Author name code: denker ADS astronomy entries on 2022-09-14 author:"Denker, Carsten" ------------------------------------------------------------------------ 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 Bibcode: 2022AN....34323996D Altcode: 2022arXiv220606076D The strong chromospheric absorption lines Ca H & 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 & 82 days in 2018 & 2019 and derive the Ca H & 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. Title: Solar Hα excess during Solar Cycle 24 from full-disk filtergrams of the Chromospheric Telescope Authors: Diercke, A.; Kuckein, C.; Cauley, P. W.; Poppenhäger, K.; Alvarado-Gómez, J. D.; Dineva, E.; Denker, C. Bibcode: 2022A&A...661A.107D Altcode: 2022arXiv220304357D Context. The chromospheric Hα spectral line is a strong line in the spectrum of the Sun and other stars. In the stellar regime, this spectral line is already used as a powerful tracer of stellar activity. For the Sun, other tracers, such as Ca II K, are typically used to monitor solar activity. Nonetheless, the Sun is observed constantly in Hα with globally distributed ground-based full-disk imagers.
Aims: The aim of this study is to introduce the imaging Hα excess and deficit as tracers of solar activity and compare them to other established indicators. Furthermore, we investigate whether the active region coverage fraction or the changing Hα excess in the active regions dominates temporal variability in solar Hα observations.
Methods: We used observations of full-disk Hα filtergrams of the Chromospheric Telescope and morphological image processing techniques to extract the imaging Hα excess and deficit, which were derived from the intensities above or below 10% of the median intensity in the filtergrams, respectively. These thresholds allowed us to filter for bright features (plage regions) and dark absorption features (filaments and sunspots). In addition, the thresholds were used to calculate the mean intensity ImeanE/D for Hα excess and deficit regions. We describe the evolution of the Hα excess and deficit during Solar Cycle 24 and compare it to the mean intensity and other well established tracers: the relative sunspot number, the F10.7 cm radio flux, and the Mg II index. In particular, we tried to determine how constant the Hα excess and number density of Hα excess regions are between solar maximum and minimum. The number of pixels above or below the intensity thresholds were used to calculate the area coverage fraction of Hα excess and deficit regions on the Sun, which was compared to the imaging Hα excess and deficit and the respective mean intensities averaged for the length of one Carrington rotation. In addition, we present the Hα excess and mean intensity variation of selected active regions during their disk passage in comparison to the number of pixels of Hα excess regions.
Results: The Hα excess and deficit follow the behavior of the solar activity over the course of the cycle. They both peak around solar maximum, whereby the peak of the Hα deficit is shortly after the solar maximum. Nonetheless, the correlation of the monthly averages of the Hα excess and deficit is high with a Spearman correlation of ρ = 0.91. The Hα excess is closely correlated to the chromospheric Mg II index with a correlation of 0.95. The highest correlation of the Hα deficit is found with the F10.7 cm radio flux, with a correlation of 0.89, due to their peaks after the solar activity maximum. Furthermore, the Hα deficit reflects the cyclic behavior of polar crown filaments and their disappearance shortly before the solar maximum. We investigated the mean intensity distribution for Hα excess regions for solar minimum and maximum. The shape of the distributions for solar minimum and maximum is very similar, but with different amplitudes. Furthermore, we found that the area coverage fraction of Hα excess regions and the Hα excess are strongly correlated with an overall Spearman correlation of 0.92. The correlation between the Hα excess and the mean intensity of Hα excess regions is 0.75. The correlation of the area coverage fraction and the mean intensity of Hα excess regions is in general relatively low (ρ = 0.45) and only for few active regions is this correlation above 0.7. The weak correlation between the area coverage fraction and mean intensity leaves us pessimistic that the degeneracy between these two quantities can be broken for the modeling of unresolved stellar surfaces. Title: Multiple Stokes I inversions for inferring magnetic fields in the spectral range around Cr I 5782 Å Authors: Kuckein, C.; Balthasar, H.; Quintero Noda, C.; Diercke, A.; Trelles Arjona, J. C.; Ruiz Cobo, B.; Felipe, T.; Denker, C.; Verma, M.; Kontogiannis, I.; Sobotka, M. Bibcode: 2021A&A...653A.165K Altcode: 2021arXiv210711116K
Aims: In this work, we explore the spectral window containing Fraunhofer lines formed in the solar photosphere, around the magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0, and 5783.8 Å, with Landé g-factors between 1.6 and 2.5. The goal is to simultaneously analyze 15 spectral lines, comprising Cr I, Cu I, Fe I, Mn I, and Si I lines, without the use of polarimetry, to infer the thermodynamic and magnetic properties in strongly magnetized plasmas using an inversion code.
Methods: Our study is based on a new setup at the Vacuum Tower Telescope (VTT, Tenerife), which includes fast spectroscopic scans in the wavelength range around the Cr I 5781.75 Å line. The oscillator strengths log(gf) of all spectral lines, as well as their response functions to temperature, magnetic field, and Doppler velocity, were determined using the Stokes Inversion based on Response functions (SIR) code. Snapshot 385 of the enhanced network simulation from the Bifrost code serves to synthesize all the lines, which are, in turn, inverted simultaneously with SIR to establish the best inversion strategy. We applied this strategy to VTT observations of a sunspot belonging to NOAA 12723 on 2018 September 30 and compared the results to full-disk vector field data obtained with the Helioseismic and Magnetic Imager (HMI).
Results: The 15 simultaneously inverted intensity profiles (Stokes I) delivered accurate temperatures and Doppler velocities when compared with the simulations. The derived magnetic fields and inclinations achieve the best level of accuracy when the fields are oriented along the line-of-sight (LOS) and less accurate when the fields are transverse to the LOS. In general, the results appear similar to what is reported in the HMI vector-field data, although some discrepancies exist.
Conclusions: The analyzed spectral range has the potential to deliver thermal, dynamic, and magnetic information for strongly magnetized features on the Sun, such as pores and sunspots, even without the use of polarimetry. The highest sensitivity of the lines is found in the lower photosphere, on average, around log τ = −1. The multiple-line inversions provide smooth results across the whole field of view (FOV). The presented spectral range and inversion strategy will be used for future VTT observing campaigns. Title: 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. Bibcode: 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. 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 Bibcode: 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 & 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 & 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. 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. Bibcode: 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. Title: Filigree in the Surroundings of Polar Crown and High-Latitude Filaments Authors: Diercke, Andrea; Kuckein, Christoph; Verma, Meetu; Denker, Carsten Bibcode: 2021SoPh..296...35D Altcode: 2020arXiv201204349D High-resolution observations of polar crown and high-latitude filaments are scarce. We present a unique sample of such filaments observed in high-resolution Hα narrow-band filtergrams and broad-band images, which were obtained with a new fast camera system at the Vacuum Tower Telescope (VTT), Tenerife, Spain. The Chromospheric Telescope (ChroTel) provided full-disk context observations in Hα , Ca II K, and He I 10830 Å. The Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) provided line-of-sight magnetograms and ultraviolet (UV) 1700 Å filtergrams, respectively. We study filigree in the vicinity of polar crown and high-latitude filaments and relate their locations to magnetic concentrations at the filaments' footpoints. Bright points are a well studied phenomenon in the photosphere at low latitudes, but they were not yet studied in the quiet network close to the poles. We examine size, area, and eccentricity of bright points and find that their morphology is very similar to their counterparts at lower latitudes, but their sizes and areas are larger. Bright points at the footpoints of polar crown filaments are preferentially located at stronger magnetic flux concentrations, which are related to bright regions at the border of supergranules as observed in UV filtergrams. Examining the evolution of bright points on three consecutive days reveals that their amount increases while the filament decays, which indicates they impact the equilibrium of the cool plasma contained in filaments. Title: Classification of High-resolution Solar Hα Spectra Using t-distributed Stochastic Neighbor Embedding Authors: Verma, Meetu; Matijevič, Gal; Denker, Carsten; Diercke, Andrea; Dineva, Ekaterina; Balthasar, Horst; Kamlah, Robert; Kontogiannis, Ioannis; Kuckein, Christoph; Pal, Partha S. Bibcode: 2021ApJ...907...54V Altcode: 2020arXiv201113214V The Hα spectral line is a well-studied absorption line revealing properties of the highly structured and dynamic solar chromosphere. Typical features with distinct spectral signatures in Hα include filaments and prominences, bright active-region plages, superpenumbrae around sunspots, surges, flares, Ellerman bombs, filigree, and mottles and rosettes, among others. This study is based on high-spectral resolution Hα spectra obtained with the Echelle spectrograph of the Vacuum Tower Telescope (VTT) located at Observatorio del Teide, Tenerife, Spain. The t-distributed stochastic neighbor embedding (t-SNE) is a machine-learning algorithm, which is used for nonlinear dimensionality reduction. In this application, it projects Hα spectra onto a two-dimensional map, where it becomes possible to classify the spectra according to results of cloud model (CM) inversions. The CM parameters optical depth, Doppler width, line-of-sight velocity, and source function describe properties of the cloud material. Initial results of t-SNE indicate its strong discriminatory power to separate quiet-Sun and plage profiles from those that are suitable for CM inversions. In addition, a detailed study of various t-SNE parameters is conducted, the impact of seeing conditions on the classification is assessed, results for various types of input data are compared, and the identified clusters are linked to chromospheric features. Although t-SNE proves to be efficient in clustering high-dimensional data, human inference is required at each step to interpret the results. This exploratory study provides a framework and ideas on how to tailor a classification scheme toward specific spectral data and science questions. Title: 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. Bibcode: 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. Title: Observational study of chromospheric heating by acoustic waves Authors: Abbasvand, V.; Sobotka, M.; Švanda, M.; Heinzel, P.; García-Rivas, M.; Denker, C.; Balthasar, H.; Verma, M.; Kontogiannis, I.; Koza, J.; Korda, D.; Kuckein, C. Bibcode: 2020A&A...642A..52A Altcode: 2020arXiv200802688A
Aims: Our aim is to investigate the role of acoustic and magneto-acoustic waves in heating the solar chromosphere. Observations in strong chromospheric lines are analyzed by comparing the deposited acoustic-energy flux with the total integrated radiative losses.
