when employed in magnetographs, especially that
they can be tuned by only applying electric fields. However, anisotropic
crystalline etalons can also introduce undesired birefringent effects
that corrupt the polarization of the incoming light. In particular,
uniaxial Fabry-Pérots, such as LiNbO<SUB>3</SUB> etalons, are
birefringent when illuminated with an oblique beam. The farther the
incidence from the normal, the larger the induced retardance between the
two orthogonal polarization states. The application of high voltages,
as well as fabrication defects, can also change the direction of
the optical axis of the crystal, introducing birefringence even at
normal illumination. Here we obtain analytical expressions for the
induced retardance and for the Mueller matrix of uniaxial etalons
located in both collimated and telecentric configurations. We also
evaluate the polarimetric behavior of Z-cut crystalline etalons with
the incident angle, with the orientation of the optical axis, and with
the f-number of the incident beam for the telecentric case. We study
artificial signals produced in the output Stokes vector in the two
configurations. Last, we discuss the polarimetric dependence of the
imaging response of the etalon for both collimated and telecentric
setups.
---------------------------------------------------------
Title: Photospheric Magnetic Fields of the Trailing Sunspots in
Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
R.; von der Lühe, O.; Waldmann, T.
2019ASPC..526..291V Altcode: 2018arXiv180507752V
The solar magnetic field is responsible for all aspects of solar
activity. Sunspots are the main manifestation of the ensuing solar
activity. Combining high-resolution and synoptic observations has
the ambition to provide a comprehensive description of the sunspot
growth and decay processes. Active region NOAA 12396 emerged on 2015
August 3 and was observed three days later with the 1.5-meter GREGOR
solar telescope on 2015 August 6. High-resolution spectropolarimetric
data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
with the chromospheric He I λ1083.0 nm triplet. These near-infrared
spectropolarimetric observations were complemented by synoptic
line-of-sight magnetograms and continuum images of the Helioseismic
and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO).
---------------------------------------------------------
Title: On Fabry-Pérot Etalon-based Instruments. I. The Isotropic Case
Authors: Bailén, F. J.; Orozco Suárez, D.; del Toro Iniesta, J. C.
2019ApJS..241....9B Altcode: 2019arXiv190306403B
Here we assess the spectral and imaging properties of Fabry-Pérot
etalons when located in solar magnetographs. We discuss the chosen
configuration (collimated or telecentric) for both ideal and real
cases. For the real cases, we focus on the effects caused by the
polychromatic illumination of the filter by the irregularities in
the optical thickness of the etalon and by deviations from the ideal
illumination in both setups. We first review the general properties of
Fabry-Pérots and we then address the different sources of degradation
of the spectral transmission profile. We review and extend the general
treatment of defects followed by different authors. We discuss the
differences between the point spread functions (PSFs) of the collimated
and telecentric configurations for both monochromatic and (real)
quasi-monochromatic illumination of the etalon. The PSF corresponding
to collimated mounts is shown to have a better performance, although
it varies from point to point due to an apodization of the image
inherent to this configuration. This is in contrast to the (perfect)
telecentric case, where the PSF remains constant but produces artificial
velocities and magnetic field signals because of its strong spectral
dependence. We find that the unavoidable presence of imperfections in
the telecentrism produces a decrease of flux of photons and a shift,
a broadening and a loss of symmetrization of both the spectral and PSF
profiles over the field of view, thus compromising their advantages
over the collimated configuration. We evaluate these effects for
different apertures of the incident beam.
---------------------------------------------------------
Title: Quiet Sun magnetic fields: an observational view
Authors: Bellot Rubio, Luis; Orozco Suárez, David
2019LRSP...16....1B Altcode:
The quiet Sun is the region of the solar surface outside of sunspots,
pores, and plages. In continuum intensity it appears dominated by
granular convection. However, in polarized light the quiet Sun exhibits
impressive magnetic activity on a broad range of scales, from the 30,000
km of supergranular cells down to the smallest magnetic features of
about 100 km resolvable with current instruments. Quiet Sun fields are
observed to evolve in a coherent way, interacting with each other as
they are advected by the horizontal photospheric flows. They appear and
disappear over surprisingly short time scales, bringing large amounts
of magnetic flux to the solar surface. For this reason they may be
important contributors to the heating of the chromosphere. Peering into
such fields is difficult because of the weak signals they produce, which
are easily affected, and even completely hidden, by photon noise. Thus,
their evolution and nature remain largely unknown. In recent years
the situation has improved thanks to the advent of high-resolution,
high-sensitivity spectropolarimetric measurements and the application
of state-of-the-art Zeeman and Hanle effect diagnostics. Here we review
this important aspect of solar magnetism, paying special attention
to the techniques used to observe and characterize the fields,
their evolution on the solar surface, and their physical properties
as revealed by the most recent analyses. We identify the main open
questions that need to be addressed in the future and offer some ideas
on how to solve them.
---------------------------------------------------------
Title: Study of the polarization produced by the Zeeman effect in
the solar Mg I b lines
Authors: Quintero Noda, C.; Uitenbroek, H.; Carlsson, M.; Orozco
Suárez, D.; Katsukawa, Y.; Shimizu, T.; Ruiz Cobo, B.; Kubo, M.; Oba,
T.; Kawabata, Y.; Hasegawa, T.; Ichimoto, K.; Anan, T.; Suematsu, Y.
2018MNRAS.481.5675Q Altcode: 2018arXiv181001067Q; 2018MNRAS.tmp.2566Q
The next generation of solar observatories aim to understand the
magnetism of the solar chromosphere. Therefore, it is crucial to
understand the polarimetric signatures of chromospheric spectral
lines. For this purpose, we here examine the suitability of the three
Fraunhofer Mg I b<SUB>1</SUB>, b<SUB>2</SUB>, and b<SUB>4</SUB> lines
at 5183.6, 5172.7, and 5167.3 Å, respectively. We start by describing
a simplified atomic model of only six levels and three line transitions
for computing the atomic populations of the 3p-4s (multiplet number
2) levels involved in the Mg I b line transitions assuming non-local
thermodynamic conditions and considering only the Zeeman effect using
the field-free approximation. We test this simplified atom against
more complex ones finding that, although there are differences in the
computed profiles, they are small compared with the advantages provided
by the simple atom in terms of speed and robustness. After comparing
the three Mg I lines, we conclude that the most capable one is the
b<SUB>2</SUB> line as b<SUB>1</SUB> forms at similar heights and always
shows weaker polarization signals, while b<SUB>4</SUB> is severely
blended with photospheric lines. We also compare Mg I b<SUB>2</SUB>
with the K I D<SUB>1</SUB> and Ca II 8542 Å lines finding that the
former is sensitive to the atmospheric parameters at heights that
are in between those covered by the latter two lines. This makes Mg I
b<SUB>2</SUB> an excellent candidate for future multiline observations
that aim to seamlessly infer the thermal and magnetic properties of
different features in the lower solar atmosphere.
---------------------------------------------------------
Title: SOPHISM: Software Instrument Simulator
Authors: Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Orozco
Suárez, D.; Martínez Pillet, V.; Bonet, J. A.; Feller, A.;
Hirzberger, J.; Lagg, A.; Piqueras, J.; Gasent Blesa, J. L.
2018ascl.soft10017B Altcode:
SOPHISM models astronomical instrumentation from the entrance
of the telescope to data acquisition at the detector, along with
software blocks dealing with, for example, demodulation, inversion,
and compression. The code performs most analyses done with light
in astronomy, such as differential photometry, spectroscopy, and
polarimetry. The simulator offers flexibility and implementation of new
effects and subsystems, making it user-adaptable for a wide variety
of instruments. SOPHISM can be used for all stages of instrument
definition, design, operation, and lifetime tracking evaluation.
---------------------------------------------------------
Title: SOPHISM: An End-to-end Software Instrument Simulator
Authors: Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Orozco
Suárez, D.; Martínez Pillet, V.; Bonet, J. A.; Feller, A.;
Hirzberger, J.; Lagg, A.; Piqueras, J.; Gasent Blesa, J. L.
2018ApJS..237...35B Altcode:
We present a software simulator for the modeling of astronomical
instrumentation, which includes platform effects and software
processing. It is an end-to-end simulator, from the entrance of
the telescope to the data acquisition at the detector, along with
software blocks dealing, e.g., with demodulation, inversion, and
compression. Developed following the Solar Orbiter/Polarimetric
and Helioseismic Imager (SO/PHI) instrument, it comprises elements
such as a filtergraph, polarimetric modulator, detector, vibrations,
and accumulations. Through these, the simulator performs most of the
analyses that can be done with light in astronomy, such as differential
photometry, spectroscopy, and polarimetry. The simulator is coded
with high flexibility and ease of implementation of new effects and
subsystems. Thus, it allows for the user to adapt it to a wide variety
of instruments, even not exclusively solar ones, as illustrated with
an example of application to a night-time observation. The simulator
can provide support in the phase of instrument design and help assess
tolerances and test solutions to underperformances arising during the
instrument operations. All this makes SOPHISM a very valuable tool
for all the stages of astronomical instrument definition, design,
operation, and lifetime tracking evaluation.
---------------------------------------------------------
Title: Sunrise Chromospheric Infrared spectroPolarimeter (SCIP)
for the SUNRISE balloon-borne solar observatory
Authors: Suematsu, Yoshinori; Katsukawa, Yukio; Hara, Hirohisa;
Ichimoto, Kiyoshi; Shimizu, Toshifumi; Kubo, Masahito; Barthol,
Peter; Riethmueller, Tino; Gandorfer, Achim; Feller, Alex; Orozco
Suárez, David; Del Toro Iniesta, Jose Carlos; Kano, Ryouhei; Ishikawa,
Shin-nosuke; Ishikawa, Ryohko; Tsuzuki, Toshihiro; Uraguchi, Fumihiro;
Quintero Noda, Carlos; Tamura, Tomonori; Oba, Takayoshi; Kawabata,
Yusuke; Nagata, Shinichi; Anan, Tetsu; Cobos Carrascosa, Juan Pedro;
Lopez Jimenez, Antonio Carlos; Balaguer Jimenez, Maria; Solanki, Sami
2018cosp...42E3285S Altcode:
The SUNRISE balloon-borne solar observatory carries a 1 m aperture
optical telescope, and allows us to perform seeing-free continuous
observations at visible-IR wavelengths from an altitude higher than
35 km. In the past two flights, in 2009 and 2013, observations mainly
focused on fine structures of photospheric magnetic fields. For the
third flight planned for 2021, we are developing a new instrument
for conducting spectro-polarimetry of spectral lines formed over a
larger height range in the solar atmosphere from the photosphere to
the chromosphere. Targets of the spectro-polarimetric observation
are (1) to determine 3D magnetic structure from the photosphere to
the chromosphere, (2) to trace MHD waves from the photosphere to the
chromosphere, and (3) to reveal the mechanism driving chromospheric
jets, by measuring height- and time-dependent velocities and magnetic
fields. To achieve these goals, a spectro-polarimeter called SCIP
(Sunrise Chromospheric Infrared spectroPolarimeter) is designed to
observe near-infrared spectrum lines sensitive to solar magnetic
fields. The spatial and spectral resolutions are 0.2 arcsec and
200,000, respectively, while 0.03% polarimetric sensitivity is
achieved within a 10 sec integration time. The optical system employs
an Echelle grating and off-axis aspheric mirrors to observe the two
wavelength ranges centered at 850 nm and 770 nm simultaneously by
two cameras. Polarimetric measurements are performed using a rotating
waveplate and polarization beam-splitters in front of the cameras. For
detecting minute polarization signals with good precision, we carefully
assess the temperature dependence of polarization optics, and make
the opto-structural design that minimizes the thermal deformation
of the spectrograph optics. Another key technique is to attain good
(better than 30 msec) synchronization among the rotating phase of
the waveplate, read-out timing of cameras, and step timing of a
slit-scanning mirror. On-board accumulation and data processing are
also critical because we cannot store all the raw data read-out from the
cameras. We demonstrate that we can reduce the data down to almost 10%
with loss-less image compression and without sacrificing polarimetric
information in the data. The SCIP instrument is developed by internal
collaboration among Japanese institutes including Japan Aerospace
Exploration Agency (JAXA), the Spanish Sunrise consortium, and the
German Max Planck Institute for Solar System Research (MPS) with a
leadership of the National Astronomical Observatory of Japan (NAOJ).
---------------------------------------------------------
Title: The quick RTE inversion on FPGA for DKIST
Authors: Cobos Carrascosa, J. P.; Ramos Mas, J. L.; Aparicio del
Moral, B.; Hernández Expósito, D.; Sánchez Gómez, A.; Balaguer,
M.; López Jiménez, A. C.; Orozco Suárez, D.; del Toro Iniesta, J. C.
2018SPIE10707E..0LC Altcode:
In this contribution we present a multi-core system-on-chip, embedded on
FPGA, for real-time data processing, to be used in the Daniel K. Inouye
Solar Telescope (DKIST). Our system will provide "quick-look" magnetic
field vector and line-of-sight velocity maps to help solar physicists
to react to specific solar events or features during observations or
to address specific phenomena while analyzing the data off line. The
stand-alone device will be installed at the National Solar Observatory
(NSO) Data Center. It will be integrated in the processing data pipeline
through a software interface, and is competitive in computing speed
to complex computer clusters.
---------------------------------------------------------
Title: Image compression on reconfigurable FPGA for the SO/PHI
space instrument
Authors: Hernández Expósito, D.; Cobos Carrascosa, J. P.; Ramos
Mas, J. L.; Rodríguez Valido, M.; Orozco Suárez, D.; Hirzberger,
J.; Woch, J.; Solanki, S.; del Toro Iniesta, J. C.
