denker

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Author name code: denker
ADS astronomy entries on 2022-09-14
author:"Denker, Carsten"

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Title: Characterization of chromospheric activity based on
Sun‑as‑a‑star spectral and disk‑resolved activity indices
Authors: Dineva, Ekaterina; Pearson, Jeniveve; Ilyin, Ilya; Verma,
Meetu; Diercke, Andrea; Strassmeier, Klaus G.; Denker, Carsten
2022AN....34323996D Altcode: 2022arXiv220606076D
The strong chromospheric absorption lines Ca H &amp; K are tightly
connected to stellar surface magnetic fields. Only for the Sun, spectral
activity indices can be related to evolving magnetic features on the
solar disk. The Solar Disk-Integrated (SDI) telescope feeds the Potsdam
Echelle Polarimetric and Spectroscopic Instrument (PEPSI) of the Large
Binocular Telescope (LBT) at Mt. Graham International Observatory
(MGIO), Arizona, U.S.A. We present high-resolution, high-fidelity
spectra that were recorded on 184 &amp; 82 days in 2018 &amp; 2019 and
derive the Ca H &amp; K emission ratio, i.e., the S-index. In addition,
we compile excess brightness and area indices based on full-disk Ca
K line-core filtergrams of the Chromospheric Telescope (ChroTel) at
Observatorio del Teide, Tenerife, Spain and full-disk ultraviolet (UV)
1600~Å images of the Atmospheric Imaging Assembly (AIA) on board the
Solar Dynamics Observatory (SDO). Thus, Sun-as-a-star spectral indices
are related to their counterparts derived from resolved images of
the solar chromosphere. All indices display signatures of rotational
modulation, even during the very low magnetic activity in the minimum
of Solar Cycle 24. Bringing together different types of activity
indices has the potential to join disparate chromospheric datasets,
yielding a comprehensive description of chromospheric activity across
many solar cycles.

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Title: Solar Hα excess during Solar Cycle 24 from full-disk
filtergrams of the Chromospheric Telescope
Authors: Diercke, A.; Kuckein, C.; Cauley, P. W.; Poppenhäger, K.;
Alvarado-Gómez, J. D.; Dineva, E.; Denker, C.
2022A&A...661A.107D Altcode: 2022arXiv220304357D
Context. The chromospheric Hα spectral line is a strong line in
the spectrum of the Sun and other stars. In the stellar regime,
this spectral line is already used as a powerful tracer of stellar
activity. For the Sun, other tracers, such as Ca II K, are typically
used to monitor solar activity. Nonetheless, the Sun is observed
constantly in Hα with globally distributed ground-based full-disk
imagers. Aims: The aim of this study is to introduce the imaging
Hα excess and deficit as tracers of solar activity and compare them to
other established indicators. Furthermore, we investigate whether the
active region coverage fraction or the changing Hα excess in the active
regions dominates temporal variability in solar Hα observations. Methods: We used observations of full-disk Hα filtergrams of the
Chromospheric Telescope and morphological image processing techniques
to extract the imaging Hα excess and deficit, which were derived
from the intensities above or below 10% of the median intensity in
the filtergrams, respectively. These thresholds allowed us to filter
for bright features (plage regions) and dark absorption features
(filaments and sunspots). In addition, the thresholds were used to
calculate the mean intensity ImeanE/D for Hα
excess and deficit regions. We describe the evolution of the Hα excess
and deficit during Solar Cycle 24 and compare it to the mean intensity
and other well established tracers: the relative sunspot number, the
F10.7 cm radio flux, and the Mg II index. In particular, we tried to
determine how constant the Hα excess and number density of Hα excess
regions are between solar maximum and minimum. The number of pixels
above or below the intensity thresholds were used to calculate the area
coverage fraction of Hα excess and deficit regions on the Sun, which
was compared to the imaging Hα excess and deficit and the respective
mean intensities averaged for the length of one Carrington rotation. In
addition, we present the Hα excess and mean intensity variation of
selected active regions during their disk passage in comparison to the
number of pixels of Hα excess regions. Results: The Hα excess
and deficit follow the behavior of the solar activity over the course
of the cycle. They both peak around solar maximum, whereby the peak
of the Hα deficit is shortly after the solar maximum. Nonetheless,
the correlation of the monthly averages of the Hα excess and deficit
is high with a Spearman correlation of ρ = 0.91. The Hα excess is
closely correlated to the chromospheric Mg II index with a correlation
of 0.95. The highest correlation of the Hα deficit is found with the
F10.7 cm radio flux, with a correlation of 0.89, due to their peaks
after the solar activity maximum. Furthermore, the Hα deficit reflects
the cyclic behavior of polar crown filaments and their disappearance
shortly before the solar maximum. We investigated the mean intensity
distribution for Hα excess regions for solar minimum and maximum. The
shape of the distributions for solar minimum and maximum is very
similar, but with different amplitudes. Furthermore, we found that the
area coverage fraction of Hα excess regions and the Hα excess are
strongly correlated with an overall Spearman correlation of 0.92. The
correlation between the Hα excess and the mean intensity of Hα excess
regions is 0.75. The correlation of the area coverage fraction and the
mean intensity of Hα excess regions is in general relatively low (ρ =
0.45) and only for few active regions is this correlation above 0.7. The
weak correlation between the area coverage fraction and mean intensity
leaves us pessimistic that the degeneracy between these two quantities
can be broken for the modeling of unresolved stellar surfaces.

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Title: Multiple Stokes I inversions for inferring magnetic fields
in the spectral range around Cr I 5782 Å
Authors: Kuckein, C.; Balthasar, H.; Quintero Noda, C.; Diercke, A.;
Trelles Arjona, J. C.; Ruiz Cobo, B.; Felipe, T.; Denker, C.; Verma,
M.; Kontogiannis, I.; Sobotka, M.
2021A&A...653A.165K Altcode: 2021arXiv210711116K
 Aims: In this work, we explore the spectral window containing
Fraunhofer lines formed in the solar photosphere, around the
magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0,
and 5783.8 Å, with Landé g-factors between 1.6 and 2.5. The goal is
to simultaneously analyze 15 spectral lines, comprising Cr I, Cu I,
Fe I, Mn I, and Si I lines, without the use of polarimetry, to infer
the thermodynamic and magnetic properties in strongly magnetized
plasmas using an inversion code. Methods: Our study is based
on a new setup at the Vacuum Tower Telescope (VTT, Tenerife), which
includes fast spectroscopic scans in the wavelength range around
the Cr I 5781.75 Å line. The oscillator strengths log(gf) of all
spectral lines, as well as their response functions to temperature,
magnetic field, and Doppler velocity, were determined using the Stokes
Inversion based on Response functions (SIR) code. Snapshot 385 of the
enhanced network simulation from the Bifrost code serves to synthesize
all the lines, which are, in turn, inverted simultaneously with SIR to
establish the best inversion strategy. We applied this strategy to VTT
observations of a sunspot belonging to NOAA 12723 on 2018 September
30 and compared the results to full-disk vector field data obtained
with the Helioseismic and Magnetic Imager (HMI). Results: The
15 simultaneously inverted intensity profiles (Stokes I) delivered
accurate temperatures and Doppler velocities when compared with the
simulations. The derived magnetic fields and inclinations achieve
the best level of accuracy when the fields are oriented along the
line-of-sight (LOS) and less accurate when the fields are transverse to
the LOS. In general, the results appear similar to what is reported in
the HMI vector-field data, although some discrepancies exist. 
Conclusions: The analyzed spectral range has the potential to deliver
thermal, dynamic, and magnetic information for strongly magnetized
features on the Sun, such as pores and sunspots, even without the use
of polarimetry. The highest sensitivity of the lines is found in the
lower photosphere, on average, around log τ = −1. The multiple-line
inversions provide smooth results across the whole field of view
(FOV). The presented spectral range and inversion strategy will be
used for future VTT observing campaigns.

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Title: Study Of Global-scale Surface Flows Of The Sun In Past 10
Solar Cycles
Authors: Li, Q.; Xu, Y.; Verma, M.; Denker, C.; Wang, H.
2021AAS...23811323L Altcode:
Surface flows have played essential roles in predicting solar cycles and
have connections with the solar dynamo signatures. In order to provide
the surface flows, such as meridional flows, differential rotation,
and zonal flows, in 10 solar cycles, as input for the dynamo and solar
cycle modeling, we track the flows from Halpha images as a proxy for
magnetic features using Local Correlation Tracking (LCT) tool. We aim
to provide the long-term observational constraints of surface flows,
including hemispheric and latitudinal dependence. In this work, we
present the updated results of the derived flow maps using the HMI/MDI
data from Solar Dynamics Observatory (SDO) and H-alpha data from
Kanzelho ̈he Solar Observatory (KSO), respectively, in order to have
a comprehensive analysis over Solar Cycle 23 and 24. The signatures of
torsional oscillation in ~ eight-year period and excessive meridional
flow can be observed along with the Solar Maximum/Minimum from both
photosphere and chromosphere.

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Title: Characterization of Chromospheric Activity Based on
Sun-as-a-star Spectral and Disk-resolved Observations
Authors: Dineva, Ekaterina; Pearson, Jeniveve; Verman, Meetu; Ilyin,
Ilya; Strassmeier, Klaus G.; Denker, Carsten
2021csss.confE.130D Altcode:
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI)
is a state-of-the-art, thermally stabilized, fiber-fed, high-resolution
spectrograph for the Large Binocular Telescope (LBT) at Mt. Graham,
Arizona. It can be fed with sunlight from the Solar Disk-Integrated
(SDI) telescope. Synoptic solar observations with PEPSI/SDI produce
daily spectra with high signal-to-noise ratio, providing access to
unprecedented, quasi-continuous, long-term, disk-integrated spectra of
the Sun with high spectral and temporal resolution. The observed spectra
contain a multitude of photospheric and chromospheric spectral lines
in the wavelength range of 380 910 nm. Strong chromospheric absorption
lines, such as the Ca II H &amp; K lines, are powerful diagnostic
tools for solar activity studies, since they trace the variations
of the solar magnetic field. Derivation of activity indices, such
as the Ca II H &amp; K emission ratio S-index provides insight into
the chromospheric magnetic field and its variability over the solar
activity cycle. The well known relation between solar calcium indices
and UV flux variations motivates us to compute an excess brightness
indices from Ca II K full-disk images from of the Chromospheric
Telescope (ChroTel) at the Observatory del Teide on Tenerife, Spain
and UV data of the Solar Dynamics Observatory (SDO). We present a
set of indices representing magnetic activity at various heights in
the solar atmosphere. In the present work, we carefully compare the
indices computed from various datasets and discuss the differences in
terms of physical and observational properties.

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Title: Wavelength Dependence of Image Quality Metrics and Seeing
Parameters and Their Relation to Adaptive Optics Performance
Authors: Kamlah, R.; Verma, M.; Diercke, A.; Denker, C.
2021SoPh..296...29K Altcode: 2020arXiv201104346K
Ground-based solar observations are severely affected by Earth's
turbulent atmosphere. As a consequence, observed image quality and
prevailing seeing conditions are closely related. Partial correction
of image degradation is nowadays provided in real time by adaptive
optics (AO) systems. In this study, different metrics of image
quality are compared with parameters characterizing the prevailing
seeing conditions, i.e. Median Filter Gradient Similarity (MFGS),
Median Filter Laplacian Similarity (MFLS), Helmli-Scherer mean,
granular rms-contrast, differential image motion, and Fried-parameter
r0. The quiet-Sun observations at disk center were carried
out at the Vacuum Tower Telescope (VTT), Observatorio del Teide
(OT), Izaña, Tenerife, Spain. In July and August 2016, time series
of short-exposure images were recorded with the High-resolution Fast
Imager (HiFI) at various wavelengths in the visible and near-infrared
parts of the spectrum. Correlation analysis yields the wavelength
dependence of the image quality metrics and seeing parameters, and
Uniform Manifold Approximation and Projection (UMAP) is employed to
characterize the seeing on a particular observing day. In addition, the
image quality metrics and seeing parameters are used to determine the
field dependence of the correction provided by the AO system. Management
of high-resolution imaging data from large-aperture, ground-based
telescopes demands reliable image quality metrics and meaningful
characterization of prevailing seeing conditions and AO performance. The
present study offers guidance on how retrieving such information ex
post facto.

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Title: Filigree in the Surroundings of Polar Crown and High-Latitude
Filaments
Authors: Diercke, Andrea; Kuckein, Christoph; Verma, Meetu; Denker,
Carsten
2021SoPh..296...35D Altcode: 2020arXiv201204349D
High-resolution observations of polar crown and high-latitude filaments
are scarce. We present a unique sample of such filaments observed in
high-resolution Hα narrow-band filtergrams and broad-band images,
which were obtained with a new fast camera system at the Vacuum Tower
Telescope (VTT), Tenerife, Spain. The Chromospheric Telescope (ChroTel)
provided full-disk context observations in Hα , Ca II K, and He I 10830
Å. The Helioseismic and Magnetic Imager (HMI) and the Atmospheric
Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO)
provided line-of-sight magnetograms and ultraviolet (UV) 1700 Å
filtergrams, respectively. We study filigree in the vicinity of polar
crown and high-latitude filaments and relate their locations to magnetic
concentrations at the filaments' footpoints. Bright points are a well
studied phenomenon in the photosphere at low latitudes, but they were
not yet studied in the quiet network close to the poles. We examine
size, area, and eccentricity of bright points and find that their
morphology is very similar to their counterparts at lower latitudes,
but their sizes and areas are larger. Bright points at the footpoints of
polar crown filaments are preferentially located at stronger magnetic
flux concentrations, which are related to bright regions at the border
of supergranules as observed in UV filtergrams. Examining the evolution
of bright points on three consecutive days reveals that their amount
increases while the filament decays, which indicates they impact the
equilibrium of the cool plasma contained in filaments.

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Title: Classification of High-resolution Solar Hα Spectra Using
t-distributed Stochastic Neighbor Embedding
Authors: Verma, Meetu; Matijevič, Gal; Denker, Carsten; Diercke,
Andrea; Dineva, Ekaterina; Balthasar, Horst; Kamlah, Robert;
Kontogiannis, Ioannis; Kuckein, Christoph; Pal, Partha S.
2021ApJ...907...54V Altcode: 2020arXiv201113214V
The Hα spectral line is a well-studied absorption line
revealing properties of the highly structured and dynamic solar
chromosphere. Typical features with distinct spectral signatures in
Hα include filaments and prominences, bright active-region plages,
superpenumbrae around sunspots, surges, flares, Ellerman bombs,
filigree, and mottles and rosettes, among others. This study is
based on high-spectral resolution Hα spectra obtained with the
Echelle spectrograph of the Vacuum Tower Telescope (VTT) located at
Observatorio del Teide, Tenerife, Spain. The t-distributed stochastic
neighbor embedding (t-SNE) is a machine-learning algorithm, which
is used for nonlinear dimensionality reduction. In this application,
it projects Hα spectra onto a two-dimensional map, where it becomes
possible to classify the spectra according to results of cloud model
(CM) inversions. The CM parameters optical depth, Doppler width,
line-of-sight velocity, and source function describe properties of
the cloud material. Initial results of t-SNE indicate its strong
discriminatory power to separate quiet-Sun and plage profiles from
those that are suitable for CM inversions. In addition, a detailed
study of various t-SNE parameters is conducted, the impact of seeing
conditions on the classification is assessed, results for various types
of input data are compared, and the identified clusters are linked
to chromospheric features. Although t-SNE proves to be efficient
in clustering high-dimensional data, human inference is required at
each step to interpret the results. This exploratory study provides
a framework and ideas on how to tailor a classification scheme toward
specific spectral data and science questions.

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Title: Study of Global-Scale Surface Flows of the Sun in Past 10
Solar Cycles
Authors: Li, Q.; Xu, Y.; Verma, M.; Denker, C.; Wang, H.
2020AGUFMSH0020025L Altcode:
Surface flows have played essential roles in predicting solar cycles
and connecting the signatures of the solar dynamo. In order to provide
the surface flows, such as meridional flows, differential rotation,
and zonal flows, in 10 solar cycles, as input for the dynamo and
solar cycle modeling, we track the flows from Halpha images as a
proxy for magnetic features using Local Correlation Tracking (LCT)
tool. In this work, we present the preliminary result of the derived
flow maps using the Halpha data from Kanzelho ̈he Solar Observatory
(KSO). The correlation between the chromospheric flows and surface
flows makes deriving the surface flows on a wide range of time-scales
achievable. We aim to provide the long-term observational constraints
of surface flows, including hemispheric and latitudinal dependence.

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Title: Observational study of chromospheric heating by acoustic waves
Authors: Abbasvand, V.; Sobotka, M.; Švanda, M.; Heinzel, P.;
García-Rivas, M.; Denker, C.; Balthasar, H.; Verma, M.; Kontogiannis,
I.; Koza, J.; Korda, D.; Kuckein, C.
2020A&A...642A..52A Altcode: 2020arXiv200802688A
 Aims: Our aim is to investigate the role of acoustic and
magneto-acoustic waves in heating the solar chromosphere. Observations
in strong chromospheric lines are analyzed by comparing the deposited
acoustic-energy flux with the total integrated radiative losses. Methods: Quiet-Sun and weak-plage regions were observed in the Ca
II 854.2 nm and Hα lines with the Fast Imaging Solar Spectrograph
(FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and
in the Hα and Hβ lines with the echelle spectrograph attached
to the Vacuum Tower Telescope on 2018 December 11 and 2019 June
6. The deposited acoustic energy flux at frequencies up to 20 mHz
was derived from Doppler velocities observed in line centers and
wings. Radiative losses were computed by means of a set of scaled
non-local thermodynamic equilibrium 1D hydrostatic semi-empirical
models obtained by fitting synthetic to observed line profiles. 
Results: In the middle chromosphere (h = 1000-1400 km), the radiative
losses can be fully balanced by the deposited acoustic energy flux in
a quiet-Sun region. In the upper chromosphere (h &gt; 1400 km), the
deposited acoustic flux is small compared to the radiative losses in
quiet as well as in plage regions. The crucial parameter determining
the amount of deposited acoustic flux is the gas density at a given
height. Conclusions: The acoustic energy flux is efficiently
deposited in the middle chromosphere, where the density of gas is
sufficiently high. About 90% of the available acoustic energy flux in
the quiet-Sun region is deposited in these layers, and thus it is a
major contributor to the radiative losses of the middle chromosphere. In
the upper chromosphere, the deposited acoustic flux is too low, so that
other heating mechanisms have to act to balance the radiative cooling.

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Title: Study of Global-Scale Surface Flows of the Sun in Past 10
Solar Cycles
Authors: Li, Q.; Xu, Y.; Denker, C.; Verma, M.; Wang, H.
2020SPD....5120901L Altcode:
Surface flows have played essential roles in predicting solar cycles
and have connections with the signatures of the solar dynamo. In order
to provide the surface flows, such as meridional flows, differential
rotation, and zonal flows, in 10 solar cycles, as input for the dynamo
and solar cycle modeling, we track the flows from Halpha images as
a proxy for magnetic features using Local Correlation Tracking (LCT)
tool. In this work, we present the preliminary result of the derived
flow maps using the Halpha data from Kanzelho ̈he Solar Observatory
(KSO). The correlation between the chromospheric flows and surface
flows makes deriving the surface flows on a wide range of time-scales
achievable. We aim to provide the long-term observational constraints
of surface flows, including hemispheric and latitudinal dependence.

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Title: High-resolution Spectroscopy of an Erupting Minifilament and
Its Impact on the Nearby Chromosphere
Authors: Kontogiannis, I.; Dineva, E.; Diercke, A.; Verma, M.; Kuckein,
C.; Balthasar, H.; Denker, C.
2020ApJ...898..144K Altcode: 2020arXiv200701564K
We study the evolution of a minifilament eruption in a quiet region
at the center of the solar disk and its impact on the ambient
atmosphere. We used high spectral resolution imaging spectroscopy in
Hα acquired by the echelle spectrograph of the Vacuum Tower Telescope,
Tenerife, Spain; photospheric magnetic field observations from the
Helioseismic Magnetic Imager; and UV/EUV imaging from the Atmospheric
Imaging Assembly of the Solar Dynamics Observatory. The Hα line
profiles were noise-stripped using principal component analysis
and then inverted to produce physical and cloud model parameter
maps. The minifilament formed between small-scale, opposite-polarity
magnetic features through a series of small reconnection events, and
it erupted within an hour after its appearance in Hα. Its development
and eruption exhibited similarities to large-scale erupting filaments,
indicating the action of common mechanisms. Its eruption took place in
two phases, namely, a slow rise and a fast expansion, and it produced
a coronal dimming, before the minifilament disappeared. During its
eruption, we detected a complicated velocity pattern, indicative of
a twisted, thread-like structure. Part of its material returned to
the chromosphere, producing observable effects on nearby low-lying
magnetic structures. Cloud model analysis showed that the minifilament
was initially similar to other chromospheric fine structures, in terms
of optical depth, source function, and Doppler width, but it resembled a
large-scale filament on its course to eruption. High spectral resolution
observations of the chromosphere can provide a wealth of information
regarding the dynamics and properties of minifilaments and their
interactions with the surrounding atmosphere.

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Title: Solar observatory Einstein Tower: Data release of the digitized
solar full-disk photographic plate archive
Authors: Pal, Partha S.; Verma, Meetu; Rendtel, Jürgen; González
Manrique, Sergio Javier; Enke, Harry; Denker, Carsten
2020AN....341..575P Altcode: 2020arXiv200714744P
We present solar full-disk observations that were recorded
at the Einstein Tower during the years 1943-1991 (solar cycles
18-22). High-school students from Potsdam and Berlin digitized more than
3,500 full-disk images during 2-3-week internships at Leibniz-Institut
für Astrophysik Potsdam (AIP). The digital images cover a 15 cm × 15
cm region on photographic plates, which were scanned at a resolution
of 7,086 × 7,086 pixels. The raw data are monochromatic 8-bit images
in the tagged image file format (TIFF). These images were calibrated
and saved with improved photometric precision as 16-bit images with
2,048 × 2,048 pixels in the Flexible Image Transport System (FITS)
format, which contains extensive headers describing the full-disk
images and the observations. The various calibration steps include,
for example, accurate measurements of the solar radius, determination
of the limb-darkening function, and establishing an accurate coordinate
system. The contrast-enhanced and limb-darkening corrected images,
as well as the raw data, are freely available to researchers and
the general public in a publicly accessible repository. The data are
published as a special data release of the Archives of Photographic
PLates for Astronomical USE (APPLAUSE) project.

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Title: The dynamics of a solar arch filament system from the
chromosphere to the photosphere
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Diercke, A.; Collados, M.; Gömöry, P.; Zhong, S.; Hou, Y.; Denker, C.
2020sea..confE.199G Altcode:
We study the dynamics of plasma along the legs of an arch filament
system (AFS) from the chromosphere to the photosphere, observed with
high-cadence spectroscopic data from two ground-based solar telescopes:
the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph
in the He I 10830 Å range and the Swedish Solar Telescope (La Palma)
using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542
Å and Fe I 6173 Å spectral lines. The temporal evolution of the
draining of the plasma was followed along the legs of a single arch
filament from the chromosphere to the photosphere. The average Doppler
velocities inferred at the upper chromosphere from the He I 10830 Å
triplet reach velocities up to 20-24 km s-1, and in the lower
chromosphere and upper photosphere the Doppler velocities reach up to
11 km s-1 and 1.5 km s-1 in the case of the Ca II
8542 Å and Si I 10827 Å spectral lines, respectively. The evolution
of the Doppler velocities at different layers of the solar atmosphere
(chromosphere and upper photosphere) shows that they follow the same
line-of-sight (LOS) velocity patern, which confirms the observational
evidence that the plasma drains toward the photosphere as proposed in
models of AFSs. The observations and the nonlinear force-free field
(NLFFF) extrapolations demonstrate that the magnetic field loops of
the AFS rise with time.

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Title: The STIX Aspect System (SAS): The Optical Aspect System of
the Spectrometer/Telescope for Imaging X-Rays (STIX) on Solar Orbiter
Authors: Warmuth, A.; Önel, H.; Mann, G.; Rendtel, J.; Strassmeier,
K. G.; Denker, C.; Hurford, G. J.; Krucker, S.; Anderson, J.;
Bauer, S. -M.; Bittner, W.; Dionies, F.; Paschke, J.; Plüschke,
D.; Sablowski, D. P.; Schuller, F.; Senthamizh Pavai, V.; Woche, M.;
Casadei, D.; Kögl, S.; Arnold, N. G.; Gröbelbauer, H. -P.; Schori,
D.; Wiehl, H. J.; Csillaghy, A.; Grimm, O.; Orleanski, P.; Skup,
K. R.; Bujwan, W.; Rutkowski, K.; Ber, K.
2020SoPh..295...90W Altcode:
The Spectrometer/Telescope for Imaging X-rays (STIX) is a remote
sensing instrument on Solar Orbiter that observes the hard X-ray
bremsstrahlung emission of solar flares. This paper describes the
STIX Aspect System (SAS), a subunit that measures the pointing of
STIX relative to the Sun with a precision of ±4″, which
is required to accurately localize the reconstructed X-ray images on
the Sun. The operating principle of the SAS is based on an optical
lens that images the Sun onto a plate that is perforated by small
apertures arranged in a cross-shaped configuration of four radial
arms. The light passing through the apertures of each arm is detected
by a photodiode. Variations of spacecraft pointing and of distance
from the Sun cause the solar image to move over different apertures,
leading to a modulation of the measured lightcurves. These signals are
used by ground analysis to calculate the locations of the solar limb,
and hence the pointing of the telescope.

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Title: High-resolution spectroscopy of a surge in an emerging
flux region
Authors: Verma, M.; Denker, C.; Diercke, A.; Kuckein, C.; Balthasar,
H.; Dineva, E.; Kontogiannis, I.; Pal, P. S.; Sobotka, M.
2020A&A...639A..19V Altcode: 2020arXiv200503966V
 Aims: The regular pattern of quiet-Sun magnetic fields was
disturbed by newly emerging magnetic flux, which led a day later to
two homologous surges after renewed flux emergence, affecting all
atmospheric layers. Hence, simultaneous observations in different
atmospheric heights are needed to understand the interaction of
rising flux tubes with the surrounding plasma, in particular by
exploiting the important diagnostic capabilities provided by the
strong chromospheric Hα line regarding morphology and energetic
processes in active regions. Methods: A newly emerged active
region NOAA 12722 was observed with the Vacuum Tower Telescope (VTT)
at Observatorio del Teide, Tenerife, Spain, on 11 September 2018. High
spectral resolution observations using the echelle spectrograph in the
chromospheric Hαλ6562.8 Å line were obtained in the early growth
phase. Noise-stripped Hα line profiles yield maps of line-core and
bisector velocities, which were contrasted with velocities inferred
from Cloud Model inversions. A high-resolution imaging system recorded
simultaneously broad- and narrowband Hα context images. The Solar
Dynamics Observatory provided additional continuum images, line-of-sight
(LOS) magnetograms, and UV and extreme UV (EUV) images, which link the
different solar atmospheric layers. Results: The active region
started as a bipolar region with continuous flux emergence when a new
flux system emerged in the leading part during the VTT observations,
resulting in two homologous surges. While flux cancellation at the
base of the surges provided the energy for ejecting the cool plasma,
strong proper motions of the leading pores changed the magnetic
field topology making the region susceptible to surging. Despite
the surge activity in the leading part, an arch filament system in
the trailing part of the old flux remained stable. Thus, stable
and violently expelled mass-loaded ascending magnetic structures
can coexist in close proximity. Investigating the height dependence
of LOS velocities revealed the existence of neighboring strong up-
and downflows. However, downflows occur with a time lag. The opacity
of the ejected cool plasma decreases with distance from the base of
the surge, while the speed of the ejecta increases. The location at
which the surge becomes invisible in Hα corresponds to the interface
where the surge brightens in He IIλ304 Å. Broad-shouldered and
dual-lobed Hα profiles suggests accelerated or decelerated and
highly structured LOS plasma flows. Significantly broadened Hα
profiles imply significant heating at the base of the surges, which
is also supported by bright kernels in UV and EUV images uncovered
by swaying motions of dark fibrils at the base of the surges. 
Conclusions: The interaction of newly emerging flux with pre-existing
flux concentrations of a young, diffuse active region provided
suitable conditions for two homologous surges. High-resolution
spectroscopy revealed broadened and dual-lobed Hα profiles
tracing accelerated or decelerated flows of cool plasma along the
multi-threaded structure of the surge. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936762/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Magnetic Flux Emergence in a Coronal Hole
Authors: Palacios, Judith; Utz, Dominik; Hofmeister, Stefan; Krikova,
Kilian; Gömöry, Peter; Kuckein, Christoph; Denker, Carsten; Verma,
Meetu; González Manrique, Sergio Javier; Campos Rozo, Jose Iván;
Koza, Július; Temmer, Manuela; Veronig, Astrid; Diercke, Andrea;
Kontogiannis, Ioannis; Cid, Consuelo
2020SoPh..295...64P Altcode: 2020arXiv200611779P
A joint campaign of various space-borne and ground-based observatories,
comprising the Japanese Hinode mission (Hinode Observing Plan 338,
20 - 30 September 2017), the GREGOR solar telescope, and the Vacuum
Tower Telescope (VTT), investigated numerous targets such as pores,
sunspots, and coronal holes. In this study, we focus on the coronal
hole region target. On 24 September 2017, a very extended non-polar
coronal hole developed patches of flux emergence, which contributed
to the decrease of the overall area of the coronal hole. These flux
emergence patches erode the coronal hole and transform the area into a
more quiet-Sun-like area, whereby bipolar magnetic structures play an
important role. Conversely, flux cancellation leads to the reduction
of opposite-polarity magnetic fields and to an increase in the area
of the coronal hole.

---------------------------------------------------------
Title: Monitoring solar activity with PEPSI
Authors: Dineva, Ekaterina; Denker, Carsten; Strassmeier, Klaus G.;
Ilyin, Ilya; Pevtsov, Alexei A.
2020IAUGA..30..351D Altcode:
Synoptic Sun-as-a-star observations are carried out with the Potsdam
Echelle Polarimetric and Spectroscopic Instrument (PEPSI), which
receives light from the Solar Disk-Integration (SDI) telescope. Daily
spectra are produced with a high signal-to-noise ratio, providing access
to unprecedented quasi-continuous, long-term, disk-integrated spectra
of the Sun with high spectral and temporal resolution. We developed
tools to monitor and study solar activity on different time-scales
ranging from daily changes, over periods related to solar rotation,
to annual and decadal trends. Strong chromospheric absorption lines,
such as the Ca ii H &amp; K λ3934 &amp; 3968 Å lines, are powerful
diagnostic tools for solar activity studies, since they trace the
variations of the solar magnetic field. Other lines, such as Hα λ6563
Å line and the near-infrared (NIR) Ca ii λ8542 Å line, provide
additional information on the physical properties in this highly
complex and dynamic atmospheric layer. Currently, we work on a data
pipeline for extraction, calibration, and analysis of the PEPSI/SDI
data. We compare the SDI data with daily spectra from the Integrated
Sunlight Spectrometer (ISS), which is part of the Synoptic Long-Term
Investigation of the Sun (SOLIS) facility operated by the U.S. National
Solar Observatory (NSO). This facilitates cross-calibration and
validation of the SDI data.

---------------------------------------------------------
Title: Synoptic maps in three wavelengths of the Chromospheric
Telescope
Authors: Diercke, Andrea; Denker, Carsten
2020IAUGA..30..339D Altcode:
The Chromospheric Telescope (ChroTel) observes the entire solar disk
since 2011 in three different chromospheric wavelengths: Hα, Ca II K,
and He I. The instrument records full-disk images of the Sun every three
minutes in these different spectral ranges. The ChroTel observations
cover the rising and decaying phase of solar cycle 24. We started
analyzing the ChroTel time-series and created synoptic maps of the
entire observational period in all three wavelength bands. The maps
will be used to analyze the poleward migration of quiet-Sun filaments
in solar cycle 24.

---------------------------------------------------------
Title: Tracking Downflows from the Chromosphere to the Photosphere
in a Solar Arch Filament System
Authors: González Manrique, Sergio Javier; Kuckein, Christoph;
Pastor Yabar, Adur; Diercke, Andrea; Collados, Manuel; Gömöry,
Peter; Zhong, Sihui; Hou, Yijun; Denker, Carsten
2020ApJ...890...82G Altcode: 2020arXiv200107078G
We study the dynamics of plasma along the legs of an arch filament
system (AFS) from the chromosphere to the photosphere, observed with
high-cadence spectroscopic data from two ground-based solar telescopes:
the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph
in the He I 10830 Å range and the Swedish Solar Telescope (La Palma)
using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542
Å and Fe I 6173 Å spectral lines. The temporal evolution of the
draining of the plasma was followed along the legs of a single arch
filament from the chromosphere to the photosphere. The average Doppler
velocities inferred at the upper chromosphere from the He I 10830 Å
triplet reach velocities up to 20-24 km s-1, and in the lower
chromosphere and upper photosphere the Doppler velocities reach up to
11 km s-1 and 1.5 km s-1 in the case of the Ca II
8542 Å and Si I 10827 Å spectral lines, respectively. The evolution
of the Doppler velocities at different layers of the solar atmosphere
(chromosphere and upper photosphere) shows that they follow the same
line-of-sight (LOS) velocity pattern, which confirms the observational
evidence that the plasma drains toward the photosphere as proposed
in models of AFSs. The Doppler velocity maps inferred from the lower
photospheric Ca I 10839 Å or Fe I 6173 Å spectral lines do not
show the same LOS velocity pattern. Thus, there is no evidence that
the plasma reaches the lower photosphere. The observations and the
nonlinear force-free field (NLFFF) extrapolations demonstrate that
the magnetic field loops of the AFS rise with time. We found flow
asymmetries at different footpoints of the AFS. The NLFFF values of
the magnetic field strength help us to explain these flow asymmetries.

---------------------------------------------------------
Title: The magnetic structure and dynamics of a decaying active region
Authors: Kontogiannis, Ioannis; Kuckein, Christoph; González
Manrique, Sergio Javier; Felipe, Tobias; Verma, Meetu; Balthasar,
Horst; Denker, Carsten
2020IAUS..354...53K Altcode:
We study the evolution of the decaying active region NOAA 12708, from
the photosphere up to the corona using high resolution, multi-wavelength
GREGOR observations taken on May 9, 2018. We utilize spectropolarimetric
scans of the 10830 Å spectral range by the GREGOR Infrared Spectrograph
(GRIS), spectral imaging time-series in the Na ID2 spectral
line by the GREGOR Fabry-Pérot Interferometer (GFPI) and context
imaging in the Ca IIH and blue continuum by the High-resolution Fast
Imager (HiFI). Context imaging in the UV/EUV from the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO)
complements our dataset. The region under study contains one pore with a
light-bridge, a few micro-pores and extended clusters of magnetic bright
points. We study the magnetic structure from the photosphere up to the
upper chromosphere through the spectropolarimetric observations in He
II and Si I and through the magnetograms provided by the Helioseismic
and Magnetic Imager (HMI). The high-resolution photospheric images
reveal the complex interaction between granular-scale convective
motions and a range of scales of magnetic field concentrations in
unprecedented detail. The pore itself shows a strong interaction with
the convective motions, which eventually leads to its decay, while,
under the influence of the photospheric flow field, micro-pores
appear and disappear. Compressible waves are generated, which are
guided towards the upper atmosphere along the magnetic field lines of
the various magnetic structures within the field-of-view. Modelling
of the He i absorption profiles reveals high velocity components,
mostly associated with magnetic bright points at the periphery
of the active region, many of which correspond to asymmetric Si I
Stokes-V profiles revealing a coupling between upper photospheric
and upper chromospheric dynamics. Time-series of Na ID2
spectral images reveal episodic high velocity components at the same
locations. State-of-the-art multi-wavelength GREGOR observations allow
us to track and understand the mechanisms at work during the decay
phase of the active region.

---------------------------------------------------------
Title: Measuring the etalon quality of the GREGOR Fabry-Pérot
interferometer
Authors: Verma, Meetu; Denker, Carsten
2020JATIS...6a5001V Altcode:
Imaging spectropolarimetry is an important observational tool in solar
physics because it provides fast-cadence spectral scans with high
spectral resolution, large field-of-view, and inherent suitability
for post facto image restoration. Fabry-Pérot etalons are the key
optical elements of these instruments. Their optical quality critically
defines the instrument's performance. The two etalons of the GREGOR
Fabry-Pérot interferometer were used for more than 10 years, raising
questions about the potential deterioration of etalon coatings. We
present an assessment of the etalons' optical quality, describe the
inspection method based on Zernike polynomials, discuss the field
dependence of the finesse and its consequences for instrument design,
and investigate the impact of the measurement technique to achieve plate
parallelism. We find that extended exposure to sunlight affects the
etalon coatings, i.e., lowering the peak transmission and leaving an
imprint of the pupil of the GREGOR solar telescope on the etalon that
is directly exposed to sunlight. The finesse of both etalons, however,
remains high, so the impact on imaging spectropolarimetry is negligible.

---------------------------------------------------------
Title: Sun-as-a-star observations of the 2017 August 21 solar eclipse
Authors: Dineva, Ekaterina; Denker, Carsten; Verma, Meetu; Strassmeier,
Klaus G.; Ilyin, Ilya; Milic, Ivan
2020IAUS..354..473D Altcode:
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI)
is a state-of-the-art, thermally stabilized, fiber-fed, high-resolution
spectrograph for the Large Binocular Telescope (LBT) at Mt. Graham,
Arizona. During daytime the instrument is fed with sunlight from the
10-millimeter aperture, fully automated, binocular Solar Disk-Integrated
(SDI) telescope. The observed Sun-as-a-star spectra contain a multitude
of photospheric and chromospheric spectral lines in the wavelength
ranges 4200-4800 Å and 5300-6300 Å. One of the advantages of PEPSI
is that solar spectra are recorded in the exactly same manner as
nighttime targets. Thus, solar and stellar spectra can be directly
compared. PEPSI/SDI recorded 116 Sun-as-a-star spectra during the
2017 August 21 solar eclipse. The observed maximum obscuration was
61.6%. The spectra were taken with a spectral resolution of ≈ 250000
and an exposure time of 0.3 s. The high-spectral resolution facilitates
detecting subtle changes in the spectra while the Moon passes the solar
disk. Sun-as-a-star spectra are affected by changing contributions due
to limb darkening and solar differential rotation, and to a lesser
extend by supergranular velocity pattern and the presence of active
regions on the solar surface. The goal of this study is to investigate
the temporal evolution of the chromospheric Na D doublet during the
eclipse and to compare observations with synthetic line profiles
computed with the state-of-the-art Bifrost code.

