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Author name code: heyvaerts
ADS astronomy entries on 2022-09-14
author:"Heyvaerts, Jean"
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Title: General solution for the vacuum electromagnetic field in the
surroundings of a rotating star
Authors: Bonazzola, S.; Mottez, F.; Heyvaerts, J.
2020arXiv200702539B Altcode:
Aims. Many recent observations of pulsars and magnetars can
be interpreted in terms of neutron stars (NS) with multipole
electromagnetic fields. As a first approximation, we investigate the
multipole magnetic and electric fields in the environment of a rotating
star when this environment is deprived of plasma. Methods. We compute a
multipole expansion of the electromagnetic field in vacuum for a given
magnetic field on the conducting surface of the rotating star. Then, we
consider a few consequences of multipole fields of pulsars. Results. We
provide an explicit form of the solution. For each spherical harmonic of
the magnetic field, the expansion contains a finite number of terms. A
multipole magnetic field can provide an explanation for the stable
sub-structures of pulses, and they offer a solution to the problem of
current closure in pulsar magnetospheres. Conclusions. This computation
generalises the widely used model of a rotating star in vacuum with
a dipole field. It can be especially useful as a first approximation
to the electromagnetic environment of a compact star, for instance a
neutron star, with an arbitrarily magnetic field.
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Title: Magnetic coupling of planets and small bodies with a pulsar
wind (Corrigendum)
Authors: Mottez, F.; Heyvaerts, J.
2020A&A...639C...2M Altcode:
No abstract at ADS
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Title: Dressed diffusion and friction coefficients in inhomogeneous
multicomponent self-gravitating systems
Authors: Heyvaerts, Jean; Fouvry, Jean-Baptiste; Chavanis,
Pierre-Henri; Pichon, Christophe
2017MNRAS.469.4193H Altcode: 2017arXiv170606009H
General self-consistent expressions for the coefficients of
diffusion and dynamical friction in a stable, bound, multicomponent
self-gravitating, and inhomogeneous system are derived. They account
for the detailed dynamics of the colliding particles and their
self-consistent dressing by collective gravitational interactions. The
associated Fokker-Planck equation is shown to be fully consistent with
the corresponding inhomogeneous Balescu-Lenard equation and, in the weak
self-gravitating limit, to the inhomogeneous Landau equation. Hence,
it provides an alternative derivation to both and demonstrates their
equivalence. The corresponding stochastic Langevin equations are
presented: they can be a practical alternative to numerically solving
the inhomogeneous Fokker-Planck and Balescu-Lenard equations. The
present formalism allows for a self-consistent description of the
secular evolution of different populations covering a spectrum
of masses, with a proper accounting of the induced secular mass
segregation, which should be of interest to various astrophysical
contexts, from galactic centres to protostellar discs.
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Title: Do asteroids evaporate near pulsars? Induction heating by
pulsar waves revisited
Authors: Kotera, Kumiko; Mottez, Fabrice; Voisin, Guillaume;
Heyvaerts, Jean
2016A&A...592A..52K Altcode: 2016arXiv160505746K
<BR /> Aims: We investigate the evaporation of close-by pulsar
companions, such as planets, asteroids, and white dwarfs, by induction
heating. <BR /> Methods: Assuming that the outflow energy is dominated
by a Poynting flux (or pulsar wave) at the location of the companions,
we calculate their evaporation timescales, by applying the Mie
theory. <BR /> Results: Depending on the size of the companion compared
to the incident electromagnetic wavelength, the heating regime varies
and can lead to a total evaporation of the companion. In particular,
we find that inductive heating is mostly inefficient for small
pulsar companions, although it is generally considered the dominant
process. <BR /> Conclusions: Small objects like asteroids can survive
induction heating for 10<SUP>4</SUP> yr at distances as small as 1
R<SUB>⊙</SUB> from the neutron star. For degenerate companions,
induction heating cannot lead to evaporation and another source
of heating (likely by kinetic energy of the pulsar wind) has to be
considered. It was recently proposed that bodies orbiting pulsars are
the cause of fast radio bursts; the present results explain how those
bodies can survive in the pulsar's highly energetic environment.
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Title: General solution for the vacuum electromagnetic field in the
surroundings of a rotating star
Authors: Bonazzola, S.; Mottez, F.; Heyvaerts, J.
2015A&A...573A..51B Altcode:
<BR /> Aims: Many recent observations of pulsars and magnetars can be
interpreted in terms of neutron stars with multipole electromagnetic
fields. As a first approximation, we investigate the multipole
magnetic and electric fields in the environment of a rotating star when
this environment is deprived of plasma. <BR /> Methods: We compute a
multipole expansion of the electromagnetic field in vacuum for a given
magnetic field on the conducting surface of the rotating star. Then,
we consider a few consequences of multipole fields of pulsars. <BR />
Results: We provide an explicit form of the solution. For each spherical
harmonic of the magnetic field, the expansion contains a finite number
of terms. A multipole magnetic field can provide an explanation for
the stable sub-structures of pulses, and they offer a solution to the
problem of current closure in pulsar magnetospheres. <BR /> Conclusions:
This computation generalises the widely used model of a rotating star
in vacuum with a dipole field. It can be especially useful as a first
approximation to the electromagnetic environment of a compact star,
for instance a neutron star, with an arbitrarily magnetic field.
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Title: Towards a theory of extremely intermittent
pulsars. II. Asteroids at a close distance
Authors: Mottez, F.; Bonazzola, S.; Heyvaerts, J.
2013A&A...555A.126M Altcode: 2013arXiv1305.6726M
<BR /> Aims: We investigate whether there may be one or many companions
orbiting at close distance to the light cylinder around the extremely
intermittent pulsars PSR B1931+24 and PSR J1841-0500. These pulsars,
behaving in a standard way when they are active, also "switch off" for
durations of several days, during which their magnetospheric activity
is interrupted or reduced. <BR /> Methods: We constrained our analysis
on eight fundamental properties of PSR B1931+24 that summarise the
observations. We considered that the disruption/activation of the
magnetospheric activity would be caused by the direct interaction
of the star with the Alfvén wings emanating from the companions. We
also considered the recurrence period of 70 days to be the period of
precession of the periastron of the companions orbit. We analysed
in which way the time scale of the "on/off" pseudo-cycle would
be conditioned by the precession of the periastron and not by the
orbital time scale, and we derived a set of orbital constraints that
we solved. We then compared the model, based on PSR 1931+24, with the
known properties of PSR 1841+0500. <BR /> Results: We conclude that
PSR B1931+24 may be surrounded at a close distance to the star by
a stream of small bodies of kilometric or sub-kilometric sizes that
could originate from the tidal disruption of a body of moderate size
that fell at a close distance to the neutron star on an initially very
eccentric orbit. This scenario is also compatible with the properties
of PSR J1841-0500, although the properties of PSR J1841-0500 are,
as of now, less constrained. <BR /> Conclusions: These results
raise new questions. Why are the asteroids not yet evaporated? What
kind of interaction can explain the disruption of the magnetospheric
activity? These questions are the object of two Papers in preparation
that will complete the present analysis.
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Title: Towards a theory of extremely intermittent pulsars. I. Does
something orbit PSR B1931+24?
Authors: Mottez, F.; Bonazzola, S.; Heyvaerts, J.
2013A&A...555A.125M Altcode: 2013arXiv1305.6724M
<BR /> Aims: We investigate whether one or many companions are
orbiting the extremely intermittent pulsar PSR B1931+24. <BR />
Methods: We constrained our analysis on previous observations of eight
fundamental properties of PSR B1931+24. The most puzzling properties
are the intermittent nature of the pulsar's activity, with active
and quiet phases that alternate quasi-periodically; the variation of
the slowing-down rate of its period between active and quiet phases;
and because there are no timing residuals, it is highly unlikely that
the pulsar has a massive companion. Here, we examine the effects that
one putative companion immersed in the magnetospheric plasma or the
wind of the pulsar might have, as well as the associated electric
current distribution. We analysed several possibilities for the
distance and orbit of this hypothetical companion and the nature of
its interaction with the neutron star. <BR /> Results: We show that if
the quasi-periodic behaviour of PSR B1931+24 was caused by a companion
orbiting the star with a period of 35 or 70 days, the radio emissions,
usually considered to be those of the pulsar would in that specific case
be emitted in the companion's environment. We analysed four possible
configurations and conclude that none of them would explain the whole
set of peculiar properties of PSR 1931+24. We furthermore considered a
period of 70 days for the precession of the periastron associated to
an orbit very close to the neutron star. This hypothesis is analysed
in a companion paper.
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Title: Polarization transfer in relativistic magnetized plasmas
Authors: Heyvaerts, Jean; Pichon, Christophe; Prunet, Simon; Thiébaut,
Jérôme
2013MNRAS.430.3320H Altcode: 2013MNRAS.tmp..843H; 2012arXiv1211.7352H
The polarization transfer coefficients of a relativistic magnetized
plasma are derived. These results apply to any momentum distribution
function of the particles, isotropic or anisotropic. Particles interact
with the radiation either in a non-resonant mode when the frequency
of the radiation exceeds their characteristic synchrotron emission
frequency or quasi-resonantly otherwise. These two classes of particles
contribute differently to the polarization transfer coefficients. For
a given frequency, this dichotomy corresponds to a regime change in
the dependence of the transfer coefficients on the parameters of the
particle's population, since these parameters control the relative
weight of the contribution of each class of particles. Our results apply
to either regimes as well as the intermediate one. The derivation of the
transfer coefficients involves an exact expression of the conductivity
tensor of the relativistic magnetized plasma that has not been used
hitherto in this context. Suitable expansions valid at frequencies
much larger than the cyclotron frequency allow us to analytically
perform the summation over all resonances at high harmonics of the
relativistic gyrofrequency.
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Title: The magnetic coupling of planets and small bodies with a
pulsar's wind
Authors: Mottez, F.; Heyvaerts, J.
2012sf2a.conf..597M Altcode: 2012arXiv1210.0684M
We investigate the electromagnetic interaction of a relativistic stellar
wind with a planet or a smaller body in orbit around a pulsar. This
may be relevant to objects such as PSR B1257+12 and PSR B1620-26 that
are expected to hold a planetary system, or to pulsars with suspected
asteroids or comets. Most models of pulsar winds predict that,
albeit highly relativistic, they are slower than Alfvén waves. In
that case, a pair of stationary Alfvén waves, called Alfvén wings
(AW), is expected to form on the sides of the planet. The wings expand
far into the pulsar's wind and they could be strong sources of radio
emissions. The Alfvén wings would cause a significant drift over
small bodies such as asteroids and comets.
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Title: The magnetic wake of planets and small bodies in a pulsar's
wind
Authors: Mottez, F.; Heyvaerts, J.
2012epsc.conf..153M Altcode: 2012espc.conf..153M
We investigate the electromagnetic interaction of a relativistic
and magnetized stellar wind with a planet or a smaller body in orbit
around a pulsar. This may be relevant to objects such as PSR B1257+12
and PSR B1620-26 that are expected to hold a planetary system, or
to other pulsars with suspected asteroids or comets. Most models
predict that, albeit highly relativistic, pulsar's winds are slower
than Alfvén waves. In that case, a pair of stationary Alfvén waves,
called Alfvén wings (AW), is expected to form on the sides of the
planet. They are the magnetic wake of the body into the plasma flow,
like the wake of a boat left into the sea (with a similar shape). The
theory of Alfvén wings was initially developed in the context of the
Io- Jupiter interaction. We have extended it to relativistic winds,
and we have studied the possible consequences that could be relevant
for observations : possible radio emissions from pulsar's planets,
and a magnetic force configuration that can deeply modify the orbit
of the smaller bodies (asteroids, comets).
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Title: Non-linear simple relativistic Alfvén waves in astrophysical
plasmas
Authors: Heyvaerts, J.; Lehner, T.; Mottez, F.
2012A&A...542A.128H Altcode:
<BR /> Aims: Large amplitude MHD perturbations are generated in
magnetized tenuous relativistically moving plasmas, such as winds
emitted by compact stellar objects or galactic nuclei, when a rapid
change occurs at their boundaries or when an obstacle is present in
them. These perturbations may involve relativistic motions in the
rest-frame of the unperturbed plasma. In this paper, we calculate
the characteristics and the structure of relativistic non-linear
Alfvén waves. <BR /> Methods: We establish these properties for
special-relativistic perturbations occurring in a particular type
of non-linear waves, the simple waves. <BR /> Results: We derive
the conditions applicable to Alfvénic perturbations in a cold
flow. We calculate the characteristics of these perturbations and
the structure of wave trains of finite extent in the propagation
direction of these characteristics, as observed in the unperturbed
fluid proper frame. We determine the velocity of the characteristics
with respect to any observer. This velocity is found to be a first
integral, constant in time and space. This implies that relativistic
Alfvénic perturbations are channeled, in the unperturbed fluid proper
frame, by the unperturbed magnetic field and travel along this field
neither steepening nor breaking into shocks. For finite wave trains,
the Lorentz factor is found to be limited by some maximum value that
we calculate and that depends on the ratio of proper magnetic energy
density to material energy density in the unperturbed fluid.
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Title: The magnetic coupling of planets and small bodies with a
pulsar's wind
Authors: Mottez, F.; Heyvaerts, J.
2011epsc.conf...23M Altcode: 2011DPS....43...23M
We investigate the electromagnetic interaction of a relativistic stellar
wind with a planet or a smaller body in orbit around a pulsar. This
may be relevant to objects such as PSR B1257+12 and PSR B1620-26 that
are expected to hold a planetary system, or to pulsars with suspected
asteroids or comets. Most models of pulsar winds predict that, albeit
highly relativistic, they are slower than Alfvén waves. In that
case, a pair of stationary Alfvén waves, called Alfvén wings (AW),
is expected to form on the sides of the planet. The wings expands far
into the pulsar's wind. We have extended the theory of Alfvén wings,
initially developed in the context of the Io-Jupiter interaction,
to relativistic winds, and we have studied the possible consequences
that could be relevant for observations.
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Title: Magnetic coupling of planets and small bodies with a pulsar
wind
Authors: Mottez, F.; Heyvaerts, J.
2011A&A...532A..21M Altcode: 2011arXiv1106.0657M
<BR /> Aims: We investigate the electromagnetic interaction of a
relativistic stellar wind with a planet or a smaller body in orbit
around the star. This may be relevant to objects orbiting a pulsar
that are expected to hold a planetary system, such as PSR B1257+12 and
PSR B1620-26, or to pulsars with suspected asteroids or comets. <BR
/> Methods: We extend the theory of Alfvén wings to relativistic
winds. <BR /> Results: When the wind is relativistic but slower than
the total Alfvén speed, a system of electric currents carried by
a stationary Alfvénic structure is driven by the planet or by its
surroundings.For an Earth-like planet around a "standard" second
pulsar, the associated current can reach the same magnitude as the
Goldreich-Julian current that powers the pulsar's magnetosphere.
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Title: A magnetic thrust action on small bodies orbiting a pulsar
Authors: Mottez, F.; Heyvaerts, J.
2011A&A...532A..22M Altcode: 2011arXiv1106.0659M
<BR /> Aims: We investigate the electromagnetic interaction of
a relativistic stellar wind with small bodies in orbit around the
star. <BR /> Methods: Based on our work on the theory of Alfvén wings
to relativistic winds presented in a companion paper, we estimate the
force exerted by the associated current system on orbiting bodies and
evaluate the resulting orbital drift. <BR /> Results: This Alfvénic
structure is found to have no significant influence on planets or
smaller bodies orbiting a millisecond pulsar. On the time scale of
millions of years, it can however affect the orbit of bodies with a
diameter of 100 km around standard pulsars with a period P ~ 1 s and a
magnetic field B ~ 10<SUP>8</SUP> T. Kilometer-sized bodies experience
drastic orbital changes on a time scale of 10<SUP>4</SUP> years.
