Author name code: engvold ADS astronomy entries on 2022-09-14 author:"Engvold, Oddbjorn" ------------------------------------------------------------------------ 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: Synergies among the IAU Offices Authors: Govender, Kevin; Cheung, Sze-Leung; Aretxaga, Itziar; Engvold, Oddbjørn Bibcode: 2020IAUGA..30..563G Altcode: No abstract at ADS Title: IAU's Interaction with Young Astronomers Authors: Engvold, Oddbjorn Bibcode: 2019IAUS..349...75E Altcode: The IAU promotes astronomy as a tool to strengthen science education of young people in developing regions through its International Schools for Young Astronomers (ISYA) and a Teaching for Astronomy Development (TAD) programme. This article describes briefly the strategy, organization and development of these programmes. The contents of the courses, tutorials and aims for longer-term effects of these programmes are described with focus on the ISYAs. Title: Preface Authors: Engvold, Oddbjørn; Vial, Jean-Claude; Skumanich, Andrew Bibcode: 2019sgsp.bookD..17E Altcode: No abstract at ADS Title: Chapter 12.2 - High-Resolution Ground-Based Observations of the Sun Authors: Engvold, Oddbjørn; Zirker, Jack B. Bibcode: 2019sgsp.book..419E Altcode: To investigate the small-scale interactions between magnetic and velocity fields that underlie many solar phenomena, solar physicists need higher spatial and temporal resolution. As a result, they are gradually introducing telescopes with meter-class mirrors and instruments with more sensitivity. Adaptive optics systems have been developed to minimize, in real time, the image distortions caused by the Earth's atmosphere. Post facto image correcting techniques facilitate further reduction of the distortions. Combinations of instruments now observe simultaneously and record the many aspects of a dynamic solar feature. The infrared spectrum, out to 2 μm and beyond to submillimeters, is used to a greater extent. The first of a new generation of 4-m telescopes is being built and 8-m telescopes are being designed. The future beckons for ground-based solar research. In this chapter, we survey these developments. Title: Chapter 1 - Discoveries and Concepts: The Sun's Role in Astrophysics Authors: Zirker, Jack B.; Engvold, Oddbjørn Bibcode: 2019sgsp.book....1Z Altcode: The Sun has had an important role in the development of stellar astrophysics. The discoveries of solar magnetism, solar wind, and global acoustic vibrations, to name only a few, have launched completely new topics for research in stellar physics. In addition, concepts such as magnetic reconnection and neutrino mass first arose in attempts to explain puzzling solar phenomena.

This volume is intended to remind astronomers, physicists, and students of the Sun's key role, which is based in part on its proximity and its commonality with other stars. After a short survey of the subject, successive chapters will describe the status and future progress in several topics in solar physics that are relevant to stellar physics. We begin with the simplest characteristic of the Sun, its luminosity. Title: The Sun as a Guide to Stellar Physics Authors: Engvold, Oddbjørn; Vial, Jean-Claude; Skumanich, Andrew Bibcode: 2019sgsp.book.....E Altcode: No abstract at ADS Title: The Parallel Worlds of Christoph Scheiner and Galileo Galilei Authors: Engvold, Oddbjørn; Zirker, Jack B. Bibcode: 2016JHA....47..332E Altcode: No abstract at ADS Title: Distinguishing between coronal cloud prominences and channel prominences and their associations with solar and stellar flares Authors: Martin, Sara F.; Engvold, Oddbjorn; Lin, Yong; da Silva, Jacqueline Alves Bibcode: 2016IAUS..320..278M Altcode: To better understand the differences between coronal cloud prominences and channel prominences, we systematically identified and analyzed coronal cloud prominences recorded in SDO/AIA images at 304 Å from 2010 May 20 through 2012 April 28. For the 225 cases identified, their numbers vary directly with the sunspot number. Their durations are typically less than 3 days. Their most frequent maximum height is 90,000 + and - 10,000 km. We offer our hypothesis that many coronal cloud prominences originate from some of the mass of previously erupted filaments ejected high out of their filament channels; subsequently part of this mass falls and collects in leaky magnetic troughs among coronal magnetic fields which constrain the leaked mass to slowly drain downward along curved trajectories where it appears as coronal rain. Currently there is inadequate evidence for a convincing correspondence between either coronal cloud prominences or channel prominences with stellar prominences detected to date. Title: Observing Cascades of Solar Bullets at High Resolution. II. Authors: Scullion, E.; Engvold, O.; Lin, Y.; Rouppe van der Voort, L. Bibcode: 2015ApJ...814..123S Altcode: High resolution observations from the Swedish 1-m Solar Telescope revealed bright, discrete, blob-like structures (which we refer to as solar bullets) in the Hα 656.28 nm line core that appear to propagate laterally across the solar atmosphere as clusters in active regions (ARs). These small-scale structures appear to be field aligned and many bullets become triggered simultaneously and traverse collectively as a cluster. Here, we conduct a follow-up study on these rapidly evolving structures with coincident observations from the Solar Dynamics Observatory/Atmospheric Imaging Assembly. With the co-aligned data sets, we reveal (a) an evolving multithermal structure in the bullet cluster ranging from chromospheric to at least transition region temperatures, (b) evidence for cascade-like behavior and corresponding bidirectional motions in bullets within the cluster, which indicate that there is a common source of the initial instability leading to bullet formation, and (c) a direct relationship between co-incident bullet velocities observed in Hα and He ii 30.4 nm and an inverse relationship with respect to bullet intensity in these channels. We find evidence supporting that bullets are typically composed of a cooler, higher density core detectable in Hα with a less dense, hotter, and fainter co-moving outer sheath. Bullets unequivocally demonstrate the finely structured nature of the AR corona. We have no clear evidence for bullets being associated with locally heated (or cooled), fast flowing plasma. Fast MHD pulses (such as solitons) could best describe the dynamic properties of bullets whereas the presence of a multithermal structure is new. Title: Distinguishing Between Different Types of Prominences Associated with Solar Flares Authors: Martin, Sara F.; Engvold, Oddbjorn; Lin, Yong Bibcode: 2015IAUGA..2255962M Altcode: In the early days of solar astronomy, any feature that extended above the solar limb was called a prominence. However, many such coronal features have been sufficiently studied to justify more specific names such as flare loops, surges, and flaring arches. Each of these named phenomena has different properties and involves different physical processes from other solar prominences. If we exclude these well-identified phenomena, we find that the majority of the remaining prominences can be grouped into only two categories that are distinctly different from each other. The main two types are (1) channel prominences or channel filaments when seen against the solar disk and (2) coronal cloud prominences, including narrow, down-flows named coronal rain. We illustrate the many significant differences between channel prominences and coronal cloud prominences. One of the fundamental differences is that channel prominences often have patterns of mass motions useful in anticipating many flares while coronal cloud prominences tend to occur hours after major solar flares. We also raise the question of whether the much taller coronal cloud prominences could have a counterpart in prominences on solar-like stars with magnetic fields of greater magnitude than the Sun. Title: Description and Classification of Prominences Authors: Engvold, Oddbjørn Bibcode: 2015ASSL..415...31E Altcode: Solar prominences are bright cloud-like structures when observed beyond the solar limb and they appear as dark filamentary objects which are termed filaments when seen against the solar disk. The aims of prominence classifications were from the start to establish references and frameworks for understanding the physical conditions for their formation and development through interplay with the solar magnetic environment. The multi-thermal nature of solar prominences became fully apparent once observations from space in UV, VUV, EUV and X-rays could be made. The cool prominence plasma is thermally shielded from the much hotter corona and supported in the field of gravity by small- and large-scale magnetic fields of the filament channels. High cadence, subarcsecond observing facilities on ground and in space have firmly proven the highly dynamic nature of solar prominences down to the smallest observed structural sizes of 100 km. The origin of the ubiquitous oscillations and flowing of the plasma over a variety of spatial and temporal scales, whether the cool dense plasma originates from below via levitation, injections by reconnection or results from condensation processes, are central issues in prominence research today. The unveiling of instabilities leading to prominences eruptions and Coronal Mass Ejections is another important challenge. The objective of this chapter is to review the main characteristics of various types of prominences and their associated magnetic environments, which will all be addressed in details in the following chapters of this book. Title: Solar Prominences Authors: Vial, Jean-Claude; Engvold, Oddbjørn Bibcode: 2015ASSL..415.....V Altcode: No abstract at ADS Title: The Build-Up to Eruptive Solar Events Viewed as the Development of Chiral Systems Authors: Martin, S. F.; Panasenco, O.; Berger, M. A.; Engvold, O.; Lin, Y.; Pevtsov, A. A.; Srivastava, N. Bibcode: 2012ASPC..463..157M Altcode: 2012arXiv1212.3646M When we examine the chirality or observed handedness of the chromospheric and coronal structures involved in the long-term build-up to eruptive events, we find that they evolve in very specific ways to form two and only two sets of large-scale chiral systems. Each system contains spatially separated components with both signs of chirality, the upper portion having negative (positive) chirality and the lower part possessing positive (negative) chirality. The components within a system are a filament channel (represented partially by sets of chromospheric fibrils), a filament (if present), a filament cavity, sometimes a sigmoid, and always an overlying arcade of coronal loops. When we view these components as parts of large-scale chiral systems, we more clearly see that it is not the individual components of chiral systems that erupt but rather it is the approximate upper parts of an entire evolving chiral system that erupts. We illustrate the typical pattern of build-up to eruptive solar events first without and then including the chirality in each stage of the build-up. We argue that a complete chiral system has one sign of handedness above the filament spine and the opposite handedness in the barbs and filament channel below the filament spine. If the spine has handedness, the observations favor its having the handedness of the filament cavity and coronal loops above. As the separate components of a chiral system form, we show that the system appears to maintain a balance of right-handed and left-handed features, thus preserving an initial near-zero net helicity. We further argue that the chiral systems allow us to identify key sites of energy transformation and stored energy later dissipated in the form of concurrent CMEs, erupting filaments and solar flares. Each individual chiral system may produce many successive eruptive events above a single filament channel. Because major eruptive events apparently do not occur independent of, or outside of, these unique chiral systems, we hypothesize that the development of chiral systems: (1) are fundamental to the occurrence of eruptive solar events and (2) preserve an approximate balance between positive and negative helicity (right and left-handed chirality) while preparing to release energy in the form of CMEs, erupting filaments, and flares. Title: Astronomy and Astrophysics, Volume II Authors: Engvold, Oddbjørn; Stabell, Rolf; Czerny, Bozena; Lattanzio, John Bibcode: 2012aaa2.book.....E Altcode: No abstract at ADS Title: Astronomy and Astrophysics, Volume I Authors: Engvold, Oddbjørn; Stabell, Rolf; Czerny, Bozena; Lattanzio, John Bibcode: 2012aaa1.book.....E Altcode: No abstract at ADS Title: Prominence seismology using ground- and space-based observations Authors: Ballester, J. L.; Arregui, I.; Oliver, R.; Terradas, J.; Soler, R.; Lin, Y.; Engvold, O.; Langagen, O.; Rouppe van der Voort, L. H. M. Bibcode: 2012EAS....55..169B Altcode: Ground- and space-based observations have confirmed the presence of oscillatory motions in prominences and they have been interpreted in terms of magnetohydrodynamic (MHD) waves. This interpretation opens the door to perform prominence seismology, whose main aim is to determine physical parameters in magnetic and plasma structures (prominences) that are difficult to measure by direct means. Here, two prominence seismology applications are presented. Title: Small-scale, Dynamic Bright Blobs in Solar Filaments and Active Regions Authors: Lin, Y.; Engvold, O.; Rouppe van der Voort, L. H. M. Bibcode: 2012ApJ...747..129L Altcode: 2012arXiv1201.0406L High-cadence high spatial resolution observations in Hα with the Swedish 1 m Solar Telescope on La Palma have revealed the existence of small-scale highly dynamic bright blobs. A fast wavelength tuning spectropolarimeter provides spectral information of these structures. The blobs slide along thin magnetic threads at speeds in the range from 45 km s-1 to 111 km s-1. The blobs have a slightly elongated shape and their lengths increase by a factor of three from close to half an arcsecond when they first appear until they disappear one to two minutes later. The brightest blobs show the highest speed. The widths of the Hα line emission of the blobs correspond to non-thermal velocities in the plasma less than 10 km s-1, which implies that they are not the result of shock-driven heating. The dynamic character of the bright blobs is similar to what can be expected from an MHD fast-mode pulse. Title: Relating a Prominence Observed from the Solar Optical Telescope on the Hinode Satellite to Known 3-D Structures of Filaments Authors: Martin, S. F.; Panasenco, O.; Agah, Y.; Engvold, O.; Lin, Y. Bibcode: 2009ASPC..415..183M Altcode: We address only a first step in relating limb and disk observations by illustrating and comparing the spines and barbs of three different quiescent prominences and filaments observed in Hα by three different telescopes. Although the appearance of the three quiescent prominences is quite different, we show that each consists of a spine, barbs extending from the spine, and arcs at the base of some of the curtains of barb threads. Title: Swaying Threads of a Solar Filament Authors: Lin, Y.; Soler, R.; Engvold, O.; Ballester, J. L.; Langangen, Ø.; Oliver, R.; Rouppe van der Voort, L. H. M. Bibcode: 2009ApJ...704..870L Altcode: 2009arXiv0909.2792L From recent high-resolution observations obtained with the Swedish 1 m Solar Telescope in La Palma, we detect swaying motions of individual filament threads in the plane of the sky. The oscillatory characters of these motions are comparable with oscillatory Doppler signals obtained from corresponding filament threads. Simultaneous recordings of motions in the line of sight and in the plane of the sky give information about the orientation of the oscillatory plane. These oscillations are interpreted in the context of the magnetohydrodynamic (MHD) theory. Kink MHD waves supported by the thread body are proposed as an explanation of the observed thread oscillations. On the basis of this interpretation and by means of seismological arguments, we give an estimation of the thread Alfvén speed and magnetic field strength by means of seismological arguments. Title: Inter-Division IX-X-XI Working Group Astronomy from The Moon Authors: Baliunas, Sallie L.; Kondo, Yoji; Kaifu, Norio; Engvold, Oddbjørn; Kaifu, Norio; Okuda, Haruyuki; Terzian, Yervant Bibcode: 2009IAUTA..27..356B Altcode: During the period the Working Group had proposed and was granted renewed status by Division XI Space and High-Energy Astrophysics. Additionally the Working Group requested to be extended to Division IX Optical and Infrared Techniques, Division X Radio Astronomy, as well as Division XI. Title: On small active region filaments, fibrils and surges Authors: Lin, Y.; Martin, S. F.; Engvold, O.; Rouppe van der Voort, L. H. M.; van Noort, M. Bibcode: 2008AdSpR..42..803L Altcode: High resolution Hα images and magnetograms (0.2 arc s) of an active region were obtained in alternating time series at 42 s cadences using the Swedish 1-m Solar Telescope on 2004 August 21. The Hα filtergrams reveal an active region filament and surges consisting of thread-like structures which have widths similar to the widths of chromospheric fibrils, both recorded down to the resolution limit in the best images. All observed structures in the active region appear highly dynamic. Fibrils show counterstreaming strongly resembling the counterstreaming threads in filaments. Streaming, along the threads of surges extending more than 10 arc s, is higher in speed (∼20 km s-1) than in the filament and fibrils and appears to flow independently over and above the chromospheric fibrils. Blue shifts seen in the Hα Dopplergrams confirm the outward mass motion of the surges. However, in at least one case, we also see simultaneous downflows from the same site but in the opposite direction and downward toward the chromosphere. We suggest that the site between these two outward and downward flows identifies the place where magnetic reconnection could occur and thereby cause of the surge. This appears to imply that the reconnection site is in the high chromosphere or low corona. Title: A Method of Resolving the 180-Degree Ambiguity by Employing the Chirality of Solar Features Authors: Martin, S. F.; Lin, Y.; Engvold, O. Bibcode: 2008SoPh..250...31M Altcode: 2008SoPh..tmp..105M The 180-degree ambiguity in magnetic field direction along polarity reversal boundaries can be resolved often and reliably by the chiral method. The chiral method requires (1) identification of the chirality of at least one solar feature related to a polarity reversal boundary along which the field direction is sought and (2) knowledge of the polarity of the network magnetic field on at least one side of the polarity reversal boundary. In the context of the Sun, chirality is an observable signature of the handedness of the magnetic field of a solar feature. We concentrate on how to determine magnetic field direction from chirality definitions and illustrate the technique in eight examples. The examples cover the spectrum of polarity boundaries associated with filament channels and filaments ranging from those connected with active regions to those on the quiet Sun. The applicability of the chiral method to all categories of filaments supports the view that active region filaments and quiescent filaments are the extreme ends in a continuous spectrum of filaments. Title: The Unique 3D Magnetic Structure of Filaments Authors: Lin, Y.; Engvold, O.; Martin, S.; Panasenco, O. Bibcode: 2008AGUSMSH23A..05L Altcode: Filaments in active regions most clearly have the form of long thin ribbons as seen in Hα. The ribbon structure is also readily demonstrated for quiescent filaments when seen from an end view as a filament is transported across the east or west limb due to solar rotation. In addition to the primary ribbon structure, filaments also have shorter, secondary structures called barbs which connect some threads of the main ribbon structure to the chromosphere; these are also seen in the end view of filaments at the limb. This connection with the chromosphere is corroborated in high resolution images of filaments recorded against the disk at the 1-meter Swedish Solar Telescope (SST). In these high resolution Hα movies, the lower parts of all threads are recognizable because they move less freely than the higher parts. The connection of the ends of the threads of the main filament ribbon and the ends of the filament barbs to the chromosphere/photosphere is strong evidence alone that filaments have their own magnetic fields separate from surrounding coronal magnetic fields. The chirality (handedness) of filaments provides further evidence that filaments have their own magnetic fields. The two forms of dextral and sinistral chirality are generally manifest in the relative direction of the deviation of barbs from the main ribbon. However, the sign of chirality is most clear in the thread structure of all barbs seen in Hα images from the SST. From a number of characteristics of the observed mass motions of filament threads of the order of several to tens of kilometers per second, we have previously concluded that filament threads are field-aligned. Therefore we use the threads and their mass motions to construct the 3D configuration of filament magnetic fields. We end this presentation with movies of filaments from STEREO/SECCHI/EUVI consistent with our thread model of filaments. Title: Observational aspects of prominence oscillations Authors: Engvold, Oddbjørn Bibcode: 2008IAUS..247..152E Altcode: 