scholarly journals Loss of magnetic flux and angular momentum from molecular clouds

1991 ◽  
Vol 147 ◽  
pp. 67-74
Author(s):  
Takenori Nakano
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Flux ◽  
Molecular Clouds ◽  
Loss Rate ◽  
Momentum Loss ◽  
Angular Momentum Loss ◽  
The Magnetic Field ◽  
Flux Loss

The magnetic field and the angular momentum are major obstacles against cloud contraction. I will review recent results on magnetic flux loss rate and angular momentum loss rate and will investigate a gross feature of cloud contraction.

scholarly journals Loss of magnetic flux and angular momentum from molecular clouds

1991 ◽  
Vol 147 ◽  
pp. 67-74
Author(s):  
Takenori Nakano
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Flux ◽  
Molecular Clouds ◽  
Loss Rate ◽  
Momentum Loss ◽  
Angular Momentum Loss ◽  
The Magnetic Field ◽  
Flux Loss

The magnetic field and the angular momentum are major obstacles against cloud contraction. I will review recent results on magnetic flux loss rate and angular momentum loss rate and will investigate a gross feature of cloud contraction.

scholarly journals Magnetic Fields in OH Maser Clouds

1974 ◽  
Vol 60 ◽  
pp. 275-292 ◽  
Author(s):  
R. D. Davies
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Field Data ◽  
Zeeman Splitting ◽  
Galactic Rotation ◽  
Magnetic Field Data ◽  
The Magnetic Field ◽  
Maser Sources

Observations of Class I OH maser sources show a range of features which are predicted on the basis of Zeeman splitting in a source magnetic field. Magnetic field strengths of 2 to 7 mG are derived for eight OH maser sources. The fields in all the clouds are directed in the sense of galactic rotation. A model of W3 OH is proposed which incorporates the magnetic field data. It is shown that no large amount of magnetic flux or angular momentum has been lost since the condensation from the interstellar medium began.

scholarly journals Hollow Cylindrical Lobes with a Helical Velocity Field of the L1551 Bipolar Flow

1987 ◽  
Vol 115 ◽  
pp. 287-300
Author(s):  
Yutaka Uchida ◽  
Norio Kaifu ◽  
Kazunari Shibata ◽  
Saeko S. Hayashi ◽  
Tetsuo Hasegawa
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Star Formation ◽  
Velocity Field ◽  
Formation Process ◽  
High Spatial Resolution ◽  
Cylindrical Structure ◽  
Angular Momentum Loss ◽  
Show Evidence ◽  
The Magnetic Field

Observations of the structure and the velocity field in the L1551 bipolar flow were made with the 45m telescope at Nobeyama in the 115GHz 12CO J = 1 – 0 line with high spatial resolution. It was found that the bipolar flow lobes have a clear hollow cylindrical structure and show evidence of a helical velocity field. They appear to rotate in the same direction as the CS disk found by Kaifu et al. (1984). The velocity of the flow in the bipolar directions increases with distance up to ∼ 3′ from the central object, IRS 5. These characteristics coincide with those predicted by the magnetodynamic theory proposed by Uchida and Shibata and indicate the essential importance of the magnetic field in producing such flows and also in the star-formation process itself through the enhancement of angular-momentum loss.

scholarly journals Stellar Winds and Spindown in Solar Type Stars

1983 ◽  
Vol 102 ◽  
pp. 449-460 ◽  
Author(s):  
I.W. Roxburgh
Keyword(s):  
Angular Momentum ◽  
Loss Rate ◽  
Neutrino Flux ◽  
Flow Speed ◽  
Stellar Winds ◽  
Sudden Increase ◽  
Momentum Loss ◽  
Rotational Discontinuity ◽  
Angular Momentum Loss ◽  
Solar Type

