scholarly journals Magnetic fields in Bok globules: multi-wavelength polarimetry as tracer across large spatial scales

2018 ◽  
Vol 618 ◽  
pp. A163 ◽  
Author(s):  
S. Jorquera ◽  
G. H.-M. Bertrang
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Wavelength Range ◽  
Near Infrared ◽  
Spatial Scales ◽  
Field Structure ◽  
Bok Globules ◽  
The Magnetic Field ◽  
Complex Density

Context. The role of magnetic fields in the process of star formation is a matter of continuous debate. Clear observational proof of the general influence of magnetic fields on the early phase of cloud collapse is still pending. In an earlier study on Bok globules with simple structures, we find strong indications of dominant magnetic fields across large spatial scales. Aims. The aim of this study is to test the magnetic field influence across Bok globules with more complex density structures. Methods. We apply near-infrared polarimetry to trace the magnetic field structure on scales of 104–105 au (~0.05–0.5pc) in selected Bok globules. The combination of these measurements with archival data in the optical and sub-mm wavelength range allows us to characterize the magnetic field on scales of 103–106 au (~0.005–5pc). Results. We present polarimetric data in the near-infrared wavelength range for the three Bok globules CB34, CB56, and [OMK2002]18, combined with archival polarimetric data in the optical wavelength range for CB34 and CB56, and in the submillimeter wavelength range for CB34 and [OMK2002]18. We find a strong polarization signal (P ≥ 2%) in the near-infrared for all three globules. For CB34, we detect a connection between the structure on scales of 104–105 au (~0.05–0.5pc) to 105–106 au (~0.5–5pc). For CB56, we trace aligned polarization segments in both the near-infrared and optical data, suggesting a connection of the magnetic field structure across the whole globule. In the case of [OMK2002]18, we find ordered polarization structures on scales of 104–105 au (~0.05–0.5pc). Conclusions. We find strongly aligned polarization segments on large scales which indicate dominant magnetic fields across Bok globules with complex density structures. To reconcile our findings in globules, the lowest mass clouds known, and the results on intermediate (e.g. Taurus) and more massive (e.g. Orion) clouds, we postulate a mass-dependent role of magnetic fields, whereby magnetic fields appear to be dominant on low and high mass but rather subdominant on intermediate mass clouds.

Observations of magnetic fields in star-forming clouds

2018 ◽  
Vol 14 (A30) ◽  
pp. 101-101
Author(s):  
Juan D. Soler
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Spatial Scales ◽  
Cloud Formation ◽  
Star Forming ◽  
Formation And Evolution ◽  
Under Construction ◽  
The Magnetic Field

AbstractThis review examines observations of magnetic fields in molecular clouds, that is, at spatial scales ranging from tens to tenths of parsecs and densities up to hundreds of particles per cubic centimetre. I will briefly summarize the techniques for observing and mapping magnetic fields in molecular clouds. I will review important examples of observational results obtained using each technique and their implications for our understanding of the role of the magnetic field in molecular cloud formation and evolution. Finally, I will briefly discuss the prospects for advances in our observational capabilities with telescopes and instruments now beginning operation or under construction.

scholarly journals What Density of Magnetosheath Sodium Ions Can Provide the Observed Decrease in the Magnetic Field of the “Double Magnetopause” during the First MESSENGER Flyby?

Symmetry ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1168
Author(s):  
Elena Belenkaya ◽  
Ivan Pensionerov
Keyword(s):  
Magnetic Field ◽  
Analytical Approach ◽  
Field Structure ◽  
Sodium Ions ◽  
Plasma Parameters ◽  
Calculation Results ◽  
Magnetizing Current ◽  
The Magnetic Field ◽  
Density Excess

On 14 January 2008, the MESSENGER spacecraft, during its first flyby around Mercury, recorded the magnetic field structure, which was later called the “double magnetopause”. The role of sodium ions penetrating into the Hermean magnetosphere from the magnetosheath in generation of this structure has been discussed since then. The violation of the symmetry of the plasma parameters at the magnetopause is the cause of the magnetizing current generation. Here, we consider whether the change in the density of sodium ions on both sides of the Hermean magnetopause could be the cause of a wide diamagnetic current in the magnetosphere at its dawn-side boundary observed during the first MESSENGER flyby. In the present paper, we propose an analytical approach that made it possible to determine the magnetosheath Na+ density excess providing the best agreement between the calculation results and the observed magnetic field in the double magnetopause.

