Author name code: scharmer ADS astronomy entries on 2022-09-14 author:"Scharmer, Goran B." ------------------------------------------------------------------------ Title: SSTRED: Data- and metadata-processing pipeline for CHROMIS and CRISP Authors: Löfdahl, Mats G.; Hillberg, Tomas; de la Cruz Rodríguez, Jaime; Vissers, Gregal; Andriienko, Oleksii; Scharmer, Göran B.; Haugan, Stein V. H.; Fredvik, Terje Bibcode: 2021A&A...653A..68L Altcode: 2018arXiv180403030L Context. Data from ground-based, high-resolution solar telescopes can only be used for science with calibrations and processing, which requires detailed knowledge about the instrumentation. Space-based solar telescopes provide science-ready data, which are easier to work with for researchers whose expertise is in the interpretation of data. Recently, data-processing pipelines for ground-based instruments have been constructed.
Aims: We aim to provide observers with a user-friendly data pipeline for data from the Swedish 1-meter Solar Telescope (SST) that delivers science-ready data together with the metadata needed for proper interpretation and archiving.
Methods: We briefly describe the CHROMospheric Imaging Spectrometer (CHROMIS) instrument, including its (pre)filters, as well as recent upgrades to the CRisp Imaging SpectroPolarimeter (CRISP) prefilters and polarization optics. We summarize the processing steps from raw data to science-ready data cubes in FITS files. We report calibrations and compensations for data imperfections in detail. Misalignment of Ca II data due to wavelength-dependent dispersion is identified, characterized, and compensated for. We describe intensity calibrations that remove or reduce the effects of filter transmission profiles as well as solar elevation changes. We present REDUX, a new version of the MOMFBD image restoration code, with multiple enhancements and new features. It uses projective transforms for the registration of multiple detectors. We describe how image restoration is used with CRISP and CHROMIS data. The science-ready output is delivered in FITS files, with metadata compliant with the SOLARNET recommendations. Data cube coordinates are specified within the World Coordinate System (WCS). Cavity errors are specified as distortions of the WCS wavelength coordinate with an extension of existing WCS notation. We establish notation for specifying the reference system for Stokes vectors with reference to WCS coordinate directions. The CRIsp SPectral EXplorer (CRISPEX) data-cube browser has been extended to accept SSTRED output and to take advantage of the SOLARNET metadata.
Results: SSTRED is a mature data-processing pipeline for imaging instruments, developed and used for the SST/CHROMIS imaging spectrometer and the SST/CRISP spectropolarimeter. SSTRED delivers well-characterized, science-ready, archival-quality FITS files with well-defined metadata. The SSTRED code, as well as REDUX and CRISPEX, is freely available through git repositories. Title: Design and Performance Analysis of a Highly Efficient Polychromatic Full Stokes Polarization Modulator for the CRISP Imaging Spectrometer Authors: de Wijn, A. G.; de la Cruz Rodríguez, J.; Scharmer, G. B.; Sliepen, G.; Sütterlin, P. Bibcode: 2021AJ....161...89D Altcode: 2021arXiv210201231D We present the design and performance of a polychromatic polarization modulator for the CRisp Imaging SpectroPolarimeter (CRISP) Fabry-Perot tunable narrow-band imaging spectropolarimer at the Swedish 1 m Solar Telescope (SST). We discuss the design process in depth, compare two possible modulator designs through a tolerance analysis, and investigate thermal sensitivity of the selected design. The trade-offs and procedures described in this paper are generally applicable in the development of broadband polarization modulators. The modulator was built and has been operational since 2015. Its measured performance is close to optimal between 500 and 900 nm, and differences between the design and as-built modulator are largely understood. We show some example data, and briefly review scientific work that used data from SST/CRISP and this modulator. Title: High-resolution observations of the solar photosphere, chromosphere, and transition region. A database of coordinated IRIS and SST observations Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Carlsson, M.; de la Cruz Rodríguez, J.; Bose, S.; Chintzoglou, G.; Drews, A.; Froment, C.; Gošić, M.; Graham, D. R.; Hansteen, V. H.; Henriques, V. M. J.; Jafarzadeh, S.; Joshi, J.; Kleint, L.; Kohutova, P.; Leifsen, T.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Ortiz, A.; Pereira, T. M. D.; Popovas, A.; Quintero Noda, C.; Sainz Dalda, A.; Scharmer, G. B.; Schmit, D.; Scullion, E.; Skogsrud, H.; Szydlarski, M.; Timmons, R.; Vissers, G. J. M.; Woods, M. M.; Zacharias, P. Bibcode: 2020A&A...641A.146R Altcode: 2020arXiv200514175R NASA's Interface Region Imaging Spectrograph (IRIS) provides high-resolution observations of the solar atmosphere through ultraviolet spectroscopy and imaging. Since the launch of IRIS in June 2013, we have conducted systematic observation campaigns in coordination with the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides complementary high-resolution observations of the photosphere and chromosphere. The SST observations include spectropolarimetric imaging in photospheric Fe I lines and spectrally resolved imaging in the chromospheric Ca II 8542 Å, Hα, and Ca II K lines. We present a database of co-aligned IRIS and SST datasets that is open for analysis to the scientific community. The database covers a variety of targets including active regions, sunspots, plages, the quiet Sun, and coronal holes. Title: Dissecting bombs and bursts: non-LTE inversions of low-atmosphere reconnection in SST and IRIS observations Authors: Vissers, G. J. M.; de la Cruz Rodríguez, J.; Libbrecht, T.; Rouppe van der Voort, L. H. M.; Scharmer, G. B.; Carlsson, M. Bibcode: 2019A&A...627A.101V Altcode: 2019arXiv190502035V Ellerman bombs and UV bursts are transient brightenings that are ubiquitously observed in the lower atmospheres of active and emerging flux regions. As they are believed to pinpoint sites of magnetic reconnection in reconfiguring fields, understanding their occurrence and detailed evolution may provide useful insight into the overall evolution of active regions. Here we present results from inversions of SST/CRISP and CHROMIS, as well as IRIS data of such transient events. Combining information from the Mg II h & k, Si IV, and Ca II 8542 Å and Ca II H & K lines, we aim to characterise their temperature and velocity stratification, as well as their magnetic field configuration. We find average temperature enhancements of a few thousand kelvin, close to the classical temperature minimum and similar to previous studies, but localised peak temperatures of up to 10 000-15 000 K from Ca II inversions. Including Mg II appears to generally dampen these temperature enhancements to below 8000 K, while Si IV requires temperatures in excess of 10 000 K at low heights, but may also be reproduced with secondary temperature enhancements of 35 000-60 000 K higher up. However, reproducing Si IV comes at the expense of overestimating the Mg II emission. The line-of-sight velocity maps show clear bi-directional jet signatures for some events and strong correlation with substructure in the intensity images in general. Absolute line-of-sight velocities range between 5 and 20 km s-1 on average, with slightly larger velocities towards, rather than away from, the observer. The inverted magnetic field parameters show an enhancement of the horizontal field co-located with the brightenings at heights similar to that of the temperature increase. We are thus able to largely reproduce the observational properties of Ellerman bombs with the UV burst signature (e.g. intensities, profile asymmetries, morphology, and bi-directional jet signatures), with temperature stratifications peaking close to the classical temperature minimum. Correctly modelling the Si IV emission in agreement with all other diagnostics is however an outstanding issue and remains paramount in explaining its apparent coincidence with Hα emission. Fine-tuning the approach (accounting for resolution differences, fitting localised temperature enhancements, and/or performing spatially coupled inversions) is likely necessary in order to obtain better agreement between all considered diagnostics. Title: Is the sky the limit?. Performance of the revamped Swedish 1-m Solar Telescope and its blue- and red-beam reimaging systems Authors: Scharmer, G. B.; Löfdahl, M. G.; Sliepen, G.; de la Cruz Rodríguez, J. Bibcode: 2019A&A...626A..55S Altcode: 2019arXiv190505588S We discuss the use of measurements of the solar granulation contrast as a measure of optical quality. We demonstrate that for data recorded with a telescope that uses adaptive optics and/or post-processing to compensate for many low- and high-order aberrations, the RMS granulation contrast is directly proportional to the Strehl ratio calculated from the residual (small-scale) wavefront error (static and/or from seeing). We demonstrate that the wings of the high-order compensated point spread function for the Swedish 1-m Solar Telescope (SST) are likely to extend to a radius of not more than about 2″, which is consistent with earlier conclusions drawn from stray-light compensation of sunspot images. We report on simultaneous measurements of seeing and solar granulation contrast averaged over 2 s time intervals at several wavelengths from 525 nm to 853.6 nm on the red-beam (CRISP beam) and wavelengths from 395 nm to 484 nm on the blue-beam (CHROMIS beam). These data were recorded with the SST, which has been revamped with an 85-electrode adaptive mirror and a new tip-tilt mirror, both of which were polished to exceptionally high optical quality. Compared to similar data obtained with the previous 37-electrode adaptive mirror in 2009 and 2011, there is a significant improvement in image contrast. The highest 2 s average image contrasts measured in April 2015 through 0.3-0.9 nm interference filters at 525 nm, 557 nm, 630 nm, and 853.5 nm with compensation only for the diffraction limited point spread function of SST are 11.8%, 11.8%, 10.2%, and 7.2%, respectively. Similarly, the highest 2 s contrasts measured at 395 nm, 400 nm, and 484 nm in May 2016 through 0.37-1.3 nm filters are 16%, 16%, and 12.5%, respectively. The granulation contrast observed with SST compares favorably to measured values with SOT on Hinode and with Sunrise as well as major ground-based solar telescopes. Simultaneously with the above wideband red-beam data, we also recorded narrowband continuum images with the CRISP imaging spectropolarimeter. We find that contrasts measured with CRISP are entirely consistent with the corresponding wideband contrasts, demonstrating that any additional image degradation by the CRISP etalons and telecentric optical system is marginal or even insignificant. Finally, we discuss the origin of the 48 nm RMS wavefront error needed to bring consistency between the measured granulation contrast and that obtained from 3D simulations of convection. Title: The Dark Side of Penumbral Microjets: Observations in Hα Authors: Buehler, D.; Esteban Pozuelo, S.; de la Cruz Rodriguez, J.; Scharmer, G. B. Bibcode: 2019ApJ...876...47B Altcode: 2019arXiv190501245B We present data of 10 penumbral microjets (PMJs) observed in a Hα, Ca II 8542 Å, and Fe I 6302 Å line pair with the Swedish 1 m Solar Telescope (SST) with CRISP and Ca II K with SST/CHROMIS in active region NOAA 12599 on 2016 October 12 at μ = 0.68. All four Stokes parameters of the Ca II 8542 Å and Fe I 6302 Å lines were observed and a series of test pixels were inverted using the Stockholm inversion code. Our analysis revealed for the first time that PMJs are visible in Hα, where they appear as dark features with average line-of-sight (LOS) upflows of 1.1 ± 0.6 km s-1, matching the LOS velocities from the inversions. Based on the Hα observations we extend the previous average length and lifetime of PMJs to 2815 ± 530 km and 163 ± 25 s, respectively. The plane-of-sky (POS) velocities of our PMJs of up to 17 km s-1 tend to give increased velocities with distance traveled. Furthermore, two of our PMJs with significant Stokes V signal indicate that the PMJs possess an increased LOS magnetic field of up to 100 G compared to the local pre-/post- PMJ magnetic field, which propagates as quickly as the PMJs’ POS velocities. Finally, we present evidence that PMJs display an on average 1 minute gradual precursory brightening that only manifests itself in the cores of the Ca II lines. We conclude that PMJs are not ordinary jets but likely are manifestations of heat fronts that propagate at the local Alfvén velocity. Title: Observationally Based Models of Penumbral Microjets Authors: Esteban Pozuelo, S.; de la Cruz Rodríguez, J.; Drews, A.; Rouppe van der Voort, L.; Scharmer, G. B.; Carlsson, M. Bibcode: 2019ApJ...870...88E Altcode: 2018arXiv181107881E We study the polarization signals and physical parameters of penumbral microjets (PMJs) by using high spatial resolution data taken in the Fe I 630 nm pair, Ca II 854.2 nm, and Ca II K lines with the CRISP and CHROMIS instruments at the Swedish 1 m Solar Telescope. We infer their physical parameters, such as physical observables in the photosphere and chromospheric velocity diagnostics, by different methods, including inversions of the observed Stokes profiles with the STiC code. PMJs harbor overall brighter Ca II K line profiles and conspicuous polarization signals in Ca II 854.2 nm, specifically in circular polarization that often shows multiple lobes mainly due to the shape of Stokes I. They usually overlap photospheric regions with a sheared magnetic field configuration, suggesting that magnetic reconnections could play an important role in the origin of PMJs. The discrepancy between their low LOS velocities and the high apparent speeds reported on earlier, as well as the existence of different vertical velocity gradients in the chromosphere, indicate that PMJs might not be entirely related to mass motions. Instead, PMJs could be due to perturbation fronts induced by magnetic reconnections occurring in the deep photosphere that propagate through the chromosphere. This reconnection may be associated with current heating that produces temperature enhancements from the temperature minimum region. Furthermore, enhanced collisions with electrons could also increase the coupling to the local conditions at higher layers during the PMJ phase, giving a possible explanation for the enhanced emission in the overall Ca II K profiles emerging from these transients. Title: Chromospheric heating during flux emergence in the solar atmosphere Authors: Leenaarts, Jorrit; de la Cruz Rodríguez, Jaime; Danilovic, Sanja; Scharmer, Göran; Carlsson, Mats Bibcode: 2018A&A...612A..28L Altcode: 2017arXiv171200474L Context. The radiative losses in the solar chromosphere vary from 4 kW m-2 in the quiet Sun, to 20 kW m-2 in active regions. The mechanisms that transport non-thermal energy to and deposit it in the chromosphere are still not understood. Aim. We aim to investigate the atmospheric structure and heating of the solar chromosphere in an emerging flux region.
Methods: We have used observations taken with the CHROMIS and CRISP instruments on the Swedish 1-m Solar Telescope in the Ca II K , Ca II 854.2 nm, Hα, and Fe I 630.1 nm and 630.2 nm lines. We analysed the various line profiles and in addition perform multi-line, multi-species, non-local thermodynamic equilibrium (non-LTE) inversions to estimate the spatial and temporal variation of the chromospheric structure.
Results: We investigate which spectral features of Ca II K contribute to the frequency-integrated Ca II K brightness, which we use as a tracer of chromospheric radiative losses. The majority of the radiative losses are not associated with localised high-Ca II K-brightness events, but instead with a more gentle, spatially extended, and persistent heating. The frequency-integrated Ca II K brightness correlates strongly with the total linear polarization in the Ca II 854.2 nm, while the Ca II K profile shapes indicate that the bulk of the radiative losses occur in the lower chromosphere. Non-LTE inversions indicate a transition from heating concentrated around photospheric magnetic elements below log τ500 = -3 to a more space-filling and time-persistent heating above log τ500 = -4. The inferred gas temperature at log τ500 = -3.8 correlates strongly with the total linear polarization in the Ca II 854.2 nm line, suggesting that that the heating rate correlates with the strength of the horizontal magnetic field in the low chromosphere.

Movies attached to Figs. 1 and 4 are available at https://www.aanda.org/ Title: Three-dimensional modeling of the Ca II H and K lines in the solar atmosphere Authors: Bjørgen, Johan P.; Sukhorukov, Andrii V.; Leenaarts, Jorrit; Carlsson, Mats; de la Cruz Rodríguez, Jaime; Scharmer, Göran B.; Hansteen, Viggo H. Bibcode: 2018A&A...611A..62B Altcode: 2017arXiv171201045B Context. CHROMIS, a new imaging spectrometer at the Swedish 1-m Solar Telescope (SST), can observe the chromosphere in the H and K lines of Ca II at high spatial and spectral resolution. Accurate modeling as well as an understanding of the formation of these lines are needed to interpret the SST/CHROMIS observations. Such modeling is computationally challenging because these lines are influenced by strong departures from local thermodynamic equilibrium, three-dimensional radiative transfer, and partially coherent resonance scattering of photons. Aim. We aim to model the Ca II H and K lines in 3D model atmospheres to understand their formation and to investigate their diagnostic potential for probing the chromosphere.
Methods: We model the synthetic spectrum of Ca II using the radiative transfer code Multi3D in three different radiation-magnetohydrodynamic model atmospheres computed with the Bifrost code. We classify synthetic intensity profiles according to their shapes and study how their features are related to the physical properties in the model atmospheres. We investigate whether the synthetic data reproduce the observed spatially-averaged line shapes, center-to-limb variation and compare this data with SST/CHROMIS images.