---------------------------------------------------------
Title: Cloud model inversions of strong chromospheric absorption
lines using principal component analysis
Authors: Dineva, Ekaterina; Verma, Meetu; González Manrique, Sergio
J.; Schwartz, Pavol; Denker, Carsten
2020AN....341...64D Altcode: 2019arXiv191210476D
High-resolution spectroscopy of strong chromospheric absorption
lines delivers nowadays several millions of spectra per observing
day, when using fast scanning devices to cover large regions on
the solar surface. Therefore, fast and robust inversion schemes are
needed to explore the large data volume. Cloud model (CM) inversions
of the chromospheric Hα line are commonly employed to investigate
various solar features including filaments, prominences, surges, jets,
mottles, and (macro-) spicules. The choice of the CM was governed by
its intuitive description of complex chromospheric structures as clouds
suspended above the solar surface by magnetic fields. This study is
based on observations of active region NOAA 11126 in Hα, which were
obtained November 18-23, 2010 with the echelle spectrograph of the
vacuum tower telescope at the Observatorio del Teide, Spain. Principal
component analysis reduces the dimensionality of spectra and conditions
noise-stripped spectra for CM inversions. Modeled Hα intensity and
contrast profiles as well as CM parameters are collected in a database,
which facilitates efficient processing of the observed spectra. Physical
maps are computed representing the line-core and continuum intensity,
absolute contrast, equivalent width, and Doppler velocities, among
others. Noise-free spectra expedite the analysis of bisectors. The data
processing is evaluated in the context of "big data," in particular
with respect to automatic classification of spectra.

---------------------------------------------------------
Title: Emergence of small-scale magnetic flux in the quiet Sun
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.; Gontikakis,
C.; Kuckein, C.; Verma, M.; Denker, C.
2020A&A...633A..67K Altcode: 2019arXiv191202496K
Context. We study the evolution of a small-scale emerging flux region
(EFR) in the quiet Sun, from its emergence in the photosphere to
its appearance in the corona and its decay. Aims: We track
processes and phenomena that take place across all atmospheric layers;
we explore their interrelations and compare our findings with those from
recent numerical modelling studies. Methods: We used imaging
as well as spectral and spectropolarimetric observations from a suite
of space-borne and ground-based instruments. Results: The EFR
appears in the quiet Sun next to the chromospheric network and shows all
morphological characteristics predicted by numerical simulations. The
total magnetic flux of the region exhibits distinct evolutionary phases,
namely an initial subtle increase, a fast increase with a Co-temporal
fast expansion of the region area, a more gradual increase, and a slow
decay. During the initial stages, fine-scale G-band and Ca II H bright
points coalesce, forming clusters of positive- and negative-polarity
in a largely bipolar configuration. During the fast expansion, flux
tubes make their way to the chromosphere, pushing aside the ambient
magnetic field and producing pressure-driven absorption fronts that
are visible as blueshifted chromospheric features. The connectivity
of the quiet-Sun network gradually changes and part of the existing
network forms new connections with the newly emerged bipole. A few
minutes after the bipole has reached its maximum magnetic flux, the
bipole brightens in soft X-rays forming a coronal bright point. The
coronal emission exhibits episodic brightenings on top of a long
smooth increase. These coronal brightenings are also associated
with surge-like chromospheric features visible in Hα, which can
be attributed to reconnection with adjacent small-scale magnetic
fields and the ambient quiet-Sun magnetic field. Conclusions:
The emergence of magnetic flux even at the smallest scales can be the
driver of a series of energetic phenomena visible at various atmospheric
heights and temperature regimes. Multi-wavelength observations reveal
a wealth of mechanisms which produce diverse observable effects during
the different evolutionary stages of these small-scale structures.

---------------------------------------------------------
Title: Measuring the Etalon Quality of the GREGOR Fabry-Pérot
Interferometer
Authors: Verma, Meetu; Denker, Carsten
2020arXiv200101203V Altcode:
Imaging spectropolarimetry is an important observational tool in solar
physics because of fast-cadence spectral scans with high-spectral
resolution, large field-of-view, and its inherent suitability for
post-facto image restoration. Fabry-Pérot etalons are the key optical
elements of these instruments. Their optical quality critically defines
the instrument's performance. The two etalons of the GREGOR Fabry-Pérot
Interferometer (GFPI) were used for more than 10~years, raising
questions about the potential deterioration of etalons coatings. We
present an assessment of the etalons optical quality, describe the
inspection method based on Zernike polynomials, discuss the field
dependence of the finesse and its consequences for instrument design,
and investigate the impact of the measurement technique to achieve
plate parallelism. We find that extended exposure to sunlight affects
the etalon coatings, i.e., lowering the peak transmission and leaving
an imprint of the pupil of the GREGOR solar telescope on the etalon
that is directly exposed to sunlight. The finesse of both etalons,
however, remains high so that the impact on imaging spectropolarimetry
is negligible.

---------------------------------------------------------
Title: Revisiting the building blocks of solar magnetic fields
by GREGOR
Authors: Utz, Dominik; Kuckein, Christoph; Campos Rozo, Jose Iván;
González Manrique, Sergio Javier; Balthasar, Horst; Gömöry,
Peter; Hernández, Judith Palacios; Denker, Carsten; Verma, Meetu;
Kontogiannis, Ioannis; Krikova, Kilian; Hofmeister, Stefan; Diercke,
Andrea
2020IAUS..354...38U Altcode:
The Sun is our dynamic host star due to its magnetic fields causing
plentiful of activity in its atmosphere. From high energetic flares
and coronal mass ejections (CMEs) to lower energetic phenomena such
as jets and fibrils. Thus, it is of crucial importance to learn about
formation and evolution of solar magnetic fields. These fields cover a
wide range of spatial and temporal scales, starting on the larger end
with active regions harbouring complex sunspots, via isolated pores,
down to the smallest yet resolved elements - so-called magnetic bright
points (MBPs). Here, we revisit the various manifestations of solar
magnetic fields by the largest European solar telescope in operation,
the 1.5-meter GREGOR telescope. We show images from the High-resolution
Fast Imager (HiFI) and spectropolarimetric data from the GREGOR Infrared
Spectrograph (GRIS). Besides, we outline resolved convective features
inside the larger structures - so-called light-bridges occurring on
large to mid-sized scales.

---------------------------------------------------------
Title: Chromospheric Synoptic Maps of Polar Crown Filaments
Authors: Diercke, A.; Denker, C.
2019SoPh..294..152D Altcode: 2019arXiv191007943D
Polar crown filaments form above the polarity inversion line between the
old magnetic flux of the previous cycle and the new magnetic flux of
the current cycle. Studying their appearance and their properties can
lead to a better understanding of the solar cycle. We use full-disk
data of the Chromospheric Telescope (ChroTel) at the Observatorio
del Teide, Tenerife, Spain, which were taken in three different
chromospheric absorption lines (Hα λ 6563 Å, Ca II K λ 3933 Å,
and He I λ 10830 Å), and we create synoptic maps. In addition,
the spectroscopic He I data allow us to compute Doppler velocities
and to create synoptic Doppler maps. ChroTel data cover the rising
and decaying phase of Solar Cycle 24 on about 1000 days between 2012
and 2018. Based on these data, we automatically extract polar crown
filaments with image-processing tools and study their properties. We
compare contrast maps of polar crown filaments with those of quiet-Sun
filaments. Furthermore, we present a super-synoptic map summarizing the
entire ChroTel database. In summary, we provide statistical properties,
i.e. number and location of filaments, area, and tilt angle for both
the maximum and the declining phase of Solar Cycle 24. This demonstrates
that ChroTel provides a promising data set to study the solar cycle.

---------------------------------------------------------
Title: Dynamics and connectivity of an extended arch filament system
Authors: Diercke, A.; Kuckein, C.; Denker, C.
2019A&A...629A..48D Altcode: 2019arXiv190801510D
 Aims: In this study, we analyzed a filament system, which
expanded between moving magnetic features (MMFs) of a decaying sunspot
and opposite flux outside of the active region from the nearby
quiet-Sun network. This configuration deviated from a classical
arch filament system (AFS), which typically connects two pores in
an emerging flux region. Thus, we called this system an extended
AFS. We contrasted classical and extended AFSs with an emphasis on the
complex magnetic structure of the latter. Furthermore, we examined the
physical properties of the extended AFS and described its dynamics
and connectivity. Methods: The extended AFS was observed
with two instruments at the Dunn Solar Telescope (DST). The Rapid
Oscillations in the Solar Atmosphere (ROSA) imager provided images
in three different wavelength regions, which covered the dynamics of
the extended AFS at different atmospheric heights. The Interferometric
Bidimensional Spectropolarimeter (IBIS) provided spectroscopic Hα data
and spectropolarimetric data that was obtained in the near-infrared
(NIR) Ca IIλ8542 Å line. We derived the corresponding line-of-sight
(LOS) velocities and used He IIλ304 Å extreme ultraviolet (EUV)
images of the Atmospheric Imaging Assembly (AIA) and LOS magnetograms
of the Helioseismic and Magnetic Imager (HMI) on board the Solar
Dynamics Observatory (SDO) as context data. Results: The
NIR Ca II Stokes-V maps are not suitable to definitively define a
clear polarity inversion line and to classify this chromospheric
structure. Nevertheless, this unusual AFS connects the MMFs of a
decaying sunspot with the network field. At the southern footpoint,
we measured that the flux decreases over time. We find strong downflow
velocities at the footpoints of the extended AFS, which increase
in a time period of 30 min. The velocities are asymmetric at both
footpoints with higher velocities at the southern footpoint. An EUV
brigthening appears in one of the arch filaments, which migrates from
the northern footpoint toward the southern one. This activation likely
influences the increasing redshift at the southern footpoint. Conclusions: The extended AFS exhibits a similar morphology as
classical AFSs, for example, threaded filaments of comparable length
and width. Major differences concern the connection from MMFs around the
sunspot with the flux of the neighboring quiet-Sun network, converging
footpoint motions, and longer lifetimes of individual arch filaments
of about one hour, while the extended AFS is still very dynamic. Movies associated to Figs. 5, 6, and 12 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201935583/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Polarimetry with the GREGOR Fabry-Pérot Interferometer
Authors: Balthasar, H.; Gisler, D.; González Manrique, S. J.; Kuckein,
C.; Verma, M.; Denker, C.
2019spw..confE...3B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Background-Subtracted Solar Activity Maps
Authors: Denker, C.; Verma, M.
2019SoPh..294...71D Altcode: 2019arXiv190506057D
We introduce the concept of a Background-subtracted Solar Activity
Map (BaSAM) as a new quantitative tool to assess and visualize the
temporal variation of the photospheric magnetic field and the UV
λ 160 nm intensity. The method utilizes data of the Solar Dynamics
Observatory (SDO) and is applicable to both full-disk observations and
regions-of-interest. We illustrate and discuss the potential of BaSAM
resorting to datasets representing solar minimum and maximum conditions:
i) Contributions of quiet-Sun magnetic fields, i.e. the network and
(decaying) plage, to solar activity can be better determined when their
variation is measured with respect to the background given by "deep"
magnetograms. ii) Flaring and intermittent brightenings are easily
appraised in BaSAMs of the UV intensity. iii) Both magnetic-field and
intensity variations demonstrated that the flux system of sunspots is
well connected to the surrounding supergranular cells. In addition,
producing daily full-disk BaSAMs for the entire mission time of SDO
provides a unique tool to analyze solar cycle variations, showing
how vigorous or frail the variations of magnetic-field and intensity
features are.

---------------------------------------------------------
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.
2019ASPC..526..217B Altcode: 2018arXiv180401789B
We observed an arch filament system (AFS) in a sunspot group with the
GREGOR Infrared Spectrograph attached to the GREGOR solar telescope. The
AFS was located between the leading sunspot of negative polarity and
several pores of positive polarity forming the following part of the
sunspot group. We recorded five spectro-polarimetric scans of this
region. The spectral range included the spectral lines Si I 1082.7
nm, He I 1083.0 nm, and Ca I 1083.9 nm. In this work we concentrate
on the silicon line which is formed in the upper photosphere. The
line profiles are inverted with the code 'Stokes Inversion based
on Response functions' to obtain the magnetic field vector. The
line-of-sight velocities are determined independently with a Fourier
phase method. Maximum velocities are found close to the ends of AFS
fibrils. These maximum values amount to 2.4 km s-1 next
to the pores and to 4 km s-1 at the sunspot side. Between
the following pores, we encounter an area of negative polarity that
is decreasing during the five scans. We interpret this by new emerging
positive flux in this area canceling out the negative flux. In summary,
our findings confirm the scenario that rising magnetic flux tubes
cause the AFS.

---------------------------------------------------------
Title: Photospheric Magnetic Fields of the Trailing Sunspots in
Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
R.; von der Lühe, O.; Waldmann, T.
2019ASPC..526..291V Altcode: 2018arXiv180507752V
The solar magnetic field is responsible for all aspects of solar
activity. Sunspots are the main manifestation of the ensuing solar
activity. Combining high-resolution and synoptic observations has
the ambition to provide a comprehensive description of the sunspot
growth and decay processes. Active region NOAA 12396 emerged on 2015
August 3 and was observed three days later with the 1.5-meter GREGOR
solar telescope on 2015 August 6. High-resolution spectropolarimetric
data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
with the chromospheric He I λ1083.0 nm triplet. These near-infrared
spectropolarimetric observations were complemented by synoptic
line-of-sight magnetograms and continuum images of the Helioseismic
and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO).

---------------------------------------------------------
Title: Calibration of full-disk He I 10830 Å filtergrams of the
Chromospheric Telescope
Authors: Shen, Zili; Diercke, Andrea; Denker, Carsten
2019AAS...23340101S Altcode:
The Chromospheric Telescope (ChroTel) is a small 10-cm robotic telescope
at Observatorio del Teide on Tenerife (Spain), which observes the
entire solar disk in Hα, Ca II K, and He I 10830 Å. We present
a new calibration method that includes limb-darkening correction,
removal of non-uniform filter transmission, and determination of
He I Doppler velocities. Chromospheric full-disk filtergrams are
often obtained with Lyot filters, which may display non-uniform
transmission causing large-scale intensity variations across the solar
disk. After the removal of a 2D symmetric limb-darkening function
from full-disk images, transmission artifacts remain and are even
more distinct. Zernike polynomials with a Noll index up to j = 36 are
well-suited to reconstruct the large-scale intensity variations of the
background. Zernike coefficients show a distinct temporal evolution for
ChroTel data, which is likely related to the telescope's alt-azimuth
mount that introduces image rotation. The intensity variations in the
He I filtergrams could be removed resulting in flat full-disk data. In
addition, applying this calibration to sets of seven filtergrams that
cover the He I triplet facilitates determining chromospheric Doppler
velocities. To validate the method, we use three data sets with varying
levels of solar activity. The Doppler velocities are benchmarked with
respect to co-temporal high-resolution spectroscopic data of the GREGOR
Infrared Spectrograph (GRIS). ChroTel Doppler velocities derived from
line-wing difference images and from spectral line fitting match those
of GRIS Dopplergrams. From this comparison, it was possible to derive a
velocity analog and full-disk Dopplergrams of ChroTel. Furthermore, the
Zernike technique can be applied to ChroTel Hα and Ca II K data. The
calibration method for ChroTel filtergrams can be easily adapted to
other full-disk data exhibiting unwanted large-scale variations and
provide valuable context data for near-infrared spectropolarimetry.

---------------------------------------------------------
Title: Deciphering the atmosphere of HAT-P-12b: solving discrepant
results
Authors: Alexoudi, X.; Mallonn, M.; von Essen, C.; Turner, J. D.;
Keles, E.; Southworth, J.; Mancini, L.; Ciceri, S.; Granzer, T.;
Denker, C.; Dineva, E.; Strassmeier, K. G.
2018A&A...620A.142A Altcode: 2018arXiv181002172A
Context. Two independent investigations of the atmosphere of the
hot Jupiter HAT-P-12b by two different groups resulted in discrepant
solutions. Using broad-band photometry from the ground, one study found
a flat and featureless transmission spectrum that was interpreted as
gray absorption by dense cloud coverage. The second study made use of
Hubble Space Telescope (HST) observations and found Rayleigh scattering
at optical wavelengths caused by haze. Aims: The main purpose
of this work is to determine the source of this inconsistency and
provide feedback to prevent similar discrepancies in future analyses of
other exoplanetary atmospheres. Methods: We studied the observed
discrepancy via two methods. With further broad-band observations in the
optical wavelength regions, we strengthened the previous measurements in
precision, and with a homogeneous reanalysis of the published data, we
were able to assess the systematic errors and the independent analyses
of the two different groups. Results: Repeating the analysis
steps of both works, we found that deviating values for the orbital
parameters are the reason for the aforementioned discrepancy. Our
work showed a degeneracy of the planetary spectral slope with these
parameters. In a homogeneous reanalysis of all data, the two literature
data sets and the new observations converge to a consistent transmission
spectrum, showing a low-amplitude spectral slope and a tentative
detection of potassium absorption. The transit light curves
of HAT-P-12b 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/620/A142">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A142</A>

---------------------------------------------------------
Title: sTools - a software package for data reduction of GREGOR
instruments and general data analysis
Authors: Kuckein, Christoph; Denker, Carsten; Verma, Meetu; Balthasar,
Horst; Diercke, Andrea; González Manrique, Sergio Javier; Dineva,
Ekaterina; Kontogiannis, Ioannis; Shen, Zili
2018csc..confE.105K Altcode:
The optical solar physics group at AIP is responsible for the GREGOR
Fabry-Perot Interferometer (GFPI) and the large-format facility cameras
(Blue Imaging Channel (BIC) and High-resolution Fast Imager (HiFI))
at the 1.5-meter GREGOR solar telescope (Tenerife, Spain). Since
the »Early Science Phase« of the telescope in 2014, the group
developed a data reduction pipeline for these two instruments. The
pipeline »sTools« is based on the Interactive Data Language
(IDL) and delivers reduced and image-restored data with a minimum
of user interaction. Furthermore, it creates quick-look data and
builds a webpage with an overview of the observations and their
statistics (http://gregor.aip.de). However, during the last years,
sTools continuously evolved and currently hosts many additional
routines for data analysis: (1) A local correlation tracking (LCT)
algorithm adapted for both high-resolution (GREGOR and Hinode) and
synoptic full-disk (SDO) data. (2) A new quantitative tool, i.e.,
a Background-subtracted Solar Activity Map (BaSAM), to assess and
visualize the temporal variation of the photospheric magnetic field
and the EUV 160 nm intensity. This method utilizes SDO data and is
applicable to both full-disk observations and regions-of-interest. (3)
Calibration of synoptic full-disk data from the Chromospheric Telescope
(ChroTel) including extraction of Doppler velocities from He I 1083
nm filtergrams. (4) Analysis tools for sun-as-a-star spectroscopy
for the Solar Disk-Integrated (SDI) telescope of the Potsdam Echelle
Polarimetric and Spectroscopic Instrument (PEPSI). sTools is licensed
under a creative commons license and is freely available, after
registration, at the abovementioned website.

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Title: The Effects of Stellar Activity on Optical High-resolution
Exoplanet Transmission Spectra
Authors: Cauley, P. Wilson; Kuckein, Christoph; Redfield, Seth;
Shkolnik, Evgenya L.; Denker, Carsten; Llama, Joe; Verma, Meetu
2018AJ....156..189C Altcode: 2018arXiv180809558C
Chromospherically sensitive atomic lines display different spectra
in stellar active regions, spots, and the photosphere, raising the
possibility that exoplanet transmission spectra are contaminated by
the contrast between various portions of the stellar disk. To explore
this effect, we performed transit simulations of G-type and K-type
stars for the spectral lines Ca II K at 3933 Å, Na I 5890 Å, H I
6563 Å (Hα), and He I 10830 Å. We find that strong facular emission
and large coverage fractions can contribute a non-negligible amount
to transmission spectra, especially for Hα, Ca II K, and Na I D,
while spots and filaments are comparatively unimportant. The amount of
contamination depends strongly on the location of the active regions
and the intrinsic emission strength. In particular, active regions
must be concentrated along the transit chord in order to produce a
consistent in-transit signal. Mean absorption signatures in Na I and
Hα, for example, can reach ≈0.2% and 0.3%, respectively, for transits
of active latitudes with line emission similar in strength to moderate
solar flares. Transmission spectra of planets transiting active stars,
such as HD 189733, are likely contaminated by the contrast effect,
although the tight constraints on active region geometry and emission
strength make it unlikely that consistent in-transit signatures are due
entirely to the contrast effect. He I 10830 Å is not strongly affected
and absorption signatures are likely diluted, rather than enhanced,
by stellar activity. He I 10830 Å should thus be considered a priority
for probing extended atmospheres, even in the case of active stars.

---------------------------------------------------------
Title: Counter-streaming flows in a giant quiet-Sun filament
Authors: Diercke, Andrea; Kuckein, Christoph; Verma, Meetu; Denker,
Carsten
2018csc..confE.104D Altcode:
A giant solar filament was visible on the solar surface between 2011
November 8-23. The filament stretched over more than half a solar
diameter. Multi-wavelength data from the SDO instrument AIA (171, 193,
304, and 211 A) were used to examine counter-streaming flows within
the spine of the filament. H-alpha images from the Kanzelhöhe Solar
Observatory provided context information. We apply local correlation
tracking (LCT) to a two-hour time series on 2011 November 16 of the AIA
images to derive horizontal flow velocities of the filament. To enhance
the contrast of the AIA images, noise adaptive fuzzy equalization
(NAFE) is employed, which allows us to identify and quantify
counter-streaming flows in the filament. We detect counter-streaming
flows in the filament, which are visible in the time-lapse movies in all
examined AIA wavelength bands. In the time-lapse movies, we see that
these persistent flows lasted for at least two hours. Furthermore, by
applying LCT to the images we clearly determine counter-streaming flows
in time series of 171 A and 193 A images. In the 304 A wavelength band,
we only see minor indications for counter-streaming flows with LCT,
while in the 211 A wavelength band the counter-streaming flows are not
detectable. The average horizontal flows reach mean flow speeds of 0.5
km/s. The highest horizontal flow speeds are identified in the 171
A band with flow speeds of up to 2.5 km/s. The results are averaged
over a time series of 90 min. Because the LCT sampling window has a
finite width, a spatial degradation cannot be avoided leading to lower
estimates of the flow velocities as compared to feature tracking or
Doppler measurements. The counter-streaming flows cover about 15-20%
of the whole area of the EUV filament channel and are located in the
central part of the spine. In conclusion, we confirm the omnipresence
of counter-streaming flows also in giant quiet-Sun filaments.

---------------------------------------------------------
Title: Calibration of full-disk He I 10 830 Å filtergrams of the
Chromospheric Telescope
Authors: Shen, Z.; Diercke, A.; Denker, C.
2018AN....339..661S Altcode: 2018arXiv181204404S
The Chromospheric Telescope (ChroTel) is a small 10-cm robotic telescope
at Observatorio del Teide on Tenerife (Spain), which observes the
entire sun in Hα, Ca II K, and He I 10 830 Å. We present a new
calibration method that includes limb-darkening correction, removal
of nonuniform filter transmission, and determination of He I Doppler
velocities. Chromospheric full-disk filtergrams are often obtained
with Lyot filters, which may display nonuniform transmission causing
large-scale intensity variations across the solar disk. Removal of a
2D symmetric limb-darkening function from full-disk images results
in a flat background. However, transmission artifacts remain and
are even more distinct in these contrast-enhanced images. Zernike
polynomials are uniquely appropriate to fit these large-scale intensity
variations of the background. The Zernike coefficients show a distinct
temporal evolution for ChroTel data, which is likely related to the
telescope's alt-azimuth mount that introduces image rotation. In
addition, applying this calibration to sets of seven filtergrams that
cover the He I triplet facilitates the determination of chromospheric
Doppler velocities. To validate the method, we use three datasets with
varying levels of solar activity. The Doppler velocities are benchmarked
with respect to cotemporal high-resolution spectroscopic data of the
GREGOR Infrared Spectrograph (GRIS). Furthermore, this technique can
be applied to ChroTel Hα and Ca II K data. The calibration method
for ChroTel filtergrams can be easily adapted to other full-disk data
exhibiting unwanted large-scale variations. The spectral region of the
He I triplet is a primary choice for high-resolution near-infrared
spectropolarimetry. Here, the improved calibration of ChroTel data
will provide valuable context data.

---------------------------------------------------------
Title: VizieR Online Data Catalog: HAT-P-12b 2016-2017 light curve
(Alexoudi+, 2018)
Authors: Alexoudi, X.; Mallonn, M.; von Essen, C.; Turner, J. D.;
Keles, E.; Southworth, J.; Mancini, L.; Ciceri, S.; Granzer, T.;
Denker, C.; Dineva, E.; Strassmeier, K. G.
2018yCat..36200142A Altcode:
Photometric observations of the transiting exoplanet HAT-P-12b in
2016-2017 with different ground-based facilities. These observations
made use of the 1.2m STELLA robotic telescope (5 transits at Sloan g'),
the 3.5m Telescopio Nazionale Galileo (TNG) on Roque de los Muchachos
Observatory (1 transit at Johnson B), the 1.23m (two transits at
Johnson B) and 2.2m (1 transit at Johnson B) telescopes of Calar Alto
Observatory and the 3.5m (1 transit at Johnson B) Astrophysics Research
Consortium (ARC) telescope from the Apache Point Observatory. (2
data files).

---------------------------------------------------------
Title: Temporal evolution of arch filaments as seen in He I 10 830 Å
Authors: González Manrique, S. J.; Kuckein, C.; Collados, M.; Denker,
C.; Solanki, S. K.; Gömöry, P.; Verma, M.; Balthasar, H.; Lagg,
A.; Diercke, A.
2018A&A...617A..55G Altcode: 2018arXiv180700728G
 Aims: We study the evolution of an arch filament system (AFS)
and of its individual arch filaments to learn about the processes
occurring in them. Methods: We observed the AFS at the
GREGOR solar telescope on Tenerife at high cadence with the very
fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS)
in the He I 10 830 Å spectral range. The He I triplet profiles
were fitted with analytic functions to infer line-of-sight (LOS)
velocities to follow plasma motions within the AFS. Results:
We tracked the temporal evolution of an individual arch filament
over its entire lifetime, as seen in the He I 10 830 Å triplet. The
arch filament expanded in height and extended in length from 13″ to
21″. The lifetime of this arch filament is about 30 min. About 11
min after the arch filament is seen in He I, the loop top starts to
rise with an average Doppler velocity of 6 km s-1. Only two
minutes later, plasma drains down with supersonic velocities towards
the footpoints reaching a peak velocity of up to 40 km s-1
in the chromosphere. The temporal evolution of He I 10 830 Å profiles
near the leading pore showed almost ubiquitous dual red components of
the He I triplet, indicating strong downflows, along with material
nearly at rest within the same resolution element during the whole
observing time. Conclusions: We followed the arch filament as it
carried plasma during its rise from the photosphere to the corona. The
material then drained toward the photosphere, reaching supersonic
velocities, along the legs of the arch filament. Our observational
results support theoretical AFS models and aids in improving future
models. The movie associated to Fig. 3 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201832684/olm">https://www.aanda.org/</A>

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Title: High-resolution imaging and near-infrared spectroscopy of
penumbral decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; Rezaei,
R.; Sobotka, M.; Deng, N.; Wang, H.; Tritschler, A.; Collados, M.;
Diercke, A.; González Manrique, S. J.
2018A&A...614A...2V Altcode: 2018arXiv180103686V
 Aims: Combining high-resolution spectropolarimetric and imaging
data is key to understanding the decay process of sunspots as it
allows us to scrutinize the velocity and magnetic fields of sunspots
and their surroundings. Methods: Active region NOAA 12597
was observed on 2016 September 24 with the 1.5-meter GREGOR solar
telescope using high-spatial-resolution imaging as well as imaging
spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal
proper motions were estimated with local correlation tracking, whereas
line-of-sight (LOS) velocities were computed with spectral line fitting
methods. The magnetic field properties were inferred with the "Stokes
Inversions based on Response functions" (SIR) code for the Si I and Ca
I NIR lines. Results: At the time of the GREGOR observations,
the leading sunspot had two light bridges indicating the onset of
its decay. One of the light bridges disappeared, and an elongated,
dark umbral core at its edge appeared in a decaying penumbral sector
facing the newly emerging flux. The flow and magnetic field properties
of this penumbral sector exhibited weak Evershed flow, moat flow, and
horizontal magnetic field. The penumbral gap adjacent to the elongated
umbral core and the penumbra in that penumbral sector displayed LOS
velocities similar to granulation. The separating polarities of a new
flux system interacted with the leading and central part of the already
established active region. As a consequence, the leading spot rotated
55° clockwise over 12 h. Conclusions: In the high-resolution
observations of a decaying sunspot, the penumbral filaments facing the
flux emergence site contained a darkened area resembling an umbral core
filled with umbral dots. This umbral core had velocity and magnetic
field properties similar to the sunspot umbra. This implies that the
horizontal magnetic fields in the decaying penumbra became vertical
as observed in flare-induced rapid penumbral decay, but on a very
different time-scale.

---------------------------------------------------------
Title: On the extent of the moat flow in axisymmetric sunspots
Authors: Verma, M.; Kummerow, P.; Denker, C.
2018AN....339..268V Altcode: 2018arXiv180504356V
Unipolar, axisymmetric sunspots are figuratively called "theoretician's
sunspots" because their simplicity supposedly makes them more suitable
for theoretical descriptions or numerical models. On November 18, 2013,
a very large specimen (active region NOAA 11899) crossed the central
meridian of the sun. The moat flow associated with this very large spot
is quantitatively compared to that of a medium and a small sunspot to
determine the extent of the moat flow in different environments. We
employ continuum images and magnetograms of the Helioseismic and
Magnetic Imager (HMI) as well as extreme ultraviolet (EUV) images at
λ160 nm of the Atmospheric Imaging Assembly (AIA), both on board the
Solar Dynamics Observatory (SDO), to measure horizontal proper motions
with Local Correlation Tracking (LCT) and flux transport velocities
with the Differential Affine Velocity Estimator (DAVE). We compute
time-averaged flow maps (±6 hr around meridian passage) and radial
averages of photometric, magnetic, and flow properties. Flow fields of
a small- and a medium-sized axisymmetric sunspot provide the context
for interpreting the results. All sunspots show outward moat flow and
the advection of moving magnetic features (MMFs). However, the extent
of the moat flow varies from spot to spot, and a correlation of flow
properties with size is tenuous, if at all present. The moat flow
is asymmetric and predominantly in the east-west direction, whereby
deviations are related to the tilt angle of the sunspot group as well
as to the topology and activity level of the trailing plage.

---------------------------------------------------------
Title: High-cadence Imaging and Imaging Spectroscopy at the
GREGOR Solar Telescope—A Collaborative Research Environment for
High-resolution Solar Physics
Authors: Denker, Carsten; Kuckein, Christoph; Verma, Meetu; González
Manrique, Sergio J.; Diercke, Andrea; Enke, Harry; Klar, Jochen;
Balthasar, Horst; Louis, Rohan E.; Dineva, Ekaterina
2018ApJS..236....5D Altcode: 2018arXiv180210146D
In high-resolution solar physics, the volume and complexity
of photometric, spectroscopic, and polarimetric ground-based
data significantly increased in the last decade, reaching data
acquisition rates of terabytes per hour. This is driven by the
desire to capture fast processes on the Sun and the necessity
for short exposure times “freezing” the atmospheric seeing,
thus enabling ex post facto image restoration. Consequently,
large-format and high-cadence detectors are nowadays used in
solar observations to facilitate image restoration. Based on our
experience during the “early science” phase with the 1.5 m
GREGOR solar telescope (2014-2015) and the subsequent transition
to routine observations in 2016, we describe data collection and
data management tailored toward image restoration and imaging
spectroscopy. We outline our approaches regarding data processing,
analysis, and archiving for two of GREGOR’s post-focus instruments
(see <A href="http://gregor.aip.de">http://gregor.aip.de</A>), i.e.,
the GREGOR Fabry-Pérot Interferometer (GFPI) and the newly installed
High-Resolution Fast Imager (HiFI). The heterogeneous and complex
nature of multidimensional data arising from high-resolution solar
observations provides an intriguing but also a challenging example for
“big data” in astronomy. The big data challenge has two aspects: (1)
establishing a workflow for publishing the data for the whole community
and beyond and (2) creating a collaborative research environment
(CRE), where computationally intense data and postprocessing tools are
colocated and collaborative work is enabled for scientists of multiple
institutes. This requires either collaboration with a data center or
frameworks and databases capable of dealing with huge data sets based on
virtual observatory (VO) and other community standards and procedures.

---------------------------------------------------------
Title: Counter-streaming flows in a giant quiet-Sun filament observed
in the extreme ultraviolet
Authors: Diercke, A.; Kuckein, C.; Verma, M.; Denker, C.
2018A&A...611A..64D Altcode: 2018arXiv180101036D
Aim. The giant solar filament was visible on the solar surface from
2011 November 8-23. Multiwavelength data from the Solar Dynamics
Observatory (SDO) were used to examine counter-streaming flows
within the spine of the filament. Methods: We use data from
two SDO instruments, the Atmospheric Imaging Assembly (AIA) and the
Helioseismic and Magnetic Imager (HMI), covering the whole filament,
which stretched over more than half a solar diameter. Hα images from
the Kanzelhöhe Solar Observatory (KSO) provide context information
of where the spine of the filament is defined and the barbs are
located. We apply local correlation tracking (LCT) to a two-hour time
series on 2011 November 16 of the AIA images to derive horizontal flow
velocities of the filament. To enhance the contrast of the AIA images,
noise adaptive fuzzy equalization (NAFE) is employed, which allows us
to identify and quantify counter-streaming flows in the filament. We
observe the same cool filament plasma in absorption in both Hα and
EUV images. Hence, the counter-streaming flows are directly related to
this filament material in the spine. In addition, we use directional
flow maps to highlight the counter-streaming flows. Results:
We detect counter-streaming flows in the filament, which are visible
in the time-lapse movies in all four examined AIA wavelength bands
(λ171 Å, λ193 Å, λ304 Å, and λ211 Å). In the time-lapse
movies we see that these persistent flows lasted for at least two
hours, although they became less prominent towards the end of the
time series. Furthermore, by applying LCT to the images we clearly
determine counter-streaming flows in time series of λ171 Å and
λ193 Å images. In the λ304 Å wavelength band, we only see minor
indications for counter-streaming flows with LCT, while in the λ211
Å wavelength band the counter-streaming flows are not detectable
with this method. The diverse morphology of the filament in Hα
and EUV images is caused by different absorption processes, i.e.,
spectral line absorption and absorption by hydrogen and helium continua,
respectively. The horizontal flows reach mean flow speeds of about 0.5
km s-1 for all wavelength bands. The highest horizontal
flow speeds are identified in the λ171 Å band with flow speeds of
up to 2.5 km s-1. The results are averaged over a time
series of 90 minutes. Because the LCT sampling window has finite
width, a spatial degradation cannot be avoided leading to lower
estimates of the flow velocities as compared to feature tracking or
Doppler measurements. The counter-streaming flows cover about 15-20%
of the whole area of the EUV filament channel and are located in
the central part of the spine. Conclusions: Compared to the
ground-based observations, the absence of seeing effects in AIA
observations reveal counter-streaming flows in the filament even
with a moderate image scale of 0. ”6 pixel-1. Using
a contrast enhancement technique, these flows can be detected
and quantified with LCT in different wavelengths. We confirm the
omnipresence of counter-streaming flows also in giant quiet-Sun
filaments. A movie associated to Fig. 6 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201730536/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Image Quality in High-resolution and High-cadence Solar Imaging
Authors: Denker, C.; Dineva, E.; Balthasar, H.; Verma, M.; Kuckein,
C.; Diercke, A.; González Manrique, S. J.
2018SoPh..293...44D Altcode: 2018arXiv180200760D
Broad-band imaging and even imaging with a moderate bandpass (about 1
nm) provides a photon-rich environment, where frame selection (lucky
imaging) becomes a helpful tool in image restoration, allowing us to
perform a cost-benefit analysis on how to design observing sequences
for imaging with high spatial resolution in combination with real-time
correction provided by an adaptive optics (AO) system. This study
presents high-cadence (160 Hz) G-band and blue continuum image sequences
obtained with the High-resolution Fast Imager (HiFI) at the 1.5-meter
GREGOR solar telescope, where the speckle-masking technique is used
to restore images with nearly diffraction-limited resolution. The
HiFI employs two synchronized large-format and high-cadence sCMOS
detectors. The median filter gradient similarity (MFGS) image-quality
metric is applied, among others, to AO-corrected image sequences of
a pore and a small sunspot observed on 2017 June 4 and 5. A small
region of interest, which was selected for fast-imaging performance,
covered these contrast-rich features and their neighborhood, which were
part of Active Region NOAA 12661. Modifications of the MFGS algorithm
uncover the field- and structure-dependency of this image-quality
metric. However, MFGS still remains a good choice for determining image
quality without a priori knowledge, which is an important characteristic
when classifying the huge number of high-resolution images contained in
data archives. In addition, this investigation demonstrates that a fast
cadence and millisecond exposure times are still insufficient to reach
the coherence time of daytime seeing. Nonetheless, the analysis shows
that data acquisition rates exceeding 50 Hz are required to capture a
substantial fraction of the best seeing moments, significantly boosting
the performance of post-facto image restoration.

---------------------------------------------------------
Title: Ca II 8542 Å brightenings induced by a solar microflare
Authors: Kuckein, C.; Diercke, A.; González Manrique, S. J.; Verma,
M.; Löhner-Böttcher, J.; Socas-Navarro, H.; Balthasar, H.; Sobotka,
M.; Denker, C.
2017A&A...608A.117K Altcode: 2017arXiv170906861K
 Aims: We study small-scale brightenings in Ca II 8542 Å
line-core images to determine their nature and effect on localized
heating and mass transfer in active regions. Methods:
High-resolution two-dimensional spectroscopic observations of a solar
active region in the near-infrared Ca II 8542 Å line were acquired
with the GREGOR Fabry-Pérot Interferometer attached to the 1.5-m GREGOR
telescope. Inversions of the spectra were carried out using the NICOLE
code to infer temperatures and line-of-sight (LOS) velocities. Response
functions of the Ca II line were computed for temperature and LOS
velocity variations. Filtergrams of the Atmospheric Imaging Assembly
(AIA) and magnetograms of the Helioseismic and Magnetic Imager (HMI)
were coaligned to match the ground-based observations and to follow the
Ca II brightenings along all available layers of the atmosphere. 
Results: We identified three brightenings of sizes up to 2” × 2”
that appeared in the Ca II 8542 Å line-core images. Their lifetimes
were at least 1.5 min. We found evidence that the brightenings belonged
to the footpoints of a microflare (MF). The properties of the observed
brightenings disqualified the scenarios of Ellerman bombs or Interface
Region Imaging Spectrograph (IRIS) bombs. However, this MF shared some
common properties with flaring active-region fibrils or flaring arch
filaments (FAFs): (1) FAFs and MFs are both apparent in chromospheric
and coronal layers according to the AIA channels; and (2) both show
flaring arches with lifetimes of about 3.0-3.5 min and lengths of
20” next to the brightenings. The inversions revealed heating by
600 K at the footpoint location in the ambient chromosphere during
the impulsive phase. Connecting the footpoints, a dark filamentary
structure appeared in the Ca II line-core images. Before the
start of the MF, the spectra of this structure already indicated
average blueshifts, meaning upward motions of the plasma along the
LOS. During the impulsive phase, these velocities increased up to -
2.2 km s-1. The structure did not disappear during the
observations. Downflows dominated at the footpoints. However, in
the upper photosphere, slight upflows occurred during the impulsive
phase. Hence, bidirectional flows are present in the footpoints
of the MF. Conclusions: We detected Ca II brightenings that
coincided with the footpoint location of an MF. The MF event led to
a rise of plasma in the upper photosphere, both before and during the
impulsive phase. Excess mass, previously raised to at most chromospheric
layers, slowly drained downward along arches toward the footpoints
of the MF. The movie associated to Fig. 2 is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201731319/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: sTools - a data reduction pipeline for the GREGOR Fabry-Pérot
Interferometer and the High-resolution Fast Imager at the GREGOR
solar telescope
Authors: Kuckein, C.; Denker, C.; Verma, M.; Balthasar, H.; González
Manrique, S. J.; Louis, R. E.; Diercke, A.
2017IAUS..327...20K Altcode: 2017arXiv170101670K
A huge amount of data has been acquired with the GREGOR Fabry-Pérot
Interferometer (GFPI), large-format facility cameras, and since 2016
with the High-resolution Fast Imager (HiFI). These data are processed
in standardized procedures with the aim of providing science-ready data
for the solar physics community. For this purpose, we have developed a
user-friendly data reduction pipeline called “sTools” based on the
Interactive Data Language (IDL) and licensed under creative commons
license. The pipeline delivers reduced and image-reconstructed data
with a minimum of user interaction. Furthermore, quick-look data are
generated as well as a webpage with an overview of the observations and
their statistics. All the processed data are stored online at the GREGOR
GFPI and HiFI data archive of the Leibniz Institute for Astrophysics
Potsdam (AIP). The principles of the pipeline are presented together
with selected high-resolution spectral scans and images processed
with sTools.

