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Author name code: kuperus
ADS astronomy entries on 2022-09-14
author:"Kuperus, Max"
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Title: The effect of delays on filament oscillations and stability
Authors: van den Oord, G. H. J.; Schutgens, N. A. J.; Kuperus, M.
1998A&A...339..225V Altcode:
We discuss the linear response of a filament to perturbations, taking
the finite communication time between the filament and the photosphere
into account. The finite communication time introduces delays in the
system. Recently Schutgens (1997ab) investigated the solutions of the
delay equation for vertical perturbations. In this paper we expand his
analysis by considering also horizontal and coupled oscillations. The
latter occur in asymmetric coronal fields. We also discuss the effect
of Alfven wave emission on filament oscillations and show that wave
emission is important for stabilizing filaments. We introduce a fairly
straightforward method to study the solutions of delay equations
as a function of the filament-photosphere communication time. A
solution can be described by a linear combination of damped harmonic
oscillations each characterized by a frequency, a damping/growth
time and, accordingly, a quality factor. As a secondary result of
our analysis we show that, within the context of line current models,
Kippenhahn/Schlüter-type filament equilibria can never be stable in
the horizontal and the vertical direction at the same time but we also
demonstrate that Kuperus/Raadu-type equilibria can account for both
an inverse or a normal polarity signature. The diagnostic value of our
analysis for determining, e.g., the filament current from observations
of oscillating filaments is discussed.
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Title: Prominence Oscillations and the Influence of the Distant
Photosphere
Authors: Schutgens, N. A. J.; Kuperus, M.; van den Oord, G. H. J.
1998ASPC..150..147S Altcode: 1998IAUCo.167..147S; 1998npsp.conf..147S
No abstract at ADS
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Title: The Double Inverse Polarity Paradigm|The Sign of Magnetic
Fields in Quiescent Prominences
Authors: Kuperus, Max
1996SoPh..169..349K Altcode:
A model is presented for the origin of inverse polarity magnetic
fields in the perpendicular as well as in the axial direction of
quiescent prominences. The model is based on the presence of a discrete
coronal arcade structure where magnetic separating surfaces can be
identified. On the crossing of these separating surfaces magnetic
reconnection driven by photospheric shear and converging motions can
create the observed field direction in quiescent prominences.
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Title: A magnetic explanation for the rapid burster.
Authors: Kuijpers, J.; Kuperus, M.
1994A&A...286..491K Altcode:
The main observations of Type II bursts in the low-mass X-ray binary
MXB 1730-335 (the Rapid Burster) can be understood if the neutron star's
magnetic field is strong (7 x 10^11^ - 2 x 10^12^ gauss at the surface)
and rotationally symmetric around the axis of a steadily accreting
disk. We show that a Keplerian disk of matter develops inside the
pressure balance radius where it is compressed into a very thin disk
by the external magnetic field. At the inner edge of the disk a ring
of matter is suspended in the stellar magnetic field and corotates
with the star. During quiescence the disk penetrates more and more
into the magnetosphere, the ring accumulates gas and shifts to lower
altitudes. The stellar field sets a maximum to the amount of supported
gas. As soon as the threshold is passed an ideal mhd instability occurs,
the matter ring falls onto the surface and triggers a violent burst of
accretion. As the stellar field relaxes outward accretion onto the star
continues to be enhanced until a new magnetic equilibrium is attained,
the burst ends and a smaller ring is left at higher altitudes. As the
(steady) external accretion continues the ring load increases again
and moves inward until the threshold is reached and the sequence
repeats. Such a bursting behaviour only occurs if the star is an
aligned rotator.
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Title: A magnetic explanation for the rapid burster
Authors: Kuijpers, J.; Kuperus, M.
1994SSRv...68..333K Altcode:
The observations of X-ray Type II bursts from the low-mass X-ray
binary MXB 1730-335 can be explained by a particular form of magnetic
gating in the presence of steady external accretion. The requirements
are a strong magnetic field of the neutron star (7×10<SUP>11</SUP>
2×10<SUP>12</SUP> gauss at the surface), rotational symmetry and
alignment of the field axis with the axis of a steadily accreting disk
to within 6°.
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Title: Foreword
Authors: van den Oord, Bert; Kuijpers, Jan; Kuperus, Max; Benz, A. O.;
Brown, J. C.; Einaudi, G.; Kuperus, M.; Raadu, M. A.; Trottet, G.;
van den Oord, G. H. J.; Vlahos, L.; Zheleznyakov, V. V.; Wijburg,
Marion; Fletcher, Lyndsay; Volwerk, Martin
1994SSRv...68D..17V Altcode:
No abstract at ADS
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Title: Accretion disk flares in energetic radiation fields. A model
for hard X-rays from black hole candidates.
Authors: van Oss, R. F.; van den Oord, G. H. J.; Kuperus, M.
1993A&A...270..275V Altcode:
An investigation is conducted of the magnetic flares in the energetic
radiation field of an accretion-disk corona, whose X-ray emission
may be the source of the hard power-law component in the X-ray
spectra of galactic black-hole candidates in their 'high' spectral
state. The concept of the low plasma-beta accretion-disk corona (ADC),
which produces the hard X-rays via inverse Compton scattering of
lower-energy photons from the disk on enegetic electrons in the corona,
is elaborated. A spectrum is derived for the up-scattered radiation
from current sheets in the ADC; this spectrum mimics a power-law above
a critical photon energy.
