Author name code: deltoro-iniesta
ADS astronomy entries on 2022-09-14
author:"Del Toro Iniesta, Jose Carlos"
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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: 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: Nice memories from a collaboration on sunspots
Authors: del Toro Iniesta, J.
Bibcode: 2022fysr.confE..52D
Altcode:
Back in 1994, when I still was at the IAC, I had the idea of using the
(by then) new SIR inversion code to a full vector spectropolarimetric
map of a sunspot as obtained with the HAO's Advanced Stokes
Polarimeter. The opportunity was open to study the three-dimensional
structure of sunspots from a semi-empirical basis. A collaboration
between HAO and IAC had already started a few years earlier with the
stays in HAO of Jorge Sánchez Almeida and Valentín Martínez Pillet
(today's NSO director) as postdocs. Direct contact with the champions
of ASP, Andy and Bruce, Bruce and Andy, was hence granted and I readily
suggested them to undertake the study with their data and our code in
the frame of the PhD thesis of a new student of mine, Carlos Westendorp
Plaza. A few years later (1997), the discovery that penumbral material
comes back to the solar interior at the external penumbral border was
published in the Nature journal. The paper was followed by a series in
ApJ on an optical tomography of a sunspot. The friendly and enriching
discussions with Andy and Bruce remain as one of the most rewarding
experiences in my (already long) career.
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: 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: SUNRISE Chromospheric Infrared spectroPolarimeter (SCIP)
for SUNRISE III: Scan mirror mechanism
Authors: Oba, Takayoshi; Shimizu, Toshifumi; Katsukawa, Yukio; Kubo,
Masahito; Uraguchi, Fumihiro; Tsuzuki, Toshihiro; Tamura, Tomonori;
Shinoda, Kazuya; Kodeki, Kazuhide; Fukushima, Kazuhiko; Gandorfer,
Achim; del Toro Iniesta, Jose Carlos
Bibcode: 2020SPIE11445E..4FO
Altcode:
The SUNRISE Chromospheric Infrared spectroPolarimeter (SCIP) is a
balloon-borne long-slit spectrograph for SUNRISE III to precisely
measure magnetic fields in the solar atmosphere. The scan mirror
mechanism (SMM) is installed in the optical path to the entrance slit
of the SCIP to move solar images focused on the slit for 2-dimensional
mapping. The SMM is required to have (1) the tilt stability better
than 0.035″ (3σ) on the sky angle for the diffraction-limited
spatial resolution of 0.2″, (2) step response shorter than 32 msec
for rapid scanning observations, and (3) good linearity (i.e. step
uniformity) over the entire field-of-view (60″x60″). To achieve
these performances, we have developed a flight-model mechanism
and its electronics, in which the mirror tilt is controlled by
electromagnetic actuators with a closed-loop feedback logic with
tilt angles from gap-based capacitance sensors. Several optical
measurements on the optical bench verified that the mechanism meets
the requirements. In particular, the tilt stability achives better
than 0.012″ (3σ). Thermal cycling and thermal vacuum tests have
been completed to demonstrate the performance in the vacuum and the
operational temperature range expected in the balloon flight. We
found a small temperature dependence in the step uniformity and this
dependence will be corrected to have 2-demensional maps with the
sub-arcsec spatial accuracy in the data post-processing.
Title: Sunrise Chromospheric Infrared spectroPolarimeter (SCIP)
for SUNRISE III: polarization modulation unit
Authors: Kubo, Masahito; Shimizu, Toshifumi; Katsukawa, Yukio;
Kawabata, Yusuke; Anan, Tetsu; Ichimoto, Kiyoshi; Shinoda, Kazuya;
Tamura, Tomonori; Nodomi, Yoshifumi; Nakayama, Satoshi; Yamada, Takuya;
Tajima, Takao; Nakata, Shimpei; Nakajima, Yoshihito; Okutani, Kousei;
Feller, Alex; del Toro Iniesta, Jose Carlos
Bibcode: 2020SPIE11447E..A3K
Altcode:
Polarization measurements of the solar chromospheric lines at
high precision are key to present and future solar telescopes for
understanding magnetic field structures in the chromosphere. The
Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) for Sunrise
III is a spectropolarimeter with a polarimetric precision of 0.03 %
(1 σ). The key to high-precision polarization measurements using
SCIP is a polarization modulation unit that rotates a waveplate
continuously at a constant speed. The rotating mechanism is a DC
brushless motor originally developed for a future space mission, and
its control logic was originally developed for the sounding rocket
experiment CLASP. Because of our requirement on a speed of rotation
(0.512 s/rotation) that was 10 times faster than that of CLASP, we
optimized the control logic for the required faster rotation. Fast
polarization modulation is essential for investigating the fine-scale
magnetic field structures related to the dynamical chromospheric
phenomena. We have verified that the rotation performance can achieve
the polarization precision of 0.03 % (1 σ) required by SCIP and such
a significant rotation performance is maintained under thermal vacuum
conditions by simulating the environment of the Sunrise III balloon
flight. The waveplate was designed as a pair of two birefringent
plates made of quartz and sapphire to achieve a constant retardation
in a wide wavelength range. We have confirmed that the retardation
is almost constant in the 770 nm and 850nm wavelength bands of SCIP
under the operational temperature conditions.
Title: Sunrise Chromospheric Infrared spectroPolarimeter (SCIP)
for SUNRISE III: opto-mechanical analysis and design
Authors: Uraguchi, Fumihiro; Tsuzuki, Toshihiro; Katsukawa, Yukio;
Hara, Hirohisa; Iwamura, Satoru; Kubo, Masahito; Nodomi, Yoshifumi;
Suematsu, Yoshinori; Kawabata, Yusuke; Shimizu, Toshifumi; Gandorfer,
Achim; del Toro Iniesta, Jose Carlos
Bibcode: 2020SPIE11447E..ABU
Altcode:
The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) is a
near-IR spectro-polarimeter instrument newly designed for Sunrise III,
a balloon-borne solar observatory with a 1-m diameter telescope. In
order to achieve the strict requirements the SCIP wavefront error, it is
necessary to quantify the errors due to environmen- tal effects such as
gravity and temperature variation under the observation conditions. We
therefore conducted an integrated opto-mechanical analysis incorporating
mechanical and thermal disturbances into a finite element model of
the entire SCIP structure to acquire the nodal displacements of each
optical element, then fed them back to the optical analysis software
in the form of rigid body motion and surface deformation fitted by
polynomials. This method allowed us to determine the error factors
having a significant influence on optical performance. For example,
no significant wavefront degradation was associated with the structural
mountings because the optical element mounts were well designed based
on quasi-kinematic constraints. In contrast, we found that the main
factor affecting wavefront degradation was the rigid body motions of
the optical elements, which must be mini- mized within the allowable
level. Based on these results, we constructed the optical bench using a
sandwich panel as the optical bench consisting of an aluminum-honeycomb
core and carbon fiber reinforced plastic skins with a high stiffness
and low coefficient of thermal expansion. We then confirmed that the
new opto-mechanical model achieved the wavefront error requirement. In
this paper, we report the details of this integrated opto-mechanical
analysis, including the wavefront error budgeting and the design of
the opto-mechanics.
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: Solar Orbiter: connecting remote sensing and in situ
measurements
Authors: Horbury, T. S.; Auchere, F.; Antonucci, E.; Berghmans, D.;
Bruno, R.; Carlsson, M.; del Toro Iniesta, J. C.; Fludra, A.; Harra,
L.; Hassler, D.; Heinzel, P.; Howard, R. A.; Krucker, S.; Livi, S. A.;
Long, D.; Louarn, P.; Maksimovic, M.; Mueller, D.; Owen, C. J.; Peter,
H.; Rochus, P. L.; Rodriguez-Pacheco, J.; Romoli, M.; Schühle, U.;
Solanki, S. K.; Teriaca, L.; Wimmer-Schweingruber, R. F.; Zouganelis,
Y.; Laker, R.
Bibcode: 2020AGUFMSH038..10H
Altcode:
A key science goal of the Solar Orbiter mission is to make connections
between phenomena on the Sun and their manifestations in interplanetary
space. To that end, the spacecraft carries a carefully tailored
payload of six remote sensing instruments and four making in situ
measurements. During June 2020, while the spacecraft was around 0.5
AU from the Sun, the remote sensing instruments operated for several
days. While this was primarily an engineering activity, the resulting
observations provided outstanding measurements and represent the ideal
first opportunity to investigate the potential for making connections
between the remote sensing and in situ payloads on Solar Orbiter. We present a preliminary analysis of the available remote sensing and
in situ observations, showing how connections can be made, and discuss
the potential for further, more precise mapping to be performed as
the mission progresses.
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: Autonomous on-board data processing and instrument calibration
software for the Polarimetric and Helioseismic Imager on-board the
Solar Orbiter mission
Authors: Albert, Kinga; Hirzberger, Johann; Kolleck, Martin; Jorge,
Nestor Albelo; Busse, Dennis; Rodríguez, Julian Blanco; Carrascosa,
Juan Pedro Cobos; Fiethe, Björn; Gandorfer, Achim; Germerott, Dietmar;
Guan, Yejun; Guerrero, Lucas; Gutierrez-Marques, Pablo; Expósito,
David Hernández; Lange, Tobias; Michalik, Harald; Suárez, David
Orozco; Schou, Jesper; Solanki, Sami K.; del Toro Iniesta, José
Carlos; Woch, Joachim
Bibcode: 2020JATIS...6d8004A
Altcode:
A frequent problem arising for deep space missions is the discrepancy
between the amount of data desired to be transmitted to the ground
and the available telemetry bandwidth. A part of these data consists
of scientific observations, being complemented by calibration data
to help remove instrumental effects. We present our solution for this
discrepancy, implemented for the Polarimetric and Helioseismic Imager
on-board the Solar Orbiter mission, the first solar spectropolarimeter
in deep space. We implemented an on-board data reduction system that
processes calibration data, applies them to the raw science observables,
and derives science-ready physical parameters. This process reduces
the raw data for a single measurement from 24 images to five, thus
reducing the amount of downlinked data, and in addition, renders the
transmission of the calibration data unnecessary. Both these on-board
actions are completed autonomously.
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: The Solar Orbiter mission. Science overview
Authors: Müller, D.; St. Cyr, O. C.; Zouganelis, I.; Gilbert, H. R.;
Marsden, R.; Nieves-Chinchilla, T.; Antonucci, E.; Auchère, F.;
Berghmans, D.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic,
M.; Owen, C. J.; Rochus, P.; Rodriguez-Pacheco, J.; Romoli, M.;
Solanki, S. K.; Bruno, R.; Carlsson, M.; Fludra, A.; Harra, L.;
Hassler, D. M.; Livi, S.; Louarn, P.; Peter, H.; Schühle, U.;
Teriaca, L.; del Toro Iniesta, J. C.; Wimmer-Schweingruber, R. F.;
Marsch, E.; Velli, M.; De Groof, A.; Walsh, A.; Williams, D.
Bibcode: 2020A&A...642A...1M
Altcode: 2020arXiv200900861M
Aims: Solar Orbiter, the first mission of ESA's Cosmic Vision
2015-2025 programme and a mission of international collaboration between
ESA and NASA, will explore the Sun and heliosphere from close up and
out of the ecliptic plane. It was launched on 10 February 2020 04:03
UTC from Cape Canaveral and aims to address key questions of solar and
heliospheric physics pertaining to how the Sun creates and controls
the Heliosphere, and why solar activity changes with time. To answer
these, the mission carries six remote-sensing instruments to observe
the Sun and the solar corona, and four in-situ instruments to measure
the solar wind, energetic particles, and electromagnetic fields. In
this paper, we describe the science objectives of the mission, and how
these will be addressed by the joint observations of the instruments
onboard.
Methods: The paper first summarises the mission-level
science objectives, followed by an overview of the spacecraft and
payload. We report the observables and performance figures of each
instrument, as well as the trajectory design. This is followed by a
summary of the science operations concept. The paper concludes with a
more detailed description of the science objectives.
Results:
Solar Orbiter will combine in-situ measurements in the heliosphere
with high-resolution remote-sensing observations of the Sun to address
fundamental questions of solar and heliospheric physics. The performance
of the Solar Orbiter payload meets the requirements derived from the
mission's science objectives. Its science return will be augmented
further by coordinated observations with other space missions and
ground-based observatories. ARRAY(0x207ce98)
Title: PMI: The Photospheric Magnetic Field Imager
Authors: Staub, Jan; Fernandez-Rico, German; Gandorfer, Achim; Gizon,
Laurent; Hirzberger, Johann; Kraft, Stefan; Lagg, Andreas; Schou,
Jesper; Solanki, Sami K.; del Toro Iniesta, Jose Carlos; Wiegelmann,
Thomas; Woch, Joachim
Bibcode: 2020JSWSC..10...54S
Altcode:
We describe the design and the capabilities of the Photospheric Magnetic
field Imager (PMI), a compact and lightweight vector magnetograph,
which is being developed for ESA's Lagrange mission to the Lagrange
L5 point. After listing the design requirements and give a scientific
justification for them, we describe the technical implementation and
the design solution capable of fulfilling these requirements. This is
followed by a description of the hardware architecture as well as the
operations principle. An outlook on the expected performance concludes
the paper.
Title: On the Magnetic Nature of an Exploding Granule as Revealed
by Sunrise/IMaX
Authors: Guglielmino, Salvo L.; Martínez Pillet, Valentín; Ruiz
Cobo, Basilio; Bellot Rubio, Luis R.; del Toro Iniesta, José Carlos;
Solanki, Sami K.; Riethmüller, Tino L.; Zuccarello, Francesca
Bibcode: 2020ApJ...896...62G
Altcode: 2020arXiv200503371G
We study the photospheric evolution of an exploding granule
observed in the quiet Sun at high spatial (∼0"3) and temporal
(31.5 s) resolution by the imaging magnetograph Sunrise/IMaX in 2009
June. These observations show that the exploding granule is cospatial
to a magnetic flux emergence event occurring at mesogranular scale
(up to ∼12 Mm2 area). Using a modified version of the
SIR code for inverting the IMaX spectropolarimetric measurements, we
obtain information about the magnetic configuration of this photospheric
feature. In particular, we find evidence of highly inclined emerging
fields in the structure, carrying a magnetic flux content up to ∼4
× 1018 Mx. The balance between gas and magnetic pressure
in the region of flux emergence, compared with a very quiet region of
the Sun, indicates that the additional pressure carried by the emerging
flux increases the total pressure by about 5% and appears to allow the
granulation to be modified, as predicted by numerical simulations. The
overall characteristics suggest that a multipolar structure emerges
into the photosphere, resembling an almost horizontal flux sheet. This
seems to be associated with exploding granules. Finally, we discuss
the origin of such flux emergence events.
Title: The SO/PHI instrument on Solar Orbiter and its data products
Authors: Solanki, Sami K.; Hirzberger, Johann; Wiegelmann, Thomas;
Gandorfer, Achim; Woch, Joachim; del Toro Iniesta, José Carlos
Bibcode: 2020EGUGA..2217904S
Altcode:
A central instrument of Solar Orbiter is the Polarimetric and
Helioseismic Imager, SO/PHI. It is a vector magnetograph that also
provides data for helioseismology. SO/PHI is composed of two telescopes,
a full-disk telescope (FDT) and a high-resolution telescope (HRT). The
HRT will observe at a resolution as high as 200 km on the solar
surface, while the FDT will obtain the magnetic field and velocity of
the full solar disc whenever it observes. SO/PHI will be the first
solar spectro-polarimeter to leave the Sun-Earth line, opening up
some unique perspectives, such as the first detailed view of the solar
poles. This will allow not just a more precise and exact mapping of the
polar magnetic field than possible so far, but will also enable us to
follow the dynamics of individual magnetic features at high latitudes
and to determine solar surface and sub-surface flows right up to the
poles. In addition to its standard data products (vector magnetograms,
continuum images and maps of the line-of-sight velocity), SO/PHI will
also provide higher-level data products. These will include synoptic
charts, local magnetic field extrapolations starting from HRT data and
global magnetic field extrapolations (from FDT data) with potential
field source-surface (PFSS) models and possibly also non-potential
models such as NLFFF (non-linear force-free fields), magnetostatics
and MHD. The SO/PHI data products will usefully complement the data
taken by other instruments on Solar Orbiter and on Solar Probe, as
well as instruments on the ground or in Earth orbit. Combining with
observations by Earth-based and near-Earth telescopes will enable
new types of investigations, such as stereoscopic polarimetry and
stereoscopic helioseismology.
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: The Polarimetric and Helioseismic Imager on Solar Orbiter
Authors: Mueller, D.; Solanki, S. K.; del Toro Iniesta, J. C.
Bibcode: 2019AGUFMSH21D3292M
Altcode:
The Polarimetric and Helioseismic Imager on the Solar Orbiter mission
(SO/PHI) is 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. It will provide
valuable supporting observations for Parker Solar Probe. 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 (LCVRs). The line and the
nearby continuum are sampled at six wavelength points and the data are
recorded by a 2k x 2k CMOS detector. To save valuable telemetry, the
raw data are reduced already on board, including being inverted under
the assumption of a Milne-Eddington atmosphere. SO/PHI is composed of
two telescopes, the Full Disc Telescope (FDT), covers the full solar
disc at all phases of the orbit, while the High Resolution Telescope
(HRT), can resolve structures as small as 200 km on the Sun at closest
perihelion. The standard data products of SO/PHI are maps of the
photospheric magnetic field vector, line-of-sight velocity and continuum
intensity with a highest cadence of one minute. The operational modes
of SO/PHI are kept highly flexible allowing to adjust to the actual
science goal chosen for a Solar Orbiter operation window.
Title: Performance Analysis of the SO/PHI Software Framework for
On-board Data Reduction
Authors: Albert, K.; Hirzberger, J.; Busse, D.; Rodríguez, J. Blanco;
Castellanos Duran, J. S.; Cobos Carrascosa, J. P.; Fiethe, B.;
Gandorfer, A.; Guan, Y.; Kolleck, M.; Lagg, A.; Lange, T.; Michalik,
H.; Solanki, S. K.; del Toro Iniesta, J. C.
Bibcode: 2019ASPC..523..151A
Altcode: 2019arXiv190508690A
The Polarimetric and Helioseismic Imager (PHI) is the first deep-space
solar spectropolarimeter, on-board the Solar Orbiter (SO) space
mission. It faces: stringent requirements on science data accuracy, a
dynamic environment, and severe limitations on telemetry volume. SO/PHI
overcomes these restrictions through on-board instrument calibration
and science data reduction, using dedicated firmware in FPGAs. This
contribution analyses the accuracy of a data processing pipeline by
comparing the results obtained with SO/PHI hardware to a reference
from a ground computer. The results show that for the analyzed pipeline
the error introduced by the firmware implementation is well below the
requirements of SO/PHI.
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: On the Magnetic Nature of Solar Exploding Granules
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo,
B.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.; Solanki, S. K.;
Zuccarello, F.
Bibcode: 2019ASPC..526..299G
Altcode:
We report on spectropolarimetric observations acquired by the imaging
magnetograph SUNRISE/IMaX at high spatial 0.''3 and temporal (31.5 s)
resolution during the first science flight of this balloon-borne solar
observatory. We describe the photospheric evolution of an exploding
granule observed in the quiet Sun. This granule is cospatial with
a magnetic flux emergence event occurring at mesogranular scales
(up to ∼12 Mm2 area). Using a modified version of the
SIR code, we show that we can estimate the longitudinal field also
in the presence of a residual cross-talk in these IMaX longitudinal
measurements. We determine the magnetic flux content of the structure
(∼3 ×1018 Mx), which appears to have a multipolar
configuration, and discuss the origin of such flux emergence events.
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: 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: The High Resolution Telescope (HRT) of the Polarimetric and
Helioseismic Imager (PHI) onboard Solar Orbiter
Authors: Gandorfer, A.; Grauf, B.; Staub, J.; Bischoff, J.; Woch, J.;
Hirzberger, J.; Solanki, S. K.; Álvarez-Herrero, A.; García Parejo,
P.; Schmidt, W.; Volkmer, R.; Appourchaux, T.; del Toro Iniesta, J. C.
