scholarly journals Relative alignment between dense molecular cores and ambient magnetic field: the synergy of numerical models and observations

2020 ◽  
Vol 494 (2) ◽  
pp. 1971-1987 ◽  
Author(s):  
Che-Yu Chen ◽  
Erica A Behrens ◽  
Jasmin E Washington ◽  
Laura M Fissel ◽  
Rachel K Friesen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Numerical Models ◽  
Field Orientation ◽  
Relative Significance ◽  
Star Forming ◽  
Ambient Magnetic Field ◽  
Core Field ◽  
Dense Cores ◽  
Background Magnetic Field ◽  
The Magnetic Field

ABSTRACT The role played by magnetic field during star formation is an important topic in astrophysics. We investigate the correlation between the orientation of star-forming cores (as defined by the core major axes) and ambient magnetic field directions in (i) a 3D magnetohydrodynamic simulation, (ii) synthetic observations generated from the simulation at different viewing angles, and (iii) observations of nearby molecular clouds. We find that the results on relative alignment between cores and background magnetic field in synthetic observations slightly disagree with those measured in fully 3D simulation data, which is partly because cores identified in projected 2D maps tend to coexist within filamentary structures, while 3D cores are generally more rounded. In addition, we examine the progression of magnetic field from pc to core scale in the simulation, which is consistent with the anisotropic core formation model that gas preferably flows along the magnetic field towards dense cores. When comparing the observed cores identified from the Green Bank Ammonia Survey and Planck polarization-inferred magnetic field orientations, we find that the relative core–field alignment has a regional dependence among different clouds. More specifically, we find that dense cores in the Taurus molecular cloud tend to align perpendicular to the background magnetic field, while those in Perseus and Ophiuchus tend to have random (Perseus) or slightly parallel (Ophiuchus) orientations with respect to the field. We argue that this feature of relative core–field orientation could be used to probe the relative significance of the magnetic field within the cloud.

scholarly journals Is the Magnetic Field Preserved During Core Formation?

2004 ◽  
Vol 221 ◽  
pp. 97-103
Author(s):  
Brenda C. Matthews ◽  
Shih-Ping Lai ◽  
Richard M. Crutcher ◽  
Christine D. Wilson
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Position Angle ◽  
Dark Cloud ◽  
Field Orientation ◽  
Nearby Star ◽  
Star Forming ◽  
Ordered Fields ◽  
Field Geometry ◽  
The Magnetic Field

We present recent JCMT and BIMA array polarimetry data of nearby star-forming regions in order to compare the core and cloud-scale magnetic field geometries in two regions of Orion. The similarity of the magnetic field geometry in these cores to that of their ambient clouds is contrasted with JCMT data toward the Barnard 1 dark cloud in Perseus, which reveal a different magnetic field orientation between the majority of the cores and the surrounding cloud; each of the cores exhibits a different mean polarization position angle. We conclude that the preservation of the magnetic field geometry is better in cores formed within clouds with ordered large scale structures. In Barnard 1, the cores may quickly exhibit a different polarization pattern if they have, for example, rotation which differs from the large scale cloud motions, or a weaker component of ordered fields. This could also explain why the cores exhibit such different geometries from each other in Barnard 1.

scholarly journals Maser polarization with ALMA

2012 ◽  
Vol 8 (S287) ◽  
pp. 64-68
Author(s):  
Andrés F. Pérez-Sánchez ◽  
Wouter Vlemmings
Keyword(s):  
Magnetic Field ◽  
Zeeman Splitting ◽  
Molecular State ◽  
Stimulated Emission ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Field Orientation ◽  
Maser Emission ◽  
Star Forming ◽  
The Magnetic Field

