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.
Bibcode: 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.
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
Bibcode: 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.
Title: Magnetic properties of short-lived penumbral microjets
Authors: Tapia, Azaymi Siu; Bellot Rubio, L. R.; Gafeira, Ricardo;
Orozco Suárez, David
Bibcode: 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.
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.
Bibcode: 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.
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.
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 (HRIEUV, 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.
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.
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.
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.
Bibcode: 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.
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.
Bibcode: 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.
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.
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.
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.
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.
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.
Bibcode: 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.
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.
Bibcode: 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-2 day-1), and provide
about 70% of the total instantaneous IN flux detected in the interior
of the supergranule.
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
Bibcode: 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−1. 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.
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.
Bibcode: 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.
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.
Bibcode: 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.
Aims: In this work we discuss
the application of convolutional neural networks (CNNs) as a tool to
advantageously initialize Stokes profile inversions.
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.
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.
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.
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.
Bibcode: 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.
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.
Bibcode: 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.
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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.
Bibcode: 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.
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.
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.
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.
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.
Bibcode: 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.
Bibcode: 2020A&A...642A..11S
Altcode: 2019arXiv190311061S
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.
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
LiNbO3 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.
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.
Bibcode: 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.
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.
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.
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.
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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 LiNbO3 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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 b1, b2, and b4 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
b2 line as b1 forms at similar heights and always
shows weaker polarization signals, while b4 is severely
blended with photospheric lines. We also compare Mg I b2
with the K I D1 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
b2 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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 D2 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.
Bibcode: 2018A&A...610A..79Q
Altcode: 2018arXiv180101655Q
Of the two solar lines, K I D1 and D2, almost
all attention so far has been devoted to the D1 line, as
D2 is severely affected by an O2 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 O2 band on the K I D2
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 O2 is still present, albeit much weaker, at the expected
balloon altitude. We applied the obtained O2 transmittance
to K I D2 synthetic polarimetric spectra and found that in
the absence of line-of-sight motions, the residual O2 has
a negligible effect on the K I D2 line. On the other hand,
for Doppler-shifted K I D2 data, the residual O2
might alter the shape of the Stokes profiles. However, the residual
O2 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 D2 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.
Bibcode: 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.
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.
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.
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.
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 2017MNRAS.470.1453Q
Altcode: 2017arXiv170510002Q
We characterize the K I D1 & D2 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 (ApJS 229, 1, 6)
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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\prime\prime )
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.
Bibcode: 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.
Bibcode: 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-1 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-1. 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-2. 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.
Bibcode: 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
km2 s-1, 80-90 km2 s-1,
and 25-70 km2 s-1, 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.
Bibcode: 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.
Bibcode: 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-1. 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.
Bibcode: 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 }2 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.
Bibcode: 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}-11+49 km
s-1 and {15}-15+34 km s-1,
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.
Bibcode: 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.
Bibcode: 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-1
and 1.2 km s-1, 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 × 1017 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.
Bibcode: 2016A&A...596A...2B
Altcode: 2016arXiv160708165B
Context. Some models for the topology of the magnetic field in
sunspot penumbrae predict regions free of magnetic fields or with
only dynamically weak fields in the deep photosphere.
Aims:
We aim to confirm or refute the existence of weak-field regions in
the deepest photospheric layers of the penumbra.
Methods:
We investigated the magnetic field at log τ5 = 0 is
by inverting spectropolarimetric data of two different sunspots
located very close to disk center with a spatial resolution of
approximately 0.4-0.45''. The data have been recorded using the GRIS
instrument attached to the 1.5-m solar telescope GREGOR at the El
Teide observatory. The data include three Fe I lines around 1565 nm,
whose sensitivity to the magnetic field peaks half a pressure scale
height deeper than the sensitivity of the widely used Fe I spectral
line pair at 630 nm. Before the inversion, the data were corrected
for the effects of scattered light using a deconvolution method with
several point spread functions.
Results: At log τ5
= 0 we find no evidence of regions with dynamically weak (B<
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.
Bibcode: 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-1 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.
Bibcode: 2016A&A...596A...8J
Altcode: 2016arXiv160801988J
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.
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.
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.
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.
Bibcode: 2016A&A...596A...6L
Altcode: 2016arXiv160506324L
Context. Investigations of the magnetism of the quiet Sun are hindered
by extremely weak polarization signals in Fraunhofer spectral
lines. Photon noise, straylight, and the systematically different
sensitivity of the Zeeman effect to longitudinal and transversal
magnetic fields result in controversial results in terms of the strength
and angular distribution of the magnetic field vector.
Aims:
The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
spatial straylight and photon noise into account.
Methods: Highly
sensitive full Stokes measurements of a quiet-Sun region at disk center
in the deep photospheric Fe I lines in the 1.56 μm region were obtained
with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
diagnostics based directly on the shape and strength of the profiles
were applied to the GRIS data. We made use of the magnetic line ratio
technique, which was tested against realistic magneto-hydrodynamic
simulations (MURaM).
Results: About 80% of the GRIS spectra
of a very quiet solar region show polarimetric signals above a 3σ
level. Area and amplitude asymmetries agree well with small-scale
surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields.
Conclusions:
The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
are so far unique in the combination of high spatial resolution scans
and high magnetic field sensitivity. Nevertheless, the unavoidable
effect of spatial straylight and the resulting dilution of the weak
Stokes profiles means that inversion techniques still bear a high risk
of misinterpretating the data.
Title: 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.
Bibcode: 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.
Bibcode: 2016A&A...596A..59F
Altcode: 2016arXiv161104803F
Context. Active regions are the most prominent manifestations of solar
magnetic fields; their generation and dissipation are fundamental
problems in solar physics. Light bridges are commonly present during
sunspot decay, but a comprehensive picture of their role in the
removal of the photospheric magnetic field is still lacking.
Aims: We study the three-dimensional configuration of a sunspot,
and in particular, its light bridge, during one of the last stages of
its decay.
Methods: We present the magnetic and thermodynamical
stratification inferred from full Stokes inversions of the photospheric
Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
Infrared Spectrograph of the GREGOR telescope at the Observatorio del
Teide, Tenerife, Spain. The analysis is complemented by a study of
continuum images covering the disk passage of the active region, which
are provided by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory.
Results: The sunspot shows a light bridge
with penumbral continuum intensity that separates the central umbra from
a smaller umbra. We find that in this region the magnetic field lines
form a canopy with lower magnetic field strength in the inner part. The
photospheric light bridge is dominated by gas pressure (high-β),
as opposed to the surrounding umbra, where the magnetic pressure
is higher. A convective flow is observed in the light bridge. This
flow is able to bend the magnetic field lines and to produce field
reversals. The field lines merge above the light bridge and become
as vertical and strong as in the surrounding umbra. We conclude that
this occurs because two highly magnetized regions approach each other
during the sunspot evolution.