scholarly journals PRISMA: A Mission to Study Interior and Surface of Stars

1994 ◽  
Vol 147 ◽  
pp. 540-544
Author(s):  
P. Lemaire
Keyword(s):  
Convection Zone ◽  
Stellar Surface ◽  
Direct Access ◽  
The Core ◽  
Active Structures ◽  
Deep Interior ◽  
Accuracy Of Measurements ◽  
The Waves ◽  
The Magnetic Field

AbstractNew technics such as asteroseismology are able to sound the deep interior of stars and to provide the data that will constrain the modelisation of the core. This information will be combined with data collected from the stellar surface which give direct access to measurements of the radiative losses, angular momentum losses and distribution of active structures. From the two sets of data, the key role of the convection zone will be clarified, as the convection zone excites the waves that propagate through the whole star and generates the magnetic field that structures the stellar surface. The PRISMA mission was developed to collect the data needed for detecting the oscillations by very accurate photometry (micromagnitude) and to derive the surface activity and rotation from accurate ultraviolet spectroscopy. A short description of the model payload is given with the observational constraints related to the needed accuracy of measurements. Following the non-selection by ESA in may 1993, some following perspectives are described.

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 The Toroidal Magnetic Field inside the Sun

1991 ◽  
Vol 130 ◽  
pp. 187-189
Author(s):  
V.N. Krivodubskij ◽  
A.E. Dudorov ◽  
A.A. Ruzmaikin ◽  
T.V. Ruzmaikina
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Convection Zone ◽  
The Sun ◽  
Poloidal Magnetic Field ◽  
Radial Gradient ◽  
The Core ◽  
Large Scale Magnetic Field ◽  
Magnetic Buoyancy ◽  
The Magnetic Field

Analysis of the fine structure of the solar oscillations has enabled us to determine the internal rotation of the Sun and to estimate the magnitude of the large-scale magnetic field inside the Sun. According to the data of Duvall et al. (1984), the core of the Sun rotates about twice as fast as the solar surface. Recently Dziembowski et al. (1989) have showed that there is a sharp radial gradient in the Sun’s rotation at the base of the convection zone, near the boundary with the radiative interior. It seems to us that the sharp radial gradients of the angular velocity near the core of the Sun and at the base of the convection zone, acting on the relict poloidal magnetic field Br, must excite an intense toroidal field Bф, that can compensate for the loss of the magnetic field due to magnetic buoyancy.

scholarly journals Asteroseismology of white dwarf stars

1997 ◽  
Vol 181 ◽  
pp. 367-380
Author(s):  
G. Vauclair
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Rate Of Change ◽  
Direct Access ◽  
Dwarf Stars ◽  
Fundamental Parameters ◽  
The Core ◽  
White Dwarf Stars ◽  
The Magnetic Field ◽  
Theoretical Developments

The theoretical potential of white dwarf asteroseismology is summarized. It is shown how one can derive fundamental parameters on the internal structure and evolution of these stars. The analysis of the non-radial g-modes permits in principle to determine the total mass, the rotation rate, the magnetic field strength. The mass of the outer layers, left on top of the carbon/oxygen core, can be determined as well as the structure of the transition zone between the core and the outer layers, giving an “a posteriori” unique information on the efficiency of the previous mass loss episodes. When measurable, the rate of change of the pulsation periods gives direct access to the evolutionary time scale and to the chemical composition of the core. These theoretical expectations are compared with the observations of variable white dwarfs in the three known instability strips for the planetary nebulae nuclei and PG1159 stars, for the DB and DA white dwarfs. Emphasis is put on results obtained from multi-sites photometric campaigns. Prospects on both theoretical developments and observations conclude the review.