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Title: Accretion Disk Flares in Energetic Radiation Fields
Authors: van Oss, R. F.; van den Oord, G. H. J.; Kuperus, M.
1993IAUS..157..217V Altcode:
No abstract at ADS
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Title: The Effect of Retardation on the Stability of Current Filaments
Authors: van den Oord, G. H. J.; Kuperus, M.
1992SoPh..142..113V Altcode:
We investigate the influence of the finite Alfvén velocity on the
evolution of an active region filament. In general, variations of
a current result in variations of the magnetic fields which spread
around with the Alfvén velocity. As a consequence of the fact that a
magnetic field can only change with the Alfvén velocity, a filament
will experience the photospheric boundary conditions as these were at
an Alfvén travel time back in time. The inclusion of this retardation
effect in the momentum equation of a filament leads effectively to
an extra force term. This force contribution acts in the direction in
which the filament moves and has therefore a destabilizing effect on
the filament. Because a moving filament acts as an antenna of Alfvén
waves, the filament loses energy by the emission process. This leads to
a radiative damping term in the equation of motion of the filament. In
general, the radiative damping will be sufficiently strong to counteract
the retardation instability. Numerical simulations show that during
the energy build-up phase a filament follows the van Tend-Kuperus
equilibrium curve. After the van Tend-Kuperus equilibrium has
disappeared the filament goes through a transient phase moving with a
sub-Alfvénic velocity upward. At greater heights the repulsive Lorentz
force of the photospheric surface current magnetic field is balanced
by the radiative damping, resulting in a decreasing filament velocity.
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Title: Retardation effects and the origin of filament oscillations.
Authors: Kuperus, M.; van den Oord, G. H. J.
1992ESASP.346...39K Altcode: 1992ssts.rept...39K
A filament current subject to a perturbation experiences the
photospheric boundary an Alfvén bounce time later. This retardation
effect gives rise to an extra force which causes the filament to
oscillate around an equilibrium position, emitting Alfvén waves which
damp the filament oscillations. The onset of filament oscillations is a
natural consequence of the presence of the inert photospheric boundary
and the finite Alfvén speed. Numerical simulations are presented that
show the evolution of a filament in a bipolar magnetic field as the
filament current slowly increases. The emission of waves during this
evolution is an important energy source for the coronal heating.
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Title: The Effect of Coupling of a Corona to the Turbulence in an
Accretion Disk
Authors: Geertsema, G. T.; Kuperus, M.
1992A&A...254..426G Altcode:
Assuming a preferred length scale at which energy flows from
magnetohydrodynamic turbulence in a thin accretion disk to a
magnetically coupled corona, we investigate the differences between
the energy dissipated in the accretion disk and the energy flowing
into the corona. The study shows that the turbulence is very stable
even against a strong coronal energy sink. A weak coronal energy sink
reduces the amplitude of the fluctuations in the turbulent energy. <P
/>The temporal spectra of the disk turbulence i.e. the dissipated energy
and of the energy flowing into the corona are compared. The slopes of
the power spectra of the energy which flows into the corona are steeper
than those for the dissipated energy. A case of strong coronal coupling
is further examined. Remarkable peaks occur in the Fourier spectra,
which we identify with energy bursts in the total turbulent energy.
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Title: Book reviews
Authors: Linssen, P. F. J.; Valníček, B.; Pecker, Jean-Claude;
Marov, M. Ya; Abalakin, V. K.; Achterberg, A.; Kuperus, M.; Sterzik, M.
1991SSRv...56..419L Altcode:
No abstract at ADS
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Title: Book Review: Accretion disks and magnetic fields in
astrophysics / Kluwer, 1989
Authors: Kuperus, M.
1991SSRv...56..422K Altcode:
No abstract at ADS
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Title: Book Review: An introduction to Alfven waves / Adam Hilger,
1988
Authors: Kuperus, M.
1990SSRv...53..347K Altcode: 1990SSRv...53..347C
No abstract at ADS
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Title: Magnetohydrodynamics of accretion disks.
Authors: Kuperus, M.
1990CoPhR..12..275K Altcode:
Accretion disks in close binary systems originate when mass overflow
occurs from the primary star onto the compact star. When the compact
star is a neutron star or a black hole the inner parts of the thin disk
extend to the Alfvén radius respectively a few times the Schwarzschild
radius. In the Keplerian rotating highly turbulent inner parts of the
accretion disk magnetic fields are strongly amplified and expelled from
the disk thus leading to the formation of a magnetically structured
accretion disk corona. The magnetic energy supplied to the corona is
radiated by inverse Compton scattering of soft X-ray photons produced in
the disk by the viscous heating of the accreting matter. The interaction
of the inner parts of an accretion disk with the magnetosphere around
a neutron star leads to channeled accretion onto the magnetic poles,
resulting in the phenomenon of X-ray pulsars. The interaction of disk
coronal structures with the relatively weak magnetic fields of old fast
spinning neutron stars leads to a new form of interaction around the
so called beat frequency that can be used as a model for quasiperiodic
oscillations in low-mass X-ray binaries.
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Title: Accretion disk coronae
Authors: Kuperus, M.
1989HiA.....8..535K Altcode:
No abstract at ADS
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Title: Coupling of an accretion disk corona with a weakly magnetic
neutron star and a possible relation with quasi-periodic oscillations.
Authors: Stollman, G. M.; Kuperus, M.