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Title: A Balescu-Lenard-type kinetic equation for the collisional
evolution of stable self-gravitating systems
Authors: Heyvaerts, J.
2010MNRAS.407..355H Altcode: 2010MNRAS.tmp.1045H
A kinetic equation for the collisional evolution of stable, bound,
self-gravitating and slowly relaxing systems is established, which
is valid when the number of constituents is very large. It accounts
for the detailed dynamics and self-consistent dressing by collective
gravitational interaction of the colliding particles, for the system's
inhomogeneity and for different constituents' masses. It describes
the coupled evolution of collisionally interacting populations, such
as stars in a thick disc and the molecular clouds off which they
scatter. <P />The kinetic equation derives from the BBGKY hierarchy
in the limit of weak, but non-vanishing, binary correlations, an
approximation which is well justified for large stellar systems. The
evolution of the 1-body distribution function is described in
action-angle space. The collective response is calculated using a
biorthogonal basis of pairs of density-potential functions. <P />The
collision operators are expressed in terms of the collective response
function allowed by the existing distribution functions at any given
time and involve particles in resonant motion. These equations are shown
to satisfy an H theorem. Because of the inhomogeneous character of the
system, the relaxation causes the potential as well as the orbits of the
particles to secularly evolve. The changing orbits also cause the angle
Fourier coefficients of the basis potentials to change with time. We
derive the set of equations which describes this coupled evolution
of distribution functions, potential and basis Fourier coefficients
for spherically symmetric systems. In the homogeneous limit, which
sacrifices the description of the evolution of the spatial structure of
the system but retains the effect of collective gravitational dressing,
the kinetic equation reduces to a form similar to the Balescu-Lenard
equation of plasma physics.
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Title: A Balescu-Lenard type kinetic equation fot the collisional
evolution of stable self-gravitating systems
Authors: Heyvaerts, Jean
2010arXiv1005.0195H Altcode:
A kinetic equation for the collisional evolution of stable, bound,
self gravitating and slowly relaxing systems is established, which
is valid when the number of constituents is very large. It accounts
for the detailed dynamics and self consistent dressing by collective
gravitational interaction of the colliding particles, for the system's
inhomogeneity and for different constituent's masses. The evolution
of the one-body distribution function is described in action angle
space. The collision operators are expressed in terms of the collective
response function allowed by the existing distribution functions at
any given time and involve particles in resonant motions. The set of
equations which describe the coupled evolution of the distribution
functions and of the potential is derived for spherical systems. In the
homogeneous limit, which sacrifices the description of the evolution
of the spatial structure of the system, but retains the effects of
collective gravitational dressing, the kinetic equation reduces to a
form similar to the Balescu-Lenard equation of plasma physics.
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Title: Luminosity of a quark star undergoing torsional oscillations
and the problem of γ-ray bursts
Authors: Heyvaerts, J.; Bonazzola, S.; Bejger, M.; Haensel, P.
2009A&A...496..317H Altcode: 2008arXiv0811.1090H
Aims: We discuss whether the winding-up of the magnetic field
by differential rotation in a new-born quark star can produce a
sufficiently-high, energy, emission rate of sufficiently long duration
to explain long gamma-ray bursts. <BR />Methods: In the context of
magnetohydrodynamics, we study the torsional oscillations and energy
extraction from a new-born, hot, differentially-rotating quark star. <BR
/>Results: The new-born compact star is a rapid rotator that produces a
relativistic, leptonic wind. The star's torsional oscillation modulates
this wind emission considerably when it is odd and of sufficient
amplitude, which is relatively easy to reach. Odd oscillations may occur
just after the formation of a quark star. Other asymmetries can cause
similar effects. The buoyancy of wound-up magnetic fields is inhibited,
or its effects are limited, by a variety of different mechanisms. Direct
electromagnetic emission by the torsional oscillation in either an
outside vacuum or the leptonic wind surrounding the compact object is
found to be insignificant. In contrast, the twist given to the outer
magnetic field by an odd torsional oscillation is generally sufficient
to open the star's magnetosphere. The Poynting emission of the star
in its leptonic environment is then radiated from all of its surface
and is enhanced considerably during these open episodes, tapping at
the bulk rotational energy of the star. This results in intense energy
shedding in the first tens of minutes after the collapse of magnetized
quark stars with an initial poloidal field of order of 10<SUP>14</SUP>
Gauss, sufficient to explain long gamma-ray bursts.
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Title: Coronal Heating at Separators and Separatrices
Authors: Priest, E. R.; Longcope, D. W.; Heyvaerts, J.
2005ApJ...624.1057P Altcode:
Several ways have been proposed for heating the solar corona by magnetic
reconnection in current sheets, depending on the nature of both the
coronal magnetic field and the photospheric driving. Two ways that
have recently been considered involve the formation of such current
sheets either along separatrices (surfaces that separate topologically
distinct regions) or along separators (intersections of separatrices
linking one null point to another). The effect of slow photospheric
motions on complex coronal magnetic configurations will in general
be to generate three forms of electric current, namely, nonsingular
distributed currents, singular currents on separatrices and singular
currents on separators. These currents are not mutually exclusive
but will in general coexist in the same configuration. The aim of
this paper is to compare energy storage and heating that occurs at
separatrices and separators. We use reduced MHD to model coronal loops
that are much longer than they are wide, and we construct a series of
examples for the formation of current sheets along separatrices and
separators. We deduce that coronal heating is of comparable importance
at separatrices and separators. Separatrices are twice as effective
for observed small footpoint motions, while separators are twice as
effective in the initial build-up of a new flux domain.
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Title: Effects of Complexity on the Flux-Tube Tectonics Model
Authors: Close, R. M.; Heyvaerts, J. F.; Priest, E. R.
2004SoPh..225..267C Altcode:
The quiet-Sun magnetic field emerges through the solar photosphere
in a multitude of mixed-polarity magnetic concentrations and is
subsequently tangled up into intricate regions of interconnecting
flux. Moreover, since these discrete concentrations are likely to be
extremely small in size, with fluxes of around only 10<SUP>17</SUP>
Mx, the number of such flux sources in, say, a supergranule, will be
extremely large. The flux-tube tectonics model of Priest, Heyvaerts,
and Title (2002) demonstrated how the formation and dissipation of
current sheets along the separatrices that separate the regions of
different connectivity are likely to make an important contribution
to coronal heating. Since the full complexity of the magnetic field
is below present observable scales, this study examines the effect
of having the magnetic flux emerge through configurations structured
on smaller and smaller scales. It is found that, by fixing the amount
of flux emerging into a given 2D region, the main factors influencing
the current build-up along the separatrices are the number of sources
through which the flux emerges and the spatial distribution of the
sources on the photosphere. The free energy (i.e., that above potential)
is stored lower and lower in the atmosphere as the complexity of the
system increases. A simple comparison is then made between coronal
heating by separator currents and by separatrix currents. It is
found that both result in comparable amounts of energy release, with
separatrix heating being the more dominant.
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Title: Structuring and support by Alfvén waves around prestellar
cores
Authors: Folini, D.; Heyvaerts, J.; Walder, R.
2004A&A...414..559F Altcode: 2003astro.ph.10525F
Observations of molecular clouds show the existence of starless, dense
cores, threaded by magnetic fields. Observed line widths indicate
these dense condensates to be embedded in a supersonically turbulent
environment. Under these conditions, the generation of magnetic waves is
inevitable. In this paper, we study the structure and support of a 1D
plane-parallel, self-gravitating slab, as a monochromatic, circularly
polarized Alfvén wave is injected in its central plane. Dimensional
analysis shows that the solution must depend on three dimensionless
parameters. To study the nonlinear, turbulent evolution of such a slab,
we use 1D high resolution numerical simulations. For a parameter range
inspired by molecular cloud observations, we find the following. 1)
A single source of energy injection is sufficient to force persistent
supersonic turbulence over several hydrostatic scale heights. 2)
The time averaged spatial extension of the slab is comparable to the
extension of the stationary, analytical WKB solution. Deviations,
as well as the density substructure of the slab, depend on the
wave-length of the injected wave. 3) Energy losses are dominated by
loss of Poynting-flux and increase with increasing plasma beta. 4)
Good spatial resolution is mandatory, making similar simulations in
3D currently prohibitively expensive.
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Title: Course 1: Accretion and Ejection-Related MHD
Authors: Heyvaerts, Jean
2004adjh.conf....3H Altcode: 2004LHSS...78....3H
This lecture is an introduction to MHD. Relevant equations, both in the
classical and special-relativistic regimes are derived. The magnetic
field evolution is considered both in the perfect-MHD limit and when
weak resistivity is present, giving rise to reconnection flows. A
short section gives a flavour of dynamo theory. Examples of simple
stationnary flows and equilibria are then presented. Stationnary,
axisymmetric, rotating perfect-MHD winds and jets are discussed in some
more detail. Their asymptotic structure is described. The last sections
deal with small motions about an equilibrium and stability. These
issues are illustrated by a few classical examples. The last section
discusses linear aspects of the magneto-rotationnal instability.
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Title: Cross-field charge transport by the diocotron instability in
pulsar magnetospheres with gaps
Authors: Pétri, J.; Heyvaerts, J.; Bonazzola, S.
2003A&A...411..203P Altcode:
In a previous work, we have shown by linear analysis that a thin charged
disk in differential rotation in the magnetosphere of a neutron star
with vacuum gaps is unstable to a collisionless instability induced
in non-neutral plasmas by differential rotation, the diocotron
instability. In this paper we study the long-time-scale evolution
of this instability in the non-linear regime by means of both direct
numerical simulations and a quasilinear model. We show that, when the
disk is externally fed with charged particles produced by a moderate
pair creation activity in the magnetosphere, the diocotron instability
causes diffusion of the charged particles across the magnetic
field lines outwards. An equatorial cross-field electric current is
observed to form, carrying a net charge flux radially outwards. This
constitutes a hitherto ignored charge transport mechanism in the pulsar
magnetosphere. We briefly discuss how this turbulent charge transport
mechanism could bear on the problem of electric current closure in
pulsar's magnetospheres. <P />Appendices A and B are only available
in electronic form at\ http://www.edpsciences.org
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Title: Global Asymptotic Solutions for Nonrelativistic
Magnetohydrodynamic Jets and Winds
Authors: Heyvaerts, Jean; Norman, Colin
2003ApJ...596.1270H Altcode: 2003astro.ph..9128H
We present general and global analytical solutions, valid from
pole to equator, for the asymptotic structure of nonrelativistic,
rotating, stationary, axisymmetric, polytropic, unconfined, perfect MHD
winds. The standard five Lagrangian first integrals along field lines
are assumed known. The asymptotic structure of such winds consists
of field regions virtually devoid of poloidal current. We show that a
Hamilton-Jacobi equation, or equivalently a Grad-Shafranov equation,
gives the asymptotic structure in the field regions. These field regions
are bordered by current-carrying boundary layers around the polar axis
and near null magnetic surfaces. Current closure is achieved in a number
of separate cells bordered by null surfaces. The solution is given in
the form of matched asymptotics separately valid outside and inside
these boundary layers. The polar boundary layer is pressure supported
against the pinching force exerted by the axial poloidal current and
has the structure of a current pinch, while the null-surface boundary
layers have the structure of current sheet pinches. We establish a
consistency relation between the residual poloidal current at large
distances and the axial pressure. We find a similar relation for the
current sheets at null surfaces. We further consider the case where the
polar boundary layer is force-free. The geometry of magnetic surfaces
in all parts of the asymptotic domain is explicitly deduced in terms
of the first integrals. The solutions have the following general
properties:1. For winds that are kinetic energy-dominated at infinity
we derive WKBJ analytic solutions whose magnetic surfaces focus into
paraboloids. The current slowly weakens as the inverse of the logarithm
of the distance to the wind source, while the axial plasma density
falls off as a negative power of this logarithm.2. For winds carrying
Poynting flux at large distances the solutions asymptotically approach
to nested cylindrical and conical magnetic surfaces.
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Title: Kinetic Energy Flux versus Poynting Flux in Magnetohydrodynamic
Winds and Jets: The Intermediate Regime
Authors: Heyvaerts, Jean; Norman, Colin
2003ApJ...596.1256H Altcode: 2003astro.ph..9143H
We show that the formal asymptotic limit for all rotating polytropic
axisymmetric perfect MHD flows is a kinetic energy-dominated wind
that collimates to paraboloids around the symmetry axis. We reach this
result by showing that another a priori possible solution with finite
Poynting flux can be excluded on the following physical grounds: (1)
the wind velocity does not exceed the fast mode speed everywhere and
(2) the circumpolar current increases with distance from the source. We
show that asymptotic hoop stress collimation is mathematically robust
and we give strong arguments why recent “anticollimation” claims are
not correct. However, in practice, because of the very slow logarithmic
decline of the circumpolar current with increasing distance from the
source, there is a broad intermediate regime with significant Poynting
flux. This intermediate regime, rather than the mathematically exact
asymptotic regime, may well apply along the finite length of the jet. We
briefly discuss peculiarities that would be associated with Poynting
jets in the intermediate regime. Force-free initial conditions in the
near field are most likely to produce such jets, in which most of the
energy flux is electromagnetic.
---------------------------------------------------------
Title: Global Asymptotic Solutions for Relativistic
Magnetohydrodynamic Jets and Winds
Authors: Heyvaerts, Jean; Norman, Colin
2003ApJ...596.1240H Altcode: 2003astro.ph..9132H
We consider relativistic, stationary, axisymmetric, polytropic,
unconfined, perfect MHD winds, assuming their five Lagrangian first
integrals to be known. The asymptotic structure consists of field
regions bordered by boundary layers along the polar axis and at null
surfaces, such as the equatorial plane, which have the structure of
charged column or sheet pinches supported by plasma or magnetic poloidal
pressure. In each field-region cell, the proper current (defined here as
the ratio of the asymptotic poloidal current to the asymptotic Lorentz
factor) remains constant. Our solution is given in the form of matched
asymptotic solutions separately valid outside and inside the boundary
layers. A Hamilton-Jacobi equation, or equivalently a Grad-Shafranov
equation, gives the asymptotic structure in the field regions of
winds that carry Poynting flux to infinity. An important consistency
relation is found to exist between axial pressure, axial current,
and asymptotic Lorentz factor. We similarly derive WKB-type analytic
solutions for winds that are kinetic energy-dominated at infinity and
whose magnetic surfaces focus to paraboloids. The density on the axis
in the polar boundary column is shown to slowly fall off as a negative
power of the logarithm of the distance to the wind source. The geometry
of magnetic surfaces in all parts of the asymptotic domain, including
boundary layers, is explicitly deduced in terms of the first integrals.
---------------------------------------------------------
Title: Magnetized accretion
Authors: Heyvaerts, J.
2003EAS.....7..309H Altcode:
This lecture reviews in simple terms the general subject of large
scale magnetic field coupling to plasma flows in the vicinity of
accreting compact stars. The relevant astrophysical phenomenology is
summarized. Disk interaction with the magnetosphere of accreting stars
is first discussed, in particular the structure of the magnetopause,
its stability and plasma ejection in so-called propeller systems. The
physics of accretion/ejection is then considered. Acceleration and
focusing mechanisms of jets from accretion disks around compact stars
or black holes and the question of the self-consistency of accretion
and ejection are described. By contrast, small scale MHD turbulence in
disks is not discussed, neither are accretion columns near the polar
caps of neutron stars or white dwarfs. The reader is only assumed to
have some basic knowledge of astrophysics and of fluid mechanics and
electromagnetism.