Methods: Quiet-Sun and weak-plage regions were observed in the Ca II 854.2 nm and Hα lines with the Fast Imaging Solar Spectrograph (FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and in the Hα and Hβ lines with the echelle spectrograph attached to the Vacuum Tower Telescope on 2018 December 11 and 2019 June 6. The deposited acoustic energy flux at frequencies up to 20 mHz was derived from Doppler velocities observed in line centers and wings. Radiative losses were computed by means of a set of scaled non-local thermodynamic equilibrium 1D hydrostatic semi-empirical models obtained by fitting synthetic to observed line profiles.
Results: In the middle chromosphere (h = 1000-1400 km), the radiative losses can be fully balanced by the deposited acoustic energy flux in a quiet-Sun region. In the upper chromosphere (h > 1400 km), the deposited acoustic flux is small compared to the radiative losses in quiet as well as in plage regions. The crucial parameter determining the amount of deposited acoustic flux is the gas density at a given height.
Conclusions: The acoustic energy flux is efficiently deposited in the middle chromosphere, where the density of gas is sufficiently high. About 90% of the available acoustic energy flux in the quiet-Sun region is deposited in these layers, and thus it is a major contributor to the radiative losses of the middle chromosphere. In the upper chromosphere, the deposited acoustic flux is too low, so that other heating mechanisms have to act to balance the radiative cooling. Title: 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. Bibcode: 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. Title: High-resolution Spectroscopy of an Erupting Minifilament and Its Impact on the Nearby Chromosphere Authors: Kontogiannis, I.; Dineva, E.; Diercke, A.; Verma, M.; Kuckein, C.; Balthasar, H.; Denker, C. Bibcode: 2020ApJ...898..144K Altcode: 2020arXiv200701564K We study the evolution of a minifilament eruption in a quiet region at the center of the solar disk and its impact on the ambient atmosphere. We used high spectral resolution imaging spectroscopy in Hα acquired by the echelle spectrograph of the Vacuum Tower Telescope, Tenerife, Spain; photospheric magnetic field observations from the Helioseismic Magnetic Imager; and UV/EUV imaging from the Atmospheric Imaging Assembly of the Solar Dynamics Observatory. The Hα line profiles were noise-stripped using principal component analysis and then inverted to produce physical and cloud model parameter maps. The minifilament formed between small-scale, opposite-polarity magnetic features through a series of small reconnection events, and it erupted within an hour after its appearance in Hα. Its development and eruption exhibited similarities to large-scale erupting filaments, indicating the action of common mechanisms. Its eruption took place in two phases, namely, a slow rise and a fast expansion, and it produced a coronal dimming, before the minifilament disappeared. During its eruption, we detected a complicated velocity pattern, indicative of a twisted, thread-like structure. Part of its material returned to the chromosphere, producing observable effects on nearby low-lying magnetic structures. Cloud model analysis showed that the minifilament was initially similar to other chromospheric fine structures, in terms of optical depth, source function, and Doppler width, but it resembled a large-scale filament on its course to eruption. High spectral resolution observations of the chromosphere can provide a wealth of information regarding the dynamics and properties of minifilaments and their interactions with the surrounding atmosphere. Title: 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 Bibcode: 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. Title: The dynamics of a solar arch filament system from the chromosphere to the photosphere Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.; Diercke, A.; Collados, M.; Gömöry, P.; Zhong, S.; Hou, Y.; Denker, C. Bibcode: 2020sea..confE.199G Altcode: We study the dynamics of plasma along the legs of an arch filament system (AFS) from the chromosphere to the photosphere, observed with high-cadence spectroscopic data from two ground-based solar telescopes: the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph in the He I 10830 Å range and the Swedish Solar Telescope (La Palma) using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542 Å and Fe I 6173 Å spectral lines. The temporal evolution of the draining of the plasma was followed along the legs of a single arch filament from the chromosphere to the photosphere. The average Doppler velocities inferred at the upper chromosphere from the He I 10830 Å triplet reach velocities up to 20-24 km s-1, and in the lower chromosphere and upper photosphere the Doppler velocities reach up to 11 km s-1 and 1.5 km s-1 in the case of the Ca II 8542 Å and Si I 10827 Å spectral lines, respectively. The evolution of the Doppler velocities at different layers of the solar atmosphere (chromosphere and upper photosphere) shows that they follow the same line-of-sight (LOS) velocity patern, which confirms the observational evidence that the plasma drains toward the photosphere as proposed in models of AFSs. The observations and the nonlinear force-free field (NLFFF) extrapolations demonstrate that the magnetic field loops of the AFS rise with time. Title: 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. Bibcode: 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. Title: High-resolution spectroscopy of a surge in an emerging flux region Authors: Verma, M.; Denker, C.; Diercke, A.; Kuckein, C.; Balthasar, H.; Dineva, E.; Kontogiannis, I.; Pal, P. S.; Sobotka, M. Bibcode: 2020A&A...639A..19V Altcode: 2020arXiv200503966V
Aims: The regular pattern of quiet-Sun magnetic fields was disturbed by newly emerging magnetic flux, which led a day later to two homologous surges after renewed flux emergence, affecting all atmospheric layers. Hence, simultaneous observations in different atmospheric heights are needed to understand the interaction of rising flux tubes with the surrounding plasma, in particular by exploiting the important diagnostic capabilities provided by the strong chromospheric Hα line regarding morphology and energetic processes in active regions.
Methods: A newly emerged active region NOAA 12722 was observed with the Vacuum Tower Telescope (VTT) at Observatorio del Teide, Tenerife, Spain, on 11 September 2018. High spectral resolution observations using the echelle spectrograph in the chromospheric Hαλ6562.8 Å line were obtained in the early growth phase. Noise-stripped Hα line profiles yield maps of line-core and bisector velocities, which were contrasted with velocities inferred from Cloud Model inversions. A high-resolution imaging system recorded simultaneously broad- and narrowband Hα context images. The Solar Dynamics Observatory provided additional continuum images, line-of-sight (LOS) magnetograms, and UV and extreme UV (EUV) images, which link the different solar atmospheric layers.
Results: The active region started as a bipolar region with continuous flux emergence when a new flux system emerged in the leading part during the VTT observations, resulting in two homologous surges. While flux cancellation at the base of the surges provided the energy for ejecting the cool plasma, strong proper motions of the leading pores changed the magnetic field topology making the region susceptible to surging. Despite the surge activity in the leading part, an arch filament system in the trailing part of the old flux remained stable. Thus, stable and violently expelled mass-loaded ascending magnetic structures can coexist in close proximity. Investigating the height dependence of LOS velocities revealed the existence of neighboring strong up- and downflows. However, downflows occur with a time lag. The opacity of the ejected cool plasma decreases with distance from the base of the surge, while the speed of the ejecta increases. The location at which the surge becomes invisible in Hα corresponds to the interface where the surge brightens in He IIλ304 Å. Broad-shouldered and dual-lobed Hα profiles suggests accelerated or decelerated and highly structured LOS plasma flows. Significantly broadened Hα profiles imply significant heating at the base of the surges, which is also supported by bright kernels in UV and EUV images uncovered by swaying motions of dark fibrils at the base of the surges.
Conclusions: The interaction of newly emerging flux with pre-existing flux concentrations of a young, diffuse active region provided suitable conditions for two homologous surges. High-resolution spectroscopy revealed broadened and dual-lobed Hα profiles tracing accelerated or decelerated flows of cool plasma along the multi-threaded structure of the surge.