1988A&A...203..104S Altcode:
We propose a mechanism whereby rotating, weakly magnetized neutron
stars, which are thought to be present in some low mass X-ray binaries,
may lose energy to the accretion disk via an electrodynamical coupling
between the magnetic field of the star and magnetic loops in a disk
corona. This mechanism may solve some of the problems posed by the
observations of these systems. In particular, the properties of
the power spectra of some of the sources, in which quasi-periodic
oscillations are observed, can be explained, and especially it can
be understood why the lowfrequency noise in some sources may be much
reduced in power with respect to the power in the oscillations.
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Title: Equivalent circuit representation of Alfven waves
Authors: Scheurwater, R.; Kuperus, M.
1988A&A...194..213S Altcode:
By applying basic electric circuit theory to the linearized MHD
equations the authors determine the voltage and current distribution
in the magnetoplasma associated with the Alfvén waves and derive
an expression for the input impedance. The input impedance, which
is a function of both the plasma parameters and the frequency of the
Alfvén waves, in general, may be represented by an equivalent electric
circuit. The authors construct equivalent circuit representations for
different ranges of the plasma parameters and frequency and calculate
the quality factors for the circuits in the vicinity of the natural
frequencies.
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Title: Accretion disk coronae and the contribution to angular-momentum
transport in the disk
Authors: Burn, H.; Kuperus, M.
1988A&A...192..165B Altcode:
The differential rotation of an accretion disk amplifies the magnetic
field in a standard thin accretion disk and drives large flux cells
out of the disk which form an accretion disk corona. These cells, which
are treated as force-free arcades in this paper are sheared by the same
differential rotation. The reaction force of these cells that acts on
the disk plasma is described in the frame work of an effective shear
stress and can give a significant contribution to the total angular
momentum transport in the corona-disk system.
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Title: Report of IAU Commission 12: Radiation and structure of the
solar atmosphere (Radiation et structure de l'atmosphère solaire).
Authors: Kuperus, M.
1988IAUTA..20...91K Altcode:
No abstract at ADS
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Title: Varying self-inductance and energy storage in a sheared
force-free arcade
Authors: Zuccarello, F.; Burm, H.; Kuperus, M.; Raadu, M.; Spicer,
D. S.
1987A&A...180..218Z Altcode:
The authors utilize an electric circuit analogy to model the build-up
and storage of magnetic energy in the coronal loops known to exist
in the atmosphere of the Sun. The parameterization of magnetic energy
storage in an electric circuit analogue uses a bulk current I flowing
in the circuit and a self-inductance L. Because the self-inductance is
determined by the geometry of the magnetic configuration any change in
its dimensions will change L. If L is increased, the amount of magnetic
energy stored and the rate at which magnetic energy is stored are both
increased. One way of increasing L is to shear the magnetic field lines
and increase their effective geometrical length. Using the force-free
field approximation for a magnetic arcade whose field lines are sheared
by photospheric motions, the authors demonstrate that the increase
of magnetic energy is initially due to the increase of the current
intensity I and later mainly due to the increase of the self-inductance.
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Title: Accretion disk electrodynamics.
Authors: Kuperus, M.
1987gac..conf..195K Altcode:
Contents: 1. The standard thin disk. 2. Turbulent dynamo in accretion
disks. 3. Electrodynamic coupling of accretion-disk coronae. 4. The
interaction of a neutron star with an accretion disk: Spin up of
neutron stars. Quasiperiodic oscillations.
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Title: Black hole accretion disks. Electrodynamic coupling of
accretion-diskcoronae and the partitioning of soft and hard X-ray
emission.
Authors: Kuperus, M.; Ionson, J. A.
1985A&A...148..309K Altcode:
It is demonstrated that the observed large ratio of hard to soft
X-ray emission and the bimodel behavior of black hole accreting X-ray
sources such as Cygnus X-1 can be described in terms of a magnetically
structured accretion disk corona which is electrodynamically coupled
to the disk turbulent motions while the disk is thermodynamically
coupled to the corona as described by a feedback parameter delta. The
observed ratio of hard to soft X-ray emission is independent of the disk
thickness, and weakly dependent of the disk parameter alpha relating
the disk viscous stresses to the total pressure. Observed values of
the luminosity ratio point towards strong differences of the feedback
of the low state compared to the high state, in the sense that low
state means small feedback (delta less than 0.2) and high state means
strong feedback delta of about 0.5.
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Title: Solar physics: "progress in solar hydromagnetics".
Authors: Kuperus, M.
1985plph.conf..997K Altcode:
No abstract at ADS
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Title: The role of differential rotation in magnetic energy storage.
Authors: Zappala, R. A.; Zuccarello, F.; Kuperus, M.
1984ESASP.220..159Z Altcode: 1984ESPM....4..159Z
The authors investigate a possible mechanism for magnetic energy
storage in coronal loops without making assumptions about dissipative
mechanisms.
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Title: Black hole accretion disks - Coronal stabilization of the
Lightman-Eardley instability
Authors: Ionson, J. A.; Kuperus, M.
1984ApJ...284..389I Altcode:
Physical processes by which the presence of a corona around a black hole
can raise the threshold of onset of the Lightman-Eardley (L-E, 1976)
instability are explored analytically. The L-E model predicts that an
optically thick disk becomes unstable when the disk radiation pressure
exceeds the disk gas pressure. The model has important implications
for the validity of either the coronal disk or two-temperature disk
models for accretion zones around black holes. It is shown that a
corona can dissipate accreting gravitational energy through radiative
cooling. Specific ratios of hard/soft X-rays are quantified for stable
and unstable conditions. X-ray spectra from Cyg X-1 are cited as
residing below the instability threshold value and thus are supportive
of the coronal disk model.