2018SPIE10707E..2FH Altcode:
In this paper we present a novel FPGA implementation of the Consultative
Committee for Space Data Systems Image Data Compression (CCSDS-IDC
122.0-B-1) for performing image compression aboard the Polarimetric
Helioseismic Imager instrument of the ESA's Solar Orbiter mission. This
is a System-On-Chip solution based on a light multicore architecture
combined with an efficient ad-hoc Bit Plane Encoder core. This hardware
architecture performs an acceleration of 30 times with respect to a
software implementation running into space-qualified processors, like
LEON3. The system stands out over other FPGA implementations because
of the low resource usage, which does not use any external memory,
and of its configurability.
---------------------------------------------------------
Title: Getting Ready for the Third Science Flight of SUNRISE
Authors: Barthol, Peter; Katsukawa, Yukio; Lagg, Andreas; Solanki,
Sami K.; Kubo, Masahito; Riethmueller, Tino; Martínez Pillet,
Valentin; Gandorfer, Achim; Feller, Alex; Berkefeld, . Thomas; Orozco
Suárez, David; Del Toro Iniesta, Jose Carlos; Bernasconi, Pietro;
Álvarez-Herrero, Alberto; Quintero Noda, Carlos
2018cosp...42E.215B Altcode:
SUNRISE is a balloon-borne, stratospheric solar observatory dedicated
to the investigation of the structure and dynamics of the Sun's
magnetic field and its interaction with convective plasma flows and
waves. The previous science flights of SUNRISE in 2009 and 2013 have
led to many new scientific results, so far described in around 90
refereed publications. This success has shown the huge potential of the
SUNRISE concept and the recovery of the largely intact payload offers
the opportunity for a third flight.The scientific instrumentation of
SUNRISE 3 will have extended capabilities in particular to measure
magnetic fields, plasma velocities and temperatures with increased
sensitivity and over a larger height range in the solar atmosphere, from
the convectively dominated photosphere up to the still poorly understood
chromosphere. The latter is the key interaction region between magnetic
field, waves and radiation and plays a central role in transporting
energy to the outer layers of the solar atmosphere including the
corona.SUNRISE 3 will carry 2 new grating-based spectro-polarimeters
with slit-scanning and context imaging with slitjaw cameras. The
SUNRISE UV Spectro-polarimeter and Imager (SUSI) will explore the rich
near-UV range between 300 nm and 430 nm which is poorly accessible
from the ground. The SUNRISE Chromospheric Infrared spectro-Polarimeter
(SCIP) will sample 2 spectral windows in the near-infrared, containing
many spectral lines highly sensitive to magnetic fields at different
formation heights. In addition to the two new instruments the Imaging
Magnetograph eXperiment (IMaX), an etalon-based tunable filtergraph and
spectro-polarimeter flown on both previous missions, will be upgraded
to IMaX+, enhancing its cadence and giving access to 2 spectral lines
in the visible spectral range. All three instruments will allow
investigating both the photosphere and the chromosphere and will
ideally complement each other in terms of sensitivity, height coverage
and resolution.A new gondola with a sophisticated attitude control
system including roll damping will provide improved pointing/tracking
performance. Upgraded image stabilization with higher bandwidth will
further reduce residual jitter, maximizing the quality of the science
data.SUNRISE 3 is a joint project of the German Max-Planck-Institut für
Sonnensystemforschung together with the Spanish SUNRISE consortium, the
Johns Hopkins University Applied Physics Laboratory, USA, the German
Kiepenheuer Institut für Sonnenphysik, the National Astronomical
Observatory of Japan and the Japan Aerospace eXploraion Agency (JAXA).
---------------------------------------------------------
Title: Autonomous on-board data processing and instrument calibration
software for the SO/PHI
Authors: Albert, K.; Hirzberger, J.; Busse, D.; Lange, T.; Kolleck, M.;
Fiethe, B.; Orozco Suárez, D.; Woch, J.; Schou, J.; Blanco Rodriguez,
J.; Gandorfer, A.; Guan, Y.; Cobos Carrascosa, J. P.; Hernández
Expósito, D.; del Toro Iniesta, J. C.; Solanki, S. K.; Michalik, H.
2018SPIE10707E..0OA Altcode: 2018arXiv181003493A
The extension of on-board data processing capabilities is an
attractive option to reduce telemetry for scientific instruments
on deep space missions. The challenges that this presents, however,
require a comprehensive software system, which operates on the limited
resources a data processing unit in space allows. We implemented such
a system for the Polarimetric and Helioseismic Imager (PHI) on-board
the Solar Orbiter (SO) spacecraft. It ensures autonomous operation
to handle long command-response times, easy changing of the processes
after new lessons have been learned and meticulous book-keeping of all
operations to ensure scientific accuracy. This contribution presents
the requirements and main aspects of the software implementation,
followed by an example of a task implemented in the software frame,
and results from running it on SO/PHI. The presented example shows
that the different parts of the software framework work well together,
and that the system processes data as we expect. The flexibility of
the framework makes it possible to use it as a baseline for future
applications with similar needs and limitations as SO/PHI.
---------------------------------------------------------
Title: Solar polarimetry in the K I D<SUB>2</SUB> line : A novel
possibility for a stratospheric balloon
Authors: Quintero Noda, C.; Villanueva, G. L.; Katsukawa, Y.; Solanki,
S. K.; Orozco Suárez, D.; Ruiz Cobo, B.; Shimizu, T.; Oba, T.; Kubo,
M.; Anan, T.; Ichimoto, K.; Suematsu, Y.
2018A&A...610A..79Q Altcode: 2018arXiv180101655Q
Of the two solar lines, K I D<SUB>1</SUB> and D<SUB>2</SUB>, almost
all attention so far has been devoted to the D<SUB>1</SUB> line, as
D<SUB>2</SUB> is severely affected by an O<SUB>2</SUB> atmospheric
band. This, however, makes the latter appealing for balloon and space
observations from above (most of) the Earth's atmosphere. We estimate
the residual effect of the O<SUB>2</SUB> band on the K I D<SUB>2</SUB>
line at altitudes typical for stratospheric balloons. Our aim is to
study the feasibility of observing the 770 nm window. Specifically,
this paper serves as a preparation for the third flight of the Sunrise
balloon-borne observatory. The results indicate that the absorption
by O<SUB>2</SUB> is still present, albeit much weaker, at the expected
balloon altitude. We applied the obtained O<SUB>2</SUB> transmittance
to K I D<SUB>2</SUB> synthetic polarimetric spectra and found that in
the absence of line-of-sight motions, the residual O<SUB>2</SUB> has
a negligible effect on the K I D<SUB>2</SUB> line. On the other hand,
for Doppler-shifted K I D<SUB>2</SUB> data, the residual O<SUB>2</SUB>
might alter the shape of the Stokes profiles. However, the residual
O<SUB>2</SUB> absorption is sufficiently weak at stratospheric levels
that it can be divided out if appropriate measurements are made,
something that is impossible at ground level. Therefore, for the
first time with Sunrise III, we will be able to perform polarimetric
observations of the K I D<SUB>2</SUB> line and, consequently, we will
have improved access to the thermodynamics and magnetic properties of
the upper photosphere from observations of the K I lines.
---------------------------------------------------------
Title: Detection of emission in the Si I 1082.7 nm line core in
sunspot umbrae
Authors: Orozco Suárez, D.; Quintero Noda, C.; Ruiz Cobo, B.;
Collados Vera, M.; Felipe, T.
2017A&A...607A.102O Altcode: 2017arXiv170906773O
Context. Determining empirical atmospheric models for the solar
chromosphere is difficult since it requires the observation and
analysis of spectral lines that are affected by non-local thermodynamic
equilibrium (NLTE) effects. This task is especially difficult in sunspot
umbrae because of lower continuum intensity values in these regions
with respect to the surrounding brighter granulation. Umbral data is
therefore more strongly affected by the noise and by the so-called
scattered light, among other effects. <BR /> Aims: The purpose of this
study is to analyze spectropolarimetric sunspot umbra observations
taken in the near-infrared Si I 1082.7 nm line taking NLTE effects into
account. Interestingly, we detected emission features at the line core
of the Si I 1082.7 nm line in the sunspot umbra. Here we analyze the
data in detail and offer a possible explanation for the Si I 1082.7 nm
line emission. <BR /> Methods: Full Stokes measurements of a sunspot
near disk center in the near-infrared spectral range were obtained
with the GRIS instrument installed at the German GREGOR telescope. A
point spread function (PSF) including the effects of the telescope,
the Earth's atmospheric seeing, and the scattered light was constructed
using prior Mercury observations with GRIS and the information provided
by the adaptive optics system of the GREGOR telescope during the
observations. The data were then deconvolved from the PSF using a
principal component analysis deconvolution method and were analyzed
via the NICOLE inversion code, which accounts for NLTE effects in the
Si I 1082.7 nm line. The information of the vector magnetic field was
included in the inversion process. <BR /> Results: The Si I 1082.7 nm
line seems to be in emission in the umbra of the observed sunspot after
the effects of scattered light (stray light coming from wide angles)
are removed. We show how the spectral line shape of umbral profiles
changes dramatically with the amount of scattered light. Indeed, the
continuum levels range, on average, from 44% of the quiet Sun continuum
intensity to about 20%. Although very low, the inferred levels are in
line with current model predictions and empirical umbral models. The Si
I 1082.7 nm line is in emission after adding more that 30% of scattered
light so that it is very sensitive to a proper determination of the
PSF. Additionally, we have thoroughly investigated whether the emission
is a byproduct of the particular deconvolution technique but have not
found any evidence to the contrary. Only the circular polarization
signals seem to be more sensitive to the deconvolution strategy
because of the larger amount of noise in the umbra. Interestingly,
current umbral empirical models are not able to reproduce the emission
in the deconvolved umbral Stokes profiles. The results of the NLTE
inversions suggests that to obtain the emission in the Si I 1082.7 nm
line, the temperature stratification should first have a hump located
at about log τ = -2 and start rising at lower heights when moving into
the transition region. <BR /> Conclusions: This is, to our knowledge,
the first time the Si I 1082.7 nm line is seen in emission in sunspot
umbrae. The results show that the temperature stratification of current
umbral models may be more complex than expected with the transition
region located at lower heights above sunspot umbrae. Our finding might
provide insights into understanding why the sunspot umbra emission in
the millimeter spectral range is less than that predicted by current
empirical umbral models.
---------------------------------------------------------
Title: Chromospheric polarimetry through multiline observations of
the 850-nm spectral region - II. A magnetic flux tube scenario
Authors: Quintero Noda, C.; Kato, Y.; Katsukawa, Y.; Oba, T.; de la
Cruz Rodríguez, J.; Carlsson, M.; Shimizu, T.; Orozco Suárez, D.;
Ruiz Cobo, B.; Kubo, M.; Anan, T.; Ichimoto, K.; Suematsu, Y.
2017MNRAS.472..727Q Altcode: 2017arXiv170801333Q
In this publication, we continue the work started in Quintero Noda et
al., examining this time a numerical simulation of a magnetic flux
tube concentration. Our goal is to study if the physical phenomena
that take place in it, in particular, the magnetic pumping, leaves
a specific imprint on the examined spectral lines. We find that the
profiles from the interior of the flux tube are periodically doppler
shifted following an oscillation pattern that is also reflected in
the amplitude of the circular polarization signals. In addition, we
analyse the properties of the Stokes profiles at the edges of the flux
tube discovering the presence of linear polarization signals for the Ca
II lines, although they are weak with an amplitude around 0.5 per cent
of the continuum intensity. Finally, we compute the response functions
to perturbations in the longitudinal field, and we estimate the field
strength using the weak-field approximation. Our results indicate
that the height of formation of the spectral lines changes during the
magnetic pumping process, which makes the interpretation of the inferred
magnetic field strength and its evolution more difficult. These results
complement those from previous works, demonstrating the capabilities and
limitations of the 850-nm spectrum for chromospheric Zeeman polarimetry
in a very dynamic and complex atmosphere.
---------------------------------------------------------
Title: The Maximum Entropy Limit of Small-scale Magnetic Field
Fluctuations in the Quiet Sun
Authors: Gorobets, A. Y.; Berdyugina, S. V.; Riethmüller, T. L.;
Blanco Rodríguez, J.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
Gizon, L.; Hirzberger, J.; van Noort, M.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..233....5G Altcode: 2017arXiv171008361G
The observed magnetic field on the solar surface is characterized by a
very complex spatial and temporal behavior. Although feature-tracking
algorithms have allowed us to deepen our understanding of this behavior,
subjectivity plays an important role in the identification and tracking
of such features. In this paper, we continue studies of the temporal
stochasticity of the magnetic field on the solar surface without relying
either on the concept of magnetic features or on subjective assumptions
about their identification and interaction. We propose a data analysis
method to quantify fluctuations of the line-of-sight magnetic field by
means of reducing the temporal field’s evolution to the regular Markov
process. We build a representative model of fluctuations converging to
the unique stationary (equilibrium) distribution in the long time limit
with maximum entropy. We obtained different rates of convergence to the
equilibrium at fixed noise cutoff for two sets of data. This indicates
a strong influence of the data spatial resolution and mixing-polarity
fluctuations on the relaxation process. The analysis is applied to
observations of magnetic fields of the relatively quiet areas around an
active region carried out during the second flight of the Sunrise/IMaX
and quiet Sun areas at the disk center from the Helioseismic and
Magnetic Imager on board the Solar Dynamics Observatory satellite.
