Ambipolar diffusion, cloud cores, and star formation: Two-dimensional, cylindrically symmetric contraction. II - Results and a length scale for protostellar cores. III - A further parameter study and magnetically controlled accretion rate

1992 ◽  
Vol 390 ◽  
pp. 144 ◽  
Author(s):  
Telemachos Ch. Mouschovias ◽  
Scott A. Morton
Keyword(s):  
Star Formation ◽  
Accretion Rate ◽  
Ambipolar Diffusion ◽  
Parameter Study ◽  
Length Scale ◽  
Two Dimensional ◽  
Cylindrically Symmetric ◽  
Cloud Cores

scholarly journals Magnetic Fields in Molecular Clouds—Observation and Interpretation

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 41
Author(s):  
Hua-Bai Li
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Zeeman Effect ◽  
Ambipolar Diffusion ◽  
Grain Alignment ◽  
The Past ◽  
Turbulence Velocity ◽  
Cloud Cores ◽  
Dust Grain

The Zeeman effect and dust grain alignment are two major methods for probing magnetic fields (B-fields) in molecular clouds, largely motivated by the study of star formation, as the B-field may regulate gravitational contraction and channel turbulence velocity. This review summarizes our observations of B-fields over the past decade, along with our interpretation. Galactic B-fields anchor molecular clouds down to cloud cores with scales around 0.1 pc and densities of 104–5 H2/cc. Within the cores, turbulence can be slightly super-Alfvénic, while the bulk volumes of parental clouds are sub-Alfvénic. The consequences of these largely ordered cloud B-fields on fragmentation and star formation are observed. The above paradigm is very different from the generally accepted theory during the first decade of the century, when cloud turbulence was assumed to be highly super-Alfvénic. Thus, turbulence anisotropy and turbulence-induced ambipolar diffusion are also revisited.

Quasi-mode damping in two-dimensional fully non-uniform coronal loops

2005 ◽  
Vol 364 (1839) ◽  
pp. 529-532 ◽  
Author(s):  
I Arregui ◽  
T Van Doorsselaere ◽  
J Andries ◽  
M Goossens ◽  
D Kimpe
Keyword(s):  
Plasma Density ◽  
Flux Tube ◽  
Equilibrium Model ◽  
Coronal Loop ◽  
Density Contrast ◽  
Length Scale ◽  
Coronal Loops ◽  
Two Dimensional ◽  
Equilibrium Models ◽  
Cylindrically Symmetric

Resonantly damped fast kink quasi-modes are computed in fully resistive magnetohydrodynamics for fully non-uniform two-dimensional equilibrium models. The equilibrium model is a straight cylindrically symmetric flux tube with a plasma density that is non-uniform both across and along the loop. The variation of density across the loop can cover the whole loop. Our results indicate that the period and damping of coronal loop oscillations mainly depend on the density contrast and the inhomogeneity length-scale and are independent of the details of longitudinal stratification. This study extends previous studies on coronal loop oscillations, and allows for a better comparison between observations and theory.

scholarly journals On the emergent system mass function: the contest between accretion and fragmentation

2020 ◽  
Vol 500 (2) ◽  
pp. 1697-1707
Author(s):  
Paul C Clark ◽  
Anthony P Whitworth
Keyword(s):  
Star Formation ◽  
Standard Deviation ◽  
Mass Distribution ◽  
Power Law ◽  
Accretion Rate ◽  
Mass Function ◽  
High Mass ◽  
New Model ◽  
System Formation ◽  
Low Mass

ABSTRACT We propose a new model for the evolution of a star cluster’s system mass function (SMF). The model involves both turbulent fragmentation and competitive accretion. Turbulent fragmentation creates low-mass seed proto-systems (i.e. single and multiple protostars). Some of these low-mass seed proto-systems then grow by competitive accretion to produce the high-mass power-law tail of the SMF. Turbulent fragmentation is relatively inefficient, in the sense that the creation of low-mass seed proto-systems only consumes a fraction, ${\sim }23{{\ \rm per\ cent}}$ (at most ${\sim }50{{\ \rm per\ cent}}$), of the mass available for star formation. The remaining mass is consumed by competitive accretion. Provided the accretion rate on to a proto-system is approximately proportional to its mass (dm/dt ∝ m), the SMF develops a power-law tail at high masses with the Salpeter slope (∼−2.3). If the rate of supply of mass accelerates, the rate of proto-system formation also accelerates, as appears to be observed in many clusters. However, even if the rate of supply of mass decreases, or ceases and then resumes, the SMF evolves homologously, retaining the same overall shape, and the high-mass power-law tail simply extends to ever higher masses until the supply of gas runs out completely. The Chabrier SMF can be reproduced very accurately if the seed proto-systems have an approximately lognormal mass distribution with median mass ${\sim } 0.11 \, {\rm M}_{\odot }$ and logarithmic standard deviation $\sigma _{\log _{10}({M/M}_\odot)}\sim 0.47$).

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