2007IAUS..247..152E Seismology has become a powerful tool in studies of the magnetic structure of solar prominences and filaments. Reversely, analytical and numerical models are guided by available information about the spatial and thermodynamical structure of these enigmatic structures. The present invited paper reviews recent observational results on oscillations and waves as well as details about small-scale structures and dynamics of prominences and filaments. Title: Filament Substructures and their Interrelation Authors: Lin, Y.; Martin, S. F.; Engvold, O. Bibcode: 2008ASPC..383..235L Altcode: The main structural components of solar filaments, their spines, barbs, and legs at the extreme ends of the spine, are illustrated from recent high-resolution observations. The thread-like structures appear to be present in filaments everywhere and at all times. They are the fundamental elements of solar filaments. The interrelation of the spines, barbs and legs are discussed. From observations, we present a conceptual model of the magnetic field of a filament. We suggest that only a single physical model is needed to explain filaments in a continuous spectrum represented by active region filaments at one end and quiescent filaments at the other end. Title: Chromospheric and coronal manifestations of photospheric cancelling magnetic fields Authors: Panasenco, Olga; Martin, Sara F.; Engvold, Oddbjorn Bibcode: 2008cosp...37.2336P Altcode: 2008cosp.meet.2336P We discuss observable changes in solar features interpreted as evidences of the transfer of magnetic fields from the photosphere to the chromosphere and corona. In the photospheric level, new or decayed active region magnetic fields of opposite polarity encounter each other and cancel along a pre-existing polarity reversal boundary. Concurrently, in the chromospheric level of the solar atmosphere, the cancelling fields appear to lead to the creation and maintenance of a filament channel. The channel is identified by systematic changes in the orientation of fibrils in the chromosphere. We deduce that invisible extensions of the magnetic fields of the chromospheric fibrils into the corona could represent the beginning of the formation of a filament cavity in the low corona, before and/or during the initial appearance of a filament threads. When the filament channel is fully developed, such that there is a local magnetic field aligned with the polarity reversal boundary, the cancelling fields are then associated with the transfer of plasma, as well as magnetic field, into the low corona. We suggest this plasma is observed as new filament threads. Title: Chromospheric observations of erupting filaments with the Optical Solar Patrol Network (OSPaN) telescope Authors: Cliver, Edward; Balasubramaniam, K. S.; Cliver, E. W.; Engvold, O.; Pevtsov, A.; Martin, S.; Panasenco, O. Bibcode: 2008cosp...37..562C Altcode: 2008cosp.meet..562C Using AFRL/NSO OSPaN telescope chromospheric images, we present movies and analyses of the eruption of a quiescent filament (11 June 2003) and an active region filament (13 May 2005). In both cases, widely separated regions of the solar surface were affected by the eruptions, either via the Moreton waves they generated (inferred from winking filaments) or through direct magnetic connection (manifested by sequential chromospheric brightenings). We investigate the topology of the magnetic fields in which these eruptions occur and use Doppler measurements to understand the dynamics of the eruptions. Title: Executive Committee Working Group Young Astronomers Events Authors: Gerbaldi, Michèle; De Greve, Jean-Pierre; Dovčiak, Michal; Engvold, Oddbjørn; Guinan, Edward F.; Hearnshaw, John B.; Johnston-Hollitt, Melanie; Pasachoff, Jay M.; Percy, John R.; Ribas, Ignasi; White, James C.; Dovčiak, Michal; Goosmann, René; Pecháček, Tomáš; Stoklasová, Ivana Bibcode: 2007IAUTB..26..242G Altcode: At the IAU XXV General Assembly in Sydney, 2003, a questionnaire on the perception of participation of “young astronomers” at IAU meeting was distributed. Following the conclusions from the analysis of this questionnaire, the IAU EC recommended in 2004 that the “young astronomers” concept at the next GA in Prague should be worked out with specific activities. Title: Division XI / Wg: Astronomy from the Moon Authors: Baliunas, Sallie L.; Kondo, Yoji; Kaifu, Norio; Engvold, Oddbjorn; Kaifu, Norio; Okuda, Haruyuki; Terzian, Yervant; Wamsteker, Willem Bibcode: 2007IAUTB..26..208B Altcode: The Business Meeting opened with a recall of the memory of a member of the Organizing Committee, Willem Wamsteker. N. Kaifu, past president of the Working Group, was thanked for his outstanding service. Title: Evidence of Traveling Waves in Filament Threads Authors: Lin, Y.; Engvold, O.; Rouppe van der Voort, L. H. M.; van Noort, M. Bibcode: 2007SoPh..246...65L Altcode: High-resolution Hα filtergrams (0.2″) obtained with the Swedish 1-m Solar Telescope resolve numerous very thin, thread-like structures in solar filaments. The threads are believed to represent thin magnetic flux tubes that must be longer than the observable threads. We report on evidence for small-amplitude (1 - 2 km s−1) waves propagating along a number of threads with an average phase velocity of 12 km s−1 and a wavelength of 4″. The oscillatory period of individual threads vary from 3 to 9 minutes. Temporal variation of the Doppler velocities averaged over a small area containing a number of individual threads shows a short-period (3.6 minutes) wave pattern. These short-period oscillations could possibly represent fast modes in accordance with numerical fibril models proposed by Díaz et al. (Astron. Astrophys.379, 1083, 2001). In some cases, it is clear that the propagating waves are moving in the same direction as the mass flows. Title: Reports on Astronomy 2003-2005 (IAU XXVIA) Authors: Engvold, Oddbjorn Bibcode: 2007reas.book.....E Altcode: No abstract at ADS Title: Comparisons of the Spines of Prominences (Filaments) in Hα and He II (304Å) Images Authors: Martin, Sara F.; Engvold, O.; Lin, Y. Bibcode: 2007AAS...21012006M Altcode: 2007BAAS...39..245M Prominence (filament) spines are being analyzed in Hα images from ground-based observatories and in He II 304 Αngstrom (Å) images from the EIT experiment on board the SoHO satellite. Our comparisons show the spines of quiescent prominences are often longer and slightly taller in He II 304Å images than seen in Hα images. Spines are also sharper and more clearly defined in He II 304Å than in Hα images. The prominences (filaments) in some cases appear earlier and can also last longer in 304Å than in Hα. Examples are shown on the disk and above the limb where the spines of separate filaments (prominences) merge in 304Å images before they appear to merge in Hα. In one case, the spine of a quiescent filament disappears in Hα but remains visible in He II images. These observations are consistent with our measurements of a typical quiescent prominence that shows the Hα brightness decreases with height in the prominence, whereas the brightness at He II 304Å slightly increases with height. Thus we find that the spines of quiescent prominences are always more readily visible in 304Å than in Hα. The relative variation of prominence brightness with height reflects a difference in conditions for excitation of these two lines. This is consistent with a presumed increase of temperature with height, in combination with a slight decrease of electron density with height and with the theory that the He II 304Å line is controlled by EUV radiation from the surrounding corona, whereas Hα is influenced by radiation from the chromosphere below. SFM acknowledges support from NSF grant ATM-0519249 and Y.L. from Norwegian Research Council grant FRINAT171012. Title: Reports on Astronomy 2003-2005 (IAU XXVIA) Authors: Engvold, Oddbjorn Bibcode: 2007IAUTA..26.....E Altcode: No abstract at ADS Title: The IAU Role Authors: Engvold, Oddbjørn Bibcode: 2007IAUS..236..467E Altcode: No abstract at ADS Title: A Simple Method of Resolving the 180 Degree Ambiguity Employing the Chirality of Solar Features Authors: Martin, Sara F.; Lin, Y.; Engvold, O. Bibcode: 2006SPD....37.0129M Altcode: 2006BAAS...38..220M The 180 degree ambiguity in magnetic field direction along polarity reversal boundaries can be resolved simply and reliably by a technique that we name "chiral method". For a given polarity boundary, the chiral method requires identifying the chirality of at least one solar feature related to the polarity boundary, familiarity with the one-to-one associations between the chirality of solar features, and the polarity of the network magnetic field on at least one side of the polarity boundary. We demonstrate the technique in 6 examples. The examples cover the spectrum of polarity boundaries associated with filament channels and filaments ranging from those associated with active regions to those on the quiet Sun.The applicability of the chiral method to all categories of filaments supports the view that active region filaments and quiescent filaments are the extreme ends in a continuous spectrum of filaments. An example is shown of a filament where the chirality could not be determined in low resolution images because of lack of consistency in barb orientation; however, at high resolution, all threads of this barb were found to be consistent with just one sense of chirality. The chiral method is almost universally applicable because many types of data, that reveal chirality in solar features, are now readily available over the world-wide web. Solar features that most commonly reveal chirality are filaments, filament channels, sigmoids, and both quiescent and dynamic coronal loop systems. Assuming that the chirality of the solar features is identified correctly, the method is fail-safe and physically meaningful because chirality is an observational representation of the helicity and there are clear differences between left-handed and right-handed solar structures.Support from US NSF grant ATM-0209395 and NASA grant NAG5-10852 are acknowledged for S.F.M. and Y.L. Title: "Coronal Cloud" Prominences And Their Association With Coronal Mass Ejections Authors: Lin, Yong; Martin, S. F.; Engvold, O. Bibcode: 2006SPD....37.0121L Altcode: 2006BAAS...38Q.219L "Coronal cloud" prominences appear to form as bright knots of mass condensing out of the corona while some of their mass also continuously drains down along curved streamers to the chromosphere. Movies of such "suspended cloud" prominences were recorded in Hα by Dunn as early as the 1950s (1976, Solar Physics 49, 283). They have been also observed in HeI 10830 Å and EIT 304 Å .Four Hα "coronal clouds" were recorded at Helio Research (2004/09/16-17, 2004/11/16-17 and 2005/12/12). Their apparent heights are estimated in the range between 66,000-240,000 km, much higher than the more common prominences and filaments with spines and barbs. Near the surface, the downflows accelerate at a typical speed of 40 km s-1. By comparing the positions of the coronal clouds with magnetograms several days prior to or after the coronal clouds were observed at the limb, we are able to show that the condensations of mass are located above or adjacent to complex active regions. The condensations of the fainter coronal clouds have a V-shaped appearance which suggests to us that these concentrations of mass might be trapped at junctions of separatrix magnetic surfaces.For each of our 4 cases, LASCO movies show a CME 1-2 days prior to the "coronal clouds" and encompassing or overlapping the range of latitudes. In one case, the LASCO movie also shows a downflow after the CME which is radially above the coronal cloud. We suggest that downflows associated with CMEs provide the mass for "coronal clouds" formation even though the downflows are not clearly observed in three of the 4 cases; the downflows could be blocked from our sight by the LASCO occulting disk and/or obscured by the more prevalent outflows of mass.Support from US NSF grant ATM-0209395 and NASA grant NAG5-10852 are acknowledged. Title: Editorial Appreciation Authors: Engvold, Oddbjørn; Harvey, Jack; Leibacher, John; Sakurai, Takashi; Švestka, Zdeněk; van Driel-Gesztelyi, Lidia; Solar Physics editors Bibcode: 2006SoPh..233....1E Altcode: No abstract at ADS Title: Dynamics of an active region filament, fibrils and surges in high resolution Authors: Lin, Y.; Martin, S. F.; Engvold, O.; Rouppe van der Voort, L. H. M.; van Noort, M. Bibcode: 2006cosp...36.3193L Altcode: 2006cosp.meet.3193L High resolution H alpha and magnetograms 0 2 arc sec of an active region were obtained in alternating time series at 42 sec cadences using the Swedish 1-m Solar Telescope on 2004 August 21 The 79 times 52 arcsec field of view was centered at N11 W5 The H alpha filtergrams reveal an active region filament and surges consisting of thread-like structures which have widths similar to the widths of chromospheric fibrils both recorded down to the resolution limit in the best images All observed structures in the active region are highly dynamic The flow speeds in some active filament threads 25 km s -1 are higher than typical speeds in quiescent filament threads Fibrils show counterstreaming strongly resembling the counterstreaming threads in filaments The transverse speeds of mass within fibrils are comparable to the typical speeds of mass flows in quiescent filament threads sim 10 km s -1 Streaming along the threads of surges extending more than 10 arc sec is higher in speed sim 20 km s -1 than in the filament and fibrils and appears to flow over the chromospheric fibrils Small surges near one end of the filament appear to flow into the filament thereby mass seems to be added to the filament Blue shifts seen in the H alpha Dopplergrams confirm the outward mass motion of the surges However in at least one case we also see simultaneous red shifts from the same site in the opposite direction toward the chromosphere We suggest that the site between these two opposite motions identifies the place where magnetic Title: Evidence for the Formation of Faint, High Prominences in the Aftermath of two Faint CMEs Authors: Martin, S. F.; Engvold, O. Bibcode: 2005AAS...20720401M Altcode: 2005BAAS...37.1502M On 16 and 17 September 2004, changes in two unusually high prominences were recorded for intervals of several hours in the Hα line at Helio Research using a 10-inch aperture telescope equipped with a narrow band (1/10 fwhm) filter. The high prominences, each reaching an altitude 200,000 km, appeared above a long low-lying prominence that was well-observed crossing the limb and had a maximum altitude of 60,000 km. The lower prominence had a horizontal axis and barbs while the high prominence in Hα consisted of many strands of nearly vertical structure but with only a few threads with mass streaming downward close to the chromosphere. Because there were no apparent geometric properties or mass flows in common between the high prominences and the low one, it is deduced that the high prominences were associated with photospheric polarity reversal boundaries and filament channels that were at least 20-33 degrees beyond the west limb and associated with a large decaying active region. Additionally, LASCO movies revealed two faint CMEs on 14 Sep (19:12 UT) and 15 Sep (21:24 UT) evidently from the backside of the Sun and near the same position angles as the high prominences. These events were also most likely related to the polarity reversal boundaries within or on the border of the large active region beyond the west limb. We suggest that each of the high prominences developed in the 1-2 day aftermath of each of the successive CMEs. We further suggest that the prominences are related to the formation of current sheets anticipated by (Lin and Forbes 2000) or magnetic interfaces (Lin and van Ballegooijen 2001) that, in either case, are continuing to evolve one to two days after the eruptive events. Support from NSF grant ATM-0209395 is acknowledged. Title: Preface Authors: Rottman, G.; Woods, T.; George, V.; Harvey, J.; Švestka, Z.; Engvold, O. Bibcode: 2005SoPh..230....1R Altcode: No abstract at ADS Title: Editorial Authors: Engvold, Oddbjorn; Harvey, Jack; Švestka, Zdenek Bibcode: 2005SoPh..229....1E Altcode: No abstract at ADS Title: Solar Filaments and Photospheric Network Authors: Lin, Yong; Wiik, Jun Elin; Engvold, Oddbjørn; Van Der Voort, Luc Rouppe; Frank, Zoe A. Bibcode: 2005SoPh..227..283L Altcode: The locations of barbs of quiescent solar filaments are compared with the photospheric/chromospheric network, which thereby serves as a proxy of regions with enhanced concentrations of magnetic flux. The study covers quiet regions, where also the photospheric network as represented by flow converging regions, i.e., supergranular cell boundaries, contain largely weak magnetic fields. It is shown that close to 65% of the observed end points of barbs falls within the network boundaries. The remaining fraction points into the inner areas of the network cells. This confirms earlier findings (Lin et al., Solar Physics, 2004) that quiescent filaments are basically connected with weaker magnetic fields in the photosphere below. Title: Thin Threads of Solar Filaments Authors: Lin, Yong; Engvold, OddbjØrn; der Voort, Luc Rouppe van; Wiik, Jun Elin; Berger, Thomas E. Bibcode: 2005SoPh..226..239L Altcode: High-resolution images obtained in Hα with the new Swedish Solar Telescope at La Palma, Spain, have been used for studies of fine-scale threads in solar filaments. The widths of the thin threads are ≤0.3 arcsec. The fact that the width of the thinnest threads is comparable to the diffraction limit of the telescope of about 0.14 arcsec, at the wavelength of Hα, suggests that even thinner threads may exist. Assuming that the threads represent thin magnetic strings, we conclude that only a small fraction of these are filled with observable absorbing plasma, at a given time. The absorbing plasma is continuously flowing along the thread structures at velocities 15± 10 kms−1, which suggests that the flows must be field-aligned. In one case where a bundle of thin threads appears to be rooted in the nearby photosphere, we find that the individual threads connects with intergranular, dark lanes in the photosphere. We do not find signs of typical network fields at the `roots' of the fine threads, as normally evidenced by bright points in associated G-band images. It is suggested that filament threads are rooted in relatively weak magnetic fields. Title: Highlights of Astronomy. Volume 13, as presented at the XXVth General Assembly of the IAU - 2003 Authors: Engvold, Oddbjörn Bibcode: 2005HiA....13.....E Altcode: Contents: Preface. I. Joint discussions - 1. Non-electromagnetic windows for astrophysics. 2. Mercury. 3. Magnetic field & helicity in the Sun & heliosphere. 4. Astrophysical impact of abundances in globular clusters. 6. Extragalactic globular clusters & their host galaxies. 7. The Sun & the heliosphere as an integrated system. 8. Large telescopes and Virtual Observatory: visions for the future. 9. Astrotomography. 10. Evolution in galaxy clusters: a multi-wavelength approach. 11. Dynamics and evolution of dense stellar systems. 12. Solar and solar-like oscillations: insights & challenges for the Sun and stars. 13. Extragalactic binaries. 14. Formation of cometary material. 15. Elemental abundances in old stars & damped Lyman-alpha systems. 16. The International Celestial Reference System: Maintenance & future realization. 17. Atomic data for X-ray astronomy. 18. Quasar cores & jets. 19. Physical properties and morphology of small solar system bodies. 20. Frontiers of high resolution spectroscopy. 21. The astrochemistry of external galaxies. Special scientific sessions: 1. Recent progress in planetary exploration. 2. Astronomy in Antarctica. 3. A new classification scheme for double stars. 4. Effective teaching and learning of astronomy. Title: Preface: Highlights of Astronomy. Volume 13 Authors: Engvold, Oddbjörn Bibcode: 2005HiA....13D..29E Altcode: No abstract at ADS Title: Structures and Dynamics of Solar Filaments - challenges in observing and modeling Authors: Engvold, Oddbjørn Bibcode: 2004IAUS..223..187E Altcode: 2005IAUS..223..187E Fundamental information about the nature of solar filaments and governing physical processes are retained in their small-scale structure and dynamics. The paper reviews some recent high resolution studies of filaments, with emphasize on potential impact on current understanding of their physical nature. Title: Separation of high resolution spectra of the multiple star system UX Ari Authors: Aarum Ulvås, V.; Engvold, O. Bibcode: 2003A&A...402.1043A Altcode: This paper presents a technique for separation of individual components in composite stellar spectra. The technique is based on a comparison of residual depths of the component spectral lines to residual depths of the corresponding spectral lines of a single star of the same spectral class. We apply the technique to high resolution spectra of the RS CVn system UX Ari, where the spectral lines from all three components are well resolved. The deduced variations in the relative flux of the primary component agree well with simultaneously obtained photometric observations of UX Ari. The starspots causing the light curve variations and the facular areas causing the chromospheric emission seem to be separated by about 180o in longitude on the surface of the primary component. We also find that the secondary component of UX Ari is subject to some chromospheric activity. Finally, some fundamental parameters of the third star in the spectrum are derived and discussed.

Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Title: Why does the spotted UX Ari system get bluer as it gets darker? Authors: Aarum Ulvås, V.; Engvold, O. Bibcode: 2003A&A...399L..11A Altcode: We present simplified calculations of UX Ari B-V colour index and V magnitude for a range of parameter values. The results of our calculations are compared to previously published measurements. We find that our calculations reproduce the well established colour-brightness relation (UX Ari gets bluer as it gets darker) only if the dark spots on the surface of the K star are accompanied by bright facular areas. There is currently an ambiguity between the temperature of the facular areas and the portion of the stellar surface occupied by them. Title: Preface Authors: Lin, R.; Dennis, B.; Benz, A.; Harvey, J.; Engvold, O.; švestka, Z. Bibcode: 2002SoPh..210....1L Altcode: No abstract at ADS Title: Magnetic cancellation and small-scale activity in an AR filament Authors: Schmieder, B.; Engvold, O.; Yong, Lin; Deng, Y. Y.; Mein, N. Bibcode: 2002ESASP.505..223S Altcode: 2002solm.conf..223S; 2002IAUCo.188..223S A long set of observations obtained with the VTT/MSDP spectrograph in September 1998 (8 to 11) allows us to follow the formation of a complex filament in and around a nest of active regions during its disk passage. Continuous shear of magnetic field in this region can explain the formation and the relative stability of the filament structure before the occurrence of a flare which leads to important changes in the magnetic configuration. The corona overlying the region and the flare, as well, is observed by TRACE. The studied filament is stable on long term time scale. However, high spatial and temporal observations obtained in La Palma (SVST) show high Doppler shifts and strong transverse motions of absorbing blobs along the filament. These velocities are directly related to magnetic activity as observed with the SVST. A small scale magnetic analysis shows emergence of MMFs (Moving Magnetic Features) around a decaying sunspot and canceling flux with the neighbor network. Magnetic reconnection could occur and explain the ejection of blobs along the new magnetic field lines. Formation of the transient blobs is discussed. Title: Filament activation and magnetic reconnection Authors: Deng, Yuanyong; Lin, Yong; Schmieder, Brigitte; Engvold, OddbjØrn Bibcode: 2002SoPh..209..153D Altcode: A curved filament in a decaying active region (AR 8329) was observed on 9 September 1998 with a combination of several instruments. The main data base is a 4-hour long time series of 1 min cadence using the Lockheed tunable filter mounted in the Swedish Vacuum Solar Tower in La Palma (SVST). Filtergrams obtained at several wavelength positions in Hα images are used to derive Doppler images. Interleaved images in the magnetic sensitive Fe i 6302.5 Å line yield corresponding magnetograms. Supplementing observations are collected from TRACE and the French Multi-Channel Double Pass spectrograph (MSDP) mounted in the German VTT in Tenerife. The filament, which consists of several discrete fragments with nearly horizontal fine structures, undergoes activity and counter-streaming bulk flow, but without erupting. The magnetic field inversion line of this active region is complex and strongly influenced by intrusion of a positive polarity area in a following negative polarity of the region. The positive polarity area contains a small sunspot surrounded by moving magnetic features (MMFs). The MMFs interact directly with the parasitic polarities in the filament channel, and thereby gives rise to merging and canceling magnetic flux. When the interaction occurs at the location of the feet (`barbs') of the filament notable activations are observed (ejection of `blobs'). The ejections of `blobs' are preceded by twist of filament threads and the `blobs' move along downward bending field lines towards the photosphere close to the sound speed. Title: On the Nature of Prominence Absorption and Emission in Highly Ionized Iron and in Neutral Hydrogen Authors: Engvold, Oddbjørn; Jakobsson, Hans; Tandberg-Hanssen, Einar; Gurman, Joe B.; Moses, Daniel Bibcode: 2001SoPh..202..293E Altcode: We have studied the behavior of the emission in the highly ionized EUV lines Fe ix/x, 171 Å, Fe xii, 195 Å, and Fe xv, 284 Å observed in quiescent prominences. Kucera, Andretta, and Poland (1998) have explained the absorption of other highly ionized metallic EUV lines as due to absorption in the hydrogen continuum. However, since the authors noticed deviations from the expected λ3 dependence of the absorption strengths, we have explored the possibility that emission in EUV iron lines can influence the observations. We propose the existence of a hot, i.e., million-degree plasma component of the prominence-corona transition region (PCTR), where the EUV iron lines originate. We find that (i) neither of the two scenarios alone reproduces observations; (ii) both emission and absorption increase prior to eruption; (iii) the measurements of Kucera, Andretta, and Poland's 14 May event are strongly affected by hot PCTR emission. Title: Solar Prominence Fine Structure Authors: Engvold, O. Bibcode: 2000eaa..bookE2280E Altcode: A clear feature of high-resolution observations of quiescent PROMINENCES, both on the disk and at the limb, is the presence of fine-scale fibril structures. The fine structure of prominences provides vital clues to questions such as how prominences form and how they are supported. Magnetic fields permeate the prominence plasma and play a decisive role in shaping the fine structure and its dynamic... Title: Emergence of sheared magnetic flux tubes in an active region observed with the SVST and TRACE Authors: Deng, Y. Y.; Schmieder, B.; Engvold, O.; DeLuca, E.; Golub, L. Bibcode: 2000SoPh..195..347D Altcode: The active region NOAA AR 8331 was a target of an international ground-based observational campaign in the Canaries and coordinated with space instruments (TRACE and Yohkoh). We focus our study on observations obtained with the SVST at LaPalma, and with TRACE. On 10 September 1998, arch-filament systems were observed with high spatial and temporal resolution, from the lower to the upper atmosphere of the Sun, during five hours. Flux tubes emerged with increasing shear, which apparently led to energy release and heating in the overlying corona. A model for filament formation by the emergence of U-shaped loops from the subphotosphere, as proposed by Rust and Kumar (1994), is supported by the present observations. The coronal response to these events is visualized by rising, medium-scale loop brightenings. The low-lying X-ray loops show short-lived, bright knots which are thought to result from interaction between different loop systems. Title: Modeling of prominence threads in magnetic fields: Levitation by incompressible MHD waves Authors: Pécseli, Hans; Engvold, OddbjØrn Bibcode: 2000SoPh..194...73P Altcode: The nature of thin, highly inclined threads observed in quiescent prominences has puzzled solar physicists for a long time. When assuming that the threads represent truly inclined magnetic fields, the supporting mechanism of prominence plasma against gravity has remained an open issue. This paper examines the levitation of prominence plasma exerted by weakly damped MHD waves in nearly vertical magnetic flux tubes. It is shown that the wave damping, and resulting `radiation pressure', caused predominantly by ion-neutral collisions in the `cold' prominence plasma, may balance the acceleration of gravity provided the oscillation frequency is ω≈ 2 rad s−1 (f≈0.5 Hz). Such short wave periods may be the result of small-scale magnetic reconnections in the highly fragmentary magnetic field of quiescent prominences. In the proposed model, the wave induced levitation acts predominantly on plasma - neutral gas mixtures. Title: The Physics of the Solar Corona and Transition Region Authors: Engvold, Oddbjorn; Harvey, John Bibcode: 2000psct.conf.....E Altcode: The Sun's magnetic field is responsible for the spectacularly dynamic and intricate phenomenon that we call the corona. The past decade has seen an enormous increase in our understanding of this part of the solar outer atmosphere, both as a result of observations and because of rapid advances in numerical studies. The YOHKOH satellite has observed the Sun now for over six years, producing spectacular sequences of images that convey the complexity of the corona. The imaging and spectroscopic instruments on SOHO have added information on the cooler part of the corona. And since April of 1998 TRACE has given us very high resolution images of the 1-2 MK corona, at cadences that allow detailed observations of field oscillations, loop evolution, mass ejecta, etc. This volume contains papers contributed to a workshop (held in August 1999, in Monterey, California) that was dedicated to an exploration of the most recent results on the solar corona, as well as on the transition region and low solar wind. The diverse presentations at the meeting revolved around one key theme: the entire outer atmosphere of the Sun is intrinsically dynamic, evolving so rapidly that even the concept of a single local temperature for a single fluid often breaks down. Moreover, the corona is an intrinsically nonlinear and nonlocal medium. These aspects are discussed in these proceedings that include both papers that review recent developments (both based on observations and on theoretical/numerical modeling), and original research papers based on observations from many different observatories. The papers presented at the meeting add up to such a size that they are distributed over two Topical Issues of Solar Physics (December 1999 and April 2000), which are reprinted in two bound volumes. MAIL: http://www.wkap.nl/boordfrm.htm?0-7923-6357-4+1 Title: Commission 10: Solar Activity: (Activite Solaire) Authors: Ai, G.; Benz, A.; Dere, K. P.; Engvold, O.; Gopalswamy, N.; Hammer, R.; Hood, A.; Jackson, B. V.; Kim, I.; Marten, P. C.; Poletto, G.; Rozelot, J. P.; Sanchez, A. J.; Shibata, K.; van Driel-Geztelyi, L. Bibcode: 2000IAUTA..24...67A Altcode: No abstract at ADS Title: Division II: The Sun and Heliosphere: (Le Soleil et Heliosphere) Authors: Foukal, Peter; Ai, Guoxiang; Benz, Arnold; Engvold, Oddbjorn; Solanki, Sami; Vandas, Marek; Verheest, Frank Bibcode: 2000IAUTA..24...65F Altcode: No abstract at ADS Title: Bright Rims of Solar Prominences Authors: Hansen, I.; Engvold, O.; Schmieder, B.; Mein, N.; Mein, P. Bibcode: 1999ESASP.448..491H Altcode: 1999mfsp.conf..491H; 1999ESPM....9..491H No abstract at ADS Title: A Study of Hydrogen Density in Emerging Flux Loops from a Coordinated TRACE and Canary Islands Observation Campaign Authors: Schmieder, B.; Deluca, E.; Mein, N.; Mein, P.; Malherbe, J. M.; Wilken, V.; Staiger, J.; Engvold, O.; Hanssen, I. Bibcode: 1999ESASP.448..653S Altcode: 1999mfsp.conf..653S; 1999ESPM....9..653S No abstract at ADS Title: Fine-Structures and Dynamics of a Filament in EUV lines: SOHO/CDS and SUMER, TRACE Authors: Schmieder, B.; Engvold, O.; Wiik, J. E.; Deluca, E. Bibcode: 1999ESASP.446..599S Altcode: 1999soho....8..599S No abstract at ADS Title: The Wilson-Bappu effect of the MgII K line - dependence on stellar temperature, activity and metallicity Authors: Elgarøy, Øystein; Engvold, Oddbjørn; Lund, Niels Bibcode: 1999A&A...343..222E Altcode: The Wilson-Bappu effect is investigated using accurate absolute magnitudes of 65 stars obtained through early release of data from the Hipparcos satellite together with MgII k line widths determined from high resolution spectra observed with the International Ultraviolet Explorer (IUE) observatory. Stars of spectral classes F, G, K and M and luminosity classes I-V are represented in the sample. Wilson-Bappu relations for the Mg II k line for stars of different temperatures i.e. spectral classes are determined. The relation varies with spectral class and there is a significant scatter of the line widths around the regression lines. The sample contains slowly rotating stars of different activity levels and is suitable for investigations of a possible relation between line width and stellar activity. A difference in behavior between dwarfs and giants (and supergiants) of spectral class K seems to be present. Magnetic activity affects the width of the Mg II k line in dwarfs. Metallicity is found to influence the Mg II k line width in giants and supergiants. Possible interpretations of the new results are briefly discussed. Title: Investigation of the spot distribution and surface differential rotation on x Authors: Aarum, Vidar; Engvold, Oddbjorn; Berdyugina, Svetlana; Dummler, Rudolf Bibcode: 1999noao.prop...68A Altcode: The purpose of the programme is to determine the starspot distribution on the primary component of x using Doppler imaging. Special attention is given to the possible existence of a polar spot and a technique to separate the spectra of the individual components. Studying the system over several years provides information on the star's surface differential rotation. Title: Counter-streaming gas flows in solar prominences as evidence for vertical magnetic fields Authors: Zirker, J. B.; Engvold, O.; Martin, S. F. Bibcode: 1998Natur.396..440Z Altcode: Solar prominences are sheets of relatively cool and dense gas embedded in the surrounding hotter corona. An erupting prominence can inject a mass of up to 1015g into the solar wind as part of a coronal mass ejection. These eruptions must depend critically on the topology of the prominence's magnetic field. In all present models,, the prominence hangs on horizontal or helical field lines, while an overlying magnetic arcade temporarily restrains the prominence from erupting. Such models are inconsistent, however, with the slow upward vertical gas flows that are seen in prominences. Here we report counter-streaming flows along closely spaced vertical regions of a prominence, between its top and the lower solar atmosphere. As the flows must be aligned with the magnetic field, this observation implies that a field connects the prominence directly to the photosphere, contrary to all existing models. These magnetic `tethers' might help prevent a prominence from erupting. Title: Identification of FeH molecular lines in the spectrum of a sunspot umbra Authors: Fawzy, D. E.; Youssef, N. H.; Engvold, O. Bibcode: 1998A&AS..129..435F Altcode: A high resolution spectrum of a large -\ sunspot umbra is used for identification of two bands (2-0) and (2-1) of the (4) Delta - (4) Delta system of the FeH molecule, in addition to the previously identified bands (0-0) and (1-0) of the same system. The spectrum was obtained with FTS of the McMath-Pierce Solar Telescope of NSO/NOAO at Kitt Peak. Title: Observations Authors: Engvold, O. Bibcode: 1998ESASP.421..239E Altcode: 1998sjcp.conf..239E No abstract at ADS Title: Observations of Filament Structure and Dynamics (Review) Authors: Engvold, O. Bibcode: 1998ASPC..150...23E Altcode: 1998npsp.conf...23E; 1998IAUCo.167...23E No abstract at ADS Title: Physics of the Sun and Heliosphere in the ERA of Space Probes: Scientific Highlights of SOHO, ULYSSES and Yohko Authors: Engvold, O.; Deubner, F. L.; Ripken, H. Bibcode: 1998HiA....11..827E Altcode: No abstract at ADS Title: Velocity Fields of a Filament Region Observed with Ground-Based Telescopes and from SOHO Authors: Mein, P.; Schmieder, B.; Malherbe, J. -M.; Wiik, J. E.; Engvold, O.; Brekke, P.; Zirker, J. B.; Poland, A. I.; Delaboudiniere, J. -P.; Staiger, J. Bibcode: 1998ASPC..150..135M Altcode: 1998npsp.conf..135M; 1998IAUCo.167..135M No abstract at ADS Title: Plasma Streaming as Indicator of Field Topology in a Quiescent Filament Authors: Zirker, J. B.; Engvold, O.; Martin, S. F. Bibcode: 1997AAS...19112004Z Altcode: 1997BAAS...29.1402Z Although it is generally accepted that quiescent filaments have strong horizontal axial magnetic field (Leroy,1984) the field configuration in the legs (``barbs'' or ``feet'') is controversial. Previous observations indicate both rising and falling Doppler motions in such appendages, at speeds less than ``free-fall'' (Dunn,1960; Yi et al,1991; Zirker et al, 1994). Such observations could be consistent with the presence of horizontal magnetic fields that are slowly drifting up and down carrying plasma with them. However the H alpha fine-structure strongly suggests the presence of vertical or highly inclined magnetic field lines. Without vector field observations it is difficult to choose between these alternatives. In an attempt to clarify the issue, H alpha observations of a quiescent filament were made during its passage across the disk, from 12 to 20 April, 1993 at the Big Bear Observatory. Remarkable high-speed flows (of order 20 km/s ) were seen along the axial "spine" of the filament. Substantially slower motions were detected in the barbs. The paradox of non-free-fall motions in the predominantly vertically directed threads of barbs, will be discussed briefly. Bommier,V., Landi Degli'Innocenti,E., Leroy, J-L., and Sahal-Brechot, S.: 1994, Solar Phys. 154,231 Dunn, R.B.,1960, Ph D Thesis, Harvard University Engvold,O.: 1976,Solar Phys.49,283. Leroy,J-L. Bommier,V. nd Sahal Brechot,S.:1984, Astronomy and Astrophysics, 131,33. Yi,Z.,Engvold,O. and Keil,S.L.: 1991, Solar Phys. 132,63. Zirker,J.B.,Engvold,O.and Yi,Z. 1994, Solar Phys. 150,81. Title: Solar Physics Announces CD-ROM Authors: Svestka, Zdenek; Howard, Robert