Author name code: kuckein
ADS astronomy entries on 2022-09-14
author:"Kuckein, Christoph"
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Title: The European Solar Telescope
Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.;
Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein,
C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz
Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados,
M.; the EST team
Bibcode: 2022arXiv220710905Q
Altcode:
The European Solar Telescope (EST) is a project aimed at studying
the magnetic connectivity of the solar atmosphere, from the deep
photosphere to the upper chromosphere. Its design combines the knowledge
and expertise gathered by the European solar physics community during
the construction and operation of state-of-the-art solar telescopes
operating in visible and near-infrared wavelengths: the Swedish 1m Solar
Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR,
the French Télescope Héliographique pour l'Étude du Magnétisme
et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope
(DOT). With its 4.2 m primary mirror and an open configuration, EST will
become the most powerful European ground-based facility to study the Sun
in the coming decades in the visible and near-infrared bands. EST uses
the most innovative technological advances: the first adaptive secondary
mirror ever used in a solar telescope, a complex multi-conjugate
adaptive optics with deformable mirrors that form part of the optical
design in a natural way, a polarimetrically compensated telescope design
that eliminates the complex temporal variation and wavelength dependence
of the telescope Mueller matrix, and an instrument suite containing
several (etalon-based) tunable imaging spectropolarimeters and several
integral field unit spectropolarimeters. This publication summarises
some fundamental science questions that can be addressed with the
telescope, together with a complete description of its major subsystems.
Title: Solar Hα excess during Solar Cycle 24 from full-disk
filtergrams of the Chromospheric Telescope
Authors: Diercke, A.; Kuckein, C.; Cauley, P. W.; Poppenhäger, K.;
Alvarado-Gómez, J. D.; Dineva, E.; Denker, C.
Bibcode: 2022A&A...661A.107D
Altcode: 2022arXiv220304357D
Context. The chromospheric Hα spectral line is a strong line in
the spectrum of the Sun and other stars. In the stellar regime,
this spectral line is already used as a powerful tracer of stellar
activity. For the Sun, other tracers, such as Ca II K, are typically
used to monitor solar activity. Nonetheless, the Sun is observed
constantly in Hα with globally distributed ground-based full-disk
imagers.
Aims: The aim of this study is to introduce the imaging
Hα excess and deficit as tracers of solar activity and compare them to
other established indicators. Furthermore, we investigate whether the
active region coverage fraction or the changing Hα excess in the active
regions dominates temporal variability in solar Hα observations.
Methods: We used observations of full-disk Hα filtergrams of the
Chromospheric Telescope and morphological image processing techniques
to extract the imaging Hα excess and deficit, which were derived
from the intensities above or below 10% of the median intensity in
the filtergrams, respectively. These thresholds allowed us to filter
for bright features (plage regions) and dark absorption features
(filaments and sunspots). In addition, the thresholds were used to
calculate the mean intensity ImeanE/D for Hα
excess and deficit regions. We describe the evolution of the Hα excess
and deficit during Solar Cycle 24 and compare it to the mean intensity
and other well established tracers: the relative sunspot number, the
F10.7 cm radio flux, and the Mg II index. In particular, we tried to
determine how constant the Hα excess and number density of Hα excess
regions are between solar maximum and minimum. The number of pixels
above or below the intensity thresholds were used to calculate the area
coverage fraction of Hα excess and deficit regions on the Sun, which
was compared to the imaging Hα excess and deficit and the respective
mean intensities averaged for the length of one Carrington rotation. In
addition, we present the Hα excess and mean intensity variation of
selected active regions during their disk passage in comparison to the
number of pixels of Hα excess regions.
Results: The Hα excess
and deficit follow the behavior of the solar activity over the course
of the cycle. They both peak around solar maximum, whereby the peak
of the Hα deficit is shortly after the solar maximum. Nonetheless,
the correlation of the monthly averages of the Hα excess and deficit
is high with a Spearman correlation of ρ = 0.91. The Hα excess is
closely correlated to the chromospheric Mg II index with a correlation
of 0.95. The highest correlation of the Hα deficit is found with the
F10.7 cm radio flux, with a correlation of 0.89, due to their peaks
after the solar activity maximum. Furthermore, the Hα deficit reflects
the cyclic behavior of polar crown filaments and their disappearance
shortly before the solar maximum. We investigated the mean intensity
distribution for Hα excess regions for solar minimum and maximum. The
shape of the distributions for solar minimum and maximum is very
similar, but with different amplitudes. Furthermore, we found that the
area coverage fraction of Hα excess regions and the Hα excess are
strongly correlated with an overall Spearman correlation of 0.92. The
correlation between the Hα excess and the mean intensity of Hα excess
regions is 0.75. The correlation of the area coverage fraction and the
mean intensity of Hα excess regions is in general relatively low (ρ =
0.45) and only for few active regions is this correlation above 0.7. The
weak correlation between the area coverage fraction and mean intensity
leaves us pessimistic that the degeneracy between these two quantities
can be broken for the modeling of unresolved stellar surfaces.
Title: Observational evidence for two-component distributions
describing solar magnetic bright points
Authors: Berrios Saavedra, Gerardine; Utz, Dominik; Vargas Domínguez,
Santiago; Campos Rozo, José Iván; González Manrique, Sergio Javier;
Gömöry, Peter; Kuckein, Christoph; Balthasar, Horst; Zelina, Peter
Bibcode: 2022A&A...657A..79B
Altcode: 2021arXiv211012404B
Context. High-resolution observations of the solar photosphere reveal
the presence of fine structures, in particular the so-called Magnetic
Bright Points (MBPs), which are small-scale features associated with
strong magnetic field regions of the order of kilogauss (kG). It
is especially relevant to study these magnetic elements, which are
extensively detected in all moments during the solar cycle, in order to
establish their contribution to the behavior of the solar atmosphere,
and ultimately a plausible role within the coronal heating problem.
Aims: Characterisation of size and velocity distributions of MBPs in
the solar photosphere in two different datasets of quiet Sun images
acquired with high-resolution solar instruments i.e. Solar Optical
Telescope SOT/Hinode and the High-resolution Fast Imager HiFI/GREGOR,
in the G-band (4308 Å).
Methods: In order to detect the
MBPs, an automatic segmentation and identification algorithm is
used. Next, the identified features were tracked to measure their
proper motions. Finally, a statistical analysis of hundreds of MBPs is
carried out, generating histograms for areas, diameters and horizontal
velocities.
Results: This work establishes that areas and
diameters of MBPs display log-normal distributions that are well-fitted
by two different components, whereas the velocity vector components
follow Gaussians and the vector magnitude a Rayleigh distribution
revealing again for all vector elements a two component composition.
Conclusions: The results can be interpreted as due to the presence of
two different populations of MBPs in the solar photosphere one likely
related to stronger network magnetic flux elements and the other one
to weaker intranetwork flux elemens. In particular this work concludes
on the effect of the different spatial resolution of GREGOR and Hinode
telescopes, affecting detections and average values.
Title: Multiple Stokes I inversions for inferring magnetic fields
in the spectral range around Cr I 5782 Å
Authors: Kuckein, C.; Balthasar, H.; Quintero Noda, C.; Diercke, A.;
Trelles Arjona, J. C.; Ruiz Cobo, B.; Felipe, T.; Denker, C.; Verma,
M.; Kontogiannis, I.; Sobotka, M.
Bibcode: 2021A&A...653A.165K
Altcode: 2021arXiv210711116K
Aims: In this work, we explore the spectral window containing
Fraunhofer lines formed in the solar photosphere, around the
magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0,
and 5783.8 Å, with Landé g-factors between 1.6 and 2.5. The goal is
to simultaneously analyze 15 spectral lines, comprising Cr I, Cu I,
Fe I, Mn I, and Si I lines, without the use of polarimetry, to infer
the thermodynamic and magnetic properties in strongly magnetized
plasmas using an inversion code.
Methods: Our study is based
on a new setup at the Vacuum Tower Telescope (VTT, Tenerife), which
includes fast spectroscopic scans in the wavelength range around
the Cr I 5781.75 Å line. The oscillator strengths log(gf) of all
spectral lines, as well as their response functions to temperature,
magnetic field, and Doppler velocity, were determined using the Stokes
Inversion based on Response functions (SIR) code. Snapshot 385 of the
enhanced network simulation from the Bifrost code serves to synthesize
all the lines, which are, in turn, inverted simultaneously with SIR to
establish the best inversion strategy. We applied this strategy to VTT
observations of a sunspot belonging to NOAA 12723 on 2018 September
30 and compared the results to full-disk vector field data obtained
with the Helioseismic and Magnetic Imager (HMI).
Results: The
15 simultaneously inverted intensity profiles (Stokes I) delivered
accurate temperatures and Doppler velocities when compared with the
simulations. The derived magnetic fields and inclinations achieve
the best level of accuracy when the fields are oriented along the
line-of-sight (LOS) and less accurate when the fields are transverse to
the LOS. In general, the results appear similar to what is reported in
the HMI vector-field data, although some discrepancies exist.
Conclusions: The analyzed spectral range has the potential to deliver
thermal, dynamic, and magnetic information for strongly magnetized
features on the Sun, such as pores and sunspots, even without the use
of polarimetry. The highest sensitivity of the lines is found in the
lower photosphere, on average, around log τ = −1. The multiple-line
inversions provide smooth results across the whole field of view
(FOV). The presented spectral range and inversion strategy will be
used for future VTT observing campaigns.
Title: Properties of the inner penumbra boundary and temporal
evolution of a decaying sunspot (Corrigendum)
Authors: Benko, M.; González Manrique, S. J.; Balthasar, H.; Gömöry,
P.; Kuckein, C.; Jurčák, J.
Bibcode: 2021A&A...652C...7B
Altcode:
No abstract at ADS
Title: Evidence For Two-component Distributions Describing Magnetic
Bright Points In The Solar Photosphere
Authors: Vargas Domínguez, S.; Berrios Saavedra, G.; Utz, D.;
Campos Rozo, J. I.; González Manrique, S.; Gömöry, Peter; Kuckein,
Christoph; Balthasar, Horst; Zelina, Peter
Bibcode: 2021AAS...23811310V
Altcode:
High-resolution observations of the Sun reveal the presence of Magnetic
Bright Points (MBPs), which are small-scale features associated with
strong magnetic field regions, that are found all over the solar
photosphere. In this work, we characterize some physical properties
and dynamics of MBPs in a quiet Sun region by using time series of
images acquired with the High-resolution Fast Imager HiFI/GREGOR and
Solar Optical Telescope SOT/Hinode in the G-band (4308 Angstrom). An
automated segmentation algorithm is used to identify the MBPs and
track their evolution. The results show observational evidence for
two-component distributions of areas, diameters and velocities, that
can be interpreted as corresponding to different populations of MBPs.
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
Bibcode: 2021SoPh..296...70R
Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
Title: Filigree in the Surroundings of Polar Crown and High-Latitude
Filaments
Authors: Diercke, Andrea; Kuckein, Christoph; Verma, Meetu; Denker,
Carsten
Bibcode: 2021SoPh..296...35D
Altcode: 2020arXiv201204349D
High-resolution observations of polar crown and high-latitude filaments
are scarce. We present a unique sample of such filaments observed in
high-resolution Hα narrow-band filtergrams and broad-band images,
which were obtained with a new fast camera system at the Vacuum Tower
Telescope (VTT), Tenerife, Spain. The Chromospheric Telescope (ChroTel)
provided full-disk context observations in Hα , Ca II K, and He I 10830
Å. The Helioseismic and Magnetic Imager (HMI) and the Atmospheric
Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO)
provided line-of-sight magnetograms and ultraviolet (UV) 1700 Å
filtergrams, respectively. We study filigree in the vicinity of polar
crown and high-latitude filaments and relate their locations to magnetic
concentrations at the filaments' footpoints. Bright points are a well
studied phenomenon in the photosphere at low latitudes, but they were
not yet studied in the quiet network close to the poles. We examine
size, area, and eccentricity of bright points and find that their
morphology is very similar to their counterparts at lower latitudes,
but their sizes and areas are larger. Bright points at the footpoints of
polar crown filaments are preferentially located at stronger magnetic
flux concentrations, which are related to bright regions at the border
of supergranules as observed in UV filtergrams. Examining the evolution
of bright points on three consecutive days reveals that their amount
increases while the filament decays, which indicates they impact the
equilibrium of the cool plasma contained in filaments.
Title: Classification of High-resolution Solar Hα Spectra Using
t-distributed Stochastic Neighbor Embedding
Authors: Verma, Meetu; Matijevič, Gal; Denker, Carsten; Diercke,
Andrea; Dineva, Ekaterina; Balthasar, Horst; Kamlah, Robert;
Kontogiannis, Ioannis; Kuckein, Christoph; Pal, Partha S.
Bibcode: 2021ApJ...907...54V
Altcode: 2020arXiv201113214V
The Hα spectral line is a well-studied absorption line
revealing properties of the highly structured and dynamic solar
chromosphere. Typical features with distinct spectral signatures in
Hα include filaments and prominences, bright active-region plages,
superpenumbrae around sunspots, surges, flares, Ellerman bombs,
filigree, and mottles and rosettes, among others. This study is
based on high-spectral resolution Hα spectra obtained with the
Echelle spectrograph of the Vacuum Tower Telescope (VTT) located at
Observatorio del Teide, Tenerife, Spain. The t-distributed stochastic
neighbor embedding (t-SNE) is a machine-learning algorithm, which
is used for nonlinear dimensionality reduction. In this application,
it projects Hα spectra onto a two-dimensional map, where it becomes
possible to classify the spectra according to results of cloud model
(CM) inversions. The CM parameters optical depth, Doppler width,
line-of-sight velocity, and source function describe properties of
the cloud material. Initial results of t-SNE indicate its strong
discriminatory power to separate quiet-Sun and plage profiles from
those that are suitable for CM inversions. In addition, a detailed
study of various t-SNE parameters is conducted, the impact of seeing
conditions on the classification is assessed, results for various types
of input data are compared, and the identified clusters are linked
to chromospheric features. Although t-SNE proves to be efficient
in clustering high-dimensional data, human inference is required at
each step to interpret the results. This exploratory study provides
a framework and ideas on how to tailor a classification scheme toward
specific spectral data and science questions.
Title: Observational study of chromospheric heating by acoustic waves
Authors: Abbasvand, V.; Sobotka, M.; Švanda, M.; Heinzel, P.;
García-Rivas, M.; Denker, C.; Balthasar, H.; Verma, M.; Kontogiannis,
I.; Koza, J.; Korda, D.; Kuckein, C.
Bibcode: 2020A&A...642A..52A
Altcode: 2020arXiv200802688A
Aims: Our aim is to investigate the role of acoustic and
magneto-acoustic waves in heating the solar chromosphere. Observations
in strong chromospheric lines are analyzed by comparing the deposited
acoustic-energy flux with the total integrated radiative losses.
