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Author name code: carlqvist
ADS astronomy entries on 2022-09-14
author:"Carlqvist, Per"
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Title: Twisted Crab fingers revisited
Authors: Carlqvist, Per
2015Ap&SS.357...47C Altcode:
Narrowband images of the Crab Nebula captured by the Hubble Space
Telescope have earlier shown that the nebula does not only present
a network of broad, bright filaments crossing the nebula but also
numerous so-called fingers mostly pointing inwards. Using archival
Hubble images we have in some detail studied the morphology of a great
number of such fingers. This scrutiny has revealed that practically
all the fingers are made up of filaments. Most of the larger fingers
show overall shapes that are similar to either of the two letters V
and Y. In many of these fingers it is also possible to see internal
details. Interestingly, a number of the larger, Y-shaped fingers
turn out to have a stem that consists of intertwined filaments. By
contrast with this, the smaller fingers usually appear only as diffuse
and sometimes incomplete pegs. In none of the smaller fingers is it
possible to find any plain, internal structure. The observational
results obtained are compared with the properties of a previously
proposed model of the fingers. The model suggests that the fingers
have evolved out of magnetized filaments. The evolution should lead
to fingers with overall shapes that are similar to either a V or a Y,
very much in agreement with the observations. In addition to this,
the model prescribes that the stems of the Y-shaped fingers should be
made up of intertwined filaments. From all these points of agreement
we conclude that the properties of the fingers observed lend strong
support to the model.
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Title: Model of outgrowths in the spiral galaxies NGC 4921 and NGC
7049 and the origin of spiral arms
Authors: Carlqvist, Per
2013Ap&SS.343..689C Altcode: 2012Ap&SS.tmp..380C; 2012arXiv1211.3628C
NGC 4921 and 7049 are two spiral galaxies presenting narrow, distinct
dust features. A detailed study of the morphology of those features
has been carried out using Hubble Space Telescope archival images. NGC
4921 shows a few but well-defined dust arms midway to its centre while
NGC 7049 displays many more dusty features, mainly collected within
a ring-shaped formation. Numerous dark and filamentary structures,
called outgrowths, are found to protrude from the dusty arms in
both galaxies. The outgrowths point both outwards and inwards in
the galaxies. Mostly they are found to be V-shaped or Y-shaped with
the branches connected to dark arm filaments. Often the stem of
the Y appears to consist of intertwined filaments. Remarkably, the
outgrowths show considerable similarities to elephant trunks in H ii
regions. A model of the outgrowths, based on magnetized filaments,
is proposed. The model provides explanations of both the shapes and
orientations of the outgrowths. Most important, it can also give an
account for their intertwined structures. It is found that the longest
outgrowths are confusingly similar to dusty spiral arms. This suggests
that some of the outgrowths can develop into such arms. The time-scale
of the development is estimated to be on the order of the rotation
period of the arms or shorter. Similar processes may also take place
in other spiral galaxies. If so, the model of the outgrowths can offer
a new approach to the old winding problem of spiral arms.
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Title: Dark mammoth trunks in the merging galaxy NGC 1316 and a
mechanism of cosmic double helices
Authors: Carlqvist, Per
2010Ap&SS.327..267C Altcode: 2010Ap&SS.tmp..120C; 2010arXiv1003.5818C
NGC 1316 is a giant, elliptical galaxy containing a complex network of
dark, dust features. The morphology of these features has been examined
in some detail using a Hubble Space Telescope, Advanced Camera for
Surveys image. It is found that most of the features are constituted
of long filaments. There also exist a great number of dark structures
protruding inwards from the filaments. Many of these structures are
strikingly similar to elephant trunks in H ii regions in the Milky
Way Galaxy, although much larger. The structures, termed mammoth
trunks, generally are filamentary and often have shapes resembling the
letters V or Y. In some of the mammoth trunks the stem of the Y can
be resolved into two or more filaments, many of which showing signs of
being intertwined. A model of the mammoth trunks, related to a recent
theory of elephant trunks, is proposed. Based on magnetized filaments,
the model is capable of giving an account of the various shapes of
the mammoth trunks observed, including the twined structures.
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Title: Filamentary structures in planetary nebulae
Authors: Dahlgren, Hanna; Carlqvist, Per; Gahm, Gösta F.
2007Ap&SS.310...65D Altcode: 2007Ap&SS.tmp..134D
We have studied small-scale, filamentary features in 14 planetary
nebulae and found that some structures are recurrent and shaped like the
letters V and Y, with the apex or stem pointing toward the central parts
of the nebula. Two such filaments containing dust, one in NGC 3132 and
one in NGC 7293, were investigated in more detail. The mass and density
of the filaments were obtained from extinction measurements, and their
physical properties were derived. We propose that the structures are
confined by magnetic fields, and derive magnetic field strengths of
about 10<SUP>−8</SUP> T, in line with earlier estimates. We also
estimate the magnitude of the electric currents that we expect are
generated in these dynamic systems. We propose a theory where the
magnetic fields control the sculpting and evolution of small-scale
filaments. This theory demonstrates how the substructures may form
magnetized flux ropes that are twisted around each other, in the shape
of double helices. Similar structures, and with similar origin, are
found in many other astrophysical environments.