---------------------------------------------------------
Title: Flows along arch filaments observed in the GRIS `very fast
spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; 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.
2017IAUS..327...28G Altcode: 2017arXiv170102206G
A new generation of solar instruments provides improved spectral,
spatial, and temporal resolution, thus facilitating a better
understanding of dynamic processes on the Sun. High-resolution
observations often reveal multiple-component spectral line profiles,
e.g., in the near-infrared He i 10830 Å triplet, which provides
information about the chromospheric velocity and magnetic fine
structure. We observed an emerging flux region, including two small
pores and an arch filament system, on 2015 April 17 with the `very
fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
situated at the 1.5-meter GREGOR solar telescope at Observatorio del
Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
per minute) spectral scans of the solar surface and its potential to
follow dynamic processes on the Sun. We demonstrate the performance
of the `very fast spectroscopic mode' by tracking chromospheric
high-velocity features in the arch filament system.
---------------------------------------------------------
Title: Solar polarimetry through the K I lines at 770 nm
Authors: Quintero Noda, C.; Uitenbroek, H.; Katsukawa, Y.; Shimizu,
T.; Oba, T.; Carlsson, M.; Orozco Suárez, D.; Ruiz Cobo, B.; Kubo,
M.; Anan, T.; Ichimoto, K.; Suematsu, Y.
2017MNRAS.470.1453Q Altcode: 2017arXiv170510002Q
We characterize the K I D<SUB>1</SUB> & D<SUB>2</SUB> lines in
order to determine whether they could complement the 850 nm window,
containing the Ca II infrared triplet lines and several Zeeman sensitive
photospheric lines, that was studied previously. We investigate the
effect of partial redistribution on the intensity profiles, their
sensitivity to changes in different atmospheric parameters, and
the spatial distribution of Zeeman polarization signals employing a
realistic magnetohydrodynamic simulation. The results show that these
lines form in the upper photosphere at around 500 km, and that they
are sensitive to the line-of-sight velocity and magnetic field strength
at heights where neither the photospheric lines nor the Ca II infrared
lines are. However, at the same time, we found that their sensitivity
to the temperature essentially comes from the photosphere. Then, we
conclude that the K I lines provide a complement to the lines in the
850 nm window for the determination of atmospheric parameters in the
upper photosphere, especially for the line-of-sight velocity and the
magnetic field.
---------------------------------------------------------
Title: Erratum: Morphological Properties of
Slender CaII H Fibrils Observed by sunrise II (<A
href="http://doi.org/10.3847/1538-4365/229/1/6">ApJS 229, 1, 6</A>)
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
2017ApJS..230...11G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Slender Ca II H Fibrils Mapping Magnetic Fields in the Low
Solar Chromosphere
Authors: Jafarzadeh, S.; Rutten, R. J.; Solanki, S. K.; Wiegelmann, T.;
Riethmüller, T. L.; van Noort, M.; Szydlarski, M.; Blanco Rodríguez,
J.; Barthol, P.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.;
Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Schmidt, W.
2017ApJS..229...11J Altcode: 2016arXiv161003104J
A dense forest of slender bright fibrils near a small solar active
region is seen in high-quality narrowband Ca II H images from the SuFI
instrument onboard the Sunrise balloon-borne solar observatory. The
orientation of these slender Ca II H fibrils (SCF) overlaps with the
magnetic field configuration in the low solar chromosphere derived
by magnetostatic extrapolation of the photospheric field observed
with Sunrise/IMaX and SDO/HMI. In addition, many observed SCFs are
qualitatively aligned with small-scale loops computed from a novel
inversion approach based on best-fit numerical MHD simulation. Such
loops are organized in canopy-like arches over quiet areas that differ
in height depending on the field strength near their roots.
---------------------------------------------------------
Title: Magneto-static Modeling from Sunrise/IMaX: Application to an
Active Region Observed with Sunrise II
Authors: Wiegelmann, T.; Neukirch, T.; Nickeler, D. H.; Solanki, S. K.;
Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller,
T. L.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229...18W Altcode: 2017arXiv170101458N; 2017arXiv170101458W
Magneto-static models may overcome some of the issues facing force-free
magnetic field extrapolations. So far they have seen limited use
and have faced problems when applied to quiet-Sun data. Here we
present a first application to an active region. We use solar vector
magnetic field measurements gathered by the IMaX polarimeter during
the flight of the Sunrise balloon-borne solar observatory in 2013
June as boundary conditions for a magneto-static model of the higher
solar atmosphere above an active region. The IMaX data are embedded
in active region vector magnetograms observed with SDO/HMI. This work
continues our magneto-static extrapolation approach, which was applied
earlier to a quiet-Sun region observed with Sunrise I. In an active
region the signal-to-noise-ratio in the measured Stokes parameters
is considerably higher than in the quiet-Sun and consequently the
IMaX measurements of the horizontal photospheric magnetic field allow
us to specify the free parameters of the model in a special class of
linear magneto-static equilibria. The high spatial resolution of IMaX
(110-130 km, pixel size 40 km) enables us to model the non-force-free
layer between the photosphere and the mid-chromosphere vertically
by about 50 grid points. In our approach we can incorporate some
aspects of the mixed beta layer of photosphere and chromosphere, e.g.,
taking a finite Lorentz force into account, which was not possible with
lower-resolution photospheric measurements in the past. The linear model
does not, however, permit us to model intrinsic nonlinear structures
like strongly localized electric currents.
---------------------------------------------------------
Title: The Second Flight of the Sunrise Balloon-borne Solar
Observatory: Overview of Instrument Updates, the Flight, the Data,
and First Results
Authors: Solanki, S. K.; Riethmüller, T. L.; Barthol, P.; Danilovic,
S.; Deutsch, W.; Doerr, H. -P.; Feller, A.; Gandorfer, A.; Germerott,
D.; Gizon, L.; Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.;
Lagg, A.; Meller, R.; Tomasch, G.; van Noort, M.; Blanco Rodríguez,
J.; Gasent Blesa, J. L.; Balaguer Jiménez, M.; Del Toro Iniesta,
J. C.; López Jiménez, A. C.; Orozco Suarez, D.; Berkefeld, T.;
Halbgewachs, C.; Schmidt, W.; Álvarez-Herrero, A.; Sabau-Graziati,
L.; Pérez Grande, I.; Martínez Pillet, V.; Card, G.; Centeno, R.;
Knölker, M.; Lecinski, A.
2017ApJS..229....2S Altcode: 2017arXiv170101555S
The Sunrise balloon-borne solar observatory, consisting of a 1 m
aperture telescope that provides a stabilized image to a UV filter
imager and an imaging vector polarimeter, carried out its second science
flight in 2013 June. It provided observations of parts of active regions
at high spatial resolution, including the first high-resolution images
in the Mg II k line. The obtained data are of very high quality, with
the best UV images reaching the diffraction limit of the telescope
at 3000 Å after Multi-Frame Blind Deconvolution reconstruction
accounting for phase-diversity information. Here a brief update is
given of the instruments and the data reduction techniques, which
includes an inversion of the polarimetric data. Mainly those aspects
that evolved compared with the first flight are described. A tabular
overview of the observations is given. In addition, an example time
series of a part of the emerging active region NOAA AR 11768 observed
relatively close to disk center is described and discussed in some
detail. The observations cover the pores in the trailing polarity of
the active region, as well as the polarity inversion line where flux
emergence was ongoing and a small flare-like brightening occurred in
the course of the time series. The pores are found to contain magnetic
field strengths ranging up to 2500 G, and while large pores are clearly
darker and cooler than the quiet Sun in all layers of the photosphere,
the temperature and brightness of small pores approach or even exceed
those of the quiet Sun in the upper photosphere.
---------------------------------------------------------
Title: A Tale of Two Emergences: Sunrise II Observations of Emergence
Sites in a Solar Active Region
Authors: Centeno, R.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger,
J.; Riethmüller, T. L.; van Noort, M.; Orozco Suárez, D.; Berkefeld,
T.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229....3C Altcode: 2016arXiv161003531C
In 2013 June, the two scientific instruments on board the second Sunrise
mission witnessed, in detail, a small-scale magnetic flux emergence
event as part of the birth of an active region. The Imaging Magnetograph
Experiment (IMaX) recorded two small (∼ 5<SUP>\prime\prime</SUP> )
emerging flux patches in the polarized filtergrams of a photospheric Fe
I spectral line. Meanwhile, the Sunrise Filter Imager (SuFI) captured
the highly dynamic chromospheric response to the magnetic fields pushing
their way through the lower solar atmosphere. The serendipitous capture
of this event offers a closer look at the inner workings of active
region emergence sites. In particular, it reveals in meticulous detail
how the rising magnetic fields interact with the granulation as they
push through the Sun’s surface, dragging photospheric plasma in
their upward travel. The plasma that is burdening the rising field
slides along the field lines, creating fast downflowing channels at
the footpoints. The weight of this material anchors this field to the
surface at semi-regular spatial intervals, shaping it in an undulatory
fashion. Finally, magnetic reconnection enables the field to release
itself from its photospheric anchors, allowing it to continue its
voyage up to higher layers. This process releases energy that lights
up the arch-filament systems and heats the surrounding chromosphere.
---------------------------------------------------------
Title: Photospheric Response to an Ellerman Bomb-like Event—An
Analogy of Sunrise/IMaX Observations and MHD Simulations
Authors: Danilovic, S.; Solanki, S. K.; Barthol, P.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.;
Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.;
Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229....5D Altcode: 2016arXiv160903817D
Ellerman Bombs are signatures of magnetic reconnection, which is an
important physical process in the solar atmosphere. How and where they
occur is a subject of debate. In this paper, we analyze Sunrise/IMaX
data, along with 3D MHD simulations that aim to reproduce the exact
scenario proposed for the formation of these features. Although
the observed event seems to be more dynamic and violent than the
simulated one, simulations clearly confirm the basic scenario for the
production of EBs. The simulations also reveal the full complexity of
the underlying process. The simulated observations show that the Fe I
525.02 nm line gives no information on the height where reconnection
takes place. It can only give clues about the heating in the aftermath
of the reconnection. However, the information on the magnetic field
vector and velocity at this spatial resolution is extremely valuable
because it shows what numerical models miss and how they can be
improved.
---------------------------------------------------------
Title: Transverse Oscillations in Slender Ca II H Fibrils Observed
with Sunrise/SuFI
Authors: Jafarzadeh, S.; Solanki, S. K.; Gafeira, R.; van Noort, M.;
Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco Suárez, D.;
Riethmüller, T. L.; Schmidt, W.
2017ApJS..229....9J Altcode: 2016arXiv161007449J
We present observations of transverse oscillations in slender Ca II
H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long
time series of high- (spatial and temporal-) resolution seeing-free
observations in a 1.1 Å wide passband covering the line core of Ca
II H 3969 Å from the second flight of the Sunrise balloon-borne solar
observatory. The entire field of view, spanning the polarity inversion
line of an active region close to the solar disk center, is covered with
bright, thin, and very dynamic fine structures. Our analysis reveals
the prevalence of transverse waves in SCFs with median amplitudes and
periods on the order of 2.4 ± 0.8 km s<SUP>-1</SUP> and 83 ± 29 s,
respectively (with standard deviations given as uncertainties). We
find that the transverse waves often propagate along (parts of) the
SCFs with median phase speeds of 9 ± 14 km s<SUP>-1</SUP>. While the
propagation is only in one direction along the axis in some of the
SCFs, propagating waves in both directions, as well as standing waves
are also observed. The transverse oscillations are likely Alfvénic
and are thought to be representative of magnetohydrodynamic kink
waves. The wave propagation suggests that the rapid high-frequency
transverse waves, often produced in the lower photosphere, can
penetrate into the chromosphere with an estimated energy flux of ≈15
kW m<SUP>-2</SUP>. Characteristics of these waves differ from those
reported for other fibrillar structures, which, however, were observed
mainly in the upper solar chromosphere.
---------------------------------------------------------
Title: Kinematics of Magnetic Bright Features in the Solar Photosphere
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Barthol, P.;
Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon,
L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Riethmüller, T. L.; Schmidt, W.; van Noort, M.
2017ApJS..229....8J Altcode: 2016arXiv161007634J
Convective flows are known as the prime means of transporting magnetic
fields on the solar surface. Thus, small magnetic structures are good
tracers of turbulent flows. We study the migration and dispersal
of magnetic bright features (MBFs) in intergranular areas observed
at high spatial resolution with Sunrise/IMaX. We describe the flux
dispersal of individual MBFs as a diffusion process whose parameters are
computed for various areas in the quiet-Sun and the vicinity of active
regions from seeing-free data. We find that magnetic concentrations
are best described as random walkers close to network areas (diffusion
index, γ =1.0), travelers with constant speeds over a supergranule
(γ =1.9{--}2.0), and decelerating movers in the vicinity of flux
emergence and/or within active regions (γ =1.4{--}1.5). The three
types of regions host MBFs with mean diffusion coefficients of 130
km<SUP>2</SUP> s<SUP>-1</SUP>, 80-90 km<SUP>2</SUP> s<SUP>-1</SUP>,
and 25-70 km<SUP>2</SUP> s<SUP>-1</SUP>, respectively. The MBFs in
these three types of regions are found to display a distinct kinematic
behavior at a confidence level in excess of 95%.