AbstractOnce ALMA full polarization capabilities are offered, (sub-)mm polarization studies will enter a new era. It will become possible to perform detailed studies of polarized maser emission towards for example massive star forming regions and late-type stars such as (post-) Asymptotic Giant Branch stars and young Planetary Nebulae. In these environments, SiO, H2O and HCN are molecules that can naturally generate polarized maser emission observable by ALMA. The maser polarization can then be used to derive the strength and morphology of the magnetic field in the masing regions. However, in order to derive, in particular, the magnetic field orientation from maser linear polarization, a number of conditions involving the rate of stimulated emission, molecular state decay and Zeeman splitting need to be satisfied. In this work, we discuss these conditions for the maser transitions in the ALMA frequency range and highlight the optimum transitions to further our understanding of star formation and evolved star magnetic fields.

scholarly journals Outflows, cores, and magnetic field orientations in W43-MM1 as seen by ALMA

2020 ◽  
Vol 640 ◽  
pp. A111
Author(s):  
C. Arce-Tord ◽  
F. Louvet ◽  
P. C. Cortes ◽  
F. Motte ◽  
C. L. H. Hull ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Mass ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
Mass Star ◽  
Star Forming ◽  
The Core ◽  
Dense Cores ◽  
The Impact ◽  
The Magnetic Field

Aims. It has been proposed that the magnetic field, which is pervasive in the interstellar medium, plays an important role in the process of massive star formation. To better understand the impact of the magnetic field at the pre- and protostellar stages, high-angular resolution observations of polarized dust emission toward a large sample of massive dense cores are needed. We aim to reveal any correlation between the magnetic field orientation and the orientation of the cores and outflows in a sample of protostellar dense cores in the W43-MM1 high-mass star-forming region. Methods. We used the Atacama Large Millimeter Array in Band 6 (1.3 mm) in full polarization mode to map the polarized emission from dust grains at a physical scale of ~2700 au. We used these data to measure the orientation of the magnetic field at the core scale. Then, we examined the relative orientations of the core-scale magnetic field, of the protostellar outflows, and of the major axis of the dense cores determined from a 2D Gaussian fit in the continuum emission. Results. We find that the orientation of the dense cores is not random with respect to the magnetic field. Instead, the dense cores are compatible with being oriented 20–50° with respect to the magnetic field. As for the outflows, they could be oriented 50–70° with respect to the magnetic field, or randomly oriented with respect to the magnetic field, which is similar to current results in low-mass star-forming regions. Conclusions. The observed alignment of the position angle of the cores with respect to the magnetic field lines shows that the magnetic field is well coupled with the dense material; however, the 20–50° preferential orientation contradicts the predictions of the magnetically-controlled core-collapse models. The potential correlation of the outflow directions with respect to the magnetic field suggests that, in some cases, the magnetic field is strong enough to control the angular momentum distribution from the core scale down to the inner part of the circumstellar disks where outflows are triggered.

scholarly journals NGC 4631: The Unusual Star Forming Region Around CM67 — CO Observations with NMA and Pico Veleta

1994 ◽  
Vol 140 ◽  
pp. 363-365 ◽  
Author(s):  
M. Krause ◽  
G. Golla ◽  
K.-I. Morita ◽  
R. Wielebinski
Keyword(s):  
Magnetic Field ◽  
Central Region ◽  
Formation Rate ◽  
Radio Continuum ◽  
Field Orientation ◽  
Hii Region ◽  
Star Forming ◽  
Radio Halo ◽  
Star Forming Regions ◽  
The Magnetic Field

The late-type edge-on spiral galaxy NGC 4631 is known for its high star formation rate and extended radio halo with a uniform magnetic field component ordered predominantly perpendicular to the plane of the galaxy in the inner 6 kpc (assuming a distance of 7.5 Mpc, 1′ = 2.2 kpc) (Hummel et al. 1988; Golla, Ph.D., in preparation). The strongest radio continuum source of NGC 4631 is located at the eastern edge of the central region near a giant HII region complex CM67 (Crillon and Monnet 1969). The magnetic field orientation going out from the central region and especially from the region CM67 as well as the prominent north eastern low frequency radio spur (cf. Hummel et al. 1991) indicate a close connection between the synchrotron emission of the radio halo of NGC 4631 and star forming regions/CM67 in the disk (Golla and Hummel, in preparation). Probably cosmic rays from star forming regions in the disk propagate along the magnetic field Unes into the halo.

