Author name code: schmidt
ADS astronomy entries on 2022-09-14
author:"Schmidt, Wolfgang" AND aff:"Freiburg" 
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Title: The magnetic drivers of campfires seen by the Polarimetric
    and Helioseismic Imager (PHI) on Solar Orbiter
Authors: Kahil, F.; Hirzberger, J.; Solanki, S. K.; Chitta, L. P.;
   Peter, H.; Auchère, F.; Sinjan, J.; Orozco Suárez, D.; Albert,
   K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero, A.; Blanco
   Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero, L.; Gutiérrez
   Márquez, P.; Kolleck, M.; del Toro Iniesta, J. C.; Volkmer, R.;
   Woch, J.; Fiethe, B.; Gómez Cama, J. M.; Pérez-Grande, I.; Sanchis
   Kilders, E.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Calchetti,
   D.; Carmona, M.; Deutsch, W.; Fernández-Rico, G.; Fernández-Medina,
   A.; García Parejo, P.; Gasent-Blesa, J. L.; Gizon, L.; Grauf, B.;
   Heerlein, K.; Lagg, A.; Lange, T.; López Jiménez, A.; Maue, T.;
   Meller, R.; Michalik, H.; Moreno Vacas, A.; Müller, R.; Nakai,
   E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub, J.; Strecker, H.;
   Torralbo, I.; Valori, G.; Aznar Cuadrado, R.; Teriaca, L.; Berghmans,
   D.; Verbeeck, C.; Kraaikamp, E.; Gissot, S.
Bibcode: 2022A&A...660A.143K
Altcode: 2022arXiv220213859K
  Context. The Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter
  (SO) spacecraft observed small extreme ultraviolet (EUV) bursts,
  termed campfires, that have been proposed to be brightenings near the
  apexes of low-lying loops in the quiet-Sun atmosphere. The underlying
  magnetic processes driving these campfires are not understood. <BR
  /> Aims: During the cruise phase of SO and at a distance of 0.523
  AU from the Sun, the Polarimetric and Helioseismic Imager on Solar
  Orbiter (SO/PHI) observed a quiet-Sun region jointly with SO/EUI,
  offering the possibility to investigate the surface magnetic field
  dynamics underlying campfires at a spatial resolution of about 380
  km. <BR /> Methods: We used co-spatial and co-temporal data of the
  quiet-Sun network at disc centre acquired with the High Resolution
  Imager of SO/EUI at 17.4 nm (HRI<SUB>EUV</SUB>, cadence 2 s) and the
  High Resolution Telescope of SO/PHI at 617.3 nm (HRT, cadence 2.5
  min). Campfires that are within the SO/PHI−SO/EUI common field
  of view were isolated and categorised according to the underlying
  magnetic activity. <BR /> Results: In 71% of the 38 isolated events,
  campfires are confined between bipolar magnetic features, which seem to
  exhibit signatures of magnetic flux cancellation. The flux cancellation
  occurs either between the two main footpoints, or between one of the
  footpoints of the loop housing the campfire and a nearby opposite
  polarity patch. In one particularly clear-cut case, we detected the
  emergence of a small-scale magnetic loop in the internetwork followed
  soon afterwards by a campfire brightening adjacent to the location
  of the linear polarisation signal in the photosphere, that is to
  say near where the apex of the emerging loop lays. The rest of the
  events were observed over small scattered magnetic features, which
  could not be identified as magnetic footpoints of the campfire hosting
  loops. <BR /> Conclusions: The majority of campfires could be driven
  by magnetic reconnection triggered at the footpoints, similar to the
  physical processes occurring in the burst-like EUV events discussed
  in the literature. About a quarter of all analysed campfires, however,
  are not associated to such magnetic activity in the photosphere, which
  implies that other heating mechanisms are energising these small-scale
  EUV brightenings.

Title: Newly formed downflow lanes in exploding granules in the
    solar photosphere
Authors: Ellwarth, M.; Fischer, C. E.; Vitas, N.; Schmiz, S.;
   Schmidt, W.
Bibcode: 2021A&A...653A..96E
Altcode: 2021arXiv210700582E
  Context. Exploding granules have drawn renewed interest because of
  their interaction with the magnetic field (either emerging or already
  present). Especially the newly forming downflow lanes developing in
  their centre seem to be eligible candidates for the intensification
  of magnetic fields. We analyse spectroscopic data from two different
  instruments in order to study the intricate velocity pattern within
  the newly forming downflow lanes in detail. <BR /> Aims: We aim to
  examine general properties of a number of exploding granules, such
  as their lifetime and extend. To gain a better understanding of the
  formation process of the developing intergranular lane in exploding
  granules, we study the temporal evolution and height dependence of the
  line-of-sight velocities at their formation location. Additionally, we
  search for evidence that exploding granules act as acoustic sources. <BR
  /> Methods: We investigated the evolution of several exploding granules
  using data taken with the Interferometric Bidimensional Spectrometer and
  the Imaging Magnetograph eXperiment. Velocities for different heights
  of the solar atmosphere were determined by computing bisectors of the
  Fe I 6173.0 Å and the Fe I 5250.2 Å lines. We performed a wavelet
  analysis to study the intensity and velocity oscillations within
  and around exploding granules. We also compared our observational
  findings with predictions of numerical simulations. <BR /> Results:
  Exploding granules have significantly longer lifetimes (10 to 15 min)
  than regular granules. Exploding granules larger than 3.8″ form an
  independent intergranular lane during their decay phase, while smaller
  granules usually fade away or disappear into the intergranular area
  (we find only one exception of a smaller exploding granule that also
  forms an intergranular lane). For all exploding granules that form a new
  intergranular downflow lane, we find a temporal height-dependent shift
  with respect to the maximum of the downflow velocity. Our suggestion
  that this results from a complex atmospheric structure within the newly
  forming downflow lane is supported by the comparison with synthesised
  profiles inferred from the simulations. We found an enhanced wavelet
  power with periods between 120 s to 190 s seen in the intensity and
  velocity oscillations of high photospheric or chromospheric spectral
  lines in the region of the dark core of an exploding granule.

Title: On the (in)stability of sunspots
Authors: Strecker, H.; Schmidt, W.; Schlichenmaier, R.; Rempel, M.
Bibcode: 2021A&A...649A.123S
Altcode: 2021arXiv210311487S
  Context. The stability of sunspots is one of the long-standing unsolved
  puzzles in the field of solar magnetism and the solar cycle. The thermal
  and magnetic structure of the sunspot beneath the solar surface is
  not accessible through observations, thus processes in these regions
  that contribute to the decay of sunspots can only be studied through
  theoretical and numerical studies. <BR /> Aims: We study the effects
  that destabilise and stabilise the flux tube of a simulated sunspot
  in the upper convection zone. The depth-varying effects of fluting
  instability, buoyancy forces, and timescales on the flux tube are
  analysed. <BR /> Methods: We analysed a numerical simulation of a
  sunspot calculated with the MURaM code. The simulation domain has a
  lateral extension of more than 98 Mm × 98 Mm and extends almost 18
  Mm below the solar surface. The analysed data set of 30 hours shows a
  stable sunspot at the solar surface. We studied the evolution of the
  flux tube at defined horizontal layers (1) by means of the relative
  change in perimeter and area, that is, its compactness; and (2) with
  a linear stability analysis. <BR /> Results: The simulation shows a
  corrugation along the perimeter of the flux tube (sunspot) that proceeds
  fastest at a depth of about 8 Mm below the solar surface. Towards
  the surface and towards deeper layers, the decrease in compactness is
  damped. From the stability analysis, we find that above a depth of 2
  Mm, the sunspot is stabilised by buoyancy forces. The spot is least
  stable at a depth of about 3 Mm because of the fluting instability. In
  deeper layers, the flux tube is marginally unstable. The stability
  of the sunspot at the surface affects the behaviour of the field
  lines in deeper layers by magnetic tension. Therefore the fluting
  instability is damped at depths of about 3 Mm, and the decrease in
  compactness is strongest at a depth of about 8 Mm. The more vertical
  orientation of the magnetic field and the longer convective timescale
  lead to slower evolution of the corrugation process in layers deeper
  than 10 Mm. <BR /> Conclusions: The formation of large intrusions of
  field-free plasma below the surface destabilises the flux tube of
  the sunspot. This process is not visible at the surface, where the
  sunspot is stabilised by buoyancy forces. The onset of sunspot decay
  occurs in deeper layers, while the sunspot still appears stable in
  the photosphere. The intrusions eventually lead to the disruption
  and decay of the sunspot. <P />The animation is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202040199/olm">https://www.aanda.org</A>
  <P />This paper is mainly based on Part I of
  the Ph.D. thesis "On the decay of sunspots", <A
  href="https://freidok.uni-freiburg.de/data/165760">https://freidok.uni-freiburg.de/data/165760</A>

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: Power spectrum of turbulent convection in the solar photosphere
Authors: Yelles Chaouche, L.; Cameron, R. H.; Solanki, S. K.;
   Riethmüller, T. L.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.;
   Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort,
   M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
   D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2020A&A...644A..44Y
Altcode: 2020arXiv201009037Y
  The solar photosphere provides us with a laboratory for understanding
  turbulence in a layer where the fundamental processes of transport
  vary rapidly and a strongly superadiabatic region lies very closely
  to a subadiabatic layer. Our tools for probing the turbulence are
  high-resolution spectropolarimetric observations such as have recently
  been obtained with the two balloon-borne SUNRISE missions, and numerical
  simulations. Our aim is to study photospheric turbulence with the
  help of Fourier power spectra that we compute from observations
  and simulations. We also attempt to explain some properties of the
  photospheric overshooting flow with the help of its governing equations
  and simulations. We find that quiet-Sun observations and smeared
  simulations are consistent with each other and exhibit a power-law
  behavior in the subgranular range of their Doppler velocity power
  spectra with a power-law index of ≈ - 2. The unsmeared simulations
  exhibit a power law that extends over the full range between the
  integral and Taylor scales with a power-law index of ≈ - 2.25. The
  smearing, reminiscent of observational conditions, considerably reduces
  the extent of the power-law-like portion of the power spectra. This
  suggests that the limited spatial resolution in some observations
  might eventually result in larger uncertainties in the estimation of
  the power-law indices. The simulated vertical velocity power spectra
  as a function of height show a rapid change in the power-law index
  (at the subgranular range) from roughly the optical depth unity layer,
  that is, the solar surface, to 300 km above it. We propose that the
  cause of the steepening of the power-law index is the transition from
  a super- to a subadiabatic region, in which the dominant source of
  motions is overshooting convection. A scale-dependent transport of
  the vertical momentum occurs. At smaller scales, the vertical momentum
  is more efficiently transported sideways than at larger scales. This
  results in less vertical velocity power transported upward at small
  scales than at larger scales and produces a progressively steeper
  vertical velocity power law below 180 km. Above this height, the
  gravity work progressively gains importance at all relevant scales,
  making the atmosphere progressively more hydrostatic and resulting
  in a gradually less steep power law. Radiative heating and cooling of
  the plasma is shown to play a dominant role in the plasma energetics
  in this region, which is important in terms of nonadiabatic damping
  of the convective motions.

Title: The Daniel K. Inouye Solar Telescope - Observatory Overview
Authors: Rimmele, Thomas R.; Warner, Mark; Keil, Stephen L.; Goode,
   Philip R.; Knölker, Michael; Kuhn, Jeffrey R.; Rosner, Robert R.;
   McMullin, Joseph P.; Casini, Roberto; Lin, Haosheng; Wöger, Friedrich;
   von der Lühe, Oskar; Tritschler, Alexandra; Davey, Alisdair; de Wijn,
   Alfred; Elmore, David F.; Fehlmann, André; Harrington, David M.;
   Jaeggli, Sarah A.; Rast, Mark P.; Schad, Thomas A.; Schmidt, Wolfgang;
   Mathioudakis, Mihalis; Mickey, Donald L.; Anan, Tetsu; Beck, Christian;
   Marshall, Heather K.; Jeffers, Paul F.; Oschmann, Jacobus M.; Beard,
   Andrew; Berst, David C.; Cowan, Bruce A.; Craig, Simon C.; Cross,
   Eric; Cummings, Bryan K.; Donnelly, Colleen; de Vanssay, Jean-Benoit;
   Eigenbrot, Arthur D.; Ferayorni, Andrew; Foster, Christopher; Galapon,
   Chriselle Ann; Gedrites, Christopher; Gonzales, Kerry; Goodrich, Bret
   D.; Gregory, Brian S.; Guzman, Stephanie S.; Guzzo, Stephen; Hegwer,
   Steve; Hubbard, Robert P.; Hubbard, John R.; Johansson, Erik M.;
   Johnson, Luke C.; Liang, Chen; Liang, Mary; McQuillen, Isaac; Mayer,
   Christopher; Newman, Karl; Onodera, Brialyn; Phelps, LeEllen; Puentes,
   Myles M.; Richards, Christopher; Rimmele, Lukas M.; Sekulic, Predrag;
   Shimko, Stephan R.; Simison, Brett E.; Smith, Brett; Starman, Erik;
   Sueoka, Stacey R.; Summers, Richard T.; Szabo, Aimee; Szabo, Louis;
   Wampler, Stephen B.; Williams, Timothy R.; White, Charles
Bibcode: 2020SoPh..295..172R
Altcode:
  We present an overview of the National Science Foundation's Daniel
  K. Inouye Solar Telescope (DKIST), its instruments, and support
  facilities. The 4 m aperture DKIST provides the highest-resolution
  observations of the Sun ever achieved. The large aperture of
  DKIST combined with state-of-the-art instrumentation provide the
  sensitivity to measure the vector magnetic field in the chromosphere
  and in the faint corona, i.e. for the first time with DKIST we will
  be able to measure and study the most important free-energy source
  in the outer solar atmosphere - the coronal magnetic field. Over its
  operational lifetime DKIST will advance our knowledge of fundamental
  astronomical processes, including highly dynamic solar eruptions
  that are at the source of space-weather events that impact our
  technological society. Design and construction of DKIST took over two
  decades. DKIST implements a fast (f/2), off-axis Gregorian optical
  design. The maximum available field-of-view is 5 arcmin. A complex
  thermal-control system was implemented in order to remove at prime
  focus the majority of the 13 kW collected by the primary mirror and
  to keep optical surfaces and structures at ambient temperature, thus
  avoiding self-induced local seeing. A high-order adaptive-optics
  system with 1600 actuators corrects atmospheric seeing enabling
  diffraction limited imaging and spectroscopy. Five instruments, four
  of which are polarimeters, provide powerful diagnostic capability
  over a broad wavelength range covering the visible, near-infrared,
  and mid-infrared spectrum. New polarization-calibration strategies
  were developed to achieve the stringent polarization accuracy
  requirement of 5×10<SUP>−4</SUP>. Instruments can be combined and
  operated simultaneously in order to obtain a maximum of observational
  information. Observing time on DKIST is allocated through an open,
  merit-based proposal process. DKIST will be operated primarily in
  "service mode" and is expected to on average produce 3 PB of raw
  data per year. A newly developed data center located at the NSO
  Headquarters in Boulder will initially serve fully calibrated data to
  the international users community. Higher-level data products, such as
  physical parameters obtained from inversions of spectro-polarimetric
  data will be added as resources allow.

Title: The Polarimetric and Helioseismic Imager on Solar Orbiter
Authors: Solanki, S. K.; del Toro Iniesta, J. C.; Woch, J.; Gandorfer,
   A.; Hirzberger, J.; Alvarez-Herrero, A.; Appourchaux, T.; Martínez
   Pillet, V.; Pérez-Grande, I.; Sanchis Kilders, E.; Schmidt, W.;
   Gómez Cama, J. M.; Michalik, H.; Deutsch, W.; Fernandez-Rico, G.;
   Grauf, B.; Gizon, L.; Heerlein, K.; Kolleck, M.; Lagg, A.; Meller, R.;
   Müller, R.; Schühle, U.; Staub, J.; Albert, K.; Alvarez Copano, M.;
   Beckmann, U.; Bischoff, J.; Busse, D.; Enge, R.; Frahm, S.; Germerott,
   D.; Guerrero, L.; Löptien, B.; Meierdierks, T.; Oberdorfer, D.;
   Papagiannaki, I.; Ramanath, S.; Schou, J.; Werner, S.; Yang, D.;
   Zerr, A.; Bergmann, M.; Bochmann, J.; Heinrichs, J.; Meyer, S.;
   Monecke, M.; Müller, M. -F.; Sperling, M.; Álvarez García, D.;
   Aparicio, B.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Cobos
   Carracosa, J. P.; Girela, F.; Hernández Expósito, D.; Herranz, M.;
   Labrousse, P.; López Jiménez, A.; Orozco Suárez, D.; Ramos, J. L.;
   Barandiarán, J.; Bastide, L.; Campuzano, C.; Cebollero, M.; Dávila,
   B.; Fernández-Medina, A.; García Parejo, P.; Garranzo-García, D.;
   Laguna, H.; Martín, J. A.; Navarro, R.; Núñez Peral, A.; Royo, M.;
   Sánchez, A.; Silva-López, M.; Vera, I.; Villanueva, J.; Fourmond,
   J. -J.; de Galarreta, C. Ruiz; Bouzit, M.; Hervier, V.; Le Clec'h,
   J. C.; Szwec, N.; Chaigneau, M.; Buttice, V.; Dominguez-Tagle, C.;
   Philippon, A.; Boumier, P.; Le Cocguen, R.; Baranjuk, G.; Bell,
   A.; Berkefeld, Th.; Baumgartner, J.; Heidecke, F.; Maue, T.; Nakai,
   E.; Scheiffelen, T.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Blanco
   Rodríguez, J.; Domingo, V.; Ferreres Sabater, A.; Gasent Blesa,
   J. L.; Rodríguez Martínez, P.; Osorno Caudel, D.; Bosch, J.; Casas,
   A.; Carmona, M.; Herms, A.; Roma, D.; Alonso, G.; Gómez-Sanjuan, A.;
   Piqueras, J.; Torralbo, I.; Fiethe, B.; Guan, Y.; Lange, T.; Michel,
   H.; Bonet, J. A.; Fahmy, S.; Müller, D.; Zouganelis, I.
Bibcode: 2020A&A...642A..11S
Altcode: 2019arXiv190311061S
  <BR /> Aims: This paper describes the Polarimetric and Helioseismic
  Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and
  helioseismology instrument to observe the Sun from outside the Sun-Earth
  line. It is the key instrument meant to address the top-level science
  question: How does the solar dynamo work and drive connections between
  the Sun and the heliosphere? SO/PHI will also play an important role
  in answering the other top-level science questions of Solar Orbiter,
  while hosting the potential of a rich return in further science. <BR
  /> Methods: SO/PHI measures the Zeeman effect and the Doppler shift
  in the Fe I 617.3 nm spectral line. To this end, the instrument
  carries out narrow-band imaging spectro-polarimetry using a tunable
  LiNbO<SUB>3</SUB> Fabry-Perot etalon, while the polarisation modulation
  is done with liquid crystal variable retarders. The line and the nearby
  continuum are sampled at six wavelength points and the data are recorded
  by a 2k × 2k CMOS detector. To save valuable telemetry, the raw data
  are reduced on board, including being inverted under the assumption of
  a Milne-Eddington atmosphere, although simpler reduction methods are
  also available on board. SO/PHI is composed of two telescopes; one,
  the Full Disc Telescope, covers the full solar disc at all phases of
  the orbit, while the other, the High Resolution Telescope, can resolve
  structures as small as 200 km on the Sun at closest perihelion. The high
  heat load generated through proximity to the Sun is greatly reduced by
  the multilayer-coated entrance windows to the two telescopes that allow
  less than 4% of the total sunlight to enter the instrument, most of
  it in a narrow wavelength band around the chosen spectral line. <BR />
  Results: SO/PHI was designed and built by a consortium having partners
  in Germany, Spain, and France. The flight model was delivered to
  Airbus Defence and Space, Stevenage, and successfully integrated into
  the Solar Orbiter spacecraft. A number of innovations were introduced
  compared with earlier space-based spectropolarimeters, thus allowing
  SO/PHI to fit into the tight mass, volume, power and telemetry budgets
  provided by the Solar Orbiter spacecraft and to meet the (e.g. thermal)
  challenges posed by the mission's highly elliptical orbit.

Title: Subpixel real-time jitter detection algorithm and
    implementation for polarimetric and helioseismic imager
Authors: Roma, David; Carmona, Manuel; Bosch, Jose; Casas, Albert;
   Herms, Atila; Lopez, Manel; Ruiz, Oscar; Sabater, Josep; Berkefeld,
   Thomas; Maue, Thorsten; Nakai, Eiji; Schmidt, Wolfgang; Soltau, Dirk;
   Volkmer, Reiner; Gomez, Jose M.
Bibcode: 2019JATIS...5c9003R
Altcode:
  The polarimetric and helioseismic imager instrument for the Solar
  Orbiter mission from the European Space Agency requires a high
  stability while capturing images, specially for the polarimetric
  ones. For this reason, an image stabilization system has been included
  in the instrument. It uses global motion estimation techniques to
  estimate the jitter in real time with subpixel resolution. Due to
  instrument requirements, the algorithm has to be implemented in a Xilinx
  Virtex-4QV field programmable gate array. The algorithm includes a 2-D
  paraboloid interpolation algorithm based on 2-D bisection. We describe
  the algorithm implementation and the tests that have been made to
  verify its performance. The jitter estimation has a mean error of 125
  pixel of the correlation tracking camera. The paraboloid interpolation
  algorithm provides also better results in terms of resources and time
  required for the calculation (at least a 20% improvement in both cases)
  than those based on direct calculation.

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: Convective blueshifts in the solar
    atmosphere. III. High-accuracy observations of spectral lines in
    the visible
Authors: Löhner-Böttcher, J.; Schmidt, W.; Schlichenmaier, R.;
   Steinmetz, T.; Holzwarth, R.
Bibcode: 2019A&A...624A..57L
Altcode: 2019arXiv190107606L
  Context. Convective motions in the solar atmosphere cause spectral lines
  to become asymmetric and shifted in wavelength. For photospheric lines,
  this differential Doppler shift varies from the solar disk center
  to the limb. <BR /> Aims: Precise and comprehensive observations of
  the convective blueshift and its center-to-limb variation improve
  our understanding of the atmospheric hydrodynamics and ensuing line
  formation, and provide the basis to refine 3D models of the solar
  atmosphere. <BR /> Methods: We performed systematical spectroscopic
  measurements of the convective blueshift of the quiet Sun with the
  Laser Absolute Reference Spectrograph (LARS) at the German Vacuum
  Tower Telescope. The spatial scanning of the solar disk covered
  11 heliocentric positions each along four radial (meridional and
  equatorial) axes. The high-resolution spectra of 26 photospheric
  to chromospheric lines in the visible range were calibrated with a
  laser frequency comb to absolute wavelengths at the 1 m s<SUP>-1</SUP>
  accuracy. Applying ephemeris and reference corrections, the bisector
  analysis provided line asymmetries and Doppler shifts with an
  uncertainty of only few m s<SUP>-1</SUP>. To allow for a comparison
  with other observations, we convolved the results to lower spectral
  resolutions. <BR /> Results: All spectral line bisectors exhibit
  a systematic center-to-limb variation. Typically, a blueshifted
  "C"-shaped curve at disk center transforms into a less blueshifted
  "\"-shape toward the solar limb. The comparison of all lines reveals
  the systematic dependence of the convective blueshift on the line
  depth. The blueshift of the line minima describe a linear decrease
  with increasing line depths. The slope of the center-to-limb variation
  develops a reversal point at heliocentric positions between μ = 0.7
  and 0.85, seen as the effect of horizontal granular flows in the mid
  photosphere. Line minima formed in the upper photosphere to chromosphere
  exhibit hardly any blueshift or even a slight redshift. Synthetic
  models yield considerable deviations from the observed center-to-limb
  variation. <BR /> Conclusions: The obtained Doppler shifts of the
  quiet Sun can serve as an absolute reference for other observations,
  the relative calibration of Dopplergrams, and the necessary refinement
  of atmospheric models. Based on this, the development of high-precision
  models of stellar surface convection will advance the detection of
  (potentially habitable) exoplanets by radial velocity measurements. <P
  />The reduced spectra are only available at the CDS via anonymous ftp to
  <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/624/A57">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/624/A57</A>

Title: Convective blueshifts in the solar
    atmosphere. II. High-accuracy observations of the Fe I 6173.3 Å
    line and deviations of full-disk Dopplergrams
Authors: Stief, F.; Löhner-Böttcher, J.; Schmidt, W.; Steinmetz,
   T.; Holzwarth, R.
Bibcode: 2019A&A...622A..34S
Altcode: 2018arXiv181108685S
  Context. Granular convective motions reach into the lower solar
  atmosphere, typically causing photospheric spectral lines to exhibit
  a differential line shift. This Doppler shift to shorter wavelengths
  is commonly known as convective blueshift. <BR /> Aims: Spectroscopic
  high-accuracy measurements provide us with a refined determination of
  the absolute convective blueshift and its atmospheric distribution from
  disk center to the solar limb. <BR /> Methods: We performed systematic
  observations of the quiet Sun with the Laser Absolute Reference
  Spectrograph (LARS) at the German Vacuum Tower Telescope. The solar disk
  was scanned along the meridian and the equator, from the disk center
  toward the limb. The solar spectrum around 6173 Å was calibrated with a
  laser frequency comb on an absolute wavelength scale with an accuracy
  of a few meters per second. We applied a bisector analysis on the
  spectral lines to reveal the changes of convective blueshift and line
  asymmetry at different heliocentric positions. <BR /> Results: Being a
  signature for convective motions, the bisector curve of Fe I 6173.3 Å
  describes a "C"-shape at disk center. When approaching the solar limb,
  the bisector transforms into a "\"-shape. The analysis of the time- and
  bisector-averaged line shifts yields three distinct results. Firstly,
  the center-to-limb variation of Doppler velocities measured with
  LARS reveals a significant discrepancy (up to 200 m s<SUP>-1</SUP>)
  to the full-disk Dopplergrams of the Helioseismic and Magnetic Imager
  (HMI). Secondly, we obtained a significant decrease of convective
  blueshift toward the solar limb. Thirdly, the line-of-sight effect of
  solar activity, including p-mode oscillations and supergranular flows,
  leads to a scatter of up to ±100 m s<SUP>-1</SUP> at intermediate
  heliocentric positions. <BR /> Conclusions: The accurate observation of
  the absolute convective blueshift with LARS allows the identification
  of systematic discrepancy with Doppler velocities measured by HMI. The
  center-to-limb variation of HMI suffers from an additional blueshift for
  μ &lt; 0.9 that is incompatible with our results. LARS measurements
  can be taken as a reference for the correction of systematic errors
  in the synoptic HMI Dopplergrams.

