Author name code: rutten-rob ADS astronomy entries on 2022-09-14 author:("Rutten, Robert J." OR ="Rutten, Rob" OR ="Rutten, Robert" OR ="Rutten, R.J.") NOT =author:"Rutten, R." ------------------------------------------------------------------------ Title: Cornelis de Jager: In Memoriam Authors: Rutten, Robert J.; Engvold, Oddbjørn; Nieuwenhuizen, Adrianus C. T. Bibcode: 2022SoPh..297...15R Altcode: 2022arXiv220111496R Cornelis ("Kees") de Jager, the co-founder of the journal Solar Physics, passed away on 27 May 2021. He was an exemplary human being, a great scientist, and he had a large impact on our field. In this tribute, we first briefly summarize his life and career and then describe some of his solar activities, from his Ph.D. thesis on the hydrogen lines in 1952 to the book on cycle-climate relations that he completed last year. Title: Compendium solar spectrum formation Authors: Rutten, Robert J. Bibcode: 2021arXiv210302369R Altcode: The solar spectrum conveys most of our diagnostics to find out how our star works. They must be understood for utilization, but solar spectrum formation is complex because the interaction of matter and radiation within the solar atmosphere suffers non-local control in space, wavelength, and time. These complexities are summarized and illustrated with classic literature. They combine in chromospheric spectrum formation. Title: Small-scale solar surface magnetism Authors: Rutten, Robert Bibcode: 2020smvc.book...29R Altcode: 2021arXiv210514533R This contribution to "Solar Magnetic Variability and Climate" reviews small-scale magnetic features on the solar surface, in particular, the strong-field but tiny magnetic concentrations that constitute network and plage and represent most magnetism outside sunspots and filaments. Where these are mostly of the same polarity, as in active region plage, their occurrence varies with the activity variations measured by the sunspot number, but when they appear bipolar-mixed on small scales they can also result from granular-scale dynamo action that does not vary with the cycle. Title: SolO campfires in SDO images Authors: Rutten, Robert J. Bibcode: 2020arXiv200900376R Altcode: I present the appearance of "Solar Orbiter campfires" in simultaneous images from the Solar Dynamics Observatory where most are visible although less sharp. I also show such features elsewhere in the SDO database. I show some in detail and discuss their nature. Title: Solar Hα features with hot onsets. IV. Network fibrils Authors: Rutten, Robert J.; Rouppe van der Voort, Luc H. M.; De Pontieu, Bart Bibcode: 2019A&A...632A..96R Altcode: 2019arXiv190809315R Even in quiet areas underneath coronal holes the solar chromosphere contains ubiquitous heating events. They tend to be small scale and short lived, hence difficult to identify. Here we do not address their much-debated contribution to outer-atmosphere heating, but their aftermaths. We performed a statistical analysis of high-resolution observations in the Balmer Hα line to suggest that many slender dark Hα fibrils spreading out from network represent cooling gas that outlines tracks of preceding rapid type II spicule events or smaller similar but as yet unresolved heating agents in which the main gas constituent, hydrogen, ionizes at least partially. Subsequent recombination then causes dark Hα fibrils enhanced by nonequilibrium overopacity. We suggest that the extraordinary fibrilar appearance of the Hα chromosphere around network results from intermittent, frequent small-scale prior heating.

Movies associated to Fig. 3 and blinkers are available at https://www.aanda.org Title: Non-Equilibrium Spectrum Formation Affecting Solar Irradiance Authors: Rutten, Robert J. Bibcode: 2019SoPh..294..165R Altcode: 2019arXiv190804624R This is an overview of non-equilibrium aspects of the formation of solar continua and lines affecting the contributions by magnetic network and plage to spectrally resolved solar irradiance. After a brief summary of these contributions and a compact refresher of solar spectrum formation, the emphasis is on graphical exposition. Major obstacles for simulation-based irradiance studies are how to cope with NLTE scattering in the violet and ultraviolet line haze and how to cope with retarded hydrogen opacities in infrared and mm radiation. Title: Automating Ellerman bomb detection in ultraviolet continua Authors: Vissers, Gregal J. M.; Rouppe van der Voort, Luc H. M.; Rutten, Robert J. Bibcode: 2019A&A...626A...4V Altcode: 2019arXiv190107975V Ellerman bombs are transient brightenings in the wings of Hα 6563 Å that pinpoint photospheric sites of magnetic reconnection in solar active regions. Their partial visibility in the 1600 Å and 1700 Å continua registered routinely by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) offers a unique opportunity to inventory such magnetic-field disruptions throughout the AIA database if a reliable recipe for their detection can be formulated. This is done here. We have improved and applied an Hα Ellerman bomb detection code to ten data sets spanning viewing angles from solar disc centre to the limb. They combine high-quality Hα imaging spectroscopy from the Swedish 1 m Solar Telescope with simultaneous AIA imaging around 1600 Å and 1700 Å. A trial grid of brightness, lifetime and area constraints is imposed on the AIA images to define optimal recovery of the 1735 Ellerman bombs detected in Hα. The best results when optimising simultaneously for recovery fraction and reliability are obtained from 1700 Å images by requiring 5σ brightening above the average 1700 Å nearby quiet-Sun intensity, lifetime above one minute, area of 1-18 AIA pixels. With this recipe 27% of the AIA detections are Hα-detected Ellerman bombs while it recovers 19% of these (of which many are smaller than the AIA resolution). Better yet, among the top 10% AIA 1700 Å detections selected with combined brightness, lifetime and area thresholds as many as 80% are Hα Ellerman bombs. Automated selection of the best 1700 Å candidates therefore opens the entire AIA database for detecting most of the more significant photospheric reconnection events. This proxy is applicable as a flux-dynamics tell-tale in studying any Earth-side solar active region since early 2010 up to the present. Title: Solar Ultraviolet Bursts Authors: Young, Peter R.; Tian, Hui; Peter, Hardi; Rutten, Robert J.; Nelson, Chris J.; Huang, Zhenghua; Schmieder, Brigitte; Vissers, Gregal J. M.; Toriumi, Shin; Rouppe van der Voort, Luc H. M.; Madjarska, Maria S.; Danilovic, Sanja; Berlicki, Arkadiusz; Chitta, L. P.; Cheung, Mark C. M.; Madsen, Chad; Reardon, Kevin P.; Katsukawa, Yukio; Heinzel, Petr Bibcode: 2018SSRv..214..120Y Altcode: 2018arXiv180505850Y The term "ultraviolet (UV) burst" is introduced to describe small, intense, transient brightenings in ultraviolet images of solar active regions. We inventorize their properties and provide a definition based on image sequences in transition-region lines. Coronal signatures are rare, and most bursts are associated with small-scale, canceling opposite-polarity fields in the photosphere that occur in emerging flux regions, moving magnetic features in sunspot moats, and sunspot light bridges. We also compare UV bursts with similar transition-region phenomena found previously in solar ultraviolet spectrometry and with similar phenomena at optical wavelengths, in particular Ellerman bombs. Akin to the latter, UV bursts are probably small-scale magnetic reconnection events occurring in the low atmosphere, at photospheric and/or chromospheric heights. Their intense emission in lines with optically thin formation gives unique diagnostic opportunities for studying the physics of magnetic reconnection in the low solar atmosphere. This paper is a review report from an International Space Science Institute team that met in 2016-2017. Title: Solar ALMA predictions: tutorial Authors: Rutten, R. J. Bibcode: 2017IAUS..327....1R Altcode: 2016arXiv161105308R I have proposed that long Hα fibrils are caused by heating events of which the tracks are afterwards outlined by contrails of cooling gas with extraordinary Hα opacity and yet larger opacity at the ALMA wavelengths. Here I detail the radiative transfer background. Title: Slender Ca II H Fibrils Mapping Magnetic Fields in the Low Solar Chromosphere Authors: Jafarzadeh, S.; Rutten, R. J.; Solanki, S. K.; Wiegelmann, T.; Riethmüller, T. L.; van Noort, M.; Szydlarski, M.; Blanco Rodríguez, J.; Barthol, P.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez, D.; Schmidt, W. Bibcode: 2017ApJS..229...11J Altcode: 2016arXiv161003104J A dense forest of slender bright fibrils near a small solar active region is seen in high-quality narrowband Ca II H images from the SuFI instrument onboard the Sunrise balloon-borne solar observatory. The orientation of these slender Ca II H fibrils (SCF) overlaps with the magnetic field configuration in the low solar chromosphere derived by magnetostatic extrapolation of the photospheric field observed with Sunrise/IMaX and SDO/HMI. In addition, many observed SCFs are qualitatively aligned with small-scale loops computed from a novel inversion approach based on best-fit numerical MHD simulation. Such loops are organized in canopy-like arches over quiet areas that differ in height depending on the field strength near their roots. Title: Solar H-alpha features with hot onsets. III. Long fibrils in Lyman-alpha and with ALMA Authors: Rutten, R. J. Bibcode: 2017A&A...598A..89R Altcode: 2016arXiv160901122R In H-alpha most of the solar surface is covered by dense canopies of long opaque fibrils, but predictions for quiet-Sun observations with ALMA have ignored this fact. Comparison with Ly-alpha suggests that the extraordinary opacity of H-alpha fibrils is caused by hot precursor events. Application of a recipe that assumes momentary Saha-Boltzmann extinction during their hot onset to millimeter wavelengths suggests that ALMA will observe H-alpha-like fibril canopies, not acoustic shocks underneath, and will yield data more interesting than if these canopies were transparent.

An additional file is available at the end of the PDF file of this article.This study is offered as compliment to M.W.M. de Graauw. Our ways, objects, instruments and spectral domains parted after the 1970 eclipse but converge here. Title: Observations and diagnostics of the solar chromosphere Authors: Rutten, Rob Bibcode: 2017psio.confE..42R Altcode: No abstract at ADS Title: Solar Hα features with hot onsets. II. A contrail fibril Authors: Rutten, R. J.; Rouppe van der Voort, L. H. M. Bibcode: 2017A&A...597A.138R Altcode: 2016arXiv160907616R The solar chromosphere observed in Hα consists mostly of narrow fibrils. The longest typically originate in network or plage and arch far over adjacent internetwork. We use data from multiple telescopes to analyze one well-observed example in a quiet area. It resulted from the earlier passage of an accelerating disturbance in which the gas was heated to high temperature as in the spicule-II phenomenon. After this passage a dark Hα fibril appeared as a contrail. We use Saha-Boltzmann extinction estimation to gauge the onset and subsequent visibilities in various diagnostics and conclude that such Hα fibrils can indeed be contrail phenomena, not indicative of the thermodynamic and magnetic environment when they are observed but of more dynamic happenings before. They do not connect across internetwork cells but represent launch tracks of heating events and chart magnetic field during launch, not at present. Title: Reconnection brightenings in the quiet solar photosphere Authors: Rouppe van der Voort, Luc H. M.; Rutten, Robert J.; Vissers, Gregal J. M. Bibcode: 2016A&A...592A.100R Altcode: 2016arXiv160603675R We describe a new quiet-Sun phenomenon which we call quiet-Sun Ellerman-like brightenings (QSEB). QSEBs are similar to Ellerman bombs (EB) in some respects but differ significantly in others. EBs are transient brightenings of the wings of the Balmer Hα line that mark strong-field photospheric reconnection in complex active regions. QSEBs are similar but smaller and less intense Balmer-wing brightenings that occur in quiet areas away from active regions. In the Hα wing, we measure typical lengths of less than 0.5 arcsec, widths of 0.23 arcsec, and lifetimes of less than a minute. We discovered them using high-quality Hα imaging spectrometry from the Swedish 1-m Solar Telescope (SST) and show that, in lesser-quality data, they cannot be distinguished from more ubiquitous facular brightenings, nor in the UV diagnostics currently available from space platforms. We add evidence from concurrent SST spectropolarimetry that QSEBs also mark photospheric reconnection events, but in quiet regions on the solar surface.

