Author name code: riethmueller
ADS astronomy entries on 2022-09-14
author:"Riethmueller, Tino L."
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Title: Polarimetric calibration of the Sunrise UV Spectropolarimeter
and Imager
Authors: Iglesias, F. A.; Feller, A.; Gandorfer, A.; Lagg, A.;
Riethmüller, T. L.; Solanki, S. K.; Katsukawa, Y.; Kubo, M.;
Zucarelli, G.; Sanchez, M.; Sunrise Team
Bibcode: 2022BAAA...63..305I
Altcode:
Sunrise is an optical observatory mounted in a stratospheric balloon,
developed to study magnetic fields in the solar atmosphere with very
high resolution. In its third flight, Sunrise carry the Sunrise UV
Spectropolarimeter and Imager (SUSI), that operates in the 313-430 nm
range, covering thousands of spectral lines not accessible from the
ground and thus largely unexplored. SUSI does not include a polarimetric
calibration unit on board. We report about the development status of
SUSI and the preliminary results of its calibration.
Title: Multi-scale deep learning for estimating horizontal velocity
fields on the solar surface
Authors: Ishikawa, Ryohtaroh T.; Nakata, Motoki; Katsukawa, Yukio;
Masada, Youhei; Riethmüller, Tino L.
Bibcode: 2022A&A...658A.142I
Altcode: 2021arXiv211112518I
Context. The dynamics in the photosphere is governed by the multi-scale
turbulent convection termed as granulation and supergranulation. It is
important to derive three-dimensional velocity vectors to understand the
nature of the turbulent convection and to evaluate the vertical Poynting
flux toward the upper atmosphere. The line-of-sight component of the
velocity can be obtained by observing the Doppler shifts. However,
it is difficult to obtain the velocity component perpendicular to the
line of sight, which corresponds to the horizontal velocity in disk
center observations.
Aims: We present a new method based on a
deep neural network that can estimate the horizontal velocity from
the spatial and temporal variations of the intensity and vertical
velocity. We suggest a new measure for examining the performance of
the method.
Methods: We developed a convolutional neural network
model with a multi-scale deep learning architecture. The method consists
of multiple convolutional kernels with various sizes of receptive
fields, and performs convolution for spatial and temporal axes. The
network is trained with data from three different numerical simulations
of turbulent convection. Furthermore, we introduced a novel coherence
spectrum to assess the horizontal velocity fields that were derived for
each spatial scale.
Results: The multi-scale deep learning method
successfully predicts the horizontal velocities for each convection
simulation in terms of the global correlation coefficient, which is
often used to evaluate the prediction accuracy of the methods. The
coherence spectrum reveals the strong dependence of the correlation
coefficients on the spatial scales. Although the coherence spectra
are higher than 0.9 for large-scale structures, they drastically
decrease to less than 0.3 for small-scale structures, wherein the
global correlation coefficient indicates a high value of approximately
0.95. By comparing the results of the three convection simulations, we
determined that this decrease in the coherence spectrum occurs around
the energy injection scales, which are characterized by the peak of
the power spectra of the vertical velocities.
Conclusions: The
accuracy for the small-scale structures is not guaranteed solely by
the global correlation coefficient. To improve the accuracy on small
scales, it is important to improve the loss function for enhancing
the small-scale structures and to utilize other physical quantities
related to the nonlinear cascade of convective eddies as input data.
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: The SUNRISE UV Spectropolarimeter and imager for SUNRISE III
Authors: Feller, Alex; Gandorfer, Achim; Iglesias, Francisco A.;
Lagg, Andreas; Riethmüller, Tino L.; Solanki, Sami K.; Katsukawa,
Yukio; Kubo, Masahito
Bibcode: 2020SPIE11447E..AKF
Altcode:
Sunrise is a balloon-borne solar observatory dedicated to the
investigation of key processes of the magnetic field and the plasma
flows in the lower solar atmosphere. The observatory operates in
the stratosphere at an altitude of around 37 km in order to avoid
image degradation due to turbulence in the Earth's atmosphere and to
access the UV range. The third science flight of Sunrise will carry new
instrumentation which samples the solar spectrum over a broad wavelength
domain from the UV to the near IR and covers an extended height range in
the solar atmosphere. A key feature of the Sunrise UV Spectropolarimeter
and Imager (SUSI) operating between 309 nm and 417 nm, is its capability
to simultaneously record a large number of spectral lines. By combining
the spectral and polarization information of many individual lines
with different formation heights and sensitivities, the accuracy and
the height resolution of the inferred atmospheric parameters can be
significantly increased. The spectral bands of SUSI are selected one
at a time by rotating a diffraction grating with respect to a fixed
polarimetry unit. The spatial and spectral field of view on the 2k x
2k cameras is 59" and 2.0 - 2.3 nm, respectively. A further innovation
is the numerical restoration of the spectrograph scans by means of
synchronized 2D context imaging, a technique that has recently produced
impressive results at ground-based solar observatories.
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: 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: 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: Science Requirement Document (SRD) for the European Solar
Telescope (EST) (2nd edition, December 2019)
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.;
Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.;
Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse,
K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.;
Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller,
T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno,
J.; Utz, D.; Zuccarello, F.
Bibcode: 2019arXiv191208650S
Altcode:
The European Solar Telescope (EST) is a research infrastructure
for solar physics. It is planned to be an on-axis solar telescope
with an aperture of 4 m and equipped with an innovative suite of
spectro-polarimetric and imaging post-focus instrumentation. The EST
project was initiated and is driven by EAST, the European Association
for Solar Telescopes. EAST was founded in 2006 as an association
of 14 European countries. Today, as of December 2019, EAST consists
of 26 European research institutes from 18 European countries. The
Preliminary Design Phase of EST was accomplished between 2008 and
2011. During this phase, in 2010, the first version of the EST Science
Requirement Document (SRD) was published. After EST became a project
on the ESFRI roadmap 2016, the preparatory phase started. The goal
of the preparatory phase is to accomplish a final design for the
telescope and the legal governance structure of EST. A major milestone
on this path is to revisit and update the Science Requirement Document
(SRD). The EST Science Advisory Group (SAG) has been constituted by
EAST and the Board of the PRE-EST EU project in November 2017 and has
been charged with the task of providing with a final statement on the
science requirements for EST. Based on the conceptual design, the SRD
update takes into account recent technical and scientific developments,
to ensure that EST provides significant advancement beyond the current
state-of-the-art. The present update of the EST SRD has been developed
and discussed during a series of EST SAG meetings. The SRD develops
the top-level science objectives of EST into individual science
cases. Identifying critical science requirements is one of its main
goals. Those requirements will define the capabilities of EST and the
post-focus instrument suite. The technical requirements for the final
design of EST will be derived from the SRD.