F.; Engvold, Oddbjorn Bibcode: 1997SoPh..176..443S Altcode: No abstract at ADS Title: A numerical simulation of the Wilson-Bappu relationship Authors: Cheng, Q. -Q.; Engvold, O.; Elgaroy, O. Bibcode: 1997A&A...327.1155C Altcode: { A numerical investigation of Wilson-Bappu relationship for CaII H and K lines in a series of non-active late-type main sequence stars is performed. Atmospheric models are constructed with given effective temperatures and surface gravities using a time-dependent hydrodynamic code. Mechanical heating by acoustic waves is included in the simulations. Radiative energy losses are treated by using tabulated Rosseland mean opacities in the photosphere, solving the transfer equation for the strongest lines in the chromosphere, and assuming optically thin emissivities in the corona. In the static (time-averaged) atmospheres, we find that the calculated profiles of the CaII K line for different stars show a Wilson-Bappu relationship which is in good agreement with the empirical form. In different stars the lines are formed at an atmospheric height where the column mass density, which is related to the line opacity, is different, and the full width at half maximum of the CaII line emission core broadens as a result of increasing column mass density in the chromosphere. A correct choice of turbulence velocity is important for the calculation of line width in later dwarf stars. It is well known that stellar atmospheres are dynamic. A more realistic approach is therefore to average line profiles resulting from dynamic atmospheres that represent different instants (phases) of acoustic waves. We find that the time-averaged line profiles in dynamic atmospheres are asymmetric with strong emission on the violet side of the line center. With increasing atmospheric heating the line intensity increases and the base emission line width broadens, while the variation of peak width is not significant. } % Title: Stellar activity and the Wilson-Bappu relation. Authors: Elgaroy, O.; Engvold, O.; Joras, P. Bibcode: 1997A&A...326..165E Altcode: The MgII h and k lines of 78 single stars observed with the International Ultraviolet Explorer (IUE) observatory have been analyzed. Stars of spectral classes F, G, K and M and luminosity classes I-V are represented in the sample. From these data it is shown that the Wilson-Bappu relation for the Mg II h and k lines is fulfilled over a range of 18 magnitudes, i.e. from M_v_=+12 to M_v_=-6. The sample contains slowly rotating stars of different activity levels and is suitable for investigations of a possible relation between line width and stellar activity. It is found that active stars have broader lines and show a larger variation in line widths than quiet stars. Observations of the active RS CVn binary σ Gem taken at epochs when it shows different levels of activity, clearly demonstrate line broadening following higher activity. Possible implications of the new results for the interpretation of the Wilson-Bappu relation are briefly discussed. Title: ROSAT observations of the RSCVn binary σ Geminorum. Authors: Yi, Z.; Elgaroy, O.; Engvold, O.; Westergaard, N. J. Bibcode: 1997A&A...318..791Y Altcode: X-ray observations of the RSCVn system σ Geminorum have been undertaken with the ROSAT observatory. Several spectra of very good signal-to-noise ratio were obtained. Spectral fitting using metal abundances amounting to 50% of solar values reveal two temperature components at 2MK and 12MK. Previous EXOSAT observations showed another component at 40MK. Particular interest is focused on the temporal variations of the X-ray emission. It is found that variations occur on time scales ranging from years to hours and minutes. Title: Division II: Sun & heliosphere. Reports 1996 from IAU Commissions 10, 12 and 49. Authors: Engvold, O.; Deubner, F. -L.; Ripken, H. Bibcode: 1997IAUTA..23..119E Altcode: Commissions 10: Solar activity, 12: Solar radiation & structure, 49: The interplanetary plasma & the heliosphere. Title: Problem areas in prominence research. Authors: Engvold, O. Bibcode: 1997smf..conf..105E Altcode: The review discusses current problems in physics of solar prominences. The significance of prominence structure is examined in terms of its relation to prominence formation, support against gravity, and how prominences in general interact with the neighboring atmosphere. Title: Reports from IAU Commission 10: Solar activity. Authors: Engvold, O. Bibcode: 1997IAUTA..23..121E Altcode: No abstract at ADS Title: Filament channels in the corona. Authors: Engvold, O. Bibcode: 1997ASIC..494..125E Altcode: 1997topr.conf..125E Filament channels, where filaments (prominences) are formed, are relative long-lived, narrow lanes between extended areas of magnetic field of opposite polarity. The channels are characterized by arcades of magnetic loops overlying an inner low-density cavity. The author reviews the observational bases, including small- to large-scale structure and dynamics, showing how filament channels differ from "normal" corona. One may subsequently understand better the conditions that lead to formation of filaments. Title: Oscillations in quiescent filaments from observations in H alpha Authors: Yi, Z.; Engvold, O. Bibcode: 1996ASPC..109..173Y Altcode: 1996csss....9..173Y No abstract at ADS Title: Dynamics of solar magnetic arches in the photosphere and the chromosphere. Authors: Mein, P.; Demoulin, P.; Mein, N.; Engvold, O.; Molowny-Horas, R.; Heinzel, P.; Gontikakis, C. Bibcode: 1996A&A...305..343M Altcode: Mass motions in chromospheric arch filaments have been observed with imaging spectroscopy (MSDP) at the VTT telescope of the Teide Observatory. Coordinated observations of time sequences of continuum images were carried out at the SVST telescope of the Observatorio del Roque de los Muchachos, which provided transverse velocities of photospheric tracers, by "local correlation tracking." Hα profiles along 3 arch filaments are analysed in terms of "differential cloud MODel", to discuss the Doppler velocities of chromospheric material. Models of ascending arches with downflows in both legs are investigated. The gas pressure is neglected, but the free-fall equations are integrated versus time (non-stationary case). We first assume circular lines of force with constant radius. We can account for chromospheric velocities, but we cannot fit the slow motion of footpoints derived from photospheric tracers. A better agreement is obtained by assuming lines of force with fixed footpoints and variable radius. Typical values are: half distance between footpoints of 10 to 15Mm, upward velocity at the top of loops of 4km/s after an integration time of 800s. The obtained values are consistent with the sizes and the lifetime of arch filaments. Title: Performance test of the slow wavefront sensor for the large Earth-based solar telescope LEST Authors: Owner-Petersen, M.; Jensen, M.; Engvold, O. Bibcode: 1996ESOC...54..393O Altcode: 1996adop.conf..393O No abstract at ADS Title: Mapping of Chrosmospheric Active Regions on UX Ari Authors: Engvold, O. Bibcode: 1996iue..prop.5151E Altcode: No abstract at ADS Title: Ultraviolet intensity variations of the RS CVn variable σ Geminorum Authors: Elgarøy, Ø.; Engvold, O.; Joraas, P. Bibcode: 1995IAUS..176P.165E Altcode: No abstract at ADS Title: Flows in Quiescent Prominences Authors: Zirker, Jack B.; Engvold, Oddbjorn; Yi, Zhang Bibcode: 1994SoPh..150...81Z Altcode: Earlier studies of quiescent prominences claim that there is a systematic downward directed motion of the small-scale structure. Disk observations, on the other hand, have detected mass motions both upwards and downwards. The earlier high-resolution observations of limb prominences have been re-examined using local cross-correlation techniques for measurements of motion perpendicular to the line of sight. The new measurements reveal flow speeds and directions that are in good agreement with current Doppler measurements on the disk. Title: The Near-Infrared Capabilities of LEST Authors: Engvold, O. Bibcode: 1994IAUS..154..579E Altcode: No abstract at ADS Title: Filament oscillations as evidence for Alfvén waves Authors: Jensen, Eberhart; Yi, Zhang; Engvold, Oddbjorn Bibcode: 1994SoPh..149..209J Altcode: High resolution observations of quiescent filaments show oscillations that are strongly tied to their fine threads. It is shown that neither slow nor fast MHD modes may account for the observations, which rather are in accordance with Alfvén waves. Title: Cold Matter in Filament Channels (Invited) Authors: Engvold, O. Bibcode: 1994scs..conf..297E Altcode: 1994IAUCo.144..297E The formation of cold filaments in the low corona is a central research area in solar physics. Their basic properties are not well understood, but they may be crucial for the mass and magnetic flux balance in the solar corona. The review discusses multi-wavelength observational results and theoretical modelling of filament channels and quiescent filaments. Title: Dynamics of solar magnetic arches in photosphere and chromosphere Authors: Mein, P.; Mein, N.; Démoulin, P.; Gontikakis, C.; Engvold, O.; Molowby, R. Bibcode: 1994smf..conf..366M Altcode: No abstract at ADS Title: An Overview of the LEST Live Optics Authors: Andersen, T.; Engvold, O.; Jakobsson, H. Bibcode: 1993rtpf.conf...53A Altcode: No abstract at ADS Title: Design of the LEST Slow Wavefront Sensor Authors: Owner-Petersen, M.; Darvann, T.; Engvold, O. Bibcode: 1993rtpf.conf...63O Altcode: No abstract at ADS Title: Prospects for future ground-based solar observations. Authors: Engvold, O. Bibcode: 1993ESASP1157...55E Altcode: 1993srfs.book...55E The complementary aspects of solar ground-based and space instrumentation are discussed and plans for future ground-based solar observing facilities are reviewed. Title: Filigree, magnetic fields, and flows in the photosphere Authors: Yi, Zhang; Engvold, Oddbjorn Bibcode: 1993SoPh..144....1Y Altcode: The interaction between small-scale magnetic fields and horizontal photospheric flows has been studied from observations of high angular resolution obtained with the Lockheed narrowband filter in the Swedish Vacuum Solar Telescope at La Palma. The measured magnetic flux density (αB) is in the range from a detection limit of ≈ 10 G to about 500 G, showing a good correspondence with the filigree. The magnetic flux elements take part in the local flows towards downdrafts at the supergranulation cell boundaries. The measured flux density, as well as the associated filigree intensity, decrease as the structures approach the downdrafts, presumably as a result of increased tilting and possibly submergence of flux into the downdrafts. Title: Small-Scale Magnetic Structures and Supergranulation Flows Authors: Zhang, Y.; Jensen, E.; Engvold, O. Bibcode: 1993ASPC...46..232Z Altcode: 1993mvfs.conf..232Z; 1993IAUCo.141..232Z No abstract at ADS Title: Active Region Evolution Through Coordinated Observations Authors: Mein, N.; Mein, P.; Schmieder, B.; Engvold, O.; Molowny, R.; Ai, G. X. Bibcode: 1993ASPC...46...63M Altcode: 1993mvfs.conf...63M; 1993IAUCo.141...63M No abstract at ADS Title: LEST: the large Earth-based solar telescope. Authors: Engvold, O. Bibcode: 1992EN.....23..203E Altcode: Realising LEST, a truly next-generation solar telescope in terms of dimensions, innovative optics, and dome design, will mark a new era of international cooperation in solar physics and astrophysics. Title: Absolute redshifts in the C iv 1548 Å line in the transition region of the quiet Sun Authors: Henze, William; Engvold, Oddbjorn Bibcode: 1992SoPh..141...51H Altcode: Observations with the UVSP instrument on the SMM spacecraft were made at the polar limb and disk center for the accurate determination of Doppler shifts of the CIV 1548 Å emission line formed at 105 K in the transition region of the quiet Sun. Individual data points representing 3 arc sec square pixels yield both redshifts and blueshifts, but the mean values from four different days of observations are toward the red. The mean redshifts are in the range 4-8 km s-1 and are produced by nearly vertically directed flows; the uncertainty associated with the mean values correspond to ±0.5 km s-1. The redshift increases with brightness of the CIV line. Title: The Prominence-Corona Transition Region in transverse magnetic fields Authors: Drago, Franca Chiuderi; Engvold, Oddbjørn; Jensen, Eberhart Bibcode: 1992SoPh..139...47D Altcode: An emission measure analysis is performed for the Prominence-Corona Transition Region (PCTR) under the assumption that the cool matter of quiescent filaments is contained in long, thin magnetic flux loops imbedded in hot coronal cavity gas. Consequently, there is a transition region around each thread. Title: The Prominence / Corona Transition Region in Transverse Magnetic Fields Authors: Chuideri Drago, Franca; Engvold, Oddbjorn; Jensen, Eberhart Bibcode: 1992SoPh..139...47C Altcode: An emission measure analysis is performed for the Prominence-Corona Transition Region (PCTR) under the assumption that the cool matter of quiescent filaments is contained in long, thin magnetic flux loops imbedded in hot coronal cavity gas. Consequently, there is a transition region around each thread. Comparison of the model and observations implies that the temperature gradient is perpendicular to the magnetic lines of force in the lower part of the PCTR (T < 105 K). It is shown that in this layer the heating given by the divergence of the transverse conduction fails to account for the observed UV and EUV emission by several orders of magnitude. It is, therefore, suggested that the heating of these layers could be due to dissipation of Alfvén waves. In the high-temperature layers (T ≥ 105 K), where the plasma β ≥ 1, the temperature gradient is governed by radiative cooling balancing conductive heating from the surrounding hot coronal gas. Also in these outer layers the presence of magnetic fields reduces notably the thermal conduction relative to the ideal field-free case. Numerical modelling gives good agreement with observed DEM; the inferred value of the flux carried by Alfvén waves, as well as that of the damping length, greatly support the suggested form of heating. The model assumes that about 1/3 of the volume is occupied by threads and the rest by hot coronal cavity matter. The brightness of the EUV emission will depend on the angle between the thread structure and the line of sight, which may lead to a difference in brightness from observations at the limb and on the disk. Title: UV Observations of Limb-Crossing of Active Regions on Sigma Geminorum Authors: Engvold, O. Bibcode: 1992iue..prop.4410E Altcode: No abstract at ADS Title: Are stellar flares a result of magnetic reconnection? Authors: Elgarøy, Ø.; Engvold, O. Bibcode: 1992mrpa.work..193E Altcode: In stellar flares enormous amounts of energy are released during very short times. No theory satisfactorily explains the phenomenon. Observations of flare stars support the suggestion that the rise time of stellar flares contains information on the volume in which energy is released. Possible non-magnetic energy sources fall short of explaining stellar flares. Solar flares may occur as a result of magnetic field reconnection. It is shown that considerable difficulties arise when the same mechanism is adopted to the stellar case. Some possible solutions are indicated. Title: Vertical Velocities and Oscillations in Quiescent Filaments Authors: Yi, Zhang; Engvold, Oddbjorn Bibcode: 1991SoPh..134..275Y Altcode: 1991SoPh..134..275Z Analysis of He Iλ 10 830 Å spectral observations of a large, quiescent filament reveals a pronounced oscillatory behaviour of the vertical mass motion. The filament is situated in a quiet region more than 15° away from the nearest active region. Title: Structure and oscillations in quiescent filaments from observations in He i λ10830 å Authors: Yi, Zhang; Engvold, Oddbjorn; Keil, Stephen L. Bibcode: 1991SoPh..132...63Y Altcode: 1991SoPh..132...63Z Observations of two quiescent filaments show oscillatory variations in Doppler shift and central intensity of the He I λ10830 Å line. Title: Large Earth-based Solar Telescope-LEST Authors: Engvold, Oddbjorn Bibcode: 1991AdSpR..11e.157E Altcode: 1991AdSpR..11..157E The Large Earth-based Solar Telescope (LEST) will be a powerful, next-generation solar telescope with unprecedented angular resolution and highly accurate polarimetry, that will serve the World's community of solar scientists into the next century. The project is run by the LEST Foundation which has its seat at the Royal Swedish Academy of Sciences in Stockholm. Being initially a European project (Germany, Israel, Italy, Norway, Spain, Sweden, and Switzerland) the LEST has grown to include also Australia and USA.

The LEST design is underway. The optical design is a 2.4 m aperture, ``polarization-free'' concept based on a modified Gregorian system. An actively controlled NNT-type main mirror, a high precision pointing and tracking system, a helium-filled light path and thin entrance window, together with an integrated Adaptive Optics system, will provide near diffraction-limited performance of the telescope.

LEST will be placed on La Palma, Canary Islands, near the Caldera rim on the Roque de los Muchachos observatory. This site offers superb seeing conditions which will enable LEST to reach its scientific goals.

The construction of LEST will begin early 1993, and the telescope is ready for ``first light'' in 1996.