Bibcode: 2018SPIE10698E..4NG
Altcode:
Solar Orbiter is a joint mission of ESA and NASA scheduled for
launch in 2020. Solar Orbiter is a complete and unique heliophysics
mission, combining remote sensing and in-situ analysis; its special
elliptical orbit allows viewing the Sun from a distance of only 0.28
AU, and - leaving the ecliptic plane - to observe the solar poles from
a hitherto unexplored vantage point. One of the key instruments for
Solar Orbiter's science is the "Polarimetric and Helioseismic Imager"
(PHI), which will provide maps of the solar surface magnetic fields and
the gas flows on the visible solar surface. Two telescopes, a full disc
imager, and a high resolution channel feed a common Fabry-Perot based
tunable filter and thus allow sampling a single Fraunhofer line at 617.3
nm with high spectral resolution; a polarization modulation system
makes the system sensitive to the full state of polarization. From
the analysis of the Doppler shift and the magnetically induced Zeeman
polarization in this line, the magnetic field and the line-of-sight
gas motions can be detected for each point in the image. In this
paper we describe the opto-mechanical system design of the high
resolution telescope. It is based on a decentred Ritchey-Chrétien
two-mirror telescope. The telescope includes a Barlow type magnifier
lens group, which is used as in-orbit focus compensator, and a beam
splitter, which sends a small fraction of the collected light onto
a fast camera, which provides the error signals for the actively
controlled secondary mirror compensating for spacecraft jitter and other
disturbances. The elliptical orbit of the spacecraft poses high demands
on the thermo-mechanical stability. The varying size of the solar disk
image requires a special false-light suppression architecture, which is
briefly described. In combination with a heat-rejecting entrance window,
the optical energy impinging on the polarimetric and spectral analysis
system is efficiently reduced. We show how the design can preserve the
diffraction-limited imaging performance over the design temperature
range of -20°C to +60°C. The decentred hyperbolical mirrors require
special measures for the inter-alignment and their alignment with
respect to the mechanical structure. A system of alignment flats and
mechanical references is used for this purpose. We will describe the
steps of the alignment procedure, and the dedicated optical ground
support equipment, which are needed to reach the diffraction limited
performance of the telescope. We will also report on the verification
of the telescope performance, both - in ambient condition - and in
vacuum at different temperatures.
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: 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: Convectively Driven Sinks and Magnetic Fields in the Quiet-Sun
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.;
Schmidt, Wolfgang
Bibcode: 2017ApJS..229...14R
Altcode: 2016arXiv161007622R
We study the relation between mesogranular flows, convectively
driven sinks and magnetic fields using high spatial resolution
spectropolarimetric data acquired with the Imaging Magnetograph
eXperiment on board Sunrise. We obtain the horizontal velocity
flow fields of two quiet-Sun regions (31.2 × 31.2 Mm2)
via local correlation tracking. Mesogranular lanes and the central
position of sinks are identified using Lagrange tracers. We find
6.7× {10}-2 sinks per Mm2 in the two observed
regions. The sinks are located at the mesogranular vertices and turn
out to be associated with (1) horizontal velocity flows converging to a
central point and (2) long-lived downdrafts. The spatial distribution
of magnetic fields in the quiet-Sun is also examined. The strongest
magnetic fields are preferentially located at sinks. We find that 40% of
the pixels with longitudinal components of the magnetic field stronger
than 500 G are located in the close neighborhood of sinks. In contrast,
the small-scale magnetic loops detected by Martínez González et al. in
the same two observed areas do not show any preferential distribution
at mesogranular scales. The study of individual examples reveals
that sinks can play an important role in the evolution of quiet-Sun
magnetic features.
Title: Far side Helioseismology with Solar Orbiter
Authors: Appourchaux, T.; Birch, A.; Gizon, L. C.; Löptien, B.;
Schou, J.; Solanki, S. K.; del Toro Iniesta, J. C.; Gandorfer, A.;
Hirzberger, J.; Alvarez-Herrero, A.; Woch, J. G.; Schmidt, W.
Bibcode: 2016AGUFMSH43A2554A
Altcode:
The Solar Orbiter mission, to be launched in October 2018, will
carry a suite of remote sensing and in-situ instruments, including
the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
high-cadence images of the Sun in intensity and Doppler velocity
suitable for carrying out novel helioseismic studies. The orbit
of the Solar Orbiter spacecraft will reach a solar latitude up to
34 degrees by the end of the extended mission and thus will enable
the first local helioseismology studies of the polar regions. The
full range of Earth-Sun-spacecraft angles provided by the orbit will
enable helioseismology from two vantage points by combining PHI with
another instrument: stereoscopic helioseismology will allow the study
of the deep solar interior and a better understanding of the physics
of solar oscillations in both quiet Sun and sunspots. In this paper
we will review the helioseismic objectives achievable with PHI, and
will also give a short status report of the development of the Flight
Model of PHI.
Title: Inversion of the radiative transfer equation for polarized
light
Authors: del Toro Iniesta, Jose Carlos; Ruiz Cobo, Basilio
Bibcode: 2016LRSP...13....4D
Altcode: 2016arXiv161010039D
Since the early 1970s, inversion techniques have become the most
useful tool for inferring the magnetic, dynamic, and thermodynamic
properties of the solar atmosphere. Inversions have been proposed
in the literature with a sequential increase in model complexity:
astrophysical inferences depend not only on measurements but also on
the physics assumed to prevail both on the formation of the spectral
line Stokes profiles and on their detection with the instrument. Such
an intrinsic model dependence makes it necessary to formulate specific
means that include the physics in a properly quantitative way. The core
of this physics lies in the radiative transfer equation (RTE), where the
properties of the atmosphere are assumed to be known while the unknowns
are the four Stokes profiles. The solution of the (differential)
RTE is known as the direct or forward problem. From an observational
point of view, the problem is rather the opposite: the data are made
up of the observed Stokes profiles and the unknowns are the solar
physical quantities. Inverting the RTE is therefore mandatory. Indeed,
the formal solution of this equation can be considered an integral
equation. The solution of such an integral equation is called the
inverse problem. Inversion techniques are automated codes aimed at
solving the inverse problem. The foundations of inversion techniques
are critically revisited with an emphasis on making explicit the many
assumptions underlying each of them.
Title: The RTE inversion on FPGA aboard the solar orbiter PHI
instrument
Authors: Cobos Carrascosa, J. P.; Aparicio del Moral, B.; Ramos Mas,
J. L.; Balaguer, M.; López Jiménez, A. C.; del Toro Iniesta, J. C.
Bibcode: 2016SPIE.9913E..42C
Altcode:
In this work we propose a multiprocessor architecture to reach high
performance in floating point operations by using radiation tolerant
FPGA devices, and under narrow time and power constraints. This
architecture is used in the PHI instrument that carries out the
scientific analysis aboard the ESA's Solar Orbiter mission. The
proposed architecture, in a SIMD flavor, is aimed to be an accelerator
within the Data Processing Unit (it is composed by a main Leon
processor and two FPGAs) for carrying out the RTE inversion on
board the spacecraft using a relatively slow FPGA device - Xilinx
XQR4VSX55-. The proposed architecture squeezes the FPGA resources
in order to reach the computational requirements and improves the
ground-based system performance based on commercial CPUs regarding time
and power consumption. In this work we demonstrate the feasibility of
using this FPGA devices embedded in the SO/PHI instrument. With that
goal in mind, we perform tests to evaluate the scientific results and
to measure the processing time and power consumption for carrying out
the RTE inversion.
Title: Flux appearance and disappearance rates in the solar
internetwork
Authors: Gosic, Milan; Bellot Rubio, Luis; Del Toro Iniesta, Jose
Carlos; Orozco Suarez, David; Katsukawa, Yukio
Bibcode: 2016SPD....4740105G
Altcode:
The solar internetwork contains weak and highly dynamic magnetic
fields that are essential to understanding the solar magnetism at small
spatial and temporal scales. Therefore, it is important to determine
how these fields are maintained on the solar surface. Using unique
Hinode observations, we follow the evolution of individual magnetic
elements in the interior of two supergranular cells at the disk
center. From up to 38 hr of continuous measurements, we show that
magnetic flux appears in internetwork regions at a rate of 120±3
Mx cm-2 day-1 (3.7±0.4 × 1024 Mx
day-1 over the entire solar surface). Flux disappears from
the internetwork at a rate of 125±6 Mx cm-2 day-1
(3.9±0.5 × 1024 Mx day-1) through fading of
magnetic elements, cancellation between opposite-polarity features,
and interactions with network patches, which converts internetwork
elements into network features. The removal of flux from supergranules
occurs mainly through fading and interactions with network, at nearly
the same rate of about 50 Mx cm-2 day-1. Our
results demonstrate that the sources and sinks of internetwork magnetic
flux are well balanced, reflecting the steady-state nature of the quiet
Sun. Using the instantaneous flux appearance and disappearance rates,
we successfully reproduce, for the first time, the temporal evolution
of the total unsigned flux in the interior of supergranular cells.
Title: The Solar Internetwork. II. Flux Appearance and Disappearance
Rates
Authors: Gošić, M.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.;
Orozco Suárez, D.; Katsukawa, Y.
Bibcode: 2016ApJ...820...35G
Altcode: 2016arXiv160205892G
Small-scale internetwork magnetic fields are important ingredients of
the quiet Sun. In this paper we analyze how they appear and disappear
on the solar surface. Using high resolution Hinode magnetograms,
we follow the evolution of individual magnetic elements in the
interior of two supergranular cells at the disk center. From up to
38 hr of continuous measurements, we show that magnetic flux appears
in internetwork regions at a rate of 120 ± 3 Mx cm-2
day-1 (3.7 ± 0.4 × 1024 Mx day-1
over the entire solar surface). Flux disappears from the internetwork
at a rate of 125 ± 6 Mx cm-2 day-1 (3.9
± 0.5 × 1024 Mx day-1) through fading of
magnetic elements, cancelation between opposite-polarity features,
and interactions with network patches, which converts internetwork
elements into network features. Most of the flux is lost through
fading and interactions with the network, at nearly the same rate of
about 50 Mx cm-2 day-1. Our results demonstrate
that the sources and sinks of internetwork magnetic flux are well
balanced. Using the instantaneous flux appearance and disappearance
rates, we successfully reproduce the time evolution of the total
unsigned flux in the two supergranular cells.
Title: Long-term trends of magnetic bright points. I. Number of
magnetic bright points at disc centre
Authors: Utz, D.; Muller, R.; Thonhofer, S.; Veronig, A.; Hanslmeier,
A.; Bodnárová, M.; Bárta, M.; del Toro Iniesta, J. C.
Bibcode: 2016A&A...585A..39U
Altcode: 2015arXiv151107767U
Context. The Sun shows an activity cycle that is caused by its varying
global magnetic field. During a solar cycle, sunspots, I.e. extended
regions of strong magnetic fields, occur in activity belts that are
slowly migrating from middle to lower latitudes, finally arriving
close to the equator during the cycle maximum phase. While this
and other facts about the strong extended magnetic fields have been
well known for centuries, much less is known about the solar cycle
evolution of small-scale magnetic fields. Thus the question arises
if similar principles exist for small-scale magnetic fields.
Aims: To address this question, we study magnetic bright points (MBPs)
as proxies for such small-scale, kG solar magnetic fields. This study is
based on a homogeneous data set that covers a period of eight years. The
number of detected MBPs versus time is analysed to find out if there
is an activity cycle for these magnetic features too and, if so, how
it is related to the sunspot cycle.
Methods: An automated MBP
identification algorithm was applied to the synoptic Hinode/SOT G-band
data over the period November 2006 to August 2014, I.e. covering the
decreasing phase of Cycle 23 and the rise, maximum, and early decrease
of Cycle 24. This data set includes, at the moment of investigation, a
total of 4162 images, with about 2.9 million single MBP detections.
Results: After a careful preselection and monthly median filtering
of the data, the investigation revealed that the number of MBPs close
to the equator is coupled to the global solar cycle but shifted in time
by about 2.5 yr. Furthermore, the instantaneous number of detected MBPs
depends on the hemisphere, with one hemisphere being more prominent,
I.e. showing a higher number of MBPs. After the end of Cycle 23 and at
the starting point of Cycle 24, the more active hemisphere changed from
south to north. Clear peaks in the detected number of MBPs are found
at latitudes of about ±7°, in congruence with the positions of the
sunspot belts at the end of the solar cycle.
Conclusions: These
findings suggest that there is indeed a coupling between the activity of
MBPs close to the equator with the global magnetic field. The results
also indicate that a significant fraction of the magnetic flux that
is visible as MBPs close to the equator originates from the sunspot
activity belts. However, even during the minimum of MBP activity,
a percentage as large as 60% of the maximum number of detected MBPs
has been observed, which may be related to solar surface dynamo action.
Title: Future of Inversion Tools
Authors: del Toro Iniesta, J. C.; Ruiz Cobo, B.
Bibcode: 2015AGUFMSH21C..02D
Altcode:
Since the early 1970's, inversion techniques have become the most
useful tool for inferring the magnetic, dynamic and thermodynamic
properties of the solar atmosphere. They have evolved with model
dependence as a driver: astrophysical inferences do not only depend
on measurements but also on the physics assumed to prevail both on the
formation of the spectral line Stokes profiles and on their detection
with the instrument. Such an intrinsic model dependence makes it
necessary to formulate specific means that include the physics in a
proper quantitative way. The core of this physics is in the radiative
transfer equation (RTE), where the properties of the atmosphere are
assumed to be known while the unknowns are the four Stokes profiles. The
solution of the (differential) RTE is known as the direct or forward
problem. From an observational point of view, the problem is rather
the opposite: the data are made up of the observed Stokes profiles and
the unknowns are the solar physical quantities. Inverting the RTE is
therefore mandatory. Indeed, the formal solution of this equation can
be considered an integral equation. The solution of such an integral
equation is called the inverse problem. Inversion techniques are
automated codes aimed at solving the inverse problem. The foundations
of inversion techniques are critically revisited with an emphasis
on making explicit the many assumptions underlying each of them. An
incremental complexity procedure is advised for the implementation in
practice. Coarse details of the profiles or coarsely sampled profiles
should be reproduced first with simple model atmospheres (with, for
example, a few physical quantities that are constant with optical
depth). If the Stokes profiles are well sampled and differences
between synthetic and observed ones are larger than the noise, then
the inversion should proceed by using more complex models (that is,
models where physical quantities vary with depth or, eventually, with
more than one component). Significant improvements are expected as
well from the use of new inversion techniques that take the spatial
degradation by the instruments into account.
Title: The Polarimetric and Helioseismic Imager for Solar Orbiter:
SO/PHI
Authors: Solanki, Sami K.; del Toro Iniesta, Jose Carlos; Woch,
Joachim; Gandorfer, Achim; Hirzberger, Johann; Schmidt, Wolfgang;
Appourchaux, Thierry; Alvarez-Herrero, Alberto
Bibcode: 2015IAUS..305..108S
Altcode: 2015arXiv150203368S
The Solar Orbiter is the next solar physics mission of the European
Space Agency, ESA, in collaboration with NASA, with a launch planned in
2018. The spacecraft is designed to approach the Sun to within 0.28 AU
at perihelion of a highly eccentric orbit. The proximity with the Sun
will also allow its observation at uniformly high resolution at EUV and
visible wavelengths. Such observations are central for learning more
about the magnetic coupling of the solar atmosphere. At a later phase
in the mission the spacecraft will leave the ecliptic and study the
enigmatic poles of the Sun from a heliographic latitude of up to 33°.
Title: Dynamics of Multi-cored Magnetic Structures in the Quiet Sun
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.;
Schmidt, Wolfgang
Bibcode: 2015ApJ...810...79R
Altcode: 2015arXiv150806998R
We report on the dynamical interaction of quiet-Sun magnetic fields and
granular convection in the solar photosphere as seen by Sunrise. We
use high spatial resolution (0.″15-0.″18) and temporal cadence
(33 s) spectropolarimetric Imaging Magnetograph eXperiment data,
together with simultaneous CN and Ca ii H filtergrams from Sunrise
Filter Imager. We apply the SIR inversion code to the polarimetric
data in order to infer the line of sight velocity and vector magnetic
field in the photosphere. The analysis reveals bundles of individual
flux tubes evolving as a single entity during the entire 23 minute data
set. The group shares a common canopy in the upper photospheric layers,
while the individual tubes continually intensify, fragment and merge in
the same way that chains of bright points in photometric observations
have been reported to do. The evolution of the tube cores are driven
by the local granular convection flows. They intensify when they
are “compressed” by surrounding granules and split when they are
“squeezed” between two moving granules. The resulting fragments
are usually later regrouped in intergranular lanes by the granular
flows. The continual intensification, fragmentation and coalescence of
flux results in magnetic field oscillations of the global entity. From
the observations we conclude that the magnetic field oscillations first
reported by Martínez González et al. correspond to the forcing by
granular motions and not to characteristic oscillatory modes of thin
flux tubes.
Title: Magnetic bright point dynamics and evolutions observed by
Sunrise/IMaX and other instruments
Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L.; Thonhofer,
S.; Jurčák, J.
Bibcode: 2015hsa8.conf..689U
Altcode:
In this proceeding we will have a closer look on recent observations
and results regarding the dynamics and evolution of so-called magnetic
bright points (MBPs). MBPs are manifestations of kG magnetic field
strong flux concentrations seen in the solar photosphere. They belong
to the class of small-scale solar magnetic features with diameters
starting from low values around the current observational resolution
limit - about 100 km - up to a few hundred km. They might play an
important role in several key research questions like the total solar
irradiance variation (TSI variation) as well as the solar atmospheric
heating problem. Especially their dynamic behaviour is of interest
for the heating problem as they might trigger all kinds of MHD waves
which travel up to the higher solar atmospheric layers, where they can
get damped leading to a heating of the plasma. Furthermore they might
engage in magnetic field reconnection processes leading consequently
also to a heating. Due to these reasons, and also for the sake of a
better understanding of the physical processes involved on small-scales,
detailed investigations on the dynamical behaviour and evolution of
such magnetic field proxies like MBPs is in order. In this conference
proceeding we wish to give in a first part an overview about the
obtained knowledge so far. In a second part we highlight recent results
regarding the dynamical evolution of plasma parameters of MBPs such as
magnetic field strength, temperature, and line of sight velocity. This
proceeding is completed by an outlook on what can and should be done
in the near future with available data from recent telescopes.
Title: Long time variations of Magnetic Bright Points observed
by Hinode/SOT
Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot-Rubio, L.;
Bodnárová, M.; Muller, R.; Bárta, M.; Thonhofer, S.; Hanslmeier, A.
Bibcode: 2015CEAB...39...91U
Altcode:
Magnetic bright points (MBPs) are manifestations of small-scale solar
magnetic flux concentrations, best observable due to their high contrast
in molecular bands like the G-band. Moreover, they are among the most
interesting magnetic features to be studied in high spatial and temporal
resolution in the solar photosphere. Their relevance for solar physics
is not only given by their contribution to fundamental solar plasma
physics on small scales but in addition due to their involvement in
processes like the solar atmospheric heating problem (chromosphere
and corona), their influence on granulation and hence the convective
energy transport, as well as their contribution to the variations in
total solar irradiance caused by their higher relative intensity. In
this ongoing study we focus on the long-time evolution of statistical
parameters of MBPs over the solar cycle. Are parameters like the mean
intensity, average size/diameter, and number of MBPs per unit surface
element variable with time? If so, how do these parameters vary and is
there a relationship to the solar cycle? In the actual contribution
we will discuss preliminary results regarding the variation of the
number of MBPs with time. We saw a decrease in the number of MBPs for
the first years of observation (2006 until 2011) with two distinct
local minima in the years 2009 and 2011. After 2011 the number of MBPs
is increasing again along with an increase in general solar activity
(as seen by the number of sunspots, flares, and CMEs).
Title: The Formation and Disintegration of Magnetic Bright Points
Observed by Sunrise/IMaX
Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.;
Jurčák, J.; Martínez Pillet, V.; Solanki, S. K.; Schmidt, W.
Bibcode: 2014ApJ...796...79U
Altcode: 2014arXiv1411.3240U
The evolution of the physical parameters of magnetic bright points
(MBPs) located in the quiet Sun (mainly in the interwork) during
their lifetime is studied. First, we concentrate on the detailed
description of the magnetic field evolution of three MBPs. This
reveals that individual features follow different, generally complex,
and rather dynamic scenarios of evolution. Next, we apply statistical
methods on roughly 200 observed MBP evolutionary tracks. MBPs are found
to be formed by the strengthening of an equipartition field patch,
which initially exhibits a moderate downflow. During the evolution,
strong downdrafts with an average velocity of 2.4 km s-1
set in. These flows, taken together with the concurrent strengthening of
the field, suggest that we are witnessing the occurrence of convective
collapses in these features, although only 30% of them reach kG field
strengths. This fraction might turn out to be larger when the new 4
m class solar telescopes are operational as observations of MBPs with
current state of the art instrumentation could still be suffering from
resolution limitations. Finally, when the bright point disappears
(although the magnetic field often continues to exist) the magnetic
field strength has dropped to the equipartition level and is generally
somewhat weaker than at the beginning of the MBP's evolution. Also,
only relatively weak downflows are found on average at this stage of
the evolution. Only 16% of the features display upflows at the time
that the field weakens, or the MBP disappears. This speaks either for
a very fast evolving dynamic process at the end of the lifetime, which
could not be temporally resolved, or against strong upflows as the cause
of the weakening of the field of these magnetic elements, as has been
proposed based on simulation results. It is noteworthy that in about 10%
of the cases, we observe in the vicinity of the downflows small-scale
strong (exceeding 2 km s-1) intergranular upflows related
spatially and temporally to these downflows. The paper is complemented
by a detailed discussion of aspects regarding the applied methods,
the complementary literature, and in depth analysis of parameters
like magnetic field strength and velocity distributions. An important
difference to magnetic elements and associated bright structures in
active region plage is that most of the quiet Sun bright points display
significant downflows over a large fraction of their lifetime (i.e.,
in more than 46% of time instances/measurements they show downflows
exceeding 1 km s-1).
