Author name code: kuckein
ADS astronomy entries on 2022-09-14
author:"Kuckein, Christoph" 
------------------------------------------------------------------------  

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. <BR /> 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. <BR
  /> 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 I<SUB>mean</SUB><SUP>E/D</SUP> 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. <BR /> 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. <BR
  /> 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). <BR /> 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. <BR /> 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. <BR
  /> 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
  <BR /> 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. <BR /> 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). <BR /> 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. <BR />
  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
  <BR /> 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. <BR
  /> 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. <BR />
  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 &gt; 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. <BR /> 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 D<SUB>2</SUB>) 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
  <BR /> 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. <BR /> 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. <BR /> Results: The
  erupting-filament material presents the following physical conditions:
  (1) ubiquitous upward motions with peak LOS velocities of ∼73 km
  s<SUP>-1</SUP>; (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 (&lt;2.5 min) remained constant. <BR /> Conclusions:
  The analyzed filament eruption belongs to the fast rising phase, with
  total velocities of about 124 km s<SUP>-1</SUP>. 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. <P />Movies attached to Figs. 1 and 3 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202038408/olm">https://www.aanda.org</A>

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<SUP>-1</SUP>, and in the lower
  chromosphere and upper photosphere the Doppler velocities reach up to
  11 km s<SUP>-1</SUP> and 1.5 km s<SUP>-1</SUP> 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 (&lt;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
  <BR /> 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. <BR /> 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. <BR /> 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. <BR />
  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. <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201936762/olm">https://www.aanda.org</A>

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<SUP>-1</SUP>, and in the lower
  chromosphere and upper photosphere the Doppler velocities reach up to
  11 km s<SUP>-1</SUP> and 1.5 km s<SUP>-1</SUP> 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 ID<SUP>2</SUP> 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 ID<SUP>2</SUP>
  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. <BR /> 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. <BR /> Methods: We used imaging
  as well as spectral and spectropolarimetric observations from a suite
  of space-borne and ground-based instruments. <BR /> 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. <BR /> 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
  <BR /> Aims: The expansion with height of the solar photospheric
  magnetic field and the plasma flows is investigated for three
  isolated bright points (BPs). <BR /> 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 D<SUB>2</SUB>
  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. <BR /> 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 D<SUB>2</SUB>
  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 D<SUB>2</SUB> and Si I lines. The inferred flows
  from Na I D<SUB>2</SUB> Doppler shifts are rather slow in BPs (≲1 km
  s<SUP>-1</SUP>). 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<SUP>-1</SUP>. The
  slower component is slightly blueshifted. <BR /> 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
  <BR /> 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. <BR /> 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. <BR /> 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. <BR
  /> 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. <P
  />Movies associated to Figs. 5, 6, and 12 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201935583/olm">https://www.aanda.org</A>

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<SUP>-1</SUP> next
  to the pores and to 4 km s<SUP>-1</SUP> 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. <BR /> 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. <BR />
  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. <BR
  /> 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. <BR /> 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. <P />The movie associated to Fig. 2 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201834367/olm">https://www.aanda.org</A>

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. <BR /> 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. <BR /> 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. <BR /> 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. <BR />
  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. <BR /> 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. <BR
  /> 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. <BR />
  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. <BR /> 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
  <BR /> 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. <BR /> 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. <BR /> 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<SUP>-1</SUP>. Only two
  minutes later, plasma drains down with supersonic velocities towards
  the footpoints reaching a peak velocity of up to 40 km s<SUP>-1</SUP>
  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. <BR /> 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. <P />The movie associated to Fig. 3 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201832684/olm">https://www.aanda.org/</A>

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
  <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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 <A href="http://gregor.aip.de">http://gregor.aip.de</A>), 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. <BR /> 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. <BR /> 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<SUP>-1</SUP> 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<SUP>-1</SUP>. 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. <BR /> 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<SUP>-1</SUP>. 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. <P />A movie associated to Fig. 6 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201730536/olm">https://www.aanda.org</A>

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
  <BR /> 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. <BR /> 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. <BR />
  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<SUP>-1</SUP>. 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. <BR /> 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. <P />The movie associated to Fig. 2 is available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201731319/olm">http://www.aanda.org</A>

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
  <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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. <P />Movies attached to Figs. 1 and 3 are available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201731374/olm">http://www.aanda.org</A>

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
  <BR /> 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. <BR /> 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). <BR /> 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. <BR /> 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. <P
  />The movie associated to Figs. 4 and 5 is available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201730644/olm">http://www.aanda.org</A>

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<SUP>-1</SUP>. 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. <P />Movies associated to Figs. 1 and 2 are available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201527966/olm">http://www.aanda.org</A>

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<SUP>-1</SUP> in the chromospheric helium
  line. Our findings can be explained with new emerging flux where the
  matter flows downward along the field lines of rising flux tubes,
  in agreement with earlier results.