---------------------------------------------------------
Title: A Flux-Tube Tectonics Model for Solar Coronal Heating Driven
by the Magnetic Carpet
Authors: Priest, Eric R.; Heyvaerts, Jean F.; Title, Alan M.
2002ApJ...576..533P Altcode:
We explore some of the consequences of the magnetic carpet for coronal
heating. Observations show that most of the magnetic flux in the
quiet Sun emerges as ephemeral regions and then quickly migrates
to supergranule boundaries. The original ephemeral concentrations
fragment, merge, and cancel over a time period of 10-40 hr. Since
the network photospheric flux is likely to be concentrated in units
of 10<SUP>17</SUP> Mx or smaller, there will be myriads of coronal
separatrix surfaces caused by the highly fragmented photospheric
magnetic configuration in the quiet network. We suggest that the
formation and dissipation of current sheets along these separatrices
are an important contribution to coronal heating. The dissipation of
energy along sharp boundaries we call, by analogy with geophysical
plate tectonics, the tectonics model of coronal heating. Similar to
the case on Earth, the relative motions of the photospheric sources
will drive the formation and dissipation of current sheets along a
hierarchy of such separatrix surfaces at internal dislocations in the
corona. In our preliminary assessment of such dissipation we find
that the heating is fairly uniform along the separatrices, so that
each elementary coronal flux tube is heated uniformly. However, 95%
of the photospheric flux closes low down in the magnetic carpet and
the remaining 5% forms large-scale connections, so the magnetic carpet
will be heated more effectively than the large-scale corona. This
suggests that unresolved observations of coronal loops should exhibit
enhanced heating near their feet in the carpet, while the upper parts of
large-scale loops should be heated rather uniformly but less strongly.
---------------------------------------------------------
Title: Diocotron instability in pulsar electrospheres. I. Linear
analysis
Authors: Pétri, J.; Heyvaerts, J.; Bonazzola, S.
2002A&A...387..520P Altcode:
In a previous work, we have shown that the electrospheric plasma of
a pulsar's magnetosphere with vacuum gaps is subject to differential
rotation in the equatorial belt. Here we examine the stability of a
simplified model of this belt. The model consists of a charged thin
plasma disc in differential rotation, embedded in a dipolar magnetic
field anchored in the neutron star. In the linearized electrostatic
perturbation approximation, this disc appears to be unstable to the
so-called diocotron instability. We present several eigenspectra
and eigenfunctions for different disc models, which differ by the
total charge of the disc-star system. Velocity and electric field
perturbations are also shown in the disc plane for a few fast-growing
modes. Increasing the total charge has a stabilizing effect, in the
sense that the growth rate of the fastest-growing eigenvalue decreases
with total charge and eventually vanishes. When the system is unstable,
the growth rates are of the order of the azimuthal rotation rate. This
means that the diocotron instability, which develops in a few pulsar's
periods, should be very efficient in causing particles to migrate
across magnetic surfaces.
---------------------------------------------------------
Title: Global static electrospheres of charged pulsars
Authors: Pétri, J.; Heyvaerts, J.; Bonazzola, S.
2002A&A...384..414P Altcode:
In this paper we present self-consistent models of the magnetosphere
of inactive, charged, aligned rotator pulsars. We have devised an
efficient semi-analytical and numerical algorithm to construct such
models. The only free parameter is the total charge of the system. These
charge-separated “electrospheres" consist of an equatorial belt
carrying charge of one sign, partially in differential rotation, and of
two oppositely charged domes located over the poles which corotate with
the neutron star. The dependence of the shape of these plasma-filled
regions surrounding the star on the total charge of the system and
of their differential rotation is investigated. It is shown that our
solutions are stable to vacuum breakdown by electron-positron pair
production in most of the light-cylinder volume, except perhaps in the
case of millisecond pulsars. The small regions where vacuum breakdown
occurs are shown to behave merely as an effective extension of the
star's volume. We have also found that no permanent null-charged wind
emanating from the polar caps can exist in a stationary state. Indeed,
for a given total charge of the system determined by the net outgoing
charged flux, the potential configuration becomes unfavorable to
particles escaping to infinity. Finally, we have shown that the
geometric and kinematic structure of the electrosphere is uniquely
determined by the total charge of the system.
---------------------------------------------------------
Title: Asymptotic structure of MHD winds and jets
Authors: Heyvaerts, J.; Norman, C.
2001A&AT...20..295H Altcode:
We describe asymptotic solutions for stationary, axisymmetric,
perfect MHD, polytropic winds, both classical and relativistic. They
are expressed as field-region solutions and current-carrying boundary
layer solutions smoothly joined by asymptotic matching. The vicinity of
the polar axis is one of these boundary layers. In general, the boundary
layers are null surfaces. It is argued that the boundary layer regions,
in particular the axial one, should stand out observationally because
of their larger density and activity. We associate the axial boundary
layer with a jet. Current closure is self-consistently achieved in
these solutions, which we obtain both in the case of vanishing or
non-vanishing circumpolar asymptotic current. It is shown that the
total current about the polar axis is simply related to the set of the
five first integrals which characterize the flow and that non-vanishing
values of this quantity are not available to all winds, but only to a
restricted class which we present here. We show that winds of this class
separate clearly into an axial jet and a circum-equatorial conical wind.
---------------------------------------------------------
Title: Magnetohydrodynamics of Astrophysical Winds
Authors: Heyvaerts, J.
2000eaa..bookE2227H Altcode:
Stellar mass loss became an issue when Parker (1958) first introduced
the concept of the solar wind. Such a thermal wind results from
coronal heating processes indirectly associated with the existence of a
convection zone, also responsible, with rotation, for the star's dynamo
action (see articles on SOLAR WIND: THEORY, CORONAL HEATING MECHANISMS,
SOLAR INTERIOR: CONVECTION ZONE and MAGNETOHYDROD...
---------------------------------------------------------
Title: Coronal Heating Mechanisms
Authors: Heyvaerts, J.
2000eaa..bookE2269H Altcode:
Evidence for a hot coronal medium...
---------------------------------------------------------
Title: A Method to Determine the Heating Mechanisms of the Solar
Corona
Authors: Priest, E. R.; Foley, C. R.; Heyvaerts, J.; Arber, T. D.;
Mackay, D.; Culhane, J. L.; Acton, L. W.
2000ApJ...539.1002P Altcode:
One of the paradigms about coronal heating has been the belief that the
mean or summit temperature of a coronal loop is completely insensitive
to the nature of the heating mechanisms. However, we point out that
the temperature profile along a coronal loop is highly sensitive to
the form of the heating. For example, when a steady state heating
is balanced by thermal conduction, a uniform heating function makes
the heat flux a linear function of distance along the loop, while
T<SUP>7/2</SUP> increases quadratically from the coronal footpoints;
when the heating is concentrated near the coronal base, the heat flux
is small and the T<SUP>7/2</SUP> profile is flat above the base;
when the heat is focused near the summit of a loop, the heat flux
is constant and T<SUP>7/2</SUP> is a linear function of distance
below the summit. It is therefore important to determine how the
heat deposition from particular heating mechanisms varies spatially
within coronal structures such as loops or arcades and to compare it
to high-quality measurements of the temperature profiles. We propose
a new two-part approach to try and solve the coronal heating problem,
namely, first of all to use observed temperature profiles to deduce the
form of the heating, and second to use that heating form to deduce the
likely heating mechanism. In particular, we apply this philosophy to
a preliminary analysis of Yohkoh observations of the large-scale solar
corona. This gives strong evidence against heating concentrated near the
loop base for such loops and suggests that heating uniformly distributed
along the loop is slightly more likely than heating concentrated at
the summit. The implication is that large-scale loops are heated in
situ throughout their length, rather than being a steady response
to low-lying heating near their feet or at their summits. Unless
waves can be shown to produce a heating close enough to uniform, the
evidence is therefore at present for these large loops more in favor
of turbulent reconnection at many small randomly distributed current
sheets, which is likely to be able to do so. In addition, we suggest
that the decline in coronal intensity by a factor of 100 from solar
maximum to solar minimum is a natural consequence of the observed
ratio of magnetic field strength in active regions and the quiet Sun;
the altitude of the maximum temperature in coronal holes may represent
the dissipation height of Alfvén waves by turbulent phase mixing;
and the difference in maximum temperature in closed and open regimes
may be understood in terms of the roles of the conductive flux there.
---------------------------------------------------------
Title: Astrophysical MHD jets
Authors: Heyvaerts, J.
2000NuPhS..80...51H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Introduction to MHD
Authors: Heyvaerts, Jean
2000LNP...553....1H Altcode: 2000tech.conf....1H
LNP 553, p. 1 ff.
---------------------------------------------------------
Title: Outflows from magnetic rotators. II. Asymptotic structure
and collimation
Authors: Lery, T.; Heyvaerts, J.; Appl, S.; Norman, C. A.
1999A&A...347.1055L Altcode: 1999astro.ph..2365L
The asymptotic structure of outflows from rotating magnetized objects
confined by a uniform external pressure is calculated. The flow is
assumed to be perfect MHD, polytropic, axisymmetric and stationary. The
well known associated first integrals together with the confining
external pressure, which is taken to be independent of the distance
to the source, determine the asymptotic structure. The integrals are
provided by solving the flow physics for the base within the framework
of the model developed in Paper I (Lery et al. 1998), which assumes
conical geometry below the fast mode surface, and ensures the Alfvén
regularity condition. Far from the source, the outflow collimate
cylindrically. Slow (i.e. with small rotation parameter omega )
rigid rotators give rise to diffuse electric current distribution in
the asymptotic region. They are dominated by gas pressure. Fast rigid
rotators have a core-envelope structure in which a current carrying core
is surrounded by an essentially current free region where the azimuthal
magnetic field dominates. The total asymptotic poloidal current carried
away decreases steadily with the external pressure. A sizeable finite
current remains present for fast rotators even at exceedingly small,
but still finite, pressure.
---------------------------------------------------------
Title: Astrophysical Jets
Authors: Heyvaerts, J.
1998tx19.confE.372H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Influence of viscosity laws on the transition to the
self-gravitating part of accretion disks
Authors: Bardou, Anne; Heyvaerts, Jean; Duschl, Wolfgang J.
1998A&A...337..966B Altcode:
In this paper we obtain a new solution for accretion disks influenced
by self-gravity using the viscosity law proposed by Heyvaerts et
al. (1996). We show how to solve analytically the problem taking
into account self-gravity. Using this new viscosity law, we obtain a
slightly different solution (compared with the standard one) for the
transition between the non self-gravitating and the self-gravitating
part of the disk but no solution in the self-gravitating part where
additional viscosity mechanisms may play a role.
---------------------------------------------------------
Title: Outflows from magnetic rotators. I. Inner structure
Authors: Lery, T.; Heyvaerts, J.; Appl, S.; Norman, C. A.
1998A&A...337..603L Altcode: 1999astro.ph..2364L
A simplified model for the stationary, axisymmetric structure of
magnetized winds with a polytropic equation of state is presented. The
shape of the magnetic surfaces is assumed to be known (conical
in this paper) within the fast magnetosonic surface. The model is
non-self-similar. Rather than solving the equilibrium perpendicular
to the flux surfaces everywhere, solutions are found at the Alfven
surface where it takes the form of the Alfven regularity condition and
at the base of the flow. This constrains the Transfield equilibrium in
that the Alfven regularity condition is imposed and the regularity of
the magnetic surfaces at the Alfven critical surface is ensured. The
model imposes criticality conditions at the slow and fast magnetosonic
critical points using the Bernoulli equation. These Alfven regularity
and criticality conditions are used to evaluate three constants of
motion, the total energy, angular momentum, and the ratio of mass to
magnetic flux alpha , as well as the shape of the critical surfaces. The
rotation rate Omega and the polytropic constant Q as a function of
the magnetic surfaces, together with the mass-to-magnetic flux ratio
on the axis alpha_0 entirely specify the model. Analytic results
are given for limiting cases, and parameter studies are performed by
numerical means. The model accepts any boundary conditions. Numerical
calculations yield the value of the rotation parameter omega . Rotators
can be defined as slow, intermediate or fast according to whether
omega is much less or close to unity or near its maximum value for fast
rotators, ((3)/(2))((3)/(2)) . Given the properties of astrophysical
objects with outflows, the model allows their classification in terms
of the rotation parameter. Critical surfaces are nearly spherical for
slow rotators, but become strongly distorted for rapid rotators. The
fast point remains at a finite distance for finite entropy flows, in
contrast to cold flows.It is found that for a given mass loss rate,
the rotation rate is limited.
---------------------------------------------------------
Title: Nature of the heating mechanism for the diffuse solar corona
Authors: Priest, E. R.; Foley, C. R.; Heyvaerts, J.; Arber, T. D.;
Culhane, J. L.; Acton, L. W.
1998Natur.393..545P Altcode:
The temperature of the Sun's outer atmosphere (the corona) exceeds that
of the solar surface by about two orders of magnitude, but the nature
of the coronal heating mechanisms has long been a mystery. The corona
is a magnetically dominated environment, consisting of a variety of
plasma structures including X-ray bright points, coronal holes and
coronal loops. The latter are closed magnetic structures that occur
over a range of scales and are anchored at each end in the solar
surface. Large-scale regions of diffuse emission are made up of many
long coronal loops. Here we present X-ray observations of the diffuse
corona from which we deduce its likely heating mechanism. We find that
the observed variation in temperature along a loop is highly sensitive
to the spatial distribution of the heating. From a comparison of
the observations and models we conclude that uniform heating gives
the best fit to the loop temperature distribution, enabling us to
eliminate previously suggested mechanisms of low-lying heating near
the footpoints of a loop. Our findings favour turbulent breaking and
reconnection of magnetic field lines as the heating mechanism of the
diffuse solar corona.
---------------------------------------------------------
Title: Alfven wave support of a dwarf molecular cloud. I. an
isothermal model.
Authors: Martin, C. E.; Heyvaerts, J.; Priest, E. R.
1997A&A...326.1176M Altcode:
Dwarf (or dark) molecular clouds and molecular clumps have a lifetime
which is greater than their dynamical time and must therefore be, in an
average sense, in mechanical equilibrium. Equilibrium perpendicular to
a global magnetic field is by magnetic forces and it is proposed that
along the field the gas is supported by an Alfven wave pressure force. A
self-consistent analytical model, utilising a WKB approximation, is
developed for such support. It is found that Alfven waves are indeed
a good candidate for this support, generating model cloud thicknesses
consistent with observations. The effect of damping by the linear
process of ion-neutral friction is considered. It is found that the
damping of the waves is not a necessary condition for the support of
the cloud although weak damping is an advantage. The possible sources
of these waves are discussed.
---------------------------------------------------------
Title: Instabilities in Magnetized Jets: An Origin for Knots?
Authors: Lery, T.; Appl, S.; Heyvaerts, J.; Norman, C. A.
1997AAS...190.5506L Altcode: 1997BAAS...29R1108L
No abstract at ADS
---------------------------------------------------------
Title: Instabilities in MHD Jets
Authors: Lery, T.; Heyvaerts, J.; Appl, S.; Norman, C. A.
1997AAS...190.4117L Altcode: 1997BAAS...29Q.835L
No abstract at ADS
---------------------------------------------------------
Title: Interaction Of A Stellar Magnetic Field With A Turbulent
Accretion Disk
Authors: Bardou, A.; Heyvaerts, J.