---------------------------------------------------------
Title: Spectropolarimetric Evidence for a Siphon Flow along an
Emerging Magnetic Flux Tube
Authors: Requerey, Iker S.; Ruiz Cobo, B.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Blanco Rodríguez, J.; Solanki, S. K.; Barthol,
P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.;
van Noort, M.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229...15R Altcode: 2016arXiv161106732R
We study the dynamics and topology of an emerging magnetic flux
concentration using high spatial resolution spectropolarimetric data
acquired with the Imaging Magnetograph eXperiment on board the sunrise
balloon-borne solar observatory. We obtain the full vector magnetic
field and the line of sight (LOS) velocity through inversions of
the Fe I line at 525.02 nm with the SPINOR code. The derived vector
magnetic field is used to trace magnetic field lines. Two magnetic flux
concentrations with different polarities and LOS velocities are found
to be connected by a group of arch-shaped magnetic field lines. The
positive polarity footpoint is weaker (1100 G) and displays an upflow,
while the negative polarity footpoint is stronger (2200 G) and shows
a downflow. This configuration is naturally interpreted as a siphon
flow along an arched magnetic flux tube.
---------------------------------------------------------
Title: Morphological Properties of Slender Ca II H Fibrils Observed
by SUNRISE II
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
2017ApJS..229....6G Altcode: 2016arXiv161200319G
We use seeing-free high spatial resolution Ca II H data obtained by
the SUNRISE observatory to determine properties of slender fibrils
in the lower solar chromosphere. In this work we use intensity images
taken with the SuFI instrument in the Ca II H line during the second
scientific flight of the SUNRISE observatory to identify and track
elongated bright structures. After identification, we analyze theses
structures to extract their morphological properties. We identify
598 slender Ca II H fibrils (SCFs) with an average width of around
180 km, length between 500 and 4000 km, average lifetime of ≈400
s, and average curvature of 0.002 arcsec<SUP>-1</SUP>. The maximum
lifetime of the SCFs within our time series of 57 minutes is ≈2000
s. We discuss similarities and differences of the SCFs with other
small-scale, chromospheric structures such as spicules of type I and
II, or Ca II K fibrils.
---------------------------------------------------------
Title: A New MHD-assisted Stokes Inversion Technique
Authors: Riethmüller, T. L.; Solanki, S. K.; Barthol, P.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; van Noort, M.; Blanco Rodríguez, J.;
Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez
Pillet, V.; Knölker, M.
2017ApJS..229...16R Altcode: 2016arXiv161105175R
We present a new method of Stokes inversion of spectropolarimetric
data and evaluate it by taking the example of a Sunrise/IMaX
observation. An archive of synthetic Stokes profiles is obtained
by the spectral synthesis of state-of-the-art magnetohydrodynamics
(MHD) simulations and a realistic degradation to the level of the
observed data. The definition of a merit function allows the archive
to be searched for the synthetic Stokes profiles that best match the
observed profiles. In contrast to traditional Stokes inversion codes,
which solve the Unno-Rachkovsky equations for the polarized radiative
transfer numerically and fit the Stokes profiles iteratively, the new
technique provides the full set of atmospheric parameters. This gives
us the ability to start an MHD simulation that takes the inversion
result as an initial condition. After a relaxation process of half an
hour solar time we obtain physically consistent MHD data sets with
a target similar to the observation. The new MHD simulation is used
to repeat the method in a second iteration, which further improves
the match between observation and simulation, resulting in a factor
of 2.2 lower mean {χ }<SUP>2</SUP> value. One advantage of the new
technique is that it provides the physical parameters on a geometrical
height scale. It constitutes a first step toward inversions that give
results consistent with the MHD equations.
---------------------------------------------------------
Title: Oscillations on Width and Intensity of Slender Ca II H Fibrils
from Sunrise/SuFI
Authors: Gafeira, R.; Jafarzadeh, S.; Solanki, S. K.; Lagg, A.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
2017ApJS..229....7G Altcode: 2017arXiv170102801G
We report the detection of oscillations in slender Ca II H fibrils
(SCFs) from high-resolution observations acquired with the Sunrise
balloon-borne solar observatory. The SCFs show obvious oscillations in
their intensity, but also their width. The oscillatory behaviors are
investigated at several positions along the axes of the SCFs. A large
majority of fibrils show signs of oscillations in intensity. Their
periods and phase speeds are analyzed using a wavelet analysis. The
width and intensity perturbations have overlapping distributions
of the wave period. The obtained distributions have median values
of the period of 32 ± 17 s and 36 ± 25 s, respectively. We
find that the fluctuations of both parameters propagate in
the SCFs with speeds of {11}<SUB>-11</SUB><SUP>+49</SUP> km
s<SUP>-1</SUP> and {15}<SUB>-15</SUB><SUP>+34</SUP> km s<SUP>-1</SUP>,
respectively. Furthermore, the width and intensity oscillations have a
strong tendency to be either in anti-phase or, to a smaller extent, in
phase. This suggests that the oscillations of both parameters are caused
by the same wave mode and that the waves are likely propagating. Taking
all the evidence together, the most likely wave mode to explain all
measurements and criteria is the fast sausage mode.
---------------------------------------------------------
Title: Solar Coronal Loops Associated with Small-scale Mixed Polarity
Surface Magnetic Fields
Authors: Chitta, L. P.; Peter, H.; Solanki, S. K.; Barthol, P.;
Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van
Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco
Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229....4C Altcode: 2016arXiv161007484C
How and where are coronal loops rooted in the solar lower
atmosphere? The details of the magnetic environment and its evolution
at the footpoints of coronal loops are crucial to understanding the
processes of mass and energy supply to the solar corona. To address
the above question, we use high-resolution line-of-sight magnetic
field data from the Imaging Magnetograph eXperiment instrument on the
Sunrise balloon-borne observatory and coronal observations from the
Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory
of an emerging active region. We find that the coronal loops are
often rooted at the locations with minor small-scale but persistent
opposite-polarity magnetic elements very close to the larger dominant
polarity. These opposite-polarity small-scale elements continually
interact with the dominant polarity underlying the coronal loop through
flux cancellation. At these locations we detect small inverse Y-shaped
jets in chromospheric Ca II H images obtained from the Sunrise Filter
Imager during the flux cancellation. Our results indicate that magnetic
flux cancellation and reconnection at the base of coronal loops due
to mixed polarity fields might be a crucial feature for the supply of
mass and energy into the corona.
---------------------------------------------------------
Title: Moving Magnetic Features around a Pore
Authors: Kaithakkal, A. J.; Riethmüller, T. L.; Solanki, S. K.; Lagg,
A.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; vanNoort,
M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229...13K Altcode: 2016arXiv160905664K
Spectropolarimetric observations from Sunrise/IMaX, obtained in 2013
June, are used for a statistical analysis to determine the physical
properties of moving magnetic features (MMFs) observed near a pore. MMFs
of the same and opposite polarity, with respect to the pore, are found
to stream from its border at an average speed of 1.3 km s<SUP>-1</SUP>
and 1.2 km s<SUP>-1</SUP>, respectively, with mainly same-polarity MMFs
found further away from the pore. MMFs of both polarities are found to
harbor rather weak, inclined magnetic fields. Opposite-polarity MMFs
are blueshifted, whereas same-polarity MMFs do not show any preference
for up- or downflows. Most of the MMFs are found to be of sub-arcsecond
size and carry a mean flux of ∼1.2 × 10<SUP>17</SUP> Mx.
---------------------------------------------------------
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. <BR /> Aims:
We aim to confirm or refute the existence of weak-field regions in
the deepest photospheric layers of the penumbra. <BR /> Methods:
We investigated the magnetic field at log τ<SUB>5</SUB> = 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. <BR /> Results: At log τ<SUB>5</SUB>
= 0 we find no evidence of regions with dynamically weak (B<
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: Spectropolarimetric observations of an arch filament system
with the GREGOR solar telescope
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.;
Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann,
A.; 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.
2016AN....337.1050B Altcode: 2016arXiv160901514B
Arch filament systems occur in active sunspot groups, where a fibril
structure connects areas of opposite magnetic polarity, in contrast to
active region filaments that follow the polarity inversion line. We
used the GREGOR Infrared Spectrograph (GRIS) to obtain the full
Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0
nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line
to investigate the photospheric magnetic field and velocities, and
use the line core intensities and velocities of the helium line to
study the chromospheric plasma. The individual fibrils of the arch
filament system connect the sunspot with patches of magnetic polarity
opposite to that of the spot. These patches do not necessarily coincide
with pores, where the magnetic field is strongest. Instead, areas are
preferred not far from the polarity inversion line. These areas exhibit
photospheric downflows of moderate velocity, but significantly higher
downflows of up to 30 km s<SUP>-1</SUP> in the chromospheric helium
line. Our findings can be explained with new emerging flux where the
matter flows downward along the field lines of rising flux tubes,
in agreement with earlier results.
---------------------------------------------------------
Title: Upper chromospheric magnetic field of a sunspot penumbra:
observations of fine structure
Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados,
M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar,
H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.;
Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe,
O.; Waldmann, T.
2016A&A...596A...8J Altcode: 2016arXiv160801988J
<BR /> Aims: The fine-structure of the magnetic field in a sunspot
penumbra in the upper chromosphere is to be explored and compared
to that in the photosphere. <BR /> Methods: Spectropolarimetric
observations with high spatial resolution were recorded with the 1.5-m
GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The
observed spectral domain includes the upper chromospheric Hei triplet
at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å
spectral lines. The upper chromospheric magnetic field is obtained
by inverting the Hei triplet assuming a Milne-Eddington-type model
atmosphere. A height-dependent inversion was applied to the Sii 10
827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic
field. <BR /> Results: We find that the inclination of the magnetic
field varies in the azimuthal direction in the photosphere and in the
upper chromosphere. The chromospheric variations coincide remarkably
well with the variations in the inclination of the photospheric field
and resemble the well-known spine and interspine structure in the
photospheric layers of penumbrae. The typical peak-to-peak variations
in the inclination of the magnetic field in the upper chromosphere
are found to be 10°-15°, which is roughly half the variation in
the photosphere. In contrast, the magnetic field strength of the
observed penumbra does not vary on small spatial scales in the upper
chromosphere. <BR /> Conclusions: Thanks to the high spatial resolution
of the observations that is possible with the GREGOR telescope at 1.08
microns, we find that the prominent small-scale fluctuations in the
magnetic field inclination, which are a salient part of the property
of sunspot penumbral photospheres, also persist in the chromosphere,
although at somewhat reduced amplitudes. Such a complex magnetic
configuration may facilitate penumbral chromospheric dynamic phenomena,
such as penumbral micro-jets or transient bright dots.
---------------------------------------------------------
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. <BR /> 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. <BR /> 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). <BR /> 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. <BR /> 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: Flow and magnetic field properties in the trailing sunspots
of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator 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.
2016AN....337.1090V Altcode:
Improved measurements of the photospheric and chromospheric
three-dimensional magnetic and flow fields are crucial for a precise
determination of the origin and evolution of active regions. We present
an illustrative sample of multi-instrument data acquired during a
two-week coordinated observing campaign in August 2015 involving,
among others, the GREGOR solar telescope (imaging and near-infrared
spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
and Interface Region Imaging Spectrograph (IRIS). The observations
focused on the trailing part of active region NOAA 12396 with complex
polarity inversion lines and strong intrusions of opposite polarity
flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
spectral profiles in the photospheric Si I λ1082.7 nm line, the
chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
provided maps of Doppler velocity and magnetic field at different
atmospheric heights. We compare quick-look maps with those obtained
with the “Stokes Inversions based on Response functions” (SIR)
code, which furnishes deeper insight into the magnetic properties
of the region. We find supporting evidence that newly emerging flux
and intruding opposite polarity flux are hampering the formation
of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
expected after cessation of flux emergence in proximity to the sunspots.
---------------------------------------------------------
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. <BR />
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. <BR /> 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. <BR /> 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. <P />Movies associated to Figs. 2 and 13
are available at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Fitting peculiar spectral profiles in He I 10830Å absorption
features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1057G Altcode: 2016arXiv160300679G
The new generation of solar instruments provides better
spectral, spatial, and temporal resolution for a better
understanding of the physical processes that take place on the
Sun. Multiple-component profiles are more commonly observed with these
instruments. Particularly, the He I 10830 Å triplet presents such
peculiar spectral profiles, which give information on the velocity
and magnetic fine structure of the upper chromosphere. The purpose
of this investigation is to describe a technique to efficiently fit
the two blended components of the He I 10830 Å triplet, which are
commonly observed when two atmospheric components are located within
the same resolution element. The observations used in this study were
taken on 2015 April 17 with the very fast spectroscopic mode of the
GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
telescope, located at the Observatorio del Teide, Tenerife, Spain. We
apply a double-Lorentzian fitting technique using Levenberg-Marquardt
least-squares minimization. This technique is very simple and much
faster than inversion codes. Line-of-sight Doppler velocities can
be inferred for a whole map of pixels within just a few minutes. Our
results show sub- and supersonic downflow velocities of up to 32 km
s<SUP>-1</SUP> for the fast component in the vicinity of footpoints of
filamentary structures. The slow component presents velocities close
to rest.