Title: The Solar Internetwork. I. Contribution to the Network
Magnetic Flux
Authors: Gošić, M.; Bellot Rubio, L. R.; Orozco Suárez, D.;
Katsukawa, Y.; del Toro Iniesta, J. C.
Bibcode: 2014ApJ...797...49G
Altcode: 2014arXiv1408.2369G
The magnetic network (NE) observed on the solar surface harbors a
sizable fraction of the total quiet Sun flux. However, its origin and
maintenance are not well known. Here we investigate the contribution
of internetwork (IN) magnetic fields to the NE flux. IN fields permeate
the interior of supergranular cells and show large emergence rates. We
use long-duration sequences of magnetograms acquired by Hinode and
an automatic feature tracking algorithm to follow the evolution of NE
and IN flux elements. We find that 14% of the quiet Sun (QS) flux is
in the form of IN fields with little temporal variations. IN elements
interact with NE patches and modify the flux budget of the NE either
by adding flux (through merging processes) or by removing it (through
cancellation events). Mergings appear to be dominant, so the net flux
contribution of the IN is positive. The observed rate of flux transfer
to the NE is 1.5 × 1024 Mx day-1 over the entire
solar surface. Thus, the IN supplies as much flux as is present in the
NE in only 9-13 hr. Taking into account that not all the transferred
flux is incorporated into the NE, we find that the IN would be able
to replace the entire NE flux in approximately 18-24 hr. This renders
the IN the most important contributor to the NE, challenging the view
that ephemeral regions are the main source of flux in the QS. About 40%
of the total IN flux eventually ends up in the NE.
Title: The History of a Quiet-Sun Magnetic Element Revealed by
IMaX/SUNRISE
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
Rubio, Luis R.; Bonet, José A.; Martínez Pillet, Valentín; Solanki,
Sami K.; Schmidt, Wolfgang
Bibcode: 2014ApJ...789....6R
Altcode: 2014arXiv1405.2837R
Isolated flux tubes are considered to be fundamental magnetic building
blocks of the solar photosphere. Their formation is usually attributed
to the concentration of magnetic field to kG strengths by the convective
collapse mechanism. However, the small size of the magnetic elements in
quiet-Sun areas has prevented this scenario from being studied in fully
resolved structures. Here, we report on the formation and subsequent
evolution of one such photospheric magnetic flux tube, observed in
the quiet Sun with unprecedented spatial resolution (0.''15-0.''18)
and high temporal cadence (33 s). The observations were acquired by
the Imaging Magnetograph eXperiment on board the SUNRISE balloon-borne
solar observatory. The equipartition field strength magnetic element
is the result of the merging of several same polarity magnetic flux
patches, including a footpoint of a previously emerged loop. The
magnetic structure is then further intensified to kG field strengths
by convective collapse. The fine structure found within the flux
concentration reveals that the scenario is more complex than can be
described by a thin flux tube model with bright points and downflow
plumes being established near the edges of the kG magnetic feature. We
also observe a daisy-like alignment of surrounding granules and a
long-lived inflow toward the magnetic feature. After a subsequent
weakening process, the field is again intensified to kG strengths. The
area of the magnetic feature is seen to change in anti-phase with the
field strength, while the brightness of the bright points and the speed
of the downflows varies in phase. We also find a relation between the
brightness of the bright point and the presence of upflows within it.
Title: Comparison between Mg II k and Ca II H Images Recorded by
SUNRISE/SuFI
Authors: Danilovic, S.; Hirzberger, J.; Riethmüller, T. L.; Solanki,
S. K.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Gizon, L.; Knölker,
M.; Schmidt, W.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.
Bibcode: 2014ApJ...784...20D
Altcode:
We present a comparison of high-resolution images of the solar surface
taken in the Mg II k and Ca II H channels of the Filter Imager on the
balloon-borne solar observatory SUNRISE. The Mg and Ca lines are sampled
with 0.48 nm and 0.11 nm wide filters, respectively. The two channels
show remarkable qualitative and quantitative similarities in the quiet
Sun, in an active region plage and during a small flare. However, the Mg
filtergrams display 1.4-1.7 times higher intensity contrast and appear
more smeared and smoothed in the quiet Sun. In addition, the fibrils
in a plage are wider. Although the exposure time is 100 times longer
for Mg images, the evidence suggests that these differences cannot be
explained only with instrumental effects or the evolution of the solar
scene. The differences at least partially arise because of different
line-formation heights, the stronger response of Mg k emission peaks
to the higher temperatures, and the larger height range sampled by
the broad Mg filter used here. This is evidently manifested during
the flare when a surge in Mg evolves differently than in Ca.
Title: Time evolution of a single, quiet-Sun magnetic structure
Authors: Requerey, Iker S.; Bonet, José Antonio; Solanki, Sami K.;
Bellot Rubio, L. R.; Del Toro Iniesta, Jose Carlos
Bibcode: 2014cosp...40E2828R
Altcode:
Isolated flux tubes are considered to be fundamental magnetic building
blocks of the solar photosphere. Their formation is usually attributed
to the concentration of magnetic field to kG strengths by the convective
instability mechanism. However, the small size of the magnetic elements
in quiet-Sun areas has prevented this scenario from being studied
in fully resolved structures. Here we report on the formation and
subsequent evolution of a photospheric magnetic flux tube, observed
in the quiet Sun with unprecedented spatial resolution (0. ('') 15 -
0. ('') 18) and high temporal cadence (33 s). The observations were
acquired by the Imaging Magnetograph Experiment (IMaX) aboard the
textsc{Sunrise} balloon-borne solar observatory. The equipartition
field strength magnetic element is reached from the merging of
several magnetic flux patches in a mesogranule-sized sink. The
magnetic structure is then further intensified to kG field strengths by
convective collapse and granular compression. The fine structure found
within the flux concentration reveal that the scenario is more complex
than a canonical flux tube model. After a subsequent weakening process,
the field is further intensified to kG strengths. Seen as a whole, the
evolution of the magnetic structure is compatible with oscillations in
all basic physical quantities. A discussion on whether this evolution
fits to the current theoretical descriptions is also presented.
Title: New insights into the evolution of magnetic bright point
plasma parameters
Authors: Utz, Dominik; Hanslmeier, Arnold; Bellot Rubio, L. R.;
Del Toro Iniesta, Jose Carlos; Jurcak, Jan
Bibcode: 2014cosp...40E3448U
Altcode:
The dynamics within the solar atmosphere are governed by the Suńs
magnetic fields. In the recent years the resolution limits were steadily
driven up by better and better instruments and telescopes (like Hinode,
Sunrise, NST, Gregor, ..) leading to higher resolved data. Therefore
the interest in ever smaller magnetic field structures within the solar
atmosphere rises. Among the smallest yet identified structures are
so-called magnetic bright points (MBPs). These features are thought to
be made up of single flux tubes and they have been studied exhaustively
in the Fraunhofer G-band since the 70´s of the last century. They are
important features not only due to their small scale (about 200 km in
diameter) and hence used as proxies for the smallest solar magnetic
field physics and processes, but also because they are involved in
topics like the chromospheric/coronal heating problem or the total
solar irradiance variation. In the current contribution we want to
study the evolution of important plasma parameters of MBPs, such
as temperature, magnetic field strength and line of sight velocity,
to get a deeper understanding of the involved physics and occuring
processes. Among the used data will be G-band filtergam data from
Hinode/SOT and spectro-polarimetric data from the IMaX instrument
onboard the Sunrise mission.
Title: Inversions of Stokes profiles revisited
Authors: Del Toro Iniesta, Jose Carlos
Bibcode: 2014cosp...40E.666D
Altcode:
The last thirty years have witnessed the appearance of a number
of techniques that have revolutionized our way to measure magnetic
fields, namely, the so-called inversions of the radiative transfer
equation techniques. Starting from simple models and solutions
of the transfer equation and ending with sophisticated processes
including full numeric solution of the equation and instrumental
effects at the same time, passing through different model approaches
and mathematical tools, inversion techniques have become common usage
for solar observers. A revision of the ideas, hypotheses, advantages,
limitations, and constraints behind inversions is presented, beginning
with critical reviews of commonly accepted approximations that are
becoming useless as long as new instrumentation is providing better
and better observables. The advent of state-of-the-art computing tools
increase our capabilities for finer analyses of these new observations.
Title: New insights into the temporal evolution of MBPs
Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.;
Jurčak, J.; Thonhofer, S.; Bodnárová, M.; Hanslmeier, A.; Lemmerer,
B.; Piantschitsch, I.; Guttenbrunner, S.
Bibcode: 2014CEAB...38...73U
Altcode:
Magnetic bright points (MBPs) are among the most fascinating and
interesting manifestations of small-scale solar magnetic fields. In the
present work the temporal evolution of MBPs is followed in data sets
taken by the Hinode satellite. The analysed data and obtained results
confirm a recently presented study done with Sunrise/IMaX data, namely
that MBPs are features undergoing fast evolution with magnetic fields
starting around the equipartition field strength, then showing strong
downflows (between 2 to 4 km/s) causing the magnetic field to amplify
into the kG range (700 to 1500 G) before dissolving again. Furthermore
the initial field inclinations depend on the initial magnetic field
strengths and show an evolution with more vertical angles at some
point during the evolution.
Title: First High-resolution Images of the Sun in the 2796 Å Mg II
k Line
Authors: Riethmüller, T. L.; Solanki, S. K.; Hirzberger, J.;
Danilovic, S.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Gizon, L.;
Knölker, M.; Schmidt, W.; Del Toro Iniesta, J. C.
Bibcode: 2013ApJ...776L..13R
Altcode: 2013arXiv1309.5213R
We present the first high-resolution solar images in the Mg II k 2796
Å line. The images, taken through a 4.8 Å broad interference filter,
were obtained during the second science flight of Sunrise in 2013 June
by the Sunrise Filter Imager (SuFI) instrument. The Mg II k images
display structures that look qualitatively very similar to images taken
in the core of Ca II H. The Mg II images exhibit reversed granulation
(or shock waves) in the internetwork regions of the quiet Sun, at
intensity contrasts that are similar to those found in Ca II H. Very
prominent in Mg II are bright points, both in the quiet Sun and in plage
regions, particularly near the disk center. These are much brighter than
at other wavelengths sampled at similar resolution. Furthermore, Mg II k
images also show fibril structures associated with plage regions. Again,
the fibrils are similar to those seen in Ca II H images, but tend to
be more pronounced, particularly in weak plage.
Title: Is Magnetic Reconnection the Cause of Supersonic Upflows in
Granular Cells?
Authors: Borrero, J. M.; Martínez Pillet, V.; Schmidt, W.; Quintero
Noda, C.; Bonet, J. A.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.
Bibcode: 2013ApJ...768...69B
Altcode: 2013arXiv1303.2557B
In a previous work, we reported on the discovery of supersonic magnetic
upflows on granular cells in data from the SUNRISE/IMaX instrument. In
the present work, we investigate the physical origin of these events
employing data from the same instrument but with higher spectral
sampling. By means of the inversion of Stokes profiles we are able
to recover the physical parameters (temperature, magnetic field,
line-of-sight velocity, etc.) present in the solar photosphere at the
time of these events. The inversion is performed in a Monte-Carlo-like
fashion, that is, repeating it many times with different initializations
and retaining only the best result. We find that many of the events are
characterized by a reversal in the polarity of the magnetic field along
the vertical direction in the photosphere, accompanied by an enhancement
in the temperature and by supersonic line-of-sight velocities. In
about half of the studied events, large blueshifted and redshifted
line-of-sight velocities coexist above/below each other. These features
can be explained in terms of magnetic reconnection, where the energy
stored in the magnetic field is released in the form of kinetic
and thermal energy when magnetic field lines of opposite polarities
coalesce. However, the agreement with magnetic reconnection is not
perfect and, therefore, other possible physical mechanisms might also
play a role.
Title: A Magnetic Bright Point Case Study
Authors: Utz, D.; Jurčák, J.; Bellot-Rubio, L.; del Toro Iniesta,
J. C.; Thonhofer, S.; Hanslmeier, A.; Veronig, A.; Muller, R.;
Lemmerer, B.
Bibcode: 2013CEAB...37..459U
Altcode:
Due to its magnetic fields our host star - the Sun - becomes the
interesting object for research as we know it. The magnetic fields
themselves cover different spatial, lifetime and strength scales and
reach down from enormous flux concentrations like active sunspot
groups to single isolated magnetic flux tubes and even weaker,
predominantly inclined intranetwork structures. Flux tubes can be seen
in filtergram observations as magnetic bright points (MBPs). They are
of interest for research not only due to their sheer existence but
due to their important role in atmospheric heating (wave heating as
well as reconnection processes), to their role in the understanding
of creation and annihilation of magnetic fields as well as to their
influence on the total solar irradiance variation. In this study we
present a close look onto an evolutionary track of an MBP from its
formation to its disintegration. Physical quantities of MBPs like
their magnetic field strength and inclination, their line-of-sight
velocity, and their temperature at different heights are inferred
from the inversion of spectropolarimetric data. Original data are
taken from the Sunrise/IMaX instrument and constitute a time series
of some 60 min. The presented case resembles the convective collapse
model and is in agreement with previous studies.
Title: Inversions of L12-2 IMaX data of an emerging flux mantle
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo,
B.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.; Solanki, S. K.;
Sunrise/IMaX Team
Bibcode: 2013MmSAI..84..355G
Altcode:
We present the analysis of a flux emergence event observed with
the IMaX magnetograph flown aboard the SUNRISE balloon. IMaX took a
15' sequence with cadence of 31 s along the Fe I line at 525.0 nm,
acquiring only Stokes I and V at 12 line positions (L12-2 mode). This
sequence shows the emergence of a flux mantle at mesogranular scale,
cospatial with a large exploding granule. An undesired cross-talk
between Stokes U and V was found in such L12-2 data. We show that the
use of a modified version of the SIR inversion code is able to remove
such effect in inferring the physical quantities of interest.
Title: SIR: Stokes Inversion based on Response functions
Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.
Bibcode: 2012ascl.soft12008R
Altcode:
SIR is a general-purpose code capable of dealing with gradients of
the physical quantities with height. It admits one and two-component
model atmospheres. It allows the recovery of the stratification of the
temperature, the magnetic field vector, and the line of sight velocity
through the atmosphere, and the micro- and macroturbulence velocities
- which are assumed to be constant with depth. It is based on the
response functions, which enter a Marquardt nonlinear least-squares
algorithm in a natural way. Response functions are calculated at the
same time as the full radiative transfer equation for polarized light
is integrated, which determines values of many free parameters in a
reasonable computation time. SIR demonstrates high stability, accuracy,
and uniqueness of results, even when simulated observations present
signal-to-noise ratios of the order of the lowest acceptable values
in real observations.
Title: Resolving the Internal Magnetic Structure of the Solar Network
Authors: Martínez González, M. J.; Bellot Rubio, L. R.; Solanki,
S. K.; Martínez Pillet, V.; Del Toro Iniesta, J. C.; Barthol, P.;
Schmidt, W.
Bibcode: 2012ApJ...758L..40M
Altcode: 2012arXiv1209.2584M
We analyze the spectral asymmetry of Stokes V (circularly polarized)
profiles of an individual network patch in the quiet Sun observed
by Sunrise/IMaX. At a spatial resolution of 0farcs15-0farcs18, the
network elements contain substructure which is revealed by the spatial
distribution of Stokes V asymmetries. The area asymmetry between the
red and blue lobes of Stokes V increases from nearly zero at the core
of the structure to values close to unity at its edges (single-lobed
profiles). Such a distribution of the area asymmetry is consistent
with magnetic fields expanding with height, i.e., an expanding
magnetic canopy (which is required to fulfill pressure balance and
flux conservation in the solar atmosphere). Inversion of the Stokes
I and V profiles of the patch confirms this picture, revealing a
decreasing field strength and increasing height of the canopy base
from the core to the periphery of the network patch. However, the
non-roundish shape of the structure and the presence of negative area
and amplitude asymmetries reveal that the scenario is more complex than
a canonical flux tube expanding with height surrounded by downflows.
Title: Assessing the Behavior of Modern Solar Magnetographs and
Spectropolarimeters
Authors: Del Toro Iniesta, J. C.; Martínez Pillet, V.
Bibcode: 2012ApJS..201...22D
Altcode: 2012arXiv1205.4845D
The design and later use of modern spectropolarimeters and magnetographs
require a number of tolerance specifications that allow the developers
to build the instrument and then the scientists to interpret the data
accuracy. Such specifications depend both on device-specific features
and on the physical assumptions underlying the particular measurement
technique. Here we discuss general properties of every magnetograph,
such as the detectability thresholds for the vector magnetic field and
the line-of-sight velocity, as well as specific properties of a given
type of instrument, namely, that based on a pair of nematic liquid
crystal variable retarders and a Fabry-Pérot etalon (or several) for
carrying out the light polarization modulation and spectral analysis,
respectively. We derive formulae that give the detection thresholds
in terms of the signal-to-noise ratio of the observations and the
polarimetric efficiencies of the instrument. Relationships are also
established between inaccuracies in the solar physical quantities and
instabilities in the instrument parameters. Such relationships allow,
for example, one to translate scientific requirements for the velocity
or the magnetic field into requirements for temperature or voltage
stability. We also demonstrate that this type of magnetograph can
theoretically reach the optimum polarimetric efficiencies of an ideal
polarimeter, regardless of the optics in between the modulator and the
analyzer. Such optics induce changes in the instrument parameters that
are calculated.
Title: The Frontier between Small-scale Bipoles and Ephemeral Regions
in the Solar Photosphere: Emergence and Decay of an Intermediate-scale
Bipole Observed with SUNRISE/IMaX
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Bonet, J. A.;
del Toro Iniesta, J. Carlos; Bellot Rubio, L. R.; Solanki, S. K.;
Schmidt, W.; Gandorfer, A.; Barthol, P.; Knölker, M.
Bibcode: 2012ApJ...745..160G
Altcode: 2011arXiv1110.1405G
We report on the photospheric evolution of an intermediate-scale (≈4
Mm footpoint separation) magnetic bipole, from emergence to decay,
observed in the quiet Sun at high spatial (0farcs3) and temporal (33 s)
resolution. The observations were acquired by the Imaging Magnetograph
Experiment imaging magnetograph during the first science flight of the
SUNRISE balloon-borne solar observatory. The bipole flux content is 6 ×
1017 Mx, representing a structure bridging the gap between
granular scale bipoles and the smaller ephemeral regions. Footpoints
separate at a speed of 3.5 km s-1 and reach a maximum
distance of 4.5 Mm before the field dissolves. The evolution of the
bipole is revealed to be very dynamic: we found a proper motion of
the bipole axis and detected a change of the azimuth angle of 90° in
300 s, which may indicate the presence of some writhe in the emerging
structure. The overall morphology and behavior are in agreement with
previous analyses of bipolar structures emerging at the granular scale,
but we also found several similarities with emerging flux structures
at larger scales. The flux growth rate is 2.6 × 1015 Mx
s-1, while the mean decay rate is one order of magnitude
smaller. We describe in some detail the decay phase of the bipole
footpoints that includes break up into smaller structures, and
interaction with preexisting fields leading to cancellation, but it
appears to be dominated by an as-yet unidentified diffusive process
that removes most of the flux with an exponential flux decay curve. The
diffusion constant (8 × 102 km2 s-1)
associated with this decay is similar to the values used to describe
the large-scale diffusion in flux transport models.
Title: Magnetic field emergence in mesogranular-sized exploding
granules observed with sunrise/IMaX data
Authors: Palacios, J.; Blanco Rodríguez, J.; Vargas Domínguez, S.;
Domingo, V.; Martínez Pillet, V.; Bonet, J. A.; Bellot Rubio, L. R.;
Del Toro Iniesta, J. C.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
Berkefeld, T.; Schmidt, W.; Knölker, M.