---------------------------------------------------------
Title: Flows along arch filaments observed in the GRIS `very fast
spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
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: High-resolution imaging spectroscopy of two micro-pores and
an arch filament system in a small emerging-flux region
Authors: González Manrique, S. J.; Bello González, N.; Denker, C.
2017A&A...600A..38G Altcode: 2017arXiv170310140G
Context. Emerging flux regions mark the first stage in the accumulation
of magnetic flux eventually leading to pores, sunspots, and (complex)
active regions. These flux regions are highly dynamic, show a variety
of fine structure, and in many cases live only for a short time (less
than a day) before dissolving quickly into the ubiquitous quiet-Sun
magnetic field. Aims: The purpose of this investigation is to
characterize the temporal evolution of a minute emerging flux region,
the associated photospheric and chromospheric flow fields, and the
properties of the accompanying arch filament system. We aim to explore
flux emergence and decay processes and investigate if they scale with
structure size and magnetic flux contents. Methods: This study
is based on imaging spectroscopy with the Göttingen Fabry-Pérot
Interferometer at the Vacuum Tower Telescope, Observatorio del Teide,
Tenerife, Spain on 2008 August 7. Photospheric horizontal proper motions
were measured with Local correlation tracking using broadband images
restored with multi-object multi-frame blind deconvolution. Cloud model
(CM) inversions of line scans in the strong chromospheric absorption
Hαλ656.28 nm line yielded CM parameters (Doppler velocity, Doppler
width, optical thickness, and source function), which describe the
cool plasma contained in the arch filament system. Results:
The high-resolution observations cover the decay and convergence of two
micro-pores with diameters of less than one arcsecond and provide decay
rates for intensity and area. The photospheric horizontal flow speed
is suppressed near the two micro-pores indicating that the magnetic
field is already sufficiently strong to affect the convective energy
transport. The micro-pores are accompanied by a small arch filament
system as seen in Hα, where small-scale loops connect two regions
with Hα line-core brightenings containing an emerging flux region
with opposite polarities. The Doppler width, optical thickness,
and source function reach the largest values near the Hα line-core
brightenings. The chromospheric velocity of the cloud material is
predominantly directed downwards near the footpoints of the loops
with velocities of up to 12 km s-1, whereas loop tops show
upward motions of about 3 km s-1. Some of the loops exhibit
signs of twisting motions along the loop axis. Conclusions:
Micro-pores are the smallest magnetic field concentrations leaving a
photometric signature in the photosphere. In the observed case, they
are accompanied by a miniature arch filament system indicative of newly
emerging flux in the form of Ω-loops. Flux emergence and decay take
place on a time-scale of about two days, whereas the photometric decay
of the micro-pores is much more rapid (a few hours), which is consistent
with the incipient submergence of Ω-loops. Considering lifetime and
evolution timescales, impact on the surrounding photospheric proper
motions, and flow speed of the chromospheric plasma at the loop tops
and footpoints, the results are representative for the smallest emerging
flux regions still recognizable as such.

---------------------------------------------------------
Title: Wings of the butterfly: Sunspot groups for 1826-2015
Authors: Leussu, R.; Usoskin, I. G.; Senthamizh Pavai, V.; Diercke,
A.; Arlt, R.; Denker, C.; Mursula, K.
2017A&A...599A.131L Altcode:
The spatio-temporal evolution of sunspot activity, the so-called Maunder
butterfly diagram, has been continously available since 1874 using
data from the Royal Greenwich Observatory, extended by SOON network
data after 1976. Here we present a new extended butterfly diagram
of sunspot group occurrence since 1826, using the recently digitized
data from Schwabe (1826-1867) and Spörer (1866-1880). The wings of
the diagram are separated using a recently developed method based
on an analysis of long gaps in sunspot group occurrence in different
latitude bands. We define characteristic latitudes, corresponding to
the start, end, and the largest extent of the wings (the F, L, and
H latitudes). The H latitudes (30°-45°) are highly significantly
correlated with the strength of the wings (quantified by the total sum
of the monthly numbers of sunspot groups). The F latitudes (20°-30°)
depict a weak tendency, especially in the southern hemisphere, to follow
the wing strength. The L latitudes (2°-10°) show no clear relation to
the wing strength. Overall, stronger cycle wings tend to start at higher
latitudes and have a greater wing extent. A strong (5-6)-cycle periodic
oscillation is found in the start and end times of the wings and in the
overlap and gaps between successive wings of one hemisphere. While the
average wing overlap is zero in the southern hemisphere, it is two to
three months in the north. A marginally significant oscillation of about
ten solar cycles is found in the asymmetry of the L latitudes. The new
long database of butterfly wings provides new observational constraints
to solar dynamo models that discuss the spatio-temporal distribution
of sunspot occurrence over the solar cycle and longer. Digital
data for Fig. 1 are available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A131">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A131</A>

---------------------------------------------------------
Title: Center-to-limb variation of the velocity field in and around
a sunspot with light-bridges
Authors: Denker, Carsten; Verma, Meetu; Balthasar, Horst; Diercke,
Andrea; González Manrique, S. J.; Löhner-Böttcher, Johannes;
Kuckein, Christoph; Sobotka, Michal
2017psio.confE.104D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Velocity fields in sunspots derived from observations with
the GREGOR Fabry-Pérot Interferometer
Authors: Balthasar, H.; Denker, C.; Diercke, A.; González Manrique,
S. J.; Kuckein, C.; Louis, R. E.; Verma, M., Löhner-Böttcher, J.;
Sobotka, M.
2017psio.confE.105B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Slipping reconnection in a solar flare observed in high
resolution with the GREGOR solar telescope
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.;
Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.;
Volkmer, R.; Waldmann, T.
2016A&A...596A...1S Altcode: 2016arXiv160500464S
A small flare ribbon above a sunspot umbra in active region 12205 was
observed on November 7, 2014, at 12:00 UT in the blue imaging channel
of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference
filter. Context observations from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical
Telescope (SOT) onboard Hinode, and the Interface Region Imaging
Spectrograph (IRIS) show that this ribbon is part of a larger one
that extends through the neighboring positive polarities and also
participates in several other flares within the active region. We
reconstructed a time series of 140 s of Ca II H images by means of the
multiframe blind deconvolution method, which resulted in spatial and
temporal resolutions of 0.1″ and 1 s. Light curves and horizontal
velocities of small-scale bright knots in the observed flare ribbon
were measured. Some knots are stationary, but three move along the
ribbon with speeds of 7-11 km s-1. Two of them move in the
opposite direction and exhibit highly correlated intensity changes,
which provides evidence of a slipping reconnection at small spatial
scales. Movies associated to Figs. 1 and 2 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201527966/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Editor's Note
Authors: Louis, Rohan Eugene; Mann, Gottfried; Denker, Carsten
2016AN....337.1001L Altcode:
No abstract at ADS

---------------------------------------------------------
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.
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. Aims:
We aim to confirm or refute the existence of weak-field regions in
the deepest photospheric layers of the penumbra. Methods:
We investigated the magnetic field at log τ5 = 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. Results: At log τ5
= 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.
2016AN....337.1050B Altcode: 2016arXiv160901514B
Arch filament systems occur in active sunspot groups, where a fibril
structure connects areas of opposite magnetic polarity, in contrast to
active region filaments that follow the polarity inversion line. We
used the GREGOR Infrared Spectrograph (GRIS) to obtain the full
Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0
nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line
to investigate the photospheric magnetic field and velocities, and
use the line core intensities and velocities of the helium line to
study the chromospheric plasma. The individual fibrils of the arch
filament system connect the sunspot with patches of magnetic polarity
opposite to that of the spot. These patches do not necessarily coincide
with pores, where the magnetic field is strongest. Instead, areas are
preferred not far from the polarity inversion line. These areas exhibit
photospheric downflows of moderate velocity, but significantly higher
downflows of up to 30 km s-1 in the chromospheric helium
line. Our findings can be explained with new emerging flux where the
matter flows downward along the field lines of rising flux tubes,
in agreement with earlier results.

---------------------------------------------------------
Title: 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.
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. Aims: We study the topology of the penumbral magnetic
field in the lower photosphere, focusing on regions where it returns
below the surface. 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. 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.
2016A&A...596A...3V Altcode: 2016arXiv160507462V
Context. The solar magnetic field is responsible for all aspects
of solar activity. Thus, emergence of magnetic flux at the surface
is the first manifestation of the ensuing solar activity. 
Aims: Combining high-resolution and synoptic observations aims to
provide a comprehensive description of flux emergence at photospheric
level and of the growth process that eventually leads to a mature
active region. Methods: The small active region NOAA 12118
emerged on 2014 July 17 and was observed one day later with the 1.5-m
GREGOR solar telescope on 2014 July 18. High-resolution time-series
of blue continuum and G-band images acquired in the blue imaging
channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were
complemented by synoptic line-of-sight magnetograms and continuum
images obtained with the Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO). Horizontal proper motions and
horizontal plasma velocities were computed with local correlation
tracking (LCT) and the differential affine velocity estimator (DAVE),
respectively. Morphological image processing was employed to measure
the photometric and magnetic area, magnetic flux, and the separation
profile of the emerging flux region during its evolution. 
Results: The computed growth rates for photometric area, magnetic
area, and magnetic flux are about twice as high as the respective
decay rates. The space-time diagram using HMI magnetograms of five days
provides a comprehensive view of growth and decay. It traces a leaf-like
structure, which is determined by the initial separation of the two
polarities, a rapid expansion phase, a time when the spread stalls,
and a period when the region slowly shrinks again. The separation
rate of 0.26 km s-1 is highest in the initial stage, and
it decreases when the separation comes to a halt. Horizontal plasma
velocities computed at four evolutionary stages indicate a changing
pattern of inflows. In LCT maps we find persistent flow patterns such
as outward motions in the outer part of the two major pores, a diverging
feature near the trailing pore marking the site of upwelling plasma and
flux emergence, and low velocities in the interior of dark pores. We
detected many elongated rapidly expanding granules between the two
major polarities, with dimensions twice as large as the normal granules.

---------------------------------------------------------
Title: Solar physics at the Einstein Tower
Authors: Denker, C.; Heibel, C.; Rendtel, J.; Arlt, K.; Balthasar,
Juergen H.; Diercke, A.; González Manrique, S. J.; Hofmann, A.;
Kuckein, C.; Önel, H.; Senthamizh Pavai, V.; Staude, J.; Verman, M.
2016AN....337.1105D Altcode: 2016arXiv160906949D
The solar observatory Einstein Tower ({Einsteinturm}) at the
Telegrafenberg in Potsdam is both a landmark of modern architecture
and an important place for solar physics. Originally built for
high-resolution spectroscopy and measuring the gravitational redshift,
research shifted over the years to understanding the active Sun and
its magnetic field. Nowadays, telescope and spectrographs are used for
research and development, i.e., testing instruments and in particular
polarization optics for advanced instrumentation deployed at major
European and international astronomical and solar telescopes. In
addition, the Einstein Tower is used for educating and training of the
next generation astrophysicists as well as for education and public
outreach activities directed at the general public. This article
comments on the observatory's unique architecture and the challenges
of maintaining and conserving the building. It describes in detail the
characteristics of telescope, spectrographs, and imagers; it portrays
some of the research and development activities.

---------------------------------------------------------
Title: 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.
2016A&A...596A...8J Altcode: 2016arXiv160801988J
 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. 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. 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. 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.
2016A&A...596A...7S Altcode: 2016arXiv160707094S
Context. The various mechanisms of magneto-convective energy transport
determine the structure of sunspots and active regions. 
Aims: We characterise the appearance of light bridges and other
fine-structure details and elaborate on their magneto-convective
nature. 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. 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. 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.
2016A&A...596A...6L Altcode: 2016arXiv160506324L
Context. Investigations of the magnetism of the quiet Sun are hindered
by extremely weak polarization signals in Fraunhofer spectral
lines. Photon noise, straylight, and the systematically different
sensitivity of the Zeeman effect to longitudinal and transversal
magnetic fields result in controversial results in terms of the strength
and angular distribution of the magnetic field vector. Aims:
The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
spatial straylight and photon noise into account. Methods: Highly
sensitive full Stokes measurements of a quiet-Sun region at disk center
in the deep photospheric Fe I lines in the 1.56 μm region were obtained
with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
diagnostics based directly on the shape and strength of the profiles
were applied to the GRIS data. We made use of the magnetic line ratio
technique, which was tested against realistic magneto-hydrodynamic
simulations (MURaM). Results: About 80% of the GRIS spectra
of a very quiet solar region show polarimetric signals above a 3σ
level. Area and amplitude asymmetries agree well with small-scale
surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields. Conclusions:
The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
are so far unique in the combination of high spatial resolution scans
and high magnetic field sensitivity. Nevertheless, the unavoidable
effect of spatial straylight and the resulting dilution of the weak
Stokes profiles means that inversion techniques still bear a high risk
of misinterpretating the data.

---------------------------------------------------------
Title: Flow and magnetic field properties in the trailing sunspots
of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
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.
2016A&A...596A..59F Altcode: 2016arXiv161104803F
Context. Active regions are the most prominent manifestations of solar
magnetic fields; their generation and dissipation are fundamental
problems in solar physics. Light bridges are commonly present during
sunspot decay, but a comprehensive picture of their role in the
removal of the photospheric magnetic field is still lacking. 
Aims: We study the three-dimensional configuration of a sunspot,
and in particular, its light bridge, during one of the last stages of
its decay. Methods: We present the magnetic and thermodynamical
stratification inferred from full Stokes inversions of the photospheric
Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
Infrared Spectrograph of the GREGOR telescope at the Observatorio del
Teide, Tenerife, Spain. The analysis is complemented by a study of
continuum images covering the disk passage of the active region, which
are provided by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory. Results: The sunspot shows a light bridge
with penumbral continuum intensity that separates the central umbra from
a smaller umbra. We find that in this region the magnetic field lines
form a canopy with lower magnetic field strength in the inner part. The
photospheric light bridge is dominated by gas pressure (high-β),
as opposed to the surrounding umbra, where the magnetic pressure
is higher. A convective flow is observed in the light bridge. This
flow is able to bend the magnetic field lines and to produce field
reversals. The field lines merge above the light bridge and become
as vertical and strong as in the surrounding umbra. We conclude that
this occurs because two highly magnetized regions approach each other
during the sunspot evolution. Movies associated to Figs. 2 and 13
are available at <A href="http://www.aanda.org">http://www.aanda.org</A>

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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.
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. Aims: We present
high-precision spectro-polarimetric data with high spatial resolution
(0.4”) of the very quiet Sun at 1.56 μm obtained with the GREGOR
telescope to shed some light on this complex magnetism. Methods:
We used inversion techniques in two main approaches. First, we assumed
that the observed profiles can be reproduced with a constant magnetic
field atmosphere embedded in a field-free medium. Second, we assumed
that the resolution element has a substructure with either two constant
magnetic atmospheres or a single magnetic atmosphere with gradients of
the physical quantities along the optical depth, both coexisting with
a global stray-light component. Results: Half of our observed
quiet-Sun region is better explained by magnetic substructure within
the resolution element. However, we cannot distinguish whether this
substructure comes from gradients of the physical parameters along the
line of sight or from horizontal gradients (across the surface). In
these pixels, a model with two magnetic components is preferred, and
we find two distinct magnetic field populations. The population with
the larger filling factor has very weak ( 150 G) horizontal fields
similar to those obtained in previous works. We demonstrate that the
field vector of this population is not constrained by the observations,
given the spatial resolution and polarimetric accuracy of our data. The
topology of the other component with the smaller filling factor is
constrained by the observations for field strengths above 250 G:
we infer hG fields with inclinations and azimuth values compatible
with an isotropic distribution. The filling factors are typically
below 30%. We also find that the flux of the two polarities is not
balanced. From the other half of the observed quiet-Sun area 50% are
two-lobed Stokes V profiles, meaning that 23% of the field of view
can be adequately explained with a single constant magnetic field
embedded in a non-magnetic atmosphere. The magnetic field vector and
filling factor are reliable inferred in only 50% based on the regular
profiles. Therefore, 12% of the field of view harbour hG fields with
filling factors typically below 30%. At our present spatial resolution,
70% of the pixels apparently are non-magnetised.

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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.
2016AN....337.1057G Altcode: 2016arXiv160300679G
The new generation of solar instruments provides better
spectral, spatial, and temporal resolution for a better
understanding of the physical processes that take place on the
Sun. Multiple-component profiles are more commonly observed with these
instruments. Particularly, the He I 10830 Å triplet presents such
peculiar spectral profiles, which give information on the velocity
and magnetic fine structure of the upper chromosphere. The purpose
of this investigation is to describe a technique to efficiently fit
the two blended components of the He I 10830 Å triplet, which are
commonly observed when two atmospheric components are located within
the same resolution element. The observations used in this study were
taken on 2015 April 17 with the very fast spectroscopic mode of the
GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
telescope, located at the Observatorio del Teide, Tenerife, Spain. We
apply a double-Lorentzian fitting technique using Levenberg-Marquardt
least-squares minimization. This technique is very simple and much
faster than inversion codes. Line-of-sight Doppler velocities can
be inferred for a whole map of pixels within just a few minutes. Our
results show sub- and supersonic downflow velocities of up to 32 km
s-1 for the fast component in the vicinity of footpoints of
filamentary structures. The slow component presents velocities close
to rest.

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Title: Sunspot group tilt angle measurements from historical
observations
Authors: Senthamizh Pavai, V.; Arlt, R.; Diercke, A.; Denker, C.;
Vaquero, J. M.
2016AdSpR..58.1468S Altcode: 2016arXiv160302510S
Sunspot positions from various historical sets of solar drawings
are analyzed with respect to the tilt angles of bipolar sunspot
groups. Data by Scheiner, Hevelius, Staudacher, Zucconi, Schwabe, and
Spörer deliver a series of average tilt angles spanning a period of
270 years, additional to previously found values for 20th-century data
obtained by other authors. We find that the average tilt angles before
the Maunder minimum were not significantly different from the modern
values. However, the average tilt angles of a period 50 years after
the Maunder minimum, namely for cycles 0 and 1, were much lower and
near zero. The normal tilt angles before the Maunder minimum suggest
that it was not abnormally low tilt angles which drove the solar cycle
into a grand minimum.

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Title: Giant quiescent solar filament observed with high-resolution
spectroscopy
Authors: Kuckein, C.; Verma, M.; Denker, C.
2016A&A...589A..84K Altcode: 2016arXiv160302505K
 Aims: An extremely large filament was studied in various
layers of the solar atmosphere. The inferred physical parameters
and the morphological aspects are compared with smaller quiescent
filaments. Methods: A giant quiet-Sun filament was observed
with the high-resolution Echelle spectrograph at the Vacuum Tower
Telescope at Observatorio del Teide, Tenerife, Spain, on 2011 November
15. A mosaic of spectra (ten maps of 100″ × 182″) was recorded
simultaneously in the chromospheric absorption lines Hα and Na I
D2. Physical parameters of the filament plasma were derived
using cloud model (CM) inversions and line core fits. The spectra
were complemented with full-disk filtergrams (He I λ10830 Å, Hα,
and Ca II K) of the Chromospheric Telescope (ChroTel) and full-disk
magnetograms of the Helioseismic and Magnetic Imager (HMI). 
Results: The filament had extremely large linear dimensions (~817
arcsec), which corresponds to about 658 Mm along a great circle on
the solar surface. A total amount of 175119 Hα contrast profiles
were inverted using the CM approach. The inferred mean line-of-sight
(LOS) velocity, Doppler width, and source function were similar to
previous works of smaller quiescent filaments. However, the derived
optical thickness was higher. LOS velocity trends inferred from the
Hα line core fits were in accord but weaker than those obtained with
CM inversions. Signatures of counter-streaming flows were detected
in the filament. The largest brightening conglomerates in the line
core of Na I D2 coincided well with small-scale magnetic
fields as seen by HMI. Mixed magnetic polarities were detected close
to the ends of barbs. The computation of photospheric horizontal flows
based on HMI magnetograms revealed flow kernels with a size of 5-8
Mm and velocities of 0.30-0.45 km s-1 at the ends of the
filament. Conclusions: The physical properties of extremely
large filaments are similar to their smaller counterparts, except for
the optical thickness, which in our sample was found to be higher. We
found that a part of the filament, which erupted the day before,
is in the process of reestablishing its initial configuration.

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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.
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.

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Title: GREGOR observations of a small flare above a sunspot
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
J.; Liu, W.
2016IAUS..320...68S Altcode:
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 0.1 nm Ca II H interference
filter. Context observations from SDO/AIA, Hinode/SOT, and IRIS show
that the ribbon is a part of a larger one that extends through the
neighboring positive polarities and also participates in several
other flares within the active region. A 140 second long time series
of Ca II H images was reconstructed by means of the Multi-Frame
Blind Deconvolution method, giving the respective spatial and
temporal resolutions of 0”.1 and 1 s. Light curves and horizontal
velocities of small-scale bright knots in the observed flare ribbon
were measured. Some knots are stationary but three move along the
ribbon with speeds of 7-11 km s-1. Two of them move in the
opposite direction and exhibit highly correlated intensity changes,
providing evidence for the presence of slipping reconnection at small
spatial scales.

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Title: GREGOR observations of a small flare above a sunspot
Authors: Sobotka, Michal; Dudik, Jaroslav; Denker, Carsten; Balthasar,
Horst; Jurcak, Jan; Liu, Wenjuan; GREGOR Team
2015IAUGA..2246841S Altcode:
A small flare ribbon above a sunspot with a light bridge was observed on
7 November 2014 around 12:00 UT in the blue imaging channel of GREGOR,
using a 0.1 nm Ca II H interference filter. Context observations from
SDO/AIA, Hinode/SOT and IRIS show that the ribbon is a part of a larger
ribbon extending through the neighbouring negative polarities that also
participates in several other flares within the active region. A 140
s long time series of Ca II H images was reconstructed by means of the
Multi Frame Blind Deconvolution method, giving the respective spatial
and temporal resolutions of 0.1" and 1 s. Light curves and horizontal
velocities of small-scale brightenings in the flare ribbon located
above an umbral core were measured. Some of them are stationary but
three brightenings move in opposite directions along the ribbon with
speeds of 7 - 11 km/s. Expecting that the brightenings correspond to
footpoints of flare loops, their motions can be interpreted in terms
of the slipping reconnection model.

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Title: PEPSI: The high-resolution échelle spectrograph and
polarimeter for the Large Binocular Telescope
Authors: Strassmeier, K. G.; Ilyin, I.; Järvinen, A.; Weber, M.;
Woche, M.; Barnes, S. I.; Bauer, S. -M.; Beckert, E.; Bittner, W.;
Bredthauer, R.; Carroll, T. A.; Denker, C.; Dionies, F.; DiVarano,
I.; Döscher, D.; Fechner, T.; Feuerstein, D.; Granzer, T.; Hahn,
T.; Harnisch, G.; Hofmann, A.; Lesser, M.; Paschke, J.; Pankratow,
S.; Plank, V.; Plüschke, D.; Popow, E.; Sablowski, D.
2015AN....336..324S Altcode: 2015arXiv150506492S
PEPSI is the bench-mounted, two-arm, fibre-fed and stabilized Potsdam
Echelle Polarimetric and Spectroscopic Instrument for the 2×8.4 m
Large Binocular Telescope (LBT). Three spectral resolutions of either
43 000, 120 000 or 270 000 can cover the entire optical/red wavelength
range from 383 to 907 nm in three exposures. Two 10.3k×10.3k CCDs with
9-μm pixels and peak quantum efficiencies of 94-96 % record a total of
92 échelle orders. We introduce a new variant of a wave-guide image
slicer with 3, 5, and 7 slices and peak efficiencies between 92-96
%. A total of six cross dispersers cover the six wavelength settings
of the spectrograph, two of them always simultaneously. These are made
of a VPH-grating sandwiched by two prisms. The peak efficiency of the
system, including the telescope, is 15 % at 650 nm, and still 11 %
and 10 % at 390 nm and 900 nm, respectively. In combination with
the 110 m2 light-collecting capability of the LBT, we
expect a limiting magnitude of ≈ 20th mag in V in the low-resolution
mode. The R = 120 000 mode can also be used with two, dual-beam Stokes
IQUV polarimeters. The 270 000-mode is made possible with the 7-slice
image slicer and a 100-μm fibre through a projected sky aperture of
0.74 arcsec, comparable to the median seeing of the LBT site. The 43
000-mode with 12-pixel sampling per resolution element is our bad
seeing or faint-object mode. Any of the three resolution modes can
either be used with sky fibers for simultaneous sky exposures or with
light from a stabilized Fabry-Pérot étalon for ultra-precise radial
velocities. CCD-image processing is performed with the dedicated
data-reduction and analysis package PEPSI-S4S. Its full error
propagation through all image-processing steps allows an adaptive
selection of parameters by using statistical inferences and robust
estimators. A solar feed makes use of PEPSI during day time and a 500-m
feed from the 1.8 m VATT can be used when the LBT is busy otherwise. In
this paper, we present the basic instrument design, its realization,
and its characteristics. Some pre-commissioning first-light spectra
shall demonstrate the basic functionality.

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Title: Chromospheric Rapid Blueshifted Excursions Observed with IBIS
and their Association with Photospheric Magnetic Field Evolution
Authors: Deng, Na; Chen, Xin; Liu, Chang; Jing, Ju; Tritschler,
Alexandra; Reardon, Kevin P.; Lamb, Derek A.; Deforest, Craig E.;
Denker, Carsten; Wang, Shuo; Liu, Rui; Wang, Haimin
2015ApJ...799..219D Altcode: 2014arXiv1412.4038D
Chromospheric rapid blueshifted excursions (RBEs) are suggested to
be the disk counterparts of type II spicules at the limb and believed
to contribute to the coronal heating process. Previous identification
of RBEs was mainly based on feature detection using Dopplergrams. In
this paper, we study RBEs on 2011 October 21 in a very quiet region at
the disk center, which were observed with the high-cadence imaging
spectroscopy of the Ca II 8542 Å line from the Interferometric
Bidimensional Spectrometer (IBIS). By using an automatic spectral
analysis algorithm, a total of 98 RBEs are identified during an 11
minute period. Most of these RBEs have either a round or elongated
shape, with an average area of 1.2 arcsec2. The detailed
temporal evolution of spectra from IBIS makes possible a quantitative
determination of the velocity (~16 km s-1) and acceleration
(~400 m s-2) of Ca II 8542 RBEs, and reveals an additional
deceleration (~-160 m s-2) phase that usually follows the
initial acceleration. In addition, we also investigate the association
of RBEs with the concomitant photospheric magnetic field evolution,
using coordinated high-resolution and high-sensitivity magnetograms
made by Hinode. Clear examples are found where RBEs appear to be
associated with the preceding magnetic flux emergence and/or the
subsequent flux cancellation. However, further analysis with the aid
of the Southwest Automatic Magnetic Identification Suite does not
yield a significant statistical association between these RBEs and
magnetic field evolution. We discuss the implications of our results
in the context of understanding the driving mechanism of RBEs.

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Title: Digitization of sunspot drawings by Spörer made in 1861-1894
Authors: Diercke, A.; Arlt, R.; Denker, C.
2015AN....336...53D Altcode: 2014arXiv1411.7790D
Most of our knowledge about the Sun's activity cycle arises from
sunspot observations over the last centuries since telescopes
have been used for astronomy. The German astronomer Gustav Spörer
observed almost daily the Sun from 1861 until the beginning of 1894
and assembled a 33-year collection of sunspot data covering a total
of 445 solar rotation periods. These sunspot drawings were carefully
placed on an equidistant grid of heliographic longitude and latitude
for each rotation period, which were then copied to copper plates for a
lithographic reproduction of the drawings in astronomical journals. In
this article, we describe in detail the process of capturing these data
as digital images, correcting for various effects of the aging print
materials, and preparing the data for contemporary scientific analysis
based on advanced image processing techniques. With the processed
data we create a butterfly diagram aggregating sunspot areas, and we
present methods to measure the size of sunspots (umbra and penumbra)
and to determine tilt angles of active regions. A probability density
function of the sunspot area is computed, which conforms to contemporary
data after rescaling.

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Title: The Magnetic Configuration of a δ-Spot
Authors: Balthasar, H.; Beck, C.; Louis, R. E.; Verma, M.; Denker, C.
2014ASPC..489...39B Altcode: 2013arXiv1312.5128B
Sunspots, which harbor both magnetic polarities within one penumbra, are
called δ-spots. They are often associated with flares. Nevertheless,
there are only very few detailed observations of the spatially resolved
magnetic field configuration. We present an investigation performed
with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope
in Tenerife. We observed a sunspot with a main umbra and several
additional umbral cores, one of them with opposite magnetic polarity
(the δ-umbra). The δ-spot is divided into two parts by a line along
which central emissions of the spectral line Ca &lt;font size=2&gt;II
854.2 nm appear. The Evershed flow comming from the main umbra ends
at this line. In deep photospheric layers, we find an almost vertical
magnetic field for the δ-umbra, and the magnetic field decreases
rapidly with height, faster than in the main umbra. The horizontal
magnetic field in the direction connecting main and δ-umbra is rather
smooth, but in one location next to a bright penumbral feature at
some distance to the δ-umbra, we encounter a change of the magnetic
azimuth by 90° from one pixel to the next. Near the δ-umbra, but
just outside, we encounter a blue-shift of the spectral line profiles
which we interpret as Evershed flow away from the δ-umbra. Significant
electric current densities are observed at the dividing line of the
spot and inside the δ-umbra.

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Title: Horizontal flow fields observed in Hinode G-band
images. IV. Statistical properties of the dynamical environment
around pores
Authors: Verma, M.; Denker, C.
2014A&A...563A.112V Altcode: 2014arXiv1401.4818V
Context. Solar pores are penumbra-lacking magnetic features, that
mark two important transitions in the spectrum of magnetohydrodynamic
processes: (1) the magnetic field becomes sufficiently strong to
suppress the convective energy transport and (2) at some critical point
some pores develop a penumbra and become sunspots. Aims: The
purpose of this statistical study is to comprehensively describe solar
pores in terms of their size, perimeter, shape, photometric properties,
and horizontal proper motions. The seeing-free and uniform data of the
Japanese Hinode mission provide an opportunity to compare flow fields
in the vicinity of pores in different environments and at various
stages of their evolution. Methods: The extensive database of
high-resolution G-band images observed with the Hinode Solar Optical
Telescope (SOT) is a unique resource to derive statistical properties
of pores using advanced digital image processing techniques. The study
is based on two data sets: (1) photometric and morphological properties
inferred from single G-band images cover almost seven years from 2006
October 25 to 2013 August 31; and (2) horizontal flow fields derived
from 356 one-hour sequences of G-band images using local correlation
tracking (LCT) for a shorter period of time from 2006 November 3 to
2008 January 6 comprising 13 active regions. Results: A total
of 7643/2863 (single/time-averaged) pores builds the foundation
of the statistical analysis. Pores are preferentially observed at
low latitudes in the southern hemisphere during the deep minimum of
solar cycle No. 23. This imbalance reverses during the rise of cycle
No. 24, when the pores migrate from high to low latitudes. Pores
are rarely encountered in quiet-Sun G-band images, and only about
10% of pores exist in isolation. In general, pores do not exhibit a
circular shape. Typical aspect ratios of the semi-major and -minor
axes are 3:2 when ellipses are fitted to pores. Smaller pores (more
than two-thirds are smaller than 5 Mm2) tend to be more
circular, and their boundaries are less corrugated. Both the area and
perimeter length of pores obey log-normal frequency distributions. The
frequency distribution of the intensity can be reproduced by two
Gaussians representing dark and bright components. Bright features
resembling umbral dots and even light bridges cover about 20% of the
pores' area. Averaged radial profiles show a peak in the intensity at
normalized radius RN = r/Rpore = 2.1, followed
by maxima of the divergence at RN = 2.3 and the radial
component of the horizontal velocity at RN = 4.6. The
divergence is negative within pores strongly suggesting converging
flows towards the center of pores, whereas exterior flows are directed
towards neighboring supergranular boundaries. The photometric radius of
pores, where the intensity reaches quiet-Sun levels at RN
= 1.4, corresponds to the position where the divergence is zero at
RN = 1.6. Conclusions: Morphological and photometric
properties as well as horizontal flow fields have been obtained for
a statistically meaningful sample of pores. This provides critical
boundary conditions for MHD simulations of magnetic flux concentrations,
which eventually evolve into sunspots or just simply erode and fade
away. Numerical models of pores (and sunspots) have to fit within these
confines, and more importantly ensembles of pores have to agree with
the frequency distributions of observed parameters.

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Title: The association between sunspot magnetic fields and
superpenumbral fibrils
Authors: Louis, R. E.; Balthasar, H.; Kuckein, C.; Gömöry, P.;
Puschmann, K. G.; Denker, C.
2014AN....335..161L Altcode: 2013arXiv1312.1879L
Spectropolarimetric observations of a sunspot were carried out with
the Tenerife Infrared Polarimeter at Observatorio del Teide, Tenerife,
Spain. Maps of the physical parameters were obtained from an inversion
of the Stokes profiles observed in the infrared Fe I line at 15 648
Å. The regular sunspot consisted of a light bridge which separated the
two umbral cores of the same polarity. One of the arms of the light
bridge formed an extension of a penumbral filament which comprised
weak and highly inclined magnetic fields. In addition, the Stokes V
profiles in this filament had an opposite sign as the sunspot and some
resembled Stokes Q or U. This penumbral filament terminated abruptly
into another at the edge of the sunspot, where the latter was relatively
vertical by about 30o. Chromospheric H\alpha and He II 304
Åfiltergrams revealed three superpenumbral fibrils on the limb-side
of the sunspot, in which one fibril extended into the sunspot and was
oriented along the highly inclined penumbral counterpart of the light
bridge. An intense, elongated brightening was observed along this fibril
that was co-spatial with the intersecting penumbral filaments in the
photosphere. Our results suggest that the disruption in the sunspot
magnetic field at the location of the light bridge could be the source
of reconnection that led to the intense chromospheric brightening and
facilitated the supply of cool material in maintaining the overlying
superpenumbral fibrils.

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Title: Near-infrared spectropolarimetry of a δ-spot
Authors: Balthasar, H.; Beck, C.; Louis, R. E.; Verma, M.; Denker, C.
2014A&A...562L...6B Altcode: 2014arXiv1401.4386B
Sunspots harboring umbrae of both magnetic polarities within a common
penumbra (δ-spots) are often but not always related to flares. We
present first near-infrared observations (Fe i λ1078.3 nm and Si i
λ1078.6 nm spectra) obtained with the Tenerife Infrared Polarimeter at
the Vacuum Tower Telescope in Tenerife on 2012 June 17, which afford
accurate and sensitive diagnostics to scrutinize the complex fields
along the magnetic neutral line of a δ-spot within active region NOAA
11504. We examined the vector magnetic field, line-of-sight (LOS)
velocities, and horizontal proper motions of this rather inactive
δ-spot. We find a smooth transition of the magnetic vector field
from the main umbra to that of opposite polarity (δ-umbra), but a
discontinuity of the horizontal magnetic field at some distance from the
δ-umbra on the polarity inversion line. The magnetic field decreases
faster with height by a factor of two above the δ-umbra. The latter is
surrounded by its own Evershed flow. The Evershed flow coming from the
main umbra ends at a line dividing the spot into two parts. This line
is marked by the occurrence of central emission in the Ca iiλ854.2 nm
line. Along this line, high chromospheric LOS-velocities of both signs
appear. We detect a shear flow within the horizontal flux transport
velocities parallel to the dividing line.

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Title: Sunspot splitting triggering an eruptive flare
Authors: Louis, Rohan E.; Puschmann, Klaus G.; Kliem, Bernhard;
Balthasar, Horst; Denker, Carsten
2014A&A...562A.110L Altcode: 2013arXiv1311.5054L
 Aims: We investigate how the splitting of the leading sunspot
and associated flux emergence and cancellation in active region NOAA
11515 caused an eruptive M5.6 flare on 2012 July 2. Methods:
Continuum intensity, line-of-sight magnetogram, and dopplergram data
of the Helioseismic and Magnetic Imager were employed to analyse
the photospheric evolution. Filtergrams in Hα and He I 10830 Å of
the Chromospheric Telescope at the Observatorio del Teide, Tenerife,
track the evolution of the flare. The corresponding coronal conditions
were derived from 171 Å and 304 Å images of the Atmospheric Imaging
Assembly. Local correlation tracking was utilized to determine
shear flows. Results: Emerging flux formed a neutral line
ahead of the leading sunspot and new satellite spots. The sunspot
splitting caused a long-lasting flow towards this neutral line, where
a filament formed. Further flux emergence, partly of mixed polarity,
as well as episodes of flux cancellation occurred repeatedly at
the neutral line. Following a nearby C-class precursor flare with
signs of interaction with the filament, the filament erupted nearly
simultaneously with the onset of the M5.6 flare and evolved into a
coronal mass ejection. The sunspot stretched without forming a light
bridge, splitting unusually fast (within about a day, complete ≈6 h
after the eruption) in two nearly equal parts. The front part separated
strongly from the active region to approach the neighbouring active
region where all its coronal magnetic connections were rooted. It
also rotated rapidly (by 4.9° h-1) and caused significant
shear flows at its edge. Conclusions: The eruption resulted
from a complex sequence of processes in the (sub-)photosphere and
corona. The persistent flows towards the neutral line likely caused
the formation of a flux rope that held the filament. These flows,
their associated flux cancellation, the emerging flux, and the
precursor flare all contributed to the destabilization of the flux
rope. We interpret the sunspot splitting as the separation of two
flux bundles differently rooted in the convection zone and only
temporarily joined in the spot. This explains the rotation as the
continued rise of the separating flux, and it implies that at least
this part of the sunspot was still connected to its roots deep in
the convection zone. Movie available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201321106/olm">http://www.aanda.org</A>

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Title: High-resolution spectroscopy of a giant solar filament
Authors: Kuckein, Christoph; Denker, Carsten; Verma, Meetu
2014IAUS..300..437K Altcode: 2013arXiv1309.7861K
High-resolution spectra of a giant solar quiescent filament were
taken with the Echelle spectrograph at the Vacuum Tower Telescope
(VTT; Tenerife, Spain). A mosaic of various spectroheliograms (Hα,
Hα+/-0.5 Å and Na D2) were chosen to examine the filament
at different heights in the solar atmosphere. In addition, full-disk
images (He i 10830 Å and Ca ii K) of the Chromspheric Telescope and
full-disk magnetograms of the Helioseismic and Magnetic Imager were
used to complement the spectra. Preliminary results are shown of
this filament, which had extremely large linear dimensions (~740”)
and was observed in November 2011 while it traversed the northern
solar hemisphere.