Title: Moving Magnetic Features around a Pore
Authors: Kaithakkal, A.; Riethmueller, T.; Solanki, S. K.; Lagg, A.
Bibcode: 2019ASPC..526..307K
Altcode:
Moving magnetic features (MMFs) are small-scale magnetic elements
observed to move radially outward from sunspots. Some studies have
reported the presence of MMFs around pores as well. We analyzed data
from SunriseII/IMaX observations obtained on 2013 June 12 between
23:39:10 and 23:55:37 UT. IMaX scanned the Fe I 5250.225 Å spectral
line at eight wavelength positions and recorded the full Stokes vector
at each of these positions. The field of view covered a large pore
(μ = 0.93) with pixel scale of 0″.055. MMFs of opposite (positive)
and same (negative) polarity as the pore were observed to stream
from the pore boundary. We carried out a statistical analysis of the
physical properties of MMFs and the main results are: 1) the number
of opposite polarity MMFs within 1.5 Mm from the pore border, when
they were first identified, is twice that of the same polarity MMFs. 2)
Only 11% of the chosen MMFs appear to be monopolar and they all have the
same polarity as the pore. 3) Majority of MMFs of both polarities move
away from the pore border with an average speed of 1.5 km/s. However,
they do not always follow a smooth radial track and some of them even
move in tangential direction to the pore. 4) MMFs of opposite polarity
show a preferential up-flow whereas those of the same polarity do not
show any preference. 5) MMFs of both polarities are characterized by
inclined fields. This work, presented in an oral contribution
at this Workshop, has been published on The Astrophysical Journal
Supplement Series (Kaithakkal et al. 2017).
Title: The potential of many-line inversions of photospheric
spectropolarimetric data in the visible and near UV
Authors: Riethmüller, T. L.; Solanki, S. K.
Bibcode: 2019A&A...622A..36R
Altcode: 2018arXiv181203757R
Our knowledge of the lower solar atmosphere is mainly obtained from
spectropolarimetric observations, which are often carried out in the red
or infrared spectral range and almost always cover only a single or a
few spectral lines. Here we compare the quality of Stokes inversions of
only a few spectral lines with many-line inversions. In connection with
this, we have also investigated the feasibility of spectropolarimetry
in the short-wavelength range, 3000 Å-4300 Å, where the line density
but also the photon noise are considerably higher than in the red,
so that many-line inversions could be particularly attractive in
that wavelength range. This is also timely because this wavelength
range will be the focus of a new spectropolarimeter in the third
science flight of the balloon-borne solar observatory SUNRISE. For
an ensemble of state-of-the-art magneto-hydrodynamical atmospheres we
synthesize exemplarily spectral regions around 3140 Å (containing 371
identified spectral lines), around 4080 Å (328 lines), and around
6302 Å (110 lines). The spectral coverage is chosen such that at a
spectral resolving power of 150 000 the spectra can be recorded by a
2K × 2K detector. The synthetic Stokes profiles are degraded with a
typical photon noise and afterward inverted. The atmospheric parameters
of the inversion of noisy profiles are compared with the inversion
of noise-free spectra. We find that significantly more information
can be obtained from many-line inversions than from a traditionally
used inversion of only a few spectral lines. We further find that
information on the upper photosphere can be significantly more reliably
obtained at short wavelengths. In the mid and lower photosphere, the
many-line approach at 4080 Å provides equally good results as the
many-line approach at 6302 Å for the magnetic field strength and the
line-of-sight (LOS) velocity, while the temperature determination is
even more precise by a factor of three. We conclude from our results
that many-line spectropolarimetry should be the preferred option in
the future, and in particular at short wavelengths it offers a high
potential in solar physics.
Title: Intensity contrast of solar plage as a function of magnetic
flux at high spatial resolution
Authors: Kahil, F.; Riethmüller, T. L.; Solanki, S. K.
Bibcode: 2019A&A...621A..78K
Altcode: 2018arXiv181105759K
Magnetic elements have an intensity contrast that depends on the type
of region they are located in (for example quiet Sun, or active region
plage). Observed values also depend on the spatial resolution of the
data. Here we investigate the contrast-magnetic field dependence in
active region plage observed near disk center with SUNRISE during
its second flight in 2013. The wavelengths under study range from
the visible at 525 nm to the near ultraviolet (NUV) at 300 nm and
397 nm. We use quasi-simultaneous spectropolarimetric and photometric
data from the Imaging Magnetograph eXperiment (IMaX) and the Sunrise
Filter Imager (SuFI), respectively. We find that in all wavelength
bands, the contrast exhibits a qualitatively similar dependence on
the line-of-sight magnetic field, BLOS, as found in the
quiet Sun, with the exception of the continuum at 525 nm. There, the
contrast of plage magnetic elements peaks for intermediate values of
BLOS and decreases at higher field strengths. By comparison,
the contrast of magnetic elements in the quiet Sun saturates at its
maximum value at large BLOS. We find that the explanation
of the turnover in contrast in terms of the effect of finite spatial
resolution of the data is incorrect with the evidence provided by the
high-spatial resolution SUNRISE data, as the plage magnetic elements are
larger than the quiet Sun magnetic elements and are well-resolved. The
turnover comes from the fact that the core pixels of these larger
magnetic elements are darker than the quiet Sun. We find that plages
reach lower contrast than the quiet Sun at disk center at wavelength
bands formed deep in the photosphere, such as the visible continuum
and the 300 nm band. This difference decreases with formation height
and disappears in the Ca II H core, in agreement with empirical models
of magnetic element atmospheres.
