A Dynamo Model for Magnetic Stars with Long Periods

1976 ◽  
Vol 32 ◽  
pp. 39-42
Author(s):  
M. Schüssler
Keyword(s):  
Magnetic Field ◽  
Main Sequence ◽  
Convection Zone ◽  
Dynamo Model ◽  
Magnetic Stars ◽  
Order Of Magnitude ◽  
Linear Effects ◽  
The Right ◽  
Right Order ◽  
The Magnetic Field

SummaryA α - effect dynamo model is presented which can be relevant for the group of magnetic stars.with observed periods between 1 y and 72 ys. The model is based on an axisymmetric α2- dynamo including non-linear effects due to the “cut off α- effect”; no differential rotation is taken into account. There are oscilliations of the magnetic field with periods in the right order of magnitude under the assumption of an outer convection zone between R ≥ r ≥.5 R ….7R. In the sense of this model therefore these stars should be young objects passing from their Hayashi track down to the main sequence.

scholarly journals Generation of Coronal Currents by the Solar Convection Zone

2001 ◽  
Vol 18 (4) ◽  
pp. 329-335 ◽  
Author(s):  
D. J. Galloway ◽  
Y. Uchida ◽  
N. O. Weiss
Keyword(s):  
Convection Zone ◽  
Energy State ◽  
Minimum Energy ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
Poynting Flux ◽  
Available Energy ◽  
Order Of Magnitude ◽  
The Right ◽  
Right Order

AbstractSolar flares are thought to be caused by reconnection of magnetic fields and their associated electric currents in the solar corona. The currents have to be there to provide available energy over and above the current-free minimum energy state, but what generates them has been little discussed. This paper investigates the idea that twisting motions in the turbulent convection zone below may provide a natural source for the currents and explain some of their properties. The twists generate upward-propagating Alfvén waves with a Poynting flux of the right order of magnitude to power a flare. Depending on the depth it takes place, the twisting event that initiates a particular flare may occur hours, days or even months before the flare itself.

scholarly journals The effect of toroidal magnetic fields in the overshoot layer on the eigenfrequencies of stellar oscillations

1988 ◽  
Vol 123 ◽  
pp. 167-170
Author(s):  
Gaetano Belvedere
Keyword(s):  
Magnetic Field ◽  
Main Sequence ◽  
Convection Zone ◽  
High Order ◽  
Stable Region ◽  
Flux Tubes ◽  
Frequency Splitting ◽  
Acoustic Modes ◽  
Stellar Oscillations ◽  
The Magnetic Field

The overshoot layer in stellar convection zones is slightly subadiabatic and can be considered as a stable region for storage of magnetic flux. Belvedere, Pidatella and Stix (1986) estimated the size of the overshoot layer and computed the magnetic field strength, beyond which toroidal flux tubes become unstable to buoyancy, for a number of main sequence spectral types ranging from F5 to K0. Here we estimate the relative frequency perturbation of high order acoustic modes due to the presence of a non-oblique axisymmetric magnetic field in the overshoot layer. We find that increases with the advancing spectral type, the predicted frequency splitting being large enough to be detected by observations, at least for the Sun.We conclude that magnetic field induced frequency splitting of high order acoustic modes may well be due to a toroidal field of relatively moderate strength just beneath the bottom of the convection zone.

scholarly journals First magnetic stars

2008 ◽  
Vol 4 (S259) ◽  
pp. 399-400
Author(s):  
Iosif I. Romanyuk ◽  
Dimitry O. Kudryavtsev
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Main Sequence ◽  
Published Data ◽  
Rotating Stars ◽  
Exponential Law ◽  
Chemically Peculiar ◽  
Magnetic Stars ◽  
The Magnetic Field

AbstractThis contribution dedicated to the analysis of the magnetism of chemically peculiar (CP) stars of the upper Main Sequence. We use our own measurements and published data to compile a catalog of magnetic CP stars containing a total of 326 objects with confidently detected magnetic fields and 29 stars which are very likely to possess magnetic field. Our analysis shows that the number of magnetic CP stars decreases with increasing field strength in accordance with exponential law, hotter and faster rotating stars have stronger fields. Intensity of depressions in the continua correlates with the magnetic field strength.

Meridional flow in the Sun’s convection zone is a single cell in each hemisphere

Science ◽  
2020 ◽  
Vol 368 (6498) ◽  
pp. 1469-1472 ◽  
Author(s):  
Laurent Gizon ◽  
Robert H. Cameron ◽  
Majid Pourabdian ◽  
Zhi-Chao Liang ◽  
Damien Fournier ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Single Cell ◽  
Convection Zone ◽  
Solar Surface ◽  
Meridional Flow ◽  
Data Sources ◽  
Dynamo Model ◽  
Solar Cycles ◽  
Flux Transport ◽  
The Magnetic Field

The Sun’s magnetic field is generated by subsurface motions of the convecting plasma. The latitude at which the magnetic field emerges through the solar surface (as sunspots) drifts toward the equator over the course of the 11-year solar cycle. We use helioseismology to infer the meridional flow (in the latitudinal and radial directions) over two solar cycles covering 1996–2019. Two data sources are used, which agree during their overlap period of 2001–2011. The time-averaged meridional flow is shown to be a single cell in each hemisphere, carrying plasma toward the equator at the base of the convection zone with a speed of ~4 meters per second at 45° latitude. Our results support the flux-transport dynamo model, which explains the drift of sunspot-emergence latitudes through the meridional flow.