1997ASPC..121..205B Altcode: 1997apro.conf..205B; 1997IAUCo.163..205B
No abstract at ADS
---------------------------------------------------------
Title: Asymptotic Structure of Rotating MHD Winds and its Relation
to Wind Boundary Conditions
Authors: Heyvaerts, J.; Norman, C. A.
1997IAUS..182..275H Altcode:
Approximate asymptotic solutions for rotating MHD winds are obtained
analytically in terms of the first integrals of the motion. It
is shown that the paraxial region of such winds is a line-shaped
boundary layer which has, even at large distances, the structure
of a pressure-supported current pinch. A necessary condition for
cylindrically focused asymptotics to be possible is derived. A
simplified model by which the asymptotic structure of such winds can
be obtained in terms of general boundary conditions at the wind source
is introduced. Results of semi numerical solutions of the model are
reported. The model is analytically solved in the limit of very fast
rotators, giving in this particular case an explicit and complete
description of the wind outputs and asymptotic structure in terms of
arbitrary boundary conditions at the wind source.
---------------------------------------------------------
Title: Outflows of magnetized rotators: structure and collimation
Authors: Lery, Thibaut; Heyvaerts, Jean; Appl, Stefan; Norman, Colin A.
1997IAUS..182P.152L Altcode:
How can outflows such as astrophysical winds and jets form and
collimate ? What differences exhibit these two types of plasma flows
? This work makes an attempt to answer those questions thanks to a
simple model that deals with the time-independent and axisymmetric
MHD equations. The geometry of magnetic surfaces has been assumed to
be conical up to the fast magnetosonic critical point. The transversal
force balance is calculated along the Alfven surface, and the critically
conditions are derived from the Bernoulli equation at the two other
critical points. They are used to calculate the specific energy,
the angular momentum and the mass loss rate, that are constant for
each flux surface. This allows to deal with the asymptotic structure
in pressure equilibrium with the surrounding medium. The choice of
boundary conditions is unrestricted. It is found that rigid slow
rotators, associated to stellar winds, carry a diffused poloidal
current, and are gas pressure dominated. On the other hand, rigid
fast rotators, corresponding to jets, carry a current concentrated
around the polar axis, show strongly distorted critical surfaces and
are magnetic pressure dominated at the border of the jet. Regardless
the class of rotator, the angular velocity is bounded from above for
a given mass loss rate, and regardless an external confining pressure,
the collimation of magnetic rotators is asymptotically cylindrical.
---------------------------------------------------------
Title: Magnetic Field Diffusion in Self-consistently Turbulent
Accretion Disks
Authors: Heyvaerts, J.; Priest, E. R.; Bardou, A.
1996ApJ...473..403H Altcode:
We show how the level of turbulence in accretion disks can be derived
from a self-consistency requirement that the associated effective
viscosity should match the instantaneous accretion rate. This method
is applicable when turbulence has a direct energy cascade. Only
limited information on the origin and properties of the turbulence,
such as its injection scale and anisotropy, is needed. The method
is illustrated by considering the case of turbulence originating
from the magnetic shearing instability. The corresponding effective
kinematic viscosity coefficient is shown to scale as the 1/3 power
of surface mass density at a given radius in optically thick disks,
and to be describable by a Shakura-Sunyaev law with α≍0.04. Mass
flow in disks fed at a localized hot spot is calculated for accretion
regimes driven by such turbulence, as well as passive magnetic field
diffusion and dragging. An important result of this analysis is that
thin disks supported by turbulence driven by the magnetic shearing
instability, and more generally any turbulence with injection scale
of order of the disk thickness, are very low magnetic Reynolds number
systems. Turbulent viscosity-driven solutions with negligible field
dragging and no emission of cold winds or jets are natural consequences
of such regimes. Disks of accreting objects that are magnetized enough
to be shielded by a magnetopause, however, may not operate in their
innermost regions in the magnetic shearing instability regime. The
possibility therefore remains to be explored of centrifugally driven
winds emanating from such regions.
---------------------------------------------------------
Title: Outflows of magnetized rotators: structure and collimation.
Authors: Lery, T.; Appl, S.; Heyvaerts, J.
1996AGAb...12..195L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: (Erratum) Stationary subalfvenic and low-β MHD flows in
solar coronal loops and arcades.
Authors: Surlantzis, G.; Demoulin, P.; Heyvaerts, J.; Sauty, C.
1996A&A...310..351S Altcode:
Erratum to Astron. Astrophys. 284, 985-999 (1994)
---------------------------------------------------------
Title: Electric current concentration and kink instability in
line-tied coronal loops.
Authors: Baty, H.; Heyvaerts, J.
1996A&A...308..935B Altcode:
A fully three dimensional non-linear magnetohydrodynamic (MHD)
simulation of the evolution of ideal kink modes in line-tied cylindrical
coronal loops is presented. Two distinct initially unstable equilibria
are considered: the uniform- twist force-free Gold-Hoyle profile,
and a more realistic non force free field with variable and localized
twist profile. In this latter case the instability non-linearly
develops at the axial midplane of the loop a current concentration
radially localized at a resonant point r_s_, where the condition
{vec}(k).{vec}(B)=0 is satisfied, {vec}(k) being the local wave
vector of the mode and {vec}(B) the equilibrium magnetic field. No
such fine scale current structure forms for the Gold-Hoyle profile
since {vec}(k).{vec}(B) then never vanishes. This current concentration
extends along all the loop length down to the photosphere, and it takes
the form of an helical ribbon of intense current with a weakly variable
helicity along the axial direction. A kinked bifurcated equilibrium is
reached in which the current concentration generated is non singular in
the sense that this has a non-zero thickness. Moreover, the non-linear
perturbed current seems to develop a filamentary structure superposed
on the current layer. We discuss the resistive dissipation mechanism
of such fine-scale structures.
---------------------------------------------------------
Title: Interaction of a stellar magnetic field with a turbulent
accretion disk.
Authors: Bardou, A.; Heyvaerts, J.
1996A&A...307.1009B Altcode:
This paper studies systems where a central magnetized object is
surrounded by a turbulent accretion disk. In such systems, magnetic
field lines are embedded in the disk. The purpose here is to find a
stationary magnetic configuration in the corona. The magnetic field
of the central star is considered to be dipolar in the absence of the
accretion disk. In the presence of a thin, turbulent and keplerian
accretion disk, the configuration is not dipolar anymore. We look for
a stationary solution. We show that the interaction of the disk with
the magnetic field stretches magnetic field lines along the disk and
that most of the non-magnetospheric magnetic flux is expelled outside
the disk. A few field lines might open.
---------------------------------------------------------
Title: Outflows of magnetized rotators: structure and collimation.
Authors: Lery, T.; Appl, S.; Heyvaerts, J.
1996AGAb...12..237L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotating MHD Winds
Authors: Heyvaerts, J.
1996LNP...468...31H Altcode: 1996plas.conf...31H
No abstract at ADS
---------------------------------------------------------
Title: Collimation of MHD outflows.
Authors: Heyvaerts, J.; Norman, C. A.
1996ASIC..481..459H Altcode:
This paper discusses the magnetic focusing of MHD winds, in
particular the possibility that they asymptotically converge to a
cylindrical geometry. Basics of magnetized rotating MHD winds are
quickly reviewed. The condition for the solution to remain regular at
the Alfvén surface is discussed and explicitly expressed in terms
of surface functions which determine the flow solution. Theorems
are established, which constrain the asymptotic shape of rotating
polytropic MHD winds. In particular it is proved that winds which
carry a non-vanishing Poynting flux and poloidal current to infinity
must contain a cylindrically collimated core, whereas other winds
focus parabolically.
---------------------------------------------------------
Title: Interaction of turbulent accretion disks with embedded
magnetic fields.
Authors: Heyvaerts, J. F.; Bardou, A.; Priest, E. R.
1996ASIC..481..659H Altcode:
The authors show that the level of turbulence in accretion disks can
be derived from a self-consistency requirement that the associated
effective viscosity should match the instantaneous accretion rate. When
turbulence originates in the magnetic shearing instability, the
effective kinematic viscosity coefficient is shown to be describable
by a Shakura-Sunyaev law with α ≍ 0.04. It is shown that thin disks
suported by any turbulence with injection scale of order of the disk
thickness, are very low magnetic Reynolds number systems. Turbulent
viscosity-driven solutions with negligible field dragging and no
emission of cold winds or jets are natural consequences of such
regimes. Such disks are shown to expell the magnetic field of the
accreting object from their Keplerian regions radially outwards,
resulting in a flux distribution in the disk which differs very much
from a dipolar one.
---------------------------------------------------------
Title: Outflows of magnetized rotators: structure and collimation
Authors: Lery, T.; Appl, S.; Heyvaerts, J.
1996AGM....12.J237L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Disques d'accrétion turbulents auto-cohérents.
Authors: Bardou, A.; Heyvaerts, J.; Priest, E.
1995JAF....49...51B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Erratum - Turbulent Coronal Heating
Authors: Inverarity, G. W.; Priest, E. R.; Heyvaerts, J.
1995A&A...299..640I Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Turbulent coronal heating. I. Sheared arcade.
Authors: Inverarity, G. W.; Priest, E. R.; Heyvaerts, J.
1995A&A...293..913I Altcode:
The model of Heyvaerts & Priest for heating the solar corona by
turbulent processes in a sheared arcade is examined in more detail by
numerically solving their basic equations for the turbulent viscosity,
magnetic diffusivity, velocity and energy flux density. A weighted
spectrum for the mean square velocity in the photosphere and a
scale-dependent turbulent viscosity and magnetic diffusivity for local
eddy relaxation are introduced which improve the self-consistency of
the model. Estimates are made of the turbulent variables listed above
which are found to accord well with the requirements for heating a
solar active region (=~10^7^erg/cm^2^/s).
---------------------------------------------------------
Title: Closing address
Authors: Heyvaerts, J.
1994SSRv...68..371H Altcode:
Impressions from the workshop are summarized. Difficulties within
the present observational and theoretical context are outlined and
directions for fruitful future work are indicated. The workshop
subtitle, “the interface between MHD and plasma physics”, still
appears to be a goal for the future, though some encouraging results
have been reported at this workshop.
---------------------------------------------------------
Title: Stationary subalfvenic and low-β MHD flows in solar coronal
loops and arcades.
Authors: Surlantzis, G.; Demoulin, P.; Heyvaerts, J.; Sauty, C.
1994A&A...284..985S Altcode:
We present general two-dimensional solutions for low-β and subalfvenic
stationary MHD flow. Our method of solution applies to any type of
boundary conditions. It solves for the pertubation of the magnetic
configuration brought about by flows and by the development of
shock waves in it. Solutions in cartesian and cylindrical geometries
are presented to model flows in coronal loops and counter-Evershed
flows above spots. In symmetrical magnetic configurations, when the
distribution of pressure at the foot points is symmetrical, the flow is
necessarily subsonic. Otherwise it can become supersonic at the summit
of the magnetic field line and then passes through a shock. Such shocks
can be very inclined to the magnetic field and the shocked material may
form a dense hot sheet around a cooler core, a situation which seems to
be observed in cool loops. For asymmetrical magnetic configurations,
the flow accelerates towards the low gas pressure foot point and
could be subsonic or trans-sonic depending on the pressure difference
between the foot points. Loops can have a significant density contrast
against their environment only if their energy flux differs markedly
from the background one. In asymmetrical loops one leg can be much
less dense than the other and poorly visible. Near spots, the sign
of the difference of pressure between the two foot points is such as
to drive a reverse Evershed flow towards the spot. Additional effects
would be needed to drive a direct Evershed flow.
---------------------------------------------------------
Title: Magnetic Energy Dissipation and Coronal Heating by DC Currents
Authors: Heyvaerts, J.
1994ASIC..422...25H Altcode: 1994coma.conf...25H
No abstract at ADS
---------------------------------------------------------
Title: MHD Equilibria in Uniform Gravity
Authors: Surlantzis, G.; Démoulin, P.; Heyvaerts, J.; Sauty, C.
1993ASSL..183..629S Altcode: 1993pssc.symp..629S
No abstract at ADS
---------------------------------------------------------
Title: Jeans collapse of turbulent gas clouds - Tentative theory
Authors: Bonazzola, S.; Perault, M.; Puget, J. L.; Heyvaerts, J.;
Falgarone, E.; Panis, J. F.
1992JFM...245....1B Altcode:
The conditions for gravitational instability in a statistically
homogeneous turbulent fluid is investigated using a renormalization
technique, with particular reference to the problem of stability of
molecular clouds and the origin of protostellar density fluctuations. It
is shown how turbulence at scales smaller than the potentially
collapsing scale builds up a turbulent pressure force that effectively
resists compression if the kinetic energy is sufficient to balance
gravitational attraction.
---------------------------------------------------------
Title: Physics of coronal loops: heating and reconnection.
Authors: Heyvaerts, J.
1992ESASP.344...69H Altcode: 1992spai.rept...69H
The importance of small scale structures in the current distribution
is outlined, and the smallest size that these current structures might
have is discussed. It is shown that they must be dynamic, turbulent,
structures. The physical processes that may be at the origin of the
formation of such structures are discussed. The braiding of field
lines, the phase mixing of oscillations in inhomogeneous magnetic
configurations, and a number of secondary instabilities are likely to be
the dominant ones. A selfconsistent calculation of a large scale coronal
flow with associated turbulence is described. This parameter-free
theory gives, as a function of boundary motions which cause it, the
rate of coronal heating by fine scaled DC current structures.
---------------------------------------------------------
Title: A Self-consistent Turbulent Model for Solar Coronal Heating
Authors: Heyvaerts, J.; Priest, E. R.
1992ApJ...390..297H Altcode:
The rate of solar coronal heating induced by the slow random
motions of the dense photosphere is calculated in the framework of an
essentially parameter-free model. This model assumes that these motions
maintain the corona in a state of small-scale MHD turbulence. The
associated dissipative effects then allow a large-scale stationary
state to be established. The solution for the macroscopic coronal
flow and the heating flux is first obtained assuming the effective
(turbulent) dissipation coefficients to be known. In a second step
these coefficients are calculated by the self-consistency argument
that they should result from the level of turbulence associated with
this very heating flux. For the sake of tractability the derivation
is restricted to a two-dimensional situation where boundary flows are
translationally symmetric. The resulting value of the heating rate and
the predicted level of microturbulent velocity compare satisfactorily
with the observational data.
---------------------------------------------------------
Title: Design Rationale of the Solar Ultraviolet Network / Sun
Authors: Dame, L.; Acton, L.; Bruner, M. E.; Connes, P.; Cornwell,
T. J.; Curdt, W.; Foing, B. H.; Hammer, R.; Harrison, R.; Heyvaerts,
J.; Karabin, M.; Marsch, E.; Martic, M.; Mattic, W.; Muller, R.;
Patchett, B.; Roca-Cortes, T.; Rutten, R. J.; Schmidt, W.; Title,
A. M.; Tondello, G.; Vial, J. C.; Visser, H.
1992ESOC...39..995D Altcode: 1992hrii.conf..995D
No abstract at ADS
---------------------------------------------------------
Title: Magnetohydrodynamic Effects in Active Galactic Nuclei
Accretion Disks
Authors: Heyvaerts, J.
1992pagn.conf..445H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetohydrodynamic Forces in Astrophysical Disks and Jets
Authors: Heyvaerts, J.