Title: Linear Polarization Features in the Quiet-Sun Photosphere:
Structure and Dynamics
Authors: Kianfar, S.; Jafarzadeh, S.; Mirtorabi, M. T.; Riethmüller,
T. L.
Bibcode: 2018SoPh..293..123K
Altcode: 2018arXiv180704633K
We present detailed characteristics of linear polarization features
(LPFs) in the quiet-Sun photosphere from high-resolution observations
obtained with SUNRISE/IMaX. We explore differently treated data
with various noise levels in linear polarization signals, from which
structure and dynamics of the LPFs are studied. Physical properties
of the detected LPFs are also obtained from the results of Stokes
inversions. The number of LPFs and their sizes and polarization signals
are found to be strongly dependent on the noise level and on the spatial
resolution. While the linear polarization with a signal-to-noise ratio
≥4.5 covers about 26% of the entire area in the least noisy data in
our study (with a noise level of 1.7 ×10−4 in the unit of
Stokes I continuum), the detected (spatially resolved) LPFs cover about
10% of the area at any given time, with an occurrence rate on the order
of 8 ×10−3s−1 arcsec−2. The LPFs
were found to be short lived (in the range of 30 - 300 s), relatively
small structures (radii of ≈0.1 - 1.5 arcsec), highly inclined,
posing hG fields, and they move with an average horizontal speed of
1.2 km s−1. The LPFs were observed (almost) equally on
both upflow and downflow regions, with an intensity contrast always
larger than that of the average quiet Sun.
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: 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: The Small-scale Structure of Photospheric Convection Retrieved
by a Deconvolution Technique Applied to Hinode/SP Data
Authors: Oba, T.; Riethmüller, T. L.; Solanki, S. K.; Iida, Y.;
Quintero Noda, C.; Shimizu, T.
Bibcode: 2017ApJ...849....7O
Altcode: 2017arXiv170906933O
Solar granules are bright patterns surrounded by dark channels, called
intergranular lanes, in the solar photosphere and are a manifestation of
overshooting convection. Observational studies generally find stronger
upflows in granules and weaker downflows in intergranular lanes. This
trend is, however, inconsistent with the results of numerical
simulations in which downflows are stronger than upflows through the
joint action of gravitational acceleration/deceleration and pressure
gradients. One cause of this discrepancy is the image degradation caused
by optical distortion and light diffraction and scattering that takes
place in an imaging instrument. We apply a deconvolution technique to
Hinode/SP data in an attempt to recover the original solar scene. Our
results show a significant enhancement in both the convective upflows
and downflows but particularly for the latter. After deconvolution,
the up- and downflows reach maximum amplitudes of -3.0 km s-1
and +3.0 km s-1 at an average geometrical height of roughly
50 km, respectively. We found that the velocity distributions after
deconvolution match those derived from numerical simulations. After
deconvolution, the net LOS velocity averaged over the whole field of
view lies close to zero as expected in a rough sense from mass balance.
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: Estimation of the Magnetic Flux Emergence Rate in the Quiet
Sun from Sunrise Data
Authors: Smitha, H. N.; Anusha, L. S.; Solanki, S. K.; Riethmüller,
T. L.
Bibcode: 2017ApJS..229...17S
Altcode: 2016arXiv161106432S
Small-scale internetwork (IN) features are thought to be the major
source of fresh magnetic flux in the quiet Sun. During its first science
flight in 2009, the balloon-borne observatory Sunrise captured images of
the magnetic fields in the quiet Sun at a high spatial resolution. Using
these data we measure the rate at which the IN features bring magnetic
flux to the solar surface. In a previous paper it was found that the
lowest magnetic flux in small-scale features detected using the Sunrise
observations is 9 × 1014 Mx. This is nearly an order of
magnitude smaller than the smallest fluxes of features detected in
observations from the Hinode satellite. In this paper, we compute the
flux emergence rate (FER) by accounting for such small fluxes, which
was not possible before Sunrise. By tracking the features with fluxes
in the range {10}15{--}{10}18 Mx, we measure an
FER of 1100 {Mx} {{cm}}-2 {{day}}-1. The smaller
features with fluxes ≤slant {10}16 Mx are found to be the
dominant contributors to the solar magnetic flux. The FER found here
is an order of magnitude higher than the rate from Hinode, obtained
with a similar feature tracking technique. A wider comparison with the
literature shows, however, that the exact technique of determining the
rate of the appearance of new flux can lead to results that differ by
up to two orders of magnitude, even when applied to similar data. The
causes of this discrepancy are discussed and first qualitative
explanations proposed.
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: Brightness of Solar Magnetic Elements As a Function of Magnetic
Flux at High Spatial Resolution
Authors: Kahil, F.; Riethmüller, T. L.; Solanki, S. K.
Bibcode: 2017ApJS..229...12K
Altcode: 2017arXiv170100759K
We investigate the relationship between the photospheric magnetic
field of small-scale magnetic elements in the quiet-Sun (QS) at disk
center and the brightness at 214, 300, 313, 388, 397, and 525.02
nm. To this end, we analyzed spectropolarimetric and imaging time
series acquired simultaneously by the Imaging Magnetograph eXperiment
magnetograph and the SuFI filter imager on board the balloon-borne
observatory {{S}}{{UNRISE}} during its first science flight in 2009,
with high spatial and temporal resolution. We find a clear dependence
of the contrast in the near ultraviolet and the visible on the
line-of-sight component of the magnetic field, B LOS, which
is best described by a logarithmic model. This function effectively
represents the relationship between the Ca II H-line emission and
B LOS and works better than the power-law fit adopted
by previous studies. This, along with the high contrast reached
at these wavelengths, will help with determining the contribution
of small-scale elements in the QS to the irradiance changes for
wavelengths below 388 nm. At all wavelengths, including the continuum
at 525.40 nm, the intensity contrast does not decrease with increasing
B LOS. This result also strongly supports the fact that
{{S}}{{UNRISE}} has resolved small strong magnetic field elements in the
internetwork, resulting in constant contrasts for large magnetic fields
in our continuum contrast at 525.40 nm versus the B LOS
scatterplot, unlike the turnover obtained in previous observational
studies. This turnover is due to the intermixing of the bright magnetic
features with the dark intergranular lanes surrounding them.
Title: The dark side of solar photospheric G-band bright points
Authors: Riethmüller, T. L.; Solanki, S. K.