---------------------------------------------------------
Title: GREGOR Fabry-Pérot interferometer and its companion the blue
imaging solar spectrometer
Authors: Puschmann, Klaus G.; Denker, Carsten; Balthasar, Horst; Louis,
Rohan E.; Popow, Emil; Woche, Manfred; Beck, Christian; Seelemann,
Thomas; Volkmer, Reiner
2013OptEn..52h1606P Altcode: 2013arXiv1302.7157P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-m GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI allows
fast narrow-band imaging and postfactum image restoration. The
retrieved physical parameters will be a fundamental building block
for understanding the dynamic sun and its magnetic field at spatial
scales down to ∼50 km on the solar surface. The GFPI is a tunable
dual-etalon system in a collimated mounting. It is designed for
spectrometric and spectropolarimetric observations between 530-860
nm and 580-660 nm, respectively, and possesses a theoretical spectral
resolution of R≈250,000. Large-format, high-cadence charged coupled
device detectors with sophisticated computer hard- and software enable
the scanning of spectral lines in time-spans equivalent to the evolution
time of solar features. The field-of-view (FOV) of 50″×38″ covers
a significant fraction of the typical area of active regions in the
spectroscopic mode. In case of Stokes-vector spectropolarimetry,
the FOV reduces to 25″×38″. The main characteristics of the GFPI
including advanced and automated calibration and observing procedures
are presented. Improvements in the optical design of the instrument
are discussed and first observational results are shown. Finally,
the first concrete ideas for the integration of a second FPI, the blue
imaging solar spectrometer, are laid out, which will explore the blue
spectral region below 530 nm.

---------------------------------------------------------
Title: Statistical characteristics of horizontal proper motions in
the vicinity of pores
Authors: Verma, Meetu; Denker, Carsten
2013IAUS..294..321V Altcode: 2012arXiv1210.5145V
Movement and coalescence of magnetic elements could explain the
evolution and growth of pores. There have been numerous studies focusing
on flow fields in and around individual pores. We have undertaken a
systematic study of the statistical properties of such flows. Data of
the Hinode Solar Optical Telescope offer an opportunity for this type
of research, because of the uniform data quality and absence of seeing
so that pores can directly be compared in different environments and at
various stages of their evolution. We analyzed about 220 time-series
of G-band images using local correlation tracking. The thus computed
flow maps make up a database, which covers various scenes on the
solar surface. We use an isolated pore to illustrate the statistical
parameters collected for further statistical analyses, which include
information about morphology, horizontal flows, evolutionary stage
(young, mature, or decaying), complexity of the surrounding magnetic
field, and proximity to sunspots or cluster of G-band bright points.

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Title: Digitization of Spörer's sunspot drawings
Authors: Diercke, Andrea; Arlt, Rainer; Denker, Carsten
2013IAUS..294...63D Altcode: 2012arXiv1210.5856D
Much of our knowledge about the solar dynamo is based on sunspot
observations. It is thus desirable to extend the set of positional and
morphological data of sunspots into the past. Gustav Spörer observed
in Germany from Anklam (1861-1873) and Potsdam (1874-1894). He left
detailed prints of sunspot groups, which we digitized and processed
to mitigate artifacts left in the print by the passage of time. After
careful geometrical correction, the sunspot data are now available
as synoptic charts for almost 450 solar rotation periods. Individual
sunspot positions can thus be precisely determined and spot areas
can be accurately measured using morphological image processing
techniques. These methods also allow us to determine tilt angles of
active regions (Joy's law) and to assess the complexity of an active
region.

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Title: High-Cadence and High-Resolution Halpha Imaging Spectroscopy
of a Circular Flare's Remote Ribbon with IBIS
Authors: Deng, Na; Tritschler, A.; Jing, J.; Chen, X.; Liu, C.;
Reardon, K. P.; Denker, C.; Xu, Y.; Wang, H.
2013SPD....4440404D Altcode:
We present an unprecedented high-resolution halpha imaging
spectroscopic observation of a C4.1 flare taken with IBIS on 2011
October 22. The flare consists of a main circular ribbon that occurred
in a parasitic magnetic configuration and a remote ribbon that was
observed by the IBIS. Such a circular-ribbon flare with a remote
brightening is predicted in 3D fan-spine reconnection but so far has
been rarely reported. During the flare impulsive phase, we define
"core" and "halo" structures in the observed ribbon. Examining the
halpha emission spectra averaged in the flare core and halo areas,
we find that only those from the flare cores show typical nonthermal
electron beam heating characteristics. These characteristics include:
broad and centrally reversed emission spectra, excess emission in
the red wing with regard to the blue wing (i.e., red asymmetry),
and redshifted bisectors of the emission spectra. We also observe
rather quick timescales for the heating (30 s) and cooling (14--33
s) in the flare core locations. Therefore, we suggest that the flare
cores revealed by IBIS track the sites of electron beam precipitation
with exceptional spatial and temporal resolution. The flare cores
show two-stage motion (a parallel motion along the ribbon followed
by an expansion motion perpendicular to the ribbon) during the two
impulsive phases of the flare. Some cores jump quickly (30 km/s)
between discrete magnetic elements implying reconnection involving
different flux tubes. We observe a very high temporal correlation
(&gt;0.9) between the integrated halpha and HXR emission during the
flare impulsive phase. A short time delay (4.6 s) is also found in the
halpha emission spikes relative to HXR bursts. The ionization timescale
of the cool chromosphere and the extra time taken for the electrons
to travel to the remote ribbon site may contribute to this delay.

---------------------------------------------------------
Title: Evaluating local correlation tracking using CO5BOLD simulations
of solar granulation
Authors: Verma, M.; Steffen, M.; Denker, C.
2013A&A...555A.136V Altcode: 2013arXiv1305.6033V
Context. Flows on the solar surface are intimately linked to
solar activity, and local correlation tracking (LCT) is one of the
standard techniques for capturing the dynamics of these processes by
cross-correlating solar images. However, the link between contrast
variations in successive images to the underlying plasma motions has
to be quantitatively confirmed. Aims: Radiation hydrodynamics
simulations of solar granulation (e.g., CO5BOLD) provide
access to both the wavelength-integrated, emergent continuum intensity
and the three-dimensional velocity field at various heights in the
solar atmosphere. Thus, applying LCT to continuum images yields
horizontal proper motions, which are then compared to the velocity
field of the simulated (non-magnetic) granulation. In this study, we
evaluate the performance of an LCT algorithm previously developed for
bulk-processing Hinode G-band images, establish it as a quantitative
tool for measuring horizontal proper motions, and clearly work out
the limitations of LCT or similar techniques designed to track optical
flows. Methods: Horizontal flow maps and frequency distributions
of the flow speed were computed for a variety of LCT input parameters
including the spatial resolution, the width of the sampling window,
the time cadence of successive images, and the averaging time used to
determine persistent flow properties. Smoothed velocity fields from
the hydrodynamics simulation at three atmospheric layers (log τ = -1,
0, and +1) served as a point of reference for the LCT results. 
Results: LCT recovers many of the granulation properties, e.g., the
shape of the flow speed distributions, the relationship between mean
flow speed and averaging time, and also - with significant smoothing
of the simulated velocity field - morphological features of the
flow and divergence maps. However, the horizontal proper motions are
grossly underestimated by as much as a factor of three. The LCT flows
match best the flows deeper in the atmosphere at log τ = +1. 
Conclusions: Despite the limitations of optical flow techniques, they
are a valuable tool in describing horizontal proper motions on the Sun,
as long as the results are not taken at face value but with a proper
understanding of the input parameter space and the limitations inherent
to the algorithm. Movies are available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: High-cadence and High-resolution Hα Imaging Spectroscopy of
a Circular Flare's Remote Ribbon with IBIS
Authors: Deng, Na; Tritschler, Alexandra; Jing, Ju; Chen, Xin; Liu,
Chang; Reardon, Kevin; Denker, Carsten; Xu, Yan; Wang, Haimin
2013ApJ...769..112D Altcode: 2013arXiv1304.4171D
We present an unprecedented high-resolution Hα imaging spectroscopic
observation of a C4.1 flare taken with the Interferometric Bidimensional
Spectrometer (IBIS) in conjunction with the adaptive optics system
at the 76 cm Dunn Solar Telescope on 2011 October 22 in the active
region NOAA 11324. Such a two-dimensional spectroscopic observation
covering the entire evolution of a flare ribbon with high spatial (0.”1
pixel-1 image scale), cadence (4.8 s), and spectral (0.1 Å
step size) resolution is rarely reported. The flare consists of a main
circular ribbon that occurred in a parasitic magnetic configuration and
a remote ribbon that was observed by the IBIS. Such a circular-ribbon
flare with a remote brightening is predicted in three-dimensional
fan-spine reconnection but so far has been rarely studied. During
the flare impulsive phase, we define "core" and "halo" structures in
the observed ribbon based on IBIS narrowband images in the Hα line
wing and line center. Examining the Hα emission spectra averaged in
the flare core and halo areas, we find that only those from the flare
cores show typical nonthermal electron beam heating characteristics that
have been revealed by previous theoretical simulations and observations
of flaring Hα line profiles. These characteristics include broad and
centrally reversed emission spectra, excess emission in the red wing
with regard to the blue wing (i.e., red asymmetry), and redshifted
bisectors of the emission spectra. We also observe rather quick
timescales for the heating (~30 s) and cooling (~14-33 s) in the flare
core locations. Therefore, we suggest that the flare cores revealed by
IBIS track the sites of electron beam precipitation with exceptional
spatial and temporal resolution. The flare cores show two-stage
motion (a parallel motion along the ribbon followed by an expansion
motion perpendicular to the ribbon) during the two impulsive phases
of the flare. Some cores jump quickly (30 km s-1) between
discrete magnetic elements implying reconnection involving different
flux tubes. We observe a very high temporal correlation (gsim 0.9)
between the integrated Hα and hard X-rays (HXR) emission during the
flare impulsive phase. A short time delay (4.6 s) is also found in the
Hα emission spikes relative to HXR bursts. The ionization timescale
of the cool chromosphere and the extra time taken for the electrons
to travel to the remote ribbon site may contribute to this delay.

---------------------------------------------------------
Title: The GREGOR Solar Telescope on Tenerife
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello González, N.; Berkefeld, T.;
Collados Vera, M.; Hofmann, A.; Kneer, F.; Lagg, A.; Puschmann, K. G.;
Schmidt, D.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.
2012ASPC..463..365S Altcode: 2012arXiv1202.4289S
2011 was a successful year for the GREGOR project. The telescope was
finally completed in May with the installation of the 1.5-meter primary
mirror. The installation of the first-light focal plane instruments was
completed by the end of the year. At the same time, the preparations
for the installation of the high-order adaptive optics were finished,
its integration to the telescope is scheduled for early 2012. This
paper describes the telescope and its instrumentation in their present
first-light configuration, and provides a brief overview of the science
goals of GREGOR.

---------------------------------------------------------
Title: The GREGOR Solar Telescope
Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt,
W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von
der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.;
Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.
2012IAUSS...6E.203D Altcode:
The 1.5-meter GREGOR solar telescope is a new facility for
high-resolution observations of the Sun. The telescope is located at the
Spanish Observatorio del Teide on Tenerife. The telescope incorporates
advanced designs for a foldable-tent dome, an open steel-truss telescope
structure, and active and passive means to minimize telescope and mirror
seeing. Solar fine structure can be observed with a dedicated suite
of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot
Interferometer", and the "Grating Infrared Spectrograph". All post-focus
instruments benefit from a high-order (multi-conjugate) adaptive optics
system, which enables observations close to the diffraction limit of
the telescope. The inclusion of a spectrograph for stellar activity
studies and the search for solar twins expands the scientific usage
of the GREGOR to the nighttime domain. We report on the successful
commissioning of the telescope until the end of 2011 and the first
steps towards science verification in 2012.

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Title: The GREGOR Fabry-Pérot Interferometer: A New Instrument for
High-Resolution Spectropolarimetric Solar Observations
Authors: Puschmann, K. G.; Balthasar, H.; Bauer, S. -M.; Hahn, T.;
Popow, E.; Seelemann, T.; Volkmer, R.; Woche, M.; Denker, C.
2012ASPC..463..423P Altcode: 2011arXiv1111.5509P
Fabry-Pérot interferometers have advantages over slit spectrographs
because they allow fast narrow-band imaging and post-factum image
reconstruction of the retrieved data. Temperature, plasma velocity,
and magnetic field maps can be derived from inversions of spectral
lines, thus, advancing our understanding of the dynamic Sun and its
magnetic fields at the smallest spatial scales. The GREGOR Fabry-Pérot
Interferometer (GFPI) is one of two first-light instruments of the
1.5-meter GREGOR solar telescope, which is currently being commissioned
at the Observatorio del Teide, Tenerife, Spain. The GFPI operates close
to the diffraction limit of GREGOR, thus, providing access to fine
structures as small as 60 km on the solar surface. The field-of-view
of 52″×40″ is sufficiently large to cover significant area
fraction of active regions. The GFPI is a tuneable dual-etalon system
in a collimated mounting. Equipped with a full-Stokes polarimeter,
it records spectropolarimetric data with a spectral resolution of R
≍ 250,000 over the wavelength range from 530-860 nm. Large-format,
high-cadence CCD detectors with powerful computer hard- and software
facilitate scanning of spectral lines in time spans corresponding
to the evolution time-scale of solar features. We present the main
characteristics of the GFPI including the latest developments in
software, mechanical mounts, and optics.

---------------------------------------------------------
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.
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.
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: 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.
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: Editors' note
Authors: Denker, Carsten; Feller, Alex; Schmidt, Wolfgang; von der
Lühe, Oskar
2012AN....333....1D Altcode:
This topical issue of Astronomische Nachrichten/Astronomical Notes is a
collection of reference articles covering the GREGOR solar telescope,
its science capabilities, its subsystems, and its dedicated suite
of instruments for high-resolution observations of the Sun. Because
ground-based telescopes have life spans of several decades, it is
only natural that they continuously reinvent themselves. Literally,
the GREGOR telescope builds on the foundations of the venerable
Gregory-Coudé Telescope (GCT) at Observatorio del Teide, Tenerife,
Spain. Acknowledging the fact that new discoveries in observational
solar physics are driven by larger apertures to collect more photons
and to scrutinize the Sun in finer detail, the GCT was decommissioned
and the building was made available to the GREGOR project.

---------------------------------------------------------
Title: The GREGOR Fabry-Pérot Interferometer
Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.;
Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados,
M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.;
Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer,
R.; Wittmann, A. D.; Woche, M.
2012AN....333..880P Altcode: 2012arXiv1210.2921P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-meter GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two
tunable etalons in collimated mounting. Thanks to its large-format,
high-cadence CCD detectors with sophisticated computer hard- and
software it is capable of scanning spectral lines with a cadence
that is sufficient to capture the dynamic evolution of the solar
atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well
suited for quiet Sun and sunspot observations. However, in the vector
spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The
spectral coverage in the spectroscopic mode extends from 530-860 nm
with a theoretical spectral resolution of R ≈ 250,000, whereas in
the vector spectropolarimetric mode the wavelength range is at present
limited to 580-660 nm. The combination of fast narrow-band imaging and
post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales
down to ∼50 km on the solar surface.

---------------------------------------------------------
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.
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: The GREGOR Fabry-Perot interferometer: status report and
prospects
Authors: Puschmann, Klaus G.; Balthasar, Horst; Beck, Christian;
Louis, Rohan E.; Popow, Emil; Seelemann, Thomas; Volkmer, Reiner;
Woche, Manfred; Denker, Carsten
2012SPIE.8446E..79P Altcode: 2012arXiv1207.2084P
The GREGOR Fabry-Ṕerot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-meter GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI allows
fast narrow-band imaging and post-factum image restoration. The
retrieved physical parameters will be a fundamental building block
for understanding the dynamic Sun and its magnetic field at spatial
scales down to 50 km on the solar surface. The GFPI is a tunable
dual-etalon system in a collimated mounting. It is designed for
spectropolarimetric observations over the wavelength range from 530-860
nm with a theoretical spectral resolution of R ≍ 250,000. The GFPI is
equipped with a full-Stokes polarimeter. Large-format, high-cadence CCD
detectors with powerful computer hard- and software enable the scanning
of spectral lines in time spans equivalent to the evolution time of
solar features. The field-of-view of 50”×38” covers a significant
fraction of the typical area of active regions. We present the main
characteristics of the GFPI including advanced and automated calibration
and observing procedures. We discuss improvements in the optical design
of the instrument and show first observational results. Finally, we
lay out first concrete ideas for the integration of a second FPI, the
Blue Imaging Solar Spectrometer, which will explore the blue spectral
region below 530 nm.

---------------------------------------------------------
Title: Horizontal flow fields observed in Hinode G-band
images. III. The decay of a satellite sunspot and the role of magnetic
flux removal in flaring
Authors: Verma, M.; Denker, C.
2012A&A...545A..92V Altcode: 2012arXiv1207.6219V
Context. Emergence of magnetic flux plays an important role in the
initiation of flares. However, the role of submerging magnetic flux
in prompting flares is more ambiguous, not the least because of the
scarcity of observations. Aims: The flare-prolific active
region NOAA 10930 offered both a developing δ-spot and a decaying
satellite sunspot of opposite polarity. The objective of this study
is to characterize the photometric decay of the satellite sunspot as
well as the evolution of photospheric and chromospheric horizontal
proper motions in its surroundings. Methods: We apply the local
correlation tracking technique to a 16-h time-series of Hinode G-band
and Ca ii H images and study the horizontal proper motions in the
vicinity of the satellite sunspot on 2006 December 7. Decorrelation
times were computed to measure the lifetime of solar features in
intensity and flow maps. Results: We observed shear flows
in the dominant umbral cores of the satellite sunspot. These flows
vanished once the penumbra had disappeared. This slow penumbral decay
had an average rate of 152 Mm2 day-1 over an
11-h period. Typical lifetimes of intensity features derived from an
autocorrelation analysis are 3-5 min for granulation, 25-35 min for
G-band bright points, and up to 200-235 min for penumbrae, umbrae,
and pores. Long-lived intensity features (i.e., the dominant umbral
cores) are not related to long-lived flow features in the northern
part of the sunspot, where flux removal, slowly decaying penumbrae,
and persistent horizontal flows of up to 1 km s-1 contribute
to the erosion of the sunspot. Finally, the restructuring of magnetic
field topology was responsible for a homologous M2.0 flare, which shared
many characteristics with an X6.5 flare on the previous day. 
Conclusions: Notwithstanding the prominent role of δ-spots in flaring,
we conclude based on the decomposition of the satellite sunspot, the
evolution of the surrounding flow fields, and the timing of the M2.0
flare that the vanishing magnetic flux in the decaying satellite sunspot
played an instrumental role in triggering the homologous M2.0 flare
and the eruption of a small Hα filament. The strong magnetic field
gradients of the neighboring δ-spot merely provided the vehicle for
the strongest flare emission about 10 min after the onset of the flare.

---------------------------------------------------------
Title: Horizontal flows concurrent with an X2.2 flare in the active
region NOAA 11158
Authors: Beauregard, L.; Verma, M.; Denker, C.
2012AN....333..125B Altcode: 2012arXiv1201.2800B
Horizontal proper motions were measured with local correlation tracking
(LCT) techniques in active region NOAA 11158 on 2011 February 15 at a
time when a major (X2.2) solar flare occurred. The measurements are
based on continuum images and magnetograms of the Helioseismic and
Magnetic Imager on board the Solar Dynamics Observatory. The observed
shear flows along the polarity inversion line were rather weak (a few
100 m s-1). The counter-streaming region shifted toward
the north after the flare. A small circular area with flow speeds of
up to 1.2 km s-1 appeared after the flare near a region
of rapid penumbral decay. The LCT signal in this region was provided
by small-scale photospheric brigthenings, which were associated with
fast traveling moving magnetic features. Umbral strengthening and
rapid penumbral decay was observed after the flare. Both phenomena
were closely tied to kernels of white-light flare emission. The
white-light flare only lasted for about 15 min and peaked 4 min
earlier than the X-ray flux. In comparison to other major flares,
the X2.2 flare in active region NOAA 11158 only produced diminutive
photospheric signatures.

---------------------------------------------------------
Title: Horizontal flow fields observed in Hinode G-band
images. II. Flow fields in the final stages of sunspot decay
Authors: Verma, M.; Balthasar, H.; Deng, N.; Liu, C.; Shimizu, T.;
Wang, H.; Denker, C.
2012A&A...538A.109V Altcode: 2011arXiv1112.1589V
Context. Generation and dissipation of magnetic fields is a fundamental
physical process on the Sun. In comparison to flux emergence and the
initial stages of sunspot formation, the demise of sunspots still
lacks a comprehensive description. Aims: The evolution of
sunspots is most commonly discussed in terms of their intensity and
magnetic field. Here, we present additional information about the
three-dimensional flow field in the vicinity of sunspots towards
the end of their existence. Methods: We present a subset of
multi-wavelengths observations obtained with the Japanese Hinode
mission, the Solar Dynamics Observatory (SDO), and the Vacuum Tower
Telescope (VTT) at Observatorio del Teide, Tenerife, Spain during the
time period 2010 November 18-23. Horizontal proper motions were derived
from G-band and Ca ii H images, whereas line-of-sight velocities were
extracted from VTT echelle Hα λ656.28 nm spectra and Fe i λ630.25 nm
spectral data of the Hinode/Spectro-Polarimeter, which also provided
three-dimensional magnetic field information. The Helioseismic and
Magnetic Imager on board SDO provided continuum images and line-of-sight
magnetograms, in addition to the high-resolution observations for the
entire disk passage of the active region. Results: We perform
a quantitative study of photospheric and chromospheric flow fields
in and around decaying sunspots. In one of the trailing sunspots of
active region NOAA 11126, we observe moat flow and moving magnetic
features (MMFs), even after its penumbra had decayed. We also detect
a superpenumbral structure around this pore. We find that MMFs follow
well-defined, radial paths from the spot all the way to the border of
a supergranular cell surrounding the spot. In contrast, flux emergence
near the other sunspot prevents the establishment of similar well
ordered flow patterns, which could be discerned around a tiny pore of
merely 2 Mm diameter. After the disappearance of the sunspots/pores,
a coherent patch of abnormal granulation remained at their location,
which was characterized by more uniform horizontal proper motions, low
divergence values, and smaller photospheric Doppler velocities. This
region, thus, differs significantly from granulation and other areas
covered by G-band bright points. We conclude that this peculiar flow
pattern is a signature of sunspot decay and the dispersal of magnetic
flux.

---------------------------------------------------------
Title: Velocity fields in and around sunspots at the highest
resolution
Authors: Denker, Carsten; Verma, Meetu
2011IAUS..273..204D Altcode: 2010arXiv1009.1995D
The flows in and around sunspots are rich in detail. Starting with
the Evershed flow along low-lying flow channels, which are cospatial
with the horizontal penumbral magnetic fields, Evershed clouds
may continue this motion at the periphery of the sunspot as moving
magnetic features in the sunspot moat. Besides these well-ordered
flows, peculiar motions are found in complex sunspots, where they
contribute to the build-up or relaxation of magnetic shear. In
principle, the three-dimensional structure of these velocity fields
can be captured. The line-of-sight component of the velocity vector is
accessible with spectroscopic measurements, whereas local correlation
or feature tracking techniques provide the means to assess horizontal
proper motions. The next generation of ground-based solar telescopes
will provide spectropolarimetric data resolving solar fine structure
with sizes below 50 km. Thus, these new telescopes with advanced
post-focus instruments act as a `zoom lens' to study the intricate
surface flows associated with sunspots. Accompanied by `wide-angle'
observations from space, we have now the opportunity to describe
sunspots as a system. This review reports recent findings related
to flows in and around sunpots and highlights the role of advanced
instrumentation in the discovery process.

---------------------------------------------------------
Title: Horizontal flow fields observed in Hinode G-band
images. I. Methods
Authors: Verma, M.; Denker, C.
2011A&A...529A.153V Altcode: 2011arXiv1103.2622V
Context. The interaction of plasma motions and magnetic fields is
an important mechanism, which drives the solar activity in all its
facets. For example, photospheric flows are responsible for the
advection of magnetic flux, the redistribution of flux during the
decay of sunspots, and the build-up of magnetic shear in flaring
active regions. Aims: Systematic studies based on G-band
data from the Japanese Hinode mission provide the means to gather
statistical properties of horizontal flow fields. This facilitates
comparative studies of solar features, e.g., G-band bright points,
magnetic knots, pores, and sunspots at various stages of evolution and
in distinct magnetic environments, which advances our understanding of
the dynamic Sun. Methods: We adapted local correlation tracking
(LCT) to measure horizontal flow fields based on G-band images obtained
with the Solar Optical Telescope on board Hinode. A total of about
200 time-series with a duration between 1-16 h and a cadence between
15-90 s were analyzed. Selecting a high-cadence (Δt = 15 s) as well
as a long-duration (ΔT = 16 h) time-series enabled us to optimize and
validate the LCT input parameters, which ensures a robust, reliable,
uniform, and accurate processing of a huge data volume. Results:
The LCT algorithm produces best results for G-band images with a cadence
of 60-90 s. If the cadence is lower, the velocity of slowly moving
features will not be reliably detected. If the cadence is higher, the
scene on the Sun will have evolved too much to bear any resemblance with
the earlier situation. Consequently, in both instances horizontal proper
motions are underestimated. The most reliable and yet detailed flow maps
are produced using a Gaussian kernel with a size of 2560 km × 2560 km
and a full-width-at-half-maximum (FWHM) of 1200 km (corresponding to
the size of a typical granule) as sampling window. Conclusions:
Horizontal flow maps and graphics for visualizing the properties of
photospheric flow fields are typical examples for value-added data
products, which can be extracted from solar databases. The results of
this study will be made available within the "small projects" section
of the German Astrophysical Virtual Observatory (GAVO).

---------------------------------------------------------
Title: Observations of On-Disk Type I and II Spicules
Authors: Deng, Na; Denker, C.; Verma, M.; Shimizu, T.; Liu, C.;
Wang, H.
2011SPD....42.1737D Altcode: 2011BAAS..43S.1737D
A coordinated observing campaign was carried out during 2010
November 16-30 using German Vacuum Tower Telescope (VTT) and Hinode
to investigate properties of small-scale spicules on the solar
disk. The high-spectral resolution Echelle spectrograph at the VTT
on Tenerife acquired spectra of the chromospheric halpha (656.28 nm)
and photospheric Fe I (656.92 nm) lines in a region centered on a
small pore. Hinode mission provides high-cadence vector magnetograms,
G-band and Ca II H images, EIS and XRT observations of the same
region. We present statistical properties of spicules (type I and II),
such as spectral characteristics, velocities, spatial distribution and
temporal evolution, paying particular attention to type II spicules or
chromospheric jets. We investigate the photospheric magnetic structure,
flow field and their evolution attempting to find the origin of
chromospheric jets. The vertical extent of identified chromospheric
jets in the transition region and corona will be studied using EIS
and XRT observations in conjunction with SDO observations.

---------------------------------------------------------
Title: Polarimetry with GREGOR
Authors: Balthasar, H.; Bello González, N.; Collados, M.; Denker,
C.; Feller, A.; Hofmann, A.; Lagg, A.; Nagaruju, L.; Puschmann, K. G.;
Soltau, D.; Volkmer, R.
2011ASPC..437..351B Altcode:
A brief description of the new 1.5-meter solar telescope GREGOR located
at the Observatorio del Teide in Tenerife will be given. GREGOR will
provide a spatial resolution of about 75 km on the Sun, and with its
light collecting capability we will be able to study the development
of small magnetic features with high cadence. From the beginning,
it will be equipped with the GREGOR Fabry-Pérot Interferometer
(GFPI) for the visible spectral range and with a GRating Infrared
Spectrograph (GRIS). Both postfocus instruments can be combined
with a polarimeter, and in both cases the light is modulated by two
ferro-electric liquid crystals. A calibration unit can be inserted to
determine the instrumental polarization. Because of the altazimuthal
mount, time-dependent rotation of the polarimetric reference plane
is introduced, and we have to develop a polarization model of the
telescope. Measurements to verify this model are in preparation.

---------------------------------------------------------
Title: GREGOR telescope: start of commissioning
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvana, M.; Kneer, F.; Lagg, A.; Popow,
E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K.
2010SPIE.7733E..0KV Altcode: 2010SPIE.7733E..18V
With the integration of a 1-meter Cesic primary mirror the GREGOR
telescope pre-commissioning started. This is the first time, that
the entire light path has seen sunlight. The pre-commissioning period
includes testing of the main optics, adaptive optics, cooling system,
and pointing system. This time was also used to install a near-infrared
grating spectro-polarimeter and a 2D-spectropolarimeter for the visible
range as first-light science instruments. As soon as the final 1.5
meter primary mirror is installed, commissioning will be completed,
and an extended phase of science verification will follow. In the near
future, GREGOR will be equipped with a multi-conjugate adaptive optics
system that is presently under development at KIS.

---------------------------------------------------------
Title: The GREGOR Fabry-Perot interferometer: a new instrument for
high-resolution solar observations
Authors: Denker, Carsten; Balthasar, Horst; Hofmann, Axel; Bello
González, Nazaret; Volkmer, Reiner
2010SPIE.7735E..6MD Altcode: 2010SPIE.7735E.217D
The GREGOR Fabry-Ṕerot Interferometer (GFPI) is one of the first-light
instruments of the 1.5-meter GREGOR solar telescope currently being
commissioned at Observatorio del Teide (OT), Tenerife, Spain. A
spectral resolution of R ~ 250, 000 over the wavelength range from
530-860 nm can be achieved using a tunable dual etalon system. A high
spectral resolving power is needed to extract physical parameters
(e.g., temperature, plasma velocity and the magnetic field vector) from
inversions of photospheric and chromospheric spectral lines. The GFPI
is outfitted with a polarimeter, which accurately measures the full
Stokes vector. Precision polarimetry is facilitated by a calibration
unit in the immediate vicinity of GREGOR's secondary focus. The GFPI
operates close to the diffraction limit of GREGOR, thus providing
access to fine structures as small as 60 km on the solar surface. The
field-of-view (FOV) of 52" × 40" is sufficiently large to cover
significant portions of active regions. Large-format, high-cadence
CCD detectors are an integral part of the instrument to ensure that
scans of spectral lines can be obtained in time spans corresponding
to the evolution time scale of solar phenomena such as granulation,
evolving magnetic fields or dynamic chromospheric features. Besides
describing the technical features of the GFPI and providing a status
report on commissioning the instrument, we will use two-dimensional
spectropolarimetric data obtained with the Vacuum Tower Telescope
(VTT) at OT to illustrate GFPI's science capabilities.

---------------------------------------------------------
Title: The Big Bear Solar Observatory Ca II K-line index for solar
cycle 23
Authors: Naqvi, M. F.; Marquette, W. H.; Tritschler, A.; Denker, C.
2010AN....331..696N Altcode:
No abstract at ADS

---------------------------------------------------------
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.
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: Instrument and data analysis challenges for imaging
spectro-polarimetry
Authors: Denker, C.
2010AN....331..648D Altcode: 2010arXiv1002.1792D
The next generation of solar telescopes will enable us to resolve the
fundamental scales of the solar atmosphere, i.e., the pressure scale
height and the photon mean free path. High-resolution observations
of small-scale structures with sizes down to 50 km require complex
post-focus instruments, which employ adaptive optics (AO) and benefit
from advanced image restoration techniques. The GREGOR Fabry-Pérot
Interferometer (GFPI) will serve as an example of such an instrument
to illustrate the challenges that are to be expected in instrumentation
and data analysis with the next generation of solar telescopes.

---------------------------------------------------------
Title: Optical context observations for LOFAR
Authors: Denker, C.
2009sksp.conf....7D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A full-Stokes polarimeter for the GREGOR Fabry-Perot
interferometer
Authors: Balthasar, Horst; Bello González, N.; Collados, M.; Denker,
C.; Hofmann, A.; Kneer, F.; Puschmann, K. G.
2009IAUS..259..665B Altcode:
One of the first post-focus instruments of the new solar telescope
GREGOR will be a Fabry-Perot spectrometer, which is an upgrade of the
Göttingen Fabry-Perot interferometer at the Vacuum Tower Telescope
(VTT) on Tenerife. This spectrometer is equipped with a full-Stokes
polarimeter. The modulation is performed with two ferroelectric liquid
crystals, one acting nominally as quarter-wave plate, and the other as
half-wave plate. A modified Savart plate serves as polarimetric beam
splitter. With the present liquid crystals, the optimum wavelength range
of this polarimeter is between 580 and 660 nm. The spectro-polarimeter
will benefit from the capabilities of the new telescope GREGOR which
will provide a spatial resolution of about 0″.1 (75 km on the solar
surface). Thus we will be able to investigate small magnetic features,
and we will study their development with high cadence.

---------------------------------------------------------
Title: Mini-filaments - small-scale analogues of solar eruptive
events?
Authors: Denker, Carsten; Tritschler, Alexandra
2009IAUS..259..223D Altcode:
Mini-filaments are a small-scale phenomenon of the solar chromosphere,
which frequently occur across the entire disk (see e.g. Wang, Li,
Denker, et al. 2000). They share a variety of characteristics with
their larger-scale cousins and may serve as a proxy for more complex
systems. They play an important role in the energy and mass supply
to the corona. In the case of small-scale eruptive filaments, only
a single, small-scale loop system is involved. Furthermore, they are
supported by simple magnetic field configurations (see Livi, Wang &amp;
Martin 1985), either magnetic bipoles or well-defined multipoles,
easing their theoretical description. Since mini-filaments are small
(just a few tens of seconds of arc) but highly dynamic (eruptions
can occur within just a few minutes), they are an ideal target for
high-resolution two-dimensional spectroscopy. We present a preliminary
analysis of two-dimensional Hα spectroscopic data accompanied by
broad-band speckle-restored images to demonstrate that chromospheric
small-scale phenomena can serve as building blocks for our understanding
of solar eruptive events such as filament/prominence eruptions and
even coronal mass ejections (CMEs).

---------------------------------------------------------
Title: High-resolution observations of extremely bright penumbral
grains
Authors: Denker, C.; Tritschler, A.; Deng, N.; Verdoni, A. P.
2008AN....329..773D Altcode:
We observed a cluster of extremely bright penumbral grains located at
the inner limb-side penumbra of the leading sunspot in active region
NOAA 10892. The penumbral grains in the cluster showed a typical peak
intensity of 1.58 times the intensity I_0 of the granulation surrounding
the sunspot. The brightest specimen even reached values of 1.8--2.0
I_0, thus, exceeding the temperatures of the brightest granules in the
immediate surroundings of the sunspot. We find that the observed sample
of extremely bright penumbral grains is an intermittent phenomenon,
that disappears on time scales of hours. Horizontal flow maps indicating
proper motions reveal that the cluster leaves a distinct imprint on
the penumbral flow field. We find that the divergence line co-located
with the cluster is displaced from the middle penumbra closer towards
the umbra and that the radial outflow velocities are significantly
increased to speeds in excess of 2 km s^{-1}. The extremely bright
penumbral grains, which are located at the inner limb-side penumbra,
are also discernible in off-band Hα images down to Hα ± 0.045 nm. We
interpret the observations in the context of the moving flux tube model
arguing that hotter than normal material is rapidly ascending along
the inner footpoint of the embedded flux tube, i.e., the ascending hot
material is the cause of the extremely bright penumbral grains. This
study is based on speckle-reconstructed broad-band images taken at 600
nm and chromospheric Hα observations obtained with two-dimensional
spectroscopy. All data were taken with adaptive optics under very
good seeing conditions at the Dunn Solar Telescope, National Solar
Observatory/Sacramento Peak, New Mexico on 2006 June 10.

---------------------------------------------------------
Title: First-Light Science Cases for the GREGOR Fabry-Perot
Interferometer
Authors: Denker, C.; Balthasar, H.; Bello González, N.; Collados,
M.; Kneer, H. F. Nicklas; Puschmann, K. G.
2008ESPM...12..6.8D Altcode:
The light-gathering capacity and resolving power of the 1.5-meter
aperture GREGOR telescope will provide solar observations of
the full Stokes vector with high temporal, spectral and spatial
resolution. As one of the first-light instruments, the GREGOR
Fabry-Perot Interferometer (GFPI) is well suited for observations
with adaptive optics (AO) correction. Post-facto image correction
(speckle masking imaging and deconvolution) will further enhance
the data quality to approach the diffraction-limited resolution of
the telescope. We will describe the GFPI optical design and its basic
operating procedures. Instruments characteristics such as field-of-view,
cadence, spectral resolution, and spectroscopic/polarimetric observing
modes will result in boundary conditions, which have to be carefully
considered in optimizing the scientific outcome of the first-light
observations. We will present two science cases for quiet Sun and
active region studies to illustrate the capabilities of this imaging
spectro-polarimeter.

---------------------------------------------------------
Title: Concepts for Multi-wavelength Observations with the 1.5 m
Solar Telescope GREGOR
Authors: Schmidt, W.; Beck, C.; Denker, C.; Soltau, D.; Volkmer, R.
2008ESPM...12.2.72S Altcode:
The initial instrumentation of the 1.5 m solar telescope GREGOR on
Tenerife will include a grating spectrograph with a spectro-polarimeter
for the near infrared and a dual Fabry-Perot filter spectro-polarimeter
for the "red" wavelength range from 530 to 860 nm. Both instruments
are based on their predecessors that are presently operated at
the Vacuum-Tower Telescope on Tenerife. In order to fully exploit
the scientific capability of GREGOR, simultaneous multi-wavelength
observations are necessary. Such observations will allow studying the
coupling of different layers of the solar atmosphere. Simultaneous
measurements of the magnetic field, using different spectral lines,
increase the sensitivity and the accuracy of such measurements. We
present concepts for multi-wavelength observations with GREGOR based
on the first-light instruments. As a first step, fast large-format CCD
cameras will be used in the slit-jaw imaging system of the spectrograph
or in an additional medium-band imaging channel for post-facto image
restoration combined with the spectro-polarimeter. These observations
with high spatial resolution would provide the context for the
spectrally resolved data. Beyond simple time-share concepts, the
different characteristics of imaging and spectrograph-based instruments
require more sophisticated approaches, which should neither sacrifice
adaptive optics performance nor diminish polarimetric efficiency and
accuracy. Here, we will discuss a beam splitter option and variants
of scanning spectrograph systems. Finally, we introduce a concept for
a second-generation instrument the "Blue Imaging Solar Spectrometer"
(BLISS), a dual Fabry-Perot interferometer to explore the blue solar
spectrum (from 380 to 530 nm) in tandem with the "red" instrument.