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Title: Book-Review - Solar and Stellar Magnetic Fields - Origins
and Coronal Effects
Authors: Stenflo, J. O.; Kuperus, M.
1984SSRv...38..387S Altcode:
No abstract at ADS
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Title: Book reviews
Authors: Kuijpers, Jan; Kleczek, Josip; Lamers, H. J. G. L. M.; Kruit,
P. C. V. D.; Kuperus, M.; Knott, K.
1984SSRv...38..385K Altcode:
No abstract at ADS
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Title: Book-Review - Solar Magnetohydrodynamics
Authors: Priest, E. R.; Kuperus, M.
1983SSRv...36..424P Altcode:
No abstract at ADS
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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
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Title: Spatially coherent oscillations in microwave bursts.
Authors: Kattenberg, A.; Kuperus, M.
1983SoPh...85..185K Altcode:
Solar microwave burst observations (made with the WSRT) with high
time and high spatial resolution show large-scale (> 8000 km)
short-period (1.5 s) modulations of the source. It is argued that
an interpretation in terms of Alfvén oscillations in the microwave
source is ruled out by this observation. Instead it must be the
source of the fast electrons, that produce the microwaves, that is
oscillating. The fluctuating acceleration region is identified with
a volume where a sheared field is compressed against a flux tube by
an unstable current. MHD oscillations in the overlying fluxtube are
caused by the pushing force. The rapidly expanding current plays a
major role in the flare theory of van Tend and Kuperus (1978).
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Title: Electrodynamics of the Outer Solar Atmosphere
Authors: Kuperus, M.
1983SSRv...34...47K Altcode:
The structure of the outer solar atmosphere and its magnetic coupling
to the photospheric motions indicate the existence of large-scale
current systems. The heating and the dynamics of coronal structures is
therefore governed by electrodynamic coupling of these structures to the
underlying photosphere. In a structured corona, the heating is enhanced
because of several processes such as resonance absorption of Alfvénic
surface waves, anomalous Joule heating, reconnection and the related
topological dissipation. The global thermal and dynamic behaviour of
coronal structures can be fruitfully described in terms of equivalent
electrodynamic circuits, taking into account the paramount role of the
photospheric boundaries. Coronal current systems may be stable, as in
the case of coronal loops, but occassionally they show catastrophic
behaviour if the current intensity surpasses a critical threshold.
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Title: A thermal catastrophe in a resonantly heated coronal loop
Authors: Martens, P. C. H.; Kuperus, M.
1983IAUS..102..397M Altcode:
A theory for the thermal stability of hot coronal loops is presented,
which is based on the resonant electrodynamic heating theory of Ionson
(1982) and the evaporation/condensation scenario of Krall and Antiochos
(1980). The theory predicts that gradual changes in the length of
a loops or in its magnetic field strength can trigger catastrophic
changes in the X-ray visibility of the loop, without the need for
a change in the magnetic field topology. A natural explanation is
thereby given for the observations of X-ray brightenings in loops and
loop evacuations with coronal rain.
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Title: Resonant electrodynamic heating and the thermal stability of
coronal loops
Authors: Martens, P. C. H.; Kuperus, M.
1982A&A...113..324M Altcode:
The resonant electrodynamic heating theory of Ionson (1982) and the
evaporation/condensation scenario of Krall and Antiochos (1980) are
invoked by a theory of hot coronal loop thermal stability. The theory
predicts that gradual changes in loop length or magnetic field strength
can trigger catastrophic X-ray visibility changes in the loop without
accompanying changes in magnetic field topology. This is judged to
constitute a natural explanation for observed X-ray brightening in
loops, as well as loop evacuations with coronal rain.
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Title: Heating processes of the solar corona
Authors: Kuperus, M.
1981ESASP.161..113K Altcode: 1981plas.work..113K
No abstract at ADS
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Title: Heating processes of the solar corona
Authors: Kuperus, M.
1981plap.rept..113K Altcode:
Coronal heating processes are discussed in the context of the magnetic
structure of the solar corona. Existing theories are divided into
acoustic theories, where the magnetic field plays a passive role,
and electrodynamic theories where the magnetic field plays an active
role in the sense that transversal waves are possible. The dissipation
mechanisms are shock wave dissipation in the acoustic theory and viscous
and Joule dissipation of Alfven waves in the electrodynamic theory. The
dissipation of Alfven waves appears to be much more effective in
a structured medium than in a homogeneous medium. Anomalous Joule
heating is likely to be important as a steady heating mechanism.
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Title: The Eruption of Active Region Filaments and its Relation to
the Triggering of a Solar Flare
Authors: Kuperus, M.; van Tend, W.
1981SoPh...71..125K Altcode:
The formation and eruption of active region filaments is supposed to
be caused by the increase of a concentrated current embedded in the
active region background magnetic field of an active region according
to the theory of Van Tend and Kuperus (1978).
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Title: On the theory of coronal heating mechanisms
Authors: Kuperus, M.; Ionson, J. A.; Spicer, D. S.