Movies are available at https://www.aanda.org Title: Magnetic Flux Emergence in a Coronal Hole Authors: Palacios, Judith; Utz, Dominik; Hofmeister, Stefan; Krikova, Kilian; Gömöry, Peter; Kuckein, Christoph; Denker, Carsten; Verma, Meetu; González Manrique, Sergio Javier; Campos Rozo, Jose Iván; Koza, Július; Temmer, Manuela; Veronig, Astrid; Diercke, Andrea; Kontogiannis, Ioannis; Cid, Consuelo Bibcode: 2020SoPh..295...64P Altcode: 2020arXiv200611779P A joint campaign of various space-borne and ground-based observatories, comprising the Japanese Hinode mission (Hinode Observing Plan 338, 20 - 30 September 2017), the GREGOR solar telescope, and the Vacuum Tower Telescope (VTT), investigated numerous targets such as pores, sunspots, and coronal holes. In this study, we focus on the coronal hole region target. On 24 September 2017, a very extended non-polar coronal hole developed patches of flux emergence, which contributed to the decrease of the overall area of the coronal hole. These flux emergence patches erode the coronal hole and transform the area into a more quiet-Sun-like area, whereby bipolar magnetic structures play an important role. Conversely, flux cancellation leads to the reduction of opposite-polarity magnetic fields and to an increase in the area of the coronal hole. Title: Monitoring solar activity with PEPSI Authors: Dineva, Ekaterina; Denker, Carsten; Strassmeier, Klaus G.; Ilyin, Ilya; Pevtsov, Alexei A. Bibcode: 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 & K λ3934 & 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 Bibcode: 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 Bibcode: 2020ApJ...890...82G Altcode: 2020arXiv200107078G We study the dynamics of plasma along the legs of an arch filament system (AFS) from the chromosphere to the photosphere, observed with high-cadence spectroscopic data from two ground-based solar telescopes: the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph in the He I 10830 Å range and the Swedish Solar Telescope (La Palma) using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542 Å and Fe I 6173 Å spectral lines. The temporal evolution of the draining of the plasma was followed along the legs of a single arch filament from the chromosphere to the photosphere. The average Doppler velocities inferred at the upper chromosphere from the He I 10830 Å triplet reach velocities up to 20-24 km s-1, and in the lower chromosphere and upper photosphere the Doppler velocities reach up to 11 km s-1 and 1.5 km s-1 in the case of the Ca II 8542 Å and Si I 10827 Å spectral lines, respectively. The evolution of the Doppler velocities at different layers of the solar atmosphere (chromosphere and upper photosphere) shows that they follow the same line-of-sight (LOS) velocity pattern, which confirms the observational evidence that the plasma drains toward the photosphere as proposed in models of AFSs. The Doppler velocity maps inferred from the lower photospheric Ca I 10839 Å or Fe I 6173 Å spectral lines do not show the same LOS velocity pattern. Thus, there is no evidence that the plasma reaches the lower photosphere. The observations and the nonlinear force-free field (NLFFF) extrapolations demonstrate that the magnetic field loops of the AFS rise with time. We found flow asymmetries at different footpoints of the AFS. The NLFFF values of the magnetic field strength help us to explain these flow asymmetries. Title: The magnetic structure and dynamics of a decaying active region Authors: Kontogiannis, Ioannis; Kuckein, Christoph; González Manrique, Sergio Javier; Felipe, Tobias; Verma, Meetu; Balthasar, Horst; Denker, Carsten Bibcode: 2020IAUS..354...53K Altcode: We study the evolution of the decaying active region NOAA 12708, from the photosphere up to the corona using high resolution, multi-wavelength GREGOR observations taken on May 9, 2018. We utilize spectropolarimetric scans of the 10830 Å spectral range by the GREGOR Infrared Spectrograph (GRIS), spectral imaging time-series in the Na ID2 spectral line by the GREGOR Fabry-Pérot Interferometer (GFPI) and context imaging in the Ca IIH and blue continuum by the High-resolution Fast Imager (HiFI). Context imaging in the UV/EUV from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) complements our dataset. The region under study contains one pore with a light-bridge, a few micro-pores and extended clusters of magnetic bright points. We study the magnetic structure from the photosphere up to the upper chromosphere through the spectropolarimetric observations in He II and Si I and through the magnetograms provided by the Helioseismic and Magnetic Imager (HMI). The high-resolution photospheric images reveal the complex interaction between granular-scale convective motions and a range of scales of magnetic field concentrations in unprecedented detail. The pore itself shows a strong interaction with the convective motions, which eventually leads to its decay, while, under the influence of the photospheric flow field, micro-pores appear and disappear. Compressible waves are generated, which are guided towards the upper atmosphere along the magnetic field lines of the various magnetic structures within the field-of-view. Modelling of the He i absorption profiles reveals high velocity components, mostly associated with magnetic bright points at the periphery of the active region, many of which correspond to asymmetric Si I Stokes-V profiles revealing a coupling between upper photospheric and upper chromospheric dynamics. Time-series of Na ID2 spectral images reveal episodic high velocity components at the same locations. State-of-the-art multi-wavelength GREGOR observations allow us to track and understand the mechanisms at work during the decay phase of the active region. Title: Measuring the etalon quality of the GREGOR Fabry-Pérot interferometer Authors: Verma, Meetu; Denker, Carsten Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 2020A&A...633A..67K Altcode: 2019arXiv191202496K Context. We study the evolution of a small-scale emerging flux region (EFR) in the quiet Sun, from its emergence in the photosphere to its appearance in the corona and its decay.
Aims: We track processes and phenomena that take place across all atmospheric layers; we explore their interrelations and compare our findings with those from recent numerical modelling studies.
Methods: We used imaging as well as spectral and spectropolarimetric observations from a suite of space-borne and ground-based instruments.
Results: The EFR appears in the quiet Sun next to the chromospheric network and shows all morphological characteristics predicted by numerical simulations. The total magnetic flux of the region exhibits distinct evolutionary phases, namely an initial subtle increase, a fast increase with a Co-temporal fast expansion of the region area, a more gradual increase, and a slow decay. During the initial stages, fine-scale G-band and Ca II H bright points coalesce, forming clusters of positive- and negative-polarity in a largely bipolar configuration. During the fast expansion, flux tubes make their way to the chromosphere, pushing aside the ambient magnetic field and producing pressure-driven absorption fronts that are visible as blueshifted chromospheric features. The connectivity of the quiet-Sun network gradually changes and part of the existing network forms new connections with the newly emerged bipole. A few minutes after the bipole has reached its maximum magnetic flux, the bipole brightens in soft X-rays forming a coronal bright point. The coronal emission exhibits episodic brightenings on top of a long smooth increase. These coronal brightenings are also associated with surge-like chromospheric features visible in Hα, which can be attributed to reconnection with adjacent small-scale magnetic fields and the ambient quiet-Sun magnetic field.
Conclusions: The emergence of magnetic flux even at the smallest scales can be the driver of a series of energetic phenomena visible at various atmospheric heights and temperature regimes. Multi-wavelength observations reveal a wealth of mechanisms which produce diverse observable effects during the different evolutionary stages of these small-scale structures. Title: Measuring the Etalon Quality of the GREGOR Fabry-Pérot Interferometer Authors: Verma, Meetu; Denker, Carsten Bibcode: 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 Bibcode: 2020IAUS..354...38U Altcode: The Sun is our dynamic host star due to its magnetic fields causing plentiful of activity in its atmosphere. From high energetic flares and coronal mass ejections (CMEs) to lower energetic phenomena such as jets and fibrils. Thus, it is of crucial importance to learn about formation and evolution of solar magnetic fields. These fields cover a wide range of spatial and temporal scales, starting on the larger end with active regions harbouring complex sunspots, via isolated pores, down to the smallest yet resolved elements - so-called magnetic bright points (MBPs). Here, we revisit the various manifestations of solar magnetic fields by the largest European solar telescope in operation, the 1.5-meter GREGOR telescope. We show images from the High-resolution Fast Imager (HiFI) and spectropolarimetric data from the GREGOR Infrared Spectrograph (GRIS). Besides, we outline resolved convective features inside the larger structures - so-called light-bridges occurring on large to mid-sized scales. Title: Chromospheric Synoptic Maps of Polar Crown Filaments Authors: Diercke, A.; Denker, C. Bibcode: 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. Bibcode: 2019A&A...629A..48D Altcode: 2019arXiv190801510D
Aims: In this study, we analyzed a filament system, which expanded between moving magnetic features (MMFs) of a decaying sunspot and opposite flux outside of the active region from the nearby quiet-Sun network. This configuration deviated from a classical arch filament system (AFS), which typically connects two pores in an emerging flux region. Thus, we called this system an extended AFS. We contrasted classical and extended AFSs with an emphasis on the complex magnetic structure of the latter. Furthermore, we examined the physical properties of the extended AFS and described its dynamics and connectivity.
Methods: The extended AFS was observed with two instruments at the Dunn Solar Telescope (DST). The Rapid Oscillations in the Solar Atmosphere (ROSA) imager provided images in three different wavelength regions, which covered the dynamics of the extended AFS at different atmospheric heights. The Interferometric Bidimensional Spectropolarimeter (IBIS) provided spectroscopic Hα data and spectropolarimetric data that was obtained in the near-infrared (NIR) Ca IIλ8542 Å line. We derived the corresponding line-of-sight (LOS) velocities and used He IIλ304 Å extreme ultraviolet (EUV) images of the Atmospheric Imaging Assembly (AIA) and LOS magnetograms of the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) as context data.
Results: The NIR Ca II Stokes-V maps are not suitable to definitively define a clear polarity inversion line and to classify this chromospheric structure. Nevertheless, this unusual AFS connects the MMFs of a decaying sunspot with the network field. At the southern footpoint, we measured that the flux decreases over time. We find strong downflow velocities at the footpoints of the extended AFS, which increase in a time period of 30 min. The velocities are asymmetric at both footpoints with higher velocities at the southern footpoint. An EUV brigthening appears in one of the arch filaments, which migrates from the northern footpoint toward the southern one. This activation likely influences the increasing redshift at the southern footpoint.
Conclusions: The extended AFS exhibits a similar morphology as classical AFSs, for example, threaded filaments of comparable length and width. Major differences concern the connection from MMFs around the sunspot with the flux of the neighboring quiet-Sun network, converging footpoint motions, and longer lifetimes of individual arch filaments of about one hour, while the extended AFS is still very dynamic.