---------------------------------------------------------
Title: PEPSI: the Potsdam Echelle Polarimetric and Spectroscopic
Instrument for the LBT
Authors: Strassmeier, K. G.; Woche, M.; Ilyin, I.; Popow, E.; Bauer,
S. -M.; Dionies, F.; Fechner, T.; Weber, M.; Hofmann, A.; Storm,
J.; Materne, R.; Bittner, W.; Bartus, J.; Granzer, T.; Denker, C.;
Carroll, T.; Kopf, M.; DiVarano, I.; Beckert, E.; Lesser, M.
2008SPIE.7014E..0NS Altcode: 2008SPIE.7014E..21S
We present the status of PEPSI, the bench-mounted fibre-fed and
stabilized "Potsdam Echelle Polarimetric and Spectroscopic Instrument"
for the 2×8.4m Large Binocular Telescope in southern Arizona. PEPSI
is under construction at AIP and is scheduled for first light in
2009/10. Its ultra-high-resolution mode will deliver an unprecedented
spectral resolution of approximately R=310,000 at high efficiency
throughout the entire optical/red wavelength range 390-1050nm without
the need for adaptive optics. Besides its polarimetric Stokes IQUV mode,
the capability to cover the entire optical range in three exposures at
resolutions of 40,000, 130,000 and 310,000 will surpass all existing
facilities in terms of light-gathering-power times spectral-coverage
product. A solar feed will make use of the spectrograph also during day
time. As such, we hope that PEPSI will be the most powerful spectrometer
of its kind for the years to come.

---------------------------------------------------------
Title: Optical Design of Multilayer Achromatic Waveplate by Simulated
Annealing Algorithm
Authors: Ma, Jun; Wang, Jing-Shan; Denker, Carsten; Wang, Hai-Min
2008ChJAA...8..349M Altcode:
We applied a Monte Carlo method — simulated annealing algorithm
— to carry out the design of multilayer achromatic waveplate. We
present solutions for three-, six- and ten-layer achromatic
waveplates. The optimized retardance settings are found to be
89°51‧39″+/-0°33‧37″ and 89°54‧46″+/-0°22‧4″ for
the six- and ten-layer waveplates, respectively, for a wavelength range
from 1000 nm to 1800 nm. The polarimetric properties of multilayer
waveplates are investigated based on several numerical experiments. In
contrast to previously proposed three-layer achromatic waveplate, the
fast axes of the new six- and ten-layer achromatic waveplate remain
at fixed angles, independent of the wavelength. Two applications of
multilayer achromatic waveplate are discussed, the general-purpose phase
shifter and the birefringent filter in the Infrared Imaging Magnetograph
(IRIM) system of the Big Bear Solar Observatory (BBSO). We also checked
an experimental method to measure the retardance of waveplates.

---------------------------------------------------------
Title: Solar Physics and the Solar-Stellar Connection at Dome C
Authors: Denker, C.; Strassmeier, K. G.
2008EAS....33...97D Altcode: 2007arXiv0712.1471D
Solar magnetic fields evolve on many time-scales, e.g., the generation,
migration, and dissipation of magnetic flux during the 22-year magnetic
cycle of the Sun. Active regions develop and decay over periods of
weeks. The build-up of magnetic shear in active regions can occur
within less than a day. At the shortest time-scales, the magnetic
field topology can change rapidly within a few minutes as the result of
eruptive events such as flares, filament eruptions, and coronal mass
ejections. The unique daytime seeing characteristics at Dome C, i.e.,
continuous periods of very good to excellent seeing during almost the
entire Antarctic summer, allow us to address many of the top science
cases related to the evolution of solar magnetic fields. We introduce
the Advanced Solar Photometric Imager and Radiation Experiment and
present the science cases for synoptic solar observations at Dome
C. Furthermore, common science cases concerning the solar-stellar
connection are discussed in the context of the proposed International
Concordia Explorer Telescope.

---------------------------------------------------------
Title: Science with ICE-T: Exoplanets and stellar/solar activity
Authors: Strassmeier, K. G.; Granzer, T.; Denker, C.; Fuhrmann, C.;
Fügner, D.; Woche, M.; Divarano, I.; Cutispoto, G.; Herber, A.;
Horne, K.; Rafanelli, P.; Bortoletto, F.; Ribas, I.; Tosti, G.
2008EAS....33..199S Altcode:
We present the science case for ICE-T, the International Concordia
Explorer Telescope, a double telescope optimized for ultra-high and
ultra wide field optical time-series photometry from Dome C. ICE-T
consists of two 60 cm 8^circ×8°-FOV Schmidt telescopes for Sloan
g and i photometry and one independent 25 cm, solar, full-disk, Ca
ii-K imaging telescope on a single mount. ICE-T is therefore operable
during night and day. A 28 cm narrow-field Maksutov spectrophotometric
telescope for night-time aerosol measurements (TAVERN-SP) will be
provided by AWI early on and operated in parallel with IRAIT and
later with ICE-T. The low scintillation noise and the long continuous
darkness are among the unique properties for high precision optical
time-series photometry.

---------------------------------------------------------
Title: Flow Field Evolution of a Decaying Sunspot
Authors: Deng, Na; Choudhary, Debi Prasad; Tritschler, Alexandra;
Denker, Carsten; Liu, Chang; Wang, Haimin
2007ApJ...671.1013D Altcode: 2007arXiv0709.3340D
We study the evolution of the flows and horizontal proper motions
in and around a decaying follower sunspot based on time sequences
of two-dimensional spectroscopic observations in the visible and
white-light imaging data obtained over 6 days from 2005 June 7 to
12. During this time period the sunspot decayed gradually to a pore. The
spectroscopic observations were obtained with the Fabry-Pérot-based
Visible-Light Imaging Magnetograph (VIM) in conjunction with the
high-order adaptive optics (AO) system operated at the 65 cm vacuum
reflector of the Big Bear Solar Observatory (BBSO). We apply local
correlation tracking (LCT) to the speckle-reconstructed time sequences
of white-light images around 600 nm to infer horizontal proper motions,
while the Doppler shifts of the scanned Fe I line at 630.15 nm are
used to calculate line-of-sight (LOS) velocities with subarcsecond
resolution. We find that the dividing line between radial inward and
outward proper motions in the inner and outer penumbra, respectively,
survives the decay phase. In particular the moat flow is still
detectable after the penumbra disappeared. Based on our observations,
three major processes removed flux from the sunspot: (1) fragmentation
of the umbra, (2) flux cancelation of moving magnetic features (MMFs; of
the same polarity as the sunspot) that encounter the leading opposite
polarity network and plages areas, and (3) flux transport by MMFs
(of the same polarity as the sunspot) to the surrounding network and
plage regions that have the same polarity as the sunspot.

---------------------------------------------------------
Title: Two-Dimensional Spectroscopy of Photospheric Shear Flows in
a Small δ Spot
Authors: Denker, C.; Deng, N.; Tritschler, A.; Yurchyshyn, V.
2007SoPh..245..219D Altcode: 2007arXiv0708.3490D
In recent high-resolution observations of complex active regions,
long-lasting and well-defined regions of strong flows were identified
in major flares and associated with bright kernels of visible,
near-infrared, and X-ray radiation. These flows, which occurred in the
proximity of the magnetic neutral line, significantly contributed to
the generation of magnetic shear. Signatures of these shear flows are
strongly curved penumbral filaments, which are almost tangential to
sunspot umbrae rather than exhibiting the typical radial filamentary
structure. Solar active region NOAA 10756 was a moderately complex
βδ sunspot group, which provided an opportunity to extend previous
studies of such shear flows to quieter settings. We conclude that
shear flows are a common phenomenon in complex active regions and δ
spots. However, they are not necessarily a prerequisite condition for
flaring. Indeed, in the present observations, the photospheric shear
flows along the magnetic neutral line are not related to any change of
the local magnetic shear. We present high-resolution observations of
NOAA 10756 obtained with the 65-cm vacuum reflector at Big Bear Solar
Observatory (BBSO). Time series of speckle-reconstructed white-light
images and two-dimensional spectroscopic data were combined to study
the temporal evolution of the three-dimensional vector flow field
in the βδ sunspot group. An hour-long data set of consistent high
quality was obtained, which had a cadence of better than 30 seconds
and subarcsecond spatial resolution.

---------------------------------------------------------
Title: The thermal environment of the fiber glass dome for the new
solar telescope at Big Bear Solar Observatory
Authors: Verdoni, A. P.; Denker, C.; Varsik, J. R.; Shumko, S.; Nenow,
J.; Coulter, R.
2007SPIE.6689E..0YV Altcode: 2007SPIE.6689E..28V; 2007arXiv0708.0622V
The New Solar Telescope (NST) is a 1.6-meter off-axis Gregory-type
telescope with an equatorial mount and an open optical support
structure. To mitigate the temperature fluctuations along the exposed
optical path, the effects of local/dome-related seeing have to be
minimized. To accomplish this, NST will be housed in a 5/8-sphere
fiberglass dome that is outfitted with 14 active vents evenly spaced
around its perimeter. The 14 vents house louvers that open and close
independently of one another to regulate and direct the passage
of air through the dome. In January 2006, 16 thermal probes were
installed throughout the dome and the temperature distribution was
measured. The measurements confirmed the existence of a strong thermal
gradient on the order of 5° Celsius inside the dome. In December 2006,
a second set of temperature measurements were made using different
louver configurations. In this study, we present the results of these
measurements along with their integration into the thermal control
system (ThCS) and the overall telescope control system (TCS).

---------------------------------------------------------
Title: Statistical study of low-energy heliosphere particle fluxes
from 1.4 to 5 AU over a solar cycle
Authors: Denker, C.; Reza, J. Z.; Nelson, A. J.; Patterson, J. D.;
Armstrong, T. P.; Maclennan, C. G.; Lanzerotti, L. J.
2007SpWea...5.7002D Altcode:
Throughout the entire Ulysses mission, the Heliosphere Instrument
for Spectra, Composition, and Anisotropy at Low Energies (HI-SCALE)
has collected measurements of low-energy interplanetary ions and
electrons. Time series of electron, proton, and ion fluxes have been
obtained since 1990. We present statistical studies of high-resolution
ion and electron energy spectra (~50 keV to ~5 MeV) as measured by
the HI-SCALE instrument on the Ulysses spacecraft over a time interval
longer than a solar cycle (1990 to 2004). Ulysses is the only spacecraft
that continually measured the inner (~1.4 to ~5 AU) heliosphere particle
population during these years. The data thus provide measures of the
lower-energy population of particles that a spacecraft traveling outward
from Earth would have encountered and that also could have impacted
the atmosphere and surface of Mars and of its satellites during this
interval. Comparisons of Ulysses particle fluxes with those from the
Electron, Proton, and Alpha Monitor (EPAM) instrument on the Advanced
Composition Explorer (ACE) spacecraft (the HI-SCALE backup instrument)
have shown that azimuthal and heliolatitude dependencies of particle
fluxes in the inner heliosphere following solar events are not as
extreme as might be expected. Thus the Ulysses measurements, while
taken over a range of heliolatitudes, can provide important statistical
information that can be used to estimate the low-energy radiation
dosages and potential sputtering fluxes to planetary surfaces and to
heliosphere spacecraft surfaces and solar arrays over a solar cycle.

---------------------------------------------------------
Title: The Local Seeing Environment at Big Bear Solar Observatory
Authors: Verdoni, Angelo; Denker, Carsten
2007PASP..119..793V Altcode:
The site survey for the Advanced Technology Solar Telescope (ATST)
of the National Solar Observatory was initiated in 2002 to find
the best location for a 4 m aperture solar telescope. At the
end of a 4 year survey, three sites (Big Bear Solar Observatory
[BBSO] in California, Mees Solar Observatory [MSO] on Haleakala,
Maui, Hawaii, and Observatorio Roque de los Muchachos, on La Palma,
Spain) were identified as excellent sites for high-resolution solar
observations. MSO was ultimately chosen as the future ATST site. We
present a subset of the ATST site survey data, focusing on the local
seeing environment at BBSO. In particular, we are interested in the
seeing characteristics at a mountain lake-site observatory, its relation
to the local environment and climate, and its implications for the 1.6
m New Solar Telescope (NST) currently being built at BBSO. We find a
close correlation of very good seeing conditions with the prevailing
wind direction and speed. The observatory building, located at the
end of a 300 m causeway, is surrounded by the cool waters of Big Bear
Lake, which effectively suppress the ground-layer seeing. Very good
seeing conditions from sunrise to sunset are a unique feature of BBSO,
which makes it ideally suited for synoptic observations and sustained
high-resolution studies of solar activity and space weather.

---------------------------------------------------------
Title: Synoptic Observing at Big Bear Solar Observatory
Authors: Denker, C.; Naqvi, M.; Deng, N.; Tritschler, A.; Marquette,
W. H.
2007ASPC..368..515D Altcode:
Synoptic solar observations in the chromospheric absorption lines
Ca II K and Hα have a long tradition at Big Bear Solar Observatory
(BBSO). The advent of the New Solar Telescope (NST) will shift the
focus of BBSO's synoptic observing program toward high-resolution
observations. We present an overview of the telescopes and
instrumentation and show some of the most recent results. This includes
Ca II K data to track solar irradiance variations, Hα full-disk data to
monitor eruptive events, Dopplergrams from two-dimensional spectroscopy,
as well as image restorations of diffraction-limited quality.

---------------------------------------------------------
Title: Two-dimensional Spectroscopy Of Chromospheric And Photospheric
Sunspot Fine-structure
Authors: Denker, Carsten; Verdoni, A. P.; Naqvi, M.; Deng, N.;
Tritschler, A.
2007AAS...21010002D Altcode: 2007BAAS...39..227D
In preparation for the future 1.6-meter New Solar Telescope (NST) at
Big Bear Solar Observatory, a suite of instruments has been developed
for observations with high-spatial and high-temporal resolution. Two of
these instruments, a fast CCD camera system for image restoration and
the Visible-light Imaging Magnetograph (VIM), were moved to the National
Solar Observatory/Sacramento Peak, while NST is under construction. In
this study, we report results of observations obtained with the
high-order adaptive optics system at the Dunn Solar Telescope on 2006
June 10. We observed active region NOAA 10892 in broad-band continuum
(600 nm) and in the chromsopheric lines (Hα and Na D2). We
obtained photospheric and chromospheric flow fields based on local
correlation tracking and Doppler measurements and discuss them in
the context of sunspot fine-structure. This work was supported
by NSF under grants ATM 00-86999, ATM 02-36945, IIS ITR 03-24816,
and AST MRI 00-79482 and by NASA under grant NAG 5-12782.

---------------------------------------------------------
Title: Three-Dimensional Structure of Evershed Flows
Authors: Deng, Na; Choudhary, D. P.; Denker, C.; Verdoni, A.;
Tritschler, A.
2007AAS...210.9506D Altcode: 2007BAAS...39..224D
The Evershed flow is known as the unceasing radially outward mass flow
in sunspot penumbrae observed in the photosphere, which is most clearly
seen near the solar limb. The Evershed flow reverses its direction in
the chromosphere, where an inward mass flow is observed. In order to
quantitatively explore the three-dimensional structure of the Evershed
flow from photosphere to chromosphere, we observed a sunspot group
(NOAA 10892) at the limb using the Horizontal Spectrograph (HSG)
at the National Solar Observatory/Sacramento Peak (NSO/SP) on 2006
June 04. Spectral data sets were obtained simultaneously at four solar
absorbtion lines: Fe 630.15 nm and 630.25 nm (photosphere), NaD 588.99
nm (lower chromosphere), and Hα 656.28 nm (chromosphere). Spectral
analysis and different methods of determining Doppler velocities will
be presented and compared. This work is supported by NSF under
grant ATM 02-36945, ATM 03-42560, ATM 05-48260 and MRI AST 00-79482
and by NASA under grant NAG 5-13661.

---------------------------------------------------------
Title: Observations of Quiet Sun Chromosphere Dynamics
Authors: Verdoni, Angelo; Denker, C.; Deng, N.; Tritschler, A.
2007AAS...21010003V Altcode: 2007BAAS...39..228V
The quiet Sun shows a multitude of fine structure in both the
photosphere and chromosphere. Observations with high spatial and
temporal resolution are required to study their dynamics. In June 2006,
simultaneous broad-band continuum (600 nm) and narrow-band spectroscopic
(Hα and Na 589.0 nm) data were obtained of a quiet Sun region near disk
center using the Dunn Solar Telescope and high-order adaptive optics
at the National Solar Observatory/Sacramento Peak. The time-series
of continuum data was restored using the speckle masking technique
to achieve almost diffraction-limited resolution across the entire
field-of-view (80" by 80"). The spectroscopic data were taken with a
two-dimensional spectrometer, which is currently being upgraded for
spectro-polarimetry. The Visible-light Imaging Magnetograph (VIM) is
a telecentric two-dimensional Fabry-Perot based spectro-polarimeter,
which will become one of the first-light instruments of the future
1.6-meter New Solar Telescope (NST) at Big Bear Solar Observatory
(BBSO). This work was supported by NSF under grants ATM 00-86999,
ATM 02-36945, IIS ITR 03-24816, and AST MRI 00-79482 and by NASA under
grant NAG 5-12782.

---------------------------------------------------------
Title: Field-Dependent Adaptive Optics Correction Derived with the
Spectral Ratio Technique
Authors: Denker, C.; Deng, N.; Rimmele, T. R.; Tritschler, A.;
Verdoni, A.
2007SoPh..241..411D Altcode:
In this empirical study, we compare high-resolution observations
obtained with the 65-cm vacuum reflector at Big Bear Solar Observatory
(BBSO) in 2005 and with the Dunn Solar Telescope (DST) at the National
Solar Observatory/Sacramento Peak (NSO/SP) in 2006. We measure the
correction of the high-order adaptive optics (AO) systems across
the field of view (FOV) using the spectral ratio technique, which
is commonly employed in speckle masking imaging, and differential
image motion measurements. The AO correction is typically much larger
(10” to 25”) than the isoplanatic angle and
can be described by a radially symmetric function with a central core
and extended wings. The full-width at half-maximum (FWHM) of the core
represents a measure of the AO correction. The average FWHM values
for BBSO and NSO/SP are 23.5” and 18.2”,
respectively. The extended wings of the function show that the
AO systems still contribute to an improved speckle reconstruction
at the periphery of the 80”×80” FOV. The
major differences in the level of AO correction between BBSO and
NSO/SP can be explained by different contributions of ground-layer-
and free-atmosphere-dominated seeing, as well as different FOVs of
the wavefront sensors. In addition, we find an anisotropic spectral
ratio in sunspot penumbrae caused by the quasi-one-dimensional nature
of penumbral filaments, which introduces a significant error in the
estimation of the Fourier amplitudes during the image restoration
process.

---------------------------------------------------------
Title: Adaptive Optics at the Big Bear Solar Observatory: Instrument
Description and First Observations
Authors: Denker, Carsten; Tritschler, Alexandra; Rimmele, Thomas R.;
Richards, Kit; Hegwer, Steve L.; Wöger, Friedrich
2007PASP..119..170D Altcode:
In 2004 January, the Big Bear Solar Observatory (BBSO) was equipped with
a high-order adaptive optics (AO) system built in collaboration with
the National Solar Observatory (NSO) at Sacramento Peak. The hardware is
almost identical to the AO system operated at the NSO Dunn Solar Tower
(DST), incorporating a 97 actuator deformable mirror, a Shack-Hartmann
wave-front sensor with 76 subapertures, and an off-the-shelf digital
signal processor system. However, the BBSO optical design is quite
different. It had to be adapted to the 65 cm vacuum reflector and
the downstream postfocus instrumentation. In this paper, we describe
the optical design, demonstrate the AO performance, and use image
restoration techniques to illustrate the image quality that can be
achieved with the new AO system.

---------------------------------------------------------
Title: Ground-based solar facilities in the U.S.A.
Authors: Denker, C.; Gary, D. E.; Rimmele, T. R.
2007msfa.conf...31D Altcode:
In this review, we present the status of new ground-based facilities
for optical and radio observations of the Sun in the United States. The
4-meter aperture Advanced Technology Solar Telescope (ATST) under the
stewardship of the National Solar Observatory (NSO) has successfully
completed its design phase and awaits funding approval. The 1.6-meter
aperture New Solar Telescope (NST) at Big Bear Solar Observatory
(BBSO) is currently under construction. Complementing these optical
telescopes is the Frequency Agile Solar Radiotelescope (FASR)
an instrument for dynamic broadband imaging spectroscopy covering
a multitude of radio frequencies from 50 MHz to 20 GHz. Imaging
spectroscopy and polarimetry are common features of these telescopes,
which will provide new insight regarding the evolution and nature of
solar magnetic fields. High-resolution observations of solar activity,
bridging the solar atmosphere from the photosphere to the corona, will
be obtained with a dedicated suite of instruments. Special emphasis
of this review will be put on the interplay between instrumentation
and scientific discovery.

---------------------------------------------------------
Title: Solar image restoration
Authors: Löfdahl, M. G.; van Noort, M. J.; Denker, C.
2007msfa.conf..119L Altcode:
Image restoration is used to repair solar images degraded by the
turbulence in Earth's atmosphere. Restoration algorithms are based on
models of the optical system that produce the images from the solar
source of radiation, through Earth's atmosphere and telescope/instrument
optics, to the detectors recording the data. In this review, these
model components are discussed in the context of two very different
classes of image restoration methods, i.e., Speckle Imaging and Phase
Diversity/Multi-Frame Blind Deconvolution, which have been successfully
used during the last two decades. The strengths and weaknesses of
these two approaches are discussed, as well as some variants and
recent progress.

---------------------------------------------------------
Title: Multiwavelength Study of Flow Fields in Flaring Super Active
Region NOAA 10486
Authors: Deng, N.; Xu, Y.; Yang, G.; Cao, W.; Liu, C.; Rimmele, T. R.;
Wang, H.; Denker, C.
2006AGUFMSH31B..06D Altcode:
We present high resolution observations of horizontal flow fields
measured by Local Correlation Tracking from intensity images in three
wavelengths, i.e., G-Band (GB), White-Light (WL), and Near InfraRed
(NIR). The observations were obtained on 2003 October~29 within
the flaring super active region NOAA~10486, which was the source of
several X-class flares, including an X10 flare that occurred near
the end of the observing run. The data were obtained at National
Solar Observatory/Sacramento Peak (NSO/SP) using the newly developed
high-order Adaptive Optics (AO) system. We also use Dopplergrams
and magnetograms from MDI on board SOHO to study the line-of-sight
flow and magnetic field. We observe persistent and long-lived (at
least 5 hours) strong horizontal and vertical shear flows (both in
the order of 1 km s-1) along the magnetic Neutral Line (NL) until
the X10 flare occurred. From lower photospheric level (NIR), the
direction of the flows does not change up to the upper photosphere
(GB), while the flow speeds in the shear motion regions decrease and
on the contrary those in regions without shear motions increase with
increasing altitude. Right after the X10 flare, the magnetic gradient
decreased, while both horizontal and vertical shear flows dramatically
enhanced near the flaring NL. Our results suggest that photospheric
shear flows and local magnetic shear near the NL can increase after
the flare, which may be the result of shear release in the overlying
large-scale magnetic system or the reflection of a twisted or sheared
flux emergence carrying enough energy from subphotosphere.

---------------------------------------------------------
Title: Progress on the 1.6-meter New Solar Telescope at Big Bear
Solar Observatory
Authors: Denker, C.; Goode, P. R.; Ren, D.; Saadeghvaziri, M. A.;
Verdoni, A. P.; Wang, H.; Yang, G.; Abramenko, V.; Cao, W.; Coulter,
R.; Fear, R.; Nenow, J.; Shoumko, S.; Spirock, T. J.; Varsik, J. R.;
Chae, J.; Kuhn, J. R.; Moon, Y.; Park, Y. D.; Tritschler, A.
2006SPIE.6267E..0AD Altcode: 2006SPIE.6267E..10D
The New Solar Telescope (NST) project at Big Bear Solar Observatory
(BBSO) now has all major contracts for design and fabrication in place
and construction of components is well underway. NST is a collaboration
between BBSO, the Korean Astronomical Observatory (KAO) and Institute
for Astronomy (IfA) at the University of Hawaii. The project will
install a 1.6-meter, off-axis telescope at BBSO, replacing a number
of older solar telescopes. The NST will be located in a recently
refurbished dome on the BBSO causeway, which projects 300 meters into
the Big Bear Lake. Recent site surveys have confirmed that BBSO is
one of the premier solar observing sites in the world. NST will be
uniquely equipped to take advantage of the long periods of excellent
seeing common at the lake site. An up-to-date progress report will
be presented including an overview of the project and details on the
current state of the design. The report provides a detailed description
of the optical design, the thermal control of the new dome, the optical
support structure, the telescope control systems, active and adaptive
optics systems, and the post-focus instrumentation for high-resolution
spectro-polarimetry.

---------------------------------------------------------
Title: The thermal control of the new solar telescope at Big Bear
Observatory
Authors: Verdoni, Angelo P.; Denker, Carsten
2006SPIE.6267E..0MV Altcode: 2006SPIE.6267E..20V
We present the basic design of the THermal Control System (THCS) for the
1.6-meter New Solar Telescope (NST) at the Big Bear Solar Observatory
(BBSO), California. The NST is an off-axis Gregorian telescope with
an equatorial mount and an open support structure. Since the telescope
optics is exposed to the air, it is imperative to control the local/dome
seeing, i.e., temperature fluctuations along the exposed optical
path have to be minimized. To accomplish this, a THCS is implemented
to monitor the dome environment and interact with the louver system
of the dome to optimize instrument performance. In addition, an air
knife is used to minimize mirror seeing. All system components have
to communicate with the Telescope Control System (TCS), a hierarchical
system of computers linking the various aspects of the entire telescope
system, e.g., the active mirror control, adaptive optics, dome and
telescope tracking, weather station, etc. We will provide an initial
thermal model of the dome environment and first measurements taken in
the recently replaced BBSO dome.

---------------------------------------------------------
Title: The telescope control system of the New Solar Telescope at
Big Bear Solar Observatory
Authors: Yang, G.; Varsik, J. R.; Shumko, S.; Denker, C.; Choi, S.;
Verdoni, A. P.; Wang, H.
2006SPIE.6274E..1YY Altcode: 2006SPIE.6274E..62Y
The New Solar Telescope (NST) is an advanced solar telescope at Big Bear
Solar Observatory (BBSO). It features a 1.6-m clear aperture with an
off-axis Gregorian configuration. An open structure will be employed
to improve the local seeing. The NST Telescope Control System (TCS)
is a complex system, which provides powerful and robust control over
the entire telescope system. At the same time, it needs to provide
a simple and clear user interface to scientists and observers. We
present an overview of the design and implementation of the TCS as
a distributed system including its several subsystems such as the
Telescope Pointing and Tracking Subsystem, Wavefront Sensing Subsystem
etc. The communications between different subsystems are handled by
the Internet Communication Engine (Ice) middleware.

---------------------------------------------------------
Title: High-Resolution Studies of Complex Solar Active Regions
Authors: Deng, Na; Wang, H.; Liu, C.; Yang, G.; Xu, Y.; Tritschler,
A.; Cao, W.; Rimmele, T. R.; Denker, C.
2006SPD....37.3401D Altcode: 2006BAAS...38..258D
Most Flares and CMEs occur or originate in solar active regions,
typically in sunspots with complex magnetic fields such as
delta-spots. Rapid and substantial changes of the sunspot structure have
been discovered to be associated with flares/CMEs. Rapid penumbral decay
and umbral enhancements are intensity changes, which are interpreted as
signatures of magnetic reconnection during the flare. The magnetic field
lines switch from an inclined to a more vertical orientation. Strong and
long-lived shear flows near the flaring magnetic inversion line have
been detected using Local Correlation Tracking (LCT) techniques based
on multi-wavelength high resolution observations. A newly observed and
important phenomenon is the increased local shear flow and magnetic
shear right after the flare in spite of theoretical models requiring
an overall decrease in the magnetic free energy. The emergence of a
twisted or pre-sheared flux rope near the neutral line is a possible
interpretation. Using high-order adaptive optics combined post-facto
speckle masking image reconstruction, we can obtain time-series with
highly improved image quality and spatial resolution in the order of
0.14" or about 100 km on the solar surface. We combine the observed
longitudinal Dopplergrams obtained with two-dimensional imaging
spectrometer and transverse LCT flow maps derived from time-series
of speckle reconstructed images to create real local 3D flow maps
(view from above). Using these precise 3D flow maps observed in a
typical sunspot in the course of its center to limb disc passage,
we observe distinct division line between radially inward and outward
flow in the penumbra and its evolution during the decaying phase of
the sunspot. The inclination angles of penumbral flow channels are
also calculated.Acknowledgments: This work is supported by NSF under
grant ATM 03-42560, ATM 03-13591, ATM 02-36945, ATM 05-48952, and MRI
AST 00-79482 and by NASA under grant NAG 5-13661.

---------------------------------------------------------
Title: Two-Dimensional Spectroscopy at Big Bear Solar Observatory
Authors: Denker, Carsten; Deng, N.; Tritschler, A.
2006SPD....37.3702D Altcode:
Two-dimensional spectroscopy is an important tool to measure the
physical parameters related to solar activity in both the photosphere
and chromosphere. We present a description of the visible-light
post-focus instrumentation at the Big Bear Solar Observatory (BBSO)
including adaptive optics and image restoration. We report the first
science observations obtained with two-dimensional spectroscopy during
the 2005 observing season. In particular we discuss the properties
of flows associated with a small delta-spot in solar active region
NOAA 10756.

---------------------------------------------------------
Title: Multiwavelength Study of Flow Fields in Flaring Super Active
Region NOAA 10486
Authors: Deng, Na; Xu, Yan; Yang, Guo; Cao, Wenda; Liu, Chang; Rimmele,
Thomas R.; Wang, Haimin; Denker, Carsten
2006ApJ...644.1278D Altcode:
We present high-resolution observations of horizontal flow fields
measured by local correlation tracking from intensity images in three
wavelengths, i.e., G band (GB), white light (WL), and near-infrared
(NIR). The observations were obtained on 2003 October 29 within
the flaring super active region NOAA 10486, which was the source of
several X-class flares, including an X10 flare that occurred near
the end of the observing run. The data were obtained at National
Solar Observatory/Sacramento Peak (NSO/SP) using the newly developed
high-order adaptive optics (AO) system. We also use Dopplergrams
and magnetograms from MDI on board SOHO to study the line-of-sight
flow and magnetic field. We observe persistent and long-lived (at
least 5 hr) strong horizontal and vertical shear flows (both in the
order of 1 km s-1) along the magnetic neutral line (NL)
until the X10 flare occurred. From lower photospheric level (NIR),
the direction of the flows does not change up to the upper photosphere
(GB), while the flow speeds in the shear motion regions decrease and,
on the contrary, those in regions without shear motions increase with
increasing altitude. Right after the X10 flare, the magnetic gradient
decreased, while both horizontal and vertical shear flows dramatically
enhanced near the flaring NL. Our results suggest that photospheric
shear flows and local magnetic shear near the NL can increase after
the flare, which may be the result of shear release in the overlying
large-scale magnetic system or the reflection of a twisted or sheared
flux emergence carrying enough energy from the subphotosphere.

---------------------------------------------------------
Title: Integrating seeing measurements into the operations of solar
telescopes
Authors: Denker, C.; Verdoni, A. P.
2006SPIE.6267E..0LD Altcode: 2006SPIE.6267E..19D
The New Solar Telescope (NST) is an innovative 1.6-meter, off-axis,
open telescope currently being developed and built at the Big Bear Solar
Observatory (BBSO). The observatory is situated on a small peninsula in
Big Bear Lake, a mountain lake at an altitude of about 2100 m in the
San Bernardino Mountains of Southern California. The lake effectively
suppresses the boundary layer seeing. Thus, providing consistently
very good daytime seeing conditions. BBSO has been identified by the
site survey for the Advanced Technology Solar Telescope (ATST) as one
of the best sites for solar observations. It is uniquely qualified for
long-duration observations requiring high-spatial resolution. This type
of observations is typically encountered in solar activity monitoring
and space weather forecast. The ATST site survey has collected more than
two years of data linking seeing conditions to geographical parameters
and local climate. We have integrated these data in a MySQL database
and we will use this information in connection with a real-time seeing
monitor and weather station to predict the seeing conditions at Big
Bear such that scheduling and prioritization of observing programs
(e.g., synoptic vs. high-resolution modes) becomes possible.

---------------------------------------------------------
Title: The first light of the Infrared Imaging Magnetographat Big
Bear Solar Observatory
Authors: Cao, Wenda; Ma, J.; Jing, J.; Xu, Y.; Denker, C.; Wang, H.;
Goode, P.
2006SPD....37.0612C Altcode: 2006BAAS...38..227C
The InfraRed Imaging Magnetograph (IRIM) system developed by Big Bear
Solar Observatory (BBSO) has been put into preliminary operation. It
is one of the first imaging spectro-polarimeters working at 1565 nm,
and is used for the observations of the Sun at its opacity minimum,
exposing the deepest photospheric layers. The tandem system of a 4.2 nm
interference filter, an unique 0.25 nm birefringent Lyot filter and a
Fabry-Perot etalon is capable of providing a bandpass as low as 0.01
nm in a telecentric configuration. A fixed quarter wave plate and a
nematic liquid crystal variable retarder are employed for analyzing
the circular polarization of the Zeeman components. The longitudinal
magnetic field is measured for highly Zeeman-sensitive Fe I line at
1564.85 nm (Lande factor g = 3). The polarimetric data, with a field of
view (FOV) 145" × 145", were recorded by a 1024 × 1024 pixel, 14-bit
HgCdTe CMOS focal plane array camera. Benefiting from the Correlation
Tracking system (CT) and newly developed Adaptive Optics (AO) system,
the first imaging polarimetric observations at 1565 nm were made at the
diffraction limit on 1 July 2005 using BBSO's 65 cm telescope. After
comparing the magnetograms from IRIM with those taken by the Michelson
Doppler Imager (MDI) on board SOHO, it was found that all the magnetic
features matched very well in both sets of magnetograms. Also, Stokes
V profiles obtained from the Fabry-Perot etalon scanning data provide
access to both the true magnetic field strength and filling factor of
the small-scale magnetic flux elements. In this paper, we present the
design, fabrication, and calibration of IRIM, as well as the results
of the first scientific observations.

---------------------------------------------------------
Title: Site testing for the Advanced Technology Solar Telescope
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.;
Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn,
M.; Radick, R.; Rimmele, T.; Socas-Navarro, H.; Streander, K.
2006SPIE.6267E..1TH Altcode: 2006SPIE.6267E..59H
The Advanced Solar Technology Telescope (ATST) is a 4-m solar telescope
being designed for high spatial, spectral and temporal resolution,
as well as IR and low-scattered light observations. The overall
limit of performance of the telescope is strongly influenced by the
qualities of the site at which it is located. Six sites were tested
with a seeing monitor and a sky brightness instrument for 1.5 to 2
years. The sites were Big Bear (California), Haleakala (Hawaii), La
Palma (Canary Islands, Spain), Panguitch Lake (Utah), Sacramento Peak
(New Mexico), and San Pedro Martir (Baja California, Mexico). In this
paper we will describe the methods and results of the site survey,
which chose Haleakala as the location of the ATST.

---------------------------------------------------------
Title: High-Resolution Observations of Multiwavelength Emissions
during Two X-Class White-Light Flares
Authors: Xu, Yan; Cao, Wenda; Liu, Chang; Yang, Guo; Jing, Ju; Denker,
Carsten; Emslie, A. Gordon; Wang, Haimin
2006ApJ...641.1210X Altcode:
We observed two X-class white-light flares (WLFs) on 2003 October 29
(~20:40 UT) and November 2 (~17:16 UT) using the Dunn Solar Telescope
(DST) and its High-Order Adaptive Optics (HOAO) system in several
wavelengths. The spatial resolution was close to the diffraction limit
of DST's 76 cm aperture, and the cadence was as high as 2 s. This
is the first time that WLFs have been observed in the near-infrared
(NIR) wavelength region. We present a detailed study in this paper
comparing photospheric continuum observations during the two events with
corresponding line-of-sight magnetograms from the Solar and Heliospheric
Observatory (SOHO) Michelson Doppler Imager (MDI) and hard X-ray (HXR)
data from the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). We
also discuss several models that provide possible mechanisms to explain
these continuum enhancements, especially in the NIR.

---------------------------------------------------------
Title: The Statistical Properties of Low Energy Heliosphere Particle
Fluxes from 1.4 to 5 AU Over a Solar Cycle
Authors: Denker, C.; Lanzerotti, L. J.; Wang, H.; Maclennan, C. G.;
Armstrong, T. P.; Patterson, J. D.
2006cosp...36.2953D Altcode: 2006cosp.meet.2953D
We present statistical studies of high resolution ion and electron
energy spectra sim 50 keV to sim 5 MeV as measured by the HI-SCALE
instrument on the Ulysses spacecraft over a time interval longer than a
solar cycle from launch in 1990 to nearly the present Ulysses was the
only spacecraft that continually measured the inner sim 1 4 to sim 5
AU heliosphere particle population during these years The data thus
provide measures of the lower energy population of particles that a
spacecraft traveling outward from Earth would have encountered and that
also impacted the atmosphere and surface of Mars and the surfaces of the
Martian satellites Phobos and Deimos during this interval Comparisons
of Ulysses particle fluxes with those from the EPAM instrument on
the ACE spacecraft the HI-SCALE back-up instrument have shown that it
is common for the particle fluxes in the inner heliosphere following
solar events to be distributed quite uniformly in heliolatitude Thus
the Ulysses measurements while taken over a range of heliolatitudes
can provide important statistical information that can be used to
estimate the low energy radiation dosages and potential sputtering
fluxes to planetary surfaces and to heliosphere spacecraft surfaces
and solar arrays over a solar cycle

---------------------------------------------------------
Title: The Visible--Light Magnetograph at the Big Bear Solar
Observatory: Hardware and Software
Authors: Shumko, S.; Abramenko, V.; Denker, C.; Goode, P.; Tritschler,
A.; Varsik, J.
2005ASPC..347..509S Altcode: 2005adass..14..509S
In this paper we report about the current status of the control and
acquisition software package developed to control the visible-light
imaging magnetograph (VIM) system at the Big Bear Solar Observatory
(BBSO). The instrument is designed to perform high-spatial and
high-temporal observations of the solar photosphere and chromosphere
utilizing the remodeled Coudé-feed of the 65 cm vacuum telescope.