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Title: Rotating elephant trunks
Authors: Gahm, G. F.; Carlqvist, P.; Johansson, L. E. B.; Nikolić, S.
2006A&A...454..201G Altcode:
Aims.We investigate the structure and velocity of cold molecular
pillars, "elephant trunks", in expanding H II regions.<BR /> Methods:
.The trunks are seen in silhouette against the bright background in
our Hα images. All trunks are filamentary, and show signs of being
twisted. Four such trunks in NGC 7822, IC 1805, the Rosette Nebula,
and DWB 44 were selected, and then mapped mainly in <SUP>12</SUP>CO and
<SUP>13</SUP>CO. We determine the mass and density of the trunks. Most
of the mass is concentrated in a head facing the central cluster,
and in sub-filaments forming the body of the trunk that is connected
to V-shaped filaments to the outer expanding shell.<BR /> Results:
.We discovered that all four trunks rotate as rigid bodies (to a first
approximation) about their major axes, and that at least two trunks
are stretching along their major axes, meaning that the massive heads
are lagging behind in the general expansion of the H II regions. The
rotational periods are of the order of a few million years - similar
to the age of the clusters. Rotation, then, is responsible for the
twisted appearance of many elephant trunks, since they are rooted in the
outer shells. The trunks carry surprisingly large amounts of angular
momentum, 3× 10<SUP>48</SUP>{-}2× 10<SUP>50</SUP> kg m<SUP>2</SUP>
s<SUP>-1</SUP>, with corresponding rotational energies of up to
10<SUP>37</SUP> J. However, we estimate the total magnetic energies
to be even larger. The trunks continuously reshape, and the formation
of twined, and in many cases helical, sub-filaments can be understood
as a consequence of electromagnetic and inertia forces inside the
trunks. A theory based on the concept of magnetically twisted trunks is
developed further, where the initial angular momentum is a consequence
of the twisting of parent filaments containing mass condensations. Our
results also suggest a new process of removing angular momentum from
parent molecular clouds.<BR />
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Title: A remarkable double helix in the V838 Mon nebula
Authors: Carlqvist, P.
2005A&A...436..231C Altcode:
In the beginning of 2002 the previously unnoted star V838 Mon
had a powerful outburst. The star is surrounded by pre-existing,
dusty clouds which are illuminated by the star in an expanding,
parabolic layer. Spectacular images captured by the Hubble Space
Telescope Advanced Camera for Surveys show that the clouds are to a
great extent built up by filaments and concentric shells. One of the
most remarkable features is a filamentary structure forming a double
helix. The structure, which has a projected length and width of ~ 9
arcsec and ∼ 1.4 arcsec, respectively, points almost radially towards
V838 Mon. In order to reveal the geometry of the double helix in some
more detail, a three-dimensional computer model of the structure has
been constructed. The model also assists in determining the expansion
rate of the light echoes along the double helix. By means of the
expansion rate and the tilt of the double helix the distance to V838
Mon is determined to be 2.4 ± 0.5 kpc. A theory of the double helix,
based on a magnetized and twisted filament, is presented. Dynamic and
magnetic forces play an essential role in the shaping of the double
helix. The theory is supported by a mechanical analogy model. Double
helices in other cosmic environments are also discussed.
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Title: A new mechanism for the crab fingers
Authors: Carlqvist, P.
2004Ap&SS.289...47C Altcode:
Images of the outer filamentary parts of the Crab Nebula, earlier
obtained with the Hubble Space Telescope WFPC2, are reconsidered. On
inspection of the images it is found that most of the mainly radially
oriented fingers possess an internal structure, usually in the form of
two or more filaments.For some of the fingers there are clear signs
that the filaments are twistedaround each other. A mechanism for the
fingers taking the internal structureinto account is proposed. The
mechanism is based on the reshaping of magnetizedfilaments under the
influence of inertia and magnetic forces. When interacting with an
expanding shell, driven by the pressure of the synchrotron nebula, part
of such a filament may develop into a double helix pointing radially
inwards. For this transformation to take place it is required that the
magnetic field within the filament is sufficiently twisted and that
the filament containsa mass condensation. The finger is identified
with the double helix. Similar structures of double helices are found
to be present also in other environments.
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Title: Theory of twisted trunks
Authors: Carlqvist, P.; Gahm, G. F.; Kristen, H.