Bibcode: 2012A&A...537A..21P
Altcode: 2011arXiv1110.4555P
We report on magnetic field emergences covering significant
areas of exploding granules. The balloon-borne mission Sunrise
provided high spatial and temporal resolution images of the solar
photosphere. Continuum images, longitudinal and transverse magnetic
field maps and Dopplergrams obtained by IMaX onboard Sunrise are
analyzed by local correlation traking (LCT), divergence calculation
and time slices, Stokes inversions and numerical simulations are also
employed. We characterize two mesogranular-scale exploding granules
where ~1018 Mx of magnetic flux emerges. The emergence
of weak unipolar longitudinal fields (~100 G) start with a single
visible magnetic polarity, occupying their respective granules' top
and following the granular splitting. After a while, mixed polarities
start appearing, concentrated in downflow lanes. The events last around
20 min. LCT analyses confirm mesogranular scale expansion, displaying
a similar pattern for all the physical properties, and divergence
centers match between all of them. We found a similar behaviour
with the emergence events in a numerical MHD simulation. Granule
expansion velocities are around 1 kms-1 while magnetic
patches expand at 0.65 kms-1. One of the analyzed events
evidences the emergence of a loop-like structure. Advection of
the emerging magnetic flux features is dominated by convective
motion resulting from the exploding granule due to the magnetic
field frozen in the granular plasma. Intensification of the
magnetic field occurs in the intergranular lanes, probably
because of being directed by the downflowing plasma. Movies
associated to Figs. 2-4 are available in electronic form at http://www.aanda.org
Title: Space-qualified liquid-crystal variable retarders for
wide-field-of-view coronagraphs
Authors: Uribe-Patarroyo, N.; Alvarez-Herrero, A.; García Parejo,
P.; Vargas, J.; Heredero, R. L.; Restrepo, R.; Martínez Pillet, V.;
del Toro Iniesta, J. C.; López, A.; Fineschi, S.; Capobianco, G.;
Georges, M.; López, M.; Boer, G.; Manolis, I.
Bibcode: 2011SPIE.8148E..10U
Altcode: 2011SPIE.8148E..31U
Liquid-crystal variable retarders (LCVRs) are an emergent technology
for space-based polarimeters, following its success as polarization
modulators in ground-based polarimeters and ellipsometers. Wide-field
double nematic LCVRs address the high angular sensitivity of nematic
LCVRs at some voltage regimes. We present a work in which wide-field
LCVRs were designed and built, which are suitable for wide-field-of-view
instruments such as polarimetric coronagraphs. A detailed model of
their angular acceptance was made, and we validated this technology
for space environmental conditions, including a campaign studying the
effects of gamma, proton irradiation, vibration and shock, thermo-vacuum
and ultraviolet radiation.
Title: The Sun at high resolution: first results from the Sunrise
mission
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller,
A.; Gandorfer, A.; Hirzberger, J.; Lagg, A.; Riethmüller, T. L.;
Schüssler, M.; Wiegelmann, T.; Bonet, J. A.; Pillet, V. Martínez;
Khomenko, E.; del Toro Iniesta, J. C.; Domingo, V.; Palacios, J.;
Knölker, M.; González, N. Bello; Borrero, J. M.; Berkefeld, T.;
Franz, M.; Roth, M.; Schmidt, W.; Steiner, O.; Title, A. M.
Bibcode: 2011IAUS..273..226S
Altcode:
The Sunrise balloon-borne solar observatory consists of a 1m aperture
Gregory telescope, a UV filter imager, an imaging vector polarimeter,
an image stabilization system and further infrastructure. The first
science flight of Sunrise yielded high-quality data that reveal the
structure, dynamics and evolution of solar convection, oscillations
and magnetic fields at a resolution of around 100 km in the quiet
Sun. Here we describe very briefly the mission and the first results
obtained from the Sunrise data, which include a number of discoveries.
Title: Diagnostics for spectropolarimetry and magnetography
Authors: del Toro Iniesta, Jose Carlos; Pillet, Valentín Martínez
Bibcode: 2011IAUS..273...37D
Altcode: 2010arXiv1010.0504D
An assessment on the capabilities of modern spectropolarimeters and
magnetographs is in order since most of our astrophysical results rely
upon the accuracy of the instrumentation and on the sensitivity of
the observables to variations of the sought physical parameters. A
contribution to such an assessment will be presented in this talk
where emphasis will be made on the use of the so-called response
functions to gauge the probing capabilities of spectral lines and on
an analytical approach to estimate the uncertainties in the results
in terms of instrumental effects. The Imaging Magnetograph eXperiment
(IMaX) and the Polarimetric and Helioseismic Imager (PHI) will be used
as study cases.
Title: Ubiquitous quiet-Sun jets
Authors: Martínez Pillet, V.; Del Toro Iniesta, J. C.; Quintero
Noda, C.
Bibcode: 2011A&A...530A.111M
Altcode: 2011arXiv1104.5564M
Context. IMaX/Sunrise has recently reported the temporal evolution
of highly dynamic and strongly Doppler shifted Stokes V signals in
the quiet Sun.
Aims: We attempt to identify the same quiet-Sun
jets in the Hinode spectropolarimeter (SP) data set.
Methods:
We generate combinations of linear polarization magnetograms with blue-
and redshifted far-wing circular polarization magnetograms to allow an
easy identification of the quiet-Sun jets.
Results: The jets are
identified in the Hinode data where both red- and blueshifted cases
are often found in pairs. They appear next to regions of transverse
fields that exhibit quiet-Sun neutral lines. They also have a clear
tendency to occur in the outer boundary of the granules. These regions
always display highly displaced and anomalous Stokes V profiles.
Conclusions: The quiet Sun is pervaded with jets formed when new field
regions emerge at granular scales loaded with horizontal field lines
that interact with their surroundings. This interaction is suggestive
of some form of reconnection of the involved field lines that generates
the observed high speed flows.
Title: Small-scale flux emergence events observed by Sunrise/IMaX
Authors: Guglielmino, S. L.; Pillet, V. Martínez; del Toro Iniesta,
J. C.; Rubio, L. R. Bellot; Zuccarello, F.; Solanki, S. K.; Solanki
Bibcode: 2011IAUS..274..140G
Altcode:
Thanks to the unprecedented combination of high spatial resolution
(0''.2) and high temporal cadence (33 s) spectropolarimetric
measurements, the IMaX magnetograph aboard the Sunrise balloon-borne
telescope is revealing new insights about the plasma dynamics
of the all-pervasive small-scale flux concentrations in the quiet
Sun. We present the result of a case study concerning the appearance
of a bipole, with a size of about 4'' and a flux content of 5 ×
1017 Mx, with strong signal of horizontal fields during
the emergence. We analyze the data set using the SIR inversion code
and obtain indications about the three-dimensional shape of the bipole
and its evolution with time.
Title: Mesogranulation and the Solar Surface Magnetic Field
Distribution
Authors: Yelles Chaouche, L.; Moreno-Insertis, F.; Martínez Pillet,
V.; Wiegelmann, T.; Bonet, J. A.; Knölker, M.; Bellot Rubio, L. R.;
del Toro Iniesta, J. C.; Barthol, P.; Gandorfer, A.; Schmidt, W.;
Solanki, S. K.
Bibcode: 2011ApJ...727L..30Y
Altcode: 2010arXiv1012.4481Y
The relation of the solar surface magnetic field with mesogranular
cells is studied using high spatial (≈100 km) and temporal (≈30
s) resolution data obtained with the IMaX instrument on board
SUNRISE. First, mesogranular cells are identified using Lagrange
tracers (corks) based on horizontal velocity fields obtained through
local correlation tracking. After ≈20 minutes of integration, the
tracers delineate a sharp mesogranular network with lanes of width
below about 280 km. The preferential location of magnetic elements in
mesogranular cells is tested quantitatively. Roughly 85% of pixels with
magnetic field higher than 100 G are located in the near neighborhood
of mesogranular lanes. Magnetic flux is therefore concentrated in
mesogranular lanes rather than intergranular ones. Second, magnetic
field extrapolations are performed to obtain field lines anchored in
the observed flux elements. This analysis, therefore, is independent
of the horizontal flows determined in the first part. A probability
density function (PDF) is calculated for the distribution of distances
between the footpoints of individual magnetic field lines. The PDF has
an exponential shape at scales between 1 and 10 Mm, with a constant
characteristic decay distance, indicating the absence of preferred
convection scales in the mesogranular range. Our results support
the view that mesogranulation is not an intrinsic convective scale
(in the sense that it is not a primary energy-injection scale of solar
convection), but also give quantitative confirmation that, nevertheless,
the magnetic elements are preferentially found along mesogranular lanes.
Title: The Imaging Magnetograph eXperiment (IMaX) for the Sunrise
Balloon-Borne Solar Observatory
Authors: Martínez Pillet, V.; del Toro Iniesta, J. C.;
Álvarez-Herrero, A.; Domingo, V.; Bonet, J. A.; González Fernández,
L.; López Jiménez, A.; Pastor, C.; Gasent Blesa, J. L.; Mellado, P.;
Piqueras, J.; Aparicio, B.; Balaguer, M.; Ballesteros, E.; Belenguer,
T.; Bellot Rubio, L. R.; Berkefeld, T.; Collados, M.; Deutsch, W.;
Feller, A.; Girela, F.; Grauf, B.; Heredero, R. L.; Herranz, M.;
Jerónimo, J. M.; Laguna, H.; Meller, R.; Menéndez, M.; Morales, R.;
Orozco Suárez, D.; Ramos, G.; Reina, M.; Ramos, J. L.; Rodríguez,
P.; Sánchez, A.; Uribe-Patarroyo, N.; Barthol, P.; Gandorfer, A.;
Knoelker, M.; Schmidt, W.; Solanki, S. K.; Vargas Domínguez, S.
Bibcode: 2011SoPh..268...57M
Altcode: 2010SoPh..tmp..181M; 2010arXiv1009.1095M
The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter
built by four institutions in Spain that flew on board the Sunrise
balloon-borne solar observatory in June 2009 for almost six days over
the Arctic Circle. As a polarimeter, IMaX uses fast polarization
modulation (based on the use of two liquid crystal retarders),
real-time image accumulation, and dual-beam polarimetry to reach
polarization sensitivities of 0.1%. As a spectrograph, the instrument
uses a LiNbO3 etalon in double pass and a narrow band
pre-filter to achieve a spectral resolution of 85 mÅ. IMaX uses the
high-Zeeman-sensitive line of Fe I at 5250.2 Å and observes all four
Stokes parameters at various points inside the spectral line. This
allows vector magnetograms, Dopplergrams, and intensity frames to be
produced that, after reconstruction, reach spatial resolutions in the
0.15 - 0.18 arcsec range over a 50×50 arcsec field of view. Time
cadences vary between 10 and 33 s, although the shortest one only
includes longitudinal polarimetry. The spectral line is sampled in
various ways depending on the applied observing mode, from just two
points inside the line to 11 of them. All observing modes include
one extra wavelength point in the nearby continuum. Gauss equivalent
sensitivities are 4 G for longitudinal fields and 80 G for transverse
fields per wavelength sample. The line-of-sight velocities are estimated
with statistical errors of the order of 5 - 40 m s−1. The
design, calibration, and integration phases of the instrument,
together with the implemented data reduction scheme, are described in
some detail.
Title: The Sunrise Mission
Authors: Barthol, P.; Gandorfer, A.; Solanki, S. K.; Schüssler,
M.; Chares, B.; Curdt, W.; Deutsch, W.; Feller, A.; Germerott, D.;
Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.; Meller, R.;
Müller, R.; Riethmüller, T. L.; Tomasch, G.; Knölker, M.; Lites,
B. W.; Card, G.; Elmore, D.; Fox, J.; Lecinski, A.; Nelson, P.;
Summers, R.; Watt, A.; Martínez Pillet, V.; Bonet, J. A.; Schmidt,
W.; Berkefeld, T.; Title, A. M.; Domingo, V.; Gasent Blesa, J. L.;
del Toro Iniesta, J. C.; López Jiménez, A.; Álvarez-Herrero, A.;
Sabau-Graziati, L.; Widani, C.; Haberler, P.; Härtel, K.; Kampf,
D.; Levin, T.; Pérez Grande, I.; Sanz-Andrés, A.; Schmidt, E.
Bibcode: 2011SoPh..268....1B
Altcode: 2010arXiv1009.2689B; 2010SoPh..tmp..224B
The first science flight of the balloon-borne Sunrise telescope took
place in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset
Island in northern Canada. We describe the scientific aims and
mission concept of the project and give an overview and a description
of the various hardware components: the 1-m main telescope with its
postfocus science instruments (the UV filter imager SuFI and the imaging
vector magnetograph IMaX) and support instruments (image stabilizing
and light distribution system ISLiD and correlating wavefront sensor
CWS), the optomechanical support structure and the instrument mounting
concept, the gondola structure and the power, pointing, and telemetry
systems, and the general electronics architecture. We also explain
the optimization of the structural and thermal design of the complete
payload. The preparations for the science flight are described,
including AIV and ground calibration of the instruments. The course
of events during the science flight is outlined, up to the recovery
activities. Finally, the in-flight performance of the instrumentation
is discussed.
Title: SUNRISE: Instrument, Mission, Data, and First Results
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
Gandorfer, A.; Hirzberger, J.; Riethmüller, T. L.; Schüssler, M.;
Bonet, J. A.; Martínez Pillet, V.; del Toro Iniesta, J. C.; Domingo,
V.; Palacios, J.; Knölker, M.; Bello González, N.; Berkefeld, T.;
Franz, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.127S
Altcode: 2010arXiv1008.3460S
The SUNRISE balloon-borne solar observatory consists of a 1 m aperture
Gregory telescope, a UV filter imager, an imaging vector polarimeter,
an image stabilization system, and further infrastructure. The first
science flight of SUNRISE yielded high-quality data that revealed the
structure, dynamics, and evolution of solar convection, oscillations,
and magnetic fields at a resolution of around 100 km in the quiet
Sun. After a brief description of instruments and data, the first
qualitative results are presented. In contrast to earlier observations,
we clearly see granulation at 214 nm. Images in Ca II H display narrow,
short-lived dark intergranular lanes between the bright edges of
granules. The very small-scale, mixed-polarity internetwork fields
are found to be highly dynamic. A significant increase in detectable
magnetic flux is found after phase-diversity-related reconstruction
of polarization maps, indicating that the polarities are mixed right
down to the spatial resolution limit and probably beyond.
Title: Supersonic Magnetic Upflows in Granular Cells Observed with
SUNRISE/IMAX
Authors: Borrero, J. M.; Martínez-Pillet, V.; Schlichenmaier, R.;
Solanki, S. K.; Bonet, J. A.; del Toro Iniesta, J. C.; Schmidt, W.;
Barthol, P.; Gandorfer, A.; Domingo, V.; Knölker, M.
Bibcode: 2010ApJ...723L.144B
Altcode: 2010arXiv1009.1227B
Using the IMaX instrument on board the SUNRISE stratospheric balloon
telescope, we have detected extremely shifted polarization signals
around the Fe I 5250.217 Å spectral line within granules in the solar
photosphere. We interpret the velocities associated with these events
as corresponding to supersonic and magnetic upflows. In addition, they
are also related to the appearance of opposite polarities and highly
inclined magnetic fields. This suggests that they are produced by the
reconnection of emerging magnetic loops through granular upflows. The
events occupy an average area of 0.046 arcsec2 and last for
about 80 s, with larger events having longer lifetimes. These supersonic
events occur at a rate of 1.3 × 10-5 occurrences per second
per arcsec2.
Title: Detection of Vortex Tubes in Solar Granulation from
Observations with SUNRISE
Authors: Steiner, O.; Franz, M.; Bello González, N.; Nutto, Ch.;
Rezaei, R.; Martínez Pillet, V.; Bonet Navarro, J. A.; del Toro
Iniesta, J. C.; Domingo, V.; Solanki, S. K.; Knölker, M.; Schmidt,
W.; Barthol, P.; Gandorfer, A.
Bibcode: 2010ApJ...723L.180S
Altcode: 2010arXiv1009.4723S
We have investigated a time series of continuum intensity maps and
corresponding Dopplergrams of granulation in a very quiet solar region
at the disk center, recorded with the Imaging Magnetograph eXperiment
(IMaX) on board the balloon-borne solar observatory SUNRISE. We
find that granules frequently show substructure in the form of lanes
composed of a leading bright rim and a trailing dark edge, which move
together from the boundary of a granule into the granule itself. We
find strikingly similar events in synthesized intensity maps from an
ab initio numerical simulation of solar surface convection. From cross
sections through the computational domain of the simulation, we conclude
that these granular lanes are the visible signature of (horizontally
oriented) vortex tubes. The characteristic optical appearance of vortex
tubes at the solar surface is explained. We propose that the observed
vortex tubes may represent only the large-scale end of a hierarchy of
vortex tubes existing near the solar surface.
Title: Where the Granular Flows Bend
Authors: Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; del Toro
Iniesta, J. C.; Gandorfer, A.; Bonet, J. A.; Domingo, V.; Schmidt,
W.; Barthol, P.; Knölker, M.
Bibcode: 2010ApJ...723L.159K
Altcode: 2010arXiv1008.0517K
Based on IMaX/SUNRISE data, we report on a previously undetected
phenomenon in solar granulation. We show that in a very narrow region
separating granules and intergranular lanes, the spectral line width
of the Fe I 5250.2 Å line becomes extremely small. We offer an
explanation of this observation with the help of magneto-convection
simulations. These regions with extremely small line widths correspond
to the places where the granular flows bend from upflow in granules
to downflow in intergranular lanes. We show that the resolution and
image stability achieved by IMaX/SUNRISE are important requisites to
detect this interesting phenomenon.
Title: Bright Points in the Quiet Sun as Observed in the Visible
and Near-UV by the Balloon-borne Observatory SUNRISE
Authors: Riethmüller, T. L.; Solanki, S. K.; Martínez Pillet, V.;
Hirzberger, J.; Feller, A.; Bonet, J. A.; Bello González, N.; Franz,
M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; del Toro Iniesta,
J. C.; Domingo, V.; Gandorfer, A.; Knölker, M.; Schmidt, W.
Bibcode: 2010ApJ...723L.169R
Altcode: 2010arXiv1009.1693R
Bright points (BPs) are manifestations of small magnetic elements
in the solar photosphere. Their brightness contrast not only gives
insight into the thermal state of the photosphere (and chromosphere) in
magnetic elements, but also plays an important role in modulating the
solar total and spectral irradiance. Here, we report on simultaneous
high-resolution imaging and spectropolarimetric observations of
BPs using SUNRISE balloon-borne observatory data of the quiet Sun
at the disk center. BP contrasts have been measured between 214 nm
and 525 nm, including the first measurements at wavelengths below
388 nm. The histograms of the BP peak brightness show a clear trend
toward broader contrast distributions and higher mean contrasts at
shorter wavelengths. At 214 nm, we observe a peak brightness of up to
five times the mean quiet-Sun value, the highest BP contrast so far
observed. All BPs are associated with a magnetic signal, although in
a number of cases it is surprisingly weak. Most of the BPs show only
weak downflows, the mean value being 240 m s-1, but some
display strong down- or upflows reaching a few km s-1.
Title: Transverse Component of the Magnetic Field in the Solar
Photosphere Observed by SUNRISE
Authors: Danilovic, S.; Beeck, B.; Pietarila, A.; Schüssler, M.;
Solanki, S. K.; Martínez Pillet, V.; Bonet, J. A.; del Toro Iniesta,
J. C.; Domingo, V.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.149D
Altcode: 2010arXiv1008.1535D
We present the first observations of the transverse component of
a photospheric magnetic field acquired by the imaging magnetograph
SUNRISE/IMaX. Using an automated detection method, we obtain statistical
properties of 4536 features with significant linear polarization
signal. We obtain a rate of occurrence of 7 × 10-4
s-1 arcsec-2, which is 1-2 orders of magnitude
larger than the values reported by previous studies. We show that
these features have no characteristic size or lifetime. They appear
preferentially at granule boundaries with most of them being caught
in downflow lanes at some point. Only a small percentage are entirely
and constantly embedded in upflows (16%) or downflows (8%).
Title: Detection of Large Acoustic Energy Flux in the Solar Atmosphere
Authors: Bello González, N.; Franz, M.; Martínez Pillet, V.; Bonet,
J. A.; Solanki, S. K.; del Toro Iniesta, J. C.; Schmidt, W.; Gandorfer,
A.; Domingo, V.; Barthol, P.; Berkefeld, T.; Knölker, M.
Bibcode: 2010ApJ...723L.134B
Altcode: 2010arXiv1009.4795B
We study the energy flux carried by acoustic waves excited by convective
motions at sub-photospheric levels. The analysis of high-resolution
spectropolarimetric data taken with IMaX/SUNRISE provides a total
energy flux of ~6400-7700 W m-2 at a height of ~250 km
in the 5.2-10 mHz range, i.e., at least twice the largest energy
flux found in previous works. Our estimate lies within a factor of
two of the energy flux needed to balance radiative losses from the
chromosphere according to the estimates of Anderson & Athay and
revives interest in acoustic waves for transporting energy to the
chromosphere. The acoustic flux is mainly found in the intergranular
lanes but also in small rapidly evolving granules and at the bright
borders, forming dark dots and lanes of splitting granules.
