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Author name code: suetterlin
ADS astronomy entries on 2022-09-14
author:"Suetterlin, Peter" 

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Title: Design and Performance Analysis of a Highly Efficient
    Polychromatic Full Stokes Polarization Modulator for the CRISP
    Imaging Spectrometer
Authors: de Wijn, A. G.; de la Cruz Rodríguez, J.; Scharmer, G. B.;
   Sliepen, G.; Sütterlin, P.
2021AJ....161...89D    Altcode: 2021arXiv210201231D
  We present the design and performance of a polychromatic polarization
  modulator for the CRisp Imaging SpectroPolarimeter (CRISP) Fabry-Perot
  tunable narrow-band imaging spectropolarimer at the Swedish 1 m Solar
  Telescope (SST). We discuss the design process in depth, compare
  two possible modulator designs through a tolerance analysis, and
  investigate thermal sensitivity of the selected design. The trade-offs
  and procedures described in this paper are generally applicable in the
  development of broadband polarization modulators. The modulator was
  built and has been operational since 2015. Its measured performance
  is close to optimal between 500 and 900 nm, and differences between
  the design and as-built modulator are largely understood. We show some
  example data, and briefly review scientific work that used data from
  SST/CRISP and this modulator.

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Title: CRISPRED: CRISP imaging spectropolarimeter data reduction
    pipeline
Authors: de la Cruz Rodríguez, J.; Löfdahl, M. G.; Sütterlin, P.;
   Hillberg, T.; Rouppe van der Voort, L.
2017ascl.soft08003D    Altcode:
  CRISPRED reduces data from the CRISP imaging spectropolarimeter at
  the Swedish 1 m Solar Telescope (SST). It performs fitting routines,
  corrects optical aberrations from atmospheric turbulence as well as
  from the optics, and compensates for inter-camera misalignments,
  field-dependent and time-varying instrumental polarization, and
  spatial variation in the detector gain and in the zero level offset
  (bias). It has an object-oriented IDL structure with computationally
  demanding routines performed in C subprograms called as dynamically
  loadable modules (DLMs).

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Title: CRISPRED: A data pipeline for the CRISP imaging
    spectropolarimeter
Authors: de la Cruz Rodríguez, J.; Löfdahl, M. G.; Sütterlin, P.;
   Hillberg, T.; Rouppe van der Voort, L.
2015A&A...573A..40D    Altcode: 2014arXiv1406.0202D
  The production of science-ready data from major solar telescopes
  requires expertise beyond that of the typical observer. This is
  a consequence of the increasing complexity of instruments and
  observing sequences, which require calibrations and corrections
  for instrumental and seeing effects that are not only difficult to
  measure, but are also coupled in ways that require careful analysis
  in the design of the correction procedures. Modern space-based
  telescopes have data-processing pipelines capable of routinely
  producing well-characterized data products. High resolution imaging
  spectropolarimeters at ground-based telescopes need similar data
  pipelines.We present new methods for flat-fielding spectropolarimetric
  data acquired with telecentric Fabry-Perot instruments and a new
  approach for accurate camera co-alignment for image restoration. We
  document a procedure that forms the basis of current state-of-the-art
  processing of data from the CRISP imaging spectropolarimeter at the
  Swedish 1 m Solar Telescope (SST). By collecting, implementing, and
  testing a suite of computer programs, we have defined a data reduction
  pipeline for this instrument. This pipeline, CRISPRED, streamlines the
  process of making science-ready data.It is implemented and operated
  in IDL, with time-consuming steps delegated to C.CRISPRED will also be
  the basis for the data pipeline of the forthcoming CHROMIS instrument.

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Title: Ellerman bombs: fallacies, fads, usage
Authors: Rutten, Robert J.; Vissers, Gregal J. M.; Rouppe van der
   Voort, Luc H. M.; Sütterlin, Peter; Vitas, Nikola
2013JPhCS.440a2007R    Altcode: 2013arXiv1304.1364R
  Ellerman bombs are short-lived brightenings of the outer wings of Hα
  that occur in active regions with much flux emergence. We point out
  fads and fallacies in the extensive Ellerman bomb literature, discuss
  their appearance in various spectral diagnostics, and advocate their
  use as indicators of field reconfiguration in active-region topography
  using AIA 1700 Å images.

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Title: Opposite polarity field with convective downflow and its
    relation to magnetic spines in a sunspot penumbra
Authors: Scharmer, G. B.; de la Cruz Rodriguez, J.; Sütterlin, P.;
   Henriques, V. M. J.
2013A&A...553A..63S    Altcode: 2012arXiv1211.5776S
  We discuss NICOLE inversions of Fe i 630.15 nm and 630.25 nm Stokes
  spectra from a sunspot penumbra recorded with the CRISP imaging
  spectropolarimeter on the Swedish 1-m Solar Telescope at a spatial
  resolution close to 0.15 arcsec. We report on narrow, radially extended
  lanes of opposite polarity field, located at the boundaries between
  areas of relatively horizontal magnetic field (the intra-spines) and
  much more vertical field (the spines). These lanes harbor convective
  downflows of about 1 km s<SUP>-1</SUP>. The locations of these downflows
  close to the spines agree with predictions from the convective gap
  model (the "gappy penumbra") proposed six years ago, and more recent
  three-dimensional magnetohydrodynamic simulations. We also confirm the
  existence of strong convective flows throughout the entire penumbra,
  showing the expected correlation between temperature and vertical
  velocity, and having vertical root mean square velocities of about
  1.2 km s<SUP>-1</SUP>.

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Title: Search for Alfvén waves in a bright network element observed
    in Hα
Authors: Koza, J.; Sütterlin, P.; Gömöry, P.; Rybák, J.;
   Kučera, A.
2013CoSka..43....5K    Altcode: 2013arXiv1304.4027K
  Alfvén waves are considered as potential transporters of energy
  heating the solar corona. We seek spectroscopic signatures of the
  Alfvén waves in the chromosphere occupied by a bright network element,
  investigating temporal variations of the spectral width, intensity,
  Dopplershift, and the asymmetry of the core of the Hα spectral
  line observed by the tunable Lyot filter installed on the Dutch Open
  Telescope. The spectral characteristics are derived through the fitting
  of five intensity samples, separated from each other by 0.35 Å, by a
  4<SUP>th</SUP>-order polynomial. The bright network element displays
  the most pronounced variations of the Dopplershift varying from 0 to 4
  km s<SUP>-1</SUP> about the average of 1.5 km s<SUP>-1</SUP>. This fact
  implies a persistent redshift of the Hα core with a redward asymmetry
  of about 0.5 km s<SUP>-1</SUP>, suggesting an inverse-C bisector. The
  variations of the core intensity up to ±10 % and the core width up to
  ±5 % about the respective averages are much less pronounced, but still
  detectable. The core intensity variations lag behind the Dopplershift
  variations about 2.1 min. The Hα core width tends to correlate with
  the Dopplershift and anticorrelate with the asymmetry, suggesting that
  more redshifted Hα profiles are wider and the broadening of the Hα
  core is accompanied with a change of the core asymmetry from redward
  to blueward. We also found a striking anticorrelation between the
  core asymmetry and the Dopplershift, suggesting a change of the core
  asymmetry from redward to blueward with an increasing redshift of the
  Hα core. The data and the applied analysis do not show meaningful
  tracks of Alfvén waves in the selected network element.

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Title: Large-field high-resolution mosaic movies
Authors: Hammerschlag, Robert H.; Sliepen, Guus; Bettonvil, Felix
   C. M.; Jägers, Aswin P. L.; Sütterlin, Peter; Martin, Sara F.
2012SPIE.8444E..06H    Altcode:
  Movies with fields-of-view larger than normal for high-resolution
  telescopes will give a better understanding of processes on the
  Sun, such as filament and active region developments and their
  possible interactions. New active regions can influence, by their
  emergence, their environment to the extent of possibly serving
  as an igniter of the eruption of a nearby filament. A method to
  create a large field-of-view is to join several fields-of-view into
  a mosaic. Fields are imaged quickly one after another using fast
  telescope-pointing. Such a pointing cycle has been automated at the
  Dutch Open Telescope (DOT), a high-resolution solar telescope located
  on the Canary Island La Palma. The observer can draw with the computer
  mouse the desired total field in the guider-telescope image of the
  whole Sun. The guider telescope is equipped with an H-alpha filter and
  electronic enhancement of contrast in the image for good visibility of
  filaments and prominences. The number and positions of the subfields
  are calculated automatically and represented by an array of bright
  points indicating the subfield centers inside the drawn rectangle of
  the total field on the computer screen with the whole-sun image. When
  the exposures start the telescope repeats automatically the sequence of
  subfields. Automatic production of flats is also programmed including
  defocusing and fast motion over the solar disk of the image field. For
  the first time mosaic movies were programmed from stored information
  on automated telescope motions from one field to the next. The mosaic
  movies fill the gap between whole-sun images with limited resolution
  of synoptic telescopes including space instruments and small-field
  high-cadence movies of high-resolution solar telescopes.