Bibcode: 2017A&A...598A.123R
Altcode: 2016arXiv161207887R
Bright, small-scale magnetic elements found mainly in intergranular
lanes at the solar surface are named bright points (BPs). They show
high contrasts in Fraunhofer G-band observations and are described
by nearly vertical slender flux tubes or sheets. A recent comparison
between BP observations in the ultraviolet (UV) and visible spectral
range recorded with the balloon-borne observatory Sunrise and
state-of-the-art magnetohydrodynamical (MHD) simulations revealed
a kilogauss magnetic field for 98% of the synthetic BPs. Here we
address the opposite question, namely which fraction of pixels hosting
kilogauss fields coincides with an enhanced G-band brightness. We
carried out 3D radiation MHD simulations for three magnetic activity
levels (corresponding to the quiet Sun, weak and strong plage)
and performed a full spectral line synthesis in the G-band. Only 7%
of the kilogauss pixels in our quiet-Sun simulation coincide with a
brightness lower than the mean quiet-Sun intensity, while 23% of the
pixels in the weak-plage simulation and even 49% in the strong-plage
simulation are associated with a local darkening. Dark strong-field
regions are preferentially found in the cores of larger flux patches
that are rare in the quiet Sun, but more common in plage regions,
often in the vertices of granulation cells. The significant brightness
shortfall in the core of larger flux patches coincides with a slight
magnetic field weakening. Kilogauss elements in the quiet Sun are,
on average, brighter than similar features in plage regions. Almost
all strong-field pixels display a more or less vertical magnetic field
orientation. Hence, in the quiet Sun, G-band BPs correspond almost
one-to-one with kilogauss elements. In weak plage, the correspondence
is still very good, but not perfect.
Title: Flux emergence rate in the quiet Sun from Sunrise data
Authors: Smitha, H. N.; Anusha, L. S.; Solanki, S. K.; Riethmüller,
T. L.
Bibcode: 2017psio.confE.106S
Altcode:
No abstract at ADS
Title: Probing deep photospheric layers of the quiet Sun with high
magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
Schmidt, D.; Kiess, C.; Nicklas, H.
Bibcode: 2016A&A...596A...6L
Altcode: 2016arXiv160506324L
Context. Investigations of the magnetism of the quiet Sun are hindered
by extremely weak polarization signals in Fraunhofer spectral
lines. Photon noise, straylight, and the systematically different
sensitivity of the Zeeman effect to longitudinal and transversal
magnetic fields result in controversial results in terms of the strength
and angular distribution of the magnetic field vector.
Aims:
The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
spatial straylight and photon noise into account.
Methods: Highly
sensitive full Stokes measurements of a quiet-Sun region at disk center
in the deep photospheric Fe I lines in the 1.56 μm region were obtained
with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
diagnostics based directly on the shape and strength of the profiles
were applied to the GRIS data. We made use of the magnetic line ratio
technique, which was tested against realistic magneto-hydrodynamic
simulations (MURaM).
Results: About 80% of the GRIS spectra
of a very quiet solar region show polarimetric signals above a 3σ
level. Area and amplitude asymmetries agree well with small-scale
surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields.
Conclusions:
The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
are so far unique in the combination of high spatial resolution scans
and high magnetic field sensitivity. Nevertheless, the unavoidable
effect of spatial straylight and the resulting dilution of the weak
Stokes profiles means that inversion techniques still bear a high risk
of misinterpretating the data.
Title: Sunrise Mission Highlights
Authors: Riethmüller, Tino L.; Solanki, Sami K.
Bibcode: 2015arXiv151103487R
Altcode:
Solar activity is controlled by the magnetic field, which also causes
the variability of the solar irradiance that in turn is thought to
influence the climate on Earth. The magnetic field manifests itself
in the form of structures of different sizes, starting with sunspots
(10-50 Mm) down to the smallest known magnetic features that often
have spatial extents of 100 km or less. The study of the fine scale
structure of the Sun's magnetic field has been hampered by the limited
spatial resolution of the available observations. This has recently
changed thanks to new space and ground-based telescopes. A significant
step forward has been taken by the Sunrise observatory, built around
the largest solar telescope to leave the ground, and containing two
science instruments. Sunrise had two successful long-duration science
flights on a stratospheric balloon in June 2009 (solar activity minimum)
and in June 2013 (at a high activity level) and a number of scientific
results have been obtained that have greatly advanced our understanding
of solar magnetism, with data analysis still ongoing. After a brief
introduction to the Sunrise mission, an overview of a selection of
these results will be given.
Title: Comparison of solar photospheric bright points between Sunrise
observations and MHD simulations
Authors: Riethmüller, T. L.; Solanki, S. K.; Berdyugina, S. V.;
Schüssler, M.; Martínez Pillet, V.; Feller, A.; Gandorfer, A.;
Hirzberger, J.
Bibcode: 2014A&A...568A..13R
Altcode: 2014arXiv1406.1387R
Bright points (BPs) in the solar photosphere are thought to be the
radiative signatures (small-scale brightness enhancements) of magnetic
elements described by slender flux tubes or sheets located in the darker
intergranular lanes in the solar photosphere. They contribute to the
ultraviolet (UV) flux variations over the solar cycle and hence may
play a role in influencing the Earth's climate. Here we aim to obtain
a better insight into their properties by combining high-resolution
UV and spectro-polarimetric observations of BPs by the Sunrise
Observatory with 3D compressible radiation magnetohydrodynamical
(MHD) simulations. To this end, full spectral line syntheses are
performed with the MHD data and a careful degradation is applied
to take into account all relevant instrumental effects of the
observations. In a first step it is demonstrated that the selected
MHD simulations reproduce the measured distributions of intensity at
multiple wavelengths, line-of-sight velocity, spectral line width,
and polarization degree rather well. The simulated line width also
displays the correct mean, but a scatter that is too small. In
the second step, the properties of observed BPs are compared with
synthetic ones. Again, these are found to match relatively well,
except that the observations display a tail of large BPs with strong
polarization signals (most likely network elements) not found in the
simulations, possibly due to the small size of the simulation box. The
higher spatial resolution of the simulations has a significant effect,
leading to smaller and more numerous BPs. The observation that most BPs
are weakly polarized is explained mainly by the spatial degradation,
the stray light contamination, and the temperature sensitivity of the Fe
i line at 5250.2 Å. Finally, given that the MHD simulations are highly
consistent with the observations, we used the simulations to explore
the properties of BPs further. The Stokes V asymmetries increase with
the distance to the center of the mean BP in both observations and
simulations, consistent with the classical picture of a production
of the asymmetry in the canopy. This is the first time that this has
been found also in the internetwork. More or less vertical kilogauss
magnetic fields are found for 98% of the synthetic BPs underlining
that basically every BP is associated with kilogauss fields. At the
continuum formation height, the simulated BPs are on average 190 K
hotter than the mean quiet Sun, the mean BP field strength is found to
be 1750 G, and the mean inclination is 17°, supporting the physical
flux-tube paradigm to describe BPs. On average, the synthetic BPs
harbor downflows increasing with depth. The origin of these downflows
is not yet understood very well and needs further investigation.