---------------------------------------------------------
Title: Flux appearance and disappearance rates in the solar
internetwork
Authors: Gosic, Milan; Bellot Rubio, Luis; Del Toro Iniesta, Jose
Carlos; Orozco Suarez, David; Katsukawa, Yukio
2016SPD....4740105G Altcode:
The solar internetwork contains weak and highly dynamic magnetic
fields that are essential to understanding the solar magnetism at small
spatial and temporal scales. Therefore, it is important to determine
how these fields are maintained on the solar surface. Using unique
Hinode observations, we follow the evolution of individual magnetic
elements in the interior of two supergranular cells at the disk
center. From up to 38 hr of continuous measurements, we show that
magnetic flux appears in internetwork regions at a rate of 120±3
Mx cm<SUP>-2</SUP> day<SUP>-1</SUP> (3.7±0.4 × 10<SUP>24</SUP> Mx
day<SUP>-1</SUP> over the entire solar surface). Flux disappears from
the internetwork at a rate of 125±6 Mx cm<SUP>-2</SUP> day<SUP>-1</SUP>
(3.9±0.5 × 10<SUP>24</SUP> Mx day<SUP>-1</SUP>) through fading of
magnetic elements, cancellation between opposite-polarity features,
and interactions with network patches, which converts internetwork
elements into network features. The removal of flux from supergranules
occurs mainly through fading and interactions with network, at nearly
the same rate of about 50 Mx cm<SUP>-2</SUP> day<SUP>-1</SUP>. Our
results demonstrate that the sources and sinks of internetwork magnetic
flux are well balanced, reflecting the steady-state nature of the quiet
Sun. Using the instantaneous flux appearance and disappearance rates,
we successfully reproduce, for the first time, the temporal evolution
of the total unsigned flux in the interior of supergranular cells.
---------------------------------------------------------
Title: The Solar Internetwork. II. Flux Appearance and Disappearance
Rates
Authors: Gošić, M.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.;
Orozco Suárez, D.; Katsukawa, Y.
2016ApJ...820...35G Altcode: 2016arXiv160205892G
Small-scale internetwork magnetic fields are important ingredients of
the quiet Sun. In this paper we analyze how they appear and disappear
on the solar surface. Using high resolution Hinode magnetograms,
we follow the evolution of individual magnetic elements in the
interior of two supergranular cells at the disk center. From up to
38 hr of continuous measurements, we show that magnetic flux appears
in internetwork regions at a rate of 120 ± 3 Mx cm<SUP>-2</SUP>
day<SUP>-1</SUP> (3.7 ± 0.4 × 10<SUP>24</SUP> Mx day<SUP>-1</SUP>
over the entire solar surface). Flux disappears from the internetwork
at a rate of 125 ± 6 Mx cm<SUP>-2</SUP> day<SUP>-1</SUP> (3.9
± 0.5 × 10<SUP>24</SUP> Mx day<SUP>-1</SUP>) through fading of
magnetic elements, cancelation between opposite-polarity features,
and interactions with network patches, which converts internetwork
elements into network features. Most of the flux is lost through
fading and interactions with the network, at nearly the same rate of
about 50 Mx cm<SUP>-2</SUP> day<SUP>-1</SUP>. Our results demonstrate
that the sources and sinks of internetwork magnetic flux are well
balanced. Using the instantaneous flux appearance and disappearance
rates, we successfully reproduce the time evolution of the total
unsigned flux in the two supergranular cells.
---------------------------------------------------------
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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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. <P />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: 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
& Asensio Ramos (2013A&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. <P />(1 data file).
---------------------------------------------------------
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: The Solar Internetwork. I. Contribution to the Network
Magnetic Flux
Authors: Gošić, M.; Bellot Rubio, L. R.; Orozco Suárez, D.;
Katsukawa, Y.; del Toro Iniesta, J. C.
2014ApJ...797...49G Altcode: 2014arXiv1408.2369G
The magnetic network (NE) observed on the solar surface harbors a
sizable fraction of the total quiet Sun flux. However, its origin and
maintenance are not well known. Here we investigate the contribution
of internetwork (IN) magnetic fields to the NE flux. IN fields permeate
the interior of supergranular cells and show large emergence rates. We
use long-duration sequences of magnetograms acquired by Hinode and
an automatic feature tracking algorithm to follow the evolution of NE
and IN flux elements. We find that 14% of the quiet Sun (QS) flux is
in the form of IN fields with little temporal variations. IN elements
interact with NE patches and modify the flux budget of the NE either
by adding flux (through merging processes) or by removing it (through
cancellation events). Mergings appear to be dominant, so the net flux
contribution of the IN is positive. The observed rate of flux transfer
to the NE is 1.5 × 10<SUP>24</SUP> Mx day<SUP>-1</SUP> over the entire
solar surface. Thus, the IN supplies as much flux as is present in the
NE in only 9-13 hr. Taking into account that not all the transferred
flux is incorporated into the NE, we find that the IN would be able
to replace the entire NE flux in approximately 18-24 hr. This renders
the IN the most important contributor to the NE, challenging the view
that ephemeral regions are the main source of flux in the QS. About 40%
of the total IN flux eventually ends up in the NE.
---------------------------------------------------------
Title: Pair separation of magnetic elements in the quiet Sun
Authors: Giannattasio, F.; Berrilli, F.; Biferale, L.; Del Moro, D.;
Sbragaglia, M.; Bellot Rubio, L.; Gošić, M.; Orozco Suárez, D.
2014A&A...569A.121G Altcode: 2014arXiv1409.1010G
The dynamic properties of the quiet Sun photosphere can be investigated
by analyzing the pair dispersion of small-scale magnetic fields
(i.e., magnetic elements). By using 25 h-long Hinode magnetograms
at high spatial resolution (0.3 arcsec), we tracked 68 490 magnetic
element pairs within a supergranular cell near the disk center. The
computed pair separation spectrum, calculated on the whole set of
particle pairs independently of their initial separation, points
out what is known as a super-diffusive regime with spectral index
γ = 1.55 ± 0.05, in agreement with the most recent literature, but
extended to unprecedented spatial and temporal scales (from granular
to supergranular). Furthermore, for the first time, we investigated
here the spectrum of the mean square displacement of pairs of magnetic
elements, depending on their initial separation r<SUB>0</SUB>. We found
that there is a typical initial distance above (below) which the pair
separation is faster (slower) than the average. A possible physical
interpretation of such a typical spatial scale is also provided.
---------------------------------------------------------
Title: High speed magnetized flows in the quiet Sun
Authors: Quintero Noda, C.; Borrero, J. M.; Orozco Suárez, D.;
Ruiz Cobo, B.
2014A&A...569A..73Q Altcode: 2014arXiv1407.7477Q
Context. We analyzed spectropolarimetric data recorded with
Hinode/SP in quiet-Sun regions located at the disk center. We found
single-lobed Stokes V profiles showing highly blue- and red-shifted
signals. Oftentimes both types of events appear to be related to
each other. <BR /> Aims: We aim to set constraints on the nature and
physical causes of these highly Doppler-shifted signals, as well as to
study their spatial distribution, spectropolarimetric properties, size,
and rate of occurrence. Also, we plan to retrieve the variation of the
physical parameters with optical depth through the photosphere. <BR />
Methods: We have examined the spatial and polarimetric properties of
these events using a variety of data from the Hinode spacecraft. We
have also inferred the atmospheric stratification of the physical
parameters by means of the inversion of the observed Stokes profiles
employing the Stokes Inversion based on Response functions (SIR)
code. Finally, we analyzed their evolution using a time series from
the same instrument. <BR /> Results: Blue-shifted events tend to appear
over bright regions at the edge of granules, while red-shifted events
are seen predominantly over dark regions on intergranular lanes. Large
linear polarization signals can be seen in the region that connects
them. The magnetic structure inferred from the time series revealed that
the structure corresponds to a Ω-loop, with one footpoint always over
the edge of a granule and the other inside an intergranular lane. The
physical parameters obtained from the inversions of the observed
Stokes profiles in both events show an increase with respect to the
Harvard-Smithonian reference atmosphere in the temperature at log
τ<SUB>500</SUB> ∈ (-1, -3) and a strong magnetic field, B ≥ 1 kG,
at the bottom of the atmosphere that quickly decreases upward until
vanishing at log τ<SUB>500</SUB> ≈ -2. In the blue-shifted events,
the LOS velocities change from upflows at the bottom to downflows at
the top of the atmosphere. Red-shifted events display the opposite
velocity stratification. The change of sign in LOS velocity happens at
the same optical depth in which the magnetic field becomes zero. <BR
/> Conclusions: The physical mechanism that best explains the inferred
magnetic field configuration and flow motions is a siphon flow along an
arched magnetic flux tube. Further investigation is required, however,
as the expected features of a siphon flow cannot be unequivocally
identified.
---------------------------------------------------------
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. <BR /> 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. <BR
/> 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. <BR /> 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. <P />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: Photospheric downward plasma motions in the quiet Sun
Authors: Quintero Noda, C.; Ruiz Cobo, B.; Orozco Suárez, D.
2014A&A...566A.139Q Altcode: 2014arXiv1405.1561Q
Context. We analyze spectropolarimetric data taken with the Hinode
spacecraft in quiet solar regions at the disk center. Distorted
redshifted Stokes V profiles are found that show a characteristic
evolution that always follows the same sequence of phases. <BR /> Aims:
We aim to characterize the statistical properties of these events
and recover the stratification of the relevant physical quantities
to understand the nature of the mechanism behind them. <BR />
Methods: We studied the statistical properties of these events using
spectropolarimetric data from Hinode/SP. We also examined the upper
photosphere and the low chromosphere using Mg i b<SUB>2</SUB> and Ca
ii h data from Hinode. Finally, we applied the SIRGAUSS inversion code
to the polarimetric data to infer the atmospheric stratification of the
physical parameters. We also obtained these physical parameters taking
into account dynamical terms in the equation of motion. <BR /> Results:
The Stokes V profiles display a bump that evolves in four different
time steps, and the total process lasts 108 seconds. The Stokes I shows
a strongly bent red wing and the continuum signal exhibits a bright
point inside an intergranular lane. This bright point is correlated
with a strong redshift in the Mg i b<SUB>2</SUB> line and a bright
feature in Ca ii h images. The model obtained from the inversion of
the Stokes profiles is hotter than the average quiet-Sun model, with a
vertical magnetic field configuration and field strengths in the range
of kG values. It also presents a line of sight velocity stratification
with a Gaussian perturbation, the center of which is moving to deeper
layers with time. The Gaussian perturbation is also found in the gas
pressure and density stratification obtained taking into account
dynamical terms in the equation of motion. <BR /> Conclusions: We
have examined a particular type of event that can be described as a
plasmoid of hot plasma that is moving downward from the top of the
photosphere, placed over intergranular lanes and always related to
strong magnetic field concentrations. We argue that the origin of this
plasmoid might be magnetic reconnection that is taking place in the
chromosphere. <P />Appendix A is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201423461/olm">http://www.aanda.org</A>
---------------------------------------------------------
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<SUP>-1</SUP>. 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<SUP>-1</SUP>) and large
Doppler widths (~10 km s<SUP>-1</SUP>) 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: Flux emergence in the solar internetwork and its contribution
to the network
Authors: Gosic, Milan; Katsukawa, Yukio; Orozco Suarez, David; Bellot
Rubio, L. R.
2014cosp...40E1055G Altcode:
Network and internetwork magnetic fields are believed to play a
crucial role in the energy budget of the solar atmosphere. Therefore,
it is essential to understand how they are maintained on the
solar surface. Using high resolution Hinode/NFI magnetograms at
disk center, we automatically follow quiet Sun magnetic elements
from their appearance to disappearance. From up to 40 hours of
continuous measurements, we derive the flux emergence rate in the
solar internetwork to be around 40 Mx cm(-2) day(-1) . We show
that internetwork fields appearing in the interior of individual
supergranular cells contribute flux to the surrounding network at
a rate of 2×10(19) Mx h(-1) . In only 10-20 hours, internetwork
elements can transfer as much flux as resides in network features,
establishing them as the most important source of flux for the network
and the quiet Sun flux budget.
---------------------------------------------------------
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: Diffusion of Solar Magnetic Elements up to Supergranular
Spatial and Temporal Scales
Authors: Giannattasio, F.; Del Moro, D.; Berrilli, F.; Bellot Rubio,
L.; Gošić, M.; Orozco Suárez, D.
2013ApJ...770L..36G Altcode: 2013arXiv1305.4006G
The study of spatial and temporal scales on which small magnetic
structures (magnetic elements) are organized in the quiet Sun
may be approached by determining how they are transported on the
solar photosphere by convective motions. The process involved
is diffusion. Taking advantage of Hinode high spatial resolution
magnetograms of a quiet-Sun region at the disk center, we tracked
20,145 magnetic elements. The large field of view (~50 Mm) and the
long duration of the observations (over 25 hr without interruption at
a cadence of 90 s) allowed us to investigate the turbulent flows at
unprecedented large spatial and temporal scales. In the field of view
an entire supergranule is clearly recognizable. The magnetic element
displacement spectrum shows a double-regime behavior: superdiffusive
(γ = 1.34 ± 0.02) up to granular spatial scales (~1500 km) and
slightly superdiffusive (γ = 1.20 ± 0.05) up to supergranular scales.
---------------------------------------------------------
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: Polar Field Reversal Observations with Hinode
Authors: Shiota, D.; Tsuneta, S.; Shimojo, M.; Sako, N.; Orozco Suarez,
D.; Ishikawa, R.