2003A&A...403..399C Altcode:
Using the 2.6 m Nordic Optical Telescope we have observed a large number
of elephant trunks in several H II regions. Here, we present a small
selection of this material consisting of a few large, well-developed
trunks, and some smaller ones. We find that: (i) the well-developed
trunks are made up of dark filaments and knots which show evidence of
twisted structures, (ii) the trunks are connected with essentially
two filamentary legs running in V-shape, and (iii) all trunks have
the maximum extinction in their heads. We advance a theory of twisted
elephant trunks which is based on the presence of magnetic flux ropes
in molecular clouds where hot OB stars are formed. If the rope contains
a local condensation it may adopt a V-shape as the H II region around
the hot stars expands. If, in addition, the magnetic field in the
rope is sufficiently twisted, the rope may form a double helix at
the apex of the V. The double helix is identified with the twisted
elephant trunks. In order to illustrate the mechanisms behind the
double helix we have constructed a mechanical analogy model of the
magnetic flux rope in which the rope has been replaced by a bundle
of elastic strings loaded by a weight. Experiments with the model
clearly show that part of the bundle will transform into a double
helix when the twist of the bundle is sufficiently large. We have also
worked out a simple theoretical model of a mass-loaded magnetic flux
rope. Numerical calculations show that a double helix will indeed form
when the twist of the rope exceeds a certain critical limit. Numerical
model calculations are applied to both the analogy model experiments
and one of the well-developed elephant trunks. On the basis of our
model we also suggest a new interpretation of the so called EGGs. <P
/>The double helix mechanism is quite general, and should be active
also in other suitable environments. One such environment may be the
shell of supernova remnants. Another example is the expanding bubble
outlined by the North Celestial Pole Loop. <P />Based on observations
collected at the Nordic Optical Telescope, La Palma, Spain.
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Title: The threaded molecular clumps of Chamaeleon III
Authors: Gahm, G. F.; Lehtinen, K.; Carlqvist, P.; Harju, J.; Juvela,
M.; Mattila, K.
2002A&A...389..577G Altcode:
We have mapped large areas in the Chamaeleon III complex of
molecular clouds with the SEST in <SUP>13</SUP>CO(J=1-0) and in
C<SUP>18</SUP>O(J=1-0). The stronger CO emission coincides with
areas of cold dust emission, which is distributed in long, but thin,
wavy filaments. We identify some 40 clumps of enhanced CO emission
in these filaments. In the southern part of Cha III the clumps are
equidistant along the main zig-zag shaped filament. Here we find two
systems of filaments moving at different radial velocities. At least
part of the zig-zag patterns visible on optical images may be caused
by overlapping filaments. All clumps are small (typically 0.02-0.05 pc
in radius), and of small mass (typically 0.1-0.7 M<SUB>sun</SUB>, when
assuming the “standard” C<SUP>18</SUP>O/H<SUB>2</SUB> column density
ratio). Also the average number densities are small, n(H<SUB>2</SUB>) =
1x 10<SUP>4</SUP> - 8x 10<SUP>4</SUP> cm<SUP>-3</SUP>, and the density
contrast between clump and interclump gas is only ~ 10. In addition
the values of |E<SUB>pot</SUB>|/E<SUB>kin</SUB> are unusually small,
0.03-0.33. These clumps have smaller masses than those so far identified
in other molecular clouds. Previously reported clumps of larger masses
in Cha III turn out to be composed of assemblies of clumps. There are
no signs of star formation in Cha III (unlike Cha I and Cha II), and
our results indicate also that such activity is not expected. However,
with the velocity dispersion of 0.2 km s<SUP>-1</SUP> the clumps would
leave the thin filaments on short timescales, and if the clumps as
such are not confined by some external force, they would also lose
their identity on even shorter timescales. We discuss the possibility
that the clumps are confined by electromagnetic forces, and show that
this may work with reasonable assumptions on the required magnetic
field strength. We also discuss the possibility that the clumps are
attached to magnetic ropes along the filamentary axis, in which case
the clumps could swing back and forth perpendicularly to the axis,
like they were threaded on elastic strings. Based on observations made
with the Swedish ESO Submillimetre Telescope (SEST), Chile.
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Title: Formation of Twisted Elephant Trunks in the Rosette Nebula
Authors: Carlqvist, P.; Gahm, G. F.; Kristen, H.
2002Ap&SS.280..405C Altcode:
New observations show that dark elephant trunks in the Rosette nebula
are often built up by thin filaments. In several of the trunks the
filaments seem to form a twisted pattern. This pattern is hard to
reconcile with current theory. We propose a new model for the formation
of twisted elephant trunks in which electromagnetic forces play an
important role. The model considers the behaviour of a twisted magnetic
filament in a molecular cloud, where a cluster of hot stars has been
recently born. As a result of stellar winds, and radiation pressure,
electromagnetic forces, and inertia forces part of the filament can
develop into a double helix pointing towards the stars. The double
helix represents the twisted elephant trunk. A simple analogy experiment
visualizes and supports the trunk model.
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Title: Linear polarization and molecular filamentary clouds
Authors: Harjunpää, P.; Kaas, A. A.; Carlqvist, P.; Gahm, G. F.