Results: The spatially-averaged synthetic line profiles show too low central emission peaks, and too small separation between the peaks. The trends of the observed center-to-limb variation of the profiles properties are reproduced by the models. The Ca II H and K line profiles provide a temperature diagnostic of the temperature minimum and the temperature at the formation height of the emission peaks. The Doppler shift of the central depression is an excellent probe of the velocity in the upper chromosphere. Title: Intermittent Reconnection and Plasmoids in UV Bursts in the Low Solar Atmosphere Authors: Rouppe van der Voort, L.; De Pontieu, B.; Scharmer, G. B.; de la Cruz Rodríguez, J.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Guo, L. J.; Jafarzadeh, S.; Pereira, T. M. D.; Hansteen, V. H.; Carlsson, M.; Vissers, G. Bibcode: 2017ApJ...851L...6R Altcode: 2017arXiv171104581R Magnetic reconnection is thought to drive a wide variety of dynamic phenomena in the solar atmosphere. Yet, the detailed physical mechanisms driving reconnection are difficult to discern in the remote sensing observations that are used to study the solar atmosphere. In this Letter, we exploit the high-resolution instruments Interface Region Imaging Spectrograph and the new CHROMIS Fabry-Pérot instrument at the Swedish 1-m Solar Telescope (SST) to identify the intermittency of magnetic reconnection and its association with the formation of plasmoids in so-called UV bursts in the low solar atmosphere. The Si IV 1403 Å UV burst spectra from the transition region show evidence of highly broadened line profiles with often non-Gaussian and triangular shapes, in addition to signatures of bidirectional flows. Such profiles had previously been linked, in idealized numerical simulations, to magnetic reconnection driven by the plasmoid instability. Simultaneous CHROMIS images in the chromospheric Ca II K 3934 Å line now provide compelling evidence for the presence of plasmoids by revealing highly dynamic and rapidly moving brightenings that are smaller than 0.″2 and that evolve on timescales of the order of seconds. Our interpretation of the observations is supported by detailed comparisons with synthetic observables from advanced numerical simulations of magnetic reconnection and associated plasmoids in the chromosphere. Our results highlight how subarcsecond imaging spectroscopy sensitive to a wide range of temperatures combined with advanced numerical simulations that are realistic enough to compare with observations can directly reveal the small-scale physical processes that drive the wide range of phenomena in the solar atmosphere. Title: SST/CHROMIS: a new window to the solar chromosphere Authors: Scharmer, Goran Bibcode: 2017psio.confE..85S Altcode: No abstract at ADS Title: Recent results and future DMs for astronomy and for space applications at CILAS Authors: Sinquin, Jean-Christophe; Bastard, Arnaud; Beaufort, Emmanuel; Berkefeld, Thomas; Cadiergues, Laurent; Costes, Vincent; Cousty, Raphaël.; Dekhtiar, Charles; Di Gesu, Frédéric; Gilbert, Xavier; Grèzes-Besset, Catherine; Groeninck, Denis; Hartung, Markus; Krol, Hélène; Moreau, Aurélien; Morin, Pierre; Pagès, Hubert; Palomo, Richard; Scharmer, Göran; Soltau, Dirk; Véran, Jean-Pierre Bibcode: 2014SPIE.9148E..0GS Altcode: We present recent experimental results obtained with CILAS deformable mirrors (DMs) or demonstration prototypes in solar and night-time astronomy (with ground-based telescopes) as well as observation of the Earth (with space telescopes). These important results have been reached thanks to CILAS technology range composed of monomorph and piezostack deformable mirrors, drivers and optical coatings. For instance, the monomorph technology, due to a simple architecture can offer a very good reliability for space applications. It can be used for closed or open loop correction of the primary mirror deformation (thermal and polishing aberrations, absence of gravity). It can also allow a real-time correction of wavefront aberrations introduced by the atmosphere up to relatively high spatial and temporal frequencies for ground-based telescopes. The piezostack technology is useful for very high order correction at high frequency and under relatively low operational temperature (down to -30°C), which is required for future Extremely Large Telescopes (ELTs). This wide range of applications is exposed through recent examples of DMs performances in operation and results obtained with breadboards, allowing promising DMs for future needs. Title: Response to "Stray-light correction in 2D spectroscopy" by R. Schlichenmaier and M. Franz Authors: Scharmer, G. B. Bibcode: 2014A&A...561A..31S Altcode: 2013arXiv1310.4630S We discuss a recent paper by Schlichenmaier & Franz (SF; 2013, A&A, 555, A84), in which the claim is made that the penumbral dark downflows detected for the first time with the Swedish 1-m Solar Telescope (SST) by Scharmer et al. and Joshi et al. could be produced by overcompensation for straylight. We show that the analysis of SF is fundamentally flawed, because it ignores the constraints on the strength of such straylight from 3D convection simulations and on the spatial extent of the straylight point spread function from the measured minimum intensity in the sunspot umbra. Furthermore, we show that the claim made by SF, that the spatial straylight of Hinode is less than 10%, is false. We conclude that the analysis of SF is of no relevance in relation to the straylight compensation method applied to the SST data. Title: Opposite polarity field with convective downflow and its relation to magnetic spines in a sunspot penumbra Authors: Scharmer, G. B.; de la Cruz Rodriguez, J.; Sütterlin, P.; Henriques, V. M. J. Bibcode: 2013A&A...553A..63S Altcode: 2012arXiv1211.5776S We discuss NICOLE inversions of Fe i 630.15 nm and 630.25 nm Stokes spectra from a sunspot penumbra recorded with the CRISP imaging spectropolarimeter on the Swedish 1-m Solar Telescope at a spatial resolution close to 0.15 arcsec. We report on narrow, radially extended lanes of opposite polarity field, located at the boundaries between areas of relatively horizontal magnetic field (the intra-spines) and much more vertical field (the spines). These lanes harbor convective downflows of about 1 km s-1. The locations of these downflows close to the spines agree with predictions from the convective gap model (the "gappy penumbra") proposed six years ago, and more recent three-dimensional magnetohydrodynamic simulations. We also confirm the existence of strong convective flows throughout the entire penumbra, showing the expected correlation between temperature and vertical velocity, and having vertical root mean square velocities of about 1.2 km s-1. Title: SST/CRISP observations of convective flows in a sunspot penumbra Authors: Scharmer, G. B.; Henriques, V. M. J. Bibcode: 2012A&A...540A..19S Altcode: 2011arXiv1109.1301S Context. Recent discoveries of intensity correlated downflows in the interior of a sunspot penumbra provide direct evidence for overturning convection, adding to earlier strong indications of convection from filament dynamics observed far from solar disk center, and supporting recent simulations of sunspots.
Aims: Using spectropolarimetric observations obtained at a spatial resolution approaching 0.1 arcsec with the Swedish 1-m Solar Telescope (SST) and its spectropolarimeter CRISP, we investigate whether the convective downflows recently discovered in the C i line at 538.03 nm can also be detected in the wings of the Fe i line at 630.15 nm.
Methods: We make azimuthal fits of the measured LOS velocities in the core and wings of the 538 nm and 630 nm lines to disentangle the vertical and horizontal flows. To investigate how these depend on the continuum intensity, the azimuthal fits are made separately for each intensity bin. By using spatially high-pass filtered measurements of the LOS component of the magnetic field, the flow properties are determined separately for magnetic spines (relatively strong and vertical field) and inter-spines (weaker and more horizontal field).
Results: The dark convective downflows discovered recently in the 538.03 nm line are evident also in the 630.15 nm line, and have similar strength. This convective signature is the same in spines and inter-spines. However, the strong radial (Evershed) outflows are found only in the inter-spines.
Conclusions: At the spatial resolution of the present SST/CRISP data, the small-scale intensity pattern seen in continuum images is strongly related to a convective up/down flow pattern that exists everywhere in the penumbra. Earlier failures to detect the dark convective downflows in the interior penumbra can be explained by inadequate spatial resolution in the observed data. Title: Sources of straylight in the post-focus imaging instrumentation of the Swedish 1-m Solar Telescope Authors: Löfdahl, M. G.; Scharmer, G. B. Bibcode: 2012A&A...537A..80L Altcode: 2011arXiv1110.2663L Context. Recently measured straylight point spread functions (PSFs) in Hinode/SOT make granulation contrast in observed data and synthetic magnetohydrodynamic (MHD) data consistent. Data from earthbound telescopes also need accurate correction for straylight and fixed optical aberrations.
Aims: We aim to develop a method for measuring straylight in the post-focus imaging optics of the Swedish 1-m Solar Telescope (SST).
Methods: We removed any influence from atmospheric turbulence and scattering by using an artificial target. We measured integrated straylight from three different sources in the same data: ghost images caused by reflections in the near-detector optics, PSFs corresponding to wavefront aberrations in the optics by using phase diversity, and extended scattering PSF wings of unknown origin by fitting to a number of different kernels. We performed the analysis separately in the red beam and the blue beam.
Results: Wavefront aberrations, which possibly originate in the bimorph mirror of the adaptive optics, are responsible for a wavelength-dependent straylight of 20-30% of the intensity in the form of PSFs with 90% of the energy contained within a radius of 0.6 arcsec. There are ghost images that contribute at the most a few percent of straylight. The fraction of other sources of scattered light from the post-focus instrumentation of the SST is only ~10-3 of the recorded intensity. This contribution has wide wings with a FWHM ~16'' in the blue and ~34'' in the red.
Conclusions: The present method seems to work well for separately estimating wavefront aberrations and the scattering kernel shape and fraction. Ghost images can be expected to remain at the same level for solar observations. The high-order wavefront aberrations possibly caused by the AO bimorph mirror dominate the measured straylight but are likely to change when imaging the Sun. We can therefore make no firm statements about the origin of straylight in SST data, but strongly suspect wavefront aberrations to be the dominant source. Title: Detection of Convective Downflows in a Sunspot Penumbra Authors: Scharmer, G. B.; Henriques, V. M. J.; Kiselman, D.; de la Cruz Rodríguez, J. Bibcode: 2011Sci...333..316S Altcode: The fine structure and dynamics of sunspots and the strong outflow in their outer filamentary part—the penumbra—have puzzled astronomers for more than a century. Recent theoretical models and three-dimensional numerical simulations explain the penumbral filaments and their radiative energy output as the result of overturning convection. Here, we describe the detection of ubiquitous, relatively dark downward flows of up to 1 kilometer per second (km/s) in the interior penumbra, using imaging spectropolarimetric data from the Swedish 1-meter Solar Telescope. The dark downflows are omnipresent in the interior penumbra, distinguishing them from flows in arched flux tubes, and are associated with strong (3 to 3.5 km/s) radial outflows. They are thus part of a penumbral convective flow pattern, with the Evershed flow representing the horizontal component of that convection. Title: Small-scale convection signatures associated with a strong plage solar magnetic field Authors: Narayan, G.; Scharmer, G. B. Bibcode: 2010A&A...524A...3N Altcode: 2010arXiv1007.4673N Context. Solar convection in a strong plage, in which the magnetic field is vertical and strong over extended regions, but much weaker than in the umbrae of large sunspots, has so far not been well studied. This has been mostly because of a lack of spectropolarimetric data at adequate spatial resolution. The combination of a large solar telescope, such as the Swedish 1-m Solar Telescope, adaptive optics, powerful image reconstruction techniques, and a high-fidelity imaging spectropolarimeter is, however, capable of producing such data.
Aims: In this work, we study and quantify the properties of strong-field small-scale convection and compare these observed properties with those predicted by numerical simulations.
Methods: We analyze spectropolarimetric 630.25 nm data from a unipolar ephemeral region near the Sun center. We use line-of-sight velocities and magnetic field measurements obtained with Milne-Eddington inversion techniques along with measured continuum intensities and Stokes V amplitude asymmetry at a spatial resolution of 0.15 arcsec to establish statistical relations between the measured quantities. We also study these properties for different types of distinct magnetic features, such as micropores, bright points, ribbons, flowers, and strings.
Results: We present the first direct observations of a small-scale granular magneto-convection pattern within extended regions of a strong (more than 600 G on average) magnetic field. Along the boundaries of the flux concentrations, we see mostly downflows and asymmetric Stokes V profiles, consistent with synthetic line profiles calculated from MHD simulations. We note the frequent occurrence of bright downflows along these boundaries. In the interior of the flux concentrations, we observe an up/down flow pattern that we associate with small-scale magnetoconvection, appearing similar to that of field-free granulation but with scales 4 times smaller. Measured rms velocities are 70% of those of nearby field-free granulation, even though the average radiative flux is not lower than that of the quiet Sun. The interiors of these flux concentrations are dominated by upflows. Title: Striation and convection in penumbral filaments Authors: Spruit, H. C.; Scharmer, G. B.; Löfdahl, M. G. Bibcode: 2010A&A...521A..72S Altcode: 2010arXiv1008.0932S Observations with the 1-m Swedish Solar Telescope of the flows seen in penumbral filaments are presented. Time sequences of bright filaments show overturning motions strikingly similar to those seen along the walls of small isolated structures in the active regions. The filaments show outward propagating striations with inclination angles suggesting that they are aligned with the local magnetic field. We interpret it as the equivalent of the striations seen in the walls of small isolated magnetic structures. Their origin is then a corrugation of the boundary between an overturning convective flow inside the filament and the magnetic field wrapping around it. The outward propagation is a combination of a pattern motion due to the downflow observed along the sides of bright filaments, and the Evershed flow. The observed short wavelength of the striation argues against the existence of a dynamically significant horizontal field inside the bright filaments. Its intensity contrast is explained by the same physical effect that causes the dark cores of filaments, light bridges and “canals”. In this way striation represents an important clue to the physics of penumbral structure and its relation with other magnetic structures on the solar surface. We put this in perspective with results from the recent 3-D radiative hydrodynamic simulations.

4 movies are only available in electronic form at http://www.aanda.org Title: High-order aberration compensation with multi-frame blind deconvolution and phase diversity image restoration techniques Authors: Scharmer, G. B.; Löfdahl, M. G.; van Werkhoven, T. I. M.; de la Cruz Rodríguez, J. Bibcode: 2010A&A...521A..68S Altcode: 2010arXiv1007.1236S Context. For accurately measuring intensities and determining magnetic field strengths of small-scale solar (magnetic) structure, knowledge of and compensation for the point spread function is crucial. For images recorded with the Swedish 1-meter Solar Telescope (SST), restoration with multi-frame blind deconvolution (MFBD) and joint phase diverse speckle (JPDS) methods lead to remarkable improvements in image quality but granulation contrasts that are too low, indicating additional stray light.
Aims: We propose a method to compensate for stray light from high-order atmospheric aberrations not included in MFBD and JPDS processing.
Methods: To compensate for uncorrected aberrations, a reformulation of the image restoration process is proposed that allows the average effect of hundreds of high-order modes to be compensated for by relying on Kolmogorov statistics for these modes. The applicability of the method requires simultaneous measurements of Fried's parameter r0. The method is tested with simulations as well as real data and extended to include compensation for conventional stray light.
Results: We find that only part of the reduction of granulation contrast in SST images is due to uncompensated high-order aberrations. The remainder is still unaccounted for and attributed to stray light from the atmosphere, the telescope with its re-imaging system and to various high-altitude seeing effects.
Conclusions: We conclude that statistical compensation of high-order modes is a viable method to reduce the loss of contrast occurring when a limited number of aberrations is explicitly compensated for with MFBD and JPDS processing. We show that good such compensation is possible with only 10 recorded frames. The main limitation of the method is that already MFBD and JPDS processing introduces high-order compensation that, if not taken into account, can lead to over-compensation. Title: Site-seeing measurements for the European Solar Telescope Authors: Berkefeld, Th.; Bettonvil, F.; Collados, M.; López, R.; Martín, Y.; Peñate, J.; Pérez, A.; Scharmer, G. B.; Sliepen, G.; Soltau, D.; Waldmann, T. A.; van Werkhoven, T. Bibcode: 2010SPIE.7733E..4IB Altcode: 2010SPIE.7733E.141B Seeing measurements are crucial for the optimum design of (multi-conjugate) adaptive optics systems operating at solar telescopes. For the design study of the 4-meter European Solar Telescope, to be located in the Canary Islands, several instruments have been constructed and operated, at the Observatorio del Roque de los Muchachos (La Palma) and at the Observatorio del Teide (Tenerife), to measure the properties of the ground layer and medium-high altitude turbulence. Several units of short (42.34 cm) and two long (323.06 cm) scintillometer bars are, or are to be, installed at both observatories. In addition to them, two wide-field wavefront sensors will be attached to the optical beams of the Swedish tower, on La Palma, and of the German VTT, on Tenerife, simultaneously used with the normal operation of the telescopes. These wavefront sensors are of Shack-Hartmann type with ~1 arcminute field of view. In this contribution, the instruments setup and their performance are described. Title: Adaptive optics and MCAO for the 4-m European Solar Telescope EST Authors: Soltau, D.; Berkefeld, T.; Sánchez Capuchino, J.; Collados Vera, M.; Del Moro, D.; Löfdahl, M.; Scharmer, G. Bibcode: 2010SPIE.7736E..0US Altcode: 2010SPIE.7736E..27S A consortium of more than 20 European solar physics institution from 15 different countries is conducting a design study for a 4 m class solar telescope which shall be situated at the Canary Islands. In this paper we introduce the AO and MCAO design concept for EST. A ground layer deformable mirror is combined with an arrangement of four deformable layer mirrors. A combination of Shack-Hartmann wave front sensors with wide and narrow fields of view is used to control the system and to achieve a corrected field of view of one arcmin. Title: S-DIMM+ height characterization of day-time seeing using solar granulation Authors: Scharmer, G. B.; van Werkhoven, T. I. M. Bibcode: 2010A&A...513A..25S Altcode: 2010arXiv1002.3151S Context. To evaluate site quality and to develop multi-conjugative adaptive optics systems for future large solar telescopes, characterization of contributions to seeing from heights up to at least 12 km above the telescope is needed.