The movies are available in electronic form at http://www.aanda.org Title: Hα features with hot onsets. I. Ellerman bombs Authors: Rutten, R. J. Bibcode: 2016A&A...590A.124R Altcode: 2016arXiv160103280R Ellerman bombs are transient brightenings of the wings of the Balmer lines that uniquely mark reconnection in the solar photosphere. They are also bright in strong Ca II and ultraviolet lines and in ultraviolet continua, but they are not visible in the optical continuum and the Na I D and Mg I b lines. These discordant visibilities invalidate all published Ellerman bomb modeling. I argue that the assumption of Saha-Boltzmann lower-level populations is informative to estimate bomb-onset opacities for these diverse diagnostics, even and especially for Hα, and employ such estimates to gauge the visibilities of Ellerman bomb onsets in all of them. They constrain Ellerman bomb formation to temperatures 10 000-20 000 K and hydrogen densities around 1015 cm-3. Similar arguments likely hold for Hα visibility in other transient phenomena with hot and dense onsets. Title: Ellerman Bombs at High Resolution. III. Simultaneous Observations with IRIS and SST Authors: Vissers, G. J. M.; Rouppe van der Voort, L. H. M.; Rutten, R. J.; Carlsson, M.; De Pontieu, B. Bibcode: 2015ApJ...812...11V Altcode: 2015arXiv150700435V Ellerman bombs (EBs) are transient brightenings of the extended wings of the solar Balmer lines in emerging active regions. We describe their properties in the ultraviolet lines sampled by the Interface Region Imaging Spectrograph (IRIS), using simultaneous imaging spectroscopy in Hα with the Swedish 1-m Solar Telescope (SST) and ultraviolet images from the Solar Dynamics Observatory for Ellerman bomb detection and identification. We select multiple co-observed EBs for detailed analysis. The IRIS spectra strengthen the view that EBs mark reconnection between bipolar kilogauss fluxtubes with the reconnection and the resulting bi-directional jet located within the solar photosphere and shielded by overlying chromospheric fibrils in the cores of strong lines. The spectra suggest that the reconnecting photospheric gas underneath is heated sufficiently to momentarily reach stages of ionization normally assigned to the transition region and the corona. We also analyze similar outburst phenomena that we classify as small flaring arch filaments and ascribe to reconnection at a higher location. They have different morphologies and produce hot arches in million-Kelvin diagnostics. Title: Ellerman Bombs at High Resolution. IV. Visibility in Na I and Mg I Authors: Rutten, R. J.; Rouppe van der Voort, L. H. M.; Vissers, G. J. M. Bibcode: 2015ApJ...808..133R Altcode: 2015arXiv150604426R Ellerman bombs are transient brightenings of the wings of the solar Balmer lines that mark reconnection in the photosphere. Ellerman noted in 1917 that he did not observe such brightenings in the Na i D and Mg i b lines. This non-visibility should constrain EB interpretation, but has not been addressed in published bomb modeling. We therefore test Ellerman’s observation and confirm it using high-quality imaging spectrometry with the Swedish 1-m Solar Telescope. However, we find a diffuse brightness in these lines that seems to result from prior EBs. We tentatively suggest this is a post-bomb hot-cloud phenomenon also found in recent EB spectroscopy in the ultraviolet. Title: Ellerman Bombs at High Resolution. II. Triggering, Visibility, and Effect on Upper Atmosphere Authors: Vissers, Gregal J. M.; Rouppe van der Voort, Luc H. M.; Rutten, Robert J. Bibcode: 2013ApJ...774...32V Altcode: 2013arXiv1307.1547V We use high-resolution imaging spectroscopy with the Swedish 1-m Solar Telescope (SST) to study the transient brightenings of the wings of the Balmer Hα line in emerging active regions that are called Ellerman bombs. Simultaneous sampling of Ca II 8542 Å with the SST confirms that most Ellerman bombs also occur in the wings of this line, but with markedly different morphology. Simultaneous images from the Solar Dynamics Observatory (SDO) show that Ellerman bombs are also detectable in the photospheric 1700 Å continuum, again with differing morphology. They are also observable in 1600 Å SDO images, but with much contamination from C IV emission in transition-region features. Simultaneous SST spectropolarimetry in Fe I 6301 Å shows that Ellerman bombs occur at sites of strong-field magnetic flux cancellation between small bipolar strong-field patches that rapidly move together over the solar surface. Simultaneous SDO images in He II 304 Å, Fe IX 171 Å, and Fe XIV 211 Å show no clear effect of the Ellerman bombs on the overlying transition region and corona. These results strengthen our earlier suggestion, based on Hα morphology alone, that the Ellerman bomb phenomenon is a purely photospheric reconnection phenomenon. Title: Ellerman bombs: fallacies, fads, usage Authors: Rutten, Robert J.; Vissers, Gregal J. M.; Rouppe van der Voort, Luc H. M.; Sütterlin, Peter; Vitas, Nikola Bibcode: 2013JPhCS.440a2007R Altcode: 2013arXiv1304.1364R Ellerman bombs are short-lived brightenings of the outer wings of Hα that occur in active regions with much flux emergence. We point out fads and fallacies in the extensive Ellerman bomb literature, discuss their appearance in various spectral diagnostics, and advocate their use as indicators of field reconfiguration in active-region topography using AIA 1700 Å images. Title: Twists to Solar Spicules Authors: Rutten, R. J. Bibcode: 2013ASPC..470...49R Altcode: 2012arXiv1205.5114R Type-II solar spicules appear as long, thin, highly dynamic strands of field-tied matter that feed significant mass and energy to the corona and solar wind. A recent result is that they exhibit torsional Alfvén waves in addition to accelerating outflows and swaying motions due to transverse Alfvénic waves. I summarize this finding and then re-interpret older observations in its light: the striking similarity of near-limb scenes in the outer blue and red wings of H α, and the tilts of absorption lines with respect to emission lines in eclipse spectra taken in 1973. Title: LEMUR: Large European module for solar Ultraviolet Research. European contribution to JAXA's Solar-C mission Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric; Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len; Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green, Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem, Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet, Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto, Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu, Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele; Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas; Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann, Thomas; Winter, Berend; Young, Peter Bibcode: 2012ExA....34..273T Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T The solar outer atmosphere is an extremely dynamic environment characterized by the continuous interplay between the plasma and the magnetic field that generates and permeates it. Such interactions play a fundamental role in hugely diverse astrophysical systems, but occur at scales that cannot be studied outside the solar system. Understanding this complex system requires concerted, simultaneous solar observations from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at high spatial resolution (between 0.1'' and 0.3''), at high temporal resolution (on the order of 10 s, i.e., the time scale of chromospheric dynamics), with a wide temperature coverage (0.01 MK to 20 MK, from the chromosphere to the flaring corona), and the capability of measuring magnetic fields through spectropolarimetry at visible and near-infrared wavelengths. Simultaneous spectroscopic measurements sampling the entire temperature range are particularly important. These requirements are fulfilled by the Japanese Solar-C mission (Plan B), composed of a spacecraft in a geosynchronous orbit with a payload providing a significant improvement of imaging and spectropolarimetric capabilities in the UV, visible, and near-infrared with respect to what is available today and foreseen in the near future. The Large European Module for solar Ultraviolet Research (LEMUR), described in this paper, is a large VUV telescope feeding a scientific payload of high-resolution imaging spectrographs and cameras. LEMUR consists of two major components: a VUV solar telescope with a 30 cm diameter mirror and a focal length of 3.6 m, and a focal-plane package composed of VUV spectrometers covering six carefully chosen wavelength ranges between 170 Å and 1270 Å. The LEMUR slit covers 280'' on the Sun with 0.14'' per pixel sampling. In addition, LEMUR is capable of measuring mass flows velocities (line shifts) down to 2 km s - 1 or better. LEMUR has been proposed to ESA as the European contribution to the Solar C mission. Title: The quiet-Sun photosphere and chromosphere Authors: Rutten, R. J. Bibcode: 2012RSPTA.370.3129R Altcode: 2011arXiv1110.6606R The overall structure and the fine structure of the solar photosphere outside active regions are largely understood, except possibly important roles of a turbulent near-surface dynamo at its bottom, internal gravity waves at its top, and small-scale vorticity. Classical 1D static radiation-escape modelling has been replaced by 3D time-dependent MHD simulations that come closer to reality. The solar chromosphere, in contrast, remains ill-understood although its pivotal role in coronal mass and energy loading makes it a principal research area. Its fine structure defines its overall structure, so that hard-to-observe and hard-to-model small-scale dynamical processes are the key to understanding. However, both chromospheric observation and chromospheric simulation presently mature towards the required sophistication. The open-field features seem of greater interest than the easier-to-see closed-field features. Title: Ubiquitous Torsional Motions in Type II Spicules Authors: De Pontieu, B.; Carlsson, M.; Rouppe van der Voort, L. H. M.; Rutten, R. J.; Hansteen, V. H.; Watanabe, H. Bibcode: 2012ApJ...752L..12D Altcode: 2012arXiv1205.5006D Spicules are long, thin, highly dynamic features that jut out ubiquitously from the solar limb. They dominate the interface between the chromosphere and corona and may provide significant mass and energy to the corona. We use high-quality observations with the Swedish 1 m Solar Telescope to establish that so-called type II spicules are characterized by the simultaneous action of three different types of motion: (1) field-aligned flows of order 50-100 km s-1, (2) swaying motions of order 15-20 km s-1, and (3) torsional motions of order 25-30 km s-1. The first two modes have been studied in detail before, but not the torsional motions. Our analysis of many near-limb and off-limb spectra and narrowband images using multiple spectral lines yields strong evidence that most, if not all, type II spicules undergo large torsional modulation and that these motions, like spicule swaying, represent Alfvénic waves propagating outward at several hundred km s-1. The combined action of the different motions explains the similar morphology of spicule bushes in the outer red and blue wings of chromospheric lines, and needs to be taken into account when interpreting Doppler motions to derive estimates for field-aligned flows in spicules and determining the Alfvénic wave energy in the solar atmosphere. Our results also suggest that large torsional motion is an ingredient in the production of type II spicules and that spicules play an important role in the transport of helicity through the solar atmosphere. Title: Chromospheric backradiation in ultraviolet continua and Hα Authors: Rutten, R. J.; Uitenbroek, H. Bibcode: 2012A&A...540A..86R Altcode: 2012arXiv1203.0396R A recent paper states that ultraviolet backradiation from the solar transition region and upper chromosphere strongly affects the degree of ionization of minority stages at the top of the photosphere, i.e., in the temperature minimum of the one-dimensional static model atmospheres presented in that paper. We show that this claim is incompatible with observations and we demonstrate that the pertinent ionization balances are instead dominated by outward photospheric radiation, as in older static models. We then analyze the formation of Hα in the above model and show that it has significant backradiation across the opacity gap by which Hα differs from other strong scatttering lines. Title: Graphical introduction to chromospheric line formation Authors: Rutten, Rob Bibcode: 2012decs.confE.110R Altcode: The basics of chromospheric line formation theory were laid out in the 1960s and 1970s by e.g., Thomas, Avrett, Hummer, Jefferies, Mihalas, Shine, Milkey. Since then there has been a long silence, without much progress in understanding the chromosphere or its diagnostics. At present, the situation changes thanks to better ground-based observing, space-based monitoring, and increasingly realistic numerical simulations. There is a now a strong need to revamp classical one-dimensional static modeling as basis for chromospheric line interpretation into 3D dynamic understanding of the major diagnostics, including IRIS's Mg II h&k. In this introduction I aim to explain the old wisdom in tutorial fashion, using cartoons and graphs as means towards an intuitive grasp of fads and fallacies of chromospheric line formation. Title: Ellerman Bombs at High Resolution. I. Morphological Evidence for Photospheric Reconnection Authors: Watanabe, Hiroko; Vissers, Gregal; Kitai, Reizaburo; Rouppe van der Voort, Luc; Rutten, Robert J. Bibcode: 2011ApJ...736...71W Altcode: 2011arXiv1105.4008W High-resolution imaging-spectroscopy movies of solar active region NOAA 10998 obtained with the Crisp Imaging Spectropolarimeter at the Swedish 1-m Solar Telescope show very bright, rapidly flickering, flame-like features that appear intermittently in the wings of the Balmer Hα line in a region with moat flows and likely some flux emergence. They show up at regular Hα blue-wing bright points that outline the magnetic network, but flare upward with much larger brightness and distinct "jet" morphology seen from aside in the limbward view of these movies. We classify these features as Ellerman bombs and present a morphological study of their appearance at the unprecedented spatial, temporal, and spectral resolution of these observations. The bombs appear along the magnetic network with footpoint extents up to 900 km. They show apparent travel away from the spot along the pre-existing network at speeds of about 1 km s-1. The bombs flare repetitively with much rapid variation at timescales of seconds only, in the form of upward jet-shaped brightness features. These reach heights of 600-1200 km and tend to show blueshifts; some show bi-directional Doppler signature and some seem accompanied with an Hα surge. They are not seen in the core of Hα due to shielding by overlying chromospheric fibrils. The network where they originate has normal properties. The morphology of these jets strongly supports deep-seated photospheric reconnection of emergent or moat-driven magnetic flux with pre-existing strong vertical network fields as the mechanism underlying the Ellerman bomb phenomenon. Title: Quiet-Sun imaging asymmetries in Na I D1 compared with other strong Fraunhofer lines Authors: Rutten, R. J.; Leenaarts, J.; Rouppe van der Voort, L. H. M.; de Wijn, A. G.; Carlsson, M.; Hansteen, V. Bibcode: 2011A&A...531A..17R Altcode: 2011arXiv1104.4307R Imaging spectroscopy of the solar atmosphere using the Na I D1 line yields marked asymmetry between the blue and red line wings: sampling a quiet-Sun area in the blue wing displays reversed granulation, whereas sampling in the red wing displays normal granulation. The Mg I b2 line of comparable strength does not show this asymmetry, nor does the stronger Ca II 8542 Å line. We demonstrate the phenomenon with near-simultaneous spectral images in Na I D1, Mg I b2, and Ca II 8542 Å from the Swedish 1-m Solar Telescope. We then explain it with line-formation insights from classical 1D modeling and with a 3D magnetohydrodynamical simulation combined with NLTE spectral line synthesis that permits detailed comparison with the observations in a common format. The cause of the imaging asymmetry is the combination of correlations between intensity and Dopplershift modulation in granular overshoot and the sensitivity to these of the steep profile flanks of the Na I D1 line. The Mg I b2 line has similar core formation but much wider wings due to larger opacity buildup and damping in the photosphere. Both lines obtain marked core asymmetry from photospheric shocks in or near strong magnetic concentrations, less from higher-up internetwork shocks that produce similar asymmetry in the spatially averaged Ca II 8542 Å profile. Title: The quiet chromosphere. Old wisdom, new insights, future needs Authors: Rutten, Robert J. Bibcode: 2010MmSAI..81..565R Altcode: 2010arXiv1002.1482R; 2010MmSAI..81....1R The introduction to this review summarizes chromosphere observation with two figures. The first part showcases the historical emphasis on the eclipse chromosphere in the development of NLTE line formation theory and criticizes 1D modeling. The second part advertises recent breakthroughs after many decades of standstill. The third part discusses what may or should come next. Title: Waves in the chromosphere: observations Authors: Rutten, R. J. Bibcode: 2010arXiv1012.1196R Altcode: I review the literature on observational aspects of waves in the solar chromosphere in the first part of this contribution. High-frequency waves are invoked to build elaborate cool-star chromosphere heating theories but have not been detected decisively so far, neither as magnetic modes in network elements nor as acoustic modes in below-the-canopy internetwork regions. Three-minute upward-propagating acoustic shocks are thoroughly established through numerical simulation as the cause of intermittent bright internetwork grains, but their pistoning and their role in the low-chromosphere energy budget remain in debate. Three-minute wave interaction with magnetic canopies is a newer interest, presently progressing through numerical simulation. Three-minute umbral flashes and running penumbral waves seem a similar acoustic-shock phenomenon awaiting numerical simulation. The low-frequency network Doppler modulation remains enigmatic. In the second part, I address low-frequency ultraviolet brightness variations of the internetwork chromosphere in more detail. They contribute about half of the internetwork brightness modulation and presumably figure in cool-star basal flux. They appear to be a mixture of inverse-contrast granular overshoot at small scales and gravity-wave interference at mesogranular scales. I present TRACE evidence for the latter interpretation, and speculate that the low-frequency brightness minima map canopy heights. Title: The Irkutsk Barium filter for narrow-band wide-field high-resolution solar images at the Dutch Open Telescope Authors: Hammerschlag, Robert H.; Skomorovsky, Valery I.; Bettonvil, Felix C. M.; Kushtal, Galina I.; Olshevsky, Vyacheslav L.; Rutten, Robert J.; Jägers, Aswin P. L.; Sliepen, Guus; Snik, Frans Bibcode: 2010SPIE.7735E..85H Altcode: 2010SPIE.7735E.265H A wide-field birefringent filter for the barium II line at 455.4nm is developed in Irkutsk. The Barium line is excellent for Doppler-shift measurements because of low thermal line-broadening and steep flanks of the line profile. The filter width is 0.008nm and the filter is tunable over 0.4nm through the whole line and far enough in the neighboring regions. A fast tuning system with servomotor is developed at the Dutch Open Telescope (DOT). Observations are done in speckle mode with 10 images per second and Keller-VonDerLühe reconstruction using synchronous images of a nearby bluecontinuum channel at 450.5nm. Simultaneous observation of several line positions, typically 3 or 5, are made with this combination of fast tuning and speckle. All polarizers are birefringent prisms which largely reduced the light loss compared to polarizing sheets. The advantage of this filter over Fabry-Perot filters is its wide field due to a large permitted entrance angle and no need of polishing extremely precise surfaces. The BaII observations at the DOT occur simultaneously with those of a fast-tunable birefringent H-alpha filter. This gives the unique possibility of simultaneous speckle-reconstructed observations of velocities in photosphere (BaII) and chromosphere (H-alpha). Title: Solar Spectroscopy and (Pseudo-)Diagnostics of the Solar Chromosphere Authors: Rutten, Robert J. Bibcode: 2010ASSP...17..163R Altcode: 2009arXiv0905.2623R; 2010rast.conf..163R; 2010rasp.book..163R I first review trends in current solar spectrometry and then concentrate on comparing various spectroscopic diagnostics of the solar chromosphere. Some are actually not at all chromospheric but just photospheric or clapotispheric and do not convey information on chromospheric heating, even though this is often assumed. Balmer Hα is the principal displayer of the closed-field chromosphere, but it is unclear how chromospheric fibrils gain their large Hα opacity. The open-field chromosphere seems to harbor most if not all coronal heating and solar wind driving, but is hardly seen in optical diagnostics. Title: The Quiet Solar Atmosphere Observed and Simulated in Na I D1 Authors: Leenaarts, J.; Rutten, R. J.; Reardon, K.; Carlsson, M.; Hansteen, V. Bibcode: 2010ApJ...709.1362L Altcode: 2009arXiv0912.2206L The Na I D1 line in the solar spectrum is sometimes attributed to the solar chromosphere. We study its formation in quiet-Sun network and internetwork. We first present high-resolution profile-resolved images taken in this line with the imaging spectrometer Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope and compare these to simultaneous chromospheric images taken in Ca II 8542 Å and Hα. We then model Na I D1 formation by performing three-dimensional (3D) non-local thermodynamic equilibrium profile synthesis for a snapshot from a 3D radiation-magnetohydrodynamics simulation. We find that most Na I D1 brightness is not chromospheric but samples the magnetic concentrations that make up the quiet-Sun network in the photosphere, well below the height where they merge into chromospheric canopies, with aureoles from 3D resonance scattering. The line core is sensitive to magneto-acoustic shocks in and near magnetic concentrations, where shocks occur deeper than elsewhere, and may provide evidence of heating deep within magnetic concentrations. Title: Magnetic Coupling between the Interior and Atmosphere of the Sun Authors: Hasan, S. S.; Rutten, R. J. Bibcode: 2010ASSP...19.....H Altcode: 2010mcia.conf.....H No abstract at ADS Title: Dual-Line Spectral Imaging of the Chromosphere Authors: Cauzzi, G.; Reardon, K.; Rutten, R. J.; Tritschler, A.; Uitenbroek, H. Bibcode: 2010ASSP...19..513C Altcode: 2010mcia.conf..513C Hα filtergrams are notoriously difficult to interpret, "beautiful to view but not fit for analysis." We try to remedy this by using the IBIS bi-dimensional spectrometer at the Dunn Solar Telescope at NSO/Sacramento Peak to compare the quiet-sun chromosphere observed in Hα to what is observed simultaneously in Ca II 854.2 nm, sampling both lines with high angular and spectral resolution and extended coverage of space, time, and wavelength. Per (x, y, t) pixel we measured the intensity and Dopplershift of the minimum of each line's profile at that pixel, as well as the width of their inner chromospheric cores. A paper submitted to A&A (December 2008) compares these measurements in detail. Title: The solar chromosphere at high resolution with IBIS. IV. Dual-line evidence of heating in chromospheric network Authors: Cauzzi, G.; Reardon, K.; Rutten, R. J.; Tritschler, A.; Uitenbroek, H. Bibcode: 2009A&A...503..577C Altcode: 2009arXiv0906.2083C The structure and energy balance of the solar chromosphere remain poorly known. We used the imaging spectrometer IBIS at the Dunn Solar Telescope to obtain fast-cadence, multi-wavelength profile sampling of Hα and Ca ii 854.2 nm over a sizable two-dimensional field of view encompassing quiet-Sun network. We provide a first inventory of how the quiet chromosphere appears in these two lines by comparing basic profile measurements in the form of image displays, temporal-average displays, time slices, and pixel-by-pixel correlations. We find that the two lines can be markedly dissimilar in their rendering of the chromosphere, but that, nevertheless, both show evidence of chromospheric heating, particularly in and around network: Hα in its core width and Ca ii 854.2 nm in its brightness. We discuss venues for improved modeling. Title: Dynamic Lyα jets Authors: Koza, J.; Rutten, R. J.; Vourlidas, A. Bibcode: 2009A&A...499..917K Altcode: 2008arXiv0807.4889K Context: The solar chromosphere and transition region are highly structured and complex regimes. A recent breakthrough has been the identification of dynamic fibrils observed in Hα as caused by field-aligned magnetoacoustic shocks.
Aims: We seek to find whether such dynamic fibrils are also observed in Lyα.
Methods: We used a brief sequence of four high-resolution Lyα images of the solar limb taken by the Very high Angular resolution ULtraviolet Telescope (VAULT), which displays many extending and retracting Lyα jets. We measured their top trajectories and fitted parabolas to the 30 best-defined ones.
Results: Most jet tops move supersonically. Half of them decelerate, sometimes superballistically, the others accelerate. This bifurcation may arise from incomplete sampling of recurrent jets.
Conclusions: The similarities between dynamic Lyα jets and Hα fibrils suggest that the magnetoacoustic shocks causing dynamic Hα fibrils also affect dynamic Lyα jets. Title: Explanation of the activity sensitivity of Mn I 5394.7 Å Authors: Vitas, N.; Viticchiè, B.; Rutten, R. J.; Vögler, A. Bibcode: 2009A&A...499..301V Altcode: 2008arXiv0811.3555V There is a long-standing debate why the Mn i 5394.7 Å line in the solar irradiance spectrum brightens more at higher activity than other photospheric lines. The claim that this is caused by spectral interlocking to chromospheric emission in the Mg ii h & k lines is disputed. In this paper we settle this issue, using classical one-dimensional modeling for demonstration and modern three-dimensional MHD simulation for verification and analysis. The unusual sensitivity of the Mn i 5394.7 Å line to solar activity is due to its excessive hyperfine structure. This overrides the thermal and granular Doppler smearing through which the other, narrower, photospheric lines lose such sensitivity. We take the nearby Fe i 5395.2 Å line as example of the latter, and analyze the formation of both lines in detail to demonstrate and explain the granular Doppler brightening which affects all narrow photospheric lines. Neither the chromosphere nor Mg ii h & k emission play a role, nor is it correct to describe the activity sensitivity of Mn i 5394.7 Å in terms of plage models with outward increasing temperature contrast. The Mn i 5394.7 Å line represents a proxy diagnostic of strong-field magnetic concentrations in the deep solar photosphere comparable to the G band and the blue wing of Hα, but not a better one than these. The Mn i lines are more promising as diagnostics of weak fields in high-resolution Stokes polarimetry. Title: Hα as a Chromospheric Diagnostic Authors: Rutten, R. J. Bibcode: 2008ASPC..397...54R Altcode: I first illustrate with images from the Dutch Open Telescope (DOT) that Hα is the principal diagnostic of the solar chromosphere. The DOT movies at http://dot.astro.uu.nl demonstrate this fact even more vividly.