Methods: Quiet-Sun and weak-plage regions were observed in the Ca
II 854.2 nm and Hα lines with the Fast Imaging Solar Spectrograph
(FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and
in the Hα and Hβ lines with the echelle spectrograph attached
to the Vacuum Tower Telescope on 2018 December 11 and 2019 June
6. The deposited acoustic energy flux at frequencies up to 20 mHz
was derived from Doppler velocities observed in line centers and
wings. Radiative losses were computed by means of a set of scaled
non-local thermodynamic equilibrium 1D hydrostatic semi-empirical
models obtained by fitting synthetic to observed line profiles.
Results: In the middle chromosphere (h = 1000-1400 km), the radiative
losses can be fully balanced by the deposited acoustic energy flux in
a quiet-Sun region. In the upper chromosphere (h > 1400 km), the
deposited acoustic flux is small compared to the radiative losses in
quiet as well as in plage regions. The crucial parameter determining
the amount of deposited acoustic flux is the gas density at a given
height.
Conclusions: The acoustic energy flux is efficiently
deposited in the middle chromosphere, where the density of gas is
sufficiently high. About 90% of the available acoustic energy flux in
the quiet-Sun region is deposited in these layers, and thus it is a
major contributor to the radiative losses of the middle chromosphere. In
the upper chromosphere, the deposited acoustic flux is too low, so that
other heating mechanisms have to act to balance the radiative cooling.
Title: Chromospheric Resonances above Sunspots and Potential
Seismological Applications
Authors: Felipe, Tobias; Kuckein, Christoph; González Manrique,
Sergio Javier; Milic, Ivan; Sangeetha, C. R.
Bibcode: 2020ApJ...900L..29F
Altcode: 2020arXiv200810623F
Oscillations in sunspot umbrae exhibit remarkable differences
between the photosphere and chromosphere. We evaluate two competing
scenarios proposed for explaining those observations: a chromospheric
resonant cavity and waves traveling from the photosphere to upper
atmospheric layers. We have employed numerical simulations to
analyze the oscillations in both models. They have been compared with
observations in the low (Na I D2) and high (He I 10830 Å)
chromosphere. The nodes of the resonant cavity can be detected as
phase jumps or power dips, although the identification of the latter
is not sufficient to claim the existence of resonances. In contrast,
phase differences between velocity and temperature fluctuations reveal
standing waves and unequivocally prove the presence of an acoustic
resonator above umbrae. Our findings offer a new seismic method to probe
active region chromospheres through the detection of resonant nodes.
Title: Determining the dynamics and magnetic fields in He I 10830
Å during a solar filament eruption
Authors: Kuckein, C.; González Manrique, S. J.; Kleint, L.; Asensio
Ramos, A.
Bibcode: 2020A&A...640A..71K
Altcode: 2020arXiv200610473K
Aims: We investigate the dynamics and magnetic properties of
the plasma, including the line-of-sight velocity (LOS) and optical
depth, as well as the vertical and horizontal magnetic fields,
belonging to an erupted solar filament.
Methods: The filament
eruption was observed with the GREGOR Infrared Spectrograph at
the 1.5-meter GREGOR telescope on July 3, 2016. We acquired three
consecutive full-Stokes slit-spectropolarimetric scans in the He
I 10830 Å spectral range. The Stokes I profiles were classified
using the machine learning k-means algorithm and then inverted with
different initial conditions using the HAZEL code.
Results: The
erupting-filament material presents the following physical conditions:
(1) ubiquitous upward motions with peak LOS velocities of ∼73 km
s-1; (2) predominant large horizontal components of the
magnetic field, on average, in the range of 173-254 G, whereas the
vertical components of the fields are much lower, on average between
39 and 58 G; (3) optical depths in the range of 0.7-1.1. The average
azimuth orientation of the field lines between two consecutive
raster scans (<2.5 min) remained constant.
Conclusions:
The analyzed filament eruption belongs to the fast rising phase, with
total velocities of about 124 km s-1. The orientation of the
magnetic field lines does not change from one raster scan to the other,
indicating that the untwisting phase has not yet started. The untwisting
appears to start about 15 min after the beginning of the filament
eruption. Movies attached to Figs. 1 and 3 are available at https://www.aanda.org
Title: High-resolution Spectroscopy of an Erupting Minifilament and
Its Impact on the Nearby Chromosphere
Authors: Kontogiannis, I.; Dineva, E.; Diercke, A.; Verma, M.; Kuckein,
C.; Balthasar, H.; Denker, C.
Bibcode: 2020ApJ...898..144K
Altcode: 2020arXiv200701564K
We study the evolution of a minifilament eruption in a quiet region
at the center of the solar disk and its impact on the ambient
atmosphere. We used high spectral resolution imaging spectroscopy in
Hα acquired by the echelle spectrograph of the Vacuum Tower Telescope,
Tenerife, Spain; photospheric magnetic field observations from the
Helioseismic Magnetic Imager; and UV/EUV imaging from the Atmospheric
Imaging Assembly of the Solar Dynamics Observatory. The Hα line
profiles were noise-stripped using principal component analysis
and then inverted to produce physical and cloud model parameter
maps. The minifilament formed between small-scale, opposite-polarity
magnetic features through a series of small reconnection events, and
it erupted within an hour after its appearance in Hα. Its development
and eruption exhibited similarities to large-scale erupting filaments,
indicating the action of common mechanisms. Its eruption took place in
two phases, namely, a slow rise and a fast expansion, and it produced
a coronal dimming, before the minifilament disappeared. During its
eruption, we detected a complicated velocity pattern, indicative of
a twisted, thread-like structure. Part of its material returned to
the chromosphere, producing observable effects on nearby low-lying
magnetic structures. Cloud model analysis showed that the minifilament
was initially similar to other chromospheric fine structures, in terms
of optical depth, source function, and Doppler width, but it resembled a
large-scale filament on its course to eruption. High spectral resolution
observations of the chromosphere can provide a wealth of information
regarding the dynamics and properties of minifilaments and their
interactions with the surrounding atmosphere.
Title: The dynamics of a solar arch filament system from the
chromosphere to the photosphere
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Diercke, A.; Collados, M.; Gömöry, P.; Zhong, S.; Hou, Y.; Denker, C.
Bibcode: 2020sea..confE.199G
Altcode:
We study the dynamics of plasma along the legs of an arch filament
system (AFS) from the chromosphere to the photosphere, observed with
high-cadence spectroscopic data from two ground-based solar telescopes:
the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph
in the He I 10830 Å range and the Swedish Solar Telescope (La Palma)
using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542
Å and Fe I 6173 Å spectral lines. The temporal evolution of the
draining of the plasma was followed along the legs of a single arch
filament from the chromosphere to the photosphere. The average Doppler
velocities inferred at the upper chromosphere from the He I 10830 Å
triplet reach velocities up to 20-24 km s-1, and in the lower
chromosphere and upper photosphere the Doppler velocities reach up to
11 km s-1 and 1.5 km s-1 in the case of the Ca II
8542 Å and Si I 10827 Å spectral lines, respectively. The evolution
of the Doppler velocities at different layers of the solar atmosphere
(chromosphere and upper photosphere) shows that they follow the same
line-of-sight (LOS) velocity patern, which confirms the observational
evidence that the plasma drains toward the photosphere as proposed in
models of AFSs. The observations and the nonlinear force-free field
(NLFFF) extrapolations demonstrate that the magnetic field loops of
the AFS rise with time.
Title: Chromospheric resonant cavities in umbrae: unequivocal
detection and seismic applications
Authors: Felipe, T.; Kuckein, C.; González Manrique, S. J.; Milic,
I.; Sangeetha, C. R.
Bibcode: 2020sea..confE.196F
Altcode:
Umbral chromospheric oscillations exhibit significant differences
compared to their photospheric counterparts. We evaluate two competing
scenarios proposed for explaining those observations: a chromospheric
resonant cavity and waves traveling from the photosphere to upper
atmospheric layers. The oscillatory signatures of both models have been
determined from numerical simulations, and they have been compared to
observations. We find that a high-frequency peak in the He I 10830 Å
power spectra cannot discriminate between both theories, contrary to the
claims of Jess et al. (2019). In contrast, phase differences between
velocity and temperature fluctuations reveal a standing pattern and
unequivocally prove the presence of an acoustic cavity above umbrae. Our
findings offer a new seismic method to probe sunspot chromospheres
through the identification of resonant nodes in phase spectra.
Title: Determining the dynamics and magnetic fields in the
chromospheric He I 10830 Å triplet during a solar filament eruption
Authors: Kuckein, C.; González Manrique, S. J.; Kleint, L.; Asensio
Ramos, A.
Bibcode: 2020sea..confE.202K
Altcode:
We investigate the dynamics and magnetic properties of the plasma, such
as line-of-sight velocity (LOS), optical depth, vertical and horizontal
magnetic fields, belonging to an erupted solar filament. The filament
eruption was observed with the GREGOR Infrared Spectrograph (GRIS)
at the 1.5-meter GREGOR telescope on 2016 July 3. Three consecutive
full-Stokes slit-spectropolarimetric scans in the He I 10830 Å
spectral range were acquired. The Stokes I profiles were classified
using the machine learning k-means algorithm and then inverted with
different initial conditions using the inversion code HAZEL. The
erupting-filament material presents the following physical conditions:
(i) ubiquitous upward motions with peak LOS velocities of ∼73 km/s;
(ii) predominant large horizontal components of the magnetic field, on
average, in the range of 173-254 G, whereas the vertical components of
the fields are much lower, on average between 39-58 G; (iii) optical
depths in the range of 0.7-1.1. The average azimuth orientation of
the field lines between two consecutive raster scans (<2.5 minutes)
remained constant. The analyzed filament eruption belonged to the fast
rising phase, with total velocities of about 124 km/s.
Title: High-resolution spectroscopy of a surge in an emerging
flux region
Authors: Verma, M.; Denker, C.; Diercke, A.; Kuckein, C.; Balthasar,
H.; Dineva, E.; Kontogiannis, I.; Pal, P. S.; Sobotka, M.
Bibcode: 2020A&A...639A..19V
Altcode: 2020arXiv200503966V
Aims: The regular pattern of quiet-Sun magnetic fields was
disturbed by newly emerging magnetic flux, which led a day later to
two homologous surges after renewed flux emergence, affecting all
atmospheric layers. Hence, simultaneous observations in different
atmospheric heights are needed to understand the interaction of
rising flux tubes with the surrounding plasma, in particular by
exploiting the important diagnostic capabilities provided by the
strong chromospheric Hα line regarding morphology and energetic
processes in active regions.
Methods: A newly emerged active
region NOAA 12722 was observed with the Vacuum Tower Telescope (VTT)
at Observatorio del Teide, Tenerife, Spain, on 11 September 2018. High
spectral resolution observations using the echelle spectrograph in the
chromospheric Hαλ6562.8 Å line were obtained in the early growth
phase. Noise-stripped Hα line profiles yield maps of line-core and
bisector velocities, which were contrasted with velocities inferred
from Cloud Model inversions. A high-resolution imaging system recorded
simultaneously broad- and narrowband Hα context images. The Solar
Dynamics Observatory provided additional continuum images, line-of-sight
(LOS) magnetograms, and UV and extreme UV (EUV) images, which link the
different solar atmospheric layers.
Results: The active region
started as a bipolar region with continuous flux emergence when a new
flux system emerged in the leading part during the VTT observations,
resulting in two homologous surges. While flux cancellation at the
base of the surges provided the energy for ejecting the cool plasma,
strong proper motions of the leading pores changed the magnetic
field topology making the region susceptible to surging. Despite
the surge activity in the leading part, an arch filament system in
the trailing part of the old flux remained stable. Thus, stable
and violently expelled mass-loaded ascending magnetic structures
can coexist in close proximity. Investigating the height dependence
of LOS velocities revealed the existence of neighboring strong up-
and downflows. However, downflows occur with a time lag. The opacity
of the ejected cool plasma decreases with distance from the base of
the surge, while the speed of the ejecta increases. The location at
which the surge becomes invisible in Hα corresponds to the interface
where the surge brightens in He IIλ304 Å. Broad-shouldered and
dual-lobed Hα profiles suggests accelerated or decelerated and
highly structured LOS plasma flows. Significantly broadened Hα
profiles imply significant heating at the base of the surges, which
is also supported by bright kernels in UV and EUV images uncovered
by swaying motions of dark fibrils at the base of the surges.
Conclusions: The interaction of newly emerging flux with pre-existing
flux concentrations of a young, diffuse active region provided
suitable conditions for two homologous surges. High-resolution
spectroscopy revealed broadened and dual-lobed Hα profiles
tracing accelerated or decelerated flows of cool plasma along the
multi-threaded structure of the surge. Movies are available at https://www.aanda.org
Title: Magnetic Flux Emergence in a Coronal Hole
Authors: Palacios, Judith; Utz, Dominik; Hofmeister, Stefan; Krikova,
Kilian; Gömöry, Peter; Kuckein, Christoph; Denker, Carsten; Verma,
Meetu; González Manrique, Sergio Javier; Campos Rozo, Jose Iván;
Koza, Július; Temmer, Manuela; Veronig, Astrid; Diercke, Andrea;
Kontogiannis, Ioannis; Cid, Consuelo
Bibcode: 2020SoPh..295...64P
Altcode: 2020arXiv200611779P
A joint campaign of various space-borne and ground-based observatories,
comprising the Japanese Hinode mission (Hinode Observing Plan 338,
20 - 30 September 2017), the GREGOR solar telescope, and the Vacuum
Tower Telescope (VTT), investigated numerous targets such as pores,
sunspots, and coronal holes. In this study, we focus on the coronal
hole region target. On 24 September 2017, a very extended non-polar
coronal hole developed patches of flux emergence, which contributed
to the decrease of the overall area of the coronal hole. These flux
emergence patches erode the coronal hole and transform the area into a
more quiet-Sun-like area, whereby bipolar magnetic structures play an
important role. Conversely, flux cancellation leads to the reduction
of opposite-polarity magnetic fields and to an increase in the area
of the coronal hole.