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Title: Sunlight refraction in the mesosphere of Venus during the
    transit on June 8th, 2004
Authors: Tanga, P.; Widemann, T.; Sicardy, B.; Pasachoff, J. M.;
   Arnaud, J.; Comolli, L.; Rondi, A.; Rondi, S.; Sütterlin, P.
2012Icar..218..207T    Altcode: 2011arXiv1112.3136T
  Many observers in the past gave detailed descriptions of the telescopic
  aspect of Venus during its extremely rare transits across the Solar
  disk. In particular, at the ingress and egress, the portion of the
  planet’s disk outside the Solar photosphere has been repeatedly
  perceived as outlined by a thin, bright arc (“aureole”). Those
  historical visual observations allowed inferring the existence of
  Venus’ atmosphere, the bright arc being correctly ascribed to the
  refraction of light by the outer layers of a dense atmosphere. On June
  8th, 2004, fast photometry based on electronic imaging devices allowed
  the first quantitative analysis of the phenomenon. Several observers
  used a variety of acquisition systems to image the event - ranging from
  amateur-sized to professional telescopes and cameras - thus collecting
  for the first time a large amount of quantitative information on this
  atmospheric phenomenon. In this paper, after reviewing some elements
  brought by the historical records, we give a detailed report of the
  ground based observations of the 2004 transit. Besides confirming the
  historical descriptions, we perform the first photometric analysis of
  the aureole using various acquisition systems. The spatially resolved
  data provide measurements of the aureole flux as a function of the
  planetocentric latitude along the limb. A new differential refraction
  model of solar disk through the upper atmosphere allows us to relate
  the variable photometry to the latitudinal dependency of scale-height
  with temperature in the South polar region, as well as the latitudinal
  variation of the cloud-top layer altitude. We compare our measurements
  to recent analysis of the Venus Express VIRTIS-M, VMC and SPICAV/SOIR
  thermal field and aerosol distribution. Our results can be used a
  starting point for new, more optimized experiments during the 2012
  transit event.

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Title: Multi-wavelength fine structure and mass flows in solar
    microflares
Authors: Berkebile-Stoiser, S.; Gömöry, P.; Veronig, A. M.; Rybák,
   J.; Sütterlin, P.
2009A&A...505..811B    Altcode:
  Aims: We study the multi-wavelength characteristics at high spatial
  resolution, as well as chromospheric evaporation signatures of solar
  microflares. To this end, we analyze the fine structure and mass
  flow dynamics in the chromosphere, transition region and corona of
  three homologous microflares (GOES class &lt;A9/0.7 with/without
  background), which occurred on July 4, 2006 in AR 10898. <BR
  />Methods: A multi-wavelength analysis using temporally and spatially
  highly resolved imaging data from the Dutch open telescope (Hα,
  Ca ii H), the transition region and coronal explorer (17.1 nm),
  the extreme-ultraviolet imaging telescope (19.5 nm), and the Reuven
  Ramaty high energy solar spectroscopic imager (≳3 keV) was carried
  out. EUV line spectra provided by the coronal diagnostic spectrometer
  are searched for Doppler shifts in order to study associated
  plasma flows at chromospheric (He i, T∼3.9× 10<SUP>4</SUP> K),
  transition region (e.g. O v, T∼ 2.6× 10<SUP>5</SUP> K), and
  coronal temperatures (Si xii, T∼ 2× 10<SUP>6</SUP> K). RHESSI
  X-ray spectra provide information about non-thermal electrons. <BR
  />Results: The multi-wavelength appearance of the microflares is in
  basic agreement with the characteristics of large flares. For the
  first event, a complex flare sequence is observed in TRACE 17.1 nm
  images (T≈ 1 MK), which show several brightenings, narrow loops
  of enhanced emission, and an EUV jet. EIT 19.5 nm data (T≈ 1.5 MK)
  exhibit similar features for the third event. DOT measurements show
  finely structured chromospheric flare brightenings for all three events,
  loop-shaped fibrils of increased emission between Hα brightenings, as
  well as a similar feature in Ca ii. For all three events, a RHESSI X-ray
  source (3-8 keV, T ≳ 10 MK) is located in between two chromospheric
  brightenings situated in magnetic flux of opposite polarity. We find
  the flow dynamics associated with the events to be very complex. In
  the chromosphere and transition region, CDS observed downflows for
  the first (v ≲ 40 km s<SUP>-1</SUP>), and upflows for the second
  event (v ≲ 40 km s<SUP>-1</SUP>). During the third microflare, we
  find upflows of ≲ 20 km s<SUP>-1</SUP> and also weak downflows of
  ≲20 km s<SUP>-1</SUP> in two separate brightenings. For all three
  microflares, multi-component fitting is needed for several profiles
  of He i, O v, and Ne vi lines observed at the flare peaks, which
  indicate spatially unresolved, oppositely directed flows of ≲180
  km s<SUP>-1</SUP>. We interpret these flows as twisting motions of
  the flare loops. Loop-shaped fibrils in between Hα brightenings
  showing opposite flow directions (v≈5 km s<SUP>-1</SUP>) are also
  observed in DOT Hα Dopplergrams. RHESSI X-ray spectra show evidence
  of non-thermal bremsstrahlung for two of the three microflares. The
  electron beam flux density deposited in the chromosphere for these
  events is estimated to straddle the threshold heating flux between
  gentle and explosive evaporation. <P />Appendix A and the movie are
  only available in electronic form at http://www.aanda.org

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Title: Multi-wavelength Observations of Microflares Near an Active
    Region
Authors: Bein, B.; Veronig, A.; Rybak, J.; Gömöry, P.;
   Berkebile-Stoiser, S.; Sütterlin, P.
2009CEAB...33..179B    Altcode:
  We study the multi-wavelength characteristics of a microflaring active
  region (AR 10898) near disc centre. The analysed data were from the
  4^{th} of July 2006, and were recorded by DOT (Hα, Ca II H), RHESSI
  (X-rays), TRACE (EUV) and SOHO/MDI (magnetograms). The identified
  microflare events were studied with respect to their magnetic field
  configuration and their multi-wavelength time evolution.

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Title: CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
Authors: Scharmer, G. B.; Narayan, G.; Hillberg, T.; de la Cruz
   Rodriguez, J.; Löfdahl, M. G.; Kiselman, D.; Sütterlin, P.; van
   Noort, M.; Lagg, A.
2008ApJ...689L..69S    Altcode: 2008arXiv0806.1638S
  We discuss penumbral fine structure in a small part of a pore,
  observed with the CRISP imaging spectropolarimeter at the Swedish
  1-m Solar Telescope (SST), close to its diffraction limit of
  0.16”. Milne-Eddington inversions applied to these Stokes data
  reveal large variations of field strength and inclination angle over
  dark-cored penumbral intrusions and a dark-cored light bridge. The
  mid-outer part of this penumbra structure shows ~0.3” wide spines,
  separated by ~1.6” (1200 km) and associated with 30° inclination
  variations. Between these spines, there are no small-scale magnetic
  structures that easily can be identified with individual flux tubes. A
  structure with nearly 10° more vertical and weaker magnetic field is
  seen midway between two spines. This structure is cospatial with the
  brightest penumbral filament, possibly indicating the location of a
  convective upflow from below.

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Title: Photospheric flows around a quiescent filament at Large and
    small scale and their ffects on filament destabilization
Authors: Roudier, Th.; Malherbe, J. M.; Švanda, M.; Molodij, G.;
   Keil, S.; Sütterlin, P.; Schmieder, B.; Bommier, V.; Aulanier, G.;
   Meunier, N.; Rieutord, M.; Rondi, S.
2008sf2a.conf..569R    Altcode:
  We study the influence of large and small scales photospheric
  motions on the destabilization of an eruptive filament, observed
  on October 6, 7, and 8, 2004 as part of an international observing
  campaign (JOP 178). Large-scale horizontal flows are invetigated
  from a series of MDI/SOHO full-disc Dopplergrams and magnetograms
  from THEMIS. Small-scale horizontal flows were derived using local
  correlation tracking on TRACE satellite, Dutch Open Telescope (DOT)
  and The Dunn Solar telescope (DST) data. The topology of the flow field
  changed significantly during the filament eruptive phase, suggesting
  a possible coupling between the surface flow field and the coronal
  magnetic field. We measured an increase of the shear below the point
  where the eruption starts and a decrease in shear after the eruption. We
  conclude that there is probably a link between changes in surface flow
  and the disappearance of the eruptive filament.