V. Heating and Dynamics of Chromosphere and Corona

1988 ◽  
Vol 20 (1) ◽  
pp. 100-102
Author(s):  
G.E. Brueckner
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Acoustic Waves ◽  
Convection Zone ◽  
Flux Tubes ◽  
Magnetic Structures ◽  
Convective Motions ◽  
Field Lines ◽  
The Magnetic Field

The crucial role of magnetic fields in any mechanism to heat the outer solar atmosphere has been generally accepted by all authors. However, there is still no agreement about the detailed function of the magnetic field. Heating mechanisms can be divided up into 4 classes: (I) The magnetic field plays a passive role as a suitable medium for the propagation of Alfvén waves from the convection zone into the corona (Ionson, 1984). (II) In closed magnetic structures the slow random shuffling of field lines by convective motions below the surface induces electric currents in the corona which heat it by Joule dissipation (Heyvaerts and Priest, 1984). (Ill) Emerging flux which is generated in the convection zone reacts with ionized material while magnetic field lines move through the chromosphere, transition zone and corona. Rapid field line annihilation, reconnection and drift currents result in heating and material ejection (Brueckner, 1987; Brueckner et al., 1987; Cook et al., 1987). (IV) Acoustic waves which could heat the corona can be guided by magnetic fields. Temperature distribution, wave motions and shock formation are highly dependent on the geometry of the flux tubes (Ulmschneider and Muchmore, 1986; Ulmschneider, Muchmore and Kalkofen, 1987).

Analysis of Reactor Magnetic Circuit Based on ANSYS Command Flow

2011 ◽  
Vol 383-390 ◽  
pp. 2256-2261
Author(s):  
Po Yang ◽  
Zhong Dong Yin ◽  
Ruo Chen Cui ◽  
Ning Kong
Keyword(s):  
Graphical User Interface ◽  
Structural Design ◽  
Reactive Power ◽  
Magnetic Circuit ◽  
Element Analysis ◽  
The Core ◽  
The Common ◽  
Controllable Reactor ◽  
The Magnetic Field

Controllable reactor is the common equipment in the modern power system, which plays an important role in voltage control and reactive power compensation. The core structure of reactor effects the magnetic field distribution in the core and the loss of reactor. In this paper, the models of two kinds of classic reactors are built by the ANSYS command flow method, and explain the differences between magnetic valve controllable reactor and common reactor. This paper points out the advantages of command flow compared with the graphical user interface and the important role of ANSYS finite element analysis in the structural design of reactor.

scholarly journals Under and over-adiabatic electrons through a perpendicular collisionless shock: theory versus simulations

2005 ◽  
Vol 23 (12) ◽  
pp. 3685-3698 ◽  
Author(s):  
P. Savoini ◽  
B. Lembège ◽  
V. Krasnosselskhik ◽  
Y. Kuramitsu
Keyword(s):  
Shock Front ◽  
Lower Percentage ◽  
Collisionless Shock ◽  
The Core ◽  
High Injection ◽  
Theory Versus ◽  
Particle Simulations ◽  
Core Part ◽  
The Magnetic Field

Abstract. Test particle simulations are performed in order to analyze in detail the dynamics of transmitted electrons through a supercritical, strictly perpendicular, collisionless shock. In addition to adiabatic particles, two distinct nonadiabatic populations are observed surprisingly: (i) first, an over-adiabatic population characterized by an increase in the gyrating velocity higher than that expected from the conservation of the magnetic moment µ, and (ii) second, an under-adiabatic population characterized by a decrease in this velocity. Results show that both nonadiabatic populations have their pitch angle more aligned along the magnetic field than the adiabatic one at the time these hit the shock front. The formation of "under" and "over-adiabatic" particles strongly depends on their local injection conditions through the large amplitude cross-shock potential present within the shock front. A simplified theoretical model validates these results and points out the important role of the electric field as seen by the electrons. A classification shows that both nonadiabatic electrons are issued from the core part of the upstream distributionÊ function. In contrast, suprathermal and tail electrons only contribute to the adiabatic population; nevertheless, the core part of the upstream distribution contributes at a lower percentage to the adiabatic electrons. Under-adiabatic electrons are characterized by small injection angles θinj≤90°, whereas "over-adiabatic" particles have high injection angles θinj>90° (where θinj is the angle between the local gyrating velocity vector and the shock normal).