Movies associated to Figs. 5, 6, and 12 are available at https://www.aanda.org Title: Polarimetry with the GREGOR Fabry-Pérot Interferometer Authors: Balthasar, H.; Gisler, D.; González Manrique, S. J.; Kuckein, C.; Verma, M.; Denker, C. Bibcode: 2019spw..confE...3B Altcode: No abstract at ADS Title: Background-Subtracted Solar Activity Maps Authors: Denker, C.; Verma, M. Bibcode: 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. Bibcode: 2019ASPC..526..217B Altcode: 2018arXiv180401789B We observed an arch filament system (AFS) in a sunspot group with the GREGOR Infrared Spectrograph attached to the GREGOR solar telescope. The AFS was located between the leading sunspot of negative polarity and several pores of positive polarity forming the following part of the sunspot group. We recorded five spectro-polarimetric scans of this region. The spectral range included the spectral lines Si I 1082.7 nm, He I 1083.0 nm, and Ca I 1083.9 nm. In this work we concentrate on the silicon line which is formed in the upper photosphere. The line profiles are inverted with the code 'Stokes Inversion based on Response functions' to obtain the magnetic field vector. The line-of-sight velocities are determined independently with a Fourier phase method. Maximum velocities are found close to the ends of AFS fibrils. These maximum values amount to 2.4 km s-1 next to the pores and to 4 km s-1 at the sunspot side. Between the following pores, we encounter an area of negative polarity that is decreasing during the five scans. We interpret this by new emerging positive flux in this area canceling out the negative flux. In summary, our findings confirm the scenario that rising magnetic flux tubes cause the AFS. Title: Photospheric Magnetic Fields of the Trailing Sunspots in Active Region NOAA 12396 Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer, C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2019ASPC..526..291V Altcode: 2018arXiv180507752V The solar magnetic field is responsible for all aspects of solar activity. Sunspots are the main manifestation of the ensuing solar activity. Combining high-resolution and synoptic observations has the ambition to provide a comprehensive description of the sunspot growth and decay processes. Active region NOAA 12396 emerged on 2015 August 3 and was observed three days later with the 1.5-meter GREGOR solar telescope on 2015 August 6. High-resolution spectropolarimetric data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together with the chromospheric He I λ1083.0 nm triplet. These near-infrared spectropolarimetric observations were complemented by synoptic line-of-sight magnetograms and continuum images of the Helioseismic and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Title: Calibration of full-disk He I 10830 Å filtergrams of the Chromospheric Telescope Authors: Shen, Zili; Diercke, Andrea; Denker, Carsten Bibcode: 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. Bibcode: 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 http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A142 Title: sTools - a software package for data reduction of GREGOR instruments and general data analysis Authors: Kuckein, Christoph; Denker, Carsten; Verma, Meetu; Balthasar, Horst; Diercke, Andrea; González Manrique, Sergio Javier; Dineva, Ekaterina; Kontogiannis, Ioannis; Shen, Zili Bibcode: 2018csc..confE.105K Altcode: The optical solar physics group at AIP is responsible for the GREGOR Fabry-Perot Interferometer (GFPI) and the large-format facility cameras (Blue Imaging Channel (BIC) and High-resolution Fast Imager (HiFI)) at the 1.5-meter GREGOR solar telescope (Tenerife, Spain). Since the »Early Science Phase« of the telescope in 2014, the group developed a data reduction pipeline for these two instruments. The pipeline »sTools« is based on the Interactive Data Language (IDL) and delivers reduced and image-restored data with a minimum of user interaction. Furthermore, it creates quick-look data and builds a webpage with an overview of the observations and their statistics (http://gregor.aip.de). However, during the last years, sTools continuously evolved and currently hosts many additional routines for data analysis: (1) A local correlation tracking (LCT) algorithm adapted for both high-resolution (GREGOR and Hinode) and synoptic full-disk (SDO) data. (2) A new quantitative tool, i.e., a Background-subtracted Solar Activity Map (BaSAM), to assess and visualize the temporal variation of the photospheric magnetic field and the EUV 160 nm intensity. This method utilizes SDO data and is applicable to both full-disk observations and regions-of-interest. (3) Calibration of synoptic full-disk data from the Chromospheric Telescope (ChroTel) including extraction of Doppler velocities from He I 1083 nm filtergrams. (4) Analysis tools for sun-as-a-star spectroscopy for the Solar Disk-Integrated (SDI) telescope of the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI). sTools is licensed under a creative commons license and is freely available, after registration, at the abovementioned website. Title: The Effects of Stellar Activity on Optical High-resolution Exoplanet Transmission Spectra Authors: Cauley, P. Wilson; Kuckein, Christoph; Redfield, Seth; Shkolnik, Evgenya L.; Denker, Carsten; Llama, Joe; Verma, Meetu Bibcode: 2018AJ....156..189C Altcode: 2018arXiv180809558C Chromospherically sensitive atomic lines display different spectra in stellar active regions, spots, and the photosphere, raising the possibility that exoplanet transmission spectra are contaminated by the contrast between various portions of the stellar disk. To explore this effect, we performed transit simulations of G-type and K-type stars for the spectral lines Ca II K at 3933 Å, Na I 5890 Å, H I 6563 Å (Hα), and He I 10830 Å. We find that strong facular emission and large coverage fractions can contribute a non-negligible amount to transmission spectra, especially for Hα, Ca II K, and Na I D, while spots and filaments are comparatively unimportant. The amount of contamination depends strongly on the location of the active regions and the intrinsic emission strength. In particular, active regions must be concentrated along the transit chord in order to produce a consistent in-transit signal. Mean absorption signatures in Na I and Hα, for example, can reach ≈0.2% and 0.3%, respectively, for transits of active latitudes with line emission similar in strength to moderate solar flares. Transmission spectra of planets transiting active stars, such as HD 189733, are likely contaminated by the contrast effect, although the tight constraints on active region geometry and emission strength make it unlikely that consistent in-transit signatures are due entirely to the contrast effect. He I 10830 Å is not strongly affected and absorption signatures are likely diluted, rather than enhanced, by stellar activity. He I 10830 Å should thus be considered a priority for probing extended atmospheres, even in the case of active stars. Title: Counter-streaming flows in a giant quiet-Sun filament Authors: Diercke, Andrea; Kuckein, Christoph; Verma, Meetu; Denker, Carsten Bibcode: 2018csc..confE.104D Altcode: A giant solar filament was visible on the solar surface between 2011 November 8-23. The filament stretched over more than half a solar diameter. Multi-wavelength data from the SDO instrument AIA (171, 193, 304, and 211 A) were used to examine counter-streaming flows within the spine of the filament. H-alpha images from the Kanzelhöhe Solar Observatory provided context information. We apply local correlation tracking (LCT) to a two-hour time series on 2011 November 16 of the AIA images to derive horizontal flow velocities of the filament. To enhance the contrast of the AIA images, noise adaptive fuzzy equalization (NAFE) is employed, which allows us to identify and quantify counter-streaming flows in the filament. We detect counter-streaming flows in the filament, which are visible in the time-lapse movies in all examined AIA wavelength bands. In the time-lapse movies, we see that these persistent flows lasted for at least two hours. Furthermore, by applying LCT to the images we clearly determine counter-streaming flows in time series of 171 A and 193 A images. In the 304 A wavelength band, we only see minor indications for counter-streaming flows with LCT, while in the 211 A wavelength band the counter-streaming flows are not detectable. The average horizontal flows reach mean flow speeds of 0.5 km/s. The highest horizontal flow speeds are identified in the 171 A band with flow speeds of up to 2.5 km/s. The results are averaged over a time series of 90 min. Because the LCT sampling window has a finite width, a spatial degradation cannot be avoided leading to lower estimates of the flow velocities as compared to feature tracking or Doppler measurements. The counter-streaming flows cover about 15-20% of the whole area of the EUV filament channel and are located in the central part of the spine. In conclusion, we confirm the omnipresence of counter-streaming flows also in giant quiet-Sun filaments. Title: Calibration of full-disk He I 10 830 Å filtergrams of the Chromospheric Telescope Authors: Shen, Z.; Diercke, A.; Denker, C. Bibcode: 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. Bibcode: 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. Bibcode: 2018A&A...617A..55G Altcode: 2018arXiv180700728G
Aims: We study the evolution of an arch filament system (AFS) and of its individual arch filaments to learn about the processes occurring in them.
Methods: We observed the AFS at the GREGOR solar telescope on Tenerife at high cadence with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) in the He I 10 830 Å spectral range. The He I triplet profiles were fitted with analytic functions to infer line-of-sight (LOS) velocities to follow plasma motions within the AFS.
Results: We tracked the temporal evolution of an individual arch filament over its entire lifetime, as seen in the He I 10 830 Å triplet. The arch filament expanded in height and extended in length from 13″ to 21″. The lifetime of this arch filament is about 30 min. About 11 min after the arch filament is seen in He I, the loop top starts to rise with an average Doppler velocity of 6 km s-1. Only two minutes later, plasma drains down with supersonic velocities towards the footpoints reaching a peak velocity of up to 40 km s-1 in the chromosphere. The temporal evolution of He I 10 830 Å profiles near the leading pore showed almost ubiquitous dual red components of the He I triplet, indicating strong downflows, along with material nearly at rest within the same resolution element during the whole observing time.
Conclusions: We followed the arch filament as it carried plasma during its rise from the photosphere to the corona. The material then drained toward the photosphere, reaching supersonic velocities, along the legs of the arch filament. Our observational results support theoretical AFS models and aids in improving future models.

The movie associated to Fig. 3 is available at https://www.aanda.org/ Title: High-resolution imaging and near-infrared spectroscopy of penumbral decay Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; Rezaei, R.; Sobotka, M.; Deng, N.; Wang, H.; Tritschler, A.; Collados, M.; Diercke, A.; González Manrique, S. J. Bibcode: 2018A&A...614A...2V Altcode: 2018arXiv180103686V
Aims: Combining high-resolution spectropolarimetric and imaging data is key to understanding the decay process of sunspots as it allows us to scrutinize the velocity and magnetic fields of sunspots and their surroundings.
Methods: Active region NOAA 12597 was observed on 2016 September 24 with the 1.5-meter GREGOR solar telescope using high-spatial-resolution imaging as well as imaging spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal proper motions were estimated with local correlation tracking, whereas line-of-sight (LOS) velocities were computed with spectral line fitting methods. The magnetic field properties were inferred with the "Stokes Inversions based on Response functions" (SIR) code for the Si I and Ca I NIR lines.
Results: At the time of the GREGOR observations, the leading sunspot had two light bridges indicating the onset of its decay. One of the light bridges disappeared, and an elongated, dark umbral core at its edge appeared in a decaying penumbral sector facing the newly emerging flux. The flow and magnetic field properties of this penumbral sector exhibited weak Evershed flow, moat flow, and horizontal magnetic field. The penumbral gap adjacent to the elongated umbral core and the penumbra in that penumbral sector displayed LOS velocities similar to granulation. The separating polarities of a new flux system interacted with the leading and central part of the already established active region. As a consequence, the leading spot rotated 55° clockwise over 12 h.