Title: Absolute velocity measurements in sunspot umbrae
Authors: Löhner-Böttcher, J.; Schmidt, W.; Schlichenmaier, R.;
   Doerr, H. -P.; Steinmetz, T.; Holzwarth, R.
Bibcode: 2018A&A...617A..19L
Altcode: 2018arXiv180408304L
  Context. In sunspot umbrae, convection is largely suppressed by the
  strong magnetic field. Previous measurements reported on negligible
  convective flows in umbral cores. Based on this, numerous studies have
  taken the umbra as zero reference to calculate Doppler velocities of
  the ambient active region. <BR /> Aims: We aim to clarify the amount of
  convective motion in the darkest part of umbrae, by directly measuring
  Doppler velocities with an unprecedented accuracy and precision. <BR />
  Methods: We performed spectroscopic observations of sunspot umbrae with
  the Laser Absolute Reference Spectrograph (LARS) at the German Vacuum
  Tower Telescope. A laser frequency comb enabled the calibration of
  the high-resolution spectrograph and absolute wavelength positions for
  13 observation sequences. A thorough spectral calibration, including
  the measurement of the reference wavelength, yielded Doppler shifts
  of the spectral line Ti I 5713.9 Å with an uncertainty of around 5
  m s<SUP>-1</SUP>. A bisector analysis gave the depth-dependent line
  asymmetry. <BR /> Results: The measured Doppler shifts are a composition
  of umbral convection and magneto-acoustic waves. For the analysis of
  convective shifts, we temporally averaged each sequence to reduce the
  superimposed wave signal. Compared to convective blueshifts of up to
  -350 m s<SUP>-1</SUP> in the quiet Sun, sunspot umbrae yield strongly
  reduced convective blueshifts around -30 m s<SUP>-1</SUP>. We find
  that the velocity in a sunspot umbra correlates significantly with the
  magnetic field strength, but also with the umbral temperature defining
  the depth of the Ti I 5713.9 Å line. The vertical upward motion
  decreases with increasing field strength. Extrapolating the linear
  approximation to zero magnetic field reproduces the measured quiet Sun
  blueshift. In the same manner, we find that the convective blueshift
  decreases as a function of increasing line depth. <BR /> Conclusions:
  Simply taking the sunspot umbra as a zero velocity reference for the
  calculation of photospheric Dopplergrams can imply a systematic velocity
  error reaching 100 m s<SUP>-1</SUP>, or more. Setting up a relationship
  between vertical velocities and magnetic field strength provides a
  remedy for solar spectropolarimetry. We propose a novel approach of
  substantially increasing the accuracy of the Doppler velocities of a
  sunspot region by including the magnetic field information to define
  the umbral reference velocity.

Title: Convective blueshifts in the solar atmosphere. I. Absolute
    measurements with LARS of the spectral lines at 6302 Å
Authors: Löhner-Böttcher, J.; Schmidt, W.; Stief, F.; Steinmetz,
   T.; Holzwarth, R.
Bibcode: 2018A&A...611A...4L
Altcode: 2017arXiv171207059L
  Context. The solar convection manifests as granulation and
  intergranulation at the solar surface. In the photosphere, convective
  motions induce differential Doppler shifts to spectral lines. The
  observed convective blueshift varies across the solar disk. Aim. We
  focus on the impact of solar convection on the atmosphere and aim
  to resolve its velocity stratification in the photosphere. <BR />
  Methods: We performed high-resolution spectroscopic observations of the
  solar spectrum in the 6302 Å range with the Laser Absolute Reference
  Spectrograph at the Vacuum Tower Telescope. A laser frequency comb
  enabled the calibration of the spectra to an absolute wavelength scale
  with an accuracy of 1 m s<SUP>-1</SUP>. We systematically scanned the
  quiet Sun from the disk center to the limb at ten selected heliocentric
  positions. The analysis included 99 time sequences of up to 20 min in
  length. By means of ephemeris and reference corrections, we translated
  wavelength shifts into absolute line-of-sight velocities. A bisector
  analysis on the line profiles yielded the shapes and convective shifts
  of seven photospheric lines. <BR /> Results: At the disk center,
  the bisector profiles of the iron lines feature a pronounced C-shape
  with maximum convective blueshifts of up to -450 m s<SUP>-1</SUP> in
  the spectral line wings. Toward the solar limb, the bisectors change
  into a "\"-shape with a saturation in the line core at a redshift of
  +100 m s<SUP>-1</SUP>. The center-to-limb variation of the line core
  velocities shows a slight increase in blueshift when departing the
  disk center for larger heliocentric angles. This increase in blueshift
  is more pronounced for the magnetically less active meridian than
  for the equator. Toward the solar limb, the blueshift decreases and
  can turn into a redshift. In general, weaker lines exhibit stronger
  blueshifts. <BR /> Conclusions: Best spectroscopic measurements enabled
  the accurate determination of absolute convective shifts in the solar
  photosphere. We convolved the results to lower spectral resolution to
  permit a comparison with observations from other instruments.

Title: The Maximum Entropy Limit of Small-scale Magnetic Field
    Fluctuations in the Quiet Sun
Authors: Gorobets, A. Y.; Berdyugina, S. V.; Riethmüller, T. L.;
   Blanco Rodríguez, J.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
   Gizon, L.; Hirzberger, J.; van Noort, M.; Del Toro Iniesta, J. C.;
   Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..233....5G
Altcode: 2017arXiv171008361G
  The observed magnetic field on the solar surface is characterized by a
  very complex spatial and temporal behavior. Although feature-tracking
  algorithms have allowed us to deepen our understanding of this behavior,
  subjectivity plays an important role in the identification and tracking
  of such features. In this paper, we continue studies of the temporal
  stochasticity of the magnetic field on the solar surface without relying
  either on the concept of magnetic features or on subjective assumptions
  about their identification and interaction. We propose a data analysis
  method to quantify fluctuations of the line-of-sight magnetic field by
  means of reducing the temporal field’s evolution to the regular Markov
  process. We build a representative model of fluctuations converging to
  the unique stationary (equilibrium) distribution in the long time limit
  with maximum entropy. We obtained different rates of convergence to the
  equilibrium at fixed noise cutoff for two sets of data. This indicates
  a strong influence of the data spatial resolution and mixing-polarity
  fluctuations on the relaxation process. The analysis is applied to
  observations of magnetic fields of the relatively quiet areas around an
  active region carried out during the second flight of the Sunrise/IMaX
  and quiet Sun areas at the disk center from the Helioseismic and
  Magnetic Imager on board the Solar Dynamics Observatory satellite.

Title: Flows along arch filaments observed in the GRIS `very fast
    spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
   Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
   Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
   R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
   A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
   W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
   J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2017IAUS..327...28G
Altcode: 2017arXiv170102206G
  A new generation of solar instruments provides improved spectral,
  spatial, and temporal resolution, thus facilitating a better
  understanding of dynamic processes on the Sun. High-resolution
  observations often reveal multiple-component spectral line profiles,
  e.g., in the near-infrared He i 10830 Å triplet, which provides
  information about the chromospheric velocity and magnetic fine
  structure. We observed an emerging flux region, including two small
  pores and an arch filament system, on 2015 April 17 with the `very
  fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
  situated at the 1.5-meter GREGOR solar telescope at Observatorio del
  Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
  per minute) spectral scans of the solar surface and its potential to
  follow dynamic processes on the Sun. We demonstrate the performance
  of the `very fast spectroscopic mode' by tracking chromospheric
  high-velocity features in the arch filament system.

Title: LARS: An Absolute Reference Spectrograph for solar
    observations. Upgrade from a prototype to a turn-key system
Authors: Löhner-Böttcher, J.; Schmidt, W.; Doerr, H. -P.; Kentischer,
   T.; Steinmetz, T.; Probst, R. A.; Holzwarth, R.
Bibcode: 2017A&A...607A..12L
Altcode: 2017arXiv170701573L
  Context. We designed a Laser-based Absolute Reference Spectrograph
  (LARS) for ultra-precise solar observations. The high-resolution
  echelle spectrograph of the Vacuum Tower Telescope is supported by
  a laser frequency comb to calibrate the solar spectrum on an absolute
  wavelength scale. In this article, we describe the scientific instrument
  and focus on the upgrades carried out in the last two years to turn the
  prototype into a turn-key system. <BR /> Aims: The goal was to improve
  the short-term and long-term stability of the systems, and to enable
  a user-friendly and more versatile operation of the instrument. <BR />
  Methods: The first upgrade involved the modernization of the frequency
  comb. The laser system generating the comb spectrum was renewed. The
  Fabry-Pérot cavities were adjusted to filter to a repetition
  frequency of 8 GHz. A technologically matured photonic crystal fiber was
  implemented for spectral broadening which simplified and stabilized the
  setup. The new control software facilitates an automated operation of
  the frequency comb. The second, quite recent upgrade was performed on
  the optics which feed the sunlight into a single-mode fiber connected
  to the spectrograph. A motorized translation stage was deployed to allow
  the automated selection of three different fields of view with diameters
  of 1'', 3'', and 10'' for the analysis of the solar spectrum. <BR />
  Results: The successful upgrades allow for long-term observations
  of up to several hours per day with a stable spectral accuracy of 1
  m s<SUP>-1</SUP> limited by the spectrograph. The instrument covers
  a wavelength range between 480 nm and 700 nm in the visible. Stable,
  user-friendly operation of the instrument is supported. The selection
  of the pre-aligned fiber to change the field of view can now be done
  within seconds. <BR /> Conclusions: LARS offers the possibility to
  observe absolute wavelength positions of spectral lines and Doppler
  velocities in the solar atmosphere. First results demonstrate the
  capabilities of the instrument for solar science. The accurate
  measurement of the solar convection, p-modes, and atmospheric waves
  will enhance our knowledge of the solar atmosphere and its physical
  conditions to improve current atmospheric models.

Title: Erratum: Morphological Properties of
    Slender CaII H Fibrils Observed by sunrise II (<A
href="http://doi.org/10.3847/1538-4365/229/1/6">ApJS 229, 1, 6</A>)
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
   van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
   J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
   Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..230...11G
Altcode:
  No abstract at ADS

Title: Slender Ca II H Fibrils Mapping Magnetic Fields in the Low
    Solar Chromosphere
Authors: Jafarzadeh, S.; Rutten, R. J.; Solanki, S. K.; Wiegelmann, T.;
   Riethmüller, T. L.; van Noort, M.; Szydlarski, M.; Blanco Rodríguez,
   J.; Barthol, P.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.;
   Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
   D.; Schmidt, W.
Bibcode: 2017ApJS..229...11J
Altcode: 2016arXiv161003104J
  A dense forest of slender bright fibrils near a small solar active
  region is seen in high-quality narrowband Ca II H images from the SuFI
  instrument onboard the Sunrise balloon-borne solar observatory. The
  orientation of these slender Ca II H fibrils (SCF) overlaps with the
  magnetic field configuration in the low solar chromosphere derived
  by magnetostatic extrapolation of the photospheric field observed
  with Sunrise/IMaX and SDO/HMI. In addition, many observed SCFs are
  qualitatively aligned with small-scale loops computed from a novel
  inversion approach based on best-fit numerical MHD simulation. Such
  loops are organized in canopy-like arches over quiet areas that differ
  in height depending on the field strength near their roots.

Title: Magneto-static Modeling from Sunrise/IMaX: Application to an
    Active Region Observed with Sunrise II
Authors: Wiegelmann, T.; Neukirch, T.; Nickeler, D. H.; Solanki, S. K.;
   Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller,
   T. L.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
   Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...18W
Altcode: 2017arXiv170101458N; 2017arXiv170101458W
  Magneto-static models may overcome some of the issues facing force-free
  magnetic field extrapolations. So far they have seen limited use
  and have faced problems when applied to quiet-Sun data. Here we
  present a first application to an active region. We use solar vector
  magnetic field measurements gathered by the IMaX polarimeter during
  the flight of the Sunrise balloon-borne solar observatory in 2013
  June as boundary conditions for a magneto-static model of the higher
  solar atmosphere above an active region. The IMaX data are embedded
  in active region vector magnetograms observed with SDO/HMI. This work
  continues our magneto-static extrapolation approach, which was applied
  earlier to a quiet-Sun region observed with Sunrise I. In an active
  region the signal-to-noise-ratio in the measured Stokes parameters
  is considerably higher than in the quiet-Sun and consequently the
  IMaX measurements of the horizontal photospheric magnetic field allow
  us to specify the free parameters of the model in a special class of
  linear magneto-static equilibria. The high spatial resolution of IMaX
  (110-130 km, pixel size 40 km) enables us to model the non-force-free
  layer between the photosphere and the mid-chromosphere vertically
  by about 50 grid points. In our approach we can incorporate some
  aspects of the mixed beta layer of photosphere and chromosphere, e.g.,
  taking a finite Lorentz force into account, which was not possible with
  lower-resolution photospheric measurements in the past. The linear model
  does not, however, permit us to model intrinsic nonlinear structures
  like strongly localized electric currents.

Title: The Second Flight of the Sunrise Balloon-borne Solar
Observatory: Overview of Instrument Updates, the Flight, the Data,
    and First Results
Authors: Solanki, S. K.; Riethmüller, T. L.; Barthol, P.; Danilovic,
   S.; Deutsch, W.; Doerr, H. -P.; Feller, A.; Gandorfer, A.; Germerott,
   D.; Gizon, L.; Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.;
   Lagg, A.; Meller, R.; Tomasch, G.; van Noort, M.; Blanco Rodríguez,
   J.; Gasent Blesa, J. L.; Balaguer Jiménez, M.; Del Toro Iniesta,
   J. C.; López Jiménez, A. C.; Orozco Suarez, D.; Berkefeld, T.;
   Halbgewachs, C.; Schmidt, W.; Álvarez-Herrero, A.; Sabau-Graziati,
   L.; Pérez Grande, I.; Martínez Pillet, V.; Card, G.; Centeno, R.;
   Knölker, M.; Lecinski, A.
Bibcode: 2017ApJS..229....2S
Altcode: 2017arXiv170101555S
  The Sunrise balloon-borne solar observatory, consisting of a 1 m
  aperture telescope that provides a stabilized image to a UV filter
  imager and an imaging vector polarimeter, carried out its second science
  flight in 2013 June. It provided observations of parts of active regions
  at high spatial resolution, including the first high-resolution images
  in the Mg II k line. The obtained data are of very high quality, with
  the best UV images reaching the diffraction limit of the telescope
  at 3000 Å after Multi-Frame Blind Deconvolution reconstruction
  accounting for phase-diversity information. Here a brief update is
  given of the instruments and the data reduction techniques, which
  includes an inversion of the polarimetric data. Mainly those aspects
  that evolved compared with the first flight are described. A tabular
  overview of the observations is given. In addition, an example time
  series of a part of the emerging active region NOAA AR 11768 observed
  relatively close to disk center is described and discussed in some
  detail. The observations cover the pores in the trailing polarity of
  the active region, as well as the polarity inversion line where flux
  emergence was ongoing and a small flare-like brightening occurred in
  the course of the time series. The pores are found to contain magnetic
  field strengths ranging up to 2500 G, and while large pores are clearly
  darker and cooler than the quiet Sun in all layers of the photosphere,
  the temperature and brightness of small pores approach or even exceed
  those of the quiet Sun in the upper photosphere.

Title: A Tale of Two Emergences: Sunrise II Observations of Emergence
    Sites in a Solar Active Region
Authors: Centeno, R.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
   Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger,
   J.; Riethmüller, T. L.; van Noort, M.; Orozco Suárez, D.; Berkefeld,
   T.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....3C
Altcode: 2016arXiv161003531C
  In 2013 June, the two scientific instruments on board the second Sunrise
  mission witnessed, in detail, a small-scale magnetic flux emergence
  event as part of the birth of an active region. The Imaging Magnetograph
  Experiment (IMaX) recorded two small (∼ 5<SUP>\prime\prime</SUP> )
  emerging flux patches in the polarized filtergrams of a photospheric Fe
  I spectral line. Meanwhile, the Sunrise Filter Imager (SuFI) captured
  the highly dynamic chromospheric response to the magnetic fields pushing
  their way through the lower solar atmosphere. The serendipitous capture
  of this event offers a closer look at the inner workings of active
  region emergence sites. In particular, it reveals in meticulous detail
  how the rising magnetic fields interact with the granulation as they
  push through the Sun’s surface, dragging photospheric plasma in
  their upward travel. The plasma that is burdening the rising field
  slides along the field lines, creating fast downflowing channels at
  the footpoints. The weight of this material anchors this field to the
  surface at semi-regular spatial intervals, shaping it in an undulatory
  fashion. Finally, magnetic reconnection enables the field to release
  itself from its photospheric anchors, allowing it to continue its
  voyage up to higher layers. This process releases energy that lights
  up the arch-filament systems and heats the surrounding chromosphere.

Title: Photospheric Response to an Ellerman Bomb-like Event—An
    Analogy of Sunrise/IMaX Observations and MHD Simulations
Authors: Danilovic, S.; Solanki, S. K.; Barthol, P.; Gandorfer,
   A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.;
   Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.;
   Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....5D
Altcode: 2016arXiv160903817D
  Ellerman Bombs are signatures of magnetic reconnection, which is an
  important physical process in the solar atmosphere. How and where they
  occur is a subject of debate. In this paper, we analyze Sunrise/IMaX
  data, along with 3D MHD simulations that aim to reproduce the exact
  scenario proposed for the formation of these features. Although
  the observed event seems to be more dynamic and violent than the
  simulated one, simulations clearly confirm the basic scenario for the
  production of EBs. The simulations also reveal the full complexity of
  the underlying process. The simulated observations show that the Fe I
  525.02 nm line gives no information on the height where reconnection
  takes place. It can only give clues about the heating in the aftermath
  of the reconnection. However, the information on the magnetic field
  vector and velocity at this spatial resolution is extremely valuable
  because it shows what numerical models miss and how they can be
  improved.

Title: Transverse Oscillations in Slender Ca II H Fibrils Observed
    with Sunrise/SuFI
Authors: Jafarzadeh, S.; Solanki, S. K.; Gafeira, R.; van Noort, M.;
   Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer,
   A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco Suárez, D.;
   Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....9J
Altcode: 2016arXiv161007449J
  We present observations of transverse oscillations in slender Ca II
  H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long
  time series of high- (spatial and temporal-) resolution seeing-free
  observations in a 1.1 Å wide passband covering the line core of Ca
  II H 3969 Å from the second flight of the Sunrise balloon-borne solar
  observatory. The entire field of view, spanning the polarity inversion
  line of an active region close to the solar disk center, is covered with
  bright, thin, and very dynamic fine structures. Our analysis reveals
  the prevalence of transverse waves in SCFs with median amplitudes and
  periods on the order of 2.4 ± 0.8 km s<SUP>-1</SUP> and 83 ± 29 s,
  respectively (with standard deviations given as uncertainties). We
  find that the transverse waves often propagate along (parts of) the
  SCFs with median phase speeds of 9 ± 14 km s<SUP>-1</SUP>. While the
  propagation is only in one direction along the axis in some of the
  SCFs, propagating waves in both directions, as well as standing waves
  are also observed. The transverse oscillations are likely Alfvénic
  and are thought to be representative of magnetohydrodynamic kink
  waves. The wave propagation suggests that the rapid high-frequency
  transverse waves, often produced in the lower photosphere, can
  penetrate into the chromosphere with an estimated energy flux of ≈15
  kW m<SUP>-2</SUP>. Characteristics of these waves differ from those
  reported for other fibrillar structures, which, however, were observed
  mainly in the upper solar chromosphere.

Title: Kinematics of Magnetic Bright Features in the Solar Photosphere
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Barthol, P.;
   Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon,
   L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
   D.; Riethmüller, T. L.; Schmidt, W.; van Noort, M.
Bibcode: 2017ApJS..229....8J
Altcode: 2016arXiv161007634J
  Convective flows are known as the prime means of transporting magnetic
  fields on the solar surface. Thus, small magnetic structures are good
  tracers of turbulent flows. We study the migration and dispersal
  of magnetic bright features (MBFs) in intergranular areas observed
  at high spatial resolution with Sunrise/IMaX. We describe the flux
  dispersal of individual MBFs as a diffusion process whose parameters are
  computed for various areas in the quiet-Sun and the vicinity of active
  regions from seeing-free data. We find that magnetic concentrations
  are best described as random walkers close to network areas (diffusion
  index, γ =1.0), travelers with constant speeds over a supergranule
  (γ =1.9{--}2.0), and decelerating movers in the vicinity of flux
  emergence and/or within active regions (γ =1.4{--}1.5). The three
  types of regions host MBFs with mean diffusion coefficients of 130
  km<SUP>2</SUP> s<SUP>-1</SUP>, 80-90 km<SUP>2</SUP> s<SUP>-1</SUP>,
  and 25-70 km<SUP>2</SUP> s<SUP>-1</SUP>, respectively. The MBFs in
  these three types of regions are found to display a distinct kinematic
  behavior at a confidence level in excess of 95%.

Title: Spectropolarimetric Evidence for a Siphon Flow along an
    Emerging Magnetic Flux Tube
Authors: Requerey, Iker S.; Ruiz Cobo, B.; Del Toro Iniesta, J. C.;
   Orozco Suárez, D.; Blanco Rodríguez, J.; Solanki, S. K.; Barthol,
   P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.;
   van Noort, M.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...15R
Altcode: 2016arXiv161106732R
  We study the dynamics and topology of an emerging magnetic flux
  concentration using high spatial resolution spectropolarimetric data
  acquired with the Imaging Magnetograph eXperiment on board the sunrise
  balloon-borne solar observatory. We obtain the full vector magnetic
  field and the line of sight (LOS) velocity through inversions of
  the Fe I line at 525.02 nm with the SPINOR code. The derived vector
  magnetic field is used to trace magnetic field lines. Two magnetic flux
  concentrations with different polarities and LOS velocities are found
  to be connected by a group of arch-shaped magnetic field lines. The
  positive polarity footpoint is weaker (1100 G) and displays an upflow,
  while the negative polarity footpoint is stronger (2200 G) and shows
  a downflow. This configuration is naturally interpreted as a siphon
  flow along an arched magnetic flux tube.

Title: Morphological Properties of Slender Ca II H Fibrils Observed
    by SUNRISE II
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
   van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
   J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
   Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....6G
Altcode: 2016arXiv161200319G
  We use seeing-free high spatial resolution Ca II H data obtained by
  the SUNRISE observatory to determine properties of slender fibrils
  in the lower solar chromosphere. In this work we use intensity images
  taken with the SuFI instrument in the Ca II H line during the second
  scientific flight of the SUNRISE observatory to identify and track
  elongated bright structures. After identification, we analyze theses
  structures to extract their morphological properties. We identify
  598 slender Ca II H fibrils (SCFs) with an average width of around
  180 km, length between 500 and 4000 km, average lifetime of ≈400
  s, and average curvature of 0.002 arcsec<SUP>-1</SUP>. The maximum
  lifetime of the SCFs within our time series of 57 minutes is ≈2000
  s. We discuss similarities and differences of the SCFs with other
  small-scale, chromospheric structures such as spicules of type I and
  II, or Ca II K fibrils.

Title: A New MHD-assisted Stokes Inversion Technique
Authors: Riethmüller, T. L.; Solanki, S. K.; Barthol, P.; Gandorfer,
   A.; Gizon, L.; Hirzberger, J.; van Noort, M.; Blanco Rodríguez, J.;
   Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez
   Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...16R
Altcode: 2016arXiv161105175R
  We present a new method of Stokes inversion of spectropolarimetric
  data and evaluate it by taking the example of a Sunrise/IMaX
  observation. An archive of synthetic Stokes profiles is obtained
  by the spectral synthesis of state-of-the-art magnetohydrodynamics
  (MHD) simulations and a realistic degradation to the level of the
  observed data. The definition of a merit function allows the archive
  to be searched for the synthetic Stokes profiles that best match the
  observed profiles. In contrast to traditional Stokes inversion codes,
  which solve the Unno-Rachkovsky equations for the polarized radiative
  transfer numerically and fit the Stokes profiles iteratively, the new
  technique provides the full set of atmospheric parameters. This gives
  us the ability to start an MHD simulation that takes the inversion
  result as an initial condition. After a relaxation process of half an
  hour solar time we obtain physically consistent MHD data sets with
  a target similar to the observation. The new MHD simulation is used
  to repeat the method in a second iteration, which further improves
  the match between observation and simulation, resulting in a factor
  of 2.2 lower mean {χ }<SUP>2</SUP> value. One advantage of the new
  technique is that it provides the physical parameters on a geometrical
  height scale. It constitutes a first step toward inversions that give
  results consistent with the MHD equations.

Title: Oscillations on Width and Intensity of Slender Ca II H Fibrils
    from Sunrise/SuFI
Authors: Gafeira, R.; Jafarzadeh, S.; Solanki, S. K.; Lagg, A.;
   van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
   J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
   Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....7G
Altcode: 2017arXiv170102801G
  We report the detection of oscillations in slender Ca II H fibrils
  (SCFs) from high-resolution observations acquired with the Sunrise
  balloon-borne solar observatory. The SCFs show obvious oscillations in
  their intensity, but also their width. The oscillatory behaviors are
  investigated at several positions along the axes of the SCFs. A large
  majority of fibrils show signs of oscillations in intensity. Their
  periods and phase speeds are analyzed using a wavelet analysis. The
  width and intensity perturbations have overlapping distributions
  of the wave period. The obtained distributions have median values
  of the period of 32 ± 17 s and 36 ± 25 s, respectively. We
  find that the fluctuations of both parameters propagate in
  the SCFs with speeds of {11}<SUB>-11</SUB><SUP>+49</SUP> km
  s<SUP>-1</SUP> and {15}<SUB>-15</SUB><SUP>+34</SUP> km s<SUP>-1</SUP>,
  respectively. Furthermore, the width and intensity oscillations have a
  strong tendency to be either in anti-phase or, to a smaller extent, in
  phase. This suggests that the oscillations of both parameters are caused
  by the same wave mode and that the waves are likely propagating. Taking
  all the evidence together, the most likely wave mode to explain all
  measurements and criteria is the fast sausage mode.

Title: Solar Coronal Loops Associated with Small-scale Mixed Polarity
    Surface Magnetic Fields
Authors: Chitta, L. P.; Peter, H.; Solanki, S. K.; Barthol, P.;
   Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van
   Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco
   Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....4C
Altcode: 2016arXiv161007484C
  How and where are coronal loops rooted in the solar lower
  atmosphere? The details of the magnetic environment and its evolution
  at the footpoints of coronal loops are crucial to understanding the
  processes of mass and energy supply to the solar corona. To address
  the above question, we use high-resolution line-of-sight magnetic
  field data from the Imaging Magnetograph eXperiment instrument on the
  Sunrise balloon-borne observatory and coronal observations from the
  Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory
  of an emerging active region. We find that the coronal loops are
  often rooted at the locations with minor small-scale but persistent
  opposite-polarity magnetic elements very close to the larger dominant
  polarity. These opposite-polarity small-scale elements continually
  interact with the dominant polarity underlying the coronal loop through
  flux cancellation. At these locations we detect small inverse Y-shaped
  jets in chromospheric Ca II H images obtained from the Sunrise Filter
  Imager during the flux cancellation. Our results indicate that magnetic
  flux cancellation and reconnection at the base of coronal loops due
  to mixed polarity fields might be a crucial feature for the supply of
  mass and energy into the corona.

Title: Moving Magnetic Features around a Pore
Authors: Kaithakkal, A. J.; Riethmüller, T. L.; Solanki, S. K.; Lagg,
   A.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; vanNoort,
   M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
   D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...13K
Altcode: 2016arXiv160905664K
  Spectropolarimetric observations from Sunrise/IMaX, obtained in 2013
  June, are used for a statistical analysis to determine the physical
  properties of moving magnetic features (MMFs) observed near a pore. MMFs
  of the same and opposite polarity, with respect to the pore, are found
  to stream from its border at an average speed of 1.3 km s<SUP>-1</SUP>
  and 1.2 km s<SUP>-1</SUP>, respectively, with mainly same-polarity MMFs
  found further away from the pore. MMFs of both polarities are found to
  harbor rather weak, inclined magnetic fields. Opposite-polarity MMFs
  are blueshifted, whereas same-polarity MMFs do not show any preference
  for up- or downflows. Most of the MMFs are found to be of sub-arcsecond
  size and carry a mean flux of ∼1.2 × 10<SUP>17</SUP> Mx.