Title: Magnetic Loops in the Quiet Sun
Authors: Wiegelmann, T.; Solanki, S. K.; Borrero, J. M.; Martínez
Pillet, V.; del Toro Iniesta, J. C.; Domingo, V.; Bonet, J. A.;
Barthol, P.; Gandorfer, A.; Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.185W
Altcode: 2010arXiv1009.4715W
We investigate the fine structure of magnetic fields in the atmosphere
of the quiet Sun. We use photospheric magnetic field measurements from
SUNRISE/IMaX with unprecedented spatial resolution to extrapolate
the photospheric magnetic field into higher layers of the solar
atmosphere with the help of potential and force-free extrapolation
techniques. We find that most magnetic loops that reach into the
chromosphere or higher have one footpoint in relatively strong magnetic
field regions in the photosphere. Ninety-one percent of the magnetic
energy in the mid-chromosphere (at a height of 1 Mm) is in field
lines, whose stronger footpoint has a strength of more than 300 G,
i.e., above the equipartition field strength with convection. The
loops reaching into the chromosphere and corona are also found to be
asymmetric in the sense that the weaker footpoint has a strength B <
300 G and is located in the internetwork (IN). Such loops are expected
to be strongly dynamic and have short lifetimes, as dictated by the
properties of the IN fields.
Title: SUNRISE/IMaX Observations of Convectively Driven Vortex Flows
in the Sun
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Palacios,
J.; Martínez Pillet, V.; Solanki, S. K.; del Toro Iniesta, J. C.;
Domingo, V.; Berkefeld, T.; Schmidt, W.; Gandorfer, A.; Barthol, P.;
Knölker, M.
Bibcode: 2010ApJ...723L.139B
Altcode: 2010arXiv1009.1992B
We characterize the observational properties of the convectively driven
vortex flows recently discovered on the quiet Sun, using magnetograms,
Dopplergrams, and images obtained with the 1 m balloon-borne SUNRISE
telescope. By visual inspection of time series, we find some 3.1
× 10-3 vortices Mm-2 minute-1,
which is a factor of ~1.7 larger than previous estimates. The mean
duration of the individual events turns out to be 7.9 minutes, with
a standard deviation of 3.2 minutes. In addition, we find several
events appearing at the same locations along the duration of the time
series (31.6 minutes). Such recurrent vortices show up in the proper
motion flow field map averaged over the time series. The typical
vertical vorticities are lsim6 × 10-3 s-1,
which corresponds to a period of rotation of some 35 minutes. The
vortices show a preferred counterclockwise sense of rotation, which
we conjecture may have to do with the preferred vorticity impinged by
the solar differential rotation.
Title: Retrieval of solar magnetic fields from high-spatial resolution
filtergraph data: the Imaging Magnetograph eXperiment (IMaX)
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Martínez Pillet,
V.; Bonet, J. A.; Vargas Domínguez, S.; Del Toro Iniesta, J. C.
Bibcode: 2010A&A...522A.101O
Altcode: 2010arXiv1006.5510O
Context. The design of modern instruments does not only imply thorough
studies of instrumental effects but also a good understanding of the
scientific analysis planned for the data.
Aims: We investigate
the reliability of Milne-Eddington (ME) inversions of high-resolution
magnetograph measurements such as those to be obtained with the Imaging
Magnetograph eXperiment (IMaX) aboard the Sunrise balloon. We also
provide arguments to choose either Fe I 525.02 or 525.06 nm as the
most suitable line for IMaX.
Methods: We reproduce an IMaX
observation using magnetoconvection simulations of the quiet Sun
and synthesizing the four Stokes profiles emerging from them. The
profiles are degraded by spatial and spectral resolution, noise,
and limited wavelength sampling, just as real IMaX measurements. We
invert these data and estimate the uncertainties in the retrieved
physical parameters caused by the ME approximation and the spectral
sampling.
Results: It is possible to infer the magnetic field
strength, inclination, azimuth, and line-of-sight velocity from
standard IMaX measurements (4 Stokes parameters, 5 wavelength points,
and a signal-to-noise ratio of 1000) applying ME inversions to any
of the Fe I lines at 525 nm. We also find that telescope diffraction
has important effects on the spectra coming from very high resolution
observations of inhomogeneous atmospheres. Diffration reduces the
amplitude of the polarization signals and changes the asymmetry of
the Stokes profiles.
Conclusions: The two Fe I lines at 525 nm
meet the scientific requirements of IMaX, but Fe I 525.02 nm is to be
preferred because it leads to smaller uncertainties in the retrieved
parameters and offers a better detectability of the weakest (linear)
polarization signals prevailing in the quiet Sun.
Title: Surface Waves in Solar Granulation Observed with SUNRISE
Authors: Roth, M.; Franz, M.; Bello González, N.; Martínez Pillet,
V.; Bonet, J. A.; Gandorfer, A.; Barthol, P.; Solanki, S. K.;
Berkefeld, T.; Schmidt, W.; del Toro Iniesta, J. C.; Domingo, V.;
Knölker, M.
Bibcode: 2010ApJ...723L.175R
Altcode: 2010arXiv1009.4790R
Solar oscillations are expected to be excited by turbulent flows in
the intergranular lanes near the solar surface. Time series recorded
by the IMaX instrument on board the SUNRISE observatory reveal solar
oscillations at high spatial resolution, which allow the study of
the properties of oscillations with short wavelengths. We analyze
two time series with synchronous recordings of Doppler velocity and
continuum intensity images with durations of 32 minutes and 23 minutes,
respectively, recorded close to the disk center of the Sun to study
the propagation and excitation of solar acoustic oscillations. In
the Doppler velocity data, both the standing acoustic waves and the
short-lived, high-degree running waves are visible. The standing
waves are visible as temporary enhancements of the amplitudes of the
large-scale velocity field due to the stochastic superposition of
the acoustic waves. We focus on the high-degree small-scale waves by
suitable filtering in the Fourier domain. Investigating the propagation
and excitation of f- and p 1-modes with wavenumbers k>1.4
Mm-1, we also find that exploding granules contribute to
the excitation of solar p-modes in addition to the contribution of
intergranular lanes.
Title: Fully Resolved Quiet-Sun Magnetic flux Tube Observed with
the SUNRISE/IMAX Instrument
Authors: Lagg, A.; Solanki, S. K.; Riethmüller, T. L.; Martínez
Pillet, V.; Schüssler, M.; Hirzberger, J.; Feller, A.; Borrero,
J. M.; Schmidt, W.; del Toro Iniesta, J. C.; Bonet, J. A.; Barthol, P.;
Berkefeld, T.; Domingo, V.; Gandorfer, A.; Knölker, M.; Title, A. M.
Bibcode: 2010ApJ...723L.164L
Altcode: 2010arXiv1009.0996L
Until today, the small size of magnetic elements in quiet-Sun areas has
required the application of indirect methods, such as the line-ratio
technique or multi-component inversions, to infer their physical
properties. A consistent match to the observed Stokes profiles could
only be obtained by introducing a magnetic filling factor that specifies
the fraction of the observed pixel filled with magnetic field. Here,
we investigate the properties of a small magnetic patch in the quiet
Sun observed with the IMaX magnetograph on board the balloon-borne
telescope SUNRISE with unprecedented spatial resolution and low
instrumental stray light. We apply an inversion technique based on
the numerical solution of the radiative transfer equation to retrieve
the temperature stratification and the field strength in the magnetic
patch. The observations can be well reproduced with a one-component,
fully magnetized atmosphere with a field strength exceeding 1 kG and
a significantly enhanced temperature in the mid to upper photosphere
with respect to its surroundings, consistent with semi-empirical flux
tube models for plage regions. We therefore conclude that, within the
framework of a simple atmospheric model, the IMaX measurements resolve
the observed quiet-Sun flux tube.
Title: Two-dimensional solar spectropolarimetry with the KIS/IAA
Visible Imaging Polarimeter
Authors: Beck, C.; Bellot Rubio, L. R.; Kentischer, T. J.; Tritschler,
A.; Del Toro Iniesta, J. C.
Bibcode: 2010A&A...520A.115B
Altcode: 2010arXiv1007.1153B
Context. Spectropolarimetry at high spatial and spectral resolution
is a basic tool to characterize the magnetic properties of the solar
atmosphere.
Aims: We introduce the KIS/IAA Visible Imaging
Polarimeter (VIP), a new post-focus instrument that upgrades the TESOS
spectrometer at the German Vacuum Tower Telescope (VTT) into a full
vector polarimeter. VIP is a collaboration between the Kiepenheuer
Institut für Sonnenphysik (KIS) and the Instituto de Astrofísica
de Andalucía (IAA-CSIC).
Methods: We describe the optical
setup of VIP, the data acquisition procedure, and the calibration of
the spectropolarimetric measurements. We show examples of data taken
between 2005 and 2008 to illustrate the potential of the instrument.
Results: VIP is capable of measuring the four Stokes profiles of
spectral lines in the range from 420 to 700 nm with a spatial resolution
better than 0farcs5. Lines can be sampled at 40 wavelength positions
in 60 s, achieving a noise level of about 2 × 10-3 with
exposure times of 300 ms and pixel sizes of 0farcs17 × 0farcs17 (2
× 2 binning). The polarization modulation is stable over periods of a
few days, ensuring high polarimetric accuracy. The excellent spectral
resolution of TESOS allows the use of sophisticated data analysis
techniques such as Stokes inversions. One of the first scientific
results of VIP presented here is that the ribbon-like magnetic
structures of the network are associated with a distinct pattern of
net circular polarization away from disk center.
Conclusions:
VIP performs spectropolarimetric measurements of solar magnetic fields
at a spatial resolution that is only slightly worse than that of the
Hinode spectropolarimeter, while providing a 2D field field of view and
the possibility to observe up to four spectral regions sequentially
with high cadence. VIP can be used as a stand-alone instrument or in
combination with other spectropolarimeters and imaging systems of the
VTT for extended wavelength coverage.
Title: Milne-Eddington inversion of the Fe I line pair at 630 nm
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Del Toro Iniesta,
J. C.
Bibcode: 2010A&A...518A...3O
Altcode: 2010arXiv1005.5013S; 2010arXiv1005.5013O
Context. The iron lines at 630.15 and 630.25 nm are often used to
determine the physical conditions of the solar photosphere. A common
approach is to invert them simultaneously under the Milne-Eddington
approximation. The same thermodynamic parameters are employed for the
two lines, except for their opacities, which are assumed to have a
constant ratio.
Aims: We aim at investigating the validity of
this assumption, since the two lines are not exactly the same.
Methods: We use magnetohydrodynamic simulations of the quiet
Sun to examine the behavior of the ME thermodynamic parameters and
their influence on the retrieval of vector magnetic fields and flow
velocities.
Results: Our analysis shows that the two lines can
be coupled and inverted simultaneously using the same thermodynamic
parameters and a constant opacity ratio. The inversion of two lines
is significantly more accurate than single-line inversions because of
the larger number of observables.
Title: Applicability of Milne-Eddington inversions to high spatial
resolution observations of the quiet Sun
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Vögler, A.; Del
Toro Iniesta, J. C.
Bibcode: 2010A&A...518A...2O
Altcode: 2010arXiv1005.5012O
Context. The physical conditions of the solar photosphere change on
very small spatial scales both horizontally and vertically. Such a
complexity may pose a serious obstacle to the accurate determination
of solar magnetic fields.
Aims: We examine the applicability of
Milne-Eddington (ME) inversions to high spatial resolution observations
of the quiet Sun. Our aim is to understand the connection between
the ME inferences and the actual stratifications of the atmospheric
parameters.
Methods: We use magnetoconvection simulations of
the solar surface to synthesize asymmetric Stokes profiles such as
those observed in the quiet Sun. We then invert the profiles with the
ME approximation. We perform an empirical analysis of the heights of
formation of ME measurements and analyze the uncertainties brought
about by the ME approximation. We also investigate the quality of the
fits and their relationship with the model stratifications.
Results: The atmospheric parameters derived from ME inversions of
high-spatial resolution profiles are reasonably accurate and can be
used for statistical analyses of solar magnetic fields, even if the
fit is not always good. We also show that the ME inferences cannot be
assigned to a specific atmospheric layer: different parameters sample
different ranges of optical depths, and even the same parameter
may trace different layers depending on the physical conditions
of the atmosphere. Despite this variability, ME inversions tend
to probe deeper layers in granules than in intergranular lanes. Figure 10 and appendix are only available in electronic form at http://www.aanda.org
Title: The IMaX polarimeter for the solar telescope SUNRISE of the
NASA long duration balloon program
Authors: Alvarez-Herrero, A.; Martínez-Pillet, V.; Del Toro Iniesta,
J. C.; Domingo, V.
Bibcode: 2010EPJWC...505002A
Altcode:
On June 8th 2009 the SUNRISE mission was successfully launched. This
mission consisted of a 1m aperture solar telescope on board of a
stratospheric balloon within the Long Duration Balloon NASA program. The
flight followed the foreseen circumpolar trajectory over the Artic
and the duration was 5 days and 17 hours. One of the two postfocal
instruments onboard was IMaX, the Imaging Magnetograph eXperiment. This
instrument is a solar magnetograph which is a diffraction limited imager
capable to resolve 100 km on the solar surface, and simultaneously
a high sensitivity polarimeter (<10-3) and a high
resolution spectrograph (bandwidth <70mÅ). The magnetic vectorial
map can be extracted thanks to the well-know Zeeman effect, which takes
place in the solar atoms, allowing to relate polarization and spectral
measurements to magnetic fields. The technological challenge of the IMaX
development has a special relevance due to the utilization of innovative
technologies in the Aeroespacial field and it is an important precedent
for future space missions such as Solar Orbiter from ESA. Among these
novel technologies the utilization of Liquid Crystal Variable Retarders
(LCVRs) as polarization modulators and a LiNbO3 etalon as
tunable spectral filter are remarkable. Currently the data obtained
is being analyzed and the preliminary results show unprecedented
information about the solar dynamics.
Title: Size matters
Authors: del Toro Iniesta, J. C.; Orozco Suárez, D.
Bibcode: 2010AN....331..558D
Altcode: 2010arXiv1002.3106D
The new generation of ground-based, large-aperture solar telescopes
promises to significantly increase our capabilities to understand the
many basic phenomena taking place in the Sun at all atmospheric layers
and how they relate to each other. A (non-exhaustive) summary of the
main scientific arguments to pursue these impressive technological goals
is presented. We illustrate how imaging, polarimetry, and spectroscopy
can benefit from the new telescopes and how several wavelength bands
should be observed to study the atmospheric coupling from the upper
convection zone all the way to the corona. The particular science case
of sunspot penumbrae is barely discussed as a specific example.
Title: On Spectropolarimetric Measurements with Visible Lines
Authors: del Toro Iniesta, J. C.; Orozco Suárez, D.; Bellot Rubio,
L. R.
Bibcode: 2010ApJ...711..312D
Altcode: 2010arXiv1001.3022D
The ability of new instruments for providing accurate inferences of
vector magnetic fields and line-of-sight velocities of the solar
plasma depends a great deal on the sensitivity to these physical
quantities of the spectral lines chosen to be measured. Recently,
doubts have been raised about visible Stokes profiles to provide
a clear distinction between weak fields and strong ones filling a
small fraction of the observed area. The goal of this paper is to
give qualitative and quantitative arguments that help in settling the
debate since several instruments that employ visible lines are either
operating or planned for the near future. The sensitivity of the Stokes
profiles is calculated through the response functions (RFs), for e.g.,
by Ruiz Cobo & Del Toro Iniesta. Both theoretical and empirical
evidences are gathered in favor of the reliability of visible Stokes
profiles. The RFs are also used for estimating the uncertainties in
the physical quantities due to noise in observations. A useful formula
has been derived that takes into account the measurement technique
(number of polarization measurements, polarimetric efficiencies, and
number of wavelength samples), the model assumptions (number of free
parameters and the filling factor), and the radiative transfer (RFs). We
conclude that a scenario with a weak magnetic field can reasonably
be distinguished with visible lines from another with a strong field
but a similar Stokes V amplitude, provided that the Milne-Eddington
approximation is good enough to describe the solar atmosphere and the
polarization signal is at least 3 or 4 times larger than the typical
rms noise of 10-3 I c reached in the observations.
Title: ASTRONET: Public Outreach
Authors: Ros, R. M.; Fosbury, R.; Christensen, L. L.; Del Toro Iniesta,
J. C.; Fucili, L.; Hill, R.; Lorenzen, D.; Madsen, C.; Newsam, A.;
Pickwick, A.; Radeva, V.
Bibcode: 2009CAPJ....5...26R
Altcode:
We have all seen the spectacular images that the Hubble Space Telescope
and other such observatories have revealed to the world. Their haunting
splendour inspires and compels us as artists. But how can we capture
the elusive essence of space in our own work?
Title: ASTRONET Panel E: Education, recruitment/training &
public outreach
Authors: Hill, Robert; Ros, Rosa Maria; Fosbury, Robert; Christensen,
Lars Lindberg; Fucili, Leonarda; Lorenzen, Dirk; del Toro Iniesta, Jose
Carlos; Madsen, Claus; Newsam, Andy; Pickwick, Alan; Radeva, Veselka
Bibcode: 2008ca07.conf..166H
Altcode:
ASTRONET was created by a group of European funding agencies in order
to establish a comprehensive long-term plan for the development of
European astronomy. The objective of this effort is to consolidate
and reinforce the world-leading position that European astronomy has
attained at the beginning of this 21st century. This presentation
concentrates on the work of Panel E.
Title: Magnetic field emergence in quiet Sun granules
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; del Toro Iniesta,
J. C.; Tsuneta, S.
Bibcode: 2008A&A...481L..33O
Altcode: 2007arXiv0712.2663O
Aims:We describe a new form of small-scale magnetic flux emergence in
the quiet Sun. This process seems to take vertical magnetic fields
from subsurface layers to the photosphere, where they appear above
granular convection cells.
Methods: High-cadence time series
of spectropolarimetric measurements obtained by Hinode in a quiet
region near disk center are analyzed. We extract line parameters from
the observed Stokes profiles and study their evolution with time.
Results: The circular polarization maps derived from the observed Fe
I 630 nm lines show clear magnetic signals emerging at the center of
granular cells. We do not find any evidence for linear polarization
signals associated with these events. The magnetic flux patches grow
with time, occupying a significant fraction of the granular area. The
signals then fade until they disappear completely. The typical lifetime
of these events is of the order of 20 min. No significant changes in
the chromosphere are seen to occur in response to the emergence, as
revealed by co-spatial Ca II H filtergrams. The Stokes I and V profiles
measured in the emerging flux concentrations show strong asymmetries
and Doppler shifts.
Conclusions: The origin of these events is
unclear at present, but we suggest that they may represent the emergence
of vertical fields lines from the bottom of the photosphere, possibly
dragged by the convective upflows of granules. Preliminary inversions
of the Stokes spectra indicate that this scenario is compatible with
the observations, although the emergence of vertical field lines is
not free from conceptual problems.
Title: Temporal evolution of the Evershed flow in
sunspots. II. Physical properties and nature of Evershed clouds
Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Borrero, J. M.;
Del Toro Iniesta, J. C.
Bibcode: 2008A&A...477..273C
Altcode: 2007arXiv0709.1601C
Context: Evershed clouds (ECs) represent the most conspicuous
variation of the Evershed flow in sunspot penumbrae.
Aims:
We determine the physical properties of ECs from high spatial and
temporal resolution spectropolarimetric measurements. This information
is used to investigate the nature of the EC phenomenon.
Methods:
The Stokes profiles of four visible and three infrared spectral lines
are subject to inversions based on simple one-component models as well
as more sophisticated realizations of penumbral flux tubes embedded
in a static ambient field (uncombed models).
Results: According
to the one-component inversions, the EC phenomenon can be understood
as a perturbation of the magnetic and dynamic configuration of the
penumbral filaments along which the ECs move. The uncombed inversions,
on the other hand, suggest that ECs are the result of enhancements
in the visibility of penumbral flux tubes. We conjecture that
these enhancements are caused by a perturbation of the thermodynamic
properties of the tubes, rather than by changes in the vector magnetic
field. This mechanism is investigated performing numerical experiments
of thick penumbral tubes in mechanical equilibrium with a background
field.
Conclusions: While the one-component inversions confirm
many of the properties indicated by a simple line parameter analysis
(Paper I of this series), we give more credit to the results of the
uncombed inversions because they take into account, at least in an
approximate manner, the fine structure of the penumbra. Appendix
A is only available in electronic form at http://www.aanda.org
Title: Temporal evolution of the Evershed flow in
sunspots. I. Observational characterization of Evershed clouds
Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; Del Toro
Iniesta, J. C.
Bibcode: 2007A&A...475.1067C
Altcode: 2007arXiv0707.2629C
Context: The magnetic and kinematic properties of the photospheric
Evershed flow are relatively well known, but not completely
understood. The evolution of the flow with time, which is mainly due
to the appearance of velocity packets called Evershed clouds (ECs),
may provide information to further constrain its origin.
Aims:
We undertake a detailed analysis of the evolution of the Evershed flow
by studying the properties of ECs. In this first paper we determine
the sizes, proper motions, location in the penumbra, and frequency
of appearance of ECs, as well as their typical Doppler velocities,
linear and circular polarization signals, Stokes V area asymmetries,
and continuum intensities.
