scholarly journals Magnetic fields of Sun-like stars

2013 ◽  
Vol 9 (S302) ◽  
pp. 180-189 ◽  
Author(s):  
Rim Fares
Keyword(s):  
Solar Cycle ◽  
Magnetic Fields ◽  
Stellar Evolution ◽  
Large Scale ◽  
Observational Constraints ◽  
Field Generation ◽  
Magnetic Cycles ◽  
Host Stars

AbstractMagnetic fields play an important role at all stages of stellar evolution. In Sun-like stars, they are generated in the outer convective layers. Studying the large-scale magnetic fields of these stars enlightens our understanding of the field properties and gives us observational constraints for the field generation models. In this review, I summarise the current observational picture of the large-scale magnetic fields of Sun-like stars, in particular solar-twins and planet-host stars. I will discuss the observations of large-scale magnetic cycles, and compare these to the solar cycle.

scholarly journals Sun-like Stars: magnetic fields, cycles and exoplanets

2015 ◽  
Vol 11 (A29A) ◽  
pp. 360-364
Author(s):  
Rim Fares
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Observational Constraints ◽  
The Sun ◽  
Field Generation ◽  
Large Scale Magnetic Field ◽  
Planetary Orbits ◽  
Activity Cycles ◽  
Magnetic Cycles

AbstractIn Sun-like stars, magnetic fields are generated in the outer convective layers. They shape the stellar environment, from the photosphere to planetary orbits. Studying the large-scale magnetic field of those stars enlightens our understanding of the field properties and gives us observational constraints for field generation dynamo models. It also sheds light on how “normal” the Sun is among Sun-like stars. In this contribution, I will review the field properties of Sun-like stars, focusing on solar twins and planet hosting stars. I will discuss the observed large-scale magnetic cycles, compare them to stellar activity cycles, and link that to what we know about the Sun. I will also discuss the effect of large-scale stellar fields on exoplanets, exoplanetary emissions (e.g. radio), and habitability.

scholarly journals Stellar models of rotating, pre-main sequence low-mass stars with magnetic fields

2013 ◽  
Vol 9 (S302) ◽  
pp. 112-113 ◽  
Author(s):  
Luiz T. S. Mendes ◽  
Natália R. Landin ◽  
Luiz P. R. Vaz
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Large Scale ◽  
Main Sequence ◽  
Stellar Structure ◽  
Low Mass Stars ◽  
Large Scale Magnetic Field ◽  
Low Mass ◽  
Structure Equations ◽  
Stellar Models

AbstractWe report our present efforts for introducing magnetic fields in the ATON stellar evolution code code, which now evolved to truly modifying the stellar structure equations so that they can incorporate the effects of an imposed, large-scale magnetic field. Preliminary results of such an approach, as applied to low-mass stellar models, are presented and discussed.

scholarly journals Dynamo models of the solar cycle

2020 ◽  
Vol 17 (1) ◽  
Author(s):  
Paul Charbonneau
Keyword(s):  
Solar Cycle ◽  
Large Scale ◽  
Chaotic Behavior ◽  
Critical Discussion ◽  
Solar Convection ◽  
Current State ◽  
Hydromagnetic Dynamo ◽  
Magnetic Cycles ◽  
Dynamo Process ◽  
Key Questions

AbstractThis paper reviews recent advances and current debates in modeling the solar cycle as a hydromagnetic dynamo process. Emphasis is placed on (relatively) simple dynamo models that are nonetheless detailed enough to be comparable to solar cycle observations. After a brief overview of the dynamo problem and of key observational constraints, I begin by reviewing the various magnetic field regeneration mechanisms that have been proposed in the solar context. I move on to a presentation and critical discussion of extant solar cycle models based on these mechanisms, followed by a discussion of recent magnetohydrodynamical simulations of solar convection generating solar-like large-scale magnetic cycles. I then turn to the origin and consequences of fluctuations in these models and simulations, including amplitude and parity modulation, chaotic behavior, and intermittency. The paper concludes with a discussion of our current state of ignorance regarding various key questions relating to the explanatory framework offered by dynamo models of the solar cycle.