LEST marks a new era of international cooperation in solar physics and astrophysics. Title: Structure and dynamics of solar prominences. Authors: Engvold, O. Bibcode: 1991joso.proc.....E Altcode: Some questions about the formation and existence of solar prominences are considered. Title: LEST Mini-Workshop: Entrance windows of solar telescopes Authors: Engvold, O.; Andersen, T. Bibcode: 1991ewst.conf.....E Altcode: 1991LFTR...46.....E These proceedings present discussions such as manufacture, design and mounting of thin entrance windows with application to LEST. Title: An Ultraviolet Spectral Atlas of a Prominence Authors: Engvold, Oddbjorn; Hansteen, V.; Kjeldseth-Moe, O.; Brueckner, G. E. Bibcode: 1990Ap&SS.170..179E Altcode: The ultraviolet spectrum of a large prominence has been observed with the High Resolution Telescope and Spectrograph (HRTS) on SPACELAB 2, 5 August, 1985. The spectrum covers the wavelength range λλ1335 1670 Å and shows numerous emission lines from gas at chromospheric and transition region temperatures. An Atlas of the prominence spectrum has been made showing absolute calibrated intensities on an accurate wavelength scale. The Atlas includes for comparison the corresponding UV-spectrum from an average quiet solar region. Title: Deviation from the Wilson-Bappu relationship in faint red dwarf stars. Authors: Elgaroy, O.; Engvold, O.; Carlsson, M. Bibcode: 1990A&A...234..308E Altcode: New observations of the Mg II h and k lines on red dwarf stars have been carried out with the International Ultraviolet Explorer observatory. It is found that several of the dwarf stars in the sample have Mg II h and k lines which are narrower than expected from the Wilson-Bappu relationship, that is established for stars brighter than M(v) about 7. The deviations may depend on the Mg II h and k line opacity. Evidence is presented in favor of the suggestion that the optical thickness of the Mg II lines in faint red dwarfs depends on the level of activity of the stars. Calculations based on models for the sun and YZ CMi (Mv = 12.3) support the observational results. Title: Absolute Flows in the Solar Transition Region Authors: Engvold, Oddbjorn; Henze, William Bibcode: 1990Ap&SS.170..173E Altcode: It is the objective of the present study to establish an absolute scale for flows in the solar transition region in observations obtained with the UVSP/SMM. By use of the polar limbs as reference one finds that the downflows range between 3 and 10 km s-1. The brighter regions show the largest downward flows. Title: Hvar Reference Atmosphere of Quiescent Prominences Authors: Engvold, Oddbjørn; Hirayama, Tadashi; Leroy, Jean Louis; Priest, Eric R.; Tandberg-Hanssen, Einar Bibcode: 1990LNP...363..294E Altcode: 1990IAUCo.117..294E; 1990doqp.coll..294E No abstract at ADS Title: Addendum to the LEST Design report. Authors: Engvold, O.; Andersen, T. Bibcode: 1990LFTR...42.....E Altcode: The design modification and other major issues are presented in this addendum to the LEST Design report. Implementation of some of the modifications has budgetary consequences. The resulting revised budget is included. Title: The Prominence/corona Transition Region Analyzed from SL-2 HRTS Authors: Engvold, O.; Hansteen, V.; Kjeldseth-Moe, O.; Brueckner, G. E. Bibcode: 1990LNP...363..250E Altcode: 1990IAUCo.117..250E; 1990doqp.coll..250E The ultraviolet spectrum of a large prominence has been observed with the High Resolution Telescope and Spectrograph (HRTS) on Spacelab 2 August 5, 1985. The spectrum covers the wavelength range 1335-1670Å and shows numerous emission lines from gas at chromospheric and transition region temperatures. A spectral atlas of these data is available. The data reveals a variation with height of the line intensities. The prominence becomes hotter with height. A value of ~ 0.12 dyn cm-2 for the gas pressure in the prominence-corona transition region is obtained from line ratios. The resolved fine structure of the He II 1640.400Å line indicates that a major part of this emission comes from cold gas. A broad Fe XI 1467.080Å suggests high velocities in the coronal cavity region. The Fe XI line in the cavity region is a factor ~ 5 less bright in the normal corona at the same height. Assuming that the temperature is the same in the two regions the present obervations suggest that the pressure in the cavity region is lower by a similar factor. Title: Modelling of the prominence-corona transition region. Authors: Engvold, O.; Kjeldseth-Moe, O. Bibcode: 1990ppst.conf..165E Altcode: Empirical modeling of the PC transition region is based on observed intensities of EUV and UV lines, and emission at radio wavelengths. Analysis of EUV and UV lines in quiescent prominences show that the transition region between prominences and corona is very thin and in general similar to the Chromosphere-Corona (CC) transition region. This review discusses observations, methods and some recent results. Title: The LEST project Authors: Engvold, O. Bibcode: 1990nwus.book..451E Altcode: No abstract at ADS Title: New Observational Aspects Authors: Engvold, O. Bibcode: 1990IAUS..138..469E Altcode: No abstract at ADS Title: Vertical Flows in a Quiescent Filament Authors: You, J. Q.; Engvold, O. Bibcode: 1990LNP...363..262Y Altcode: 1990IAUCo.117..262Y; 1990doqp.coll..262Y High resolution spectra of the H, and Ca II H and K lines were observed simultaneously for a quiescent filament on the solar disk on 27 July, 1974. The narrow absorption line profiles of the disk filament show asymmetries which give rise to differences in flow velocities derived from measurements of line center positions. The bi-sector at a higher intensity level of the three lines gives consistent values for vertical flow velocities. The velcities range from -1.7 to +2.7 km s -1, and mean value 0.5 km s -1, for H, and -1.9 to 2.5 km s -1, and mean value 0.3 km s -1, for the Ca II H and K lines. Title: LEST design. Status of the design of the Large Earth-Based Solar Telescope Authors: Andersen, Torben E.; Engvold, Oddbjorn Bibcode: 1990ldsd.book.....A Altcode: No abstract at ADS Title: Distribution of Velocities in the Pre-Eruptive Phase of a Quiescent Prominence Authors: Engvold, Oddbjørn; Jensen, Eberhart; Zhang, Yi; Brynildsen, Nils Bibcode: 1990LNP...363..263E Altcode: 1990IAUCo.117..263E; 1990doqp.coll..263E High resolution Ca II K line spectra of a large quiescent prominence were obtained about one hour before a prominence eruption May 2nd 1974. The observations were made with the main spectrograph of the vacuum tower of Sacramento Peak Observatory. The observed velocities in a wide range from -50 to +25 km/s suggest that the very initial stages of destabilization of the prominence were in fact recorded. The distribution of line intensities and line widths versus line shift suggest that one observes 3 threads in the line-of-sight for low velocities. For larger shifts one is evidently able to observe individual threads. Title: Vertical Flows in the Solar Transition Region Authors: Henze, W.; Engvold, O. Bibcode: 1989BAAS...21Q.840H Altcode: No abstract at ADS Title: Addendum to Technical Report No. 38: comments of the LEST Site Investigation Team on the referee's reports. Authors: Brandt, P. N.; Erasmus, D. A.; Kusoffsky, U.; Righini, A.; Rodriguez, A.; Engvold, O. Bibcode: 1989attr.book.....B Altcode: No abstract at ADS Title: Results and conclusions from the meteorological phase of the LEST site survey. Authors: Brandt, P. N.; Erasmus, D. A.; Kusoffsky, U.; Righini, A.; Rodríguez, A.; Engvold, O. Bibcode: 1989rcfm.book.....B Altcode: No abstract at ADS Title: Examples of high resolution observations of solar fine structures made at La Palma. Authors: Jensen, E.; Engvold, O.; Scharmer, G. B. Bibcode: 1989ftsa.conf...67J Altcode: Two video films from the Swedish Vacuum Solar Telescope at La Palma were shown. Some basic parameters of the telescope are given. Title: Vertical Flows in a Quiescent Filament Authors: Jian-Yi, You; Engvold, O. Bibcode: 1989HvaOB..13..197J Altcode: No abstract at ADS Title: Distribution of velocities in the Pre-Eruptive Phase of a Quiscent Prominence Authors: Engvold, O.; Jensen, E.; Zhang, Yi; Brynildsen, N. Bibcode: 1989HvaOB..13..205E Altcode: No abstract at ADS Title: Prominence environment Authors: Engvold, Oddbjorn Bibcode: 1989ASSL..150...47E Altcode: 1989dsqs.work...47E; 1988dsqs.work...47E Studies of prominences vis a vis the surrounding corona provide insight into basic questions about the formation of prominences, their stability and support, and their mass and energy balance. The present review discusses observational and theoretical results on helmet streamers, cavities, filament channels, and the prominence-corona transition sheath. Title: Transition Zone Dynamics in Yellow Giants and Supergiants Authors: Engvold, O. Bibcode: 1989iue..prop.3594E Altcode: No abstract at ADS Title: Vertical flows in a quiescent filament. Authors: You, Jian-Qi; Engvold, O. Bibcode: 1989HvaOB..13..197Y Altcode: High resolution spectra of the Hα, and Ca II H and K lines were observed simultaneously for a quiescent filament on the solar disk on 27 July, 1974. The narrow absorption line profiles of the disk filament show asymmetries which give rise to differences in flow velocities. The vertical flow velocities range from -1.7 to +2.7 km s-1, and mean value 0.5 km s-1, for Hα, and -1.9 to 2.5 km s-1, and mean value 0.3 km s-1, for the Ca II H and K lines. Title: Gas Flows in the Transition Region above Sunspots Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Engvold, O.; Maltby, P.; Bartoe, J. -D. F.; Brueckner, G. E.; Cook, J. W.; Dere, K. P.; Socker, D. G. Bibcode: 1988ApJ...334.1066K Altcode: Strong downflows and moderate upflows in the transition region over a sunspot have been observed with the HRTS on Spacelab 2 in 1985. The flows are persistent in the sense that they are seen in the same spot for 5 days. The downflows are prominent in regions of limited extent (4arcsec - 6arcsec), and flow velocities are in the range 40 - 80 km s-1 and are thus supersonic. Upward flows have smaller velocities, 5 - 20 km s-1, but may extend over a larger area. In the downflowing regions there is always an appreciable amount of gas at rest in the line of sight. Flow speeds derived from the profiles of different lines formed in the transition region between 30,000 and 230,000K are very similar implying constant downflow in this temperature range. Title: Downflow Velocity in the Solar Transition Region Authors: Henze, W.; Engvold, O. Bibcode: 1988BAAS...20..703H Altcode: No abstract at ADS Title: Ultraviolet emission lines and optical photometry of the flare star AT Microscopii. Authors: Elgaroy, O.; Joras, P.; Engvold, O.; Jensen, E.; Pettersen, B. R.; Ayres, T. R.; Ambruster, C.; Linsky, J. L.; Clark, M.; Kunkel, W.; Marang, F. Bibcode: 1988A&A...193..211E Altcode: Ultraviolet spectra of the dwarf flare star binary AT Mic (dM 4.5e+dM 4.5e) were obtained with the IUE spacecraft on three days in September 1985. A high-resolution short-wavelength spectrum was exposed for 25 hours. Simultaneous optical monitoring in the U-band was performed during part of the IUE observations. At the time of observation AT Mic was flaring at an average rate of 1.3 flares per hour. On the average 9% of the energy in the U-band was due to the detected flare activity. From the observed high resolution spectra, line wavelengths, widths and fluxes were derived, and the effects of the binary structure of AT Mic on the spectral lines were evaluated. The ultraviolet emission line spectrum is similar in character to that of flare regions on the Sun and other stars. Title: Far-ultraviolet and X-ray emission of the long period RS CVn star sigma Geminorum. Authors: Engvold, O.; Ayres, T. R.; Elgaroy, O.; Jensen, E.; Joras, P. B.; Kjeldseth-Moe, O.; Linsky, J. L.; Schnopper, H. W.; Westergaard, N. J. Bibcode: 1988A&A...192..234E Altcode: The new UV and X-ray observations of σ Gem support the theory that large active regions associated with starspots are responsible for the enhanced line emission commonly seen in RS CVn systems. The rotational modulation of the UV line fluxes increases with temperature of the line-forming region. The X-ray emission from the stellar corona, on the other hand, shows only a barely detectable variation with rotational phase. One may infer that the coronal active regions of the system are not co-spatial with the activity in the transition region below, and/or occupy a significantly larger surface area. An equally probable explanation, however, is that the X-ray emission is emitted from huge, stellar sized loops. Title: Redshifts of High Temperature Emission Lines in the Far-Ultraviolet Spectra of Late-Type Stars. II. New, Precise Measurements of Dwarfs and Giants Authors: Ayres, Thomas R.; Jensen, Eberhard; Engvold, Oddbjorn Bibcode: 1988ApJS...66...51A Altcode: Results are presented from an IUE SWP camera investigation of the occurrence of gasdynamic flows, analogous to the downdrafts of 10 to the 5th K material observed over magnetic active regions of the sun, among stars of late spectral type. The SWP calibration spectra study conducted documents the existence of local, small, persistent distortions of the echelle wavelength scales that are of unknown origin. Attention is given to the enormous widths of the stellar high-excitation emission lines in both the dwarfs and the giants, with respect to the comparatively small, subsonic Doppler shifts; the widths are typically an order of magnitude greater than the redshifts. Title: The ultraviolet variability of Betelgeuse Authors: Joras, P.; Engvold, O.; Elgarøy, O. Bibcode: 1988ASSL..143..311J Altcode: 1988acse.conf..311J Observations of the red, bright supergiant star α Ori using the IUE satellite during the past 8 years, show significant variations in the UV line fluxes. Furthermore, different types of lines do not show the same variability. The short term fluctuations in visual brightness, which are believed to be associated with transient phenomena in the stellar atmosphere, are well correlated with UV line flux variations. Title: LEST update. Authors: Stenflo, J. O.; Engvold, O. Bibcode: 1988LFTR...34.....S Altcode: No abstract at ADS Title: Prominence environment. Authors: Engvold, O. Bibcode: 1988dssp.conf...51E Altcode: Studies of prominences vis-a-vis the surrounding corona provide insight to basic questions about prominence formation, their stability and support, mass and energy balance. This review discusses observational and theoretical results on helmet streamers, coronal voids, cavities, filament channels, and the prominence-corona transition sheath. Title: Proposal for an alignment system for the primary and secondary mirrorof LEST. Authors: Heier, H.; Engvold, O.; Dunn, R. B. Bibcode: 1988LFTR...32.....H Altcode: The tolerances of tilt and decentration of the secondary mirror of LEST relative to the primary mirror are very tight. The tilt tolerance is 10 arc sec and the decentration tolerance is 80 μm. In order to be able to align the secondary and primary mirrors to these tolerances, the authors propose to equip the telescope with two auxiliary optical systems. Title: The prominence-corona transition region. Authors: Engvold, Oddbjorn Bibcode: 1988sscd.conf..151E Altcode: The prominence-corona (P-C) transition region is highly fragmented and the area filling of emission may occasionally be as small as 0.02. The P-C plasma is threaded with magnetic flux tubes, highly inclined with the long axis of the prominence. Line-of-sight velocities (r.m.s.) increases with temperature to ≍30 km s-1 at T = 105K. Emission measure and model calculations suggest that the P-C transition region is less steep than the corresponding region (C-C) for the quiet Sun. More precise values for the area filling factors and for possible flow velocities are required to make realistic models of the P-C transition region. Title: Microflares in the Solar Magnetic Network Authors: Porter, J. G.; Moore, R. L.; Reichmann, E. J.; Engvold, O.; Harvey, K. L. Bibcode: 1987ApJ...323..380P Altcode: It is suggested that the events observed by HRTS are microflares in tiny magnetic bipoles (some in cell interiors but most in the magnetic network) and that these same events, when strong enough and frequent enough in some of the larger bipoles, sustain X-ray bright points. In this paper, the authors present new evidence in favor of this hypothesis. Using C IV spectroheliograms in combination with magnetograms and He I λ10,830 spectroheliograms they find that impulsive heating events of the class observed by HRTS are common at small bipoles in the network, both at bipoles corresponding to X-ray bright points and at many weaker bipoles that show no sustained enhanced coronal brightness. Title: Observations and modelling of the prominence/corona transition region. Authors: Engvold, O.; Kjeldseth-Moe, O.; Bartoe, J. -D. F.; Brueckner, G. E. Bibcode: 1987ESASP.275...21E Altcode: 1987sspp.symp...21E The construction of inhomogeneous temperature transition region models for solar prominences is considered. Models based on UV line intensities from SO82B on Apollo Telescope Mount (ATM)/Skylab and the High Resolution Telescope and Spectrograph (HRTS) on Spacelab 2 are derived. The modeled structures of the transition region are in the form of thin tubes, similar to the prominence structures seen in the cool core. An expression for the thickness of the transition region around prominences is given, and mechanisms for energy transport are discussed. Uncertainties and possible improvements in the modeling are pointed out. Title: EUV Line Flux Variations and Activity in Alpha Orionis Authors: Elgaroy, O.; Engvold, O.; Joeras, P. Bibcode: 1987ESASP.270..337E Altcode: 1987erbp.symp..337E Studies of the red, bright supergiant star Alpha Orionis, using the IUE over an eight-year period show significant variations in the EUV line fluxes of the star. Neither the long term cyclic variation in radial velocity and in visual brightness, nor the relative position of the orbiting inner stellar companion of the triplet stellar system, seem to be connected with observed fluctuations in EUV line fluxes. Short term fluctuations in optical brightness (B magnitude) believed to be associated with transient (active) regions in the atmosphere of the star, are well correlated with EUV line flux variations. Title: A Deep, Doppler-Compensated IUE SWP Echellogram of the KO Primary of HR 1099 Authors: Bennett, J. O.; Ayres, T. R.; Jensen, E.; Engvold, O. Bibcode: 1987BAAS...19R.706B Altcode: 1987BAAS...19Z.706B No abstract at ADS Title: Proceedings of the workshop on adaptive optics in solar observations,Freiburg, September 8 - 9, 1987. Authors: Merkle, F.; Engvold, O.; Falomo, R.; Mattig, W. Bibcode: 1987pwoa.book.....M Altcode: No abstract at ADS Title: The Wilson-Bappu Relationship - a Barometric Effect Authors: Engvold, O.; Elgaroøy, Ø. Bibcode: 1987LNP...291..315E Altcode: 1987LNP87.291..315E; 1987csss....5..315E Optically thick lines in the UV spectra of late type stars obey a Wilson-Bappu type relationship. Optically thin lines reveal no width-luminosity relationship. Consequently, there is no systematic variation in Doppler broadening with stellar luminosity. Title: Site testing. Meeting on the LEST site survey held at Roque de los Muchachos, La Palma, 18 - 19 February 1987. Authors: Engvold, O.; Hauge, Ø. Bibcode: 1987stmo.book.....E Altcode: No abstract at ADS Title: Objectives and conditions for the LEST site survey. Authors: Engvold, O. Bibcode: 1987LFTR...26....7E Altcode: No abstract at ADS Title: Old and New Views of Solar Prominences Authors: Livingston, W. C.; Engvold, O.; Jensen, E. Bibcode: 1987Ast....15...18L Altcode: No abstract at ADS Title: Optical telescope for LEST site survey. Authors: Bonaccini, D.; Dunn, R. B.; Engvold, O. Bibcode: 1987LFTR...28..233B Altcode: The authors propose a telescope of 40-cm aperture for the optical site-testing campaign for the LEST. They have chosen a helium-filled compact design with a f/2.54 spherical primary whose aberrations are corrected by a lens-mirror combination with all spherical surfaces. A scheme for taking TV images of the granulation, determining Ro and measuring the size of the isoplanatic patch is proposed. Title: Adaptive optics in solar observations Authors: Merkle, Fritz; Engvold, O.; Falomo, R. Bibcode: 1987aoso.conf.....M Altcode: No abstract at ADS Title: X-ray spectrum of sigma Geminorum : an RS Canum Venaticorum type binary. Authors: Singh, K. P.; Slijkhuis, S.; Westergaard, N. J.; Schnopper, H. W.; Elgaroy, O.; Engvold, O.; Joras, P. Bibcode: 1987MNRAS.224..481S Altcode: The binary system Sigma Gem has been observed on three occasions during 1984 November 17-21 with the medium-energy and the low-energy detectors on the Exosat Observatory. Spectral analysis of the data obtained over the energy range of 0.05-6.0 keV shows evidence for a bimodal temperature distribution of emission measure in an optically thin thermal equilibrium plasma with one component of about 5 million K and the other one of about 40 million K. It is found that the lower-temperature component is the dominant source of X-ray emission. The data are interpreted in terms of emission from two types of hot coronal loops with constant pressure on the surface of the visible red giant star in the binary. The two systems of coronal loops correspond to the two temperature plasma components measured. The observed variations in the luminosity of the system are probably due to the rotational effects on the smaller, cooler loops confined to certain regions on the surface of the late-type giant star. Title: A Deep, Doppler-compensated SWP Echelle Exposure of UX Arietis Authors: Engvold, O. Bibcode: 1987iue..prop.2999E Altcode: No abstract at ADS Title: Prominence Environment Authors: Engvold, O. Bibcode: 1987dssp.work...57E Altcode: 1987ASSL..150...57E No abstract at ADS Title: Transition Zone Flows in Sunspots Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Engvold, O.; Maltby, P.; Bartoe, J. -D. F.; Brueckner, G. E. Bibcode: 1987rfsm.conf..317K Altcode: Downflow in the transition region over sunspots first detected on HRTS rocket flights, seems to be a general phenomenon. Although details in the flow pattern appear to change over a period of minutes, the phenomenon itself persists for days. While the mechanism producing the observed redshifts is not understood it seems most likely that they are produced by actual downflow of gas in thin filamentary structures. This may be inferred from the co-existence within the same spatial resolution element of tubes with strong downflows and tubes where the gas is at rest. Thus the line profiles result from an unresolved fine structure in a similar fashion that Evershed effect in the photosphere produces "flag"-like line profiles in visual lines. Title: Deep SWP Echelle Exposures of the Solar-Twin Alpha CentauriaA (G2 V) and Its Companion Alpha Centauri B (K1 V) Authors: Engvold, O. Bibcode: 1987iue..prop.3029E Altcode: No abstract at ADS Title: Temperatures of quiescent prominences measured from hydrogen Paschen and Ca II IR lines. Authors: Engvold, Oddbjorn; Brynildsen, Nils Bibcode: 1986NASCP2442...97E Altcode: 1986copp.nasa...97E During 12 to 17 September 1983 a number of prominences were observed with the McMatch solar telescope of National Solar Observatories, using the Fourier transform spectrometer with a InSb detector (Brault 1979). The present study refers to three prominences observed 13 and 14 September. Prominence A: Large quiescent prominence at S28 E90 Prominence B. Stable prominence in weakly enhanced magnetic region at about NO8 E90 Prominence C: Quiescent prominence at N30 E90. Spectra were obtained at a total of 15 different locations in the three prominences in the wavelength range lambda, lambda 7740 to 14,000 Angstroms. The observed differences between Texc and Tkin are hardly significant. Researchers conclude that the two methods for temperature determination when applied to optically thin lines give reasonably consistent results, i.e., the population of the excited levels of hydrogen is collisionally controlled. The well known increase in T and V towards the edge of equiescent prominences (Hirayama 1964) is not corroborated by the present data. One explanation for this could be that prominence A is atypical. The optical thickness of prominence emission lines tends to increase from center to edges as demonstrated by the case of He I lambda 10830 angstroms. If line opacity plays a significant role in earlier center to edge determinations of T and V, a smaller variation would be expected from measurements in optically thin lines, such as in the present case. Title: Vertical motions in quiescent prominences observed in the He I λ10830 Å line. Authors: Engvold, Oddbjorn; Keil, Stephen L. Bibcode: 1986NASCP2442..169E Altcode: 1986copp.nasa..169E The observations contain two-dimensional spectral scans of a total of 17 different prominences on the solar disk from the period 3 to 9 May 1981, using the main spectrograph of the solar vacuum telescope at Sacramento Peak. The following conclusions may be drawn from the data: (1) Blue shifts are much more common than red shifts. In many cases more than 90 per cent of the projected prominence area is associated with blue shifts. (2) The darkest prominence regions show the largest blue shift (v less than 3 km s-1). (3) Red shifts are most commonly seen at prominence edges. (4) The general pattern of prominence velocity persists for several hours. On the scale of about 10 arcsec and less, changes are detectable in the course of 2 to 5 minutes. The observed predominance of the blue shifts is largely in agreement with earlier results from H alpha (cf. Martres et al. 1981). It cannot, however, be concluded definitely that the observed shift really represents a net flow of matter. The situation could possibly be analogous to that of the solar transition region where lines such as C IV lambda 1548 angstroms seem to indicate a net inflow, which can hardly be true, at velocities greater than 4 km s(-1) in the quiet Sun (Athay et al. 1983; Gurman and Athay 1983). If the typical structure element of the prominence is sub-resolution, i.e., 2 to 3 arcsec or worse, as in the present case, an apparent net shift could result if the ascending and the decending elements have different temperature and/or pressure. Different lines could then indicate different flow velocities and even opposite directions. Title: Optical systems for the LEST polarimeter - a feasibility study. Authors: Heier, H.; Engvold, O.; Bertani, D.; Cetica, M.; Iorio-Fili, D. Bibcode: 1986LFTR...17.....H Altcode: The authors have studied the effect of the polarimeter optics on the image of the LEST solar telescope both with and without an auxiliary collimating system making a parallel beam in the polarimeter space. Title: Progress Report: Precise Measurements of Radial Velocities of Far-Ultraviolet Emission Lines in Stars of Late Spectral Type Authors: Ayres, T.; Engvold, O.; Jensen, E.; Linsky, J. Bibcode: 1986LNP...254...94A Altcode: 1986csss....4...94A Recent high-dispersion, far-ultraviolet IUE spectra of the G-type supergiant β Draconis contain evidence for organized, persistent downflows of gas, apparently confined to a high-density component of the stellar transition zone. Title: A Deep High-Dispersion, Doppler Compensated SWP Exposure of The Primary of the HR 1099 System Authors: Engvold, O. Bibcode: 1986iue..prop.2707E Altcode: No abstract at ADS Title: On the variability of Sigma Geminorum - an interesting candidate for X-ray studies. Authors: Elgaroey, O.; Engvold, O.; Joraas, P. Bibcode: 1985ESASP.239..117E Altcode: 1985cxrs.work..117E Observations of Sigma Gem in UV show that high excitation line fluxes increase with the emergence of a dark region from behind the approaching limb. A moderate increase in X-ray intensity occurs, together with the coming into view of another, weaker, spot region. Further observations of rotational modulation effects are desirable. Title: Evidence for Systematic Flows in the Transition Region around Prominences Authors: Engvold, O.; Tandberg-Hanssen, E.; Reichmann, E. Bibcode: 1985SoPh...96...35E Altcode: The solar transition region in the neighbourhood of prominences has been studied from observations with the Ultraviolet Spectrometer and Polarimeter of NASA's Solar Maximum Mission satellite. Dopplergrams from observations of the transition-region lines CIV λ 1548 Å and SiIV λ 1393 Å, which are formed at about 105 K, give velocity amplitudes typically in the range ± 15 km s-1. Prominences are found to be located very close to dividing lines between areas of up- and down-draughts in the transition-region. The observed pattern suggests that the 105 K gas flows take place within arcades of magnetic loops, which most likely are part of the supporting magnetic structure for the prominence matter. An additional band of blue-ward Doppler shifts is frequently seen close to quiescent prominences. This may be the source of outward flowing matter along the helmet streamers above filament channels. Title: Excitation mechanisms in the atmospheres of yellow and red giant and supergiant stars. Authors: Engvold, O.; Kjeldseth Moe, O.; Jensen, E.; Joras, P. Bibcode: 1985ESA7..R....151E Altcode: No abstract at ADS Title: A proposal for the LEST control system. Authors: Engvold, O.; Andersen, T. E.; Carlsson, M.; Jensen, J. R.; Klim, K. Bibcode: 1985LFTR...15.....E Altcode: Contents: Trends in development of computers and peripherals. Trends in telescope control and operation. Control system requirements for LEST. Proposed LEST control system. Remote control of LEST. Cost estimate. Estimated total cost of control and data reduction system. Title: LEST optical system: Study of solutions for the mirror figures. Authors: Engvold, O.; Brahde, R.; Heier, H. Bibcode: 1985LFTR...10.....E Altcode: The performance of the proposed three-mirror concept for LEST has been analysed in search for solutions that minimize the Seidel spherical aberration, coma, astigmatism, and higher order aberrations. One finds that the combination of paraboloidal surface figure of the primary mirror and ellipsoidals for the secondary and tertiary is suitable for LEST. Title: Simulated Correlation Tracking on Solar Granulation Authors: Andreassen, O.; Engvold, O.; Muller, R. Bibcode: 1985LNP...233...91A Altcode: 1985hrsp.proc...91A The applicability of low contrast granulation images of the sun to telescope tracking over an extended period of time is evaluated. The reliability of correlation tracking in solar telescopes is tested by simulating correlation tracking in a time series of high resolution images of solar granulation. The cross correlation power for images recorded on May 16, 1979 at the Pic-du-Midi Observatory, France is calculated. The relationships between the cross-correlation peak value and time, and the peak value and the overlap area of the two images are analyzed. The data reveal that the granulation structure observed during good seeing shows identifiable peak values of the cross-correlation for time differences less than 8-9 minutes. Examples of the correlation scheme applied to areas of 21 arcsec x 21 arcsec are presented. It is noted that the cross-correlation technique is useful for recognizing an area of the sun for tracking over periods that are several times the lifetime of granules. Title: Excitation mechanisms in the atmospheres of yellow and red giant and supergiant stars Authors: Engvold, O.; Moe, O. K.; Jensen, E.; Joraas, P. Bibcode: 1985ESASP.229..151E Altcode: 1985erbp.symp..151E Far ultraviolet emission line spectra of 16 cool giant and supergiant stars have been obtained with the IUE satellite of ESA, NASA and UK. The bright emission lines in the spectra of these stars are produced primarily through radiative excitation. The formation of chromospheric lines of O I and S I are discussed. The spectra of stars with Teff ≥ 4300K contain emission lines formed at temperatures of 8×104K and 105K which implies that these stars must have transition regions and hot coronas. Title: Den tekniske løsning for LEST. Authors: Engvold, O. Bibcode: 1985ATi....18...51E Altcode: No abstract at ADS Title: The Large European Solar Telescope Authors: Engvold, O. Bibcode: 1985LNP...233...15E Altcode: 1985hrsp.proc...15E The design of the Large European Solar Telescope (LEST) is described. The telescope is a Gregorian system and the optical system is to be used for active and adaptive optics. The mirrors and alignment system for LEST are examined. The high precision tracking of the telescope is achieved by combining low and high frequency response systems. The LEST is placed on a tower to reduce ground turbulence and has an alt-azimuth mount. The three components of the dome, which support the telescope tube, the telescope tube design, and the mirror support system are analyzed. Instrument stations and auxiliary telescope facilities are located underground. The LEST can be operated with the astronomer observing at the site, with the astronomer present in a control station, or with the staff performing an astronomer's written instructions. Diagrams of the LEST's optical system and telescope tube, mounting, and dome structure are provided. Title: The Planning and Preliminary Design of LEST-A Solar Telescope for High Spatial Resolution and Polarimetric Observations Authors: Engvold, O. Bibcode: 1985spit.conf.1126E Altcode: No abstract at ADS Title: The large European solar telescope Authors: Engvold, O. Bibcode: 1985LNP...233...13E Altcode: No abstract at ADS Title: A Deep SWP Echelle Exposure of a Red Dwarf Flare Star: At Microscopii Authors: Engvold, O. Bibcode: 1985iue..prop.2339E Altcode: No abstract at ADS Title: A progress report on the analysis of long exposure SWP high resolution spectra of cool stars. Authors: Linsky, J. L.; Ayres, T. R.; Brown, A.; Carpenter, K.; Jordan, C.; Judge, P.; Gustafsson, B.; Eriksson, K.; Saxner, M.; Engvold, O.; Jensen, E.; Moe, O. K.; Simon, T. Bibcode: 1984NASCP2349..445L Altcode: 1984fiue.rept..445L; 1984IUE84......445L The IUE is the first experiment with sufficient sensitivity to obtain high resolution spectra (lambda/delta lambda is approximately 10,000) of many cool stars in the vitally important 1200 to 2000 A spectral region. These data provide qualitatively new information with which to understand the properties of and structures in the outer atmospheres of these stars. Also, these cool star spectra will be extremely useful in planning for the Space Telescope High Resolution Spectrograph, which will be 1000 times more sensitive than IUE but will be hampered by limited observing time and limited spectral bandwidth in each exposure. Very long exposure, high disperson SWP spectra of many stars located throughout the cool half of the HR diagram were obtained. These 12 to 21 hour exposures were obtained by combining NASA and Vilspa shifts so as to obtain the longest possible exposures at times of low background. Included are dwarf stars of spectral type G0 V to M2 V, G9.5 III to M5 II giants, G2 Ib to M2 Iab supergiants, a number of RS CVn-type systems, and Barium stars. Title: Precise measurements of radial velocities of emission lines in the far-ultraviolet spectra of late-type stars. Authors: Ayres, T. R.; Engvold, O.; Moe, D. K.; Simon, T.; Jordan, C.; Judge, P.; Brown, A.; Linsky, J. L. Bibcode: 1984NASCP2349..468A Altcode: 1984fiue.rept..468A; 1984IUE84......468A The radial velocities of emission lines in deep short wave prime camera echelle exposures of several late-type dwarf and giant stars were measured. The goal was to search for absolute and differential Doppler shifts of emission lines formed at different temperatures in the stellar outer atmospheres analogous to the redshifts of C IV lambda 1548 (10 to the 5th power K) which occur in the solar transition zone. Existing images, taken without the precise radial velocity precautions, of five dwarf stars, four giant stars, and three supergiants are reanalyzed. Title: A Precise Radial Velocity Study of SI III) Lambda 1892 and C III) Lambda 1909 Emission of Beta Draconis Winds or Antiwin Authors: Engvold, O. Bibcode: 1984iue..prop.1996E Altcode: No abstract at ADS Title: Limb Crossing of an Active Region on Sigma Gem Authors: Engvold, O. Bibcode: 1984iue..prop.1995E Altcode: No abstract at ADS Title: Preliminary Results from Studies of High Resolution Line Spectra in Late-type Giant and Supergiant Stars Authors: Engvold, O.; Kjeldseth Moe, O.; Jensen, E.; Jordan, C.; Stencel, R.; Linsky, J. Bibcode: 1984LNP...193..359E Altcode: 1984csss....3..359E No abstract at ADS Title: A wind tunnel study of the LEST structure. Authors: Engvold, O.; Fossum, B.; Holdø, A. E. Bibcode: 1984LFTR....6.....E Altcode: This study focuses on the flow pattern and the associated structural generated turbulence in front of the protubing telescope aperture of LEST. The object is to survey and to