Title: Tracking Downflows from the Chromosphere to the Photosphere
in a Solar Arch Filament System
Authors: González Manrique, Sergio Javier; Kuckein, Christoph;
Pastor Yabar, Adur; Diercke, Andrea; Collados, Manuel; Gömöry,
Peter; Zhong, Sihui; Hou, Yijun; Denker, Carsten
Bibcode: 2020ApJ...890...82G
Altcode: 2020arXiv200107078G
We study the dynamics of plasma along the legs of an arch filament
system (AFS) from the chromosphere to the photosphere, observed with
high-cadence spectroscopic data from two ground-based solar telescopes:
the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph
in the He I 10830 Å range and the Swedish Solar Telescope (La Palma)
using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542
Å and Fe I 6173 Å spectral lines. The temporal evolution of the
draining of the plasma was followed along the legs of a single arch
filament from the chromosphere to the photosphere. The average Doppler
velocities inferred at the upper chromosphere from the He I 10830 Å
triplet reach velocities up to 20-24 km s-1, and in the lower
chromosphere and upper photosphere the Doppler velocities reach up to
11 km s-1 and 1.5 km s-1 in the case of the Ca II
8542 Å and Si I 10827 Å spectral lines, respectively. The evolution
of the Doppler velocities at different layers of the solar atmosphere
(chromosphere and upper photosphere) shows that they follow the same
line-of-sight (LOS) velocity pattern, which confirms the observational
evidence that the plasma drains toward the photosphere as proposed
in models of AFSs. The Doppler velocity maps inferred from the lower
photospheric Ca I 10839 Å or Fe I 6173 Å spectral lines do not
show the same LOS velocity pattern. Thus, there is no evidence that
the plasma reaches the lower photosphere. The observations and the
nonlinear force-free field (NLFFF) extrapolations demonstrate that
the magnetic field loops of the AFS rise with time. We found flow
asymmetries at different footpoints of the AFS. The NLFFF values of
the magnetic field strength help us to explain these flow asymmetries.
Title: Capabilities of bisector analysis of the Si I 10 827 Å line
for estimating line-of-sight velocities in the quiet Sun
Authors: González Manrique, S. J.; Quintero Noda, C.; Kuckein, C.;
Ruiz Cobo, B.; Carlsson, M.
Bibcode: 2020A&A...634A..19G
Altcode: 2020arXiv200100508G
We examine the capabilities of a fast and simple method to infer
line-of-sight (LOS) velocities from observations of the photospheric
Si I 10 827 Å line. This spectral line is routinely observed together
with the chromospheric He I 10 830 Å triplet as it helps to constrain
the atmospheric parameters. We study the accuracy of bisector analysis
and a line core fit of Si I 10 827 Å. We employ synthetic profiles
starting from the Bifrost enhanced network simulation. The profiles are
computed solving the radiative transfer equation, including non-local
thermodynamic equilibrium effects on the determination of the atomic
level populations of Si I. We found a good correlation between the
inferred velocities from bisectors taken at different line profile
intensities and the original simulation velocity at given optical
depths. This good correlation means that we can associate bisectors
taken at different line-profile percentages with atmospheric layers
that linearly increase as we scan lower spectral line intensities. We
also determined that a fit to the line-core intensity is robust and
reliable, providing information about atmospheric layers that are
above those accessible through bisectors. Therefore, by combining
both methods on the Si I 10 827 Å line, we can seamlessly trace the
quiet-Sun LOS velocity stratification from the deep photosphere to
higher layers until around logτ = -3.5 in a fast and straightforward
way. This method is ideal for generating quick-look reference images
for future missions like the Daniel K. Inoue Solar Telescope and the
European Solar Telescope, for example.
Title: The magnetic structure and dynamics of a decaying active region
Authors: Kontogiannis, Ioannis; Kuckein, Christoph; González
Manrique, Sergio Javier; Felipe, Tobias; Verma, Meetu; Balthasar,
Horst; Denker, Carsten
Bibcode: 2020IAUS..354...53K
Altcode:
We study the evolution of the decaying active region NOAA 12708, from
the photosphere up to the corona using high resolution, multi-wavelength
GREGOR observations taken on May 9, 2018. We utilize spectropolarimetric
scans of the 10830 Å spectral range by the GREGOR Infrared Spectrograph
(GRIS), spectral imaging time-series in the Na ID2 spectral
line by the GREGOR Fabry-Pérot Interferometer (GFPI) and context
imaging in the Ca IIH and blue continuum by the High-resolution Fast
Imager (HiFI). Context imaging in the UV/EUV from the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO)
complements our dataset. The region under study contains one pore with a
light-bridge, a few micro-pores and extended clusters of magnetic bright
points. We study the magnetic structure from the photosphere up to the
upper chromosphere through the spectropolarimetric observations in He
II and Si I and through the magnetograms provided by the Helioseismic
and Magnetic Imager (HMI). The high-resolution photospheric images
reveal the complex interaction between granular-scale convective
motions and a range of scales of magnetic field concentrations in
unprecedented detail. The pore itself shows a strong interaction with
the convective motions, which eventually leads to its decay, while,
under the influence of the photospheric flow field, micro-pores
appear and disappear. Compressible waves are generated, which are
guided towards the upper atmosphere along the magnetic field lines of
the various magnetic structures within the field-of-view. Modelling
of the He i absorption profiles reveals high velocity components,
mostly associated with magnetic bright points at the periphery
of the active region, many of which correspond to asymmetric Si I
Stokes-V profiles revealing a coupling between upper photospheric
and upper chromospheric dynamics. Time-series of Na ID2
spectral images reveal episodic high velocity components at the same
locations. State-of-the-art multi-wavelength GREGOR observations allow
us to track and understand the mechanisms at work during the decay
phase of the active region.
Title: Coordinated observations between China and Europe to follow
active region 12709
Authors: González Manrique, S. J.; Kuckein, C.; Gömöry, P.; Yuan,
S.; Xu, Z.; Rybák, J.; Balthasar, H.; Schwartz, P.
Bibcode: 2020IAUS..354...58G
Altcode: 2020IAUS..354...58M; 2019arXiv191208611G
We present the first images of a coordinated campaign to follow active
region NOAA 12709 on 2018 May 13 as part of a joint effort between
three observatories (China-Europe). The active region was close to
disk center and enclosed a small pore, a tight polarity inversion line
and a filament in the chromosphere. The active region was observed
with the 1.5-meter GREGOR solar telescope on Tenerife (Spain) with
spectropolarimetry using GRIS in the He i 10830 Å spectral range
and with HiFI using two broad-band filter channels. In addition,
the Lomnicky Stit Observatory (LSO, Slovakia) recorded the same
active region with the new Solar Chromospheric Detector (SCD) in
spectroscopic mode at Hα 6562 Å. The third ground-based telescope
was located at the Fuxian Solar Observatory (China), where the active
region was observed with the 1-meter New Vacuum Solar Telescope
(NVST), using the Multi-Channel High Resolution Imaging System at
Hα 6562 Å. Overlapping images of the active region from all three
telescopes will be shown as well as preliminary Doppler line-of-sight
(LOS) velocities. The potential of such observations are discussed.
Title: Emergence of small-scale magnetic flux in the quiet Sun
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.; Gontikakis,
C.; Kuckein, C.; Verma, M.; Denker, C.
Bibcode: 2020A&A...633A..67K
Altcode: 2019arXiv191202496K
Context. We study the evolution of a small-scale emerging flux region
(EFR) in the quiet Sun, from its emergence in the photosphere to
its appearance in the corona and its decay.
Aims: We track
processes and phenomena that take place across all atmospheric layers;
we explore their interrelations and compare our findings with those from
recent numerical modelling studies.
Methods: We used imaging
as well as spectral and spectropolarimetric observations from a suite
of space-borne and ground-based instruments.
Results: The EFR
appears in the quiet Sun next to the chromospheric network and shows all
morphological characteristics predicted by numerical simulations. The
total magnetic flux of the region exhibits distinct evolutionary phases,
namely an initial subtle increase, a fast increase with a Co-temporal
fast expansion of the region area, a more gradual increase, and a slow
decay. During the initial stages, fine-scale G-band and Ca II H bright
points coalesce, forming clusters of positive- and negative-polarity
in a largely bipolar configuration. During the fast expansion, flux
tubes make their way to the chromosphere, pushing aside the ambient
magnetic field and producing pressure-driven absorption fronts that
are visible as blueshifted chromospheric features. The connectivity
of the quiet-Sun network gradually changes and part of the existing
network forms new connections with the newly emerged bipole. A few
minutes after the bipole has reached its maximum magnetic flux, the
bipole brightens in soft X-rays forming a coronal bright point. The
coronal emission exhibits episodic brightenings on top of a long
smooth increase. These coronal brightenings are also associated
with surge-like chromospheric features visible in Hα, which can
be attributed to reconnection with adjacent small-scale magnetic
fields and the ambient quiet-Sun magnetic field.
Conclusions:
The emergence of magnetic flux even at the smallest scales can be the
driver of a series of energetic phenomena visible at various atmospheric
heights and temperature regimes. Multi-wavelength observations reveal
a wealth of mechanisms which produce diverse observable effects during
the different evolutionary stages of these small-scale structures.
Title: Revisiting the building blocks of solar magnetic fields
by GREGOR
Authors: Utz, Dominik; Kuckein, Christoph; Campos Rozo, Jose Iván;
González Manrique, Sergio Javier; Balthasar, Horst; Gömöry,
Peter; Hernández, Judith Palacios; Denker, Carsten; Verma, Meetu;
Kontogiannis, Ioannis; Krikova, Kilian; Hofmeister, Stefan; Diercke,
Andrea
Bibcode: 2020IAUS..354...38U
Altcode:
The Sun is our dynamic host star due to its magnetic fields causing
plentiful of activity in its atmosphere. From high energetic flares
and coronal mass ejections (CMEs) to lower energetic phenomena such
as jets and fibrils. Thus, it is of crucial importance to learn about
formation and evolution of solar magnetic fields. These fields cover a
wide range of spatial and temporal scales, starting on the larger end
with active regions harbouring complex sunspots, via isolated pores,
down to the smallest yet resolved elements - so-called magnetic bright
points (MBPs). Here, we revisit the various manifestations of solar
magnetic fields by the largest European solar telescope in operation,
the 1.5-meter GREGOR telescope. We show images from the High-resolution
Fast Imager (HiFI) and spectropolarimetric data from the GREGOR Infrared
Spectrograph (GRIS). Besides, we outline resolved convective features
inside the larger structures - so-called light-bridges occurring on
large to mid-sized scales.
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: Height variation of magnetic field and plasma flows in isolated
bright points
Authors: Kuckein, Christoph
Bibcode: 2019A&A...630A.139K
Altcode: 2019arXiv190905550K
Aims: The expansion with height of the solar photospheric
magnetic field and the plasma flows is investigated for three
isolated bright points (BPs).
Methods: The BPs were observed
simultaneously with three different instruments attached to the 1.5 m
GREGOR telescope: (1) filtergrams of Ca II H and blue continuum (4505
Å) with the HiFI, (2) imaging spectroscopy of the Na I D2
line at 5890 Å with the GFPI, and (3) slit spectropolarimetry in the 1
μm spectral range with the GRIS. Spectral-line inversions were carried
out for the Si I 10827 Å Stokes profiles.
Results: Bright points
are identified in the Ca II H and blue continuum filtergrams. Moreover,
they are also detected in the blue wing of the Na I D2
and Si I 10827 Å lines, as well as in the Ca I 10839 Å line-core
images. We carried out two studies to validate the expansion of
the magnetic field with height. On the one hand, we compare the
photospheric Stokes V signals of two different spectral lines that
are sensitive to different optical depths (Ca I vs. Si I). The area
at which the Stokes V signal is significantly large is almost three
times larger for the Si I line - sensitive to higher layers - than
for the Ca I one. On the other hand, the inferred line-of-sight (LOS)
magnetic fields at two optical depths (log τ = -1.0 vs. -2.5) from
the Si I line reveal spatially broader fields in the higher layer,
up to 51% more extensive in one of the BPs. The dynamics of BPs are
tracked along the Na I D2 and Si I lines. The inferred flows
from Na I D2 Doppler shifts are rather slow in BPs (≲1 km
s-1). However, the Si I line shows intriguing Stokes profiles
with important asymmetries. The analysis of these profiles unveils
the presence of two components, a fast and a slow one, within the same
resolution element. The faster one, with a smaller filling factor of
∼0.3, exhibits LOS velocities of about 6 km s-1. The
slower component is slightly blueshifted.
Conclusions: The
present work provides observational evidence for the expansion of the
magnetic field with height. Moreover, fast flows are likely present
in BPs but are sometimes hidden because of observational limitations.
Title: Dynamics and connectivity of an extended arch filament system
Authors: Diercke, A.; Kuckein, C.; Denker, C.
Bibcode: 2019A&A...629A..48D
Altcode: 2019arXiv190801510D
Aims: In this study, we analyzed a filament system, which
expanded between moving magnetic features (MMFs) of a decaying sunspot
and opposite flux outside of the active region from the nearby
quiet-Sun network. This configuration deviated from a classical
arch filament system (AFS), which typically connects two pores in
an emerging flux region. Thus, we called this system an extended
AFS. We contrasted classical and extended AFSs with an emphasis on the
complex magnetic structure of the latter. Furthermore, we examined the
physical properties of the extended AFS and described its dynamics
and connectivity.
Methods: The extended AFS was observed
with two instruments at the Dunn Solar Telescope (DST). The Rapid
Oscillations in the Solar Atmosphere (ROSA) imager provided images
in three different wavelength regions, which covered the dynamics of
the extended AFS at different atmospheric heights. The Interferometric
Bidimensional Spectropolarimeter (IBIS) provided spectroscopic Hα data
and spectropolarimetric data that was obtained in the near-infrared
(NIR) Ca IIλ8542 Å line. We derived the corresponding line-of-sight
(LOS) velocities and used He IIλ304 Å extreme ultraviolet (EUV)
images of the Atmospheric Imaging Assembly (AIA) and LOS magnetograms
of the Helioseismic and Magnetic Imager (HMI) on board the Solar
Dynamics Observatory (SDO) as context data.
Results: The
NIR Ca II Stokes-V maps are not suitable to definitively define a
clear polarity inversion line and to classify this chromospheric
structure. Nevertheless, this unusual AFS connects the MMFs of a
decaying sunspot with the network field. At the southern footpoint,
we measured that the flux decreases over time. We find strong downflow
velocities at the footpoints of the extended AFS, which increase
in a time period of 30 min. The velocities are asymmetric at both
footpoints with higher velocities at the southern footpoint. An EUV
brigthening appears in one of the arch filaments, which migrates from
the northern footpoint toward the southern one. This activation likely
influences the increasing redshift at the southern footpoint.
Conclusions: The extended AFS exhibits a similar morphology as
classical AFSs, for example, threaded filaments of comparable length
and width. Major differences concern the connection from MMFs around the
sunspot with the flux of the neighboring quiet-Sun network, converging
footpoint motions, and longer lifetimes of individual arch filaments
of about one hour, while the extended AFS is still very dynamic. Movies associated to Figs. 5, 6, and 12 are available at https://www.aanda.org
Title: Polarimetry with the GREGOR Fabry-Pérot Interferometer
Authors: Balthasar, H.; Gisler, D.; González Manrique, S. J.; Kuckein,
C.; Verma, M.; Denker, C.