The angular momentum loss produced by stellar winds is reviewed and a simple model of angular momentum loss with multipole fields is presented in which the field is potential when the flow speed is less than the Alfvén speed, and radial when greater than the Alfvén speed. The simpler the magnetic geometry, the larger is the angular momentum loss rate. This result is used to explain the rotational discontinuity across the Vaughan-Preston gap as being due to a sudden increase in angular momentum loss when the dynamo field switches from a quadropole to a dipole geometry.The evolution of the internal rotation of stars as a result of surface angular momentum loss is considered. In the absence of a magnetic field, differential rotation can drive instabilities which then transport angular momentum out from the interior down the angular velocity gradient. Other instabilities such as that caused by the build up of 3He can also transport angular momentum outwards. If angular momentum is transported by such weak turbulence, it also makes the star more homogeneous than standard evolutionary models and lowers the predicted value of the solar neutrino flux.The recent results on rotational splitting of solar oscillations are considered: these suggest that the inside of the sun is spinning faster than the surface and are compatible with models in which angular momentum is transported by mild turbulence. But data is scarce — and in such circumstances the speculations of the theorist must be viewed with caution!

scholarly journals Spin evolution and saturation: new insights through 3D MHD simulations of young solar analogs

2019 ◽  
Vol 82 ◽  
pp. 233-240
Author(s):  
V. Réville ◽  
A.S. Brun
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Large Scale ◽  
Stellar Surface ◽  
Doppler Imaging ◽  
Momentum Loss ◽  
Mhd Simulations ◽  
Spin Evolution ◽  
Angular Momentum Loss ◽  
Solar Analogs

We examine how 3D MHD simulations can deliver clues on the mechanisms at the origin of angular momentum loss saturation of rapidly rotating solar-like stars. Based on a study of six targets, whose magnetic field has been observed by Zeeman Doppler Imaging (ZDI), we find that the saturation could be explained by a extremely strong coverage of the stellar surface of a large scale dipolar mode, in disagreement with recent works.

scholarly journals A nonextensive approach for the angular momentum loss rate in low-mass stars

2012 ◽  
Vol 8 (S294) ◽  
pp. 197-198
Author(s):  
Daniel B. de Freitas ◽  
J. R. De Medeiros
Keyword(s):  
Angular Momentum ◽  
Loss Rate ◽  
Rotational Velocity ◽  
Low Mass Stars ◽  
New Approach ◽  
Momentum Loss ◽  
Angular Momentum Loss ◽  
Low Mass

AbstractThe present study demonstrates that behavior of rotational velocity as a function of stellar age is consistent using Tsallis' nonextensive formalism, resulting in a new approach to understanding the stellar rotational scenario.

scholarly journals The Magnetic Field in Highly Dense Molecular Clouds

1990 ◽  
Vol 140 ◽  
pp. 268-268
Author(s):  
M.S. El-Nawawy
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Molecular Clouds ◽  
Ambipolar Diffusion ◽  
Ohmic Dissipation ◽  
The Magnetic Field ◽  
Dissipation Processes

General forms of the B-ρ relation are investigated in both the isothermal and the non-isothermal regions. The magnetic flux dissipation either by ambipolar diffusion or by Ohmic dissipation has been restudied. The rates of heating due to the magnetic dissipation processes have been calculated in comparison with the rate of compressional heating.

scholarly journals The Rate of Angular Momentum Loss from Cloud Cores

1990 ◽  
Vol 140 ◽  
pp. 281-286
Author(s):  
Takenori Nakano
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Rotation Axis ◽  
Ambient Medium ◽  
Interstellar Clouds ◽  
Angular Momentum Loss ◽  
Field Lines ◽  
Cloud Cores ◽  
The Magnetic Field ◽  
Alfven Velocity

The angular momentum is one of the major obstacles to the contraction of interstellar clouds. An efficient process of removing the angular momentum from the cloud is via transport along the magnetic field lines to the ambient medium. When the magnetic field is nearly uniform and the direction of the field lines is parallel to the rotation axis, the spin-down time of the cloud is given by σ/2ρVA, where σ is the column density of the cloud along the field lines, and ρ and VA are the density and the Alfvén velocity, respectively, in the ambient medium (Ebert et al. 1960; Mouschovias & Paleologou 1980). However, this is for a cloud with weak gravity. Because a cloud with strong gravity has contracted dragging the field lines, the ambient field is considerably distorted from uniformity. The spin-down time of such a cloud is shorter than given above (Gillis, Mestel & Paris 1974, 1979).

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

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