Title: Convectively Driven Sinks and Magnetic Fields in the Quiet-Sun
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
   Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.;
   Schmidt, Wolfgang
Bibcode: 2017ApJS..229...14R
Altcode: 2016arXiv161007622R
  We study the relation between mesogranular flows, convectively
  driven sinks and magnetic fields using high spatial resolution
  spectropolarimetric data acquired with the Imaging Magnetograph
  eXperiment on board Sunrise. We obtain the horizontal velocity
  flow fields of two quiet-Sun regions (31.2 × 31.2 Mm<SUP>2</SUP>)
  via local correlation tracking. Mesogranular lanes and the central
  position of sinks are identified using Lagrange tracers. We find
  6.7× {10}<SUP>-2</SUP> sinks per Mm<SUP>2</SUP> in the two observed
  regions. The sinks are located at the mesogranular vertices and turn
  out to be associated with (1) horizontal velocity flows converging to a
  central point and (2) long-lived downdrafts. The spatial distribution
  of magnetic fields in the quiet-Sun is also examined. The strongest
  magnetic fields are preferentially located at sinks. We find that 40% of
  the pixels with longitudinal components of the magnetic field stronger
  than 500 G are located in the close neighborhood of sinks. In contrast,
  the small-scale magnetic loops detected by Martínez González et al. in
  the same two observed areas do not show any preferential distribution
  at mesogranular scales. The study of individual examples reveals
  that sinks can play an important role in the evolution of quiet-Sun
  magnetic features.

Title: Far side Helioseismology with Solar Orbiter
Authors: Appourchaux, T.; Birch, A.; Gizon, L. C.; Löptien, B.;
   Schou, J.; Solanki, S. K.; del Toro Iniesta, J. C.; Gandorfer, A.;
   Hirzberger, J.; Alvarez-Herrero, A.; Woch, J. G.; Schmidt, W.
Bibcode: 2016AGUFMSH43A2554A
Altcode:
  The Solar Orbiter mission, to be launched in October 2018, will
  carry a suite of remote sensing and in-situ instruments, including
  the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
  high-cadence images of the Sun in intensity and Doppler velocity
  suitable for carrying out novel helioseismic studies. The orbit
  of the Solar Orbiter spacecraft will reach a solar latitude up to
  34 degrees by the end of the extended mission and thus will enable
  the first local helioseismology studies of the polar regions. The
  full range of Earth-Sun-spacecraft angles provided by the orbit will
  enable helioseismology from two vantage points by combining PHI with
  another instrument: stereoscopic helioseismology will allow the study
  of the deep solar interior and a better understanding of the physics
  of solar oscillations in both quiet Sun and sunspots. In this paper
  we will review the helioseismic objectives achievable with PHI, and
  will also give a short status report of the development of the Flight
  Model of PHI.

Title: 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: Magnetic field reconstruction based on sunspot oscillations
Authors: Löhner-Böttcher, J.; Bello González, N.; Schmidt, W.
Bibcode: 2016AN....337.1040L
Altcode: 2016arXiv160105925L
  The magnetic field of a sunspot guides magnetohydrodynamic waves
  toward higher atmospheric layers. In the upper photosphere and lower
  chromosphere, wave modes with periods longer than the acoustic
  cut-off period become evanescent. The cut-off period essentially
  changes due to the atmospheric properties, e.g., increases for
  larger zenith inclinations of the magnetic field. In this work, we
  aim at introducing a novel technique of reconstructing the magnetic
  field inclination on the basis of the dominating wave periods in
  the sunspot chromosphere and upper photosphere. On 2013 August 21,
  we observed an isolated, circular sunspot (NOAA11823) for 58 min in
  a purely spectroscopic multi-wavelength mode with the Interferometric
  Bidimensional Spectro-polarimeter (IBIS) at the Dunn Solar Telescope. By
  means of a wavelet power analysis, we retrieved the dominating wave
  periods and reconstructed the zenith inclinations in the chromosphere
  and upper photosphere. The results are in good agreement with the
  lower photospheric HMI magnetograms. The sunspot's magnetic field
  in the chromosphere inclines from almost vertical (0<SUP>°</SUP>)
  in the umbra to around 60<SUP>°</SUP> in the outer penumbra. With
  increasing altitude in the sunspot atmosphere, the magnetic field of
  the penumbra becomes less inclined. We conclude that the reconstruction
  of the magnetic field topology on the basis of sunspot oscillations
  yields consistent and conclusive results. The technique opens up a
  new possibility to infer the magnetic field inclination in the solar
  chromosphere.

Title: Daniel K. Inouye Solar Telescope: High-resolution observing
    of the dynamic Sun
Authors: Tritschler, A.; Rimmele, T. R.; Berukoff, S.; Casini, R.;
   Kuhn, J. R.; Lin, H.; Rast, M. P.; McMullin, J. P.; Schmidt, W.;
   Wöger, F.; DKIST Team
Bibcode: 2016AN....337.1064T
Altcode:
  The 4-m aperture Daniel K. Inouye Solar Telescope (DKIST) formerly
  known as the Advanced Technology Solar Telescope (ATST) is currently
  under construction on Haleakalā (Maui, Hawai'i) projected to
  start operations in 2019. At the time of completion, DKIST will be
  the largest ground-based solar telescope providing unprecedented
  resolution and photon collecting power. The DKIST will be equipped
  with a set of first-light facility-class instruments offering unique
  imaging, spectroscopic and spectropolarimetric observing opportunities
  covering the visible to infrared wavelength range. This first-light
  instrumentation suite will include: a Visible Broadband Imager (VBI) for
  high-spatial and -temporal resolution imaging of the solar atmosphere; a
  Visible Spectro-Polarimeter (ViSP) for sensitive and accurate multi-line
  spectropolarimetry; a Fabry-Pérot based Visible Tunable Filter
  (VTF) for high-spatial resolution spectropolarimetry; a fiber-fed
  Diffraction-Limited Near Infra-Red Spectro-Polarimeter (DL-NIRSP)
  for two-dimensional high-spatial resolution spectropolarimetry
  (simultaneous spatial and spectral information); and a Cryogenic Near
  Infra-Red Spectro-Polarimeter (Cryo-NIRSP) for coronal magnetic field
  measurements and on-disk observations of, e.g., the CO lines at 4.7
  μm. We will provide an overview of the DKIST's unique capabilities
  with strong focus on the first-light instrumentation suite, highlight
  some of the additional properties supporting observations of transient
  and dynamic solar phenomena, and touch on some operational strategies
  and the DKIST critical science plan.

Title: Deep probing of the photospheric sunspot penumbra: no evidence
    of field-free gaps
Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.;
   Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.;
   Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe,
   O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.;
   Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.;
   Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H.
Bibcode: 2016A&A...596A...2B
Altcode: 2016arXiv160708165B
  Context. Some models for the topology of the magnetic field in
  sunspot penumbrae predict regions free of magnetic fields or with
  only dynamically weak fields in the deep photosphere. <BR /> Aims:
  We aim to confirm or refute the existence of weak-field regions in
  the deepest photospheric layers of the penumbra. <BR /> Methods:
  We investigated the magnetic field at log τ<SUB>5</SUB> = 0 is
  by inverting spectropolarimetric data of two different sunspots
  located very close to disk center with a spatial resolution of
  approximately 0.4-0.45''. The data have been recorded using the GRIS
  instrument attached to the 1.5-m solar telescope GREGOR at the El
  Teide observatory. The data include three Fe I lines around 1565 nm,
  whose sensitivity to the magnetic field peaks half a pressure scale
  height deeper than the sensitivity of the widely used Fe I spectral
  line pair at 630 nm. Before the inversion, the data were corrected
  for the effects of scattered light using a deconvolution method with
  several point spread functions. <BR /> Results: At log τ<SUB>5</SUB>
  = 0 we find no evidence of regions with dynamically weak (B&lt;
  500 Gauss) magnetic fields in sunspot penumbrae. This result is much
  more reliable than previous investigations made on Fe I lines at 630
  nm. Moreover, the result is independent of the number of nodes employed
  in the inversion, is independent of the point spread function used to
  deconvolve the data, and does not depend on the amount of stray light
  (I.e., wide-angle scattered light) considered.

Title: Spectropolarimetric observations of an arch filament system
    with the GREGOR solar telescope
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
   Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.;
   Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann,
   A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.;
   Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
   M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016AN....337.1050B
Altcode: 2016arXiv160901514B
  Arch filament systems occur in active sunspot groups, where a fibril
  structure connects areas of opposite magnetic polarity, in contrast to
  active region filaments that follow the polarity inversion line. We
  used the GREGOR Infrared Spectrograph (GRIS) to obtain the full
  Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0
  nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line
  to investigate the photospheric magnetic field and velocities, and
  use the line core intensities and velocities of the helium line to
  study the chromospheric plasma. The individual fibrils of the arch
  filament system connect the sunspot with patches of magnetic polarity
  opposite to that of the spot. These patches do not necessarily coincide
  with pores, where the magnetic field is strongest. Instead, areas are
  preferred not far from the polarity inversion line. These areas exhibit
  photospheric downflows of moderate velocity, but significantly higher
  downflows of up to 30 km s<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: Magnetic fields of opposite polarity in sunspot penumbrae
Authors: Franz, M.; Collados, M.; Bethge, C.; Schlichenmaier, R.;
   Borrero, J. M.; Schmidt, W.; Lagg, A.; Solanki, S. K.; Berkefeld,
   T.; Kiess, C.; Rezaei, R.; Schmidt, D.; Sigwarth, M.; Soltau, D.;
   Volkmer, R.; von der Luhe, O.; Waldmann, T.; Orozco, D.; Pastor Yabar,
   A.; Denker, C.; Balthasar, H.; Staude, J.; Hofmann, A.; Strassmeier,
   K.; Feller, A.; Nicklas, H.; Kneer, F.; Sobotka, M.
Bibcode: 2016A&A...596A...4F
Altcode: 2016arXiv160800513F
  Context. A significant part of the penumbral magnetic field returns
  below the surface in the very deep photosphere. For lines in the
  visible, a large portion of this return field can only be detected
  indirectly by studying its imprints on strongly asymmetric and
  three-lobed Stokes V profiles. Infrared lines probe a narrow layer
  in the very deep photosphere, providing the possibility of directly
  measuring the orientation of magnetic fields close to the solar
  surface. <BR /> Aims: We study the topology of the penumbral magnetic
  field in the lower photosphere, focusing on regions where it returns
  below the surface. <BR /> Methods: We analyzed 71 spectropolarimetric
  datasets from Hinode and from the GREGOR infrared spectrograph. We
  inferred the quality and polarimetric accuracy of the infrared data
  after applying several reduction steps. Techniques of spectral
  inversion and forward synthesis were used to test the detection
  algorithm. We compared the morphology and the fractional penumbral
  area covered by reversed-polarity and three-lobed Stokes V profiles for
  sunspots at disk center. We determined the amount of reversed-polarity
  and three-lobed Stokes V profiles in visible and infrared data of
  sunspots at various heliocentric angles. From the results, we computed
  center-to-limb variation curves, which were interpreted in the context
  of existing penumbral models. <BR /> Results: Observations in visible
  and near-infrared spectral lines yield a significant difference in the
  penumbral area covered by magnetic fields of opposite polarity. In
  the infrared, the number of reversed-polarity Stokes V profiles is
  smaller by a factor of two than in the visible. For three-lobed Stokes
  V profiles the numbers differ by up to an order of magnitude.

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: Upper chromospheric magnetic field of a sunspot penumbra:
    observations of fine structure
Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados,
   M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar,
   H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.;
   Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.;
   Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe,
   O.; Waldmann, T.
Bibcode: 2016A&A...596A...8J
Altcode: 2016arXiv160801988J
  <BR /> Aims: The fine-structure of the magnetic field in a sunspot
  penumbra in the upper chromosphere is to be explored and compared
  to that in the photosphere. <BR /> Methods: Spectropolarimetric
  observations with high spatial resolution were recorded with the 1.5-m
  GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The
  observed spectral domain includes the upper chromospheric Hei triplet
  at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å
  spectral lines. The upper chromospheric magnetic field is obtained
  by inverting the Hei triplet assuming a Milne-Eddington-type model
  atmosphere. A height-dependent inversion was applied to the Sii 10
  827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic
  field. <BR /> Results: We find that the inclination of the magnetic
  field varies in the azimuthal direction in the photosphere and in the
  upper chromosphere. The chromospheric variations coincide remarkably
  well with the variations in the inclination of the photospheric field
  and resemble the well-known spine and interspine structure in the
  photospheric layers of penumbrae. The typical peak-to-peak variations
  in the inclination of the magnetic field in the upper chromosphere
  are found to be 10°-15°, which is roughly half the variation in
  the photosphere. In contrast, the magnetic field strength of the
  observed penumbra does not vary on small spatial scales in the upper
  chromosphere. <BR /> Conclusions: Thanks to the high spatial resolution
  of the observations that is possible with the GREGOR telescope at 1.08
  microns, we find that the prominent small-scale fluctuations in the
  magnetic field inclination, which are a salient part of the property
  of sunspot penumbral photospheres, also persist in the chromosphere,
  although at somewhat reduced amplitudes. Such a complex magnetic
  configuration may facilitate penumbral chromospheric dynamic phenomena,
  such as penumbral micro-jets or transient bright dots.

Title: Active region fine structure observed at 0.08 arcsec resolution
Authors: Schlichenmaier, R.; von der Lühe, O.; Hoch, S.; Soltau, D.;
   Berkefeld, T.; Schmidt, D.; Schmidt, W.; Denker, C.; Balthasar, H.;
   Hofmann, A.; Strassmeier, K. G.; Staude, J.; Feller, A.; Lagg, A.;
   Solanki, S. K.; Collados, M.; Sigwarth, M.; Volkmer, R.; Waldmann,
   T.; Kneer, F.; Nicklas, H.; Sobotka, M.
Bibcode: 2016A&A...596A...7S
Altcode: 2016arXiv160707094S
  Context. The various mechanisms of magneto-convective energy transport
  determine the structure of sunspots and active regions. <BR />
  Aims: We characterise the appearance of light bridges and other
  fine-structure details and elaborate on their magneto-convective
  nature. <BR /> Methods: We present speckle-reconstructed images taken
  with the broad-band imager (BBI) at the 1.5 m GREGOR telescope in the
  486 nm and 589 nm bands. We estimate the spatial resolution from the
  noise characteristics of the image bursts and obtain 0.08″ at 589
  nm. We describe structure details in individual best images as well
  as the temporal evolution of selected features. <BR /> Results: We
  find branched dark lanes extending along thin (≈1″) light bridges
  in sunspots at various heliocentric angles. In thick (≳ 2″) light
  bridges the branches are disconnected from the central lane and have a Y
  shape with a bright grain toward the umbra. The images reveal that light
  bridges exist on varying intensity levels and that their small-scale
  features evolve on timescales of minutes. Faint light bridges show
  dark lanes outlined by the surrounding bright features. Dark lanes are
  very common and are also found in the boundary of pores. They have a
  characteristic width of 0.1″ or smaller. Intergranular dark lanes of
  that width are seen in active region granulation. <BR /> Conclusions: We
  interpret our images in the context of magneto-convective simulations
  and findings: while central dark lanes in thin light bridges are
  elevated and associated with a density increase above upflows, the dark
  lane branches correspond to locations of downflows and are depressed
  relative to the adjacent bright plasma. Thick light bridges with central
  dark lanes show no projection effect. They have a flat elevated plateau
  that falls off steeply at the umbral boundary. There, Y-shaped filaments
  form as they do in the inner penumbra. This indicates the presence of
  inclined magnetic fields, meaning that the umbral magnetic field is
  wrapped around the convective light bridge.

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: 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: The Polarimetric and Helioseismic Imager for Solar Orbiter:
    SO/PHI
Authors: Solanki, Sami K.; del Toro Iniesta, Jose Carlos; Woch,
   Joachim; Gandorfer, Achim; Hirzberger, Johann; Schmidt, Wolfgang;
   Appourchaux, Thierry; Alvarez-Herrero, Alberto
Bibcode: 2015IAUS..305..108S
Altcode: 2015arXiv150203368S
  The Solar Orbiter is the next solar physics mission of the European
  Space Agency, ESA, in collaboration with NASA, with a launch planned in
  2018. The spacecraft is designed to approach the Sun to within 0.28 AU
  at perihelion of a highly eccentric orbit. The proximity with the Sun
  will also allow its observation at uniformly high resolution at EUV and
  visible wavelengths. Such observations are central for learning more
  about the magnetic coupling of the solar atmosphere. At a later phase
  in the mission the spacecraft will leave the ecliptic and study the
  enigmatic poles of the Sun from a heliographic latitude of up to 33°.

Title: Where does the Thermospheric Ionospheric GEospheric Research
    (TIGER) Program go?
Authors: Schmidtke, G.; Avakyan, S. V.; Berdermann, J.; Bothmer,
   V.; Cessateur, G.; Ciraolo, L.; Didkovsky, L.; Dudok de Wit, T.;
   Eparvier, F. G.; Gottwald, A.; Haberreiter, M.; Hammer, R.; Jacobi,
   Ch.; Jakowski, N.; Kretzschmar, M.; Lilensten, J.; Pfeifer, M.;
   Radicella, S. M.; Schäfer, R.; Schmidt, W.; Solomon, S. C.; Thuillier,
   G.; Tobiska, W. K.; Wieman, S.; Woods, T. N.
Bibcode: 2015AdSpR..56.1547S
Altcode:
  At the 10th Thermospheric Ionospheric GEospheric Research (TIGER/COSPAR)
  symposium held in Moscow in 2014 the achievements from the start of
  TIGER in 1998 were summarized. During that period, great progress was
  made in measuring, understanding, and modeling the highly variable
  UV-Soft X-ray (XUV) solar spectral irradiance (SSI), and its effects
  on the upper atmosphere. However, after more than 50 years of work the
  radiometric accuracy of SSI observation is still an issue and requires
  further improvement. Based on the extreme ultraviolet (EUV) data from
  the SOLAR/SolACES, and SDO/EVE instruments, we present a combined data
  set for the spectral range from 16.5 to 105.5 nm covering a period
  of 3.5 years from 2011 through mid of 2014. This data set is used
  in ionospheric modeling of the global Total Electron Content (TEC),
  and in validating EUV SSI modeling. For further investigations the
  period of 3.5 years is being extended to about 12 years by including
  data from SOHO/SEM and TIMED/SEE instruments. Similarly, UV data are
  used in modeling activities. After summarizing the results, concepts
  are proposed for future real-time SSI measurements with in-flight
  calibration as experienced with the ISS SOLAR payload, for the
  development of a space weather camera for observing and investigating
  space weather phenomena in real-time, and for providing data sets for
  SSI and climate modeling. Other planned topics are the investigation
  of the relationship between solar EUV/UV and visible/near-infrared
  emissions, the impact of X-rays on the upper atmosphere, the development
  of solar EUV/UV indices for different applications, and establishing a
  shared TIGER data system for EUV/UV SSI data distribution and real-time
  streaming, also taking into account the achievements of the FP7 SOLID
  (First European SOLar Irradiance Data Exploitation) project. For further
  progress it is imperative that coordinating activities in this special
  field of solar-terrestrial relations and solar physics is emphasized.

Title: Dynamics of Multi-cored Magnetic Structures in the Quiet Sun
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
   Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.;
   Schmidt, Wolfgang
Bibcode: 2015ApJ...810...79R
Altcode: 2015arXiv150806998R
  We report on the dynamical interaction of quiet-Sun magnetic fields and
  granular convection in the solar photosphere as seen by Sunrise. We
  use high spatial resolution (0.″15-0.″18) and temporal cadence
  (33 s) spectropolarimetric Imaging Magnetograph eXperiment data,
  together with simultaneous CN and Ca ii H filtergrams from Sunrise
  Filter Imager. We apply the SIR inversion code to the polarimetric
  data in order to infer the line of sight velocity and vector magnetic
  field in the photosphere. The analysis reveals bundles of individual
  flux tubes evolving as a single entity during the entire 23 minute data
  set. The group shares a common canopy in the upper photospheric layers,
  while the individual tubes continually intensify, fragment and merge in
  the same way that chains of bright points in photometric observations
  have been reported to do. The evolution of the tube cores are driven
  by the local granular convection flows. They intensify when they
  are “compressed” by surrounding granules and split when they are
  “squeezed” between two moving granules. The resulting fragments
  are usually later regrouped in intergranular lanes by the granular
  flows. The continual intensification, fragmentation and coalescence of
  flux results in magnetic field oscillations of the global entity. From
  the observations we conclude that the magnetic field oscillations first
  reported by Martínez González et al. correspond to the forcing by
  granular motions and not to characteristic oscillatory modes of thin
  flux tubes.

Title: The photospheric solar oxygen project. III. Investigation of
    the centre-to-limb variation of the 630 nm [O I]-Ni I blend
Authors: Caffau, E.; Ludwig, H. -G.; Steffen, M.; Livingston, W.;
   Bonifacio, P.; Malherbe, J. -M.; Doerr, H. -P.; Schmidt, W.
Bibcode: 2015A&A...579A..88C
Altcode: 2015arXiv150600931C
  Context. The solar photospheric abundance of oxygen is still a matter
  of debate. For about ten years some determinations have favoured a
  low oxygen abundance which is at variance with the value inferred by
  helioseismology. Among the oxygen abundance indicators, the forbidden
  line at 630 nm has often been considered the most reliable even
  though it is blended with a Ni i line. In Papers I and II of this
  series we reported a discrepancy in the oxygen abundance derived
  from the 630 nm and the subordinate [O I] line at 636 nm in dwarf
  stars, including the Sun. <BR /> Aims: Here we analyse several,
  in part new, solar observations of the centre-to-limb variation
  of the spectral region including the blend at 630 nm in order to
  separate the individual contributions of oxygen and nickel. <BR />
  Methods: We analyse intensity spectra observed at different limb
  angles in comparison with line formation computations performed on a
  CO5BOLD 3D hydrodynamical simulation of the solar atmosphere. <BR />
  Results: The oxygen abundances obtained from the forbidden line at
  different limb angles are inconsistent if the commonly adopted nickel
  abundance of 6.25 is assumed in our local thermodynamic equilibrium
  computations. With a slightly lower nickel abundance, A(Ni) ≈ 6.1,
  we obtain consistent fits indicating an oxygen abundance of A(O) = 8.73
  ± 0.05. At this value the discrepancy with the subordinate oxygen
  line remains. <BR /> Conclusions: The derived value of the oxygen
  abundance supports the notion of a rather low oxygen abundance in the
  solar photosphere. However, it is disconcerting that the forbidden
  oxygen lines at 630 and 636 nm give noticeably different results,
  and that the nickel abundance derived here from the 630 nm blend is
  lower than expected from other nickel lines.

Title: Variation in sunspot properties between 1999 and 2014
Authors: Rezaei, R.; Beck, C.; Lagg, A.; Borrero, J. M.; Schmidt,
   W.; Collados, M.
Bibcode: 2015A&A...578A..43R
Altcode:
  <BR /> Aims: We study the variation in the magnetic field strength,
  area, and continuum intensity of umbrae in solar cycles 23 and 24. <BR
  /> Methods: We analyzed a sample of 374 sunspots observed from 1999
  until 2014 with the Tenerife Infrared Polarimeter at the German
  Vacuum Tower Telescope and the Facility InfRared Spectropolarimeter
  at the Dunn Solar Telescope. The sample of field strength, area,
  and intensities was used to trace any long-term or cyclic trend of
  umbral properties in the last 15 years. <BR /> Results: Sunspots
  are systematically weaker, that is, have a weaker field strength and
  stronger continuum intensity, toward the end of cycle 23 than they
  had at the maximum of cycle 23. The linear trend reverses with the
  onset of cycle 24. We find that the field strength decreases in the
  declining phase of cycle 23 by about 112 (± 16) G yr<SUP>-1</SUP>,
  while it increases in the rising phase of cycle 24 by about 138 (±
  72) G yr<SUP>-1</SUP>. The umbral intensity shows the opposite trend:
  the intensity increases with a rate of 0.7 (± 0.3)% of I<SUB>c</SUB>
  yr<SUP>-1</SUP> toward the end of cycle 23 and decreases with a rate
  of 3.8 (± 1.5)% of I<SUB>c</SUB> yr<SUP>-1</SUP> toward the maximum of
  cycle 24. The distribution of the umbral maximum field strength in cycle
  24 is similar to that of cycle 23, but is slightly shifted toward lower
  values by about 80 G, corresponding to a possible long-term gradient in
  umbral field strength of about 7 ± 4 G yr<SUP>-1</SUP>. If instead of
  the maximum umbral field we consider the average value over the entire
  umbra, the distribution shifts by about 44 Gauss. <BR /> Conclusions:
  The umbral brightness decreases in the rising stage of a solar cycle,
  but increases from maximum toward the end of the cycle. Our results
  do not indicate a drastic change of the solar cycle toward a grand
  minimum in the near future.

Title: Comb-calibrated solar spectroscopy through a multiplexed
    single-mode fiber channel
Authors: Probst, R. A.; Wang, L.; Doerr, H. -P.; Steinmetz, T.;
   Kentischer, T. J.; Zhao, G.; Hänsch, T. W.; Udem, Th; Holzwarth,
   R.; Schmidt, W.
Bibcode: 2015NJPh...17b3048P
Altcode: 2015arXiv150204942P
  We investigate a new scheme for astronomical spectrograph calibration
  using the laser frequency comb at the Solar Vacuum Tower Telescope on
  Tenerife. Our concept is based upon a single-mode fiber channel, that
  simultaneously feeds the spectrograph with comb light and sunlight. This
  yields nearly perfect spatial mode matching between the two sources. In
  combination with the absolute calibration provided by the frequency
  comb, this method enables extremely robust and accurate spectroscopic
  measurements. The performance of this scheme is compared to a sequence
  of alternating comb and sunlight, and to absorption lines from Earth’s
  atmosphere. We also show how the method can be used for radial-velocity
  detection by measuring the well-explored 5 min oscillations averaged
  over the full solar disk. Our method is currently restricted to solar
  spectroscopy, but with further evolving fiber-injection techniques it
  could become an option even for faint astronomical targets.