I then summarize, on the basis of the recent numerical simulations by

Leenaarts et al. (2007),

why Halpha; is such an omnipresent diagnostic of the chromosphere. The ubiquity of Hα fibrils in both hot and cool gas is due to (i)- the presence of shocks everywhere, guided by the magnetic field into dynamic fibrils near the network and pushing the canopy and transition region upward in weaker-field internetwork regions, (ii)- the large rate difference between the fast hydrogen ionization/recombination balancing in hot shocks and the slow balancing in cool post-shock gas, and (iii)- the large excitation energy of Hα's nis2 lower level, causing strong coupling to the ion population. These three facts combine to cause appreciable Hα opacity throughout the chromosphere, enormously in excess of instantaneous Saha-Boltzmann partitioning in cool post-shock gas. Thus, sluggish post-shock recombination causes Hα to be visible everywhere.

Finally, I address Hα observing. Since Hinode's Hα imaging is affected by bubbles and limited in cadence, the DOT may serve as a complementary facility furnishing profile-sampling Hα image sequences at the same 0.3 arcsec angular resolution as Hinode whenever the La Palma seeing is good. However, imminent loss of DOT funding requires outside financing of an on-site observer for DOT utilization in co-pointed joint observing. Title: DOT Tomography of the Solar Atmosphere VII. Chromospheric Response to Acoustic Events Authors: Rutten, R. J.; van Veelen, B.; Sütterlin, P. Bibcode: 2008SoPh..251..533R Altcode: 2008arXiv0801.0374R; 2008SoPh..tmp...28R We use synchronous movies from the Dutch Open Telescope sampling the G band, Ca II H, and Hα with five-wavelength profile sampling to study the response of the chromosphere to acoustic events in the underlying photosphere. We first compare the visibility of the chromosphere in Ca II H and Hα, demonstrate that studying the chromosphere requires Hα data, and summarize recent developments in understanding why this is so. We construct divergence and vorticity maps of the photospheric flow field from the G-band images and locate specific events through the appearance of bright Ca II H grains. The reaction of the Hα chromosphere is diagnosed in terms of brightness and Doppler shift. We show and discuss three particular cases in detail: a regular acoustic grain marking shock excitation by granular dynamics, a persistent flasher, which probably marks magnetic-field concentration, and an exploding granule. All three appear to buffet overlying fibrils, most clearly in Dopplergrams. Although our diagnostic displays to dissect these phenomena are unprecedentedly comprehensive, adding even more information (photospheric Doppler tomography and magnetograms along with chromospheric imaging and Doppler mapping in the ultraviolet) is warranted. Title: Dynamic Fibrils in Ly-alpha Authors: Koza, J.; Rutten, R. J.; Vourlidas, A.; Suetterlin, P. Bibcode: 2008ESPM...12.2.16K Altcode: We have detected dynamic fibrils (DFs) in Ly-alpha filtergrams taken with the rocket-borne Very high Angular resolution ULtraviolet Telescope (VAULT). Although the data consist of only a 1-min sequence of 4 images taken near the solar limb during the second VAULT flight, they enable us to identify and study the time evolution of over 50 DFs. Most show parabolic trajectories in their angular extent, with supersonic maximum velocities. The measured decelerations vary from sub-ballistic to super-ballistic. The similarities with DFs seen in Halpha suggest a common cause, possibly the presence of hot transition-region interfaces around cool oscillation-fed jets. Title: Concluding remarks Authors: Rutten, R. J. Bibcode: 2008ESPM...12..7.1R Altcode: No abstract at ADS Title: On the solar abundance of indium Authors: Vitas, N.; Vince, I.; Lugaro, M.; Andriyenko, O.; Gošić, M.; Rutten, R. J. Bibcode: 2008MNRAS.384..370V Altcode: 2008MNRAS.tmp...25V; 2007arXiv0711.2166V The generally adopted value for the solar abundance of indium is over six times higher than the meteoritic value. We address this discrepancy through numerical synthesis of the 451.13-nm line on which all indium abundance studies are based, both for the quiet Sun and the sunspot umbra spectrum, employing standard atmosphere models and accounting for hyperfine structure and Zeeman splitting in detail. The results, as well as a re-appraisal of indium nucleosynthesis, suggest that the solar indium abundance is close to the meteoritic value, and that some unidentified ion line causes the 451.13-nm feature in the quiet-Sun spectrum. Title: Search for photospheric footpoints of quiet Sun transition region loops Authors: Sánchez Almeida, J.; Teriaca, L.; Sütterlin, P.; Spadaro, D.; Schühle, U.; Rutten, R. J. Bibcode: 2007A&A...475.1101S Altcode: 2007arXiv0709.3451S Context: The footpoints of quiet Sun Transition Region (TR) loops do not seem to coincide with the photospheric magnetic structures appearing in traditional low-sensitivity magnetograms.
Aims: We look for the so-far unidentified photospheric footpoints of TR loops using G-band bright points (BPs) as proxies for photospheric magnetic field concentrations.
Methods: We compare TR measurements with SoHO/SUMER and photospheric magnetic field observations obtained with the Dutch Open Telescope.
Results: Photospheric BPs are associated with bright TR structures, but they seem to avoid the brightest parts of the structure. BPs appear in regions that are globally redshifted, but they avoid extreme velocities. TR explosive events are not clearly associated with BPs.
Conclusions: The observations are not inconsistent with the BPs being footpoints of TR loops, although we have not succeeded to uniquely identify particular BPs with specific TR loops. Title: Non-equilibrium hydrogen ionization in 2D simulations of the solar atmosphere Authors: Leenaarts, J.; Carlsson, M.; Hansteen, V.; Rutten, R. J. Bibcode: 2007A&A...473..625L Altcode: 2007arXiv0709.3751L Context: The ionization of hydrogen in the solar chromosphere and transition region does not obey LTE or instantaneous statistical equilibrium because the timescale is long compared with important hydrodynamical timescales, especially of magneto-acoustic shocks. Since the pressure, temperature, and electron density depend sensitively on hydrogen ionization, numerical simulation of the solar atmosphere requires non-equilibrium treatment of all pertinent hydrogen transitions. The same holds for any diagnostic application employing hydrogen lines.
Aims: To demonstrate the importance and to quantify the effects of non-equilibrium hydrogen ionization, both on the dynamical structure of the solar atmosphere and on hydrogen line formation, in particular Hα.
Methods: We implement an algorithm to compute non-equilibrium hydrogen ionization and its coupling into the MHD equations within an existing radiation MHD code, and perform a two-dimensional simulation of the solar atmosphere from the convection zone to the corona.
Results: Analysis of the simulation results and comparison to a companion simulation assuming LTE shows that: a) non-equilibrium computation delivers much smaller variations of the chromospheric hydrogen ionization than for LTE. The ionization is smaller within shocks but subsequently remains high in the cool intershock phases. As a result, the chromospheric temperature variations are much larger than for LTE because in non-equilibrium, hydrogen ionization is a less effective internal energy buffer. The actual shock temperatures are therefore higher and the intershock temperatures lower. b) The chromospheric populations of the hydrogen n = 2 level, which governs the opacity of Hα, are coupled to the ion populations. They are set by the high temperature in shocks and subsequently remain high in the cool intershock phases. c) The temperature structure and the hydrogen level populations differ much between the chromosphere above photospheric magnetic elements and above quiet internetwork. d) The hydrogen n = 2 population and column density are persistently high in dynamic fibrils, suggesting that these obtain their visibility from being optically thick in Hα also at low temperature.

Movie and Appendix A are only available in electronic form at http://www.aanda.org Title: Chromospheric and Transition-Region Dynamics in Plage Authors: de Wijn, A. G.; de Pontieu, B.; Rutten, R. J. Bibcode: 2007ASPC..368..137D Altcode: We study the dynamical interaction of the solar chromosphere with the transition region in mossy and non-mossy active-region plage. We carefully align image sequences taken with the Transition Region And Coronal Explorer (TRACE) in the ultraviolet passbands around 1550, 1600, and 1700 Å and the extreme ultraviolet passbands at 171 and 195 Å. We compute Fourier phase-difference spectra that are spatially averaged separately over mossy and non-mossy plage to study temporal modulations as a function of temporal frequency. The 1550 versus 171 Å comparison shows zero phase difference in non-mossy plage. In mossy plage, the phase differences between all UV and EUV passbands show pronounced upward trends with increasing frequency, which abruptly changes into zero phase difference beyond 4 -- 6 mHz. The phase difference between the 171 and 195 Å sequences exhibits a shallow dip below 3 mHz and then also turns to zero phase difference beyond this value. We attribute the various similarities between the UV and EUV diagnostics that are evident in the phase-difference diagrams to the contribution of the C IV resonance lines in the 1550 and 1600 Å passbands. The strong upward trend at the lower frequencies indicates the presence of upward-traveling disturbances. It points to correspondence between the lower chromosphere and the upper transition region, perhaps by slow-mode magnetosonic disturbances, or by a connection between chromospheric and coronal heating mechanisms. The transition from this upward trend to zero phase difference at higher frequencies is due to the intermittent obscuration by fibrils that occult the foot points of hot loops, which are bright in the EUV and C IV lines, in oscillatory manner. Title: ESMN in Memoriam (1998 -- 2006) Authors: Rutten, R. J. Bibcode: 2007ASPC..368...21R Altcode: The EC-FP5 European Solar Magnetism Network (ESMN) was terminated during this conference. Together with its FP4 predecessor, the European Solar Magnetometry Network (ESMN), it funded 22 postdoc and 9 graduate-student appointments at nine solar physics groups in Western Europe, it enhanced Europe-wide collaboration in solar physics, and it contributed to the integration of East-European groups in West-European enterprises. Its unfortunate demise results from lack of further fortune in the FP6 lottery. The FP6-funded Utrecht-Stockholm-Oslo graduate school in solar physics represents offspring, the FP6 Solaire network is a partial replacement, and the EAST undertaking and pledge to build an EST is a most worthy FP7 stake. The EC's policy shifts from postdoc to predoc funding and from requiring (too) small to requiring (too) large consortia are criticized. Title: Aperture Increase Options for the Dutch Open Telescope Authors: Hammerschlag, R. H.; Bettonvil, F. C. M.; Jägers, A. P. L.; Rutten, R. J. Bibcode: 2007ASPC..368..573H Altcode: 2007astro.ph..3638H This paper is an invitation to the international community to participate in the usage and a substantial upgrade of the Dutch Open Telescope on La Palma (DOT, http://dot.astro.uu.nl).

We first give a brief overview of the approach, design, and current science capabilities of the DOT. It became a successful 0.2-arcsec-resolution solar movie producer through its combination of (i) an excellent site, (ii) effective wind flushing through the fully open design and construction of both the 45-cm telescope and the 15-m support tower, (iii) special designs which produce extraordinary pointing stability of the tower, equatorial mount, and telescope, (iv) simple and excellent optics with minimum wavefront distortion, and (v) large-volume speckle reconstruction including narrow-band processing. The DOT's multi-camera multi-wavelength speckle imaging system samples the solar photosphere and chromosphere simultaneously in various optical continua, the G band, Ca II H (tunable throughout the blue wing), and Hα (tunable throughout the line). The resulting DOT data sets are all public. The DOT database (http://dotdb.phys.uu.nl/DOT) now contains many tomographic image sequences with 0.2-0.3 arcsec resolution and up to multi-hour duration. You are welcome to pull them over for analysis.

The main part of this contribution outlines DOT upgrade designs implementing larger aperture. The motivation for aperture increase is the recognition that optical solar physics needs the substantially larger telescope apertures that became useful with the advent of adaptive optics and viable through the DOT's open principle, both for photospheric polarimetry at high resolution and high sensitivity and for chromospheric fine-structure diagnosis at high cadence and full spectral sampling.

Our upgrade designs for the DOT are presented in an incremental sequence of five options of which the simplest (Option I) achieves 1.4 m aperture using the present tower, mount, fold-away canopy, and multi-wavelength speckle imaging and processing systems. The most advanced (Option V) offers unblocked 2.5 m aperture in an off-axis design with a large canopy, a wide 30-m high support tower, and image transfer to a groundbased optics lab for advanced instrumentation. All five designs employ adaptive optics. The important advantages of fully open, wind-transparent and wind-flushed structure, polarimetric constancy, and absence of primary-image rotation remain. All designs are relatively cheap through re-using as much of the existing DOT hardware as possible.

Realization of an upgrade requires external partnership(s). This report about DOT upgrade options therefore serves also as initial documentation for potential partners. Title: Observing the Solar Chromosphere Authors: Rutten, R. J. Bibcode: 2007ASPC..368...27R Altcode: 2007astro.ph..3637R This review is split into two parts: one on chromospheric line formation in answer to the frequent question ``where is my line formed'', and one presenting state-of-the-art imagery of the chromosphere. In the first part I specifically treat the formation of the Na D lines, Ca II H&K, and Hα. In the second I show DOT, IBIS, VAULT, and TRACE images as evidence that the chromosphere consists of fibrils of intrinsically different types. The straight-up ones are hottest. The slanted ones are filled by shocks and likely possess thin transition sheaths to coronal plasma. The ones hovering horizontally over ``clapotispheric'' cell interiors outline magnetic canopies and are buffeted by shocks, most violently in the quietest regions.

