engvold

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Author name code: engvold
ADS astronomy entries on 2022-09-14
author:"Engvold, Oddbjorn"

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Title: Cornelis de Jager: In Memoriam
Authors: Rutten, Robert J.; Engvold, Oddbjørn; Nieuwenhuizen,
Adrianus C. T.
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.

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Title: Synergies among the IAU Offices
Authors: Govender, Kevin; Cheung, Sze-Leung; Aretxaga, Itziar;
Engvold, Oddbjørn
2020IAUGA..30..563G Altcode:
No abstract at ADS

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Title: IAU's Interaction with Young Astronomers
Authors: Engvold, Oddbjorn
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.

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Title: Preface
Authors: Engvold, Oddbjørn; Vial, Jean-Claude; Skumanich, Andrew
2019sgsp.bookD..17E Altcode:
No abstract at ADS

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Title: Chapter 12.2 - High-Resolution Ground-Based Observations of
the Sun
Authors: Engvold, Oddbjørn; Zirker, Jack B.
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 Î¼m 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.

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Title: Chapter 1 - Discoveries and Concepts: The Sun's Role in
Astrophysics
Authors: Zirker, Jack B.; Engvold, Oddbjørn
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.

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Title: The Sun as a Guide to Stellar Physics
Authors: Engvold, Oddbjørn; Vial, Jean-Claude; Skumanich, Andrew
2019sgsp.book.....E Altcode:
No abstract at ADS

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Title: The Parallel Worlds of Christoph Scheiner and Galileo Galilei
Authors: Engvold, Oddbjørn; Zirker, Jack B.
2016JHA....47..332E Altcode:
No abstract at ADS

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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
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.

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Title: Observing Cascades of Solar Bullets at High Resolution. II.
Authors: Scullion, E.; Engvold, O.; Lin, Y.; Rouppe van der Voort, L.
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.

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Title: Distinguishing Between Different Types of Prominences
Associated with Solar Flares
Authors: Martin, Sara F.; Engvold, Oddbjorn; Lin, Yong
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.

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Title: Description and Classification of Prominences
Authors: Engvold, Oddbjørn
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.

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Title: Solar Prominences
Authors: Vial, Jean-Claude; Engvold, Oddbjørn
2015ASSL..415.....V Altcode:
No abstract at ADS

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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.
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.

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Title: Astronomy and Astrophysics, Volume II
Authors: Engvold, Oddbjørn; Stabell, Rolf; Czerny, Bozena; Lattanzio,
John
2012aaa2.book.....E Altcode:
No abstract at ADS

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Title: Astronomy and Astrophysics, Volume I
Authors: Engvold, Oddbjørn; Stabell, Rolf; Czerny, Bozena; Lattanzio,
John
2012aaa1.book.....E Altcode:
No abstract at ADS

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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.
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.

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Title: Small-scale, Dynamic Bright Blobs in Solar Filaments and
Active Regions
Authors: Lin, Y.; Engvold, O.; Rouppe van der Voort, L. H. M.
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.

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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.
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.

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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.
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.

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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
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.

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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.
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.

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Title: A Method of Resolving the 180-Degree Ambiguity by Employing
the Chirality of Solar Features
Authors: Martin, S. F.; Lin, Y.; Engvold, O.
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.

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Title: The Unique 3D Magnetic Structure of Filaments
Authors: Lin, Y.; Engvold, O.; Martin, S.; Panasenco, O.
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.

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Title: Observational aspects of prominence oscillations
Authors: Engvold, Oddbjørn
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.

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Title: Filament Substructures and their Interrelation
Authors: Lin, Y.; Martin, S. F.; Engvold, O.
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.

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Title: Chromospheric and coronal manifestations of photospheric
cancelling magnetic fields
Authors: Panasenco, Olga; Martin, Sara F.; Engvold, Oddbjorn
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.

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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.
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.

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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
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.

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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
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.

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Title: Evidence of Traveling Waves in Filament Threads
Authors: Lin, Y.; Engvold, O.; Rouppe van der Voort, L. H. M.; van
Noort, M.
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.

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Title: Reports on Astronomy 2003-2005 (IAU XXVIA)
Authors: Engvold, Oddbjorn
2007reas.book.....E Altcode:
No abstract at ADS

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Title: Comparisons of the Spines of Prominences (Filaments) in Hα
and He II (304Å) Images
Authors: Martin, Sara F.; Engvold, O.; Lin, Y.
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.