Title: DKIST: Observing the Sun at High Resolution
Authors: Tritschler, A.; Rimmele, T. R.; Berukoff, S.; Casini, R.;
   Craig, S. C.; Elmore, D. F.; Hubbard, R. P.; Kuhn, J. R.; Lin, H.;
   McMullin, J. P.; Reardon, K. P.; Schmidt, W.; Warner, M.; Woger, F.
Bibcode: 2015csss...18..933T
Altcode:
  The 4-m aperture Daniel K. Inouye Solar Telescope (DKIST) formerly
  known as the Advanced Technology Solar Telescope (ATST) and currently
  under construction on Haleakalā (Maui, Hawai'i) will be the largest
  solar ground-based telescope and leading resource for studying the
  dynamic Sun and its phenomena at high spatial, spectral and temporal
  resolution. Accurate and sensitive polarimetric observations at
  high-spatial resolution throughout the solar atmosphere including the
  corona is a high priority and a major science driver. As such the DKIST
  will offer a combination of state-of-the-art instruments with imaging
  and/or spectropolarimetric capabilities covering a broad wavelength
  range. This first-light instrumentation suite will include: a Visible
  Broadband Imager (VBI) for high-spatial and -temporal resolution
  imaging of the solar atmosphere; a Visible Spectro-Polarimeter (ViSP)
  for sensitive and accurate multi-line spectropolarimetry; a double
  Fabry-Pérot based Visible Tunable Filter (VTF) for high-spatial
  resolution spectropolarimetry; a fiber-fed 2D Diffraction-Limited Near
  Infra-Red Spectro-Polarimeter (DL-NIRSP); and a Cryogenic Near Infra-Red
  Spectro-Polarimeter (Cryo-NIRSP) for coronal magnetic field measurements
  and on-disk observations of e.g. the CO lines at 4.7 microns. We
  will provide a brief overview of the DKIST's unique capabilities to
  perform spectroscopic and spectropolarimetric measurements of the solar
  atmosphere using its first-light instrumentation suite, the status of
  the construction project, and how facility and data access is provided
  to the US and international community.

Title: The Formation and Disintegration of Magnetic Bright Points
    Observed by Sunrise/IMaX
Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.;
   Jurčák, J.; Martínez Pillet, V.; Solanki, S. K.; Schmidt, W.
Bibcode: 2014ApJ...796...79U
Altcode: 2014arXiv1411.3240U
  The evolution of the physical parameters of magnetic bright points
  (MBPs) located in the quiet Sun (mainly in the interwork) during
  their lifetime is studied. First, we concentrate on the detailed
  description of the magnetic field evolution of three MBPs. This
  reveals that individual features follow different, generally complex,
  and rather dynamic scenarios of evolution. Next, we apply statistical
  methods on roughly 200 observed MBP evolutionary tracks. MBPs are found
  to be formed by the strengthening of an equipartition field patch,
  which initially exhibits a moderate downflow. During the evolution,
  strong downdrafts with an average velocity of 2.4 km s<SUP>-1</SUP>
  set in. These flows, taken together with the concurrent strengthening of
  the field, suggest that we are witnessing the occurrence of convective
  collapses in these features, although only 30% of them reach kG field
  strengths. This fraction might turn out to be larger when the new 4
  m class solar telescopes are operational as observations of MBPs with
  current state of the art instrumentation could still be suffering from
  resolution limitations. Finally, when the bright point disappears
  (although the magnetic field often continues to exist) the magnetic
  field strength has dropped to the equipartition level and is generally
  somewhat weaker than at the beginning of the MBP's evolution. Also,
  only relatively weak downflows are found on average at this stage of
  the evolution. Only 16% of the features display upflows at the time
  that the field weakens, or the MBP disappears. This speaks either for
  a very fast evolving dynamic process at the end of the lifetime, which
  could not be temporally resolved, or against strong upflows as the cause
  of the weakening of the field of these magnetic elements, as has been
  proposed based on simulation results. It is noteworthy that in about 10%
  of the cases, we observe in the vicinity of the downflows small-scale
  strong (exceeding 2 km s<SUP>-1</SUP>) intergranular upflows related
  spatially and temporally to these downflows. The paper is complemented
  by a detailed discussion of aspects regarding the applied methods,
  the complementary literature, and in depth analysis of parameters
  like magnetic field strength and velocity distributions. An important
  difference to magnetic elements and associated bright structures in
  active region plage is that most of the quiet Sun bright points display
  significant downflows over a large fraction of their lifetime (i.e.,
  in more than 46% of time instances/measurements they show downflows
  exceeding 1 km s<SUP>-1</SUP>).

Title: The History of a Quiet-Sun Magnetic Element Revealed by
    IMaX/SUNRISE
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
   Rubio, Luis R.; Bonet, José A.; Martínez Pillet, Valentín; Solanki,
   Sami K.; Schmidt, Wolfgang
Bibcode: 2014ApJ...789....6R
Altcode: 2014arXiv1405.2837R
  Isolated flux tubes are considered to be fundamental magnetic building
  blocks of the solar photosphere. Their formation is usually attributed
  to the concentration of magnetic field to kG strengths by the convective
  collapse mechanism. However, the small size of the magnetic elements in
  quiet-Sun areas has prevented this scenario from being studied in fully
  resolved structures. Here, we report on the formation and subsequent
  evolution of one such photospheric magnetic flux tube, observed in
  the quiet Sun with unprecedented spatial resolution (0.''15-0.''18)
  and high temporal cadence (33 s). The observations were acquired by
  the Imaging Magnetograph eXperiment on board the SUNRISE balloon-borne
  solar observatory. The equipartition field strength magnetic element
  is the result of the merging of several same polarity magnetic flux
  patches, including a footpoint of a previously emerged loop. The
  magnetic structure is then further intensified to kG field strengths
  by convective collapse. The fine structure found within the flux
  concentration reveals that the scenario is more complex than can be
  described by a thin flux tube model with bright points and downflow
  plumes being established near the edges of the kG magnetic feature. We
  also observe a daisy-like alignment of surrounding granules and a
  long-lived inflow toward the magnetic feature. After a subsequent
  weakening process, the field is again intensified to kG strengths. The
  area of the magnetic feature is seen to change in anti-phase with the
  field strength, while the brightness of the bright points and the speed
  of the downflows varies in phase. We also find a relation between the
  brightness of the bright point and the presence of upflows within it.

Title: Properties of sunspot umbrae observed in cycle 24
Authors: Kiess, Christoph; Rezaei, Reza; Schmidt, Wolfgang
Bibcode: 2014A&A...565A..52K
Altcode: 2014arXiv1402.2881K
  <BR /> Aims: There is an ongoing debate whether the solar activity cycle
  is overlaid with a long-term decline that may lead to another grand
  minimum in the near future. We used the size, intensity, and magnetic
  field strength of sunspot umbrae to compare the present cycle 24 with
  the previous one. <BR /> Methods: We used data of the Helioseismic and
  Magnetic Imager on board the Solar Dynamics Observatory and selected
  all sunspots between May 2010 and October 2012, using one image per
  day. We created two subsets of this dataset with a manual tracking
  algorithm, both without duplication. One contains each sunspot (910
  umbrae within 488 spots) and was used to analyze the distribution of
  umbral areas, selected with an automated thresholding method. The other
  subset contains 205 fully evolved sunspots. We estimated their magnetic
  field and the total magnetic flux and discuss the relations between
  umbral size, minimum continuum intensity, maximum field strength,
  and total magnetic flux. <BR /> Results: We find non-linear relations
  between umbral minimum intensity and size and between maximum magnetic
  field strength and size. The field strength scales linearly with
  the intensity and the umbral size scales roughly linearly with the
  total magnetic flux, while the size and field strength level off with
  stronger flux. When separated into hemispheres and averaged temporally,
  the southern umbrae show a temporal increase in size and the northern
  umbrae remain constant. We detected no temporal variation in the umbral
  mean intensity. The probability density function of the umbral area
  in the ascending phase of the current solar cycle is similar to that
  of the last solar cycle. <BR /> Conclusions: From our investigation
  of umbral area, magnetic field, magnetic flux, and umbral intensity
  of the sunspots of the rising phase of cycle 24, we do not find a
  significant difference to the previous cycle, and hence no indication
  for a long-term decline of solar activity.

Title: Comparison between Mg II k and Ca II H Images Recorded by
    SUNRISE/SuFI
Authors: Danilovic, S.; Hirzberger, J.; Riethmüller, T. L.; Solanki,
   S. K.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Gizon, L.; Knölker,
   M.; Schmidt, W.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.
Bibcode: 2014ApJ...784...20D
Altcode:
  We present a comparison of high-resolution images of the solar surface
  taken in the Mg II k and Ca II H channels of the Filter Imager on the
  balloon-borne solar observatory SUNRISE. The Mg and Ca lines are sampled
  with 0.48 nm and 0.11 nm wide filters, respectively. The two channels
  show remarkable qualitative and quantitative similarities in the quiet
  Sun, in an active region plage and during a small flare. However, the Mg
  filtergrams display 1.4-1.7 times higher intensity contrast and appear
  more smeared and smoothed in the quiet Sun. In addition, the fibrils
  in a plage are wider. Although the exposure time is 100 times longer
  for Mg images, the evidence suggests that these differences cannot be
  explained only with instrumental effects or the evolution of the solar
  scene. The differences at least partially arise because of different
  line-formation heights, the stronger response of Mg k emission peaks
  to the higher temperatures, and the larger height range sampled by
  the broad Mg filter used here. This is evidently manifested during
  the flare when a surge in Mg evolves differently than in Ca.

Title: Prominence Science with ATST Instrumentation
Authors: Rimmele, Thomas; Berger, Thomas; Casini, Roberto; Elmore,
   David; Kuhn, Jeff; Lin, Haosheng; Schmidt, Wolfgang; Wöger, Friedrich
Bibcode: 2014IAUS..300..362R
Altcode:
  The 4m Advance Technology Solar Telescope (ATST) is under construction
  on Maui, HI. With its unprecedented resolution and photon collecting
  power ATST will be an ideal tool for studying prominences and filaments
  and their role in producing Coronal Mass Ejections that drive Space
  Weather. The ATST facility will provide a set of first light instruments
  that enable imaging and spectroscopy of the dynamic filament and
  prominence structure at 8 times the resolution of Hinode. Polarimeters
  allow high precision chromospheric and coronal magnetometry at visible
  and infrared (IR) wavelengths. This paper summarizes the capabilities
  of the ATST first-light instrumentation with focus on prominence and
  filament science.

Title: Dynamics of the Fe II 396.94 nm emission line observed at
    solar disk center
Authors: Schmidt, W.; Fisher, J.
Bibcode: 2013A&A...560A..50S
Altcode:
  <BR /> Aims: We have studied the structure and dynamics of the upper
  photosphere and lower chromosphere of the quiet Sun. <BR /> Methods:
  We analyzed a sequence of scans of slit spectra of the Ca II H line
  at 396.8 nm, with a spectral resolution of 850 000, and a spatial
  resolution of about one arcsec, taken in the quiet Sun at disk center,
  with a duration of about 55 min and an area coverage of 185″ ×
  3.5″. We used statistical methods to characterize size, lifetime,
  and dynamics of emission features of the Fe II line at 396.94 nm. <BR />
  Results: We have identified about 780 distinct features where the Fe II
  line shows emission stronger than 3% above the local continuum. Their
  lifetime is on the order of one minute, and the spatial extent is
  about or less than 2″. On average, Fe II emission features show a
  significant redshift of 1.3 km s<SUP>-1</SUP>, with respect to the
  position of the absorption line. The redshift of the Fe II emission
  is absent close to the solar limb. The Fe II emission is coupled with
  a strongly enhanced intensity level of the Ca II wings. A time line
  analysis shows that other photospheric lines show significant redshift
  one minute before, and a blueshift after, the occurrence of an emission
  event. A redshift of the Ca II H line core precedes the redshift of
  the Fe II line by about 30 s. The occurrence of the H2v emissions is
  strongly reduced before and significantly increased after the Fe II
  emission events. <BR /> Conclusions: The temporal behavior of the Fe II
  emission line and both the Ca II H line core and H2v emission suggest
  a connection between Fe II emission and chromospheric activity. The
  presence of a significant redshift during the Fe II emissions and
  the absence of this redshift near the limb suggest that the observed
  redshift is indeed caused by a downflow in the line-forming region. From
  our result concerning the intensity fluctuations in the core of the Fe
  II line, and from the magnitude of the downflow velocities we conclude
  that the Fe II emissions at 396.94 nm occur in the photosphere.

Title: First High-resolution Images of the Sun in the 2796 Å Mg II
    k Line
Authors: Riethmüller, T. L.; Solanki, S. K.; Hirzberger, J.;
   Danilovic, S.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Gizon, L.;
   Knölker, M.; Schmidt, W.; Del Toro Iniesta, J. C.
Bibcode: 2013ApJ...776L..13R
Altcode: 2013arXiv1309.5213R
  We present the first high-resolution solar images in the Mg II k 2796
  Å line. The images, taken through a 4.8 Å broad interference filter,
  were obtained during the second science flight of Sunrise in 2013 June
  by the Sunrise Filter Imager (SuFI) instrument. The Mg II k images
  display structures that look qualitatively very similar to images taken
  in the core of Ca II H. The Mg II images exhibit reversed granulation
  (or shock waves) in the internetwork regions of the quiet Sun, at
  intensity contrasts that are similar to those found in Ca II H. Very
  prominent in Mg II are bright points, both in the quiet Sun and in plage
  regions, particularly near the disk center. These are much brighter than
  at other wavelengths sampled at similar resolution. Furthermore, Mg II k
  images also show fibril structures associated with plage regions. Again,
  the fibrils are similar to those seen in Ca II H images, but tend to
  be more pronounced, particularly in weak plage.

Title: Is Magnetic Reconnection the Cause of Supersonic Upflows in
    Granular Cells?
Authors: Borrero, J. M.; Martínez Pillet, V.; Schmidt, W.; Quintero
   Noda, C.; Bonet, J. A.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.
Bibcode: 2013ApJ...768...69B
Altcode: 2013arXiv1303.2557B
  In a previous work, we reported on the discovery of supersonic magnetic
  upflows on granular cells in data from the SUNRISE/IMaX instrument. In
  the present work, we investigate the physical origin of these events
  employing data from the same instrument but with higher spectral
  sampling. By means of the inversion of Stokes profiles we are able
  to recover the physical parameters (temperature, magnetic field,
  line-of-sight velocity, etc.) present in the solar photosphere at the
  time of these events. The inversion is performed in a Monte-Carlo-like
  fashion, that is, repeating it many times with different initializations
  and retaining only the best result. We find that many of the events are
  characterized by a reversal in the polarity of the magnetic field along
  the vertical direction in the photosphere, accompanied by an enhancement
  in the temperature and by supersonic line-of-sight velocities. In
  about half of the studied events, large blueshifted and redshifted
  line-of-sight velocities coexist above/below each other. These features
  can be explained in terms of magnetic reconnection, where the energy
  stored in the magnetic field is released in the form of kinetic
  and thermal energy when magnetic field lines of opposite polarities
  coalesce. However, the agreement with magnetic reconnection is not
  perfect and, therefore, other possible physical mechanisms might also
  play a role.

Title: Evolution of the Fine Structure of Magnetic Fields in the
Quiet Sun: Observations from Sunrise/IMaX and Extrapolations
Authors: Wiegelmann, T.; Solanki, S. K.; Borrero, J. M.; Peter,
   H.; Barthol, P.; Gandorfer, A.; Martínez Pillet, V.; Schmidt, W.;
   Knölker, M.
Bibcode: 2013SoPh..283..253W
Altcode:
  Observations with the balloon-borne Sunrise/Imaging Magnetograph
  eXperiment (IMaX) provide high spatial resolution (roughly 100 km at
  disk center) measurements of the magnetic field in the photosphere of
  the quiet Sun. To investigate the magnetic structure of the chromosphere
  and corona, we extrapolate these photospheric measurements into
  the upper solar atmosphere and analyze a 22-minute long time series
  with a cadence of 33 seconds. Using the extrapolated magnetic-field
  lines as tracer, we investigate temporal evolution of the magnetic
  connectivity in the quiet Sun's atmosphere. The majority of magnetic
  loops are asymmetric in the sense that the photospheric field strength
  at the loop foot points is very different. We find that the magnetic
  connectivity of the loops changes rapidly with a typical connection
  recycling time of about 3±1 minutes in the upper solar atmosphere and
  12±4 minutes in the photosphere. This is considerably shorter than
  previously found. Nonetheless, our estimate of the energy released by
  the associated magnetic-reconnection processes is not likely to be the
  sole source for heating the chromosphere and corona in the quiet Sun.

Title: Gregor@night: The future high-resolution stellar spectrograph
    for the GREGOR solar telescope
Authors: Strassmeier, K. G.; Ilyin, I. V.; Woche, M.; Granzer,
   T.; Weber, M.; Weingrill, J.; Bauer, S. -M.; Popow, E.; Denker, C.;
   Schmidt, W.; von der Lühe, O.; Berdyugina, S.; Collados, M.; Koubsky,
   P.; Hackman, T.; Mantere, M. J.
Bibcode: 2012AN....333..901S
Altcode:
  We describe the future night-time spectrograph for the GREGOR solar
  telescope and present its science core projects. The spectrograph
  provides a 3-pixel resolution of up to R=87 000 in 45 échelle orders
  covering the wavelength range 390-900 nm with three grating settings. An
  iodine cell can be used for high-precision radial velocity work in the
  500-630 nm range. The operation of the spectrograph and the telescope
  will be fully automated without the presence of humans during night-time
  and will be based on the successful STELLA control system. Future
  upgrades include a second optical camera for even higher spectral
  resolution, a Stokes-V polarimeter and a link to the laser-frequency
  comb at the Vacuum Tower Telescope. The night-time core projects are a
  study of the angular-momentum evolution of ``The Sun in Time'' and a
  continuation of our long-term Doppler imaging of active stars.

Title: A retrospective of the GREGOR solar telescope in scientific
    literature
Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.;
   Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.;
   Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.;
   Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa,
   M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
   Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.;
   Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann,
   T.; Wiehr, E.; Wittmann, A. D.; Woche, M.
Bibcode: 2012AN....333..810D
Altcode: 2012arXiv1210.3167D
  In this review, we look back upon the literature, which had the
  GREGOR solar telescope project as its subject including science cases,
  telescope subsystems, and post-focus instruments. The articles date
  back to the year 2000, when the initial concepts for a new solar
  telescope on Tenerife were first presented at scientific meetings. This
  comprehensive bibliography contains literature until the year 2012,
  i.e., the final stages of commissioning and science verification. Taking
  stock of the various publications in peer-reviewed journals and
  conference proceedings also provides the ``historical'' context
  for the reference articles in this special issue of Astronomische
  Nachrichten/Astronomical Notes.

Title: Open-foldable domes with high-tension textile membranes:
    The GREGOR dome
Authors: Hammerschlag, R. H.; Kommers, J. N.; Visser, S.; Bettonvil,
   F. C. M.; van Schie, A. G. M.; van Leverink, S. J.; Sliepen, G.;
   Jägers, A. P. L.; Schmidt, W.; Volkmer, R.
Bibcode: 2012AN....333..830H
Altcode:
  Double layers of high-tensioned textile membranes were applied to the
  completely open-foldable dome for the GREGOR telescope for the first
  time. Simultaneous climate measurements inside and outside the dome
  have proven the thermal-insulating capability of this double-layer
  construction. The GREGOR dome is the result of the continuation of the
  ESO research on open-foldable domes with textile structures, followed by
  the research for the DOT dome with high-tensioned textile membranes. It
  cleared the way to extreme stability required for astronomical practice
  on high mountain sites with heavy storms and ice formation. The storm
  Delta with 245 km/h 1-minute mean maximum at the location of the GREGOR
  caused no problems, nor did other storms afterwards. Opening and closing
  experiences up to wind speeds of 90 km/h were without problems. New
  technical developments were implemented and tested at the GREGOR dome,
  opening the way for application to much larger domes up to the 30 m
  diameter-class range.

Title: The 1.5 meter solar telescope GREGOR
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
   Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.;
   Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann,
   A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
   Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.;
   Strassmeier, K. G.; Waldmann , T. A.
Bibcode: 2012AN....333..796S
Altcode:
  The 1.5 m telescope GREGOR opens a new window to the understanding
  of solar small-scale magnetism. The first light instrumentation
  includes the Gregor Fabry Pérot Interferometer (GFPI), a filter
  spectro-polarimeter for the visible wavelength range, the GRating
  Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The
  excellent performance of the first two instruments has already been
  demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest
  solar telescope and number 3 in the world. Its all-reflective Gregory
  design provides a large wavelength coverage from the near UV up to at
  least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR
  is equipped with a high-order adaptive optics system, with a subaperture
  size of 10 cm, and a deformable mirror with 256 actuators. The science
  goals are focused on, but not limited to, solar magnetism. GREGOR
  allows us to measure the emergence and disappearance of magnetic flux
  at the solar surface at spatial scales well below 100 km. Thanks to its
  spectro-polarimetric capabilities, GREGOR will measure the interaction
  between the plasma flows, different kinds of waves, and the magnetic
  field. This will foster our understanding of the processes that heat the
  chromosphere and the outer layers of the solar atmosphere. Observations
  of the surface magnetic field at very small spatial scales will shed
  light on the variability of the solar brightness.

Title: Mechanical design of the solar telescope GREGOR
Authors: Volkmer, R.; Eisenträger, P.; Emde, P.; Fischer, A.; von
   der Lühe, O.; Nicklas, H.; Soltau, D.; Schmidt, W.; Weis, U.
Bibcode: 2012AN....333..816V
Altcode:
  The mechanical structure of the GREGOR telescope was installed at the
  Observatorio del Teide, Tenerife, in 2004. New concepts for mounting
  and cooling of the 1.5-meter primary mirror were introduced. GREGOR
  is an open telescope, therefore the dome is completely open during
  observations to allow for air flushing through the open, but stiff
  telescope structure. Backside cooling system of the primary mirror
  keeps the mirror surface close to ambient temperature to prevent mirror
  seeing. The large collecting area of the primary mirror results in high
  energy density at the field stop at the prime focus of the primary
  which needs to be removed. The optical elements are supported by
  precision alignment systems and should provide a stable solar image
  at the optical lab. The coudé train can be evacuated and serves
  as a natural barrier between the outer environmental conditions and
  the air-conditioned optical laboratory with its sensitive scientific
  instrumentation. The telescope was successfully commissioned and will
  start its nominal operation during 2013.

Title: GRIS: The GREGOR Infrared Spectrograph
Authors: Collados, M.; López, R.; Páez, E.; Hernández, E.; Reyes,
   M.; Calcines, A.; Ballesteros, E.; Díaz, J. J.; Denker, C.; Lagg,
   A.; Schlichenmaier, R.; Schmidt, W.; Solanki, S. K.; Strassmeier,
   K. G.; von der Lühe, O.; Volkmer, R.
Bibcode: 2012AN....333..872C
Altcode:
  This paper describes the main characteristics of GRIS (GREGOR Infrared
  Spectrograph), the grating spectrograph installed in the recently
  inaugurated (May 2012) 1.5-meter GREGOR telescope located at the
  Observatorio del Teide in Tenerife. The spectrograph has a standard
  Czerny-Turner configuration with parabolic collimator and camera mirrors
  that belong to the same conic surface. Although nothing prevents its
  use at visible wavelengths, the spectrograph will be initially used
  in combination with the infrared detector of the Tenerife Infrared
  Polarimeter (TIP-II) in standard spectroscopic mode as well as for
  spectropolarimetric measurements.

Title: A Laser Frequency Comb System for Absolute Calibration of
    the VTT Echelle Spectrograph
Authors: Doerr, H. -P.; Steinmetz, T.; Holzwarth, R.; Kentischer,
   T.; Schmidt, W.
Bibcode: 2012SoPh..280..663D
Altcode: 2012arXiv1204.0948D; 2012SoPh..tmp...59D
  A wavelength calibration system based on a laser frequency comb (LFC)
  was developed in a co-operation between the Kiepenheuer-Institut für
  Sonnenphysik, Freiburg, Germany and the Max-Planck-Institut für
  Quantenoptik, Garching, Germany for permanent installation at the
  German Vacuum Tower Telescope (VTT) on Tenerife, Canary Islands. The
  system was installed successfully in October 2011. By simultaneously
  recording the spectra from the Sun and the LFC, for each exposure a
  calibration curve can be derived from the known frequencies of the
  comb modes that is suitable for absolute calibration at the meters
  per second level. We briefly summarize some topics in solar physics
  that benefit from absolute spectroscopy and point out the advantages
  of LFC compared to traditional calibration techniques. We also sketch
  the basic setup of the VTT calibration system and its integration with
  the existing echelle spectrograph.

Title: Resolving the Internal Magnetic Structure of the Solar Network
Authors: Martínez González, M. J.; Bellot Rubio, L. R.; Solanki,
   S. K.; Martínez Pillet, V.; Del Toro Iniesta, J. C.; Barthol, P.;
   Schmidt, W.
Bibcode: 2012ApJ...758L..40M
Altcode: 2012arXiv1209.2584M
  We analyze the spectral asymmetry of Stokes V (circularly polarized)
  profiles of an individual network patch in the quiet Sun observed
  by Sunrise/IMaX. At a spatial resolution of 0farcs15-0farcs18, the
  network elements contain substructure which is revealed by the spatial
  distribution of Stokes V asymmetries. The area asymmetry between the
  red and blue lobes of Stokes V increases from nearly zero at the core
  of the structure to values close to unity at its edges (single-lobed
  profiles). Such a distribution of the area asymmetry is consistent
  with magnetic fields expanding with height, i.e., an expanding
  magnetic canopy (which is required to fulfill pressure balance and
  flux conservation in the solar atmosphere). Inversion of the Stokes
  I and V profiles of the patch confirms this picture, revealing a
  decreasing field strength and increasing height of the canopy base
  from the core to the periphery of the network patch. However, the
  non-roundish shape of the structure and the presence of negative area
  and amplitude asymmetries reveal that the scenario is more complex than
  a canonical flux tube expanding with height surrounded by downflows.

Title: Variation in sunspot properties between 1999 and 2011 as
    observed with the Tenerife Infrared Polarimeter
Authors: Rezaei, R.; Beck, C.; Schmidt, W.
Bibcode: 2012A&A...541A..60R
Altcode: 2012arXiv1203.1444R
  <BR /> Aims: We study the variation in the magnetic field strength
  and the umbral intensity of sunspots during the declining phase of
  the solar cycle No. 23 and in the beginning of cycle No. 24. <BR />
  Methods: We analyze a sample of 183 sunspots observed from 1999 until
  2011 with the Tenerife Infrared Polarimeter (TIP) at the German Vacuum
  Tower Telescope (VTT). The magnetic field strength is derived from the
  Zeeman splitting of the Stokes-V signal in one near-infrared spectral
  line, either Fe i 1564.8 nm, Fe i 1089.6 nm, or Si i 1082.7 nm. This
  avoids the effects of the unpolarized stray light from the field-free
  quiet Sun surroundings that can affect the splitting seen in Stokes-I
  in the umbra. The minimum umbral continuum intensity and umbral area are
  also measured. <BR /> Results: We find that there is a systematic trend
  for sunspots in the late stage of the solar cycle No. 23 to be weaker,
  i.e., to have a smaller maximum magnetic field strength than those at
  the start of the cycle. The decrease in the field strength with time of
  about 94 Gyr<SUP>-1</SUP> is well beyond the statistical fluctuations
  that would be expected because of the larger number of sunspots close
  to cycle maximum (14 Gyr<SUP>-1</SUP>). In the same time interval, the
  continuum intensity of the umbra increases with a rate of 1.3 (±0.4)%
  of I<SUB>c</SUB> yr<SUP>-1</SUP>, while the umbral area does not show
  any trend above the statistical variance. Sunspots in the new cycle
  No. 24 show higher field strengths and lower continuum intensities
  than those at the end of cycle No. 23, interrupting the trend. <BR />
  Conclusions: Sunspots have an intrinsically weaker field strength and
  brighter umbrae at the late stages of solar cycles compared to their
  initial stages, without any significant change in their area. The abrupt
  increase in field strength in sunspots of the new cycle suggests that
  the cyclic variations are dominating over any long-term trend that
  continues across cycles. We find a slight decrease in field strength
  and an increase in intensity as a long-term trend across the cycles.