1999A&A...349..912H Altcode:
We have carried out deep CCD polarimetry in the I band in selected
fields in three filamentary, molecular clouds: the L1400 complex,
L204, and MBM25, at galactic latitudes 4degr , 21degr , and 31degr ,
respectively. I magnitudes and the degree and direction of linear
polarization were measured with satisfactory accuracies for 387
stars down to I=19.5. Typical uncertainties of the degree and angle
of polarization are ΔP{~}0.5% and Δθ{~}10degr . We also derived
extinctions from star counts in and around the observed fields. In
the L1400 complex we imaged a 48 arcmin(2) field in the H and K bands,
providing independent measures of extinction based on the E(H-K) colour
excess. Our measurements show that the patterns of polarization are
remarkably smooth over the fields studied, particularly in the L1400
complex. There is no indication of any statistically significant
difference in polarization angle and degree between obscured and
non-obscured regions. MBM25, with the lowest levels of extinction and
polarization, shows some anomalies in the polarization vectors, but
the statistics is here less good. Our method opens the possibility
to study small-scale irregularities in the polarization pattern on
angular scales down to a few arcseconds. Comparing the extinction
A_V and P/A_V in the field observed in the H and K bands we find that
P/A_V can attain high values (close to the P=3 A_V relation) only for
small values of A_V. Modelling the stellar content along the line of
sight reveals that we, for magnitudes around I=19, sample stars at
very large distances behind the clouds. Our general conclusion is that
the interstellar filaments contribute very little to the polarization
measured. This is in line with recent results obtained for other cloud
regions comprising less detailed spatial scale and a smaller depth in
brightness. Using a semi-empirical version of the Davis-Greenstein
mechanism we have calculated the polarization for simple models of
the three clouds studied, and find that it is considerably smaller
than the typical background polarization, a result in consonance with
the polarimetric measurements. For MBM25 we derive a new distance of
~ 145 pc from Hipparcos parallaxes of two stars surrounded by bright
nebulosities, on the assumption that the stars are physically associated
with the cloud. Based on observations made with the Nordic Optical
Telescope, operated on the island of La Palma jointly by Denmark,
Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del
Roque de los Muchachos of the Instituto de Astrofisica de Canarias.
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Title: Molecular Filamentary Clouds, Structures and Polarization
Authors: Gahm, G. F.; Carlqvist, P.; Harjunpää, P.; Kaas, A. A.;
Kristen, H.
1999anot.conf..155G Altcode:
No abstract at ADS
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Title: Helical structures in a Rosette elephant trunk
Authors: Carlqvist, Per; Kristen, Helmuth; Gahm, Gosta F.
1998A&A...332L...5C Altcode:
We discuss small-scale, helical, interstellar filaments on the basis
of optical observations of an elephant trunk in the Rosette nebula. The
trunk studied is composed of a number of sinusoidal or serpentine-like
dark filaments, preferentially in the outer part of the trunk, where
their wavelength is 7-9 times the trunk radius. The diameters are down
to the limit of resolution of 1.0 arcsec, corresponding to 1600 au, and
ranging up to about 6400 au. At some positions filament crossings give
rise to enhanced extinction. We suggest that the sinusoidal filaments
are helices lined up by magnetic fields. We derive average extinctions
of 0.5-1.0 mag in the filaments, implying molecular densities of
n_H2 ~ 10(4) cm(-3) . From existing data on the Rosette HiI region,
we conclude that the surrounding kinetic and dynamic pressure and the
background radiation field suffice to balance even the denser filaments
and to exert drag forces on the trunk as a whole, consistent with
evidence of stretching of the trunk. The helical magnetic structures
imply the presence of electric currents along the trunk axis. These
currents should form a nearly force-free geometry and are consistent
with a model consisting of 4-7 helical cables on the surface of a
cylinder and which produce the observed wavelength of the helices. We
suggest that the Rosette elephant trunks form an interconnected system
of rope-like structures which are relics from filamentary skeletons
of magnetic fields in the primordial cloud. Based on observations
collected at the Nordic Optical Telescope, La Palma, Spain
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Title: Polarization models of filamentary molecular clouds.
Authors: Carlqvist, P.; Kristen, H.
1997A&A...324.1115C Altcode:
We study numerically the linear polarization and extinction of light
from background stars in three types of models of elongated molecular
clouds by following the development of the Stokes parameters. The
clouds are assumed to be of cylindrical shape and penetrated by a
helical magnetic field {vec}(B). In the first two models we study
only the relative magnitude of the polarization assuming that the
polarization is proportional to B<SUP>mu</SUP>^, where primarily
μ=2. Provided there is no background/foreground polarization present
we find from the cylindrically symmetric Model I that the angle of
polarization has a bimodal character with the polarization being either
parallel with or perpendicular to the axis of the filament. For some
magnetic-field geometries both angles may exist in one and the same
filament. It is concluded that it is not a straightforward task to find
the magnetic-field-line pattern from the polarization pattern. If
a background/foreground polarization exists or, as in Model II,
the filament is not cylindrically symmetric, the bimodal character
of the angle of polarization is lost. By means of Model III we have,
using semi-empirical methods based on the Davis-Greenstein mechanism,
estimated the absolute degree of polarization in the filamentary
molecular cloud L204. It is found that the polarization produced by
the model is much less than the polarization observed. We therefore
conclude that most of the polarization measured in the L204 cloud is
not produced in the cloud itself but is constituted by a large-scale
background/foreground polarization.
