scholarly journals SMA observations of polarized dust emission in solar-type Class 0 protostars: Magnetic field properties at envelope scales

2018 ◽  
Vol 616 ◽  
pp. A139 ◽  
Author(s):  
Maud Galametz ◽  
Anaëlle Maury ◽  
Josep M. Girart ◽  
Ramprasad Rao ◽  
Qizhou Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Dust Emission ◽  
Point Of View ◽  
Continuum Emission ◽  
Small Scale ◽  
Theoretical Point ◽  
Multiple Systems ◽  
Linearly Polarized ◽  
Solar Type ◽  
The Magnetic Field

Aims. Although from a theoretical point of view magnetic fields are believed to play a significant role during the early stages of star formation, especially during the main accretion phase, the magnetic field strength and topology is poorly constrained in the youngest accreting Class 0 protostars that lead to the formation of solar-type stars. Methods. We carried out observations of the polarized dust continuum emission with the SMA interferometer at 0.87 mm to probe the structure of the magnetic field in a sample of 12 low-mass Class 0 envelopes in nearby clouds, including both single protostars and multiple systems. Our SMA observations probed the envelope emission at scales ~600 − 5000 au with a spatial resolution ranging from 600 to 1500 au depending on the source distance. Results. We report the detection of linearly polarized dust continuum emission in all of our targets with average polarization fractions ranging from 2% to 10% in these protostellar envelopes. The polarization fraction decreases with the continuum flux density, which translates into a decrease with the H2 column density within an individual envelope. Our analysis show that the envelope-scale magnetic field is preferentially observed either aligned or perpendicular to the outflow direction. Interestingly, our results suggest for the first time a relation between the orientation of the magnetic field and the rotational energy of envelopes, with a larger occurrence of misalignment in sources in which strong rotational motions are detected at hundreds to thousands of au scales. We also show that the best agreement between the magnetic field and outflow orientation is found in sources showing no small-scale multiplicity and no large disks at ~100 au scales.

Magnetically regulated collapse in the B335 protostar ?

2018 ◽  
Vol 14 (A30) ◽  
pp. 117-117
Author(s):  
A. J. Maury ◽  
J. M. Girart ◽  
Q. Zhang
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Dust Emission ◽  
Flux Ratio ◽  
Point Of View ◽  
Continuum Emission ◽  
Poloidal Magnetic Field ◽  
Core Mass ◽  
Protostellar Collapse ◽  
The Magnetic Field

AbstractThe role of the magnetic field during protostellar collapse is still poorly constrained from an observational point of view, and only few constraints exist that shed light on the magnetic braking efficiency during the main accretion phase. I presented our ALMA polarimetric observations of the thermal dust continuum emission at 1.3 mm, towards the B335 Class 0 protostar (Maury et al. 2018a). Linearly polarized dust emission is detected at all scales probed by our observations (50 to 1000 au). The magnetic field structure has a very ordered topology in the inner envelope, with a transition from a large-scale poloidal magnetic field, in the outflow direction, to strongly pinched in the equatorial direction. We compared our data to a family of magnetized protostellar collapse models. We show that only models with an initial core mass-to-flux ratio μ∼5-6 are able to reproduce the observed properties of B335, especially the upper-limits on its disk size, its large-scale envelope rotation β and the pronounced magnetic field lines pinching observed in our ALMA data. In these MHD models, the magnetic field is dynamically relevant to regulate the typical outcome of protostellar collapse, suggesting a magnetically-regulated disk formation scenarios is at work in B335.

scholarly journals QUANTUM CORRECTIONS TO CONDUCTIVITY FOR SEMICONDUCTORS WITH VARIOUS STRUCTURES

2011 ◽  
Vol 25 (14) ◽  
pp. 1915-1929
Author(s):  
S. A. ALAVI ◽  
A. TATAR
Keyword(s):  
Magnetic Field ◽  
Strong Relationship ◽  
Point Of View ◽  
Quantum Corrections ◽  
Theoretical Point ◽  
Quantum Well Structures ◽  
Temperature Ranges ◽  
Heavily Doped ◽  
Low Magnetic Field ◽  
The Magnetic Field