1991assm.conf..399H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A solar interferometric mission for ultrahigh resolution
imaging and spectroscopy: SIMURIS
Authors: Damé, L.; Acton, L.; Bruner, M.; Connes, P.; Cornwell, T.;
Foing, B. H.; Heyvaerts, J.; Lemaire, P.; Martić, M.; Muller, R.;
Porteneuve, J.; Roca Cortés, T.; Riehl, J.; Rutten, R.; Séchaud,
M.; Smith, P.; Thorne, A. P.; Title, A. M.; Vial, J. -C.; Visser,
H.; Weigelt, G.
1991AdSpR..11a.383D Altcode: 1991AdSpR..11..383D
SIMURIS is an interferometric investigation of the very fine structure
of the solar atmosphere from the photosphere to the corona. It was
proposed to ESA /1/, November 30 1989, for the Next Medium Size
Mission - M2, and accepted in February 1990 for an Assessment Study
in the context of the Space Station. The main scientific objectives
will be outlined, and the ambitious model payload featuring the Solar
Ultraviolet Network (SUN), a 2 m long monolithic array of 4 telescopes
of Ø20 cm, and the Imaging Fourier Transform Spectrometer (IFTS),
an UV and Visible Imaging Fourier Transform Spectrometer coupled to
a Ø40 cm Gregory, described.
---------------------------------------------------------
Title: Solar physics at ultrahigh resolution from the space station
with the Solar Ultraviolet Network (SUN)
Authors: Damé, L.; Acton, L.; Bruner, M.; Connes, P.; Cornwell,
T.; Foing, B.; Heyvaerts, J.; Lemaire, P.; Martić, M.; Muller, R.;
Roca Cortés, T.; Riehl, J.; Rutten, R.; Title, A. M.; Vial, J. -C.;
Visser, H.; Weigelt, G.
1991AdSpR..11e.267D Altcode: 1991AdSpR..11..267D
The SUN experiment is a UV and visible Space Interferometer aimed at
ultra-high resolution in the solar atmosphere. It has been proposed
to ESA as part of the SIMURIS Mission Proposal which has recently
been accepted for an Assessment Study in the framework of the
Space Station. The 4 × 20 cm telescopes of the SUN linear array are
non-redundantly placed to cover a 2 m baseline, and the instrument makes
full use of stabilized interferometry potential, the 4 telescopes being
co-aligned and co-phased on a reference field on the sun. After a brief
outline of the scientific objectives, the concept of the instrument
is described, and its image reconstruction potential is illustrated.
---------------------------------------------------------
Title: The Role of Magnetic Fields in Accretion Disks.
Authors: Heyvaerts, J.
1991sepa.conf..109H Altcode: 1991IAUCo.129..109H
No abstract at ADS
---------------------------------------------------------
Title: Basic Hydrodynamics
Authors: Heyvaerts, Jean
1991LNP...373..313H Altcode: 1991lsse.conf..313H
No abstract at ADS
---------------------------------------------------------
Title: MHD forces in astrophysical disks and jets.
Authors: Heyvaerts, J.
1991gamp.conf..399H Altcode:
Accretion disks and jets are found to be associated with several kinds
of astrophysical objects which are briefly described. Observational
evidence and theoretical arguments indicating that accretion disks are
likely to be magnetized are presented, and the consequences for the
structure and evolution of disks are discussed. It is shown that dynamo
action in the disk results in a magnetized coronal halo around it. Being
stressed by the disk's differential rotation, the halo is heated
by a process similar to solar coronal heating. Conversely, Lorentz
forces are exerted on the disk, which cause non-local interaction and
redistribution of angular momentum. The disk, even at relatively low
magnetization, may become non-keplerian, and eventually differential
rotation may come to be frozen. A model incorporating these effects
is outlined. If the disk is threaded by an open field configuration,
the latter can support a rotating magnetized wind. It is shown that
such a wind can remove angular momentum from the disk, thus allowing
a secular contraction of it to take place. Finally, the shape of the
wind in regions remote from its source is discussed. Recent results
(Heyvaerts and Norman, 1989) show that the asymptotic form of the
momentum equation perpendicular to flux surfaces implies that, for
almost all such winds, the asymptotic structure consists of a family
of nested cylindrical surfaces, potentially explaining the collimation
of the observed "jets", in particular the famous jets from active
galactic nuclei without resorting to any external confinement.
---------------------------------------------------------
Title: Possible scenarios of coronal loops reconnection/heating
processes to be observed at high spatial resolution
Authors: Dame, L.; Heyvaerts, J.; Foing, B. H.
1991AdSpR..11a.327D Altcode: 1991AdSpR..11..327D
Recent improvements in interferometric techniques could allow to
achieve 0.01 arcsec angular resolution on the Sun, i.e. 10 km. Such
a high resolution is of direct interest to understand the coronal
loop structure since current observations at low resolution cannot
distinguish between major dissipation/heating theories which all involve
very small scale dissipating processes. Three simplified scenarios of
loop instabilities are investigated in this paper and the resulting fine
structure and contrast that they might induce on observable quantities
(temperature, density) are deduced.
---------------------------------------------------------
Title: High Resolution Solar Physics from the Space Station with
Interferometric Techniques: The Solar Ultraviolet Network (SUN) -
Instrument &Objectives
Authors: Damé, L.; Acton, L.; Bruner, M.; Connes, P.; Cornwell, T.;
Foing, B.; Heyvaerts, J.; Jalin, R.; Lemaire, Ph.; Martic, M.; Moreau,
B.; Muller, R.; Roca Cortés, T.; Riehl, J.; Rutten, R.; Title, A. M.;
Vial, J. -C.; Visser, H.; Weigelt, G.
1990PDHO....7..262D Altcode: 1990dysu.conf..262D; 1990ESPM....6..262D
No abstract at ADS
---------------------------------------------------------
Title: The Collimation of Magnetohydrodynamic Winds - Bipolar Flows
and Jets
Authors: Norman, C. A.; Heyvaerts, J.
1990IAUS..140..353N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Heating by DC Currents
Authors: Heyvaerts, J.
1990IAUS..142..207H Altcode:
Recent views on dc current coronal heating are presented. The relation
to ac mechanisms, the importance of MHD turbulence in both processes,
and the convergence of recently proposed ideas are outlined. Attention
is given to the role of the field line stochasticity in coronal
structures and tentative theories of the 'extrinsic' and 'intrinsic'
type.
---------------------------------------------------------
Title: The Collimation of Magnetized Winds
Authors: Heyvaerts, Jean; Norman, Colin
1989ApJ...347.1055H Altcode:
It is established that any stationary axisymmetric magnetized wind
will collimate along the symmetry axis at large distances from the
source. This result is proved by consideration of the asymoptotic
properties of the transfield equation, keeping the exact conserved
quantities along field lines. The only consistent nonsingular
solution with a nonvanishing poloidal current approaches a cylindrical
structure. For singular solutions or those with a vanishing poloidal
current, the asymptotic solutions can be paraboloidal. This result
only applies to pure wind boundary conditions on the surface of the
source. It is shown how the boundary conditions and the critical
point analysis are related in our asymptotic analysis. This result
demonstrates that axisymmetric magnetized flows tend generally to
collimate, and it is hypothesized that this is the natural reason why
there are so many collimated flows and jets.
---------------------------------------------------------
Title: Solar Ultraviolet Network: an interferometric investigation
of the fundamental solar astrophysical scales
Authors: Dame, Luc; Moreau, Bernard G.; Cornwell, Timothy J.;
Visser, H.; Title, Alan M.; Acton, Loren W.; Aime, Claude; Braam,
Bart M.; Bruner, Marilyn E.; Connes, Pierre; Faucherre, Michel; Foing,
B. H.; Haisch, Bernhard M.; Hoekstra, Roel; Heyvaerts, Jean; Jalin,
Rene; Lemaire, Philippe; Martic, Milena; Muller, R.; Noens, J. C.;
Porteneuve, Jacques; Schulz-Luepertz, E.; von der Luehe, Oskar
1989SPIE.1130..126D Altcode:
The Solar UV Network (SUN) presently proposed is an interferometric
system, based on the principles of stabilized interferometry, which
will be capable of solar observations with spatial resolutions better
than 0.013 arcsec. SUN will consist of four 20-cm diameter telescopes
aligned nonredundantly on a 2-m baseline. SUN is judged to be ideally
deployable by the NASA Space Station, if implemented on a pointing
platform whose performance is of the order of the Instrument Pointing
System flown on Spacelab 2. The compact, nonredundant configuration of
SUN's telescopes will allow high-resolution imaging of a 2 x 2 arcsec
field on the solar disk.
---------------------------------------------------------
Title: A model for a non-Keplerian magnetic accretion disk with a
magnetically heated corona
Authors: Heyvaerts, J. F.; Priest, E. R.
1989A&A...216..230H Altcode:
MHD stresses are used to model a thin disk dynamically interacting with
a self-created magnetic corona. A simple model of the coronal magnetic
structure produced by the turbulent MHD relaxation of the stresses
exerted by the disk's differential rotation can explain the effect
of coronal heating and the back reaction of the corona on the energy
balance and angular momentum flow in the disk. The results show the
disk to acquire a non-Keplerian rotation profile, with the trailing
foot point of the magnetic loops being accelerated, and the leading
one being decelerated, in comparison to a Keplerian distribution. It
is found that the coronal heating and non-Keplerian effects are weak
when the coronal scale becomes much larger than the disk size.
---------------------------------------------------------
Title: MHD Aspects of Galactic Center Physics (review)
Authors: Heyvaerts, J.
1989IAUS..136..301H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: La formation doctorale à l'heure européenne.
Authors: Heyvaerts, J.
1989JAF....34...26H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Topological catastrophe in massive current sheets.
Authors: Peterle, P.; Heyvaerts, J.
1989sasf.confP.285P Altcode: 1989IAUCo.104P.285P; 1988sasf.conf..285P
A two-dimensional sheet model for solar filaments (Kippenhahn and
Schlüter configuration) is considered. The authors investigate the
quasi-static evolution of gravito-magnetohydrostatic equilibria in
exploring the response of massive current sheets to a slow continuous
variation of the mass/flux ratio with fixed boundary conditions. A
catastrophic behavior of the field topology is found to occur in the
sequence following the formation of a cusp point (bifurcation).
---------------------------------------------------------
Title: A Magnetic Loop Model for Structure and Activity in the
Galactic Center
Authors: Heyvaerts, Jean; Norman, Colin; Pudritz, Ralph E.
1988ApJ...330..718H Altcode:
A simple model for the production and propagation of magnetized loops in
the Galactic center is developed. It is found that a magnetized model
can reproduce the filamentary, asymmetric structures on all scales
from 100 pc to subparsec scales in the Galactic center. The radio and
molecular gas morphology on all scales inside the Galactic center lobe
may be explained in terms of the expansion of strongly magnetized loops
and their interaction with the 2-5 pc torus and 30-50 pc portion of the
center lobe. The magnetic loops have a toroidal field which explains
the braided appearance of the radio continuum emission on the 2 pc
scale. The barlike feature on the 2 pc radio continuum maps can be
viewed as a piece of a magnetic loop with field strength about 0.01 G
which is colliding and reconnecting with the ionized inner edge of the 2
pc molecular torus. The loop-torus interaction feeds energetic particles
and shear Alfven waves into the torus, and deposits mass and energy.
---------------------------------------------------------
Title: Magnetohydrodynamic Modes of a Periodic Magnetic Medium
Authors: Berton, R.; Heyvaerts, J.
1987SoPh..109..201B Altcode:
The oscillations of a magnetic medium periodic in the x-direction with
B parallel to z, have been studied. The case with no gravity and a
stepwise profile for B(x), allowing a normal mode analysis, has been
examined and dispersion relations have been derived. The dispersion
curves in the diagram k<SUB>z</SUB> − ω display two types of modes,
kink and sausage, like in the isolated slab, but the profiles are
different and depend on Bloch's number k<SUB>0</SUB>. Moreover, modes
usually absent in the isolated slab (propagating and tunelling) appear
here, connecting surface- or body-wave domains. The detectability
of this characteristic structure of the diagnostic diagram on the
observations is discussed, and prospects for a more realistic analysis
including gravity are given.
---------------------------------------------------------
Title: About the interest of Solar Interferometric Observations
Authors: Heyvaerts, J.
1987ESASP.273...11H Altcode: 1987ois..work...11H
It is shown that the understanding of some basic solar physical
processes calls for high spatial resolution observation on the
visible and in EUV lines. These processes are of general astrophysical
interest. The scientific return expected from UV line observations of
coronal loops with an angular resolution of 0arcsec.01 across the loop
is described in some more detail.
---------------------------------------------------------
Title: Solar interferometry with a 4-aperture non-redondant and
stabilised network
Authors: Dame, L.; Aime, C.; Faucherre, M.; Heyvaerts, J.
1987ESASP.273..189D Altcode: 1987ois..work..189D
The design of a solar interferometer is intrinsically complex since
many requirements, often found separately, and difficult by themselves,
are brought together: UV spectral range, limb observations, resolved
structures (low contrast) and time resolution. The stabilized
interferometry technique, applied to a non-redundant array of 4
telescopes, provides an elegant solution to those complex problems.
---------------------------------------------------------
Title: A magnetic loop model for activity in the Galactic centre
Authors: Heyvaerts, Jean; Pudritz, Ralph E.; Norman, Colin A.
1987AIPC..155..176H Altcode: 1987gace.conf..176H
We propose that radio structures on 0.1-100 pc scales in the galactic
centre radio lobe (GCL) are manifestations of magnetic activity in
a central source object. The observations indicate that truly one
dimensional structures occur and we hold that this is strong evidence
for magnetic loops. They are generated on subpc scales and expand
out to 10-100 pc. Their interaction with the 2 pc molecular torus as
well as the GCL on 30-50 pc scales reproduces the observed irregular
ionized and molecular emission on 2 pc scales, as well as the bridge,
radio arc, and thread-like filaments on the larger ones. The Sgr A radio
lobe itself (on 10 pc scales) is comprised of a system of lower energy
magnetized loops which have been trapped in the molecular torus. The
main thrust of this theory is that all of these exotic structures may
be understood within the framework of one rather simple model.
---------------------------------------------------------
Title: Jeans collapse in a turbulent medium
Authors: Bonazzola, S.; Heyvaerts, J.; Falgarone, E.; Perault, M.;
Puget, J. L.
1987A&A...172..293B Altcode:
According to the classical Jeans criterion, all the observed molecular
clouds of mass M greater than 100 solar masses, radius R greater than
1 pc and gas kinetic temperature Tk less than 30 K are gravitationally
unstable. However, millimetric and infrared observations show that
low mass dense cores (M greater than 3 solar masses) can collapse and
form stars within clouds for which there is no evidence for global
collapse. It is shown that, if the power spectrum of the turbulent
internal motions which support them against gravity is steep enough,
the molecular clouds are stable as long as their gas density remains
close to the observed low mean densities (a few 100 per cu cm). For
larger densities, only a narrow range of scales become gravitationally
unstable. In that context, unstable low mass dense cores eventually form
only when the density fluctuations within the clouds happen to be large.
---------------------------------------------------------
Title: Formation à et par la recherche en astronomie: mythes et
réalités.
Authors: Heyvaerts, J.
1987JAF....30...10H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Jeans criterion in a turbulent medium
Authors: Bonazzola, S.; Falgarone, E.; Heyvaerts, J.; Perault, M.;
Puget, J. L.