Bibcode: 2019spw..confE...3B
Altcode:
No abstract at ADS
Title: Spectropolarimetric Observations of an Arch Filament System
with GREGOR
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kučera, A.; Schwartz, P.; Berkefeld, T.; Collados, M.;
Denker, C.; Feller, A.; Hofmann, A.; Schlichenmaier, R.; Schmidt,
D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau,
D.; Staude, J.; Strassmeier, K. G.; von der Lühe, O.
Bibcode: 2019ASPC..526..217B
Altcode: 2018arXiv180401789B
We observed an arch filament system (AFS) in a sunspot group with the
GREGOR Infrared Spectrograph attached to the GREGOR solar telescope. The
AFS was located between the leading sunspot of negative polarity and
several pores of positive polarity forming the following part of the
sunspot group. We recorded five spectro-polarimetric scans of this
region. The spectral range included the spectral lines Si I 1082.7
nm, He I 1083.0 nm, and Ca I 1083.9 nm. In this work we concentrate
on the silicon line which is formed in the upper photosphere. The
line profiles are inverted with the code 'Stokes Inversion based
on Response functions' to obtain the magnetic field vector. The
line-of-sight velocities are determined independently with a Fourier
phase method. Maximum velocities are found close to the ends of AFS
fibrils. These maximum values amount to 2.4 km s-1 next
to the pores and to 4 km s-1 at the sunspot side. Between
the following pores, we encounter an area of negative polarity that
is decreasing during the five scans. We interpret this by new emerging
positive flux in this area canceling out the negative flux. In summary,
our findings confirm the scenario that rising magnetic flux tubes
cause the AFS.
Title: Photospheric Magnetic Fields of the Trailing Sunspots in
Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2019ASPC..526..291V
Altcode: 2018arXiv180507752V
The solar magnetic field is responsible for all aspects of solar
activity. Sunspots are the main manifestation of the ensuing solar
activity. Combining high-resolution and synoptic observations has
the ambition to provide a comprehensive description of the sunspot
growth and decay processes. Active region NOAA 12396 emerged on 2015
August 3 and was observed three days later with the 1.5-meter GREGOR
solar telescope on 2015 August 6. High-resolution spectropolarimetric
data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
with the chromospheric He I λ1083.0 nm triplet. These near-infrared
spectropolarimetric observations were complemented by synoptic
line-of-sight magnetograms and continuum images of the Helioseismic
and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO).
Title: Spiral-shaped wavefronts in a sunspot umbra
Authors: Felipe, T.; Kuckein, C.; Khomenko, E.; Thaler, I.
Bibcode: 2019A&A...621A..43F
Altcode: 2018arXiv181011257F
Context. Solar active regions show a wide variety of oscillatory
phenomena. The presence of the magnetic field leads to the appearance
of several wave modes whose behavior is determined by the sunspot
thermal and magnetic structure.
Aims: We aim to study the
relation between the umbral and penumbral waves observed at the high
photosphere and the magnetic field topology of the sunspot.
Methods: Observations of the sunspot in active region NOAA 12662
obtained with the GREGOR telescope (Observatorio del Teide, Tenerife,
Spain) were acquired on 2017 June 17. The data set includes a temporal
series in the Fe I 5435 Å line obtained with the imaging spectrograph
GREGOR Fabry-Pérot Interferometer (GFPI) and a spectropolarimetric
raster map acquired with the GREGOR Infrared Spectrograph (GRIS)
in the 10 830 Å spectral region. The Doppler velocity deduced from
the restored Fe I 5435 Å line has been determined, and the magnetic
field vector of the sunspot has been inferred from spectropolarimetric
inversions of the Ca I 10 839 Å and the Si I 10 827 Å lines.
Results: A two-armed spiral wavefront has been identified in the
evolution of the two-dimensional velocity maps from the Fe I 5435 Å
line. The wavefronts initially move counterclockwise in the interior
of the umbra, and develop into radially outward propagating running
penumbral waves when they reach the umbra-penumbra boundary. The
horizontal propagation of the wavefronts approximately follows the
direction of the magnetic field, which shows changes in the magnetic
twist with height and horizontal position.
Conclusions:
The spiral wavefronts are interpreted as the visual pattern of slow
magnetoacoustic waves which propagate upward along magnetic field
lines. Their apparent horizontal propagation is due to their sequential
arrival to different horizontal positions at the formation height of the
Fe I 5435 Å line, as given by the inclination and orientation of the
magnetic field. The movie associated to Fig. 2 is available at https://www.aanda.org
Title: Properties of the inner penumbral boundary and temporal
evolution of a decaying sunspot
Authors: Benko, M.; González Manrique, S. J.; Balthasar, H.; Gömöry,
P.; Kuckein, C.; Jurčák, J.
Bibcode: 2018A&A...620A.191B
Altcode: 2018arXiv181013185B
Context. It has been empirically determined that the umbra-penumbra
boundaries of stable sunspots are characterized by a constant value of
the vertical magnetic field.
Aims: We analyzed the evolution
of the photospheric magnetic field properties of a decaying sunspot
belonging to NOAA 11277 between August 28-September 3, 2011. The
observations were acquired with the spectropolarimeter on-board of
the Hinode satellite. We aim to prove the validity of the constant
vertical magnetic-field boundary between the umbra and penumbra in
decaying sunspots.
Methods: A spectral-line inversion technique
was used to infer the magnetic field vector from the full-Stokes
profiles. In total, eight maps were inverted and the variation of
the magnetic properties in time were quantified using linear or
quadratic fits.
Results: We find a linear decay of the umbral
vertical magnetic field, magnetic flux, and area. The penumbra showed
a linear increase of the vertical magnetic field and a sharp decay
of the magnetic flux. In addition, the penumbral area quadratically
decayed. The vertical component of the magnetic field is weaker on the
umbra-penumbra boundary of the studied decaying sunspot compared to
stable sunspots. Its value seem to be steadily decreasing during the
decay phase. Moreover, at any time of the sunspot decay shown, the inner
penumbra boundary does not match with a constant value of the vertical
magnetic field, contrary to what is seen in stable sunspots.
Conclusions: During the decaying phase of the studied sunspot, the
umbra does not have a sufficiently strong vertical component of the
magnetic field and is thus unstable and prone to be disintegrated by
convection or magnetic diffusion. No constant value of the vertical
magnetic field is found for the inner penumbral boundary.
Title: sTools - a software package for data reduction of GREGOR
instruments and general data analysis
Authors: Kuckein, Christoph; Denker, Carsten; Verma, Meetu; Balthasar,
Horst; Diercke, Andrea; González Manrique, Sergio Javier; Dineva,
Ekaterina; Kontogiannis, Ioannis; Shen, Zili
Bibcode: 2018csc..confE.105K
Altcode:
The optical solar physics group at AIP is responsible for the GREGOR
Fabry-Perot Interferometer (GFPI) and the large-format facility cameras
(Blue Imaging Channel (BIC) and High-resolution Fast Imager (HiFI))
at the 1.5-meter GREGOR solar telescope (Tenerife, Spain). Since
the »Early Science Phase« of the telescope in 2014, the group
developed a data reduction pipeline for these two instruments. The
pipeline »sTools« is based on the Interactive Data Language
(IDL) and delivers reduced and image-restored data with a minimum
of user interaction. Furthermore, it creates quick-look data and
builds a webpage with an overview of the observations and their
statistics (http://gregor.aip.de). However, during the last years,
sTools continuously evolved and currently hosts many additional
routines for data analysis: (1) A local correlation tracking (LCT)
algorithm adapted for both high-resolution (GREGOR and Hinode) and
synoptic full-disk (SDO) data. (2) A new quantitative tool, i.e.,
a Background-subtracted Solar Activity Map (BaSAM), to assess and
visualize the temporal variation of the photospheric magnetic field
and the EUV 160 nm intensity. This method utilizes SDO data and is
applicable to both full-disk observations and regions-of-interest. (3)
Calibration of synoptic full-disk data from the Chromospheric Telescope
(ChroTel) including extraction of Doppler velocities from He I 1083
nm filtergrams. (4) Analysis tools for sun-as-a-star spectroscopy
for the Solar Disk-Integrated (SDI) telescope of the Potsdam Echelle
Polarimetric and Spectroscopic Instrument (PEPSI). sTools is licensed
under a creative commons license and is freely available, after
registration, at the abovementioned website.
Title: The Effects of Stellar Activity on Optical High-resolution
Exoplanet Transmission Spectra
Authors: Cauley, P. Wilson; Kuckein, Christoph; Redfield, Seth;
Shkolnik, Evgenya L.; Denker, Carsten; Llama, Joe; Verma, Meetu
Bibcode: 2018AJ....156..189C
Altcode: 2018arXiv180809558C
Chromospherically sensitive atomic lines display different spectra
in stellar active regions, spots, and the photosphere, raising the
possibility that exoplanet transmission spectra are contaminated by
the contrast between various portions of the stellar disk. To explore
this effect, we performed transit simulations of G-type and K-type
stars for the spectral lines Ca II K at 3933 Å, Na I 5890 Å, H I
6563 Å (Hα), and He I 10830 Å. We find that strong facular emission
and large coverage fractions can contribute a non-negligible amount
to transmission spectra, especially for Hα, Ca II K, and Na I D,
while spots and filaments are comparatively unimportant. The amount of
contamination depends strongly on the location of the active regions
and the intrinsic emission strength. In particular, active regions
must be concentrated along the transit chord in order to produce a
consistent in-transit signal. Mean absorption signatures in Na I and
Hα, for example, can reach ≈0.2% and 0.3%, respectively, for transits
of active latitudes with line emission similar in strength to moderate
solar flares. Transmission spectra of planets transiting active stars,
such as HD 189733, are likely contaminated by the contrast effect,
although the tight constraints on active region geometry and emission
strength make it unlikely that consistent in-transit signatures are due
entirely to the contrast effect. He I 10830 Å is not strongly affected
and absorption signatures are likely diluted, rather than enhanced,
by stellar activity. He I 10830 Å should thus be considered a priority
for probing extended atmospheres, even in the case of active stars.
Title: Counter-streaming flows in a giant quiet-Sun filament
Authors: Diercke, Andrea; Kuckein, Christoph; Verma, Meetu; Denker,
Carsten
Bibcode: 2018csc..confE.104D
Altcode:
A giant solar filament was visible on the solar surface between 2011
November 8-23. The filament stretched over more than half a solar
diameter. Multi-wavelength data from the SDO instrument AIA (171, 193,
304, and 211 A) were used to examine counter-streaming flows within
the spine of the filament. H-alpha images from the Kanzelhöhe Solar
Observatory provided context information. We apply local correlation
tracking (LCT) to a two-hour time series on 2011 November 16 of the AIA
images to derive horizontal flow velocities of the filament. To enhance
the contrast of the AIA images, noise adaptive fuzzy equalization
(NAFE) is employed, which allows us to identify and quantify
counter-streaming flows in the filament. We detect counter-streaming
flows in the filament, which are visible in the time-lapse movies in all
examined AIA wavelength bands. In the time-lapse movies, we see that
these persistent flows lasted for at least two hours. Furthermore, by
applying LCT to the images we clearly determine counter-streaming flows
in time series of 171 A and 193 A images. In the 304 A wavelength band,
we only see minor indications for counter-streaming flows with LCT,
while in the 211 A wavelength band the counter-streaming flows are not
detectable. The average horizontal flows reach mean flow speeds of 0.5
km/s. The highest horizontal flow speeds are identified in the 171
A band with flow speeds of up to 2.5 km/s. The results are averaged
over a time series of 90 min. Because the LCT sampling window has a
finite width, a spatial degradation cannot be avoided leading to lower
estimates of the flow velocities as compared to feature tracking or
Doppler measurements. The counter-streaming flows cover about 15-20%
of the whole area of the EUV filament channel and are located in the
central part of the spine. In conclusion, we confirm the omnipresence
of counter-streaming flows also in giant quiet-Sun filaments.
Title: Height variation of the cutoff frequency in a sunspot umbra
Authors: Felipe, T.; Kuckein, C.; Thaler, I.
Bibcode: 2018A&A...617A..39F
Altcode: 2018arXiv180605856F
Context. In the solar atmosphere, the acoustic cutoff frequency is
a local quantity that depends on atmospheric height. It separates
low-frequency evanescent waves from high-frequency propagating
waves.
Aims: We measure the cutoff frequency of slow
magnetoacoustic waves at various heights of a sunspot umbra and compare
the results with the estimations from several analytical formulae.
Methods: We analyzed the oscillations in the umbra of a sunspot
belonging to active region NOAA 12662 observed in the 10 830 Å spectral
region with the GREGOR Infrared Spectrograph and in the Fe I 5435 Å
line with the GREGOR Fabry-Pérot Interferometer. Both instruments
are attached to the GREGOR telescope at the Observatorio del Teide,
Tenerife, Spain. We computed the phase and amplification spectra between
the velocity measured from various pairs of lines that sample various
heights of the solar atmosphere. The cutoff frequency and its height
variation were estimated from the inspection of the spectra.
Results: At the deep umbral photosphere the cutoff frequency is around
5 mHz and it increases to 6 mHz at higher photospheric layers. At the
chromosphere the cutoff is 3.1 mHz. A comparison of the observationally
determined cutoff with the theoretically predicted values reveals
an agreement in the general trend and a reasonable match at the
chromosphere, but also significant quantitative differences at the
photosphere.
Conclusions: Our analyses show strong evidence of
the variation of the cutoff frequency with height in a sunspot umbra,
which is not fully accounted for by current analytical estimations. This
result has implications for our understanding of wave propagation, the
seismology of active regions, and the evaluation of heating mechanisms
based on compressible waves.
Title: Temporal evolution of arch filaments as seen in He I 10 830 Å
Authors: González Manrique, S. J.; Kuckein, C.; Collados, M.; Denker,
C.; Solanki, S. K.; Gömöry, P.; Verma, M.; Balthasar, H.; Lagg,
A.; Diercke, A.
Bibcode: 2018A&A...617A..55G
Altcode: 2018arXiv180700728G
Aims: We study the evolution of an arch filament system (AFS)
and of its individual arch filaments to learn about the processes
occurring in them.
Methods: We observed the AFS at the
GREGOR solar telescope on Tenerife at high cadence with the very
fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS)
in the He I 10 830 Å spectral range. The He I triplet profiles
were fitted with analytic functions to infer line-of-sight (LOS)
velocities to follow plasma motions within the AFS.
Results:
We tracked the temporal evolution of an individual arch filament
over its entire lifetime, as seen in the He I 10 830 Å triplet. The
arch filament expanded in height and extended in length from 13″ to
21″. The lifetime of this arch filament is about 30 min. About 11
min after the arch filament is seen in He I, the loop top starts to
rise with an average Doppler velocity of 6 km s-1. Only two
minutes later, plasma drains down with supersonic velocities towards
the footpoints reaching a peak velocity of up to 40 km s-1
in the chromosphere. The temporal evolution of He I 10 830 Å profiles
near the leading pore showed almost ubiquitous dual red components of
the He I triplet, indicating strong downflows, along with material
nearly at rest within the same resolution element during the whole
observing time.