scholarly journals Stellar dynamos with solar and antisolar differential rotations: Implications to magnetic cycles of slowly rotating stars

2019 ◽  
Vol 491 (3) ◽  
pp. 3155-3164 ◽  
Author(s):  
Bidya Binay Karak ◽  
Aparna Tomar ◽  
Vindya Vashishth
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Mean Field ◽  
Rotation Period ◽  
Toroidal Field ◽  
Dynamo Model ◽  
Cycle Period ◽  
Rotating Stars ◽  
Magnetic Cycles

ABSTRACT Simulations of magnetohydrodynamics convection in slowly rotating stars predict antisolar differential rotation (DR) in which the equator rotates slower than poles. This antisolar DR in the usual αΩ dynamo model does not produce polarity reversal. Thus, the features of large-scale magnetic fields in slowly rotating stars are expected to be different than stars having solar-like DR. In this study, we perform mean-field kinematic dynamo modelling of different stars at different rotation periods. We consider antisolar DR for the stars having rotation period larger than 30 d and solar-like DR otherwise. We show that with particular α profiles, the dynamo model produces magnetic cycles with polarity reversals even with the antisolar DR provided, the DR is quenched when the toroidal field grows considerably high and there is a sufficiently strong α for the generation of toroidal field. Due to the antisolar DR, the model produces an abrupt increase of magnetic field exactly when the DR profile is changed from solar-like to antisolar. This enhancement of magnetic field is in good agreement with the stellar observational data as well as some global convection simulations. In the solar-like DR branch, with the decreasing rotation period, we find the magnetic field strength increases while the cycle period shortens. Both of these trends are in general agreement with observations. Our study provides additional support for the possible existence of antisolar DR in slowly rotating stars and the presence of unusually enhanced magnetic fields and possibly cycles that are prone to production of superflare.

scholarly journals Observations of the Solar Corona from Space

2020 ◽  
Vol 216 (8) ◽  
Author(s):  
Ester Antonucci ◽  
Louise Harra ◽  
Roberto Susino ◽  
Daniele Telloni
Keyword(s):  
Solar Cycle ◽  
Solar Corona ◽  
Large Scale ◽  
Coronal Holes ◽  
Active Regions ◽  
Coronal Emission ◽  
Field Patterns ◽  
Magnetic Cycles ◽  
Outer Corona

AbstractSpace observations of the atmosphere of the Sun, obtained in half a century of dedicated space missions, provide a well established picture of the medium and large-scale solar corona, which is highly variable with the level of solar activity through a solar cycle and evolves with the long-term evolution of the magnetic cycles. In this review, we summarize the physical properties and dynamics of the medium and large-scale corona, consisting primarily of active regions, streamers and coronal holes; describe the dependence of coronal patterns on the magnetic field patterns changing through the solar cycle and the properties of the regions of open magnetic flux channeling the solar wind; the ubiquitous presence of fluctuations in the outer corona; the rotational properties of the large-scale corona; and the persistent hemispheric asymmetries in the emergence of magnetic fields and the distribution of the coronal emission.

scholarly journals Large-Scale Flow Patterns in the Solar Atmosphere

1990 ◽  
Vol 142 ◽  
pp. 101-105
Author(s):  
K.R. Sivaraman
Keyword(s):  
Solar Cycle ◽  
Magnetic Fields ◽  
Time Evolution ◽  
Large Scale ◽  
Opposite Polarity ◽  
Meridional Flow ◽  
The Sun ◽  
Solar Cycle Variation ◽  
Large Scale Flow ◽  
Good Agreement