1986inpr.conf...41B Altcode:
According to the classical Jeans analysis, all the molecular clouds
of mass larger than a few 100 M(solar), size larger than about 1pc and
kinetic temperature Tk less than 30K are gravitationally unstable. We
have shown that in clouds supported by internal supersonic motions,
local gravitational instabilities may appear within molecular clouds
which are globally stable. The argument is threefold: (1) when the
turbulent kinetic energy is included into the internal energy term,
the virial equilibrium condition shows that molecular clouds such as
those observed, which are gravitationally unstable according to the
Jeans criterion, are indeed globally stable if supported by a turbulent
velocity field of power spectrum steeper than 3; (2) 2D compressible
hydrodynamical simulations show that a supersonic turbulent velocity
field generates a turbulent pressure within clouds, the gradients of
which stabilize the unstable scales (i.e., the largest scales and the
cloud itself) against gravitational collapse; (3) an analysis similar to
the Jeans approach but including the turbulent pressure gradient term,
gives basically the same results as those given in (1). Clouds of mean
density lower than a critical value are found to be stable even though
more massive than their Jeans mass. In clouds of mean density larger
than that critical value, the gravitational instability appears only
over a range of scales smaller than the cloud size, the largest scales
being stable. In practice, the observed mean densities are lower than
this critical value: the observation of a small number of cores and
stars of a few solar masses embedded in clouds of several hundred
solar masses can only be understood in terms of small scale density
fluctuations of large amplitude generated by the supersonic turbulence
which would occasionally overtake the limit of gravitational stability.
---------------------------------------------------------
Title: Gamma-Ray Bursts
Authors: Heyvaerts, J.
1986ppm..conf..180H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Quasistatic Evolution of Magnetic Arcades in the Sun : Ideal
and Dissipative Case (Invited paper)
Authors: Heyvaerts, J.
1986mrt..conf..121H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Fine Structures - Their Importance in the Sun's Physics
and Their Observation
Authors: Heyvaerts, J.
1985ESASP.235..169H Altcode: 1985shpp.rept..169H; 1985fmsh.work..169H
An overview of the structures in the sun's atmosphere is given. The
essential role of these structures in the physics of the sun's
convective zone and atmosphere is stressed, and it is emphasized
that the same physics is crucial in a number of other systems of
planetological or astrophysical interest. The problem of solar coronal
heating is evocated with some more detail, and its relation to the
solar wind acceleration problem is discussed. The diagnosing of non
thermal heating phenomena is shown to involve elaborate observations
with high spectral, spatial and temporal resolution. It is concluded
that the SOHO project, presently considered by ESA, appears in this
respect to be the best next step to take.
---------------------------------------------------------
Title: Spectra of gamma-ray bursts
Authors: Hameury, J. M.; Lasota, J. P.; Bonazzola, S.; Heyvaerts, J.
1985ApJ...293...56H Altcode:
It is shown that gamma-ray burst spectra are basically thermal
synchrotron spectra emitted in a cold 'photosphere' by electrons excited
to high Landau levels by high-energy photons that are beamed along
the magnetic field lines. The high-energy radiation is produced in a
corona by the interaction of soft, thermal photons and synchrotron
photons with one-dimensional, relativistic electrons in a strong
magnetic field. These coronal electrons are accelerated by short-scale
magnetic reconnection. The physical parameters of the coronal layer
are self-consistently determined. Monte Carlo simulations that include
Compton and resonant scattering produce spectra in good agreement with
the observations between 20 keV and 1 MeV. It is speculated that the
recently discovered high-energy tail of the spectrum is formed in the
outer corona and the wind zone. It is also shown that the emission is
strongly anisotropic, and consequently, the most intense bursts need
not be the closest.
---------------------------------------------------------
Title: Anomalous magnetic field diffusion during star formation
Authors: Norman, C.; Heyvaerts, J.
1985A&A...147..247N Altcode:
The authors discuss the physics of magnetic field dissipation and
reconnection during protostellar formation. In their analysis of
quasi-equilibrium collapse they have incorporated both ambipolar
diffusion and magnetic dissipation processes. Both the final flux
and angular momentum problems can be resolved in their model which
incorporates some of the detailed physics that was previously lacking in
such theories. The energy input during flux destruction is considerable
and the authors have speculated that consequences may include the
formation of a hot corona with an observable X-ray flux, and the
pumping of OH masers. Radio emission may be observable in this phase.
---------------------------------------------------------
Title: Energy dissipation mechanisms in the solar corona
Authors: Heyvaerts, J.
1985IAUS..107...95H Altcode:
Present ideas concerning the electric heating of the solar corona are
reviewed. More detailed consideration is given to the dissipation of
MHD waves in strong horizontal gradients of the Alfven velocity. Then
the evolution of dc currents in the solar corona is considered. Some
theories aiming at the evaluation of the net rate of energy dissipation
by such mechanisms are described. A short account is given of a recent
analytical study based on a generalization of Taylor's hypothesis
concerning the evolution of magnetic helicity in plasma with a large
magnetic Reynolds number.
---------------------------------------------------------
Title: Mechanisms of magnetic heating of the solar corona.
Authors: Heyvaerts, J.
1984ESASP.220..123H Altcode: 1984ESPM....4..123H
Present ideas concerning the electric heating of the solar corona
are briefly reviewed. The author considers mechanisms of MHD wave
dissipation in strong horizontal gradients of the Alfvén velocity,
as well as turbulence associated dissipation. Then he considers the
evolution of D.C. coronal currents in the presence of active magnetic
reconnection, and stresses the interest of considering the existence
of approximate global invariants associated with such phenomena.
---------------------------------------------------------
Title: Coronal heating by reconnection in DC current systems -
A theory based on Taylor's hypothesis
Authors: Heyvaerts, J.; Priest, E. R.
1984A&A...137...63H Altcode:
The rate of coronal heating expected from complex reconnection
processes is analyzed by adapting Taylor's hypothesis to solar and
stellar physical conditions. The fact that the magnetic helicity of
a region which is not a closed flux tube is not a gauge-invariant
quantity is addressed, and the time evolution of a magnetic arcade
undergoing slow footpoint motions and infinitely rapid relaxation by
reconnection is calculated. It is shown that, when the stresses are
relaxed instantaneously the amount of heating vanishes exactly. A
second order theory is developed which permits the heating effect
due to a small but finite reconnection time to be calculated. It is
concluded that DC current coronal heating is mainly due to motions
comparable in size to or smaller than the characteristic size of
the magnetic structure, and that these motions must tend to produce a
nonconstant alpha force-free magnetic structure. The theory illuminates
the connection between general coronal heating and solar flares.
---------------------------------------------------------
Title: The production of gamma-rays in gamma-ray burst sources
Authors: Bonazzola, S.; Hameury, J. M.; Heyvaerts, J.; Lasota, J. P.
1984A&A...136...89B Altcode:
The authors propose, as a model for gamma-ray bursts, that the energy
released by the thermonuclear runaway at the surface of a magnetized
neutron star is converted into gamma-ray photons by small scale
magnetic field reconnection. Most of the energy flux is transported
up to the atmosphere by Alfvén waves, driven by oscillatory
magnetoconvection. The electric field created by reconnection
accelerates electrons to very high energies. The excitation of
Landau levels by collisions is followed by gamma-ray synchrotron
emission. The time scales, energies, and luminosities involved agree
with the observations.
---------------------------------------------------------
Title: Resonant reception in the Solar System of gravitational waves
from external sources
Authors: Bonazzola, S.; Carter, B.; Heyvaerts, J.; Lasota, J. P.
1984Natur.308..163B Altcode:
Here we aim to point out the rather stringent limitations, particularly
those due to frequency stability requirements, that can be placed on
conceivable (for example, binary) sources of any gravitational waves
that might be detected by resonant stimulation of an oscillation mode in
the Solar System. This question has recently been raised by widespread
informal discussions<SUP>1,2</SUP> of the possibility that unexpectedly
persistent low-frequency (160-min period) oscillations observed in the
Sun<SUP>3</SUP> might be due to such a mechanism<SUP>4</SUP>. We show
here that this particular possibility can be excluded.
---------------------------------------------------------
Title: Radiative transfer in optically thick hot astrophysical
plasmas.
Authors: Heyvaerts, J.
1984PhST....7...94H Altcode: 1984PhyS....7...94H
Inelastic radiation transfer in hot plasmas is reviewed. It is shown
that a variety of situations can be described by combining a Kompaneets
type of transfer equation with suitable photon sources. Some emphasis
is put on the particular case of very magnetized plasmas (B ≅
10<SUP>12</SUP>G). It is shown that the spectrum of magnetized X-ray
sources is best understood as resonant-scattering cooling of very hot
photons in a medium with negative temperature gradient.
---------------------------------------------------------
Title: Magnétohydrostatique.
Authors: Heyvaerts, J.
1984cms..conf..179H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Thermonuclear flashes on magnetized neutron stars as a model
for gamma-ray bursts
Authors: Hameury, J. M.; Bonazzola, S.; Heyvaerts, J.; Lasota, J. P.
1984AdSpR...3j.297H Altcode: 1984AdSpR...3..297H
We propose, as a model for gamma ray bursts, that the energy
released by a thermonuclear runaway at the surface of a slowly
accreting, magnetized neutron star, is converted into gamma ray
photons by small scale magnetic field reconnection. Most of the
energy flux is transported up to the atmosphere by Alfvén waves,
driven by oscillatory magnetoconvection. The electric field created by
reconnection accelerates electrons to very high energies. The excitation
of Landau levels by collisions is followed by gamma ray synchrotron
emission. The time scales, energies, and luminosities involved agree
with the observations.
---------------------------------------------------------
Title: Thermonuclear Flashes on Magnetized Neutron Stars as a Model
for Gamma-Ray Bursts
Authors: Hameury, J. M.; Bonazzola, S.; Heyvaerts, J.; Lasota, J. P.
1984heac.conf..297H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mechanisms for Heating the Solar Corona by the Dissipation
of AC or DC Currents
Authors: Heyvaerts, J.
1984apoa.conf..318H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Gamma-ray Bursts: a Model
Authors: Hameury, J. M.; Bonazzola, S.; Heyvaerts, J.; Lasota, J. P.
1984ASIC..134..345H Altcode: 1984pcnr.conf..345H
The authors propose, as a model for gamma-ray bursters, that the
energy released by a thermonuclear runaway under the surface of a
slowly accreting, magnetized, neutron star, is transported up to the
atmosphere by Alfvén waves, driven by overstable magnetoconvection. In
the atmosphere, the short scale magnetic field lines reconnection
generates an electric field. The electrons accelerated by this process
produce gamma-rays by inverse Compton scatterings with blackbody
photons of a few keV.
---------------------------------------------------------
Title: Magnetohydrostatics in the polar caps of the gamma-ray
burst sources
Authors: Hameury, J. M.; Bonazzola, S.; Heyvaerts, J.; Lasota, J. P.
1983A&A...128..369H Altcode:
The ability of the magnetic field existing at the surface of a neutron
star to confine a layer of hydrogen inside the polar caps has been
studied. It is found that, except for low values of the magnetic field
(less than 10 to the 11th G), diffusion across the field lines is
negligible. A numerical solution of the magnetohydrostatic equations
shows that the disruption of the field lines can occur only if the
ratio beta of the gas pressure to the magnetic pressure exceeds L/h (L
= polar cap radius, h = height of the accreted layer). When the amount
of accreted matter reaches the critical value at which a thermonuclear
flash is triggered, the value of the critical magnetic field is a few
times 10 to the 11th G; it is much smaller than what is deduced from
Mazets line features (Mazets et al., 1981), i.e. about 5 x 10 to the
12th G. It is therefore concluded that the magnetic field acts as a
stiff container, and that it is not distorted on a large scale either
before or during the burst.
---------------------------------------------------------
Title: Current sheet models for solar prominences. II - Energetics
and condensation process
Authors: Malherbe, J. M.; Priest, E. R.; Forbes, T. G.; Heyvaerts, J.
1983A&A...127..153M Altcode:
A steady state dynamic model for solar prominences of the Kuperus and
Raadu type was previously proposed by Malherbe and Priest (1983), but
only the motion through series of quasi-static states was investigated
there. The mechanisms for formation, condensation and cooling of
plasma in this model are studied. As hot coronal material approaches
the filament sheet, it is expected to cool and condense. Cold material
is then carried up through the prominence by rising magnetic field
lines due to converging photospheric motions below the filament. Two
possible ways are suggested of triggering a thermal instability and so
producing such a stationary condensation process: a larger pressure in
the sheet, or a smaller wave heating in the reconnected field than in
the surrounding corona. This paper presents a simple model to simulate
the plasma condensation: the thermodynamics of the cooling process,
as well as the dynamics of new material entering the prominence sheet,
are described in detail.
---------------------------------------------------------
Title: The final state of a solar flare.
Authors: Norman, C. A.; Heyvaerts, J.
1983A&A...124L...1N Altcode:
It is shown that the final state of a solar flare is a force free field
with constant α where α is determined by the boundary conditions. This
result is independent of the details of magnetic energy build up and
release. The crucial assumptions are that during the period of rapid
magnetic energy release the effects of slow photospheric foot point
motions can be neglected and that magnetic field reconnection occurs
in regions whose total volume is small compared to that of the overall
configuration.
---------------------------------------------------------
Title: Gravitational settling in layers accreted on neutron stars
and its relations to gamma ray bursts
Authors: Hameury, J. M.; Heyvaerts, J.; Bonazzola, S.
1983A&A...121..259H Altcode:
The use of Hansen's (1978) diffusion coefficient has reduced
metallicities by two to three orders of magnitude in the present
study of the possibility of the occurrence of hydrogen-helium flashes
at the surface of accreting neutron stars, which takes into account
heavy element depletion due to sedimentation. The abundance profile
is found to be Rayleigh-Taylor unstable under the influence of a mean
molecular weight gradient when there is no magnetic field, in which
case metallicity is reduced. The minimum hydrogen flash-associated
accretion rate is of the order of 10 to the -15th solar masses/year
per sq km, rendering these neutron stars only marginally detectable
in the X-ray emission range by the Einstein satellite.
---------------------------------------------------------
Title: A mathematical model of solar flares.
Authors: Heyvaerts, J.; Lasry, J. -M.; Schatzman, M.; Witomski, P.
1983QApMa..41....1H Altcode:
The phenomenon of solar flares is modeled assuming that the magnetic
field is force-free and that its evolution is quasi-static. This
model is simplified so as to be tractable and yields a semi-linear
elliptic equation in a half-plane depending on a parameter lambda which
describes the time evolution. It is proved that there are (at least)
two branches of solutions which have distinct asymptotic behaviors
at infinity. The upper branch exists for all lambda greater than 0,
but the lower branch exists only on a finite interval /0, lambda exp
c/. As stable solutions must have the same asymptotic behavior as the
lower branch of solutions, and as this is impossible after lambda exp
c, it is contended that no stable solution exists after lambda exp c
and that a solar flare is thus triggered.
---------------------------------------------------------
Title: Can γ-ray bursts originate from low-mass binaries?
Authors: Ventura, J.; Bonazzola, S.; Hameury, J. M.; Heyvaerts, J.
1983Natur.301..491V Altcode:
γ-Ray bursts have been attributed to binary systems<SUP>1-3</SUP> with
the burst resulting from an accretion instability<SUP>1,2</SUP>, or a
thermonuclear explosion at the surface of an accreting magnetic neutron
star<SUP>4-6</SUP>. Recent deep sky surveys in the X-ray<SUP>7-9</SUP>
and optical wavelengths (S. Illovaiski and C. Chevalier, personal
communication), impose stringent new limitations on the theory. Assuming
an average distance of ~300 pc, these observations limit the optical
absolute magnitude of bursters in quiescence to M<SUB>v</SUB>>13
and their X-ray luminosity to <10<SUP>31</SUP> erg s<SUP>-1</SUP>
for polar cap accretion (K. Hurley, S. Illovaiski and G. Pizzichini,
personal communication). If these are local binary systems in
our Galaxy, as suggested by their isotropic distribution in the
sky<SUP>10,11</SUP>, the binary companion would clearly have to
be a very low mass object. Although very peculiar, the presence of
such an `invisible' companion is possibly hinted at by the recently
proposed identification of the 19 November 1978 γ-ray burst to
a 1928 optical transient event lasting <=10 min discovered by
Schaefer<SUP>12</SUP>. Motivated by these data, we examine here the
possibility of obtaining such low luminosity systems as the evolutionary
end products of galactic low-mass binary systems with a neutron star
primary.