Conclusions: We followed the arch filament as it
carried plasma during its rise from the photosphere to the corona. The
material then drained toward the photosphere, reaching supersonic
velocities, along the legs of the arch filament. Our observational
results support theoretical AFS models and aids in improving future
models. The movie associated to Fig. 3 is available at https://www.aanda.org/
Title: High-resolution imaging and near-infrared spectroscopy of
penumbral decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; Rezaei,
R.; Sobotka, M.; Deng, N.; Wang, H.; Tritschler, A.; Collados, M.;
Diercke, A.; González Manrique, S. J.
Bibcode: 2018A&A...614A...2V
Altcode: 2018arXiv180103686V
Aims: Combining high-resolution spectropolarimetric and imaging
data is key to understanding the decay process of sunspots as it
allows us to scrutinize the velocity and magnetic fields of sunspots
and their surroundings.
Methods: Active region NOAA 12597
was observed on 2016 September 24 with the 1.5-meter GREGOR solar
telescope using high-spatial-resolution imaging as well as imaging
spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal
proper motions were estimated with local correlation tracking, whereas
line-of-sight (LOS) velocities were computed with spectral line fitting
methods. The magnetic field properties were inferred with the "Stokes
Inversions based on Response functions" (SIR) code for the Si I and Ca
I NIR lines.
Results: At the time of the GREGOR observations,
the leading sunspot had two light bridges indicating the onset of
its decay. One of the light bridges disappeared, and an elongated,
dark umbral core at its edge appeared in a decaying penumbral sector
facing the newly emerging flux. The flow and magnetic field properties
of this penumbral sector exhibited weak Evershed flow, moat flow, and
horizontal magnetic field. The penumbral gap adjacent to the elongated
umbral core and the penumbra in that penumbral sector displayed LOS
velocities similar to granulation. The separating polarities of a new
flux system interacted with the leading and central part of the already
established active region. As a consequence, the leading spot rotated
55° clockwise over 12 h.
Conclusions: In the high-resolution
observations of a decaying sunspot, the penumbral filaments facing the
flux emergence site contained a darkened area resembling an umbral core
filled with umbral dots. This umbral core had velocity and magnetic
field properties similar to the sunspot umbra. This implies that the
horizontal magnetic fields in the decaying penumbra became vertical
as observed in flare-induced rapid penumbral decay, but on a very
different time-scale.
Title: High-cadence Imaging and Imaging Spectroscopy at the
GREGOR Solar Telescope—A Collaborative Research Environment for
High-resolution Solar Physics
Authors: Denker, Carsten; Kuckein, Christoph; Verma, Meetu; González
Manrique, Sergio J.; Diercke, Andrea; Enke, Harry; Klar, Jochen;
Balthasar, Horst; Louis, Rohan E.; Dineva, Ekaterina
Bibcode: 2018ApJS..236....5D
Altcode: 2018arXiv180210146D
In high-resolution solar physics, the volume and complexity
of photometric, spectroscopic, and polarimetric ground-based
data significantly increased in the last decade, reaching data
acquisition rates of terabytes per hour. This is driven by the
desire to capture fast processes on the Sun and the necessity
for short exposure times “freezing” the atmospheric seeing,
thus enabling ex post facto image restoration. Consequently,
large-format and high-cadence detectors are nowadays used in
solar observations to facilitate image restoration. Based on our
experience during the “early science” phase with the 1.5 m
GREGOR solar telescope (2014-2015) and the subsequent transition
to routine observations in 2016, we describe data collection and
data management tailored toward image restoration and imaging
spectroscopy. We outline our approaches regarding data processing,
analysis, and archiving for two of GREGOR’s post-focus instruments
(see http://gregor.aip.de), i.e.,
the GREGOR Fabry-Pérot Interferometer (GFPI) and the newly installed
High-Resolution Fast Imager (HiFI). The heterogeneous and complex
nature of multidimensional data arising from high-resolution solar
observations provides an intriguing but also a challenging example for
“big data” in astronomy. The big data challenge has two aspects: (1)
establishing a workflow for publishing the data for the whole community
and beyond and (2) creating a collaborative research environment
(CRE), where computationally intense data and postprocessing tools are
colocated and collaborative work is enabled for scientists of multiple
institutes. This requires either collaboration with a data center or
frameworks and databases capable of dealing with huge data sets based on
virtual observatory (VO) and other community standards and procedures.
Title: Counter-streaming flows in a giant quiet-Sun filament observed
in the extreme ultraviolet
Authors: Diercke, A.; Kuckein, C.; Verma, M.; Denker, C.
Bibcode: 2018A&A...611A..64D
Altcode: 2018arXiv180101036D
Aim. The giant solar filament was visible on the solar surface from
2011 November 8-23. Multiwavelength data from the Solar Dynamics
Observatory (SDO) were used to examine counter-streaming flows
within the spine of the filament.
Methods: We use data from
two SDO instruments, the Atmospheric Imaging Assembly (AIA) and the
Helioseismic and Magnetic Imager (HMI), covering the whole filament,
which stretched over more than half a solar diameter. Hα images from
the Kanzelhöhe Solar Observatory (KSO) provide context information
of where the spine of the filament is defined and the barbs are
located. We apply local correlation tracking (LCT) to a two-hour time
series on 2011 November 16 of the AIA images to derive horizontal flow
velocities of the filament. To enhance the contrast of the AIA images,
noise adaptive fuzzy equalization (NAFE) is employed, which allows us
to identify and quantify counter-streaming flows in the filament. We
observe the same cool filament plasma in absorption in both Hα and
EUV images. Hence, the counter-streaming flows are directly related to
this filament material in the spine. In addition, we use directional
flow maps to highlight the counter-streaming flows.
Results:
We detect counter-streaming flows in the filament, which are visible
in the time-lapse movies in all four examined AIA wavelength bands
(λ171 Å, λ193 Å, λ304 Å, and λ211 Å). In the time-lapse
movies we see that these persistent flows lasted for at least two
hours, although they became less prominent towards the end of the
time series. Furthermore, by applying LCT to the images we clearly
determine counter-streaming flows in time series of λ171 Å and
λ193 Å images. In the λ304 Å wavelength band, we only see minor
indications for counter-streaming flows with LCT, while in the λ211
Å wavelength band the counter-streaming flows are not detectable
with this method. The diverse morphology of the filament in Hα
and EUV images is caused by different absorption processes, i.e.,
spectral line absorption and absorption by hydrogen and helium continua,
respectively. The horizontal flows reach mean flow speeds of about 0.5
km s-1 for all wavelength bands. The highest horizontal
flow speeds are identified in the λ171 Å band with flow speeds of
up to 2.5 km s-1. The results are averaged over a time
series of 90 minutes. Because the LCT sampling window has finite
width, a spatial degradation cannot be avoided leading to lower
estimates of the flow velocities as compared to feature tracking or
Doppler measurements. The counter-streaming flows cover about 15-20%
of the whole area of the EUV filament channel and are located in
the central part of the spine.
Conclusions: Compared to the
ground-based observations, the absence of seeing effects in AIA
observations reveal counter-streaming flows in the filament even
with a moderate image scale of 0. ''6 pixel-1. Using
a contrast enhancement technique, these flows can be detected
and quantified with LCT in different wavelengths. We confirm the
omnipresence of counter-streaming flows also in giant quiet-Sun
filaments. A movie associated to Fig. 6 is available at https://www.aanda.org
Title: Image Quality in High-resolution and High-cadence Solar Imaging
Authors: Denker, C.; Dineva, E.; Balthasar, H.; Verma, M.; Kuckein,
C.; Diercke, A.; González Manrique, S. J.
Bibcode: 2018SoPh..293...44D
Altcode: 2018arXiv180200760D
Broad-band imaging and even imaging with a moderate bandpass (about 1
nm) provides a photon-rich environment, where frame selection (lucky
imaging) becomes a helpful tool in image restoration, allowing us to
perform a cost-benefit analysis on how to design observing sequences
for imaging with high spatial resolution in combination with real-time
correction provided by an adaptive optics (AO) system. This study
presents high-cadence (160 Hz) G-band and blue continuum image sequences
obtained with the High-resolution Fast Imager (HiFI) at the 1.5-meter
GREGOR solar telescope, where the speckle-masking technique is used
to restore images with nearly diffraction-limited resolution. The
HiFI employs two synchronized large-format and high-cadence sCMOS
detectors. The median filter gradient similarity (MFGS) image-quality
metric is applied, among others, to AO-corrected image sequences of
a pore and a small sunspot observed on 2017 June 4 and 5. A small
region of interest, which was selected for fast-imaging performance,
covered these contrast-rich features and their neighborhood, which were
part of Active Region NOAA 12661. Modifications of the MFGS algorithm
uncover the field- and structure-dependency of this image-quality
metric. However, MFGS still remains a good choice for determining image
quality without a priori knowledge, which is an important characteristic
when classifying the huge number of high-resolution images contained in
data archives. In addition, this investigation demonstrates that a fast
cadence and millisecond exposure times are still insufficient to reach
the coherence time of daytime seeing. Nonetheless, the analysis shows
that data acquisition rates exceeding 50 Hz are required to capture a
substantial fraction of the best seeing moments, significantly boosting
the performance of post-facto image restoration.
Title: Ca II 8542 Å brightenings induced by a solar microflare
Authors: Kuckein, C.; Diercke, A.; González Manrique, S. J.; Verma,
M.; Löhner-Böttcher, J.; Socas-Navarro, H.; Balthasar, H.; Sobotka,
M.; Denker, C.
Bibcode: 2017A&A...608A.117K
Altcode: 2017arXiv170906861K
Aims: We study small-scale brightenings in Ca II 8542 Å
line-core images to determine their nature and effect on localized
heating and mass transfer in active regions.
Methods:
High-resolution two-dimensional spectroscopic observations of a solar
active region in the near-infrared Ca II 8542 Å line were acquired
with the GREGOR Fabry-Pérot Interferometer attached to the 1.5-m GREGOR
telescope. Inversions of the spectra were carried out using the NICOLE
code to infer temperatures and line-of-sight (LOS) velocities. Response
functions of the Ca II line were computed for temperature and LOS
velocity variations. Filtergrams of the Atmospheric Imaging Assembly
(AIA) and magnetograms of the Helioseismic and Magnetic Imager (HMI)
were coaligned to match the ground-based observations and to follow the
Ca II brightenings along all available layers of the atmosphere.
Results: We identified three brightenings of sizes up to 2'' × 2''
that appeared in the Ca II 8542 Å line-core images. Their lifetimes
were at least 1.5 min. We found evidence that the brightenings belonged
to the footpoints of a microflare (MF). The properties of the observed
brightenings disqualified the scenarios of Ellerman bombs or Interface
Region Imaging Spectrograph (IRIS) bombs. However, this MF shared some
common properties with flaring active-region fibrils or flaring arch
filaments (FAFs): (1) FAFs and MFs are both apparent in chromospheric
and coronal layers according to the AIA channels; and (2) both show
flaring arches with lifetimes of about 3.0-3.5 min and lengths of
20'' next to the brightenings. The inversions revealed heating by
600 K at the footpoint location in the ambient chromosphere during
the impulsive phase. Connecting the footpoints, a dark filamentary
structure appeared in the Ca II line-core images. Before the
start of the MF, the spectra of this structure already indicated
average blueshifts, meaning upward motions of the plasma along the
LOS. During the impulsive phase, these velocities increased up to -
2.2 km s-1. The structure did not disappear during the
observations. Downflows dominated at the footpoints. However, in
the upper photosphere, slight upflows occurred during the impulsive
phase. Hence, bidirectional flows are present in the footpoints
of the MF.
Conclusions: We detected Ca II brightenings that
coincided with the footpoint location of an MF. The MF event led to
a rise of plasma in the upper photosphere, both before and during the
impulsive phase. Excess mass, previously raised to at most chromospheric
layers, slowly drained downward along arches toward the footpoints
of the MF. The movie associated to Fig. 2 is available at http://www.aanda.org
Title: Signatures of the impact of flare-ejected plasma on the
photosphere of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Rajaguru, S. P.;
Franz, M.; Kuckein, C.; Asensio Ramos, A.
Bibcode: 2017A&A...608A..97F
Altcode: 2017arXiv170806133F
Aims: We investigate the properties of a sunspot light bridge,
focusing on the changes produced by the impact of a plasma blob ejected
from a C-class flare.
Methods: We observed a sunspot in active
region NOAA 12544 using spectropolarimetric raster maps of the four
Fe I lines around 15 655 Å with the GREGOR Infrared Spectrograph,
narrow-band intensity images sampling the Fe I 6173 Å line with
the GREGOR Fabry-Pérot Interferometer, and intensity broad-band
images in G-band and Ca II H-band with the High-resolution Fast
Imager. All these instruments are located at the GREGOR telescope at
the Observatorio del Teide, Tenerife, Spain. The data cover the time
before, during, and after the flare event. The analysis is complemented
with Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager
data from the Solar Dynamics Observatory. The physical parameters of
the atmosphere at differents heights were inferred using spectral-line
inversion techniques.
Results: We identify photospheric and
chromospheric brightenings, heating events, and changes in the Stokes
profiles associated with the flare eruption and the subsequent arrival
of the plasma blob to the light bridge, after traveling along an
active region loop.
Conclusions: The measurements suggest that
these phenomena are the result of reconnection events driven by the
interaction of the plasma blob with the magnetic field topology of the
light bridge. Movies attached to Figs. 1 and 3 are available at http://www.aanda.org
Title: sTools - a data reduction pipeline for the GREGOR Fabry-Pérot
Interferometer and the High-resolution Fast Imager at the GREGOR
solar telescope
Authors: Kuckein, C.; Denker, C.; Verma, M.; Balthasar, H.; González
Manrique, S. J.; Louis, R. E.; Diercke, A.
Bibcode: 2017IAUS..327...20K
Altcode: 2017arXiv170101670K
A huge amount of data has been acquired with the GREGOR Fabry-Pérot
Interferometer (GFPI), large-format facility cameras, and since 2016
with the High-resolution Fast Imager (HiFI). These data are processed
in standardized procedures with the aim of providing science-ready data
for the solar physics community. For this purpose, we have developed a
user-friendly data reduction pipeline called ``sTools'' based on the
Interactive Data Language (IDL) and licensed under creative commons
license. The pipeline delivers reduced and image-reconstructed data
with a minimum of user interaction. Furthermore, quick-look data are
generated as well as a webpage with an overview of the observations and
their statistics. All the processed data are stored online at the GREGOR
GFPI and HiFI data archive of the Leibniz Institute for Astrophysics
Potsdam (AIP). The principles of the pipeline are presented together
with selected high-resolution spectral scans and images processed
with sTools.