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Title: Spectropolarimetry of Sunspots at 0.16 ARCSEC resolution
Authors: Scharmer, G.; Henriques, V.; Hillberg, T.; Kiselman, D.;
   Löfdahl, M.; Narayan, G.; Sütterlin, P.; van Noort, M.; de la Cruz
   Rodríguez, J.
2008ESPM...12..2.5S    Altcode:
  We present first observations of sunspots with the imaging
  spectropolarimeter CRISP, recently installed at the Swedish 1-m
  Solar Telescope (SST) on La Palma. This spectropolarimeter is based
  on a high-fidelity dual Fabry-Perot filter system. <P />Two liquid
  crystals and a polarizing beam splitter are used to reduce seeing
  induced I,Q,U,V crosstalk by simultaneously recording images with
  two 1kx1k back-illuminated Sarnoff CCD's. A third CCD simultaneously
  records broadband images through the pre-filter of the FPI filter
  system, allowing image reconstruction and co-alignment of images of
  different polarization states and at different wavelengths in Zeeman
  sensitive spectral lines. <P />The first data, recorded in April 2008,
  demonstrate the capability of this system to record high cadence,
  high S/N polarimetric data with a spatial resolution at or close to
  the diffraction limit of the SST at 630 nm, 0.16 arcsec. We discuss
  the analysis of first spectropolarimetric data for sunspots, based on
  Milne-Eddington inversion techniques.

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Title: DOT Tomography of the Solar Atmosphere VII. Chromospheric
    Response to Acoustic Events
Authors: Rutten, R. J.; van Veelen, B.; Sütterlin, P.
2008SoPh..251..533R    Altcode: 2008arXiv0801.0374R; 2008SoPh..tmp...28R
  We use synchronous movies from the Dutch Open Telescope sampling the G
  band, Ca II H, and Hα with five-wavelength profile sampling to study
  the response of the chromosphere to acoustic events in the underlying
  photosphere. We first compare the visibility of the chromosphere in
  Ca II H and Hα, demonstrate that studying the chromosphere requires
  Hα data, and summarize recent developments in understanding why this
  is so. We construct divergence and vorticity maps of the photospheric
  flow field from the G-band images and locate specific events through
  the appearance of bright Ca II H grains. The reaction of the Hα
  chromosphere is diagnosed in terms of brightness and Doppler shift. We
  show and discuss three particular cases in detail: a regular acoustic
  grain marking shock excitation by granular dynamics, a persistent
  flasher, which probably marks magnetic-field concentration, and an
  exploding granule. All three appear to buffet overlying fibrils, most
  clearly in Dopplergrams. Although our diagnostic displays to dissect
  these phenomena are unprecedentedly comprehensive, adding even more
  information (photospheric Doppler tomography and magnetograms along
  with chromospheric imaging and Doppler mapping in the ultraviolet)
  is warranted.

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Title: Dynamic Fibrils in Ly-alpha
Authors: Koza, J.; Rutten, R. J.; Vourlidas, A.; Suetterlin, P.
2008ESPM...12.2.16K    Altcode:
  We have detected dynamic fibrils (DFs) in Ly-alpha filtergrams taken
  with the rocket-borne Very high Angular resolution ULtraviolet Telescope
  (VAULT). Although the data consist of only a 1-min sequence of 4
  images taken near the solar limb during the second VAULT flight, they
  enable us to identify and study the time evolution of over 50 DFs. Most
  show parabolic trajectories in their angular extent, with supersonic
  maximum velocities. The measured decelerations vary from sub-ballistic
  to super-ballistic. The similarities with DFs seen in Halpha suggest a
  common cause, possibly the presence of hot transition-region interfaces
  around cool oscillation-fed jets.

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Title: SST/CRISP Magnetometry with Fe I 630.2 nm
Authors: Narayan, G.; Scharmer, G. B.; Hillberg, T.; Lofdahl, M.;
   van Noort, M.; Sutterlin, P.; Lagg, A.
2008ESPM...122.120N    Altcode:
  We present recent full Stokes observations in the Fe I 630.2 nm
  line with CRISP, an imaging spectropolarimeter at the Swedish 1-m
  Solar Telescope (SST). The observations reach a spatial resolution
  of 0".16, close to the diffraction limit of the SST, representing
  a major improvement over any past ground based or space based
  spectropolarimetric data. We describe the data acquisition and reduction
  methods and present results of Milne-Eddington(ME) inversions applied
  on observations of plage.

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Title: Search for photospheric footpoints of quiet Sun transition
    region loops
Authors: Sánchez Almeida, J.; Teriaca, L.; Sütterlin, P.; Spadaro,
   D.; Schühle, U.; Rutten, R. J.
2007A&A...475.1101S    Altcode: 2007arXiv0709.3451S
  Context: The footpoints of quiet Sun Transition Region (TR) loops
  do not seem to coincide with the photospheric magnetic structures
  appearing in traditional low-sensitivity magnetograms. <BR />Aims: We
  look for the so-far unidentified photospheric footpoints of TR loops
  using G-band bright points (BPs) as proxies for photospheric magnetic
  field concentrations. <BR />Methods: We compare TR measurements with
  SoHO/SUMER and photospheric magnetic field observations obtained with
  the Dutch Open Telescope. <BR />Results: Photospheric BPs are associated
  with bright TR structures, but they seem to avoid the brightest parts
  of the structure. BPs appear in regions that are globally redshifted,
  but they avoid extreme velocities. TR explosive events are not clearly
  associated with BPs. <BR />Conclusions: The observations are not
  inconsistent with the BPs being footpoints of TR loops, although we
  have not succeeded to uniquely identify particular BPs with specific
  TR loops.

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Title: Magnetic properties of G-band bright points in a sunspot moat
Authors: Beck, C.; Bellot Rubio, L. R.; Schlichenmaier, R.;
   Sütterlin, P.
2007A&A...472..607B    Altcode: 2007arXiv0707.1232B
  We present simultaneous spectropolarimetric observations of four
  visible (630 nm) and three infrared (1565 nm) spectral lines from the
  German Vacuum Tower Telescope, together with speckle-reconstructed
  filtergrams in the G-band and the Ca II H line core from the Dutch
  Open Telescope. After alignment of the data sets, we used the G-band
  intensity to locate bright points (BPs) in the moat of a regular
  sunspot. With the cospatial and cotemporal information provided by the
  polarimetric data, we characterize the magnetic, kinematic, and thermal
  properties of the BPs. We find that (a) 94% of the BPs are associated
  with magnetic fields; (b) their field strengths range between 500 and
  1400 G, with a rather flat distribution; (c) the contrast of BPs in the
  G-band depends on the angle between the vector magnetic field and the
  line of sight; (d) the BPs harbor downflows of magnetized plasma and
  exhibit Stokes V profiles with large area and amplitude asymmetries;
  (e) the magnetic interior of BPs is hotter than the immediate field-free
  surroundings by about 1000 K at equal optical depth; and (f) the mean
  effective diameter of BPs in our data set is 150 km, with very few
  BPs larger than 300 km. Most of these properties can be explained
  by the classical magnetic flux tube model. However, the wide range
  of BP parameters found in this study indicates that not all G-band
  BPs are identical to stable long-lived flux tubes or sheets of kG
  strength. <P />Appendices A-C are only available in electronic form
  at http://www.aanda.org

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Title: Photospheric flows around a quiescent filament
Authors: Rondi, S.; Roudier, Th.; Molodij, G.; Bommier, V.; Keil,
   S.; Sütterlin, P.; Malherbe, J. M.; Meunier, N.; Schmieder, B.;
   Maloney, P.
2007A&A...467.1289R    Altcode:
  Context: The horizontal photospheric flows below and around a
  filament are one of the components in the formation and evolution of
  filaments. Few studies exist because they require multiwalength time
  sequences at high spatial resolution. <BR />Aims: Our objective
  is to measure the horizontal photospheric flows associated
  with the evolution and eruption of a filament. <BR />Methods:
  We present observations obtained in 2004 during the international
  JOP 178 campaign which involved eleven instruments both in space
  and at ground based observatories. We use TRACE WL, DOT and DST
  observation to derive flow maps which are then coaligned with
  intensity images and with the vector magnetic field map obtained with
  THEMIS/MTR. <BR />Results: Several supergranulation cells cross the
  Polarity Inversion Line (PIL) and can transport magnetic flux through
  the PIL, in particular parasitic polarities. We present a detailed
  example of the formation of a secondary magnetic dip at the location
  of a filament footpoint. Large-scale converging flows, which could
  exist along the filament channel and contribute to its formation, are
  not observed. Before the filament's eruptive phase, we observe both
  parasitic and normal polarities being swept by a continuously diverging
  horizontal flow located in the filament gap. The disappearance of the
  filament initiates in this gap. Such purely horizontal motions could
  lead to destabilization of the filament and could trigger the sudden
  filament disappearance.