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Title: Reports on Astronomy 2003-2005 (IAU XXVIA)
Authors: Engvold, Oddbjorn
2007IAUTA..26.....E Altcode:
No abstract at ADS

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Title: The IAU Role
Authors: Engvold, Oddbjørn
2007IAUS..236..467E Altcode:
No abstract at ADS

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Title: A Simple Method of Resolving the 180 Degree Ambiguity Employing
the Chirality of Solar Features
Authors: Martin, Sara F.; Lin, Y.; Engvold, O.
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.
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
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.
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.
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.
2005SoPh..230....1R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Editorial
Authors: Engvold, Oddbjorn; Harvey, Jack; Švestka, Zdenek
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.
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.
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
2005HiA....13.....E Altcode:
Contents: Preface. I. Joint discussions - 1. Non-electromagnetic
windows for astrophysics. 2. Mercury. 3. Magnetic field &amp;
helicity in the Sun &amp; heliosphere. 4. Astrophysical impact of
abundances in globular clusters. 6. Extragalactic globular clusters
&amp; their host galaxies. 7. The Sun &amp; 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 &amp; challenges for the Sun and stars. 13. Extragalactic
binaries. 14. Formation of cometary material. 15. Elemental
abundances in old stars &amp; damped Lyman-alpha systems. 16. The
International Celestial Reference System: Maintenance &amp; future
realization. 17. Atomic data for X-ray astronomy. 18. Quasar cores
&amp; 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
2005HiA....13D..29E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Structures and Dynamics of Solar Filaments - challenges in
observing and modeling
Authors: Engvold, Oddbjørn
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 <ASTROBJ>UX Ari</ASTROBJ>
Authors: Aarum Ulvås, V.; Engvold, O.
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
<ASTROBJ>RS CVn</ASTROBJ> system <ASTROBJ>UX Ari</ASTROBJ>, 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 <ASTROBJ>UX
Ari</ASTROBJ>. 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 <ASTROBJ>UX
Ari</ASTROBJ> 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 <ASTROBJ>UX Ari</ASTROBJ> system get
bluer as it gets darker?
Authors: Aarum Ulvås, V.; Engvold, O.
2003A&A...399L..11A Altcode:
We present simplified calculations of <ASTROBJ>UX Ari</ASTROBJ> 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 (<ASTROBJ>UX Ari</ASTROBJ> 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.
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.
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
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
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.
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.
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
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
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.
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
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.
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.
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.
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
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
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.
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.
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.
1998ESASP.421..239E Altcode: 1998sjcp.conf..239E
No abstract at ADS

---------------------------------------------------------
Title: Observations of Filament Structure and Dynamics (Review)
Authors: Engvold, O.
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.
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.
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.
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
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.
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.
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.
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 &amp; heliosphere. Reports 1996 from IAU
Commissions 10, 12 and 49.
Authors: Engvold, O.; Deubner, F. -L.; Ripken, H.
1997IAUTA..23..119E Altcode:
Commissions 10: Solar activity, 12: Solar radiation &amp; structure,
49: The interplanetary plasma &amp; the heliosphere.

---------------------------------------------------------
Title: Problem areas in prominence research.
Authors: Engvold, O.
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.
1997IAUTA..23..121E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Filament channels in the corona.
Authors: Engvold, O.
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.
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.
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.
1996ESOC...54..393O Altcode: 1996adop.conf..393O
No abstract at ADS