Aims: We describe a method for evaluating contributions to seeing from different layers along the line-of-sight to the Sun. The method is based on Shack Hartmann wavefront sensor data recorded over a large field-of-view with solar granulation and uses only measurements of differential image displacements from individual exposures, such that the measurements are not degraded by residual tip-tilt errors.
Methods: The covariance of differential image displacements at variable field angles provides a natural extension of the work of Sarazin and Roddier to include measurements that are also sensitive to the height distribution of seeing. By extending the numerical calculations of Fried to include differential image displacements at distances much smaller and much larger than the subaperture diameter, the wavefront sensor data can be fitted to a well-defined model of seeing. The resulting least-squares fit problem can be solved with conventional methods. The method is tested with simple simulations and applied to wavefront data from the Swedish 1-m Solar Telescope on La Palma, Spain.
Results: We show that good inversions are possible with 9-10 layers, three of which are within the first 1.5 km, and a maximum distance of 16-30 km, but with poor height resolution in the range 10-30 km.
Conclusions: We conclude that the proposed method allows good measurements when Fried's parameter r0 is larger than about 7.5 cm for the ground layer and that these measurements should provide valuable information for site selection and multi-conjugate development for the future European Solar Telescope. A major limitation is the large field of view presently used for wavefront sensing, leading to uncomfortably large uncertainties in r0 at 30 km distance. Title: Convection and the Origin of Evershed Flows Authors: Nordlund, Å.; Scharmer, G. B. Bibcode: 2010ASSP...19..243N Altcode: 2009arXiv0905.0918N; 2010mcia.conf..243N Numerical simulations have by now revealed that the fine scale structure of the penumbra in general and the Evershed effect in particular is due to overturning convection, mainly confined to gaps with strongly reduced magnetic field strength. The Evershed flow is the radial component of the overturning convective flow visible at the surface. It is directed outwards - away from the umbra - because of the broken symmetry due to the inclined magnetic field. The dark penumbral filament cores visible at high resolution are caused by the "cusps" in the magnetic field that form above the gaps. Still remaining to be established are the details of what determines the average luminosity of penumbrae, the widths, lengths, and filling factors of penumbral filaments, and the amplitudes and filling factors of the Evershed flow. These are likely to depend at least partially also on numerical aspects such as limited resolution and model size, but mainly on physical properties that have not yet been adequately determined or calibrated, such as the plasma beta profile inside sunspots at depth and its horizontal profile, the entropy of ascending flows in the penumbra, etc. Title: Recent Evidence for Convection in Sunspot Penumbrae Authors: Scharmer, Göran B. Bibcode: 2009SSRv..144..229S Altcode: Whereas penumbral models during the last 15 years have been successful in explaining Evershed flows and magnetic field inclination variations in terms of flux tubes, the lack of contact between these models and a convective process needed to explain the penumbral radiative heat flux has been disturbing. We report on recent observational and theoretical evidence that challenge flux tube interpretations and conclude that the origin of penumbral filamentary structure is overturning convection. Title: Recent Evidence for Convection in Sunspot Penumbrae Authors: Scharmer, Göran B. Bibcode: 2009odsm.book..229S Altcode: Whereas penumbral models during the last 15 years have been successful in explaining Evershed flows and magnetic field inclination variations in terms of flux tubes, the lack of contact between these models and a convective process needed to explain the penumbral radiative heat flux has been disturbing. We report on recent observational and theoretical evidence that challenge flux tube interpretations and conclude that the origin of penumbral filamentary structure is overturning convection. Title: CRISP Spectropolarimetric Imaging of Penumbral Fine Structure Authors: Scharmer, G. B.; Narayan, G.; Hillberg, T.; de la Cruz Rodriguez, J.; Löfdahl, M. G.; Kiselman, D.; Sütterlin, P.; van Noort, M.; Lagg, A. Bibcode: 2008ApJ...689L..69S Altcode: 2008arXiv0806.1638S We discuss penumbral fine structure in a small part of a pore, observed with the CRISP imaging spectropolarimeter at the Swedish 1-m Solar Telescope (SST), close to its diffraction limit of 0.16''. Milne-Eddington inversions applied to these Stokes data reveal large variations of field strength and inclination angle over dark-cored penumbral intrusions and a dark-cored light bridge. The mid-outer part of this penumbra structure shows ~0.3'' wide spines, separated by ~1.6'' (1200 km) and associated with 30° inclination variations. Between these spines, there are no small-scale magnetic structures that easily can be identified with individual flux tubes. A structure with nearly 10° more vertical and weaker magnetic field is seen midway between two spines. This structure is cospatial with the brightest penumbral filament, possibly indicating the location of a convective upflow from below. Title: Recent evidence for convection in sunspot penumbrae Authors: Scharmer, G. B. Bibcode: 2008PhST..133a4015S Altcode: 2008arXiv0812.3971S Whereas penumbral models during the last 15 years have appeared successful in explaining Evershed flows and magnetic field inclination variations in terms of flux tubes, the lack of connection between these models and a convective process to explain the penumbral radiative heat flux has been disturbing. We report on recent observational and theoretical evidence that challenge these flux tube interpretations and instead suggest overturning convection as the origin of the penumbral filamentary structure. Title: Spectropolarimetry of Sunspots at 0.16 ARCSEC resolution Authors: Scharmer, G.; Henriques, V.; Hillberg, T.; Kiselman, D.; Löfdahl, M.; Narayan, G.; Sütterlin, P.; van Noort, M.; de la Cruz Rodríguez, J. Bibcode: 2008ESPM...12..2.5S Altcode: We present first observations of sunspots with the imaging spectropolarimeter CRISP, recently installed at the Swedish 1-m Solar Telescope (SST) on La Palma. This spectropolarimeter is based on a high-fidelity dual Fabry-Perot filter system.

Two liquid crystals and a polarizing beam splitter are used to reduce seeing induced I,Q,U,V crosstalk by simultaneously recording images with two 1kx1k back-illuminated Sarnoff CCD's. A third CCD simultaneously records broadband images through the pre-filter of the FPI filter system, allowing image reconstruction and co-alignment of images of different polarization states and at different wavelengths in Zeeman sensitive spectral lines.

The first data, recorded in April 2008, demonstrate the capability of this system to record high cadence, high S/N polarimetric data with a spatial resolution at or close to the diffraction limit of the SST at 630 nm, 0.16 arcsec. We discuss the analysis of first spectropolarimetric data for sunspots, based on Milne-Eddington inversion techniques. Title: SST/CRISP Magnetometry with Fe I 630.2 nm Authors: Narayan, G.; Scharmer, G. B.; Hillberg, T.; Lofdahl, M.; van Noort, M.; Sutterlin, P.; Lagg, A. Bibcode: 2008ESPM...122.120N Altcode: We present recent full Stokes observations in the Fe I 630.2 nm line with CRISP, an imaging spectropolarimeter at the Swedish 1-m Solar Telescope (SST). The observations reach a spatial resolution of 0".16, close to the diffraction limit of the SST, representing a major improvement over any past ground based or space based spectropolarimetric data. We describe the data acquisition and reduction methods and present results of Milne-Eddington(ME) inversions applied on observations of plage. Title: Convection and the Origin of Evershed Flows in Sunspot Penumbrae Authors: Scharmer, G. B.; Nordlund, Å.; Heinemann, T. Bibcode: 2008ApJ...677L.149S Altcode: 2008arXiv0802.1927S We discuss a numerical 3D radiation-MHD simulation of penumbral fine structure in a small sunspot. This simulation shows the development of short filamentary structures with horizontal flows, similar to observed Evershed flows, and an inward propagation of these structures at a speed compatible with observations. Although the lengths of these filaments are much shorter than observed, we conjecture that this simulation qualitatively reproduces the mechanisms responsible for filament formation and Evershed flows in penumbrae. We conclude that the Evershed flow represents the horizontal-flow component of overturning convection in gaps with strongly reduced field strength. The top of the flow is always directed outward—away from the umbra—because of the broken symmetry due to the inclined magnetic field. Upflows occur in the inner parts of the gaps and most of the gas turns over radially (outward and sideways), and descends back down again. The ascending, cooling, and overturning flow tends to bend magnetic field lines down, forcing a weakening of the field that makes it easier for gas located in an adjacent layer—farther in—to initiate a similar sequence of motion, aided by lateral heating, thus causing the inward propagation of the filament. Title: MHD Simulations of Penumbra Fine Structure Authors: Heinemann, T.; Nordlund, Å.; Scharmer, G. B.; Spruit, H. C. Bibcode: 2007ApJ...669.1390H Altcode: 2006astro.ph.12648H We present the results of numerical 3D magnetohydrodynamic (MHD) simulations with radiative energy transfer of fine structure in a small sunspot of about 4 Mm width. The simulations show the development of filamentary structures and flow patterns that are, except for the lengths of the filaments, very similar to those observed. The filamentary structures consist of gaps with reduced field strength relative to their surroundings. Calculated synthetic images show dark cores like those seen in the observations; the dark cores are the result of a locally elevated τ=1 surface. The magnetic field in these cores is weaker and more horizontal than for adjacent brighter structures, and the cores support a systematic outflow. Accompanying animations show the migration of the dark-cored structures toward the umbra, and fragments of magnetic flux that are carried away from the spot by a large-scale ``moat flow.'' We conclude that the simulations are in qualitative agreement with observed penumbra filamentary structures, Evershed flows, and moving magnetic features. Title: What are 'Faculae'? Authors: Berger, T. E.; Title, A. M.; Tarbell, T.; Rouppe van der Voort, L.; Löfdahl, M. G.; Scharmer, G. B. Bibcode: 2007ASPC..369..103B Altcode: We present very high resolution filtergram and magnetogram observations of solar faculae taken at the Swedish 1-meter Solar Telescope (SST) on La Palma. Three datasets with average line-of-sight angles of 16, 34, and 53 degrees are analyzed. The average radial extent of faculae is at least 400~km. In addition we find that contrast versus magnetic flux density is nearly constant for faculae at a given disk position. These facts and the high resolution images and movies reveal that faculae are not the interiors of small flux tubes - they are granules seen through the transparency caused by groups of magnetic elements or micropores ``in front of'' the granules. Previous results which show a strong dependency of facular contrast on magnetic flux density were caused by bin-averaging of lower resolution data leading to a mixture of the signal from bright facular walls and the associated intergranular lanes and micropores. The findings are relevant to studies of total solar irradiance (TSI) that use facular contrast as a function of disk position and magnetic field in order to model the increase in TSI with increasing sunspot activity. Title: Recent High Resolution Observations and Interpretations of Sunspot Fine Structure Authors: Scharmer, G. B.; Langhans, K.; Kiselman, D.; Löfdahl, M. G. Bibcode: 2007ASPC..369...71S Altcode: We review analyses made of highly resolved filtergrams, magnetograms and Dopplergrams of sunspots, recorded with the Swedish 1-meter Solar Telescope (SSTSST) on La Palma. Dark cores in penumbral filaments are shown to be directly linked to peripheral umbral dots and to dark lanes in light bridges, suggesting similar or related underlying physics. The visibility of dark cores is found to depend strongly on the azimuth angle already for spots located at small heliocentric distances. It is shown that dark cores are clearly visible close to the center of the Ca II H line, formed approximately 150--200~km above the photosphere. We conclude that the τ = 1 layer of dark-cored filaments outlines a strongly warped surface, consistent with the finding that the magnetic field strength is strongly reduced in dark cores. We show that several properties of dark-cored filaments derived from SSTSST data are consistent with results of inversions of low-resolution Stokes spectra, but also find important discrepancies with the interpretation that penumbral filaments can be identified with flux tubes. Our data are consistent with the model proposed by Spruit & Scharmer (2006), explaining dark cores as signatures of field-free convection occurring just below the visible surface of the penumbra. We discuss recent simulations of light bridges and umbral dots, providing additional support to that model. Title: Observations of dark-cored filaments in sunspot penumbrae Authors: Langhans, K.; Scharmer, G. B.; Kiselman, D.; Löfdahl, M. G. Bibcode: 2007A&A...464..763L Altcode: Context: The recent discovery of dark-cored penumbral filaments suggests that we are resolving the building blocks of sunspot penumbrae. Their properties are largely unknown but provide important clues to understanding penumbral fine structure.
Aims: Our observations provide new constraints for the different scenarios put forward to explain the structure of sunspot penumbrae.
Methods: We present an analysis of dark-cored penumbral filaments, based on intensity filtergrams (G-band, continuum and Ca II H line wing), magnetograms and Dopplergrams, obtained at heliocentric distances between 15° and 55°.