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Title: Temporal Variations in Fibril Orientation
Authors: Koza, J.; Sütterlin, P.; Kučera, A.; Rybák, J.
2007ASPC..368..115K    Altcode: 2007astro.ph..3733K
  We measure variations in orientation of fourteen dynamic fibrils as
  a function of time in a small isolated plage and nearby network using
  a 10-min time sequence of Hα filtergrams obtained by the Dutch Open
  Telescope. We found motions with average angular velocities of the
  order of 1 deg min<SUP>-1</SUP> suggesting systematic turning from
  one limit position to another, particularly apparent in the case of
  fibrils with lifetimes of a few minutes. Shorter fibrils tend to turn
  faster than longer ones, which we interpret as due to vortex flows in
  the underlying granulation that twist magnetic fields.

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Title: Magnetic properties of G-band bright points
Authors: Beck, C.; Mikurda, K.; Bellot Rubio, L. R.; Schlichenmaier,
   R.; Sütterlin, P.
2007msfa.conf..165B    Altcode:
  Bright points (BPs) visible in the G band at 430 nm are commonly used
  as tracers of magnetic fields, indicating the location of kG flux
  concentrations. To study the actual magnetic properties of G-band BPs,
  we took observations in 2003 and 2005, employing simultaneously a
  speckle setup in the G band and vector spectropolarimetry to derive
  the magnetic field vector. From the analysis of the co-aligned
  polarimetric data we find that the BPs show a broad range of field
  strengths, magnetic fluxes, and field inclinations. Many G-band
  BPs are not co-spatial with the central part of the nearby flux
  concentrations. Even at the small heliocentric angle of only 12°,
  the BPs appear projected on adjacent granules, whereas the magnetic
  field is concentrated in the intergranular lanes. Our findings support
  the view that the G-band BPs are a result of the "hot wall effect". The
  downward shift of the optical depth scale in the presence of magnetic
  fields allows to see deeper and hotter layers in the hot granules next
  to the field concentrations, where CH dissociates. Thus, information
  drawn from imaging observations of BPs has limited use to investigate
  the actual magnetic field structure, when the BPs are not co-spatial
  with the central part of the flux concentrations.

---------------------------------------------------------
Title: Polarimetric Observations of the Formation of a G-Band
    Bright Point
Authors: Beck, C.; Schmidt, W.; Bellot Rubio, L. R.; Schlichenmaier,
   R.; Sütterlin, P.; Lites, B. W.
2006ASPC..358...72B    Altcode:
  We investigate the kinematic and magnetic properties of G-band bright
  points in the moat of a regular sunspot. The analysis is based on vector
  polarimetric measurements made at the German Vacuum Tower Telescope in
  visible (630 nm) and infrared (1565 nm) spectral lines, complemented
  by high-resolution filtergrams in the G-band at 430.6 nm and the core
  of the Ca II H line at 396.7 nm from the Dutch Open Telescope. The
  spectro-polarimetric data has been inverted to derive the magnetic
  field properties of the observed region. We witness the formation of a
  G-band bright point from a patch of diffuse flux with an initial field
  strength of 0.4 kG. The magnetic field strength increases to 0.9 kG in
  the course of several minutes, accompanied by a downflow of magnetized
  plasma. A few minutes after the field intensification, a G-band bright
  point is seen at the location of the flux concentration. The formation
  of the bright point shows the signatures of convective collapse.

---------------------------------------------------------
Title: Magnetic Patches in Internetwork Areas
Authors: de Wijn, A. G.; Rutten, R. J.; Haverkamp, E. M. W. P.;
   Sütterlin, P.
2006ASPC..354...20D    Altcode:
  We present a study of internetwork magnetic elements that appear as
  bright points in G-band (photosphere) and Ca II H (low chromosphere)
  image sequences from the Dutch Open Telescope. Many bright points
  appear intermittently in groups of long-lived structures that we call
  “magnetic patches”. We develop an algorithm for the identification
  of bright points and magnetic patches. The average internetwork bright
  point lifetimes is measured to be 3.5 minutes in the G band, and 4.3
  minutes in the Ca II H. We find an internetwork bright point number
  density of 0.02 Mm^{-2} in the G-band sequence and 0.05 Mm^{-2} in
  the Ca II H sequence. The bright points show a bimodal distribution
  of the frame-to-frame horizontal velocities, with a peak at 0 km
  s^{-1} and a wide hump centered around 1.2 km s^{-1}. The patches
  last much longer than granular time scales (about nine hours) and
  outline cell-like structures on mesogranular scale. We conclude that
  transient internetwork bright points trace the locations of strong
  magnetic fields that exist before the bright point appears and remain
  after it disappears.

---------------------------------------------------------
Title: Tunable H-alpha Lyot filter with advanced servo system and
image processing: instrument design and new scientific results with
    the Dutch Open Telescope
Authors: Bettonvil, Felix C. M.; Hammerschlag, Robert H.; Sütterlin,
   Peter; Rutten, Robert J.; Jägers, Aswin P. L.; Sliepen, Guus
2006SPIE.6269E..0EB    Altcode: 2006SPIE.6269E..12B
  The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma
  is a revolutionary open solar telescope, on an excellent site, on
  top of a transparent tower of steel framework, and uses natural
  air flow to minimize local seeing. The DOT is a high-resolution
  multi-wavelength imager capable of long-duration time series aiming
  at magnetic fine structure, topology and dynamics in the photosphere
  and low- and high chromosphere. In this paper we describe the latest
  addition to the multi-wavelength imaging system: a Lyot H-alpha
  camera channel operating at a wavelength of 656.3 nm, being of major
  interest for high-chromospheric phenomena. The channel is operated
  strictly synchronous with the other channels and all data are speckle
  reconstructed. The channel permits profile sampling and delivers
  Dopplergrams in a 15 second time cadence, up to several hours long
  and adding up to a total data amount of 1.6 Terabyte/day. A dedicated
  computer (DSP, DOT Speckle Processor) has been built for processing
  the data overnight.

---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. VI. Magnetic elements
    as bright points in the blue wing of Hα
Authors: Leenaarts, J.; Rutten, R. J.; Sütterlin, P.; Carlsson, M.;
   Uitenbroek, H.
2006A&A...449.1209L    Altcode:
  High-resolution solar images taken in the blue wing of the Balmer H
  α line with the Dutch Open Telescope show intergranular magnetic
  elements as strikingly bright features, similar to, but with
  appreciably larger contrast over the surrounding granulation than
  their more familiar manifestation as G-band bright points. Part of
  this prominent appearance is due to low granular contrast, without
  granule/lane brightness reversal as, e.g., in the wings of Ca II H
  &amp; K. We use 1D and 2D radiative transfer modeling and 3D solar
  convection and magnetoconvection simulations to reproduce and explain
  the H α wing images. We find that the blue H α wing obeys near-LTE
  line formation. It appears particularly bright in magnetic elements
  through low temperature gradients. The granulation observed in the blue
  wing of H α has low contrast because of the lack of H α opacity in the
  upper photosphere, Doppler cancellation, and large opacity sensitivity
  to temperature working against source function sensitivity. We conclude
  that the blue H α wing represents a promising proxy magnetometer to
  locate and track isolated intermittent magnetic elements, a better one
  than the G band and the wings of Ca II H &amp; K although less sharp
  at given aperture.