In the absence of integral-field ultraviolet spectrometry, Hα remains the principal chromosphere diagnostic. The required fast-cadence profile-sampling imaging is an important quest for new telescope technology. Title: The Physics of Chromospheric Plasmas Authors: Heinzel, P.; Dorotovič, I.; Rutten, R. J. Bibcode: 2007ASPC..368.....H Altcode: No abstract at ADS Title: Fourier Analysis of Active-Region Plage Authors: de Wijn, A. G.; De Pontieu, B.; Rutten, R. J. Bibcode: 2007ApJ...654.1128D Altcode: 2007arXiv0706.2014D We study the dynamical interaction of the solar chromosphere with the transition region in mossy and nonmossy active-region plage. We carefully align image sequences taken with the Transition Region And Coronal Explorer (TRACE) in the ultraviolet passbands around 1550, 1600, and 1700 Å and the extreme ultraviolet passbands at 171 and 195 Å. We compute Fourier phase-difference spectra that are spatially averaged separately over mossy and nonmossy plage to study temporal modulations as a function of temporal frequency. The 1550 versus 171 Å comparison shows zero phase difference in nonmossy plage. In mossy plage, the phase differences between all UV and EUV passbands show pronounced upward trends with increasing frequency, which abruptly changes into zero phase difference beyond 4-6 mHz. The phase difference between the 171 and 195 Å sequences exhibits a shallow dip below 3 mHz and then also turns to zero phase difference beyond this value. We attribute the various similarities between the UV and EUV diagnostics that are evident in the phase-difference diagrams to the contribution of the C IV resonance lines in the 1550 and 1600 Å passbands. The strong upward trend at the lower frequencies indicates the presence of upward-traveling disturbances. It points to correspondence between the lower chromosphere and the upper transition region, perhaps by slow-mode magnetosonic disturbances, or by a connection between chromospheric and coronal heating mechanisms. The transition from this upward trend to zero phase difference at higher frequencies is due to the intermittent obscuration by fibrils that occult the footpoints of hot loops, which are bright in the EUV and C IV lines, in an oscillatory manner. Title: The Ba II 4554 / Hβ Imaging Polarimeter for the Dutch Open Telescope Authors: Snik, F.; Bettonvil, F. C. M.; Jägers, A. P. L.; Hammerschlag, R. H.; Rutten, R. J.; Keller, C. U. Bibcode: 2006ASPC..358..205S Altcode: In order to expand the high-resolution, multi-wavelength imaging capabilities of the Dutch Open Telescope (DOT), an additional polarimetric channel based on a 80 mÅ tunable Lyot filter for Ba II 4554 and Hβ has been designed and constructed. The large atomic mass and the resulting steep line wings, make Ba II 4554 particularly suitable for the creation of photospheric Dopplergrams and Stokes-V magnetograms. The line also yields a significant degree of linear (scattering) polarization for observations near the limb of the Sun, which is modified by both horizontal and vertical weak-field topologies through the Hanle effect and hyperfine-structure level crossing. The polarimeter is based on liquid crystal variable retarders (LCVRs) as polarization modulators in combination with the Lyot filter's entrance polarizer. The tunability of the LCVRs is exploited to enable specific wavelength calibration, selection of the reference frame of linear polarization, and optimization of instrumental polarization cross-talk, which for the DOT is constant in time. With the future Ba II 4554 photospheric magnetograms, we expect to be able to discern magnetic structures of about 150 km with field strengths down to 100 G, and that Hanle-type observations can be performed at a resolution of about 1 arcsec. The range of applicability of Hβ imaging polarimetry has to be explored after installation. Title: Magnetic Patches in Internetwork Areas Authors: de Wijn, A. G.; Rutten, R. J.; Haverkamp, E. M. W. P.; Sütterlin, P. Bibcode: 2006ASPC..354...20D Altcode: We present a study of internetwork magnetic elements that appear as bright points in G-band (photosphere) and Ca II H (low chromosphere) image sequences from the Dutch Open Telescope. Many bright points appear intermittently in groups of long-lived structures that we call ``magnetic patches''. We develop an algorithm for the identification of bright points and magnetic patches. The average internetwork bright point lifetimes is measured to be 3.5 minutes in the G band, and 4.3 minutes in the Ca II H. We find an internetwork bright point number density of 0.02 Mm^{-2} in the G-band sequence and 0.05 Mm^{-2} in the Ca II H sequence. The bright points show a bimodal distribution of the frame-to-frame horizontal velocities, with a peak at 0 km s^{-1} and a wide hump centered around 1.2 km s^{-1}. The patches last much longer than granular time scales (about nine hours) and outline cell-like structures on mesogranular scale. We conclude that transient internetwork bright points trace the locations of strong magnetic fields that exist before the bright point appears and remain after it disappears. Title: Fourier analysis of chromospheric and transition region emission above active region plage Authors: de Wijn, A. G.; de Pontieu, B.; Rutten, R. J. Bibcode: 2006AGUFMSH23B0364D Altcode: We study the dynamical interaction of the solar chromosphere with the transition region (TR) in mossy and non-mossy active region plage, and find evidence for correlated brightness changes or upward travelling disturbances between the low chromosphere and the upper transition region. We carefully align image sequences taken with the Transition Region and Coronal Explorer (TRACE) in the ultraviolet passbands around 1550, 1600 and 1700 Å\ (indicative of low chromosphere and low TR) and the extreme ultraviolet passbands at 171 and 195 Å\ (indicative of upper transition region). We compute Fourier phase-difference spectra that are spatially averaged separately over mossy and non-mossy plage to study temporal modulations as a function of temporal frequency. We find that in non-mossy plage there is zero phase difference between 1550 Å\ and 171 Å. In mossy plage, the phase differences between all UV and EUV passbands show pronounced upward trends with increasing frequency, which abruptly changes into zero phase differences for frequencies beyond 4-6 mHz. The phase difference between the 171 and 195 Å\ sequences exhibits a shallow dip below 3 mHz and then also turns to zero phase difference beyond this value. We attribute some of the various similarities between the UV and EUV diagnostics that are evident in the phase-difference diagrams to the contribution of the C IV resonance lines in the 1550 and 1600 Å\ passbands. The strong upward trend at lower frequencies in the phase difference between all UV passbands (including 1700 Å) and 171 Å\ indicates the presence of upward travelling disturbances. Since 1700 Å\ does not contain C IV emission (low TR), this points to a correlation between brightness changes in the lower chromosphere and the upper TR, perhaps by slow-mode disturbances, or by a connection between chromospheric and coronal heating mechanisms. We find that such correlated brightness changes first occur in the low chromosphere, and are followed about 400 s later in the upper TR. The transition from the upward trend in phase difference at low frequencies to zero phase difference at higher frequencies is due to the intermittent obscuration by fibrils. These chromospheric jets occult the footpoints of hot loops, which are bright in the EUV and C IV lines, in oscillatory manner. Title: On the Nature of the Solar Chromosphere Authors: Rutten, R. J. Bibcode: 2006ASPC..354..276R Altcode: 2007astro.ph..1379R DOT high-resolution imagery suggests that only internetwork-spanning Hα ``mottles'' constitute the quiet-Sun chromosphere, whereas more upright network ``straws'' in ``hedge rows'' reflect transition-region conditions. Title: Tunable H-alpha Lyot filter with advanced servo system and image processing: instrument design and new scientific results with the Dutch Open Telescope Authors: Bettonvil, Felix C. M.; Hammerschlag, Robert H.; Sütterlin, Peter; Rutten, Robert J.; Jägers, Aswin P. L.; Sliepen, Guus Bibcode: 2006SPIE.6269E..0EB Altcode: 2006SPIE.6269E..12B The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma is a revolutionary open solar telescope, on an excellent site, on top of a transparent tower of steel framework, and uses natural air flow to minimize local seeing. The DOT is a high-resolution multi-wavelength imager capable of long-duration time series aiming at magnetic fine structure, topology and dynamics in the photosphere and low- and high chromosphere. In this paper we describe the latest addition to the multi-wavelength imaging system: a Lyot H-alpha camera channel operating at a wavelength of 656.3 nm, being of major interest for high-chromospheric phenomena. The channel is operated strictly synchronous with the other channels and all data are speckle reconstructed. The channel permits profile sampling and delivers Dopplergrams in a 15 second time cadence, up to several hours long and adding up to a total data amount of 1.6 Terabyte/day. A dedicated computer (DSP, DOT Speckle Processor) has been built for processing the data overnight. Title: A comparison of solar proxy-magnetometry diagnostics Authors: Leenaarts, J.; Rutten, R. J.; Carlsson, M.; Uitenbroek, H. Bibcode: 2006A&A...452L..15L Altcode: Aims.We test various proxy-magnetometry diagnostics, i.e., brightness signatures of small-scale magnetic elements, for studying magnetic field structures in the solar photosphere.
Methods: .Images are numerically synthesized from a 3D solar magneto-convection simulation for, respectively, the G band at 430.5 nm, the CN band at 388.3 nm, and the blue wings of the H α, H β, Ca ii H, and Ca ii 854.2 nm lines.
Results: .Both visual comparison and scatter diagrams of the computed intensity versus the magnetic field strength show that, in particular for somewhat spatially extended magnetic elements, the blue H α wing presents the best proxy-magnetometry diagnostic, followed by the blue wing of H β. The latter yields higher diffraction-limit resolution.
Conclusions: .We recommend using the blue H α wing to locate and track small-scale photospheric magnetic elements through their brightness appearance. Title: DOT tomography of the solar atmosphere. VI. Magnetic elements as bright points in the blue wing of Hα Authors: Leenaarts, J.; Rutten, R. J.; Sütterlin, P.; Carlsson, M.; Uitenbroek, H. Bibcode: 2006A&A...449.1209L Altcode: High-resolution solar images taken in the blue wing of the Balmer H α line with the Dutch Open Telescope show intergranular magnetic elements as strikingly bright features, similar to, but with appreciably larger contrast over the surrounding granulation than their more familiar manifestation as G-band bright points. Part of this prominent appearance is due to low granular contrast, without granule/lane brightness reversal as, e.g., in the wings of Ca II H & K. We use 1D and 2D radiative transfer modeling and 3D solar convection and magnetoconvection simulations to reproduce and explain the H α wing images. We find that the blue H α wing obeys near-LTE line formation. It appears particularly bright in magnetic elements through low temperature gradients. The granulation observed in the blue wing of H α has low contrast because of the lack of H α opacity in the upper photosphere, Doppler cancellation, and large opacity sensitivity to temperature working against source function sensitivity. We conclude that the blue H α wing represents a promising proxy magnetometer to locate and track isolated intermittent magnetic elements, a better one than the G band and the wings of Ca II H & K although less sharp at given aperture. Title: Small Scale Magnetic Elements as Bright Points in the Blue Hα Wing Authors: Leenaarts, J.; Sütterlin, P.; Rutten, R. J.; Carlsson, M.; Uitenbroek, H. Bibcode: 2005ESASP.596E..15L Altcode: 2005ccmf.confE..15L No abstract at ADS Title: DOT tomography of the solar atmosphere. IV. Magnetic patches in internetwork areas Authors: de Wijn, A. G.; Rutten, R. J.; Haverkamp, E. M. W. P.; Sütterlin, P. Bibcode: 2005A&A...441.1183D Altcode: 2007arXiv0706.2008D We use G-band and Ca ii H image sequences from the Dutch Open Telescope (DOT) to study magnetic elements that appear as bright points in internetwork parts of the quiet solar photosphere and chromosphere. We find that many of these bright points appear recurrently with varying intensity and horizontal motion within longer-lived magnetic patches. We develop an algorithm for detection of the patches and find that all patches identified last much longer than the granulation. The patches outline cell patterns on mesogranular scales, indicating that magnetic flux tubes are advected by granular flows to mesogranular boundaries. Statistical analysis of the emergence and disappearance of the patches points to an average patch lifetime as long as 530±50~min (about nine hours), which suggests that the magnetic elements constituting strong internetwork fields are not generated by a local turbulent dynamo. Title: The wings of Ca II H and K as solar fluxtube diagnostics Authors: Sheminova, V. A.; Rutten, R. J.; Rouppe van der Voort, L. H. M. Bibcode: 2005A&A...437.1069S Altcode: We combine high-resolution Ca II H and K spectrograms from the Swedish Vacuum Solar Telescope with standard fluxtube modeling to derive photospheric temperature and velocity stratifications within individual magnetic elements in plage near a sunspot. We find that 1D on-axis modeling gives better consistency than spatial averaging over flaring-fluxtube geometry. Our best-fit temperature stratifications suggest that magnetic elements are close to radiative equilibrium throughout their photospheres. Their brightness excess throughout the H and K wings compared with the quiet photosphere is primarily due to low density, not to mechanical heating. We conclude that the extended H and K wings provide excellent fine-structure diagnostics for both high-resolution observations and simulations of the solar photosphere. Title: The temperature gradient in and around solar magnetic fluxtubes Authors: Sheminova, V. A.; Rutten, R. J.; Rouppe van der Voort, L. H. M. Bibcode: 2005KFNTS...5..110S Altcode: We use spectra covering the outer part of the extended wing of the solar Ca II K line observed at high angular resolution with the Swedish Vacuum Solar Telescope to test standard solar fluxtube models. The wings of the Ca II resonance lines are formed in LTE both with regard to excitation (source function) and to ionization (opacity) and, therefore, sample temperature stratifications in relatively straightforward fashion. We obtain best fits by combining steeper temperature gradients than those in the standard models for both the tube inside and the tube environment. Similarly steep gradients are also determined from a numerical magnetoconvection simulation by the late A. S. Gadun. It is found that the energy balance in the individual magnetic elements appears to be close to radiative equilibrium throughout the photosphere. Title: MAO-SIU solar physics collaborations Authors: Rutten, R. J. Bibcode: 2005KFNTS...5...11R Altcode: The Kyiv-Utrecht collaboration in solar physics has a long history and a bright future. In this report I highlight some of our joint analyses in the past, discuss the general solar physics context as I see it at present, and describe exciting research challenges which fit the Kyiv-Utrecht expertise and interests. Title: Dynamics of the solar chromosphere. V. High-frequency modulation in ultraviolet image sequences from TRACE Authors: de Wijn, A. G.; Rutten, R. J.; Tarbell, T. D. Bibcode: 2005A&A...430.1119D Altcode: 2007arXiv0706.1987D We search for signatures of high-frequency oscillations in the upper solar photosphere and low chromosphere in the context of acoustic heating of outer stellar atmospheres. We use ultraviolet image sequences of a quiet center-disk area from the Transition Region and Coronal Explorer (TRACE) mission which were taken with strict cadence regularity. The latter permits more reliable high-frequency diagnosis than in earlier work. Spatial Fourier power maps, spatially averaged coherence and phase-difference spectra, and spatio-temporal (kh,f) decompositions all contain high-frequency features that at first sight seem of considerable intrinsic interest but actually are more likely to represent artifacts of different nature. Spatially averaged phase difference measurement provides the most sensitive diagnostic and indicates the presence of acoustic modulation up to f≈20 mHz (periods down to 50 s) in internetwork areas. Title: DOT++: the Dutch Open Telescope with 1.4-m aperture Authors: Bettonvil, Felix C.; Hammerschlag, Robert H.; Sütterlin, Peter; Rutten, Robert J.; Jägers, Aswin P.; Snik, Frans Bibcode: 2004SPIE.5489..362B Altcode: The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma is a revolutionary open solar telescope, on an excellent site, on top of a transparent steel tower, and uses natural air flow to minimize local seeing. The aim is long-duration high-resolution imaging with a multi-wavelength camera system. In order to achieve this, the DOT is equipped with a diffraction limited imaging system and uses the speckle reconstruction technique for removing the remaining atmospheric turbulence. The DOT optical system is simple and consists currently of a 0.45m/F4.44 parabolic mirror and a 10x enlargement lens system. We present our plans to increase the aperture of the DOT from 0.45m to 1.4m. The mirror support and telescope top shall be redesigned, but telescope, tower, multi-wavelength camera system and speckle system remain intact. The new optical design permits user selectable choice between angular resolution and field size, as well as transversal pupil shift introducing the possibility to use obstruction free apertures up to 65cm. The design will include a low order AO system, which improves the speckle S/N substantially during moderate seeing conditions. Title: DOT tomography of the solar atmosphere. II. Reversed granulation in Ca II H Authors: Rutten, R. J.; de Wijn, A. G.; Sütterlin, P. Bibcode: 2004A&A...416..333R Altcode: High-quality simultaneous image sequences from the Dutch Open Telescope (DOT) in the G band and the Ca II H line are used to quantify the occurrence of reversed granulation as a constituent of the subsonic brightness pattern observed as a background to acoustic oscillations in the quiet-Sun internetwork atmosphere. In the middle photosphere reversed granulation constitutes a much larger part of this background than at the larger heights sampled by ultraviolet radiation. The anticorrelation with the underlying granulation reaches about 50% at a temporal delay of 2-3 min, and increases with spatial image smoothing to mesogranular resolution. We discuss the nature of reversed granulation in terms of convection reversal, gravity waves, acoustic waves, and intergranular magnetism, suggest that the internetwork background pattern is primarily a mixture of the first two ingredients, and speculate that it is also an inverse canopy mapper. Title: The Dutch Open Telescope on La Palma Authors: Rutten, R. J.; Bettonvil, F. C. M.; Hammerschlag, R. H.; Jägers, A. P. L.; Leenaarts, J.; Snik, F.; Sütterlin, P.; Tziotziou, K.; de Wijn, A. G. Bibcode: 2004IAUS..223..597R Altcode: 2005IAUS..223..597R The Dutch Open Telescope (DOT) on La Palma is an innovative solar telescope combining open telescope structure and an open support tower with a multi-wavelength imaging assembly and with synchronous speckle cameras to generate high-resolution movies which sample different layers of the solar atmosphere simultaneously and co-spatially at high resolution over long durations. The DOT test and development phase is nearly concluded. The installation of an advanced speckle processor enables full science utilization including "Open-DOT" time allocation to the international community. Co-pointing with spectropolarimeters at other Canary Island telescopes and with TRACE furnishes valuable Solar-B precursor capabilities. Title: DOT tomography of the solar atmosphere. I. Telescope summary and program definition Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. C. M.; Sütterlin, P.; de Wijn, A. G. Bibcode: 2004A&A...413.1183R Altcode: The Dutch Open Telescope (DOT) on La Palma is an innovative optical solar telescope capable of reaching 0.2 arcsec angular resolution over extended durations. The DOT presently progresses from technology testbed to a stable science configuration providing multi-wavelength imaging and multi-camera speckle data acquisition for tomographic mapping of the solar atmosphere. Large-volume speckle processing will soon enable frequent usage and community-wide time allocation, in particular for tandem operation with other solar telescopes pursuing spectropolarimetry and EUV imaging. We summarize the DOT hardware and software in the context of this increasing availability and outline the corresponding ``open-DOT'' program. Title: Dynamics of the solar chromosphere IV. Evidence for atmospheric gravity waves from TRACE Authors: Rutten, R. J.; Krijger, J. M. Bibcode: 2003A&A...407..735R Altcode: We study the low-frequency brightness modulation of internetwork regions in the low solar chromosphere using simultaneous ultraviolet and white-light image sequences from the Transition Region and Coronal Explorer (TRACE). The ultraviolet sequences exhibit a slowly varying brightness pattern in internetwork regions on which the more familiar acoustic three-minute oscillation is superimposed, with about half of the peak brightness reached in internetwork grains contributed by the low-frequency background. We address the nature of the latter, applying two-dimensional Fourier filtering to isolate it from the acoustic modulation. Spatio-temporal comparisons and selective time-delay scatter correlations between the ultraviolet and white-light low-frequency sequences establish that reversed granulation constitutes at most a minor part of the ultraviolet background. Fourier analysis shows that the meso-scale contribution dominates and consists of atmospheric gravity waves. Title: The Dutch Open Telescope Authors: Rutten, Robert J. Bibcode: 2003ASSL..288..111R Altcode: 2003ASSL..287..411R No abstract at ADS Title: La Palma observations of umbral flashes Authors: Rouppe van der Voort, L. H. M.; Rutten, R. J.; Sütterlin, P.; Sloover, P. J.; Krijger, J. M. Bibcode: 2003A&A...403..277R Altcode: We present high-quality Ca II H & K data showing chromospheric flashes in sunspot umbrae collected with the Swedish Vacuum Solar Telescope, the Dutch Open Telescope, and the Swedish 1-m Solar Telescope at the Roque de los Muchachos Observatory on La Palma. Differential movies, time slices, spectrograms, and Fourier power maps demonstrate that umbral flashes and running penumbral waves are closely related oscillatory phenomena, combining upward shock propagation with coherent wave spreading over the entire spot. We attribute the flash brightening to large redshift by post-shock material higher up. We find no obvious relation between umbral dots and umbral flashes. Title: Radiative Transfer in Stellar Atmospheres Authors: Rutten, Robert J. Bibcode: 2003rtsa.book.....R Altcode: The main topic treated in these graduate course notes is the classical theory of radiative transfer for explaining stellar spectra. It needs relatively much attention to be mastered. Radiative transfer in gaseous media that are neither optically thin nor fully opaque and scatter to boot is a key part of astrophysics but not a transparent subject. These course notes represent a middle road between Mihalas' "Stellar Atmospheres" (graduate level and up) and the books by Novotny and Boehm-Vitense (undergraduate level). They are at about the level of Gray's "The observation and analysis of stellar photospheres" but emphasize NLTE radiative transfer rather than observational techniques and data interpretation. Title: Multi-wavelength imaging system for the Dutch Open Telescope Authors: Bettonvil, Felix C.; Suetterlin, Peter; Hammerschlag, Robert H.; Jagers, Aswin P.; Rutten, Robert J. Bibcode: 2003SPIE.4853..306B Altcode: The Dutch Open Telescope (DOT) is an innovative solar telescope, completely open, on an open steel tower, without a vacuum system. The aim is long-duration high resolution imaging and in order to achieve this the DOT is equipped with a diffraction limited imaging system in combination with a data acquisition system designed for use with the speckle masking reconstruction technique for removing atmospheric aberrations. Currently the DOT is being equipped with a multi-wavelength system forming a high-resolution tomographic imager of magnetic fine structure, topology and dynamics in the photosphere and low- and high chromosphere. Finally the system will contain 6 channels: G-band (430.5 nm), Ca II H (K) (396.8 nm), H-α (656.3 nm), Ba II (455.4 nm), and two continuum channels (432 and 651 nm). Two channels are in full operation now and observations show that the DOT produces real diffraction limited movies (with 0.2" resolution) over hours in G-band (430.5 nm) and continuum (432 nm). Title: Utrecht Radiative Transfer Courses Authors: Rutten, R. J. Bibcode: 2003ASPC..288...99R Altcode: 2003sam..conf...99R The Utrecht course ``The Generation and Transport of Radiation'' teaches basic radiative transfer to second-year students. It is a much-expanded version of the first chapter of Rybicki & Lightman's ``Radiative Processes in Astrophysics''. After this course, students understand why intensity is measured per steradian, have an Eddington-Barbier feel for optically thick line formation, and know that scattering upsets LTE. The text is a computer-aided translation by Ruth Peterson of my 1992 Dutch-language course. My aim is to rewrite this course in non-computer English and make it web-available at some time. In the meantime, copies of the Peterson translation are made yearly at Uppsala -- ask them, not me. Eventually it should become a textbook.