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: Sunrise Mission Highlights
Authors: Riethmüller, T.; Solanki, S. K.; Sunrise Team
Bibcode: 2014frap.confE..34R
Altcode: 2014PoS...237E..34R
No abstract at ADS
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: Investigations of small-scale magnetic features on the
solar surface
Authors: Riethmüller, T. L.
Bibcode: 2013PhDT.........6R
Altcode: 2013arXiv1307.2410R
Solar activity is controlled by the magnetic field, which also causes
the variability of the solar irradiance that in turn is thought to
influence the climate on Earth. The magnetic field manifests itself
in the form of structures of largely different sizes. This thesis
concentrates on two types of the smallest known magnetic features:
The first part studies the properties of umbral dots, dot-like
bright features in the dark umbra of a sunspot. The obtained umbral
dot properties provide a remarkable confirmation of the results of
recent magneto-hydrodynamical simulations. Observations as well as
simulations show that umbral dots differ from their surroundings
mainly in the lowest photospheric layers, where the temperature
is enhanced and the magnetic field is weakened. In addition, the
interior of the umbral dots displays strong upflow velocities which
are surrounded by weak downflows. This qualitative agreement further
strengthens the interpretation of umbral dots as localized columns of
overturning convection. The second part of the thesis investigates
bright points, which are small-scale brightness enhancements
in the darker intergranular lanes of the quiet Sun produced by
magnetic flux concentrations. Observational data obtained by the
balloon-borne solar telescope SUNRISE are used in this thesis. For
the first time contrasts of bright points in the important ultraviolet
spectral range are determined. A comparison of observational data with
magneto-hydrodynamical simulations revealed a close correspondence, but
only after effects due to the limited spectral and spatial resolution
were carefully included. 98% of the synthetic bright points are found
to be associated with a nearly vertical kilo-Gauss field.
Title: Vertical flows and mass flux balance of sunspot umbral dots
Authors: Riethmüller, T. L.; Solanki, S. K.; van Noort, M.; Tiwari,
S. K.
Bibcode: 2013A&A...554A..53R
Altcode: 2013arXiv1305.1164R
A new Stokes inversion technique that greatly reduces the effect of the
spatial point spread function of the telescope is used to constrain
the physical properties of umbral dots (UDs). The depth-dependent
inversion of the Stokes parameters from a sunspot umbra recorded
with Hinode SOT/SP revealed significant temperature enhancements and
magnetic field weakenings in the core of the UDs in deep photospheric
layers. Additionally, we found upflows of around 960 m/s in peripheral
UDs (i.e., UDs close to the penumbra) and ≈600 m/s in central UDs. For
the first time, we also detected systematic downflows for distances
larger than 200 km from the UD center that balance the upflowing mass
flux. In the upper photosphere, we found almost no difference between
the UDs and their diffuse umbral background.
Title: Investigations of small-scale magnetic features on the
solar surface
Authors: Riethmüller, Tino L.
Bibcode: 2013PhDT.......354R
Altcode:
No abstract at ADS
Title: Structure and dynamics of isolated internetwork Ca II H bright
points observed by SUNRISE
Authors: Jafarzadeh, S.; Solanki, S. K.; Feller, A.; Lagg, A.;
Pietarila, A.; Danilovic, S.; Riethmüller, T. L.; Martínez Pillet, V.
Bibcode: 2013A&A...549A.116J
Altcode: 2012arXiv1211.4836J
Aims: We aim to improve our picture of the low chromosphere in
the quiet-Sun internetwork by investigating the intensity, horizontal
velocity, size and lifetime variations of small bright points (BPs;
diameter smaller than 0.3 arcsec) observed in the Ca II H 3968 Å
passband along with their magnetic field parameters, derived from
photospheric magnetograms.
Methods: Several high-quality
time series of disc-centre, quiet-Sun observations from the Sunrise
balloon-borne solar telescope, with spatial resolution of around 100
km on the solar surface, have been analysed to study the dynamics
of BPs observed in the Ca II H passband and their dependence on the
photospheric vector magnetogram signal.
Results: Parameters such
as horizontal velocity, diameter, intensity and lifetime histograms of
the isolated internetwork and magnetic Ca II H BPs were determined. Mean
values were found to be 2.2 km s-1, 0.2 arcsec (≈150 km),
1.48 ⟨ ICa ⟩ and 673 s, respectively. Interestingly, the
brightness and the horizontal velocity of BPs are anti-correlated. Large
excursions (pulses) in horizontal velocity, up to 15 km s-1,
are present in the trajectories of most BPs. These could excite kink
waves travelling into the chromosphere and possibly the corona, which we
estimate to carry an energy flux of 310 W m-2, sufficient to
heat the upper layers, although only marginally.
Conclusions:
The stable observing conditions of Sunrise and our technique for
identifying and tracking BPs have allowed us to determine reliable
parameters of these features in the internetwork. Thus we find, e.g.,
that they are considerably longer lived than previously thought. The
large velocities are also reliable, and may excite kink waves. Although
these wave are (marginally) energetic enough to heat the quiet corona,
we expect a large additional contribution from larger magnetic elements
populating the network and partly also the internetwork.