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Title: Multicomponent double layers and selective acceleration of
charged particles
Authors: Carlqvist, Per
1995JGR...100..205C Altcode:
Multicomponent double layers, defined as layers composed of more
than two kinds of charged particles, are supposed to constitute
the predominant type of double layer in cosmic plasmas. A model of
a steady and strong multicomponent double layer is studied in both
the nonrelativistic and relativistic approximations. In particular,
such properties of the layer as the structure, potential drop, and
current composition are investigated. It is demonstrated that the
density distribution of each kind of positive and negative particle
in the nonrelativistic multicomponent layer is of the same shape as
the density distribution of the ions and electrons, respectively, in
Langmuir's two-component layer. Also, the shape of the distribution
of the electric field corresponds to that of the two-component
layer. In the relativistic layer the charges are distributed among
two very thin layers of high positive and negative charge density
close to the high-potential and low-potential boundaries of the layer,
respectively, and a constant but low charge density in the rest of the
layer. It is shown that the potential drop across the multicomponent
layer is proportional to the thickness of the layer raised to 4/3
in the nonrelativistic case while it is directly proportional to the
thickness in the relativistic case. Current conditions prescribing the
allowed sets of current densities of the various kinds of particles
in the layer are derived in the nonrelativistic and relativistic
approximations. Correspondingly, abundance conditions for the particles
accelerated through the layer are also obtained. The abundance of the
particles accelerated by the double layer is expected generally to be
different from the abundance of the ambient plasma. It is suggested
that the abundance of the accelerated particles might serve as a means
to detect double layers, especially in space plasmas.
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Title: Manifestations of electric currents in interstellar molecular
clouds.
Authors: Carlqvist, Per; Gahm, Gosta F.
1992ITPS...20..867C Altcode:
The authors draw the attention to filamentary structures in molecular
clouds and point out the existence of subfilaments of sinusoidal shape
and also of helix like structures. For two dark clouds, the Lynds
204 complex and the Sandqvist 187-188 complex, they make a detailed
study of such shapes and in addition they find the possible existence
of helices wound around the main filaments. These features suggest the
existence of electric currents and magnetic fields in these clouds. The
authors derive the magnitudes of the currents expected to flow in
the filaments. Values of column densities, magnetic field strengths,
and directions of the fields are derived from observations. This study
shows that axial currents of the order of a few times 10<SUP>13</SUP>A
are necessary for the clouds to be in equilibrium. The corresponding
mean current densities are very small and even at the very low values
of the fractional abundance of electrons encountered in these clouds.
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Title: Manifestations of electric currents in interstellar molecular
clouds
Authors: Carlqvist, P.; Gahm, G. F.
1991STIN...9317638C Altcode:
Filamentary structures in molecular clouds and the existence of
subfilaments of sinusoidal shape and also of helixlike structures
are investigated. For two dark clouds, the Lynds 204 complex and the
Sandqvist 187-188 complex, such shapes and the possible existence of
helices wound around the main filaments are studied. All these features
suggest the existence of electric currents and magnetic fields in these
clouds. On the basis of a generalization of the Bennett pinch model,
the magnitudes of the currents expected to flow in the filaments
are derived. Values of column densities, magnetic field strengths,
and direction of the fields are derived from observations. Magnetic
fields with both toroidal and axial components are considered. The
study shows that axial currents of the order of a few times 10 to the
13th power A are necessary for the clouds to be in equilibrium. The
mean electron velocities are of the order of 0.01 to 0.00001
m/s, much lower than the thermal velocities in the clouds. It is
suggested that helical structures may evolve as a result of various
instabilities in the pinched clouds. Attention is given to the kink
instability in connection with the sinusoidal shapes. The existence
of electromagnetically controlled features in the interstellar clouds
can be tested by further observations.
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Title: Relativistic Fireworks
Authors: Laurent, Bertel; Carlqvist, Per
1991Ap&SS.181..211L Altcode:
We have studied a model of relativistic fireworks. In this model it
is assumed that a series of explosions occur. In each explosion the
fragments fly apart in arbitrary directions with a given velocity
which is a parameter in the model. We have succeeded in obtaining an
exact expression for the distribution of fragments in velocity space
aftern explosions. We present an exact solution also in the limiting
case of small velocity steps where the process turns into a diffusion
in velocity space. The development in configuration space has been
obtained through Monte-Carlo numerical simulations. The model has been
applied to metagalactic cosmology. Although single explosions cannot
reach the highest redshifts observed in the Hubble expansion the
fireworks model offers a possibility to reach thesez-values in a few
explosions. The model gives a density inhomogeneity of 20% over a tenth
of the Hubble distance as seen from a typical position. Observations
show a considerably greater irregular variation. The model gives a local
velocity dispersion which is too great to comply with observations. A
development of the model is suggested.
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Title: Cosmic electric currents and the generalized Bennett relation.