---------------------------------------------------------
Title: Mapping of Chrosmospheric Active Regions on UX Ari
Authors: Engvold, O.
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.
1995IAUS..176P.165E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Flows in Quiescent Prominences
Authors: Zirker, Jack B.; Engvold, Oddbjorn; Yi, Zhang
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.
1994IAUS..154..579E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Filament oscillations as evidence for Alfvén waves
Authors: Jensen, Eberhart; Yi, Zhang; Engvold, Oddbjorn
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.
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.
1994smf..conf..366M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: An Overview of the LEST Live Optics
Authors: Andersen, T.; Engvold, O.; Jakobsson, H.
1993rtpf.conf...53A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Design of the LEST Slow Wavefront Sensor
Authors: Owner-Petersen, M.; Darvann, T.; Engvold, O.
1993rtpf.conf...63O Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Prospects for future ground-based solar observations.
Authors: Engvold, O.
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
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.
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.
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.
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
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
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
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 &lt;
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.
1992iue..prop.4410E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Are stellar flares a result of magnetic reconnection?
Authors: Elgarøy, Ø.; Engvold, O.
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
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.
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
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.
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.
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.
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.
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
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
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.
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.
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.
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.
1990nwus.book..451E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: New Observational Aspects
Authors: Engvold, O.
1990IAUS..138..469E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Vertical Flows in a Quiescent Filament
Authors: You, J. Q.; Engvold, O.
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
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
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.
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.
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.
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.
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.
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.
1989HvaOB..13..205E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Prominence environment
Authors: Engvold, Oddbjorn
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.
1989iue..prop.3594E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Vertical flows in a quiescent filament.
Authors: You, Jian-Qi; Engvold, O.
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.
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.
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.
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.
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
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.
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.
1988LFTR...34.....S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Prominence environment.
Authors: Engvold, O.
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.
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
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.
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.
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.
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.
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.
1987pwoa.book.....M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Wilson-Bappu Relationship - a Barometric Effect
Authors: Engvold, O.; Elgaroøy, Ø.
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.
1987stmo.book.....E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Objectives and conditions for the LEST site survey.
Authors: Engvold, O.
1987LFTR...26....7E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Old and New Views of Solar Prominences
Authors: Livingston, W. C.; Engvold, O.; Jensen, E.
1987Ast....15...18L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Optical telescope for LEST site survey.
Authors: Bonaccini, D.; Dunn, R. B.; Engvold, O.
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.
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.
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.
1987iue..prop.2999E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Prominence Environment
Authors: Engvold, O.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1985ATi....18...51E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Large European Solar Telescope
Authors: Engvold, O.
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.
1985spit.conf.1126E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The large European solar telescope
Authors: Engvold, O.
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.
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.
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.
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.
1984iue..prop.1996E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Limb Crossing of an Active Region on Sigma Gem
Authors: Engvold, O.
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.
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.
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.
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.
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.
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.
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.
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.
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 &lt;
1300 Å.

---------------------------------------------------------
Title: Solar center-limb variation of the Ca II K line and the
Wilson-Bappu effect.
Authors: Engvold, O.; Marstad, N. C.
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.
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.
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.
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.
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.
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.
1983itab.rept....1W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Determination of Absolute Velocities for Emission Lines in
Late-Type Stars
Authors: Engvold, O.
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.
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.
1983ITABO..59...59K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Stellar activity.
Authors: Pettersen, B. R.; Engvold, O.
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.
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.
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.
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
1982ROLun..18...13E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Turbulent Velocity Fields in Quiescent Prominences
Authors: Jensen, E.; Engvold, O.
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.
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.
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.
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.
1981BAAS...13..885B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Large European Solar Telescope (lest) - a Preparatory Study
Authors: Engvold, O.; Hefter, M.
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.
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.
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.
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.
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.
1980fsoo.conf....7E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Protuberanser i solens korona.
Authors: Engvold, O.
1980kosm.conf..101E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Kinematics of a loop prominence.
Authors: Engvold, O.; Jensen, E.; Andersen, B. N.
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.
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.
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.
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.
1979MmArc.106....1G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Discussion
Authors: Acton, L. W.; Engvold, O.; Milkey, R. W.; Orrall, F. Q.;
Zirin, H.
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.
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.
1979phsp.coll...53M Altcode: 1979IAUCo..44...53M
No abstract at ADS

---------------------------------------------------------
Title: Discussion
Authors: Acton, L. W.; Engvold, O.; Landman, D. A.
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.
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.
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.
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.
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 &gt; 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 &gt; 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.
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.
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.
1978fsoo.conf....7E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Active edges of quiescent prominences.
Authors: Malville, J. M.; Engvold, O.; Livingston, W.
1977BAAS....9R.569M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Active Edges of Quiescent Prominences.
Authors: Malville, J. M.; Engvold, O.; Livingston, W.
1977BAAS....9..569M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The solar chemical composition.
Authors: Engvold, O.
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.
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.
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.
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.
1977BAAS....9R.315M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solen--en innforing i moderne solfysikk
Authors: Jensen, Eberhart; Engvold, Oddbjorn
1977sole.book.....J Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The fine structure of prominences. I: Observations - Halpha
filtergrams.
Authors: Engvold, O.
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.
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.
1976ATi.....9...11E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Kitt Peak National Observatory's 60-cm Vakuumteleskop
Authors: Engvold, O.
1976ATi.....9..145E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Prominence Eruption Accompanied by Twist Readjustment
Authors: Jockers, K.; Engvold, O.
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.
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) &lt; 1.2 i 0.6 &gt;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.
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
1975SoPh...40...65M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: An analytical representation for photographic characteristic
curves.
Authors: Tsubaki, T.; Engvold, O.
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.
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'.