---------------------------------------------------------
Title: Measuring and Maintaining the Plate Parallelism of Fabry-Pérot
Etalons
Authors: Denker, Carsten; Tritschler, Alexandra
2005PASP..117.1435D Altcode:
Many dynamic phenomena on the Sun require observations with high
temporal, spatial, and spectral resolution. Fabry-Pérot-based imaging
spectropolarimetry can serve these needs, especially in combination
with adaptive optics and advanced image restoration and processing
techniques. Therefore, a detailed understanding of the instrument
characteristics is the foundation for exploiting the capabilities
of these complex systems. We present a novel, efficient, and robust
algorithm for maintaining and quantifying the plate parallelism of
Fabry-Pérot etalons. The plate characteristics are quantified in
terms of Zernike polynomials, finding a direct relationship between
the voltages applied to the piezoelectric actuators, which control the
tip-tilt motion of the etalon, and the plate parallelism. The plate
defects are conveniently described by the Zernike coefficients up
to 15th order. The algorithm has been tested with the visible-light
imaging magnetograph at the Big Bear Solar Observatory in California.

---------------------------------------------------------
Title: Solar Site Survey for the Advanced Technology Solar
Telescope. I. Analysis of the Seeing Data
Authors: Socas-Navarro, H.; Beckers, J.; Brandt, P.; Briggs, J.;
Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer,
S.; Hill, F.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.;
Oncley, S.; Penn, M.; Rimmele, T.; Streander, K.
2005PASP..117.1296S Altcode: 2005astro.ph..8690S
The site survey for the Advanced Technology Solar Telescope concluded
recently after more than 2 years of data gathering and analysis. Six
locations, including lake, island, and continental sites, were
thoroughly probed for image quality and sky brightness. The present
paper describes the analysis methodology employed to determine the
height stratification of the atmospheric turbulence. This information
is crucial, because daytime seeing is often very different between the
actual telescope aperture (~30 m) and the ground. Two independent
inversion codes have been developed to simultaneously analyze
data from a scintillometer array and a solar differential image
monitor. We show here the results of applying them to a sample subset
of data from 2003 May that was used for testing. Both codes retrieve a
similar seeing stratification through the height range of interest. A
quantitative comparison between our analysis procedure and actual in
situ measurements confirms the validity of the inversions. The sample
data presented in this paper reveal a qualitatively different behavior
for the lake sites (dominated by high-altitude seeing) and the rest
(dominated by near-ground turbulence).

---------------------------------------------------------
Title: Properties of Small Dark Features Observed in the Pure
Near-Infrared and Visible Continua
Authors: Xu, Yan; Cao, Wenda; Ma, Jun; Hartkorn, Klaus; Jing, Ju;
Denker, Carsten; Wang, Haimin
2005ApJ...628L.167X Altcode:
High-resolution images in the visible and near-infrared (NIR) continua
at around 1560 nm were obtained of solar active regions NOAA AR 10707
and AR 10486 with the Dunn Solar Telescope (DST) at the National Solar
Observatory/Sacramento Peak (NSO/SP) on 2004 December 1 and 2 and
2003 October 29. The images were taken with the high-order adaptive
optics (HOAO) system, and the spatial resolution was close to the
diffraction limit of the 76 cm aperture DST in both wavelengths. For
the 2004 December run, the NIR observations were made with a newly
developed Lyot filter system, which was designed at the Center for
Solar-Terrestrial Research (CSTR)/New Jersey Institute of Technology
(NJIT). The filter has a bandpass of 2.5 Å that allows us to observe
the pure NIR continuum at the opacity minimum. Our data show that all
dark features in the NIR are also dark in the visible light. There
is no evidence showing the existence of so-called dark faculae, i.e.,
faculae that have negative contrasts in the NIR but positive contrasts
in the visible. The negative peak contrasts of these small pores are
about 50% in the visible and 25% in the NIR, and their dimensions are
in the range of 1"-4".

---------------------------------------------------------
Title: 1024 × 1024 HgCdTe CMOS camera for infrared imaging
magnetograph of Big Bear Solar Observatory
Authors: Cao, W.; Xu, Y.; Denker, C.; Wang, H.
2005SPIE.5881..245C Altcode:
The InfraRed Imaging Magnetograph (IRIM)1,2 is a
two-dimensional narrow-band solar spectro-polarimeter currently being
developed at Big Bear Solar Observatory (BBSO). It works in the near
infrared (NIR) from 1.0 μm to 1.7 μm and possesses high temporal
resolution, high spatial resolution, high spectral resolving power, high
magnetic sensitivity. As the detector of IRIM, the 1024 × 1024 HgCdTe
TCM8600 CMOS camera manufactured by the Rockwell Scientific Company
plays a very important role in acquiring the high precision solar
spectropolarimetry data. In order to make the best use of it for solar
observation, the characteristic evaluation was carried out at BBSO and
National Solar Observatory (NSO), Sacramento Peak in October 2003. The
paper presents a series of measured performance parameters including
linearity, readout noise, gain, full well capacity, hot pixels, dark,
flat field, frame rate, vacuum, low temperature control, etc., and
shows some solar infrared narrow band imaging observation results.

---------------------------------------------------------
Title: The ATST Site Survey
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J. W.; Brown, T.;
Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.;
Radick, R.; Rimmele, T.; Socas-Navarro, H.; Soltau, D.; Streander, K.
2005AGUSMSP34A..04H Altcode:
The Advanced Technology Solar Telescope (ATST) will be the world's
largest aperture solar telescope, and is being designed for high
resolution, IR, and coronal research. It must be located at a site that
maximizes the scientific return of this substantial investment. We
present the instrumentation, analysis and results of the ATST site
survey. Two instrumentation sets were deployed at each of six sites to
measure seeing as a function of height, and sky brightness as a function
of wavelength and off-limb position. Analysis software was developed
to estimate the structure function Cn2 as a function of height near
the ground, and the results were verified by comparison with in-situ
measurements. Additional software was developed to estimate the sky
brightness. The statistics of the conditions at the sites were corrected
for observing habits and the annualized hours of specific observing
conditions were estimated. These results were used to identify three
excellent sites suitable to host the ATST: Haleakala, Big Bear and La
Palma. Among them, Haleakala is proposed as the optimal location of
the ATST, La Palma and Big Bear being viable alternative sites.

---------------------------------------------------------
Title: Do Dark Faculae Exist?
Authors: Xu, Y.; Cao, W.; Ma, J.; Hartkon, K.; Jing, J.; Denker, C.;
Wang, H.
2005AGUSMSP31A..01X Altcode:
High-resolution images in visible light and the near infrared
(NIR) continuum around 1560~nm were obtained in solar active region
NOAA~10707 with the Dunn Solar Telescope (DST) at the National Solar
Observatory/Sacramento Peak (NSO/SP) on 2004 December~2 and 7. A
spatial resolution close to the diffraction limit of the 76~cm DST was
achieved with high-order adaptive optics system. The observation were
made with a near infrared tunable Lyot filter system newly developed
by Big Bear Solar Observatory (BBSO). The filter has a bandpass
of 2.5~Å. This allows us to observe the pure NIR continuum that
represents the opacity minimum. Our data show that the contrast of
faculae has the same sign in the visible and the NIR continua. There
is no evidence for the existence of so-called "dark faculae", faculae
that have negative contrasts in the NIR and positive contrasts in
visible light. We conclude that the previously observed "dark faculae"
are unresolved pores. This work is supported by NSF under grants
ATM-0313591, ATM-0236945, ATM-0233931 and AST-0307676, by NASA under
grants NAG5-10910, NAG5-10212 and NAG5-12733, and by Air Force under
grant F49620-02-1-0265 and by NSFC-10103004.

---------------------------------------------------------
Title: The New Solar Telescope at Big Bear Solar Observatory -
A Progress Report
Authors: Denker, C.; Cao, W.; Chae, J.; Coulter, R.; Kuhn, J. R.;
Marquette, W. H.; Moon, Y.; Park, Y.; Ren, D.; Tritschler, A.; Varsik,
J. R.; Wang, H.; Yang, G.; Shoumko, S.; Goode, P. R.
2005AGUSMSP43A..07D Altcode:
The New Solar Telescope (NST) is a new 1.6-meter, off-axis telescope
for the Big Bear Solar Observatory (BBSO) in California. The NST is
collaboration between BBSO, the Korean Astronomical Observatory (KAO)
and Institute for Astronomy (IfA) at the University of Hawaii. BBSO
is an ideal site for high-spatial resolution observations, since this
mountain-lake site provides consistent seeing conditions with extended
periods of excellent seeing from sunrise to sunset. These unique seeing
characteristics make BBSO ideally suited for combined high-resolution
campaigns and synoptic observations, which are essential for studies
of solar activity and space weather. In this progress report, we
present the latest information on the optical design, the optical
support structure, the telescope control system and the requisite
instrumentation for the telescope. Acknowledgements: This work has been
supported by NSF under grants ATM-0236945, ATM-0342560, MRI-0320540,
and Air Force DURIP F-49620-03-1-0271.

---------------------------------------------------------
Title: Dissertation Talk: High Resolution Observations of
Multi-Wavelength Emissions During Two X-Class White-Light Flares
Authors: Xu, Y.; Cao, W.; Liu, C.; Yang, G.; Jing, J.; Denker, C.;
Wang, H.
2005AGUSMSP51C..01X Altcode:
We observed two X-class white-light flares (WLF) on 2003 October~29
(~20:40~UT) and November~2 (~17:16 UT) using the Dunn Solar Telescope
(DST) and its High-Order Adaptive Optics (HOAO) system in several
wavelengths. The spatial resolution was close to the diffraction limit
of DST's 76~cm aperture. The temporal resolution was as high as 2~s. It
is the first time that WLFs were observed in the Near Infrared (NIR)
wavelength region. We present a detailed study in this presentation
by comparing the photospheric continuum observations during these
two events with corresponding line-of-sight (LOS) magnetograms of the
Michelson Doppler Imager (MDI) and hard X-ray (HXR) data of the Ramaty
High Energy Solar Spectroscopic Imager (RHESSI). Our observations show
that: Significant intensity enhancements were observed in the
visible and NIR continua and G-band during the impulsive phase of the
flares. The maximum intensity enhancements were 37% of white-light
and 25% of the NIR continuum during the first event, and 76% of
white-light and 66% of the NIR continuum for the second flare. The
flares were typical two ribbon flares. All ribbons showed a brighter
core surrounded by a halo structure. The ribbon separation speeds
were about 28~km/s in the first and 24~km/s in the second event based
on NIR observations. The derived electric fields in the reconnection
current sheet Ec are about 23~V~ cm-1 and 22~V~cm-1, respectively. The
NIR emission and the impulsive HXR emission up to 800~keV were well
correlated, not considering a small delay of less than two minutes. The
high resolution and high cadence images gave us the first chance to
measure the cooling time of flares close to the photosphere. We found
that the cooling process could be characterized by two steps. A quick
temperature drop, which is related to the cooling process of the bright
cores, and a relative slow decay related to the halo structures. The
fine scale is in the order of less than 30~s and a few minutes for these
two steps, respectively. Based on these observational results,
we discuss several models that provide possible mechanisms to explain
these continuum enhancements, especially in the NIR. This work is
supported by NSF under grants ATM-0313591, ATM-0236945, ATM-0233931 and
AST-0307676, by NASA under grants NAG5-10910, NAG5-10212 and NAG5-12733,
and by Air Force under grant F49620-02-1-0265 and by NSFC-10103004.

---------------------------------------------------------
Title: Automated Detection and Identification of Solar Filaments
and Sunspots
Authors: Qu, M.; Shih, F. Y.; Jing, J.; Denker, C.; Wang, H.
2005AGUSMSP31A..06Q Altcode:
We developed a procedure for the automatic detection and identification
of filaments and their disappearance. Full-disk Hα images from the Big
Bear Solar Observatory (BBSO) in California are used as the data set for
our procedure. Solar images are randomly selected starting from January
1, 1999 to September 1, 2004. We present an automatic solar filament
detection procedure using advanced image enhancement, segmentation,
pattern recognition and mathematical morphology. This procedure not
only provides the detection results of filaments, but also identifies
the spines, footpoints and disappearances of filaments. Low contrast
filaments are emphasize and sharpen by the stabilized inverse diffusion
equation (SIDE) which was introduced by Pollak et al. (2000). Adaptive
image segmentation techniques are used for selecting the threshold
based on the edge and local information. To distinguish sunspot
from filaments, an efficient feature-based classifier, the Support
Vector Machine (SVM), is utilized. Detail filament identification
is achieved by morphological thinning, pruning and adaptive edge
linking methods. Finally, the filament disappearances are detected by
comparing the spine and footpoints of the filaments on two consecutive
days. Comparing to Gao et al. (2002) and Shih and Kowalski (2003),
our procedure utilizes the image enhancement techniques to enhance
the low contrast filaments, and apply advanced pattern recognition
and morphology techniques to identify filament and sunspots. Our work
has shown the better and more complete results than other work on the
automatic filament detection.

---------------------------------------------------------
Title: First Light for the Near-Infrared Narrow-Band Tunable
Birefringent Filter of the Big Bear Solar Observatory
Authors: Cao, W.; Hartkorn, K.; Ma, J.; Wang, J.; Xu, Y.; Spirock,
T.; Denker, C.; Wang, H.
2005AGUSMSP43A..08C Altcode:
A new near-infrared, narrow-band tunable birefringent filter has
been developed by BBSO/NJIT. This filter, one of the first Lyot
filters in the near-infrared, has a FWHM of about 2.5 ~Å at the
design wavelength of 1.5648 μm and is used to observe the deepest
levels of the photosphere. New techniques were employed in the design,
including liquid crystal retarders to tune the center wavelength in
range of ± 100 ~Å. After finishing the calibration and evaluation of
the filter at the Evans Facility of the NSO at Sacramento Peak, high
spatial resolution filtergrams and imaging spectroscopy observations
were carried out at the Dunn Solar Telescope of NSO in December 2004
with the use of the high-order Adaptive Optics System. For some of
these observations, the Lyot filter was combined with a Fabry-Perot
Etalon to achieve a much higher spectral resolution. We discuss the
calibration methods and present some preliminary observation results.

---------------------------------------------------------
Title: High Resolution Chromospheric Flow Fields in Solar Active
Region NOAA 9393 Before and After an X20 Flare
Authors: Smith, G. A.; Tritschler, A.; Denker, C.
2005AGUSMSP23B..02S Altcode:
Hα full-disk images of the Sun obtained at the Big Bear Solar
Observatory (BBSO) are used to measure the chromospheric flow field
before and after the X20 flare in solar active region NOAA 9393 on
April 2, 2001. Local correlation tracking is used to determine global
(differential rotation) and local flow fields (flows in active regions
and filaments). We present high-resolution (2k × 2k pixel) flow maps to
analyze the dynamics of the chromosphere before and after the flare. If
there is a typical pattern in the motions of a flaring active region,
it can be used to predict flare activity and/or the onset of Coronal
Mass Ejections (CMEs). The high quality of the limb-darkening corrected
and contrast-enhanced Hα full-disk images make them an ideal data
set for these types of studies due to their high-temporal resolution
(1-minute cadence) and extended coverage (more than 500 filtergrams).

---------------------------------------------------------
Title: On the Relation Between Flow Fields and Magnetic Field
Evolution in Flare Productive NOAA Active Region 10486
Authors: Deng, N.; Xu, Y.; Yang, G.; Cao, W.; Rimmele, T. R.; Wang,
H.; Denker, C.
2005AGUSMSP51C..05D Altcode:
We present high resolution observations of flow fields within solar NOAA
active region 10486 before an X10 flare on October 29, 2003. From 2003
October 28 to November 4, a complex δ-sunspot located in NOAA 10486
produced dramatic flare activities in the descending phase of the solar
cycle 23. The flow fields are measured by local correlation tracking
(LCT) based on speckle masking white-light images, near-infrared (NIR)
continuum images at 1.56 μm, and G-band images obtained with the Dunn
Solar Telescope (DST) of the National Solar Observatory/Sacramento Peak
(NSO/SP). NSO's newly developed high-order adaptive optics system at
the DST was used to achieve diffraction-limited imaging with a high
signal-to-noise ratio. The spatial resolution of the images approaches
the diffraction limit of the 76 cm aperture DST of about 0.14 ″ at
527 nm. In addtion, we use longitudinal magnetograms from the Michelson
Doppler Imager (MDI) on board the Solar and Heliospheric Observatory
(SoHO) to study the evolution of photospheric magnetic field and
its correlation with flow fields in this flare productive active
region. We link strong magnetic shear and fast emergence of magnetic
flux to photospheric flows, which might trigger the flares. Our result
suggests that the time-series analysis of the photospheric flow fields
is a critical observational diagnostic for the evolution of magnetic
fields in solar active regions. This work was supported by NSF under
grant ATM 03-42560, ATM 03-13591, ATM 02-36945, and MRI AST 00-79482
and by NASA under grant NAG 5-13661.

---------------------------------------------------------
Title: Narrow-band Near Infrared Filtergram Observation of Light
Bridges and Umbral Dots
Authors: Ma, J.; Cao, W.; Denker, C.; Wang, H.
2005AGUSMSP31A..03M Altcode:
We are presenting the observations of the active region NOAA 10709
on December, 2004 using 0.12Å~narrow band filter centered around
1.56μm. The observation run was carried out using Dunn Tower
Telescope of NSO (SacPeak) with high-order AO system. The averaged
angular resolution of this observation is 0.5" or better. These high
resolution data in near infrared offer a new view on the photospheric
structures of sunspot near opacity minimum. By using the tunable near
infrared narrow band filtergram, we are able to construct magnetic
field strength map of sunspot. In particular, we will show the magnetic
structure of light bridges and umbral dots.

---------------------------------------------------------
Title: Solar Fireworks - Integrating an Exhibit on Solar Physics
and Space Science into the Science and Astronomy Curriculum of
High-School and College Students
Authors: Denker, C.; Wang, H.; Conod, K. D.; Wintemberg, T.;
Calderon, I.
2005AGUSMSH11A..03D Altcode:
Astronomers at The Newark Museum's Alice and Leonard Dreyfuss
Planetarium teamed up with the New Jersey Institute of Technology's
(NJIT) Center for Solar-Terrestrial Research (CSTR) and the Big Bear
Solar Observatory in presenting Solar Fireworks. The exhibit opened
on May 15, 2004 and features two exhibition kiosks with interactive
touch screen displays, where students and other visitors can take
"virtual tours" in the fields of solar physics, solar activity,
Sun-Earth connection, and geo-sciences. Planetarium and museum visits
are an integral part of the introductory physics and astronomy classes
at NJIT and the exhibition has been integrated in the astronomy
curriculum. For example, NJIT students of the Astronomy Club and
regular astronomy courses were closely involved in the design and
development of the exhibit. The exhibit is the latest addition to
the long-running natural science exhibit "Dynamic Earth: Revealing
Nature's Secrets" at the museum. More than 30,000 people per year attend
various programs offered by the planetarium including public shows,
more than a dozen programs for school groups, after school activities,
portable planetarium outreach, outdoor sky watches, solar observing and
other family events. More than 1,000 high school students visited the
planetarium in 2004. The exhibit is accompanied by a yearly teacher
workshop (the first one was held on October 18-20, 2004) to enhance
the learning experience of classes visiting the Newark Museum. The
planetarium and museum staff has been working with teachers of Newark
high schools and has presented many workshops for educators on a
wide range of topics from astronomy to zoology. At the conclusion
of the exhibit in December 2005, the exhibit will go "on the road"
and will be made available to schools or other museums. Finally,
the exhibit will find its permanent home at the new office complex of
CSTR at NJIT. Acknowledgements: Solar Fireworks was organized by The
Newark Museum and the New Jersey Institute of Technology's Center for
Solar-Terrestrial Research and supported by a two-year grant from
NASA's Office of Space Science Education/Public Outreach Program
(NASA NAG5-12733 EPO-02-219). http://www.bbso.njit.edu

---------------------------------------------------------
Title: Rapid Penumbral Decay Associated with an X2.3 Flare in NOAA
Active Region 9026
Authors: Deng, Na; Liu, Chang; Yang, Guo; Wang, Haimin; Denker, Carsten
2005ApJ...623.1195D Altcode:
We present observations of rapid penumbral decay associated with a
major flare in solar NOAA Active Region 9026 on 2000 June 6. Within 1.5
hr, an X2.3 flare accompanied by an 11° long filament eruption and a
full-halo coronal mass ejection (CME) originated near the neutral line
of a large δ-spot region, which was associated with significant changes
in white-light structure and magnetic field topology: an increase
of moving magnetic features (MMFs), flux emergence and cancellation,
and, in particular, the rapid disappearance of two penumbral segments
located in opposite-polarity regions on the north and south sides of
the δ-spot. The rapid penumbral decay is believed to be the result
of magnetic field topology change that was caused by rapid magnetic
reconnection during the flare, rather than part of overall long-term
evolution. We present a possible explanation of this event, using a
“magnetic breakout” model for solar flares, considering its complex
multipolar δ-configuration and associated filament eruption and CME,
i.e., previously closed magnetic field lines opened up and reconnected
at a null point above the neutral line of this δ-spot. The magnetic
breakout caused an energy release from a highly sheared magnetic field
in the umbrae and a transition of the magnetic arcades from low lying
to high lying, which led to an increase of the inclination angle of the
magnetic field lines in the peripheral penumbrae; i.e., the magnetic
field turned from more inclined to more vertical and toward the inner
umbrae. Once the magnetic field in the penumbrae was vertical enough,
the Evershed flow ceased, the manifestation of which in white-light
structure is the disappearance of peripheral penumbrae. We also discuss
other possible flare models for this event and compare them in several
observational features. The present observations provide further
evidence that highly energetic events have a distinct associated
photospheric magnetic field signature and support the findings of
recent analyses of photospheric line-of-sight magnetograms from the
Big Bear Solar Observatory (BBSO) and the Michelson Doppler Imager
(MDI) on board the Solar and Heliospheric Observatory (SOHO) that show
rapid and permanent changes of photospheric magnetic fields associated
with flares.

---------------------------------------------------------
Title: High-Spatial-Resolution Imaging Combining High-Order Adaptive
Optics, Frame Selection, and Speckle Masking Reconstruction
Authors: Denker, Carsten; Mascarinas, Dulce; Xu, Yan; Cao, Wenda;
Yang, Guo; Wang, Haimin; Goode, Philip R.; Rimmele, Thomas
2005SoPh..227..217D Altcode:
We present, for the first time, high-spatial-resolution observations
combining high-order adaptive optics (AO), frame selection, and
post-facto image correction via speckle masking. The data analysis is
based on observations of solar active region NOAA 10486 taken with the
Dunn Solar Telescope (DST) at the Sacramento Peak Observatory (SPO) of
the National Solar Observatory (NSO) on 29 October 2003. The high Strehl
ratio encountered in AO corrected short-exposure images provides highly
improved signal-to-noise ratios leading to a superior recovery of the
object's Fourier phases. This allows reliable detection of small-scale
solar features near the diffraction limit of the telescope. Speckle
masking imaging provides access to high-order wavefront aberrations,
which predominantly originate at high atmospheric layers and are only
partially corrected by the AO system. In addition, the observations
provided qualitative measures of the image correction away from the
lock point of the AO system. We further present a brief inspection
of the underlying imaging theory discussing the limitations and
prospects of this multi-faceted image reconstruction approach in
terms of the recovery of spatial information, photometric accuracy,
and spectroscopic applications.

---------------------------------------------------------
Title: Rapid Change of δ Spot Structure Associated with Seven
Major Flares
Authors: Liu, Chang; Deng, Na; Liu, Yu; Falconer, David; Goode,
Philip R.; Denker, Carsten; Wang, Haimin
2005ApJ...622..722L Altcode:
A large fraction of major flares occur in active regions that exhibit a
δ configuration. The formation and disintegration of δ configurations
is very important in understanding the evolution of photospheric
magnetic fields. In this paper we study the relationship between the
change in δ spot structures and associated major flares. We present
a new observational result that part of penumbral segments in the
outer δ spot structure decay rapidly after major flares; meanwhile,
the neighboring umbral cores and/or inner penumbral regions become
darker. Using white-light (WL) observations from the Transition Region
and Coronal Explorer (TRACE), we study the short-term evolution of δ
spots associated with seven major flares, including six X-class flares
and one M-class flare. The rapid changes, which can be identified in
the time profiles of WL mean intensity are permanent, not transient,
and thus are not due to flare emission. The co-aligned magnetic field
observations obtained with the Michelson Doppler Imager (MDI) show
substantial changes in the longitudinal magnetic field associated with
the decaying penumbrae and darkened central areas. For two events for
which vector magnetograms were available, we find that the transverse
field associated with the penumbral decay areas decreased while it
increased in the central darkened regions. Both events also show an
increase in the magnetic shear after the flares. For all the events,
we find that the locations of penumbral decay are related to flare
emission and are connected by prominent TRACE postflare loops. To
explain these observations, we propose a reconnection picture in which
the two components of a δ spot become strongly connected after the
flare. The penumbral fields change from a highly inclined to a more
vertical configuration, which leads to penumbral decay. The umbral
core and inner penumbral region become darker as a result of increasing
longitudinal and transverse magnetic field components.

---------------------------------------------------------
Title: Observations of Photosphere and Chromosphere
Authors: Denker, Carsten
2005ASSL..320....1D Altcode: 2005smp..conf....1D
No abstract at ADS

---------------------------------------------------------
Title: Photospheric Shear Flows along the Magnetic Neutral Line of
Active Region 10486 prior to an X10 Flare
Authors: Yang, Guo; Xu, Yan; Cao, Wenda; Wang, Haimin; Denker, Carsten;
Rimmele, Thomas R.
2004ApJ...617L.151Y Altcode:
We present high spatial resolution observations of proper motions in
the solar NOAA Active Region 10486 using a high-order adaptive optics
system, frame selection, and speckle-masking image reconstruction. The
data were obtained with the Dunn Solar Telescope of the National Solar
Observatory/Sacramento Peak on 2003 October 29. The resolution of the
images approaches the diffraction-limited resolution of the Dunn Solar
Telescope of about 0.14" at 527 nm. We analyzed a 2 hr time series with
a 1 minute cadence prior to an X10 white-light flare. Local correlation
tracking was used to measure the photospheric proper motions. We find
specific evidence of strong shear flows along the magnetic neutral line;
these shear flows are well defined and correlated with white-light
flare kernels in the visible and infrared. The speed along the flow
channels can reach up to 1.6 km s-1, and the separation of
channels with head-on flows can be less than 1". Counterstreaming and
complex flow patterns have been distinguishing characteristics of this
extraordinarily flare-productive active region.

---------------------------------------------------------
Title: Visible and near-infrared contrast of faculae in active region
NOAA 8518.
Authors: Xu, Y.; Yang, G.; Qiu, J.; Spirock, T. J.; Jing, J.; Denker,
C.; Wang, H.
2004ChJAA...4..481X Altcode:
No abstract at ADS

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Title: Solar site testing for the Advanced Technology Solar Telescope
Authors: Hill, Frank; Beckers, Jacques; Brandt, Peter; Briggs, John;
Brown, Timothy; Brown, W.; Collados, Manuel; Denker, Carsten; Fletcher,
Steven; Hegwer, Steven; Horst, T.; Komsa, Mark; Kuhn, Jeff; Lecinski,
Alice; Lin, Haosheng; Oncley, Steve; Penn, Matthew; Rimmele, Thomas
R.; Socas-Navarro, Hector; Streander, Kim
2004SPIE.5489..122H Altcode:
The location of the Advanced Technology Solar Telescope (ATST) is a
critical factor in the overall performance of the telescope. We have
developed a set of instrumentation to measure daytime seeing, sky
brightness, cloud cover, water vapor, dust levels, and weather. The
instruments have been located at six sites for periods of one to two
years. Here we describe the sites and instrumentation, discuss the
data reduction, and present some preliminary results. We demonstrate
that it is possible to estimate seeing as a function of height near the
ground with an array of scintillometers, and that there is a distinct
qualitative difference in daytime seeing between sites with or without
a nearby lake.

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Title: Near infrared (NIR) achromatic phase retarder
Authors: Ma, Jun; Wang, Jingshan; Cao, W.; Denker, Carsten; Wang,
Haimin
2004SPIE.5523..139M Altcode:
The tunable near InfraRed Lyot filter (TNIRLF) is one of the focal plane
instruments for Advanced Technology Solar Telescope (ATST) project of
the National Solar Observatory (NSO). Achromatic half waveplate and
quarter waveplates working from 1000 nm to 1700 nm will be used in
this filter. In this paper, we give a description of the design and
development for the synthesized achromatic waveplates using quartz
plates. The retardance variation is within 1% over the full spectral
range and we discuss the variance of optical axis.

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Title: Near-Infrared Observations at 1.56 Microns of the 2003 October
29 X10 White-Light Flare
Authors: Xu, Yan; Cao, Wenda; Liu, Chang; Yang, Guo; Qiu, Jiong;
Jing, Ju; Denker, Carsten; Wang, Haimin
2004ApJ...607L.131X Altcode:
We present high-resolution observations of an X10 white-light flare in
solar NOAA Active Region 10486 obtained with the Dunn Solar Telescope
(DST) at the National Solar Observatory/Sacramento Peak on 2003
October 29. Our investigation focuses on flare dynamics observed
in the near-infrared (NIR) continuum at 1.56 μm. This is the first
report of a white-light flare observed at the opacity minimum. The
spatial resolution was close to the diffraction limit of the 76 cm
aperture DST. The data benefited from a newly developed high-order
adaptive optics system and a state-of-the-art NIR complex metal oxide
semiconductor focal plane array. In addition, we compared hard X-ray
(HXR) data of RHESSI and magnetograms of the Michelson Doppler Imager on
board SOHO with the NIR continuum images. Although it is still possible
that some high-energy electrons penetrate deep to this layer, a more
likely explanation of the observed emission is back-warming. During
the impulsive phase of the flare, two major flare ribbons moved apart,
which were both temporally and spatially correlated with RHESSI HXR
ribbons. The maximum intensity enhancement of the two flare ribbons is
18% and 25%, respectively, compared to the quiet-Sun NIR continuum. The
separation speed of the ribbons is about 38 km s-1 in regions
with weak magnetic fields and decreases to about 19 km s-1,
where stronger magnetic fields are encountered. The derived electric
field in reconnection current sheet Ec is of the order of
45 V cm-1 during the flare maximum.

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Title: Latest Results from the ATST Site Survey
Authors: Hill, F.; Collados, M.; Navarro, H.; Beckers, J.; Brandt,
P.; Briggs, J.; Brown, T.; Denker, C.; Hegwer, S.; Horst, T.; Komsa,
M.; Kuhn, J.; Lin, H.; Oncley, S.; Penn, M.; Rimmele, T.; Soltau,
D.; Streander, K.
2004AAS...204.6909H Altcode: 2004BAAS...36..795H
We present the latest results and current status of the site survey
portion of the Advanced Technology Solar Telescope (ATST) project. The
ATST will provide high resolution solar data in the visible and IR. The
site is a major factor determining the performance of the telescope. The
most critical site characteristics are the statistics of daytime seeing
quality and sky clarity. These conditions are being measured by a suite
of instruments at three sites (Big Bear, Haleakala, La Palma). These
sites were chosen from a set of six that have been tested starting in
November 2001. The instrumentation includes a solar differential image
motion monitor, an array of scintillometers, a miniature coronagraph,
a dust monitor, and a weather station. The analysis of the data provides
an estimate of the seeing as a function of height near the ground. We
will present the latest results of the analysis of the survey data set.

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Title: Near Infrared Obsevations at 1.56 μ m of the 2003 October
29 X10 White-Light Flare
Authors: Xu, Y.; Cao, W.; Liu, C.; Yang, G.; Qiu, J.; Jing, J.;
Denker, C.; Wang, H.
2004AAS...204.4712X Altcode: 2004BAAS...36..738X
We present high resolution observations of an X10 white-light flare in
solar active region NOAA 10486 obtained with the Dunn Solar Telescope
(DST) at the National Solar Observatory/Sacramento Peak (NSO/SP) on 2003
October 29. Our investigation focusses on flare dynamics observed in the
near-infrared (NIR) continuum at 1.56 μ m. This is the first report
of a white-light flare observed in the NIR. The spatial resolution
was close to the diffraction limit of the 76 cm aperture DST. The data
benefited from a newly developed high order adaptive optics (AO) system
and a state-of-the-art NIR complex metal oxide semiconductor (CMOS)
focal plane array (FPA). In addition, we compared hard X-ray (HXR)
data of the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and
magnetograms of the Michelson Doppler Imager (MDI) onboard the Solar and
Heliospheric Observatory (SoHO) with the NIR continuum images. Since the
NIR data were observed at the opacity minimum, only the most energetic
electrons can penetrate to this layer in the deep photosphere. As a
consequence, the flare ribbons appear to be very thin (&lt;2 arcseconds)
and well defined. During the impulsive phase of the flare, two major
flare ribbons moved apart, which were both temporally and spatially
correlated with RHESSI HXR ribbons. The two ribbons ranges are 18%
to 25% brighter than the quiet sun NIR continuum. The separation speed
of the ribbons is about 38 km/s in regions with weak magnetic fields
and decreases to about 19 km/s, where stronger magnetic fields are
encountered. The derived reconnection electric field Ec
is of order 50 Vcm-1 at the flare maximum.

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Title: The VIsible and InfraRed Imaging Magnetograph (VIM-IRIM)
at Big Bear Solar Observatory
Authors: Cao, W.; Tritschler, A.; Denker, C.; Wang, H.; Shumko, S.;
Ma, J.; Wang, J.; Marquette, B.
2004AAS...204.6907C Altcode: 2004BAAS...36..795C
The Visible-light and the InfraRed Imaging Magnetograph (VIM-IRIM) are
Fabry-Perot based filtergraphs working in a telecentric configuration,
planned to upgrade the capability for measuring solar magnetic fields
at BBSO. Both filtergraph instruments are designed to work with
the combination of a narrow-band prefilter and a single Fabry-Perot
etalon. VIM and IRIM will provide high temporal resolution, high spatial
resolution (&lt; 0.2 "/pixel image scale), high spectral resolution
(&lt; 0.1 Å) simultaneous observation at 600-700 nm and 1.0-1.6 μ
m with a substantial field of view 170", respectively. Modifications
in the setup allow also for scanning different spectral lines that
cover the height range from the solar photosphere up to the solar
chromopshere. Here we describe the optical setup and present first
observations to demonstrate the feasibility of the instrument. After
the instrument has proven to work as a 2D-spectrometer, the upgrade
to a 2D spectropolarimeter is planned.

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Title: Magnetic Helicity Change Rate Associated With X-Class and
M-Class Flares
Authors: Hartkorn, K.; Wang, H.; Cao, W.; Denker, C.; Xu, Y.
2004AAS...204.3901H Altcode: 2004BAAS...36..714H
We investigate the total helicity change rate of active regions
during the time period of five X-class and five M-class flares. The
X-class flares include the X17 flare on October 28 2003 and the X11
flare on October 29 2003. For the X11 flare we have high-resolution
IR and G-band data available which allows us to compare flow fields
derived from this high-resolution data with the flow fields derived
from MDI full disc magnetograms. Four out of five regions with
X-class flares show a significant change in the helicity change rate,
while none of the five active regions with an associated M-class flare
shows this behavior. We determine the location of the helicity change
in the active regions and discuss possible causes. We also investigate
active regions with no flare activity to determine the fluctuations
of the helicity change rate due to instrumental effects.

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Title: High-Spatial Resolution Observations of Flow Fields in Solar
Active Region NOAA 10486
Authors: Yang, G.; Xu, Y.; Cao, W.; Wang, H.; Denker, C.; Rimmele,
T. R.
2004AAS...204.0210Y Altcode: 2004BAAS...36..669Y
We present high-spatial resolution observations of proper motions in
solar active region NOAA 10486 using the newly developed high-order
adaptive optics (AO) system at the Dunn Solar Telescope (DST) of the
National Solar Observatory/Sacramento Peak (NSO/SP) on 2003 October
29. The images were obtained with high-order AO, frame selection, and
speckle masking image reconstruction. We analyze a two hour time series
with 1-minute cadence in the context of an X10 white-light flare. Local
correlation tracking (LCT) was used to measure the horizontal proper
motions in the photosphere and relate them to the strong shear observed
in the magnetic field configuration.

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Title: Rapid Changes of Sunspot Structure Associated with Major
Flares in AR 10486
Authors: Liu, C.; Deng, N.; Qiu, J.; Goode, P. R.; Denker, C.; Wang, H.
2004AAS...204.4705L Altcode: 2004BAAS...36..737L
By tracing the change in TRACE white-light images, we find penumbral
segments decayed rapidly and permanently right after three X-class
solar flares. All of these three events occurred recently in NOAA
Active Region 10486, an X17 flare on 2003 October 28, an X10 flare
on 2003 October 29, and an X8.3 flare on 2003 November 2. For the X17
flare, the decaying penumbral segment is related to a section of one
of the two TRACE 1600Å ribbons, while for the X10 and X8.3 flares,
both to the 50-100 keV hard X-ray sources observed by RHESSI. We show
the changes of photospheric magnetic fields associated with these
penumbral decaying area by plotting the time profiles of magnetic flux
derived from MDI magnetograms. We also use the TRACE 195Å images to
understand the coronal environment. From all these observations, we
propose a possible explanation that magnetic fields change from a highly
inclined to a more vertical configuration after the flares, that is,
part of the penumbral magnetic field is converted into umbral fields.

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Title: Spreadsheet Toolkit for Ulysses Hi-Scale Measurements of
Interplanetary Ions and Electrons
Authors: Reza, J. Z.; Lanzerotti, L. J.; Denker, C.; Patterson, D.;
Amstrong, T. P.
2004AAS...204.7006R Altcode: 2004BAAS...36R.796R
Throughout the entire Ulysses out-of-the-ecliptic solar polar mission,
the Heliosphere Instrument for Spectra, Composition, and Anisotropy at
Low Energies (HI-SCALE) has collected measurements of interplanetary
ions and electrons. Time-series of electron and ion fluxes obtained
since 1990 have been carefully calibrated and will be stored in a data
management system, which will be publicly accessible via the WWW. The
goal of the Virtual Solar Observatory (VSO) is to provide data uniformly
and efficiently to a diverse user community. However, data dissemination
can only be a first step, which has to be followed by a suite of data
analysis tools that are tailored towards a diverse user community in
science, technology, and education. The widespread use and familiarity
of spreadsheets, which are available at low cost or open source for
many operating systems, make them an interesting tool to investigate
for the analysis of HI-SCALE data. The data are written in comma
separated variable (CSV) format, which is commonly used in spreadsheet
programs. CSV files can simply be linked as external data to spreadsheet
templates, which in turn can be used to generate tables and figures
of basic statistical properties and frequency distributions, temporal
evolution of electron and ion spectra, comparisons of various energy
channels, automatic detection of solar events, solar cycle variations,
and space weather. Exploring spreadsheet-assisted data analysis in the
context of information technology research, data base information search
and retrieval, and data visualization potentially impacts other VSO
components, where diverse user communities are targeted. Finally, this
presentation is the result of an undergraduate research project, which
will allow us to evaluate the performance of user-based spreadsheet
analysis "benchmarked" at the undergraduate skill level.