Results: In general, the visibility of dark cores degrades with increasing heliocentric distance. Based on Ca II H wing images we conclude that this is due to a geometrical 3D-effect and not due to a simple formation height effect. Only in the center-side penumbra are dark-cored filaments visible at all observed heliocentric distances. We observe that dark-cored filaments frequently split in the umbra, forming a Y-shape that disappears after a few minutes, leaving a shortened filamentary structure and a bright dot in the umbra. The dark-cored filaments have life times ≥ 90 min. The dark cores are related to a much weaker and a more horizontal magnetic field than their lateral brightenings. Where the dark-cored filaments appear in the umbra, the magnetic field is inclined by 40° with respect to the solar surface normal for both the dark core and the bright edges. With increasing distance from the umbra, the magnetic field inclination in the dark cores increases rapidly within a few thousand km. Both the magnetic field strength and inclination in the lateral brightenings show very small variations with spot-center radial distance. The velocity field possesses a strong horizontal component within the dark cores. The absolute line-of-sight (LOS) velocity is larger within the dark cores than in their lateral brightenings. The Evershed flow apparently is present primarily in the dark cores. Title: Ca IIH line wing images of sunspot penumbrae recorded with the Swedish 1-m Solar Telescope Authors: Narayan, G.; van Noort, M. J.; Scharmer, G. Bibcode: 2007msfa.conf..213N Altcode: We present recent Ca IIH images of sunspot penumbrae taken with the Swedish 1m Solar Telescope (SST) during June-July 2006 and restored to a resolution close to 0".1. Images were recorded at different Ca IIH line positions using one tunable filter, one fixed wing filter and a wide band quasi-continuum filter. Apart from the images recorded at line center (and formed under non-LTE conditions), this provides temperature information from approximately the first 200-300 km above the photosphere. Title: Magnetostatic penumbra models with field-free gaps Authors: Scharmer, G. B.; Spruit, H. C. Bibcode: 2006A&A...460..605S Altcode: 2006astro.ph..9130S We present numerical 2D magnetostatic models for sunspot penumbrae consisting of radially aligned field-free gaps in a potential magnetic field, as proposed by Spruit & Scharmer (2006, A&A, 447, 343). The shape of the gaps and the field configurations around them are computed consistently from the condition of magnetostatic pressure balance between the gap and the magnetic field. The results show that field-free gaps in the inner penumbra are cusp-shaped and bounded by a magnetic field inclined by about 70° from the vertical. Here, the magnetic component has a Wilson depression on the order 200-300 km relative to the top of the field-free gap; the gaps should thus appear as noticeably elevated features. This structure explains the large variations in field strength in the inner penumbra inferred from magnetograms and two-component inversions, and the varying appearance of the inner penumbra with viewing angle. In the outer penumbra, on the other hand, the gaps are flat-topped with a horizontal magnetic field above the middle of the gap. The magnetic field has large inclination variations horizontally, but only small fluctuations in field strength, in agreement with observations. Title: Rapid Temporal Variability of Faculae: High-Resolution Observations and Modeling Authors: De Pontieu, B.; Carlsson, M.; Stein, R.; Rouppe van der Voort, L.; Löfdahl, M.; van Noort, M.; Nordlund, Å.; Scharmer, G. Bibcode: 2006ApJ...646.1405D Altcode: We present high-resolution G-band observations (obtained with the Swedish 1 m Solar Telescope) of the rapid temporal variability of faculae, which occurs on granular timescales. By combining these observations with magnetoconvection simulations of a plage region, we show that much of this variability is not intrinsic to the magnetic field concentrations that are associated with faculae, but rather a phenomenon associated with the normal evolution and splitting of granules. We also show examples of facular variability caused by changes in the magnetic field, with movies of dynamic behavior of the striations that dominate much of the facular appearance at 0.1" resolution. Examples of these dynamics include merging, splitting, rapid motion, apparent fluting, and possibly swaying. Title: Large bearings with incorporated gears, high stiffness, and precision for the Swedish Solar Telescope (SST) on La Palma Authors: Hammerschlag, Robert H.; Bettonvil, Felix C. M.; Jägers, Aswin P. L.; Scharmer, Göran B. Bibcode: 2006SPIE.6273E..15H Altcode: 2006SPIE.6273E..34H The 1-meter Swedish Solar Telescope (SST) obtains images of the solar surface with an unprecedented resolution of 0.1 arcsec. It consists of a relatively slender tower with on top only the vacuum turret for reflecting downward the solar beam and no protective dome. This is a favourable situation to get good local seeing. Just in the case of some wind, seeing is best for daytime observations, therefore the precision bearings and drives of the elevation- and azimuth axis of the turret have to be stiff against wind. This requires line contact between the meshing teeth of the large gear wheel and the pinion. High preload forces to achieve line contact are not allowed because of appearing stick-slip effects. To reduce the risk on stick-slip a special design of the teeth for high stiffness combined with low friction and smooth transition from one tooth to the next was made. Furthermore, extreme precision in the fabrication was pursued such that relatively small contact forces give already line contact. This required a special order of the successive fabrication steps of the combination of bearing and gear teeth. An additional problem was the relatively thin section of the bearings required for a compact turret construction, needed for best local seeing and minimum wind load. Solutions for all these problems will be discussed. For the large gears the exceptional good DIN quality class 4 for the pitch precision and straightness plus direction of the teeth faces was achieved. Title: Comments on the optimization of high resolution Fabry-Pérot filtergraphs Authors: Scharmer, G. B. Bibcode: 2006A&A...447.1111S Altcode: In this paper we present results of simulations of Fabry-Pérot (FPI) system performance that address two entirely separate aspects. The first concerns the image quality of FPIs used in telecentric optical setups. We show that the image degradation from phase errors found by von der Lühe & Kentischer (2000, A&AS, 146, 499) can largely be compensated by refocusing and that the major cause of image degradation is the pupil apodization discussed by Beckers (1998, A&AS, 120, 191). We also discuss the optimization of FPI systems, considering the effects of cavity errors on the homogeneity of the instrument function (transmission profile) across the FOV when two FPIs are combined in a telecentric reimaging system. Our conclusions from several numerical experiments are that telecentric FPI systems that use two or more FPIs with high (94-95%) reflectivities are likely to show large variations in the instrument profile across the FOV unless the cavity errors are significantly smaller than 2.0 nm. We show, that such homogeneity can be obtained at relatively low "cost" in terms of increased parasitic light levels by lowering the reflectivity of the FPI with the smallest cavity separation rather then lowering the reflectivity of both FPIs. We also demonstrate that the choice of cavity ratios has a strong impact on the homogeneity of the spectral transmission profile across the FOV and that double FPI systems with cavity ratios around 0.3 perform much better than at around 0.6. Title: Fine structure, magnetic field and heating of sunspot penumbrae Authors: Spruit, H. C.; Scharmer, G. B. Bibcode: 2006A&A...447..343S Altcode: 2005astro.ph..8504S We interpret penumbral filaments as due to convection in field-free, radially aligned gaps just below the visible surface of the penumbra, intruding into a nearly potential field above. This solves the classical discrepancy between the large heat flux and the low vertical velocities observed in the penumbra. The presence of the gaps causes strong small-scale fluctuations in inclination, azimuth angle and field strength. The field is nearly horizontal in a region around the cusp-shaped top of the gap, thereby providing an environment for Evershed flows. We identify this region with the recently discovered dark penumbral cores. Its darkness has the same cause as the dark lanes in umbral light-bridges, reproduced in numerical simulations by Nordlund & Stein (2005, in preparation). We predict that the large vertical and horizontal gradients of the magnetic field inclination and azimuth in the potential field model will produce the net circular polarization seen in observations. The model also explains the significant elevation of bright filaments above their surroundings. It predicts that dark areas in the penumbra are of two different kinds: dark filament cores containing the most inclined (horizontal) fields, and regions between bright filaments, containing the least inclined field lines. Title: Simulated Solar Plages Authors: Stein, R. F.; Carlsson, M.; de Pontieu, B.; Scharmer, G.; Nordlund, Å.; Benson, D. Bibcode: 2006apri.meet...30S Altcode: No abstract at ADS Title: Inclination of magnetic fields and flows in sunspot penumbrae Authors: Langhans, K.; Scharmer, G. B.; Kiselman, D.; Löfdahl, M. G.; Berger, T. E. Bibcode: 2005A&A...436.1087L Altcode: An observational study of the inclination of magnetic fields and flows in sunspot penumbrae at a spatial resolution of 0.2 arcsec is presented. The analysis is based on longitudinal magnetograms and Dopplergrams obtained with the Swedish 1-m Solar Telescope on La Palma using the Lockheed Solar Optical Universal Polarimeter birefringent filter. Data from two sunspots observed at several heliocentric angles between 12 ° and 39 ° were analyzed. We find that the magnetic field at the level of the formation of the Fe i-line wing (630.25 nm) is in the form of coherent structures that extend radially over nearly the entire penumbra giving the impression of vertical sheet-like structures. The inclination of the field varies up to 45 ° over azimuthal distances close to the resolution limit of the magnetograms. Dark penumbral cores, and their extensions into the outer penumbra, are prominent features associated with the more horizontal component of the magnetic field. The inclination of this dark penumbral component - designated B - increases outwards from approximately 40 ° in the inner penumbra such that the field lines are nearly horizontal or even return to the solar surface already in the middle penumbra. The bright component of filaments - designated A - is associated with the more vertical component of the magnetic field and has an inclination with respect to the normal of about 35 ° in the inner penumbra, increasing to about 60 ° towards the outer boundary. The magnetogram signal is lower in the dark component B regions than in the bright component A regions of the penumbral filaments. The measured rapid azimuthal variation of the magnetogram signal is interpreted as being caused by combined fluctuations of inclination and magnetic field strength. The Dopplergrams show that the velocity field associated with penumbral component B is roughly aligned with the magnetic field while component A flows are more horizontal than the magnetic field. The observations give general support to fluted and uncombed models of the penumbra. The long-lived nature of the dark-cored filaments makes it difficult to interpret these as evidence for convective exchange of flux tubes. Our observations are in broad agreement with the two component model of Bellot Rubi et al. (2003), but do not rule out the embedded flux tube model of Solanki & Montavon (1993). Title: Solar magnetic elements at 0.1 arcsec resolution. General appearance and magnetic structure Authors: Berger, T. E.; Rouppe van der Voort, L. H. M.; Löfdahl, M. G.; Carlsson, M.; Fossum, A.; Hansteen, V. H.; Marthinussen, E.; Title, A.; Scharmer, G. Bibcode: 2004A&A...428..613B Altcode: New observations of solar magnetic elements in a remnant active region plage near disk center are presented. The observations were obtained at the recently commissioned Swedish 1-m Solar Telescope on La Palma. We examine a single 430.5 nm G-band filtergram that resolves ∼70 km (0.1 arcsec) structures and find new forms of magnetic structures in this particular region. A cotemporal Ca II H-line image is used to examine the low-chromosphere of network elements. A cotemporal Fe I 630.25 nm magnetogram that resolves structures as small as 120 km (0.18 arcsec) FWHM with a flux sensitivity of approximately 130 Mx cm-2 quantifies the magnetic structure of the region. A Ni I 676.8 nm Dopplergram establishes relative velocity patterns associated with the network features with an accuracy of about 300 m s-1. We find that magnetic flux in this region as seen in both the magnetogram and the G-band image is typically structured into larger, amorphous, ``ribbons'' which are not resolved into individual flux tubes. The measured magnetic flux density in the ribbon structures ranges from 300 to 1500 Mx cm-2, the higher values occurring at localized concentrations embedded within the ribbons. The Dopplergram indicates relative downflows associated with all magnetic elements with some indication that higher downflows occur adjacent to the peak magnetic flux location. The mean absolute magnetic flux density of the remnant plage network is about 130 Mx cm-2; in the lowest flux regions of the field-of-view, the mean absolute flux density is approximately 60 Mx cm-2. Within these quiet regions we do not find evidence of pervasive kilo-gauss strength magnetic elements as seen in recent high resolution internetwork studies. In general, the observations confirm recent 3-dimensional numerical simulations which show that the magnetic field in high-density regions such as plage is concentrated in complex structures that are not generally composed of discrete magnetic flux tubes.

Appendices are only available in electronic form at http://www.edpsciences.org Title: Observational Manifestations of Solar Magnetoconvection: Center-to-Limb Variation Authors: Carlsson, Mats; Stein, Robert F.; Nordlund, Åke; Scharmer, Göran B. Bibcode: 2004ApJ...610L.137C Altcode: 2004astro.ph..6160C We present the first center-to-limb G-band images synthesized from high-resolution simulations of solar magnetoconvection. Toward the limb the simulations show ``hilly'' granulation with dark bands on the far side, bright granulation walls, and striated faculae, similar to observations. At disk center G-band bright points are flanked by dark lanes. The increased brightness in magnetic elements is due to their lower density compared with the surrounding intergranular medium. One thus sees deeper layers where the temperature is higher. At a given geometric height, the magnetic elements are cooler than the surrounding medium. In the G band, the contrast is further increased by the destruction of CH in the low-density magnetic elements. The optical depth unity surface is very corrugated. Bright granules have their continuum optical depth unity 80 km above the mean surface, the magnetic elements 200-300 km below. The horizontal temperature gradient is especially large next to flux concentrations. When viewed at an angle, the deep magnetic elements' optical surface is hidden by the granules and the bright points are no longer visible, except where the ``magnetic valleys'' are aligned with the line of sight. Toward the limb, the low density in the strong magnetic elements causes unit line-of-sight optical depth to occur deeper in the granule walls behind than for rays not going through magnetic elements, and variations in the field strength produce a striated appearance in the bright granule walls. Title: Three-Dimensional Structure of the Active Region Photosphere as Revealed by High Angular Resolution Authors: Lites, B. W.; Scharmer, G. B.; Berger, T. E.; Title, A. M. Bibcode: 2004SoPh..221...65L Altcode: Blue continuum images of active regions at ∼ 60° from the center of the solar disk obtained with the new Swedish 1-m Solar Telescope reveal heretofore unreported structure of the magnetized solar atmosphere. Perhaps the most striking aspect of these images is that, at an angular resolution of 0.12″, they show clearly the three-dimensional structure of the photosphere. In particular, the Wilson depression of the dark floors of pores is readily apparent. Conversely, the segmented structure of light bridges running through sunspots and pores reveal that light bridges are raised above the dark surroundings. The geometry of light bridges permits estimates of the height of their central (slightly darker) ridge: typically in the range 200-450 km. These images also clearly show that facular brightenings outside of sunspots and pores occur on the disk-center side of those granules just limbward of intergranular lanes that presumably harbor the associated plage magnetic flux. In many cases the brightening extends 0.5″ or more over those granules. Furthermore, a very thin, darker lane is often found just centerward of the facular brightening. We speculate that this feature is the signature of cool down flows that surround flux tubes in dynamical models. These newly recognized observational aspects of photospheric magnetic fields should provide valuable constraints for MHD models of the magnetized photosphere, and examination of those models as viewed from oblique angles is encouraged. Title: G-band Images from MHD Convection Simulations Authors: Stein, R. F.; Carlsson, M.; Nordlund, A.; Scharmer, G. Bibcode: 2004AAS...204.8804S Altcode: 2004BAAS...36..820S High resolution magneto-convection simulations are used to calculate G-band and G-continuum images at various angles. Towards the limb the simulations show "hilly" granulation, bright granulation walls, intergranular striations and "sticking out" G-band bright features similar to observations. The increased brightness in magnetic elements is due to their lower density compared with the surrounding intergranular medium, so that one sees deeper layers where the temperature is higher. At a given geometric height, the magnetic elements are not hotter than the surrounding medium. In the G-band, the contrast is further increased by the destruction of CH in the low density magnetic elements. The optical depth unity surface is very corrugated. Bright granules have their continuum optical depth unity 80 km above the mean surface, the magnetic elements 200-300 km below. At large angles, the deep lying magnetic elements are hidden by the granules and the bright points are no longer visible. Where the "magnetic valleys" are aligned with the line of sight, they are visible as elongated structures seemingly "sticking out". Even when the deep hot surface is hidden, the low density in the