On the existence of compressional MHD oscillations in an inhomogeneous magnetoplasma

1990 ◽  
Vol 44 (2) ◽  
pp. 361-375 ◽  
Author(s):  
Andrew N. Wright
Keyword(s):  
Magnetic Field ◽  
Wave Equation ◽  
Density Distribution ◽  
Cold Plasma ◽  
Wave Equations ◽  
Perturbation Field ◽  
Plasma Density Distribution ◽  
Background Magnetic Field ◽  
Transverse Fields ◽  
The Magnetic Field

In a cold plasma the wave equation for solely compressional magnetic field perturbations appears to decouple in any surface orthogonal to the background magnetic field. However, the compressional fields in any two of these surfaces are related to each other by the condition that the perturbation field b be divergence-free. Hence the wave equations in these surfaces are not truly decoupled from one another. If the two solutions happen to be ‘matched’ (i.e. V.b = 0) then the medium may execute a solely compressional oscillation. If the two solutions are unmatched then transverse fields must evolve. We consider two classes of compressional solutions and derive a set of criteria for when the medium will be able to support pure compressional field oscillations. These criteria relate to the geometry of the magnetic field and the plasma density distribution. We present the conditions in such a manner that it is easy to see if a given magnetoplasma is able to executive either of the compressional solutions we investigate.

Effect of a static magnetic field onEscherichia coliadhesion and orientation

2016 ◽  
Vol 62 (11) ◽  
pp. 944-952 ◽  
Author(s):  
Lotfi Mhamdi ◽  
Nejib Mhamdi ◽  
Naceur Mhamdi ◽  
Philippe Lejeune ◽  
Nicole Jaffrezic ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Bacterial Adhesion ◽  
Parallel Magnetic Field ◽  
Field Orientation ◽  
Static Magnetic Fields ◽  
Preliminary Study ◽  
The Difference ◽  
The Magnetic Field

This preliminary study focused on the effect of exposure to 0.5 T static magnetic fields on Escherichia coli adhesion and orientation. We investigated the difference in bacterial adhesion on the surface of glass and indium tin oxide-coated glass when exposed to a magnetic field either perpendicular or parallel to the adhesion surface (vectors of magnetic induction are perpendicular or parallel to the adhesion surface, respectively). Control cultures were simultaneously grown under identical conditions but without exposure to the magnetic field. We observed a decrease in cell adhesion after exposure to the magnetic field. Orientation of bacteria cells was affected after exposure to a parallel magnetic field. On the other hand, no effect on the orientation of bacteria cells was observed after exposure to a perpendicular magnetic field.

Soft Robot Based on Hyperelastic Buckling Controlled by Discontinuous Magnetic Field

2021 ◽  
pp. 1-35
Author(s):  
Yingdong Xu ◽  
Dongze Yan ◽  
Kai Zhang ◽  
Xuequan Li ◽  
Y.F. Xing ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Flexible Electronics ◽  
Nonlinear Deformation ◽  
Numerical Models ◽  
Optical Path ◽  
Magnetic Composite ◽  
Soft Robot ◽  
New Ideas ◽  
Cargo Transportation ◽  
The Magnetic Field

Abstract Most untethered magnetic soft robots are controlled by a continuously applied magnetic field. The accuracy of their motion depends completely on the accuracy of external magnetic field, consequently any slight disturbance may cause a dramatic change. Here, we report a new structure and driven method design to achieve a novel magnetic soft robot, which can achieve accurate and stable locomotion with weakly dependence on the magnetic field. The robot consists of functional magnetic composite materials with one central transportation platform and four crawling arms, whose motion is mainly based on hyperelastic buckling and recovering of the arms. The robot is capable of cargo transportation with multimodal locomotion, such as crawling, climbing and turning with high adaptability to various surfaces. The robot consumes much less driven energy compared to conventional magnetic robots. Moreover, we develop theoretical and numerical models to rationally design the precisely controlled robot. Our study shows applications in terms of transportation functions, such as for optical path adjustments and photographic tasks in complex circumstances. This work also provides new ideas on how to utilize nonlinear deformation more efficiently, one could combine the benefits for both the flexible electronics and actuation applications.