Title: 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. <BR />
  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. <BR /> 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. <BR />
  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<SUP>-1</SUP> 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. <BR /> Aims:
  The information content of Stokes measurements close to the diffraction
  limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
  spatial straylight and photon noise into account. <BR /> Methods: Highly
  sensitive full Stokes measurements of a quiet-Sun region at disk center
  in the deep photospheric Fe I lines in the 1.56 μm region were obtained
  with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
  statistics and Stokes V asymmetries were analyzed and compared to a
  similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
  diagnostics based directly on the shape and strength of the profiles
  were applied to the GRIS data. We made use of the magnetic line ratio
  technique, which was tested against realistic magneto-hydrodynamic
  simulations (MURaM). <BR /> Results: About 80% of the GRIS spectra
  of a very quiet solar region show polarimetric signals above a 3σ
  level. Area and amplitude asymmetries agree well with small-scale
  surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
  analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
  range with some concentrations of kilo-Gauss fields. <BR /> Conclusions:
  The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
  are so far unique in the combination of high spatial resolution scans
  and high magnetic field sensitivity. Nevertheless, the unavoidable
  effect of spatial straylight and the resulting dilution of the weak
  Stokes profiles means that inversion techniques still bear a high risk
  of misinterpretating the data.

Title: Flow and magnetic field properties in the trailing sunspots
    of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
   C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
   M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
   Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
   R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
   Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
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. <BR />
  Aims: We study the three-dimensional configuration of a sunspot,
  and in particular, its light bridge, during one of the last stages of
  its decay. <BR /> Methods: We present the magnetic and thermodynamical
  stratification inferred from full Stokes inversions of the photospheric
  Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
  Infrared Spectrograph of the GREGOR telescope at the Observatorio del
  Teide, Tenerife, Spain. The analysis is complemented by a study of
  continuum images covering the disk passage of the active region, which
  are provided by the Helioseismic and Magnetic Imager on board the Solar
  Dynamics Observatory. <BR /> Results: The sunspot shows a light bridge
  with penumbral continuum intensity that separates the central umbra from
  a smaller umbra. We find that in this region the magnetic field lines
  form a canopy with lower magnetic field strength in the inner part. The
  photospheric light bridge is dominated by gas pressure (high-β),
  as opposed to the surrounding umbra, where the magnetic pressure
  is higher. A convective flow is observed in the light bridge. This
  flow is able to bend the magnetic field lines and to produce field
  reversals. The field lines merge above the light bridge and become
  as vertical and strong as in the surrounding umbra. We conclude that
  this occurs because two highly magnetized regions approach each other
  during the sunspot evolution. <P />Movies associated to Figs. 2 and 13
  are available at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: 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 (&lt;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. <BR /> 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. <BR /> 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. <BR /> 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<SUP>-1</SUP> 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
  <BR /> 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. <BR /> 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
  D<SUB>2</SUB>. 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). <BR />
  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 D<SUB>2</SUB> 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<SUP>-1</SUP> at the ends of the
  filament. <BR /> 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&lt;small&gt;I&lt;/small&gt; 10 830 Å triplet by the TIP 1
  spectropolarimeter, in Hα by the TESOS Fabry-Pérot interferometer, and
  in Ca &lt;small&gt;II&lt;/small&gt; 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}<SUP>-3</SUP>}
  and ∼ {{10}<SUP>-4</SUP>} g cm<SUP>-2</SUP> s<SUP>-1</SUP> 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 30<SUP>o</SUP>. 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 D<SUB>2</SUB>) 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. <BR />
  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. <BR /> 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. <BR /> Results: A ubiquitous chromospheric downflow is found
  in the faculae surrounding the filament, with an average velocity of
  1.6 km s<SUP>-1</SUP>. 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<SUP>-1</SUP>. 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<SUP>-1</SUP>. 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. <BR /> 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. <P />Appendices A and B are available in electronic form
  at <A href="http://www.aanda.org">http://www.aanda.org</A>

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
  <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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<SUP>-1</SUP>. 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. <BR />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. <BR />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. <BR />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.