We study the magnetic field dependences of the conductivity in heavily doped, strongly disordered 2D quantum well structures within wide conductivity and temperature ranges. We show that the exact analytical expression derived in our previous paper [S. A. Alavi and S. Rouhani, Phys. Lett. A320, 327 (2004)], is in better agreement with the existing equation, i.e., Hikami et al. expression [ Prog. Theor. Phys.63, 707 (1980)] and Littman and Schmid expression [J. Low Temp. Phys.69, 131 (1987)], with the experimental data even in low magnetic field for which the diffusion approximation is valid. On the other hand from theoretical point of view we observe that our equation is also rich because it establishes a strong relationship between quantum corrections to the conductivity and the quantum symmetry Suq(2). It is shown that the quantum corrections to the conductivity is the trace of Green function made by a generator of Suq(2) algebra. Using this fact we show that the quantum corrections to the conductivity can be expressed as a sum of an infinite number of Feynman diagrams.

Role of the magnetic field on the formation of solar type stars

2018 ◽  
Vol 14 (A30) ◽  
pp. 119-119
Author(s):  
Valeska Valdivia ◽  
Anaëlle J. Maury ◽  
Patrick Hennebelle
Keyword(s):  
Magnetic Field ◽  
Gravitational Collapse ◽  
Dust Emission ◽  
Stokes Parameters ◽  
Field Orientation ◽  
Magnetic Field Orientation ◽  
Solar Type ◽  
3D Topology ◽  
The Magnetic Field

AbstractMagnetic fields play a key role during the gravitational collapse of dense protostellar cores. In recent years mm and sub-mm observations of dust polarized emission have been used to unveil the morphology of the magnetic field, but this method relies on the assumption that non-spherical dust grains are well aligned with the magnetic field.Using non-ideal MHD numerical simulations, we study the evolution of the magnetic field during the gravitational collapse. We use the state-of-the-art radiative transfer code POLARIS to compute the Stokes parameters and produce synthetic observations of mm/submm polarized dust emission. We compare the results obtained using the radiative torques (RAT) mechanism to the results obtained by assuming that grains are perfectly aligned to constrain how well polarized dust emission traces the magnetic field orientation.The complexity of the magnetic field produces a mild depolarization. The depolarization observed in the inner regions is rather caused by a decrease of the dust alignment efficiency and it cannot be reproduced by just scaling down the polarisation degree obtained for a uniform efficiency. We find that the magnetic field orientation is well constrained by the polarized dust emission as long as its 3D topology remains organized.

Characterizing the youngest protostellar disks with the IRAM-PdBI and ALMA interferometers

2018 ◽  
Vol 14 (S345) ◽  
pp. 91-95
Author(s):  
Anaëlle Maury
Keyword(s):  
Magnetic Field ◽  
Line Emission ◽  
Rotating Disk ◽  
Continuum Emission ◽  
Disk Formation ◽  
Protostellar Disks ◽  
Disk Size ◽  
Solar Type ◽  
Protostellar Collapse ◽  
The Magnetic Field

AbstractI present our observations and modeling of the 1.3 mm and 3.18 mm dust continuum emission in Class 0 protostars, from the IRAM-PdBI CALYPSO survey. We show that most protostars are better reproduced by models including a disk-like dust continuum component contributing to the flux at small scales, but less than 25% of these candidate protostellar disks are resolved at radii >60 au, which favors magnetized models of rotating protostellar collapse for disk formation (Maury et al. 2019). I also present new ALMA observations of the molecular line emission in the IRAM04191 protostar, suggesting a small counter-rotating disk is detected in this young low-luminosity solar-type protostar. Finally, I show our ALMA observations of the magnetic field topology in the B335 protostar, which when compared to the typical output from protostellar collapse models, suggest the magnetic field might be responsible for constraining the disk size to remain very small in this protostar (Maury et al. 2018).

