scholarly journals Wind channeling, magnetospheres, and spindown of magnetic massive stars

2013 ◽  
Vol 9 (S302) ◽  
pp. 320-329
Author(s):  
S. P. Owocki ◽  
A. ud-Doula ◽  
R. H. D. Townsend ◽  
V. Petit ◽  
J. O. Sundqvist ◽  
...  
Keyword(s):  
Large Scale ◽  
Massive Stars ◽  
Line Emission ◽  
Balmer Line ◽  
Closed Loops ◽  
Magnetically Trapped ◽  
Mhd Simulations ◽  
Angular Momentum Loss ◽  
Weak Winds

AbstractA subpopulation (~10%) of hot, luminous, massive stars have been revealed through spectropolarimetry to harbor strong (hundreds to tens of thousand Gauss), steady, large-scale (often significantly dipolar) magnetic fields. This review focuses on the role of such fields in channeling and trapping the radiatively driven wind of massive stars, including both in the strongly perturbed outflow from open field regions, and the wind-fed “magnetospheres” that develop from closed magnetic loops. For B-type stars with weak winds and moderately fast rotation, one finds “centrifugal magnetospheres”, in which rotational support allows magnetically trapped wind to accumulate to a large density, with quite distinctive observational signatures, e.g. in Balmer line emission. In contrast, more luminous O-type stars have generally been spun down by magnetic braking from angular momentum loss in their much stronger winds. The lack of centrifugal support means their closed loops form a “dynamical magnetosphere”, with trapped material falling back to the star on a dynamical timescale; nonetheless, the much stronger wind feeding leads to a circumstellar density that is still high enough to give substantial Balmer emission. Overall, this review describes MHD simulations and semi-analytic dynamical methods for modeling the magnetospheres, the magnetically channeled wind outflows, and the associated spin-down of these magnetic massive stars.

scholarly journals A shallow water analogue of asymmetric core-collapse, and neutron star kick/spin

2011 ◽  
Vol 7 (S279) ◽  
pp. 134-137
Author(s):  
Thierry Foglizzo ◽  
Frédéric Masset ◽  
Jérôme Guilet ◽  
Gilles Durand
Keyword(s):  
Neutron Star ◽  
Shallow Water ◽  
Acoustic Waves ◽  
Large Scale ◽  
Massive Stars ◽  
Core Collapse ◽  
Hydraulic Jumps ◽  
Core Collapse Supernova ◽  
Accretion Shock

AbstractMassive stars end their life with the gravitational collapse of their core and the formation of a neutron star. Their explosion as a supernova depends on the revival of a spherical accretion shock, located in the inner 200km and stalled during a few hundred milliseconds. Numerical simulations suggest that the large scale asymmetry of the neutrino-driven explosion is induced by a hydrodynamical instability named SASI. Its non radial character is able to influence the kick and the spin of the resulting neutron star. The SWASI experiment is a simple shallow water analog of SASI, where the role of acoustic waves and shocks is played by surface waves and hydraulic jumps. Distances in the experiment are scaled down by a factor one million, and time is slower by a factor one hundred. This experiment is designed to illustrate the asymmetric nature of core-collapse supernova.

scholarly journals MHD simulations of star-disk magnetospheres and the formation of outflows and jets

2007 ◽  
Vol 3 (S243) ◽  
pp. 265-276
Author(s):  
Christian Fendt
Keyword(s):  
Numerical Simulation ◽  
Stellar Wind ◽  
Large Scale ◽  
Disk Surface ◽  
Time Dependent ◽  
Mhd Simulations ◽  
Tremendous Progress ◽  
Stellar Magnetospheres ◽  
Scale Evolution

AbstractIn this review the recent development concerning the large-scale evolution of stellar magnetospheres in interaction with the accretion disk is discussed. I put emphasis on the generation of outflows and jets from the disk and/or the star. In fact, tremendous progress has occurred over the last decade in the numerical simulation of the star-disk interaction. The role of numerical simulations is essential in this area because the processes involved are complex, strongly interrelated, and often highly time-dependent. Recent MHD simulations suggest that outflows launched from a very concentrated region tend to be un-collimated. I present preliminary results of simulations of large-scale star-disk magnetospheres loaded with matter from the stellar, resp. the disk surface demonstrating how a disk jet collimates the wind from the star and also how the stellar wind lowers the collimation degree of the disk outflow.