Methods: High-cadence, high-resolution,
full vector spectropolarimetric measurements in visible and infrared
lines are used to characterize the EC phenomenon through a simple
line-parameter analysis.
Results: ECs appear in the mid penumbra
and propagate outward along filaments having large linear polarization
signals and enhanced Evershed flows. The frequency of appearance of
ECs varies between 15 and 40 min in different filaments. ECs exhibit
the largest Doppler velocities and linear-to-circular polarization
ratios of the whole penumbra. In addition, lines formed deeper in the
atmosphere show larger Doppler velocities, much in the same way as
the “quiescent” Evershed flow. According to our observations, ECs
can be classified in two groups: type I ECs, which vanish in the outer
penumbra, and type II ECs, which cross the outer penumbral boundary and
enter the sunspot moat. Most of the observed ECs belong to type I. On
average, type II ECs can be detected as velocity structures outside
of the spot for only about 14 min. Their proper motions in the moat
are significantly reduced with respect to the ones they had in the
penumbra. Appendices A and B are only available in electronic
form at http://www.aanda.org
Title: Quiet-Sun Internetwork Magnetic Fields from the Inversion of
Hinode Measurements
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; del Toro Iniesta,
J. C.; Tsuneta, S.; Lites, B. W.; Ichimoto, K.; Katsukawa, Y.; Nagata,
S.; Shimizu, T.; Shine, R. A.; Suematsu, Y.; Tarbell, T. D.; Title,
A. M.
Bibcode: 2007ApJ...670L..61O
Altcode: 2007arXiv0710.1405O
We analyze Fe I 630 nm observations of the quiet Sun at disk center
taken with the spectropolarimeter of the Solar Optical Telescope aboard
the Hinode satellite. A significant fraction of the scanned area,
including granules, turns out to be covered by magnetic fields. We
derive field strength and inclination probability density functions from
a Milne-Eddington inversion of the observed Stokes profiles. They show
that the internetwork consists of very inclined, hG fields. As expected,
network areas exhibit a predominance of kG field concentrations. The
high spatial resolution of Hinode's spectropolarimetric measurements
brings to an agreement the results obtained from the analysis of
visible and near-infrared lines.
Title: Strategy for the Inversion of Hinode Spectropolarimetric
Measurements in the Quiet Sun
Authors: Orozco Suárez, David; Bellot Rubio, Luis R.; Del Toro
Iniesta, Jose Carlos; Tsuneta, Saku; Lites, Bruce; Ichimoto, Kiyoshi;
Katsukawa, Yukio; Nagata, Shin'ichi; Shimizu, Toshifumi; Shine,
Richard A.; Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.
Bibcode: 2007PASJ...59S.837O
Altcode: 2007arXiv0709.2033O
In this paper we propose an inversion strategy for the analysis of
spectropolarimetric measurements taken by Hinode in the quiet Sun. The
Spectro-Polarimeter of the Solar Optical Telescope aboard Hinode records
the Stokes spectra of the FeI line pair at 630.2nm with unprecendented
angular resolution, high spectral resolution, and high sensitivity. We
discuss the need to consider a local stray-light contamination to
account for the effects of telescope diffraction. The strategy is
applied to observations of a wide quiet Sun area at disk center. Using
these data we examine the influence of noise and initial guess models
in the inversion results. Our analysis yields the distributions of
magnetic field strengths and stray-light factors. They show that quiet
Sun internetwork regions consist mainly of hG fields with stray-light
contamination of about 0.8.
Title: Vector Spectropolarimetry of Dark-cored Penumbral Filaments
with Hinode
Authors: Bellot Rubio, L. R.; Tsuneta, S.; Ichimoto, K.; Katsukawa,
Y.; Lites, B. W.; Nagata, S.; Shimizu, T.; Shine, R. A.; Suematsu,
Y.; Tarbell, T. D.; Title, A. M.; del Toro Iniesta, J. C.
Bibcode: 2007ApJ...668L..91B
Altcode: 2007arXiv0708.2791B
We present spectropolarimetric measurements of dark-cored penumbral
filaments taken with Hinode at a resolution of 0.3". Our observations
demonstrate that dark-cored filaments are more prominent in polarized
light than in continuum intensity. Far from disk center, the Stokes
profiles emerging from these structures are very asymmetric and show
evidence for magnetic fields of different inclinations along the
line of sight, together with strong Evershed flows of at least 6-7 km
s-1. In sunspots closer to disk center, dark-cored penumbral
filaments exhibit regular Stokes profiles with little asymmetries due
to the vanishing line-of-sight component of the horizontal Evershed
flow. An inversion of the observed spectra indicates that the magnetic
field is weaker and more inclined in the dark cores as compared with
the surrounding bright structures. This is compatible with the idea
that dark-cored filaments are the manifestation of flux tubes carrying
hot Evershed flows.
Title: Quiet-Sun Magnetic Fields from Space-borne Observations:
Simulating Hinode's Case
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; del Toro Iniesta,
J. C.
Bibcode: 2007ApJ...662L..31O
Altcode: 2007arXiv0705.0096O
We examine whether it is possible to derive the field strength
distribution of quiet-Sun internetwork regions from very high spatial
resolution polarimetric observations in the visible. In particular,
we consider the case of the spectropolarimeter attached to the Solar
Optical Telescope aboard Hinode. Radiative magnetoconvection simulations
are used to synthesize the four Stokes profiles of the Fe I 630.2
nm lines. Once the profiles are degraded to a spatial resolution of
0.32" and added noise, we infer the atmospheric parameters by means
of Milne-Eddington inversions. The comparison of the derived values
with the real ones indicates that the visible lines yield correct
internetwork field strengths and magnetic fluxes, with uncertainties
smaller than ~150 G, when a stray-light contamination factor is
included in the inversion. Contrary to the results of ground-based
observations at 1", weak fields are retrieved wherever the field is
weak in the simulation.
Title: Introduction to Spectropolarimetry
Authors: del Toro Iniesta, Jose Carlos
Bibcode: 2007insp.book.....D
Altcode:
Preface; Acknowledgements; 1. Historical introduction; 2. A
review of some basic concepts; 3. The polarization properties
of quasi-monochromatic light; 4. Linear optical systems acting on
polarized light; 5. Solar polarimetry; 6. Absorption and dispersion;
7. The radiative transfer equation; 8. The RTE in the presence of a
magnetic field; 9. Solving the radiative transfer equation; 10. Stokes
spectrum diagnostics; 11. Inversion of the RTE; Index.
Title: The usefulness of analytic response functions
Authors: Orozco Suárez, D.; Del Toro Iniesta, J. C.
Bibcode: 2007A&A...462.1137O
Altcode: 2012arXiv1211.1502O
Aims:We introduce analytical response functions and their main
properties as an important diagnostic tool that help understand Stokes
profile formation physics and the meaning of well-known behaviors of
standard inversion codes of the radiative transfer equation often used
to measure solar magnetic fields.
Methods: A Milne-Eddington
model atmosphere is used as an example where response functions are
analytical. A sample spectral line has been chosen to show the main
qualitative properties.
Results: We show that analytic response
functions readily provide explanations for various well-known behaviors
of spectral lines, such as the sensitivity of visible lines to weak
magnetic fields or the trade-offs often detected in inversion codes
between the Milne-Eddington thermodynamic parameters. We also show
that response functions are helpful in selecting sample wavelengths
optimized for specific parameter diagnostics. Appendix A is only
available in electronic form at http://www.aanda.org
Title: S im ulation And Analysis Of VIM Measurements: Feedback On
Design Parameters
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Vargas, S.; Bonet,
J. A.; Martíez Pillet, V.; del Toro Iniesta, J. C.
Bibcode: 2007ESASP.641E..49O
Altcode: 2006astro.ph.11443O
The Visible-light Imager and Magnetograph (VIM) proposed for the
ESA Solar Orbiter mission will observe a photo spheric spectral
line at high spatial resolution. Here we simulate and interpret VIM
measurements. Realistic MHD models are used to synthesize "observed"
Stokes profiles of the photospheric Fe I 617.3 nm line. The profiles are
degraded by telescope diffraction and detector pixel size to a spatial
resolution of 162 km on the solar surface. We stufy the influence
of spectral resolving power, noise, and limited wavelength sampling
on the vector magnetic fields and line-of-sight velocities derived
from Milne-Eddington inversions of the simulated measurements. VIM
will provide reasonably accurate values of the atmospheric parametes
even with the filter widths of 120 Å and 3 wavelength positions plus
continuum, as long as the noise level is kept below 10-3 Ic.
Title: First Steps Towards the Electronic Inversion of the Radiative
Transfer Equation
Authors: Castillo Lorenzo, J. L.; Orozco Suárez, D.; Bellot Rubio,
L. R.; Jiménez, L.; Del Toro Iniesta, J. C.
Bibcode: 2006ASPC..358..177C
Altcode:
The radiative transfer equation (RTE) gives us information about how the
light streams through the medium. It must be inverted in order to obtain
the properties of the medium that generated the observation. While
there are a number of well discussed methods to approach the solution
of the inversion, none of them is suitable for the real-time analysis
of high-resolution images due to their computational requirements. This
document introduces an electronic inverter for the RTE, suitable for
real-time inversion and mainly intended for space missions and on-line
ground-based observations.
Title: Inversion of Visible and IR Stokes Profiles in Sunspots
Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; Del Toro
Iniesta, J. C.
Bibcode: 2006ASPC..358...25C
Altcode:
We present an analysis of simultaneous observations of a sunspot
in two different spectral ranges (630 nm and 1565 nm). The dataset
was acquired with the POlarimetric LIttrow Spectrograph (POLIS) and
the Tenerife Infrared Polarimeter (TIP) at the German Vacuum Tower
Telescope (VTT) of Observatorio del Teide. Inversions of both sets
of lines are carried out to retrieve physical quantities such as
temperature and magnetic fields. We find that: a) the differences
between the atmospheric parameters inferred from the two ranges
are small, demonstrating that inversion techniques provide unique
results; b) there is a cross-talk between temperature and stray light
for visible lines; c) a more realistic treatment of the stray light
contamination is required. Making use of both visible and infrared
lines we obtain < dB/dz >=-2.3±0.6 G km-1 and <
dγ/dz >=-0.019±0.015 deg km-1 in the umbra. Finally,
we show how simultaneous spectro-polarimetric observations of the Sun
in visible and infrared wavelengths improve the diagnostic capabilities
of a single spectral range alone.
Title: Milne-Eddington Response Functions and Their Applications
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Del Toro Iniesta,
J. C.
Bibcode: 2006ASPC..358..197O
Altcode:
We examine the errors in the atmospheric parameters recovered
from the inversion of spectro-polarimetric data with limited
wavelength sampling. We suggest that response functions evaluated in
Milne-Eddington atmospheres may be useful as diagnostic tools that
allow, for instance, the selection of the optimum wavelength positions
to be observed by vector magnetographs.
Title: Evershed Clouds as Precursors of Moving Magnetic Features
around Sunspots
Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; del Toro
Iniesta, J. C.
Bibcode: 2006ApJ...649L..41C
Altcode: 2006astro.ph..9108C
The relation between the Evershed flow and moving magnetic features
(MMFs) is studied using high-cadence, simultaneous spectropolarimetric
measurements of a sunspot in visible (630.2 nm) and near-infrared
(1565 nm) lines. Doppler velocities, magnetograms, and total linear
polarization maps are calculated from the observed Stokes profiles. We
follow the temporal evolution of two Evershed clouds that move radially
outward along the same penumbral filament. Eventually, the clouds
cross the visible border of the spot and enter the moat region, where
they become MMFs. The flux patch farther from the sunspot has the same
polarity of the spot, while the MMF closer to it has opposite polarity
and exhibits abnormal circular polarization profiles. Our results
provide strong evidence that at least some MMFs are the continuation
of the penumbral Evershed flow into the moat. This, in turn, suggests
that MMFs are magnetically connected to sunspots.
Title: VIP - 2D Vector Spectropolarimetry of the Solar Atmosphere
near the Diffraction Limit
Authors: Bellot Rubio, L. R.; Tritschler, A.; Kentischer, T.; Beck,
C.; Del Toro Iniesta, J. C.
Bibcode: 2006IAUJD...3E..58B
Altcode:
The KIS/IAA Vector Imaging Polarimeter (VIP) is a new instrument for
two-dimensional spectropolarimetry of the solar atmosphere. It is used
with TESOS, the triple etalon Fabry-Perot interferometer installed at
the German Vacuum Tower Telescope of Observatorio del Teide (Tenerife,
Spain). The polarimeter is based on a pair of nematic liquid crystal
retarders and a Wollaston prism. VIP and TESOS are able to observe
any spectral line in the range from 450 nm to 750 nm with a spectral
resolving power of about 250000 and spatial resolutions better than
0.5" (thanks to the Kiepenheuer Adaptive Optics System). Typically,
the four Stokes parameters of a line can be measured at 40 wavelength
points in less than 60 s, with a noise level of 1-2 x 10^-3 and a
pixel size of 0.18" x 0.18" (2x2 binning). The modulation matrix of
VIP is derived using the polarimetric calibration unit installed at
the telescope. Here we present first-light observations of VIP carried
out in November 2005. We recorded the full Stokes profiles of the 630.1
and 630.2 nm Fe I lines emerging from a solar pore and its surroundings
at a spatial resolution of ~0.4". Based on these data, we discuss the
performance and capabilities of VIP as a powerful instrument for high
spatial and temporal resolution measurements of vector magnetic fields
in the solar atmosphere.
Title: Detailed design of the imaging magnetograph experiment (IMaX):
a visible imager magnetograph for the Sunrise mission
Authors: Álvarez-Herrero, A.; Belenguer, T.; Pastor, C.; González,
L.; Heredero, R. L.; Ramos, G.; Reina, M.; Sánchez, A.; Villanueva,
J.; Sabau, L.; Martínez Pillet, V.; Bonet, J. A.; Collados, M.;
Jochum, L.; Ballesteros, E.; Medina Trujillo, J. L.; Ruiz, Cobo B.;
González, J. C.; del Toro Iniesta, J. C.; López Jiménez, A. C.;
Castillo Lorenzo, J.; Herranz, M.; Jerónimo, J. M.; Mellado, P.;
Morales, R.; Rodríguez, J.; Domingo, V.; Gasent, J. L.; Rodríquez, P.
Bibcode: 2006SPIE.6265E..4CA
Altcode: 2006SPIE.6265E.132A
In this work, it is described the Imaging Magnetograph eXperiment,
IMaX, one of the three postfocal instruments of the Sunrise mission. The
Sunrise project consists on a stratospheric balloon with a 1 m aperture
telescope, which will fly from the Antarctica within the NASA Long
Duration Balloon Program. IMaX will provide vector magnetograms
of the solar surface with a spatial resolution of 70 m. This data
is relevant for understanding how the magnetic fields emerge in
the solar surface, how they couple the photospheric base with the
million degrees of temperature of the solar corona and which are the
processes that are responsible of the generation of such an immense
temperatures. To meet this goal IMaX should work as a high sensitivity
polarimeter, high resolution spectrometer and a near diffraction
limited imager. Liquid Crystal Variable Retarders will be used as
polarization modulators taking advantage of the optical retardation
induced by application of low electric fields and avoiding mechanical
mechanisms. Therefore, the interest of these devices for aerospace
applications is envisaged. The spectral resolution required will be
achieved by using a LiNbO 3 Fabry-Perot etalon in double
pass configuration as spectral filter before the two CCDs detectors. As
well phase-diversity techniques will be implemented in order to improve
the image quality. Nowadays, IMaX project is in the detailed design
phase before fabrication, integration, assembly and verification. This
paper briefly describes the current status of the instrument and the
technical solutions developed to fulfil the scientific requirements.
Title: The many scales in the universe : JENAM 2004 astrophysics
reviews
Authors: Del Toro Iniesta, Jose Carlos; Alfaro, Emilio J.; Gorgas,
J. G.; Salvador-Sole, E.; Butcher, H.
Bibcode: 2006msu..conf.....D
Altcode:
No abstract at ADS
Title: Sensitivity of spectral lines to temperature, velocity,
and magnetic field
Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; del Toro Iniesta,
J. C.
Bibcode: 2005A&A...439..687C
Altcode:
We present an analytical and numerical study of the sensitivity of
weak solar photospheric lines to temperature, velocity, and magnetic
fields. Our investigation is based on the concept of response functions
(Landi degl'Innocenti & Landi degl'Innocenti 1977; Ruiz Cobo &
del Toro Iniesta 1994). Lines commonly used in solar spectropolarimetry,
like Fe I 630.25 nm in the visible and Fe I 1564.85 nm in the infrared,
are examined in detail as emerging from reference quiet Sun and sunspot
models. We develop a simple phenomenological model capable of describing
the response of any given line to these atmospheric parameters. We
find that: (a) the sensitivity of the lines to velocity and magnetic
fields increases with the sharpness of the intensity and circular
polarization profiles; (b) the sensitivity to temperature is determined
mainly by the variation of the source function with temperature,
which is smaller at longer wavelengths; and (c) lines quoted to be
insensitive to temperature, like Fe I 1564.85 nm and Fe I 557.61 nm,
exhibit larger changes in equivalent width than lines presumed to
have higher sensitivities to T, such as Fe I 630.25 nm. The relations
provided by our model are universal and can be used to decide which
line is better suited to measuring a given atmospheric parameter. The
results of this study are of practical interest for the design of new
instruments and for better exploitation of existing ones.
Title: The imaging magnetograph eXperiment for the SUNRISE balloon
Antarctica project
Authors: Martinez Pillet, Valentin; Bonet, Jose A.; Collados, Manuel
V.; Jochum, Lieselotte; Mathew, S.; Medina Trujillo, J. L.; Ruiz Cobo,
B.; del Toro Iniesta, Jose Carlos; Lopez Jimenez, A. C.; Castillo
Lorenzo, J.; Herranz, M.; Jeronimo, J. M.; Mellado, P.; Morales, R.;
Rodriguez, J.; Alvarez-Herrero, Alberto; Belenguer, Tomas; Heredero,
R. L.; Menendez, M.; Ramos, G.; Reina, Manuel; Pastor, C.; Sanchez,
A.; Villanueva, J.; Domingo, Vicente; Gasent, J. L.; Rodriguez, P.
Bibcode: 2004SPIE.5487.1152M
Altcode:
The SUNRISE balloon project is a high-resolution mission to study solar
magnetic fields able to resolve the critical scale of 100 km in the
solar photosphere, or about one photon mean free path. The Imaging
Magnetograph eXperiment (IMaX) is one of the three instruments that
will fly in the balloon and will receive light from the 1m aperture
telescope of the mission. IMaX should take advantage of the 15 days
of uninterrupted solar observations and the exceptional resolution
to help clarifying our understanding of the small-scale magnetic
concentrations that pervade the solar surface. For this, IMaX should
act as a diffraction limited imager able to carry out spectroscopic
analysis with resolutions in the 50.000-100.000 range and capable
to perform polarization measurements. The solutions adopted by the
project to achieve all these three demanding goals are explained in this
article. They include the use of Liquid Crystal Variable Retarders for
the polarization modulation, one LiNbO3 etalon in double pass
and two modern CCD detectors that allow for the application of phase
diversity techniques by slightly changing the focus of one of the CCDs.
Title: An orthonormal set of Stokes profiles
Authors: del Toro Iniesta, J. C.; López Ariste, A.
Bibcode: 2003A&A...412..875D
Altcode:
A family of well-known orthonormal functions, the set of Hermite
functions, is proposed as a suitable basis for expanding the
Stokes profiles of any spectral line. An expansion series thus
provides different degrees of approximation to the Stokes spectrum,
depending on the number of basis elements used (or on the number
of coefficients). Hence, an usually large number of wavelength
samples, may be substituted by a few such coefficients, thus reducing
considerably the size of data files and the analysis of observable
information. Moreover, since the set of Hermite functions is an
universal basis, it promises to help in modern inversion techniques
of the radiative transfer equation that infer the solar physical
quantities from previously compiled look-up tables or artificial neural
networks. These features appear to be particularly important in modern
solar applications producing huge amounts of spectropolarimetric data
and on near-future, on-line applications aboard spacecrafts.
Title: Accurate atomic parameters for near-infrared spectral lines
Authors: Borrero, J. M.; Bellot Rubio, L. R.; Barklem, P. S.; del
Toro Iniesta, J. C.