scholarly journals Bok globule CB 17: polarization, extinction and distance

2019 ◽  
Vol 487 (1) ◽  
pp. 475-485
Author(s):  
G B Choudhury ◽  
A Barman ◽  
H S Das ◽  
B J Medhi
Keyword(s):  
Magnetic Field ◽  
Near Infrared ◽  
Dust Emission ◽  
Continuum Emission ◽  
Magnetic Field Direction ◽  
Molecular Outflow ◽  
Bolometer Array ◽  
Imaging Receiver ◽  
Photometric Technique ◽  
The Magnetic Field

Abstract In this article, the results obtained from a polarimetric study of Bok globule CB 17 in both optical and submillimetre wavelengths are presented. Optical polarimetric observations in the R band (λ = 630 nm, Δλ = 120 nm) were conducted with the 1.04-m Sampurnanand Telescope, Aryabhatta Research Institute of observational sciencES (ARIES), in Nainital, India on 2016 March 9, while submillimetre polarimetric data are taken from the Submillimetre Common-User bolometer array POLarimeter (SCUPOL) data archive, which has been reanalysed. The contours of Herschel1 Spectral and Photometric Imaging Receiver (SPIRE) 500-μm dust continuum emission of CB 17 (typically a cometary-shaped globule) are overlaid on the Digital Sky Survey (DSS) image of CB 17 along with polarization vectors (optical and submm). The magnetic field strength at the core of the globule is estimated to be 99 μG. Using near-infrared photometric technique and Gaia data, the distance to CB 17 is found to be 253 ± 43 pc. The correlation between the various quantities of the globule is also studied. It is observed that the magnetic field in the cloud core as revealed by polarization measurements of the submillimetre dust emission is found to be almost aligned along the minor axis of the globule, which fits the magnetically regulated star formation model. A misalignment between core-scale magnetic field direction and molecular outflow direction is also found.

scholarly journals Small-scale properties of Class 0 protostars from the CALYPSO IRAM-PdBI survey

2015 ◽  
Vol 11 (S315) ◽  
pp. 114-117
Author(s):  
Anaëlle Maury ◽  
Philippe André ◽  
Sébastien Maret ◽  
Arnaud Belloche ◽  
Claudio Codella ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Angular Resolution ◽  
Dust Emission ◽  
Continuum Emission ◽  
Small Scale ◽  
High Angular Resolution ◽  
Multiple Systems ◽  
Small Scales ◽  
Molecular Lines ◽  
Scale Properties

AbstractBecause the formation of protostars is believed to be closely tied to the angular momentum problem of star formation, characterizing the properties of the youngest disks around Class 0 objects is crucial. However, not much is known on the structure of the youngest protostellar envelopes, on the small scales at which disks and multiple systems are observed around more evolved YSOs, due to a lack of comprehensive high angular resolution observations (probing <100 AU). In order to tackle this issue, we conducted a large observing program with the IRAM Plateau de Bure interferometer (PdBI): the CALYPSO survey, providing us with detailed maps of molecular lines and millimeter continuum emission, probing scales down to ~30–50 au towards a sample of 17 Class 0 protostars. Here we present our analysis of the CALYPSO dust continuum emission maps, constraining disk properties of the Class 0 protostars in our sample. We show that large, r > 50 au, disk structures are not observed in most Class 0 protostars from our sample, which can be described by various envelope models reproducing satisfactorily the intensity distribution of the dust emission at all scales from 50 au to 5000 au.

scholarly journals Genetic algorithm coupled with Bézier curves applied to the magnetic field on a solenoid axis synthesis

2016 ◽  
Vol 65 (2) ◽  
pp. 361-370 ◽  
Author(s):  
Marcin Ziolkowski ◽  
Stanislaw Gratkowski
Keyword(s):  
Magnetic Field ◽  
Genetic Algorithm ◽  
Magnetic Fields ◽  
Uniform Magnetic Field ◽  
Optimal Shape ◽  
Point Of View ◽  
Theoretical Point ◽  
Bezier Curves ◽  
Bézier Curves ◽  
The Magnetic Field