scholarly journals Simulation study of the plasma-brake effect

2014 ◽  
Vol 32 (10) ◽  
pp. 1207-1216 ◽  
Author(s):  
P. Janhunen
Keyword(s):  
Magnetic Field ◽  
High Performance ◽  
Ionospheric Plasma ◽  
Low Earth Orbit ◽  
Earth Orbit ◽  
Breaking Force ◽  
Field Orientation ◽  
Particle In Cell ◽  
Leo Satellite ◽  
The Magnetic Field

Abstract. Plasma brake is a thin, negatively biased tether that has been proposed as an efficient concept for deorbiting satellites and debris objects from low Earth orbit. We simulate the interaction with the ionospheric plasma ram flow with the plasma-brake tether by a high-performance electrostatic particle in cell code to evaluate the thrust. The tether is assumed to be perpendicular to the flow. We perform runs for different tether voltage, magnetic-field orientation and plasma-ion mass. We show that a simple analytical thrust formula reproduces most of the simulation results well. The interaction with the tether and the plasma flow is laminar (i.e. smooth and not turbulent) when the magnetic field is perpendicular to the tether and the flow. If the magnetic field is parallel to the tether, the behaviour is unstable and thrust is reduced by a modest factor. The case in which the magnetic field is aligned with the flow can also be unstable, but does not result in notable thrust reduction. We also correct an error in an earlier reference. According to the simulations, the predicted thrust of the plasma brake is large enough to make the method promising for low-Earth-orbit (LEO) satellite deorbiting. As a numerical example, we estimate that a 5 km long plasma-brake tether weighing 0.055 kg could produce 0.43 mN breaking force, which is enough to reduce the orbital altitude of a 260 kg object mass by 100 km over 1 year.

scholarly journals Magnetic Field Structure of Star Forming Regions: VLBI Spectral Line Results

1984 ◽  
Vol 110 ◽  
pp. 333-334
Author(s):  
J.A. Garcia-Barreto ◽  
B. F. Burke ◽  
M. J. Reid ◽  
J. M. Moran ◽  
A. D. Haschick
Keyword(s):  
Magnetic Field ◽  
Three Dimensional ◽  
Aperture Synthesis ◽  
Stokes Parameters ◽  
Hii Region ◽  
Star Forming ◽  
Star Forming Regions ◽  
Vlbi Observations ◽  
The Magnetic Field ◽  
Synthesis Experiment

Magnetic fields play a major role in the general dynamics of astronomical phenomena and particularly in the process of star formation. The magnetic field strength in galactic molecular clouds is of the order of few tens of μG. On a smaller scale, OH masers exhibit fields of the order of mG and these can probably be taken as representative of the magnetic field in the dense regions surrounding protostars. The OH molecule has been shown to emit highly circular and linearly polarized radiation. That it was indeed the action of the magnetic field that would give rise to the highly polarized spectrum of OH has been shown by the VLBI observations of Zeeman pairs of the 1720 and 6035 MHz by Lo et. al. and Moran et. al. VLBI observations of W3 (OH) revealed that the OH emission was coming from numerous discrete locations and that all spots fell within the continuum contours of the compact HII region. The most detailed VLBI aperture synthesis experiment of the 1665 MHz emission from W3 (OH) was carried out by Reid et. al. who found several Zeeman pairs and a characteristic maser clump size of 30 mas. In this work, we report the results of a 5 station VLBI aperture synthesis experiment of the 1665 MHz OH emission from W3 (OH) with full polarization information. We produced VLBI synthesis maps of all Stokes parameters of 16 spectral features that showed elliptical polarization. The magnitude and direction of the magnetic field have been obtained by the detection of 7 Zeeman pairs. The three dimensional orientation of the magnetic field can be obtained, following the theoretical arguments of Goldreich et. al., from the observation of π and σ components.

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