1981ARA&A..19....7K Altcode:
The present state-of-the-art of two classes of theories of coronal
heating is examined: (1) heating by acoustic processes in the
'nonmagnetic' parts of the atmosphere (the shock-wave theory is
an example); and (2) heating by electrodynamic processes in the
magnetic regions of the corona (beta much less than 1) either by
MHD waves or current heating in regions with high electric current
densities (flare-type heating). It is concluded that the mechanism
of the heating of the solar chromosphere and corona remains an open
question, especially in explaining detailed atmospheric structures. The
acoustic theory might be correct with little modification for most of
the chromosphere, but as soon as the atmosphere shows a high degree
of structure as in the corona and transition layer the magnetic field
must play a dominant role. It appears that the current heating theories
have a small range of applicability, while the MHD-wave theories are
the most promising.
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Title: On the theory of coronal heating mechanisms
Authors: Kuperus, M.; Ionson, J. A.; Spicer, D. S.
1980STIN...8115928K Altcode:
Theoretical models describing solar coronal heating mechanisms are
reviewed in some detail. The requirements of chromospheric and coronal
heating are discussed in the context of the fundamental constraints
encountered in modelling the outer solar atmosphere. Heating by acoustic
processes in the 'nonmagnetic' parts of the atmosphere is examined
with particular emphasis on the shock wave theory. Also discussed are
theories of heating by electrodynamic processes in the magnetic regions
of the corona, either magnetohydrodynamic waves or current heating
in the regions with large electric current densities (flare type
heating). Problems associated with each of the models are addressed.
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Title: Brief Report of Meeting - IAU / Solar Maximum Year
Authors: Švestka, Zdenk; Van Hoven, Gerard; Hoyng, Peter; Kuperus, Max
1980SoPh...67..379S Altcode:
No abstract at ADS
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Title: Solar and Interplanetary Dynamics
Authors: Kuperus, M.
1980IAUS...91..547K Altcode:
No abstract at ADS
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Title: Kinetic effects on the propagation of surface waves and their
relevance to the heating of the solar corona.
Authors: Kuperus, M.; Heyvaerts, J.
1980AnPh....5..483K Altcode: 1980mhda.conf..483K
No abstract at ADS
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Title: The development of coronal electric current systems in active
regions and their relation to filaments and flares.
Authors: van Tend, W.; Kuperus, M.
1978SoPh...59..115V Altcode:
The equilibrium positions of coronal currents are determined. It is
shown that the fact that the photosphere has a very large inertia as
compared to the corona, poses an important boundary condition at the
surface. Electric currents flowing in a coronal active region show
a tendency to concentrate above a neutral line. Only here equilibria
are possible, determined at low heights by the background field and at
large heights by gravity. An instability may occur when the current at
low heights exceeds a certain value. The model given is compared with
observations of the corona, of prominences, and of fibril motions. Also,
the relation with solar flares is discussed in general terms.
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Title: The triggering of plasma turbulence during fast flux emergence
in the solar corona.
Authors: Heyvaerts, J.; Kuperus, M.
1978A&A....64..219H Altcode:
The paper discusses the physics of current sheet formation in regions
of contact between old and new flux; this formation occurs during
flux emergence from the solar photosphere into the corona. Particular
attention is paid to the case of fast emergence, in which, at first,
no field-line reconnection can take place. It is shown to be almost
impossible to trigger microturbulence in the one-dimensional phase
of sheet development. An approximation based on the fact that the
sheet is very long and very thin is used to study analytically the
two-dimensional phase of flow induced by compression. It is shown
that the flow evacuates the region of the sheet where the pinching
is strongest, and that the conditions for microturbulence are easily
fulfilled there after some time. The behavior of the current sheet
after turbulence sets in is considered.
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Title: The Coronal Active Region and the Preflare Environment
Authors: Kuperus, M.; Svetska, Z.
1978pfsl.conf..169K Altcode: 1978ESPM....2..169K
No abstract at ADS
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Title: Mechanisms of Heating and Heat Transfer in the Outer Solar
Atmosphere
Authors: Chiuderi, C.; Kuperus, M.
1977ebhs.coll..223C Altcode: 1977IAUCo..36..223C
No abstract at ADS
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Title: Solar Flares
Authors: de Jager, C.; Kuperus, M.; Rosenberg, H.
1976RSPTA.281..507D Altcode: 1976RSLPT.281..507D
A summary is given of some recent observational data on solar
flares. Particularly we discuss the flare build-up process and the time
scales involved. We suggest as a possible magnetic field configuration a
multiply kinked or supertwisted flux tube. The role of plasma turbulence
and the Fermi mechanism in particle acceleration is discussed.
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Title: Physics of the Solar Atmosphere
Authors: de Jager, C.; Kuperus, M.; Rosenberg, H.
1976RSPTA.281..415D Altcode: 1976RSLPT.281..415D
A summary is given on recent results on the physics of the quiet solar
atmosphere, and active regions. This includes: solar rotation, velocity
fields and waves, magnetic field concentration, the transition region,
coronal magnetic field structure, and prominences.
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Title: Solar Flares and Magnetospheric Substorms (Invited summary)
Authors: Kuperus, M.
1976SoPh...47..361K Altcode:
No abstract at ADS
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Title: The role of plasma turbulence in the development of solar
flares.
Authors: Kuperus, M.
1976SoPh...47...79K Altcode:
The amount of energy released during a solar flare and the relatively
short timescale in which all the flare associated events occur lead to
the conclusion that a solar flare is a magnetohydrodynamic instability
taking place in a strongly turbulent plasma.
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Title: Book reviews
Authors: de Jager, C.; van Rensbergen, Walter; Kuperus, M.; Falthammar,
Carl-Gunne; Mewe, R.; Reunen, G. C. M.; Bruzek, A.; Swanenburg,
B. N.; Kleczek, J.; Millman, Peter M.; Vesseur, H. J. A.; Pacini,
F.; Monfils, A.