Conclusions: In the high-resolution observations of a decaying sunspot, the penumbral filaments facing the flux emergence site contained a darkened area resembling an umbral core filled with umbral dots. This umbral core had velocity and magnetic field properties similar to the sunspot umbra. This implies that the horizontal magnetic fields in the decaying penumbra became vertical as observed in flare-induced rapid penumbral decay, but on a very different time-scale. Title: On the extent of the moat flow in axisymmetric sunspots Authors: Verma, M.; Kummerow, P.; Denker, C. Bibcode: 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 Bibcode: 2018ApJS..236....5D Altcode: 2018arXiv180210146D In high-resolution solar physics, the volume and complexity of photometric, spectroscopic, and polarimetric ground-based data significantly increased in the last decade, reaching data acquisition rates of terabytes per hour. This is driven by the desire to capture fast processes on the Sun and the necessity for short exposure times “freezing” the atmospheric seeing, thus enabling ex post facto image restoration. Consequently, large-format and high-cadence detectors are nowadays used in solar observations to facilitate image restoration. Based on our experience during the “early science” phase with the 1.5 m GREGOR solar telescope (2014-2015) and the subsequent transition to routine observations in 2016, we describe data collection and data management tailored toward image restoration and imaging spectroscopy. We outline our approaches regarding data processing, analysis, and archiving for two of GREGOR’s post-focus instruments (see http://gregor.aip.de), i.e., the GREGOR Fabry-Pérot Interferometer (GFPI) and the newly installed High-Resolution Fast Imager (HiFI). The heterogeneous and complex nature of multidimensional data arising from high-resolution solar observations provides an intriguing but also a challenging example for “big data” in astronomy. The big data challenge has two aspects: (1) establishing a workflow for publishing the data for the whole community and beyond and (2) creating a collaborative research environment (CRE), where computationally intense data and postprocessing tools are colocated and collaborative work is enabled for scientists of multiple institutes. This requires either collaboration with a data center or frameworks and databases capable of dealing with huge data sets based on virtual observatory (VO) and other community standards and procedures. Title: Counter-streaming flows in a giant quiet-Sun filament observed in the extreme ultraviolet Authors: Diercke, A.; Kuckein, C.; Verma, M.; Denker, C. Bibcode: 2018A&A...611A..64D Altcode: 2018arXiv180101036D Aim. The giant solar filament was visible on the solar surface from 2011 November 8-23. Multiwavelength data from the Solar Dynamics Observatory (SDO) were used to examine counter-streaming flows within the spine of the filament.
Methods: We use data from two SDO instruments, the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI), covering the whole filament, which stretched over more than half a solar diameter. Hα images from the Kanzelhöhe Solar Observatory (KSO) provide context information of where the spine of the filament is defined and the barbs are located. We apply local correlation tracking (LCT) to a two-hour time series on 2011 November 16 of the AIA images to derive horizontal flow velocities of the filament. To enhance the contrast of the AIA images, noise adaptive fuzzy equalization (NAFE) is employed, which allows us to identify and quantify counter-streaming flows in the filament. We observe the same cool filament plasma in absorption in both Hα and EUV images. Hence, the counter-streaming flows are directly related to this filament material in the spine. In addition, we use directional flow maps to highlight the counter-streaming flows.
Results: We detect counter-streaming flows in the filament, which are visible in the time-lapse movies in all four examined AIA wavelength bands (λ171 Å, λ193 Å, λ304 Å, and λ211 Å). In the time-lapse movies we see that these persistent flows lasted for at least two hours, although they became less prominent towards the end of the time series. Furthermore, by applying LCT to the images we clearly determine counter-streaming flows in time series of λ171 Å and λ193 Å images. In the λ304 Å wavelength band, we only see minor indications for counter-streaming flows with LCT, while in the λ211 Å wavelength band the counter-streaming flows are not detectable with this method. The diverse morphology of the filament in Hα and EUV images is caused by different absorption processes, i.e., spectral line absorption and absorption by hydrogen and helium continua, respectively. The horizontal flows reach mean flow speeds of about 0.5 km s-1 for all wavelength bands. The highest horizontal flow speeds are identified in the λ171 Å band with flow speeds of up to 2.5 km s-1. The results are averaged over a time series of 90 minutes. Because the LCT sampling window has finite width, a spatial degradation cannot be avoided leading to lower estimates of the flow velocities as compared to feature tracking or Doppler measurements. The counter-streaming flows cover about 15-20% of the whole area of the EUV filament channel and are located in the central part of the spine.
Conclusions: Compared to the ground-based observations, the absence of seeing effects in AIA observations reveal counter-streaming flows in the filament even with a moderate image scale of 0. ''6 pixel-1. Using a contrast enhancement technique, these flows can be detected and quantified with LCT in different wavelengths. We confirm the omnipresence of counter-streaming flows also in giant quiet-Sun filaments.

A movie associated to Fig. 6 is available at https://www.aanda.org Title: Image Quality in High-resolution and High-cadence Solar Imaging Authors: Denker, C.; Dineva, E.; Balthasar, H.; Verma, M.; Kuckein, C.; Diercke, A.; González Manrique, S. J. Bibcode: 2018SoPh..293...44D Altcode: 2018arXiv180200760D Broad-band imaging and even imaging with a moderate bandpass (about 1 nm) provides a photon-rich environment, where frame selection (lucky imaging) becomes a helpful tool in image restoration, allowing us to perform a cost-benefit analysis on how to design observing sequences for imaging with high spatial resolution in combination with real-time correction provided by an adaptive optics (AO) system. This study presents high-cadence (160 Hz) G-band and blue continuum image sequences obtained with the High-resolution Fast Imager (HiFI) at the 1.5-meter GREGOR solar telescope, where the speckle-masking technique is used to restore images with nearly diffraction-limited resolution. The HiFI employs two synchronized large-format and high-cadence sCMOS detectors. The median filter gradient similarity (MFGS) image-quality metric is applied, among others, to AO-corrected image sequences of a pore and a small sunspot observed on 2017 June 4 and 5. A small region of interest, which was selected for fast-imaging performance, covered these contrast-rich features and their neighborhood, which were part of Active Region NOAA 12661. Modifications of the MFGS algorithm uncover the field- and structure-dependency of this image-quality metric. However, MFGS still remains a good choice for determining image quality without a priori knowledge, which is an important characteristic when classifying the huge number of high-resolution images contained in data archives. In addition, this investigation demonstrates that a fast cadence and millisecond exposure times are still insufficient to reach the coherence time of daytime seeing. Nonetheless, the analysis shows that data acquisition rates exceeding 50 Hz are required to capture a substantial fraction of the best seeing moments, significantly boosting the performance of post-facto image restoration. Title: Ca II 8542 Å brightenings induced by a solar microflare Authors: Kuckein, C.; Diercke, A.; González Manrique, S. J.; Verma, M.; Löhner-Böttcher, J.; Socas-Navarro, H.; Balthasar, H.; Sobotka, M.; Denker, C. Bibcode: 2017A&A...608A.117K Altcode: 2017arXiv170906861K
Aims: We study small-scale brightenings in Ca II 8542 Å line-core images to determine their nature and effect on localized heating and mass transfer in active regions.
Methods: High-resolution two-dimensional spectroscopic observations of a solar active region in the near-infrared Ca II 8542 Å line were acquired with the GREGOR Fabry-Pérot Interferometer attached to the 1.5-m GREGOR telescope. Inversions of the spectra were carried out using the NICOLE code to infer temperatures and line-of-sight (LOS) velocities. Response functions of the Ca II line were computed for temperature and LOS velocity variations. Filtergrams of the Atmospheric Imaging Assembly (AIA) and magnetograms of the Helioseismic and Magnetic Imager (HMI) were coaligned to match the ground-based observations and to follow the Ca II brightenings along all available layers of the atmosphere.
Results: We identified three brightenings of sizes up to 2'' × 2'' that appeared in the Ca II 8542 Å line-core images. Their lifetimes were at least 1.5 min. We found evidence that the brightenings belonged to the footpoints of a microflare (MF). The properties of the observed brightenings disqualified the scenarios of Ellerman bombs or Interface Region Imaging Spectrograph (IRIS) bombs. However, this MF shared some common properties with flaring active-region fibrils or flaring arch filaments (FAFs): (1) FAFs and MFs are both apparent in chromospheric and coronal layers according to the AIA channels; and (2) both show flaring arches with lifetimes of about 3.0-3.5 min and lengths of 20'' next to the brightenings. The inversions revealed heating by 600 K at the footpoint location in the ambient chromosphere during the impulsive phase. Connecting the footpoints, a dark filamentary structure appeared in the Ca II line-core images. Before the start of the MF, the spectra of this structure already indicated average blueshifts, meaning upward motions of the plasma along the LOS. During the impulsive phase, these velocities increased up to - 2.2 km s-1. The structure did not disappear during the observations. Downflows dominated at the footpoints. However, in the upper photosphere, slight upflows occurred during the impulsive phase. Hence, bidirectional flows are present in the footpoints of the MF.
Conclusions: We detected Ca II brightenings that coincided with the footpoint location of an MF. The MF event led to a rise of plasma in the upper photosphere, both before and during the impulsive phase. Excess mass, previously raised to at most chromospheric layers, slowly drained downward along arches toward the footpoints of the MF.