---------------------------------------------------------
Title: Coronal heating by phase-mixed shear Alfven waves.
Authors: Heyvaerts, J.; Priest, E. R.
1983A&A...117..220H Altcode:
The authors consider the physical processes which occur when a shear
Alfvén wave propagates in a structure with a large gradient of the
Alfvén velocity. Although these waves do not possess local resonances
(unlike magneto acoustic modes) they nevertheless suffer intense phase
mixing during which the oscillations of neighbouring field lines become
rapidly out of phase. The authors study this effect and show that the
resulting large growth of gradients dramatically enhances the viscous
and ohmic dissipation. The cases of propagating and standing waves
are considered, and a detailed calculation is given of the rate of
dissipation achieved in a finite length structure like a loop, in
the presence of a random excitation at its ends. The authors prove
that, after a long enough time, phase mixing can actually ensure the
dissipation of all the wave mechanical energy that a loop can pick up
from the excitation, in agreement with a previous claim by Ionson. The
general conclusion of the study is that phase mixing is the process
most able to ensure the dissipation of shear Alfvén waves in loops and
in open regions of strong reflectivity, and that loops, in particular,
must be in a permanent state of Kelvin-Helmholtz and tearing turbulence.
---------------------------------------------------------
Title: Observational constraints on the thermonuclear flash model
for gamma-ray bursts
Authors: Ventura, J.; Bonazzola, S.; Hameury, J. M.; Heyvaerts, J.
1983MitAG..58..111V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Thermonuclear runaways at the surface of slowly accreting
neutron stars.
Authors: Bonazzola, S.; Hameury, J. M.; Heyvaerts, J.; Ventura, J.
1982ans..conf..241B Altcode: 1982ans..conf..241H
Thermonuclear runaways at the surface of neutron stars with mass
accretion rates of the order of 10 to the -15th power solar mass/yr/sq
km are discussed. This slow accretion results in longer recurrence time
scales, of the order of a few years; the shell temperature between
two bursts is also lower and consequently the accreted material is
pushed to higher densities before the flash. A strong magnetic field
causes non-thermal emission during the flash, and may explain the
gamma-ray emission. Moreover, it focusses the accretion onto the
polar caps. The accretion rate per unit surface may then be 1000
times larger than the rate which result from spherical accretion. The
possibility of producing hydrogen-helium flashes in such conditions is
investigated. In a previous paper it was found that a metallicity Z =
.04 in the accreted layer, thermonuclear instabilities where obtained
when the accretion rate was larger than a critical value. However
depletion of the C, N, and O nuclei due to gravitational settling
seriously affect these results.
---------------------------------------------------------
Title: Hydrogen-helium flashes on accreting neutron stars as a
possible origin of gamma-ray bursts
Authors: Hameury, J. M.; Bonazzola, S.; Heyvaerts, J.; Ventura, J.
1982A&A...111..242H Altcode:
Accretion of interstellar matter on a galactic disc population of
old neutron stars can lead to thermonuclear runaway offering a very
plausible explanation for the phenomenon of gamma-ray bursts. We have
studied numerically the possibility of having hydrogen and helium
flashes in system with low accretion rates Mdot < 10<SUP>-12</SUP>
M<SUB>sun</SUB> yr<SUP>-1</SUP>. We find instabilities when the
accretion rate exceeds 3 10<SUP>-13</SUP> M<SUB>sun</SUB> (in the
absence of magnetic channeling of the accretion). Each burst is then
triggered by electron capture on protons, when the accreted envelope
reaches a mass of 3 10<SUP>23</SUP> g. The resulting hydrogen flash
will lead to helium detonation after a short heating time of several
minutes. Our conclusions are: <P />a) Only slowly moving neutron stars
(3 km s<SUP>-1</SUP> with respect to the interstellar medium) can give a
burst. <P />b) The model is compatible with the data if the old neutron
star density is ∼10<SUP>-2</SUP> PC<SUP>-3</SUP> and their velocity
dispersion is ∼50km s<SUP>-1</SUP>, somewhat lower then that of radio
pulsars. <P />c) The amount of fuel available for the detonation has
a standard value of ∼10<SUP>+23</SUP> g, but can also depend on the
neutron star's previous history. Exceptionally intense events could,
for instance, be explained by a cold neutron star entering a favorable
environment of low relative velocity. <P />d) Persistent X-ray emission
after the bursts and a gradual increase above the X-ray back ground
starting a few minutes before the burst should be a signature of the
mechanism proposed.
---------------------------------------------------------
Title: Blowing up of two-dimensional magnetohydrostatic equilibria
by an increase of electric current or pressure
Authors: Heyvaerts, J.; Lasry, J. M.; Schatzmann, M.; Witomsky, P.
1982A&A...111..104H Altcode:
General properties are deduced for a series of two-dimensional
magnetohydrostatic configurations. An existence theorem for the
Dirichlet boundary conditions on the frontier of a semiinfinite domain
is established, and the magnetic topology of the always-existing
solution is shown to be of the open type. While the existence of a
closed topology solution is also proved for the case of small currents,
this solution disappears at a bifurcation point for some finite value
of the stretching parameter lambda. The relevance of these results to
the study of eruptive solar flares and other solar active phenomena
is discussed.
---------------------------------------------------------
Title: Population III objects and the shape of the cosmological
background radiation.
Authors: Heyvaerts, J.; Puget, J. -L.
1982cp...proc..297H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High energy particle acceleration in flares
Authors: Heyvaerts, J.
1982AdSpR...2k.187H Altcode: 1982AdSpR...2..187H
Not Available <P />The permanent participants in this team at Annecy SMY
workshop (October 1981) have been, in alphabetical order : R. BOCCHIA,
S. ENOME, J. HEYVAERTS, C. KOUVELIOTOU, B. IWERS, M. PESSSES, E. RIEGER,
J.M. ROBILLOT, J. RYAN, G. TROTTET, N. VILMER, L. VLAHOS, G. WIBBERENZ
Very useful contributions by many other participants are acknowledged,
specially (but not only) by K. ANDERSON, A. BENZ, J. BROWN, M. KUNDU,
M. PICK, D. RUST, R. STEWART.
---------------------------------------------------------
Title: Magnetic reconnection: A problem of general physical and
astrophysical interest, with special implications in solar physics
Authors: Heyvaerts, J.
1982AdSpR...2i..21H Altcode: 1982AdSpR...2...21H
The astrophysical applications of magnetic reconnection are
addressed. MHD flows involving reconnection are considered for various
situations and different media, and the importance of thermal and
gravitational effects in plasma MHD flows is argued. The nature of
reconnection where the plasma is not collisional enough to be regarded
as an MHD medium is addressed, and microturbulence in reconnection
processes is discussed. Phenomena related to the nonlinear evolution of
tearing modes in time-dependent reconnection are considered, including
magnetic braiding, internal disruptions involving an apparently unique
helical mode, and situations resulting when the primary periodicity of
the tearing perturbation is inapplicable or where finite resistivity
is included.
---------------------------------------------------------
Title: Are γ-ray bursters neutron stars accreting interstellar
matter?
Authors: Bonazzola, S.; Hameury, J. M.; Heyvaerts, J.; Ventura, J.
1981SSRv...30..471B Altcode:
A model for the approximately 150 gamma-ray burst events observed
in recent years is presented. The existence of population I, old
neutron stars with a density of one/100 cu pc was considered, with an
accretion of interstellar matter at a rate defined by Bondi's law. The
thermal evolution of the subsequent thick shells was calculated,
with an eye to the possibility of thermonuclear runaway. Account was
made of the energy exchanges between the accreted shell and the star
interior, and a range of parameters was derived which would result
in a runaway. Higher accretion rates were found to lead to a runaway
when the shell reaches 50 cm in thickness and electron capture was
occurring. Various changes in burning rates, changing temperatures,
and accretion rates which would disrupt steady-state stages into
a runaway condition and subsequent gamma-ray burst are discussed,
noting that a significant role may also be played by the magnetic field.
---------------------------------------------------------
Title: Expected characteristics of pulsar gamma-ray radiation and
the problem of its location
Authors: Heyvaerts, J.; Signore, M.
1981A&A....96...36H Altcode:
The transfer of gamma rays in the near pulsar magnetosphere of a
parallel rotator is studied, with emphasis placed on determining the
parameters characterizing the emitted spectrum, namely high energy
cutoff, spectral slopes, and the energy range of secondary emission. A
systematic and analytical investigation is made of their relaxation
to the electron acceleration. It is shown that there exists a maximum
pulsar period above which pair creation in the vicinity of the crust
is impossible, whatever the electron acceleration conditions may be
---------------------------------------------------------
Title: Population III objects and the shape of the cosmological
background radiation
Authors: Heyvaerts, J.; Puget, J. -L.
1981copa.conf..297H Altcode: 1981copa.conf..297P
The spectrum of the cosmological radiation may keep track of nonthermal
processes having followed the decoupling era, in the form of departures
from a strictly Planckian spectrum. The consequences of energy and
metals release by a population of pregalactic objects is examined. The
latter are asumed to condense into dust. The formation of the universal
spectrum under these conditions is described in a self-consistent
manner. It is shown that a good enough agreement can be obtained with
presently available data. It is concluded that the observed spectrum
can be explained if the star burst occurred before the epoch z near 30
and after z near 300, with a release varying between 0.3 MeV/nucleon
for z equals 30 and 2 MeV/nucleon at z equals 200, while the mass
fraction in grains vary from 1/10,000-1/1,000,000. The results point
to the possibility that the population III even might have occurred
recently, at z near 30 to 50, this being still consistent with all
the considered constraints.
---------------------------------------------------------
Title: Recent developments in solar flare models
Authors: Heyvaerts, J.
1981soac.reptR....H Altcode:
Theoretical models which explain why and how solar flares occur are
surveyed. Processes that govern the dissipation of magnetic energy
are considered fundamental. The storage of magnetic energy and what
produces its violent conversion into thermal and suprathermal energy
are considered. A magnetic model of a flare which is presented
comprises three phases: a stable flare buildup phase evolves into
an impulsive phase which leads to the principle phase of a flare
phenomenon. The stability of the preeruptive state and current sheets
is discussed as well as the thermal equilibrium of the preeruptive
structure. Reconnection in the preeruptive state and the occurence of
spontaneous reconnection are treated. Results show that reconnection can
have different geometries and, hence, can provoke nonlinear developments
of widely varying magnitudes in the context of the solar corona.
---------------------------------------------------------
Title: Energy Balance in Current Sheets - from Petschek to Gravity
Driven Reconnection
Authors: Mercier, C.; Heyvaerts, J.
1980SoPh...68..151M Altcode:
It has been shown earlier that energy balance processes play a very
important role in the determination of the reconnection regime in the
central diffusive region of a steady Petschek flow (usually considered
elsewhere as isothermal and incompressible): as a consequence of the
plasma thermal properties, abrupt transitions in the reconnection regime
may occur for special external conditions. The regime becomes then a
dynamical one, and it was suggested that onset of plasma microturbulence
may result and act as a primary triggering mechanism in solar flares.
---------------------------------------------------------
Title: Stability of accretion column flows.
Authors: Hameury, J. M.; Bonazzola, S.; Heyvaerts, J.
1980A&A....90..359H Altcode:
The stability of both a spherically symmetric optically thin accretion
and an optically thick accretion column are examined. For optically
thick conditions, it is shown that radiation-pressure dominated flows
near the Eddington limit are, under the usual physical conditions,
unstable to a Rayleigh-Taylor type of instability. Yet an optically
thin flow is stable against radial modes, both in cases where a time lag
between accretion fluctuations and the resulting changes in luminosity
is incorporated or not. These studies indicate that realistic accretion
models should take into account strong micro-inhomogeneity likely to
be present in accretion columns.
---------------------------------------------------------
Title: Population III stars and the shape of the cosmological black
body radiation
Authors: Puget, J. L.; Heyvaerts, J.
1980A&A....83L..10P Altcode:
The paper presents a theory of the distortion of the cosmological
thermal spectrum by pregalactic dust which appears to fit the recent
data. The basic idea is to consider the possibility that the opacity of
the universe in the pregalactic phase (redshift of the order of 10 or
more) may have been dominated by dust at a wavelength near the peak of
intensity of the cosmological black body at that time. This hypothesis
is quite natural within the framework of a model of the universe in
which population III stars can produce a fraction of the observed
abundances of helium and of the heavier elements, which might condense
into dust. It is suggested that the formation of a small mass fraction
of dust (about 0.001) near z equals 10, together with sufficient energy
release, explains the shape of the observed distortion.
---------------------------------------------------------
Title: MHD stability of coronal structures.
Authors: Heyvaerts, J.
1980AnPh....5..337H Altcode: 1980mhda.conf..337H
No abstract at ADS
---------------------------------------------------------
Title: Resistive stability.
Authors: Heyvaerts, J.
1980AnPh....5..379H Altcode: 1980mhda.conf..379H
No abstract at ADS
---------------------------------------------------------
Title: Solar corona magnetohydrostatics.
Authors: Heyvaerts, J.
1980AnPh....5..315H Altcode: 1980mhda.conf..315H
No abstract at ADS
---------------------------------------------------------
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
---------------------------------------------------------
Title: Electro Magnetic Heating of Coronae
Authors: Heyvaerts, J.; Schatzman, E.
1980jfss.conf...77H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Gyro-synchrotron modulation in the moving type IV bursts.
Authors: Trottet, G.; Pick, M.; Heyvaerts, J.
1979A&A....79..164T Altcode:
Three successive moving type IV bursts were observed in association
with an eruptive prominence on April 12, 1977. The radiation which is
attributed to the gyrosynchrotron emission from energetic electrons
trapped in an expanding magnetic arch exhibits an important modulation
on a time scale of about one minute. The modulation takes predominantly
its origin in two components which are assumed to be the mirror points
of the expanding arch where the electrons are trapped. The possibility
that synchrotron radiation near the mirror points is modulated by
a mere MHD oscillation of the arch is investigated. A second kind
of explanation is proposed which involves a quasiperiodic downward
precipitation of particles.
---------------------------------------------------------
Title: Cyclotron line formation by resonant Compton-cyclotron
scattering in Hercules X-1.
Authors: Bonazzola, S.; Heyvaerts, J.; Puget, J. L.
1979A&A....78...53B Altcode:
Calculations are presented which show that a spectrum similar to
the one observed for Hercules X-1 can be generated. It is shown that
there is no straightforward way to explain how observed 'lines' are
produced. The effect of the cyclotron process as resonance scattering
and Compton diffusion on a thermal spectrum in a simple model (cold
plasma, plane-parallel geometry, isotropic scattering cross section)
is studied. It is shown that even in such a crude model, a good account
is given of the formation of the observed spectrum, continuum as well
as lines. The cold-gas approximation is shown not to be inconsistent
with the thermal balance of the accreting column.
---------------------------------------------------------
Title: Plasma and solar physics. The solar flare phenomenon
Authors: Heyvaerts, J.
1979JPhys..40...37H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Discussion
Authors: Gaizauskas, V.; Glencross, W. M.; Heyvaerts, J.