strong magnetic elements causes unit line-of-sight optical depth to occur deeper in the granule walls behind then for rays not going through magnetic elements. Flux concentrations in intergranular lanes therefore cause a striped intensity pattern. This work is funded by NSF grants AST 0205500 and ATM 99881112 and NASA grants NAG 5 12450 and NNGO4GB92G. Title: Observations of solar magnetic elements with 0.1" resolution Authors: Berger, T. E.; Rouppe van der Voort, L. H. M.; Lofdahl, M. G.; Carlsson, M.; Fossum, A.; Hansteen, V. H.; Marthinussen, E.; Title, A. M.; Scharmer, G. Bibcode: 2004AAS...204.2005B Altcode: 2004BAAS...36..686B New observations of solar magnetic elements in a remnant active region plage near disk center are presented. The observations were taken with the Swedish 1-meter Solar Telescope on La Palma. We examine a single 430.5 nm G-band filtergram that resolves ∼70 km (0.''1) structures and find new forms of magnetic structures in this particular region. A simultaneous Ca II H-line image is used to examine the low-chromosphere of network elements. A simultaneous Fe I 630.25 nm magnetogram that resolves structures as small as 120 km (0.''18) FWHM with a flux sensitivity of approximately 130 Mx cm-2 quantifies the magnetic structure of the region. A Ni I 676.8 nm Dopplergram establishes relative velocity patterns associated with the network features with an accuracy of about 300 m s-1. Magnetic flux in this region as seen in both the magnetogram and the G-band image is typically structured into larger, amorphous, ``ribbons'' with a wide range of flux density values, rather than isolated kilogauss flux tubes. We also present filtergrams and magnetograms of magnetic elements at the solar limb showing that solar faculae are resolved into bright granular walls that appear to project 350 to 500 km above the photosphere. Title: Penumbral structure at 0.1 arcsec resolution. I. General appearance and power spectra Authors: Rouppe van der Voort, L. H. M.; Löfdahl, M. G.; Kiselman, D.; Scharmer, G. B. Bibcode: 2004A&A...414..717R Altcode: We analyse sunspot filtergrams of unprecedented quality obtained by \citet{scharmer02dark} with the Swedish 1-m Solar Telescope on La Palma. The observations comprise images in three different wavelength bands: 488, 436, and 430 nm (G-band). We find that there are still unresolved penumbral filaments which must have widths smaller than 80 km. The fine structuring along the filaments is limited. Penumbral grains have internal structure and look like they are split or crossed by narrow dark structures. We calculate intensity power spectra of the penumbra from images that are corrected for seeing using the Phase Diversity technique. The effects of high order aberrations that are not corrected for are estimated to be too low to be consistent with a flat power spectrum. The penumbral power spectra do not show any signs of bumps or peaks that could correspond to a preferred scale at 0\farcs35 for the width of penumbral filaments. We argue that the power spectrum is not a very reliable source of information concerning preferred scales. Title: High resolution limb images synthesized from 3D MHD simulations Authors: Carlsson, Mats; Stein, Robert F.; Nordlund, Åke; Scharmer, Göran B. Bibcode: 2004IAUS..223..233C Altcode: 2005IAUS..223..233C We present the first center-to-limb G-band images synthesized from high resolution simulations of solar magneto-convection. Towards the limb the simulations show "hilly" granulation with dark bands on the far side, bright granulation walls and striated faculae, similar to observations. At disk center G-band bright points are flanked by dark lanes. The increased brightness in magnetic elements is due to their lower density compared with the surrounding intergranular medium. One thus sees deeper layers where the temperature is higher. At a given geometric height, the magnetic elements are cooler than the surrounding medium. In the G-band, the contrast is further increased by the destruction of CH in the low density magnetic elements. The optical depth unity surface is very corrugated. Bright granules have their continuum optical depth unity 80 km above the mean surface, the magnetic elements 200-300 km below. The horizontal temperature gradient is especially large next to flux concentrations. When viewed at an angle, the deep magnetic elements optical surface is hidden by the granules and the bright points are no longer visible, except where the "magnetic valleys" are aligned with the line of sight. Towards the limb, the low density in the strong magnetic elements causes unit line-of-sight optical depth to occur deeper in the granule walls behind than for rays not going through magnetic elements and variations in the field strength produce a striated appearance in the bright granule walls. Title: Observations of magnetoconvection in Sunspots with 100 km resolution Authors: Berger, T. E.; Löfdahl, M. G.; Scharmer, G.; Title, A. M. Bibcode: 2003SPD....34.1108B Altcode: 2003BAAS...35..828B We present new observations from the Swedish 1-meter Solar Telescope (SST) on La Palma with ∼0.1 arcsecond ( ∼100 km) resolution: the highest resolution yet achieved in solar observations. We focus on sunspot and active region magnetoconvective phenomena using G-band 4305 Å, 4877 Å continuum, 7507 Å TiO bandhead, and Ca II 3968 Å H-line filtergram movies. The G-band data are post-processed using Joint Phase Diverse Speckle wavefront restoration to create a full diffraction limited time series. Sunspot light-bridges are shown to have dark lanes less than 300 km in width that are coherent along the entire length of the bridge. Similarly, we find elongated dark ``canals'' in plage regions, particularly near pores, that appear to be highly modified intergranular downflow lanes. The canals are less than 200 km in width and are much more coherent than intergranular lanes in non-magnetic regions, often retaining their basic structure for more than one granular turn-over time. Both the light-bridge central lane and the canals appear to be the result of highly constrained flow structure in strong magnetic field regions -- an aspect of solar magnetoconvection that has not previously been observed. This reseach was supported by funding from the Royal Swedish Academy of Sciences, a SOHO Guest Investigator subcontract to California State University Northridge, and the NASA TRACE contract NAS5-38099 at Lockheed Martin. Title: The 1-meter Swedish solar telescope Authors: Scharmer, Goran B.; Bjelksjo, Klas; Korhonen, Tapio K.; Lindberg, Bo; Petterson, Bertil Bibcode: 2003SPIE.4853..341S Altcode: We describe the 1-meter Swedish solar telescope which replaces the former 50-cm solar telescope (SVST) in La Palma. The un-obscured optics consists of a singlet lens used as vacuum window and two secondary optical systems. The first of these enables narrow-band imaging and polarimetry with a minimum of optical surfaces. The second optical system uses a field mirror to re-image the pupil on a 25 cm corrector which provides a perfectly achromatic image, corrected also for atmospheric dispersion. The adaptive optics system is integrated with the design of the telescope but is sufficiently flexible to allow future upgrades. It consists of a low-order bimorph modal mirror with 37 electrodes, allowing near-diffraction-limited imaging a reasonable fraction of the observing time on La Palma. The new telescope became operational at the end of May 2002 and has already proven to be the most highly resolving solar telescope ever built. In this paper, we describe its mechanical and optical design, the polishing and testing of the optics and the instrumentation in use or planned for this telescope. Title: Adaptive optics system for the new Swedish solar telescope Authors: Scharmer, Goran B.; Dettori, Peter M.; Lofdahl, Mats G.; Shand, Mark Bibcode: 2003SPIE.4853..370S Altcode: The 1-meter Swedish solar telescope is a new solar telescope that was put in operation on the island of La Palma in the Canary Islands at the end of May 2002. The goal of this telescope is to reach its diffraction limited resolution of 0.1 arcsec in blue light. This has already been achieved by use of a low-order adaptive optics (AO)system. This paper describes the AO system initially developed for the former 50-cm Swedish Vacuum Solar Telescope (SVST) and further improved for the new telescope. Both systems use a combination of bimorph modal mirrors and Shack-Hartmann wavefront sensors. Unique to these systems are that they rely on a single workstation or a PC to do all the computations required to extract and pre-process the images, measure their positions using cross correlation techniques and for controlling the deformable mirror. This is in the present system possible by using the PERR instruction available on Compaq's Alpha architecture and in the new system using the PSADDBW instruction, available on Pentium 4 and Athlon processors. We describe both these systems with an emphasis on the performance, the ease of support and upgrades of performance. We also describe the optimization of the electrode geometry for the new 37-electrode bimorph mirror, supplied by AOPTIX Technologies, Inc., for controlling Karhunen--Loeve modes. Expected performance, based on closed-loop simulations, is discussed. Title: Phase diverse speckle inversion applied to data from the Swedish 1-meter solar telescope Authors: Lofdahl, Mats G.; Scharmer, Goran B. Bibcode: 2003SPIE.4853..567L Altcode: We report on the use of a new joint phase diverse speckle code, an implementation of a method where a single object and individual phases are estimated from several pairs of phase diverse data. The code was used on 430.5 nm G-band data collected with the newly installed Swedish 1-meter solar telescope in La Palma, equipped with a low-order adaptive optics system. We describe the algorithm briefly, show wavefront statistics and object estimates from the processing and discuss the results. We demonstrate a resolution of 0.12 arc seconds for a time sequence and a large field of view, which is a break-through for ground based solar telescopes. Title: First Results from the Swedish 1-m Solar Telescope Authors: Scharmer, G. B.; Kiselman, D.; Löfdahl, M. G.; Rouppe van der Voort, L. H. M. Bibcode: 2003ASPC..307....3S Altcode: No abstract at ADS Title: Dark cores in sunspot penumbral filaments Authors: Scharmer, Göran B.; Gudiksen, Boris V.; Kiselman, Dan; Löfdahl, Mats G.; Rouppe van der Voort, Luc H. M. Bibcode: 2002Natur.420..151S Altcode: Sunspot umbrae-the dark central regions of the spots-are surrounded by brighter filamentary penumbrae, the existence of which remains largely inexplicable. The penumbral filaments contain magnetic fields with varying inclinations and are associated with flowing gas, but discriminating between theoretical models has been difficult because the structure of the filaments has not hitherto been resolved. Here we report observations of penumbral filaments that reveal dark cores inside them. We cannot determine the nature of these dark cores, but their very existence provides a crucial test for any model of penumbrae. Our images also reveal other very small structures, in line with the view that many of the fundamental physical processes in the solar photosphere occur on scales smaller than 100km. Title: Workstation-based solar/stellar adaptive optics system Authors: Scharmer, Goran B.; Shand, Mark; Lofdahl, Mats G.; Dettori, Peter M.; Wei, Wang Bibcode: 2000SPIE.4007..239S Altcode: The microprocessors used in off-the-shelf workstations double in performance every eighteen months. The Swedish Vacuum Solar Tower (SVST) uses off-the-shelf workstations for all aspects of its on-line telescope control and data acquisition. Since 1995 workstation performance has been adequate for a correlation tracker of solar granulation controlling a tip- tilt corrector. In 2000 workstation performance permits the construction of a 20 - 50 subimage Shack-Hartmann based low- latency adaptive optics system. It is argued that workstations provide a cost-effective, upgradable, low-risk and flexible means of construction of stellar and solar adaptive optics systems. We give an overview of the adaptive optics system installed at the SVST in May 1999. The system uses a bimorph modal mirror with 19 electrodes from Laplacian Optics. For use with extended targets, such as solar fine structure, cross- correlations with 16 X 16-pixel sub-images are used. For use with point sources, a centroiding algorithm is implemented. The work station used is capable of completing all processing required by the adaptive optics system in 0.5 ms (cross-correlations) or 0.3 ms (centroiding), with potential for significant performance improvements. Title: Predictor approach to closed-loop phase-diversity wavefront sensing Authors: Lofdahl, Mats G.; Scharmer, Goran B. Bibcode: 2000SPIE.4013..737L Altcode: We present a novel and fast method for utilizing wavefront information in closed-loop phase-diverse image data. We form a 2D object-independent error function using the images at different focus positions together with OTFs of the diffraction limited system. Each coefficient in an expansion of the wavefront is estimated quickly and independently by calculating the inner produce of a corresponding predictor function and the error function. This operation is easy to parallelize. The main computational burden is in pre- processing, when the predictors are formed. This makes this method fast and therefore attractive for closed loop operation. Calculating the predictors involves error function derivatives with respect to the wavefront parameters, statistics of the parameters, noise levels and other known characteristics of the optical system. The predictors are optimized so that the RMS error in the wavefront parameters is minimized rather than consistency between estimated quantities with image data. We present simulation results that are relevant to the phasing of segmented mirrors in a space telescope, such as the NGST. Title: Coordinated MDI/TRACE/SVST Observations of Sunspots Authors: Bush, R. I.; Shine, R. A.; Brandt, P.; Sobotka, M.; Scharmer, G. Bibcode: 2000SPD....31.0122B Altcode: 2000BAAS...32R.804B During the first two weeks of June 1999, coordinated observations of sunspots were made by the MDI instrument on the SOHO spacecraft, the TRACE satellite and the Swedish Vacuum Solar Tower (SVST) at La Palma. The MDI instrument was operating in a "high resolution" mode and was obtaining 1.2 arc-second resolution magnetograms and 2.4 arc-second resolution dopplergrams at a one minute cadence. TRACE observations were made in Fe IX/X 171 Angstroms and/or Fe XII 195 Angstroms together with the 1600 Angstroms and continuum bands at a 1.0 arc-second resolution. The SVST data consist of filtergrams taken with three 2Kx2K CCD cameras with about 0.4 arc-second resolution operating in frame selection mode. The first camera used a fixed G band (4305 Angstroms) filter, the second a fixed blue continuum filter (4507 Angstroms), and the third a narrow band tunable filter which was cycled through several positions in the Hα line and the 6302 Angstroms Fe ~I line. The goal of this investigation is to detail the evolution of stable sunspots in order to understand the detailed correlation of photospheric flows and magnetic features. The high time and spatial resolution of these measurements provides a unique opportunity to explore the interactions of plasma and magnetic field at the solar surface. This work was supported by NASA grant NAG5-3077 at Stanford and NASA contract NAS5-38099 at Lockheed Martin. Title: Calibration of a Deformable Mirror and Strehl Ratio Measurements by Use of Phase Diversity Authors: Löfdahl, Mats G.; Scharmer, Göran B.; Wei, Wang Bibcode: 2000ApOpt..39...94L Altcode: No abstract at ADS Title: Coordinated Observations of Transition Region Dynamics using TRACE and the SVST Authors: Berger, T.; de Pontieu, B.; Schrijver, C.; Title, A.; Scharmer, G. Bibcode: 1999ASPC..183..365B Altcode: 1999hrsp.conf..365B No abstract at ADS Title: The New Swedish Solar Telescope Authors: Scharmer, G.; Owner-Petersen, M.; Korhonen, T.; Title, A. Bibcode: 1999ASPC..183..157S Altcode: 1999hrsp.conf..157S No abstract at ADS Title: Optimized Shack-Hartmann Wavefront Sensing for Adaptive Optics and Post Processing Authors: Scharmer, G.; Blomberg, H. Bibcode: 1999ASPC..183..239S Altcode: 1999hrsp.conf..239S No abstract at ADS Title: Object-Independent Fast Phase-Diversity Authors: Scharmer, G. Bibcode: 1999ASPC..183..330S Altcode: 1999hrsp.conf..330S No abstract at ADS Title: Correlation Tracking and Adaptive Optics Control Using Off-The-Shelf Workstation Technology Authors: Shand, M.; Scharmer, G.; Wei, W. Bibcode: 1999ASPC..183..231S Altcode: 1999hrsp.conf..231S No abstract at ADS Title: LPSP & TIP: Full Stokes Polarimeters for the Canary Islands Observatories Authors: Mártinez Pillet, V.; Collados, M.; Sánchez Almeida, J.; González, V.; Cruz-Lopez, A.; Manescau, A.; Joven, E.; Paez, E.; Diaz, J.; Feeney, O.; Sánchez, V.; Scharmer, G.; Soltau, D. Bibcode: 1999ASPC..183..264M Altcode: 1999hrsp.conf..264M No abstract at ADS Title: Fine Structures of Magnetic Field in Solar Quiet Region Authors: Zhang, H.; Scharmer, G.; Lofdahl, M.; Yi, Z. Bibcode: 1998SoPh..183..283Z Altcode: In this paper, we present a time series of Fe i λ5250.2 Å photospheric filtergrams and corresponding magnetograms in a quiet region. The relationship between fine structures of granulation and magnetic fields is analyzed. It is found that although most bright filigree features in photospheric filtergrams are related to corresponding magnetic features, they are generally not cospatial. It is also found that some bright features and their corresponding photospheric magnetic fields show fast changes within several minutes. Title: The Swedish Vacuum Solar Telescope data-acquisition and control systems Authors: Shand, Mark; Scharmer, Göran B. Bibcode: 1998NewAR..42..481S Altcode: The performance of commodity computer systems doubles approximately every 18 months. Traditionally, the design of scientific data-acquisition and control systems has tended to ignore this fact, relying instead on custom hardware developments using the technology available at the time of instrument specification. Moreover, development manpower is usually limited, causing relatively long development cycles. Often the the result is that an instrument is technologically obsolete quite early in its projected lifetime. In contrast, all the digital processing for data acquisition and control at the Swedish Vacuum Solar Telescope (SVST) on La Palma (Canary Islands) is performed with commodity workstations. The result is a flexible system with low development costs that can easily take advantage of the latest microprocessor advances. The SVST's use of commodity workstations in on-line real-time tasks is in large part made possible by its use of reconfigurable interface technology. Indeed the SVST has been a valuable proving ground for this technology. This article summarizes the instrumentation of the SVST and illustrates examples of data recorded with this instrumentation. Title: Fast phase diversity wavefront sensing for mirror control Authors: Lofdahl, Mats G.; Duncan, Alan L.; Scharmer, Goran B. Bibcode: 1998SPIE.3353..952L Altcode: We show with simulation experiments that closed-loop phase- diversity can be used without numerical guard-bands for wavefront sensing of low-order wavefronts from extended objects using broad-band filters. This may allow real-time correction at high bandwidth for certain applications. We also present a proper maximum likelihood treatment of Shack- Hartmann data, which includes an imaging model to extract curvature information from the lenslet images. We demonstrate by simple simulations that this approach should allow higher-order wavefront information to be extracted than with traditional Shack-Hartmann wavefront sensing for a given number of lenslets. Title: Comparison of Granulation Correlation Tracking (CT) and Feature Tracking (FT) Results from SOHO/MDI and the Swedish Vacuum Solar Telescope on La Palma Authors: Shine, R.; Strous, L.; Simon, G.; Berger, T.; Hurlburt, N.; Tarbell, T.; Title, A.; Scharmer, G. Bibcode: 1997SPD....28.0262S Altcode: 1997BAAS...29Q.904S We have computed photospheric velocity flow maps from simultaneous observations taken with MDI and at the Swedish Vacuum Solar Tower (SVST) on La Palma on August 15, 1996. Both sets consist of a series of photospheric images, and flow maps are computed by following the local motions of granules. The MDI data have the important advantages of very stable images and longer continuous coverage of the same area of the solar surface. This longer coverage is necessary to study the evolution of mesogranules, supergranules, and to detect possible low amplitude motions on scales larger than supergranules. However, the high resolution mode of MDI is limited by the small telescope size to about 1.2 arc seconds angular resolution and uses a 0.6 arc second pixel size. This is adequate to show granulation but has the rms constrast significantly reduced to about 2%. Early efforts adapting techniques that were successful with higher resolution ground based images gave poor results and although new methods have now been developed, there are still some problems with accuracy. On the other hand, the SVST images have much higher angular resolution (as good as 0.2 arc second) but suffer from variable atmospheric distortion. They also have a much smaller field of view. By detailed comparison of the two data sets and by using CT and FT techniques to track the motions, we hope to understand the sources of any differences between them and to develop credible correction parameters to the MDI data sets if necessary. This work was supported by NASA Grant NAG5-3077 at Stanford and Lockheed Martin, by AFOSR and the Fellows Program of AF Phillips Lab at NSO/SP, and by the Swedish Royal Academy of Sciences. Title: The IAC Solar Polarimeters: Goals and Review of Two Ongoing Projects Authors: Sanchez Almeida, J.; Collados, M.; Martinez Pillet, V.; Gonzalez Escalera, V.; Scharmer, G. B.; Shand, M.; Moll, L.; Joven, E.; Cruz, A.; Diaz, J. J.; Rodriguez, L. F.; Fuentes, J.; Jochum, L.; Paez, E.; Ronquillo, B.; Carranza, J. M.; Escudero-Sanz, I. Bibcode: 1997ASPC..118..366S Altcode: 1997fasp.conf..366S The IAC is currently developing two similar polarimeters, one for optical wavelengths and one for near infra-red wavelengths (1.5 mu m). Both instruments will provide spectra of the four Stokes parameters over 2D solar regions. The visible spectro-polarimeter will be operated at the Swedish Tower (La Palma), and it is being developed in collaboration with the Royal Swedish Academy of Sciences. We intend to take advantage of the excellent seeing conditions at this telescope, while maintaining high polarimetric precision. The IR polarimeter is being designed for the German VTT (Tenerife) which has better angular resolution in the near infra-red. This report describes the goals and technical solutions. It also briefs on the current status of the projects. Title: Evaluation of Phase-Diversity Techniques for Solar-Image Restoration Authors: Paxman, Richard G.; Seldin, John H.; Loefdahl, Mats G.; Scharmer, Goeran B.; Keller, Christoph U. Bibcode: 1996ApJ...466.1087P Altcode: Phase-diversity techniques provide a novel observational method for overcoming the effects of turbulence and instrument-induced aberrations in ground-based astronomy. Two implementations of phase-diversity techniques that differ with regard to noise model, estimator, optimization algorithm, method of regularization, and treatment of edge effects are described. Reconstructions of solar granulation derived by applying these two implementations to common data sets are shown to yield nearly identical images. For both implementations, reconstructions from phase-diverse speckle data (involving multiple realizations of turbulence) are shown to be superior to those derived from conventional phase-diversity data (involving a single realization). Phase-diverse speckle reconstructions are shown to achieve near diffraction-limited resolution and are validated by internal and external consistency tests, including a comparison with a reconstruction using a well-accepted speckle-imaging method. Title: TRACE: the Transition Region and Coronal Explorer Authors: Schrijver, C.; Title, A.; Acton, L.; Bruner, M.; Fischer, R.; Golub, L.; Harrison, R.; Lemen, J.; Rosner, R.; Scharmer, G.; Scherrer, P.; Strong, K.; Tarbell, T.; Wolfson, J. Bibcode: 1996AAS...188.6704S Altcode: 1996BAAS...28..934S The TRACE mission is designed to obtain images of the solar transition region and corona of unprecedented quality. With these images we will be able to explore quantitatively the connections between the photospheric magnetic field and the associated hot and tenuous structures in the outer atmosphere. The TRACE telescope has an aperture of 30 cm, and will observe an 8.5 x 8.5 arcminute field of view with a resolution of one arcsecond. Finely tuned coatings on four quadrants on the primary and secondary normal--incidence mirrors will allow observations in narrow EUV and UV spectral bands. The passbands are set to Fe IX, XII, and XV lines in the EUV band, while filters allow observations in C IV, Ly alpha , and the UV continuum using the UV mirror quadrant. The data thus cover temperatures from 10(4) K up to 10(7) K. The Sun--synchronous orbit allows long intervals of uninterrupted viewing. Observations at different wavelengths can be made in rapid succession with an alignment of 0.1 arcsec. Coordinated observing with TRACE, SoHO and YOHKOH will give us the first opportunity to observe all temperature regimes in the solar atmosphere, including magnetograms, simultaneously from space. TRACE is currently scheduled to be launched in October 1997. More information can be found on the web at ``http://pore1.space.lockheed.com/TRACE/welcome.html''. Title: Photospheric Surface Flows and Small Magnetic Structures in Sunspot Moats Authors: Shine, R. A.; Title, A.; Frank, Zoe; Scharmer, G. Bibcode: 1996AAS...188.3501S Altcode: 1996BAAS...28Q.871S We have computed horizontal flow maps of the photosphere around and within three different sunspots using high spatial resolution continuum movies obtained at the Swedish Vacuum Solar Telescope on La Palma on June 5, 1993, August 29, 1993, and July 14, 1994. Two of the data sets also included magnetograms and dopplergrams. A new feature found in the flow maps is azimuthal structure in the moat flows surrounding sunspots. Instead of a simple radial flow, there are zones of azimuthal divergence and convergence resulting in radial ``spokes'' of convergence. These are not uniformly distinct around the entire circumference but are seen in part of the surrounding area for all 3 sunspots. The angular spacing is about 10 to 20 degrees and the pattern persists for several hours. For one of the sunspots, we have concurrent movies made with a 3 Angstrom wide K line filter. A time average of these images shows bright spokes in the K line congruent with the convergence spokes. Much of the magnetic flux that is continually emerging and moving outward in the moat is in the vicinity of the ``spokes.'' In addition, these data show several good examples of so called ``streakers.'' These are small bright structures seen in continuum movies that appear to be emitted from the outer edge of the penumbral and travel a few thousand km at about 2 to 3 km/s before fading. We find that these are associated with a magnetic field of opposite polarity to the sunspot and that they travel toward another larger and slower moving magnetic feature with the same polarity as the sunspot. When the streaker catches up, it disappears, sometimes coincident with a brightening of the merged feature which continues outward at the previous velocity, about 0.5 km/s. This work was supported by NSF grant ATM-9213879, NASA contracts NAS8-39746 and NAS8-39747, Lockheed Independent Research Funds, and the Swedish Royal Academy of Sciences. Title: Phenomena in an emerging active region. I. Horizontal dynamics. Authors: Strous, L. H.; Scharmer, G.; Tarbell, T. D.; Title, A. M.; Zwaan, C. Bibcode: 1996A&A...306..947S Altcode: Horizontal dynamics in observations of NOAA AR 5617 are studied by tracking individual elements through the field of view. Small magnetic elements of both magnetic polarities occur everywhere in the active region, and define unipolar thread-like concentrations of magnetic field of up to 15Mm length. The horizontal granular flow field in the active region is divergent (e-time scale 2.1hours) and clockwise (time scale 32hours). Facular elements are tracers of (clumps of) fluxtubes. A hierarchy of movement of magnetic elements appears: Facular elements everywhere in the active region move obliquely toward the edges of the active region of the same polarity as their own, faster than those edges (as defined by strings of pores) move apart. The pores move along the edges toward the major sunspots of their own polarity, and the major sunspots of either polarity move apart. The separation velocity of both polarities of facular elements is about 0.84km/s, of pores about 0.73km/s, and that of the major sunspots is about 0.50km/s. Title: Motion and Evolution of Solar Magnetic Elements Authors: Berger, T. E.; Schrijver, C. J.; Shine, R. S.; Tarbell, T. D.; Title, A. M.; Scharmer, G. Bibcode: 1995AAS...18710104B Altcode: 1995BAAS...27.1426B The dynamics of sub-arcsecond solar magnetic flux tubes are analyzed based on very-high resolution movies of photospheric bright points obtained in 1994 at the 50-cm Swedish Solar Vacuum Telescope (SVST) on the island of La Palma, Spain. The bright points are imaged using a 12 Angstroms bandpass interference filter centered at 4305 Angstroms in the ``G Band'' molecular bandhead of the CH molecule. The image sets typically consist of up to 4 hours of consecutive images taken at a 10 to 20 second cadence. Spatial resolution throughout the movies averages less than 0\arcsec.5 and many frames in the sets exhibit resolution down to 0\arcsec.25. Magnetic flux elements in the photosphere are shown to move continually along the intergranular lanes at speeds of up to 5 km/sec and ranges up to several thousand km. Evolution of individual magnetic elements is dominated by the local evolution of surrounding granules. Fragmentation and merging is the fundamental mode of evolution of the majority of magnetic elements seen in our data. Rotation and folding of chains or groups of elements is also frequently observed. The time scale for the fragmentation/merging evolution of the elements is on the order of the lifetime of granulation (6--8 minutes), but significant morphological changes are seen to occur on time scales as short as 100 seconds. The concept of a stable, isolated, sub-arcsecond magnetic flux element in the solar photosphere is inconsistent with the observations presented here. Title: New Observations of Subarcsecond Photospheric Bright Points Authors: Berger, T. E.; Schrijver, C. J.; Shine, R. A.; Tarbell, T. D.; Title, A. M.; Scharmer, G. Bibcode: 1995ApJ...454..531B Altcode: We have used an interference filter centered at 4305 Å within the bandhead of the CH radical (the "G band") and real-time image selection at the Swedish Vacuum Solar Telescope on La Palma to produce very high contrast images of subarcsecond photospheric bright points at all locations on the solar disk. During the 6 day period of 1993 September 15-20 we observed active region NOAA 7581 from its appearance on the East limb to a near disk-center position on September 20. A total of 1804 bright points were selected for analysis from the disk center image using feature extraction image processing techniques. The measured FWHM distribution of the bright points in the image is subnormal with a modal value of 220 km (0".30) and an average value of 250 km (0".35). The smallest measured bright point diameter is 120 km (0".17) and the largest is 600 km (0".69). Approximately 60% of the measured bright points are circular (eccentricity ∼1.0), the average eccentricity is 1.5, and the maximum eccentricity corresponding to filigree in the image is 6.5. The peak contrast of the measured bright points is normally distributed. The contrast distribution variance is much greater than the measurement accuracy, indicating a large spread in intrinsic bright-point contrast. When referenced to an averaged "quiet-Sun area 1n the image, the modal contrast is 29% and the maximum value is 75%; when referenced to an average intergranular lane brightness in the image, the distribution has a modal value of 61 % and a maximum of 119%. The bin-averaged contrast of G-band bright points is constant across the entire measured size range. The measured area of the bright points, corrected for population and selection effects, covers about 1.8% of the total image area. Large pores and micropores occupy an additional 2% of the image area, implying a total area fraction of magnetic proxy features in the image of 3.8%. We discuss the implications of this area fraction measurement in the context of previously published measurements which show that typical active region plage has a magnetic filling factor on the order of 10% or greater. The results suggest that in the active region analyzed here, less than 50% of the small-scale magnetic flux tubes are demarcated by visible proxies such as bright points or pores. Title: 3.8-ms latency correlation tracker for active mirror control based on a reconfigurable interface to a standard workstation Authors: Shand, Mark; Wei, Wang; Scharmer, Goran B. Bibcode: 1995SPIE.2607..145S Altcode: We describe the use of a reconfigurable interface board based on FPGAs and a UNIX workstation to implement a correlation tracker with 3.8ms latency. The correlation tracker is part of an active mirror system in use at the Swedish Vacuum Solar Telescope, La Palma, Canary Islands. The reconfigurable interface is used to leverage the workstation CPU, relieving it of tasks that it performs poorly such as rapid context switching and low-level bit manipulation. The reconfigurable interface handles control of external devices, high- performance input (16 MB/s) and data preformatting. The workstation CPU, a 64-bit microprocessor, performs the bulk of the computation. For the key computations of the correlation tracker we are able to treat 8 pixels in parallel in the CPU's 64-bit integer datapath. We present the structure of the CCD interface configuration and the implementations of the key algorithms on the workstation CPU. We describe the design trade-offs that arose during the development of the system, and demonstrate the symbiosis between components implemented in software and configurable hardware. Title: Frame Selection Techniques for Solar Movies Authors: Shine, R. A.; Tarbell, T.; Title, A.; Scharmer, G.; Simon, G.; Brandt, P.; Berger, T. Bibcode: 1995SPD....26..506S Altcode: 1995BAAS...27..957S No abstract at ADS Title: Properties of Sub-Arcsecond Facular Bright Points Authors: Berger, T.; Schrijver, C.; Shine, R.; Tarbell, T.; Title, A.; Scharmer, G. Bibcode: 1995SPD....26..505B Altcode: 1995BAAS...27..957B No abstract at ADS Title: On the Relation Between Facular Bright Points and the Magnetic Field Authors: Berger, Thomas; Shine, Richard; Tarbell, Theodore; Title, Alan; Scharmer, Goran Bibcode: 1994AAS...185.8607B Altcode: 1994BAAS...26.1465B Multi-spectral images of magnetic structures in the solar photosphere are presented. The images were obtained in the summers of 1993 and 1994 at the Swedish Solar Telescope on La Palma using the tunable birefringent Solar Optical Universal Polarimeter (SOUP filter), a 10 Angstroms wide interference filter tuned to 4304 Angstroms in the band head of the CH radical (the Fraunhofer G-band), and a 3 Angstroms wide interference filter centered on the Ca II--K absorption line. Three large format CCD cameras with shuttered exposures on the order of 10 msec and frame rates of up to 7 frames per second were used to create time series of both quiet and active region evolution. The full field--of--view is 60times 80 arcseconds (44times 58 Mm). With the best seeing, structures as small as 0.22 arcseconds (160 km) in diameter are clearly resolved. Post--processing of the images results in rigid coalignment of the image sets to an accuracy comparable to the spatial resolution. Facular bright points with mean diameters of 0.35 arcseconds (250 km) and elongated filaments with lengths on the order of arcseconds (10(3) km) are imaged with contrast values of up to 60 % by the G--band filter. Overlay of these images on contemporal Fe I 6302 Angstroms magnetograms and Ca II K images reveals that the bright points occur, without exception, on sites of magnetic flux through the photosphere. However, instances of concentrated and diffuse magnetic flux and Ca II K emission without associated bright points are common, leading to the conclusion that the presence of magnetic flux is a necessary but not sufficient condition for the occurence of resolvable facular bright points. Comparison of the G--band and continuum images shows a complex relation between structures in the two bandwidths: bright points exceeding 350 km in extent correspond to distinct bright structures in the continuum; smaller bright points show no clear relation to continuum structures. Size and contrast statistical cross--comparisons compiled from measurements of over two-thousand bright point structures are presented. Preliminary analysis of the time evolution of bright points in the G--band reveals that the dominant mode of bright point evolution is fission of larger structures into smaller ones and fusion of small structures into conglomerate structures. The characteristic time scale for the fission/fusion process is on the order of minutes. Title: Wavefront sensing and image restoration from focused and defocused solar images. Authors: Löfdahl, M. G.; Scharmer, G. B. Bibcode: 1994A&AS..107..243L Altcode: We have implemented a least-squares technique for recovering phase information from simultaneously recorded focused and defocused images. The inversions are made from small subfields in order to deal with anisoplanatic image formation, such as occurring