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 Evolution of auroral substorm as viewed from MHD simulations: dynamics, energy transfer and energy conversion

2020 ◽  
Vol 4 (1) ◽  
Author(s):  
Yusuke Ebihara ◽  
Takashi Tanaka
Keyword(s):  
Energy Transfer ◽  
Large Scale ◽  
A Priori ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
The Earth ◽  
Auroral Substorm ◽  
Transient Disturbances ◽  
Global Mhd Simulation

AbstractAn auroral substorm is a visual manifestation of large-scale, transient disturbances taking place in space surrounding the Earth, and is one of the central issues in the space plasma physics. While a number of studies have been conducted, a unified picture of the overall evolution of the auroral substorm has not been drawn. This paper is aimed to overview the recently obtained results of global magnetohydrodynamics (MHD) simulations in a context of a priori presence of anomalous resistivity leading to magnetic reconnection, and to illuminate what the global MHD simulation can sufficiently reproduce the auroral transients during the auroral substorm. Some auroral transients are found to be seamlessly reproduced by the MHD simulation, including complicated auroral structures moving equatorward during the growth phase, auroral brightening starting to appear near the equatorward border of the preexisting auroral arc, and an auroral surge traveling westward. Possible energy transfer and conversion from the solar wind to the Earth are also overviewed on the basis of the MHD simulation. At least, 4 dynamo regions appear sequentially in the course of the development of the auroral substorm. Although the MHD simulation reproduces some transients, further studies are needed to investigate the role of kinetic processes.

scholarly journals Rotation and Mass Ejection: the Launching of Be-Star Disks

2004 ◽  
Vol 215 ◽  
pp. 515-524 ◽  
Author(s):  
Stanley P. Owocki
Keyword(s):  
Binary Systems ◽  
Line Emission ◽  
Circumstellar Disk ◽  
Balmer Line ◽  
Be Stars ◽  
Wide Binary ◽  
Orbital Mass ◽  
Be Star ◽  
Mass Ejection

The characteristic signature of Be Stars is the Balmer line emission understood to arise in a circumstellar disk. Unlike the accretion disks of protostars or mass-exchange binary systems, the evolved and generally single or wide-binary status of Be Stars seems to require that its disk must form from mass ejection (a.k.a. decretion) from the star itself. In this paper, I use analogies with launching orbital satellites to discuss two candidate processes (radiation, pulsation) for driving such orbital mass ejection, with particular emphasis on the role of the rapid, possibly near-critical, rotation of Be Stars in facilitating the formation of their signature disks.

scholarly journals MHD simulations of ram pressure stripping of disk galaxies

2015 ◽  
Vol 11 (S319) ◽  
pp. 143-143
Author(s):  
Mariana Ramos-Martínez ◽  
Gilberto C. Gómez
Keyword(s):  
Wind Tunnel ◽  
Galaxy Evolution ◽  
Large Scale ◽  
Galactic Disk ◽  
Disk Galaxies ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Ram Pressure ◽  
3D Mhd Simulation

AbstractThe removal of ISM of disk galaxies through ram pressure stripping (RPS) has been extensively studied in numerous simulations (see Roediger 2009 and references therein). The models show that RPS has a significant impact on galaxy evolution (truncation of the ISM will lead to a decrease in star formation and a change in galaxy color). Nevertheless, the role of magnetic fields (MFs) on the dynamics of the gas in this process has not been sufficiently studied, although the influence of the MFs on the large scale structure is well established. This motivated us to perform a 3D MHD simulation of a disk galaxy with an isothermal, non-self gravitating and magnetized gaseous disk in equilibrium with a galaxy potential (Allen & Santillán, 1991). We model RPS on the galactic disk under the wind-tunnel approximation with the use of the RAMSES code (Teyssier, 2002) in order to understand the effects of MFs in RPS.