Title: Diffusivity of Isolated Internetwork Ca II H Bright Points
    Observed by SuFI/SUNRISE
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Feller, A.;
   Pietarila, A.; Lagg, A.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
   Knoelker, M.; Martinez Pillet, V.; Schmidt, W.; Title, A.
Bibcode: 2012decs.confE..99J
Altcode:
  We analyze trajectories of the proper motion of intrinsically magnetic,
  isolated internetwork Ca II H BPs (with mean lifetime of 461 sec) to
  obtain their diffusivity behaviors. We use high spatial and temporal
  resolution image sequences of quiet-Sun, disc-centre observations
  obtained in the Ca II H 397 nm passband of the Sunrise Filter Imager
  (SuFI) on board the SUNRISE balloon-borne solar observatory. In
  order to avoid misidentification, the BPs are semi-manually selected
  and then automatically tracked. The trajectory of each BP is then
  calculated and its diffusion index is described by a power law
  exponent, using which we classify the BPs' trajectories into sub-,
  normal and super- diffusive. In addition, the corresponding diffusion
  coefficients (D) based on the observed displacements are consequently
  computed. We find a strong super-diffusivity at a height sampled by the
  SuFI/SUNRISE Ca II H passband (i.e. a height corresponding roughly to
  the temperature minimum). We find that 74% of the identified tiny BPs
  are super-diffusive, 18% move randomly (i.e. their motion corresponds
  to normal diffusion) and only 8% belong to the sub-diffusion regime. In
  addition, we find that 53% of the super-diffusion regime (i.e. 39% of
  all BPs) have the diffusivity index of 2 which are termed as "Ballistic
  BPs". Finally, we explore the distribution of diffusion index with the
  help of a simple simulation. The results suggest that the BPs are random
  walkers superposed by a systematic (background) velocity in which the
  magnitude of each component (and hence their ratio) depends on the time
  and spatial scales. We further discuss a simple sketch to explain the
  diffusivity of observed BPs while they migrate within a supergranule
  (i.e. internetwork areas) or close to the network regions.

Title: The Frontier between Small-scale Bipoles and Ephemeral Regions
in the Solar Photosphere: Emergence and Decay of an Intermediate-scale
    Bipole Observed with SUNRISE/IMaX
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Bonet, J. A.;
   del Toro Iniesta, J. Carlos; Bellot Rubio, L. R.; Solanki, S. K.;
   Schmidt, W.; Gandorfer, A.; Barthol, P.; Knölker, M.
Bibcode: 2012ApJ...745..160G
Altcode: 2011arXiv1110.1405G
  We report on the photospheric evolution of an intermediate-scale (≈4
  Mm footpoint separation) magnetic bipole, from emergence to decay,
  observed in the quiet Sun at high spatial (0farcs3) and temporal (33 s)
  resolution. The observations were acquired by the Imaging Magnetograph
  Experiment imaging magnetograph during the first science flight of the
  SUNRISE balloon-borne solar observatory. The bipole flux content is 6 ×
  10<SUP>17</SUP> Mx, representing a structure bridging the gap between
  granular scale bipoles and the smaller ephemeral regions. Footpoints
  separate at a speed of 3.5 km s<SUP>-1</SUP> and reach a maximum
  distance of 4.5 Mm before the field dissolves. The evolution of the
  bipole is revealed to be very dynamic: we found a proper motion of
  the bipole axis and detected a change of the azimuth angle of 90° in
  300 s, which may indicate the presence of some writhe in the emerging
  structure. The overall morphology and behavior are in agreement with
  previous analyses of bipolar structures emerging at the granular scale,
  but we also found several similarities with emerging flux structures
  at larger scales. The flux growth rate is 2.6 × 10<SUP>15</SUP> Mx
  s<SUP>-1</SUP>, while the mean decay rate is one order of magnitude
  smaller. We describe in some detail the decay phase of the bipole
  footpoints that includes break up into smaller structures, and
  interaction with preexisting fields leading to cancellation, but it
  appears to be dominated by an as-yet unidentified diffusive process
  that removes most of the flux with an exponential flux decay curve. The
  diffusion constant (8 × 10<SUP>2</SUP> km<SUP>2</SUP> s<SUP>-1</SUP>)
  associated with this decay is similar to the values used to describe
  the large-scale diffusion in flux transport models.

Title: Magnetic field emergence in mesogranular-sized exploding
    granules observed with sunrise/IMaX data
Authors: Palacios, J.; Blanco Rodríguez, J.; Vargas Domínguez, S.;
   Domingo, V.; Martínez Pillet, V.; Bonet, J. A.; Bellot Rubio, L. R.;
   Del Toro Iniesta, J. C.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
   Berkefeld, T.; Schmidt, W.; Knölker, M.
Bibcode: 2012A&A...537A..21P
Altcode: 2011arXiv1110.4555P
  We report on magnetic field emergences covering significant
  areas of exploding granules. The balloon-borne mission Sunrise
  provided high spatial and temporal resolution images of the solar
  photosphere. Continuum images, longitudinal and transverse magnetic
  field maps and Dopplergrams obtained by IMaX onboard Sunrise are
  analyzed by local correlation traking (LCT), divergence calculation
  and time slices, Stokes inversions and numerical simulations are also
  employed. We characterize two mesogranular-scale exploding granules
  where ~10<SUP>18</SUP> Mx of magnetic flux emerges. The emergence
  of weak unipolar longitudinal fields (~100 G) start with a single
  visible magnetic polarity, occupying their respective granules' top
  and following the granular splitting. After a while, mixed polarities
  start appearing, concentrated in downflow lanes. The events last around
  20 min. LCT analyses confirm mesogranular scale expansion, displaying
  a similar pattern for all the physical properties, and divergence
  centers match between all of them. We found a similar behaviour
  with the emergence events in a numerical MHD simulation. Granule
  expansion velocities are around 1 kms<SUP>-1</SUP> while magnetic
  patches expand at 0.65 kms<SUP>-1</SUP>. One of the analyzed events
  evidences the emergence of a loop-like structure. Advection of
  the emerging magnetic flux features is dominated by convective
  motion resulting from the exploding granule due to the magnetic
  field frozen in the granular plasma. Intensification of the
  magnetic field occurs in the intergranular lanes, probably
  because of being directed by the downflowing plasma. <P />Movies
  associated to Figs. 2-4 are available in electronic form at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

Title: Venus transit 2004: Illustrating the capability of exoplanet
    transmission spectroscopy
Authors: Hedelt, P.; Alonso, R.; Brown, T.; Collados Vera, M.; Rauer,
   H.; Schleicher, H.; Schmidt, W.; Schreier, F.; Titz, R.
Bibcode: 2011A&A...533A.136H
Altcode: 2011arXiv1107.3700H
  The transit of Venus in 2004 offered the rare possibility to remotely
  sense a well-known planetary atmosphere using ground-based absorption
  spectroscopy. Transmission spectra of Venus' atmosphere were obtained
  in the near infrared using the Vacuum Tower Telescope (VTT) in
  Tenerife. Since the instrument was designed to measure the very bright
  photosphere of the Sun, extracting Venus' atmosphere was challenging. We
  were able to identify CO<SUB>2</SUB> absorption lines in the upper
  Venus atmosphere. Moreover, the relative abundance of the three
  most abundant CO<SUB>2</SUB> isotopologues could be determined. The
  observations resolved Venus' limb, showing Doppler-shifted absorption
  lines that are probably caused by high-altitude winds. We demonstrate
  the utility of ground-based measurements in analyzing the atmospheric
  constituents of a terrestrial planet atmosphere using methods that
  might be applied in future to terrestrial extrasolar planets.

Title: The Sun at high resolution: first results from the Sunrise
    mission
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller,
   A.; Gandorfer, A.; Hirzberger, J.; Lagg, A.; Riethmüller, T. L.;
   Schüssler, M.; Wiegelmann, T.; Bonet, J. A.; Pillet, V. Martínez;
   Khomenko, E.; del Toro Iniesta, J. C.; Domingo, V.; Palacios, J.;
   Knölker, M.; González, N. Bello; Borrero, J. M.; Berkefeld, T.;
   Franz, M.; Roth, M.; Schmidt, W.; Steiner, O.; Title, A. M.
Bibcode: 2011IAUS..273..226S
Altcode:
  The Sunrise balloon-borne solar observatory consists of a 1m aperture
  Gregory telescope, a UV filter imager, an imaging vector polarimeter,
  an image stabilization system and further infrastructure. The first
  science flight of Sunrise yielded high-quality data that reveal the
  structure, dynamics and evolution of solar convection, oscillations
  and magnetic fields at a resolution of around 100 km in the quiet
  Sun. Here we describe very briefly the mission and the first results
  obtained from the Sunrise data, which include a number of discoveries.

Title: Unnoticed Magnetic Field Oscillations in the Very Quiet Sun
    Revealed by SUNRISE/IMaX
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
   R.; Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; López Ariste,
   A.; Schmidt, W.; Barthol, P.; Gandorfer, A.
Bibcode: 2011ApJ...730L..37M
Altcode: 2011arXiv1103.0145M
  We present observational evidence for oscillations of magnetic flux
  density in the quiet areas of the Sun. The majority of magnetic
  fields on the solar surface have strengths of the order of or lower
  than the equipartition field (300-500 G). This results in a myriad of
  magnetic fields whose evolution is largely determined by the turbulent
  plasma motions. When granules evolve they squash the magnetic field
  lines together or pull them apart. Here, we report on the periodic
  deformation of the shapes of features in circular polarization observed
  at high resolution with SUNRISE. In particular, we note that the
  area of patches with a constant magnetic flux oscillates with time,
  which implies that the apparent magnetic field intensity oscillates
  in antiphase. The periods associated with this oscillatory pattern
  are compatible with the granular lifetime and change abruptly, which
  suggests that these oscillations might not correspond to characteristic
  oscillatory modes of magnetic structures, but to the forcing by granular
  motions. In one particular case, we find three patches around the same
  granule oscillating in phase, which means that the spatial coherence
  of these oscillations can reach 1600 km. Interestingly, the same kind
  of oscillatory phenomenon is also found in the upper photosphere.

Title: Mesogranulation and the Solar Surface Magnetic Field
    Distribution
Authors: Yelles Chaouche, L.; Moreno-Insertis, F.; Martínez Pillet,
   V.; Wiegelmann, T.; Bonet, J. A.; Knölker, M.; Bellot Rubio, L. R.;
   del Toro Iniesta, J. C.; Barthol, P.; Gandorfer, A.; Schmidt, W.;
   Solanki, S. K.
Bibcode: 2011ApJ...727L..30Y
Altcode: 2010arXiv1012.4481Y
  The relation of the solar surface magnetic field with mesogranular
  cells is studied using high spatial (≈100 km) and temporal (≈30
  s) resolution data obtained with the IMaX instrument on board
  SUNRISE. First, mesogranular cells are identified using Lagrange
  tracers (corks) based on horizontal velocity fields obtained through
  local correlation tracking. After ≈20 minutes of integration, the
  tracers delineate a sharp mesogranular network with lanes of width
  below about 280 km. The preferential location of magnetic elements in
  mesogranular cells is tested quantitatively. Roughly 85% of pixels with
  magnetic field higher than 100 G are located in the near neighborhood
  of mesogranular lanes. Magnetic flux is therefore concentrated in
  mesogranular lanes rather than intergranular ones. Second, magnetic
  field extrapolations are performed to obtain field lines anchored in
  the observed flux elements. This analysis, therefore, is independent
  of the horizontal flows determined in the first part. A probability
  density function (PDF) is calculated for the distribution of distances
  between the footpoints of individual magnetic field lines. The PDF has
  an exponential shape at scales between 1 and 10 Mm, with a constant
  characteristic decay distance, indicating the absence of preferred
  convection scales in the mesogranular range. Our results support
  the view that mesogranulation is not an intrinsic convective scale
  (in the sense that it is not a primary energy-injection scale of solar
  convection), but also give quantitative confirmation that, nevertheless,
  the magnetic elements are preferentially found along mesogranular lanes.

Title: The Imaging Magnetograph eXperiment (IMaX) for the Sunrise
    Balloon-Borne Solar Observatory
Authors: Martínez Pillet, V.; del Toro Iniesta, J. C.;
   Álvarez-Herrero, A.; Domingo, V.; Bonet, J. A.; González Fernández,
   L.; López Jiménez, A.; Pastor, C.; Gasent Blesa, J. L.; Mellado, P.;
   Piqueras, J.; Aparicio, B.; Balaguer, M.; Ballesteros, E.; Belenguer,
   T.; Bellot Rubio, L. R.; Berkefeld, T.; Collados, M.; Deutsch, W.;
   Feller, A.; Girela, F.; Grauf, B.; Heredero, R. L.; Herranz, M.;
   Jerónimo, J. M.; Laguna, H.; Meller, R.; Menéndez, M.; Morales, R.;
   Orozco Suárez, D.; Ramos, G.; Reina, M.; Ramos, J. L.; Rodríguez,
   P.; Sánchez, A.; Uribe-Patarroyo, N.; Barthol, P.; Gandorfer, A.;
   Knoelker, M.; Schmidt, W.; Solanki, S. K.; Vargas Domínguez, S.
Bibcode: 2011SoPh..268...57M
Altcode: 2010SoPh..tmp..181M; 2010arXiv1009.1095M
  The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter
  built by four institutions in Spain that flew on board the Sunrise
  balloon-borne solar observatory in June 2009 for almost six days over
  the Arctic Circle. As a polarimeter, IMaX uses fast polarization
  modulation (based on the use of two liquid crystal retarders),
  real-time image accumulation, and dual-beam polarimetry to reach
  polarization sensitivities of 0.1%. As a spectrograph, the instrument
  uses a LiNbO<SUB>3</SUB> etalon in double pass and a narrow band
  pre-filter to achieve a spectral resolution of 85 mÅ. IMaX uses the
  high-Zeeman-sensitive line of Fe I at 5250.2 Å and observes all four
  Stokes parameters at various points inside the spectral line. This
  allows vector magnetograms, Dopplergrams, and intensity frames to be
  produced that, after reconstruction, reach spatial resolutions in the
  0.15 - 0.18 arcsec range over a 50×50 arcsec field of view. Time
  cadences vary between 10 and 33 s, although the shortest one only
  includes longitudinal polarimetry. The spectral line is sampled in
  various ways depending on the applied observing mode, from just two
  points inside the line to 11 of them. All observing modes include
  one extra wavelength point in the nearby continuum. Gauss equivalent
  sensitivities are 4 G for longitudinal fields and 80 G for transverse
  fields per wavelength sample. The line-of-sight velocities are estimated
  with statistical errors of the order of 5 - 40 m s<SUP>−1</SUP>. The
  design, calibration, and integration phases of the instrument,
  together with the implemented data reduction scheme, are described in
  some detail.

Title: The Wave-Front Correction System for the Sunrise Balloon-Borne
    Solar Observatory
Authors: Berkefeld, T.; Schmidt, W.; Soltau, D.; Bell, A.;
   Doerr, H. P.; Feger, B.; Friedlein, R.; Gerber, K.; Heidecke, F.;
   Kentischer, T.; v. d. Lühe, O.; Sigwarth, M.; Wälde, E.; Barthol,
   P.; Deutsch, W.; Gandorfer, A.; Germerott, D.; Grauf, B.; Meller, R.;
   Álvarez-Herrero, A.; Knölker, M.; Martínez Pillet, V.; Solanki,
   S. K.; Title, A. M.
Bibcode: 2011SoPh..268..103B
Altcode: 2010SoPh..tmp..236B; 2010arXiv1009.3196B
  This paper describes the wave-front correction system developed for
  the Sunrise balloon telescope, and it provides information about its
  in-flight performance. For the correction of low-order aberrations,
  a Correlating Wave-Front Sensor (CWS) was used. It consisted of a
  six-element Shack - Hartmann wave-front sensor (WFS), a fast tip-tilt
  mirror for the compensation of image motion, and an active telescope
  secondary mirror for focus correction. The CWS delivered a stabilized
  image with a precision of 0.04 arcsec (rms), whenever the coarse
  pointing was better than ± 45 arcsec peak-to-peak. The automatic
  focus adjustment maintained a focus stability of 0.01 waves in the
  focal plane of the CWS. During the 5.5 day flight, good image quality
  and stability were achieved during 33 hours, containing 45 sequences,
  which lasted between 10 and 45 min.

Title: The Sunrise Mission
Authors: Barthol, P.; Gandorfer, A.; Solanki, S. K.; Schüssler,
   M.; Chares, B.; Curdt, W.; Deutsch, W.; Feller, A.; Germerott, D.;
   Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.; Meller, R.;
   Müller, R.; Riethmüller, T. L.; Tomasch, G.; Knölker, M.; Lites,
   B. W.; Card, G.; Elmore, D.; Fox, J.; Lecinski, A.; Nelson, P.;
   Summers, R.; Watt, A.; Martínez Pillet, V.; Bonet, J. A.; Schmidt,
   W.; Berkefeld, T.; Title, A. M.; Domingo, V.; Gasent Blesa, J. L.;
   del Toro Iniesta, J. C.; López Jiménez, A.; Álvarez-Herrero, A.;
   Sabau-Graziati, L.; Widani, C.; Haberler, P.; Härtel, K.; Kampf,
   D.; Levin, T.; Pérez Grande, I.; Sanz-Andrés, A.; Schmidt, E.
Bibcode: 2011SoPh..268....1B
Altcode: 2010arXiv1009.2689B; 2010SoPh..tmp..224B
  The first science flight of the balloon-borne Sunrise telescope took
  place in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset
  Island in northern Canada. We describe the scientific aims and
  mission concept of the project and give an overview and a description
  of the various hardware components: the 1-m main telescope with its
  postfocus science instruments (the UV filter imager SuFI and the imaging
  vector magnetograph IMaX) and support instruments (image stabilizing
  and light distribution system ISLiD and correlating wavefront sensor
  CWS), the optomechanical support structure and the instrument mounting
  concept, the gondola structure and the power, pointing, and telemetry
  systems, and the general electronics architecture. We also explain
  the optimization of the structural and thermal design of the complete
  payload. The preparations for the science flight are described,
  including AIV and ground calibration of the instruments. The course
  of events during the science flight is outlined, up to the recovery
  activities. Finally, the in-flight performance of the instrumentation
  is discussed.

Title: The Filter Imager SuFI and the Image Stabilization and Light
Distribution System ISLiD of the Sunrise Balloon-Borne Observatory:
    Instrument Description
Authors: Gandorfer, A.; Grauf, B.; Barthol, P.; Riethmüller, T. L.;
   Solanki, S. K.; Chares, B.; Deutsch, W.; Ebert, S.; Feller, A.;
   Germerott, D.; Heerlein, K.; Heinrichs, J.; Hirche, D.; Hirzberger,
   J.; Kolleck, M.; Meller, R.; Müller, R.; Schäfer, R.; Tomasch,
   G.; Knölker, M.; Martínez Pillet, V.; Bonet, J. A.; Schmidt, W.;
   Berkefeld, T.; Feger, B.; Heidecke, F.; Soltau, D.; Tischenberg, A.;
   Fischer, A.; Title, A.; Anwand, H.; Schmidt, E.
Bibcode: 2011SoPh..268...35G
Altcode: 2010SoPh..tmp..176G; 2010arXiv1009.1037G
  We describe the design of the Sunrise Filter Imager (SuFI) and the
  Image Stabilization and Light Distribution (ISLiD) unit onboard the
  Sunrise balloon borne solar observatory. This contribution provides the
  necessary information which is relevant to understand the instruments'
  working principles, the relevant technical data, and the necessary
  information about calibration issues directly related to the science
  data.

Title: SUNRISE: Instrument, Mission, Data, and First Results
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
   Gandorfer, A.; Hirzberger, J.; Riethmüller, T. L.; Schüssler, M.;
   Bonet, J. A.; Martínez Pillet, V.; del Toro Iniesta, J. C.; Domingo,
   V.; Palacios, J.; Knölker, M.; Bello González, N.; Berkefeld, T.;
   Franz, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.127S
Altcode: 2010arXiv1008.3460S
  The SUNRISE balloon-borne solar observatory consists of a 1 m aperture
  Gregory telescope, a UV filter imager, an imaging vector polarimeter,
  an image stabilization system, and further infrastructure. The first
  science flight of SUNRISE yielded high-quality data that revealed the
  structure, dynamics, and evolution of solar convection, oscillations,
  and magnetic fields at a resolution of around 100 km in the quiet
  Sun. After a brief description of instruments and data, the first
  qualitative results are presented. In contrast to earlier observations,
  we clearly see granulation at 214 nm. Images in Ca II H display narrow,
  short-lived dark intergranular lanes between the bright edges of
  granules. The very small-scale, mixed-polarity internetwork fields
  are found to be highly dynamic. A significant increase in detectable
  magnetic flux is found after phase-diversity-related reconstruction
  of polarization maps, indicating that the polarities are mixed right
  down to the spatial resolution limit and probably beyond.

Title: Supersonic Magnetic Upflows in Granular Cells Observed with
    SUNRISE/IMAX
Authors: Borrero, J. M.; Martínez-Pillet, V.; Schlichenmaier, R.;
   Solanki, S. K.; Bonet, J. A.; del Toro Iniesta, J. C.; Schmidt, W.;
   Barthol, P.; Gandorfer, A.; Domingo, V.; Knölker, M.
Bibcode: 2010ApJ...723L.144B
Altcode: 2010arXiv1009.1227B
  Using the IMaX instrument on board the SUNRISE stratospheric balloon
  telescope, we have detected extremely shifted polarization signals
  around the Fe I 5250.217 Å spectral line within granules in the solar
  photosphere. We interpret the velocities associated with these events
  as corresponding to supersonic and magnetic upflows. In addition, they
  are also related to the appearance of opposite polarities and highly
  inclined magnetic fields. This suggests that they are produced by the
  reconnection of emerging magnetic loops through granular upflows. The
  events occupy an average area of 0.046 arcsec<SUP>2</SUP> and last for
  about 80 s, with larger events having longer lifetimes. These supersonic
  events occur at a rate of 1.3 × 10<SUP>-5</SUP> occurrences per second
  per arcsec<SUP>2</SUP>.

Title: Detection of Vortex Tubes in Solar Granulation from
    Observations with SUNRISE
Authors: Steiner, O.; Franz, M.; Bello González, N.; Nutto, Ch.;
   Rezaei, R.; Martínez Pillet, V.; Bonet Navarro, J. A.; del Toro
   Iniesta, J. C.; Domingo, V.; Solanki, S. K.; Knölker, M.; Schmidt,
   W.; Barthol, P.; Gandorfer, A.
Bibcode: 2010ApJ...723L.180S
Altcode: 2010arXiv1009.4723S
  We have investigated a time series of continuum intensity maps and
  corresponding Dopplergrams of granulation in a very quiet solar region
  at the disk center, recorded with the Imaging Magnetograph eXperiment
  (IMaX) on board the balloon-borne solar observatory SUNRISE. We
  find that granules frequently show substructure in the form of lanes
  composed of a leading bright rim and a trailing dark edge, which move
  together from the boundary of a granule into the granule itself. We
  find strikingly similar events in synthesized intensity maps from an
  ab initio numerical simulation of solar surface convection. From cross
  sections through the computational domain of the simulation, we conclude
  that these granular lanes are the visible signature of (horizontally
  oriented) vortex tubes. The characteristic optical appearance of vortex
  tubes at the solar surface is explained. We propose that the observed
  vortex tubes may represent only the large-scale end of a hierarchy of
  vortex tubes existing near the solar surface.

Title: Where the Granular Flows Bend
Authors: Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; del Toro
   Iniesta, J. C.; Gandorfer, A.; Bonet, J. A.; Domingo, V.; Schmidt,
   W.; Barthol, P.; Knölker, M.
Bibcode: 2010ApJ...723L.159K
Altcode: 2010arXiv1008.0517K
  Based on IMaX/SUNRISE data, we report on a previously undetected
  phenomenon in solar granulation. We show that in a very narrow region
  separating granules and intergranular lanes, the spectral line width
  of the Fe I 5250.2 Å line becomes extremely small. We offer an
  explanation of this observation with the help of magneto-convection
  simulations. These regions with extremely small line widths correspond
  to the places where the granular flows bend from upflow in granules
  to downflow in intergranular lanes. We show that the resolution and
  image stability achieved by IMaX/SUNRISE are important requisites to
  detect this interesting phenomenon.

Title: Bright Points in the Quiet Sun as Observed in the Visible
    and Near-UV by the Balloon-borne Observatory SUNRISE
Authors: Riethmüller, T. L.; Solanki, S. K.; Martínez Pillet, V.;
   Hirzberger, J.; Feller, A.; Bonet, J. A.; Bello González, N.; Franz,
   M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; del Toro Iniesta,
   J. C.; Domingo, V.; Gandorfer, A.; Knölker, M.; Schmidt, W.
Bibcode: 2010ApJ...723L.169R
Altcode: 2010arXiv1009.1693R
  Bright points (BPs) are manifestations of small magnetic elements
  in the solar photosphere. Their brightness contrast not only gives
  insight into the thermal state of the photosphere (and chromosphere) in
  magnetic elements, but also plays an important role in modulating the
  solar total and spectral irradiance. Here, we report on simultaneous
  high-resolution imaging and spectropolarimetric observations of
  BPs using SUNRISE balloon-borne observatory data of the quiet Sun
  at the disk center. BP contrasts have been measured between 214 nm
  and 525 nm, including the first measurements at wavelengths below
  388 nm. The histograms of the BP peak brightness show a clear trend
  toward broader contrast distributions and higher mean contrasts at
  shorter wavelengths. At 214 nm, we observe a peak brightness of up to
  five times the mean quiet-Sun value, the highest BP contrast so far
  observed. All BPs are associated with a magnetic signal, although in
  a number of cases it is surprisingly weak. Most of the BPs show only
  weak downflows, the mean value being 240 m s<SUP>-1</SUP>, but some
  display strong down- or upflows reaching a few km s<SUP>-1</SUP>.

Title: Transverse Component of the Magnetic Field in the Solar
    Photosphere Observed by SUNRISE
Authors: Danilovic, S.; Beeck, B.; Pietarila, A.; Schüssler, M.;
   Solanki, S. K.; Martínez Pillet, V.; Bonet, J. A.; del Toro Iniesta,
   J. C.; Domingo, V.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
   Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.149D
Altcode: 2010arXiv1008.1535D
  We present the first observations of the transverse component of
  a photospheric magnetic field acquired by the imaging magnetograph
  SUNRISE/IMaX. Using an automated detection method, we obtain statistical
  properties of 4536 features with significant linear polarization
  signal. We obtain a rate of occurrence of 7 × 10<SUP>-4</SUP>
  s<SUP>-1</SUP> arcsec<SUP>-2</SUP>, which is 1-2 orders of magnitude
  larger than the values reported by previous studies. We show that
  these features have no characteristic size or lifetime. They appear
  preferentially at granule boundaries with most of them being caught
  in downflow lanes at some point. Only a small percentage are entirely
  and constantly embedded in upflows (16%) or downflows (8%).