The Utrecht course ``Radiative Transfer in Stellar Atmospheres'' is a 30-hour course for third-year students. It treats NLTE line formation in plane-parallel stellar atmospheres at a level intermediate between the books by Novotny and Boehm-Vitense, and Mihalas' ``Stellar Atmospheres''. After this course, students appreciate that epsilon is small, that radiation can heat or cool, and that computers have changed the field. This course is web-available since 1995 and is regularly improved -- but remains incomplete. Eventually it should become a textbook.

The three Utrecht exercise sets ``Stellar Spectra A: Basic Line Formation'', ``Stellar Spectra B: LTE Line Formation'', and ``Stellar Spectra C: NLTE Line Formation'' are IDL-based computer exercises for first-year, second-year, and third-year students, respectively. They treat spectral classification, Saha-Boltzmann population statistics, the curve of growth, the FAL-C solar atmosphere model, the role of H-minus in the solar continuum, LTE formation of Fraunhofer lines, inversion tactics, the Feautrier method, classical lambda iteration, and ALI computation. The first two sets are web-available since 1998; the third will follow.

Acknowledgement. Both courses owe much to previous Utrecht courses taught by the late Kees Zwaan. The third exercise set was developed by Phil Judge, Mandy Hagenaar, and Thijs Krijger.

Reverse acknowledgement. If you are a user of this free material you might refer to this summary and so boost my citation standing. Corrections are also welcome. Title: NLTE in a Hot Hydrogen Star: Auer & Mihalas Revisited Authors: Wiersma, J.; Rutten, R. J.; Lanz, T. Bibcode: 2003ASPC..288..130W Altcode: 2003sam..conf..130W We pay tribute to two landmark papers published by Auer & Mihalas in 1969. They modeled hot-star NLTE-RE hydrogen-only atmospheres, using two simplified hydrogen atoms: ApJ 156, 157: H I levels 1, 2 and c, Lyman α the only line ApJ 156, 681: H I levels 1, 2, 3 and c, Balmer α the only line and computed LTE and NLTE models with the single line turned on and off. The results were extensively analyzed in the two papers.

Any student of stellar line formation should take these beautiful papers to heart. The final exercise in Rutten's lecture notes ``Radiative Transfer in Stellar Atmospheres'' asks the student to work through five pages of questions concerning diagrams from the first paper alone! That exercise led to the present work in which we recompute the Auer-Mihalas hot-hydrogen-star models with TLUSTY, adding results from a complete hydrogen atom for comparison.

Our motivation for this Auer-Mihalas re-visitation is twofold:

1. to add diagnostic diagrams to the ones published by Auer & Mihalas, in particular Bν, Jν, Sν graphs to illustrate the role of the radiation field, and radiative heating & cooling graphs to illustrate the radiative energy budget,