Authors: Carlqvist, Per
1988Ap&SS.144...73C Altcode:
A generalized form of the Bennett pinch is studied in both
cylindrical geometry and plane-parallel geometry. In this kind
of pinch electromagnetic forces, kinetic pressure gradient forces,
centrifugal forces, and gravitational forces may act. For each of the
two geometries considered a generalized Bennett relation is derived. By
means of these relations it is possible to describe among other things
the pure Bennett pinch, Jean's criterion in one and two dimensions,
force-free magnetic fields, gravitationally balanced magnetic pressures,
and continuous transitions between these states. The theory is applied
to electric currents in the magnetosphere, in the solar atmosphere,
and in the interstellar medium. It is pointed out that the currents
in the solar atmosphere and in the interstellar medium may lead to
pinches that are of vital importance to the phenomena of solar flares
and star formation, respectively.
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Title: On the Dynamics of the Metagalaxy
Authors: Laurent, B. E.; Bonnevier, B.; Carlqvist, P.
1988Ap&SS.144..639L Altcode:
The dynamical aspects of the metagalactic model are studied. In
particular, the consequences of high galaxy and quasar red shifts
are considered. A number of explosion mechanisms are investigated
and limits are given for the velocities they can produce. In case of
constant density in the local rest frame limits are also given for
the parameter Ω<SUB>0</SUB>, for our position in the metagalaxy,
and for the initial mass.
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Title: On the dynamics of the metagalaxy
Authors: Laurent, B. E.; Bonnevier, B.; Carlqvist, P.
1988STIN...8828852L Altcode:
The dynamical aspects of the metagalactic model are
studied. The consequences of high galaxy and quasar red shifts are
considered. Explosion mechanisms are investigated and limits for the
velocities they can produce are given. In the case of constant density
in the local rest frame, limits are also given for the parameter
omega<SUB>o,</SUB> for our position in the metagalaxy, and for the
initial mass.
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Title: On the acceleration of energetic cosmic particles by
electrostatic double layers.
Authors: Carlqvist, Per
1986ITPS...14..794C Altcode:
The capability of electrostatic double layers of accelerating
charged particles to high energies is investigated. Starting from a
one-dimensional relativistic double-layer model, a two-dimensional
relativistic double layer in a current filament is studied. It is
found that the filamentary double layer has a maximum potential drop
that depends both on the magnitude of the filamentary current and on
the composition of the layer. The results are applied to two cosmic
double layers - one in a solar electric circuit and another in a
galactic circuit. If the layers are composed of protons and electrons,
these particles may be accelerated to 10 to the 11th eV in the solar
layer, and to 10 to the 14th eV in the galactic layer. It is suggested
that the solar double layer may account for the acceleration of solar
cosmic rays, while the galactic layer may contribute to the generation
of cosmic radiation.
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Title: On the acceleration of energetic cosmic particles by
electrostatic double layers
Authors: Carlqvist, Per
1986oaec.rept.....C Altcode:
The capability of electrostatic double layers of accelerating
charged particles to high energies is investigated. Starting from a
one-dimensional, relativistic double layer model, a two-dimensional,
relativistic double layer in a current filament is studied. It is
found that the filamentary double layer has a maximum potential drop
that depends on the magnitude of the filamentary current and on the
composition of the layer. The results are applied to two cosmic double
layers: one in a solar electric circuit and another in a galactic
circuit. If the layers are composed of protons and electrons these
particles may be accelerated to 10 to the 11th power eV in the solar
layer and to 10 to the 14th power eV in the galactic layer. It is
suggested that the solar double layer may account for the acceleration
of solar cosmic rays while the galactic layer may contribute to the
generation of cosmic radiation.
---------------------------------------------------------
Title: On the physics of relativistic double layers.
Authors: Carlqvist, P.
1982Ap&SS..87...21C Altcode:
A model of a strong, time-independent, and relativistic double layer is
studied. Besides double layers having the electric field parallel to
the current the model also describes a certain type of oblique double
layers. The ‘Langmuir condition’ (ratio of ion current density to
electron current density) as well as an expression for the potential
drop of the double layer are derived. Furthermore, the distributions
of charged particles, electric field, and potential within the double
layer are clarified and discussed. It is found that the properties of
relativistic double layers differ substantially from the properties
of corresponding non-relativistic double layers.
---------------------------------------------------------
Title: Transition from the dusty plasma state to the planetesimal
state of the early solar system
Authors: Carlqvist, P.; Alfven, H.
1981STIN...8226133C Altcode:
The agreement to within a few percent between the theoretically
predicted cosmogonic shadow effect and observations of large scale
structures of the Saturnian rings and the asteroidal region is
discussed. Although the theory has to be modified, its observationally
confirmed core remains valid. A transformation from the fixed coordinate
system to a system which corotates with the plasma shows that in
the latter system the orbits of the condensed particles contain a
number of cusps where the condensed material is focused and stays for
a comparatively long time. As a result, radiative cooling decreases
the temperature, possibly by one or several orders of magnitude. This
makes the cusps form small cold high density regions in a plasma,
the major part of which is hot and dilute.
---------------------------------------------------------
Title: Electrostatic double layers and a plasma evacuation process.