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Title: The New Solar Telescope at Big Bear Solar Observatory
Authors: Denker, C.; Marquette, W. H.; Varsik, J.; Wang, H.; Goode,
P. R.; Moretto, G.; Kuhn, J.; Coulter, R.
2004AAS...204.6908D Altcode: 2004BAAS...36R.795D
The New Solar Telescope (NST) at Big Bear Solar Observatory is
the replacement of the current 65 cm vacuum telescope. We present
the optical design of this novel off-axis telescope with a 1.6 m
clear aperture. The NST has been designed to exploit the excellent
seeing conditions at a lake-site observatory and provide data with a
spatial resolution close the telescope's diffraction limit from the
visible to the near-infrared (NIR) wavelength region. The post-focus
instrumentation is located in the Coudé-room, a new optical laboratory
below the observing floor, which also hosts a high-order adaptive optics
system. The main instruments are two imaging spectro-polarimeters for
visible and NIR observations and a real-time image reconstruction system
for visible-light multi-color photometry. This unique combination of
instruments will realize its full potential in the studies of active
region evolution and space weather forecasts.

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Title: Innovative Information Technology for Space Weather Research
Authors: Wang, H.; Qu, M.; Shih, F.; Denker, C.; Gerbessiotis, A.;
Lofdahl, M.; Rees, D.; Keller, C.
2004AAS...204.5209W Altcode: 2004BAAS...36..755W
Solar activity is closely related to the near earth environment --
summarized descriptively as space weather. Changes in space weather
have adverse effect on many aspects of life and systems on earth and in
space. Real-time, high-quality data and data processing would be a key
element to forecast space weather promptly and accurately. Recently,
we obtained a funding from US National Science Foundation to apply
innovative information technology for space weather prediction. (1)
We use the technologies of image processing and pattern recognition,
such as image morphology segmentation, Support Vector Machines (SVMs),
and neural networks to detect and characterize three important solar
activities in real-time: filament eruptions, flares, and emerging flux
regions (EFRs). Combining the real time detection with the recent
statistical study on the relationship among filament eruptions,
flares, EFRs, coronal mass ejections (CMEs), and geomagnetic storms,
we are establishing real time report of solar events and automatic
forecasting of earth directed CMEs and subsequent geomagnetic storms. (2) We combine state-of-art parallel computing techniques with phase
diverse speckle imaging techniques, to yield near real-time diffraction
limited images with a cadence of approximately 10 sec. We utilize the
multiplicity of parallel paradigms to optimize the calculation of phase
diverse speckle imaging to improve calculation speed. With such data,
we can monitor flare producing active regions continuously and carry
out targeted studies of the evolution and flows in flare producing
active regions. (3) We are developing Web based software tools to
post our processed data, events and forecasting in real time, and to
be integrated with current solar activity and space weather prediction
Web pages at BBSO. This will also be a part of Virtual Solar Observatory
(VSO) being developed by the solar physics community. This research
is supported by NSF ITR program.

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Title: High Resolution Observations of Complex Magnetic Structure
in Active Region NOAA 10375
Authors: Deng, N.; Liu, C.; Wang, H.; Denker, C.; NJIT/CFSTR Team
2004AAS...204.2003D Altcode: 2004BAAS...36..686D
We observed the dynamics, spatial distribution, and temporal evolution
of magnetic fields in active region NOAA 10375 using high resolution
images. From June 9 to June 12, 2003, the NOAA 10375, which has a δ
configuration, produced major flare activity. An X1.7 event occurred
on June 9 with an associated Type II radio burst. On June 10, the
region produced numerous M-class flares including an M5.6 flare at
18:15 UT. Two X-class flares occurred on June 11. On June 12, the
region produced four M-class flares, including an M1.1 flare at 17:12
UT. We use speckle reconstructed data obtained with the new real-time
image reconstruction (RTIR) system at BBSO that is a unique instrument
for high-spatial resolution observation of the Sun. We also use high
resolution Hα data taken at the 65 cm vacuum reflector to study
chromospheric activity. In addition, we combine TRACE, MDI and RHESSI
data to study the temporal evolution and connectivity of magnetic
structures for a better understanding of active region evolution and
the dynamics of the activity. This work was supported by NSF under
grant ATM 03-42560, ATM 03-13591, and ATM 02-36945, and by NASA under
grant NAG 5-12782.

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Title: Characteristic evaluation of a near-infrared Fabry-Perot
filter for the InfraRed Imaging Magnetograph (IRIM)
Authors: Cao, Wenda; Denker, Carsten J.; Wang, Haimin; Ma, J.; Qu,
M.; Wang, Jinshan; Goode, Philip R.
2004SPIE.5171..307C Altcode:
The InfraRed Imaging Magnetograph (IRIM) is a high temporal
resolution, high spatial resolution, high spectral resolving power,
and high magnetic sensitivity solar two-dimensional narrow-band
spectro-polarimeter working in the near infrared from 1.0 μm to
1.7 μm at Big Bear Solar Observatory (BBSO). It consists of an
interference filter, a polarization analyzer, a birefringent filter,
and a Fabry-Perot etalon. As the narrowest filter of IRIM, the infrared
Fabry-Perot plays a very important role in achieving the narrow band
transmission of ~ 10 pm and high throughput between 85% and 95% for
the full wavelength range, maintaining wavelength tuning ability
from 1.0 to 1.7 μm, and assuring stability and reliability. As
the third of a series of publications describing IRIM, this paper
outlines a set of methods to evaluate the near infrared Fabry-Perot
etalon. Two-dimensional characteristic maps of the near infrared
Fabry-Perot etalon, including the bandpass ▵λ, effective finesse
Feff, peak transmission τmax, along with a free
spectral range, flatness, roughness, and stability and repeatability
were obtained with laboratory equipment. These measured results will
benefit the optimization of IRIM design and observational mode of
the future.

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Title: First results from the NSO/NJIT solar adaptive optics system
Authors: Rimmele, Thomas R.; Richards, Kit; Hegwer, Stephen; Fletcher,
Stephen; Gregory, Scott; Moretto, Gilberto; Didkovsky, Leonid V.;
Denker, Carsten J.; Dolgushin, Alexander; Goode, Philip R.; Langlois,
Maud; Marino, Jose; Marquette, William
2004SPIE.5171..179R Altcode:
The National Solar Observatory and the New Jersey Institute of
Technology have developed two 97 actuator solar adaptive optics
(AO) systems based on a correlating Shack-Hartmann wavefront sensor
approach. The first engineering run was successfully completed
at the Dunn Solar Telescope (DST) at Sacramento Peak, New Mexico
in December 2002. The first of two systems is now operational at
Sacramento Peak. The second system will be deployed at the Big Bear
Solar Observatory by the end of 2003. The correlating Shack-Hartmann
wavefront sensor is able to measure wavefront aberrations for
low-contrast, extended and time-varying objects, such as solar
granulation. The 97-actuator solar AO system operates at a loop
update rate of 2.5 kHz and achieves a closed loop bandwidth (0dB
crossover error rejection) of about 130 Hz. The AO system is capable
of correcting atmospheric seeing at visible wavelengths during median
seeing conditions at both the NSO/Sacramento Peak site and the Big Bear
Solar Observatory. We present an overview of the system design. The
servo loop was successfully closed and first AO corrected images were
recorded. We present first results from the new, high order AO system.

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Title: Rapid Penumbral Decay following Three X-Class Solar Flares
Authors: Wang, H.; Liu, C.; Qiu, J.; Deng, N.; Goode, P. R.; Denker, C.
2004ApJ...601L.195W Altcode:
We show strong evidence that penumbral segments decayed rapidly and
permanently right after three X-class solar flares. Two of the three
events occurred very recently in NOAA Active Region 10486, an X17
flare on 2003 October 28 and an X10 flare on 2003 October 29. The
third X2.3 flare was observed in solar active region NOAA AR 9026 on
2000 June 6. The locus of penumbral decay is related to flare emission,
albeit with distinct differences for each event. We present difference
images highlighting the rapid changes between pre- and postflare states
of the flaring active region, which show distinct decaying penumbral
segments and neighboring umbral cores becoming darker. Because of the
lack of spectroscopic data, we cannot exclude the possibility that
the observed changes are due to changes in the temperature structure
of the flaring atmosphere, or to a corresponding reduction in opacity
for a section of both umbra and penumbra. However, we argue against
this possibility because the observed intensity changes are permanent,
not transient. We instead propose a possible explanation that magnetic
fields change from a highly inclined to a more vertical configuration
within approximately 1 hr after the flares; i.e., part of the penumbral
magnetic field is converted into umbral fields.

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Title: Low energy SEP events of October/November 2003 at 1 and 5 AU
Authors: Lanzerotti, L. J.; Maclennan, C. G.; Denker, C.
2004cosp...35..669L Altcode: 2004cosp.meet..669L
The late October-early November solar energetic particle (SEP) events
during the declining stage of solar cycle 23 provide an outstanding
opportunity to investigate the propagation of solar-produced ions and
electrons in the inner (&lt;5 AU) heliosphere. The EPAM instrument on
the ACE spacecraft (1 AU) and the HISCALE instrument on the Ulysses
spacecraft (essentially in the ecliptic plane at 5.2 AU and about
117^o east of the Earth-Sun line) were ideally situated to measure
the in-ecliptic interplanetary particles produced by the series of
large solar events. Of particular interest is the particle event on 28
October 2003 (day 301) following the exceptionally large X17 flare in
Active Region 486. Particles were observed at both ACE and Ulysses;
quite rapid onsets of the intensities of ions were measured at both
spacecraft. Indeed, this event may have the most rapid onset of any SEP
event ever measured at 5 AU. This presentation will concentrate on an
examination of the intensities, time dependence, and radial gradients
of protons and heavy ions (Z ≥ 2) that were measured during the
series of SEPs in this time interval.

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Title: High Spatial Resolution Observations of Pores and the Formation
of a Rudimentary Penumbra
Authors: Yang, G.; Xu, Y.; Wang, H.; Denker, C.
2003ApJ...597.1190Y Altcode:
We present high spatial resolution observation of small-scale
magnetic activity in solar active region NOAA 9539. The observations
were obtained on 2001 July 15 using the 65 cm vacuum reflector and
25 cm refractor of the Big Bear Solar Observatory (BBSO). The data
sets include time series of speckle reconstructed continuum images
at 5200 Å, Hα filtergrams (blue line wing, line center, and red
line wing), and line-of-sight magnetograms. Two pores, separated by
a light bridge, were located in the central part of NOAA 9539. The
formation of penumbral filaments near the light bridge indicated
a sudden change of the local magnetic field topology from almost
vertical to strongly inclined magnetic fields, which allowed cool
material previously suspended in a filament to stream downward. During
the downward motion of the cool material, Hα Dopplergrams revealed
twisted streamlines along the filament. Finally, there are several
well-defined Hα brightenings, Ellerman bombs (EBs), occurred near
the region where the downflow of materials fell in. The EBs reside
near a magnetic inversion line and are stationary, as opposed to
EBs associated with moving magnetic features. We also found that the
horizontal flow field of the white-light images derived from local
correlation tracking is different from the previous observations. The
horizontal movements in the superpenumbrae of leading sunspot and the
following sunspots are opposite.

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Title: 1.6 M Solar Telescope in Big Bear -- The NST
Authors: Goode, Philip R.; Denker, Carsten. J.; Didkovsky, Leonid I.;
Kuhn, J. R.; Wang, Haimin
2003JKAS...36S.125G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Sun from Big Bear
Authors: Goode, Philip R.; Denker, Carsten; Wang, Haimin
2003ASSL..288..137G Altcode: 2003ASSL..287..437G
No abstract at ADS

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Title: Long-Term Seeing Characteristics at Big Bear Solar Observatory
Authors: Denker, C.; Espinosa, O. D.; Nenow, J.; Marquette, W. H.
2003SPD....34.2018D Altcode: 2003BAAS...35R.847D
We present observations of long-term seeing characteristics from June
1997 to September 2002 obtained with Seykora-type scintillometers
at Big Bear Solar Observatory (BBSO). BBSO is an ideal site for
ground-based campaign-style observations. Since BBSO is situated on a
small island in a 2,000 m high mountain lake in the cloudless mountains
of Souther California, it benefits from excellent seeing conditions all
day long. The atmospheric turbulence that degrades images originates
primarily from two layers near the ground and at the level of the jet
stream. BBSO's dome is located at the end of a 300 m long causeway
jutting into the lake. Since the lake, with its cool waters, provides
a natural inversion, and the dome has three kilometers of open water
to its west, the boundary layer seeing is effectively suppressed. In
addition, the east-west orientation of the Big Bear Valley provides a
natural channel for the prevailing winds from the west resulting in a
nearly laminar flow at the observatory site. We present a comparison
of scintillometer data with climate data and analyze a one year long
sub-set for local seeing variations near the lake shore and at the
observatory island. We would like to thank Jacques Beckers and the
National Solar Observatory for providing the scintillometer data. This
work was supported by NSF under grant ATM 00-86999, ATM 00-76602,
and ATM 02-36945 and by NASA under grant NAG 5-9682.

---------------------------------------------------------
Title: Studies of Faculae and Pores in Visible and near IR
Authors: Xu, Y.; Denker, C.; Yang, G.; Jing, J.; Ma, J.; Spirock,
T. J.; Wang, H.
2003SPD....34.1102X Altcode: 2003BAAS...35..827X
We followed active region NOAA 0030 from July 14 to 21, 2002 at Big
Bear Solar Observatory(BBSO). High resolution images at 5200 continuum
and NIR 1.56 μ were taken continuously for about 3 hours each day. We
applied speckle reconstruction technique on 5200 continuum data to get
diffraction limit images. Combined our images with MDI magnetograms,
we are able to study the structure, evolution and flows of faculae and
small pores. In addition, we obtained data of several other active
regions, NOAA 0031, 0035, 0036. These images were used to study the
Center-to-Limb variation of facular contrasts. Finally, we compare
the results of this study with that for the data sets we obtained in
August and September 1999.

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Title: High-Resolution Infrared Filter System for Solar Spectroscopy
and Polarimetry
Authors: Cao, W.; Ma, J.; Wang, J.; Goode, P. R.; Wang, H.; Denker, C.
2003SPD....34.2013C Altcode: 2003BAAS...35..846C
We report on the design of an imaging filter system working at the
near infrared (NIR) of 1.56 μ m to obtain monochromatic images
and to probe weak magnetic fields in different layers of the deep
photosphere with high temporal resolution and spatial resolution at
Big Bear Solar Observatory (BBSO). This filter system consists of
an interference filter, a birefringent filter, and a Fabry-Pérot
etalon. As the narrowest filter system, the infrared Fabry-Pérot
plays an important role in achieving narrow band transmission and
high throughput, maintaining wavelength tuning ability, and assuring
stability and reliability. In this poster, we outline a set of methods
for the evaluation and calibration of the near infrared Fabry-Pérot
etalon. Two-dimensional characteristic maps of the near infrared
Fabry-Pérot etalon, including full-width-at-half-maximum (FWHM),
effective finesse, peak transmission, along with free spectral range,
flatness, roughness, stability and repeatability were obtained with lab
equipments. Finally, by utilizing these results, a detailed analysis
of the filter performance for the Fe I 1.5648 μ m and Fe I 1.5652 μ
m Zeeman sensitive lines is presented. These results will benefit the
design of NIR spectro-polarimeter of Advanced Technology Solar Telescope
(ATST).

---------------------------------------------------------
Title: First Results of the Near Real-Time Imaging Reconstruction
System at Big Bear Solar Observatory
Authors: Yang, G.; Denker, C.; Wang, H.
2003SPD....34.0304Y Altcode: 2003BAAS...35..808Y
The Near Real-Time Imaging Reconstruction system (RTIR) at Big Bear
Solar Observatory (BBSO) is designed to obtain high spatial resolution
solar images at a cadence of 1 minute utilizing the power of parallel
processing. With this system, we can compute near diffraction-limited
images without saving huge amounts of data that are involved in the
speckle masking reconstruction algorithm. It enables us to monitor
active regions and give fast response to the solar activity. In this
poster we present the first results of our new 32-CPU Beowulf cluster
system. The images are 1024 x 1024 and the field of view (FOV) is
80” x 80”. Our target is an active region with
complex magnetic configuration. We focus on pores and small spots in
the active region with the goal of better understanding the formation
of penumbra structure. In addition we expect to study evolution of
active regions during solar flares.

---------------------------------------------------------
Title: Rapid Penumbral Decay in Active Region NOAA 9026 Associated
with Two X-Class Flares
Authors: Deng, N.; Liu, C.; Yang, G.; Wang, H.; Denker, C.
2003SPD....34.1619D Altcode: 2003BAAS...35..836D
In recent studies, we found that the longitudinal magnetic field
changes drastically during energetic M- and X-class flares. In this
poster, we show an example of rapid penumbral decay associated with
two X1.1/X2.3 flares in active region NOAA 9026 on 2000 June 6. From
about 08:00 UT to 13:30 UT, several C-class and one M-class flares
occurred in the active region. An X1.1 flare started at 13:00 UT and
reached its maximum at 13:39 UT, which was followed by another M7.1
flare at 13:56 UT. This flare reached its maximum at around 14:01 UT
and decayed quickly and ended at 14:11 UT. The largest event was an
X2.3 flare starting at 14:58 UT. It reached its peak at around 15:25
UT and since then decayed slowly. The penumbra in two distinct regions
partially disappeared as a result of the X-class flares. This event also
produced a type II radio burst (1189 km/s), a type IV radio burst, an
11-degree long filament eruption, and full-halo coronal mass ejection
(CME). Even though the penumbral decay happened in a δ -sunspot, our
observations will provide guidance for subsequent studies employing
two-dimensional spectro-polarimetry and image reconstruction, and for
models to understand active region evolution and solar activity. This work was supported by NSF under grant ATM 00-86999, ATM 00-76602,
and ATM 02-36945, and by NASA under grant NAG 5-9682.

---------------------------------------------------------
Title: Hα Full Disk Observations of Chromospheric Differential
Rotation
Authors: Smith, G. A.; Varsik, J.; Nenow, J.; Marquette, W. H.; Wang,
H.; Denker, C.
2003SPD....34.0708S Altcode: 2003BAAS...35..821S
We studied the solar chromospheric rotation profile using full-disk
Hα images of the Sun obtained at the Big Bear Solar Observatory
(BBSO). The method is based on Local Correlation Tracking (LCT). As a
unique feature the entire full-disk image is used, i. e., quiet sun
as well as solar active regions, whereas most other methods rely on
images of distinct individual features such as filaments, plages,
and sunspots. Six months of Hα full-disk data sets from June to
December 2001, which consists of 600 to 800 daily images at 30 s to 60
s cadence, have been processed and analyzed. The images were checked
for a number of problems, including overexposure, underexposure, and
skewed images. All images were normalized by having the solar disk
recentered, the dark frame subtracted, and the limb darkening function
calculated and subtracted from the image. The images are locally
cross-correlated with each other to find the displacements between
them. The angular velocities are projected onto the central meridian
and a differential rotation profile is fitted to the data (either as
Legendre polynomials or as polynomials in sin 2nθ , quad
n=0,1, 2, ..., where θ is the heliographic longitude). The currently
used settings in the processing of the six months data were optimized
for both accuracy and speed. A number of different parameters were
experimented with, such as various grid sizes, grid spacing, sampling
window sizes, weighing functions and also different implementations of
cross-correlation algorithms, to find the best combination. This
work was supported by NSF under grant ATM 00-86999, ATM 00-76602,
and ATM 02-36945 and by NASA under grant NAG 5-9682.

---------------------------------------------------------
Title: Design of Achromatic Waveplates for ATST Near IR Filter System
Authors: Ma, J.; Wang, J.; Cao, W.; Denker, C.; Wang, H.
2003SPD....34.2024M Altcode: 2003BAAS...35R.848M
Achromatic waveplates play one of the central roles in constructing
universal birefringent filters (UBF). Although it's been developed
very well by several authors in the last decades, the mechanisms and
detailed techniques which can realize the achromatism are still not
clearly categorized. Such waveplates for Infrared do not exist yet. In
the recent development of a InfraRed High Resolution Magnetograph at
BBSO, it is realized that a standard approach of designing achromatic
waveplate is needed not only for the IRHRM, but more importantly, for
the Near IR Tunable Filter for ATST. There are several theoretical
methods which are available to describe the behavior of waveplates and
polarization status of field, including algebraic tools (Jones Algebra,
Muler Matrix, Stokes Vector), and geometrical approach (Poincere Sphere,
which is Complex Analysis in fact). By using these methods, it can
be proved that a combination of waveplates could have much better
achromatic performance than a single component has. Since the
simulation of the combination of waveplates gets more and more complex,
a computer program software package for designing achromatic waveplates
is developed. Compared to the most popular commercial software package,
such as ZEMAX which uses ray-tracing approach, the recently developed
software tools is based on Transfer Functions of Optical Systems,
which will be more efficient than ray-tracing approach.

---------------------------------------------------------
Title: IRIM: An Imaging Magnetograph for High-Resoultion Solar
Observations in the Near-Infrared
Authors: Denker, Carsten J.; Ma, J.; Wang, Jingshan; Didkovsky,
Leonid V.; Varsik, John R.; Wang, Haimin; Goode, Philip R.
2003SPIE.4853..223D Altcode:
The InfraRed Imaging Magnetograph (IRIM) is an innovative magnetograph
system for near-infrared (NIR)observations of the Sun. IRIM will
provide high spatial resolution (0.2" per pixel image scale), high
temporal resolution (1-2 minutes), moderate spectral resolution
(14.0 pm), and high magnetic sensitivity covering a substantial
field-of-view (FOV: 170" circular). The bandpass of the instrument
is reduced in three steps while still providing high transmission:
(1) a 4 nm interference filter, (2) a 0.25 nm Lyot-filter, and (3)
a 14.0 pm tunable Fabry-Perot etalon. The innovative NIR Lyot-filter
was developed at the New Jersey Institute of Technology (NJIT) and
is currently being assembled at Cambridge Research Instruments. It is
the first of its kind and provides a large angle of acceptance, thus
solving many problems encountered with dual Fabry-Perot systems. The
two-dimensional line profiles will be recorded by a 1024 × 1024 pixel,
12-bit Complex Metal Oxide Semiconductor (CMOS) focal plane array (FPA)
manufactured by Rockwell Scientific Imaging, which can obtain images
at a rate of 50 fps. IRIM will utilize the remodelled Coude-feed of
the 65 cm vacuum telescope at the Big Bear Solar Observatory (BBSO)
and will benefit from an image stabilization and correction system of
independently operating Correlation Tracking (CT) and Adaptive Optics
(AO) systems.

---------------------------------------------------------
Title: Solar adaptive optics: a progress report
Authors: Rimmele, Thomas R.; Richards, Kit; Hegwer, Steven L.; Ren,
Deqing; Fletcher, S.; Gregory, Scott; Didkovsky, Leonid V.; Denker,
Carsten J.; Marquette, William; Marino, J.; Goode, Philip R.
2003SPIE.4839..635R Altcode:
We present a progress report of the solar adaptive optics (AO)
development program at the National Solar Observatory (NSO) and the
Big Bear Solar Observatory (BBSO). Examples of diffraction-limited
observations obtained with the NSO low-order solar adaptive optics
system at the Dunn Solar Telescope (DST) are presented. The design
of the high order adaptive optics systems that will be deployed at
the DST and the BBSO is discussed. The high order systems will provide
diffraction-limited observations of the Sun in median seeing conditions
at both sites.

---------------------------------------------------------
Title: High-order adaptive optical system for Big Bear Solar
Observatory
Authors: Didkovsky, Leonid V.; Dolgushyn, Alexander; Marquette,
William; Nenow, Jeff; Varsik, John; Goode, Philip R.; Hegwer, Steven
L.; Ren, Deqing; Fletcher, Steve; Richards, Kit; Rimmele, Thomas;
Denker, Carsten J.; Wang, Haimin
2003SPIE.4853..630D Altcode:
We present a high-order adaptive optical system for the 26-inch vacuum
solar telescope of Big Bear Solar Observatory. A small elliptical
tip/tilt mirror is installed at the end of the existing coude
optical path on the fast two-axis tip/tilt platform with its resonant
frequency around 3.3 kHz. A 77 mm diameter deformable mirror with 76
subapertures as well as wave-front sensors (correlation tracker and
Shack-Hartman) and scientific channels for visible and IR polarimetry
are installed on an optical table. The correlation tracker sensor
can detect differences at 2 kHz between a 32×32 reference frame
and real time frames. The WFS channel detects 2.5 kHz (in binned
mode) high-order wave-front atmosphere aberrations to improve solar
images for two imaging magnetographs based on Fabry-Perot etalons in
telecentric configurations. The imaging magnetograph channels may work
simultaneously in a visible and IR spectral windows with FOVs of about
180×180 arc sec, spatial resolution of about 0.2 arc sec/pixel and
SNR of about 400 and 600 accordingly for 0.25 sec integration time.

---------------------------------------------------------
Title: Imaging magnetographs for high-resolution solar observations
in the visible and near-infrared wavelength region
Authors: Denker, C.; Didkovsky, L.; Ma, J.; Shumko, S.; Varsik, J.;
Wang, J.; Wang, H.; Goode, P. R.
2003AN....324..332D Altcode:
The Coudé feed of the vacuum telescope (aperture D=65 cm) at the Big
Bear Solar Observatory (BBSO) is currently completely remodelled to
accommodate a correlation tracker and a high-order Adaptive Optics (AO)
system. The AO system serves two imaging magnetograph systems located at
a new optical laboratory on the observatory's 2nd floor. The
InfraRed Imaging Magnetograph (IRIM) is an innovative magnetograph
system for near-infrared (NIR) observations in the wavelength region
from 1.0 mu m to 1.6 mu m. The Visible-light Imaging Magnetograph
(VIM) is basically a twin of IRIM for observations in the wavelength
range from 550 nm to 700 nm. Both instruments were designed for high
spatial and high temporal observations of the solar photosphere and
chromosphere. Real-time data processing is an integral part of the
instruments and will enhance BBSO's capabilities in monitoring solar
activity and predicting and forecasting space weather.

---------------------------------------------------------
Title: Comparison of Facular Contrast in the Visible and Near-Infrared
Authors: Xu, Y.; Wang, H.; Denker, C.; Yang, G.; Spirock, T. J.;
Qiu, J.
2003ASPC..286..201X Altcode: 2003ctmf.conf..201X
No abstract at ADS

---------------------------------------------------------
Title: Seeing Characteristic at a Lake-Site Observatory
Authors: Denker, C.; Didkovsky, L.; Marquette, W. H.; Goode, P. R.;
Venkateswaran, K.; Rimmele, T. R.
2003ASPC..286...23D Altcode: 2003ctmf.conf...23D
No abstract at ADS

---------------------------------------------------------
Title: Speckle Masking Imaging of Pores in Solar Active Region
NOAA 9439
Authors: Yang, G.; Denker, C.; Xu, Y.; Wang, H.
2003ASPC..286..317Y Altcode: 2003ctmf.conf..317Y
No abstract at ADS

---------------------------------------------------------
Title: High-order adaptive optical system for Big Bear Solar
Observatory
Authors: Didkovsky, L. V.; Denker, C.; Goode, P. R.; Wang, H.; Rimmele,
T. R.
2003AN....324..297D Altcode:
A high-order Adaptive Optical (AO) system for the 65 cm vacuum telescope
of the Big Bear Solar Observatory (BBSO) is presented. The Coudé-exit
of the telescope has been modified to accommodate the AO system and two
imaging magnetograph systems for visible-light and near infrared (NIR)
observations. A small elliptical tip/tilt mirror directs the light into
an optical laboratory on the observatory's 2mathrm {nd}
floor just below the observing floor. A deformable mirror (DM) with
77 mm diameter is located on an optical table where it serves two
wave-front sensors (WFS), a correlation tracker (CT) and Shack-Hartman
(SH) sensor for the high-order AO system, and the scientific channels
with the imaging magnetographs. The two-axis tip/tilt platform has a
resonance frequency around 3.3 kHz and tilt range of about 2 mrad,
which corresponds to about 25” in the sky. Based on
32 x 32 pixel images, the CT detects image displacements between a
reference frame and real-time frames at a rate of 2 kHz. High-order
wave-front aberrations are detected in the SH WFS channel from slope
measurements derived from 76 sub-apertures, which are recorded with
1,280 x 1,024 pixel Complex Metal Oxide Semiconductor (CMOS) camera
manufactured by Photobit camera. In the 4 x 4 pixel binning mode,
the data acquisition rate of the CMOS device is more than 2 kHz. Both
visible-light and NIR imaging magnetographs use Fabry-Pérot etalons in
telecentric configurations for two-dimensional spectro-polarimetry. The
optical design of the AO system allows using small aperture prefilters,
such as interference or Lyot filters, and 70 mm diameter Fabry-Pérot
etalons covering a field-of-view (FOV) of about 180”
x 180”.

---------------------------------------------------------
Title: Control and Acquisition Software for the Visible-Light
Fabry-Pérot Interferometer at the Big Bear Solar Observatory
Authors: Shumko, Sergiy; Denker, Carsten J.; Varsik, John; Didkovsky,
Leonid V.; Marquette, William; Goode, Philip R.; Wang, Haimin
2002SPIE.4848..483S Altcode:
We describe our progress in the development of a software package to
control a Fabry-Pérot interferometer (FPI) at the Big Bear Solar
Observatory (BBSO). The FPI is a key part of our new Visible-Light
Imaging Magnetograph (VIM). We describe the software libraries
and methods that we use to develop the software. We also present
specifications and characteristics of this new instrument.

---------------------------------------------------------
Title: Rapid Changes of Magnetic Fields Associated with Six X-Class
Flares
Authors: Wang, Haimin; Spirock, Thomas J.; Qiu, Jiong; Ji, Haisheng;
Yurchyshyn, Vasyl; Moon, Yong-Jae; Denker, Carsten; Goode, Philip R.
2002ApJ...576..497W Altcode:
In this paper, we present the results of the study of six X-class
flares. We found significant changes in the photospheric magnetic
fields associated with all of the events. For the five events in 2001,
when coronagraph data were available, all were associated with halo
coronal mass ejections. Based on the analyses of the line-of-sight
magnetograms, all six events had an increase in the magnetic flux
of the leading polarity of order of a few times 1020 Mx
while each event had some degree of decrease in the magnetic flux
of the following polarity. The flux changes are considered impulsive
because the “changeover” time, which we defined as the time to change
from preflare to postflare state, ranged from 10 to 100 minutes. The
observed changes are permanent. Therefore, the changes are not due
to changes in the line profile caused by flare emissions. For the
three most recent events, when vector magnetograms were available,
two showed an impulsive increase of the transverse field strength
and magnetic shear after the flares, as well as new sunspot area in
the form of penumbral structure. One of the events in this study was
from the previous solar cycle. This event showed a similar increase
in all components of the magnetic field, magnetic shear, and sunspot
area. We present three possible explanations to explain the observed
changes: (1) the emergence of very inclined flux loops, (2) a change
in the magnetic field direction, and (3) the expansion of the sunspot,
which moved some flux out of Zeeman saturation. However, we have no
explanation for the polarity preference; i.e., the flux of leading
polarity tends to increase while the flux of following polarity tends
to decrease slightly.

---------------------------------------------------------
Title: Solar activity monitoring and forecasting capabilities at
Big Bear Solar Observatory
Authors: Gallagher, P. T.; Denker, C.; Yurchyshyn, V.; Spirock, T.;
Qiu, J.; Wang, H.; Goode, P. R.
2002AnGeo..20.1105G Altcode:
The availability of full-disk, high-resolution Ha

---------------------------------------------------------
Title: Properties of Faculae and Pores
Authors: Xu, Y.; Denker, C.; Spirock, T.; Qiu, J.; Jing, J.; Ma, J.;
Wang, H.
2002AAS...200.3804X Altcode: 2002BAAS...34..699X
In August/September 1999, we obtained high resolution images of several
active regions at the Big Bear Solar Observatory. The data set consists
of near-infrared (1560 nm), Ca I (610.3 nm), and broad-band (520 nm)
images. In addition, we took magnetograms with the improved digital
vector magnetograph (DVMG). All data were obtained quasi-simultaneously,
i. e., the temporal evolution of small-scale features is negligible. By
using speckle masking technique, we reconstructed images of diffraction
limit resolution. In this presentation, we present our preliminary
results from this high quality data set focussing on the following
three topics: 1. Comparison of contrasts of faculae and pores in three
wavelengths regimes which cover three different solar atmopsheric
heights. 2. Center-to-limb variation of facular contrasts. 3. The
relationship between magnetic field strength and the contrasts of
faculae and pores.

---------------------------------------------------------
Title: Near Real-Time Image Reconstruction
Authors: Denker, C.; Yang, G.; Wang, H.
2001SoPh..202...63D Altcode:
In recent years, post-facto image-processing algorithms have
been developed to achieve diffraction-limited observations of
the solar surface. We present a combination of frame selection,
speckle-masking imaging, and parallel computing which provides
real-time, diffraction-limited, 256×256 pixel images at a 1-minute
cadence. Our approach to achieve diffraction limited observations is
complementary to adaptive optics (AO). At the moment, AO is limited
by the fact that it corrects wavefront abberations only for a field
of view comparable to the isoplanatic patch. This limitation does not
apply to speckle-masking imaging. However, speckle-masking imaging
relies on short-exposure images which limits its spectroscopic
applications. The parallel processing of the data is performed on
a Beowulf-class computer which utilizes off-the-shelf, mass-market
technologies to provide high computational performance for scientific
calculations and applications at low cost. Beowulf computers have
a great potential, not only for image reconstruction, but for any
kind of complex data reduction. Immediate access to high-level data
products and direct visualization of dynamic processes on the Sun are
two of the advantages to be gained.

---------------------------------------------------------
Title: Asymmetric Behavior of Hα Footpoint Emission during the
Early Phase of an Impulsive Flare
Authors: Qiu, Jiong; Ding, Ming D.; Wang, Haimin; Gallagher, Peter T.;
Sato, Jun; Denker, Carsten; Goode, Philip R.
2001ApJ...554..445Q Altcode:
We study the impulsive phase of a C9.0 solar flare using high temporal
and spatial resolution Hα images from Big Bear Solar Observatory (BBSO)
in conjunction with high-cadence hard X-ray (HXR) observations from
Yohkoh. During the early impulsive phase, HXR emission emerged from
two kernels K1 and K2 which were connected by coronal loops observed
in soft X-ray (SXR) images from Yohkoh. In Hα, the initial rise was
observed in one flare kernel K2, which was followed within 10 s by
enhanced emission in the associated kernel K1. Such a significant
asymmetry was not observed at HXR wavelengths. Our analysis shows
that the asymmetric Hα footpoint emission cannot be explained by the
magnetic mirroring effect in which strong field footpoints show lower
precipitation rates. Instead, we study this phenomenon by investigating
the atmospheric response of the lower chromosphere to nonthermal
beam heating. From numerical simulations, it is suggested that a cool
atmosphere does not respond rapidly to beam impact, which may explain
the missing Hα emission at K1 during the early impulsive phase. At K2,
the early-phase atmosphere may be preferentially heated resulting in
the Hα emission rapidly following the HXR emission. This is due to
the fact that K2 is a compact source which received persistent energy
deposition and consequent heating in a confined area during the early
phase. K1, on the other hand, is a diffused source which therefore
experienced a lower heating rate per unity area. We propose a scenario
in which the flare loop consists of multiple magnetic “threads”
connecting the compact footpoint K2 with the diffuse footpoint K1.

---------------------------------------------------------
Title: Solar Seeing Seven Ways From Sunday
Authors: Hill, F.; Balasubramaniam, K. S.; Beckers, J. M.; Briggs,
J. W.; Hegwer, S.; Radick, R. R.; Rimmele, T. R.; Richards, K.;
Denker, C.
2001AGUSM..SP21B03H Altcode:
The Advanced Technology Solar Telescope (ATST) site survey will be
carried out with a Solar Differential Image Motion Monitor (S-DIMM)
and a six-scintillometer SHAdow BAnd Ranging (SHABAR) array. This
device will provide estimates of the Fried parameter, R0,
derived from the differential motion measurements of two images of the
same cut across the solar limb formed by two 45 mm diameter telescope
apertures 225 mm apart, and an estimate of the height dependence of the
index of refraction structure parameter, Cn2, from
the co-variance of the signals from an array of 6 scintillometers with
15 baseline separations. It will also provide a cloud cover measurement
and RMS scintillation signal. In preparation for the survey, we compare
estimates of daytime solar seeing obtained simultaneously from seven
different instruments. The observations were made at NSO/Sacramento
Peak during the period January 26 - February 5, 2001 under a variety of
seeing and transparency conditions ranging from poor to excellent. The
seven instruments were: 1. a S-DIMM/SHABAR mounted at the top of
the Dunn Solar Tower (DST) 2. an identical S-DIMM/SHABAR mounted at
ground level 3. the NSO/SP Adaptive Optics wavefront sensor providing
subaperature image motion measurements 4. a Dalsa camera providing
bursts of high-speed images for spectral ratio seeing estimates 5. a
Xedar camera obtaining granulation images for contrast and differential
stretching measurements 6. a Seykora scintillometer mounted in the
DST 7. a video camera recording a movie of the visual quality of the
image The analysis of this data set will provide the first direct
comparison of this many simultaneous solar seeing measurements, test
the ATST site survey system, and verify the SHABAR measurement of the
seeing height profile.

---------------------------------------------------------
Title: High Spatial Resolution Observations of Sunspots, Pores,
and Faculae in the Visible and Near Infrared
Authors: Denker, C.
2001AGUSM..SP41C01D Altcode:
In August/September 1999, we observed several active regions
during their disk passage on the Sun. The data set consists of
speckle reconstructed continuum images at 520~nm, near infrared
continuum obtained at 1565~nm with frame selection, and line-of-sight
magnetograms. All these data were taken simultaneously. We studied the
horizontal motions of sunspots, pores, and faculae by tracking features
in the continuum filtergrams with sizes close to the diffraction limit
of the 65~cm vacuum refractor at the Big Bear Solar Observatory. We
undertake this study to gain a better understanding of the development
of active regions and the emergence of magnetic flux. We focus our
attention on the dynamics of small-scale magnetic features such
as rudimentary penumbrae, penumbral grains, magnetic knots, and
filigree. Finally, the results of this analysis will illustrate the
prospects for near real-time image reconstruction and application
oriented parallel computing.