through the Earth's atmosphere. Parameters corresponding to the alignment of the focused-defocused images are determined simultaneously with aberration parameters. Simulations show that the method can recover wavefronts of up to 1/2 wave rms and that 15-21 Zernike coefficients can be obtained from 3"x3"-5"x5" solar granulation images using a 50 cm telescope and with noise levels of 0.4% of the average intensity. In general, the accuracy of the restored images is better than expected from the number of Zernike polynomials used to represent the wave front. We have applied the method to sequences of 100 8-bit solar granulation images obtained with the Swedish Vacuum Solar Telescope (SVST) in La Palma using subfields of 3"x3"-5"x5". These data enable a number of consistency tests, all of which demonstrate that the technique works on real data. Using averaged images obtained from each sequence we find that derived alignment parameters are consistent to within 0.02" and that wavefronts derived from different subfields and different sequences recorded close in time are virtually identical. The wavefronts derived from averaged images are also virtually identical to the average of wavefronts derived from individual images. These measurements of telescope aberrations suggest that astigmatism and coma are the major aberrations. These aberrations vary with time in a way which is consistent with a major contribution from the telescope objective and/or the first folding mirror of the alt-az tower telescope. Wavefronts derived from individual images show 50-90% correlation between Zernike coefficients 4-14 derived from nearby but independent subfields. Mosaics of 13 x 11 independently derived wavefronts from single images show smooth variations across a 12"x10" field-of-view. These results are consistent with the impression that degradation of image quality is more or less uniform across the image. Restored images in a sequence show a high degree of consistency and much more fine structure than the corresponding observed images, but occasional fringe-like artifacts can be seen. Using the results of two inversions to restore the scene removes such artifacts. We conclude that this technique provides adequate wavefront information on telescopic and atmospheric wavefront aberrations and substantial improvements in image quality. The ease of implementation as well as its tolerance to experimental errors and low cost makes it an excellent complement to or even substitute for adaptive optics for many applications. The technique is particularly well-suited for solar telescopes, where wavefront sensing over a large field-of-view is important. Title: Application of phase-diversity to solar images Authors: Lofdahl, Mats G.; Scharmer, Goran B. Bibcode: 1994SPIE.2302..254L Altcode: We have implemented a least-squares technique for recovering phase information and alignment parameters from simultaneously obtained focused and defocused solar images. Small subfields are used, in order to deal with anisoplanatism. The method is applied to sequences of 100 8-bit solar granulation images. These data enable a number of consistency tests, all of which demonstrate that the technique works. Alignment parameters derived from averaged images in a sequence are highly consistent and wavefronts derived from different subfields and different sequences recorded close in time are virtually identical. The wavefronts derived from averaged images are also virtually identical to the average of wavefronts derived from individual images. These aberrations vary with time in a way which is consistent with a major contribution from the moving elements of the alt-az tower telescope. Independently derived wavefronts from single images show high correlation between neighboring subfields and smooth variations across large fields-of-view, consistent with the impression that the image quality is more or less uniform across the image. Restored images in a sequence show a high degree of consistency and much more fine structure than the corresponding observed images. Title: High-Resolution Observations of the Evershed Effect in Sunspots Authors: Shine, R. A.; Title, A. M.; Tarbell, T. D.; Smith, K.; Frank, Z. A.; Scharmer, Goran Bibcode: 1994ApJ...430..413S Altcode: High spatial resolution movies of sunspots taken at the Swedish Solar Observatory on La Palma reveal that the Evershed effect is time dependent. Outward proper motions are visible in both the continuum and Dopplergrams. These can be tracked over most of the width of the penumbra and overlap regions that show inward moving penubral grains. The radial spacing between the moving structures is about 2000 km, and they exhibit irregular repetitive behavior with a typical interval of 10 minutes. These are probably the cause of 10 minutes oscillations sometimes seen in a penumbral power spectra. Higher velocities are spatially correlated with the relatively darker regions between bright filaments. Regions with a strong variation in the Doppler signal show peak-to-peak modulations of 1 km/s on an average velocity of about 3-4 km/s. The proper motion velocity is approximately constant from the iner penumbra and generally larger than the Doppler velocity when both are interpreted as projections of horizontal motion. Regions where thay are consistent suggest a typical horizontal velocity of 3.5 km/s. Some proper motion velocites as high as 7 km/s are seen, but these are less certain. The temporal behavoir shows a correlation between increased Doppler signal and increased continuum intensity, the opposite of the spatial correlation. When spatially averaged across filaments and over time, the averaged Evershed effect has a peak horizontal component near the outer edge of the penumbra of 2.0 km/s with evidence for a 200-400 m/s upward component. The latter depends on an uncertain absolute velocity calibration. If real it could be an actual upward component or a penumbral analogue of the convective blueshift seen in the quiet Sun. Title: Dynamics of the Evershed effect Authors: Shine, R. A.; Title, A. M.; Tarbell, T. D.; Smith, K.; Frank, Z. A.; Scharmer, G. Bibcode: 1994ASIC..433..197S Altcode: No abstract at ADS Title: Large-scale photospheric motions: first results from an extraordinary eleven-hour granulation observation Authors: Simon, G. W.; Brandt, P. N.; November, L. J.; Scharmer, G. B.; Shine, R. A. Bibcode: 1994ASIC..433..261S Altcode: No abstract at ADS Title: Phase-Diversity Restoration of Solar Images Authors: Löfdahl, Mats G.; Scharmer, Göran B. Bibcode: 1993rtpf.conf...89L Altcode: We have implemented a least-squares linearization technique for recovering phase information from simultaneously recorded focused and defocused solar images. The inversion is made from small subfields, in order to deal with anisoplanatic image formation, such as occuring through the earth's atmosphere. Simulations show that the method can recover wavefronts of approximately 1/4 wave rms and that noise levels corresponding to 8-bit images allow better reconstruction of the images than of the derived wavefronts. We find that cross-correlation techniques cannot be used to align the focused and defocused images because of cross-talk with coma and similar asymmetric aberrations. Therefore we simultaneously determine alignment and aberration parameters. We have applied the method to 8-bit solar granulation images obtained with the Swedish Vacuum Solar Telescope in La Palma using subfields of 3".1 x 3".1. The least-squares fits indicate wavefronts of approximately 0.12-0.16 waves rms. Derived alignment parameters from different subfields and different images are consistent, indicating that the wavefront is well determined by the data. Wavefronts derived from different sub fields of a single image in general show similar aberrations whereas derived wavefronts from different images only show occasional similarities, indicating a significant wavefront aberration from the lower atmosphere. The reconstructed granulation images show enhanced fine structure and an increase of the rms contrast by ~2% as compared to the observed focused image, but the rms contrasts of consequtive images indicate small errors in the derived rms wavefronts. Title: High Resolution Observations of the Evershed Flow in Sunspots Authors: Shine, R.; Title, A.; Smith, K.; Scharmer, G. Bibcode: 1993BAAS...25.1183S Altcode: No abstract at ADS Title: La Palma Observations During the CoMStOC'92 Campaign Authors: Shine, R.; Tarbell, T.; Topka, K.; Frank, Z.; Title, A.; Scharmer, G. Bibcode: 1993BAAS...25S1223S Altcode: No abstract at ADS Title: On the Magnetic and Velocity Field Geometry of Simple Sunspots Authors: Title, Alan M.; Frank, Zoe A.; Shine, Richard A.; Tarbell, Theodore D.; Topka, Kenneth P.; Scharmer, Goran; Schmidt, Wolfgang Bibcode: 1993ApJ...403..780T Altcode: It is presently shown that a simple sunspot model with azimuthal variations in inclination, but lacking azimuthal field-strength variations, is free from azimuthal Lorentz forces. The meridional currents arising from the inclination variations are parallel to the field lines, suggesting that a cylindrically symmetric magnetostatic sunspot model can be perturbed into one with azimuthal variations in inclination with adjustment of the meridional force balance. Title: On the Differences between Plage and Quiet Sun in the Solar Photosphere Authors: Title, Alan M.; Topka, Kenneth P.; Tarbell, Theodore D.; Schmidt, Wolfgang; Balke, Christiaan; Scharmer, Goran Bibcode: 1992ApJ...393..782T Altcode: Time sequences of interleaved observations of the continuum intensity, longitudinal magnetic field, vertical velocity in the midphotosphere, and the line-center intensity in Ni I 6768 A were obtained in an active-region plage and the surrounding relatively field-free area near disk center. Spacetime Fourier filtering techniques are used to separate the convective and oscillatory components of the solar atmosphere. The properties of the photosphere are found to differ qualitatively and quantitatively between the plage, where the field is 150 G or more, and its quiet surroundings. The scale of granulation is smaller, the contrast lower, and the temporal evolution slower in the plage than the quiet sun. In the plage, the vertical velocity is reduced in amplitude compared to the quiet sun, and there is little evidence of a granulation pattern, while in the quiet sun the vertical flow pattern is similar in size and shape to the underlying granulation pattern in the continuum. Title: Very high spatial resolution two-dimensional solar spectroscopy with video CCDs Authors: Johanneson, A.; Bida, T.; Lites, B.; Scharmer, G. B. Bibcode: 1992A&A...258..572J Altcode: We have developed techniques for recording and reducing spectra of solar fine structure with complete coverage of two-dimensional areas at very high spatial resolution and with a minimum of seeing-induced distortions. These new techniques permit one, for the first time, to place the quantitative measures of atmospheric structure that are afforded only by detailed spectral measurements into their proper context. The techniques comprise the simultaneous acquisition of digital spectra and slit-jaw images at video rates as the solar scene sweeps rapidly by the spectrograph slit. During data processing the slit-jaw images are used to monitor rigid and differential image motion during the scan, allowing measured spectrum properties to be remapped spatially. The resulting quality of maps of measured properties from the spectra is close to that of the best filtergrams. We present the techniques and show maps from scans over pores and small sunspots obtained at a resolution approaching 1/3 arcsec in the spectral region of the magnetically sensitive Fe I lines at 630.15 and 630.25 nm. The maps shown are of continuum intensity and calibrated Doppler velocity. More extensive spectral inversion of these spectra to yield the strength of the magnetic field and other parameters is now underway, and the results of that analysis will be presented in a following paper. Title: High Resolution Observations of the Magnetic and Velocity Field of Simple Sunspots Authors: Title, Alan M.; Frank, Zoe A.; Shine, Richard A.; Tarbell, T. D.; Topka, K. P.; Scharmer, Goran; Schmidt, Wolfgang Bibcode: 1992ASIC..375..195T Altcode: 1992sto..work..195T We have observed the disk passage of relatively simple round sunspots using a narrowband filter and a large format CCD detector and have created magnetograms, Dopplergrams, and continuum images nearly simultaneously. In addition the spectral resolution of the filter allows the construction of 'spectra' for all points in the field of view. The mean inclination of the magnetic field increases from 45-50 deg to 70-75 deg across the penumbra and there is a fluctuation of the inclination angle about the mean of about 4 +/- 18 deg. The variation in inclination is large enough that substantial amounts of magnetic field are parallel to the solar surface from the mid to outer penumbra. The Evershed flow tends to occur in the regions where the magnetic field is horizontal. This suggests that the Evershed flow is confined to the regions of horizontal fields. We show that a simple sunspot model with azimuthal variations in inclination but no azimuthal variations of field strength is free from azimuthal Lorentz forces. The meridional component of the currents which arise from the azimuthal variation in inclination are parallel to the field lines. This suggests that a cylindrically symmetric magnetostatic sunspot model can be perturbed into one with azimuthal variations in inclination with some adjustment in the meridional force balance. Title: Properties of the Smallest Magnetic Elements on the Sun Authors: Topka, K. P.; Smith, K. L.; Tarbell, T. D.; Title, A. M.; Scharmer, G. Bibcode: 1991BAAS...23.1388T Altcode: No abstract at ADS Title: High-Resolution Spectra of Solar Magnetic Features. II. Magnetic Fields of Umbral Brightenings Authors: Lites, Bruce W.; Bida, Thomas A.; Johannesson, A.; Scharmer, G. B. Bibcode: 1991ApJ...373..683L Altcode: The spectra of Fe I and Fe II Zeeman-sensitive lines enhanced by video processing of CCD images are considered. The magnetic-field variation within umbras is obtained from the nearly complete Zeeman splitting of the Stokes I profile. It is shown that small brightenings within umbrae have magnetic fields nearly equal to or slightly smaller than that of the darker surroundings; these features are also nearly at rest with respect to their surroundings. It is noted that the absence of significant motions in umbral dots implies that radiation transports most of the energy at and immediately below the surface. The small size of the dots implies that, if convective plumes transport energy below the surface of sunspot umbrae, they should have both a lateral extent and a depth of their upper boundary comparable to or smaller than the size of the dot. Title: Magnetograph Observations with the Swedish Solar Telescope on La-Palma Authors: Lundstedt, Henrik; Johannesson, Anders; Scharmer, Göran; Stenflo, Jan Olof; Kusoffsky, Ulf; Larsson, Birgitta Bibcode: 1991SoPh..132..233L Altcode: A high-resolution videomagnetograph that records the images of opposite circular polarization simultaneously has been constructed for the Swedish vacuum solar telescope at La Palma. Magnetograms are obtained by off-line integration of bursts consisting of typically 50 frames of 20 ms exposures, with bad frames rejected, and the frame-to-frame image motion of the remaining frames compensated for by cross-correlation techniques. The short exposures combined with frame selection and elimination of image motion optimizes the resolution and thereby also the S/N, allowing good magnetograms to be obtained with an effective exposure time of less than 1 s at an image scale of 0.1″ pixel−1. The advantages and limitations of the system are discussed and compared with other techniques of making filter magnetograms are discussed. Title: Fine-Scale Magnetic Field in a Sunspot Penumbra and Adjacent Photosphere Authors: Frank, Z. A.; Scharmer, G. B.; Keller, C.; Lundstedt, H. Bibcode: 1991BAAS...23.1052F Altcode: No abstract at ADS Title: Power Spectra of Flows and Magnetic Fields in the Solar Photosphere Authors: Tarbell, T. D.; Slater, G. L.; Frank, Z. A.; Topka, K. P.; Scharmer, G.; Schmidt, W. Bibcode: 1991BAAS...23.1048T Altcode: No abstract at ADS Title: Stokes Polarimetry of a Sunspot from the Swedish Solar Observatory at La Palma Authors: Topka, K. P.; Frank, Z. A.; Tarbell, T. D.; Title, A. M.; Scharmer, G. Bibcode: 1991BAAS...23Q1052T Altcode: No abstract at ADS Title: Variation of granulation properties on a mesogranular scale Authors: Brandt, P. N.; Ferguson, S.; Shine, R. A.; Tarbell, T. D.; Scharmer, G. B. Bibcode: 1991A&A...241..219B Altcode: A 79 min series of CCD images of the solar granulation with subarcsec spatial resolution is analyzed. Local correlation techniques are applied to determine horizontal displacements of the granular intensity pattern in a 14.2 by 12.2 sq arcsec field of view. The divergence of the average horizontal flow field shows mean cell sizes of 5 to 7 arcsec. Granules are selected with respect to area, brightness, lifetime, and expansion rate. It is shown that small, faint, short-lived, and fast collapsing granules are located preferentially in the negative divergence (down-draft) regions of the mesogranular flow field, while bright, long-lived, and rapidly expanding granules populate preferentially the positive divergence (up-draft) regions. The differences in area coverage range between + or - 6 percent and + or - 9 percent. Title: Swedish solar telescope: Short summary of instrumentation and observation techniques Authors: Scharmer, Goran; Lofdahl, Mats Bibcode: 1991AdSpR..11e.129S Altcode: 1991AdSpR..11..129S A short summary of the design concepts of the Swedish Solar Telescope at La Palma, is given along with the most important parts of the instrumentation and observing techniques. Our experiences from using high-speed read-out CCDs for solar observations are also discussed. The advantages of this data aquisition system are that it allows real-time frame selection for achieving high spatial resolution, that several cameras can be slaved by one seeing monitor, and that bursts of digital images can be recorded for full spatial coverage of small parts of active regions. Title: SOUP Observations of Solar Activity Authors: Shine, R. A.; Scharmer, G.; Tarbell, T. D.; Title, A. M.; Topka, K. P. Bibcode: 1991max..conf..295S Altcode: No abstract at ADS Title: High-Resolution Spectra of Solar Magnetic Features. I. Analysis of Penumbral Fine Structure Authors: Lites, B. W.; Scharmer, G. B.; Skumanich, A. Bibcode: 1990ApJ...355..329L Altcode: The Swedish Vacuum Telescope on La Palma was used to obtain spectra of the magnetic-sensitive Fe I 630.25 nm line under conditions of exceptional angular resolution (0.32 arcsec) and high spectral resolution (FWHM 2.5 pm). Simultaneous 0.02 s CCD exposures of both the spectrum and the slit-jaw image effectively 'freeze' the atmospheric seeing motions and permit unambiguous identification of the spectra of the various penumbral