Authors: Raadu, M. A.; Carlqvist, P.
1981Ap&SS..74..189R Altcode:
An evacuation process due to the growth of current driven instabilties
in a plasma is discussed. The process, which leads to localized extreme
density reductions, is related to the formation of electrostatic double
layers. The initial linear phase is treated using the superposition of
unstable plasma waves. In the long wavelength, non-dispersive limit,
a density dip — which is initially present as a small disturbance —
grows rapidly and remains localized in the plasma. The process works
for a variety of plasma conditions provided a certain current density
is exceeded. For a particular choice of plasma parameters the non-linear
development is followed, by solving the coupled Vlasov-Poisson equations
by finite difference methods. The evacuation process is found to work
even more effectively in the non-linear phase and leads to an extreme
density reduction within the dip. It is suggested that the growth of
such structures produces weak points within the plasma that can lead
to the formation of double layers.
---------------------------------------------------------
Title: Energy Source of the Solar Wind
Authors: Carlqvist, P.; Alfven, H.
1980Ap&SS..71..203C Altcode:
A direct transfer of energy from photospheric activity to the solar
wind by means of electric currents is discussed. Currents are assumed
to flow in quiescent prominences which occasionally erupt and give
rise to expanding loop-like structures in the corona, as observed
from Skylab. Due to expansion, the legs of the loops are transformed
into coronal rays which carry currents from the photosphere to the
outer parts of the corona or interplanetary medium and then back
again to the photosphere. It is proposed that energy is transferred
from photospheric activity to the solar wind in the following ways:
(1) as kinetic energy of the ejected loop matter; (2) as electric
power directly fed into the extended loops; and (3) as torsional waves
produced by fluctuations in the loop currents.
---------------------------------------------------------
Title: Energy source of the solar wind
Authors: Carlqvist, P.; Alfven, H.
1979STIN...8025266C Altcode:
A direct transfer of energy from photospheric activity to the solar
wind by means of electric currents is discussed. Currents are assumed
to flow in quiescent prominences which occasionally erupt and give
rise to expanding looplike structures in the corona as observed from
Skylab. Due to the expansion the legs of the loops are transformed into
coronal rays which carry currents from the photosphere to the outer
parts of the corona or interplanetary medium and then back again to the
photosphere. It is proposed that energy is transferred from photospheric
activity to the solar wind (1) as kinetic energy of the ejected loop
matter; (2) as electric power directly fed into the extended loops; and
(3) as torsional waves produced by fluctuations in the loop currents.
---------------------------------------------------------
Title: A flare-associated mechanism for solar surges.
Authors: Carlqvist, P.
1979SoPh...63..353C Altcode:
An ejection mechanism for solar surges is discussed. The mechanism is
closely related to an earlier proposed model for solar flares founded
on current disruption. Hence, the observed connection between surges
and flares may be explained in a simple way. The mechanism can also
offer explanations of other questions connected with surges such as
why surges tend to grow up from small bright knots emitting moustache
spectra, why strong magnetic field concentrations are observed near
the base of surges, why surges often exhibit a helical motion, and why
homologous surges are produced. Finally it is pointed out that spicules
might be generated by a mechanism similar to that discussed for surges.
---------------------------------------------------------
Title: Some Theoretical Aspects of Electrostatic Double Layers
Authors: Carlqvist, P.
1979wisp.proc...83C Altcode:
A review is presented of the main results of the theoretical work
on electrostatic double layers. The general properties of double
layers are first considered. Then the time-independent double layer is
discussed. The discussion deals with the potential drop, the thickness,
and some necessary criteria for the existence and stability of the
layer. As a complement to the study of the time-independent double
layer a few remarks are also made upon the time-dependent double
layer. Finally the question of how double layers are formed and
maintained is treated. Several possible formation mechanisms are
considered.
---------------------------------------------------------
Title: Some Theoretical Aspects of Electrostatic Double Layers
Authors: Carlqvist, P.
1979ASSL...74...83C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Some theoretical aspects of electrostatic double layers
Authors: Carlqvist, P.
1978STIN...7917790C Altcode:
The general properties of electrostatic double layers are
considered. The time-independent double layer is discussed with
emphasis on the potential drop, the thickness, and some necessary
criteria for the existence and stability of the layer. Properties of
the time-dependent double layer are also reviewed. The question of how
double layers are formed and maintained is treated. Several possible
formation mechanisms are examined.
---------------------------------------------------------
Title: Interstellar Clouds and the Formation of Stars
Authors: Alfven, H.; Carlqvist, P.