The movie associated to Fig. 2 is available at http://www.aanda.org Title: sTools - a data reduction pipeline for the GREGOR Fabry-Pérot Interferometer and the High-resolution Fast Imager at the GREGOR solar telescope Authors: Kuckein, C.; Denker, C.; Verma, M.; Balthasar, H.; González Manrique, S. J.; Louis, R. E.; Diercke, A. Bibcode: 2017IAUS..327...20K Altcode: 2017arXiv170101670K A huge amount of data has been acquired with the GREGOR Fabry-Pérot Interferometer (GFPI), large-format facility cameras, and since 2016 with the High-resolution Fast Imager (HiFI). These data are processed in standardized procedures with the aim of providing science-ready data for the solar physics community. For this purpose, we have developed a user-friendly data reduction pipeline called ``sTools'' based on the Interactive Data Language (IDL) and licensed under creative commons license. The pipeline delivers reduced and image-reconstructed data with a minimum of user interaction. Furthermore, quick-look data are generated as well as a webpage with an overview of the observations and their statistics. All the processed data are stored online at the GREGOR GFPI and HiFI data archive of the Leibniz Institute for Astrophysics Potsdam (AIP). The principles of the pipeline are presented together with selected high-resolution spectral scans and images processed with sTools. Title: Flows along arch filaments observed in the GRIS `very fast spectroscopic mode' Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.; Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier, R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2017IAUS..327...28G Altcode: 2017arXiv170102206G A new generation of solar instruments provides improved spectral, spatial, and temporal resolution, thus facilitating a better understanding of dynamic processes on the Sun. High-resolution observations often reveal multiple-component spectral line profiles, e.g., in the near-infrared He i 10830 Å triplet, which provides information about the chromospheric velocity and magnetic fine structure. We observed an emerging flux region, including two small pores and an arch filament system, on 2015 April 17 with the `very fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS) situated at the 1.5-meter GREGOR solar telescope at Observatorio del Teide, Tenerife, Spain. We discuss this method of obtaining fast (one per minute) spectral scans of the solar surface and its potential to follow dynamic processes on the Sun. We demonstrate the performance of the `very fast spectroscopic mode' by tracking chromospheric high-velocity features in the arch filament system. Title: 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. Bibcode: 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. Bibcode: 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 http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A131 Title: Center-to-limb variation of the velocity field in and around a sunspot with light-bridges Authors: Denker, Carsten; Verma, Meetu; Balthasar, Horst; Diercke, Andrea; González Manrique, S. J.; Löhner-Böttcher, Johannes; Kuckein, Christoph; Sobotka, Michal Bibcode: 2017psio.confE.104D Altcode: No abstract at ADS Title: Velocity fields in sunspots derived from observations with the GREGOR Fabry-Pérot Interferometer Authors: Balthasar, H.; Denker, C.; Diercke, A.; González Manrique, S. J.; Kuckein, C.; Louis, R. E.; Verma, M., Löhner-Böttcher, J.; Sobotka, M. Bibcode: 2017psio.confE.105B Altcode: No abstract at ADS Title: Slipping reconnection in a solar flare observed in high resolution with the GREGOR solar telescope Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák, J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann, A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.; Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann, T. Bibcode: 2016A&A...596A...1S Altcode: 2016arXiv160500464S A small flare ribbon above a sunspot umbra in active region 12205 was observed on November 7, 2014, at 12:00 UT in the blue imaging channel of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference filter. Context observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical Telescope (SOT) onboard Hinode, and the Interface Region Imaging Spectrograph (IRIS) show that this ribbon is part of a larger one that extends through the neighboring positive polarities and also participates in several other flares within the active region. We reconstructed a time series of 140 s of Ca II H images by means of the multiframe blind deconvolution method, which resulted in spatial and temporal resolutions of 0.1″ and 1 s. Light curves and horizontal velocities of small-scale bright knots in the observed flare ribbon were measured. Some knots are stationary, but three move along the ribbon with speeds of 7-11 km s-1. Two of them move in the opposite direction and exhibit highly correlated intensity changes, which provides evidence of a slipping reconnection at small spatial scales.

Movies associated to Figs. 1 and 2 are available at http://www.aanda.org Title: Editor's Note Authors: Louis, Rohan Eugene; Mann, Gottfried; Denker, Carsten Bibcode: 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. Bibcode: 2016A&A...596A...2B Altcode: 2016arXiv160708165B Context. Some models for the topology of the magnetic field in sunspot penumbrae predict regions free of magnetic fields or with only dynamically weak fields in the deep photosphere.
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< 500 Gauss) magnetic fields in sunspot penumbrae. This result is much more reliable than previous investigations made on Fe I lines at 630 nm. Moreover, the result is independent of the number of nodes employed in the inversion, is independent of the point spread function used to deconvolve the data, and does not depend on the amount of stray light (I.e., wide-angle scattered light) considered. Title: Spectropolarimetric observations of an arch filament system with the GREGOR solar telescope Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.; Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.; Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1050B Altcode: 2016arXiv160901514B Arch filament systems occur in active sunspot groups, where a fibril structure connects areas of opposite magnetic polarity, in contrast to active region filaments that follow the polarity inversion line. We used the GREGOR Infrared Spectrograph (GRIS) to obtain the full Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0 nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line to investigate the photospheric magnetic field and velocities, and use the line core intensities and velocities of the helium line to study the chromospheric plasma. The individual fibrils of the arch filament system connect the sunspot with patches of magnetic polarity opposite to that of the spot. These patches do not necessarily coincide with pores, where the magnetic field is strongest. Instead, areas are preferred not far from the polarity inversion line. These areas exhibit photospheric downflows of moderate velocity, but significantly higher downflows of up to 30 km s-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. Bibcode: 2016A&A...596A...4F Altcode: 2016arXiv160800513F Context. A significant part of the penumbral magnetic field returns below the surface in the very deep photosphere. For lines in the visible, a large portion of this return field can only be detected indirectly by studying its imprints on strongly asymmetric and three-lobed Stokes V profiles. Infrared lines probe a narrow layer in the very deep photosphere, providing the possibility of directly measuring the orientation of magnetic fields close to the solar surface.
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. Bibcode: 2016A&A...596A...3V Altcode: 2016arXiv160507462V Context. The solar magnetic field is responsible for all aspects of solar activity. Thus, emergence of magnetic flux at the surface is the first manifestation of the ensuing solar activity.
Aims: Combining high-resolution and synoptic observations aims to provide a comprehensive description of flux emergence at photospheric level and of the growth process that eventually leads to a mature active region.
Methods: The small active region NOAA 12118 emerged on 2014 July 17 and was observed one day later with the 1.5-m GREGOR solar telescope on 2014 July 18. High-resolution time-series of blue continuum and G-band images acquired in the blue imaging channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were complemented by synoptic line-of-sight magnetograms and continuum images obtained with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Horizontal proper motions and horizontal plasma velocities were computed with local correlation tracking (LCT) and the differential affine velocity estimator (DAVE), respectively. Morphological image processing was employed to measure the photometric and magnetic area, magnetic flux, and the separation profile of the emerging flux region during its evolution.
Results: The computed growth rates for photometric area, magnetic area, and magnetic flux are about twice as high as the respective decay rates. The space-time diagram using HMI magnetograms of five days provides a comprehensive view of growth and decay. It traces a leaf-like structure, which is determined by the initial separation of the two polarities, a rapid expansion phase, a time when the spread stalls, and a period when the region slowly shrinks again. The separation rate of 0.26 km s-1 is highest in the initial stage, and it decreases when the separation comes to a halt. Horizontal plasma velocities computed at four evolutionary stages indicate a changing pattern of inflows. In LCT maps we find persistent flow patterns such as outward motions in the outer part of the two major pores, a diverging feature near the trailing pore marking the site of upwelling plasma and flux emergence, and low velocities in the interior of dark pores. We detected many elongated rapidly expanding granules between the two major polarities, with dimensions twice as large as the normal granules. Title: Solar physics at the Einstein Tower Authors: Denker, C.; Heibel, C.; Rendtel, J.; Arlt, K.; Balthasar, Juergen H.; Diercke, A.; González Manrique, S. J.; Hofmann, A.; Kuckein, C.; Önel, H.; Senthamizh Pavai, V.; Staude, J.; Verman, M. Bibcode: 2016AN....337.1105D Altcode: 2016arXiv160906949D The solar observatory Einstein Tower ({Einsteinturm}) at the Telegrafenberg in Potsdam is both a landmark of modern architecture and an important place for solar physics. Originally built for high-resolution spectroscopy and measuring the gravitational redshift, research shifted over the years to understanding the active Sun and its magnetic field. Nowadays, telescope and spectrographs are used for research and development, i.e., testing instruments and in particular polarization optics for advanced instrumentation deployed at major European and international astronomical and solar telescopes. In addition, the Einstein Tower is used for educating and training of the next generation astrophysicists as well as for education and public outreach activities directed at the general public. This article comments on the observatory's unique architecture and the challenges of maintaining and conserving the building. It describes in detail the characteristics of telescope, spectrographs, and imagers; it portrays some of the research and development activities. Title: Upper chromospheric magnetic field of a sunspot penumbra: observations of fine structure Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados, M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar, H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.; Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016A&A...596A...8J Altcode: 2016arXiv160801988J
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. Bibcode: 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. Bibcode: 2016A&A...596A...6L Altcode: 2016arXiv160506324L Context. Investigations of the magnetism of the quiet Sun are hindered by extremely weak polarization signals in Fraunhofer spectral lines. Photon noise, straylight, and the systematically different sensitivity of the Zeeman effect to longitudinal and transversal magnetic fields result in controversial results in terms of the strength and angular distribution of the magnetic field vector.
Aims: The information content of Stokes measurements close to the diffraction limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of spatial straylight and photon noise into account.
Methods: Highly sensitive full Stokes measurements of a quiet-Sun region at disk center in the deep photospheric Fe I lines in the 1.56 μm region were obtained with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise statistics and Stokes V asymmetries were analyzed and compared to a similar data set of the Hinode spectropolarimeter (SOT/SP). Simple diagnostics based directly on the shape and strength of the profiles were applied to the GRIS data. We made use of the magnetic line ratio technique, which was tested against realistic magneto-hydrodynamic simulations (MURaM).
Results: About 80% of the GRIS spectra of a very quiet solar region show polarimetric signals above a 3σ level. Area and amplitude asymmetries agree well with small-scale surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss range with some concentrations of kilo-Gauss fields.