Title: Flows along arch filaments observed in the GRIS `very fast
spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2017IAUS..327...28G
Altcode: 2017arXiv170102206G
A new generation of solar instruments provides improved spectral,
spatial, and temporal resolution, thus facilitating a better
understanding of dynamic processes on the Sun. High-resolution
observations often reveal multiple-component spectral line profiles,
e.g., in the near-infrared He i 10830 Å triplet, which provides
information about the chromospheric velocity and magnetic fine
structure. We observed an emerging flux region, including two small
pores and an arch filament system, on 2015 April 17 with the `very
fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
situated at the 1.5-meter GREGOR solar telescope at Observatorio del
Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
per minute) spectral scans of the solar surface and its potential to
follow dynamic processes on the Sun. We demonstrate the performance
of the `very fast spectroscopic mode' by tracking chromospheric
high-velocity features in the arch filament system.
Title: Flare-induced changes of the photospheric magnetic field in
a δ-spot deduced from ground-based observations
Authors: Gömöry, P.; Balthasar, H.; Kuckein, C.; Koza, J.;
Veronig, A. M.; González Manrique, S. J.; Kučera, A.; Schwartz,
P.; Hanslmeier, A.
Bibcode: 2017A&A...602A..60G
Altcode: 2017arXiv170406089G
Aims: Changes of the magnetic field and the line-of-sight
velocities in the photosphere are being reported for an M-class
flare that originated at a δ-spot belonging to active region NOAA
11865.
Methods: High-resolution ground-based near-infrared
spectropolarimetric observations were acquired simultaneously in
two photospheric spectral lines, Fe I 10783 Å and Si I 10786 Å,
with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope
(VTT) in Tenerife on 2013 October 15. The observations covered several
stages of the M-class flare. Inversions of the full-Stokes vector of
both lines were carried out and the results were put into context using
(extreme)-ultraviolet filtergrams from the Solar Dynamics Observatory
(SDO).
Results: The active region showed high flaring activity
during the whole observing period. After the M-class flare, the
longitudinal magnetic field did not show significant changes along
the polarity inversion line (PIL). However, an enhancement of the
transverse magnetic field of approximately 550 G was found that
bridges the PIL and connects umbrae of opposite polarities in the
δ-spot. At the same time, a newly formed system of loops appeared
co-spatially in the corona as seen in 171 Å filtergrams of the
Atmospheric Imaging Assembly (AIA) on board SDO. However, we cannot
exclude that the magnetic connection between the umbrae already existed
in the upper atmosphere before the M-class flare and became visible
only later when it was filled with hot plasma. The photospheric
Doppler velocities show a persistent upflow pattern along the PIL
without significant changes due to the flare.
Conclusions:
The increase of the transverse component of the magnetic field after
the flare together with the newly formed loop system in the corona
support recent predictions of flare models and flare observations. The movie associated to Figs. 4 and 5 is available at http://www.aanda.org
Title: Physical properties of a group of pores as derived from Ca
II 854.2 nm observations and inversions at GREGOR
Authors: Kuckein, Christoph
Bibcode: 2017psio.confE..45K
Altcode:
No abstract at ADS
Title: Center-to-limb variation of the velocity field in and around
a sunspot with light-bridges
Authors: Denker, Carsten; Verma, Meetu; Balthasar, Horst; Diercke,
Andrea; González Manrique, S. J.; Löhner-Böttcher, Johannes;
Kuckein, Christoph; Sobotka, Michal
Bibcode: 2017psio.confE.104D
Altcode:
No abstract at ADS
Title: Velocity fields in sunspots derived from observations with
the GREGOR Fabry-Pérot Interferometer
Authors: Balthasar, H.; Denker, C.; Diercke, A.; González Manrique,
S. J.; Kuckein, C.; Louis, R. E.; Verma, M., Löhner-Böttcher, J.;
Sobotka, M.
Bibcode: 2017psio.confE.105B
Altcode:
No abstract at ADS
Title: Flare induced changes of the photospheric magnetic field in
a delta-spot deduced from ground-based observations
Authors: Gömöry, P.; Balthasar, H.; Kuckein, C.; Koza, J.;
Kuĉera, A.; González Manrique, S. J.; Schwartz, P.; Veronig, A. M.;
Hanslmeier, A.
Bibcode: 2017psio.confE.107G
Altcode:
No abstract at ADS
Title: Slipping reconnection in a solar flare observed in high
resolution with the GREGOR solar telescope
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.;
Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.;
Volkmer, R.; Waldmann, T.
Bibcode: 2016A&A...596A...1S
Altcode: 2016arXiv160500464S
A small flare ribbon above a sunspot umbra in active region 12205 was
observed on November 7, 2014, at 12:00 UT in the blue imaging channel
of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference
filter. Context observations from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical
Telescope (SOT) onboard Hinode, and the Interface Region Imaging
Spectrograph (IRIS) show that this ribbon is part of a larger one
that extends through the neighboring positive polarities and also
participates in several other flares within the active region. We
reconstructed a time series of 140 s of Ca II H images by means of the
multiframe blind deconvolution method, which resulted in spatial and
temporal resolutions of 0.1″ and 1 s. Light curves and horizontal
velocities of small-scale bright knots in the observed flare ribbon
were measured. Some knots are stationary, but three move along the
ribbon with speeds of 7-11 km s-1. Two of them move in the
opposite direction and exhibit highly correlated intensity changes,
which provides evidence of a slipping reconnection at small spatial
scales. Movies associated to Figs. 1 and 2 are available at http://www.aanda.org
Title: NLTE modeling of a small active region filament observed with
the VTT
Authors: Schwartz, P.; Balthasar, H.; Kuckein, C.; Koza, J.; Gömöry,
P.; Rybák, J.; Heinzel, P.; Kučera, A.
Bibcode: 2016AN....337.1045S
Altcode:
An active region mini-discretionary-filament was observed with the
Vacuum Tower Telescope (VTT) in Tenerife simultaneously in the He
I infrared triplet using the Tenerife Infrared Polarimeter 1 (TIP
1), in Hα with the TESOS Fabry-Pérot interferometer, and in Ca II
8542 Å with the VTT spectrograph. The spectropolarimetric data were
inverted using the HAZEL code and Hα profiles were modelled by solving
a NLTE radiative transfer in a simple isobaric and isothermal 2D slab
irradiated both from its bottom and sides from the solar surface. It was
found that the mini-discretionary-filament is composed of horizontal
fluxtubes, along which the cool plasma of T∼10 000 K can flow with
very large, even supersonic, velocities.
Title: Spectropolarimetric observations of an arch filament system
with the GREGOR solar telescope
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.;
Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.;
Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016AN....337.1050B
Altcode: 2016arXiv160901514B
Arch filament systems occur in active sunspot groups, where a fibril
structure connects areas of opposite magnetic polarity, in contrast to
active region filaments that follow the polarity inversion line. We
used the GREGOR Infrared Spectrograph (GRIS) to obtain the full
Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0
nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line
to investigate the photospheric magnetic field and velocities, and
use the line core intensities and velocities of the helium line to
study the chromospheric plasma. The individual fibrils of the arch
filament system connect the sunspot with patches of magnetic polarity
opposite to that of the spot. These patches do not necessarily coincide
with pores, where the magnetic field is strongest. Instead, areas are
preferred not far from the polarity inversion line. These areas exhibit
photospheric downflows of moderate velocity, but significantly higher
downflows of up to 30 km s-1 in the chromospheric helium
line. Our findings can be explained with new emerging flux where the
matter flows downward along the field lines of rising flux tubes,
in agreement with earlier results.
Title: Horizontal flow fields in and around a small active region. The
transition period between flux emergence and decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016A&A...596A...3V
Altcode: 2016arXiv160507462V
Context. The solar magnetic field is responsible for all aspects
of solar activity. Thus, emergence of magnetic flux at the surface
is the first manifestation of the ensuing solar activity.
Aims: Combining high-resolution and synoptic observations aims to
provide a comprehensive description of flux emergence at photospheric
level and of the growth process that eventually leads to a mature
active region.
Methods: The small active region NOAA 12118
emerged on 2014 July 17 and was observed one day later with the 1.5-m
GREGOR solar telescope on 2014 July 18. High-resolution time-series
of blue continuum and G-band images acquired in the blue imaging
channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were
complemented by synoptic line-of-sight magnetograms and continuum
images obtained with the Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO). Horizontal proper motions and
horizontal plasma velocities were computed with local correlation
tracking (LCT) and the differential affine velocity estimator (DAVE),
respectively. Morphological image processing was employed to measure
the photometric and magnetic area, magnetic flux, and the separation
profile of the emerging flux region during its evolution.
Results: The computed growth rates for photometric area, magnetic
area, and magnetic flux are about twice as high as the respective
decay rates. The space-time diagram using HMI magnetograms of five days
provides a comprehensive view of growth and decay. It traces a leaf-like
structure, which is determined by the initial separation of the two
polarities, a rapid expansion phase, a time when the spread stalls,
and a period when the region slowly shrinks again. The separation
rate of 0.26 km s-1 is highest in the initial stage, and
it decreases when the separation comes to a halt. Horizontal plasma
velocities computed at four evolutionary stages indicate a changing
pattern of inflows. In LCT maps we find persistent flow patterns such
as outward motions in the outer part of the two major pores, a diverging
feature near the trailing pore marking the site of upwelling plasma and
flux emergence, and low velocities in the interior of dark pores. We
detected many elongated rapidly expanding granules between the two
major polarities, with dimensions twice as large as the normal granules.
Title: Solar physics at the Einstein Tower
Authors: Denker, C.; Heibel, C.; Rendtel, J.; Arlt, K.; Balthasar,
Juergen H.; Diercke, A.; González Manrique, S. J.; Hofmann, A.;
Kuckein, C.; Önel, H.; Senthamizh Pavai, V.; Staude, J.; Verman, M.
Bibcode: 2016AN....337.1105D
Altcode: 2016arXiv160906949D
The solar observatory Einstein Tower ({Einsteinturm}) at the
Telegrafenberg in Potsdam is both a landmark of modern architecture
and an important place for solar physics. Originally built for
high-resolution spectroscopy and measuring the gravitational redshift,
research shifted over the years to understanding the active Sun and
its magnetic field. Nowadays, telescope and spectrographs are used for
research and development, i.e., testing instruments and in particular
polarization optics for advanced instrumentation deployed at major
European and international astronomical and solar telescopes. In
addition, the Einstein Tower is used for educating and training of the
next generation astrophysicists as well as for education and public
outreach activities directed at the general public. This article
comments on the observatory's unique architecture and the challenges
of maintaining and conserving the building. It describes in detail the
characteristics of telescope, spectrographs, and imagers; it portrays
some of the research and development activities.
Title: Probing deep photospheric layers of the quiet Sun with high
magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
Schmidt, D.; Kiess, C.; Nicklas, H.
Bibcode: 2016A&A...596A...6L
Altcode: 2016arXiv160506324L
Context. Investigations of the magnetism of the quiet Sun are hindered
by extremely weak polarization signals in Fraunhofer spectral
lines. Photon noise, straylight, and the systematically different
sensitivity of the Zeeman effect to longitudinal and transversal
magnetic fields result in controversial results in terms of the strength
and angular distribution of the magnetic field vector.
Aims:
The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
spatial straylight and photon noise into account.
Methods: Highly
sensitive full Stokes measurements of a quiet-Sun region at disk center
in the deep photospheric Fe I lines in the 1.56 μm region were obtained
with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
diagnostics based directly on the shape and strength of the profiles
were applied to the GRIS data. We made use of the magnetic line ratio
technique, which was tested against realistic magneto-hydrodynamic
simulations (MURaM).
Results: About 80% of the GRIS spectra
of a very quiet solar region show polarimetric signals above a 3σ
level. Area and amplitude asymmetries agree well with small-scale
surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields.
Conclusions:
The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
are so far unique in the combination of high spatial resolution scans
and high magnetic field sensitivity. Nevertheless, the unavoidable
effect of spatial straylight and the resulting dilution of the weak
Stokes profiles means that inversion techniques still bear a high risk
of misinterpretating the data.
Title: Flow and magnetic field properties in the trailing sunspots
of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016AN....337.1090V
Altcode:
Improved measurements of the photospheric and chromospheric
three-dimensional magnetic and flow fields are crucial for a precise
determination of the origin and evolution of active regions. We present
an illustrative sample of multi-instrument data acquired during a
two-week coordinated observing campaign in August 2015 involving,
among others, the GREGOR solar telescope (imaging and near-infrared
spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
and Interface Region Imaging Spectrograph (IRIS). The observations
focused on the trailing part of active region NOAA 12396 with complex
polarity inversion lines and strong intrusions of opposite polarity
flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
spectral profiles in the photospheric Si I λ1082.7 nm line, the
chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
provided maps of Doppler velocity and magnetic field at different
atmospheric heights. We compare quick-look maps with those obtained
with the ``Stokes Inversions based on Response functions'' (SIR)
code, which furnishes deeper insight into the magnetic properties
of the region. We find supporting evidence that newly emerging flux
and intruding opposite polarity flux are hampering the formation
of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
expected after cessation of flux emergence in proximity to the sunspots.
Title: Three-dimensional structure of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio
Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.;
Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier,
R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki,
S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.;
von der Lühe, O.; Waldmann, T.
Bibcode: 2016A&A...596A..59F
Altcode: 2016arXiv161104803F
Context. Active regions are the most prominent manifestations of solar
magnetic fields; their generation and dissipation are fundamental
problems in solar physics. Light bridges are commonly present during
sunspot decay, but a comprehensive picture of their role in the
removal of the photospheric magnetic field is still lacking.
Aims: We study the three-dimensional configuration of a sunspot,
and in particular, its light bridge, during one of the last stages of
its decay.
Methods: We present the magnetic and thermodynamical
stratification inferred from full Stokes inversions of the photospheric
Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
Infrared Spectrograph of the GREGOR telescope at the Observatorio del
Teide, Tenerife, Spain. The analysis is complemented by a study of
continuum images covering the disk passage of the active region, which
are provided by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory.
Results: The sunspot shows a light bridge
with penumbral continuum intensity that separates the central umbra from
a smaller umbra. We find that in this region the magnetic field lines
form a canopy with lower magnetic field strength in the inner part. The
photospheric light bridge is dominated by gas pressure (high-β),
as opposed to the surrounding umbra, where the magnetic pressure
is higher. A convective flow is observed in the light bridge. This
flow is able to bend the magnetic field lines and to produce field
reversals. The field lines merge above the light bridge and become
as vertical and strong as in the surrounding umbra. We conclude that
this occurs because two highly magnetized regions approach each other
during the sunspot evolution. Movies associated to Figs. 2 and 13
are available at http://www.aanda.org
Title: Inference of magnetic fields in the very quiet Sun
Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.;
Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.;
Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.;
González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.;
Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.;
Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman,
T.; Volkmer, R.