The Role of Sense of Direction and Other Factors During Navigation in a Large-Scale, Unconstrained Environment

2013 ◽  
Author(s):  
Elisabeth J. Ploran ◽  
Ericka Rovira ◽  
James C. Thompson ◽  
Raja Parasuraman
Keyword(s):  
Large Scale ◽  
Sense Of Direction

Magnetic Properties of xCeO2•(50 − x) PbO•50B2O3 Glasses and Glass Ceramics

2017 ◽  
Vol 13 (1) ◽  
pp. 4486-4494 ◽  
Author(s):  
G.El Damrawi ◽  
F. Gharghar
Keyword(s):  
Magnetic Properties ◽  
Large Scale ◽  
Glass Ceramics ◽  
Magnetic Behavior ◽  
Crystal Formation ◽  
Dual Roles ◽  
Effective Agent ◽  
Ordered Structures ◽  
Essential Change

Cerium oxide in borate glasses of composition xCeO2·(50 − x)PbO·50B2O3 plays an important role in changing both microstructure and magnetic behaviors of the system. The structural role of CeO2 as an effective agent for cluster and crystal formation in borate network is clearly evidenced by XRD technique. Both structure and size of well-formed cerium separated clusters have an effective influence on the structural properties. The cluster aggregations are documented to be found in different range ordered structures, intermediate and long range orders are the most structures in which cerium phases are involved. The nano-sized crystallized cerium species in lead borate phase are evidenced to have magnetic behavior.  The criteria of building new specific borate phase enriched with cerium as ferrimagnetism has been found to keep the magnetization in large scale even at extremely high temperature. Treating the glass thermally or exposing it to an effective dose of ionized radiation is evidenced to have an essential change in magnetic properties. Thermal heat treatment for some of investigated materials is observed to play dual roles in the glass matrix. It can not only enhance alignment processes of the magnetic moment but also increases the capacity of the crystallite species in the magnetic phases. On the other hand, reverse processes are remarked under the effect of irradiation. The magnetization was found to be lowered, since several types of the trap centers which are regarded as defective states can be produced by effect of ionized radiation. 

The Impact of Quantitative Easing on Emerging Markets – Literature Review

e-Finanse ◽  
2018 ◽  
Vol 14 (4) ◽  
pp. 67-76
Author(s):  
Piotr Bartkiewicz
Keyword(s):  
Emerging Markets ◽  
Large Scale ◽  
Empirical Literature ◽  
Quantitative Easing ◽  
Methodological Choices ◽  
The Subject ◽  
Methodological Approaches ◽  
The Impact ◽  
Sufficient Precision

AbstractThe article presents the results of the review of the empirical literature regarding the impact of quantitative easing (QE) on emerging markets (EMs). The subject is of interest to policymakers and researchers due to the increasingly larger role of EMs in the world economy and the large-scale capital flows occurring after 2009. The review is conducted in a systematic manner and takes into consideration different methodological choices, samples and measurement issues. The paper puts the summarized results in the context of transmission channels identified in the literature. There are few distinct methodological approaches present in the literature. While there is a consensus regarding the direction of the impact of QE on EMs, its size and durability have not yet been assessed with sufficient precision. In addition, there are clear gaps in the empirical findings, not least related to relative underrepresentation of the CEE region (in particular, Poland).

Age Advantages of Emotional Experience during the COVID-19 Pandemic are Robust, but Diminished Compared to Pre-pandemic Conditions

2020 ◽  
Author(s):  
Rui Sun ◽  
Disa Sauter
Keyword(s):  
Older Adults ◽  
Large Scale ◽  
Negative Emotion ◽  
Emotional Experience ◽  
Negative Emotions ◽  
Older Individuals ◽  
Selection Strategies ◽  
Scale Test ◽  
Prolonged Stress

Getting old is generally seen as unappealing, yet aging confers considerable advantages in several psychological domains (North & Fiske, 2015). In particular, older adults are better off emotionally than younger adults, with aging associated with the so-called “age advantages,” that is, more positive and less negative emotional experiences (Carstensen et al., 2011). Although the age advantages are well established, it is less clear whether they occur under conditions of prolonged stress. In a recent study, Carstensen et al (2020) demonstrated that the age advantages persist during the COVID-19 pandemic, suggesting that older adults are able to utilise cognitive and behavioural strategies to ameliorate even sustained stress. Here, we build on Carstensen and colleagues’ work with two studies. In Study 1, we provide a large-scale test of the robustness of Carstensen and colleagues’ finding that older individuals experience more positive and less negative emotions during the COVID-19 pandemic. We measured positive and negative emotions along with age information in 23,629 participants in 63 countries in April-May 2020. In Study 2, we provide a comparison of the age advantages using representative samples collected before and during the COVID-19 pandemic. We demonstrate that older people experience less negative emotion than younger people during the prolonged stress of the COVID-19 pandemic. However, the advantage of older adults was diminished during the pandemic, pointing to a likely role of older adults use of situation selection strategies (Charles, 2010).

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