investigate structural generated turbulence, and to study practical modifications of the telescope aperture structures which could lead to substantial reduction of the turbulence level. A successful structural design will also reduce vibrations resulting from the fluctuating forces and pressures produced by the air turbulence. Title: LEST design study. Authors: Andersen, T. E.; Dunn, R. B.; Engvold, O. Bibcode: 1984LFTR....7.....A Altcode: No abstract at ADS Title: Large European Solar Telescope (LEST) - A solar telescope for high spatial resolution and polarimetric observations Authors: Engvold, O. Bibcode: 1984vlti.conf..183E Altcode: 1984IAUCo..79..183E The objectives and features of the planned Large European Solar Telescope (LEST) are summarized. The goals of LEST include high spatial resolution close to 0.1 arcsec, high photon flux, adequate pointing and tracking capabilities for observations of subarcsecond solar features for extended periods of time, and provision for accurate polarimetric measurements. The optical system, polarization modulator, thin entrance window and helium-filled light path, telescope mounting and tower, and two-step tracking system are briefly described. Title: Book-Review - Instrumentation for Astronomy with Large Optical Telescopes Authors: Humphries, C. M.; Engvold, O. Bibcode: 1983SSRv...36..430H 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: Redshifts of high-temperature emission lines in the far-ultraviolet spectra of late-type stars. Authors: Ayres, T. R.; Stencel, R. E.; Linsky, J. L.; Simon, T.; Jordan, C.; Brown, A.; Engvold, O. Bibcode: 1983ApJ...274..801A Altcode: High-dispersion IUE spectra of six late-type stars exhibit small but statistically significant differential redshifts of high-temperature emission lines, like Si IV and C IV, with respect to low-temperature lines like S I and O I. A well-exposed, small-aperture spectrum of the active chromosphere binary Capella (Alpha Aurigae A: G6 II+F9 III) establishes that the high-temperature lines are redshifted in an absolute sense with respect to the accurately determined photospheric velocity of the system at single-line phase 0.50. Several possible explanations for the stellar redshifts are discused, including a warm wind (100,000 K) in which aparent redshifts are produced in optically thick lines by an accelerating outfow, and the downflowing component of a vertical circulation system for which the up-leg portion of the flow is too cool, too hot, or too tenuous to be visible in Si IV and C IV. If the second scenario is true, the stellar redshifts may provide an important phenomenological link to the downflows observed in 100,000 K species over magnetic active regions in the sun. Title: Fe II fluorescence in the atmospheres of late type giants and supergiant stars. Authors: Engvold, O.; Jensen, E.; Kjeldseth Moe, O. Bibcode: 1983ITABO..59...65E Altcode: The Fe II triplet lines λλ1785 - 88 Å of UV multiplet 191 are present in high resolution spectra of α Ori (M2 I ab) and β Gru (M3 II) observed with IUE. The middle component of the triplet system is missing in the spectra of giant stars of spectral types K1 - K5. The line flux of the Fe II triplet increases strongly with the stellar Teff. The Fe II lines are most probably formed by fluorescence with the UV radiation field of the stars at λ < 1300 Å. Title: Solar center-limb variation of the Ca II K line and the Wilson-Bappu effect. Authors: Engvold, O.; Marstad, N. C. Bibcode: 1983ITABO..55.....E Altcode: New observations of the quiet Sun Ca II K line center-to-limb (C-L) have been made. The separation of the K2 intensity peaks, the K1 intensity minima, and the intermediate width W0 (the Wilson-Bappu width) are presented. It is shown that the C-L variation of all three parameters can be accounted for as a dependence on chromospheric column mass. The corresponding Ca II K line width parameters of 41 late type stars are also shown to vary in accordance with the inferred chromospheric column mass of the stars. Title: Variability of spectral lines in full-disk observations of the sun. Authors: Barth, S. B.; Brynildsen, N.; Engvold, O. Bibcode: 1983ITABO..59...27B Altcode: Signals of solar activity have been searched for in full-disk line spectra of the sun. In the chromospheric lines Ca II H and K, and Hα, one finds that the central flux varies in concert with solar activity. Hγ shows no clear dependence on activity. Noticeable variations in the Ca II line flux are seen in the course of an hour. The photospheric Fe I λ5250 Å line tends to get deeper with increasing activity. Title: The umbra/photosphere contrast of a large sunspot in high spectral resolution. Authors: Elboth, D.; Engvold, O. Bibcode: 1983ITABO..59...15E Altcode: The relative continuum intensity I(umbra)/I(photosphere) for a large sunspot is derived from high resolution spectral observations with the Fourier Transform Spectrometer of Kitt Peak National Observatory. Preliminary results are presented. A method for straylight correction of the umbral spectrum is discussed. Title: Test of vacuum vs helium in a solar telescope. Authors: Engvold, O.; Dunn, R. B.; Livingston, W. C.; Smartt, R. N. Bibcode: 1983ApOpt..22...10E Altcode: The consequences of filling a solar telescope with helium, a gas with an exceptionally low index of refraction and a high thermal conductivity, are reported. All the tests are conducted with the solar beam present to provide normal heating. Internal seeing of the telescope is evaluated by viewing the image of an He-Ne laser beam in autocollimation reflected from the entrance window for different pressures of air or helium. The total path of the laser beam through the tank (six times) becomes about 100 m. Quantitative measurements of the wave front distortions are derived by inserting a point-diffraction interferometer near the focused image of the laser beam. Excursions of the fringe pattern yield direct measures of the wave front errors in units of the 0.633-micron laser wavelength. It is concluded that a helium-filled telescope is a realistic alternative to a vacuum telescope for solar observations. The barely detectable tank seeing with helium near atmospheric pressure could possibly be rectified either by a high reflectivity coating of the mirrors, which reduces the heat load, or by a forced circulation of the helium in the tank. Title: UV FEII Flourescence in Cool Giant and Supergiant Stars Authors: Engvold, O. Bibcode: 1983iue..prop.1613E Altcode: No abstract at ADS Title: Solar Center / Limb Variation of the CAII K Line and the Wilson / Bappu Effect Authors: Engvold, O.; Marstad, N. C. Bibcode: 1983itab.rept....1E Altcode: No abstract at ADS Title: Absorption Lines of Feh in a Sunspot Spectrum Authors: Wohl, H.; Engvold, O.; Brault, J. W. Bibcode: 1983itab.rept....1W Altcode: No abstract at ADS Title: Determination of Absolute Velocities for Emission Lines in Late-Type Stars Authors: Engvold, O. Bibcode: 1983iue..prop.1716E Altcode: No abstract at ADS Title: Absorption lines of FeH in a sunspot spectrum. Authors: Wöhl, H.; Engvold, O.; Brault, J. W. Bibcode: 1983ITABO..56.....W Altcode: The strengths of the 8690 Å and 9890 Å bands of the FeH molecule are measured in the spectrum of a large sunspot. The strongest lines attain central depths of about 20% of the continuum intensity. Title: Physical conditions in the chromosphere of α Ori. Authors: Kjeldseth Moe, O.; Engvold, O.; Jensen, E. Bibcode: 1983ITABO..59...59K Altcode: No abstract at ADS Title: Stellar activity. Authors: Pettersen, B. R.; Engvold, O. Bibcode: 1983ITABO..60...41P Altcode: The paper discusses some aspects of stellar activity that Scandinavian astronomers have proposed to study with the future Nordic Optical Telescope. It is apparent that solar-type transient phenomena are present and observable in many classes of late type stars. Observations of solar-type phenomena in stars provide informations of fundamental interest for both solar physics and stellar astrophysics. Such observational programs will absorb as much telescope time as is made available to them. Title: LEST, Large European Solar Telescope : report on a study for the Joint Organisation for Solar Obse[r]vations Authors: Engvold, O.; Hefter, M. Bibcode: 1982lest.rept.....E Altcode: No abstract at ADS Title: A High Resolution EUV Spectrum of α Ori Authors: Engvold, O.; Kjeldseth Moe, O.; Jensen, E.; Linsky, J. L.; Stencel, R. E. Bibcode: 1982BAAS...14..651E Altcode: No abstract at ADS Title: Gas Flow in the Chromosphere of α Ori Authors: Kjeldseth Moe, O.; Engvold, O.; Jensen, E.; Linsky, J. L.; Stencel, R. E. Bibcode: 1982BAAS...14..651K Altcode: No abstract at ADS Title: LEST, Large European Solar Telescope : report on a study for the Joint Organisation for Solar Obse[r]vations Authors: Engvold, Oddbjørn.; Hefter, Manfred Bibcode: 1982ROLun..18...13E Altcode: No abstract at ADS Title: Turbulent Velocity Fields in Quiescent Prominences Authors: Jensen, E.; Engvold, O. Bibcode: 1982ASSL...96..131J Altcode: 1982spls.meet..131J The results of the high resolution spectrographic temporal evolution examination of nine quiescent prominences observed during 1973-74 are presented. Digital analysis of the spectrograms was carried out by a computer controlled microphotometer, yielding a velocity interval, radial velocity distribution, and Gaussian distributions. A total of 3-4000 profiles were obtained. All but one of the velocity distributions were Gaussian, while the alpha-parameter showed large scatter, from 2.4-16 km/sec, averaging 6.3 km/sec. Most of the velocity spectra were in the supersonic range. The most probable velocity, alpha, was concluded to vary with individual prominences and changed position within each prominence. The theory of incompressible MHD turbulence was found to be inapplicable. Extension of the temporal evolution technique to disk filaments is indicated. Title: High dispersion far ultraviolet spectra of cool stars. Authors: Stencel, R. E.; Linsky, J. L.; Ayres, T. R.; Jordan, C.; Brown, A.; Engvold, O. Bibcode: 1982NASCP2238..259S Altcode: 1982auva.nasa..259S; 1982IUE82......259S; 1982NASCP2338..259S Recent far ultraviolet high dispersion spectra of two cool supergiant stars, Beta Dra (G2 Ib) and Alpha Ori (M2 Iab) are examined in the context of current questions regarding stellar chromospheres, coronae and mass loss. These stars show very different outer atmosphere structure. Beta Dra has a geometrically thin transition region with bright emission lines of 100,000 K plasma that are red-shifted, indicating downflow in magnetic flux tubes. By contrast, Alpha Ori has a cool extended chromosphere and circumstellar envelope with large mass loss. Title: Solar telescopes filled with helium Authors: Engvold, O.; Brahde, R.; Fossum, B. Bibcode: 1981PASP...93..526E Altcode: An experiment has been carried out in order to investigate the qualities of He in an optical path. It is shown that He gas may absorb a heat flux more than 30 times larger than air to produce the same optical effects. The factor increases to about 100 at 0.5 atmospheric pressure. The result supports an earlier suggestion that helium in the telescope light pass will substantially improve the internal seeing. Title: The Small Scale Velocity Field of a Quiescent Prominence Authors: Engvold, O. Bibcode: 1981SoPh...70..315E Altcode: The small scale velocity field of a large quiescent prominence is studied from simultaneous filtergrams in the red and violet wings of the Ca II K-line. Title: IUE Echelle Mode Observations Contrasting Coronal and Non-Coronal Late Type Giant and Supergiant Stars Authors: Brown, A.; Stencel, R. E.; Linsky, J. L.; Jordan, C.; Engvold, O. Bibcode: 1981BAAS...13..885B Altcode: No abstract at ADS Title: Large European Solar Telescope (lest) - a Preparatory Study Authors: Engvold, O.; Hefter, M. Bibcode: 1981siwn.conf..295E Altcode: No abstract at ADS Title: Identification of the CrH molecule in a sunspot spectrum. Authors: Engvold, O.; Woehl, H.; Brault, J. W. Bibcode: 1980A&AS...42..209E Altcode: The 6Σ+ - 6Σ+ infrared system of the CrH molecule has been identified in the spectrum of a large sunspot. Title: Thermodynamic Models and Fine Structure of Prominences Authors: Engvold, O. Bibcode: 1980SoPh...67..351E Altcode: Observed Hα brightness versus size of emission substructures of quiescent prominences are compared with values predicted from thermodynamical models. The measured size of an emission element of a given brightness is substantially less than the theoretical value. Title: The influence of spatial resolution on the Ca/+/K line width and shift in a quiescent prominence Authors: Engvold, O.; Wiehr, E.; Wittmann, A. Bibcode: 1980A&A....85..326E Altcode: A series of 17 spectrograms of the Ca+ K line in a large quiescent prominence are investigated for the effects of spatial smearing due to seeing. It is found that the full width at half- maximum (FWHM) decreases from 0.190 Å to 0.125 Å when the spatial resolution increases from 15" to about 2". High spatial resolution also facilitates the detection of large line shifts Δλ. The narrowest line profiles - which are detected in the case of high spatial resolution and large shift - yield FWHMmin ≍ 0.090 Å, which exceeds the pure thermal broadening width by a factor of 2-3. The most probable value of the resolved macroscopic velocity is found to be 23 km s-1. This velocity corresponds to an equipartition magnetic field strength of about 3.8 G. Title: Energy and mass injected by flares and eruptive prominences Authors: Engvold, O. Bibcode: 1980IAUS...91..173E Altcode: Various types of dynamic events at chromospheric levels and in the lower corona are described, and an attempt is made to evaluate their significance with respect to coronal disturbances. The strong evidence that ascending prominences and flare sprays are essential in the process that brings about observable coronal transients is considered. It is concluded that flare sprays and ascending prominences all consist of matter situated in the lower corona prior to the disruption, that surges follow pre-existing lines of force, and that eruptive prominences are driven by, and move with, the magnetic field. Title: Introduction to the workshop Authors: Engvold, O. Bibcode: 1980fsoo.conf....7E Altcode: No abstract at ADS Title: Protuberanser i solens korona. Authors: Engvold, O. Bibcode: 1980kosm.conf..101E Altcode: No abstract at ADS Title: Kinematics of a loop prominence. Authors: Engvold, O.; Jensen, E.; Andersen, B. N. Bibcode: 1979SoPh...62..331E Altcode: The kinematics of a loop system has been studied from high resolution Ca II K line spectra and Hα filtergrams recorded at Oslo Solar Observatory. Title: High Resolution CA II K Spectra of the September 8, 1977 Loop System. Authors: Albregtsen, F.; Engvold, O. Bibcode: 1979phsp.coll..246A Altcode: 1979phsp.conf..246A; 1979IAUCo..44..246A A spectrum analysis of the high resolution Ca II K line observations of the September 8, 1977 solar loop system recorded with the main spectrograph at the Oslo Solar Observatory is presented. The loop system was located at the east limb (N 10), and the planes of the individual loops appeared to be oriented at angles of 75-90 deg relative to the line of sight. The forms of the loops fit well to that of the lines of force of a dipole. The maximum brightness of individual loop structures was measured taking into account the solar radiation scattering by the earth's atmosphere. The half widths at 1/e times the maximum intensity of the emission line profiles were also measured. It is believed that the noticeable scatter of points in the graph of the value of the brightness of the loop leg structures versus the half widths can be accounted for by a time variable seeing. A curve through the points of maximum brightness versus line width is likely to be closer to the real line brightness than is the average for the observed points. It is concluded that there is an increase of brightness with increasing line width. There is also an increase in line shift with increasing line width, indicating that the velocity dispersion is velocity dependent. Measurements of the position of individual emission elements along the various loop legs as a function of time made from the H-alpha slit jaw filtergrams are also discussed. Title: Kinematics of a system of loop prominences Authors: Engvold, O.; Jensen, E.; Andersen, B. N. Bibcode: 1979phsp.coll..237E Altcode: 1979IAUCo..44..237E; 1979phsp.conf..237E An analysis of the mass motion of solar flare loop prominences is presented based on 72 K-line and Ca II spectra of a system of bright loop prominences observed on April 23, 1978 at the Oslo Solar Observatory. The spectral characteristics are compared with the simplest model possible, that of free fall of matter under gravity along the legs of the loops, assuming that the outlines of the loops reflect the form of the magnetic lines of force. The line of sight velocity is then computed as a function of distance from the top of the loop by multiplication with the cosine of the angle between the line of sight and the tangent to the dipole line of force. The spectral data are in accordance with a model where the matter starts from rest at the top of the loop and falls down along the legs. The present loop system matches the line of force of a dipole for the scale, R, of the dipole loop between 110,000 and 150,000 km. Since the observed heights of the loops are 60-90,000 km it is concluded that the dipole origin is located in the neighborhood of 50,000 km below the photosphere. Title: Discussion Authors: Acton, L. W.; Engvold, O.; Heasley, J. N.; Heyvaerts, J.; Hirayama, T.; Kundu, M. R.; Leroy, J. L.; Malville, J.; Rust, D. M.; Zirin, H. Bibcode: 1979phsp.coll...31A Altcode: 1979IAUCo..44...31A No abstract at ADS Title: Proceedings of the JOSO workshop: Future solar optical observations - needs and constraints. Firenze, November 7 - 10, 1978. Authors: Godoli, G.; Noci, G.; Righini, A.; Pacini, F.; Engvold, O.; Harvey, J. W. Bibcode: 1979MmArc.106....1G Altcode: No abstract at ADS Title: Discussion Authors: Acton, L. W.; Engvold, O.; Milkey, R. W.; Orrall, F. Q.; Zirin, H. Bibcode: 1979phsp.coll..354A Altcode: 1979IAUCo..44..354A No abstract at ADS Title: Orientation of Prominence Microstructure Relative to the Direction of the Magnetic Field. Authors: Engvold, O.; Leroy, J. L. Bibcode: 1979phsp.coll...97E Altcode: 1979phsp.conf...97E; 1979IAUCo..44...97E A set of simultaneous observations of the magnetic