1978Ap&SS..55..487A Altcode:
Part I gives a survey of the drastic revision of cosmic plasma physics
which is precipitated by the exploration of the magnetosphere throughin
situ measurements. The ‘pseudo-plasma formalism’, which until
now has almost completely dominated theoretical astrophysics, must be
replaced by an experimentally based approach involving the introduction
of a number of neglected plasma phenomena, such as electric double
layers, critical velocity, and pinch effect. The general belief that
star light is the main ionizer is shown to be doubtful; hydromagnetic
conversion of gravitational and kinetic energy may often be much
more important. In Part II the revised plasma physics is applied to
dark clouds and star formation. Magnetic fields do not necessarily
counteract the contraction of a cloud; they may just as well ‘pinch’
the cloud. Magnetic compression may be the main mechanism for forming
interstellar clouds and keeping them together. Part III treats the
formation of stars in a dusty cosmic plasma cloud. Star formation is
due to an instability, but it is very unlikely that it has anything
to do with the Jeans instability. A reasonable mechanism is that the
sedimentation of ‘dust’ (including solid bodies of different
size) is triggering off a gravitationally assisted accretion. A
‘stellesimal’ accretion analogous to the planetesimal accretion
leads to the formation of a star surrounded by a very low density hollow
in the cloud. Matter falling in from the cloud towards the star is the
raw material for the formation of planets and satellites. The study of
the evolution of a dark cloud leads to a scenario of planet formation
which is reconcilable with the results obtained from studies based on
solar system data. This means that the new approach to cosmical plasma
physics discussed in Part I logically leads to a consistent picture
of the evolution of dark clouds and the formation of solar systems.
---------------------------------------------------------
Title: Interstellar clouds and the formation of stars
Authors: Alfven, H.; Carlqvist, P.
1977STIN...7827037A Altcode:
The theory and properties of cosmic plasma are reviewed and the general
belief that star light is the main ionizer is shown to be doubtful. The
magnetohydrodynamic aspects of cosmic plasma clouds are discussed and it
is concluded that magnetic fields may pinch the cloud, while magnetic
compression may be the main mechanism for forming interstellar clouds
and keeping them together. The formation of stars in a dusty cosmic
plasma cloud is also discussed.
---------------------------------------------------------
Title: The cosmic X-ray background (reply)
Authors: Carlqvist; Laurent
1976Natur.262..822C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Annihilation of matter and antimatter and the cosmic X-ray
background
Authors: Carlqvist, P.; Laurent, B.
1976Natur.260..225C Altcode:
When optical photons are scattered against the relativistic electrons
produced by the annihilation of matter and antimatter, X-rays are
produced by the inverse Compton effect. The efficiency of this X-ray
mechanism in intergalactic space is investigated on the basis of a
simplified model. The inverse Compton spectrum obtained from the
model is in good agreement with observational data on the cosmic
X-ray background over the interval 1 keV to 100 keV. A mean electron
density calculated for the energy interval 10 MeV to 100 MeV is
about two orders of magnitude smaller than the mean atom density
of galactic material throughout the Universe. The magnetic field
required to yield a stationary spectrum for the electron energies of
interest is calculated to be greater than .00002 Gauss, indicating
an intensity of synchrotron radiation in the radio band produced by
the annihilation electrons necessary to produce the X-rays which is
higher than experiment allows. Annihilation electrons may be created
in quasars and galactic nuclei where a rapid decay in the electron
energy occurs. The annihilation electrons escape into intergalactic
space, become uniformly distributed, and produce the X-ray background
by interacting with optical photons.
---------------------------------------------------------
Title: Annihilation of matter and antimatter and the cosmic X-ray
background.
Authors: Carlqvist, P.; Laurent, B.
1975amac.book.....C Altcode: 1975STIN...7623146C
A cosmologic model for the cosmic X-ray background radiation mechanism
is suggested. This model is based on inverse Compton scattering of
galactic photons on relativistic annihilation electrons.
---------------------------------------------------------
Title: On the formation of double layers in plasmas.
Authors: Carlqvist, P.
1972CosEl...3..377C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Space-charge regions above the aurora
Authors: Carlqvist, Per; Boström, Rolf
1970JGR....75.7140C Altcode:
Observations have shown that field-aligned currents above auroras
reach such magnitudes that space-charge regions of high potential
drops can be expected. Effects of the electric fields associated with
such a space-charge region are acceleration of auroral electrons and
horizontal motions in the visual aurora.
---------------------------------------------------------
Title: Current Limitation and Solar Flares
Authors: Carlqvist, P.
1969SoPh....7..377C Altcode:
A flare model based on force-free currents in the solar atmosphere
is considered. The energy of the flare is supposed to be stored as
magnetic energy in the current system. If the current density exceeds
a certain critical limit an over-voltage may arise in the circuit
which will give rise to a rapid release of the stored energy. At the
end of the paper some results yielded by the model are compared with
observational evidence of flares.
---------------------------------------------------------
Title: Solar flares caused by high impedance regions in current
filaments
Authors: Carlqvist, P.
1968mmsf.conf..193C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Currents in the Solar Atmosphere and a Theory of Solar Flares
Authors: Alfvén, H.; Carlqvist, P.
1967SoPh....1..220A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Flares Caused by Circuit Interruptions
Authors: Jacobsen, C.; Carlqvist, P.
1964Icar....3..270J Altcode:
Interruptions in inductive electric current circuits in the Sun are
considered as possible causes of solar flares. The currents are assumed
to have a filamentary structure and the interruption to be related to
an instability well known in gas discharge physics.