Bibcode: 2003A&A...404..749B
Altcode:
A realistic two-component model of the quiet solar photosphere is
used to fit the intensity spectrum of the Sun in the wavelength
range 0.98-1.57 mu m. Our approach differs from earlier attempts in
many respects: proper account of convective inhomogeneities is made,
accurate collisional broadening parameters from quantum mechanical
computations are used, and the effects of possible blends in the local
continuum are corrected empirically. This allows us to derive oscillator
strengths and central wavelengths for virtually any unblended line of
the solar spectrum. The accuracy of the inferred atomic parameters,
about 0.06 dex for oscillator strengths and 5 mÅ at 1 mu m for central
wavelengths, is similar to that of the best laboratory measurements. We
apply our method to 83 near-infrared lines belonging to 6 different
atomic species. The availability of accurate oscillator strengths and
central wavelengths for lines of different species is essential for
the interpretation of high resolution spectroscopic observations. The
method is especially useful in the infrared, a wavelength domain where
laboratory measurements are scarce.
Title: Introduction to Spectropolarimetry
Authors: del Toro Iniesta, José Carlos
Bibcode: 2003isp..book.....D
Altcode: 2003insp.book.....D
Spectropolarimetry embraces the most complete and detailed measurement
and analysis of light, as well as its interaction with matter. This book
provides an introductory overview of the subject because it is playing
an increasingly important role in modern solar observations. Chapters
include a comprehensive description of the polarization state of
polychromatic light and its measurement; an overview of astronomical
polarimetry; and the formation of spectral lines in the presence of
a magnetic field. The text is a valuable reference for graduates and
researchers in astrophysics, solar physics and optics.
Title: IMax: a visible magnetograph for SUNRISE
Authors: Jochum, Lieselotte; Collados, Manuel; Martínez Pillet,
Valentin; Bonet, Jose A.; del Toro Iniesta, Jose Carlos; Lopez,
Antonio; Alvarez-Herrero, Alberto; Reina, Manuel; Fabregat, Juan;
Domingo, Vicente
Bibcode: 2003SPIE.4843...20J
Altcode:
The description of the Imaging Magnetograph eXperiment (IMaX) is
presented in this contribution. This is a magnetograph which will
fly by the end of 2006 on a stratospheric balloon, together with
other instruments (to be described elsewhere). Especial emphasis
is put on the scientific requirements to obtain diffraction-limited
visible magnetograms, on the optical design and several constraining
characteristics, such as the wavelength tuning or the crosstalk between
the Stokes parameters.
Title: Interpretation of observations by inversion
Authors: del Toro Iniesta, J. C.
Bibcode: 2003AN....324..383D
Altcode:
The most recent developments in inversion techniques of the
radiative transfer equation are critically reviewed and some of
their findings are summarized to illustrating their achievements. Two
significantly different approaches are currently being used that deserve
consideration, each characterized by whether or not the model solar
atmospheres are changed iteratively by the algorithm. The comparison
between the two may help in finding future inversion techniques that
can solve many challenging problems of solar physics that still need
to be properly settled. These problems themselves suggest strategies
that look more suitable than others.
Title: Accurate Atomic Parameters from the Solar Spectrum
Authors: Bellot Rubio, Luis Ramon; Borrero, Juan Manuel; Barklem,
Paul; del Toro Iniesta, Jose Carlos
Bibcode: 2003IAUJD..20E..16B
Altcode:
A realistic two-component model of the quiet solar photosphere is used
to fit the full shape of the intensity profiles of unblended lines in
the solar spectrum. Our approach differs from previous attempts in many
respects: proper account of granulation inhomogeneities is made accurate
collisional broadening parameters from quantum mechanical computations
are used and possible absorptions in the local continuum due to blends
are corrected empirically. This allows us to derive oscillator strengths
and central wavelengths for any clean line with an accuracy comparable
with that of the best laboratory measurements. The availability of
very precise atomic parameters for lines of different species is
essential for the interpretation of high resolution spectroscopic
observations. Abundance determinations and investigations of granular
motions in stellar atmospheres are among the applications that would
benefit from such accurate atomic data. As an example we determine the
oscillator strengths and central wavelengths of 100 unblended lines
in the near-infrared (0.99-1.56 microns) a wavelength domain where
laboratory measurements are particularly scarce.
Title: Solar Polarimetry and Magnetic Field Measurements
Authors: del Toro Iniesta, J. C.
Bibcode: 2001ASSL..259..183D
Altcode: 2001dysu.conf..183D
The magnetic nature of most solar (spatially resolved or unresolved)
structures is amply recognized. Magnetic fields of the Sun play a
paramount rôle in the overall thermodynamic and dynamic state of
our star. The main observable manifestation of solar magnetic fields
is the polarization of light either through the Zeeman effect on
spectral lines or through the Hanle effect (depolarization by very weak
magnetic fields of light previously polarized by scattering). Hence,
one can easily understand the increasing importance that polarimetry
is experimenting continuously in solar physics. Under the title
of this contribution a six-hour course was given during the summer
school. Clearly, the limited extension allocated for the notes in
these proceedings avoids an extensive account of the several topics
discussed: 1) a description of light as an electromagnetic wave and
the polarization properties of monochromatic, time-harmonic, plane
waves; 2) the polarization properties of polychromatic light and, in
particular, of quasi-monochromatic light; 3) the transformations of
(partially) polarized light by linear optical systems and a description
of the ways we measure the Stokes parameters by spatially and/or
temporally modulating the polarimetric signal; 4) a discussion on
specific problems relevant to solar polarimetry like seeing-induced
and instrumental polarization, or modulation and demodulation, along
with a brief description of current solar polarimeters; 5) the vector
radiative transfer equation for polarized light and its links to the
scalar one for unpolarized light, together with a summary of the Zeeman
effect and its consequences on line formation in a magnetized stellar
atmosphere; 7) an introduction of the paramount astrophysical problem,
i.e., that of finding diagnostics that enable the solar physicist to
interpret the observables in terms of the solar atmospheric quantities,
including a discussion on contribution and response functions; and 8)
a brief outline of inversion techniques as a recommended way to infer
values of the vector magnetic field and other thermodynamic and dynamic
quantities. Since most of the material presented in the lectures can
be found in the literature, I decided to focus these pages to those
topics that, in my opinion, need a particular stress and/or do not
have received much attention in previous reviews or textbooks. These
notes have been written with mostly didactical purposes so that,
skipping the customary usage, just a few references will be cited
within the text. Instead, a classified (and necessarily incomplete)
bibliography is recommended at the end.
Title: Cold, Supersonic Evershed Downflows in a Sunspot
Authors: del Toro Iniesta, Jose Carlos; Bellot Rubio, Luis R.;
Collados, Manuel
Bibcode: 2001ApJ...549L.139D
Altcode:
We report here on the discovery of supersonic Evershed downflows
in the penumbra of a sunspot. These flows are shown to occur along
spatially unresolved, very cold magnetic flux tubes whose downflowing
footpoints are found from the middle penumbra outward. Evershed
flows along magnetic field lines returning to the solar surface were
discovered by Westendorp Plaza and coworkers, but only in the outer
parts of the penumbra and beyond its visible boundary; on the other
hand, no supersonic flows of any type have ever been reported in the
photosphere of sunspots, except for the very different case of the
delta spot analyzed by Martínez Pillet and coworkers. We present
unequivocal evidence of such supersonic motions, already predicted
theoretically by the siphon-flow model, from the interpretation
of infrared spectropolarimetric observations of a sunspot with
unprecedented spatial resolution.
Title: Optical Tomography of a Sunspot. II. Vector Magnetic Field
and Temperature Stratification
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martínez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 2001ApJ...547.1130W
Altcode:
An observational determination of the three-dimensional magnetic
and thermal structure of a sunspot is presented. It has been
obtained through the application of the SIR inversion technique
(Stokes Inversion based on Response functions) on a low-noise, full
Stokes profile two-dimensional map of the sunspot as observed with
the Advanced Stokes Polarimeter. As a result of the inversion, maps
of the magnetic field strength, B, zenith angle, γ, azimuth, χ, and
temperature, T, over 25 layers at given optical depths (i.e., an optical
tomography) are obtained, of which those between logτ5=0 and
logτ5=-2.8 are considered to provide accurate information on
the physical parameters. All over the penumbra γ increases with depth,
while B is larger at the bottom layers of the inner penumbra (as in
the umbra) but larger at the top layers of the outer penumbra (as in
the canopy). The corrugation of the penumbral magnetic field already
observed by other authors has been confirmed by our different inversion
technique. Such a corrugation is especially evident in the zenith angle
maps of the intermediate layers, featuring the presence of the so-called
spines that we further characterize: spines are warmer and have a less
inclined magnetic field than the spaces between them and tend to have a
smaller gradient of γ with optical depth over the entire penumbra, but
with a field strength which is locally stronger in the middle penumbra
and locally weaker in the outer penumbra and beyond in the canopy. In
the lower layers of these external parts of the sunspot, most of the
field lines are seen to return to the solar surface, a result that is
closely connected with the Evershed effect (e.g., Westendorp et al.,
the third paper in this series). The Stokes V net area asymmetry map
as well as the average B, γ, and T radial distributions (and that
of the line-of-sight velocities; see the third paper in this series)
show a border between an inner and an outer penumbra with different
three-dimensional structure. We suggest that it is in this middle zone
where most of a new family of penumbral flux tubes (some of them with
Evershed flow) emerge interlaced (both horizontally and vertically)
among themselves and with the ``background'' magnetic field of the
penumbra. The interlacing along the line of sight is witnessed by
the indication of many points in the outer penumbra showing rapid
transitions with height between two structures, one with very weak
and inclined magnetic field at the bottom of the photosphere and the
other with a stronger and less inclined magnetic field. Over the whole
penumbra, and at all optical layers, a constant but weak deviation from
radiality of some 5° is detected for the azimuth of the vector magnetic
field, which may be in agreement with former detections but which is
not significantly higher than the size of the errors for this parameter.
Title: Optical Tomography of a Sunspot. III. Velocity Stratification
and the Evershed Effect
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martínez Pillet, V.
Bibcode: 2001ApJ...547.1148W
Altcode:
The stratification with optical depth of the line-of-sight (LOS)
velocity of a simple, isolated, round sunspot observed with the Advanced
Stokes Polarimeter (ASP; Elmore et al.) presented here completes this
series of papers that investigates the stratification in optical depths
of such a typical sunspot. These results have been obtained through the
use of the SIR technique (Stokes Inversion based on Response functions
of Ruiz Cobo & del Toro Iniesta). From these data we have confirmed
that there are strong downflowing velocities at logτ5=0
that coincide spatially with the places where the magnetic field points
downward (Westendorp Plaza et al.). Further confirmation is obtained
by the application of the same method on a different sunspot, already
analyzed with the Milne-Eddington inversion technique (Stanchfield,
Thomas, & Lites). These downflows reconcile observations that have
detected Evershed velocities outside sunspots together with suggestions
of the possible return of the flow within the penumbra. The Evershed
flow seems to be concentrated in elevated channels not thicker than 1 or
2 scale heights that are mostly located in the space between magnetic
spines, i.e., in places where the magnetic field is more inclined,
weaker in the inner-middle penumbra, and stronger in the outer penumbra
and beyond the visible limits of the sunspot. This conclusion is
based upon the tight correlation found between LOS velocities and
the (reported in the second paper of this series) magnetic field
strength and zenith angle. The upstreaming material is seen in the
inner penumbra and the downstreaming in the outer penumbra. A strong
increase with optical depth has been obtained for the LOS velocities
that provides indications of the superposition of Evershed channels
along the LOS. The differential opacity effect between the center-side
and the limb-side penumbra, already reported in the second paper in
this series, is also seen in the velocity maps and has suggested the
comparison of the vertical mass flux through the upstreaming zones
(mostly seen in the center side) and the downstreaming zones (mostly
seen in the limb side), obtaining a fairly good balance between the two.
Title: Sunspot Magnetic Fields
Authors: del Toro Iniesta, J. C.
Bibcode: 2001ASPC..248...35D
Altcode: 2001mfah.conf...35D
No abstract at ADS
Title: Sunspots: Evershed Effect
Authors: del Toro Iniesta, J.
Bibcode: 2000eaa..bookE2031D
Altcode:
The Evershed Effect is an observational effect in the penumbra of
SUNSPOTS consisting in displacements of the spectral line profiles
towards either shorter wavelengths (that is, blueshifts) in the zones
closest to the Sun's disk center or larger wavelengths (that is,
redshifts) in those zones closest to the solar limb. Since the first
detection in 1909, this effect was correctly interpreted by it...
Title: Optimum Modulation and Demodulation Matrices for Solar
Polarimetry
Authors: del Toro Iniesta, Jose Carlos; Collados, Manuel
Bibcode: 2000ApOpt..39.1637D
Altcode:
No abstract at ADS
Title: Granular and Intergranular Model Atmospheres from Inversion
of Solar Two-Dimensional Spectroscopic Data
Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Collados, M.; del
Toro Iniesta, J. C.
Bibcode: 1999ASPC..173..313R
Altcode: 1999sstt.conf..313R
No abstract at ADS
Title: Optical Tomography of a Sunspot. I. Comparison between Two
Inversion Techniques
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martínez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 1998ApJ...494..453W
Altcode:
A quantitative comparison between the Milne-Eddington (ME) inversion
technique implemented by Skumanich & Lites and the SIR (Stokes
Inversion based on Response Functions) proposed by Ruiz Cobo &
del Toro Iniesta is presented. Numerical experiments are carried
out to explore the capabilities and limitations of both diagnostic
techniques. Such experiments consist of inversions of Stokes profiles
previously synthesized in ``realistic'' solar atmospheric models. The
results show that the ME inversion provides accurate, line-of-sight
(LOS) averaged values for the input stratification of the vector
magnetic field. Its greater speed compared to SIR makes it useful for
quick analysis of large quantities of data (such as those currently
provided by modern spectropolarimeters) if one is only interested
in LOS-averaged quantities. However, the higher order description
of the atmosphere used by SIR (which acknowledges variation of the
thermal, dynamic, and magnetic parameters through the photosphere)
allows retrieval of the stratification of all these parameters to good
accuracy. This is so even in the presence of discontinuities such
as those foreseen in magnetic canopies of sunspots. The trade-offs
between thermodynamic and magnetic parameters observed in some ME
inversions are reduced considerably in the case of SIR inversions
because of the more realistic treatment of the thermodynamics in this
analysis. Notably, both allow one to extract quantitative inferences of
fairly weak magnetic fields (below 500 G), even when they are applied
to Zeeman-sensitive lines in the visible spectrum; i.e., well below
the commonly accepted limit of 500 G. The thermodynamic parameters
resulting from the ME inversion are understood theoretically in terms
of the generalized response functions introduced by Ruiz Cobo &
del Toro Iniesta and through the concept of height of formation
for inferred values proposed by Sánchez Almeida, Ruiz Cobo, &
del Toro Iniesta. The present comparison and verification of
the reliability of inversion methods is a natural first step toward
the ongoing analysis of the three-dimensional magnetic structure of
a sunspot. By using SIR (with ME results for initialization) on maps
of a whole sunspot observed by the Advanced Stokes Polarimeter, we
obtain maps at different optical layers (i.e., an optical tomography)
of the temperature, vector magnetic field, and LOS velocity. Such a
tomography will appear in subsequent papers of the present series. To
illustrate fits to the observed Stokes profiles, we show here actual
inversion results for three points observed within a sunspot: one
within the umbra, another from the outermost parts of the penumbra,
and a third from the magnetic canopy surrounding the sunspot.
Title: Evidence for a downward mass flux in the penumbral region of
a sunspot
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martinez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 1997Natur.389...47W
Altcode:
No abstract at ADS
Title: Space Certifiability of LCVRs
Authors: del Toro Iniesta, J. C.; Martinez Pillet, V.; Gonzalez
Escalera, V.
Bibcode: 1997ASPC..118..356D
Altcode: 1997fasp.conf..356D
This contribution is a report on a test campaign carried out by the
IAC, in collaboration with Construcciones Aeronauticas, S.A. (CASA) as
a main contrac tor, for exploring the capabilities of liquid crystal
variable retarders (LCVRs) to be u sed in future space missions as
the core of the modulation package of a polarimetric device, used as
a post-focus instrument of a visible solar telescope.
Title: Inversion of Stokes profiles: what's next?
Authors: Del Toro Iniesta, J. C.; Ruiz Cobo, B.
Bibcode: 1997ftst.conf...93D
Altcode:
No abstract at ADS
Title: 1st Advances in Solar Physics Euroconference: Advances in
the Physics of Sunspots
Authors: Schmieder, B.; del Toro Iniesta, J. C.; Vazquez, M.
Bibcode: 1997ASPC..118.....S
Altcode: 1997fasp.conf.....S
No abstract at ADS
Title: Inversion Techniques Applied to Sunspot Spectropolarimetric
Data
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martinez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 1997ASPC..118..197W
Altcode: 1997fasp.conf..197W
Two inversion techniques are compared: the Unno-Rachkov\-sky fitting
method (UR) and the Stokes Inversion based on Response functions
(SIR). Results with synthetic profiles in sunspot model atmospheres and
real data show that whilst UR is well suited for recovering a constant
vec B, SIR enables us to know the run with depth of vec B and the line
of sight velocity together with the temperature stratification.
Title: Optical Tomography of a Sunspot: Preliminary Results
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martinez Pillet, V.; Lites, B. W.; Skumanich, A.
Bibcode: 1997ASPC..118..202W
Altcode: 1997fasp.conf..202W
Preliminary results of the inversion of spectropolarimetric maps
of a sunspot observed with the Advanced Stokes Polarimeter (ASP) are
presented. The method used, Stokes Inversion based on Response functions
(SIR), does not assume constancy of the different parameters with
depth, thus enabling us to embark on an analysis of the information at
different layers in continuum optical depth (i.e. optical tomography),
of a sunspot's photosphere. Maps of the vector magnetic field and
other physical quantities like temperature or line-of-sight velocity at
several optical depths show a new and promising view of the structure
of a sunspot, casting light on long standing debates as those over
penumbral `corrugated' fields (spines), superpenumbral canopies,
return flux, or the nature of the Evershed effect.
Title: Heights of formation for measurements of atmospheric
parameters.
Authors: Sanchez Almeida, J.; Ruiz Cobo, B.; del Toro Iniesta, J. C.
Bibcode: 1996A&A...314..295S
Altcode:
We argue that heights of formation (HOFs) should not be assigned to
spectral lines since a single line my sample very different layers of
the atmosphere, depending on the physical parameter of interest and
the technique employed to determine it. HOFs should be assigned to
specific measurements. General expressions to compute these HOFs for
measurements are derived. The equations are subsequently used to show,
in representative solar measurements, the uncertainties produced by
assigning HOFs to lines. Only weak lines can probe a single height of
the atmosphere.
Title: Stokes Profiles Inversion Techniques
Authors: Del Toro Iniesta, J. C.; Ruiz Cobo, B.
Bibcode: 1996SoPh..164..169D
Altcode:
Inversion techniques of the radiative transfer equation for polarized
light are presented as one of the best current procedures to infer
the vector magnetic field, as well as other quantities governing the
physical state of the atmospheric layers that photons are coming
from. Several characteristics of the various available inversion
procedures are pointed out. They are mostly based on the diagnostic
contents of the spectral lines as well as on the main hypotheses
assumed in these procedures. In particular, the role of gradients in
the atmospheric quantities is emphasized as of paramount importance in
any diagnostic analysis and, hence, in any interpretation of inversion
results.
Title: Two-dimensional, high spatial resolution, solar spectroscopy
using a Correlation Tracker. II. Maps of spectral quantities.
Authors: Collados, M.; Rodriguez Hidalgo, I.; Ballesteros, E.; Ruiz
Cobo, B.; Sanchez Almeida, J.; del Toro Iniesta, J. C.
Bibcode: 1996A&AS..115..367C
Altcode:
In this paper we illustrate some of the capabilities of the Correlation
Tracker prototype developed at the Instituto de Astrofisica de
Canarias used for two-dimensional, high spatial resolution, solar
spectroscopy. Slit spectra have been taken, using the Correlation
Tracker as a stabilizer (minimizing image motion during exposures) and
as an accurate positioning device (allowing to precisely locate the
entrance slit of the spectrograph at adjacent positions on the solar
disc). Spectral information is obtained from several solar regions
of different sizes. Granules (including some exploding ones) and
intergranules are clearly resolved. Several sub-arcsecond structures
are undoubtedly distinguished as well. The two-dimensional variation
of several spectral quantities in the solar atmosphere is shown,
demonstrating the power of this technique and its future possibilities.
Title: Empirical granular/intergranular average model atmospheres.
Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Del Toro Iniesta,
J. C.; Collados, M.; Sánchez Almeida, J.
Bibcode: 1996joso.proc..162R
Altcode:
No abstract at ADS
Title: Empirical model of an average solar granule
Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.; Rodriguez Hidalgo,
I.; Collados, M.; Sanchez Almeida, J.