Title: Detection of Large Acoustic Energy Flux in the Solar Atmosphere
Authors: Bello González, N.; Franz, M.; Martínez Pillet, V.; Bonet,
   J. A.; Solanki, S. K.; del Toro Iniesta, J. C.; Schmidt, W.; Gandorfer,
   A.; Domingo, V.; Barthol, P.; Berkefeld, T.; Knölker, M.
Bibcode: 2010ApJ...723L.134B
Altcode: 2010arXiv1009.4795B
  We study the energy flux carried by acoustic waves excited by convective
  motions at sub-photospheric levels. The analysis of high-resolution
  spectropolarimetric data taken with IMaX/SUNRISE provides a total
  energy flux of ~6400-7700 W m<SUP>-2</SUP> at a height of ~250 km
  in the 5.2-10 mHz range, i.e., at least twice the largest energy
  flux found in previous works. Our estimate lies within a factor of
  two of the energy flux needed to balance radiative losses from the
  chromosphere according to the estimates of Anderson &amp; Athay and
  revives interest in acoustic waves for transporting energy to the
  chromosphere. The acoustic flux is mainly found in the intergranular
  lanes but also in small rapidly evolving granules and at the bright
  borders, forming dark dots and lanes of splitting granules.

Title: Magnetic Loops in the Quiet Sun
Authors: Wiegelmann, T.; Solanki, S. K.; Borrero, J. M.; Martínez
   Pillet, V.; del Toro Iniesta, J. C.; Domingo, V.; Bonet, J. A.;
   Barthol, P.; Gandorfer, A.; Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.185W
Altcode: 2010arXiv1009.4715W
  We investigate the fine structure of magnetic fields in the atmosphere
  of the quiet Sun. We use photospheric magnetic field measurements from
  SUNRISE/IMaX with unprecedented spatial resolution to extrapolate
  the photospheric magnetic field into higher layers of the solar
  atmosphere with the help of potential and force-free extrapolation
  techniques. We find that most magnetic loops that reach into the
  chromosphere or higher have one footpoint in relatively strong magnetic
  field regions in the photosphere. Ninety-one percent of the magnetic
  energy in the mid-chromosphere (at a height of 1 Mm) is in field
  lines, whose stronger footpoint has a strength of more than 300 G,
  i.e., above the equipartition field strength with convection. The
  loops reaching into the chromosphere and corona are also found to be
  asymmetric in the sense that the weaker footpoint has a strength B &lt;
  300 G and is located in the internetwork (IN). Such loops are expected
  to be strongly dynamic and have short lifetimes, as dictated by the
  properties of the IN fields.

Title: SUNRISE/IMaX Observations of Convectively Driven Vortex Flows
    in the Sun
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Palacios,
   J.; Martínez Pillet, V.; Solanki, S. K.; del Toro Iniesta, J. C.;
   Domingo, V.; Berkefeld, T.; Schmidt, W.; Gandorfer, A.; Barthol, P.;
   Knölker, M.
Bibcode: 2010ApJ...723L.139B
Altcode: 2010arXiv1009.1992B
  We characterize the observational properties of the convectively driven
  vortex flows recently discovered on the quiet Sun, using magnetograms,
  Dopplergrams, and images obtained with the 1 m balloon-borne SUNRISE
  telescope. By visual inspection of time series, we find some 3.1
  × 10<SUP>-3</SUP> vortices Mm<SUP>-2</SUP> minute<SUP>-1</SUP>,
  which is a factor of ~1.7 larger than previous estimates. The mean
  duration of the individual events turns out to be 7.9 minutes, with
  a standard deviation of 3.2 minutes. In addition, we find several
  events appearing at the same locations along the duration of the time
  series (31.6 minutes). Such recurrent vortices show up in the proper
  motion flow field map averaged over the time series. The typical
  vertical vorticities are lsim6 × 10<SUP>-3</SUP> s<SUP>-1</SUP>,
  which corresponds to a period of rotation of some 35 minutes. The
  vortices show a preferred counterclockwise sense of rotation, which
  we conjecture may have to do with the preferred vorticity impinged by
  the solar differential rotation.

Title: Surface Waves in Solar Granulation Observed with SUNRISE
Authors: Roth, M.; Franz, M.; Bello González, N.; Martínez Pillet,
   V.; Bonet, J. A.; Gandorfer, A.; Barthol, P.; Solanki, S. K.;
   Berkefeld, T.; Schmidt, W.; del Toro Iniesta, J. C.; Domingo, V.;
   Knölker, M.
Bibcode: 2010ApJ...723L.175R
Altcode: 2010arXiv1009.4790R
  Solar oscillations are expected to be excited by turbulent flows in
  the intergranular lanes near the solar surface. Time series recorded
  by the IMaX instrument on board the SUNRISE observatory reveal solar
  oscillations at high spatial resolution, which allow the study of
  the properties of oscillations with short wavelengths. We analyze
  two time series with synchronous recordings of Doppler velocity and
  continuum intensity images with durations of 32 minutes and 23 minutes,
  respectively, recorded close to the disk center of the Sun to study
  the propagation and excitation of solar acoustic oscillations. In
  the Doppler velocity data, both the standing acoustic waves and the
  short-lived, high-degree running waves are visible. The standing
  waves are visible as temporary enhancements of the amplitudes of the
  large-scale velocity field due to the stochastic superposition of
  the acoustic waves. We focus on the high-degree small-scale waves by
  suitable filtering in the Fourier domain. Investigating the propagation
  and excitation of f- and p <SUB>1</SUB>-modes with wavenumbers k&gt;1.4
  Mm<SUP>-1</SUP>, we also find that exploding granules contribute to
  the excitation of solar p-modes in addition to the contribution of
  intergranular lanes.

Title: Fully Resolved Quiet-Sun Magnetic flux Tube Observed with
    the SUNRISE/IMAX Instrument
Authors: Lagg, A.; Solanki, S. K.; Riethmüller, T. L.; Martínez
   Pillet, V.; Schüssler, M.; Hirzberger, J.; Feller, A.; Borrero,
   J. M.; Schmidt, W.; del Toro Iniesta, J. C.; Bonet, J. A.; Barthol, P.;
   Berkefeld, T.; Domingo, V.; Gandorfer, A.; Knölker, M.; Title, A. M.
Bibcode: 2010ApJ...723L.164L
Altcode: 2010arXiv1009.0996L
  Until today, the small size of magnetic elements in quiet-Sun areas has
  required the application of indirect methods, such as the line-ratio
  technique or multi-component inversions, to infer their physical
  properties. A consistent match to the observed Stokes profiles could
  only be obtained by introducing a magnetic filling factor that specifies
  the fraction of the observed pixel filled with magnetic field. Here,
  we investigate the properties of a small magnetic patch in the quiet
  Sun observed with the IMaX magnetograph on board the balloon-borne
  telescope SUNRISE with unprecedented spatial resolution and low
  instrumental stray light. We apply an inversion technique based on
  the numerical solution of the radiative transfer equation to retrieve
  the temperature stratification and the field strength in the magnetic
  patch. The observations can be well reproduced with a one-component,
  fully magnetized atmosphere with a field strength exceeding 1 kG and
  a significantly enhanced temperature in the mid to upper photosphere
  with respect to its surroundings, consistent with semi-empirical flux
  tube models for plage regions. We therefore conclude that, within the
  framework of a simple atmospheric model, the IMaX measurements resolve
  the observed quiet-Sun flux tube.

Title: Quiet-sun Intensity Contrasts in the Near-ultraviolet as
    Measured from SUNRISE
Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Schüssler,
   M.; Borrero, J. M.; Afram, N.; Unruh, Y. C.; Berdyugina, S. V.;
   Gandorfer, A.; Solanki, S. K.; Barthol, P.; Bonet, J. A.; Martínez
   Pillet, V.; Berkefeld, T.; Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.154H
Altcode:
  We present high-resolution images of the Sun in the near-ultraviolet
  spectral range between 214 nm and 397 nm as obtained from the first
  science flight of the 1 m SUNRISE balloon-borne solar telescope. The
  quiet-Sun rms intensity contrasts found in this wavelength range are
  among the highest values ever obtained for quiet-Sun solar surface
  structures—up to 32.8% at a wavelength of 214 nm. We compare the
  rms contrasts obtained from the observational data with theoretical
  intensity contrasts obtained from numerical magnetohydrodynamic
  simulations. For 388 nm and 312 nm the observations agree well with
  the numerical simulations whereas at shorter wavelengths discrepancies
  between observed and simulated contrasts remain.

Title: A Chromospheric Conundrum?
Authors: Judge, Philip; Knölker, Michael; Schmidt, Wolfgang;
   Steiner, Oskar
Bibcode: 2010ApJ...720..776J
Altcode: 2010arXiv1007.1203J
  We examine spectra of the Ca II H line, obtained under good seeing
  conditions with the VTT Echelle Spectrograph in 2007 June, and
  higher resolution data of the Ca II λ8542 line from Fabry-Pérot
  instruments. The VTT targets were areas near disk center which included
  quiet Sun and some dispersed plage. The infrared data included quiet
  Sun and plage associated with small pores. Bright chromospheric network
  emission patches expand little with wavelength from line wing to line
  center, i.e., with increasing line opacity and height. We argue that
  this simple observation has implications for the force and energy
  balance of the chromosphere, since bright chromospheric network
  emission is traditionally associated with enhanced local mechanical
  heating which increases temperatures and pressures. Simple physical
  considerations then suggest that the network chromosphere may not be
  able to reach horizontal force balance with its surroundings, yet the
  network is a long-lived structure. We speculate on possible reasons for
  the observed behavior. By drawing attention to a potential conundrum,
  we hope to contribute to a better understanding of a long-standing
  unsolved problem: the heating of the chromospheric network.

Title: SUNRISE Impressions from a successful science flight
Authors: Schmidt, W.; Solanki, S. K.; Barthol, P.; Berkefeld, T.;
   Gandorfer, A.; Knölker, M.; Martínez Pillet, V.; Schüssler, M.;
   Title, A.
Bibcode: 2010AN....331..601S
Altcode:
  SUNRISE is a balloon-borne telescope with an aperture of one meter. It
  is equipped with a filter imager for the UV wavelength range between
  214 nm and 400 nm (SUFI), and with a spectro-polarimeter that measures
  the magnetic field of the photosphere using the Fe I line at 525.02
  nm that has a Landé factor of 3. SUNRISE performed its first science
  flight from 8 to 14 June 2009. It was launched at the Swedish ESRANGE
  Space Center and cruised at an altitude of about 36 km and geographic
  latitudes between 70 and 74 degrees to Somerset Island in northern
  Canada. There, all data, the telescope and the gondola were successfully
  recovered. During its flight, Sunrise achieved high pointing stability
  during 33 hours, and recorded about 1.8 TB of science data. Already at
  this early stage of data processing it is clear that SUNRISE recorded
  UV images of the solar photosphere, and spectropolarimetric measurements
  of the quiet Sun's magnetic field of unprecedented quality.

Title: GREGOR solar telescope: Design and status
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S. K.;
   Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Fischer, A.;
   Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Kneer, F.;
   Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau,
   D.; Strassmeier, K. G.
Bibcode: 2010AN....331..624V
Altcode:
  The integration and verification phase of the GREGOR telescope
  reached an important milestone with the installation of the
  interim 1 m SolarLite primary mirror. This was the first time
  that the entire light path had seen sunlight. Since then extensive
  testing of the telescope and its subsystems has been carried out. The
  integration and verification phase will culminate with the delivery and
  installation of the final 1.5 m Zerodur primary mirror in the summer of
  2010. Observatory level tests and science verification will commence in
  the second half of 2010 and in 2011. This phase includes testing of the
  main optics, adaptive optics, cooling and pointing systems. In addition,
  assuming the viewpoint of a typical user, various observational modes
  of the GREGOR Fabry-Pérot Interferometer (GFPI), the Grating Infrared
  Spectrograph (GRIS), and high-speed camera systems will be tested to
  evaluate if they match the expectations and science requirements. This
  ensures that GREGOR will provide high-quality observations with its
  combination of (multi-conjugate) adaptive optics and advanced post-focus
  instruments. Routine observations are expected for 2012.

Title: Laser Frequency Combs for Astronomical Observations
Authors: Steinmetz, Tilo; Wilken, Tobias; Araujo-Hauck, Constanza;
   Holzwarth, Ronald; Hänsch, Theodor W.; Pasquini, Luca; Manescau,
   Antonio; D'Odorico, Sandro; Murphy, Michael T.; Kentischer, Thomas;
   Schmidt, Wolfgang; Udem, Thomas
Bibcode: 2008Sci...321.1335S
Altcode: 2008arXiv0809.1663S
  A direct measurement of the universe’s expansion history could be made
  by observing in real time the evolution of the cosmological redshift
  of distant objects. However, this would require measurements of Doppler
  velocity drifts of ~1 centimeter per second per year, and astronomical
  spectrographs have not yet been calibrated to this tolerance. We
  demonstrated the first use of a laser frequency comb for wavelength
  calibration of an astronomical telescope. Even with a simple analysis,
  absolute calibration is achieved with an equivalent Doppler precision
  of ~9 meters per second at ~1.5 micrometers—beyond state-of-the-art
  accuracy. We show that tracking complex, time-varying systematic
  effects in the spectrograph and detector system is a particular
  advantage of laser frequency comb calibration. This technique promises
  an effective means for modeling and removal of such systematic effects
  to the accuracy required by future experiments to see direct evidence
  of the universe’s putative acceleration.

Title: SUNRISE: High resolution UV/VIS observations of the sun from
    the stratosphere
Authors: Sunrise Team; Barthol, P.; Gandorfer, A. M.; Solanki,
   S. K.; Knölker, M.; Martinez Pillet, V.; Schmidt, W.; Title, A. M.;
   SUNRISE Team
Bibcode: 2008AdSpR..42...70S
Altcode:
  SUNRISE is an international project for the development, construction
  and operation of a balloon-borne solar telescope with an aperture
  of 1 m, working in the UV/VIS spectral domain. The main scientific
  goal of SUNRISE is to understand the structure and dynamics of the
  magnetic field in the atmosphere of the Sun. SUNRISE will provide
  near diffraction-limited images of the photosphere and chromosphere
  with an unprecedented resolution down to 35 km on the solar surface
  at wavelengths around 220 nm. Active in-flight alignment and image
  stabilization techniques are used. The focal-plane instrumentation
  consists of a polarization sensitive spectrograph, a Fabry Perot
  filter magnetograph and a phase-diverse filter imager working in
  the near UV. The first stratospheric long-duration balloon flight
  of SUNRISE is planned in summer 2009 from the Swedish ESRANGE
  station. SUNRISE is a joint project of the German Max-Planck-Institut
  für Sonnensystemforschung (MPS), Katlenburg-Lindau, with the
  Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, Germany, the
  High-Altitude Observatory (HAO), Boulder, USA, the Lockheed-Martin
  Solar and Astrophysics Laboratory (LMSAL), Palo Alto, USA, and the
  Spanish IMaX consortium. This paper will give an overview about the
  mission and a description of its scientific and technological aspects.

Title: Reversal-free Ca II H profiles: a challenge for solar
    chromosphere modeling in quiet inter-network
Authors: Rezaei, R.; Bruls, J. H. M. J.; Schmidt, W.; Beck, C.;
   Kalkofen, W.; Schlichenmaier, R.
Bibcode: 2008A&A...484..503R
Altcode: 2008arXiv0804.2325R
  Aims: We study chromospheric emission to understand the temperature
  stratification in the solar chromosphere. <BR />Methods: We observed
  the intensity profile of the Ca II H line in a quiet Sun region close
  to the disk center at the German Vacuum Tower Telescope. We analyze
  over 10<SUP>5</SUP> line profiles from inter-network regions. For
  comparison with the observed profiles, we synthesize spectra for a
  variety of model atmospheres with a non local thermodynamic equilibrium
  (NLTE) radiative transfer code. <BR />Results: A fraction of about
  25% of the observed Ca II H line profiles do not show a measurable
  emission peak in H<SUB>2v</SUB> and H<SUB>2r</SUB> wavelength bands
  (reversal-free). All of the chosen model atmospheres with a temperature
  rise fail to reproduce such profiles. On the other hand, the synthetic
  calcium profile of a model atmosphere that has a monotonic decline of
  the temperature with height shows a reversal-free profile that has much
  lower intensities than any observed line profile. <BR />Conclusions:
  The observed reversal-free profiles indicate the existence of cool
  patches in the interior of chromospheric network cells, at least
  for short time intervals. Our finding is not only in conflict with a
  full-time hot chromosphere, but also with a very cool chromosphere as
  found in some dynamic simulations.

Title: The signature of chromospheric heating in Ca II H spectra
Authors: Beck, C.; Schmidt, W.; Rezaei, R.; Rammacher, W.
Bibcode: 2008A&A...479..213B
Altcode: 2007arXiv0712.2538B
  Context: The heating process that balances the solar chromospheric
  energy losses has not yet been determined. Conflicting views exist on
  the source of the energy and the influence of photospheric magnetic
  fields on chromospheric heating. <BR />Aims: We analyze a 1-h time
  series of cospatial Ca II H intensity spectra and photospheric
  polarimetric spectra around 630 nm to derive the signature of the
  chromospheric heating process in the spectra and to investigate its
  relation to photospheric magnetic fields. The data were taken in a
  quiet Sun area on disc center without strong magnetic activity. <BR
  />Methods: We have derived several characteristic quantities of Ca
  II H to define the chromospheric atmosphere properties. We study the
  power of the Fourier transform at different wavelengths and the phase
  relations between them. We perform local thermodynamic equilibrium (LTE)
  inversions of the spectropolarimetric data to obtain the photospheric
  magnetic field, once including the Ca intensity spectra. <BR />Results:
  We find that the emission in the Ca II H line core at locations
  without detectable photospheric polarization signal is due to waves
  that propagate in around 100 s from low forming continuum layers in
  the line wing up to the line core. The phase differences of intensity
  oscillations at different wavelengths indicate standing waves for ν
  &lt; 2 mHz and propagating waves for higher frequencies. The waves
  steepen into shocks in the chromosphere. On average, shocks are both
  preceded and followed by intensity reductions. In field-free regions,
  the profiles show emission about half of the time. The correlation
  between wavelengths and the decorrelation time is significantly higher
  in the presence of magnetic fields than for field-free areas. The
  average Ca II H profile in the presence of magnetic fields contains
  emission features symmetric to the line core and an asymmetric
  contribution, where mainly the blue H2V emission peak is increased
  (shock signature). <BR />Conclusions: We find that acoustic waves
  steepening into shocks are responsible for the emission in the Ca II H
  line core for locations without photospheric magnetic fields. We suggest
  using wavelengths in the line wing of Ca II H, where LTE still applies,
  to compare theoretical heating models with observations. <P />Appendices
  are only available in electronic form at http://www.aanda.org

Title: Hinode observations reveal boundary layers of magnetic elements
    in the solar photosphere
Authors: Rezaei, R.; Steiner, O.; Wedemeyer-Böhm, S.; Schlichenmaier,
   R.; Schmidt, W.; Lites, B. W.
Bibcode: 2007A&A...476L..33R
Altcode: 2007arXiv0711.0408R
  Aims:We study the structure of the magnetic elements in network-cell
  interiors. <BR />Methods: A quiet Sun area close to the disc centre was
  observed with the spectro-polarimeter of the Solar Optical Telescope
  on board the Hinode space mission, which yielded the best spatial
  resolution ever achieved in polarimetric data of the Fe I 630 nm line
  pair. For comparison and interpretation, we synthesize a similar data
  set from a three-dimensional magneto-hydrodynamic simulation. <BR
  />Results: We find several examples of magnetic elements, either
  roundish (tube) or elongated (sheet), which show a central area of
  negative Stokes-V area asymmetry framed or surrounded by a peripheral
  area with larger positive asymmetry. This pattern was predicted
  some eight years ago on the basis of numerical simulations. Here,
  we observationally confirm its existence for the first time. <BR
  />Conclusions: We gather convincing evidence that this pattern of
  Stokes-V area asymmetry is caused by the funnel-shaped boundary of
  magnetic elements that separates the flux concentration from the
  weak-field environment. On this basis, we conclude that electric
  current sheets induced by such magnetic boundary layers are common in
  the photosphere.

Title: Opposite magnetic polarity of two photospheric lines in single
    spectrum of the quiet Sun
Authors: Rezaei, R.; Schlichenmaier, R.; Schmidt, W.; Steiner, O.
Bibcode: 2007A&A...469L...9R
Altcode: 2007arXiv0704.3135R
  Aims:We study the structure of the photospheric magnetic field of the
  quiet Sun by investigating weak spectro-polarimetric signals. <BR
  />Methods: We took a sequence of Stokes spectra of the Fe I 630.15
  nm and 630.25 nm lines in a region of quiet Sun near the disk
  center, using the POLIS spectro-polarimeter at the German VTT on
  Tenerife. The line cores of these two lines form at different heights
  in the atmosphere. The 3σ noise level of the data is about 1.8
  × 10<SUP>-3</SUP> I_c. <BR />Results: We present co-temporal and
  co-spatial Stokes-V profiles of the Fe I 630 nm line pair, where
  the two lines show opposite polarities in a single spectrum. We
  compute synthetic line profiles and reproduce these spectra with a
  two-component model atmosphere: a non-magnetic component and a magnetic
  component. The magnetic component consists of two magnetic layers with
  opposite polarity: the upper one moves upwards while the lower one moves
  downward. In-between, there is a region of enhanced temperature. <BR
  />Conclusions: The Stokes-V line pair of opposite polarity in a single
  spectrum can be understood as a magnetic reconnection event in the
  solar photosphere. We demonstrate that such a scenario is realistic,
  but the solution may not be unique.

Title: Relation between photospheric magnetic field and chromospheric
    emission
Authors: Rezaei, R.; Schlichenmaier, R.; Beck, C. A. R.; Bruls,
   J. H. M. J.; Schmidt, W.
Bibcode: 2007A&A...466.1131R
Altcode: 2007astro.ph..1896R
  Aims: We investigate the relationship between the photospheric
  magnetic field and the emission of the mid chromosphere of the
  Sun. <BR />Methods: We simultaneously observed the Stokes parameters
  of the photospheric iron line pair at 630.2 nm and the intensity
  profile of the chromospheric Ca II H line at 396.8 nm in a quiet
  Sun region at a heliocentric angle of 53°. Various line parameters
  have been deduced from the Ca II H line profile. The photospheric
  magnetic field vector has been reconstructed from an inversion of
  the measured Stokes profiles. After alignment of the Ca and Fe maps,
  a common mask has been created to define network and inter-network
  regions. We perform a statistical analysis of network and inter-network
  properties. The H-index is the integrated emission in a 0.1 nm band
  around the Ca core. We separate a non-magnetically, H<SUB>non</SUB>,
  and a magnetically, H<SUB>mag</SUB>, heated component from a
  non-heated component, H<SUB>co</SUB> in the H-index. <BR />Results:
  The average network and inter-network H-indices are equal to 12 and
  10 pm, respectively. The emission in the network is correlated with
  the magnetic flux density, approaching a value of H ≈ 10 pm for
  vanishing flux. The inter-network magnetic field is dominated by weak
  field strengths with values down to 200 G and has a mean absolute
  flux density of about 11 Mx cm<SUP>-2</SUP>. <BR />Conclusions:
  We find that a dominant fraction of the calcium emission caused by
  the heated atmosphere in the magnetic network has non-magnetic origin
  (H<SUB>mag</SUB>≈2 pm, H<SUB>non</SUB>≈3 pm). Considering the effect
  of straylight, the contribution from an atmosphere with no temperature
  rise to the H-index (H<SUB>co</SUB>≈6 pm) is about half of the
  observed H-index in the inter-network. The H-index in the inter-network
  is not correlated to any property of the photospheric magnetic field,
  suggesting that magnetic flux concentrations have a negligible role
  in the chromospheric heating in this region. The height range of the
  thermal coupling between the photosphere and low/mid chromosphere
  increases in presence of magnetic field. In addition, we demonstrate
  that a poor signal-to-noise level in the Stokes profiles leads to a
  significant over-estimation of the magnetic field strength.

Title: On the fine structure of the quiet solar Ca II K atmosphere
Authors: Tritschler, A.; Schmidt, W.; Uitenbroek, H.; Wedemeyer-Böhm,
   S.
Bibcode: 2007A&A...462..303T
Altcode: 2006astro.ph.11402T
  Aims:We investigate the morphological, dynamical, and evolutionary
  properties of the internetwork and network fine structure of the quiet
  sun at disk centre. <BR />Methods: The analysis is based on a ~6 h
  time sequence of narrow-band filtergrams centred on the inner-wing
  Ca II K2v reversal at 393.3 nm. To examine the temporal evolution of
  network and internetwork areas separately we employ a double-Gaussian
  decomposition of the mean intensity distribution. An autocorrelation
  analysis is performed to determine the respective characteristic
  time scales. In order to analyse statistical properties of the fine
  structure we apply image segmentation techniques. <BR />Results: The
  results for the internetwork are related to predictions derived from
  numerical simulations of the quiet sun. The average evolutionary time
  scale of the internetwork in our observations is 52 s. Internetwork
  grains show a tendency to appear on a mesh-like pattern with a
  mean cell size of ~4-5 arcsec. Based on this size and the spatial
  organisation of the mesh we speculate that this pattern is related to
  the existence of photospheric downdrafts as predicted by convection
  simulations. The image segmentation shows that typical sizes of both
  network and internetwork grains are in the order of 1.6 arcsec.

Title: Observation of a short-lived pattern in the solar chromosphere
Authors: Wöger, F.; Wedemeyer-Böhm, S.; Schmidt, W.; von der
   Lühe, O.
Bibcode: 2006A&A...459L...9W
Altcode: 2006astro.ph..9382W
  Aims.In this work we investigate the dynamic behavior of inter-network
  regions of the solar chromosphere.<BR /> Methods: .We observed the
  chromosphere of the quiet Sun using a narrow-band Lyot filter centered
  at the Ca II K2v emission peak with a bandpass of 0.3 Å. We achieved
  a spatial resolution of on average 0.7 arcsec at a cadence of 10 s.<BR
  /> Results: .In the inter-network we find a mesh-like pattern that
  features bright grains at the vertices. The pattern has a typical
  spatial scale of 1.95 arcsec and a mean evolution time scale of 53 s
  with a standard deviation of 10 s. A comparison of our results with a
  recent three-dimensional radiation hydrodynamical model implies that
  the observed pattern is of chromospheric origin. The measured time
  scales are not compatible with those of reversed granulation in the
  photosphere although the appearance is similar. A direct comparison
  between network and inter-network structure shows that their typical
  time scales differ by at least a factor of two.<BR /> Conclusions:
  .The existence of a rapidly evolving small-scale pattern in the
  inter-network regions supports the picture of the lower chromosphere
  as a highly dynamical and intermittent phenomenon.