Solar Internal Rotation and Dynamo Waves: A Two-Dimensional Asymptotic Solution in the Convection Zone

2000 ◽  
Vol 179 ◽  
pp. 379-380
Author(s):  
Gaetano Belvedere ◽  
Kirill Kuzanyan ◽  
Dmitry Sokoloff
Keyword(s):  
Magnetic Field ◽  
Asymptotic Solution ◽  
Internal Rotation ◽  
Convection Zone ◽  
General Idea ◽  
Dynamo Model ◽  
Axially Symmetric ◽  
Dynamo Action ◽  
Regeneration Rate ◽  
Dynamo Waves

Extended abstractHere we outline how asymptotic models may contribute to the investigation of mean field dynamos applied to the solar convective zone. We calculate here a spatial 2-D structure of the mean magnetic field, adopting real profiles of the solar internal rotation (the Ω-effect) and an extended prescription of the turbulent α-effect. In our model assumptions we do not prescribe any meridional flow that might seriously affect the resulting generated magnetic fields. We do not assume apriori any region or layer as a preferred site for the dynamo action (such as the overshoot zone), but the location of the α- and Ω-effects results in the propagation of dynamo waves deep in the convection zone. We consider an axially symmetric magnetic field dynamo model in a differentially rotating spherical shell. The main assumption, when using asymptotic WKB methods, is that the absolute value of the dynamo number (regeneration rate) |D| is large, i.e., the spatial scale of the solution is small. Following the general idea of an asymptotic solution for dynamo waves (e.g., Kuzanyan & Sokoloff 1995), we search for a solution in the form of a power series with respect to the small parameter |D|–1/3(short wavelength scale). This solution is of the order of magnitude of exp(i|D|1/3S), where S is a scalar function of position.

scholarly journals An 84-μG Magnetic Field in a Galaxy at Z=0.692?

2008 ◽  
Vol 4 (S254) ◽  
pp. 95-96
Author(s):  
Arthur M. Wolfe ◽  
Regina A. Jorgenson ◽  
Timothy Robishaw ◽  
Carl Heiles ◽  
Jason X. Prochaska
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Dynamo Model ◽  
Magnetic Field Generation ◽  
Interstellar Gas ◽  
Splitting Technique ◽  
Average Value ◽  
The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

Connecting a Star’s Convection Zone with its Corona

1995 ◽  
Vol 12 (2) ◽  
pp. 180-185 ◽  
Author(s):  
D. J. Galloway ◽  
C. A. Jones
Keyword(s):  
Magnetic Field ◽  
Convection Zone ◽  
Flux Rope ◽  
Field System ◽  
Stellar Convection ◽  
Coronal Activity ◽  
Flux Concentration ◽  
Global Understanding ◽  
The Magnetic Field

AbstractThis paper discusses problems which have as their uniting theme the need to understand the coupling between a stellar convection zone and a magnetically dominated corona above it. Interest is concentrated on how the convection drives the atmosphere above, loading it with the currents that give rise to flares and other forms of coronal activity. The role of boundary conditions appears to be crucial, suggesting that a global understanding of the magnetic field system is necessary to explain what is observed in the corona. Calculations are presented which suggest that currents flowing up a flux rope return not in the immediate vicinity of the rope but rather in an alternative flux concentration located some distance away.

scholarly journals Simulating Solar Global Magnetism in 3-D

2012 ◽  
Vol 10 (H16) ◽  
pp. 101-103
Author(s):  
A. S. Brun ◽  
A. Strugarek
Keyword(s):  
Magnetic Field ◽  
Recent Progress ◽  
Convection Zone ◽  
Thermal Structure ◽  
Solar Convection ◽  
Self Consistent ◽  
The Mean ◽  
The Magnetic Field

AbstractWe briefly present recent progress using the ASH code to model in 3-D the solar convection, dynamo and its coupling to the deep radiative interior. We show how the presence of a self-consistent tachocline influences greatly the organization of the magnetic field and modifies the thermal structure of the convection zone leading to realistic profiles of the mean flows as deduced by helioseismology.

scholarly journals Berechnung der Oberfläche von Kernmaterie mit Hilfe spezieller Einteilchen-Wellenfunktionen

1962 ◽  
Vol 17 (8) ◽  
pp. 640-649
Author(s):  
Franz Lanzl
Keyword(s):  
Surface Energy ◽  
Plane Waves ◽  
Yukawa Interaction ◽  
Range Interaction ◽  
Zero Range ◽  
Volume Energy ◽  
Order Of Magnitude ◽  
The Right ◽  
Right Order ◽  
Surface Thickness

Using a YUKAWA interaction between the nucleons the volume energy per particle and the specific surface energy are calculated. These expressions assume a very simple form for a zero range interaction. The space parts of the applied orthogonal single particle wave functions are products of plane waves and a momentum independent function which brings about the decrease in density within the surface layer. First the volume energy per particle as a function of the density in the interior of nuclear matter is minimized. The interaction parameters are so selected that the values of the volume energy per particle and the density at the minimum agree with the experimental data. Then the surface energy as a function of the surface thickness is minimized. The values of the surface energy and the surface thickness in the minimum are compared with the empirical data. They are found to be of the right order of magnitude

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