structures. These spectra reveal the magnetic field strength in penumbral filaments through an intensity fit of the Zeeman splitting of this line. The observations show that: (1) the field strength varies from about 2100 G near the umbra-penumbra boundary to about 900 G at the outer edge of the penumbra, (2) the observed fluctuation of penumbral magnetic field is much less dramatic than the fluctuation in intensity, (3) there is a suggestion of a rapid change in field inclination between some light and dark filaments near the edge of the penumbra, and (4) there is no obvious correlation between Doppler shift (in part due to the Evershed flow) and filament intensity. Title: Detailed Comparison of Quiet and Magnetic Sun Authors: Topka, K.; Ferguson, S.; Shine, R.; Tarbell, T.; Title, A.; Balke, C.; Scharmer, G.; Schmidt, W. Bibcode: 1990BAAS...22R.879T Altcode: No abstract at ADS Title: Penumbral Flows and Magnetic Fields Authors: Shine, R.; Smith, K.; Tarbell, T.; Title, A.; Scharmer, G. Bibcode: 1990BAAS...22..878S Altcode: No abstract at ADS Title: High Resolution Spectroscopy of Penumbral Fine Structure Authors: Bida, T.; Lites, B. W.; Johannesson, A.; Scharmer, G. Bibcode: 1990BAAS...22..880B Altcode: No abstract at ADS Title: Intermittency of Fine Scale Solar Magnetic Fields in the Photosphere Authors: Tarbell, T.; Acton, S.; Topka, K.; Title, A.; Schmidt, W.; Scharmer, G. Bibcode: 1990BAAS...22..878T Altcode: No abstract at ADS Title: Magnetic flux tubes and their relation to continuum and photospheric features Authors: Title, A.; Tarbell, T.; Topka, K.; Cauffman, D.; Balke, C.; Scharmer, G. Bibcode: 1990GMS....58..171T Altcode: An investigation is made of the relationship between photospheric 'filigree' light points, line-center brightness, and magnetic field, as inferred from sets of individual images and films showing a distinct difference between two classes of magnetic regions. While in the first such region the vertical velocity field is average and the magnetic field is mostly confined in narrow lanes, the granulation pattern of the second scale is much smaller, the vertical velocity is lower, and the magnetic field is less compact. Where granulation is normal, excellent correlation is obtained between bright continuum, line-center, and magnetic field line structure. Title: High-Resolution Observations of Emerging Magnetic Fields and Flux Tubes in Active Region Photosphere Authors: Tarbell, T.; Ferguson, S.; Frank, Z.; Shine, R.; Title, A.; Topka, K.; Scharmer, G. Bibcode: 1990IAUS..138..147T Altcode: No abstract at ADS Title: High Resolution Observations of the Photosphere Authors: Title, A. M.; Shine, R. A.; Tarbell, T. D.; Topka, K. P.; Scharmer, G. B. Bibcode: 1990IAUS..138...49T Altcode: No abstract at ADS Title: Intial Results of the Lockheed 1989 La Palma Observing Campaign Authors: Topka, K.; Frank, Z.; Shine, R.; Smith, K.; Tarbell, T.; Title, A.; Scharmer, G. Bibcode: 1989BAAS...21.1111T Altcode: No abstract at ADS Title: High resolution spectra of umbral fine structure from the Swedish solar observatory at La Palma Authors: Lites, B. W.; Scharmer, G. Bibcode: 1989hsrs.conf..286L Altcode: No abstract at ADS Title: Variation of granulation properties on a meso-granular scale Authors: Brandt, P. N.; Ferguson, S.; Scharmer, G. B.; Shine, R. A.; Tarbell, T. D.; Title, A. M.; Topka, K. Bibcode: 1989hsrs.conf..473B Altcode: No abstract at ADS Title: Short Term Evolution of Fine Scale Magnetic Structures Authors: Topka, K.; Frank, Z.; Shine, R.; Tarbell, T.; Title, A.; Scharmer, G.; Balke, A. Bibcode: 1989BAAS...21..842T Altcode: No abstract at ADS Title: Magnetic Field Inclination in Penumbra of a Round Sunspot Observed at Very High Spatial Resolution Authors: Title, A. M.; Frank, Z. A.; Shine, R. A.; Tarbell, T. D.; Scharmer, G. Bibcode: 1989BAAS...21Q.837T Altcode: No abstract at ADS Title: Modeling the Flow in Solar Vortices Authors: Simon, G. W.; Weiss, N. O.; Scharmer, G. B. Bibcode: 1989BAAS...21Q.829S Altcode: No abstract at ADS Title: Observations of Running Penumbral Waves Authors: Shine, R.; Tarbell, T.; Title, A.; Topka, K.; Frank, Z.; Scharmer, G. Bibcode: 1989BAAS...21..837S Altcode: No abstract at ADS Title: The Magnetic Field Strength of Umbral Dots Authors: Lites, B. W.; Bida, T. A.; Scharmer, G. B. Bibcode: 1989BAAS...21..854L Altcode: No abstract at ADS Title: High Resolution Granulation Observations from La Palma: Techniques and First Results Authors: Scharmer, G. B. Bibcode: 1989ASIC..263..161S Altcode: 1989ssg..conf..161S No abstract at ADS Title: Examples of high resolution observations of solar fine structures made at La Palma. Authors: Jensen, E.; Engvold, O.; Scharmer, G. B. Bibcode: 1989ftsa.conf...67J Altcode: Two video films from the Swedish Vacuum Solar Telescope at La Palma were shown. Some basic parameters of the telescope are given. Title: Vortex Motion of the Solar Granulation Authors: Brandt, P. N.; Scharmer, G. B.; Ferguson, S. H.; Shine, R. A.; Tarbell, T. D.; Title, A. M. Bibcode: 1989ASIC..263..305B Altcode: 1989ssg..conf..305B No abstract at ADS Title: Constraints Imposed by Very High Resolution Spectra and Images on Theoretical Simulations of Granular Convection Authors: Lites, B. W.; Nordlund, Å.; Scharmer, G. B. Bibcode: 1989ASIC..263..349L Altcode: 1989ssg..conf..349L No abstract at ADS Title: Fractal Geometry of Convective Flows and Magnetic Fields in the Solar Atmosphere Authors: Tarbell, T.; Ferguson, S.; Title, A.; Scharmer, G.; Brandt, P. Bibcode: 1988BAAS...20Q1010T Altcode: No abstract at ADS Title: Observations of Granulation in Quiet and Magnetic Sun from the Swedish Solar Observatory on LaPalma Authors: Topka, K.; Ferguson, S.; Frank, Z.; Shine, R.; Tarbell, T.; Title, A.; Wolfson, J.; Scharmer, G.; Brandt, P. Bibcode: 1988BAAS...20S1010T Altcode: No abstract at ADS Title: Solar Activity and Flare Observations from the Swedish Solar Observatory on La Palma Authors: Wolfson, J.; Ferguson, S.; Frank, Z.; Shine, R.; Tarbell, T.; Title, A.; Topka, K.; Scharmer, G.; Brandt, P.; Gurman, J. Bibcode: 1988BAAS...20..978W Altcode: No abstract at ADS Title: Measurements of Turbulent Diffusion by Solar Granulation in Quiet and Magnetic Areas Authors: Title, A.; Ferguson, S.; Tarbell, T.; Scharmer, G.; Brandt, P. Bibcode: 1988BAAS...20R1010T Altcode: No abstract at ADS Title: Vortex flow in the solar photosphere Authors: Brandt, P. N.; Scharmer, G. B.; Ferguson, S.; Shine, R. A.; Tarbell, T. D.; Title, A. M. Bibcode: 1988Natur.335..238B Altcode: Convective flow fields in the solar atmosphere play a key role in the concentration and dispersal of magnetic flux1, but because the individual flow elements-the solar granules-are a few arcsec or less in size, studies of their motions have been limited by the distortion and blurring of the Earth's atmosphere ('seeing'). We report here a very high-quality series of granulation images taken at the new Swedish Solar Observatory on La Palma (Canary Islands) which have permitted flow measurements at the sub-arcsec level. These movies show a vortex structure which visibly dominates the motion of the granules in its neighbourhood and persists for the 1.5 h duration of the movie. If such vortices are a common feature of the solar convective zone, they may provide an important mechanism for the heating of stellar chromospheres and coronae by twisting the footprints of magnetic flux tubes. Title: High Resolution Observations of Penubral Magnetic Fields Authors: Lites, B. W.; Scharmer, G. B. Bibcode: 1988BAAS...20..681L Altcode: No abstract at ADS Title: Solar Granulation Movies of Exceptional Spatial Resolution: Observations and Simulations of Horizontal Convective Flows Authors: Title, A.; Shine, R.; Ferguson, S.; Tarbell, T.; Brandt, P.; Scharmer, G. Bibcode: 1988BAAS...20R.679T Altcode: No abstract at ADS Title: Vortex Flow in Granulation Authors: Scharmer, G.; Brandt, P.; Title, A.; Shine, R.; Ferguson, S. Bibcode: 1987BAAS...19Q1118S Altcode: No abstract at ADS Title: Power Spectra of Solar Granulation Authors: Acton, D. S.; Brandt, P.; Scharmer, G.; Dunn, D.; Tarbell, T. D.; Title, A. M.; Smithson, R. C. Bibcode: 1987BAAS...19.1118A Altcode: No abstract at ADS Title: The Swedish 50 cm Vacuum Solar Telescope: Concepts and Auxiliary Instrumentation Authors: Scharmer, G. B. Bibcode: 1987rfsm.conf..349S Altcode: The paper reviews the concepts of the Swedish 50 cm vacuum solar telescope. The auxiliary instrumentation, including the Littrow spectrograph, the Image Sharpness Selector and the image acquisition system, are also discussed briefly. The strengths and weaknesses of the entire system are pointed out in order to guide future users towards optimized observing programs and procedures. Title: Concepts for the Swedish 50-cm vacuum solar telescope. Authors: Scharmer, G. B.; Brown, D. S.; Pettersson, L.; Rehn, J. Bibcode: 1985ApOpt..24.2558S Altcode: The concepts of a new major but medium-sized solar telescope are described. Located at one of the astronomical sites, La Palma, the telescope uses a doublet lens as the image forming element to minimize the number of reflecting surfaces, antireflection coatings to minimize stray light, and a separate guiding telescope outside the aperture of the telescope to avoid image degradation due to diffraction effects. Mechanically, the telescope uses the Sacramento Peak turret design which produces a minimum of local seeing effects. A short spectrograph, designed for minimum scattered light along and perpendicular to the slit, is also described. In several respects the telescope is different from other recently constructed or planned solar telescopes. Title: Steady flows in active regions observed with the HeI 10830 Å line Authors: Lites, B. W.; Keil, S. L.; Scharmer, G. B.; Wyller, A. A. Bibcode: 1985SoPh...97...35L Altcode: We show that the He I 10830 A line gives reliable Doppler shift measurements in the upper chromosphere above active regions. Persistent flow patterns in active regions observed near the solar limb show features previously noted in Dopplergrams using the CIV transition region ultraviolet emission line. Unlike the CIV measurements, however, the He I absorption shows a strong correlation with the line-of-sight velocity images in certain regions of some active regions. Title: A new approach to multi-level non-LTE radiative transfer problems. Authors: Scharmer, G. B.; Carlsson, M. Bibcode: 1985JCoPh..59...56S Altcode: A new approach to the numerical solution of multilevel, non-LTE problems is described. The standard non-LTE multilevel problem is formulated, and the statistical equilibrium equations and the radiative transfer equation are linearized. It is shown how to precondition the statistical equilibrium equations and the radiative transfer equation in a way which enables the solution of problems with strong numerical cancellation which arise from 'passive' scatterings at large optical depth. Simplifications in the numerical representation of radiative transfer processes are introduced which lead to rapid methods for setting up and solving the statistical equilibrium equations. Some calculations which have been made to test the convergence properties of the present scheme are described, and some generalizations of the present methods are briefly outlined. Title: Steady flows in active regions observed with the He I 10830 Å line. Authors: Lites, B. W.; Keil, S. L.; Scharmer, G. B.; Wyller, A. A. Bibcode: 1985cdm..proc..287L Altcode: No abstract at ADS Title: Sweden's solar and stellar telescopes on La Palma Authors: Wyller, A. A.; Scharmer, G. B. Bibcode: 1985VA.....28..467W Altcode: The astrophysical research station on La Palma of the Swedish Royal Academy of Sciences contains an 0.6m stellar telescope, used for photometry, and a solar telescope. The latter is being upgraded from a 44cm Cassegrain telescope via a 25cm lens test telescope to a 50cm lens telescope. An account is given of the new design, with attention to its principal aims of minimum reduction in practice of the MTF of the theoretical optical design and control of seeing degradation. The instruments of both the stellar telescope and the solar telescope, including the URSIES spectrograph, are described, and an account is given of some results from the first years of operation. Title: Effects of meso-scale velocity fields on the solar Ca II spectral lines. Authors: Carlsson, M.; Scharmer, G. B. Bibcode: 1985cdm..proc..137C Altcode: The effects of random mesoscale velocity fields on the solar Ca II K-line and the infrared 8542 A line are discussed, and average profiles and radiative cooling functions are compared with those obtained from a combination of microturbulence and macroturbulence. Profiles in the mesoscale regime could not be reproduced with any combination of micro- and macroturbulence owing to the fact that mesoscale velocity fields give core intensities that are much higher than those of static atmospheres. Calculations of radiative cooling in the two lines were different when mesoscale velocity fields were taken into account; this difference was due mainly to a redistribution of the radiative cooling between the lines. Title: A new method for solving multi-level non-LTE problems. Authors: Scharmer, G. B.; Carlsson, M. Bibcode: 1985ASIC..152..189S Altcode: 1985pssl.proc..189S A new scheme for solving multi-level non-LTE problems is described. This method uses an approximate operator for the relation between the intensity and the source function. This operator results in a matrix equation for the population numbers which has a simple and characteristic structure. Solutions are obtained such that the results are "exact", irrespective of the choice of the approximate operator. Title: Pannel discussion on radiative transfer methods. Authors: Kalkofen, W.; Linsky, J.; Rybicki, G.; Scharmer, G.; Weherse, R. Bibcode: 1985ASIC..152..233K Altcode: 1985pssl.proc..233K No abstract at ADS Title: Accurate solutions to non-LTE problems using approximate Lambda operators. Authors: Scharmer, G. B. Bibcode: 1984mrt..book..173S Altcode: 1984mrt..conf..173S A numerical method for the approximate solution of non-LTE problems is described. The essence of this method is the evaluation of an approximate operator, relating the intensity Iν to the source function Sν along a ray. Using this operator, an approximate matrix equation for the line-source function is derived. The solution of this equation generally gives less than 10 - 30% errors in the line-source function even when there are large gradients in the Doppler width or in the macroscopic velocity. Furthermore, a linearization method for the exact solution on non-LTE problems is presented. Title: A Linearization Method for Solving Partial Redistribution Problems Authors: Scharmer, G. B. Bibcode: 1983A&A...117...83S Altcode: A linearization method for solving partial redistribution (PRD) problems is presented. The basic idea of this method, due to Cannon et al. (1975), is the evaluation of an approximate operator which corresponds to assuming that radiation is completely redistributed over the line profile. Using this approximate operator, corrections to the line-source function are obtained iteratively with very small amounts of computing time. The present method uses a Rybicki-type of elimination scheme which requires small core storage even when the number of frequency-angle points is large.

The linearization method for solving PRD problems is combined with the linearization method of Scharmer (1981) and Scharmer and Nordlund (1982), used to solve complete redistribution problems. This decreases the computing time required to solve a given problem.

These methods for solving PRD problems are particularly efficient when the number of frequency-angle points is large and can be used even on very small computers. Existing CRD programs for solving complete redistribution problems can easily be modified to incorporate PRD. Title: DQPT: a computer program for solving non-LTE problems for two-level atoms in one-dimensional semi-infinite media with velocity fields. Authors: Scharmer, G. B.; Nordlund, Å. Bibcode: 1982StoOR..19.....S Altcode: No abstract at ADS Title: Solutions to radiative transfer problems using approximate lambda operators Authors: Scharmer, G. B. Bibcode: 1981ApJ...249..720S Altcode: An approximate analytical method and an exact numerical method for solving non-LTE problems are presented. The analytical method relies on concepts of radiative transfer theory such as the core-saturation approximation, the Eddington-Barbier relation, and the upper boundary condition, to derive a simple first-order differential equation for the line source function. The more efficient technique is developed using a linear test function and a one-point quadrature relation between the specific intensity and the source function. A 1% accuracy in the line source function can be obtained after four iterations, with a very rapid convergence and no evidence of numerical instabilities. Title: OSO-8 Observations of CAII H and K MGII H and K Lyman-Alpha and Lyman-Beta above a Sunspot Authors: Kneer, F.; Scharmer, G.; Mattig, W.; Wyller, A.; Artzner, G.; Lemaire, P.; Vial, J. C. Bibcode: 1981SoPh...69..289K Altcode: Observations with the French (L.P.S.P.) experiment on board OSO-8 of a sunspot and nearby plage region are described. The behaviour of the emission cores of the Ca II H and K and Mg II h and k resonance lines is very similar and the correspondence in intensity between the four lines persists in all observed features. In contrast, the Lyman lines show little correlation with the other lines. Their emission regions appear broader in the spectroheliograms than the underlying sunspot structure and must not necessarily possess a counterpart in lower layers. From the central intensity of Lα above the umbra an electron density of 4.3 × 1010 cm-3 ≲ne* ≲2.3 × 1011 cm-3 at 20 000 K is estimated. Title: The Wilson-Bappu effect as a result of supersonic turbulence. Authors: Scharmer, G. B. Bibcode: 1976A&A....53..341S Altcode: An analysis is performed to investigate qualitatively the possibility that a stellar chromosphere is dominated by the presence of supersonic turbulence. It is assumed that a chromosphere transforms only mechanical energy into radiation and is optically thin in the main energy-loss spectral region, that turbulence energy is distributed throughout the chromosphere in the form of turbulent eddies, and that the turbulence is supersonic. Momentum and energy conservation equations are combined with a boundary condition for the mechanical-energy input to obtain an expression for the turbulent velocity, the mechanical-energy flux is normalized relative to the photospheric radiative flux, and the dependence of chromospheric properties on surface gravity and effective temperature is examined. Assuming that the turbulent velocity is proportional to the line width of chromospheric Ca II K emission, it is concluded that the Wilson-Bappu effect implies temporally and spatially inhomogeneous chromospheres. The results are applied to the T Tauri star RU Lup, and observed widths of chromospheric emission lines are interpreted as being due to a supersonic turbulent velocity field.