scholarly journals Near Infrared Polarimetry of Dark Clouds and Star Forming Regions - Two Micron Polarization Survey of T Tauri Stars

1990 ◽  
Vol 140 ◽  
pp. 327-328
Author(s):  
M. Tamura ◽  
S. Sato
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Near Infrared ◽  
Background Field ◽  
Star Forming ◽  
Dark Clouds ◽  
Star Forming Regions ◽  
Stellar Sources ◽  
Geometrical Relationship ◽  
The Magnetic Field

Infrared polarimetry is one of the most useful methods to delineate the magnetic field structure in dark clouds and star-forming regions, where the intracloud extinction is so large that optical polarimetry is inaccessible. We have been conducting a near-infrared polarization survey of background field stars and embedded sources toward nearby dark clouds and star-forming regions (Tamura 1988). Particularly, the magnetic field structure in the denser regions of the clouds are well revealed in Heiles Cloud 2 in Taurus, ρ Oph core, and NGC1333 region in Perseus (Tamura et al. 1987; Sato et al. 1988; Tamura et al. 1988). This survey also suggests an interesting geometrical relationship between magnetic field and star-formation: the IR polarization of young stellar sources associated with mass outflow phenomena is perpendicular to the magnetic fields. This relationship suggests a presence of circumstellar matter (probably dust disk) with its plane perpendicular to the ambient magnetic field. Combining with another geometrical relationship that the elongation of the denser regions of the cloud is perpendicular to the magnetic field, the geometry suggests that the cloud contraction and subsequent star-formation have been strongly affected by the magnetic fields. Thus, it is important to study the universality of such geometrical relationship between IR polarization of young stellar sources and magnetic fields. In this paper, we report the results on a 2 micron polarization survey of 39 T Tauri stars, 8 young stellar objects and 11 background field stars in Taurus dark cloud complex.

scholarly journals Near-infrared Polarimetry and Interstellar Magnetic Fields in the Galactic Center

2012 ◽  
Vol 10 (H16) ◽  
pp. 387-387
Author(s):  
S. Nishiyama ◽  
H. Hatano ◽  
T. Nagata ◽  
M. Tamura
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Near Infrared ◽  
Galactic Center ◽  
Smooth Transition ◽  
The Magnetic Field

AbstractWe present a large-scale view of the magnetic field (MF) in the central 3° × 2° region of our Galaxy. There is a smooth transition of the large-scale MF configuration in this region.

Magnetic Fields and Disks in Star-forming Regions

1993 ◽  
Vol 10 (3) ◽  
pp. 247-249 ◽  
Author(s):  
C.M. Wright ◽  
D.K. Aitken ◽  
C.H. Smith ◽  
P.F. Roche
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Transverse Component ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Molecular Outflow ◽  
The Magnetic Field

AbstractThe star-formation process is an outstanding and largely unsolved problem in astrophysics. The role of magnetic fields is unclear but is widely considered to be important at all stages of protostellar evolution, from cloud collapse to ZAMS. For example, in some hydromagnetic models, the field may assist in removing angular momentum, thereby driving accretion and perhaps bipolar outflows.Spectropolarimetry between 8 and 13μm provides information on the direction of the transverse component of a magnetic field through the alignment of dust grains. We present results of 8–13μm spectropolarimetric observations of a number of bipolar molecular outflow sources, and compare the field directions observed with the axes of the outflows and putative disk-like structures observed to be associated with some of the objects. There is a strong correlation, though so far with limited statistics, between the magnetic field and disk orientations. We compare our results with magnetic field configurations predicted by current models for hydromagnetically driven winds from the disks around Young Stellar Objects (YSOs). Our results appear to argue against the Pudritz and Norman model and instead seem to support the Uchida and Shibata model.

scholarly journals Oscillatory convection in strong magnetic fields and origin of active regions

1968 ◽  
Vol 35 ◽  
pp. 127-130 ◽  
Author(s):  
S. I. Syrovatsky ◽  
Y. D. Zhugzhda
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Active Regions ◽  
Oscillatory Convection ◽  
Strong Magnetic Fields ◽  
Various Boundary Conditions ◽  
Convective Cells ◽  
The Magnetic Field ◽  
Polytropic Atmosphere