---------------------------------------------------------
Title: Unveiling the atmosphere of Venus during the June 2004
    solar transit
Authors: Tanga, P.; Arnaud, J.; Colas, F.; Comolli, L.; Rondi, S.,
   A.; Sicardy, B.; Suetterlin, P.; Unione Astrofili Italiani-“Planets"
   Section Team
2005DPS....37.5718T    Altcode: 2005BAAS...37.1571T
  Visual and CCD observations of Venus transiting in front of the Sun
  on June 8, 2004, revealed traces of the light passing through the
  atmosphere of the planet. As several witness of past events have
  accounted for [1][2], the event happens close to the ingress and
  egress phases, when the disk of the planet is crossing the Solar
  limb. The portion of atmosphere that is projected against the darker
  sky background appears bright, at least in part, due to refracted
  light (mainly). <P />The 2004 opportunity was the first observed by
  electronic equipment. Sets of several images were acquired by widely
  different instruments, at different wavelengths. <P />The images were
  processed in order to subtract the sky background, and normalized. The
  brightness of the atmospheric arc was measured; its spatial structure
  and its variation in time are discussed. A latitude dependence of
  the arc brightness is clearly detected, with an intensity maximum
  close to the planet polar regions. Even comparing CCD images to
  visual observations, an investigation of the variability of the arc
  brightness from one event to the other encounters several difficulties,
  mainly due to the evolution of instruments in time. <P />[1] F. Link,
  Eclipse phenomena in Astronomy, Springer Verlag (Berlin 1969) <P />[2]
  H.N. Russell, ApJ 9, 284 (1899)

---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. V. Analysis of a
    surge from AR10486
Authors: Tziotziou, K.; Tsiropoula, G.; Sütterlin, P.
2005A&A...444..265T    Altcode:
  We present an analysis of high temporal and spatial resolution CaII H
  chromospheric limb observations obtained with the Dutch Open Telescope
  (DOT). We focus on a solar surge observed both by the DOT in CaII H and
  the Transition Region and Coronal Explorer (TRACE) satellite in the
  195 Å and 1600 Å passbands. The surge is observed in active region
  AR10486 located near the solar limb, a region which two hours later
  produced the largest X-flare ever recorded. It consists of relatively
  cold gas of about 10<SUP>4</SUP>-10<SUP>5</SUP> K. In TRACE images
  the surge is followed for almost 2.5 h, shrinking and expanding at
  the same location several times. From DOT images we find outward
  propagating intensity disturbances, with velocities higher than 50
  km s<SUP>-1</SUP>, indicative of upward material motion. The latter
  is also suggested by the good correlation between the DOT and TRACE
  surge apparent height curves, their apparent time delay and a phase
  difference analysis. A spectral wavelet analysis of the brightness
  variations within and along the surge shows a predominant period of
  ~6 min, the first ever reported for this kind of structures. Magnetic
  reconnection at the bottom of the surge as its driving mechanism is
  suggested by the observed inverted "Y" shape configuration and is
  further supported by a phase difference analysis.

---------------------------------------------------------
Title: Small Scale Magnetic Elements as Bright Points in the Blue
    Hα Wing
Authors: Leenaarts, J.; Sütterlin, P.; Rutten, R. J.; Carlsson, M.;
   Uitenbroek, H.
2005ESASP.596E..15L    Altcode: 2005ccmf.confE..15L
  No abstract at ADS

---------------------------------------------------------
Title: DOT tomography of the solar atmosphere.  IV. Magnetic patches
    in internetwork areas
Authors: de Wijn, A. G.; Rutten, R. J.; Haverkamp, E. M. W. P.;
   Sütterlin, P.
2005A&A...441.1183D    Altcode: 2007arXiv0706.2008D
  We use G-band and Ca ii H image sequences from the Dutch Open
  Telescope (DOT) to study magnetic elements that appear as bright
  points in internetwork parts of the quiet solar photosphere and
  chromosphere. We find that many of these bright points appear
  recurrently with varying intensity and horizontal motion within
  longer-lived magnetic patches. We develop an algorithm for detection
  of the patches and find that all patches identified last much longer
  than the granulation. The patches outline cell patterns on mesogranular
  scales, indicating that magnetic flux tubes are advected by granular
  flows to mesogranular boundaries. Statistical analysis of the emergence
  and disappearance of the patches points to an average patch lifetime
  as long as 530±50~min (about nine hours), which suggests that the
  magnetic elements constituting strong internetwork fields are not
  generated by a local turbulent dynamo.

---------------------------------------------------------
Title: DOT++: the Dutch Open Telescope with 1.4-m aperture
Authors: Bettonvil, Felix C.; Hammerschlag, Robert H.; Sütterlin,
   Peter; Rutten, Robert J.; Jägers, Aswin P.; Snik, Frans
2004SPIE.5489..362B    Altcode:
  The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma is
  a revolutionary open solar telescope, on an excellent site, on top
  of a transparent steel tower, and uses natural air flow to minimize
  local seeing. The aim is long-duration high-resolution imaging with
  a multi-wavelength camera system. In order to achieve this, the DOT
  is equipped with a diffraction limited imaging system and uses the
  speckle reconstruction technique for removing the remaining atmospheric
  turbulence. The DOT optical system is simple and consists currently of
  a 0.45m/F4.44 parabolic mirror and a 10x enlargement lens system. We
  present our plans to increase the aperture of the DOT from 0.45m to
  1.4m. The mirror support and telescope top shall be redesigned, but
  telescope, tower, multi-wavelength camera system and speckle system
  remain intact. The new optical design permits user selectable choice
  between angular resolution and field size, as well as transversal pupil
  shift introducing the possibility to use obstruction free apertures up
  to 65cm. The design will include a low order AO system, which improves
  the speckle S/N substantially during moderate seeing conditions.

---------------------------------------------------------
Title: Asymmetrical appearance of dark-cored filaments in sunspot
    penumbrae
Authors: Sütterlin, P.; Bellot Rubio, L. R.; Schlichenmaier, R.
2004A&A...424.1049S    Altcode:
  Recent sunspot observations at unprecedented resolution have led to the
  discovery of dark cores in the bright filaments that form the penumbra
  (\citealt{scharmer02_Nat420}). The discovery paper considered spots
  at disk center only, so the properties of the dark-cored filaments
  remain largely unknown. Here we analyze a speckle-reconstructed time
  series of G-band and blue continuum images of a sunspot acquired with
  the Dutch Open Telescope. The target was located at an heliocentric
  angle of 27 deg. We confirm the existence of dark-cored penumbral
  filaments also in spots outside the disk center, and report on distinct
  differences between the center and limb-side penumbra. In the inner
  center-side penumbra, filaments are detected as two narrow bright
  streaks separated by a central obscuration. These structures move
  together as a single entity. On the limb side, dark cores are hardly
  seen. The time series is used to determine the sizes (∼200-250 km),
  proper motions (∼280 m s<SUP>-1</SUP>), and lifetimes (⪉45 min)
  of typical dark-cored filaments.

---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. II. Reversed
    granulation in Ca II H
Authors: Rutten, R. J.; de Wijn, A. G.; Sütterlin, P.
2004A&A...416..333R    Altcode:
  High-quality simultaneous image sequences from the Dutch Open Telescope
  (DOT) in the G band and the Ca II H line are used to quantify the
  occurrence of reversed granulation as a constituent of the subsonic
  brightness pattern observed as a background to acoustic oscillations
  in the quiet-Sun internetwork atmosphere. In the middle photosphere
  reversed granulation constitutes a much larger part of this background
  than at the larger heights sampled by ultraviolet radiation. The
  anticorrelation with the underlying granulation reaches about 50% at a
  temporal delay of 2-3 min, and increases with spatial image smoothing to
  mesogranular resolution. We discuss the nature of reversed granulation
  in terms of convection reversal, gravity waves, acoustic waves, and
  intergranular magnetism, suggest that the internetwork background
  pattern is primarily a mixture of the first two ingredients, and
  speculate that it is also an inverse canopy mapper.

---------------------------------------------------------
Title: The Dutch Open Telescope on La Palma
Authors: Rutten, R. J.; Bettonvil, F. C. M.; Hammerschlag, R. H.;
   Jägers, A. P. L.; Leenaarts, J.; Snik, F.; Sütterlin, P.; Tziotziou,
   K.; de Wijn, A. G.
2004IAUS..223..597R    Altcode: 2005IAUS..223..597R
  The Dutch Open Telescope (DOT) on La Palma is an innovative solar
  telescope combining open telescope structure and an open support tower
  with a multi-wavelength imaging assembly and with synchronous speckle
  cameras to generate high-resolution movies which sample different
  layers of the solar atmosphere simultaneously and co-spatially at high
  resolution over long durations. The DOT test and development phase is
  nearly concluded. The installation of an advanced speckle processor
  enables full science utilization including "Open-DOT" time allocation
  to the international community. Co-pointing with spectropolarimeters
  at other Canary Island telescopes and with TRACE furnishes valuable
  Solar-B precursor capabilities.

---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. I. Telescope summary
    and program definition
Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. C. M.;
   Sütterlin, P.; de Wijn, A. G.
2004A&A...413.1183R    Altcode:
  The Dutch Open Telescope (DOT) on La Palma is an innovative optical
  solar telescope capable of reaching 0.2 arcsec angular resolution
  over extended durations. The DOT presently progresses from technology
  testbed to a stable science configuration providing multi-wavelength
  imaging and multi-camera speckle data acquisition for tomographic
  mapping of the solar atmosphere. Large-volume speckle processing will
  soon enable frequent usage and community-wide time allocation, in
  particular for tandem operation with other solar telescopes pursuing
  spectropolarimetry and EUV imaging. We summarize the DOT hardware and
  software in the context of this increasing availability and outline
  the corresponding “open-DOT” program.