Bibcode: 2016A&A...596A...5M
Altcode: 2018arXiv180410089M
Context. Over the past 20 yr, the quietest areas of the solar surface
have revealed a weak but extremely dynamic magnetism occurring
at small scales (<500 km), which may provide an important
contribution to the dynamics and energetics of the outer layers of
the atmosphere. Understanding this magnetism requires the inference
of physical quantities from high-sensitivity spectro-polarimetric
data with high spatio-temporal resolution.
Aims: We present
high-precision spectro-polarimetric data with high spatial resolution
(0.4'') of the very quiet Sun at 1.56 μm obtained with the GREGOR
telescope to shed some light on this complex magnetism.
Methods:
We used inversion techniques in two main approaches. First, we assumed
that the observed profiles can be reproduced with a constant magnetic
field atmosphere embedded in a field-free medium. Second, we assumed
that the resolution element has a substructure with either two constant
magnetic atmospheres or a single magnetic atmosphere with gradients of
the physical quantities along the optical depth, both coexisting with
a global stray-light component.
Results: Half of our observed
quiet-Sun region is better explained by magnetic substructure within
the resolution element. However, we cannot distinguish whether this
substructure comes from gradients of the physical parameters along the
line of sight or from horizontal gradients (across the surface). In
these pixels, a model with two magnetic components is preferred, and
we find two distinct magnetic field populations. The population with
the larger filling factor has very weak ( 150 G) horizontal fields
similar to those obtained in previous works. We demonstrate that the
field vector of this population is not constrained by the observations,
given the spatial resolution and polarimetric accuracy of our data. The
topology of the other component with the smaller filling factor is
constrained by the observations for field strengths above 250 G:
we infer hG fields with inclinations and azimuth values compatible
with an isotropic distribution. The filling factors are typically
below 30%. We also find that the flux of the two polarities is not
balanced. From the other half of the observed quiet-Sun area 50% are
two-lobed Stokes V profiles, meaning that 23% of the field of view
can be adequately explained with a single constant magnetic field
embedded in a non-magnetic atmosphere. The magnetic field vector and
filling factor are reliable inferred in only 50% based on the regular
profiles. Therefore, 12% of the field of view harbour hG fields with
filling factors typically below 30%. At our present spatial resolution,
70% of the pixels apparently are non-magnetised.
Title: Fitting peculiar spectral profiles in He I 10830Å absorption
features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016AN....337.1057G
Altcode: 2016arXiv160300679G
The new generation of solar instruments provides better
spectral, spatial, and temporal resolution for a better
understanding of the physical processes that take place on the
Sun. Multiple-component profiles are more commonly observed with these
instruments. Particularly, the He I 10830 Å triplet presents such
peculiar spectral profiles, which give information on the velocity
and magnetic fine structure of the upper chromosphere. The purpose
of this investigation is to describe a technique to efficiently fit
the two blended components of the He I 10830 Å triplet, which are
commonly observed when two atmospheric components are located within
the same resolution element. The observations used in this study were
taken on 2015 April 17 with the very fast spectroscopic mode of the
GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
telescope, located at the Observatorio del Teide, Tenerife, Spain. We
apply a double-Lorentzian fitting technique using Levenberg-Marquardt
least-squares minimization. This technique is very simple and much
faster than inversion codes. Line-of-sight Doppler velocities can
be inferred for a whole map of pixels within just a few minutes. Our
results show sub- and supersonic downflow velocities of up to 32 km
s-1 for the fast component in the vicinity of footpoints of
filamentary structures. The slow component presents velocities close
to rest.
Title: Giant quiescent solar filament observed with high-resolution
spectroscopy
Authors: Kuckein, C.; Verma, M.; Denker, C.
Bibcode: 2016A&A...589A..84K
Altcode: 2016arXiv160302505K
Aims: An extremely large filament was studied in various
layers of the solar atmosphere. The inferred physical parameters
and the morphological aspects are compared with smaller quiescent
filaments.
Methods: A giant quiet-Sun filament was observed
with the high-resolution Echelle spectrograph at the Vacuum Tower
Telescope at Observatorio del Teide, Tenerife, Spain, on 2011 November
15. A mosaic of spectra (ten maps of 100″ × 182″) was recorded
simultaneously in the chromospheric absorption lines Hα and Na I
D2. Physical parameters of the filament plasma were derived
using cloud model (CM) inversions and line core fits. The spectra
were complemented with full-disk filtergrams (He I λ10830 Å, Hα,
and Ca II K) of the Chromospheric Telescope (ChroTel) and full-disk
magnetograms of the Helioseismic and Magnetic Imager (HMI).
Results: The filament had extremely large linear dimensions (~817
arcsec), which corresponds to about 658 Mm along a great circle on
the solar surface. A total amount of 175119 Hα contrast profiles
were inverted using the CM approach. The inferred mean line-of-sight
(LOS) velocity, Doppler width, and source function were similar to
previous works of smaller quiescent filaments. However, the derived
optical thickness was higher. LOS velocity trends inferred from the
Hα line core fits were in accord but weaker than those obtained with
CM inversions. Signatures of counter-streaming flows were detected
in the filament. The largest brightening conglomerates in the line
core of Na I D2 coincided well with small-scale magnetic
fields as seen by HMI. Mixed magnetic polarities were detected close
to the ends of barbs. The computation of photospheric horizontal flows
based on HMI magnetograms revealed flow kernels with a size of 5-8
Mm and velocities of 0.30-0.45 km s-1 at the ends of the
filament.
Conclusions: The physical properties of extremely
large filaments are similar to their smaller counterparts, except for
the optical thickness, which in our sample was found to be higher. We
found that a part of the filament, which erupted the day before,
is in the process of reestablishing its initial configuration.
Title: Flows in and around Active Region NOAA12118 Observed with
the GREGOR Solar Telescope and SDO/HMI
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016ASPC..504...29V
Altcode: 2016arXiv160301109V
Accurate measurements of magnetic and velocity fields in and around
solar active regions are key to unlocking the mysteries of the
formation and the decay of sunspots. High spatial resolution images
and spectral sequences with a high cadence obtained with the GREGOR
solar telescope give us an opportunity to scrutinize 3-D flow fields
with local correlation tracking and imaging spectroscopy. We present
GREGOR early science data acquired in 2014 July - August with the GREGOR
Fabry-Pérot Interferometer and the Blue Imaging Channel. Time-series
of blue continuum (λ 450.6 nm) images of the small active region
NOAA 12118 were restored with the speckle masking technique to derive
horizontal proper motions and to track the evolution of morphological
changes. In addition, high-resolution observations are discussed in
the context of synoptic data from the Solar Dynamics Observatory.
Title: Non-LTE Inversion of Spectropolarimetric and Spectroscopic
Observations of a Small Active-region Filament Observed at the VTT
Authors: Schwartz, P.; Balthasar, H.; Kuckein, C.; Koza, J.; Gömöry,
P.; Rybák, J.; Kučera, A.; Heinzel, P.
Bibcode: 2016ASPC..504..205S
Altcode:
An active region mini-filament was observed by VTT simultaneously
in the He<small>I</small> 10 830 Å triplet by the TIP 1
spectropolarimeter, in Hα by the TESOS Fabry-Pérot interferometer, and
in Ca <small>II</small> 8542 Å by the VTT spectrograph. The
spectropolarimetric data were inverted using the HAZEL code and Hα
profiles were modelled solving a NLTE radiative transfer in a simple
isobaric and isothermal 2D slab irradiated both from bottom and
sides. It was found that the mini-filament is composed of horizontal
fluxtubes, along which the cool plasma of T∼10 000 K can flow by
very large - even supersonic - velocities.
Title: Full Stokes observations in the He i 1083 nm spectral region
covering an M3.2 flare
Authors: Kuckein, Christoph; Collados, Manuel; Sainz, Rafael Manso;
Ramos, Andrés Asensio
Bibcode: 2015IAUS..305...73K
Altcode: 2015arXiv150205505K
We present an exceptional data set acquired with the Vacuum Tower
Telescope (Tenerife, Spain) covering the pre-flare, flare, and
post-flare stages of an M3.2 flare. The full Stokes spectropolarimetric
observations were recorded with the Tenerife Infrared Polarimeter in
the He i 1083.0 nm spectral region. The object under study was active
region NOAA 11748 on 2013 May 17. During the flare the chomospheric
He i 1083.0 nm intensity goes strongly into emission. However, the
nearby photospheric Si i 1082.7 nm spectral line profile only gets
shallower and stays in absorption. Linear polarization (Stokes Q and U)
is detected in all lines of the He i triplet during the flare. Moreover,
the circular polarization (Stokes V) is dominant during the flare,
being the blue component of the He i triplet much stronger than the red
component, and both are stronger than the Si i Stokes V profile. The Si
i inversions reveal enormous changes of the photospheric magnetic field
during the flare. Before the flare magnetic field concentrations of up
to ~1500 G are inferred. During the flare the magnetic field strength
globally decreases and in some cases it is even absent. After the flare
the magnetic field recovers its strength and initial configuration.
Title: Magnetic and Dynamical Photospheric Disturbances Observed
During an M3.2 Solar Flare
Authors: Kuckein, C.; Collados, M.; Manso Sainz, R.
Bibcode: 2015ApJ...799L..25K
Altcode: 2015arXiv150104207K
This Letter reports on a set of full-Stokes spectropolarimetric
observations in the near-infrared He i 10830 Å spectral region
covering the pre-flare, flare, and post-flare phases of an M3.2 class
solar flare. The flare originated on 2013 May 17 and belonged to
active region NOAA 11748. We detected strong He i 10830 Å emission
in the flare. The red component of the He i triplet peaks at an
intensity ratio to the continuum of about 1.86. During the flare,
He i Stokes V is substantially larger and appears reversed compared
to the usually larger Si i Stokes V profile. The photospheric Si i
inversions of the four Stokes profiles reveal the following: (1) the
magnetic field strength in the photosphere decreases or is even absent
during the flare phase, as compared to the pre-flare phase. However,
this decrease is not permanent. After the flare, the magnetic field
recovers its pre-flare configuration in a short time (i.e., 30 minutes
after the flare). (2) In the photosphere, the line of sight velocities
show a regular granular up- and downflow pattern before the flare
erupts. During the flare, upflows (blueshifts) dominate the area where
the flare is produced. Evaporation rates of ∼ {{10}-3}
and ∼ {{10}-4} g cm-2 s-1 have been
derived in the deep and high photosphere, respectively, capable of
increasing the chromospheric density by a factor of two in about 400 s.
Title: The association between sunspot magnetic fields and
superpenumbral fibrils
Authors: Louis, R. E.; Balthasar, H.; Kuckein, C.; Gömöry, P.;
Puschmann, K. G.; Denker, C.
Bibcode: 2014AN....335..161L
Altcode: 2013arXiv1312.1879L
Spectropolarimetric observations of a sunspot were carried out with
the Tenerife Infrared Polarimeter at Observatorio del Teide, Tenerife,
Spain. Maps of the physical parameters were obtained from an inversion
of the Stokes profiles observed in the infrared Fe I line at 15 648
Å. The regular sunspot consisted of a light bridge which separated the
two umbral cores of the same polarity. One of the arms of the light
bridge formed an extension of a penumbral filament which comprised
weak and highly inclined magnetic fields. In addition, the Stokes V
profiles in this filament had an opposite sign as the sunspot and some
resembled Stokes Q or U. This penumbral filament terminated abruptly
into another at the edge of the sunspot, where the latter was relatively
vertical by about 30o. Chromospheric H\alpha and He II 304
Åfiltergrams revealed three superpenumbral fibrils on the limb-side
of the sunspot, in which one fibril extended into the sunspot and was
oriented along the highly inclined penumbral counterpart of the light
bridge. An intense, elongated brightening was observed along this fibril
that was co-spatial with the intersecting penumbral filaments in the
photosphere. Our results suggest that the disruption in the sunspot
magnetic field at the location of the light bridge could be the source
of reconnection that led to the intense chromospheric brightening and
facilitated the supply of cool material in maintaining the overlying
superpenumbral fibrils.
Title: Magnetic, Thermal and Dynamical Evolution of AN M3.2 Two-Ribbon
Flare
Authors: Collados, Manuel; Kuckein, Christoph; Manso Sainz, Rafael;
Asensio Ramos, Andres
Bibcode: 2014cosp...40E.568C
Altcode:
On 2013, 17th May, a two-ribbon M3.2 flare took place in the solar
atmosphere on the active region AR 11748. The flare evolution was
observed at the German VTT of the Observatorio del Teide using the
instrument TIP-II, with spectropolarimetric measurements of the
photosphere (Si I at 1082.7 nm) and the chromosphere (Helium triplet
at 1083 nm). Simultaneous spectroscopic data of the chromospheric
spectral line of Ca II at 854.2 nm and filtergrams at Halpha were
also obtained. The flare evolution as observed from the ground can be
compared with the changes observed by AIA@SDO at different ultraviolet
wavelengths. The ground observations covered several hours, including
the pre-flare, impulsive, gradual and post-flare phases. We present
maps of the magnetic field, thermal and dynamical properties of the
region during its evolution from pre- to post-flare phase.
Title: Formation and evolution of an active region filament
Authors: Kuckein, Christoph; Centeno, Rebeca; Pillet, Valentín
Martínez
Bibcode: 2014IAUS..300...40K
Altcode: 2013arXiv1309.7855K
Several scenarios explaining how filaments are formed can be found in
literature. In this paper, we analyzed the observations of an active
region filament and critically evaluated the observed properties
in the context of current filament formation models. This study is
based on multi-height spectropolarimetric observations. The inferred
vector magnetic field has been extrapolated starting either from the
photosphere or from the chromosphere. The line-of-sight motions of
the filament, which was located near disk center, have been analyzed
inferring the Doppler velocities. We conclude that a part of the
magnetic structure emerged from below the photosphere.
Title: High-resolution spectroscopy of a giant solar filament
Authors: Kuckein, Christoph; Denker, Carsten; Verma, Meetu
Bibcode: 2014IAUS..300..437K
Altcode: 2013arXiv1309.7861K
High-resolution spectra of a giant solar quiescent filament were
taken with the Echelle spectrograph at the Vacuum Tower Telescope
(VTT; Tenerife, Spain). A mosaic of various spectroheliograms (Hα,
Hα+/-0.5 Å and Na D2) were chosen to examine the filament
at different heights in the solar atmosphere. In addition, full-disk
images (He i 10830 Å and Ca ii K) of the Chromspheric Telescope and
full-disk magnetograms of the Helioseismic and Magnetic Imager were
used to complement the spectra. Preliminary results are shown of
this filament, which had extremely large linear dimensions (~740'')
and was observed in November 2011 while it traversed the northern
solar hemisphere.