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Title: An Eruptive Prominence of June 10, 1973
Authors: Engvold, O.; Rustad, B. M.
1974SoPh...35..409E Altcode:
An eruptive prominence of June 10, 1973, showing ascending and expanding
motions, has been recorded spectroscopically at Oslo Solar Observatory.

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Title: N. U. Mayall-teleskopet ved Kitt Peak National Observatory.
Authors: Engvold, O.
1974ATi.....7...97E Altcode:
No abstract at ADS

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Title: A high dispersion spectrum 6610 Å to 6770 Å of a large
sunspot
Authors: Engvold, O.
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

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Title: New identifications of disk emission lines in the Ca II H
and K line wings
Authors: Engvold, O.; Halvorsen, H. D.
1973SoPh...28...23E Altcode:
No abstract at ADS

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Title: Det første bemannede rom-observatorium for solforskning.
Authors: Engvold, O.
1973ATi.....6....3E Altcode:
No abstract at ADS

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Title: The Internal Motion of Quiescent Prominences
Authors: Engvold, Oddbjörn
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).

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Title: Om solens kjemiske sammensetning og grunnstoffenes dannelse.
Authors: Engvold, O.
1972ATi.....5..121E Altcode:
No abstract at ADS

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Title: High Dispersion Spectroscopic Study of Quiescent Prominences
Authors: Engvold, O.; Livingston, W.
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.

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Title: Self-Reversal of the Lithium Resonance Doublet in Sunspots
Authors: Maltby, P.; Engvold, O.
1970SoPh...14..129M Altcode:
No abstract at ADS

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Title: Simultaneous Measurements of Magnetic Fields and Brightness
Fields Using a 4-Image Spectroheliograph
Authors: Sheeley, N. R., Jr.; Engvold, O.
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.

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Title: The Diatomic Molecules BH, BN, and BO in Sunspots and the
Solar Abundance of Boron
Authors: Engvold, O.
1970SoPh...11..183E Altcode:
Absorption band spectra of BH and BO have been searched for and not
found in spectra of sunspots.

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Title: Solar abundance determination.
Authors: Engvold, O.; Hauge, Ø.
1970bfs..conf..351E Altcode:
No abstract at ADS

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Title: Double-K_{2} Emission Line Observed in Sunspots and in
Prominences
Authors: Engvold, O.; Livingston, W.
1969PASP...81..795E Altcode:
0. ENGVOLDt Institute for Theoretical Oslo, Norway AND W. LIVINGSTON
Kitt Peak National Observatory} Tucson, Arizona fteceived September
2, 1969

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Title: On the Position of Sunspots in the Core of Hα Relative to
the Continuum
Authors: Engvold, Oddbjörn
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.

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Title: Spectroheliograms in Fe II λ4924
Authors: Sheeley, N. R., Jr.; Engvold, O.
1969BAAS....1T.292S Altcode:
No abstract at ADS

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Title: The Abundance of Beryllium in the Solar Atmosphere
Authors: Hauge, O.; Engvold, O.
1968ApL.....2..235H Altcode:
No abstract at ADS

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Title: A spectroscopic study of the Hα profile of moustaches
Authors: Engvold, O.; Maltby, P.
1968mmsf.conf..109E Altcode:
No abstract at ADS

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Title: On the K Line of CaII in Sunspots
Authors: Engvold, O.
1967SoPh....2..234E Altcode:
No abstract at ADS

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Title: On the K-line of Ca II in sunspots.
Authors: Engvold, Oddbjørn
1967ApNr...10..173E Altcode:
No abstract at ADS

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Title: Simultaneous observations of HA and the K-line of CA II in
the solar spectrum.
Authors: Engvold, Oddbjorn
1967sohk.book.....E Altcode: 1967QB461.O8n24....
No abstract at ADS

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Title: On the K-line of CaII in sunspots.
Authors: Engvold, Oddbjorn
1967oklc.book.....E Altcode: 1967QB1.A86v10n9...
No abstract at ADS

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Title: On the center-limb variation of the H- and K-line of Ca II.
Authors: Engvold, Oddbjørn
1966ApNr...10..101E Altcode:
No abstract at ADS

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Title: On the center-limb variation of the H- and K-lines of CaII.
Authors: Engvold, Oddbjorn
1966oclv.book.....E Altcode: 1966QB1.A86v10n6...
No abstract at ADS

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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
1966mclv.book.....E Altcode: 1966QB461.O8n17....
No abstract at ADS