---------------------------------------------------------
Title: La Palma observations of umbral flashes
Authors: Rouppe van der Voort, L. H. M.; Rutten, R. J.; Sütterlin,
   P.; Sloover, P. J.; Krijger, J. M.
2003A&A...403..277R    Altcode:
  We present high-quality Ca II H &amp; K data showing chromospheric
  flashes in sunspot umbrae collected with the Swedish Vacuum Solar
  Telescope, the Dutch Open Telescope, and the Swedish 1-m Solar Telescope
  at the Roque de los Muchachos Observatory on La Palma. Differential
  movies, time slices, spectrograms, and Fourier power maps demonstrate
  that umbral flashes and running penumbral waves are closely related
  oscillatory phenomena, combining upward shock propagation with coherent
  wave spreading over the entire spot. We attribute the flash brightening
  to large redshift by post-shock material higher up. We find no obvious
  relation between umbral dots and umbral flashes.

---------------------------------------------------------
Title: Motions of Isolated G-Band Bright Points in the Solar
    Photosphere
Authors: Nisenson, P.; van Ballegooijen, A. A.; de Wijn, A. G.;
   Sütterlin, P.
2003ApJ...587..458N    Altcode: 2002astro.ph.12306N
  Magnetic elements on the quiet Sun are buffeted by convective flows
  that cause lateral motions on timescales of minutes. The magnetic
  elements can be observed as bright points (BPs) in the G band at 4305
  Å. We present observations of BPs based on a long sequence of G-band
  images recorded with the Dutch Open Telescope and postprocessed using
  speckle-masking techniques. From these images we measured the proper
  motions of isolated BPs and derived the autocorrelation function of
  their velocity relative to the solar granulation pattern. The accuracy
  of BP position measurements is estimated to be less than 23 km on
  the Sun. The rms velocity of BPs (corrected for measurement errors)
  is about 0.89 km s<SUP>-1</SUP>, and the correlation time of BP motions
  is about 60 s. This rms velocity is about 3 times the velocity measured
  using cork tracking, almost certainly due to the fact that isolated BPs
  move more rapidly than clusters of BPs. We also searched for evidence
  of vorticity in the motions of G-band BPs.

---------------------------------------------------------
Title: Multi-wavelength imaging system for the Dutch Open Telescope
Authors: Bettonvil, Felix C.; Suetterlin, Peter; Hammerschlag, Robert
   H.; Jagers, Aswin P.; Rutten, Robert J.
2003SPIE.4853..306B    Altcode:
  The Dutch Open Telescope (DOT) is an innovative solar telescope,
  completely open, on an open steel tower, without a vacuum system. The
  aim is long-duration high resolution imaging and in order to achieve
  this the DOT is equipped with a diffraction limited imaging system
  in combination with a data acquisition system designed for use with
  the speckle masking reconstruction technique for removing atmospheric
  aberrations. Currently the DOT is being equipped with a multi-wavelength
  system forming a high-resolution tomographic imager of magnetic
  fine structure, topology and dynamics in the photosphere and low-
  and high chromosphere. Finally the system will contain 6 channels:
  G-band (430.5 nm), Ca II H (K) (396.8 nm), H-α (656.3 nm), Ba II
  (455.4 nm), and two continuum channels (432 and 651 nm). Two channels
  are in full operation now and observations show that the DOT produces
  real diffraction limited movies (with 0.2" resolution) over hours in
  G-band (430.5 nm) and continuum (432 nm).

---------------------------------------------------------
Title: Dutch Open Telescope: status, results, prospects
Authors: Rutten, Robert J.; Sütterlin, Peter; de Wijn, Alfred G.;
   Hammerschlag, Robert H.; Bettonvil, Felix C. M.; Hoogendoorn, Piet W.;
   Jägers, Aswin P. L.
2002ESASP.506..903R    Altcode: 2002svco.conf..903R; 2002ESPM...10..903R
  The Dutch Open Telescope (DOT) on La Palma is a revolutionary telescope
  achieving high-resolution imaging of the solar surface. The DOT combines
  a pioneering open design at an excellent wind-swept site with image
  restoration through speckle interferometry. Its open principle is now
  followed in major solar-telescope projects elsewhere. In the past three
  years the DOT became the first solar telescope to regularly obtain 0.2"
  resolution in extended image sequences, i.e., reaching the diffraction
  limit of its 45-cm primary mirror. Our aim for 2003-2005 is to turn
  the DOT into a 0.2" tomographic mapper of the solar atmosphere with
  frequent partnership in international multi-telescope campaigns through
  student-serviced time allocation. After 2005 we aim to triple the DOT
  resolution to 0.07" by increasing the aperture to 140 cm and to renew
  the speckle cameras and the speckle pipeline in order to increase
  the field size and sequence duration appreciably. These upgrades will
  maintain the DOT's niche as a tomographic high-resolution mapper in
  the era when GREGOR, Solar-B and SDO set the stage.

---------------------------------------------------------
Title: Opening the Dutch Open Telescope
Authors: Rutten, R. J.; de Wijn, A. G.; Sütterlin, P.; Bettonvil,
   F. C. M.; Hammerschlag, R. H.
2002ESASP.505..565R    Altcode: 2002IAUCo.188..565R; 2002solm.conf..565R
  We hope to "open the DOT" to the international solar physics
  community as a facility for high-resolution tomography of the solar
  atmosphere. Our aim is to do so combining peer-review time allocation
  with service-mode operation in a "hands-on-telescope" education
  program bringing students to La Palma to assist in the observing and
  processing. The largest step needed is considerable speedup of the
  DOT speckle processing.

---------------------------------------------------------
Title: THEMIS and DOT joint observations on NOAA 9716
Authors: Briand, C.; Collados, M.; Sütterlin, P.
2002ESASP.505..361B    Altcode: 2002IAUCo.188..361B; 2002solm.conf..361B
  Ephemeral magnetic emergence has been detected in a decaying β region
  observed in December 2001 simultaneously with the DOT and THEMIS. We
  present here the main characteristics of this phenomenon. Also the
  time evolution of a small group of pores is shown together with the
  time evolution of an horizontal magnetic field overlying them.

---------------------------------------------------------
Title: Fine structure in sunspots. IV. Penumbral grains in speckle
    reconstructed images
Authors: Sobotka, M.; Sütterlin, P.
2001A&A...380..714S    Altcode:
  The properties of penumbral grains (PGs) in a large regular sunspot
  are studied from a 70 min sequence of G-band images acquired on 20
  September 1999 at the Dutch Open Telescope, La Palma. The frames were
  processed using the speckle masking algorithm, resulting in an almost
  diffraction-limited time series (30 s cadence), basically free of
  atmospheric distortions. Applying feature tracking to a movie of 140
  frames yields proper motions, intensities, and lifetimes for a set of
  1058 PGs with lifetimes longer than 10 min. About 54% of the PGs move
  toward the umbra and 46% toward the photosphere. The inward-moving
  PGs are located mostly in the inner penumbra (up to 0.6 of the
  distance from the umbra to the photosphere). Their average lifetime
  and median speed are 50 min and 0.52 km s<SUP>-1</SUP>. Most of the
  outward-moving PGs are observed in the outer penumbra and their average
  lifetime and median speed are 31 min and 0.75 km s<SUP>-1</SUP>. These
  measurements confirm the previous results published by Sobotka et
  al. (\cite{sobotka99_AA348}).

---------------------------------------------------------
Title: Penumbral finestructure: need for larger telescopes
Authors: Balthasar, H.; Sütterlin, P.; Collados, M.
2001AN....322..367B    Altcode:
  We obtained at the same time G-band images at the Dutch Open Telescope
  (DOT) on La Palma and spectropolarimetric data in the near infrared
  at the German Vacuum Tower Telescope (VTT) on Tenerife. The
  spectropolarimetric data show interesting correlations. Bright
  filaments have a smaller magnetic field s trength, and higher
  Evershed velocities occur in dark structures. This result is in
  agreement with some previous observations, but also in contradiction
  to others. However, we suffer from the fact that the resolution limit
  of the VTT at a wavelength of 1.565 μm corresponds to 400 km. Spatial
  power spectra derived from the DOT data indicate a typical width of
  250 km for penumbral filaments. Obviously a solar telescope with an
  aperture of at least 1.5~m is needed to obtain sophisticated results
  for penumbral structures.