Conclusions: The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4 are so far unique in the combination of high spatial resolution scans and high magnetic field sensitivity. Nevertheless, the unavoidable effect of spatial straylight and the resulting dilution of the weak Stokes profiles means that inversion techniques still bear a high risk of misinterpretating the data. Title: Flow and magnetic field properties in the trailing sunspots of active region NOAA 12396 Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer, C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados, M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1090V Altcode: Improved measurements of the photospheric and chromospheric three-dimensional magnetic and flow fields are crucial for a precise determination of the origin and evolution of active regions. We present an illustrative sample of multi-instrument data acquired during a two-week coordinated observing campaign in August 2015 involving, among others, the GREGOR solar telescope (imaging and near-infrared spectroscopy) and the space missions Solar Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph (IRIS). The observations focused on the trailing part of active region NOAA 12396 with complex polarity inversion lines and strong intrusions of opposite polarity flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV spectral profiles in the photospheric Si I λ1082.7 nm line, the chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I λ1083.9 nm line. Carefully calibrated GRIS scans of the active region provided maps of Doppler velocity and magnetic field at different atmospheric heights. We compare quick-look maps with those obtained with the ``Stokes Inversions based on Response functions'' (SIR) code, which furnishes deeper insight into the magnetic properties of the region. We find supporting evidence that newly emerging flux and intruding opposite polarity flux are hampering the formation of penumbrae, i.e., a penumbra fully surrounding a sunspot is only expected after cessation of flux emergence in proximity to the sunspots. Title: Three-dimensional structure of a sunspot light bridge Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.; Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016A&A...596A..59F Altcode: 2016arXiv161104803F Context. Active regions are the most prominent manifestations of solar magnetic fields; their generation and dissipation are fundamental problems in solar physics. Light bridges are commonly present during sunspot decay, but a comprehensive picture of their role in the removal of the photospheric magnetic field is still lacking.
Aims: We study the three-dimensional configuration of a sunspot, and in particular, its light bridge, during one of the last stages of its decay.
Methods: We present the magnetic and thermodynamical stratification inferred from full Stokes inversions of the photospheric Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR Infrared Spectrograph of the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The analysis is complemented by a study of continuum images covering the disk passage of the active region, which are provided by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory.
Results: The sunspot shows a light bridge with penumbral continuum intensity that separates the central umbra from a smaller umbra. We find that in this region the magnetic field lines form a canopy with lower magnetic field strength in the inner part. The photospheric light bridge is dominated by gas pressure (high-β), as opposed to the surrounding umbra, where the magnetic pressure is higher. A convective flow is observed in the light bridge. This flow is able to bend the magnetic field lines and to produce field reversals. The field lines merge above the light bridge and become as vertical and strong as in the surrounding umbra. We conclude that this occurs because two highly magnetized regions approach each other during the sunspot evolution.

Movies associated to Figs. 2 and 13 are available at http://www.aanda.org Title: Inference of magnetic fields in the very quiet Sun Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.; Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.; Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.; González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.; Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman, T.; Volkmer, R. Bibcode: 2016A&A...596A...5M Altcode: 2018arXiv180410089M Context. Over the past 20 yr, the quietest areas of the solar surface have revealed a weak but extremely dynamic magnetism occurring at small scales (<500 km), which may provide an important contribution to the dynamics and energetics of the outer layers of the atmosphere. Understanding this magnetism requires the inference of physical quantities from high-sensitivity spectro-polarimetric data with high spatio-temporal resolution.
Aims: We present high-precision spectro-polarimetric data with high spatial resolution (0.4'') of the very quiet Sun at 1.56 μm obtained with the GREGOR telescope to shed some light on this complex magnetism.
Methods: We used inversion techniques in two main approaches. First, we assumed that the observed profiles can be reproduced with a constant magnetic field atmosphere embedded in a field-free medium. Second, we assumed that the resolution element has a substructure with either two constant magnetic atmospheres or a single magnetic atmosphere with gradients of the physical quantities along the optical depth, both coexisting with a global stray-light component.
Results: Half of our observed quiet-Sun region is better explained by magnetic substructure within the resolution element. However, we cannot distinguish whether this substructure comes from gradients of the physical parameters along the line of sight or from horizontal gradients (across the surface). In these pixels, a model with two magnetic components is preferred, and we find two distinct magnetic field populations. The population with the larger filling factor has very weak ( 150 G) horizontal fields similar to those obtained in previous works. We demonstrate that the field vector of this population is not constrained by the observations, given the spatial resolution and polarimetric accuracy of our data. The topology of the other component with the smaller filling factor is constrained by the observations for field strengths above 250 G: we infer hG fields with inclinations and azimuth values compatible with an isotropic distribution. The filling factors are typically below 30%. We also find that the flux of the two polarities is not balanced. From the other half of the observed quiet-Sun area 50% are two-lobed Stokes V profiles, meaning that 23% of the field of view can be adequately explained with a single constant magnetic field embedded in a non-magnetic atmosphere. The magnetic field vector and filling factor are reliable inferred in only 50% based on the regular profiles. Therefore, 12% of the field of view harbour hG fields with filling factors typically below 30%. At our present spatial resolution, 70% of the pixels apparently are non-magnetised. Title: Fitting peculiar spectral profiles in He I 10830Å absorption features Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.; Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.; Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1057G Altcode: 2016arXiv160300679G The new generation of solar instruments provides better spectral, spatial, and temporal resolution for a better understanding of the physical processes that take place on the Sun. Multiple-component profiles are more commonly observed with these instruments. Particularly, the He I 10830 Å triplet presents such peculiar spectral profiles, which give information on the velocity and magnetic fine structure of the upper chromosphere. The purpose of this investigation is to describe a technique to efficiently fit the two blended components of the He I 10830 Å triplet, which are commonly observed when two atmospheric components are located within the same resolution element. The observations used in this study were taken on 2015 April 17 with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar telescope, located at the Observatorio del Teide, Tenerife, Spain. We apply a double-Lorentzian fitting technique using Levenberg-Marquardt least-squares minimization. This technique is very simple and much faster than inversion codes. Line-of-sight Doppler velocities can be inferred for a whole map of pixels within just a few minutes. Our results show sub- and supersonic downflow velocities of up to 32 km s-1 for the fast component in the vicinity of footpoints of filamentary structures. The slow component presents velocities close to rest. Title: Sunspot group tilt angle measurements from historical observations Authors: Senthamizh Pavai, V.; Arlt, R.; Diercke, A.; Denker, C.; Vaquero, J. M. Bibcode: 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. Title: Giant quiescent solar filament observed with high-resolution spectroscopy Authors: Kuckein, C.; Verma, M.; Denker, C. Bibcode: 2016A&A...589A..84K Altcode: 2016arXiv160302505K
Aims: An extremely large filament was studied in various layers of the solar atmosphere. The inferred physical parameters and the morphological aspects are compared with smaller quiescent filaments.
Methods: A giant quiet-Sun filament was observed with the high-resolution Echelle spectrograph at the Vacuum Tower Telescope at Observatorio del Teide, Tenerife, Spain, on 2011 November 15. A mosaic of spectra (ten maps of 100″ × 182″) was recorded simultaneously in the chromospheric absorption lines Hα and Na I D2. Physical parameters of the filament plasma were derived using cloud model (CM) inversions and line core fits. The spectra were complemented with full-disk filtergrams (He I λ10830 Å, Hα, and Ca II K) of the Chromospheric Telescope (ChroTel) and full-disk magnetograms of the Helioseismic and Magnetic Imager (HMI).
Results: The filament had extremely large linear dimensions (~817 arcsec), which corresponds to about 658 Mm along a great circle on the solar surface. A total amount of 175119 Hα contrast profiles were inverted using the CM approach. The inferred mean line-of-sight (LOS) velocity, Doppler width, and source function were similar to previous works of smaller quiescent filaments. However, the derived optical thickness was higher. LOS velocity trends inferred from the Hα line core fits were in accord but weaker than those obtained with CM inversions. Signatures of counter-streaming flows were detected in the filament. The largest brightening conglomerates in the line core of Na I D2 coincided well with small-scale magnetic fields as seen by HMI. Mixed magnetic polarities were detected close to the ends of barbs. The computation of photospheric horizontal flows based on HMI magnetograms revealed flow kernels with a size of 5-8 Mm and velocities of 0.30-0.45 km s-1 at the ends of the filament.