2012AGUFMSH13C2274S Altcode:
We have been monitoring yearly variation in the Sun's polar magnetic
fields with the Solar Optical Telescope aboard Hinode to record their
evolution and expected reversal near the solar maximum. All magnetic
patches in the magnetic flux maps are automatically identified to obtain
the number density and magnetic flux density as a function of the total
magnetic flux per patch. The detected magnetic flux per patch ranges
over four orders of magnitude (10^15 -- 10^20 Mx). The higher end of
the magnetic flux in the polar regions is about one order of magnitude
larger than that of the quiet Sun, and nearly that of pores. Almost
all large patches ( > 10^18 Mx) have the same polarity, while
smaller patches have a fair balance of both polarities. The polarity
of the polar region as a whole is consequently determined only by the
large magnetic concentrations. A clear decrease in the net flux of
the polar region is detected in the slow rising phase of the current
solar cycle. The decrease is more rapid in the north polar region than
in the south. The decrease in the net flux is caused by a decrease in
the number and size of the large flux concentrations as well as the
appearance of patches with opposite polarity at lower latitudes. In
contrast, we do not see temporal change in the magnetic flux associated
with the smaller patches ( < 10^18 Mx) and that of the horizontal
magnetic fields during the years 2008--2012.
---------------------------------------------------------
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<SUP>-1</SUP>, 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<SUP>-1</SUP>. 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<SUP>-1</SUP>) with respect to
the other, thus suggesting the existence of supersonic counter-streaming
flows along the line of sight.
---------------------------------------------------------
Title: Requirements for the Analysis of Quiet-Sun Internetwork
Magnetic Elements with EST and ATST
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Katsukawa, Y.
2012ASPC..463...57O Altcode: 2012arXiv1203.2185O
The quiet-Sun internetwork is permeated by weak and highly inclined
magnetic fields whose physical properties, dynamics, and magnetic
interactions are not fully understood. High spatial resolution
magnetograms show them as discrete magnetic elements that appear/emerge
and disappear/cancel continuously over the quiet Sun surface. The
4-m European Solar Telescope (EST) and the Advanced Technology
Solar Telescope (ATST) will obtain two-dimensional, high cadence,
high precision polarimetric measurements at the diffraction limit
(30 km). Here, we compile the basic requirements for the observation
of internetwork fields with EST and ATST (field of view, cadence,
instrument configuration, etc.). More specifically, we concentrate
on the field-of-view requirements. To set them we analyze the proper
motion of internetwork magnetic elements across the solar surface. We
use 13 hours of magnetograms taken with the Hinode satellite to
identify and track thousands of internetwork magnetic element in an
isolated supergranular cell. We calculate the velocity components of
each element and the mean distance they travel. The results show that,
on average, magnetic elements in the interior of supergranular cells
move toward the network. The radial velocity is observed to depend on
the distance to the center of the supergranule. Internetwork magnetic
elements travel 4″ on average. These results suggest that ATST and
EST should cover, at least, one supergranular cell to obtain a complete
picture of the quiet Sun internetwork.
---------------------------------------------------------
Title: Turbulent diffusion on the solar photosphere through 24-hour
continuous observations of magnetic elements
Authors: Giannattasio, F.; Berrilli, F.; Del Moro, D.; Bellot Rubio,
L.; Orozco Suarez, D.; Gosic, M.
2012AGUFMSH13A2242G Altcode:
Solar atmosphere is a unique laboratory for the study of turbulent
flows under extreme conditions (e.g. very high Reynolds numbers). The
turbulent nature of the flow may be approached by determining how
magnetic flux elements are transported on the solar surface, and
measuring the spatio-temporal scales on which these small magnetic
structures are organized. The process involved is diffusion. Several
works explored this topic, both by simulations and observations,
and the results are often contradictory, ranging from fully-developed
turbulent scenarios to normal-diffusive motions. We analyze 24-hour
continuous Hinode SOT observations of a supergranular region (for the
first time these long scales are explored), studying the evolution of
the mutual distance between magnetic element pairs and its scaling laws,
in order to investigate the diffusion process. We find a super-diffusive
behavior, with a gamma index depending on the spatial scale selected.
---------------------------------------------------------
Title: The Connection between Internetwork Magnetic Elements and
Supergranular Flows
Authors: Orozco Suárez, D.; Katsukawa, Y.; Bellot Rubio, L. R.
2012ApJ...758L..38O Altcode:
The advection of internetwork magnetic elements by supergranular
convective flows is investigated using high spatial resolution, high
cadence, and high signal-to-noise ratio Na I D1 magnetograms obtained
with the Hinode satellite. The observations show that magnetic elements
appear everywhere across the quiet Sun surface. We calculate the proper
motion of these magnetic elements with the aid of a feature tracking
algorithm. The results indicate that magnetic elements appearing in
the interior of supergranules tend to drift toward the supergranular
boundaries with a non-constant velocity. The azimuthally averaged
radial velocities of the magnetic elements and of the supergranular
flow, calculated from a local correlation tracking technique applied
to Dopplergrams, are very similar. This suggests that, in the long
term, surface magnetic elements are advected by supergranular flows,
although on short timescales their very chaotic motions are driven
mostly by granular flows and other processes.
---------------------------------------------------------
Title: Power Spectra of Velocities and Magnetic Fields on the Solar
Surface and their Dependence on the Unsigned Magnetic Flux Density
Authors: Katsukawa, Y.; Orozco Suárez, D.
2012ApJ...758..139K Altcode: 2012arXiv1209.0548K
We have performed power spectral analysis of surface temperatures,
velocities, and magnetic fields, using spectropolarimetric data taken
with the Hinode Solar Optical Telescope. When we make power spectra in
a field of view covering the supergranular scale, kinetic and thermal
power spectra have a prominent peak at the granular scale while the
magnetic power spectra have a broadly distributed power over various
spatial scales with weak peaks at both the granular and supergranular
scales. To study the power spectra separately in internetwork and
network regions, power spectra are derived in small subregions extracted
from the field of view. We examine slopes of the power spectra using
power-law indices, and compare them with the unsigned magnetic flux
density averaged in the subregions. The thermal and kinetic spectra
are steeper than the magnetic ones at the subgranular scale in the
internetwork regions, and the power-law indices differ by about 2. The
power-law indices of the magnetic power spectra are close to or smaller
than -1 at that scale, which suggests the total magnetic energy mainly
comes from either the granular scale magnetic structures or both the
granular scale and smaller ones contributing evenly. The slopes of the
thermal and kinetic power spectra become less steep with increasing
unsigned flux density in the network regions. The power-law indices
of all the thermal, kinetic, and magnetic power spectra become similar
when the unsigned flux density is larger than 200 Mx cm<SUP>-2</SUP>.
---------------------------------------------------------
Title: Pervasive Linear Polarization Signals in the Quiet Sun
Authors: Bellot Rubio, L. R.; Orozco Suárez, D.
2012ApJ...757...19B Altcode: 2012arXiv1207.0692B
This paper investigates the distribution of linear polarization signals
in the quiet-Sun internetwork using ultra-deep spectropolarimetric
data. We reduce the noise of the observations as much as is feasible
by adding single-slit measurements of the Zeeman-sensitive Fe I 630 nm
lines taken by the Hinode spectropolarimeter. The integrated Stokes
spectra are employed to determine the fraction of the field of view
covered by linear polarization signals. We find that up to 69% of
the quiet solar surface at disk center shows Stokes Q or U profiles
with amplitudes larger than 0.032% (4.5 times the noise level of 7 ×
10<SUP>-5</SUP> reached by the longer integrations). The mere presence
of linear polarization in most of the quiet Sun implies that the weak
internetwork fields must be highly inclined, but we quantify this
by inverting those pixels with Stokes Q or U signals well above the
noise. This allows for a precise determination of the field inclination,
field strength, and field azimuth because the information carried by all
four Stokes spectra is used simultaneously. The inversion is performed
for 53% of the observed field of view at a noise level of 1.3 ×
10<SUP>-4</SUP> I <SUB>c</SUB>. The derived magnetic distributions are
thus representative of more than half of the quiet-Sun internetwork. Our
results confirm the conclusions drawn from previous analyses using
mainly Stokes I and V: internetwork fields are very inclined, but
except in azimuth they do not seem to be isotropically distributed.
---------------------------------------------------------
Title: Center-to-Limb Variation of the Magnetic Field Vector
Distribution in the Internetwork
Authors: Orozco Suárez, D.
2012ASPC..454...37O Altcode: 2012ASPC..454...37S
I present a comparison between the Probability Density Functions of
the magnetic field strength, inclination, azimuth, and filling factor
determined at four different heliocentric angles in the quiet Sun
internetwork. The data were acquired with the spectropolarimeter
attached to the Solar Optical Telescope onboard the Hinode
satellite. The signal-to-the-noise ratio corresponds to ∼ 3600,
measured at the continuum of Stokes I. To obtain the PDFs, the data
were subjected to a simple one component Milne-Eddington inversion. The
results show that for strong fields (above 300 G), variations on the
shape of the inclination PDF are detected, suggesting that the geometry
of the field vector changes with viewing angle. For weaker fields,
the distribution of inclinations does not vary, what concurs with the
isotropic nature of the internetwork fields.
---------------------------------------------------------
Title: Polar Field Reversal Observations with Hinode
Authors: Shiota, D.; Tsuneta, S.; Shimojo, M.; Sako, N.; Orozco
Suárez, D.; Ishikawa, R.
2012ApJ...753..157S Altcode: 2012arXiv1205.2154S
We have been monitoring yearly variation in the Sun's polar magnetic
fields with the Solar Optical Telescope aboard Hinode to record their
evolution and expected reversal near the solar maximum. All magnetic
patches in the magnetic flux maps are automatically identified to
obtain the number density and magnetic flux density as a function of
the total magnetic flux per patch. The detected magnetic flux per patch
ranges over four orders of magnitude (10<SUP>15</SUP>-10<SUP>20</SUP>
Mx). The higher end of the magnetic flux in the polar regions is about
one order of magnitude larger than that of the quiet Sun, and nearly
that of pores. Almost all large patches (>=10<SUP>18</SUP> Mx) have
the same polarity, while smaller patches have a fair balance of both
polarities. The polarity of the polar region as a whole is consequently
determined only by the large magnetic concentrations. A clear decrease
in the net flux of the polar region is detected in the slow rising phase
of the current solar cycle. The decrease is more rapid in the north
polar region than in the south. The decrease in the net flux is caused
by a decrease in the number and size of the large flux concentrations
as well as the appearance of patches with opposite polarity at lower
latitudes. In contrast, we do not see temporal change in the magnetic
flux associated with the smaller patches (<10<SUP>18</SUP> Mx)
and that of the horizontal magnetic fields during the years 2008-2012.
---------------------------------------------------------
Title: Evolution of internetwork magnetic fields inside supergranular
cells
Authors: Gosic, Milan; Katsukawa, Yukio; Bellot Rubio, Luis; Orozco
Suarez, David
2012cosp...39..657G Altcode: 2012cosp.meet..657G
To understand the formation of small-scale magnetic fields in the quiet
Sun and their contribution to the solar activity, it is essential to
investigate the properties of internetwork magnetic fields. Using
Hinode/NFI magnetograms of very high sensitivity (7 Mx/cm^{2}),
spatial resolution (0.16 arcsec/pixel), and cadence (90 s), we
follow the evolution of magnetic fields inside of a supergranular
cell located at disk center. In 5 hours of continuous measurements
covering an area of 20.8 × 23.2 arcsec^{2}, we manually track 2415
magnetic elements from appearance to disappearance and derive their
physical properties. The average values of the magnetic flux, effective
diameter, lifetime, and horizontal velocity are 3 × 10^{17} Mx, 0.5 Mm,
17 min, and 2 km/s, respectively. We also investigate how the physical
parameters of the individual elements vary as a function of time,
flux, and spatial position. Using this unique data set, we determine
with unprecedented accuracy the flux emergence and disappearance rate
in the solar internetwork.
---------------------------------------------------------
Title: Analysis of Quiet-Sun Internetwork Magnetic Fields Based on
Linear Polarization Signals
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.
2012ApJ...751....2O Altcode: 2012arXiv1203.1440O
We present results from the analysis of Fe I 630 nm measurements
of the quiet Sun taken with the spectropolarimeter of the Hinode
satellite. Two data sets with noise levels of 1.2 × 10<SUP>-3</SUP>
and 3 × 10<SUP>-4</SUP> are employed. We determine the distribution
of field strengths and inclinations by inverting the two observations
with a Milne-Eddington model atmosphere. The inversions show a
predominance of weak, highly inclined fields. By means of several tests
we conclude that these properties cannot be attributed to photon noise
effects. To obtain the most accurate results, we focus on the 27.4%
of the pixels in the second data set that have linear polarization
amplitudes larger than 4.5 times the noise level. The vector magnetic
field derived for these pixels is very precise because both circular
and linear polarization signals are used simultaneously. The inferred
field strength, inclination, and filling factor distributions agree
with previous results, supporting the idea that internetwork (IN)
fields are weak and very inclined, at least in about one quarter
of the area occupied by the IN. These properties differ from those
of network fields. The average magnetic flux density and the mean
field strength derived from the 27.4% of the field of view with clear
linear polarization signals are 16.3 Mx cm<SUP>-2</SUP> and 220 G,
respectively. The ratio between the average horizontal and vertical
components of the field is approximately 3.1. The IN fields do not
follow an isotropic distribution of orientations.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: On the Distribution of Quiet-Sun Magnetic Fields at Different
Heliocentric Angles
Authors: Orozco Suárez, D.; Katsukawa, Y.