Title: First Results from the SUNRISE Mission
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
Gandorfer, A.; Hirzberger, J.; Jafarzadeh, S.; Lagg, A.; Riethmüller,
T. L.; Schüssler, M.; Wiegelmann, T.; Bonet, J. A.; González,
M. J. M.; Pillet, V. M.; Khomenko, E.; Yelles Chaouche, L.; Iniesta,
J. C. d. T.; Domingo, V.; Palacios, J.; Knölker, M.; González,
N. B.; Borrero, J. M.; Berkefeld, T.; Franz, M.; Roth, M.; Schmidt,
W.; Steiner, O.; Title, A. M.
Bibcode: 2012ASPC..455..143S
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: 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: Performance validation of phase diversity image reconstruction
techniques
Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Gandorfer,
A.; Solanki, S. K.
Bibcode: 2011A&A...529A.132H
Altcode:
We present a performance study of a phase diversity (PD) image
reconstruction algorithm based on artificial solar images obtained
from MHD simulations and on seeing-free data obtained with the SuFI
instrument on the Sunrise balloon borne observatory. The artificial
data were altered by applying different levels of degradation with
synthesised wavefront errors and noise. The PD algorithm was modified
by changing the number of fitted polynomials, the shape of the pupil and
the applied noise filter. The obtained reconstructions are evaluated by
means of the resulting rms intensity contrast and by the conspicuousness
of appearing artifacts. The results show that PD is a robust method
which consistently recovers the initial unaffected image contents. The
efficiency of the reconstruction is, however, strongly dependent on the
number of used fitting polynomials and the noise level of the images. If
the maximum number of fitted polynomials is higher than 21, artifacts
have to be accepted and for noise levels higher than 10-3
the commonly used noise filtering techniques are not able to avoid
amplification of spurious structures.
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: The Filter Imager SuFI and the Image Stabilization and Light
Distribution System ISLiD of the Sunrise Balloon-Borne Observatory:
Instrument Description
Authors: Gandorfer, A.; Grauf, B.; Barthol, P.; Riethmüller, T. L.;
Solanki, S. K.; Chares, B.; Deutsch, W.; Ebert, S.; Feller, A.;
Germerott, D.; Heerlein, K.; Heinrichs, J.; Hirche, D.; Hirzberger,
J.; Kolleck, M.; Meller, R.; Müller, R.; Schäfer, R.; Tomasch,
G.; Knölker, M.; Martínez Pillet, V.; Bonet, J. A.; Schmidt, W.;
Berkefeld, T.; Feger, B.; Heidecke, F.; Soltau, D.; Tischenberg, A.;
Fischer, A.; Title, A.; Anwand, H.; Schmidt, E.
Bibcode: 2011SoPh..268...35G
Altcode: 2010SoPh..tmp..176G; 2010arXiv1009.1037G
We describe the design of the Sunrise Filter Imager (SuFI) and the
Image Stabilization and Light Distribution (ISLiD) unit onboard the
Sunrise balloon borne solar observatory. This contribution provides the
necessary information which is relevant to understand the instruments'
working principles, the relevant technical data, and the necessary
information about calibration issues directly related to the science
data.
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: 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: 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: Quiet-sun Intensity Contrasts in the Near-ultraviolet as
Measured from SUNRISE
Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Schüssler,
M.; Borrero, J. M.; Afram, N.; Unruh, Y. C.; Berdyugina, S. V.;
Gandorfer, A.; Solanki, S. K.; Barthol, P.; Bonet, J. A.; Martínez
Pillet, V.; Berkefeld, T.; Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.154H
Altcode:
We present high-resolution images of the Sun in the near-ultraviolet
spectral range between 214 nm and 397 nm as obtained from the first
science flight of the 1 m SUNRISE balloon-borne solar telescope. The
quiet-Sun rms intensity contrasts found in this wavelength range are
among the highest values ever obtained for quiet-Sun solar surface
structures—up to 32.8% at a wavelength of 214 nm. We compare the
rms contrasts obtained from the observational data with theoretical
intensity contrasts obtained from numerical magnetohydrodynamic
simulations. For 388 nm and 312 nm the observations agree well with
the numerical simulations whereas at shorter wavelengths discrepancies
between observed and simulated contrasts remain.
Title: Quiet-Sun intensity contrasts in the near ultraviolet
Authors: Hirzberger, Johann; Feller, Alex; Riethmüller, Tino L.;
Schüssler, Manfred; Borrero, Juan M.; Afram, Nadine; Unruh, Yvonne C.;
Berdyugina, Svetlana V.; Gandorfer, Achim; Solanki, Sami K.; Barthol,
Peter; Bonet, Jose A.; Martínez Pillet, Valentin; Berkefeld, Thomas;
Knölker, Michael; Schmidt, Wolfgang; Title, Alan M.
Bibcode: 2010arXiv1009.1050H
Altcode:
We present high-resolution images of the Sun in the near ultraviolet
spectral range between 214 nm and 397 nm as obtained from the first
science flight of the 1-m Sunrise balloon-borne solar telescope. The
quiet-Sun rms intensity contrasts found in this wavelength range
are among the highest values ever obtained for quiet-Sun solar
surface structures - up to 32.8% at a wavelength of 214 nm. We
compare with theoretical intensity contrasts obtained from numerical
magneto-hydrodynamic simulations. For 388 nm and 312 nm the observations
agree well with the numerical simulations whereas at shorter wavelengths
discrepancies between observed and simulated contrasts remain.
Title: High resolution imaging and polarimetry with SUNRISE, a
balloon-borne stratospheric solar observatory
Authors: Barthol, Peter; Chares, Bernd; Deutsch, Werner; Feller, Alex;
Gandorfer, Achim; Grauf, Bianca; Hirzberger, Johann; Meller, Reinhard;
Riethmueller, Tino; Schuessler, Manfred; Solanki, Sami K.; Knoelker,
Michael; Martinez Pillet, Valentin; Schmidt, Wolfgang; Title, Alan
Bibcode: 2010cosp...38.4063B
Altcode: 2010cosp.meet.4063B
SUNRISE is an international collaboration for the development
and operation of a meter-class balloon-borne stratospheric solar
observatory. Prime science goal is the study of structure and dynamics
of the magnetic field in the solar atmosphere and the interaction of
the magnetic field with convective plasma flows. These processes are
studied by high resolution imaging in the UV and polarimetry at visible
wavelengths. The instrument has been successfully launched on June 8,
2009 from ESRANGE, Kiruna, Northern Sweden. During the more than 5
days flight about 1.5 TByte of scientific data were collected. The
paper gives an overview of the instrument and mission, examples of
the scientific output will also be presented. SUNRISE is a joint
project of the Max-Planck-Institut fuer Sonnensystemforschung (MPS),
Katlenburg-Lindau, with the Kiepenheuer-Institut fuer Sonnenphysik
(KIS), Freiburg, the High-Altitude Observatory (HAO), Boulder, the
Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, and
the Spanish IMaX consortium.