Title: An active region filament studied simultaneously in the
chromosphere and photosphere. II. Doppler velocities
Authors: Kuckein, C.; Martínez Pillet, V.; Centeno, R.
Bibcode: 2012A&A...542A.112K
Altcode: 2012arXiv1204.5090K
Context. Paper I presents the magnetic structure, inferred for the
photosphere and the chromosphere, of a filament that developed in active
region (AR) NOAA 10781, observed on 2005 July 3 and July 5.
Aims: In this paper we complement those results with the velocities
retrieved from Doppler shifts measured at the chromosphere and the
photosphere in the AR filament area.
Methods: The velocities
and magnetic field parameters were inferred from full Stokes inversions
of the photospheric Si I 10 827 Å line and the chromospheric He i 10
830 Å triplet. Various inversion methods with different numbers of
atmospheric components and different weighting schemes of the Stokes
profiles were used. The velocities were calibrated on an absolute
scale.
Results: A ubiquitous chromospheric downflow is found
in the faculae surrounding the filament, with an average velocity of
1.6 km s-1. The filament region, however, displays upflows
in the photosphere on both days, when the linear polarization (which
samples the transverse component of the fields) is given more weight
in the inversions. The upflow speeds of the transverse fields in the
filament region average -0.15 km s-1. In the chromosphere,
the situation is different for the two days of observation. On July 3,
the chromospheric portion of the filament is moving upward as a whole
with a mean speed of -0.24 km s-1. However, on July 5 only
the section above an orphan penumbra shows localized upflow patches,
while the rest of the filament is dominated by the same downflows
observed elsewhere in the facular region. Photospheric supersonic
downflows that last for tens of minutes are detected below the filament,
close to the PIL.
Conclusions: The observed velocity pattern
in this AR filament strongly suggests a scenario where the transverse
fields are mostly dominated by upflows. The filament flux rope is seen
to be emerging at all places and both heights, with a few exceptions
in the chromosphere. This happens within a surrounding facular
region that displays a generalized downflow in the chromosphere and
localized downflows of supersonic character at the photosphere. No
large scale downflow of transverse field lines is observed at the
photosphere. Appendices A and B are available in electronic form
at http://www.aanda.org
Title: Doppler velocities studied simultaneously in the chromosphere
and photosphere of an active region filament
Authors: Kuckein, C.; Martinez Pillet, V.; Centeno, R.
Bibcode: 2012decs.confE..42K
Altcode:
We present line-of-sight velocities retrieved simultaneously at
two different heights (chromosphere and photosphere) on two days
in an active region (AR) filament. The velocities, as well as the
magnetic field parameters, were inferred from full Stokes inversions
of the photospheric Si I 10827A line and the chromospheric He I 10830A
triplet. Various inversion methods with different number of components
and different weights of the Stokes parameters were used. Moreover,
the velocities were calibrated on an absolute scale. We found a
ubiquitous chromospheric downflow in the faculae surrounding the
AR filament with an average velocity of 1.6 km/s. However, in the
filament region, upflows in the photosphere were detected, when the
Stokes signals from the transverse fields are given more weight in the
inversions. In the chromosphere, the filament is also moving upward
as a whole with a mean speed of -0.24 km/s as deduced from the He I
inversions. However, on the second day the chromospheric portion above
an orphan penumbra shows localized upflow patches while the rest of the
filament is dominated by the same downflows observed elsewhere in the
plage region. Photospheric supersonic downflows are detected below the
filament, close to the PIL, that last for tens of minutes. The observed
velocities in this AR filament strongly suggest a scenario where the
transverse fields are mostly dominated by upflows. The filament flux
rope is seen to be emerging at all heights with a few exceptions in
the chromosphere. No large scale downflow of transverse field lines
is observed in the photosphere.
Title: An active region filament studied simultaneously in the
chromosphere and photosphere. I. Magnetic structure
Authors: Kuckein, C.; Martínez Pillet, V.; Centeno, R.
Bibcode: 2012A&A...539A.131K
Altcode: 2011arXiv1112.1672K
Aims: A thorough multiwavelength, multiheight study of the
vector magnetic field in a compact active region filament (NOAA 10781)
on 2005 July 3 and 5 is presented. We suggest an evolutionary scenario
for this filament.
Methods: Two different inversion codes were
used to analyze the full Stokes vectors acquired with the Tenerife
Infrared Polarimeter (TIP-II) in a spectral range that comprises the
chromospheric He i 10 830 Å multiplet and the photospheric Si i 10
827 Å line. In addition, we used SOHO/MDI magnetograms, as well as
BBSO and TRACE images, to study the evolution of the filament and its
active region (AR). High-resolution images of the Dutch Open Telescope
were also used.
Results: An active region filament (formed
before our observing run) was detected in the chromospheric helium
absorption images on July 3. The chromospheric vector magnetic field
in this portion of the filament was strongly sheared (parallel to the
filament axis), whereas the photospheric field lines underneath had
an inverse polarity configuration. From July 3 to July 5, an opening
and closing of the polarities on either side of the polarity inversion
line (PIL) was recorded, resembling the recently discovered process
of the sliding door effect seen by Hinode. This is confirmed with both
TIP-II and SOHO/MDI data. During this time, a newly created region that
contained pores and orphan penumbrae at the PIL was observed. On July
5, a normal polarity configuration was inferred from the chromospheric
spectra, while strongly sheared field lines aligned with the PIL were
found in the photosphere. In this same data set, the spine of the
filament is also observed in a different portion of the field of view
and is clearly mapped by the silicon line core.
Conclusions:
The inferred vector magnetic fields of the filament suggest a flux rope
topology. Furthermore, the observations indicate that the filament is
divided in two parts, one which lies in the chromosphere and another
one that stays trapped in the photosphere. Therefore, only the top
of the helical structure is seen by the helium lines. The pores and
orphan penumbrae at the PIL appear to be the photospheric counterpart
of the extremely low-lying filament. We suggest that orphan penumbrae
are formed in very narrow PILs of compact ARs and are the photospheric
manifestation of flux ropes in the photosphere.
Title: The Three-dimensional Structure of an Active Region Filament
as Extrapolated from Photospheric and Chromospheric Observations
Authors: Yelles Chaouche, L.; Kuckein, C.; Martínez Pillet, V.;
Moreno-Insertis, F.
Bibcode: 2012ApJ...748...23Y
Altcode: 2012arXiv1201.2456Y
The three-dimensional structure of an active region filament is studied
using nonlinear force-free field extrapolations based on simultaneous
observations at a photospheric and a chromospheric height. To that end,
we used the Si I 10827 Å line and the He I 10830 Å triplet obtained
with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope
(Tenerife). The two extrapolations have been carried out independently
from each other and their respective spatial domains overlap in
a considerable height range. This opens up new possibilities for
diagnostics in addition to the usual ones obtained through a single
extrapolation from, typically, a photospheric layer. Among those
possibilities, this method allows the determination of an average
formation height of the He I 10830 Å signal of ≈2 Mm above the
surface of the Sun. It allows, as well, a cross-check of the obtained
three-dimensional magnetic structures to verify a possible deviation
from the force-free condition, especially at the photosphere. The
extrapolations yield a filament formed by a twisted flux rope whose
axis is located at about 1.4 Mm above the solar surface. The twisted
field lines make slightly more than one turn along the filament within
our field of view, which results in 0.055 turns Mm-1. The
convex part of the field lines (as seen from the solar surface)
constitutes dips where the plasma can naturally be supported. The
obtained three-dimensional magnetic structure of the filament depends
on the choice of the observed horizontal magnetic field as determined
from the 180° solution of the azimuth. We derive a method to check
for the correctness of the selected 180° ambiguity solution.
Title: Study of the magnetic structure of active region filaments
Authors: Kuckein, Christoph
Bibcode: 2012PhDT.......336K
Altcode: 2013PhDT.......686K
No abstract at ADS
Title: Continuous upflow of material in an active region filament
from thephotosphere to the corona
Authors: Kuckein, C.; Centeno, R.; Martinez Pillet, V.
Bibcode: 2011hsa6.conf..636K
Altcode:
Using spectropolarimetric data of an Active Region (AR) filament
we have carried out inversions in order to infer vector magnetic
fields in the photosphere (Si I line) and in the chromosphere
(He I line). Our filament lies above the polarity inversion line
(PIL) situated close to disk center and presents strong Zeeman-like
signatures in both photospheric and chromospheric lines. Pore-like
formations with both polarities are identified in the continuum under
the PIL. The azimuth ambiguity is solved at both heights using the
AZAM code. A comparison between the photospheric and chromospheric
vector magnetic fields revealed that they are well aligned in some
areas of the filament. However, especially at chromospheric heights,
the magnetic field is mostly aligned with the dark threads of the
filament. Velocity signatures indicating upflows of field lines are
found at both heights. The combination of all these findings strongly
suggests an emerging flux rope scenario.
Title: Evolution of an active region filament as observed in the
photosphere and chromosphere simultaneously
Authors: Kuckein, Christoph; Pillet, Martinez; Valentin; Centeno;
Rebeca
Bibcode: 2011sdmi.confE..99K
Altcode:
A multiwavelength study and comparison of the vector magnetic field in
a compact active region filament (NOAA 10781) for 2005 July 3rd and
5th is presented. Different inversion codes were used to analyze the
full Stokes vectors acquired with the Tenerife Infrared Polarimeter
(TIP-II) in a spectral range which comprises the chromospheric He
I 10830 A multiplet and the photospheric Si I 10827 A line. Other
data from ground- and space-based telescopes has been used to have a
complete view of the evolution of the active region (AR). We found
that the filament was clearly observed for the first time, on July
3rd, after a "sliding-door" effect a-la Okamoto et al. (2008) of
the polarity inversion line (PIL). The chromospheric vector magnetic
field in the filament was strongly sheared (parallel to the filament
axis) whereas the photospheric field lines had an inverse polarity
configuration. For July 5th we had a different field of view but still
half of it remained the same. We now observed pores and orphan-penumbral
features that emerged along the PIL. A normal polarity configuration
is inferred in the filament above these features and strongly sheared
field lines along the PIL are found below, in the photosphere. The
inferred vector magnetic fields of the filament suggest a flux
rope topology. Furthermore, the observations indicate that the
filament is divided in two parts, one of it seems to be trapped in
the photosphere. Inferred magnetic field strengths and velocity
measurements inside and below the filament will be presented. An
evolutionary scenario for this AR filament is suggested.
Title: Continuous Upflow of Material in an Active Region Filament
from the Photosphere to the Corona
Authors: Kuckein, C.; Centeno, R.; Martínez Pillet, V.
Bibcode: 2011ASPC..437..275K
Altcode: 2010arXiv1010.4260K
Using spectropolarimetric data of an Active Region (AR) filament
we have carried out inversions in order to infer vector magnetic
fields in the photosphere (Si I line) and in the chromosphere
(He I line). Our filament lies above the polarity inversion line
(PIL) situated close to disk center and presents strong Zeeman-like
signatures in both photospheric and chromospheric lines. Pore-like
formations with both polarities are identified in the continuum under
the PIL. The azimuth ambiguity is solved at both heights using the
AZAM code. A comparison between the photospheric and chromospheric
vector magnetic fields revealed that they are well aligned in some
areas of the filament. However, especially at chromospheric heights,
the magnetic field is mostly aligned with the dark threads of the
filament. Velocity signatures indicating upflows of field lines are
found at both heights. The combination of all these findings strongly
suggests an emerging flux rope scenario.
Title: Spectropolarimetric inversions of the He I 10830 Å multiplet
in an active region filament.
Authors: Kuckein, C.; Centeno, R.; Martínez Pillet, V.
Bibcode: 2010MmSAI..81..668K
Altcode: 2010arXiv1001.2434K
Full-Stokes spectropolarimetric data (in the 10830 Å region)
of an active region filament were obtained in July 2005 using
the Tenerife Infrared Polarimeter instrument. The polarization
profiles in the filament show Zeeman-like signatures. Milne-Eddington
inversions were performed to infer the chromospheric magnetic field,
inclination, azimuth, velocity and Doppler width from the He I 10830
Å multiplet. Field strengths of the order of 600-800 G were found in
the filament. Strong transverse fields at chromospheric levels were
detected near the polarity inversion line. To our knowledge, these are
the highest field strengths reliably measured in these structures. Our
findings suggest the possible presence of a flux rope.
Title: Magnetic field strength of active region filaments
Authors: Kuckein, C.; Centeno, R.; Martínez Pillet, V.; Casini, R.;
Manso Sainz, R.; Shimizu, T.
Bibcode: 2009A&A...501.1113K
Altcode: 2009arXiv0904.4876K
Aims: We study the vector magnetic field of a filament observed over a
compact active region neutral line.
Methods: Spectropolarimetric
data acquired with TIP-II (VTT, Tenerife, Spain) of the 10 830
Å spectral region provide full Stokes vectors that were analyzed
using three different methods: magnetograph analysis, Milne-Eddington
inversions, and PCA-based atomic polarization inversions.
Results:
The inferred magnetic field strengths in the filament are around 600-700
G by all these three methods. Longitudinal fields are found in the
range of 100-200 G whereas the transverse components become dominant,
with fields as high as 500-600 G. We find strong transverse fields
near the neutral line also at photospheric levels.
Conclusions:
Our analysis indicates that strong (higher than 500 G, but below kG)
transverse magnetic fields are present in active region filaments. This
corresponds to the highest field strengths reliably measured in these
structures. The profiles of the helium 10 830 Å lines observed in
this active region filament are dominated by the Zeeman effect.
Title: Testing commercial variable fiber attenuators and lenslet
arrays for equalized integral field spectroscopy applications
Authors: Gracia-Temich, F.; García-Lorenzo, B.; Padilla-Michel, Y.;
Escobar-Romero, J. F. M.; Fuensalida, J. J.; Rodríguez-Hernández,
M. A. C.; Rasilla, J. L.; Kuckein, C.; López-Rodríguez, E.
Bibcode: 2008SPIE.7014E..4CG
Altcode: 2008SPIE.7014E.142G
We have been testing at laboratory commercial variable attenuators
commonly used in telecommunication applications for their used in
astronomy. Such variable attenuators are going to be included in
the central fibers of the integral field unit (IFU) of the prototype
instrument EDiFiSE (Equalized and Diffraction-limited Field Spectrograph
Experiment). The EDiFiSE IFU is conformed by a lenslet array of 331
lenses, 331 fibers and seven variable attenuators (inserted in the seven
central fibers of the bundle). We present here the characterization
of the attenuator devices tested for their use in astronomy and,
in particular, to their application in the observation of object of
large dynamic range using equalized integral field spectroscopy. We
also present the optical tests we have carried out to characterize
the performances of two lenslet arrays acquired in the framework of
the EDiFiSE project.