It is now well established (McIntosh 1979; Makarov and Sivaraman 1983) that the filament and filament channels seen in the H-alpha spectroheliograms (or filtergrams) can be used as reliable tracers for studying the time evolution of large-scale magnetic fields on the Sun. These features represent the neutral lines between the unipolar regions of opposite polarity. Comparison of the synoptic charts compiled from H-alpha pictures with those from full-disc magnetograms for the same period shows very good agreement and hence the former can be used with confidence for time evolution studies of large-scale unipolar regions for those periods when the magnetographs did not even exist. In this paper we shall present one of the results of our study (Makarov and Sivaraman 1983, 1989) on the migration of H-alpha filaments, namely, the existence of the meridional flow on the Sun. We shall extend it further to show the participation of this meridional flow in the solar cycle variation.

scholarly journals Identifying solar-like magnetic cycles with Zeeman-Doppler-Imaging

2020 ◽  
Vol 500 (1) ◽  
pp. 1243-1260
Author(s):  
L T Lehmann ◽  
G A J Hussain ◽  
A A Vidotto ◽  
M M Jardine ◽  
D H Mackay
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Large Scale ◽  
Doppler Imaging ◽  
Small Scale ◽  
Flux Emergence ◽  
Flux Transport ◽  
Scale Field ◽  
Large Scale Field ◽  
Magnetic Cycles

ABSTRACT We are reaching the point where spectropolarimetric surveys have run for long enough to reveal solar-like magnetic activity cycles. In this paper, we investigate what would be the best strategy to identify solar-like magnetic cycles and ask which large-scale magnetic field parameters best follow a solar-type magnetic cycle and are observable with the Zeeman-Doppler-Imaging (ZDI) technique. We approach these questions using the 3D non-potential flux transport simulations of Yeates & Mackay (2012) modelling the solar vector magnetic field over 15 yr (centred on solar cycle 23). The flux emergence profile was extracted from solar synoptic maps and used as input for a photospheric flux transport model in combination with a non-potential coronal evolution model. We synthesize spectropolarimetric data from the simulated maps and reconstruct them using ZDI. The ZDI observed solar cycle is set into the context of other cool star observations and we present observable trends of the magnetic field topology with time, sunspot number, and S-index. We find that the axisymmetric energy fraction is the best parameter of the ZDI detectable large-scale field to trace solar-like cycles. Neither the surface averaged large-scale field or the total magnetic energy is appropriate. ZDI seems also to be able to recover the increase of the toroidal energy with S-index. We see further that ZDI might unveil hints of the dynamo modes that are operating and of the global properties of the small-scale flux emergence like active latitudes.

scholarly journals Dependence of solar cycles duration on the magnitude of the annual module of the sunspots magnetic field

2012 ◽  
Vol 8 (S294) ◽  
pp. 71-72 ◽  
Author(s):  
Valery N. Krivodubskij ◽  
Natalia I. Lozitska
Keyword(s):  
Solar Cycle ◽  
Magnetic Fields ◽  
Large Scale ◽  
Solar Maximum ◽  
Dynamo Model ◽  
Cycle Duration ◽  
Solar Cycles ◽  
Decline Phase ◽  
Calculated Period ◽  
Magnetic Index

AbstractThe dependence of the solar cycle duration, T, on the 3 years averaged module of the large-scale sunspots magnetic fields (30-60 arcsec), Bsp index, was investigated on the base of about 10,000 visual observations conducted during last eight (16-23) cycles. It was found that the duration T of the investigated cycles linearly depends on the index Bsp of the magnetic fields observed during 3 years on decline phase of the solar cycle (second, third and fourth years after solar maximum Tmax). Namely, the duration of the cycles T was varied between 9,5 and 12,5 years, when the magnetic index Bsp was ranged from 2450 to 2600 G. An explanation for this dependence is proposed within the framework of non-linear αΩ- dynamo model. We found the following equation for the dependence of solar dynamo-period on magnetic index: T ≈ Bsp3/2. Therefore, the large observed index Bsp, the longer calculated period T.

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