1976SSRv...18..541D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Support of Prominences Formed in Neutral Sheets
Authors: Kuperus, M.; Raadu, M. A.
1974A&A....31..189K Altcode:
Summary. It is shown that prominence filaments formed in a
magnetically neutral sheet in the corona can be supported against
gravity by magnetic forces due to induced currents in the photospheric
boundary. The supporting force is inversely proportional to the height
above the photo sphere and the filaments seem stable against small
perturbations. The adopted magnetic field configuration allows for
a prominence eruption. However, it is suggested that the so called
disparition brusque may only occur if either the prominence loses
weight by mass loss or through the influence of large scale changes
in the photospheric magnetic field. Key words: solar prominences -
neutral sheets - magnetohydrodynamics
---------------------------------------------------------
Title: The evolution of magnetic fields and unstable solar plasmas.
Authors: Kuperus, M.
1974UtrOv.295.....K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Onderzoek naar magnetohydrodynamische en plasma instabiliteiten
in de zonnekorona.
Authors: Kuperus, M.; Rosenberg, H.
1974NTNA...39..130K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Evolution of Magnetic Fields and Unstable Solar Plasmas
Authors: Kuperus, M.
1974cesra...4...17K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The next decade of theoretical solar physics.
Authors: Kuperus, M.
1974HiA.....3..133K Altcode:
The next decade in theoretical solar physics will probably be
characterized by the understanding that the sun is the nearest
cosmical laboratory in which a large class of astrophysical problems
can be studied in detail. The current state of knowledge regarding
solar physics is briefly reviewed and the most important developments
expected for the coming years are considered. Attention is given to
the neutrino problem, questions of solar oblateness, solar rotation
and convection, the structure of the photosphere and the chromosphere,
the corona, and solar magnetic fields.
---------------------------------------------------------
Title: Characteristics of non-thermally heated stellar atmospheres.
Authors: Lamers, H. J. G. L. M.; Kuperus, M.
1974ssse.conf..169L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Thermal Instability of Coronal Neutral Sheets and the Formation
of Quiescent Prominences
Authors: Raadu, M. A.; Kuperus, M.
1973SoPh...28...77R Altcode:
It is argued that the quiscent prominences are a natural consequence
of the formation and thermal instability of current sheets in the
corona. Thus observation and theory of prominences can give vital
information on the presence of currents and the topology of magnetic
fields in the corona. Conversely by developing the theory of the
structure and evolution of current sheets under coronal conditions we
can attempt to gain a comprehensive understanding of the structure,
evolution, and mass and energy balance of quiescent prominences. A
stability analysis for coronal material permeated by a vertical magnetic
field rooted in the photosphere, indicates that a condensation will take
the form of a thin vertical wedge of cool matter. The development of a
finite condensation is followed and it is shown that photospheric line
tying is only important in the initial stages. A perturbation analysis
of vertical motions at the neutral sheet shows that thermal instability
can lead to overstable oscillations. Cooling of coronal material can
lead to both upward and downward mass motions, and gravitational energy
release is important to the thermal balance of prominences. Relevant
optical and radio observations are discussed. Synoptic observations
of the development of active regions and magnetic fields are needed
to test the basic hypothesis of the formation of prominences from
neutral sheets.
---------------------------------------------------------
Title: Apollo Telescope Mount (ATM).
Authors: Kuperus, M.
1973HemD...71..167K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Physics of Solar Prominences. Report on an International
Colloquium Held at the German Solar Observatory, Anacapri, September
29 to October 1, 1971
Authors: Bruzek, Anton; Kuperus, Max
1972SoPh...24....3B Altcode:
This colloquium on solar prominences - the first ever held -
has shown that a major part of activity in prominence research in
recent years concentrated on both observation and computation of the
magnetic conditions which were found to play a crucial role for the
development and the maintainance of prominences. Remarkable progress
was made in fine-scale measurements of photospheric magnetic fields
around filaments and in internal field measurements in prominences. In
addition, important information on the structure of the magnetic fields
in the chromosphere adjacent to the filaments may be derived from high
resolution photographs of the Hα fine structure around filaments
which have become available recently; unfortunately, an unambiguous
determination of the vector field in the chromosphere is not yet
possible. <P />It is quite clear, now, that stable filaments extend
along `neutral' lines which divide regions of opposite longitudinal
magnetic fields. Different types of neutral lines are possible,
depending on the history and relationship of the opposite field
regions. There is convincing evidence that the magnetic field in the
neighbouring chromosphere may run nearly parallel to the filament
axis and that there are two field components in stable prominences:
an axial field dominant in the lower parts and a transverse field
dominant in the higher parts. <P />Methods for the computation of
possible prominence field configurations from measured longitudinal
photospheric fields were developed in recent years. In a number of
cases (e.g. for loop prominences) the observed configuration could
be perfectly represented by a force-free or even a potential field;
poor agreement was found between computed and measured field strengths
in quiescent prominences. In order to reconcile both of them it is
necessary to assume electric currents. Unambiguous solutions will not
be found until measurements of the vector field in the photosphere
and in the prominences are available. <P />The two-dimensional
Kippenhahn-Schlüter model is still considered a useful tool for the
study of prominence support and stability. However, a more refined
model taking into account both field components and considering also