2. to see the effect of adding the rest of the hydrogen atom. Title: Dynamical Behavior of the Upper Solar Photosphere Authors: Rutten, R. J. Bibcode: 2003IAUS..210..221R Altcode: No abstract at ADS Title: Solar Atmosphere Models Authors: Rutten, R. J. Bibcode: 2002JAD.....8....8R Altcode: This contribution honoring Kees de Jager's 80th birthday is a review of "one-dimensional" solar atmosphere modeling that followed on the initial "Utrecht Reference Photosphere" of Heintze, Hubenet & de Jager (1964). My starting point is the Bilderberg conference, convened by de Jager in 1967 at the time when NLTE radiative transfer theory became mature. The resulting Bilderberg model was quickly superseded by the HSRA and later by the VAL-FAL sequence of increasingly sophisticated NLTE continuum-fitting models from Harvard. They became the "standard models" of solar atmosphere physics, but Holweger's relatively simple LTE line-fitting model still persists as a favorite of solar abundance determiners. After a brief model inventory I discuss subsequent work on the major modeling issues (coherency, NLTE, dynamics) listed as to-do items by de Jager in 1968. The present conclusion is that one-dimensional modeling recovers Schwarzschild's (1906) finding that the lower solar atmosphere is grosso modo in radiative equilibrium. This is a boon for applications regarding the solar atmosphere as one-dimensional stellar example - but the real sun, including all the intricate phenomena that now constitute the mainstay of solar physics, is vastly more interesting. Title: Dutch Open Telescope: status, results, prospects Authors: Rutten, Robert J.; Sütterlin, Peter; de Wijn, Alfred G.; Hammerschlag, Robert H.; Bettonvil, Felix C. M.; Hoogendoorn, Piet W.; Jägers, Aswin P. L. Bibcode: 2002ESASP.506..903R Altcode: 2002svco.conf..903R; 2002ESPM...10..903R The Dutch Open Telescope (DOT) on La Palma is a revolutionary telescope achieving high-resolution imaging of the solar surface. The DOT combines a pioneering open design at an excellent wind-swept site with image restoration through speckle interferometry. Its open principle is now followed in major solar-telescope projects elsewhere. In the past three years the DOT became the first solar telescope to regularly obtain 0.2" resolution in extended image sequences, i.e., reaching the diffraction limit of its 45-cm primary mirror. Our aim for 2003-2005 is to turn the DOT into a 0.2" tomographic mapper of the solar atmosphere with frequent partnership in international multi-telescope campaigns through student-serviced time allocation. After 2005 we aim to triple the DOT resolution to 0.07" by increasing the aperture to 140 cm and to renew the speckle cameras and the speckle pipeline in order to increase the field size and sequence duration appreciably. These upgrades will maintain the DOT's niche as a tomographic high-resolution mapper in the era when GREGOR, Solar-B and SDO set the stage. Title: Opening the Dutch Open Telescope Authors: Rutten, R. J.; de Wijn, A. G.; Sütterlin, P.; Bettonvil, F. C. M.; Hammerschlag, R. H. Bibcode: 2002ESASP.505..565R Altcode: 2002IAUCo.188..565R; 2002solm.conf..565R We hope to "open the DOT" to the international solar physics community as a facility for high-resolution tomography of the solar atmosphere. Our aim is to do so combining peer-review time allocation with service-mode operation in a "hands-on-telescope" education program bringing students to La Palma to assist in the observing and processing. The largest step needed is considerable speedup of the DOT speckle processing. Title: European Solar Magnetism Network Authors: Rutten, Robert J. Bibcode: 2002ESASP.505..569R Altcode: 2002IAUCo.188..569R; 2002solm.conf..569R The future European Solar Magnetism Network (ESMN) will continue and expand collaborations of the past European Solar Magnetometry Network (ESMN). Both ESMN incarnations are funded by the European Commission, in the Fourth and Fifth Framework programmes respectively. The major past and future ESMN activity is the employment/deployment of European postdocs. Title: Small-scale topology of solar atmospheric dynamics. V. Acoustic events and internetwork grains Authors: Hoekzema, N. M.; Rimmele, T. R.; Rutten, R. J. Bibcode: 2002A&A...390..681H Altcode: We use high-quality observations from the Dunn Solar Telescope at NSO/Sacramento Peak to study spatio-temporal co-location of acoustic flux events in the photosphere and internetwork grains in the chromosphere. The events are diagnosed as sites with excess upward-propagating five-minute waves measured from Dopplergrams. The grains are repetitive bright internetwork features in simultaneous \CaII \KtwoV filtergrams. We find that the largest-flux sites in the granulation have appreciably larger than random probability to co-locate with exceptionally bright chromospheric internetwork grains, at an average delay of about two minutes which is likely to represent sound travel time to the chromosphere. This finding strengthens the case for acoustic grain excitation. Title: The European Solar Magnetometry Network in 2000 - 2001 Authors: Rutten, R. J. Bibcode: 2002joso.book....7R Altcode: No abstract at ADS Title: Dynamics of the solar chromosphere. III. Ultraviolet brightness oscillations from TRACE Authors: Krijger, J. M.; Rutten, R. J.; Lites, B. W.; Straus, Th.; Shine, R. A.; Tarbell, T. D. Bibcode: 2001A&A...379.1052K Altcode: We analyze oscillations in the solar atmosphere using image sequences from the Transition Region and Coronal Explorer (TRACE) in three ultraviolet passbands which sample the upper solar photosphere and low chromosphere. We exploit the absence of atmospheric seeing in TRACE data to furnish comprehensive Fourier diagnostics (amplitude maps, phase-difference spectra, spatio-temporal decomposition) for quiet-Sun network and internetwork areas with excellent sampling statistics. Comparison displays from the ground-based Ca Ii H spectrometry that was numerically reproduced by Carlsson & Stein are added to link our results to the acoustic shock dynamics in this simulation. The TRACE image sequences confirm the dichotomy in oscillatory behaviour between network and internetwork and show upward propagation above the cutoff frequency, the onset of acoustic shock formation in the upper photosphere, phase-difference contrast between pseudo-mode ridges and the interridge background, enhanced three-minute modulation aureoles around network patches, a persistent low-intensity background pattern largely made up of internal gravity waves, ubiquitous magnetic flashers, and low-lying magnetic canopies with much low-frequency modulation. The spatio-temporal occurrence pattern of internetwork grains is found to be dominated by acoustic and gravity wave interference. We find no sign of the high-frequency sound waves that have been proposed to heat the quiet chromosphere, but such measurement is hampered by non-simultaneous imaging in different passbands. We also find no signature of particular low-frequency fluxtube waves that have been proposed to heat the network. However, internal gravity waves may play a role in their excitation. Title: Ba II 4554 Å speckle imaging as solar Doppler diagnostic Authors: Sütterlin, P.; Rutten, R. J.; Skomorovsky, V. I. Bibcode: 2001A&A...378..251S Altcode: We present observations testing the Dopplergram capability of a narrow-band (80 mÅ) Lyot filter imaging the solar surface in the wings of the Ba II 4554 Å resonance line in combination with speckle reconstruction to obtain high angular resolution. The Ba II 4554 Å line is found to be an excellent tool for high-resolution Doppler mapping thanks to opacity insensitivity to temperature variations and line-width insensitivity to thermal broadening. The resulting Dopplergrams show concentrated downflows of 1.2-2.2 km;s-1 in intergranular lanes that probably mark magnetic fluxtubes. Two-wavelength profile sampling is found to suffice for high-resolution Dopplergram construction. The filter will be installed as part of a multi-wavelength speckle imaging system on the new Dutch Open Telescope. Title: DOT strategies versus Orbiter strategies Authors: Rutten, Robert J. Bibcode: 2001ESASP.493..357R Altcode: 2001sefs.work..357R No abstract at ADS Title: ESMN / European solar physics research area Authors: Rutten, Robert J. Bibcode: 2001ESASP.493..353R Altcode: 2001sefs.work..353R No abstract at ADS Title: Proxy Magnetometry with the Dutch Open Telescope Authors: Rutten, R. J.; Hammerschlag, R. H.; Sütterlin, P.; Bettonvil, F. C. M. Bibcode: 2001ASPC..236...25R Altcode: 2001aspt.conf...25R No abstract at ADS Title: A Multi-Channel Speckle Imaging System for the DOT Authors: Sütterlin, P.; Hammerschlag, R. H.; Bettonvil, F. C. M.; Rutten, R. J.; Skomorovsky, V. I.; Domyshev, G. N. Bibcode: 2001ASPC..236..431S Altcode: 2001aspt.conf..431S No abstract at ADS Title: Solar Atmospheric Dynamics (CD-ROM Directory: contribs/rutten) Authors: Rutten, R. J. Bibcode: 2001ASPC..223..117R Altcode: 2001csss...11..117R No abstract at ADS Title: The formation of G-band bright points I: Standard LTE modelling Authors: Kiselman, D.; Rutten, R. J.; Plez, B. Bibcode: 2001IAUS..203..287K Altcode: Assuming LTE, we investigate the formation of the G band in models of quiet solar photosphere and a semiempirical flux-tube model (Briand & Solanki 1995). Preliminary results agree with observations of of G-band bright-point contrast, though this a sensitive function of the amount of scattered light in the observations. Thus LTE line modelling in models constructed under the LTE assumptions seems to fit observations. This does not, however, necessarily imply that LTE is valid here. We also present LTE synthetic spectra of the same models for the full wavelength range from UV to IR. This serves to point out other promising pass bands for the observations of flux-tube structures. Title: Proxy Magnetometry of the Photosphere: Why are G-Band Bright Points so Bright? Authors: Rutten, R. J.; Kiselman, D.; Rouppe van der Voort, L.; Plez, B. Bibcode: 2001ASPC..236..445R Altcode: 2001aspt.conf..445R No abstract at ADS Title: The formation of G-band bright points. I: Standard LTE modelling Authors: Kiselman, D.; Rutten, R. J.; Plez, B. Bibcode: 2000astro.ph.10390K Altcode: Assuming LTE, we synthesise solar G band spectra from the semiempirical flux-tube model of Briand Solanki (1995). The results agree with observed G-band bright-point contrasts within the uncertainty set by the amount of scattered light. We find that it is the weakening of spectral lines within the flux tube that makes the bright-point contrast in the G band exceed the continuum contrast. We also synthesise flux-tube spectra assuming LTE for the full wavelength range from UV to IR, and identify other promising passbands for flux-tube observations. Title: Dutch Open Telescope: Status and Prospects Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. M.; Suetterlin, P. Bibcode: 2000SPD....3102107R Altcode: 2000BAAS...32.1290R The Dutch Open Telescope (DOT) on La Palma in the Canary Islands is a small but revolutionary solar telescope of which the image quality matches the superb imaging of the Swedish Vacuum Solar Telescope (from whose building the DOT is operated). The DOT is an open parabolic 45cm reflector on an open 15m high tower, relying on mirror flushing by the trade winds that bring the best seeing at La Palma to avoid internal turbulence. A water-cooled field stop in the primary image reflects most sunlight and heat out of the telescope. The first data from the DOT combined with speckle reconstruction have yielded sunspot movies of outstanding quality. At present, a multi-channel imaging system is in construction for simultaneous registration of speckle sequences in the G band, in Ca II K and in Hα. The data pipeline permits continuous speckle data acquisition up to 0.5 Tb per day. The advantage of speckle reconstruction over adaptive optics is the much larger field of the restored scene, with the DOT camera's 100x130 arcsec at 0.2 arcsec resolution. The DOT science program is to study magnetic topology and dynamics throughout the photosphere and chromosphere. Title: C. Fröhlich, M. C. E. Huber, S. K. Solanki and R. von Steiger (eds.), Solar Composition and its Evolution from Core to Corona Authors: Rutten, R. J. Bibcode: 1999SSRv...90..526R Altcode: No abstract at ADS Title: (Inter-),Network Structure and DynamicS Authors: Rutten, R. J. Bibcode: 1999ASPC..184..181R Altcode: The dynamical nature of the low solar atmosphere outside active regions is emphasized by recent observations and simulations alike. La Palma images, MDI maps, SUMER spectra, TRACE movies, hydrodynamic shock simulations and magnetohydrodynamic sheet simulations all impart non-quiet behavior to the "quiet Sun". This review begins with a brief summary of current insights and then focuses on various quiet-Sun questions that seem pertinent and solvable. Title: C. Zwaan (1928 - 16 June 1999). Authors: Rutten, R. J.; Schrijver, C. J. Bibcode: 1999SoPh..188.....R Altcode: 1999SoPh..188....0R No abstract at ADS Title: Dynamics of the Solar Chromosphere. II. Ca II H2V and K2V Grains versus Internetwork Fields Authors: Lites, B. W.; Rutten, R. J.; Berger, T. E. Bibcode: 1999ApJ...517.1013L Altcode: We use the Advanced Stokes Polarimeter at the NSO/Sacramento Peak Vacuum Tower Telescope to search for spatio-temporal correlations between enhanced magnetic fields in the quiet solar internetwork photosphere and the occurrence of Ca II H2V grains in the overlying chromosphere. We address the question of whether the shocks that produce the latter are caused by magnetism-related processes, or whether they are of purely hydrodynamic nature. The observations presented here are the first in which sensitive Stokes polarimetry is combined synchronously with high-resolution Ca II H spectrometry. We pay particular attention to the nature and significance of weak polarization signals from the internetwork domain, obtaining a robust estimate of our magnetographic noise level at an apparent flux density of only 3 Mx cm-2. For the quiet Sun internetwork area analyzed here, we find no direct correlation between the presence of magnetic features with apparent flux density above this limit and the occurrence of H2V brightenings. This result contradicts the one-to-one correspondence claimed by Sivaraman & Livingston. We also find no correspondence between H2V grains and the horizontal-field internetwork features discovered by Lites et al. Title: F.-L. Deubner, J. Christensen-Dalsgaard, and D. Kurtz (eds.), New Eyes to See Inside the Sun and Stars, Proceedings of the 185th Symposium of the International Astronomical Union held in Kyoto, Japan, August 18 22, 1997 Authors: Rutten, R. J. Bibcode: 1999SSRv...88..605R Altcode: No abstract at ADS Title: Magnetic Fields and Oscillations Authors: Rutten, Robert J. Bibcode: 1999PASP..111..380R Altcode: No abstract at ADS Title: The Dutch Open Telescope Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. C. M. Bibcode: 1999ASPC..158...57R Altcode: 1999ssa..conf...57R No abstract at ADS Title: Internetwork Grains with TRACE Authors: Rutten, R. J.; de Pontieu, B.; Lites, B. Bibcode: 1999ASPC..183..383R Altcode: 1999hrsp.conf..383R No abstract at ADS Title: Dynamics of the Quiet Solar Chromosphere Authors: Rutten, R. J.; Lites, B. W.; Berger, T. E.; Shine, R. A. Bibcode: 1999ASPC..158..249R Altcode: 1999ssa..conf..249R No abstract at ADS Title: Obituary: Cornelis Zwaan, 1928-1999 Authors: Rutten, Rob; Schrijver, Karel Bibcode: 1999BAAS...31.1612R Altcode: No abstract at ADS Title: Radiative Transfer for Grabs Authors: Rutten, R. J. Bibcode: 1999ASPC..158..306R Altcode: 1999ssa..conf..306R No abstract at ADS Title: Site tests for CLEAR by solar scintillometry Authors: Beckers, Jacques M.; Rutten, Robert J. Bibcode: 1998NewAR..42..489B Altcode: We briefly describe the ongoing site survey for the NSO CLEAR project which aims to put a large-aperture solar telescope at a superior location. The initial results indicate that lake sites are far better than mountain sites, at least in the US. Title: The Lower Solar Atmosphere Rapporteur Paper II Authors: Rutten, Robert J. Bibcode: 1998SSRv...85..269R Altcode: This “rapporteur” report discusses the solar photosphere and low chromosphere in the context of chemical composition studies. The highly dynamical nature of the photosphere does not seem to jeopardize precise determination of solar abundances in classical fashion. It is still an open question how the highly dynamical nature of the low chromosphere contributes to first ionization potential (FIP) fractionation. Title: Small-scale topology of solar atmosphere dynamics. III. Granular persistence and photospheric wave amplitudes Authors: Hoekzema, N. M.; Brandt, P. N.; Rutten, R. J. Bibcode: 1998A&A...333..322H Altcode: We use a superb five-hour sequence of 900 solar images taken at La Palma to study long-duration persistence in the solar granulation, in the context of the long-lived ``intergranular holes'' discovered by \cite*{Roudier+others1997} %T AA: intergranular plumes + BP formation and the contention that these mark sites of convective downflow plumes. We develop a procedure to locate ``persistency regions'' that contain granular brightness maxima or minima over extended periods (up to 45 min), while allowing for lateral drifts due to horizontal flows. Statistical evaluation of the co-location probability for different pixel classes is first used to quantify the likelihood of long-term stationarity for different granular brightness classes and for the persistency regions, and then to evaluate the amount of preferential alignment, at different frequencies and time delays, between excessive Fourier modulation and granular brightness and persistence. The results support the existence of long-lived intergranular holes. There is large persistency difference between the brightest and the darkest features; some of the latter have location memories as long as two hours. In addition, the darkest intergranular features are found to be sites of enhanced Fourier modulation in the 3-min acoustic regime, improving earlier results through much higher statistical significance. However, the persistency regions containing intergranular holes do not seem to produce the excess acoustic emission that would be expected above downflow plumes. Title: Small-scale topology of solar atmosphere dynamics. I. Wave sources and wave diffraction Authors: Hoekzema, N. M.; Rutten, R. J.; Brandt, P. N.; Shine, R. A. Bibcode: 1998A&A...329..276H Altcode: We study the small-scale topology of dynamical phenomena in the quiet-sun internetwork atmosphere, using short-duration Fourier analysis of high-resolution filtergram sequences to obtain statistical estimates for the co-location probability of different fine-structure elements and wave modes. In this initial paper we concentrate on the topology of short-duration Fourier amplitude maps for the photosphere and the simultaneously observed overlying chromosphere. We find that these maps portray a complex mix of global modes and locally excited waves which necessitates a statistical approach. Various aspects including mesoscale patterning indicate the presence of subsurface wave sources and of subsurface wave diffraction by convective inhomogeneities. Title: The Lower Solar Atmosphere Authors: Rutten, R. J. Bibcode: 1998sce..conf..269R Altcode: No abstract at ADS Title: Problem of iron abundance in the solar photosphere. Authors: Kostyk, R. I.; Shchukina, N. G.; Rutten, R. J. Bibcode: 1998BCrAO..94..118K Altcode: The authors analyze the causes of the discrepancies. Title: Small-scale topology of solar atmosphere dynamics. II. Granulation, K2v grains and waves Authors: Hoekzema, N. M.; Rutten, R. J. Bibcode: 1998A&A...329..725H Altcode: We continue studying the small-scale topology of dynamical phenomena in the quiet-sun internetwork atmosphere through statistical estimation of the co-location probability of different fine-structure elements and wave modes. In this paper we chart spatial alignments between the granular brightness structuring of the photosphere, Ca ii K2V brightness patterns in the chromosphere, and wave amplitude patterns in both regimes as a function of time delay between the occurrences of the various features. These charts confirm the presence of excess 2--4 min waves above dark intergranular lanes, the absence of excess 5 min waves above bright granules, the absence of expected alignments between photospheric and chromospheric wave patterning, and the broad-band nature of Ca ii K2V grain formation. In addition, they show significant alignments at large time delays that seem to be regulated by mesoscale patterning and pattern = migration. Title: The Dutch Open Telescope Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. M. Bibcode: 1997ASSL..225..289R Altcode: 1997scor.proc..289R The Dutch Open Telescope is now being installed at La Palma. It is intended for optical solar observations with high spatial resolution. Its open design aims to minimize disturbances of the local air flow and so reduce the locally-generated component of the atmospheric seeing. This paper briefly describes the design, construction, short-term plans, and longer-term prospects. Title: E. Kontizas, M. Kontizas, D.H. Morgan, and G.P. Vettolani (eds.). Wide-Faceted Field Spectroscopy, Proceedings of the 2nd Conference of the Working Group of IAU Commission 9 on "Wide-Field Imaging". Authors: Rutten, R. J. Bibcode: 1997SSRv...82..467R Altcode: No abstract at ADS Title: Modeling LiI and KI sensitivity to Pleiades activity. Authors: Stuik, R.; Bruls, J. H. M. J.; Rutten, R. J. Bibcode: 1997A&A...322..911S Altcode: We compare schematic modeling of spots and plage on the surface of cool dwarfs with Pleiades data to assess effects of magnetic activity on the strengths of the LiI and KI resonance lines in Pleiades spectra. Comprehensive LiI and KI NLTE line formation computation is combined with comparatively well-established empirical solar spot and plage stratifications for solar-like stars. For other stars, we use theoretical constructs to model spots and plage that portray recipes commonly applied in stellar activity analyses. We find that - up to B-V=~1.1 - neither the LiI 670.8nm nor the KI 769.9nm line is sensitive to the presence of a chromosphere, in contrast to what is often supposed. Instead, both lines respond to the effects of activity on the stratification in the deep photosphere. They do so in similar fashion, making the KI line a valid proxy to study LiI line formation without spread from abundance variations. The computed effects of activity on line strength are opposite between plage and spots, differ noticeably between the empirical and theoretical solar-like stratifications, and considerably affect stellar broad-band colors. Our results indicate that one can neither easily establish, nor easily exclude, magnetic activity as major provider of KI line strength variation in the Pleiades. Since LiI line formation follows KI line formation closely, the same holds for LiI and the apparent lithium abundance. Title: Ultraviolet Jets and Bright Points in the Solar Chromosphere. II. Statistical Correlations Authors: Hoekzema, N. M.; Rutten, R. J.; Cook, J. W. Bibcode: 1997ApJ...474..518H Altcode: We use HRTS-VI rocket observations of the solar chromosphere to search for relationships between high-Dopplershift ``jets'' observed in the C I lines near λ = 156 nm and internetwork ``bright points'' observed in the λ = 160 nm continuum, in sequel to the analysis by Cook et al. which failed to find a direct connection between these phenomena. We now use the same data to establish statistical correlations between C I Dopplershift and 160 nm brightness modulation in internetwork areas. These mean relations emerge only after