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  • 1.
    Carlqvist, Per
    KTH, Superseded Departments, Alfvén Laboratory.
    A new mechanism for the crab fingers2004In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 289, no 1-2, p. 47-53Article in journal (Refereed)
    Abstract [en]

    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 twisted around each other. A mechanism for the fingers taking the internal structure into account is proposed. The mechanism is based on the reshaping of magnetized filaments 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 contains a mass condensation. The finger is identified with the double helix. Similar structures of double helices are found to be present also in other environments.

  • 2.
    Carlqvist, Per
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    A remarkable double helix in the V838 Mon nebula2005In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 436, no 1, p. 231-239Article in journal (Refereed)
    Abstract [en]

    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 similar to 9 '' and similar to 1.'' 4, 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.

  • 3.
    Carlqvist, Per
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Dark mammoth trunks in the merging galaxy NGC 1316 and a mechanism of cosmic double helices2010In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 327, no 2, p. 267-278Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Carlqvist, Per
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Model of outgrowths in the spiral galaxies NGC 4921 and NGC 7049 and the origin of spiral arms2013In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 343, no 2, p. 689-712Article in journal (Refereed)
    Abstract [en]

    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.

  • 5.
    Carlqvist, Per
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Twisted Crab fingers revisited2015In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 357, no 1, article id 47Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Carlqvist, Per
    et al.
    Micronic Laser Systems AB, Sweden .
    Brattström, Patrik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    During, Carl
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Optimization of Active Vibration Control of a Laser Pattern Generator in Micro Lithography2010In: Proceedings of the 10th International Conference of the European Society for Precision Engineering and Nanotechnology, EUSPEN 2010, euspen , 2010, Vol. 1, p. 491-494Conference paper (Refereed)
    Abstract [en]

    The extreme precision requirements in semiconductor manufacturing drive the need for an active vibration isolation system in a laser pattern generator. Optimization has been performed and evaluated in a model using a high level programming tool [1]. The areas of optimization were 1) Decoupling strategies for decentralized control and 2) Improved feed forward control. Only a limited description of the model itself is given here. More about the model is presented in [2] and [3].

  • 7.
    Carlqvist, Per
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Gahm, G.
    Manifestations of Electric Currents in Interstellar Molecular Clouds1991Report (Other academic)
  • 8.
    Carlqvist, Per
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Gahm, G. F.
    Kristen, H.
    Formation of Twisted Elephant Trunks in the Rosette Nebula2002In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 280, no 4, p. 405-412Article in journal (Refereed)
    Abstract [en]

    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.

  • 9.
    Carlqvist, Per
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Gahm, G. F.
    Kristen, H.
    Theory of Twisted Trunks2003In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 403, p. 399-412Article in journal (Refereed)
    Abstract [en]

    Using the 2.6 m Nordic Optical Telescope we have observed a large number of elephant trunks in several 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 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.

    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.

  • 10.
    Dahlgren, Hanna
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Carlqvist, Per
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Gahm, Gösta F.
    Filamentary structures in planetary nebulae2007In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 310, no 1-2, p. 65-72Article in journal (Refereed)
    Abstract [en]

    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(-8) 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.

  • 11. Gahm, G F
    et al.
    Carlqvist, Per
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Johansson, L E B
    Nikolic, S
    Rotating elephant trunks2006In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 454, no 1, p. 201-212Article in journal (Refereed)
    Abstract [en]

    Aims. We investigate the structure and velocity of cold molecular pillars, "elephant trunks", in expanding HII regions. Methods. The trunks are seen in silhouette against the bright background in our Ha 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 (CO)-C-12 and (CO)-C-13. 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. 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 HII 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 x 10(48)-2 x 10(50) kg m(2) s(-1), with corresponding rotational energies of up to similar to 10(37) 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.

  • 12. Gahm, G. F.
    et al.
    Lehtinen, K.
    Carlqvist, Per
    KTH, Superseded Departments, Alfvén Laboratory.
    Harju, J.
    Juvela, M.
    Mattila, K.
    The Threaded Molecular Clumps of Chamaeleon III2002In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 389, no 2, p. 577-588Article in journal (Refereed)
    Abstract [en]

    We have mapped large areas in the complex of molecular clouds with the SEST in 13CO( J=1-0) and in C 18O( 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 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  , when assuming the "standard" C 18O/H 2 column density ratio). Also the average number densities are small, cm -3, and the density contrast between clump and interclump gas is only ~10. In addition the values of 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 turn out to be composed of assemblies of clumps. There are no signs of star formation in (unlike and ), and our results indicate also that such activity is not expected. However, with the velocity dispersion of 0.2 km s -1 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.

  • 13.
    Laurent, B. E.
    et al.
    KTH, Superseded Departments.
    Bonnevier, Björn
    KTH, Superseded Departments.
    Carlqvist, Per
    KTH, Superseded Departments.
    On the Dynamics of the Metagalaxy1988Report (Other academic)
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