2012ApJ...746..182O Altcode:
This paper presents results from the analysis of high signal-to-noise
ratio spectropolarimetric data taken at four heliocentric angles in
quiet-Sun internetwork regions with the Hinode satellite. First, we
find that the total circular and total linear polarization signals vary
with heliocentric angle, at least for fields with large polarization
signals. We also report changes on the Stokes V amplitude asymmetry
histograms with viewing angle for fields weaker than 200 G. Then,
we subject the data to a Milne-Eddington inversion and analyze
the variation of the field vector probability density functions
with heliocentric angle. Weak, highly inclined fields permeate
the internetwork at all heliocentric distances. For fields weaker
than 200 G, the distributions of field inclinations peak at 90°
and do not vary with viewing angle. The inclination distributions
change for fields stronger than 200 G. We argue that the shape of
the inclination distribution for weak fields partly results from the
presence of coherent, loop-like magnetic features at all heliocentric
distances and not from tangled fields within the field of view. We also
find that the average magnetic field strength is about 180 G (for 75%
of the pixels) and is constant with heliocentric angle. The average
vertical and horizontal magnetic field components are 70 and 150 G. The
latter (former) is slightly greater (smaller) near the limb. Finally,
the ratio between the horizontal and vertical components of the fields
ranges from ~1 for strong fields to ~3.5 for weak fields, suggesting
that the magnetic field vector is not isotropically distributed within
the field of view.
---------------------------------------------------------
Title: The Imaging Magnetograph eXperiment (IMaX) for the Sunrise
Balloon-Borne Solar Observatory
Authors: Martínez Pillet, V.; del Toro Iniesta, J. C.;
Álvarez-Herrero, A.; Domingo, V.; Bonet, J. A.; González Fernández,
L.; López Jiménez, A.; Pastor, C.; Gasent Blesa, J. L.; Mellado, P.;
Piqueras, J.; Aparicio, B.; Balaguer, M.; Ballesteros, E.; Belenguer,
T.; Bellot Rubio, L. R.; Berkefeld, T.; Collados, M.; Deutsch, W.;
Feller, A.; Girela, F.; Grauf, B.; Heredero, R. L.; Herranz, M.;
Jerónimo, J. M.; Laguna, H.; Meller, R.; Menéndez, M.; Morales, R.;
Orozco Suárez, D.; Ramos, G.; Reina, M.; Ramos, J. L.; Rodríguez,
P.; Sánchez, A.; Uribe-Patarroyo, N.; Barthol, P.; Gandorfer, A.;
Knoelker, M.; Schmidt, W.; Solanki, S. K.; Vargas Domínguez, S.
2011SoPh..268...57M Altcode: 2010SoPh..tmp..181M; 2010arXiv1009.1095M
The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter
built by four institutions in Spain that flew on board the Sunrise
balloon-borne solar observatory in June 2009 for almost six days over
the Arctic Circle. As a polarimeter, IMaX uses fast polarization
modulation (based on the use of two liquid crystal retarders),
real-time image accumulation, and dual-beam polarimetry to reach
polarization sensitivities of 0.1%. As a spectrograph, the instrument
uses a LiNbO<SUB>3</SUB> etalon in double pass and a narrow band
pre-filter to achieve a spectral resolution of 85 mÅ. IMaX uses the
high-Zeeman-sensitive line of Fe I at 5250.2 Å and observes all four
Stokes parameters at various points inside the spectral line. This
allows vector magnetograms, Dopplergrams, and intensity frames to be
produced that, after reconstruction, reach spatial resolutions in the
0.15 - 0.18 arcsec range over a 50×50 arcsec field of view. Time
cadences vary between 10 and 33 s, although the shortest one only
includes longitudinal polarimetry. The spectral line is sampled in
various ways depending on the applied observing mode, from just two
points inside the line to 11 of them. All observing modes include
one extra wavelength point in the nearby continuum. Gauss equivalent
sensitivities are 4 G for longitudinal fields and 80 G for transverse
fields per wavelength sample. The line-of-sight velocities are estimated
with statistical errors of the order of 5 - 40 m s<SUP>−1</SUP>. The
design, calibration, and integration phases of the instrument,
together with the implemented data reduction scheme, are described in
some detail.
---------------------------------------------------------
Title: Retrieval of solar magnetic fields from high-spatial resolution
filtergraph data: the Imaging Magnetograph eXperiment (IMaX)
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Martínez Pillet,
V.; Bonet, J. A.; Vargas Domínguez, S.; Del Toro Iniesta, J. C.
2010A&A...522A.101O Altcode: 2010arXiv1006.5510O
Context. The design of modern instruments does not only imply thorough
studies of instrumental effects but also a good understanding of the
scientific analysis planned for the data. <BR /> Aims: We investigate
the reliability of Milne-Eddington (ME) inversions of high-resolution
magnetograph measurements such as those to be obtained with the Imaging
Magnetograph eXperiment (IMaX) aboard the Sunrise balloon. We also
provide arguments to choose either Fe I 525.02 or 525.06 nm as the
most suitable line for IMaX. <BR /> Methods: We reproduce an IMaX
observation using magnetoconvection simulations of the quiet Sun
and synthesizing the four Stokes profiles emerging from them. The
profiles are degraded by spatial and spectral resolution, noise,
and limited wavelength sampling, just as real IMaX measurements. We
invert these data and estimate the uncertainties in the retrieved
physical parameters caused by the ME approximation and the spectral
sampling. <BR /> Results: It is possible to infer the magnetic field
strength, inclination, azimuth, and line-of-sight velocity from
standard IMaX measurements (4 Stokes parameters, 5 wavelength points,
and a signal-to-noise ratio of 1000) applying ME inversions to any
of the Fe I lines at 525 nm. We also find that telescope diffraction
has important effects on the spectra coming from very high resolution
observations of inhomogeneous atmospheres. Diffration reduces the
amplitude of the polarization signals and changes the asymmetry of
the Stokes profiles. <BR /> Conclusions: The two Fe I lines at 525 nm
meet the scientific requirements of IMaX, but Fe I 525.02 nm is to be
preferred because it leads to smaller uncertainties in the retrieved
parameters and offers a better detectability of the weakest (linear)
polarization signals prevailing in the quiet Sun.
---------------------------------------------------------
Title: Milne-Eddington inversion of the Fe I line pair at 630 nm
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Del Toro Iniesta,
J. C.
2010A&A...518A...3O Altcode: 2010arXiv1005.5013S; 2010arXiv1005.5013O
Context. The iron lines at 630.15 and 630.25 nm are often used to
determine the physical conditions of the solar photosphere. A common
approach is to invert them simultaneously under the Milne-Eddington
approximation. The same thermodynamic parameters are employed for the
two lines, except for their opacities, which are assumed to have a
constant ratio. <BR /> Aims: We aim at investigating the validity of
this assumption, since the two lines are not exactly the same. <BR
/> Methods: We use magnetohydrodynamic simulations of the quiet
Sun to examine the behavior of the ME thermodynamic parameters and
their influence on the retrieval of vector magnetic fields and flow
velocities. <BR /> Results: Our analysis shows that the two lines can
be coupled and inverted simultaneously using the same thermodynamic
parameters and a constant opacity ratio. The inversion of two lines
is significantly more accurate than single-line inversions because of
the larger number of observables.
---------------------------------------------------------
Title: Applicability of Milne-Eddington inversions to high spatial
resolution observations of the quiet Sun
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Vögler, A.; Del
Toro Iniesta, J. C.
2010A&A...518A...2O Altcode: 2010arXiv1005.5012O
Context. The physical conditions of the solar photosphere change on
very small spatial scales both horizontally and vertically. Such a
complexity may pose a serious obstacle to the accurate determination
of solar magnetic fields. <BR /> Aims: We examine the applicability of
Milne-Eddington (ME) inversions to high spatial resolution observations
of the quiet Sun. Our aim is to understand the connection between
the ME inferences and the actual stratifications of the atmospheric
parameters. <BR /> Methods: We use magnetoconvection simulations of
the solar surface to synthesize asymmetric Stokes profiles such as
those observed in the quiet Sun. We then invert the profiles with the
ME approximation. We perform an empirical analysis of the heights of
formation of ME measurements and analyze the uncertainties brought
about by the ME approximation. We also investigate the quality of the
fits and their relationship with the model stratifications. <BR />
Results: The atmospheric parameters derived from ME inversions of
high-spatial resolution profiles are reasonably accurate and can be
used for statistical analyses of solar magnetic fields, even if the
fit is not always good. We also show that the ME inferences cannot be
assigned to a specific atmospheric layer: different parameters sample
different ranges of optical depths, and even the same parameter
may trace different layers depending on the physical conditions
of the atmosphere. Despite this variability, ME inversions tend
to probe deeper layers in granules than in intergranular lanes. <P
/>Figure 10 and appendix are only available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Size matters
Authors: del Toro Iniesta, J. C.; Orozco Suárez, D.
2010AN....331..558D Altcode: 2010arXiv1002.3106D
The new generation of ground-based, large-aperture solar telescopes
promises to significantly increase our capabilities to understand the
many basic phenomena taking place in the Sun at all atmospheric layers
and how they relate to each other. A (non-exhaustive) summary of the
main scientific arguments to pursue these impressive technological goals
is presented. We illustrate how imaging, polarimetry, and spectroscopy
can benefit from the new telescopes and how several wavelength bands
should be observed to study the atmospheric coupling from the upper
convection zone all the way to the corona. The particular science case
of sunspot penumbrae is barely discussed as a specific example.
---------------------------------------------------------
Title: On Spectropolarimetric Measurements with Visible Lines
Authors: del Toro Iniesta, J. C.; Orozco Suárez, D.; Bellot Rubio,
L. R.
2010ApJ...711..312D Altcode: 2010arXiv1001.3022D
The ability of new instruments for providing accurate inferences of
vector magnetic fields and line-of-sight velocities of the solar
plasma depends a great deal on the sensitivity to these physical
quantities of the spectral lines chosen to be measured. Recently,
doubts have been raised about visible Stokes profiles to provide
a clear distinction between weak fields and strong ones filling a
small fraction of the observed area. The goal of this paper is to
give qualitative and quantitative arguments that help in settling the
debate since several instruments that employ visible lines are either
operating or planned for the near future. The sensitivity of the Stokes
profiles is calculated through the response functions (RFs), for e.g.,
by Ruiz Cobo & Del Toro Iniesta. Both theoretical and empirical
evidences are gathered in favor of the reliability of visible Stokes
profiles. The RFs are also used for estimating the uncertainties in
the physical quantities due to noise in observations. A useful formula
has been derived that takes into account the measurement technique
(number of polarization measurements, polarimetric efficiencies, and
number of wavelength samples), the model assumptions (number of free
parameters and the filling factor), and the radiative transfer (RFs). We
conclude that a scenario with a weak magnetic field can reasonably
be distinguished with visible lines from another with a strong field
but a similar Stokes V amplitude, provided that the Milne-Eddington
approximation is good enough to describe the solar atmosphere and the
polarization signal is at least 3 or 4 times larger than the typical
rms noise of 10<SUP>-3</SUP> I <SUB>c</SUB> reached in the observations.
---------------------------------------------------------
Title: Simulation and Analysis of Hinode Spectropolarimetric
Observations
Authors: Orozco Suárez, D.
2009ASPC..415...57O Altcode:
The diffraction-limited observations of the Hinode Spectro-Polarimeter
have open exciting possibilities for the analysis of the weak magnetic
signals of the solar internetwork (IN). Hinode/SP has demonstrated
that the IN is permeated by highly inclined fields with weak flux
densities. These observations are important to solve the discrepancy
between the IN field strength distributions obtained using visible
and infrared ground-based measurements. Recently, it has been argued
that the information contained in the Fe I 630 nm spectral region is
not sufficient to provide reliable field strength values. In this
contribution, radiative magnetoconvection simulations are used to
generate synthetic Hinode/SP observations, in an attempt to examine
the reliability of Milne-Eddington inversions applied to very high
spatial resolution data. The results show that ME inversions deliver
reasonably good magnetic field strengths and inclinations from Hinode/SP
measurements, provided the effects caused by telescope diffraction
are corrected. These effects can be accurately modeled using a local
stray-light contamination. If one does not account for the reduction
in polarization signals caused by diffraction, the inversion leads
to field strengths that are too weak. Finally, the implications that
telescope diffraction has on the average magnetic filling factors and
flux densities retrieved from Hinode/SP data are discussed.
---------------------------------------------------------
Title: MISMA inversion of HINODE SOT/SP data. Preliminary results
Authors: Viticchiè, B.; Berrilli, F.; Sánchez Almeida, J.; Orozco
Suárez, D.
2009MmSAI..80..255V Altcode:
We analyze full Stokes observations of a quiet Sun region at disk
center taken with the spectropolarimeter of the Solar Optical Telescope
aboard the HINODE satellite. We present the preliminary results derived
from the MISMA inversion of the observed Stokes I and V profiles. The
complete analysis has as a final goal the definition of probability
density function for the statistical description of the quiet Sun
magnetic field vector for a direct comparison with recently published
results.
---------------------------------------------------------
Title: The Magnetic Landscape of the Sun's Polar Region
Authors: Tsuneta, S.; Ichimoto, K.; Katsukawa, Y.; Lites, B. W.;
Matsuzaki, K.; Nagata, S.; Orozco Suárez, D.; Shimizu, T.; Shimojo,
M.; Shine, R. A.; Suematsu, Y.; Suzuki, T. K.; Tarbell, T. D.; Title,
A. M.
2008ApJ...688.1374T Altcode: 2008arXiv0807.4631T
We present observations of the magnetic landscape of the polar region
of the Sun that are unprecedented in terms of spatial resolution,
field of view, and polarimetric precision. They were carried out with
the Solar Optical Telescope aboard Hinode. Using a Milne-Eddington
inversion, we find many vertically oriented magnetic flux tubes
with field strengths as strong as 1 kG scattered in latitude between
70° and 90°. They all have the same polarity, consistent with the
global polarity of the polar region. The field vectors are observed to
diverge from the centers of the flux elements, consistent with a view
of magnetic fields that are expanding and fanning out with height. The
polar region is also found to have ubiquitous horizontal fields. The
polar regions are the source of the fast solar wind, which is channeled
along unipolar coronal magnetic fields whose photospheric source is
evidently rooted in the strong-field, vertical patches of flux. We
conjecture that vertical flux tubes with large expansion around the
photospheric-coronal boundary serve as efficient chimneys for Alfvén
waves that accelerate the solar wind.