extensive spatial averaging and have small amplitude, but are definitely significant. They show that both C I Dopplershift and 160 nm brightness participate in oscillatory behavior with 3 minute periodicity and mesoscale (8 Mm wavelength) as well as small-scale (1.4 Mm wavelength) spatial patterning. We find spatial and temporal phase relations between Dopplershift and brightness that confirm that jets and bright points should not be interpreted as isolated entities. Rather, they are chromospheric manifestations, with much pattern interference, of the oscillatory acoustic shock dynamics in the internetwork which also cause Ca II K2V grains. Additional small-scale modulation is present which we attribute to waves with f-mode character. Title: First Results from SOHO on Waves Near the Solar Transition Region Authors: Steffens, S.; Deubner, F. -L.; Fleck, B.; Wilhelm, K.; Schuhle, U.; Curdt, W.; Harrison, R.; Gurman, J.; Thompson, B. J.; Brekke, P.; Delaboudiniere, J. -P.; Lemaire, P.; Hessel, B.; Rutten, R. J. Bibcode: 1997ASPC..118..284S Altcode: 1997fasp.conf..284S We present first results from simultaneous observations with the CDS, EIT and SUMER instruments {please see Solar Physics 162 (1995) for a description of the instruments} onboard SOHO and the VTT at Tenerife. Our aim is to study the wave propagation, shock formation, and transmission properties of the upper chromosphere and transition region. The preliminary results presented here include the variation of velocity power spectra with height, difference in power between internetwork and network regions, and variations in mean flows displayed by different spectral lines. Title: Chromospheric Dynamics and the FIP Flip Authors: Rutten, R. J. Bibcode: 1997ASPC..118..298R Altcode: 1997fasp.conf..298R This paper consists of two parts. The first, resembling many other SOHO contributions in this volume, reports on a recent campaign in which SUMER was employed simultaneously with groundbased telescopes. The campaign is described but results are not yet in hand. The second part differs by proposing SUMER measurements and analysis to be contributed by you. It calls attention to the FIP effect, a puzzling outer-atmosphere element segregation that may have to do with quiet-sun chromospheric dynamics. SUMER data, including yours, may provide pertinent diagnostics. Title: Dutch Open Telescope: Status and Prospects Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. C. M. Bibcode: 1997ASPC..118..335R Altcode: 1997fasp.conf..335R The Dutch Open Telescope represents a new solar telescope concept. Being open rather than evacuated, it leads the way to large-aperture high resolution telescopes. It is now being installed on La Palma. Title: Ultraviolet Jets and Bright Points in the Solar Chromosphere. I. Search for One-to-One Relationships Authors: Cook, J. W.; Rutten, R. J.; Hoekzema, N. M. Bibcode: 1996ApJ...470..647C Altcode: Ultraviolet spectrograms and spectroheliograms of the solar chromosphere are used to test the suggestion of Dere, Bartoe, & Brueckner and Rutten & Uitenbroek that bright points in quiet Sun cell interiors observed at = 1600 A, chromospheric jets observed in C I lines near λ = 1560 Å, and Ca II K2v bright points are associated with each other and that they are all manifestations of the same wave interaction in the nonmagnetic chromosphere. We search for spatio-temporal connections between 1600 Å bright points and C I blue jets using data from the High Resolution Telescope and Spectrograph VI rocket flight, comparing 1600 A spectrohellograms and a cospatial C I Doppler shift map on a pixel-by-pixel basis. We find no direct evidence for spatial colocation of bright points and jets, not for instantaneous correspondence and also not when allowing for phase delays as long as 3 minutes. Also, the average brightness evolution and its rms fluctuation are not obviously different between sites of large C I blueshift and the remaining surface. Title: Book reviews Authors: Humphreys, R. M.; Kemp, S.; Savonije, G.; van der Hucht, K. A.; van der Kruit, P. C.; Miley, G.; Bumba, V.; van Nieuwkoop, J.; van Hoolst, T.; Cox, A.; Rutten, R. J.; Kleczek, J.; de Jager, Cornelis; Jerzykiewicz, M.; Zwaan, C.; Poedts, S.; Sakai, Jun-Ichi; Pecker, J. -C.; Heikkila, W.; de Jong, T.; Wilson, P. R.; Müller, E. A.; Hoyng, P.; Icke, V.; Shore, S. N.; Achterberg, A.; Lucchin, F.; Butcher, H.; Ne'Eman, Y.; Heidmann, J.; Belton, M. J. S.; de Graauw, Th.; Waters, L. B. F. M.; Pacini, F.; Hultqvist, B.; Akasofu, S. -I.; Vial, J. -C.; Schatzman, E.; van der Laan, H.; Cole, K. D.; Vanbeveren, D.; Southwood, D.; van der Klis, M.; Katgert, Peter Bibcode: 1996SSRv...76..339H Altcode: No abstract at ADS Title: The solar iron abundance: not the last word. Authors: Kostik, R. I.; Shchukina, N. G.; Rutten, R. J. Bibcode: 1996A&A...305..325K Altcode: Determinations of the solar iron abundance have converged to the meteoritic value with the FeII studies of Holweger et al. (1990), Biemont et al. (1991) and Hannaford et al. (1992) and the FeI results of Holweger et al. (1991). However, the latter authors pointed out that Blackwell et al. (1984) obtained a discordant result from similar oscillator strengths. A recent debate on this lingering discrepancy by the Oxford and Kiel contenders themselves has not clarified the issue. We do so here by showing that it stems from systematic differences between equivalent widths and oscillator strengths which masquerade as difference in fitted damping enhancement factors. We first discuss the various error sources in classical abundance determination and then emulate both sides of the debate with abundance fits of our own. Our emulation of the Oxford side shows that the abundance anomaly claimed by Blackwell et al. (1984) for solar FeI 2.2eV lines vanishes when equivalent width measurements from other authors are combined with better evaluation of the collisional damping parameter. On the Kiel side, we find that the oscillator strengths of Bard et al. (1991) used by Holweger et al. (1991) produce a suspicious trend when used to fit solar FeI lines, whereas comparable application of oscillator strengths from Oxford does not. The trend is mainly set by categories of FeI lines not measured at Oxford; for lines of overlap the two sets agree and deliver the iron abundance value A_Fe_=7.62+/-0.04 which exceeds the meteorite value. The dissimilar lines may suffer from solar line-formation effects. We conclude that the issue of the solar iron abundance remains open. Definitive oscillator strengths are still needed, as well as verification of classical abundance determination by more realistic representations of the solar photosphere and of photospheric line formation. Title: Chromospheric Oscillations Authors: Rutten, R. J. Bibcode: 1995ESASP.376a.151R Altcode: 1995heli.conf..151R; 1995soho....1..151R Concentrates on the quiet-Sun chromosphere. Its internetwork areas are dynamically dominated by the so-called chromospheric three-minute oscillation. They are interpretationally dominated by the so-called Ca II K2v and H2v grains. The main points of this review are that the one phenomenon explains the other (both ways), that the quiet-Sun chromosphere is a clapotisphere pervaded by shocks above h ≍ 1 Mm, and that the existence of the classical temperature minimum is in doubt. Title: The Determination of the Solar Iron Abundance from Fe I Lines Authors: Kostik, R. I.; Shchukina, N. G.; Rutten, R. J. Bibcode: 1995ASPC...78..399K Altcode: 1995aapn.conf..399K No abstract at ADS Title: Infrared lines as probes of solar magnetic features. VIII. MgI 12μm diagnostics of sunspots. Authors: Bruls, J. H. M. J.; Solanki, S. K.; Rutten, R. J.; Carlsson, M. Bibcode: 1995A&A...293..225B Altcode: Due to their large Zeeman sensitivity, the MgI lines at 12μm are important diagnostics of solar magnetism. The formation of their central emission features is now understood, enabling quantitative modeling and diagnostic application of these lines. We supply the first systematic analysis of solar MgI 12μm Stokes profiles employing detailed line-profile synthesis. We compute Stokes profiles of MgI 12.32μm for the quiet Sun, for sunspot penumbrae and for the extended ("superpenumbral") magnetic canopies surrounding sunspots. We use these computations to analyze recent MgI 12μm observations by Hewagama et al. (1993). Our results are the following: (1) -Saha-Boltzmann temperature sensitivity explains that the emission peaks are stronger in penumbrae than in the quiet Sun, and that they disappear in umbrae. (2) -The formation heights of the emission features are approximately the same in penumbrae and in the quiet Sun, namely τ_500_=~10^-3^. (3) -The simple Seares formula allows relatively accurate determinations of field strength and magnetic inclination. (4) -The observed excess broadening of the σ-component peaks compared with the π component in penumbrae is well explained by primarily horizontal, smooth radial variation of the magnetic field strength. Additional small-scale variations are less than {DELTA}B =~200G. (5) -The vertical field gradients dB/dz in penumbrae range from 0.7G/km to 3G/km; the larger gradients occur near the umbra, the smaller ones near the outer edge of the penumbra. (6) -The MgI 12μm lines are well-suited to measure the base heights of superpenumbral magnetic canopies. These heights range between 300km and 500km above τ_500_=1 out to twice the sunspot radius, in excellent agreement with determinations from other infrared lines. Title: Books-Received - Solar Surface Magnetism Authors: Rutten, R. J.; Schrijver, C. J. Bibcode: 1994Sci...265.1902R Altcode: No abstract at ADS Title: The non-LTE formation of Li I lines in cool stars Authors: Carlsson, M.; Rutten, R. J.; Bruls, J. H. M. J.; Shchukina, N. G. Bibcode: 1994A&A...288..860C Altcode: We study the non-LTE (non local thermodynamic equilibrium) formation of Li I lines in the spectra of cool stars for a grid of radiative-equilibrium model atmospheres with variation in effective temperature, gravity, metallicity and lithium abundance. We analyze the mechanisms by which departures from LTE (local thermodynamic equilibrium) arise for Li I lines, first for the young sun (prior to its lithium depletion) and then across the cool-star grid. There are various mechanisms which compete in their effects on emergent Li I line strengths. Their neglect produces errors in lithium abundance determinations that vary in sign as well as size, both across the stellar grid and between different Li I lines (Figs). The errors are appreciable for all cooler stars and largest for cool lithium-rich metal-poor giants. They reverse sign between lithium-rich stars and lithium-poor stars for the λ=670.8nm resonance line, but not for the λ=610.4nm subordinate line. The non-LTE corrections are large enough that they should be taken into account in ongoing debates on lithium synthesis and depletion. We provide convenient numerical approximations of our results (Table 1) to this purpose. We end the paper with some examples in which non-LTE corrections change the slope of published relationships. Title: The SIMURIS interferometric mission: Solar physics objectives and model payload Authors: Dame, L.; Rutten, R. J.; Thorne, A. P.; Vial, J. C. Bibcode: 1994AdSpR..14d.167D Altcode: 1994AdSpR..14..167D We describe the SIMURIS Mission with emphasis on the scientific goals and related capabilities of the major instruments of the model payload. Title: Book reviews Authors: Burlaga, L. F.; Kleczek, J.; Schatzman, E.; Adams, D. J.; Rutten, R. J.; van der Kruit, P. C.; de Jager, Cornelis; Trams, N. R.; Righini, Alberto; Ergma, E.; Grün, Eberhard; Icke, Vincent Bibcode: 1994SSRv...67..223B Altcode: No abstract at ADS Title: The Formation of Infrared Rydberg Lines Authors: Rutten, R. J.; Carlsson, M. Bibcode: 1994IAUS..154..309R Altcode: No abstract at ADS Title: Computation of Infrared Hydrogen Lines Authors: Carlsson, M.; Rutten, R. J. Bibcode: 1994IAUS..154..341C Altcode: No abstract at ADS Title: The Non-LTE Formation of Li I Lines from Cool Stars Authors: Carlsson, M.; Rutten, R. J.; Bruls, J. H. M. J.; Shchukina, N. G. Bibcode: 1994ASPC...64..270C Altcode: 1994csss....8..270C No abstract at ADS Title: Chromospheric oscillations Authors: Lites, B. W.; Rutten, R. J.; Thomas, J. H. Bibcode: 1994ASIC..433..159L Altcode: No abstract at ADS Title: On photospheric flows and chromospheric corks Authors: Brandt, P. N.; Rutten, R. J.; Shine, R. A.; Trujillo Bueno, J. Bibcode: 1994ASIC..433..251B Altcode: No abstract at ADS Title: Book Review: Sunspots: theory and observations / Kluwer, 1992 Authors: Rutten, R. J. Bibcode: 1994SSRv...67..227R Altcode: 1994SSRv...67..227T No abstract at ADS Title: Solar Surface Magnetism Authors: Rutten, Robert J.; Schrijver, Carolus J. Bibcode: 1994ASIC..433.....R Altcode: 1994ssm..work.....R No abstract at ADS Title: MgI 12 μm diagnostics of sunspot penumbrae Authors: Bruls, J. H. M. J.; Solanki, S. K.; Rutten, R. J.; Carlsson, M. Bibcode: 1994smf..conf..191B Altcode: No abstract at ADS Title: Dynamics of the Solar Chromosphere. I. Long-Period Network Oscillations Authors: Lites, B. W.; Rutten, R. J.; Kalkofen, W. Bibcode: 1993ApJ...414..345L Altcode: We analyze differences in solar oscillations between the chromospheric network and internetwork regions from a 1 hr sequence of spectrograms of a quiet region near disk center. The spectrograms contain Ca II H, Ca I 422.7 nm, and various Fe I blends in the Ca II H wing. They permit vertical tracing of oscillations throughout the photosphere and into the low chromosphere. We find that the rms amplitude of Ca II H line center Doppler fluctuations is about 1.5 km/s for both network and internetwork, but that the character of the oscillations differs markedly in these two regions. Within internetwork areas the chromospheric velocity power spectrum is dominated by oscillations with frequencies at and above the acoustic cutoff frequency. They are well correlated with the oscillations in the underlying photosphere, but they are much reduced in the network. In contrast, the network Ca II H line center velocity and intensity power spectra are dominated by low-frequency oscillations with periods of 5-20 min. Their signature is much clearer in our Ca II H line center measurements than in previously used diagnostics which are contaminated by signals from deeper layers. We find that these long-period oscillations are not correlated with underlying photospheric disturbances, and we discuss their nature. Title: Book reviews Authors: Murawski, K.; Grevesse, N.; Piteri, S.; Nieuwenhuyzen, H.; van der Hage, J. C. H.; Icke, Vincent; Hovenier, J. W.; Rutten, R. J.; De Greve, J. P.; Kaufmann, P.; Burki, G.; de Jager, Cornelis Bibcode: 1993SSRv...65..365M Altcode: No abstract at ADS Title: Prospects for very-high-resolution solar physics with the Simuris interferometric mission. Authors: Dame, L.; Martic, M.; Rutten, R. J. Bibcode: 1993ESASP1157..119D Altcode: 1993srfs.book..119D Simuris - the Solar, Solar System, and Stellar Interferometric Mission for Ultra-high Resolution Imaging and Spectroscopy - employs advanced interferometric techniques. Its payload includes two major instruments, which are the Solar Ultraviolet Network (SUN), an interferometric array of four 20 cm telescopes on a 2 m baseline, and the Imaging Fourier-Transform Spectrometer (IFTS), which uses light from a 40 cm Gregory telescope. Both instruments have active pointing capabilities of 3 mas stability, and in addition SUN has an active co-phasing control to 1/50th of a wavelength. EUV multi-layer telescopes complete the payload for diagnostics of the very-high-temperature plasma. Title: Book reviews Authors: Rutten, R. J.; Mewe, R.; Houziaux, L.; Cheng, Chung-Chieh; van der Klis, M.; Sylwester, Janusz; Tajima, T.; Kresák, Ľ.; Minarik, S.; de Jager, Cornelis; van der Kruit, P. C. Bibcode: 1993SSRv...65..181R Altcode: No abstract at ADS Title: Oscillations of the Magnetic Network Authors: Lites, B. W.; Rutten, R. J.; Kalkofen, W. Bibcode: 1993ASPC...46..530L Altcode: 1993mvfs.conf..530L; 1993IAUCo.141..530L No abstract at ADS Title: Stellar objectives of SIMURIS Authors: Damé, L.; Coradini, M.; Foing, B.; Rutten, R. J.; Thorne, A.; Vial, J. C. Bibcode: 1993MmSAI..64..345D Altcode: No abstract at ADS Title: Book Review: The observation and analysis of stellar photospheres / Cambridge U Press, 1992 Authors: Rutten, R. J. Bibcode: 1993SSRv...65..183R Altcode: 1993SSRv...65..183G No abstract at ADS Title: SIMURIS: High-Resolution Solar Physics Authors: Rutten, R. J.; Dame, L. Bibcode: 1993ASPC...46..184R Altcode: 1993mvfs.conf..184R; 1993IAUCo.141..184R No abstract at ADS Title: Book-Review - the Sun - a Laboratory for Astrophysics Authors: Schmelz, J. T.; Brown, J. C.; Rutten, R. J. Bibcode: 1993SSRv...65..370S Altcode: No abstract at ADS Title: The SIMURIS interferometric mission: solar physics objectives and model payload (invited paper) Authors: Damé, L.; Coradini, M.; Foing, B.; Rutten, R. J.; Thorne, A.; Vial, J. C. Bibcode: 1993MmSAI..64..333D Altcode: No abstract at ADS Title: High resolution solar physics. Authors: Rutten, Robert J. Bibcode: 1992ESASP.354..163R Altcode: 1992tsbi.rept..163R Solar physics is a prime example of the quest for high spatial resolution as the coming space frontier of astrophysics. The proximity of the Sun brings the enormous advantage that modest baselines suffice to fulfill an important goal: to resolve basic plasma processes at their characteristic scales. At such resolution, the solar atmosphere represents a plasma physics laboratory of broad interest. Concerted observations combining high spatial and temporal resolution with narrow-band diagnostics in the ultraviolet and the visible will deliver detailed insights is plasma processes that are ubiquitous in the cosmos, but resolvable only for the Sun. Space interferometry is the obvious way to fulfill this promise. Title: The formation of helioseismology lines. I. NLTE effects in alkali spectra. Authors: Bruls, J. H. M. J.; Rutten, R. J.; Shchukina, N. G. Bibcode: 1992A&A...265..237B Altcode: The authors study the NLTE formation of the solar K I and Na I resonance lines employed in helioseismology. They combine standard modeling of the solar atmosphere with comprehensive alkali model atoms, complete up to the Rydberg regime near the continuum, to study various NLTE mechanisms which interact to make the alkali population balances more complex than is the case for other minority species. In particular, they discuss a "photon suction" process which produces overpopulation of the neutral stage by driving a population flow from the reservoir in the singly ionized stage. They isolate this and other mechanisms with specifically tailored model atoms and provide a choice of simplified model atoms, trading precision against size, which are appropriate for future use in numerical simulations of the solar atmosphere. Title: The formation of helioseismology lines. II. Modeling of alkali resonance lines with granulation. Authors: Bruls, J. H. M. J.; Rutten, R. J. Bibcode: 1992A&A...265..257B Altcode: The authors model the NLTE formation of the solar Na I and K I resonance lines for an array of one-dimensional atmospheric models taken from a numerical simulation of the solar granulation by Nordlund and Stein. They discuss the nature of alkali-line sensitivity to granulation using hot and cool extremes from the simulation and study the granular modulation of diagnostics such as line bisectors and helioseismological resonance-cell response. They also show that granular structuring produces apparent spatially-averaged line broadening of similar magnitude as the ad hoc microturbulent and damping broadening invoked in traditional plane-parallel modeling. Title: Model payload and system design of the SIMURIS interferometric mission Authors: Dame, L.; Rutten, R. J.; Thorne, A. P.; Vial, J. C. Bibcode: 1992wadc.iafcZ....D Altcode: SIMURIS (Solar, Solar System, and Stellar Interferometric Mission for Ultrahigh Resolution Imaging and Spectroscopy) has been proposed to ESA as a Mission in the context of the Space Station in November 1989 in answer to the Call for the Next Medium Size Mission (M2). It has completed, since, an Assessment Study, and is now proceeding for a Phase A. SIMURIS employs advanced interferometric techniques. The payload includes two major instruments which are the Solar Ultraviolet Network (SUN), an interferometric array of four 20-cm telescopes on a 2-m baseline, and the Imaging Fourier Transform Spectrometer (IFTS) which uses light from a 40-cm Gregory telescope. Both instruments have active pointing capabilities of 3 milliarcsec stability, and SUN has, in addition, an active cophasing control to 1/50th of a wavelength. EUV multilayer telescopes complete the payload for diagnostics of the very high temperature plasma. The SIMURIS model payload will be described with emphasis on the system design of the interferometric aspects of the instruments. Title: Solar hydrogen lines in the infrared Authors: Carlsson, M.; Rutten, R. J. Bibcode: 1992A&A...259L..53C Altcode: We study recently observed H I lines in the infrared solar spectrum, employing detailed NLTE modeling to explain their formation and to evaluate their diagnostic merits. The solar infrared H I lines vary much in character, depending on opacity and wavelength; our computations reproduce the observations closely. The line wings are primarily set by Stark broadening due to metal ions and protons; the line cores are sensitive to NLTE population departure divergence which is driven by Balmer-continuum photoionization. The formation heights of the H I lines range from the deep photosphere for near-infrared line wings to the chromosphere for line cores with wavelengths greater than 10 microns; these features provide valuable diagnostics of the thermal structure of the solar atmosphere. Title: Prospects with SIMURIS. Authors: Dame, L.; Rutten, R. J. Bibcode: 1992ESASP.344...21D Altcode: 1992spai.rept...21D The authors give an introductory overview of the SIMURIS payload by briefly presenting its goals and concepts. Title: Design Rationale of the Solar Ultraviolet Network / Sun Authors: Dame, L.; Acton, L.; Bruner, M. E.; Connes, P.; Cornwell, T. J.; Curdt, W.; Foing, B. H.; Hammer, R.; Harrison, R.; Heyvaerts, J.; Karabin, M.; Marsch, E.; Martic, M.; Mattic, W.; Muller, R.; Patchett, B.; Roca-Cortes, T.; Rutten, R. J.; Schmidt, W.; Title, A. M.; Tondello, G.; Vial, J. C.; Visser, H. Bibcode: 1992ESOC...39..995D Altcode: 1992hrii.conf..995D No abstract at ADS Title: The formation of the MG I emission features near 12 microns Authors: Carlsson, M.; Rutten, R. J.; Shchukina, N. G. Bibcode: 1992A&A...253..567C Altcode: The formation of two Mg I 12-micron emission features in the solar spectrum, the existence of which was reported by Murcray et al. (1981), is explained using plane-parallel nonlocal thermodynamic equilibrium modeling with a radiative-equilibrium model atmosphere without chromosphere. It is shown that these emissions are a natural consequence of population depletion by line photon losses followed by population replenishment from the ionic reservoir in the highly excited levels. The results confirm the suggestion by Lemke and Holweger (1987) that the 12-micron lines are formed in the photosphere and disprove the claim by Zirin and Popp (1989) that the temperature minimum occurs much deeper than in standard models of the solar atmosphere. Title: Formation of the MG 112 TTM Lines Authors: Carlsson, M.; Rutten, R. J.; Shchukina, N. G. Bibcode: 1992ASPC...26..518C Altcode: 1992csss....7..518C No abstract at ADS Title: Dynamics of the Quiet Solar Atmosphere: K2v Cell Grains Versus Magnetic Elements Authors: Brandt, P. N.; Rutten, R. J.; Shine, R. A.; Trujillo Bueno, J. Bibcode: 1992ASPC...26..161B Altcode: 