thermal stability conditions is available now. It was proposed that
quiescent prominences may form in magnetically neutral sheets in
the corona where fields of opposite directions meet. <P />As for
the problem of the origin of the dense prominence material there
are still two opposite processes under discussion. The injection of
material from below, which was mainly applied to loop prominences, has
recently been considered also a possible mechanism for the formation of
quiescent prominences. On the other hand, the main objections against
the condensation mechanism could be removed: it was shown that (1)
sufficient material is available in the surrounding corona, and that
(2) coronal matter can be condensed to prominence densities and cooled
to prominence temperatures in a sufficiently short time. <P />The energy
balance in prominences is largely dependent on their fine structure. It
seems that a much better radiative loss function for optically thin
matter is now available. The problem of the heat conduction can only
be treated properly if the field configuration is known. Very little is
known on the heating of the corona and the prominence in a complicated
field configuration. For the optically thick prominences the energy
balance becomes a complicated radiative transfer problem. <P />Still
little is known on the first days of prominence development and on
the mechanism of first formation which, both, are crucial for the
unterstanding of the prominence phenomenon. As a first important step,
it was shown in high resolution Hα photographs that the chromospheric
fine structure becomes aligned along the direction of the `neutral'
line already before first filament appearance. More Hα studies and
magnetic field measurements are badly needed. <P />Recent studies
have shown that even in stable prominences strong small-scale internal
rotational or helical motions exist; they are not yet understood. On the
other hand, no generally agreed interpretation of large-scale motions of
prominences seems to exist. A first attempt to explain the ascendance
of prominences, the `Disparitions Brusques', as the result of a kink
instability was made recently. <P />New opportunities in prominence
research are offered by the study of invisible radiations: X-rays and
meterwaves provide important information, not available otherwise,
on physical conditions in the coronal surroundings of prominences;
EUV observations will provide data on the thin transition layer between
the cool prominence and the hot coronal plasma.
---------------------------------------------------------
Title: On the Directional Dependence of the Emission of Acoustic
Noise by Convective Turbulence in a Gravitational Atmosphere
Authors: Kuperus, M.
1972SoPh...22..257K Altcode:
The directional dependence of the emission of sound waves in the
solar atmosphere is studied. It is shown that quadrupole acoustic
radiation generated in convective turbulence is strongly enhanced in
the direction of the mean convective flow. The intensity in a direction
θ with the convective velocity is proportional to (1 − M<SUB>c</SUB>
cosθ)<SUP>−17/2</SUP>, where M<SUB>c</SUB> is the Mach number of the
convective motion. The influence of the atmospheric cut off frequency
on the transmitted acoustic spectrum is taken into account. It is
suggested that low frequency atmospheric oscillations may modulate
the flux of high frequency sound waves.
---------------------------------------------------------
Title: Structure and Dynamics of the Solar Corona
Authors: Kuperus, M.
1972ASSL...29....9K Altcode: 1972sun..conf....9K
No abstract at ADS
---------------------------------------------------------
Title: Physical characteristics of the solar atmosphere
Authors: Kuperus, M.
1972ppsr.conf...89K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Structure and dynamics of the solar corona.
Authors: Kuperus, M.
1972sstp.conf....9K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Analogy of Sound Waves and Shallow Water Waves
Authors: Kuperus, M.
1971A&A....12...85K Altcode:
The analogy between the propagation of shallow water waves and sound
waves is discussed. It is suggested that laboratory experiments
with shallow water in a vessel with varying depth and width can
be used to study the propagation of sound waves in a gravitational
atmosphere. It is shown that in some cases the depth and the width of
the vessel serve as the analogon for the temperature and the density
in the atmosphere. Key words: sound waves - stellar atmospheres -
analogy experiment
---------------------------------------------------------
Title: Solar radioastronomy and corona magnetohydrodynamics
Authors: Kuperus, M.
1971cesra...1....4K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Determination of the Velocity of the Exciters of Type
II Solar Radiobursts
Authors: Van Bueren, H. G.; Kuperus, M.
1970SoPh...14..208V Altcode:
Under the assumption that type II bursts are excited by strong shock
waves it is shown that the velocity determined from dynamic spectrograms
should be corrected by a term proportional to the gradient of the
shock strength. The magnitude of the correction strongly depends on
the properties of the pre-shock atmosphere and the geometry of the
shock propagation.
---------------------------------------------------------
Title: Thermally Driven Motions in a Gravitational Atmosphere
Authors: Bessey, R. J.; Kuperus, M.
1970SoPh...12..216B Altcode:
Numerical solutions of the non-linear equations of fluid dynamics for a
compressible inviscid initially isothermal atmosphere are given using
Lax' method for the integration of the equations when discontinuities
occur in the flow. The motion of the atmosphere is studied following
the heating of a thin layer in the atmosphere. It is found that
for a sufficiently large heat input the atmosphere strongly expands
towards the regions of lower densities. In most cases a shock wave is
formed which precedes the expanding region. The possible occurrence
of thermally generated motions in the solar chromosphere is discussed.
---------------------------------------------------------
Title: Thermally Driven Motions in a Gravitational Atmosphere
Authors: Bessey, R. J.; Kuperus, M.
1969cctr.conf..191B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Structure of the Transition Region between the Chromosphere
and the Corona
Authors: Kuperus, M.
1969cctr.conf....1K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Heating of the Solar Corona
Authors: Kuperus, M.