Title: The influence of image reconstruction on two-dimensional
    spectrograms of the solar photosphere
Authors: Mikurda, K.; Tritschler, A.; Schmidt, W.
Bibcode: 2006A&A...454..359M
Altcode:
  Aims.We present a spectral analysis of small-scale structures in
  the solar photosphere and investigate the influence of the speckle
  deconvolution technique on the line profiles.<BR /> Methods: . A
  short sequence of two-dimensional spectra is used, taken with the
  Telecentric Etalon Solar Spectrometer (TESOS) at the German Vacuum
  Tower Telescope on Tenerife. We observed two small pores surrounded by
  disturbed and by regular granulation in the non-magnetic neutral Iron
  line at 557.6 nm. In a first step, a speckle reconstruction is computed
  by applying an extended Knox-Thompson algorithm to the broad-band
  data. In a second step, the individual narrow-band filtergrams are
  deconvolved utilizing the information gained in the first step. We
  then perform a spectral analysis of the 2D spectra and compare the
  results obtained with the raw and the restored data.<BR /> Results:
  .Important spectral quantities, e.g. line position, line depression
  and line asymmetry are largely unchanged by the image reconstruction
  process. We derive the line asymmetry and the line-of-sight flow for
  granules and intergranular lanes and also for an isolated G-band bright
  point and find important differences between quiet and magnetically
  disturbed granulation: the granule centers in the quiet region show a
  strong asymmetry with significant blue shift (300 m/s) toward deeper
  layers, while the velocity in the disturbed area show virtually
  no height dependence. For the intergranular lanes the situation is
  reversed: no height dependence in the quiet area, significant red-shift
  toward deeper layers in the disturbed part. An isolated G-band bright
  point does not show any line-of-sight motion relative to its immediate
  surroundings. The map of LOS velocities derived from line-wing shifts
  shows a significant downflow around one of the pores measured in deep
  layers of the photosphere.<BR /> Conclusions: .In most cases we do
  not find any artefacts in the reconstructed line profiles that would
  compromise their usage for quantitative spectroscopy.

Title: Polarimetric Littrow Spectrograph - instrument calibration
    and first measurements
Authors: Beck, C.; Schmidt, W.; Kentischer, T.; Elmore, D.
Bibcode: 2005A&A...437.1159B
Altcode:
  We present first measurements and the calibration procedure for the
  Polarimetric Littrow Spectrograph (POLIS) operated at the Vacuum Tower
  Telescope on Tenerife, together with a brief summary of the technical
  characteristics of the instrument. In its present configuration,
  we achieve a polarimetric accuracy of about 3 × 10<SUP>-3</SUP>
  in the visible channel (630 nm) of the instrument. The accuracy is
  limited by cross talk among the different polarization states. The
  detection limit for polarized light is about 2 × 10<SUP>-3</SUP>
  for a 7 s exposure. Polarimetric measurements in the blue channel (Ca
  II H line, 396.7 nm) are strongly limited by the low photon flux. At
  this wavelength we present Stokes-V maps with a spatial resolution of
  about 0.5 arcs. The polarimetric quality of any spectropolarimeter is
  limited by the precision of the instrument calibration. We present
  a new method for self-calibration that reduces cross talk among the
  polarization components to 0.1%. This improvement results from a
  measurement of the retardance of the calibration waveplate with an
  accuracy of 0.1°. We demonstrate the capability of the simultaneous
  use of POLIS and the Tenerife Infrared Polarimeter which is integrated
  in the main spectrograph of the Vacuum Tower Telescope.

Title: Diagnostic spectroscopy of G-band brightenings in the
    photosphere of the sun
Authors: Langhans, K.; Schmidt, W.; Rimmele, T.
Bibcode: 2004A&A...423.1147L
Altcode:
  A detailed analysis of high-resolution spectra obtained in three
  different wavelength regions (at 430 nm, 526 nm and 569 nm) of G-band
  bright points in the solar photosphere is presented. They show an
  average intensity contrast of 11% with respect to the ``quiet'' sun
  reference. The CH lines are weakened in the bright point interior. The
  atomic lines, too, e.g. the Fe I line at 569.15 nm, weaken in the bright
  point interior. In contrast thereto, the absorption line of single
  ionized iron at 526.48 nm remains almost constant between bright point
  interior and the immediate surroundings. Line-of-sight velocities show a
  stronger downflow within bright points than in the close environment. A
  net downflow relative to the intergranular surroundings of around 80
  m/s is measured. Filling factors are calculated from a comparison with
  synthesized spectra for different flux tube models and are used to
  estimate the ``true'' velocity in bright points with respect to their
  immediate surroundings. We obtain up- and downflows in the order of one
  km s<SUP>-1</SUP>, in agreement with the magneto-convective picture of
  the formation and dispersal of magnetic flux tubes. From the different
  behavior of the metallic lines and the CH lines we conclude that the
  line-weakening process that leads to the G-band bright points is mainly
  due to hot-wall radiation. This confirms that these bright points are
  indeed magnetic flux elements.

Title: On the geometry of sunspot penumbral filaments
Authors: Schmidt, W.; Fritz, G.
Bibcode: 2004A&A...421..735S
Altcode:
  We investigate the center-to-limb variation of the brightness of
  the penumbrae of sunspots. The analysis includes narrow-band and
  broad-band continuum images of about 80 sunspots observed with the
  Vacuum Tower Telescope on Tenerife and with the Transition Region And
  Coronal Explorer (TRACE). We find that the azimuthal intensity variation
  depends on the viewing angle, i.e. on the position of the spot on the
  solar disk. With increasing viewing angle, the average intensity remains
  almost constant on the center side and on the limb side of the spot,
  but increases in the lateral parts. This is explained by the existence
  of elevated bright filaments that, when observed from the side and
  at increasing viewing angle, more and more hide the dark and deeper
  lying background. In addition to this azimuthal intensity modulation,
  we observe an enhanced brightness on the limb-side penumbra for large
  viewing angles.

Title: POLIS: A spectropolarimeter for the VTT and for GREGOR
Authors: Schmidt, W.; Beck, C.; Kentischer, T.; Elmore, D.; Lites, B.
Bibcode: 2003AN....324..300S
Altcode:
  The polarimetric Littrow Spectrograph POLIS is designed for vector
  polarimetry at high angular and spectral resolution. It measures the
  magnetic field simultaneously in the photosphere and the chromosphere
  of the sun. Both branches of the polarimetry unit are dual beam systems
  with a single rotating modulator for both wavelengths and polarizing
  beam splitters in front of each CCD camera. POLIS has been installed
  at the VTT on Tenerife and has seen First Light on 17 May 2002. A
  modified version of POLIS will be developed for the balloon mission
  Sunrise. That version will have UV capabilities down to 200 nm.

Title: GREGOR - optical design considerations
Authors: Soltau, D.; Berkefeld, Th.; von der Lühe, O.; Hofmann, A.;
   Schmidt, W.; Volkmer, R.; Wiehr, E.
Bibcode: 2003AN....324..292S
Altcode:
  After many years of successful work the Gregory Coudé Telescope
  (GCT) is going to be replaced by GREGOR. This new 1.5 m telescope is
  the result of design considerations which to a wide extent are based
  on new technologies. Special aspects of the design are presented,
  including measures to compensate for optical aberrations caused by
  instrumental and atmospheric effects (Adaptive Optics). First light
  is expected for the end of 2004.

Title: Material flow in sunspots
Authors: Schmidt, W.
Bibcode: 2003AN....324..374S
Altcode:
  Observations nowadays reveal more and more details about the small-scale
  structure of the penumbra and umbra. Recent measurements of the motions
  in the penumbra indicate that (i) the Evershed flow is confined to a
  thin photospheric layer and (ii) the material rises from and sinks to
  subphotospheric layers within the penumbra. This flow pattern solves
  the question of the mass budget of the Evershed flow in a natural
  way. The nature of umbral dots and their role for the spot's energy
  budget remains unclear, since they are obviously unresolved even in
  the best existing measurements.

Title: Observations of G-band bright structures with TESOS
Authors: Langhans, K.; Schmidt, W.; Tritschler, A.
Bibcode: 2003AN....324..354L
Altcode:
  No abstract at ADS

Title: High-resolution solar spectroscopy with TESOS - Upgrade from
    a double to a triple system
Authors: Tritschler, A.; Schmidt, W.; Langhans, K.; Kentischer, T.
Bibcode: 2002SoPh..211...17T
Altcode:
  We present the characteristics and demonstrate the performance of the
  Triple Etalon SOlar Spectrometer (TESOS) operated at the German Vacuum
  Tower Telescope (VTT) on Tenerife. The Fabry-Pérot interferometer
  TESOS is ideally suited for precise measurements of photospheric and
  chromospheric motion. Installed in 1997 and equipped with two etalons,
  TESOS has recently been completed with a third etalon and upgraded
  with two high-speed, backside-illuminated CCD cameras. The image scale
  of 0.089 arc sec pixel<SUP>−1</SUP> is adapted to the resolution of
  the telescope. The improved system enables frame rates up to 5 frames
  per second. The spectral resolution of 300 000 allows for spectral
  diagnostics of weak photospheric lines, including individual CH-lines
  within the G-band at 430.6 nm.

Title: 2D-spectroscopic observations of vec G-band bright structures
    in the solar photosphere
Authors: Langhans, K.; Schmidt, W.; Tritschler, A.
Bibcode: 2002A&A...394.1069L
Altcode:
  We took two-dimensional spectra with the filter spectrometer TESOS
  at the German Vacuum Tower Telescope, Tenerife, of an absorption
  line of the CH molecule and a Fe II-line in the G-band at 430.3
  nm. We observed a region, close to disk center of the Sun, that
  showed a lot of structures with enhanced G-band intensity (up to 1.3
  times the mean intensity of normal granulation). Our spectroscopic
  investigation of these structures suggests two classes which differ
  in their spectroscopic signature: (a) Bright structures caused by
  significant (up to 40\%) weakening of absorption lines of the CH
  molecule; (b) bright structures only caused by an enhanced continuum
  intensity. In order to distinguish between those two classes we
  introduce a Bright Point Index (BPI) defined by the ratio of the
  normalized line depressions of the Fe~II and the CH-line. The bright
  structures caused by weakening of the CH-lines have high BPI values and
  are accompanied by downflows. The remaining G-band bright structures
  have low BPI and are related to granules.

Title: Sunspot photometry with phase diversity. II. Fine-structure
    characteristics
Authors: Tritschler, A.; Schmidt, W.
Bibcode: 2002A&A...388.1048T
Altcode:
  We investigate the thermal and morphological fine structure of a small
  sunspot, which includes the determination of brightness temperatures
  and characteristic spatial scales as well as their distribution
  inside the sunspot. The identification and isolation of sunspot fine
  structure is accomplished by means of a feature-finding algorithm
  applied to a high-resolution time sequence taken simultaneously in
  three continuum bands of the solar spectrum. In order to compensate for
  seeing and instrumental effects, we apply the phase-diversity technique
  combined with a deconvolution method. The findings can be summarized
  as follows: (1) umbral dots are found to be on average 760 K cooler
  than the immediate surrounding photosphere outside the spot. (2) Some
  exceptional hot penumbral grains exceed the average temperature of the
  brightest granules of the spots surroundings by typically 150 K. (3)
  The size distribution of umbral dots and penumbral grains support the
  idea that the smallest structures are still spatially unresolved. (4)
  The distribution function of umbral dot peak intensities points to
  the existence of two umbral dot ``populations'' indicating different
  efficiency of energy transport. (5) The classification of penumbral
  filaments into ``dark'' and ``bright'' depends on the immediate
  surroundings.

Title: Sunspot photometry with phase diversity. I. Methods and global
    sunspot parameters
Authors: Tritschler, A.; Schmidt, W.
Bibcode: 2002A&A...382.1093T
Altcode:
  The global brightness structure of a small sunspot is
  investigated. Seeing and instrumental effects are compensated by
  application of the phase-diversity technique and a conventional
  deconvolution method. We calculate brightness temperatures for the
  reconstructed data in three simultaneously observed continuum bands of
  the solar spectrum (402.1 nm, 569.5 nm, 709.1 nm). The darkest umbral
  regions are on average 0.17I<SUP>sun</SUP>, 0.27I<SUP>sun</SUP> and
  0.32I<SUP>sun</SUP> bright. The corresponding temperatures lie in the
  range around 4790 K, 4600 K and 4460 K. The spatially averaged penumbral
  brightness amounts to 0.72I<SUP>sun</SUP>, 0.81I<SUP>sun</SUP> and
  0.85I<SUP>sun</SUP>, which corresponds to 5910 K, 5750 K and 5640 K,
  respectively. Although the spectral distribution of the umbral and
  penumbral intensities is consistent with former measurements, the
  derived values support the idea that there exist a real difference in
  the thermal properties between the umbrae of small and large sunspots.

Title: High resolution spectro-polarimetry with a large balloon-borne
    solar telescope
Authors: Schmidt, Wolfgang
Bibcode: 2002AdSpR..29.2055S
Altcode:
  The balloon mission "Sunrise" consists of a 1m lightweight solar
  telescope equipped with a powerful spectro-graph-polarimeter and a
  multi-channel filtergraph for the visible and the UV. The science goals
  of Sunrise are focussed on, but not limited to, the investigation of
  the solar surface magnetism. The key questions include the generation
  and maintenance of the variable magnetic field, the structure and
  dynamics of the chromosphere, and the interaction of material flow
  and magnetic field in sunspots.

Title: Center-to-limb-variation of the G-band lines at 430.5 nm
Authors: Langhans, K.; Schmidt, W.
Bibcode: 2002A&A...382..312L
Altcode:
  We measure the center-to-limb-variation of the CH lines in the
  wavelength range from 430.40 to 430.61 nm (G-band) for both quiet
  sun and for the cooler atmophere of sunspot umbrae at different
  heliographic positions. The limb effect of the CH lines is about 650
  ms<SUP>-1</SUP> at mu =0.1 with a slope similar to weak Fe lines. We
  investigate the behaviour of the CH abundance in the range of optical
  depth (tau =-0.05 to tau =-0.25) that is accessible by center-to-limb
  observations. The CH abundance decreases with height in accordance
  with recent numerical models.

Title: Height and dynamics of the quiet solar chromosphere at the limb
Authors: Muglach, K.; Schmidt, W.
Bibcode: 2001A&A...379..592M
Altcode:
  In this paper we present observations of He I 1083.0 nm, He D_3
  587.6 nm and Hβ 486.1 nm taken at various positions at the solar
  limb. We determine and compare the emission of the lines in terms
  of line-parameters. The height of the chromosphere as seen in the
  helium lines varies in space and time and reaches values between
  1100 and 1800 km above the continuum and is the same for both helium
  lines within the errors of the measurement. From a time-sequence of
  slit-spectra of about 23 min we study the oscillation signature of
  the chromosphere near the solar limb. We find velocity oscillations
  in He I 1083.0 nm that do not drop to zero near the limb as would be
  expected of vertically oriented oscillations, we even get horizontal
  oscillations in the off-limb emission data of both helium lines.

Title: GREGOR, a 1.5 m Gregory-type Telescope for Solar Observation
Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.;
   Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D.
Bibcode: 2001AGM....18.P223K
Altcode:
  GREGOR is a high-resolution solar telescope with an aperture of 1.5
  m. It will be equipped with an Adaptive Optics system and is designed
  for high-precision measurements of magnetic fields and plasma motions
  in the solar atmosphere and chromosphere with a resolution of 70 km
  on the Sun. GREGOR will replace the Gregory Coudé Teleskope at the
  Observatorio del Teide on Tenerife. We describe the optical design
  and the focal plane instrumentation. In concert with the other solar
  telescopes at Teide Observatory it will be useful for studying the
  dynamics of the solar atmosphere and the underlying processes. GREGOR
  will also serve as a test bed for next generation solar telescopes.

Title: High-resolution Solar Polarimetry with Sunrise
Authors: Schmidt, W.; Solanki, S. K.; Schüssler, M.; Curdt, W.;
   Lites, B. W.; Title, A. M.; Martinez Pillet, V.
Bibcode: 2001AGM....18S1001S
Altcode:
  Sunrise is a 1m balloon-borne solar telescope. It is equipped with
  a spectrograph polarimeter which combines vector-polarimetry in the
  visible with diagnostic spectroscopy in the visible and the UV, down
  to 200 nm. The instrumentation includes a filter-magnetograph and a
  medium-band filtergraph. The wavelength bands of the latter include
  the CH-band (430.6 nm) and a UV continuum at 205 nm. Diffraction
  limited resolution in the UV will be achieved by employing a phase
  diversity technique. The main telescope is based on a lightweight
  silicon-carbide mirror, developed within the Solar Lite program. During
  the long-duration flight at Antarctica, foreseen for late 2005, Sunrise
  will continuously observe the sun for a period of about ten days,
  with constant image quality across the full field of view. In-flight
  alignment of the telescope optics will be controlled by a wavefront
  sensor. The main goal of Sunrise is to understand the structure and
  dynamics of the magnetic field in the atmosphere of the sun. To this
  end, Sunrise will observe small magnetic flux concentrations with
  dimensions of less than 70 km with high polarimetric accuracy. At the
  same time, Sunrise will provide diffraction-limited filtergrams of
  the photosphere and chromosphere with a resolution down to 35 km at
  a wavelength of 200 nm.

Title: Small-scale flow field in a sunspot penumbra
Authors: Schmidt, W.; Schlichenmaier, R.
Bibcode: 2000A&A...364..829S
Altcode:
  We have measured velocity maps of a round sunspot near the center of
  the solar disk. We derive the small-scale velocity field of the penumbra
  in the deep photosphere. Superimposed on a radial outflow, we find up-
  and downflows, which are associated with bright and dark features: The
  flow in the dark component of the penumbra has a larger inclination
  angle with respect to the surface normal than the bright component,
  everywhere in the penumbra. The maximum inclination difference is
  8°. In the inner and mid penumbra, bright features (penumbral grains)
  are associated with an upflow of about 0.6 km s<SUP>-1</SUP>. At the
  outer spot boundary, the flow is inclined downwards predominantly in
  the dark component (-7degr ).

Title: Free-fall Downflow Observed in HE I 1083.0 Nanometers and Hβ
Authors: Schmidt, W.; Muglach, K.; Knölker, M.
Bibcode: 2000ApJ...544..567S
Altcode:
  In a short time sequence of simultaneously observed slit spectra
  of He I 1083.0 nm and Hβ we find the signature of material flowing
  toward the solar surface with up to 42 km s<SUP>-1</SUP>, in addition
  to material which is almost at rest. The constant acceleration of the
  moving material is about 200 m s<SUP>-2</SUP>. These multiple velocities
  occur in a small region of about 5<SUP>''</SUP> in a plage region. We
  observe a highly dynamical phenomenon which lasts a few minutes. The
  duration and constant acceleration suggest free fall of matter
  unobstructed by magnetic structures or along vertical field lines.

Title: Flow geometry in a sunspot penumbra
Authors: Schlichenmaier, R.; Schmidt, W.
Bibcode: 2000A&A...358.1122S
Altcode:
  We have measured the material flow in the penumbra of a large symmetric
  sunspot during the passage of the spot across the solar meridian. The
  line-of-sight velocity field has been obtained from Doppler measurements
  in a Fe II line using a filter spectrometer with a large field of
  view. From data sets taken on different days, i.e. at different view
  angles, we have reconstructed the magnitude and orientation of the
  penumbral flow field in the deep photosphere. We find upflows near
  the inner and downflows at the outer boundary of the penumbra with
  nearly horizontal outflow in between. From our measurements we derive
  the following flow geometry: narrow upflow channels rise at different
  penumbral radii, they bend outwards with a nearly horizontal outflow,
  and are finally tilted a few degrees downwards at the outer penumbral
  boundary, but still inside the spot. The flow reaches its maximum speed
  of about 3.5 km s<SUP>-1</SUP> in the outer part of the penumbra. Our
  findings are a significant step towards an understanding of the mass
  balance of the Evershed flow. The proposed geometry is consistent with
  recent numerical models of penumbral filaments.

Title: Solar equatorial plasma rotation: a comparison of different
    spectroscopic measurements
Authors: Wöhl, H.; Schmidt, W.
Bibcode: 2000A&A...357..763W
Altcode:
  We present solar equatorial rotation velocities measured with two
  different spectral lines (Fe I 557.6 nm and Ni I 676.8 nm) and two
  different spectrometers at the German Vacuum Tower Telescope (VTT) on
  Tenerife. The `classical' sidereal solar equatorial rotation velocity
  of about 2000 m/s has been confirmed. The results are compared with
  those from velocity data of the Michelson Doppler Imager (MDI) onboard
  the Solar Heliospheric Observatory (SOHO) obtained on 10 June 1996 and
  27 May 1999. From both data sets of MDI, a rotation velocity about 100
  to 200 m/s below the `classical' value cited above was found. Possible
  explanations of this discrepancy are discussed.

Title: Dynamics of solar magnetic elements
Authors: Sigwarth, M.; Balasubramaniam, K. S.; Knölker, M.;
   Schmidt, W.
Bibcode: 1999A&A...349..941S
Altcode:
  We present observational results that demonstrate a strong increase in
  the dynamic behavior of magnetic elements at the solar photosphere,
  when observed at high spatial and temporal resolution. The HAO/NSO
  Advanced Stokes Polarimeter was used to obtain an extensive set of
  high resolution Stokes-V spectra from network, intranetwork and active
  region magnetic fields at a low noise level. We performed a statistical
  analysis of Doppler shifts and asymmetries of the V spectra of FeI
  630.15 and 630.25 nm to obtain information on the dynamics of magnetic
  elements of different sizes. The spatial resolution of 0.8-1 arcsec in
  combination with high polarimetric precision allowed us to investigate
  Stokes-V spectra of magnetic elements down to a size of ~ 150 km. The
  Doppler velocity within magnetic elements as well as the amplitude and
  area asymmetries of the Stokes-V profiles show a strong dependence on
  the size of the magnetic elements as well as on the granular velocity
  in their vicinity. Applying an absolute velocity calibration we find
  that the smallest magnetic features have velocities of up to 5 km s(-1)
  in both up- and downflows whereas for larger elements or clusters of
  several flux tubes the velocities become smaller and more uniform. The
  V-profile asymmetries are larger (both positive and negative) for
  small fill fraction than for higher fill fraction within the resolution
  element. Averaged over all individual profiles, there remains a positive
  amplitude and area asymmetry and a downflow exceeding 0.5 km s(-1)
  . The properties of spatially and temporally integrated V profiles are
  consistent with results from FTS-observations. Our observations are
  in qualitative agreement with results from numerical MHD simulations.

Title: Vertical mass flux in a sunspot penumbra
Authors: Schlichenmaier, R.; Schmidt, W.
Bibcode: 1999A&A...349L..37S
Altcode:
  We present the first direct measurement of vertical motion in the
  deepest atmospheric layers of a penumbra, obtained at hitherto
  unreached spatial resolution. Isolated hot upflows in the inner
  penumbra feed the horizontal Evershed flow that is observed in the
  mid and outer penumbra. We discover cool downflows which surround the
  hot upflows in the inner penumbra. At the outer edge of the penumbra,
  the Evershed flow terminates in a ring of downflow channels. The
  upflows transport a sufficient amount of energy to account for the
  observed brightness of the penumbra. These measurements have therefore
  significant implications for understanding the mass balance and the
  energy transport in a sunspot penumbra.

Title: Center-to-limb variation of the solar oscillation. New results
    from MDI data
Authors: Schmidt, W.; Stix, M.; Wöhl, H.
Bibcode: 1999A&A...346..633S
Altcode:
  {Using 17 hours of full-disk MDI Doppler data we have investigated the
  center-to-limb variation of the oscillatory wave spectrum of the solar
  photosphere. Power distributions in the k_hnu -plane are calculated
  for fields of 20(deg) x 20(deg) on the Sun, centered at every 10(deg)
  heliographic latitude. From the center-to-limb variation of the power
  in the f mode and the lowest 7 p modes we obtain information about the
  mean inclination of the oscillatory velocity vector with respect to
  the vertical direction. We find qualitative agreement with a model of
  adiabatic waves in an isothermal atmosphere, but generally the solar
  oscillations appear to be less inclined than the model oscillations. We
  find no indication for the existence of horizontal sound waves on
  the Sun.}

Title: GREGOR, a 1.5 M Solar Telescope
Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Kneer, F.;
   Staude, J.
Bibcode: 1999AGAb...15....5V
Altcode: 1999AGM....15..A01V
  We present the design of a new large solar telescope which is going to
  be installed at the Observatorio del Teide, in the tower that presently
  houses the 45cm Gregory-Coudé-Telescope. The new telescope has an
  aperture of 1.5 meters and its optical design is basically a Gregorian
  configuration. It will be an open telescope in an azimuthal mount. An
  adaptive optics system is incorporated in the optical design as well as
  a polarimetry package. The feasibility of lightweight optics for the
  primary mirror has been investigated in an industrial pre-study. The
  focal plane instrumentation will include a high resolution filter
  spectrometer similar to the existing TESOS instrument at the VTT and
  a new spectro-polarimeter for the visible and the near UV. The latter
  instrument is presently being developed jointly by the KIS and the
  High Altitude Observatory in Boulder, USA. Budget permitting, detailed
  (Phase-B) planning will start in 2000, and the telescope will be
  developed and built in 2002 and 2003 with first light in spring of 2004.

Title: Chromospheric Oscillations Observed by SOHO/SUMER and VTT/GCT
    on Tenerife
Authors: Curdt, W.; Heinzel, P.; Schmidt, W.; von Uexküll, M.;
   Wilken, V.
Bibcode: 1999AGAb...15R..11C
Altcode: 1999AGM....15..A12C
  Previous studies have revealed various oscillations in higher Lyman
  lines of hydrogen, as observed with SUMER on SOHO (Curdt &amp; Heinzel
  1998). The assumption that these periodic phenomena might be related
  to similar effects observed in optical lines like Ca II K led to the
  idea of simultaneous observations with the SOHO/SUMER instrument and
  the VTT/GCT telescopes on Tenerife. First results are presented here
  for the Lyman series and Lyman continuum. Power spectra in network and
  internetwork regions have been derived and a preliminary interpretation
  based on the wave propagation concept is given. In SUMER spectra
  we found a well-pronounced asymmetry of all Lyman lines, which is
  related to atmospheric dynamics. The time variation of co-spatial UV
  and optical data is presented and basic characteristics are discussed.

Title: Vertical and horizontal mass flux in a sunspot penumbra.
Authors: Schlichenmaier, R.; Schmidt, W.
Bibcode: 1999AGAb...15....8S
Altcode: 1999AGM....15..A06S
  We present direct measurements of vertical and horizontal motions in
  the deepest atmospheric layers of a sunspot penumbra with a spatial
  resolution of about 0.5 arcsec. The observations have been made with
  the Vacuum Tower Telescope of the Kiepenheuer-Institut, operated
  at the Observatorio del Teide on Tenerife, using the Telecentric
  Solar Spectrometer (TESOS), which is based on two Fabry-Perot
  interferometers. &gt;From two-dimensional spectra we infer the
  line-of-sight velocities for the weak C I line at 538.0 nm, which forms
  in the deepest photospheric layers, and for the Fe II 542.5 nm line,
  a rather temperature sensitive line which forms in the mid-photosphere
  at a height of about 100 km above the continuum level. We have observed
  a fairly round sunspot (NOAA 8578) with a diameter of 32 000 km on its
  passage through the central meridian on four consecutive days. We find
  that isolated hot upflows in the inner penumbra feed the horizontal
  Evershed flow that is observed in the mid and outer penumbra. At the
  outer edge of the penumbra, the Evershed flow terminates in a ring of
  downflow channels. Measurements at various position angles allow us
  to derive the inclination angles of these flows. Based on our measured
  upflow velocities, we estimate that the heat flux that emerges from our
  brightest feature compares with the observed brightness of penumbral
  grains. These measurements have therefore profound implications for
  understanding the mass balance and the energy transport in a sunspot
  penumbra.

Title: Chromospheric Oscillations
Authors: Schmidt, W.; von Uexküll, M.
Bibcode: 1999AGM....15..A14S
Altcode:
  Sequences of high-resolution filtergrams taken at Ca K2v show regions
  in the interior of the Ca network with oscillations at 11 mHz. These
  regions do also have strong 3min oscillations. Periodic signals around
  2.2 mHz are concentrated in small scale structures located at the cell
  boundaries. The observations have been carried at at the Vacuum-Tower
  Telescope on Tenerife in May 1999, along with a coordinated SOHO-SUMER
  campaign.