field and microstructure in a prominence are used to study how the microstructures are oriented relative to the magnetic field. The observations include measurements of the polarization of the He I D3 line at 11 different positions in the prominence and simultaneous Ca II K-line filtergrams of the same prominence. The results show that horizontally and vertically oriented microstructures are associated with 'large' and 'small' angles of inclination, respectively. This is taken as evidence that the microstructure and the magnetic field have the same orientation. Title: Frequency Redistribution Effects in the Formation of Lyman a in Prominences and Their Influence on the Ratio of Hα to Lα. Authors: Milkey, R. W.; Heasley, J. N.; Schmahl, E. J.; Engvold, O. Bibcode: 1979phsp.coll...53M Altcode: 1979IAUCo..44...53M No abstract at ADS Title: Discussion Authors: Acton, L. W.; Engvold, O.; Landman, D. A. Bibcode: 1979phsp.coll...47A Altcode: 1979IAUCo..44...47A No abstract at ADS Title: Discussion Authors: Engvold, O.; Gaizauskas, Gaizauskas; Rust, D. M.; Sheeley, N.; Tandberg-Hanssen, E.; Ohman, Y.; Zirin, H. Bibcode: 1979phsp.coll..207E Altcode: 1979IAUCo..44..207E No abstract at ADS Title: Discussion Authors: Acton, L. W.; Anzer, U.; Engvold, O.; Martin, S. F.; Pneuman, G. W.; Rust, D. M.; Tandberg-Hanssen, E.; Zirin, H. Bibcode: 1979phsp.coll..164A Altcode: 1979IAUCo..44..164A No abstract at ADS Title: Discussion Authors: Anzer, U.; Engvold, O.; Spicer, D. S.; van Tend, W.; Zirin, H. Bibcode: 1979phsp.coll..331A Altcode: 1979IAUCo..44..331A No abstract at ADS Title: The Ca II line width in late type stars. The Wilson-Bappu effect. Authors: Engvold, O.; Rygh, B. O. Bibcode: 1978A&A....70..399E Altcode: Summary. The Ca II H and K line profiles are analysed from high resolution spectra of 26 late type stars and the Sun. The difference in wavelength (AK1) between the center of the K line and the K1 intensity minima of the stars yields a Wilson-Bappu type relationship. The equivalent parameter for the K2 peak intensities, AK2, provides an upper value of the Doppler widths. On the average the width AK1 is found to be > 7.8 + 1.7 Doppler widths, i.e. K1 is situated in the damping wing of the line absorption coefficient. For the Wilson-Bappu line width W0 we find that Wo > 4.8+0.6 Doppler widths. Neither K1 nor W0 are therefore noticeably influenced by the turbulent velocities in the stellar chromospheres. It is shown that W0 and AK1 are mainly determined by chromospheric mass column densities of the stars. The widths of the absorption line wings of the H and K lines broadens with increasing mass column density above the photospheres. Key words: Wilson-Bappu effect - stellar chromospheres - stellar Ca ii H and K lines. Title: The fine structure of prominences. Authors: Engvold, O.; Malville, J. M.; Livingston, W. Bibcode: 1978SoPh...60...57E Altcode: At least 1/3 of all quiescent prominences contain Doppler shifted features associated with their edges or emission gaps between prominence sub-structures. The individual spectral structures have lifetimes of 5-15 min, dimensions perpendicular to the edge of 1-2 arc sec, and may be lined along the visible edge of a prominence for distances up to 30 arc sec. The velocities average 30-40 km s-1. The emission line profiles are generally complex and may consist of several components. Their Ca II K, He I D3, and Hα line intensity ratios may be interpreted by a slightly higher temperature than average for the prominence. Title: The fine structure of prominences. IV: Spectral observations. Authors: Engvold, O. Bibcode: 1978SoPh...56...87E Altcode: High spatial resolution spectral observations of five hedgerow prominences were made in Hα, He I D3 and Ca II H and K. Title: Introduction to the workshop Authors: Engvold, O. Bibcode: 1978fsoo.conf....7E Altcode: No abstract at ADS Title: Active edges of quiescent prominences. Authors: Malville, J. M.; Engvold, O.; Livingston, W. Bibcode: 1977BAAS....9R.569M Altcode: No abstract at ADS Title: Active Edges of Quiescent Prominences. Authors: Malville, J. M.; Engvold, O.; Livingston, W. Bibcode: 1977BAAS....9..569M Altcode: No abstract at ADS Title: The solar chemical composition. Authors: Engvold, O. Bibcode: 1977PhyS...16...48E Altcode: Consideration is given to solar chemical composition in terms of the work of Goldberg et al. (1960) and the modifications which have been made to the adopted abundances of several elements. Data obtained from various sources are discussed, noting photosphere and sunspots, the chromosphere, prominences and corona, and solar flare particles and the solar wind. Solar chemical abundances of helium, lithium, beryllium, and boron are outlined. Title: The fine structure of prominences. III. Small scale Doppler shifted features. Authors: Engvold, O.; Malville, J. M. Bibcode: 1977SoPh...52..369E Altcode: Faint, Doppler shifted, emission features are detected in high resolution spectra of limb prominences. Their average line-of-sight velocity is about 3 × 106 cm s-1, their average life time is 300 s, and their angular sizes are ≲108 cm in our spectrograms. The emission line width of the spectral features increases with increasing line shift. Title: On Pikel'ner's theory of prominences. Authors: Engvold, O.; Jensen, E. Bibcode: 1977SoPh...52...37E Altcode: Pikel'ner computed a stationary solution for coronal gas streaming along a magnetic arch, which develops into a dense condensation similar to prominence matter. This paper discusses the choice of boundary conditions and presents additional solutions. Title: The Ca II emission lines in quiescent prominences. Authors: Heasley, J. N.; Milkey, R. W.; Engvold, O. Bibcode: 1977SoPh...51..315H Altcode: Observations of the Ca II H, K, and infrared triplet lines are compared with theoretical predictions from the slab models of Heasley and Milkey (1976). While the theoretical models describe the hydrogen and helium emission spectra of quiescent prominences satisfactorily the predicted Ca II lines are systematically too bright. The most likely reason for the discrepancy is the inapplicability of the symmetric slab prominence model for lines which become even moderately optically thick in prominences. Title: Magnetic Field Annihilation in Active Prominences. Authors: Malville, J. M.; Engvold, O. Bibcode: 1977BAAS....9R.315M Altcode: No abstract at ADS Title: Solen--en innforing i moderne solfysikk Authors: Jensen, Eberhart; Engvold, Oddbjorn Bibcode: 1977sole.book.....J Altcode: No abstract at ADS Title: The fine structure of prominences. I: Observations - Halpha filtergrams. Authors: Engvold, O. Bibcode: 1976SoPh...49..283E Altcode: The fine structure of nonspot prominences are studied from Hα filtergrams. The size of the smallest prominence structures increases with height above the chromosphere. Some prominences contain structures close to 1/2 arc second, which is the spatial resolution in the present data. The effective thickness of many nonspot prominences ranges between 4 × 107 cm and 1.5 × 108 cm. An apparent downward directed motion is observed in the majority of the prominences. No preferred direction of the motion is seen in regions composed of comparatively large diffuse structures. Some bright threads are visible for 1 hr and longer. Bright knots have an average observed lifetime of about 8 min. The process of condensation and subsequent destruction of prominence fine structure appears to take place on a very short time scale compared to the life time of the regions where prominences may exist. The observed Hα brightness of the prominences in the present data may be accounted for as scattered chromospheric radiation. Title: The eruptive prominence of June 8, 1974. Authors: Engvold, O.; Malville, J. Mckim; Rustad, B. M. Bibcode: 1976SoPh...48..137E Altcode: Filtergrams and spectra of a disparition brusque are discussed. The total mass of the prominence prior to eruption is estimated to be ∼-2×1015g. A prominence had erupted 41/2 days earlier from the same active region. The eruptive prominence which we observed formed some 11 0000 km above the photosphere. In the later phase of the eruption the outward acceleration approached the acceleration due to gravity at the same height. Down falling material along vertical structures was observed with velocities exceeding 100 km s−1. The vertical structures became twisted during the eruption indicating a field aligned current of approximately 1010 amps. Title: Noen resultater av soleksperimentene med ATM, Skylab. Authors: Engvold, O. Bibcode: 1976ATi.....9...11E Altcode: No abstract at ADS Title: Kitt Peak National Observatory's 60-cm Vakuumteleskop Authors: Engvold, O. Bibcode: 1976ATi.....9..145E Altcode: No abstract at ADS Title: Prominence Eruption Accompanied by Twist Readjustment Authors: Jockers, K.; Engvold, O. Bibcode: 1975SoPh...44..429J Altcode: In this note we discuss observations of two eruptive prominences. We find evidence for twisting motions in the early stages of the eruption. This twisting may be caused by a mechanism recently discussed by Parker (1974) and by Jockers (1976) wherein a magnetic flux tube, part of which has expanded because of reduction of external pressure, readjusts the magnetic torque along its axis. Title: A reduced upper limit to the solar boron abundance. Authors: Hall, D. N. B.; Engvold, O. Bibcode: 1975ApJ...197..513H Altcode: A new upper limit on the solar boron abundance has been obtained from observations of the photospheric spectrum in the 16240 A region. We flnd N0(B)/N0(H) < 1.2 i 0.6 >c 10-10. The implications of this result for the boron abundance in the primitive solar material are discussed. Subject headings: abundances, solar - spectra, infrared - spectra, solar Title: Spectral and Slitjaw Observations of an Eruptive and Untwisting Filament Authors: Jockers, K.; Engvold, O. Bibcode: 1975BAAS....7..349J Altcode: No abstract at ADS Title: A comparison of spicules in the Hα and HeII (304 Å) lines Authors: Moe, Olav Kjeldseth; Engvold, Oddbjorn; Beckers, Jacques Maurice Bibcode: 1975SoPh...40...65M Altcode: No abstract at ADS Title: An analytical representation for photographic characteristic curves. Authors: Tsubaki, T.; Engvold, O. Bibcode: 1975AASPB...9...17T Altcode: No abstract at ADS Title: Elemental abundances, isotope ratios and molecular compounds in the solar atmosphere Authors: Engvold, O.; Hauge, O. Bibcode: 1974STIN...7521202E Altcode: Solar abundances of chemical elements and solar isotope ratios are tabulated. The solar abundances of 67 elements are known. In addition, the upper limits for the abundances of 5 elements are listed. Isotope ratio investigations were carried out for 16 elements. A separate list presents 21 molecules which have been identified in the solar atmosphere and another 15 which may be termed 'possibly found'. Title: An Eruptive Prominence of June 10, 1973 Authors: Engvold, O.; Rustad, B. M. Bibcode: 1974SoPh...35..409E Altcode: An eruptive prominence of June 10, 1973, showing ascending and expanding motions, has been recorded spectroscopically at Oslo Solar Observatory. Title: N. U. Mayall-teleskopet ved Kitt Peak National Observatory. Authors: Engvold, O. Bibcode: 1974ATi.....7...97E Altcode: No abstract at ADS Title: A high dispersion spectrum 6610 Å to 6770 Å of a large sunspot Authors: Engvold, O. Bibcode: 1973A&AS...10...11E Altcode: A high dispersion spectrum (8.5 mm/A) in the range 6610-6770A of a large sunspot (Roma No 5367) has been recorded photographically at Oslo Solar Observatory. Nearly simultaneous broad band observations of umbral/photospheric contrast and drift curves across the solar limb were made in the same spectral region using a pinhole photometer. The umbral/photospheric continuum contrast corrected for parasitic light in the umbra is found to be 0.106+0.016 in this spectral range for this particular sunspot. The intensity profile of the umbral line spectrum is presented (corrected for parasitic light). A total of 1649 umbral lines are detected within the observed spectral range. Of these we find 1256 lines from the TiO molecule, 2 lines of CaH and 14 atomic lines. The wavelengths and central intensities of umbral lines are tabulated. Key words: sunspot spectrum - TiO molecular spectrum Title: New identifications of disk emission lines in the Ca II H and K line wings Authors: Engvold, O.; Halvorsen, H. D. Bibcode: 1973SoPh...28...23E Altcode: No abstract at ADS Title: Det første bemannede rom-observatorium for solforskning. Authors: Engvold, O. Bibcode: 1973ATi.....6....3E Altcode: No abstract at ADS Title: The Internal Motion of Quiescent Prominences Authors: Engvold, Oddbjörn Bibcode: 1972SoPh...23..346E Altcode: A study has been made of fine structure wavelength shift in the K line spectra from quiescent prominences. A persistent small scale motion is found in the prominence main body. In places where we see the characteristic thread like fine structure in the accompanying Hα filtergrams the average line-of-sight velocity amplitude is about 1 km s−1. A higher velocity (≈ 4 km s−1) is associated with a slightly coarser, mottled prominence fine structure. In the low lying regions, connecting the prominence body and the chromosphere, we do not detect any fine structure line shift (v ⩽ 1/2 km s−1). Title: Om solens kjemiske sammensetning og grunnstoffenes dannelse. Authors: Engvold, O. Bibcode: 1972ATi.....5..121E Altcode: No abstract at ADS Title: High Dispersion Spectroscopic Study of Quiescent Prominences Authors: Engvold, O.; Livingston, W. Bibcode: 1971SoPh...20..375E Altcode: The utility of very high dispersion spectra (5-11 mm/Å) for the study of line profile and velocity structure in quiescent prominences is demonstrated by observations, taken with the spectregraphic slit positioned normal to the limb in Hα λ6563 Å, He D3 λ5876 Å, and Ca+K λ3933 Å. The emission profiles of both Hα and the K line often show a central reversal (absorption). Emission structures in the K-line can be complex with details as narrow as 0.04 Å. Frequently this structure consists of two distinct components: a central, strong, rather narrow line, and an often displaced, weak feature of undefined profile appearing as `fuzz'. It is suggested that this fuzz indicates an exchange of matter between the prominence and the corona. Title: Self-Reversal of the Lithium Resonance Doublet in Sunspots Authors: Maltby, P.; Engvold, O. Bibcode: 1970SoPh...14..129M Altcode: No abstract at ADS Title: Simultaneous Measurements of Magnetic Fields and Brightness Fields Using a 4-Image Spectroheliograph Authors: Sheeley, N. R., Jr.; Engvold, O. Bibcode: 1970SoPh...12...69S Altcode: The use of an auxiliary beamsplitter with the Kitt Peak 15-foot spectroheliograph permits spectroheliograms to be taken simultaneously in 4 identical images of the sun. By using two of these images for a Zeeman spectroheliogram, a third image for a FeI λ4071 spectroheliogram, and the fourth image for a 6107Å continuum spectroheliogram, simultaneous measurements of magnetic fields and brightness fields have been obtained. Within the limits of intensity variations imposed by doppler shifts and brightness fluctuations of the continuum, a quantitative relation does exist between the measured values of brightness and magnetic field strength of the photospheric network. For intensities measured +0.12 Å from the core of FeI λ4071, this relation is ln(1 +ΔI/I) = α¦B¦, whereB refers to the component of magnetic field normal to the solar surface,ΔI/I is the fractional excess of brightness of the magnetic regions relative to the brightness of non-magnetic regions, and α = (6±2)%/100 gauss. Title: The Diatomic Molecules BH, BN, and BO in Sunspots and the Solar Abundance of Boron Authors: Engvold, O. Bibcode: 1970SoPh...11..183E Altcode: Absorption band spectra of BH and BO have been searched for and not found in spectra of sunspots. Title: Solar abundance determination. Authors: Engvold, O.; Hauge, Ø. Bibcode: 1970bfs..conf..351E Altcode: No abstract at ADS Title: Double-K_{2} Emission Line Observed in Sunspots and in Prominences Authors: Engvold, O.; Livingston, W. Bibcode: 1969PASP...81..795E Altcode: 0. ENGVOLDt Institute for Theoretical Oslo, Norway AND W. LIVINGSTON Kitt Peak National Observatory} Tucson, Arizona fteceived September 2, 1969 Title: On the Position of Sunspots in the Core of Hα Relative to the Continuum Authors: Engvold, Oddbjörn Bibcode: 1969SoPh....8..284E Altcode: The relative position of sunspots as observed in the core of Hα and in the continuum has been studied in 316 spectra of 84 different sunspots. We find that chromospheric features surrounding sunspots may produce apparent shifts of the spots in the core and in the wing of Hα. In addition a shift directed towards the limb is found. This shift is found to be a height effect. The difference in height between the levels of the Hα core and the continuum varies from 2300 km to 1000 km for different sunspots. Title: Spectroheliograms in Fe II λ4924 Authors: Sheeley, N. R., Jr.; Engvold, O. Bibcode: 1969BAAS....1T.292S Altcode: No abstract at ADS Title: The Abundance of Beryllium in the Solar Atmosphere Authors: Hauge, O.; Engvold, O. Bibcode: 1968ApL.....2..235H Altcode: No abstract at ADS Title: A spectroscopic study of the Hα profile of moustaches Authors: Engvold, O.; Maltby, P. Bibcode: 1968mmsf.conf..109E Altcode: No abstract at ADS Title: On the K Line of CaII in Sunspots Authors: Engvold, O. Bibcode: 1967SoPh....2..234E Altcode: No abstract at ADS Title: On the K-line of Ca II in sunspots. Authors: Engvold, Oddbjørn Bibcode: 1967ApNr...10..173E Altcode: No abstract at ADS Title: Simultaneous observations of HA and the K-line of CA II in the solar spectrum. Authors: Engvold, Oddbjorn Bibcode: 1967sohk.book.....E Altcode: 1967QB461.O8n24.... No abstract at ADS Title: On the K-line of CaII in sunspots. Authors: Engvold, Oddbjorn Bibcode: 1967oklc.book.....E Altcode: 1967QB1.A86v10n9... No abstract at ADS Title: On the center-limb variation of the H- and K-line of Ca II. Authors: Engvold, Oddbjørn Bibcode: 1966ApNr...10..101E Altcode: No abstract at ADS Title: On the center-limb variation of the H- and K-lines of CaII. Authors: Engvold, Oddbjorn Bibcode: 1966oclv.book.....E Altcode: 1966QB1.A86v10n6... No abstract at ADS Title: Measurements of the center-limb variation in the H- and K-lines of CaII in undisturbed and active regions on the sun. Authors: Engvold, Oddbjorn Bibcode: 1966mclv.book.....E Altcode: 1966QB461.O8n17.... No abstract at ADS