scholarly journals Thin current sheets and the associated wave activity observed by Solar Orbiter

2021 ◽  
Author(s):  
Daniel Graham ◽  
Yuri Khotyaintsev ◽  
Konrad Steinvall ◽  
Andris Vaivads ◽  
Milan Maksimovic ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plasma Waves ◽  
Wave Activity ◽  
Number Density ◽  
Current Sheets ◽  
Field Fluctuations ◽  
Density Perturbations ◽  
The Waves ◽  
The Magnetic Field

<p>Thin current sheets are routinely observed in the solar wind. Here we report observations of thin current sheets and the associated plasma waves using the Solar Orbiter spacecraft. The Radio and Plasma Waves (RPW) instrument provides high-resolution measurements of the electric field, number density perturbations, and magnetic field fluctuations, which we use to identify and characterise the observed waves, while the magnetic field provided by the MAG instrument is used to characterise the current sheets. We discuss the role of current sheets in the generation of the observed waves and the effects of the waves on the current sheets.<span> </span></p>

Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven Turbulence, and Solar Dynamo

2000 ◽  
Vol 179 ◽  
pp. 387-388
Author(s):  
Gaetano Belvedere ◽  
V. V. Pipin ◽  
G. Rüdiger
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Convection Zone ◽  
Solar Surface ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Magnetic Buoyancy ◽  
Alpha Effect ◽  
Current Helicity

Extended AbstractRecent numerical simulations lead to the result that turbulence is much more magnetically driven than believed. In particular the role ofmagnetic buoyancyappears quite important for the generation ofα-effect and angular momentum transport (Brandenburg & Schmitt 1998). We present results obtained for a turbulence field driven by a (given) Lorentz force in a non-stratified but rotating convection zone. The main result confirms the numerical findings of Brandenburg & Schmitt that in the northern hemisphere theα-effect and the kinetic helicityℋkin= 〈u′ · rotu′〉 are positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicityℋcurr= 〈j′ ·B′〉, which is negative in the northern hemisphere (and positive in the southern hemisphere). There has been an increasing number of papers presenting observations of current helicity at the solar surface, all showing that it isnegativein the northern hemisphere and positive in the southern hemisphere (see Rüdigeret al. 2000, also for a review).

Historical text archives and prosopography: the COEL database system

1998 ◽  
Vol 10 (1-3) ◽  
pp. 57-72 ◽  
Author(s):  
K. S. B. Keats-Rohan
Keyword(s):  
Research Tool ◽  
Direct Access ◽  
Specific Situation ◽  
Core Data ◽  
Secondary Sources ◽  
The Core ◽  
Level 3 ◽  
Full Discussion ◽  
Available Information ◽  
Level 2

The COEL database and database software, a combined reference and research tool created by historians for historians, is presented here through Screenshots illustrating the underlying theoretical model and the specific situation to which that has been applied. The key emphases are upon data integrity, and the historian's role in interpreting and manipulating what is often contentious data. From a corpus of sources (Level 1) certain core data are extracted for separate treatment at an interpretive level (Level 3), based upon a master list of the core data (Level 2). The core data are interdependent: each record in Level 2 is of interest in itself; and it either could or should be associated with an(other) record(s) as a specific entity. Sometimes the sources are ambiguous and the association is contentious, necessitating a probabilty-coding approach. The entities created by the association process can then be treated at a commentary level, introducing material external to the database, whether primary or secondary sources. A full discussion of the difficulties is provided within a synthesis of available information on the core data. Direct access to the source texts is only ever a mouse click away. Fully query able, COEL is formidable look-up and research tool for users of all levels, who remain free to exercise an alternative judgement on the associations of the core data. In principle, there is no limit on the type of text or core data that could be handled in such a system.

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