---------------------------------------------------------
Title: Magnetic field emergence in quiet Sun granules
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; del Toro Iniesta,
J. C.; Tsuneta, S.
2008A&A...481L..33O Altcode: 2007arXiv0712.2663O
Aims:We describe a new form of small-scale magnetic flux emergence in
the quiet Sun. This process seems to take vertical magnetic fields
from subsurface layers to the photosphere, where they appear above
granular convection cells. <BR />Methods: High-cadence time series
of spectropolarimetric measurements obtained by Hinode in a quiet
region near disk center are analyzed. We extract line parameters from
the observed Stokes profiles and study their evolution with time. <BR
/>Results: The circular polarization maps derived from the observed Fe
I 630 nm lines show clear magnetic signals emerging at the center of
granular cells. We do not find any evidence for linear polarization
signals associated with these events. The magnetic flux patches grow
with time, occupying a significant fraction of the granular area. The
signals then fade until they disappear completely. The typical lifetime
of these events is of the order of 20 min. No significant changes in
the chromosphere are seen to occur in response to the emergence, as
revealed by co-spatial Ca II H filtergrams. The Stokes I and V profiles
measured in the emerging flux concentrations show strong asymmetries
and Doppler shifts. <BR />Conclusions: The origin of these events is
unclear at present, but we suggest that they may represent the emergence
of vertical fields lines from the bottom of the photosphere, possibly
dragged by the convective upflows of granules. Preliminary inversions
of the Stokes spectra indicate that this scenario is compatible with
the observations, although the emergence of vertical field lines is
not free from conceptual problems.
---------------------------------------------------------
Title: Formation of Solar Magnetic Flux Tubes with Kilogauss Field
Strength Induced by Convective Instability
Authors: Nagata, Shin'ichi; Tsuneta, Saku; Suematsu, Yoshinori;
Ichimoto, Kiyoshi; Katsukawa, Yukio; Shimizu, Toshifumi; Yokoyama,
Takaaki; Tarbell, Theodore D.; Lites, Bruce W.; Shine, Richard A.;
Berger, Thomas E.; Title, Alan M.; Bellot Rubio, Luis R.; Orozco
Suárez, David
2008ApJ...677L.145N Altcode:
Convective instability has been a mechanism used to explain
the formation of solar photospheric flux tubes with kG field
strength. However, the turbulence of the Earth's atmosphere has
prevented ground-based observers from examining the hypothesis
with precise polarimetric measurement on the subarcsecond scale
flux tubes. Here we discuss observational evidence of this scenario
based on observations with the Solar Optical Telescope (SOT) aboard
Hinode. The cooling of an equipartition field strength flux tube
precedes a transient downflow reaching 6 km s<SUP>-1</SUP> and the
intensification of the field strength to 2 kG. These observations
agree very well with the theoretical predictions.
---------------------------------------------------------
Title: Diffraction-limited spectropolarimetry of quiet-sun magnetic
fields
Authors: Orozco Suárez, David
2008PhDT........82O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Quiet-Sun Internetwork Magnetic Fields from the Inversion of
Hinode Measurements
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; del Toro Iniesta,
J. C.; Tsuneta, S.; Lites, B. W.; Ichimoto, K.; Katsukawa, Y.; Nagata,
S.; Shimizu, T.; Shine, R. A.; Suematsu, Y.; Tarbell, T. D.; Title,
A. M.
2007ApJ...670L..61O Altcode: 2007arXiv0710.1405O
We analyze Fe I 630 nm observations of the quiet Sun at disk center
taken with the spectropolarimeter of the Solar Optical Telescope aboard
the Hinode satellite. A significant fraction of the scanned area,
including granules, turns out to be covered by magnetic fields. We
derive field strength and inclination probability density functions from
a Milne-Eddington inversion of the observed Stokes profiles. They show
that the internetwork consists of very inclined, hG fields. As expected,
network areas exhibit a predominance of kG field concentrations. The
high spatial resolution of Hinode's spectropolarimetric measurements
brings to an agreement the results obtained from the analysis of
visible and near-infrared lines.
---------------------------------------------------------
Title: Strategy for the Inversion of Hinode Spectropolarimetric
Measurements in the Quiet Sun
Authors: Orozco Suárez, David; Bellot Rubio, Luis R.; Del Toro
Iniesta, Jose Carlos; Tsuneta, Saku; Lites, Bruce; Ichimoto, Kiyoshi;
Katsukawa, Yukio; Nagata, Shin'ichi; Shimizu, Toshifumi; Shine,
Richard A.; Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.
2007PASJ...59S.837O Altcode: 2007arXiv0709.2033O
In this paper we propose an inversion strategy for the analysis of
spectropolarimetric measurements taken by Hinode in the quiet Sun. The
Spectro-Polarimeter of the Solar Optical Telescope aboard Hinode records
the Stokes spectra of the FeI line pair at 630.2nm with unprecendented
angular resolution, high spectral resolution, and high sensitivity. We
discuss the need to consider a local stray-light contamination to
account for the effects of telescope diffraction. The strategy is
applied to observations of a wide quiet Sun area at disk center. Using
these data we examine the influence of noise and initial guess models
in the inversion results. Our analysis yields the distributions of
magnetic field strengths and stray-light factors. They show that quiet
Sun internetwork regions consist mainly of hG fields with stray-light
contamination of about 0.8.
---------------------------------------------------------
Title: Quiet-Sun Magnetic Fields from Space-borne Observations:
Simulating Hinode's Case
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; del Toro Iniesta,
J. C.
2007ApJ...662L..31O Altcode: 2007arXiv0705.0096O
We examine whether it is possible to derive the field strength
distribution of quiet-Sun internetwork regions from very high spatial
resolution polarimetric observations in the visible. In particular,
we consider the case of the spectropolarimeter attached to the Solar
Optical Telescope aboard Hinode. Radiative magnetoconvection simulations
are used to synthesize the four Stokes profiles of the Fe I 630.2
nm lines. Once the profiles are degraded to a spatial resolution of
0.32" and added noise, we infer the atmospheric parameters by means
of Milne-Eddington inversions. The comparison of the derived values
with the real ones indicates that the visible lines yield correct
internetwork field strengths and magnetic fluxes, with uncertainties
smaller than ~150 G, when a stray-light contamination factor is
included in the inversion. Contrary to the results of ground-based
observations at 1", weak fields are retrieved wherever the field is
weak in the simulation.
---------------------------------------------------------
Title: Attempt to detect Aflven waves with Solar Optical Telescope
aboard Hinode
Authors: Tsuneta, Saku; Suematsu, Y.; Ichimoto, K.; Katsukawa, Y.;
Shimizu, T.; Nagata, S.; Orozco Suárez, D.; Lites, B.; Shine, D.;
Tarbell, T.; Title, A.
2007AAS...210.9428T Altcode: 2007BAAS...39..222T
Flux tube on the sun may carry linear and torsional Alfven waves
generated by photospheric motion. Photospheric motion of 2 km/s would
provide magnetic fluctuation of 40G for 1KG tube and for the Alfven
speed of 50km/s. This may be close to the detection limit of the Stokes
Q and U signals for flux tubes located in the sun center. However,
for flux tubes located near the limb, the fluctuation would be seen in
the Stokes V signal, and can be detectable. <P />We also may be able
to confirm the 90 degree phase shift between magnetic fluctuation and
velocity fluctuation, which is easier to observe for flux tubes near
the limb. Detection of waves would be important in terms of coronal
heating and solar wind acceleration. An attempt to detect waves along
flux tubes will be reported.
---------------------------------------------------------
Title: Magnetic Landscape Of Solar Polar Region With Solar Optical
Telescope Aboard Hinode
Authors: Tsuneta, Saku; Suematsu, Y.; Ichimoto, K.; Shimizu, T.;
Katsukawa, Y.; Nagata, S.; Orozco Suárez, D.; Lites, B.; Shine, D.;
Tarbell, T.; Title, A.
2007AAS...210.9405T Altcode: 2007BAAS...39..218T
Solar polar region is the final destination for remnant magnetic
fields due to meridional flow and granular diffusion, and is very
important for the global solar dynamo. Hinode satellite carried out
high-resolution spectro-polarimetric observations for the Northern
pole on 2006 November 22 as a part of its performance verification
program. We find ubiquitous isolated (positive and negative) patches
in the Stokes V map (i.e. fields horizontal to local surface) all over
the Arctic circle. The Q (vertical to local surface) map indicates
scattered vertical flux tubes, which have bipolar feature in the U and
V maps. This suggests canopy-like structure of the strong isolated flux
tubes. This will be compared with equatorial landscape with similar
distance from the sun center. Strong flux tube and weaker ubiquitous
horizontal fields as represented by Stokes V would have implication
to the current understanding of the global and local dynamo.
---------------------------------------------------------
Title: The usefulness of analytic response functions
Authors: Orozco Suárez, D.; Del Toro Iniesta, J. C.
2007A&A...462.1137O Altcode: 2012arXiv1211.1502O
Aims:We introduce analytical response functions and their main
properties as an important diagnostic tool that help understand Stokes
profile formation physics and the meaning of well-known behaviors of
standard inversion codes of the radiative transfer equation often used
to measure solar magnetic fields. <BR />Methods: A Milne-Eddington
model atmosphere is used as an example where response functions are
analytical. A sample spectral line has been chosen to show the main
qualitative properties. <BR />Results: We show that analytic response
functions readily provide explanations for various well-known behaviors
of spectral lines, such as the sensitivity of visible lines to weak
magnetic fields or the trade-offs often detected in inversion codes
between the Milne-Eddington thermodynamic parameters. We also show
that response functions are helpful in selecting sample wavelengths
optimized for specific parameter diagnostics. <P />Appendix A is only
available in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: S im ulation And Analysis Of VIM Measurements: Feedback On
Design Parameters
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Vargas, S.; Bonet,
J. A.; Martíez Pillet, V.; del Toro Iniesta, J. C.
2007ESASP.641E..49O Altcode: 2006astro.ph.11443O
The Visible-light Imager and Magnetograph (VIM) proposed for the
ESA Solar Orbiter mission will observe a photo spheric spectral
line at high spatial resolution. Here we simulate and interpret VIM
measurements. Realistic MHD models are used to synthesize "observed"
Stokes profiles of the photospheric Fe I 617.3 nm line. The profiles are
degraded by telescope diffraction and detector pixel size to a spatial
resolution of 162 km on the solar surface. We stufy the influence
of spectral resolving power, noise, and limited wavelength sampling
on the vector magnetic fields and line-of-sight velocities derived
from Milne-Eddington inversions of the simulated measurements. VIM
will provide reasonably accurate values of the atmospheric parametes
even with the filter widths of 120 Å and 3 wavelength positions plus
continuum, as long as the noise level is kept below 10-3 Ic.
---------------------------------------------------------
Title: First Steps Towards the Electronic Inversion of the Radiative
Transfer Equation
Authors: Castillo Lorenzo, J. L.; Orozco Suárez, D.; Bellot Rubio,
L. R.; Jiménez, L.; Del Toro Iniesta, J. C.
2006ASPC..358..177C Altcode:
The radiative transfer equation (RTE) gives us information about how the
light streams through the medium. It must be inverted in order to obtain
the properties of the medium that generated the observation. While
there are a number of well discussed methods to approach the solution
of the inversion, none of them is suitable for the real-time analysis
of high-resolution images due to their computational requirements. This
document introduces an electronic inverter for the RTE, suitable for
real-time inversion and mainly intended for space missions and on-line
ground-based observations.
---------------------------------------------------------
Title: Measuring the Magnetic Vector with the He I 10830 Å Line:
A Rich New World
Authors: Solanki, S. K.; Lagg, A.; Aznar Cuadrado, R.; Orozco Suárez,
D.; Collados, M.; Wiegelmann, T.; Woch, J.; Sasso, C.; Krupp, N.
2006ASPC..358..431S Altcode:
The triplet of the He I transitions around 10830 Å not only shows a
rich variety of Stokes profiles, but also allows the full magnetic
vector in the upper chromosphere to be probed, thus revealing
the magnetic structure of loops, current sheets, finely structured
supersonic downflows, the chromospheric layers of sunspots (supporting
the presence of uncombed fields in the penumbra), flares, and the
quiet Sun. A very brief overview of some of the observations and
results obtained so far is given.
---------------------------------------------------------
Title: Milne-Eddington Response Functions and Their Applications
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Del Toro Iniesta,
J. C.
2006ASPC..358..197O Altcode:
We examine the errors in the atmospheric parameters recovered
from the inversion of spectro-polarimetric data with limited
wavelength sampling. We suggest that response functions evaluated in
Milne-Eddington atmospheres may be useful as diagnostic tools that
allow, for instance, the selection of the optimum wavelength positions
to be observed by vector magnetographs.
---------------------------------------------------------
Title: Photospheric and Chromospheric Magnetic Structure of a Sunspot
Authors: Orozco Suarez, D.; Lagg, A.; Solanki, S. K.
2005ESASP.596E..59O Altcode: 2005ccmf.confE..59O
No abstract at ADS