Title: TESOS, a double Fabry-Perot instrument for solar spectroscopy
Authors: Kentischer, T. J.; Schmidt, W.; Sigwarth, M.; Uexkuell, M. V.
Bibcode: 1998A&A...340..569K
Altcode:
  A double Fabry-Perot spectrometer in a telecentric configuration
  (TESOS: Telecentric Etalon SOlar Spectrometer) has been developed and
  installed in the Vacuum Tower Telescope at the Observatorio del Teide,
  Tenerife. The control system allows to switch from one wavelength band
  to another within 2 seconds. The telecentric configuration provides a
  constant wavelength passband across the field of view. Servo-stabilized
  etalons and a stable thermal environment provide a wavelength stability
  of &lt;0.3 picometer per hour. We present initial results obtained
  with this instrument.

Title: Upwelling in a young sunspot
Authors: Sigwarth, M.; Schmidt, W.; Schuessler, M.
Bibcode: 1998A&A...339L..53S
Altcode:
  An upflow of with a velocity exceeding 0.5 km*s(-1) is found in the
  umbra of the preceding spot in a young active region with ongoing
  flux emergence. A weak downflow is indicated in the corresponding
  spot of follower polarity. Such a flow pattern is consistent with the
  counter-rotation flow along a rising magnetic flux loop driven by the
  Coriolis force as predicted by numerical simulations.

Title: The lithium abundance in sunspots
Authors: Ritzenhoff, S.; Schroter, E. H.; Schmidt, W.
Bibcode: 1997A&A...328..695R
Altcode:
  The solar lithium abundance was determined using an empirical model
  for an observed sunspot umbra. The atmospheric model is deduced from a
  number of spectral lines. In addition to the lithium (I) line doublets
  from Li(6) and Li(7) at 670.8 nm eight different line profiles were
  observed with high spectrographic resolution. A magnetically sensitive
  line was included in order to determine the magnetic field strength. An
  estimation for the influence of molecular blends caused by CN and
  TiO was taken into account. Under the assumption of LTE a lithium
  abundance of epsilon_Li =1.02 +/-0.12 was derived. Some evidence for the
  existence of a small but notable amount of Li(6) is found, however only
  an upper limit of Li(6/Li^7&lt;=) 0.03 can be derived. A more precise
  determination of the isotopic ratio is hampered by the uncertainties
  induced by the presence of TiO blends. <P />On the logarithmic scale,
  where the abundance of hydrogen is epsilon_H =12.

Title: Multiple velocities observed in HeI 1083 nm
Authors: Muglach, K.; Schmidt, W.; Knölker, M.
Bibcode: 1997SoPh..172..103M
Altcode: 1997SoPh..172..103S; 1997ESPM....8..103M
  We present a time sequence of slit spectra of Hei 1083.03 nm (and Hβ)
  taken with the German Vacuum Tower Telescope at Tenerife. We find the
  signature of an onset of a downflow accelerating up to 42 km/s . The
  Hei 1083.03 nm line splits into two well separated components during
  the event, one of which shows the usual absorption profile of material
  which is almost at rest. We calculate the velocity, line depth and
  area of both line profiles. Possible explanations for these observed
  multiple velocities are discussed.

Title: Phase Diversity Applied to Sunspot Observations
Authors: Tritschler, A.; Schmidt, W.; Knolker, M.
Bibcode: 1997ASPC..118..170T
Altcode: 1997fasp.conf..170T
  We present preliminary results of a multi-colour phase diversity
  experiment carried out with the Multichannel Filter System of the
  Vacuum Tower Telescope at the Observatorio del Teide on Tenerife. We
  apply phase-diversity imaging to a time sequence of sunspot filtergrams
  taken in three continuum bands and correct the seeing influence for
  each image. A newly developed phase diversity device allowing for
  the projection of both the focused and the defocused image onto a
  single CCD chip was used in one of the wavelength channels. With the
  information about the wavefront obtained by the image reconstruction
  algorithm the restoration of the other two bands can be performed as
  well. The processed and restored data set will then be used to derive
  the temperature and proper motion of the umbral dots. Data analysis
  is still under way, and final results will be given in a forthcoming
  article.

Title: Adaptive Optics at the German VTT on Tenerife
Authors: Soltau, D.; Acton, D. S.; Kentischer, Th.; Roser, M.; Schmidt,
   W.; Stix, M.; von der Luhe, O.
Bibcode: 1997ASPC..118..351S
Altcode: 1997fasp.conf..351S
  Experiences and considerations are presented which play an important
  role for an Adaptive Optics system at our telescope.

Title: Solar Magnetic Fields
Authors: Schüssler, Manfred; Schmidt, Wolfgang
Bibcode: 1994smf..conf.....S
Altcode: 1994QB539.M23S65...
  The study of solar magnetic fields includes such issues as how
  large-scale magnetic fields are generated in the Sun and how magnetic
  structures are spontaneously formed and then interact with convective
  flows. These are just a sample of the fundamental questions answered in
  this timely review of our understanding of solar magnetic fields. This
  volume collects together articles and research papers ranging from
  such topics as large-scale patterns and global dynamo action to tiny
  flux tubes, from the overshoot layer below the convection zone up to
  the corona, and from instrumental problems and theoretical methods
  to the latest ground-based and satellite observations. This volume
  provides an essential review of our knowledge to date for graduate
  students and researchers.

Title: Limb observations of the HeI 1083.0 NM line.
Authors: Schmidt, W.; Knoelker, M.; Westendorp Plaza, C.
Bibcode: 1994A&A...287..229S
Altcode:
  The He 1083.0 nm line has been observed at the solar limb and the
  strength of the line has been measured as a function of height above
  it. The maximum of the emission is found to be at 2400 km.

Title: Polarimetry and spectroscopy of a simple sunspot. 3: Velocity
    and magnetic field of sunspot umbral dots
Authors: Schmidt, W.; Balthasar, H.
Bibcode: 1994A&A...283..241S
Altcode:
  Velocities and magnetic fields in sunspot umbrae and in umbral dots
  have been determined from high resolution Stokes-I spectra obtained at
  the Vacuum Tower Telescope (VTT) on Tenerife. Except for oscillatory
  motions the umbra is at rest and flow velocities in umbral dots,
  measured at an optical depth of about 0.01, are smaller than 25
  m/s. The magnetic field strength is weakened in the dots by 10-20%
  for a central umbral dot and by 5-10% for a peripheral umbral dot. The
  line of sight decrease of magnetic field in a peripheral dot shows no
  difference to the surrounding umbra and amounts to 2.5-3 G/km.

Title: The Impact of Fragment ``L'' of Comet SL-9 on Jupiter
Authors: Schleicher, H.; Balthasar, H.; Knolker, M.; Schmidt, W.;
   Jockers, K.
Bibcode: 1994EM&P...66...13S
Altcode:
  Filtergrams of high spatial and temporal resolution were obtained in
  the methane band centred at 892 nm during the impact of fragment L of
  comet Shoemaker-Levy 9 on Jupiter. The light curve shows two maxima of
  an emission ball observed above the limb shortly after the impact. The
  second maximum was the brightest and had a short life time of about 90
  seconds. During it's life, the apparent height of the emission ball
  declined towards the surface of Jupiter; the amount of displacement
  is larger than the expected effect caused by Jupiter's rotation. About
  half an hour after the impact, a domelike feature became visible when
  the location of the impact rotated into the illuminated hemisphere
  of Jupiter.

Title: Polarimetry and spectroscopy of a simple sunspot. 2: On the
    height and temperature dependence of the magnetic field
Authors: Balthasar, H.; Schmidt, W.
Bibcode: 1993A&A...279..243B
Altcode:
  We have observed a fairly regular sunspot located near disk center
  and have taken series of spectrograms in three different photospheric
  lines. The magnetic field strength across the spot has been measured
  in different heights of the sunspot photosphere and shows a change in
  slope at the umbra-penumbra boundary. The line depression contribution
  functions have been computed in order to obtain the height of formation
  of the spectral lines used in this analysis. Along the line-of-sight,
  we find an upward decrease of the field strength of 2.5 to 3 G/km in
  the penumbra and the adjacent outer part of the umbra. A relation has
  been deduced between the magnetic field and the brightness temperature
  measured across the sunspot which is strongly nonlinear and shows
  pronounced differences between the umbra and the penumbra.

Title: On the Magnetic and Velocity Field Geometry of Simple Sunspots
Authors: Title, Alan M.; Frank, Zoe A.; Shine, Richard A.; Tarbell,
   Theodore D.; Topka, Kenneth P.; Scharmer, Goran; Schmidt, Wolfgang
Bibcode: 1993ApJ...403..780T
Altcode:
  It is presently shown that a simple sunspot model with azimuthal
  variations in inclination, but lacking azimuthal field-strength
  variations, is free from azimuthal Lorentz forces. The meridional
  currents arising from the inclination variations are parallel to the
  field lines, suggesting that a cylindrically symmetric magnetostatic
  sunspot model can be perturbed into one with azimuthal variations in
  inclination with adjustment of the meridional force balance.

Title: Polarimetry and spectroscopy of a simple sunspot. I - On the
    magnetic field of a sunspot penumbra
Authors: Schmidt, W.; Hofmann, A.; Balthasar, H.; Tarbell, T. D.;
   Frank, Z. A.
Bibcode: 1992A&A...264L..27S
Altcode:
  We investigate the magnetic field structure of a medium sized sunspot
  using high resolution magnetograms and spectrograms and derive a
  relationship between the brightness of penumbral structures and the
  inclination of the magnetic field. The field inclination to the spot
  normal is larger in the dark structures than in the bright ones. We
  show that the field strength does not vary between dark and bright
  structures. At the inner penumbral boundary the field strength is 2000
  Gauss and about 1000 Gauss at the outer penumbral edge. The line-of
  sight component of the material flow decreases rapidly within one
  arcsecond at the photospheric boundary of the spot.

Title: Chromospheric fine structure revisited
Authors: Grossmann-Doerth, U.; Schmidt, W.
Bibcode: 1992A&A...264..236G
Altcode:
  We obtained H-alpha spectra from both spicules at the limb and mottles
  at disk center. We compare our results with data obtained by other
  groups and derive two distributions of axial spicule velocity, one
  based on limb, the other on disk observations. The two distributions
  disagree. We conclude that our knowledge on the basic properties of
  the chromospheric fine structure has not much improved in the last
  two decades; it is still rather scanty.

Title: On the Differences between Plage and Quiet Sun in the Solar
    Photosphere
Authors: Title, Alan M.; Topka, Kenneth P.; Tarbell, Theodore D.;
   Schmidt, Wolfgang; Balke, Christiaan; Scharmer, Goran
Bibcode: 1992ApJ...393..782T
Altcode:
  Time sequences of interleaved observations of the continuum intensity,
  longitudinal magnetic field, vertical velocity in the midphotosphere,
  and the line-center intensity in Ni I 6768 A were obtained in an
  active-region plage and the surrounding relatively field-free area near
  disk center. Spacetime Fourier filtering techniques are used to separate
  the convective and oscillatory components of the solar atmosphere. The
  properties of the photosphere are found to differ qualitatively and
  quantitatively between the plage, where the field is 150 G or more,
  and its quiet surroundings. The scale of granulation is smaller, the
  contrast lower, and the temporal evolution slower in the plage than the
  quiet sun. In the plage, the vertical velocity is reduced in amplitude
  compared to the quiet sun, and there is little evidence of a granulation
  pattern, while in the quiet sun the vertical flow pattern is similar in
  size and shape to the underlying granulation pattern in the continuum.

Title: Beobachtungen mit dem Vakuum-Turm-Teleskop auf Teneriffa.
Authors: Schmidt, Wolfgang
Bibcode: 1992S&W....31..167S
Altcode:
  The Tenerife Vacuum Tower Telescope, which is designed to study solar
  magnetic fields with high spatial resolution, are discussed. The
  spectrograph and the structure of the associated universal filter
  are described. Observations of the magnetic field structure inside a
  sunspot umbra are presented and discussed.

Title: High Resolution Observations of the Magnetic and Velocity
    Field of Simple Sunspots
Authors: Title, Alan M.; Frank, Zoe A.; Shine, Richard A.; Tarbell,
   T. D.; Topka, K. P.; Scharmer, Goran; Schmidt, Wolfgang
Bibcode: 1992ASIC..375..195T
Altcode: 1992sto..work..195T
  We have observed the disk passage of relatively simple round sunspots
  using a narrowband filter and a large format CCD detector and have
  created magnetograms, Dopplergrams, and continuum images nearly
  simultaneously. In addition the spectral resolution of the filter
  allows the construction of 'spectra' for all points in the field of
  view. The mean inclination of the magnetic field increases from 45-50
  deg to 70-75 deg across the penumbra and there is a fluctuation of the
  inclination angle about the mean of about 4 +/- 18 deg. The variation in
  inclination is large enough that substantial amounts of magnetic field
  are parallel to the solar surface from the mid to outer penumbra. The
  Evershed flow tends to occur in the regions where the magnetic field
  is horizontal. This suggests that the Evershed flow is confined to the
  regions of horizontal fields. We show that a simple sunspot model with
  azimuthal variations in inclination but no azimuthal variations of
  field strength is free from azimuthal Lorentz forces. The meridional
  component of the currents which arise from the azimuthal variation
  in inclination are parallel to the field lines. This suggests that a
  cylindrically symmetric magnetostatic sunspot model can be perturbed
  into one with azimuthal variations in inclination with some adjustment
  in the meridional force balance.

Title: On the Umbra / Penumbra Area Ratio of Sunspots
Authors: Brandt, P. N.; Schmidt, W.; Steinegger, M.
Bibcode: 1990SoPh..129..191B
Altcode:
  The area ratio of umbra to penumbra (A<SUB>u</SUB>/A<SUB>p</SUB>) was
  investigated for a series of 126 sunspots observed around the maximum
  of solar activity in 1980. Plotting log (A<SUB>u</SUB>) as function of
  log (A<SUB>p</SUB>) a linear relation is obtained with a slope of 1.10,
  yielding an average ratio A<SUB>u</SUB>/A<SUB>p</SUB> of 0.24 for small
  spots and of 0.32 for large spots. This deviates noticeably from the
  commonly adopted constant value of A<SUB>u</SUB>/A<SUB>p</SUB> = 0.21
  (Allen, 1973) used e.g. for modelling the sunspot irradiance deficit
  (cf. Willson et al., 1981) from the Solar Geophysical Data.

Title: Sunspot Photometry and the Total Solar Irradiance Deficit
    Measured in 1980 BY ACRIM
Authors: Steinegger, M.; Brandt, P. N.; Pap, J.; Schmidt, W.
Bibcode: 1990Ap&SS.170..127S
Altcode:
  Until now a simple Photometric Sunspot Index (PSI) model was used
  (e.g. Willsonet al., 1981) to describe the contribution of sunspots
  to the solar irradiance deficit measurement by ACRIM. In this work we
  replace this model by a photometry of sunspot pictures for the period
  of 19 August to 4 September, 1980 taking into account the individual
  features, like lightbridges or umbral dots, of each spot. The main
  results of this preliminary analysis are: (1) theA <SUB>u</SUB>/A
  <SUB>p</SUB> ratios and alsos the α values vary in a wide range and
  are by no means constant as in the PSI model; (2) the general trend of
  the irradiance deficit from our analysis agrees well with the ACRIM
  measurements; (3) on some days there are differences of more than
  50% between the deficits derived from our measurements and from the
  PSI model.

Title: The solar granulation in the vicinity of sunspots
Authors: Schmidt, W.; Grossmann-Doerth, U.; Schroeter, E. H.
Bibcode: 1988A&A...197..306S
Altcode:
  The mean size of the granulation close to sunspots is about 10 percent
  smaller than the corresponding value in the normal photosphere. The
  percentage of small granules increases steadily over a distance of
  about 30 arcsedc, as one approaches the sunspots. The observed rms
  intensity-contrast of the granulation at distances of less than 10
  arcse to the penumbra is lower than in the quiet photosphere. This is
  the result of a power spectrum analysis of 11 white light pictures of
  different sunspots taken in 1980 with the 40 cm Newtonian Telescope
  of the Kiepenheuer-Institut operated at the Observatorio del Teide,
  Tenerife.

Title: Size and temperature of umbral dots
Authors: Grossmann-Doerth, U.; Schmidt, W.; Schroeter, E. H.
Bibcode: 1986A&A...156..347G
Altcode:
  In 12 white light broad band pictures of 6 different sunspots, taken
  in 1980 and 1981 with the 40 cm Newtonian Vacuum Telescope operated at
  the Observatorio del Teide (Iazaña), the authors identified nearly 100
  umbral dots and attempted to derive their temperature and diameter. They
  found strong evidence that the diameter of the dots is in the range
  0arcsec.4 to 0arcsec.9 and the temperature is several 100K up to more
  than 1000K cooler than the photosphere.

Title: Oscillations of the sun's chromosphere. III - Simultaneous
    H-alpha observations from two sites
Authors: von Uexkuell, M.; Kneer, F.; Mattig, W.; Nesis, A.;
   Schmidt, W.
Bibcode: 1985A&A...146..192V
Altcode:
  The authors analyze time sequences of Hα filtergrams taken
  simultaneously from two distant observatories, Capri and Izaña. By
  means of a coherence analysis the authors discriminate between
  instrumental effects including seeing and truly solar intensity
  fluctuations. Waves with periods as short as 60 s are present in the
  solar chromosphere; the lower limit is set by the time resolution of
  the observations.

Title: New information about solar rotation
Authors: Woehl, H.; Balthasar, H.; Koch, A.; Kueveler, G.; Roca-Cortes,
   T.; Schmidt, W.; Vazquez, M.
Bibcode: 1984S&W....23...73W
Altcode:
  It is pointed out that the phenomenon of solar rotation is known
  since the introduction of the telescope into astronomy by Galilei in
  1610. Regular measurements concerning the positions of sunspots were
  conducted with the aid of photographic plates at the Royal Greenwich
  Observatory during the time from 1874 to 1976. The obtained data
  provide an excellent basis for statistical analysis. Information
  obtained as a result of such analyses is discussed. Attention is given
  to the determination of the Wilson depression, details regarding
  solar differential rotation, plans for an evaluation of data with
  the aid of a computer, the rotation of the solar plasma, a comparison
  of sunspots and plasma, the theory of differential rotation, and new
  information concerning solar rotation partly obtained with the aid of
  solar telescopes in a Spanish observatory on the island of Tenerife.

Title: Balloon-borne imagery of the solar granulation. IV - The
    centre-to-limb variation of the intensity fluctuations
Authors: Durrant, C. J.; Mattig, W.; Nesis, A.; Schmidt, W.
Bibcode: 1983A&A...123..319D
Altcode:
  A reanalysis of the white-light photographs of the granulation obtained
  during the flight of the balloon-borne Spektrostratoskop experiment
  is presented. A detailed examination of the power spectra of the
  intensity fluctuations at various times during the flight reveals a
  steady increase in a straylight and a substantial degree of astigmatism
  that changed with the focus setting. Allowing for the latter and
  normalizing all measurements to that with the least straylight, the
  rms relative intensity fluctuation at the center of the disk at 556 nm
  is increased from the previously reported value of 8.6 percent to 11.3
  percent. The overall change of rms fluctuation from the center of the
  disk to 0.3 micron is remarkably small, dropping some 10 percent. The
  results agree quite well with those of the Soviet Solar Stratospheric
  Observatory, when corrected roughly for instrumental degradation, and
  with a granulation model in which the granular temperature perturbation
  cuts off at a height of 35 km in the atmosphere.

Title: Two comments of the sun's differential rotation
Authors: Schmidt, W.; Stix, M.
Bibcode: 1983A&A...118....1S
Altcode:
  The authors argue that the effect of rotation should be neglected
  when the convection velocity is estimated through a comparison of the
  kinetic energy with the work done by the superadiabatic temperature
  gradient. A recent model of the Sun's differential rotation by Durney
  (1981) would thus not be restricted to small rates of rotation. The
  authors present a simple model where convection cells elongated
  in north-south direction are simulated by means of an anisotropic
  turbulent viscosity tensor. The resulting mean flow has equatorial
  acceleration, as observed on the Sun, with negligible concomitant
  meridional circulation and pole-equator temperature difference.

Title: Models of solar differential rotation
Authors: Schmidt, W.
Bibcode: 1982GApFD..21...27S
Altcode:
  Models of a differentially rotating compressible convection zone
  are calculated, considering the inertial forces in the poloidal
  components of the equations of motion. Two driving mechanisms have
  been considered: latitude dependent heat transport and anisotropic
  viscosity. In the former case a meridional circulation is induced
  initially which in turn generates differential rotation, whereas
  in the latter case differential rotation is directly driven by the
  anisotropic viscosity, and the meridional circulation is a secondary
  effect. In the case of anisotropic viscosity the choice of boundary
  conditions has a big influence on the results: depending on whether or
  not the conditions of vanishing pressure perturbation are imposed at
  the bottom of the convection zone, one obtains differential rotation
  with a fast ( 10 ms-1) or a slow ( 1 ms-1) circulation. In the latter
  case the rotation law is mainly a function of radius and the rotation
  rate increases inwards if the viscosity is larger in radial direction
  than in the horizontal directions. The models with latitude dependent
  heat transport exhibit a strong dependence on the Prandtl number. For
  values of the Prandtl number less than 0.2 the pole-equator temperature
  difference and the surface velocity of the meridional circulation are
  compatible with observations. For sufficiently small values of the
  Prandtl number the convection zone becomes globally unstable like a
  layer of fluid for which the critical Rayleigh number is exceeded.

Title: Rms-value and power spectrum of the photospheric
    intensity-fluctuations
Authors: Schmidt, W.; Knoelker, M.; Schroeter, E. H.
Bibcode: 1981SoPh...73..217S
Altcode:
  The power spectrum and the rms-value of the granular intensity
  fluctuations were studied using granulation photographs of
  excellent quality obtained during the JOSO site testing campaign
  1979 at Izaña. The observed power spectrum was corrected using
  various effective modulation transfer functions of the system:
  telescope+aberrations+atmospheric seeing, assuming different
  contributions of the atmospheric seeing. With this procedure a
  lower and upper limit for the `true' power spectrum of the granular
  intensity fluctuations and thus for the rms-value could be derived:
  7.2% &lt;I<SUB>rms</SUB> &lt;12% at λ = 550 nm, with a most probable
  value of I<SUB>rms</SUB> = 10.5%. We checked the validity of the
  upper limit by applying to our data a MTF (Deubner and Mattig, 1975),
  which certainly must lead to an overcorrection. This procedure lead
  to I<SUB>rms</SUB> = 13.4%. Thus we can state that the true rms-value
  of the granular intensity fluctuations does certainly not exceed 13%
  at λ = 550 nm.

Title: The brightness distribution in sunspot penumbrae
Authors: Grossmann-Doerth, U.; Schmidt, W.
Bibcode: 1981A&A....95..366G
Altcode:
  From a set of high quality sunspot photographs the intensity
  distribution in the penumbrae as well as mean intensities and rms
  contrast were derived. For image restoration a Fourier technique was
  employed. The intensity distribution was found to be almost symmetrical
  and singly peaked.

Title: On the center to limb variation of the granular brightness
    fluctuations.
Authors: Schmidt, W.; Deubner, F. -L.; Mattig, W.; Mehltretter, J. P.
Bibcode: 1979A&A....75..223S
Altcode:
  The center to limb variation of the granular brightness contrast
  was studied on the basis of slit-jaw photographs obtained with the
  balloon-borne Spektro-Stratoskop telescope, flown at an altitude of
  about 28 km on May 17, 1975 and during the partial solar eclipse of
  April 26, 1976 on Tenerife. Positions concentrate at cosine theta
  values of about 1, 0.6 and 0.2. The granular contrast was found to
  decrease monotonically towards the solar limb, with the magnitude of
  contrast about three times smaller at cosine theta 2 than at the disk
  center. The relative center to limb variation was found to be 10.4%
  (eclipse observations by a 40 cm evacuated Newtonian reflector at 422
  nm) and 8.6% (Spektro-Stratoskop observations at 556 nm). Discrepancies
  between these results and those reported by Deubner and Mattig (1975)
  are thought to be due to corrections for photographic noise and other
  factors.

Title: Studies of granular velocities. VIII. The height dependence
    of the vertical granular velocity component.
Authors: Durrant, C. J.; Mattig, W.; Nesis, A.; Reiss, G.; Schmidt, W.
Bibcode: 1979SoPh...61..251D
Altcode:
  Spectral observations of solar velocity fields made during a partial
  solar eclipse are described. Continuum intensity measurements at
  the lunar limb allow the modulation transfer function to be derived
  and the true spatial power spectrum of the velocity field to be
  reconstructed. The oscillatory and granular components are separated
  by applying spatial filters cutting off at 3″.7. The oscillatory
  component values are in good agreement with those of Canfield (1976) but
  the granular component has substantially more power and a smaller height
  gradient. The discrepancy can be resolved by noting the uncertainties
  of the seeing corrections and of the separation into components in
  the work of Canfield.

Title: Study of the <SUP>19</SUP>F(<SUP>3</SUP>He,
    <SUP>6</SUP>Li)<SUP>16</SUP>O reaction at 11 MeV
Authors: Strohbusch, U.; Schmidt, W.; Huber, G.
Bibcode: 1971NuPhA.163..453S
Altcode:
  Angular distributions of the <SUP>19</SUP>F
  (<SUP>3</SUP>He, <SUP>6</SUP>Li)<SUP>16</SUP>O
  reaction have been measured at 11 MeV for the transitions
  <SUP>6</SUP>Li<SUB>g.s</SUB>. (<SUP>16</SUP>O<SUB>g.s</SUB>),
  <SUP>6</SUP>Li<SUB>3.56</SUB> (<SUP>16</SUP>O<SUB>g.s.</SUB>)
  and <SUP>6</SUP>Li<SUB>g.s</SUB>. (<SUP>16</SUP>O<SUB>6.06,
  6.14</SUB>). Zero-range DWBA analysis on the basis of the triton
  pickup mechanism revealed good fits for the two transitions to
  <SUP>16</SUP>O<SUB>g.s.</SUB> A ratio of 1.6 +/- 0.2 is obtained for the
  spectroscopic factors S (<SUP>6</SUP>Li<SUB>g.s</SUB>¦<SUP>3</SUP>He,
  t) and S (<SUP>6</SUP>Li<SUB>3.56</SUB>¦<SUP>3</SUP>He, t). Published
  angular distributions of the reaction <SUP>19</SUP>F(p,α)
  <SUP>16</SUP>O for E<SUB>p</SUB> = 22.8 and 30.5 MeV have been
  analysed on the basis of the same mechanism using the same triton
  well geometry as for the (<SUP>3</SUP>He, <SUP>6</SUP>Li) calculations
  and yield a spectroscopic factor S (<SUP>19</SUP>F<SUP>16</SUP>O, t)
  = 0.06. A rather strong transition <SUP>19</SUP>F (<SUP>3</SUP>He,
  <SUP>6</SUP>Li<SUB>g.s</SUB><SUP>16</SUP><SUB>6.06. 6.14</SUB> is
  observed which is not compatible with one-step triton pickup. The
  corresponding angular distribution shows no pronounced structure.