---------------------------------------------------------
Title: Results from the Big Bear Solar Observatory's New Digital
Vector Magnetograph
Authors: Spirock, T. J.; Denker, C.; Varsik, J.; Shumko, S.; Qiu,
J.; Gallagher, P.; Chae, J.; Goode, P.; Wang, H.
2001AGUSM..SP51B06S Altcode:
During the past several years the Big Bear Solar Observatory has
been involved in an aggressive program to modernize the observatory's
instrumentation. At the forefront of this effort has been the upgrade
of the observatory's digital vector magnetograph (DVMG), which has been
recently integrated into the observatory's daily observing program. The
DVMG, which is mounted on the observatory's 25 cm vacuum refractor,
is a highly sensitive, high cadence magnetograph which studies the
FeI line at 630.1 nm. An easy to use GUI observing tool has been
written to aid instrument development and data acquisition. This
tool automatically calibrates the data and generates near real-time
vector magnetograms which will aid space weather forecasting and the
support of space weather missions. Also, our plan is to integrate the
DVMG data into the HESSI Synoptic Archive. The very sensitive quiet
Sun magnetograms, produced by the DVMG, will aid the study of small
scale magnetic reconnection at the intranetwork level and its possible
contribution to the coronal heating problem. Quiet sun longitudinal and
active region vector magnetograms will be presented. Image quality,
such as bias, cross-talk, noise levels and sensitivity, will be
discussed in addition to the improvements gained in post processing
such as image selection and image alignment.

---------------------------------------------------------
Title: Near Real-Time Solar Image Reconstruction
Authors: Yang, G.; Denker, C.; Wang, H.
2001AGUSM..SP21B04Y Altcode:
We use a Linux Beowulf cluster to build a system for near real-time
solar image reconstruction with the goal to obtain diffraction limited
solar images at a cadence of one minute. This gives us immediate access
to high-level data products and enables direct visualization of dynamic
processes on the Sun. Space weather warnings and flare forecasting will
benefit from this project. The image processing algorithms are based on
the speckle masking method combined with frame selection. The parallel
programs use explicit message passing via Parallel Virtual Machine
(PVM). The preliminary results are very promising. Now, we can construct
a 256 by 256 pixel image out of 50 short-exposure images within one
minute on a Beowulf cluster with four 500~MHz CPUs. In addition,
we want to explore the possibility of applying parallel computing on
Beowulf clusters to other complex data reduction and analysis problems
that we encounter, e.g., in multi-dimensional spectro-polarimetry.

---------------------------------------------------------
Title: The new global high-resolution Hα network: preliminary
results on the chromospheric differential rotation
Authors: Steinegger, M.; Denker, C.; Goode, P. R.; Marquette, W. H.;
Varsik, J.; Wang, H.; Otruba, W.; Freislich, H.; Hanslmeier, A.; Luo,
G.; Chen, D.; Zhang, Q.
2001ESASP.464..315S Altcode: 2001soho...10..315S
A new global network for high-resolution Hα full-disk observations of
the sun has been established at the Big Bear Solar Observatory (U.S.A.),
the Kanzelhöhe Solar Observatory (Austria), and the Yunnan Astronomical
Observatory (China). Each of the three stations have a 2K×2K pixel CCD
detector available to monitor the sun with a spatial resolution of 1
arcsec per pixel and a cadence of at least 1 image per minute. Having
high-cadence data from three observing stations available enables us to
accurately track solar rotation rates and meridional motions by local
correlation (LCT) and feature tracking techniques. This includes, e.g.,
tracking over several days the motions around active regions. After
an overview of the new Hα network and its scientific objectives, we
present and discuss the first preliminary results of the determination
of the chromospheric differential rotation by LCT from a high-cadence
time-series of Hα full-disk images. The obtained equatorial rotation
rate of 13.3044 deg/day (2.6876 μrad/s) agrees well with the values
obtained by other authors. Finally, we briefly outline our future
plans for the continuation of this work.

---------------------------------------------------------
Title: The Big Bear Solar Observatory's Digital Vector Magnetograph
Authors: Spirock, T.; Denker, C.; Chen, H.; Chae, J.; Qiu, J.; Varsik,
J.; Wang, H.; Goode, P. R.; Marquette, W.
2001ASPC..236...65S Altcode: 2001aspt.conf...65S
No abstract at ADS

---------------------------------------------------------
Title: Synoptic Observations of the Sun from Big Bear Solar
Observatory (CD-ROM Directory: contribs/goode)
Authors: Goode, P. R.; Denker, C.; Marquette, W. H.; Wang, H.
2001ASPC..223..656G Altcode: 2001csss...11..656G
No abstract at ADS

---------------------------------------------------------
Title: Dynamics of Quiet Sun Magnetic Fields
Authors: Denker, C.; Spirock, T.; Varsik, J. R.; Chae, J.; Marquette,
W. H.; Wang, H.; Goode, P. R.
2001ASPC..236..463D Altcode: 2001aspt.conf..463D
No abstract at ADS

---------------------------------------------------------
Title: Multi-Wavelength Observations of Solar Fine-Structure with
High Spatial Resolution (CD-ROM Directory: contribs/denker)
Authors: Denker, C.; Spirock, T. J.; Jefferies, S. M.; Chen, H.;
Marquette, W. H.; Wang, H.; Goode, P. R.
2001ASPC..223..607D Altcode: 2001csss...11..607D
No abstract at ADS

---------------------------------------------------------
Title: Ultraviolet and Hα Emission in Ellerman Bombs
Authors: Qiu, Jiong; Ding, Ming D.; Wang, Haimin; Denker, Carsten;
Goode, Philip R.
2000ApJ...544L.157Q Altcode:
We present the first high-cadence time profiles of Ellerman bombs
(EBs) at two wavelengths, 1.3 Å in the blue wing of the Hα line and
the UV continuum at 1600 Å, and study their temporal correlation. Our
results demonstrate that 46 out of 75 EBs exhibit a good correlation at
the two wavelengths with a correlation coefficient greater than 50%,
suggesting that a common energy release produces emission at the two
wavelengths. We also find that the EBs with strong Hα emission tend
to show a good Hα-UV correlation but that the weakly correlated or
noncorrelated EBs are usually weak in Hα emission. More than half of
the Hα-UV well-correlated EBs are located at the boundaries of unipolar
magnetic areas; the others are located at, or close to, the magnetic
inversion lines. However, the majority of the weakly or noncorrelated
EBs are located at the magnetic inversion lines. Our results suggest
that the physical mechanisms and the energy distributions are quite
different in different types of EBs and that heating in the photosphere
and temperature minimum region is very important for producing EBs. The
high-cadence observations of EBs also confirm unambiguously that the
light curves of EBs generally demonstrate a fast rise and a fast decay,
with an average e-fold rising/decaying time of about 1 minute, which
distinguishes EBs from the flare phenomenon.

---------------------------------------------------------
Title: High-Cadence Observations of an Impulsive Flare
Authors: Wang, Haimin; Qiu, Jiong; Denker, Carsten; Spirock, Tom;
Chen, Hangjun; Goode, Philip R.
2000ApJ...542.1080W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High-Resolution Hα Observations of Proper Motion in NOAA 8668:
Evidence for Filament Mass Injection by Chromospheric Reconnection
Authors: Chae, Jongchul; Denker, Carsten; Spirock, Tom J.; Wang,
Haimin; Goode, Philip R.
2000SoPh..195..333C Altcode:
There have been two different kinds of explanations for the source
of cool material in prominences or filaments: coronal condensations
from above and cool plasma injections from below. In this paper, we
present observational results which support filament mass injection
by chromospheric reconnection. The observations of an active filament
in the active region NOAA 8668 were performed on 17 August 1999 at a
wavelength of Hα−0.6 Å using the 65 cm vacuum reflector, a Zeiss Hα
birefringent filter, and a 12-bit SMD digital camera of Big Bear Solar
Observatory. The best image was selected every 12 s for an hour based
on a frame selection algorithm. All the images were then co-aligned and
corrected for local distortion due to the seeing. The time-lapse movie
of the data shows that the filament was undergoing ceaseless motion. The
Hα flow field has been determined as a function of time using local
correlation tracking. Time-averaged flow patterns usually trace local
magnetic field lines, as inferred from Hα fibrils and line-of-sight
magnetograms. An interesting finding is a transient flow field in a
system of small Hα loops, some of which merge into the filament. The
flow is associated with a cancelling magnetic feature which is located
at one end of the loop system. Initially a diverging flow with speeds
below 10 km s−1 is visible at the flux cancellation
site. The flow is soon directed along the loops and accelerated up
to 40 km s−1 in a few minutes. Some part of the plasma
flow then merges into and moves along the filament. This kind of
transient flow takes place several times during the observations. Our
results clearly demonstrate that reconnection in the photosphere and
chromosphere is a likely way to supply cool material to a filament,
as well as re-organizing the magnetic field configuration, and, hence,
is important in the formation of filaments.

---------------------------------------------------------
Title: Measuring Seeing from Solar Scintillometry and the Spectral
Ratio Technique
Authors: Goode, P. R.; Wang, H.; Marquette, W. H.; Denker, C.
2000SoPh..195..421G Altcode:
In principle, the optical transfer function can be described by a
single parameter, the Fried parameter r0, which reveals
the net effect of the turbulence along the line of sight. We present
measurements of the Fried parameter obtained from the spectral ratio
technique and compare them to data from solar scintillometry and
from angle-of-arrival fluctuations. The measurements were performed
at the Big Bear Solar Observatory (BBSO) in 1997 and 1998 - before
and after a series of steps were taken to reduce dome seeing. The
results show that the dome seeing was considerably reduced and now
approaches the seeing conditions measured outside the dome. The Fried
parameter as measured by the spectral ratio technique now frequently
exceeds r0=10 cm at our lake site observatory. Accounting
for the remaining dome and window seeing, the scintillometer and the
angle-of-arrival data imply the potential for an r0&gt;20
cm for BBSO during days of good seeing.

---------------------------------------------------------
Title: Comparison of the 1998 April 29 M6.8 and 1998 November 5
M8.4 Flares
Authors: Wang, Haimin; Goode, Philip R.; Denker, Carsten; Yang, Guo;
Yurchishin, Vasyl; Nitta, Nariaki; Gurman, Joseph B.; St. Cyr, Chris;
Kosovichev, Alexander G.
2000ApJ...536..971W Altcode:
We combined, and analyzed in detail, the Hα and magnetograph data
from Big Bear Solar Observatory (BBSO), full-disk magnetograms from
the Michelson Doppler Imager (MDI) on board Solar and Heliospheric
Observatory (SOHO), coronagraph data from the Large Angle Spectrometric
Coronagraph (LASCO) of SOHO, Fe XII 195 Å data from the Extreme
ultraviolet Imaging Telescope (EIT) of SOHO, and Yohkoh soft X-ray
telescope (SXT) data of the M6.8 flare of 1998 April 29 in National
Oceanic and Atmospheric Administration (NOAA) region 8375 and the
M8.4 flare of 1998 November 5 in NOAA region 8384. These two flares
have remarkable similarities:1. Partial halo coronal mass ejections
(CMEs) were observed for both events. For the 1998 April 29 event,
even though the flare occurred in the southeast of the disk center,
the ejected material moved predominantly across the equator, and the
central part of the CME occurred in the northeast limb. The direction
in which the cusp points in the postflare SXT images determines the
dominant direction of the CMEs.2. Coronal dimming was clearly observed
in EIT Fe XII 195 Å for both but was not observed in Yohkoh SXT for
either event. Dimming started 2 hr before the onset of the flares,
indicating large-scale coronal restructuring before both flares.3. No
global or local photospheric magnetic field change was detected from
either event; in particular, no magnetic field change was found in the
dimming areas.4. Both events lasted several hours and, thus, could be
classified as long duration events (LDEs). However, they are different
in the following important aspects. For the 1998 April 29 event,
the flare and the CME are associated with an erupting filament in
which the two initial ribbons were well connected and then gradually
separated. SXT preflare images show the classical S-shape sheared
configuration (sigmoid structure). For the 1998 November 5 event, two
initial ribbons were well separated, and the SXT preflare image shows
the interaction of at least two loops. In addition, no filament eruption
was observed. We conclude that even though these two events resulted
in similar coronal consequences, they are due to two distinct physical
processes: eruption of sheared loops and interaction of two loops.

---------------------------------------------------------
Title: First Observations with the Global High-Resolution H-alpha
Network
Authors: Varsik, J. R.; Steinegger, M.; Denker, C.; Goode, P. R.;
Wang, H.; Luo, G.; Chen, D.; Zhang, Q.; Otruba, W.; Hanslmeier, A.;
Freislich, H.
2000SPD....3102108V Altcode: 2000BAAS...32..830V
We are in the final stages of establishing a three-site global network
for continuous full disk H-alpha observations based on our experience
with making high-resolution full disk H-alpha observations at Big
Bear Solar Observatory. Utilizing existing telescopes at Big Bear
Solar Observatory (USA), Kanzelhoehe Solar Observatory (Austria),
and Yunnan Astronomical Observatory (China), the three stations are
each equipped with 2K X 2K CCD detectors and will monitor the Sun at a
1 minute cadence. We expect to monitor the emergence of each new flux
region to obtain an unbiased data set in order to understand why some
regions grow to super-activity while most decay quickly, as well as a
more complete and uniform set of flare observations. We also expect
to implement automatic detection of filament eruptions. Having high
cadence data from three observing stations will also increase the
accuracy of solar rotation rates as determined by feature tracking
techniques. We will show the first data sets from the new network.

---------------------------------------------------------
Title: Center-to-Limb Variations of Small-Scale Magnetic Features
Authors: Denker, C.; Spirock, T. J.; Wang, H.; Goode, P. R.
2000SPD....31.0804D Altcode: 2000BAAS...32R.840D
During August/September 1999, we observed continuum images in the
visible (520 nm) and infrared (1600 nm) of various active regions
during their limb-to-limb passage. The images were obtained with the
65 cm vacuum reflector of the Big Bear Solar Observatory and speckle
masking has been applied to obtain almost diffraction limited images
of small-scale magnetic features such as pores, magnetic knots, and
faculae. The infrared images were taken with a new 320 x 240 pixel,
12-bit, 30 fps InGaAs CCD camera. The continuum images are complemented
by videomagnetograms obtained at Ca I (610.3 nm) with the 25 cm vacuum
refractor. We present the first results of a comprehensive study on
the relationship of magnetic field strength and continuum contrast
of small-scale magnetic features as a function of disk position. The
underlying mechanism of small-scale flux tubes is of particular
importance for solar irradiance variations over the 11 year solar
activity cycle.

---------------------------------------------------------
Title: High Cadence Flare Observations
Authors: Wang, H.; Qiu, J.; Denker, C.; Spirock, T. J.; Chen, H.;
Goode, P. R.
2000SPD....31.1406W Altcode: 2000BAAS...32..847W
We analyzed high cadence observations of a C5.7 flare of 1999 August
23 at Big Bear Solar Observatory (BBSO). The observing wavelength was
1.3 Angstroms in the blue wing of Hα line. The observations were made
with a 12-bit SMD camera with a cadence of 33 ms and an image scale of
0.3” pixel-1. In addition, the time profile of hard X-rays
obtained by BATSE (with the cadence of 1.024 s) and BBSO high resolution
magnetograms are compared with Hα observations to understand detailed
particle precipitations of this event. The important results are:
(1) In Hα -1.3 Angstroms, three flare kernels were observed in the
early phase of the flare. The flare started in a non-magnetic area at
the magnetic neutral line. We may have detected the top of a low-lying
loop which was the initial energy release site. While the other two
kernels may be the footpoints of another overlying flare loop formed
after the magnetic reconnection. (2) We analyzed the temporal behavior
of the three flare kernels in the impulsive phase when hard X-ray
emission was significant. We found that during a 7 s period, the Hα
-1.3 Angstroms brightenings at one of the footpoints showed very good
temporal correlation with the hard X-ray flux variation. Therefore,
from the spatially resolved Hα offband observations, we identified
this flare kernel as the source of hard X-ray emission. (3) From the
footpoint which exhibited best correlation with the HXR, the Hα -1.3
Angstroms emission showed high frequency fluctuation in a time scale
of a few tenths of a second. The amplitude of the fluctuation was more
than three times above the noise. Such fluctuation was not evident in
other flare kernels which did not show good correlation with the hard
X-ray emission. Therefore, the observed high frequency fluctuation
might be the real signature of fine temporal structure related to the
HXR elementary bursts.

---------------------------------------------------------
Title: First Results from the Big Bear Solar Observatory's Digital
Vectormagnetograph
Authors: Spirock, T. J.; Denker, C.; Chen, H.; Qui, J.; Goode, P. R.;
Wang, H.
2000SPD....3102109S Altcode: 2000BAAS...32..830S
During the past three years, the Big Bear Solar Observatory has begun an
aggressive program to upgrade the observatory's instrumentation. In the
forefront of this effort is the development of a highly sensitive, high
cadence, filter based, digital vector magnetograph for the observatory's
10" vacuum-refractor to replace the old video magnetograph to improve
our measurements of the FeI line at 6301A. The hardware is being
replaced by a 512 x 512, 12-bit, 30 frames per second CCD camera and
high quality polarization optics. In addition, software tools are
being written to aid instrument development by quickly evaluating
images (bias, cross talk, etc.) and to generate near real-time vector
magnetograms, which will aid space weather forecasting and the support
of space weather missions. Data acquisition, data calibration and flat
fielding methods will be discussed and quiet sun and active region
magnetograms will be presented.

---------------------------------------------------------
Title: Minifilament Eruption on the Quiet Sun. I. Observations at
Hα Central Line
Authors: Wang, Jingxiu; Li, Wei; Denker, Carsten; Lee, Chikyin; Wang,
Haimin; Goode, Philip R.; McAllister, Alan; Martin, Sara F.
2000ApJ...530.1071W Altcode:
The eruption of miniature filaments on the quiet Sun has been analyzed
from time sequences of digital Hα filtergrams obtained at Big Bear
Solar Observatory during 1997 September 18-24. The 2 days with the
best image quality were selected for this initial study. During
13 hr of time-lapse observations on these 2 days, in an effective
640”x480” area of quiet Sun close to the disk
center, 88 erupting miniature filaments were identified. On average,
these small-scale erupting filaments have a projected length of 19,000
km, an observed ejection speed of 13 km s-1, and a mean
lifetime of 50 minutes from first appearance through eruption. The
total mass and kinetic energy involved in a miniature filament
eruption is estimated to be 1013 g and 1025
ergs, respectively. They are distinguished from macrospicules by the
same criteria that large-scale filaments, before and during eruption,
are distinguished from surges. Prior to eruption, one end, both ends,
or the midsection of a miniature filament is superposed over a polarity
reversal boundary on line-of-sight magnetograms. We conclude that
miniature filaments are the small-scale analog to large-scale filaments.

---------------------------------------------------------
Title: An Overview of the New Global High-Resolution H-alpha Network
Authors: Steinegger, M.; Hanslmeier, A.; Otruba, W.; Freislich, H.;
Denker, C.; Goode, P. R.; Marquette, W. M.; Varied, J.; Wang, H.;
Luo, G.; Chen, D.; Zhang, Q.
2000HvaOB..24..179S Altcode:
In this paper we give a brief overview of the new global high resolution
H-alpha network which was recently established between the Big Bear
Solar Observatory (USA), the Kanzelhoehe Solar Observatory (Austria),
and the Yunnan Astronomical Observatory (China). A short description
of the sites, instruments, and the scientific aims, as well as some
sample data are presented.

---------------------------------------------------------
Title: The New Global High-Resolution Hα Network: First Observations
and First Results
Authors: Steinegger, M.; Denker, C.; Goode, P. R.; Marquette, W. H.;
Varsik, J.; Wang, H.; Otruba, W.; Freislich, H.; Hanslmeier, A.; Luo,
G.; Chen, D.; Zhang, Q.
2000ESASP.463..617S Altcode: 2000sctc.proc..617S
No abstract at ADS

---------------------------------------------------------
Title: Study of Umbral Dots at 1.6 Micron
Authors: Wang, J. S.; Wang, H.; Denker, C.; Spirock, T.; Goode, P.
1999AAS...194.9305W Altcode: 1999BAAS...31R.989W
We used a 320 by 240 InGaAs IR camera and a broadband filter centered at
1.565 micron to carry out a sequence of near IR observations at Big Bear
Solar Observatory. The target is a delta sunspot and our objective is
to study the properties of umbral dots in the opacity minimum. Because
of the lower scattering light in IR, we can resolve the very center of
the umbra. We discuss the contrasts, sizes, lifetimes and proper motions
of umbral dots observed in IR and compared with visible observations.

---------------------------------------------------------
Title: New Vectormagnetographs at the Big Bear Solar Observatory
Authors: Spirock, T. J.; Denker, C.; Wang, J.; Chen, H.; Wang, H.;
Goode, P. R.
1999AAS...194.7607S Altcode: 1999BAAS...31R.957S
During the past two years, the Big Bear Solar Observatory has begun an
aggressive program to upgrade the observatory's instrumentation. In
the forefront of this effort are improvements to the current
vectormagnetograph and the development of two new vectormagnetographs
systems - one in visible light and one in near infra red. In the
first case, the current filter-based video-magnetograph, on the 10"
vacuum-refractor, is being replaced by a 1k by 1k, 12-bit, 15 frames pre
second CCD camera, and higher quality polarization optics to improve
our measurments using the CaI line at 6103 Angstroms. Secondly, a
Fabry-Perot based imaging magnetograph with a spacial resolution of
0.15 arc-sec per pixel having a temporal resolution of approximately
1 min. for the Stokes-V and approximately 4 min. for the full Stokes
vector with a band-pass of 80m Angstroms is being developed for the
26" vacuum-reflector to scan the FeI line at 6302.5 Angstroms. In the
near infra red, an automated spectrograph based vectormagnetograph,
using a 12-bit, 320 by 240, 30 frames per second InGaAs CCD camera,
is being developed to study the FeI lines at 1.56485 microns and
1.56529 microns. Current plans and the status of each instrument will
be discussed and test results will be presented.

---------------------------------------------------------
Title: Large-Scale Structures of Solar Flares
Authors: Denker, C.; Marquette, W.; Wang, H.; Goode, P. R.;
Johannesson, A.
1999AAS...194.2207D Altcode: 1999BAAS...31..860D
Since December 1997, the Big Bear Solar Observatory (BBSO) has
provided daily, contrast enhanced, Hα full disk images of unsurpassed
quality, temporal resolution of about 30 s, and spatial resolution of
about 2 arcsec which allow us to study the evolution of small-scale
structures and low-contrast features. This data set has the right
qualities to allow us to study large-scale phenomena associated with
major solar flares such as Moreton waves, transient brightening of
the Hα network, filament eruptions and disappearances. In 1998, 31
flares of magnitude M3.0 or larger were observed by the Geosynchronous
Operational Environmental Satellites (GOES). Eight of them occurred
during the typical observing hours at BBSO and seven were actually
covered by Hα full disk observations presented here. We provide a
detailed description of various chromospheric disturbances initiated by
the flares, the influence of magnetic fields on their appearance, and
their association with coronal mass ejections. This work was supported
by ONR under grant N00014-97-1-1037, by NSF under grant ATM 97-14796,
and by NASA under grant NAG 5-4919 and NAG 5-7350.

---------------------------------------------------------
Title: Solar Differential Rotation Derived from H-alpha Full Disk
Images by Means of Local Correlation Tracking
Authors: Woodard, M. F.; Denker, C.; Strous, L. H.; BBSO Collaboration;
LMSAL Collaboration
1999AAS...19410007W Altcode: 1999BAAS...31..997W
We present the application of Local Correlation Tracking (LCT)
techniques to time series of contrast-enhanced H-alpha full disk images
taken as part of the synoptic observing program at Big Bear Solar
Observatory (BBS0) during the summer of 1998. A typical set of daily
H-alpha full disk images consists of 600 to 800 individual frames,
taken 30 to 60 s apart, with a 2k x 2k pixel Kodak 4.2 MegaPlus CCD
camera at BBSO's Singer telescope. For each pair of successive images,
we compute displacement vectors over a 64 x 64 element cartesian
grid covering the solar disk. The resulting daily-averaged flow maps
show predominantly solar differential rotation and proper motions in
active regions. We remap the flow maps to heliographic coordinates and
determine a Legendre polynomial expansion of the daily differential
rotation profile. We present preliminary findings regarding differential
rotation based on different types of features seen in H-alpha, such as
quiet-sun fibrils, plages, and dark filaments. We discuss the relation
of our differential rotation profiles to profiles derived by other
methods and address the question of time variability. The work at
BBSO is supported by ONR under grant N00014-97-1-1037, by NSF under
grant ATM 97-14796, and by NASA under grant NAG 5-4919. Louis Strous
is supported by NASA NAG5-3077 to Stanford University.

---------------------------------------------------------
Title: Synoptic Hα Full-Disk Observations of the Sun from Big
Bear Solar Observatory - I. Instrumentation, Image Processing,
Data Products, and First Results
Authors: Denker, C.; Johannesson, A.; Marquette, W.; Goode, P. R.;
Wang, H.; Zirin, H.
1999SoPh..184...87D Altcode:
The Big Bear Solar Observatory (BBSO) has a long tradition of synoptic
full-disk observations. Synoptic observations of contrast enhanced
full-disk images in the Ca ii K-line have been used with great success
to reproduce the H i Lα irradiance variability observed with the
Upper Atmosphere Research Satellite (UARS). Recent improvements in
data calibration procedures and image- processing techniques enable us
now to provide contrast enhanced Hα full-disk images with a spatial
resolution of approximately 2” and a temporal resolution of up to 3
frames min−1.

---------------------------------------------------------
Title: Properties of Sunspots and Pores
Authors: Denker, C.; Spirock, T.; Goode, P.; Wang, H.
1999ASPC..183..124D Altcode: 1999hrsp.conf..124D
No abstract at ADS

---------------------------------------------------------
Title: New Digital Magnetograph At Big Bear Solar Observatory
Authors: Wang, H.; Denker, C.; Spirock, T.; Goode, P. R.; Yang, S.;
Marquette, W.; Varsik, J.; Fear, R. J.; Nenow, J.; Dingley, D. D.
1998SoPh..183....1W Altcode:
A new digital magnetograph system has been installed and tested at
Big Bear Solar Observatory. The system uses part of BBSO's existing
videomagnetograph (VMG) system: a quarter wave plate, a ferro-electric
liquid crystal to switch polarizations, and a 0.25 Å bandpass Zeiss
filter tuned at Ca i 6103 Å. A new 256×256 pixels, 12-bit Dalsa
camera is used as the detector and as the driver to switch the liquid
crystal. The data rate of the camera is 90 frames s−1. The camera
is interfaced to a Pentium-166 PC with a μTech imaging board for data
acquisition and analysis. The computer has 128 MByte of RAM, and up to
700 live images can be stored in memory for quick post-exposure image
processing (image selection and alignment). We have significantly
improved the sensitivity and spatial resolution over the old BBSO
VMG system. In particular: (1) New digital image data are in 12 bits
while the video signal is digitized as 8 bits. Polarizations weaker
than 1% can not be detected by a single pair subtraction in the video
system. The digital system can detect a polarization signal of about
0.3% by a single pair subtraction. (2) Data rate of the digital system
is 90 frames s−1, that of the video system is 30 frames s−1. So
the time difference between two polarizations is reduced in the new
system. Under good seeing conditions, the data rate of 90 frames
s−1 ensures that most of the wavefront distortions are `frozen'
and fairly closely the same for the left and right circular polarized
image pairs. (3) Magnetograms are constructed after image selection
and alignment. We discuss the characteristics of this new system. We
present the results of our first tests to reconstruct magnetograms with
speckle interferometric techniques. We also present some preliminary
results on the comparison of facular/micropore contrasts and magnetic
field structure. The experiment with this small detector lays ground
for a larger format digital magnetograph system at BBSO, as well as
a future Fabry-Pérot system, which will be able to scan across the
spectral line.

---------------------------------------------------------
Title: High Spatial Resolution Observations of a Small δ Spot
Authors: Denker, Carsten; Wang, Haimin
1998ApJ...502..493D Altcode:
The Big Bear Solar Observatory (BBSO) has a long tradition of flare
observations. In this paper, we would like to direct the reader's
attention to observations of a small δ spot that produced a moderate
flare activity characterized by 18 C-class and 2 M-class flares. Active
region NOAA 8076 (BBSO 3877) was one of the first active regions in
the new solar cycle 23. We present for the first time high spatial
resolution white-light observations obtained on 1997 August 31
with the speckle masking technique to study mechanisms that trigger
flares. Almost diffraction-limited speckle reconstructions revealed
the complex and highly dynamical behavior of a small emerging δ
configuration in the central part of NOAA 8076. We found strong shear
flows and indications of strong transverse fields in the small δ
spot. The flare-producing mechanism for this small activity complex was
very similar to that of the outstanding flare-producing region NOAA 5395
of 1989 March however, on a completely opposite spatial scale. As an
important by-product, the speckle-interferometric techniques provided
information about the seeing quality at a site. We used the spectral
ratio technique to estimate the Fried parameter r0. We
measured a maximum Fried parameter of rmax0=10.3
cm and an average Fried parameter of r0 = 9.0 +/- 0.7 cm
in which the standard deviation reflects the temporal variations of
the seeing, indicating good seeing conditions during our observations.

---------------------------------------------------------
Title: Speckle Masking Imaging of Sunspots and Pores
Authors: Denker, Carsten
1998SoPh..180...81D Altcode:
In recent years, speckle interferometry has been successfully applied
to various solar phenomena and provides a powerful tool to study
solar small-scale structures. The present investigation lays special
emphasis on sunspots and sunspot pores. The observations have been
performed with the Vacuum Tower Telescope (VTT) at the Observatorio
del Teide (Tenerife) in the years from 1992 to 1994. Time series
of high-spatial-resolution observations reveal the highly dynamical
evolution of sunspot fine structures such as umbral dots, penumbral
grains or the small-scale brightenings in the vicinity of sunspots
observed in the wings of strong chromospheric absorption lines
(moustache phenomenon). The reconstructed images show small-scale
structures close to the telescopic diffraction limit of 0.16″ at 550
nm. Furthermore, the high transmission of a Fabry-Pérot interferometer
(FPI) as the principal optical element of a two-dimensional spectrometer
allows one to reconstruct directly images taken within a passband of
0.014 nm.

---------------------------------------------------------
Title: Dynamics of Solar Fine Structure: Observation with High
Spatial Resolution
Authors: Al, N.; Bendlin, C.; de Boer, C. R.; Denker, C.; Kneer, F.;
Schmitt, D.; Volkmer, R.; Wilken, V.
1998ASPC..154..553A Altcode: 1998csss...10..553A
The Sun is an ideal object for studying non-magnetic and magnetic
processes in cool stars. Here, we focus on fine structures of a
few 100 km in the solar atmosphere. Granular overshoot, motions
and waves of magnetic elements in the quiet Sun and in plages,
etc., all affect the atmospheric structure from the bottom of the
photosphere up to the corona and the solar wind. Observations with
high spatial resolution are required to reveal the dynamic behaviour
and to understand the underlying physical processes. During the past
five years, speckle methods have become an excellent tool to obtain
images of solar fine structure with diffraction-limited resolution. We
demonstrate by some examples how one can gain new insights from
speckle interferometry. Likewise, spectroscopy of solar fine structure
is also making rapid progress towards high spatial resolution. Our
two-dimensional, narrow-band spectrometer (Delta\lambda = 20-30 mAA
), working with a scanning Fabry-Perot interferometer, proves very
powerful in several aspects. We present some results obtained in Na D_2
from the quiet solar chromosphere. Using suitable observing techniques
together with image restoration, we aim at achieving diffraction-limited
resolution also for narrow-band spectroscopy.

---------------------------------------------------------
Title: Speckle measurements of the centre-to-limb variation of the
solar granulation.
Authors: Wilken, V.; de Boer, C. R.; Denker, C.; Kneer, F.
1997A&A...325..819W Altcode:
The Vacuum Tower Telescope (VTT) at the Observatorio del Teide/Tenerife
was used to perform speckle observations of photospheric granulation
from disc centre to limb at λ=550+/-5nm. Images were reconstructed
with the spectral ratio technique (von der Luehe 1984) and the
speckle masking method (Weigelt 1977, Optics Comm. 21, 55, Weigelt
&amp; Wirnitzer 1983, Optics Letters 8, 389, Lohmann et al. 1983,
Applied Optics 22, 4028). The granular rms contrast relative to the
local average intensity decreases monotonically from 13.5+/-1.0%
at disc centre to 8-9% at cosθ=0.1. The granular images as well as
the power spectra of the intensity fluctuations show a fading of the
coarse granular pattern towards the limb while smaller structures
become more pronounced off the disc centre. We identify these as the
bright worm-like structures appearing sometimes at the granular borders
(de Boer et al. 1992A&amp;A...257L...4D). This finding supports the
result from simulations of granular dynamics by Steffen et al. (1994,
Shocks in the solar photosphere and their spectroscopic signature. In:
Schuessler M., Schmidt W. (eds.) Solar Magnetic Fields, Cambridge
Univ. Press, p. 298). There the bright structures are locations of low
pressure between the centres of granules and intergranular spaces with
penetration of hot gas into the lower photosphere.

---------------------------------------------------------
Title: Two-dimensional speckle spectroscopy of the moustache
phenomenon on the Sun.
Authors: Denker, C.
1997A&A...323..599D Altcode:
This paper deals with a detailed morphological and photometric
investigation of solar small-scale features in the vicinity of an
irregular sunspot group. The observations were performed with the
Vacuum Tower Telescope at the Observatorio del Teide/Tenerife on May
18, 1994. The speckle masking method has been applied to reconstruct
almost diffraction limited filtergrams in two different wavelength
regions. For this purpose, we used the two-dimensional spectrometer of
the Universitaets-Sternwarte Goettingen which was slightly modified for
the speckle observations. In the narrow-band filtergrams, we studied the
intensity enhancement in the inner wings of the strong chromospheric
absorption line NaD_2_ (moustache phenomenon). The corresponding
filtergrams in the white-light channel show a clear correlation of
photospheric filigree and the moustache phenomenon. The bandwidth of
the small-passband channel amounts to 0.014nm. This is the highest
spectral resolution reached with speckle masking imaging so far.

---------------------------------------------------------
Title: New Digital Magnetograph at Big Bear Solar Observatory
Authors: Wang, Haimin; Denker, Carsten; Spirock, Thomas; Yang, Shu;
Goode, Philip
1997SPD....28.1503W Altcode: 1997BAAS...29..919W
A new magnetograph system has been installed and tested at Big Bear
Solar Observatory. The system uses part of BBSO's existing VMG
system: a quarter wave plate, a Ferro-Electric Liquid Crystal to
switch polarizations, and a 0.25A bandpass Zeiss filter tuned at CaI
6103A. A 256 by 256 12-bit Dalsa camera is used as the detector and
as the driver to switch the liquid crystal. The data rate of the
camera is 90 frames/s. The camera is interfaced by a Pentium-166
with a Mutech imaging board for data acquisition and analyses. The
computer has 128mb of ram, up to 700 live images can be stored in the
memory for a quick post-exposure image processing (image selection and
alignment). We have improved the sensitivity and spatial resolution
significantly over the old BBSO VMG system for the following reasons:
(1) new digital image data is in 12 bits while the video signal is below
8 bits. Polarizations weaker than 1% can not be detected by a single
pair subtraction in the video system. The digital system can detect a
polarization signal below 0.1% by a single pair subtraction. (2) Data
rate of the digital system is 90 frames/s, that of the video system
is 30 frames/s. So the time difference between two polarizations is
reduced in the new system. Under good seeing conditions, the data rate
of 90 frames/s ensures that the wavefront distortions are "frozen"
and approximately the same for the left and right circular polarized
image pairs. (3) Magnetograms are constructed after image selection and
alignment. The same system has potential for further imaging processing,
e.g. image de-stretch, and speckle interferometry. Preliminary results
will be presented at the meeting.

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Title: High Spatial Resolution Observations of a Sunspot with an
“Orphan Penumbra”
Authors: Denker, C.; Zirin, H.; Wang, H.
1997SPD....28.0245D Altcode: 1997BAAS...29..901D
We present a detailed analysis of a high spatial resolution, six
hour time-series of a stable sunspot (NOAA 5612) obtained at the
Big Bear Solar Observatory (BBSO) with the 65 cm vacuum reflector on
August 2nd, 1989 (cf. H. Zirin and H. Wang: 1991, Adv. Space. Res.,
Vol. 11, pp. 225-231). The sunspot shows an “orphan penumbra”
which exhibits motions similar to normal penumbrae. The time-series
consists of filtergrams taken at Hα , CaK, and the continuum. In
addition, magnetograms and dopplergrams were recorded with the
BBSO Video Magnetograph System. Our investigation aims at a better
understanding of moving magnetic features, penumbral fine-structures,
and characteristics of the Evershed flow. Therefore, we derived and
compared the proper motions visible in the different filtergrams,
dopplergrams, and magnetograms.

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Title: Speckle observations of sunspots.
Authors: Denker, C.
1996AGAb...12...87D Altcode:
No abstract at ADS

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Title: Untersuchung der Feinstruktur von Sonnenflecken mit Methoden
der Speckle-Interferometrie
Authors: Denker, Carsten
1996PhDT........51D Altcode:
No abstract at ADS

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Title: Untersuchung von Feinstrukturen der Sonne.
Authors: Denker, C.; de Boer, C. R.; Volkmer, R.
1996S&W....35..184D Altcode:
Fine structures are elements in the solar photosphere with sizes smaller
than 1 arcsec. The observation of such structures requires exquisite
instrumentation and reduction methods. In this article two methods are
represented: image reconstruction by means of speckle-interferometry
and two-dimensional spectro-polarimetry.

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Title: Speckle masking imaging of the moustache phenomenon.
Authors: Denker, C.; de Boer, C. R.; Volkmer, R.; Kneer, F.
1995A&A...296..567D Altcode:
We present high spatial resolution observations of a sunspot near
the solar disc centre obtained with the Vacuum Tower Telescope at the
Observatorio del Teide (Tenerife). Our investigation aims at a better
comprehension of umbral and penumbral fine structures. The speckle
masking image reconstruction technique was applied to narrow-band
filtergrams taken in the red wing of Hα. The reconstructed images
reveal small-scale structures close to the telescopic diffraction
limit of 0.19". Especially, the moustache phenomenon - the intensity
enhancement in the inner wings of strong chromospheric absorbtion lines
- is clearly discernible. The moustaches are concentrated at the outer
border of the penumbra and in its neighbourhood. There, they appear
at locations coinciding with the intergranular lanes. The moustaches
are not circular in shape. Instead they show sharp intensity peaks
surrounded by bright areas with frayed borders. Due to the high spatial
resolution achieved in the restored filtergrams and the correction for
the speckle transfer function, we find much higher intensities than
in previous investigations concerning the moustache phenomenon. The
peak intensities are sometimes larger than 1.7 times the intensity
of the granular background, i.e. the line profiles in the inner wing
of Hα exhibit emission features. Attempts to restore narrow-band
filtergrams with speckle interferometry are relatively new. In this
paper it is shown that the speckle masking technique is capable to
reconstruct images with a low signal-to-noise ratio taken within a
passband of 0.05nm.

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Title: Speckle-masking imaging of bright points (moustaches)
Authors: Denker, C.; Deboer, C. R.; Kneer, F.
1995IAUS..176P..51D Altcode:
No abstract at ADS

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Title: Speckle observations of sunspots
Authors: Denker, C.
1994smf..conf..194D Altcode:
No abstract at ADS

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Title: A Comparison of Two Wavefront Sensors
Authors: Denker, C.; Restaino, S.; Radick, R.
1993rtpf.conf...86D Altcode:
No abstract at ADS