---------------------------------------------------------
Title: Ba II 4554 Å speckle imaging as solar Doppler diagnostic
Authors: Sütterlin, P.; Rutten, R. J.; Skomorovsky, V. I.
2001A&A...378..251S    Altcode:
  We present observations testing the Dopplergram capability of a
  narrow-band (80 mÅ) Lyot filter imaging the solar surface in the
  wings of the Ba II 4554 Å resonance line in combination with speckle
  reconstruction to obtain high angular resolution. The Ba II 4554 Å line
  is found to be an excellent tool for high-resolution Doppler mapping
  thanks to opacity insensitivity to temperature variations and line-width
  insensitivity to thermal broadening. The resulting Dopplergrams show
  concentrated downflows of 1.2-2.2 km;s<SUP>-1</SUP> in intergranular
  lanes that probably mark magnetic fluxtubes. Two-wavelength
  profile sampling is found to suffice for high-resolution Dopplergram
  construction. The filter will be installed as part of a multi-wavelength
  speckle imaging system on the new Dutch Open Telescope.

---------------------------------------------------------
Title: The size of penumbral fine structure
Authors: Sütterlin, P.
2001A&A...374L..21S    Altcode:
  I present power spectra of penumbral and granular intensity variations
  from a speckle-restored G-band image sequence of sunspot NOAA 9407 taken
  on April 1, 2001 with the Dutch Open Telescope on La Palma. I compare
  spatial power spectra of the sunspot penumbra with spatial power spectra
  from granulation with and without filigree. Relative to the granular
  power distribution, the penumbral power spectrum is enhanced over a wide
  range in spatial frequency peaking at 0\farcs35. For smaller scales,
  the penumbral power distribution closely resembles that of the granular
  intensity variations. In contrast, the power spectrum of granulation
  with filigree exhibits increased power down to the resolution limit
  of 0\farcs22, indicating the presence of unresolved magnetic elements.

---------------------------------------------------------
Title: Active Region Oscillations: Results from SOHO JOP 097
Authors: O'Shea, E.; Fleck, B.; Muglach, K.; Sütterlin, P.
2001AGUSM..SH41A02O    Altcode:
  We present here an analysis of data obtained in a sunspot region,
  using the Coronal Diagnostic Spectrometer (CDS) on SOHO. These data
  were obtained in the context of the Joint Observing Program (JOP)
  97 which, together with CDS, included the Michelson Doppler Imaging
  (MDI) instrument on SOHO, the TRACE satellite and various ground
  based observatories, e.g. the DOT on La Palma. Using the lines of
  Fe XVI 335, Mg IX 368, He I 584, O III 599, Mg X 624 and O V 624 of
  CDS time series data were obtained in the pore and plage regions of
  sunspots associated with active regions AR 9166, 9166 and 9169 between
  September 19-29 2000. In addition to the time series datasets we also
  obtained 240 arcsec x 240 arcsec raster images of the sunspot regions
  examined. Using different time series analysis techniques we analyse
  the different periods of oscillation found in time series datasets and
  present the results here. This research is part of the European Solar
  Magnetometry Network supported by the EC through the TMR programme.

---------------------------------------------------------
Title: Penumbral Finestructure: Need for Larger Telescopes
Authors: Balthasar, H.; Sütterlin, P.; Collados, M.
2001AGM....18S1003B    Altcode:
  We obtained at the same time G-band images at the Dutch Open
  Telescope (DOT) on La Palma and spectropolarimetric data in the near
  infrared at the German Vacuum Tower Telescope (VTT) on Tenerife. The
  spectropolarimetric data show interesting correlations. Bright filaments
  have a smaller magnetic field strength, and higher Evershed velocities
  occur in dark structures. This result is in agreement with some previous
  observations, but also in contradiction to others. However, we suffer
  from the fact that the resolution limit of the VTT at a wavelength
  of 1.565 μm corresponding to 400 km. Spatial power spectra derived
  from the DOT data indicate a typical width of 250 km for the penumbral
  filaments. Obviously a solar telescope with an aperture of at least 1.5
  m is needed to obtain sophisticated results for penumbral structures.

---------------------------------------------------------
Title: Proxy Magnetometry with the Dutch Open Telescope
Authors: Rutten, R. J.; Hammerschlag, R. H.; Sütterlin, P.; Bettonvil,
   F. C. M.
2001ASPC..236...25R    Altcode: 2001aspt.conf...25R
  No abstract at ADS

---------------------------------------------------------
Title: A Multi-Channel Speckle Imaging System for the DOT
Authors: Sütterlin, P.; Hammerschlag, R. H.; Bettonvil, F. C. M.;
   Rutten, R. J.; Skomorovsky, V. I.; Domyshev, G. N.
2001ASPC..236..431S    Altcode: 2001aspt.conf..431S
  No abstract at ADS

---------------------------------------------------------
Title: Dutch Open Telescope: Status and Prospects
Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. M.;
   Suetterlin, P.
2000SPD....3102107R    Altcode: 2000BAAS...32.1290R
  The Dutch Open Telescope (DOT) on La Palma in the Canary Islands is
  a small but revolutionary solar telescope of which the image quality
  matches the superb imaging of the Swedish Vacuum Solar Telescope (from
  whose building the DOT is operated). The DOT is an open parabolic 45cm
  reflector on an open 15m high tower, relying on mirror flushing by the
  trade winds that bring the best seeing at La Palma to avoid internal
  turbulence. A water-cooled field stop in the primary image reflects
  most sunlight and heat out of the telescope. The first data from the
  DOT combined with speckle reconstruction have yielded sunspot movies
  of outstanding quality. At present, a multi-channel imaging system is
  in construction for simultaneous registration of speckle sequences in
  the G band, in Ca II K and in Hα. The data pipeline permits continuous
  speckle data acquisition up to 0.5 Tb per day. The advantage of speckle
  reconstruction over adaptive optics is the much larger field of the
  restored scene, with the DOT camera's 100x130 arcsec at 0.2 arcsec
  resolution. The DOT science program is to study magnetic topology and
  dynamics throughout the photosphere and chromosphere.

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Title: Applying speckle masking to spectra
Authors: Sütterlin, P.; Wiehr, E.
2000SoPh..194...35S    Altcode:
  We have applied the technique of speckle masking to spectra. The
  observation of elongated solar structures avoids the problem of missing
  information in one-dimensional spectra. Image motion perpendicular
  to the slit was diminished by a one-dimensional image stabilization
  system. The remaining influence of the Earth's atmosphere was removed
  by a modified speckle-masking algorithm, adapted to the single spatial
  dimension occurring in the spectra. The reconstructed spectra achieve
  the diffraction limit of the telescope and the spectrograph.

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Title: Solar Magnetometry with the Dutch Open Telescope
Authors: Rutten, R.; Hammerschlag, R. H.; Sutterlin, P.; Bettonvil,
   F. C. M.; van der Zalm, E. B. J.
2000ESASP.463..611R    Altcode: 2000sctc.proc..611R
  No abstract at ADS

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Title: Continuum photometry of solar white-light faculae
Authors: Sütterlin, P.; Wiehr, E.; Stellmacher, G.
1999SoPh..189...57S    Altcode:
  We have determined absolute continuum intensities and brightness
  temperatures of individual facular grains at a spatial resolution
  limited by the φ=50 cm aperture of the SVST on La Palma. A facular
  region at θ≈57° was observed simultaneously in three narrow
  continuum windows at 450.5, 658.7, and 863.5 nm. We corrected for
  image degradation by the Earth's atmosphere using the speckle masking
  method. The brightness temperatures do not exactly follow the Planck
  law. The differences of T<SUB>blue</SUB>−T<SUB>red</SUB>=220
  K and T<SUB>ir</SUB>−T<SUB>red</SUB>=−42 K reflect the
  wavelength dependence of the continuum formation depth. The (red)
  temperatures of 250 facular grains show excesses between 250
  and 450 K above their undisturbed neighborhood. The wavelength
  dependence of the relative intensity ratios C<SUB>λ</SUB>=
  [I<SUP>fac</SUP>/I<SUP>phot</SUP>] <SUB>λ</SUB>show a large scatter
  around mean values of C<SUB>blue</SUB>/C<SUB>red</SUB>=1.075 and
  C<SUB>ir</SUB>/C<SUB>red</SUB>=0.98. We determined the center-to-limb
  variation of the 863.5 nm continuum contrast for 0.17&gt;cosθ&gt;0.39
  by measuring 270 grains in reconstructed facular images. The
  upper envelope of the data points increases linearly to 1.5 at
  cos θ=0.17. Application of the mean color dependence yields green
  contrasts up to C<SUB>550</SUB>=1.7, which is far higher than previously
  observed values. The behaviour for cos θ&gt;0.17 is estimated from
  (unreconstructed) frame-selected best images taken over a time interval
  of 7 hours. Six distinct facular regions clearly discernible during
  the whole time interval indicate a slight contrast decrease towards
  the extreme limb. The observed quantities are useful for an adjustment
  of model calculations and for a discrimination of competing models.