Title: The Ultraviolet Filter Imager (SuFI) onboard the Sunrise
balloon-borne solar observatory: Instrument description and first
results
Authors: Gandorfer, Achim; Barthol, Peter; Feller, Alex; Grauf,
Bianca; Hirzberger, Johann; Riethmueller, Tino; Solanki, Sami K.;
Berkefeld, Thomas; Knoelker, Michael; Martinez Pillet, Valentin;
Schmidt, Wolfgang; Title, Alan
Bibcode: 2010cosp...38.4064G
Altcode: 2010cosp.meet.4064G
We describe the design of the near UV filter imager SuFi onboard
Sunrise, which was successfully flown in the stratosphere in June
2009. During its five days flight SuFI captured the highest contrast
images of solar granulation ever. SuFI is a diffraction limited filter
imager with an effective focal length of 121m, working in 5 distinct
wavelength bands between 210nm and 397nm. It is based on a two mirror
modified Schwarzschild microscope, which is integral part of the central
Image stabilization and light Distribution unit (ISLiD) of Sunrise,
which acts as the reimaging optics between the 1m telescope and the
science instruments. The key technical features of the instrument are
presented under the view of the specific demands of balloon-borne
optical systems. First results obtained with the instrument are
presented to demonstrate the capabilities of the instrument.
Title: UV intensity distributions of the quiet Sun observed with
Sunrise
Authors: Hirzberger, Johann; Feller, A.; Riethmueller, T.; Borrero,
J. M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knoelker, M.; Martínez Pillet, V.; Schmidt, W.; Solanki, S.; Title, A.
Bibcode: 2010cosp...38.1735H
Altcode: 2010cosp.meet.1735H
High resolution solar images in the near UV have been obtained with
the Solar UV Filtergraph (SUFI) onboard the Sunrise balloon borne
observatory, amongst others in wavelength regions not accessible
from the ground. We present intensity distributions of the quiet
Sun at different heliocentric angles, from disk center to the solar
limb. These results, obtained in spectral windows at 214 nm, 313 nm
(OH band), 388 nm (CN band) and 396.7 nm (CaIIH), represent an important
validation of numerical models of the solar photosphere and are, thus,
fundamental ingredients for our understanding of the thermal processes
in the solar surface region.
Title: Relation between the Sunrise photospheric magnetic field and
the Ca II H bright features
Authors: Jafarzadeh, Shahin; Hirzberger, J.; Feller, A.; Lagg, A.;
Solanki, S. K.; Pietarila, A.; Danilovic, S.; Riethmueller, T.;
Barthol, P.; Berkefeld, T.; Gandorfer, A.; Knülker, M.; Martínez
Pillet, V.; Schmidt, W.; Schüssler, M.; Title, A.
Bibcode: 2010cosp...38.2856J
Altcode: 2010cosp.meet.2856J
Recent observations from the Sunrise balloon-borne solar telescope
have enabled us to reach an unprecedented high spatial resolution
on the solar surface with the near-ultraviolet photo-spheric and
chromospheric images as well as the magnetograms. We use these high
resolution observations to investigate the structure of the solar
upper photosphere and lower chromosphere as well as their temporal
evolutions. We study the relation between the inter-granular Ca II
397 nm bright structures in images obtained by the Sunrise Filter
Imager (SuFI) and their corresponding photospheric vector magnetic
field computed from the Imaging Magnetogram eXperiment (IMaX)
observations. The targets under study are in a quiet Sun region and
close to disc-centre.
Title: High-resolution spectro-polarimetry of a flaring sunspot
penumbra
Authors: Hirzberger, J.; Riethmüller, T.; Lagg, A.; Solanki, S. K.;
Kobel, P.
Bibcode: 2009A&A...505..771H
Altcode: 2009arXiv0908.3803H
We present simultaneous photospheric and chromospheric observations
of the trailing sunspot in NOAA 10904 during a weak flare eruption
(GOES magnitude B7.8), obtained with the Swedish Solar Telescope
(SST) in La Palma, Canary Islands. High-resolution Ca II H images
show a typical two-ribbon structure that has been hitherto only
known for larger flares, and the flare appears in a confined region
that is discernible by a bright border. The underlying photosphere
shows a disturbed penumbral structure with intersecting branches of
penumbral filaments. High-resolution Doppler- and vector-magnetograms
exhibit oppositely directed Evershed flows and magnetic field vectors
in the individual penumbral branches, resulting in several regions
of magnetic azimuth discontinuity and several islands where the
vertical magnetic field is reversed. The discontinuity regions are
co-spatial with the locations of the onset of the flare ribbons. From
the results, we conclude that the confined flare region is detached
from the global magnetic field structure by a separatrix marked by the
bright border visible in C II H. We further conclude that the islands
of reversed vertical field appear because of flux emergence and that
the strong magnetic shear appearing in the regions of magnetic azimuth
discontinuity triggers the flare. Movies are only available in
electronic form at http://www.aanda.org
Title: Multi-Channel Observations of a Solar Flare
Authors: Hirzberger, J.; Riethmüller, T.; Solanki, S. K.; Kobel, P.
Bibcode: 2009ASPC..405..125H
Altcode:
On August 13, 2006 we performed simultaneous observations in Ca IIH,
G-band and Fe I 6303 Å of a complex sunspot in NOAA~10904 with
the Swedish Solar Telescope (SST) on La Palma, Canary Islands. From
spectro-polarimetric scans through the Fe I line with the tunable
SOUP filter we computed the full Stokes vectors at each pixel of the
field of view. At 8:47 UT a weak flare eruption (GOES class B7.8) was
registered in the line core of Ca IIH. We present the changing magnetic
field and flow topologies in the underneath penumbral photosphere
during the flaring phase. The unmatched spatial resolution of SST
observations allows detailed simultaneous mapping of chromospheric
and photospheric events.