1979phsp.coll..182G Altcode: 1979IAUCo..44..182G
No abstract at ADS
---------------------------------------------------------
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: Plasma and solar physics. The solar flare phenomenon.
Authors: Heyvaerts, J.
1979JPhys..40C..37H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Force-Free Equilibria, Solar Flares and Coronal Transients.
Authors: Heyvaerts, J.; Lasry, J. M.; Schatzman, M.; Witomsky, P.
1979phsp.coll..174H Altcode: 1979IAUCo..44..174H; 1979phsp.conf..174H
The properties of magnetic configurations able to exist in the solar
corona are considered. The solar flare phenomenon is due to the sudden
dissipation of magnetic energy in the solar corona, and it was shown
that photospheric shearing motions are essential in triggering flares
which occur in closed magnetic configurations. The flare problem
is simplified by considering 2-dimensional structures and deriving
expressions for the components of the field and the electric current
density. The shear function is considered, and it is concluded that
the current could be increased in a closed magnetic structure only up
to a certain value which depends on the current distribution. If the
current is pushed above this limit, no neighboring equilibrium can
be found and the structure undergoes a dynamical evolution driven by
unbalanceable Laplace forces towards the open configuration which is
the only equilibrium solution left. The motion could be the 'coronal
transient' which is observed to follow flares, and should be considered
as part of it.
---------------------------------------------------------
Title: Discussion
Authors: Acton, L. W.; Brueckner, J.; Heyvaerts, J.; Maltby, P.;
Spicer, D. S.
1979phsp.coll..314A Altcode: 1979IAUCo..44..314A
No abstract at ADS
---------------------------------------------------------
Title: Discussion
Authors: Gaizauskas, V.; Heyvaerts, J.; Hirayama, T.; Pneuman, G. W.;
Spicer, D. S.; Withbroe, G. L.; Zirin, H.
1979phsp.coll..301G Altcode: 1979IAUCo..44..301G
No abstract at ADS
---------------------------------------------------------
Title: Discussion
Authors: Heyvaerts, J.; Schmahl, E. J.; Spicer, D. S.
1979phsp.coll..179H Altcode: 1979IAUCo..44..179H
No abstract at ADS
---------------------------------------------------------
Title: Discussion
Authors: Heyvaerts, J.; Sheridan, K. V.; Zirin, H.
1979phsp.coll..320H Altcode: 1979IAUCo..44..320H
No abstract at ADS
---------------------------------------------------------
Title: Polarization and location of metric radiobursts in relationship
with the emergence of a new magnetic field.
Authors: Heyvaerts, J.; Kerdraon, A.; Mangeney, A.; Pick, M.;
Slottje, C.
1978A&A....66...81H Altcode:
Spike bursts have been observed in association with some solar type III
burst groups. In this event, the spikes appear according to bandwidth
and duration to be mini type I bursts. Their circular polarization
cannot be explained by emission of the ordinary mode in the magnetic
field of the dominant photospheric polarity. This observation is
interpreted by the expansion at 0.3 solar radii of magnetic loops
related to the emergence of a satellite polarity. A coronal-field
model is proposed for the whole active center. Application of the
theory of Mangeney and Veltri (1976) for type I bursts leads to a
consistent picture of the generation of these spikes.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Formation of X-ray spectra by Compton and cyclotron resonant
diffusion. Application to Hercules X-1.
Authors: Bonazzola, S.; Heyvaerts, J.; Pujet, J. L.
1978sss..meet...B3B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Problems related to Particle Acceleration and Plasma Turbulence
during the Impulsive Phase of Solar Flares
Authors: Heyvaerts, J.
1978pfsl.conf..193H Altcode: 1978ESPM....2..193H
No abstract at ADS
---------------------------------------------------------
Title: The downward motions in quiescent prominences.
Authors: Mercier, C.; Heyvaerts, J.
1977A&A....61..685M Altcode:
Two possible causes of the observed downward mass loss in quiescent
prominences are considered: Joule dissipation in subphotospheric regions
and downward diffusion of neutral atoms due to gravity. A model of
the complete electrical circuit in a quiescent prominence is examined
in which current lines are closed in the convection zone. Arguments
are presented suggesting that Joule dissipation occurs mainly in
the convection zone, and it is shown that the resulting downward
velocity of a prominence could be as high as several hundred meters
per second. The possibility is discussed that material motions in the
photosphere and the convection zone may act as a current generator in
addition to the motion of the prominence itself. Downward diffusive
motion of neutral atoms in a prominence as a result of gravity are
studied quantitatively, taking into account magnetic-field-induced
anisotropies in momentum transfer between particles. It is concluded
that this process allows only slow downward differential motions and
is therefore incapable of explaining the observed mass loss.
---------------------------------------------------------
Title: An emerging flux model for the solar phenomenon.
Authors: Heyvaerts, J.; Priest, E. R.; Rust, D. M.
1977ApJ...216..123H Altcode:
An outline is presented of the physical processes involved in the
emerging flux model, which appears to explain naturally many solar
flare observations. The separate physical phases of the basic model
include a preflare heating phase as the new flux emerges, an impulsive
phase as high-energy particles are accelerated, a flash (or explosive)
phase when the H-alpha intensity increases, and a main phase while
it decreases. The extent and morphology of the main phase emission
depend on the structure of the magnetic field region in which the new
flux finds itself imbedded. It is suggested that a (small) simple loop
flare occurs if the new flux appears in a region where no great amount
of magnetic energy in excess of potential is stored. A two-ribbon
flare occurs if the flux emerges near the polarity inversion line of
an active region that has begun to develop filaments.
---------------------------------------------------------
Title: An emerging flux model for solar flares.
Authors: Heyvaerts, J.; Priest, E.; Rust, D. M.
1977SoPh...53..255H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Broadening and anomalous shift of Pioneer 6 telemetry line. An
effect of coronal inhomogeneities useful for diagnostics.
Authors: Chastel, A. A.; Heyvaerts, J.
1976A&A....51..171C Altcode:
The observational results of Goldsten (1969) on the perturbations of
the frequency and bandwidth of the Pioneer VI 2.3 GHz telemetry signal
during its occultation by the sun are reexamined from the viewpoint of
whether the observed redshifts are of instrumental or solar origin. The
observations are shown to be unreliable since the probe frequency was
not controlled. Analysis of possible solar influences on the frequency
arising from electron density inhomogeneities on the global scale,
macroscopic scale, mesoscale, or microscopic scale shows that classical
physics can explain the observed anomalies, and that a new model of
photon-photon interaction is not needed. A likely explanation is that
in the experiment the corona was almost always being observed when
relaxing after the passage of a discontinuity, most probably a shock.
---------------------------------------------------------
Title: General-relativistic kinetic theory of waves in a massive
particle medium
Authors: Asseo, E.; Gerbal, D.; Heyvaerts, J.; Signore, M.
1976PhRvD..13.2724A Altcode:
In this paper, we give a general-relativistic kinetic theory of
waves propagating in a medium filled with massive particles. A major
difficulty of this problem is to handle simultaneously dispersive and
expansion effects. Matter itself is at the root of both phenomena, and
in our treatment they are conveniently separated by using a two-time
scale approximation. It turns out that the expansion modifies both
the amplitude and the frequency of the waves. Dispersion effects give
rise to proper modes, which are shown to be the 0, 1, and 2 helicity
components of the total field. The dispersion equations for these
different components are obtained in a general form. The propagation of
gravitational modes is examined in more detail for the two extreme cases
of cold and ultrarelativistic matter. A lower cutoff frequency appears,
and no Landau damping is found in the case of a thermalized gas.
---------------------------------------------------------
Title: Thermal evolution of current sheets and flash phase of
solar flares.
Authors: Heyvaerts, J.; Priest, E. R.
1976SoPh...47..223H Altcode:
The physical conditions in a stationary flow of the Petchek type,
allowing reconnection between flux emerging from below the solar
photosphere and a preexisting magnetic field, are discussed. It is
shown that, when rising in the solar atmosphere, the reconnection
region has at first a rather low temperature as compared with its
environment. Above a certain critical height, however, this low
temperature thermal equilibrium often ceases to be possible, and the
sheet rapidly heats, seeking a new thermal equilibrium. During this
dynamical process, current-driven microinstabilities may be triggered in
the current sheet, giving rise to an enhanced resistivity. High energy
particles might be produced by the induced electric field developed
during the rapid readjustment of MHD flows that results from this
change in the transport properties of the plasma.
---------------------------------------------------------
Title: The effect of electron density fluctuations on the fundamental
radiation of type III bursts.
Authors: Heyvaerts, J.
1975A&A....38...45H Altcode:
Summary. The effect of longwavelength electron density inhomogeneities
on the fundamental radiation ofType III bursts is discussed. It
is shown that the effective radiation transfer coefficients in the
source are mainly determined by these fluctuations if the relative
electron density of fluctuations exceeds 0.1 %. In this case both the
bandwidth in the vicinity of a given altitude and the overall size of
the source reflect the properties of the fluctuations of the electronic
density. Key words: solar radio burst - stochastic processes radiative
transfer- coronal electron density fluctuations plasma turbulence
---------------------------------------------------------
Title: The thermal instability in a magnetohydrodynamic medium.
Authors: Heyvaerts, J.
1974A&A....37...65H Altcode:
The modes that can propagate in a resistive, current carrying and
radiating plasma are studied. The energy equation includes wave
heating, radiation cooling, anisotropic thermal conduction as well as
Joule heating. It is shown that when the thermal instability occurs in
such a medium, it tends to develop field aligned fine structures. The
Joule effect, when it is sufficiently important, can be responsible
for a number of particular instabilities: a thermal Joule instability,
which can make unstable modes that would otherwise be stable when the
current is less than some threshold value, and an 'antidiffusion' mode,
the effect of which is to concentrate the electric currents in fine
field-aligned fibers. The nature and stability of modes whose frequency
is less than the characteristic thermal frequencies is also studied.
---------------------------------------------------------
Title: Coronal Electric Currents Produced by Photospheric Motions
Authors: Heyvaerts, J.
1974SoPh...38..419H Altcode:
Due to its high electrical conductivity along field lines, the
corona provides an electric coupling between those remote points
in the photosphere which are linked by coronal lines of force. This
coupling essentially acts as a shunt for potential differences induced
between such points by the electromotive fields created by photospheric
motions. As a result, important coronal currents are driven. This paper
studies the implications of this idea for a model which schematizes
both the magnetic configuration and the photospheric motions observed
in flare producting regions. In this particular geometry, coronal
currents would be mainly driven along a sheet, whose trace in the
plane of the photosphere would look as a two-ribbon structure on both
sides of an inversion line of the photospheric polarity. We show that
vertical currents of the order of 10<SUP>−2</SUP>, 10<SUP>−1</SUP>
A m<SUP>−2</SUP> can be generated, and possibly interrupted if the
photospheric flow velocity exceeds about 1 km s<SUP>−1</SUP>, then
releasing the 10<SUP>32</SUP> ergs of magnetic energy previous stored
in the circuit.
---------------------------------------------------------
Title: Pairs of Non Fundamental-Harmonic Type III Bursts
Authors: Caroubalos, C.; Heyvaerts, J.; Pick, M.; Trottet, G.
1974SoPh...37..205C Altcode:
Different forms of pairs of type III bursts have been discussed in
the literature. We report here a new aspect revealed by high time
resolution radioheliography. In some groups of these bursts, each
element appears to be split into two components. These pairs recur
with a characteristic time, and in a given group the time splitting of
the two components of each pair is the same (one second or less). The
nature of these pairs is discussed: the fundamental-harmonic hypothesis
is excluded. Alternative interpretations are reviewed.
---------------------------------------------------------
Title: A Clue to the Trigger for Both the Type III Solar Radioburst
and the Solar Flare
Authors: Priest, E. R.; Heyvaerts, J.
1974SoPh...36..433P Altcode:
Recent observations of `neutral line absorbing features' in the solar
atmosphere may give an important clue to the mechanism whereby both
type III solar radiobursts and solar flares are triggered. It is
suggested that as new satellite magnetic flux emerges at the edge
of an active region in an area of opposite polarity a neutral sheet
builds up between the new and old flux. When the sheet has a length of
about a megametre its thermal insulation from the surrounding plasma
is effective enough for a thermal instability to occur. The resulting
compression and inflow of plasma is observed in Hα on the disc as a
neutral line absorbing feature. Furthermore, the electric field of
the accompanying collisionless tearing mode instability in a thin
slab near the centre of the sheet exceeds the runaway field; it may
therefore accelerate electrons to high enough energies to produce the
type III burst which usually occurs at the same time as the absorbing
feature. Perhaps the flare which sometimes ensues is triggered when the
quasi-equilibrium state is destroyed by the development of turbulence
in the neutral sheet.
---------------------------------------------------------
Title: Physical sciences: Perturbations of Pioneer 6 telemetry signal
during solar occultation
Authors: Chastel, Arnaud A.; Heyvaerts, Jean F.
1974Natur.249...21C Altcode:
ATTENTION has been drawn recently to unexplained perturbations in the
telemetry signal of Pioneer 6 (2,300 MHz) during solar occultation. The
results<SUP>1</SUP> shown in Fig. 1 present the following odd features:
(1) An anomalous redshift is added to a normal linear redshift
due to the spacecraft oscillator. This residual redshift which is
symmetrical with respect to the centre of the Sun is of the order of z
= 5.18<SUP>-8</SUP> at four solar radii. (2) The bandwidth increases
sharply when the telemetry signal grazes the Sun. (3) There are some
extremely sharp pulses in the bandwidth. In Fig. 2 we show that these
pulses are clearly associated with a sharp increase of the redshift
and correspond to solar flares.
---------------------------------------------------------
Title: On Neutral Line Absorbing Features
Authors: Heyvaerts, J.; Priest, E.
1974cesra...4..147H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Effects of Turbulence Anisotropy on Propagation and
Electromagnetic Radiation of Particle Streams in the Solar Corona
Authors: Heyvaerts, J.; Verdier de Genouillac, G.
1974A&A....30..211H Altcode:
Summary. This paper studies the evolution of a plasmabeam instability
in the presence of non-linear effects. These consist of induced
11-scattering of Langmuir waves on the polarization clouds of
ions; Langmuir waves are considered to have all possible angular-
patterns. This problem is set in relation to Type III solar
radio-bursts, hence the parameters used are those presumed to be
characteristic of coronal conditions. Generally, the electromagnetic
radiation of Type III bursts is attributed to the conversion of Langmuir
waves. The non-linear effects have been introduced in the literature
as a mechanism for sustaining the streams of fast electrons or ions
in which such plasma waves may originate. Here we take explicitly
into account Langmuir turbulence anisotropy as it may influence this
stabilizing mechanism. Mathematical results show a saturation of
the Langmuir turbulence due to non4inear effects, but this regime is
not acceptable from a physical point of view. To complete the study,
we look into the influence of the turbulence level and anisotropy on
the electromagnetic radiation resulting from it by the two conversion
processes usually invoked for Type III bursts. We confirm Smith's result
that the fundamental radiation could be amplified in the source. Key
words: solar corona - solar radio-burst - particle stream - plasma
turbulence - plasma-beam instability
---------------------------------------------------------
Title: Plasma Physics and Solar Radioastronomy
Authors: Heyvaerts, J.; Pick, M.
1972ppsr.conf.....H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Some aspects of coronal structures
Authors: Heyvaerts, J.; Pick, M.
1972ppsr.conf..118H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Structures Coronales
Authors: Heyvaerts, Jean; Pick, Monique
1972stco.book.....H Altcode:
No abstract at ADS