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Title: Automatic guiding of the primary image of solar Gregory
    telescopes
Authors: Küveler, G.; Wiehr, E.; Thomas, D.; Harzer, M.; Bianda,
   M.; Epple, A.; Sütterlin, P.; Weisshaar, E.
1998SoPh..182..247K    Altcode:
  The primary image reflected from the field stop of solar Gregory
  telescopes is used for automatic guiding. This new system avoids
  temporal varying influences from the bending of the telescope tube by
  the main mirror's gravity and from offsets between the telescope and
  a separate guiding refractor. The required stiffness of the guider
  mechanics and the small areas of the sensors demand small f numbers
  for the guider optics, which cause problems with the image quality and
  with heat. Problems also arise from the pinhole in the telescope's
  field stop which is imaged as a dark dot on the sensor. Pointing
  errors introduced by the telescope affect shifts of the solar image
  on the sensor. These are numerically determined by Fourier methods
  which are found to be less sensitive to noise than profile centering
  methods. Several types of guiders are tested, the final equipment,
  now installed at the Gregory telescopes at Tenerife and at Locarno,
  is described.

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Title: Temperature mapping of sunspots and pores from speckle
    reconstructed three colour photometry
Authors: Suetterlin, P.; Wiehr, E.
1998A&A...336..367S    Altcode:
  The two-dimensional temperature distribution in a highly structured
  sunspot and in two small umbrae is determined from a three-colour
  photometry in narrow spectral continua. Disturbing influences from
  the earth's atmosphere are removed by speckle masking techniques,
  yielding a spatial resolution limited by the telescope's aperture. The
  corresponding colour temperatures are consistent over a range of
  more than 2000 K, although the numerical correction introduced by
  the reconstruction differs largely for the three colours. Part of the
  scatter in the temperature relation disappears when convoluting the
  final images with artificial PSFs that compensate for the different,
  colour dependent spatial resolution. The remaining spread in the
  scatter plots does not reflect noise, but is related to local
  variations of the temperature difference between the continuum
  emitting layers. This is most obvious for a small umbra which yields
  `branches' in the scatter plots the `bluer' of which corresponding to
  the limb-side umbral border. Here, the `hot rim' of a Wilson depressed
  umbra becomes visible. The temperature map of the large spot shows that
  the bright umbral dots do not reach the temperature of the non-spot
  surroundings. Instead, they exceed the 2000 K cooler umbral temperature
  minimum by 900-1300 K. The filamentary structure of the surrounding
  penumbra has spatial temperature fluctuations of typically 700 K,
  a value which fits earlier observed contrasts. However, the mean
  temperatures of 5650 K in the dark and 6250 K in the bright penumbral
  fine structures exceed former findings. Exceptionally bright penumbral
  grains are 250 K hotter than the mean solar surface and thus exceed
  even brightest granules.

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Title: Properties of solar pores
Authors: Suetterlin, Peter
1998A&A...333..305S    Altcode:
  We present the results of an extensive investigation of the properties
  of solar pores. Spectra of all 4 Stokes parameters of several magnetic
  sensitive absorption lines as well as Stokes ( I ) only spectra of lines
  with low or vanishing Lande-factor have been observed. An inversion code
  based on the Levenberg-Marquardt algorithm was written, incorporating
  the full radiative transfer equations. This code adapts a set of
  parameters that are used to represent the magnetic and thermodynamic
  state of the atmosphere to best-fit a set of observed line profiles. The
  results show that the value of all relevant parameters are intimately
  related to the size of the pores, therewith confirming the role of solar
  pores as a link between (bright) magnetic flux tubes and sunspots. In
  particular the inclination of the magnetic field lines at the outer
  rim of a pore, which is affected by the vertical field gradient, seems
  to put an upper limit on the diameter of pores where the inclination
  reaches a value that might trigger the formation of a penumbra.

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Title: Simultaneous Observations with the GCT and SoHO: High Velocity
    Events in the Upper Chromosphere
Authors: Muglach, K.; Sütterlin, P.
1998ASPC..155..341M    Altcode: 1998sasp.conf..341M
  No abstract at ADS

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Title: 3-Color Photometry of a Sunspot Using Speckle Masking
    Techniques
Authors: Sütterlin, P.; Wiehr, E.
1998ASPC..155...44S    Altcode: 1998sasp.conf...44S
  No abstract at ADS

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Title: Prominence Emissions with SUMER and Optical Telescopes
Authors: Wiehr, E.; Stellmacher, G.; de Boer, C. R.; Sütterlin, P.
1998ASPC..155..331W    Altcode: 1998sasp.conf..331W
  No abstract at ADS

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Title: Problems in measuring prominence oscillations.
Authors: Suetterlin, P.; Wiehr, E.; Bianda, M.; Kueveler, G.
1997A&A...321..921S    Altcode:
  Time variations of Doppler shifts of the Ca^+^ 8542Å emission in
  quiescent solar prominences have been measured. A new type of 'limb
  guider' assures a highly constant distance of the spectrograph slit from
  the solar limb and furthermore removes low frequency image motion in the
  direction perpendicular to the slit. Remaining image motion along the
  slit is usually removed by a correlation of subsequent spectra. This
  procedure, however, cannot be applied globally to the whole spatial
  height in the spectra if individual structures exhibit lateral motions
  along the slit or even decay or arise during the observation. We
  therefore correlate defined individual emission maxima from successive
  spectra. The finally obtained power spectra show oscillations with a
  variety of periods at restricted locations. The data favour the known
  general presence of periods near 20 and 60-min, however they give only
  slight indication for `typical' periods near 3 and 5 min.

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Title: Three colour photometry of a sunspot using speckle masking
    techniques.
Authors: Sütterlin, P.; Wiehr, E.
1997AGAb...13...10S    Altcode:
  No abstract at ADS

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Title: Emission Lines in a Quiescent Prominence Observed with the
    SUMER, VTT, a nd Gregory Telescopes
Authors: Wiehr, E.; de Boer, C. R.; Stellmacher, G.; Sutterlin, P.
1997ASPC..118..294W    Altcode: 1997fasp.conf..294W
  A number of emission lines have been observed in a quiescent prominence
  with the two German telescopes on Tenerife and with SUMER. The Gregory
  telescope monitored simultaneously the lines H_8 3889, He 3888, Ca(+\:)
  8498, the VTT simultaneously the lines H_β, He-D_3, Ca(+\:) 8542, and
  H_α slit jaw pictures on 1024 x 1024 CCDs. At the same time, SUMER
  monitored successively three combinations of EUV lines containing He
  584, He 537 in the second, and Ar, N(+) , C, C(++) , O, O(+) , O(++)
  , S(++) , S(+++) lines in the first order. Two dimensional images in
  the various EUV lines establish the anti-relation between temperature
  and Balmer brightness.

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Title: Polarimetry of Solar Pores
Authors: Sütterlin, P.; Schröter, E. H.; Muglach, K.
1996SoPh..164..311S    Altcode:
  We address the magnetic field structure of solar pores. The data
  were obtained at the Gregory Coudè telescope at Izaña using
  the AT1 CCD camera system to observe pores with three spectral
  lines: one magnetically sensitive line, recording all 4 Stokes
  profiles, and two g = 0 lines where only the intensity profiles
  were measured. The data reduction included the standard procedure
  (removing dark current and flatfielding) as well as destretching of
  the polarimetric spectra and removing the non-magnetic straylight by
  means of a 2-d deconvolution of the observed intensity variation using
  a Lucy-Richardson restoration algorithm. In the following analysis we
  first determined the temperature- and pressure stratification of the
  pore using the g = 0 lines and then applied an inversion of the Stokes
  profiles to get the parameters of the magnetic field. Across the pore
  we find a strong variation of the resulting field strength as well as
  of the inclination and the azimuth, consistent with the assumption of
  a canopy forming in the higher atmosphere.

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Title: Über die Struktur von solaren Poren 

---------------------------------------------------------
Title: Über die Struktur
von solaren Poren 

---------------------------------------------------------
Title: On the structure of solar pores;
Authors: Sütterlin, Peter Pit
1996PhDT.......153S    Altcode:
  No abstract at ADS

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Title: Neue Verarbeitungstechniken für CCD-Bilder. Einige Anregungen.
Authors: Sütterlin, P.
1994S&W....33..311S    Altcode:
  No abstract at ADS

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Title: On the magneto-thermodynamical structure of a solar pore
Authors: Sütterlin, P.; Thim, F.; Schröter, E. H.
1994smf..conf..213S    Altcode:
  No abstract at ADS

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Title: Erfahrungen mit CCD-Kameras in der Amateurastronomie.
Authors: Sütterlin, P.
1994aks..1995Q....S    Altcode:
  No abstract at ADS