Title: Brightness, distribution, and evolution of sunspot umbral dots
Authors: Riethmüller, T. L.; Solanki, S. K.; Zakharov, V.;
Gandorfer, A.
Bibcode: 2008A&A...492..233R
Altcode: 2008arXiv0812.0477R
Context: Umbral Dots (UDs) are thought to be manifestations
of magnetoconvection in sunspot umbrae. Recent advances in their
theoretical description point to the need for a thorough study of their
properties and evolution based on data with the highest currently
achievable resolution.
Aims: Our UD analysis aims to provide
parameters such as lifetimes, diameters, horizontal velocities, and
peak intensities, as well as the evolution of selected parameters.
Methods: We present a 106-min TiO (705.7 nm) time series of high
spatial and temporal resolution that contains thousands of UDs in
the umbra of a mature sunspot in the active region NOAA 10667 at μ =
0.95. The data were acquired with the 1-m Swedish Solar Telescope (SST)
on La Palma. With the help of a multilevel tracking (MLT) algorithm the
sizes, brightnesses, and trajectories of 12 836 umbral dots were found
and extensively analyzed. The MLT allows UDs with very low contrast to
be reliably identified.
Results: Inside the umbra we determine a
UD filling factor of 11%. The histogram of UD lifetimes is monotonic,
i.e. a UD does not have a typical lifetime. Three quarters of the UDs
lived for less than 150 s and showed no or little motion. The histogram
of the UD diameters exhibits a maximum at 225 km, i.e. most of the
UDs are spatially resolved. UDs display a typical horizontal velocity
of 420 m s-1 and a typical peak intensity of 51% of the
mean intensity of the quiet photosphere, making them on average 20%
brighter than the local umbral background. Almost all mobile UDs (large
birth-death distance) were born close to the umbra-penumbra boundary,
move towards the umbral center, and are brighter than average. Notably
bright and mobile UDs were also observed along a prominent UD chain,
both ends of which are located at the umbra-penumbra boundary. Their
motion started primarily at either of the ends of the chain, continued
along the chain, and ended near the chain's center. We observed the
splitting and merging of UDs and the temporal succession of both. For
the first time the evolution of brightness, size, and horizontal speed
of a typical UD could be determined in a statistically significant
way. Considerable differences between the evolution of central and
peripheral UDs are found, which point to a difference in origin.
Title: Theoretische Modellierung granularer Stroeme in duennen
Roehren mit Langevin-Gleichungen
Authors: Riethmueller, T. L.
Bibcode: 2008MsT..........2R
Altcode: 2008arXiv0812.0924R
This is the final version of the author's diploma thesis written at
the Humboldt University of Berlin in 1995. The topic is the flow of
granular material in narrow vertical pipes, driven by the gravity,
that is described by Langevin equations. Neglecting the interactions,
we can solve the resulting Fokker-Planck equation for the homogeneous
case. The consideration of inelastic collisions leads to a Boltzmann
equation. Assuming local equilibrium, the hydrodynamic equations
lead to the extension of the Langevin equation formalism for the
inhomogeneous case. For certain parameter ranges, our formalism can
also be used to describe traffic flows. We applied stability analyses
to the hydrodynamic equations and found critical densities for the
occurrence of particle clustering. We used numerical simulations of
the Langevin equations to verify our homogeneous solution as well as
the critical densities.
Title: Evidence of convective rolls in a sunspot penumbra
Authors: Zakharov, V.; Hirzberger, J.; Riethmüller, T. L.; Solanki,
S. K.; Kobel, P.
Bibcode: 2008A&A...488L..17Z
Altcode: 2008arXiv0808.2317Z
Aims: We study the recently discovered twisting motion of bright
penumbral filaments with the aim of constraining their geometry and
the associated magnetic field.
Methods: A large sunspot located
40° from disk center was observed at high resolution with the 1-m
Swedish Solar Telescope. Inversions of multi-wavelength polarimetric
data and speckle reconstructed time series of continuum images were
used to determine proper motions, as well as the velocity and magnetic
structure in penumbral filaments.
Results: The continuum movie
reveals apparent lateral motions of bright and dark structures inside
bright filaments oriented parallel to the limb, confirming recent
Hinode results. In these filaments we measure upflows of ≈1.1
km s-1 on their limbward side and weak downflows on
their centerward side. The magnetic field in them is significantly
weaker and more horizontal than in the adjacent dark filaments.
Conclusions: The data indicate the presence of vigorous convective
rolls in filaments with a nearly horizontal magnetic field. These
are separated by filaments harbouring stronger, more vertical
fields. Because of reduced gas pressure, we see deeper into the
latter. When observed near the limb, the disk-centerward side of the
horizontal-field filaments appear bright due to the hot wall effect
known from faculae. We estimate that the convective rolls transport
most of the energy needed to explain the penumbral radiative flux.
Title: Stratification of Sunspot Umbral Dots from Inversion of Stokes
Profiles Recorded by Hinode
Authors: Riethmüller, T. L.; Solanki, S. K.; Lagg, A.
Bibcode: 2008ApJ...678L.157R
Altcode: 2008arXiv0805.4324R
This work aims to constrain the physical nature of umbral dots (UDs)
using high-resolution spectropolarimetry. Full Stokes spectra recorded
by the spectropolarimeter on Hinode of 51 UDs in a sunspot close to the
disk center are analyzed. The height dependence of the temperature,
magnetic field vector, and line-of-sight velocity across each UD
is obtained from an inversion of the Stokes vectors of the two Fe I
lines at 630 nm. No difference is found at higher altitudes [-3 <=
log (τ500) <= - 2] between the UDs and the diffuse
umbral background. Below that level the difference rapidly increases,
so that at the continuum formation level [log (τ500) = 0]
we find on average a temperature enhancement of 570 K, a magnetic field
weakening of 510 G, and upflows of 800 m s-1 for peripheral
UDs, whereas central UDs display an excess temperature of on average
550 K, a field weakening of 480 G, and no significant upflows. The
results for, in particular, the peripheral UDs, including cuts of
magnetic vector and velocity through them, look remarkably similar to
the output of recent radiation MHD simulations. They strongly suggest
that UDs are produced by convective upwellings.