1992csss....7..161B No abstract at ADS Title: Ca uc(ii) H2v and K2v cell grains Authors: Rutten, Robert J.; Uitenbroek, Han Bibcode: 1991SoPh..134...15R Altcode: The bright Ca II H2v and K2v grains, which are intermittently present in the interiors of network cells in quiet-Sun areas, should provide important diagnostics of the dynamical interaction between the quiet photosphere and the chromosphere above it, but their nature has so far eluded identification. We review the extensive observational literature on these grains and on related phenomena. We resolve various contradictions, connect hitherto unconnected observations, distill new constraints and relate signatures in the measurement domain to signatures in the Fourier domain. We then review interpretations and simulation efforts, adding computations of our own to illustrate modeling options. We conclude that the grains are a hydrodynamical phenomenon in which magnetic fields do not play a major role. The grains are due to interference between a pervasive standing oscillation with about a 180 s periodicity and an 8 Mm horizontal wavelength in the chromosphere and the wave trains of the evanescent p-mode interference pattern in the upper photosphere. The roles of short-period waves, shock formation and granular piston excitation and the issue of long-lived patterning remain open; we suggest avenues for further research. Title: Photospheric dynamics and the NLTE formation of the solar K I 769.9 NM line Authors: Gomez, M. T.; Severino, G.; Rutten, R. J. Bibcode: 1991A&A...244..501G Altcode: Earlier analyses of the K I 769.9 nm resonance line are extended as a diagnostic of dynamical phenomena in the solar photosphere by evaluating the effects of dynamical variations on departures from LTE in the K I spectrum. Representative models for the solar granulation and the solar five-minute oscillation are used to estimate dynamical NLTE departures in the K I populations and to compare these to standarad plane-parallel NLTE modeling. Various NLTE mechanisms operate together in K I simultaneously with fortuitous cancellations; the resulting population departures vary less than 30 percent between dynamical perturbations. These results validate the assumption of departure invariance, i.e., adopting NLTE population departure coefficients from a standard static model for use in dynamical perturbations, as a good first-order approximation in K I 769.9 nm formation studies. Title: Long-Period Oscillations of the Chromospheric Network Authors: Lites, B. W.; Kalkofen, W.; Rutten, R. J. Bibcode: 1991BAAS...23.1050L Altcode: No abstract at ADS Title: Book-Review - Solar and Stellar Granulation Authors: Rutten, R. J.; Severino, G.; Rudiger, G. Bibcode: 1991AN....312..147R Altcode: No abstract at ADS Title: K2V Cell Grains and Chromospheric Heating (With 1 Figure) Authors: Rutten, R. J.; Uitenbroek, H. Bibcode: 1991mcch.conf...48R Altcode: No abstract at ADS Title: The solar photosphere: video movies and computer simulations. Authors: Rutten, R. J. Bibcode: 1990ComAp..14..297R Altcode: No abstract at ADS Title: Temperature Diagnostics of the Upper Photosphere Authors: Shchukina, N. G.; Shcherbina, T. G.; Rutten, R. J. Bibcode: 1990IAUS..138...29S Altcode: No abstract at ADS Title: Sun-As Line Formation Authors: Rutten, Robert J. Bibcode: 1990ASPC....9...91R Altcode: 1990csss....6...91R Spectral line formation in the upper solar photosphere and temperature-minimum region is discussed to examine the effectiveness of spatially averaged '1D' modeling in solar and stellar applications. Problems associated with NLTE radiative transfer are described for the two-level atom, one bound level with a continuum, three bound levels, and for multiple levels. Successful applications of 1D modeling are reviewed where solar photospheric optical lines are used to calibrate stellar abundance determinations. The homogeneity or 1D LTE-RE formation of the sun is doubted, and the atmosphere is described as being highly dynamic. The LTE-RE assumption can be applied to the spatially averaged upper photosphere, but the problems associated with the NLTE effects must be considered to investigate the fine elements of solar structure. Title: The Formation of the Mg I 12-Micron Emission Lines Authors: Carlsson, M.; Rutten, R. J.; Shchukina, N. G. Bibcode: 1990PDHO....7..260C Altcode: 1990dysu.conf..260C; 1990ESPM....6..260C Contents: The Mg I 12 μm line, LTE or NLTE, chromospheric formation, photospheric formation, collisional NLTE; departure diffusion. Title: Solar Oscillator Strengths as a Diagnostic Tool Authors: Gurtovenko, E. A.; Kostik, R. I.; Rutten, R. J. Bibcode: 1990IAUS..138...35G Altcode: No abstract at ADS Title: New solar oscillator strengths from Kiev Authors: Gurtovenko, E. A.; Kostik, R. I.; Rutten, R. J. Bibcode: 1990asos.conf...92G Altcode: No abstract at ADS Title: Summary Lecture Authors: Rutten, R. J. Bibcode: 1990IAUS..138..501R Altcode: No abstract at ADS Title: Book-Review - Solar and Stallar Granulation Authors: Rutten, R. J.; Severino, G. Bibcode: 1989Sci...246..137R Altcode: No abstract at ADS Title: Book-Review - Physics of Formation of Feii Lines Outside LTE Authors: Viotti, R.; Vittone, A.; Friedjung, M.; Rutten, R. J. Bibcode: 1989SSRv...50..617V Altcode: 1989IAUCo.107..617V No abstract at ADS Title: Book Review: Physics of formation of Fe II lines outside LTE (IAU Coll. 94) / Reidel, 1988 Authors: Viotti, R.; Vittone, A.; Friedjung, M.; Rutten, R. J. Bibcode: 1989SSRv...50..618V Altcode: No abstract at ADS Title: Book-Review - Space - the Next Twenty-Five Years Authors: Manno, V.; Kresák, Ľ.; de Jong, T.; Trimble, Virginia; Marov, Mikhail Ya.; Rutten, Robert J.; Vreeburg, J. P. B.; Kaufmann, P. Bibcode: 1989SSRv...50..615M Altcode: 1989IAUCo.107..615M No abstract at ADS Title: Workshop Introduction Authors: Rutten, R. J. Bibcode: 1989ASIC..263....1R Altcode: 1989ssg..conf....1R No abstract at ADS Title: The Granulation Sensitivity of Neutral Metal Lines Authors: Bruls, J. H. M. J.; Uitenbroek, H.; Rutten, R. J. Bibcode: 1989ASIC..263..311B Altcode: 1989ssg..conf..311B No abstract at ADS Title: Solar and stellar granulation Authors: Rutten, Robert J.; Severino, Giuseppe Bibcode: 1989ASIC..263.....R Altcode: 1989ssg..conf.....R No abstract at ADS Title: Granulation and the NLTE Formation of K I 769. 9 Authors: Gomez, M. T.; Severino, G.; Rutten, R. J. Bibcode: 1989ASIC..263..565G Altcode: 1989ssg..conf..565G No abstract at ADS Title: The Solar Photosphere: Video Movies and Computer Simulations Authors: Rutten, Robert J. Bibcode: 1989ComAp..14..297R Altcode: No abstract at ADS Title: The granulation sensitivity of helioseismology lines. Authors: Rutten, R. J.; Bruls, J. H. M. J.; Gomez, M. T.; Severino, G. Bibcode: 1988ESASP.286..251R Altcode: 1988ssls.rept..251R The authors address the sensitivity of the Ni I 676.78 nm GONG line and the K I 769.9 nm resonance line to the temperature fluctuations present in the solar granulation. The temperature contrasts due to granulation are probably small in the upper photosphere where the cores of these two helioseismology lines are formed. However, the cores are sensitive also to the granulation temperature contrasts in the deep photosphere, through non-local NLTE effects in their formation. The largest effects are due to the ultraviolet radiation field, which is strongly modulated by the granulation in the deep layers where it escapes and carries these contrasts upwards to the line formation height. The authors discuss the resulting NLTE mechanisms and their influence on the two lines. Title: The NLTE formation of iron lines in the solar photosphere Authors: Rutten, Robert J. Bibcode: 1988ASSL..138..185R Altcode: 1988IAUCo..94..185R; 1988pffl.proc..185R The use of solar iron lines as diagnostics of the solar photosphere is discussed. NLTE in photospheric iron lines is discussed, including NLTE mechanisms, the description of NLTE, and published NLTE modeling of Fe I and Fe II. Iron NLTE and the mean atmosphere is addressed, including empirical plane-parallel modeling from lines and from continua and radiative-equilibrium modeling. The use of NLTE to study granulation, flux tubes, and flux bifurcations in the sun is considered. Title: Oscillator Strengths from the High S/n Solar Spectrum Authors: Rutten, R. J. Bibcode: 1988IAUS..132..367R Altcode: No abstract at ADS Title: Feii Prospects in Solar Physics Authors: Rutten, R. J. Bibcode: 1988ASSL..138..317R Altcode: 1988IAUCo..94..317R; 1988pffl.proc..317R No abstract at ADS Title: Empirical gf-determination from the solar spectrum Authors: Rutten, Robert J.; Kostik, Roman I. Bibcode: 1988ASSL..138...83R Altcode: 1988IAUCo..94...83R; 1988pffl.proc...83R The reliability of Fe I and Fe II oscillator strengths determined empirically from optical solar lines is tested. A comparison is made between gfW fits to the equivalent widths and gfD fits to the depths of 354 Fe I lines and 22 Fe II lines for various combinations of input parameters. The resulting scatter diagrams provide a measure of the attainable precision. Title: Book reviews Authors: Kleczek, J.; van Gent, R. H.; Rutten, Robert J.; de Munck, J. C.; Slottje, C.; Severne, G.; Pecker, Jean-Claude; Postma, H.; Grishchuk, L. P.; Niewenhuijzen, H.; Schuiling, R. D.; van Beek, H. F.; Reijnen, G. C. M.; Heidmann, Jean; Lemaire, J.; Bleeker, Johan; Icke, V.; Neéman, Y.; Feast, M. W.; de Graaff, W. Bibcode: 1986SSRv...43..383K Altcode: No abstract at ADS Title: Book-Review - Progress in Stellar Spectral Line Formation Theory Authors: Beckman, J. E.; Crivellari, L.; Rutten, R. J. Bibcode: 1986SSRv...43Q.384B Altcode: No abstract at ADS Title: Book-Review - the A-Stars - Problems and Perspectives Authors: Wolff, S. C.; Rutten, R. J. Bibcode: 1985SSRv...41..396W Altcode: No abstract at ADS Title: Book-Review - Stellar Atmospheric Structural Patterns Authors: Thoma, R. N.; Rutten, R. J. Bibcode: 1985SSRv...41..394T Altcode: No abstract at ADS Title: Velocity Field in the Region of the Temperature Minimum of the Solar Atmosphere - Preliminary Results of a Determination of the Amplitude of the General Velocity Field Authors: Gurtovenko, E. A.; Sheminova, V. A.; Rutten, R. J. Bibcode: 1985SvA....29...72G Altcode: No abstract at ADS Title: Velocity field in the region of the temperature minimum of the solar atmosphere - Preliminary results of a determination of the amplitude of the general velocity field Authors: Gurtovenko, E. A.; Sheminova, V. A.; Rutten, R. J. Bibcode: 1985AZh....62..124G Altcode: The weak Fraunhofer lines in the near wings of H, K Ca II lines have been analysed to study the velocity amplitude of the general velocity field in the middle and outer photospheric layers. The results confirm the basic well-known data on the velocity amplitude in the middle photospheric layers. Besides, it is shown that the radial and tangential components of the velocity amplitude continue to decrease with height also in the outer photosphere. Title: Clean lines in the solar flux spectrum Authors: Rutten, R. J.; van der Zalm, E. B. J. Bibcode: 1984A&AS...55..171R Altcode: Profile parameters of 602 unblended lines in the Sacramento Peak Atlas of the visual solar irradiance spectrum are profiled and compared to earlier measurements of the same lines in the Jungfraujoch Atlas of the solar disk-center intensity spectrum. The expected effects of solar rotation and of center-to-limb variations in the intensity profiles are discussed and compared to the actual trends. Finally, the spread is discussed. Title: Revision of solar equivalent widths, Fe I oscillator strengths and the solar iron abundance. Authors: Rutten, R. J.; van der Zalm, E. B. J. Bibcode: 1984A&AS...55..143R Altcode: The authors employ detailed modelling of solar Fe I and Fe II lines to calibrate the correction of equivalent widths for contamination by unresolved blends. They then determine the equivalent widths of 750 clean lines in the Jungfraujoch Atlas of the optical solar spectrum, and they compare these to the values given for the Utrecht Atlas by Moore et al. (1966). The authors also select clean Fe I lines, discuss their NLTE formation, construct a NLTE Fe I curve of growth, provide new oscillator strengths for weak Fe I lines, and revise the solar iron abundance to NFe/NH = (4.3±0.5)10-5. The authors use the results to appraise the basis and methods of classical stellar abundance determination. Title: Spectral Lines: Diagnostics Authors: Rutten, R. J. Bibcode: 1984ssdp.conf..379R Altcode: The author discusses three aspects of employing spatially-averaged solar lines as diagnostics of small-scale photospheric structure: (1) partial redistribution vs. turbulence, (2) advertising the extreme limb, (3) quality of mean models. Title: One Eye Closed - Two Eyes Closed Authors: Rutten, R. J. Bibcode: 1984ssdp.conf..446R Altcode: No abstract at ADS Title: Book-Review - Automated Data Retrieval in Astronomy Authors: Jaschek, G.; Heintz, W.; Rutten, R. J. Bibcode: 1983SSRv...36..417J Altcode: No abstract at ADS Title: Book reviews Authors: Kleczek, J.; Nussbaumer, H.; van der Hucht, K. A.; De Greve, J. P.; Ooms, G.; Rutten, R. J.; van der Laan, H.; Jäger, F. W.; Reijnen, G. C. M.; Bijleveld, W.; Kistemaker, J.; de Jager, C.; Mustel, E. R.; Ne'Eman, Y.; Priest, E. R.; Stiller, H.; Seifert, W.; Namba, O.; Kuperus, M.; Hoekstra, Roel; Stumpers, F. L. H. M.; Frank, S.; Zimmerman, J. T. F.; De Loore, C.; Gendrin, R.; Schrijver, J.; Mulder, P. S.; Pounds, K. A.; Young, R. S.; Houziaux, L.; Engvold, O.; Bok, B. J.; de Graaff, W. Bibcode: 1983SSRv...36..415K Altcode: No abstract at ADS Title: Empirical NLTE analyses of solar spectral lines. IV - The Fe I curve of growth Authors: Rutten, R. J.; Zwaan, C. Bibcode: 1983A&A...117...21R Altcode: The effects of departures from local thermodynamic equilibrium on the equivalent widths of solar Fe I lines are studied as an example for the analysis of the stellar curve of growth. The solar curve of growth obtained is based on the nonlocal thermodynamic equilibrium (NLTE) modeling of the solar spectrum of Lites (1972, 1973) and the best available oscillator strengths for 991 Fe I lines. The empirical curve obtained relating the equivalent width-wavelength ratio to the oscillator strength under NLTE is shown to differ appreciably from curves neglecting the NLTE ionization departures, although these effects may be corrected by assuming a NLTE-masking model. Theoretical NLTE curves of growth are also presented, and splittings due to wavelength dependency, differences in NLTE excitation, and variation in collisional damping, which are largely hidden by noise in observed values, are discussed. A new value for the solar iron abundance of 0.000047 times the hydrogen abundance is also derived. Title: NLTE masking and the Kiev Fe I oscillator strengths. Authors: Rutten, R. J. Bibcode: 1983HiA.....6..801R Altcode: This paper describes the empirical solar-spectrum determinations of the oscillator strengths of 860 Fe I lines by Gurtovenko and Kostik (1981), and attempts to show their particular value for abundance analyses of cool stars. Title: Empirical NLTE analyses of solar spectral lines. III - Iron lines versus LTE models of the photosphere Authors: Rutten, R. J.; Kostik, R. I. Bibcode: 1982A&A...115..104R Altcode: We compare observational indications of departures from LTE in solar Fe I lines with published NLTE computations in the context of discrepancies between empirical LTE and NLTE models of the solar atmosphere. We find that the importance of departures from LTE in Fe I and similar spectra is often underestimated through neglect of opacity departures. We demonstrate with numerical experiments that the peculiarities of the LTE models are artifacts due to the neglect of NLTE departures; in particular, we so explain the Holweger-Müller LTE model quantitatively. However, we show also that the NLTE formation of most optical metal lines is fortuitously well-mimicked by LTE computation when using LTE models. Thus, LTE-derived metal abundances and empirical oscillator strengths happen to be fairly precise. The same may hold for the use of theoretical radiative- equilibrium models in stellar abundance determinations. Title: Rhe sun as a star. Authors: Rutten, R. J.; Cram, L. E. Bibcode: 1981NASSP.450..473R Altcode: 1981suas.nasa..473R The ways in which solar astrophysics serves to improve the methodology for the interpretation of stellar observations and the construction of stellar atmospheric models are summarized. The astrophysical processes highlighted are: stellar mass; stellar rotation; stellar magnetism; stellar composition; stellar companions; and evolutionary history. Title: On the formation of Fe II lines in stellar spectra. I. Solar spatial intensity variation of lambda 3969.4. Authors: Cram, L. E.; Rutten, R. J.; Lites, B. W. Bibcode: 1980ApJ...241..374C Altcode: High-spatial-resolution solar observations of the weak Fe II lambda 3969.4 line are employed to study non-local thermodynamic equilibrium effects in Fe II line formation. This line is superposed on the wing of the Ca II H line, which raises its height of formation. The line shows extraordinary spatial intensity variations, including emission features whose contrast increases toward the limb. Observed profiles of the Fe II resonance lines in the UV are used to define formation parameters in a 15-level atomic model computation, which shows that Fe II subordinate lines are generally formed out of local thermodynamic equilibrium as a result of pumping by UV line-wing photons from the deep photosphere. For the lambda 3969.4 line, this pumping results in large sensitivity to the atmospheric structure in layers deeper than the layer of formation of the H-wing background intensity. The absence of intense emission cores in the Fe II resonance lines, the effects of partially coherent scattering, and the effects of chromospheric and photospheric inhomogeneities are discussed. It is found that emission of lambda 3969.4 provides a diagnostic of the inhomogeneous structure of the deep photosphere, for the sun and for late-type stars. Title: Solar limb emission lines near CA II H & K and their spatial intensity variations Authors: Rutten, R. J.; Stencel, R. E. Bibcode: 1980A&AS...39..415R Altcode: The paper employs solar observations of high spatial and spectral resolution to identify emission lines seen in the extended wings of Ca II H & K near the solar limb. Emission lines in the wings of H & K represent valuable diagnostics of the atmospheres of cool stars, with a varying information content which depends on their particular formation mechanism. In solar spectrograms different emission line formation mechanisms can be distinguished by the character of the spatial intensity variation (SIV) apparent in the lines. Various classes of H & K emission features, their spatial intensity variations and their formation mechanisms (of which some pose further problems) are discussed. A new extended list of line identifications is compiled based on their formation class and compared with other line lists. Evidence is found that stellar luminosity-sensitive lines tend to show large spatial intensity variation on the sun. Title: Report from the discussion group on two dimensional spectroscopy Authors: Righini, A.; Rutten, R. J. Bibcode: 1980fsoo.conf..308R Altcode: No abstract at ADS Title: Afbuiging van straling door de zon. 1. De zonsverduistering van 1919. Authors: Rutten, R. J. Bibcode: 1980Zenit...7..276R Altcode: No abstract at ADS Title: Afbuiging van straling door de zon. 2. Nieuwe metingen. Authors: Rutten, R. J. Bibcode: 1980Zenit...7..372R Altcode: No abstract at ADS Title: An open LEST? Authors: Hammerschlag, R. H.; Rutten, R. J. Bibcode: 1980fsoo.conf..115H Altcode: No abstract at ADS Title: Solar observations with high spectral purity: needs and constraints (This paper was actually presented at the end of session 4.) Authors: Rutten, R. J. Bibcode: 1980fsoo.conf..221R Altcode: No abstract at ADS Title: Diagnostic Use of Feii H and K Wing Emission Lines Authors: Cram, L. E.; Rutten, R. J.; Lites, B. W. Bibcode: 1980LNP...114..102C Altcode: 1980IAUCo..51..102C; 1980sttu.coll..102C No abstract at ADS Title: Partial redistribution in the solar photospheric Ba II spectrum. Authors: Rutten, R. J.; Milkey, R. W. Bibcode: 1979ApJ...231..277R Altcode: Recent studies of the effects of partial frequency redistribution (PRD) on the formation of strong chromospheric resonance lines are extended to weaker lines formed in the photosphere. Methods that have been derived to compute the PRD formation of the Ca II spectrum are applied to the solar Ba II spectrum. It is found that PRD is important in the formation of the 4554-A resonance line, and the results confirm that its effects on the line source function explain the emission wings of this line observed near the limb. Source function structure and line profiles for Ba II 4554 A and Ba II 5854 A are discussed; they may serve as an example for estimating effects of PRD in other photospheric lines in stellar atmospheres. Title: An open LEST (Large European Solar Telescope)? Authors: Hammerschlag, R. H.; Rutten, R. J. Bibcode: 1979MmArc.106..115H Altcode: No abstract at ADS Title: Solar observations with high spectral purity: needs and constraints. Authors: Rutten, R. J. Bibcode: 1979MmArc.106..221R Altcode: No abstract at ADS Title: Report from the discussion on two-dimensional spectroscopy requirements for Lest (Large European Solar Telescope). Authors: Righini, A.; Rutten, R. J. Bibcode: 1979MmArc.106..308R Altcode: No abstract at ADS Title: Empirical NLTE analyses of solar spectral lines. II: The formation of the Ba II lambda 4554 resonance line. Authors: Rutten, R. J. Bibcode: 1978SoPh...56..237R Altcode: The center-to-limb behaviour of the Ba II λ4554 resonance line is analyzed together with data from the extreme limb, flash intensities and profiles of other Ba II lines. An empirical NLTE method is employed in which the observed profiles are compared with synthesized profiles based on a standard one-dimensional model atmosphere, with the line source function, the barium abundance, the collisional damping and the atmospheric turbulence as free parameters. Title: Report from the discussion group on two dimensional spectroscopy Authors: Righini, A.; Rutten, R. J. Bibcode: 1978fsoo.conf..308R Altcode: No abstract at ADS Title: Solar observations with high spectral purity: needs and constraints Authors: Rutten, R. J. Bibcode: 1978fsoo.conf..221R Altcode: No abstract at ADS Title: An open LEST? Authors: Hammerschlag, R. H.; Rutten, R. J. Bibcode: 1978fsoo.conf..115H Altcode: No abstract at ADS Title: Extreme limb observations of Ba II λ 4554 and Mg i λ 4571 Authors: Rutten, R. J. Bibcode: 1977SoPh...51....3R Altcode: Profiles of the Ba II λ 4554 resonance line and the Mg I λ 4571 intercombination line are presented, observed near the limb of the Sun. They are obtained from eclipse spectrograms with good spectroscopic resolution and an accurate height calibration. The reduction of the observations is described and detailed profiles are given for a range of viewing angles (1/cos θ = 4 - 22). Title: Report of the Dutch expedition to the 1970 March 7 solar eclipse. Authors: Houtgast, J.; Namba, C.; Rutten, R. J. Bibcode: 1976PKNAW..79..221H Altcode: No abstract at ADS Title: Report of the Dutch expedition to the 1970 March 7 solar eclipse. Ch. 1. Authors: Houtgast, J.; Namba, O.; Rutten, R. J. Bibcode: 1976seob.conf....3H Altcode: No abstract at ADS Title: Solar Eclipse Observations and Ba II line formation Authors: Rutten, Robert Jelle Rob Bibcode: 1976PhDT.......177R Altcode: No abstract at ADS Title: Report of the Dutch expedition to the 1970 March 7 solar eclipse. Authors: Houtgast, J.; Namba, O.; Rutten, R. J. Bibcode: 1976PRNAA..79..221H Altcode: 1976RNAAS..79..221H No abstract at ADS