Abstract Electromagnetic arrangements which create a magnetic field of required distribution and magnitude are widely used in electrical engineering. Development of new accurate designing methods is still a valid topic of technical investigations. From the theoretical point of view the problem belongs to magnetic fields synthesis theory. This paper discusses a problem of designing a shape of a solenoid which produces a uniform magnetic field on its axis. The method of finding an optimal shape is based on a genetic algorithm (GA) coupled with Bézier curves.

scholarly journals No-z Model for Magnetic Fields of Different Astrophysical Objects and Stability of the Solutions

Data ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 4
Author(s):  
Evgeny Mikhailov ◽  
Daniela Boneva ◽  
Maria Pashentseva
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Point Of View ◽  
Accretion Discs ◽  
Wide Range ◽  
Astrophysical Objects ◽  
Alpha Effect ◽  
The Stability ◽  
The Magnetic Field

A wide range of astrophysical objects, such as the Sun, galaxies, stars, planets, accretion discs etc., have large-scale magnetic fields. Their generation is often based on the dynamo mechanism, which is connected with joint action of the alpha-effect and differential rotation. They compete with the turbulent diffusion. If the dynamo is intensive enough, the magnetic field grows, else it decays. The magnetic field evolution is described by Steenbeck—Krause—Raedler equations, which are quite difficult to be solved. So, for different objects, specific two-dimensional models are used. As for thin discs (this shape corresponds to galaxies and accretion discs), usually, no-z approximation is used. Some of the partial derivatives are changed by the algebraic expressions, and the solenoidality condition is taken into account as well. The field generation is restricted by the equipartition value and saturates if the field becomes comparable with it. From the point of view of mathematical physics, they can be characterized as stable points of the equations. The field can come to these values monotonously or have oscillations. It depends on the type of the stability of these points, whether it is a node or focus. Here, we study the stability of such points and give examples for astrophysical applications.

Long-period variations in the magnetic field of small-scale solar structures

2016 ◽  
Vol 56 (8) ◽  
pp. 1052-1059 ◽  
Author(s):  
P. V. Strekalova ◽  
Yu. A. Nagovitsyn ◽  
A. Riehokainen ◽  
V. V. Smirnova
Keyword(s):  
Magnetic Field ◽  
Small Scale ◽  
Long Period ◽  
Period Variations ◽  
The Magnetic Field

scholarly journals Investigating the Magnetospheres of Rapidly Rotating B-type Stars

2016 ◽  
Vol 12 (S329) ◽  
pp. 369-372
Author(s):  
C. L. Fletcher ◽  
V. Petit ◽  
Y. Nazé ◽  
G. A. Wade ◽  
R. H. Townsend ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Centrifugal Force ◽  
Point Of View ◽  
Closed Field ◽  
Theoretical Point ◽  
X Rays ◽  
Rapid Rotation ◽  
X Ray ◽  
Surface Magnetic Field

AbstractRecent spectropolarimetric surveys of bright, hot stars have found that ~10% of OB-type stars contain strong (mostly dipolar) surface magnetic fields (~kG). The prominent paradigm describing the interaction between the stellar winds and the surface magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the stellar wind plasma is forced to move along the closed field loops of the magnetic field, colliding at the magnetic equator, and creating a shock. As the shocked material cools radiatively it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and characterizing the hot wind material confined by the magnetic fields of these stars. Some B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. The added centrifugal force due to rapid rotation is predicted to cause faster wind outflows along the field lines, leading to higher shock temperatures and harder X-rays. However, this is not observed in all rapidly rotating magnetic B-type stars. In order to address this from a theoretical point of view, we use the X-ray Analytical Dynamical Magnetosphere (XADM) model, originally developed for slow rotators, with an implementation of new rapid rotational physics. Using X-ray spectroscopy from ESA’s XMM-Newton space telescope, we observed 5 rapidly rotating B-types stars to add to the previous list of observations. Comparing the observed X-ray luminosity and hardness ratio to that predicted by the XADM allows us to determine the role the added centrifugal force plays in the magnetospheric X-ray emission of these stars.

Sign in / Sign up

Export Citation Format

Share Document