Bibcode: 1996ASPC..109..155R
Altcode: 1996csss....9..155R
No abstract at ADS
Title: On the discovery of the Zeeman effect on the sun and in
the laboratory
Authors: del Toro Iniesta, Jose Carlos
Bibcode: 1996VA.....40..241D
Altcode:
The origin of the discoveries, both on the Sun and in the laboratory,
of the action of a magnetic field on spectral lines—the so-called
Zeeman effect—is studied. The paper embraces the period from 1866,
first date of which the author is aware of observed evidences about the
widening of spectral lines in sunspots (as compared to those formed
in the photosphere), until 1908, year in which the magnetic filed in
sunspots is definitely discovered. The interval between 1896-1897,
and 1908 is mainly dealt with from an astrophysical standpoint,
although there are plenty of important contributions from laboratory
experiments. The reason is two-fold: on the one hand, the significant
role played by the Zeeman effect on the development of quantum mechanics
has suggested major historical studies that have already appeared in
the literature and that are mainly concerned with laboratory—but not
with astrophysical—spectroscopy; on the other hand, the understanding
of the sizeable delay between Zeeman's and Hale's discoveries (12
years) seems to be of concern after accounting for the fact that the
findings by the first author were soon brought to the notice of the
astrophysical community.
Title: LTE polarized radiative transfer through interlaced
atmospheres.
Authors: del Toro Iniesta, J. C.; Ruiz Cobo, B.; Bellot Rubio, L. R.;
Collados, M.
Bibcode: 1995A&A...294..855D
Altcode:
We show that the solution of the radiative transfer equation (RTE)
through a line of sight that pierces several times two alternate
atmospheres can be obtained in terms of the solutions of the RTE
through both single atmospheres separately considered. This also
applies to the response functions of the observed Stokes spectrum
to perturbations of the physical quantities. The analytic solution
of the RTE in case that the single atmospheres are Milne-Eddington
is presented. The simplification of the solution in the case of a
longitudinal or transversal (with constant azimuth) magnetic field
is presented as well. Finally, as a numerical example, we synthesize
the Stokes I- and V-spectrum emerging from a thin magnetic flux tube,
achieving a considerable decrease in computation time with respect to
conventional integrations and without loss of accuracy.
Title: Observed differences between large and small sunspots.
Authors: Collados, M.; Martinez Pillet, V.; Ruiz Cobo, B.; del Toro
Iniesta, J. C.; Vazquez, M.
Bibcode: 1994A&A...291..622C
Altcode:
We confirm recent results about the differences in temperature
and magnetic field strength between the umbra of large and small
sunspots. Five Stokes I- and V-spectra from the darkest cores of
three different umbrae have been analysed with the inversion code
of the radiative transfer equation by Ruiz Cobo & del Toro
Iniesta (1992). The run with depth of temperature, magnetic field
(strength and inclination) and velocity along the line of sight are
obtained. The larger sunspots turn out to be cooler and possesing
a larger magnetic field strength, practically throughout the whole
atmosphere. Neither significant gradients of the line-of-sight velocity,
nor of the magnetic field inclination, are detected in any of the
spots analysed. Two model atmospheres are given corresponding to hot
(small) and cool (large) sunspots. The models are, to a large extent,
free from effects of penumbral/photospheric stray-light because it is
nearly absent in the large spots and because in the small one, where
it is important for the Stokes I-profile, only Stokes V is considered
to obtain the model atmosphere. These are the first umbral models in
the literature for which a simultaneous determination of the magnetic
field and thermodynamic stratifications is presented. The implications
of these stratifications for the energy transport in sunspot umbrae
are discussed.
Title: On the Temperature and Velocity through the Photosphere of
a Sunspot Penumbra
Authors: del Toro Iniesta, J. C.; Tarbell, T. D.; Ruiz Cobo, B.
Bibcode: 1994ApJ...436..400D
Altcode:
We investigate the structure in depth of a sunspot penumbra by means
of the inversion code of the radiative transfer equation proposed
by Ruiz Cobo & del Toro Iniesta (1992), applied to a set of
filtergrams of a sunspot, scanning the Fe I line at 5576.1 A, with
a sampling interval of 30 mA, from -120 to 120 mA from line center
(data previously analyzed by Title et al. 1993). The temperature
structure of this penumbra is obtained for each of the 801 pixels
selected (0.32 sec x 0.32 sec). On the average, the temperatures seem
to decrease as we move inward, but the differences are of the order
of the rms values (approximately equal 100-200 K) at a given distance
to sunspot center. The outer parts of the penumbra have also a bigger
curvature in the T versus log tau5 relation than the inner
parts. We realize, however, that these differences might be influenced
by possible stray light effects. Compared to the quiet Sun, penumbral
temperatures are cooler at deep layers and hotter at high layers. A mean
penumbral model atmosphere is presented. The asymmetries observed in the
intensity profile (the line is magnetically insensitive) are deduced
to be produced by strong gradients of the line-of-sight velocity that
sharply vary spatially along slices of almost constant distance to
sunspot center. These variations suggest that such gradients are not
only needed to explain the broadband circular polarization observed
in sunspots (see Sanchez Almeida & Lites 1992) but are a main
characteristic of the fine-scale penumbra. The results are compatible
with an Evershed flow present everywhere, but its gradient with depth
turns out to vary so that the flow seems to be mainly concentrated in
some penumbral fibrils when studied through Dopplergrams. Finally,
as by-products of this study, we put constraints to the practical
usefulness of the Eddington-Barbier relation, and we explain the values
of the Fourier Dopplergrams to be carrying information of layers around
the centroid of the generalized response function of Dopplergrams to
velocity fluctuations.
Title: On the sensitivity of Stokes profiles to physical quantities.
Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.
Bibcode: 1994A&A...283..129R
Altcode: 1994A&A...283..129C
A thorough analysis of the sensitivities of the four Stokes profiles to
the physical quantities involved in the local thermodynamic equilibrium
(LTE) line formation is presented. We point out the ambiguities
on the definition of a mean depth of formation of a given spectral
line and on the use of Contribution Functions for the ascription of a
measure to a given depth in the atmosphere. Response Functions behave
like partial derivatives of the Stokes spectrum at a given depth
of the atmosphere. They provide the sensitivities of the observed
spectrum to the physical quantities characterizing the state of the
atmosphere. After a theoretical generalization of any measured parameter
over the spectrum, we extend the concept of Response Functions for such
parameters; in detail are discussed the properties and sensitivities
of the equivalent width, the Stokes V peaks distance, the line-ratio
method, and the centre of gravity method. Of particualr interest are
the following results : (1) a constant and longitudinal magnetic field
can desaturate a spectral line with a Zeeman pattern other than a pure
Zeeman triplet; (2) saturation is readily understood as a consequence
of an enhencement of the photon supply; and (3) methods to measure
magnetic field strength are sensitive to temperature variations,
mostly if a field strength gradient is present through the photosphere.
Title: Vertical Stratification of a Sunspot Penumbra
Authors: del Toro Iniesta, J. C.; Tarbell, T. D.; Ruiz Cobo, B.
Bibcode: 1993BAAS...25Q1221D
Altcode:
No abstract at ADS
Title: Inversion of Stokes Profiles
Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.
Bibcode: 1992ApJ...398..375R
Altcode:
An inversion code of Stokes line profiles is presented. It allows
the recovery of the stratification of the temperature, the magnetic
field vector, and the line of sight velocity through the atmosphere,
and the micro- and macroturbulence velocities - which are assumed
to be constant with depth. It is based on the response functions,
which enter a Marquardt nonlinear least-squares algorithm in a natural
way. Response functions are calculated at the same time as the full
radiative transfer equation for polarized light is integrated. This
enables us to obtain values of many free parameters in a reasonable
computation time. Many numerical experiments have been performed in
order to check the behavior of the code. These experiments reveal the
high stability, accuracy, and uniqueness of the results, even when
simulated observations present signal-to-noise ratios of the order of
the lowest acceptable values in real observations.
Title: From Filtergrams to Physical Atmospheric Magnitudes: A
Prospective Diagnostic
Authors: del Toro Iniesta, J. C.; Tarbell, T.; Ruiz Cobo, B.
Bibcode: 1992AAS...181.8115D
Altcode: 1992BAAS...24.1255D
No abstract at ADS
Title: Spectropolarimetry of active regions.
Authors: Del Toro Iniesta, J. C.; Martínez Pillet, V.; Vázquez, M.
Bibcode: 1991sopo.work..224D
Altcode:
A circular analyzer has been used at the focal plane of a telescope in
days of absence of instrumental polarization to simultaneously record
I±V spectrograms at two different wavelength ranges: ≡6300 Å and
≡3930 - 3970 Å. The observations have been analyzed within two,
also different, frames: on the one hand, an empirical relationship
between brightness temperature and the magnetic field strength has been
found for sunspot umbrae, which allows a determination of the Wilson
depression; on the other, estimates of the chromospheric longitudinal
component of the magnetic field (magnetic flux if the filling factor
is not unity) in two umbrae, in a penumbra, and in a plage have been
found by using profiles of the resonance lines H and K of Ca II. A
ratio of order 2 - 3 between the longitudinal components of the field
at the chromospheric height of formation of the Ca II lines and the
photospheric height of formation of the 6302.5 Å Fe I line is also
found in umbrae.
Title: Circular Polarization of the CA II H and K Lines in Solar
Quiet and Active Regions
Authors: Martinez Pillet, V.; Garcia Lopez, R. J.; del Toro Iniesta,
J. C.; Rebolo, R.; Vazquez, M.; Beckman, J. E.; Char, S.
Bibcode: 1990ApJ...361L..81M
Altcode:
A representative set of profiles is presented for the Ca II H resonace
line in Stokes V and I, for the quiet sun, plages, sunspot umbrae,
and a flare, as well as one example of the Ca II K line in a sunspot
penumbra. The degree of polarization is highest in the spots and zero
in the quiet sun, within error limits. The V profile asymmetries are,
however, highest in the flare. The spectra of the Ca II K line are
used to obtain a linear relation between V(lambda) and -dI/d(lambda)
and a value for B(parallel) of 820 + or - 40 G using the weak-field
approximation.
Title: Numerical Test of a New V-Profile Inversion Technique
Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.; Collados, M.;
Sanchez Almeida, J.
Bibcode: 1990Ap&SS.170..113R
Altcode:
The diagnostic method proposed by Landi Degl'Innocenti and Landolfi
(1982), based on the observation of circular polarization, has been
generalized to derive the thermodynamic properties of unresolved
magnetic elements in the solar atmosphere. The final aim is to derive
the height dependence of several parameters of the flux tube atmosphere
(such as temperature, magnetic field and velocity distributions,
macroturbulence and filling factor). We have used a perturbation
method based on the concept of response functions for the Stokes
profiles introduced by Landi Degl'Innocenti and Landi Degl'Innocenti
(1977). We present here the preliminary results of invertingV-profiles
by an iterative standard least-squares technique, which allows to find
the magnetic 1-D atmosphere consistent with simulated data.
Title: Facular points and small-scale magnetic elements
Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.;
Martinez Pillet, V.; Ruiz Cobo, B.
Bibcode: 1990Ap&SS.170....9D
Altcode:
We present spectroscopic observations, with high spatial resolution, of
Ca ii K bright points very near the disc centre. Magnetic concentrations
have been detected in these network (facular) points by only using
intensity profiles of the well-known pair of lines Fe i5250.22 Å and
5247.06 Å. No brightening of these structures with respect to the quiet
photosphere can be ascertained within an accuracy threshold of 1.2%.
Title: Velocity Fields Associated with the Magnetic Component of
Solar Faculae
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.
Bibcode: 1990Ap&SS.170...31S
Altcode:
The StokesV asymmetries observed in solar faculae can be interpreted
by invoking the presence of magnetic and velocity fields variations
along the line-of-sight. By means of a perturbative approach, we
develop the theoretical dependence on magnetic and velocity fields
of the StokesV profile around its zero-crossing point. We find that
the empirical curves of growth for theV zero-crossing point and the
slope, as well as the curve of growth for the integral (previously
derived by Sánchez Almeidaet al., 1989, through the same approach),
are reproduced quite well with a single atmosphere which assumes such
simultaneous variations. The depth dependence of the fields that give
the best fit in our model presents several striking properties which
cannot be released without totally compromising the goodness of the
fit. Namely, the magnetic field strength increases towards the observer
while the downflowing velocity field decreases. Both variations must
occur co-spatially, in the same atmospheric layers. This fact seems to
contradict theoretical models for the fanning out parts of magnetic
concentrations which foresee a sharp separation between a static
magnetic layer and a deep zone with velocity fields. We discuss a
possible solution of such contradiction in terms of a finite optical
thickness of the boundary layer between zones with and without magnetic
field in faculae.
Title: Are small-scale magnetic concentrations spatially coincident
with bright facular points?
Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.;
Martinez Pillet, V.; Ruiz Cobo, B.
Bibcode: 1990A&A...233..570D
Altcode:
The usually assumed identification of small-scale magnetic
concentrations with bright facular or network points on the photosphere
is observationally checked by using high spatial resolution spectra
of Ca II K bright points very near the disk center. The detection of
spatially unresolved magnetic structures is made via a new differential
analysis of the well-known pair of Fe I lines 5247.06 A and 5250.22
A; these concentrations are present in the central part of a line
weakening zone, which is of some 2 arcsec wide. No continuum intensity
enhancement with respect to the quiet photosphere can be ascertained of
these structures, within an accuracy threshold of 1.2 percent. In spite
of this, magnetic concentrations brighter than the quiet photosphere
are compatible with the observations, but if so, they must be narrower
than 0.2 arcsec.
Title: Spectropolarimetry of solar faculae - High spatial resolution
results
Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.;
Semel, M.
Bibcode: 1990A&A...227..591D
Altcode:
A new method to measure the magnetic field strength of small-scale
solar magnetic concentrations is presented. It is based on the center
of gravity method (Semel, 1967), is independent of radiative transfer
calculations and only observable parameters are needed. This method
also provides parameters like filling factor (area fraction occupied by
the tubes), continuum intensity contrast between flux tubes and their
surroundings, in a two-component model scheme. The method is applied
to spectropolarimetric high spatial resolution data. Local variations
of the above parameters inside single faculae are found. This result
suggests some indications about flux tube evolution. A comparison with
low spatial resolution results is also made.
Title: On the generation of the net circular polarization observed
in solar faculae
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.
Bibcode: 1989A&A...222..311S
Altcode:
The net circular polarization observed in solar faculae (Stenflo et
al., 1984) follows a law expected from the combination of velocity
and magnetic field gradients in the photosphere. To show this, the
theoretical curve of growth (net circular polarization produced by
a single line versus its absorption coefficient) predicted by this
mechanism is developed. An empirical curve of growth with more than
80 Fe I lines is also constructed. The agreement between theory and
observation seems to point toward this mechanism as responsible for
circular polarization in faculae at the disk center.
Title: Les facules solaires ou comment observer l'invisible.
Authors: Sanchez Almeida, J.; Collados, M.; Del Toro Iniesta, J. C.
Bibcode: 1989Rech...20..810S
Altcode: 1989Rech...20..810A
No abstract at ADS
Title: An explanation for the Stokes V asymmetry in solar faculae
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.
Bibcode: 1988A&A...201L..37S
Altcode:
The asymmetry in the Stokes V profile observed in solar faculae
can be explained by assuming that the magnetic field increases with
height while downflow speed decreases. The MHD compatibility of such
solution is briefly discussed together with an observational test for
that possibility.
Title: Magnetic field strength in solar flux tubes - A model
atmosphere independent determination
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.;
Solanki, S. K.
Bibcode: 1988A&A...196..266S
Altcode:
The "line ratio method" (Stenflo, 1973) has been extensively used in
the past to carry out measurements of the magnetic field strength in
spatially unresolved magnetic flux concentrations. The authors present
here a new variant of this technique, which is particularly simple as
it does not depend on any radiative transfer calculations and thus the
assumption of a model atmosphere is not required. General properties
of the transfer equation lead to a relationship between the circular
polarization generated by two lines which are identical except for
their Landé factors. This can be used to directly determine the field
strength from the measured line profiles. In order to test the method
the authors have applied it to experimental data. A comparison with
the traditional line ratio method is shown.
Title: Photometry of sunspot penumbrae
Authors: Collados, M.; del Toro Iniesta, J. C.; Vazquez, M.
Bibcode: 1988A&A...195..315C
Altcode:
The authors present the results of a statistical analysis of the
penumbra of sunspots. The intensity distribution, and several
parameters derived from it, is analysed at different heliocentric
angles and positions on the spot. It has revealed, on the one hand,
that a two-component model is compatible with the observations and
that both components lie at the same height, and on the other, that
the penumbral asymmetry found by Collados et al. (1987) is confirmed
under a photometrical point of view, the western penumbra being slightly
shorter than the eastern one.
Title: On the Age Dependence of the Asymmetry of Penumbrae of Sunspots
Authors: Collados, M.; del Toro Iniesta, J. C.; Vazquez, M.; Woehl, H.
Bibcode: 1988SoPh..117..199C
Altcode:
The age dependence of the recently described asymmetry of penumbrae
of large stable sunspots was analyzed. Young sunspots showed shorter
eastern penumbrae, which differed by a maximum of ± 10 % from their
mean width. For older sunspots the western penumbrae became smaller
than the mean penumbra reaching differences of 20 % for spots of two
months age.
Title: A Statistical Study of the Geometrical Wilson Effect
Authors: Collados, M.; del Toro Iniesta, J. C.; Vazquez, M.
Bibcode: 1987SoPh..112..281C
Altcode:
An analysis has been carried out of the centre-to-limb variation of the
apparent sizes of the umbra, penumbra and whole spot. It has revealed
that the umbral size decreases with height. We have interpreted this
result in terms of the penumbral geometrical height scale. A value
of 230 km, which is larger than that of the photosphere or the umbra,
explains the observed decrease. An intrinsic asymmetry in the penumbra
of old sunspots has also been found, the western penumbra being slightly
shorter that the rest of the penumbra. This explains why the inverse
Wilson effect is present, preferentially, in the western hemisphere,
as found in previous investigations. A comparison with other works is
also made.
Title: Observations of the Magnetic Fine Structure of a Facula
Authors: del Toro Iniesta, J. C.; Semel, M.; Collados, M.
Bibcode: 1987rfsm.conf..122D
Altcode:
No abstract at ADS
Title: Continuum intensity and magnetic flux of solar fluxtubes.
Authors: Del Toro Iniesta, J. C.; Semel, M.; Collados, M.; Sánchez
Almeida, J.
Bibcode: 1987PAICz..66..265D
Altcode: 1987eram....1..265D
The continuum contrast between fluxtubes and their quiet background,
and the magnetic flux carried by these magnetic elements, have been
determined at different points of a solar facula, in the frame of a
two-component model from spectropolarimetric observations of 1arcsec
spatial resolution. Local spatial variations of these two parameters
have been obtained.
Title: The Wilson Effect in Sunspots
Authors: Collados, M.; del Toro Iniesta, J. C.; Vázquez, M.
Bibcode: 1987rfsm.conf..183C
Altcode:
An analysis of the center to limb variation of the geometrical
properties of spots has been carried out. It has revealed that spots do
not have a symmetrical behaviour with respect to the centre of solar
disk. Thus, the Wilson effect is not zero at δ = 0°, but at δ ≡
45°W. Moreover, the inverse Wilson effect is the general rule in that
interval, while the normal phenomenon is maximum at a heliocentric
angle of 40° - 50°E.
Title: Intensity profiles in fluxtubes.
Authors: Sanches Almeida, J.; Collados, M.; del Toro Iniesta, J. C.;
Solanki, S. K.
Bibcode: 1987PAICz..66..261S
Altcode: 1987eram....1..261S
Spectroscopic analysis of the light coming from an atmosphere is a
powerful tool for revealing its properties. The problem when using
conventional spectroscopy for solar fluxtubes is their unresolved
character: magnetic and non-magnetic regions of a plage have to be
observed as a whole. With the aim of obtaining the true intensity
spectrum of an unresolved tube, the authors have developed a simple
method which can reconstruct the intensity generated in the magnetic
component. Only observed parameters are used: intensity and circular
polarization in the plage and intensity in the quiet photosphere.
Title: The Intensity Distribution in Sunspot Penumbras
Authors: Collados, M.; del Toro Iniesta, J. C.; Vázquez, M.
Bibcode: 1987rfsm.conf..214C
Altcode:
The intensity distribution of the penumbra at different stages of
evolution has been analyzed. The results have been different for both
evolved and primitive penumbras. While the former present almost
symmetrical, single-peaked histograms, the same does not occur for
the latter, their distributions being, preferentially, asymmetrical
or double-peaked. These results are interpreted in terms of bright
and dark elements. Thus, an evolutionary process has been proposed to
explain the diverse characteristics found at the different stages.
Title: Observations of the magnetic fine structure of a facula.
Authors: Del Toro Iniesta, J. C.; Semel, M.; Collados, M.
Bibcode: 1987rfsm.conf..127D
Altcode:
Simultaneous spectropolarimetric observations of a facula have
been carried out in 10 spectral lines with a spatial resolution of
1arcsec. Local variations of the magnetic field strength and the filling
factor of fluxtubes were obtained. The analysis of the velocities inside
fluxtubes shows that positive and negative Doppler shifts are present,
at the same time, at different points of the facula.