1969SSRv....9..713K Altcode:
In this paper a discussion is given of the present state of the
theory of the heating of the solar corona by shock waves. Arguments
are presented why the main contribution to the mechanical energy flux
is of acoustic origin, while estimates for the amount of acoustic
energy generated in the convection zone as well as the deviations
from isotropy are given. During propagation through the atmosphere
acoustic waves develop into shock waves after a distance of a few
scale heights in the chromosphere. The heating of the outer layers by
dissipation of shock waves is found to be sufficient to account for
the observed radiative and corpuscular energy losses. Much emphasis is
laid on the competitive role played by the four fundamental processes
of energy transfer: mechanical heating, radiation, heat conduction and
convection of energy in establishing the equilibrium structure of the
corona. The atmosphere may be divided in several regions according to
the predominance of one of the energy processes mentioned above. The
physical properties of the chromosphere and the solar wind are discussed
only where they are intimately connected with the problem of the heating
of the corona. The most important aspects of the influence of a magnetic
field on the structure and the heating of the corona in magnetically
active regions are briefly mentioned. Special attention is paid to
the strong channelling of heat flow along the field lines and its
consequences for the structure and dynamics of the chromosphere-corona
transition layer.
---------------------------------------------------------
Title: Oscillatory Phenomena in Quiescent Prominences
Authors: Kleczek, J.; Kuperus, M.
1969SoPh....6...72K Altcode:
A model for horizontal oscillations of prominences is presented. It
is found that the model of a freely oscillating prominence surrounded
by coronal matter explains satisfactorily the observed periods and
damping times, as well as the changes in the prominence shape.
---------------------------------------------------------
Title: Magnetic Fields and the Temperature Structure of the
Chromosphere-Corona Interface
Authors: Kopp, Roger A.; Kuperus, Max
1968SoPh....4..212K Altcode:
The temperature structure of the transition region between the
chromosphere and corona is discussed in the context of current ideas
about magnetic fields in these layers. Magnetic channeling of the
downward conductive heat flow from the corona into the regions of
enhanced field at the supergranulation boundaries is proposed as a
mechanism for explaining the measured intensities of solar ultraviolet
emission lines which originate in layers with temperatures below
10<SUP>5</SUP> °K. It is shown that nearly all of the observed
ultraviolet line emission originates in interspicule regions, and that
this emission plays an important part in the energy balance of the
cooler layers of the transition region. It is suggested that certain
motions observed in the upper chromosphere may represent the earliest
visual evidence for conversion of inflowing conduction energy into
kinetic motions.
---------------------------------------------------------
Title: Magnetic Fields and the Temperature Structure of the
Chromosphere-Corona Interface.
Authors: Kopp, Roger A.; Kuperus, Max
1968AJS....73Q..67K Altcode:
The temperature structure of the transition region between the
chromosphere and corona is discussed in the context of current ideas
about magnetic fields in these layers. Magnetic channeling of the
downward conductive heat flow from the corona into the regions of
enhanced field at the supergranulation boundaries is proposed as a
mechanism for explaining the measured intensities of solar ultraviolet
lines which are emitted by layers with temperatures below 10~ 0K. It is
suggested that nearly all of the observed ultraviolet line emission
originates in interspicule regions, and that this emission plays
an important part in the energy balance of the cooler layers of the
transition region.
---------------------------------------------------------
Title: The Nature of Quiescent Solar Prominences
Authors: Kuperus, Max; Tandberg-Hanssen, Einar
1967SoPh....2...39K Altcode:
Quiescent prominences occur as long-lasting cool sheets of matter in
the surrounding hot corona at the base of coronal streamers. Seen on
the disk they appear as dark filaments dividing regions of opposite
magnetic polarity.
---------------------------------------------------------
Title: On the Origin of Spicules in the Chromosphere-Corona Transition
Region
Authors: Kuperus, Max; Athay, R. Grant
1967SoPh....1..361K Altcode:
Qualitative arguments are presented to show that in the
chromosphere-corona transition region the energy which is transported
downwards by heat conduction cannot be disposed of by radiative losses
only. The region therefore is unstable and forced to be in motion,
which may give rise to spicule-like phenomena.
---------------------------------------------------------
Title: Book reviews
Authors: Kuperus, M.; Nijboer, B. R. A.
1967SSRv....6..892K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Heating of the Solar Corona by Photospheric Waves
Authors: Kuperus, M.
1966IAUTB..12..564K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the thermal generation of magnetic fields in the ionization
zone of rotating stars
Authors: Kuperus, M.
1966BAN....18..353K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The transfer of mechanical energy in the sun and the heating
of the corona
Authors: Kuperus, Max
1965RAOU...17.....K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Transfer of Mechanical Energy in the Sun and the Heating
of the Corona
Authors: Kuperus, M.
1965RAOU...17....1K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The transfer of mechanical energy in the sun and the heating
of the corona
Authors: Kuperus, Max
1965PhDT........55K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the selection concentration in a prominence observed during
the total solar eclipse of oktober 2nd 1959.
Authors: Koelbloed, D.; Kuperus, M.
1963PRNAA..66Q..36K Altcode: 1963RNAAS..66Q..36K
No abstract at ADS
---------------------------------------------------------
Title: On the electron concentration in a prominence observed during
the total solar eclipse of october 2nd. 1959.
Authors: Kuperus, M.; Koelbloed, D.
1963PRNAA..66R..36K Altcode: 1963RNAAS..66R..36K
No abstract at ADS
---------------------------------------------------------
Title: The acoustic energy flux of the Sun and the formation of
the corona
Authors: de Jager, C.; Kuperus, M.
1961BAN....16...71D Altcode:
No abstract at ADS