Conclusions: The physical properties of extremely large filaments are similar to their smaller counterparts, except for the optical thickness, which in our sample was found to be higher. We found that a part of the filament, which erupted the day before, is in the process of reestablishing its initial configuration. Title: Flows in and around Active Region NOAA12118 Observed with the GREGOR Solar Telescope and SDO/HMI Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke, A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann, A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert, M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016ASPC..504...29V Altcode: 2016arXiv160301109V Accurate measurements of magnetic and velocity fields in and around solar active regions are key to unlocking the mysteries of the formation and the decay of sunspots. High spatial resolution images and spectral sequences with a high cadence obtained with the GREGOR solar telescope give us an opportunity to scrutinize 3-D flow fields with local correlation tracking and imaging spectroscopy. We present GREGOR early science data acquired in 2014 July - August with the GREGOR Fabry-Pérot Interferometer and the Blue Imaging Channel. Time-series of blue continuum (λ 450.6 nm) images of the small active region NOAA 12118 were restored with the speckle masking technique to derive horizontal proper motions and to track the evolution of morphological changes. In addition, high-resolution observations are discussed in the context of synoptic data from the Solar Dynamics Observatory. Title: GREGOR observations of a small flare above a sunspot Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák, J.; Liu, W. Bibcode: 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. 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 Bibcode: 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. 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. Bibcode: 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. 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 Bibcode: 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. Title: Digitization of sunspot drawings by Spörer made in 1861-1894 Authors: Diercke, A.; Arlt, R.; Denker, C. Bibcode: 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. Title: The Magnetic Configuration of a δ-Spot Authors: Balthasar, H.; Beck, C.; Louis, R. E.; Verma, M.; Denker, C. Bibcode: 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 <font size=2>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. Title: Horizontal flow fields observed in Hinode G-band images. IV. Statistical properties of the dynamical environment around pores Authors: Verma, M.; Denker, C. Bibcode: 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. Title: The association between sunspot magnetic fields and superpenumbral fibrils Authors: Louis, R. E.; Balthasar, H.; Kuckein, C.; Gömöry, P.; Puschmann, K. G.; Denker, C. Bibcode: 2014AN....335..161L Altcode: 2013arXiv1312.1879L Spectropolarimetric observations of a sunspot were carried out with the Tenerife Infrared Polarimeter at Observatorio del Teide, Tenerife, Spain. Maps of the physical parameters were obtained from an inversion of the Stokes profiles observed in the infrared Fe I line at 15 648 Å. The regular sunspot consisted of a light bridge which separated the two umbral cores of the same polarity. One of the arms of the light bridge formed an extension of a penumbral filament which comprised weak and highly inclined magnetic fields. In addition, the Stokes V profiles in this filament had an opposite sign as the sunspot and some resembled Stokes Q or U. This penumbral filament terminated abruptly into another at the edge of the sunspot, where the latter was relatively vertical by about 30o. Chromospheric H\alpha and He II 304 Åfiltergrams revealed three superpenumbral fibrils on the limb-side of the sunspot, in which one fibril extended into the sunspot and was oriented along the highly inclined penumbral counterpart of the light bridge. An intense, elongated brightening was observed along this fibril that was co-spatial with the intersecting penumbral filaments in the photosphere. Our results suggest that the disruption in the sunspot magnetic field at the location of the light bridge could be the source of reconnection that led to the intense chromospheric brightening and facilitated the supply of cool material in maintaining the overlying superpenumbral fibrils. Title: Near-infrared spectropolarimetry of a δ-spot Authors: Balthasar, H.; Beck, C.; Louis, R. E.; Verma, M.; Denker, C. Bibcode: 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. Title: Sunspot splitting triggering an eruptive flare Authors: Louis, Rohan E.; Puschmann, Klaus G.; Kliem, Bernhard; Balthasar, Horst; Denker, Carsten Bibcode: 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 http://www.aanda.org Title: High-resolution spectroscopy of a giant solar filament Authors: Kuckein, Christoph; Denker, Carsten; Verma, Meetu Bibcode: 2014IAUS..300..437K Altcode: 2013arXiv1309.7861K High-resolution spectra of a giant solar quiescent filament were taken with the Echelle spectrograph at the Vacuum Tower Telescope (VTT; Tenerife, Spain). A mosaic of various spectroheliograms (Hα, Hα+/-0.5 Å and Na D2) were chosen to examine the filament at different heights in the solar atmosphere. In addition, full-disk images (He i 10830 Å and Ca ii K) of the Chromspheric Telescope and full-disk magnetograms of the Helioseismic and Magnetic Imager were used to complement the spectra. Preliminary results are shown of this filament, which had extremely large linear dimensions (~740'') and was observed in November 2011 while it traversed the northern solar hemisphere. Title: 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 Bibcode: 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 Bibcode: 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. Title: Digitization of Spörer's sunspot drawings Authors: Diercke, Andrea; Arlt, Rainer; Denker, Carsten Bibcode: 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. 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. Bibcode: 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 (>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. Bibcode: 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 http://www.aanda.org 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. 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. Bibcode: 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. Bibcode: 2012AN....333..901S Altcode: We describe the future night-time spectrograph for the GREGOR solar telescope and present its science core projects. The spectrograph provides a 3-pixel resolution of up to R=87 000 in 45 échelle orders covering the wavelength range 390-900 nm with three grating settings. An iodine cell can be used for high-precision radial velocity work in the 500-630 nm range. The operation of the spectrograph and the telescope will be fully automated without the presence of humans during night-time and will be based on the successful STELLA control system. Future upgrades include a second optical camera for even higher spectral resolution, a Stokes-V polarimeter and a link to the laser-frequency comb at the Vacuum Tower Telescope. The night-time core projects are a study of the angular-momentum evolution of ``The Sun in Time'' and a continuation of our long-term Doppler imaging of active stars. Title: A retrospective of the GREGOR solar telescope in scientific literature Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.; Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.; Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa, M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann, T.; Wiehr, E.; Wittmann, A. D.; Woche, M. Bibcode: 2012AN....333..810D Altcode: 2012arXiv1210.3167D In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post-focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer-reviewed journals and conference proceedings also provides the ``historical'' context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes. Title: The 1.5 meter solar telescope GREGOR Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.; Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Waldmann , T. A. Bibcode: 2012AN....333..796S Altcode: The 1.5 m telescope GREGOR opens a new window to the understanding of solar small-scale magnetism. The first light instrumentation includes the Gregor Fabry Pérot Interferometer (GFPI), a filter spectro-polarimeter for the visible wavelength range, the GRating Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The excellent performance of the first two instruments has already been demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest solar telescope and number 3 in the world. Its all-reflective Gregory design provides a large wavelength coverage from the near UV up to at least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR is equipped with a high-order adaptive optics system, with a subaperture size of 10 cm, and a deformable mirror with 256 actuators. The science goals are focused on, but not limited to, solar magnetism. GREGOR allows us to measure the emergence and disappearance of magnetic flux at the solar surface at spatial scales well below 100 km. Thanks to its spectro-polarimetric capabilities, GREGOR will measure the interaction between the plasma flows, different kinds of waves, and the magnetic field. This will foster our understanding of the processes that heat the chromosphere and the outer layers of the solar atmosphere. Observations of the surface magnetic field at very small spatial scales will shed light on the variability of the solar brightness. Title: Editors' note Authors: Denker, Carsten; Feller, Alex; Schmidt, Wolfgang; von der Lühe, Oskar Bibcode: 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. Bibcode: 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. Bibcode: 2012AN....333..872C Altcode: This paper describes the main characteristics of GRIS (GREGOR Infrared Spectrograph), the grating spectrograph installed in the recently inaugurated (May 2012) 1.5-meter GREGOR telescope located at the Observatorio del Teide in Tenerife. The spectrograph has a standard Czerny-Turner configuration with parabolic collimator and camera mirrors that belong to the same conic surface. Although nothing prevents its use at visible wavelengths, the spectrograph will be initially used in combination with the infrared detector of the Tenerife Infrared Polarimeter (TIP-II) in standard spectroscopic mode as well as for spectropolarimetric measurements. Title: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 2010AN....331..624V Altcode: The integration and verification phase of the GREGOR telescope reached an important milestone with the installation of the interim 1 m SolarLite primary mirror. This was the first time that the entire light path had seen sunlight. Since then extensive testing of the telescope and its subsystems has been carried out. The integration and verification phase will culminate with the delivery and installation of the final 1.5 m Zerodur primary mirror in the summer of 2010. Observatory level tests and science verification will commence in the second half of 2010 and in 2011. This phase includes testing of the main optics, adaptive optics, cooling and pointing systems. In addition, assuming the viewpoint of a typical user, various observational modes of the GREGOR Fabry-Pérot Interferometer (GFPI), the Grating Infrared Spectrograph (GRIS), and high-speed camera systems will be tested to evaluate if they match the expectations and science requirements. This ensures that GREGOR will provide high-quality observations with its combination of (multi-conjugate) adaptive optics and advanced post-focus instruments. Routine observations are expected for 2012. Title: Instrument and data analysis challenges for imaging spectro-polarimetry Authors: Denker, C. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 & 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 2004ChJAA...4..481X Altcode: No abstract at ADS 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 Bibcode: 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. Title: Near infrared (NIR) achromatic phase retarder Authors: Ma, Jun; Wang, Jingshan; Cao, W.; Denker, Carsten; Wang, Haimin Bibcode: 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. 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 Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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 (<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. 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. Bibcode: 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 (< 0.2 "/pixel image scale), high spectral resolution (< 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. Title: Magnetic Helicity Change Rate Associated With X-Class and M-Class Flares Authors: Hartkorn, K.; Wang, H.; Cao, W.; Denker, C.; Xu, Y. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. 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 Bibcode: 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. 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. Bibcode: 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. 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 Bibcode: 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. Title: Rapid Penumbral Decay following Three X-Class Solar Flares Authors: Wang, H.; Liu, C.; Qiu, J.; Deng, N.; Goode, P. R.; Denker, C. Bibcode: 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. Title: Low energy SEP events of October/November 2003 at 1 and 5 AU Authors: Lanzerotti, L. J.; Maclennan, C. G.; Denker, C. Bibcode: 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 (<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. Title: High Spatial Resolution Observations of Pores and the Formation of a Rudimentary Penumbra Authors: Yang, G.; Xu, Y.; Wang, H.; Denker, C. Bibcode: 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. 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 Bibcode: 2003JKAS...36S.125G Altcode: No abstract at ADS Title: The Sun from Big Bear Authors: Goode, Philip R.; Denker, Carsten; Wang, Haimin Bibcode: 2003ASSL..288..137G Altcode: 2003ASSL..287..437G No abstract at ADS Title: Long-Term Seeing Characteristics at Big Bear Solar Observatory Authors: Denker, C.; Espinosa, O. D.; Nenow, J.; Marquette, W. H. Bibcode: 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. Bibcode: 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. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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>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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 & 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&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. Bibcode: 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 Bibcode: 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. Title: High Spatial Resolution Observations of a Sunspot with an ``Orphan Penumbra'' Authors: Denker, C.; Zirin, H.; Wang, H. Bibcode: 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. Title: Speckle observations of sunspots. Authors: Denker, C. Bibcode: 1996AGAb...12...87D Altcode: No abstract at ADS Title: Untersuchung der Feinstruktur von Sonnenflecken mit Methoden der Speckle-Interferometrie Authors: Denker, Carsten Bibcode: 1996PhDT........51D Altcode: No abstract at ADS Title: Untersuchung von Feinstrukturen der Sonne. Authors: Denker, C.; de Boer, C. R.; Volkmer, R. Bibcode: 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. Title: Speckle masking imaging of the moustache phenomenon. Authors: Denker, C.; de Boer, C. R.; Volkmer, R.; Kneer, F. Bibcode: 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. Title: Speckle-masking imaging of bright points (moustaches) Authors: Denker, C.; Deboer, C. R.; Kneer, F. Bibcode: 1995IAUS..176P..51D Altcode: No abstract at ADS Title: Speckle observations of sunspots Authors: Denker, C. Bibcode: 1994smf..conf..194D Altcode: No abstract at ADS Title: A Comparison of Two Wavefront Sensors Authors: Denker, C.; Restaino, S.; Radick, R. Bibcode: 1993rtpf.conf...86D Altcode: No abstract at ADS