The convection in a compressible inhomogeneous conducting fluid in the presence of a vertical uniform magnetic field has been studied. It is shown that a new mode of oscillatory convection occurs, which exists in arbitrarily strong magnetic fields. The convective cells are stretched along the magnetic field, their horizontal dimensions are determined by radiative cooling. Criteria for convective instability in a polytropic atmosphere are obtained for various boundary conditions in the case when the Alfvén velocity is higher compared with the velocity of sound.The role of oscillatory convection in the origin of sunspots and active regions is discussed.

scholarly journals Distortion of magnetic fields in the pre-stellar core Barnard 68

2008 ◽  
Vol 4 (S259) ◽  
pp. 107-108 ◽  
Author(s):  
Ryo Kandori ◽  
Motohide Tamura ◽  
Ken-ichi Tatematsu ◽  
Nobuhiko Kusakabe ◽  
Yasushi Nakajima ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Near Infrared ◽  
Flux Ratio ◽  
Field Structure ◽  
Wide Field ◽  
Stellar Core ◽  
The Core ◽  
Cloud Cores ◽  
The Stability

AbstractMagnetic fields are believed to play an important role in controlling the stability and contraction of molecular cloud cores. In the present study, magnetic fields of a cold pre-stellar core, Barnard 68, have been mapped based on wide-field near-infrared polarimetric observations of background stars. A distinct “hourglass-shaped” magnetic field is identified toward the core, as the observational evidence of magnetic field structure distorted by mass accumulation in a pre-stellar core. Our findings on the geometry of magnetic fields as well as the mass-to-magnetic flux ratio are presented.

scholarly journals No-z model: results and perspectives for accretion discs

2021 ◽  
pp. 490-494
Author(s):  
E. A. Mikhailov ◽  
M. V. Pashentsevay
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Magnetic Fields ◽  
Variable Stars ◽  
Field Structure ◽  
Accretion Discs ◽  
Astrophysical Objects ◽  
The Galaxy ◽  
Galaxy Center ◽  
The Magnetic Field

Accretion discs surround different compact astrophysical objects such as black holes, neutron stars and white dwarfs. Also they are situated in systems of variable stars and near the galaxy center. Magnetic fields play an important role in evolution and hydrodynamics of the accretion discs: for example, they can describe such processes as the transition of the angular momentum. There are different approaches to explain the magnetic fields, but most interesting of them are connected with dynamo generation. As for disc, it is quite useful to take no-$z$ approximation which has been developed for galactic discs to solve the dynamo equations. It takes into account that the disc is quite thin, and we can solve the equations only for two plane components of the field. Here we describe the time dependence of the magnetic field for different distances from the center of the disc. Also we compare the results with another approaches which take into account more complicated field structure.

scholarly journals ALMA reveals the coherence of the magnetic field geometry in OH 231.8+4.2

2020 ◽  
Vol 495 (4) ◽  
pp. 4297-4305
Author(s):  
L Sabin ◽  
R Sahai ◽  
W H T Vlemmings ◽  
Q Zhang ◽  
A A Zijlstra ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Dust Emission ◽  
Polarization Data ◽  
Central System ◽  
Emission Analysis ◽  
Intermediate Mass Stars ◽  
Field Geometry ◽  
The Magnetic Field

ABSTRACT In a continuing effort to investigate the role of magnetic fields in evolved low- and intermediate-mass stars (principally regarding the shaping of their envelopes), we present new Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution polarization data obtained for the nebula OH 231.8+4.2. We found that the polarized emission likely arises from aligned grains in the presence of magnetic fields rather than radiative alignment and self-scattering. The ALMA data show well organized electric field orientations in most of the nebula and the inferred magnetic field vectors (rotated by 90°) trace an hourglass morphology centred on the central system of the nebula. One region in the southern part of OH 231.8+4.2 shows a less organized distribution probably due to the shocked environment. These findings, in conjunction with earlier investigations (maser studies and dust emission analysis at other scales and wavelengths) suggest an overall magnetic hourglass located inside a toroidal field. We propose the idea that the magnetic field structure is closely related to the architecture of a magnetic tower and that the outflows were therefore magnetically launched. While the current dynamical effect of the fields might be weak in the equatorial plane principally due to the evolution of the envelope, it would still be affecting the outflows. In that regard, the measurement of the magnetic field at the stellar surface, which is still missing, combined with a full magnetohydrodynamic treatment are required to better understand and constrain the events occurring in OH 231.8+4.2.

Sign in / Sign up

Export Citation Format

Share Document