scholarly journals Investigations of cosmic magnetism at the Crimean Astrophysical Observatory. I. Magnetic field in the interstellar medium and secondary effects of stellar magnetism

2020 ◽  
Vol 1 (2) ◽  
pp. 13-25
Author(s):  
Roal'd Gershberg ◽  
Ilya Alekseev ◽  
Nataly Bondar
Keyword(s):  
Magnetic Field ◽  
Interstellar Medium ◽  
Crimean Astrophysical Observatory ◽  
Secondary Effects ◽  
Low Mass Stars ◽  
Type Activity ◽  
Solar Type ◽  
Low Mass ◽  
The Magnetic Field

We summarize the main results obtained at the Crimean Astrophysical Observatory for the magnetic field of the interstellar medium and magnetism in the middle- and low-mass stars with the solar-type activity.

scholarly journals Exploring Flaring Behaviour on Low Mass Stars, Solar-type Stars and the Sun

2019 ◽  
Vol 15 (S354) ◽  
pp. 384-391
Author(s):  
L. Doyle ◽  
G. Ramsay ◽  
J. G. Doyle ◽  
P. F. Wyper ◽  
E. Scullion ◽  
...  
Keyword(s):  
High Energy ◽  
The Sun ◽  
Low Mass Stars ◽  
Highly Active ◽  
Rotation Phase ◽  
Solar Type ◽  
Low Mass ◽  
Insight Into ◽  
Reconnection Model ◽  
High Cadence

AbstractWe report on our project to study the activity in both the Sun and low mass stars. Utilising high cadence, Hα observations of a filament eruption made using the CRISP spectropolarimeter mounted on the Swedish Solar Telescope has allowed us to determine 3D velocity maps of the event. To gain insight into the physical mechanism which drives the event we have qualitatively compared our observation to a 3D MHD reconnection model. Solar-type and low mass stars can be highly active producing flares with energies exceeding erg. Using K2 and TESS data we find no correlation between the number of flares and the rotation phase which is surprising. Our solar flare model can be used to aid our understanding of the origin of flares in other stars. By scaling up our solar model to replicate observed stellar flare energies, we investigate the conditions needed for such high energy flares.

scholarly journals Non-ideal magnetohydrodynamics versus turbulence – I. Which is the dominant process in protostellar disc formation?

2020 ◽  
Vol 495 (4) ◽  
pp. 3795-3806 ◽  
Author(s):  
James Wurster ◽  
Benjamin T Lewis
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Rotation Axis ◽  
Low Mass Stars ◽  
Rotation Rates ◽  
Ideal Mhd ◽  
Low Mass ◽  
Dominant Process ◽  
Ideal Magnetohydrodynamics ◽  
Disc Formation

ABSTRACT Non-ideal magnetohydrodynamics (MHD) is the dominant process. We investigate the effect of magnetic fields (ideal and non-ideal) and turbulence (sub- and transsonic) on the formation of circumstellar discs that form nearly simultaneously with the formation of the protostar. This is done by modelling the gravitational collapse of a 1 M⊙ gas cloud that is threaded with a magnetic field and imposed with both rotational and turbulent velocities. We investigate magnetic fields that are parallel/antiparallel and perpendicular to the rotation axis, two rotation rates, and four Mach numbers. Disc formation occurs preferentially in the models that include non-ideal MHD where the magnetic field is antiparallel or perpendicular to the rotation axis. This is independent of the initial rotation rate and level of turbulence, suggesting that subsonic turbulence plays a minimal role in influencing the formation of discs. Aside from first core outflows that are influenced by the initial level of turbulence, non-ideal MHD processes are more important than turbulent processes during the formation of discs around low-mass stars.

The impact of magnetism on tidal dynamics in the convective envelope of low-mass stars

2019 ◽  
Vol 15 (S354) ◽  
pp. 195-199
Author(s):  
A. Astoul ◽  
S. Mathis ◽  
C. Baruteau ◽  
F. Gallet ◽  
A. Strugarek ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Orbital Evolution ◽  
Magnetic Contribution ◽  
Low Mass Stars ◽  
Convective Envelope ◽  
Tidal Waves ◽  
Tidal Interactions ◽  
Rotational Evolution ◽  
Low Mass ◽  
The Impact

AbstractFor the shortest period exoplanets, star-planet tidal interactions are likely to have played a major role in the ultimate orbital evolution of the planets and on the spin evolution of the host stars. Although low-mass stars are magnetically active objects, the question of how the star’s magnetic field impacts the excitation, propagation and dissipation of tidal waves remains open. We have derived the magnetic contribution to the tidal interaction and estimated its amplitude throughout the structural and rotational evolution of low-mass stars (from K to F-type). We find that the star’s magnetic field has little influence on the excitation of tidal waves in nearly circular and coplanar Hot-Jupiter systems, but that it has a major impact on the way waves are dissipated.

scholarly journals What Sets the Magnetic Field Strength and Cycle Period in Solar-type Stars?

2019 ◽  
Vol 880 (1) ◽  
pp. 6 ◽  
Author(s):  
G. Guerrero ◽  
B. Zaire ◽  
P. K. Smolarkiewicz ◽  
E. M. de Gouveia Dal Pino ◽  
A. G. Kosovichev ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Cycle Period ◽  
Solar Type ◽  
The Magnetic Field

scholarly journals Non-ideal magnetohydrodynamics versus turbulence II: Which is the dominant process in stellar core formation?

2020 ◽  
Vol 495 (4) ◽  
pp. 3807-3818 ◽  
Author(s):  
James Wurster ◽  
Benjamin T Lewis
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Rotation Axis ◽  
Core Formation ◽  
Low Mass Stars ◽  
Stellar Core ◽  
Ideal Mhd ◽  
Low Mass ◽  
Dominant Process ◽  
Ideal Magnetohydrodynamics

ABSTRACT Non-ideal magnetohydrodynamics (MHD) is the dominant process. We investigate the effect of magnetic fields (ideal and non-ideal) and turbulence (sub- and transsonic) on the formation of protostars by following the gravitational collapse of 1 M⊙ gas clouds through the first hydrostatic core to stellar densities. The clouds are imposed with both rotational and turbulent velocities, and are threaded with a magnetic field that is parallel/antiparallel or perpendicular to the rotation axis; we investigate two rotation rates and four Mach numbers. The initial radius and mass of the stellar core are only weakly dependent on the initial parameters. In the models that include ideal MHD, the magnetic field strength implanted in the protostar at birth is much higher than observed, independent of the initial level of turbulence; only non-ideal MHD can reduce this strength to near or below the observed levels. This suggests that not only is ideal MHD an incomplete picture of star formation, but that the magnetic fields in low mass stars are implanted later in life by a dynamo process. Non-ideal MHD suppresses magnetically launched stellar core outflows, but turbulence permits thermally launched outflows to form a few years after stellar core formation.

scholarly journals The Hα Emission of the PMS Star Serpens/SVS 2

1990 ◽  
Vol 140 ◽  
pp. 318-318
Author(s):  
A.I. Gomez De Castro
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Major Axis ◽  
Mass Star ◽  
Polarization Pattern ◽  
Bipolar Structure ◽  
Dust Disk ◽  
Hα Emission ◽  
Low Mass ◽  
The Magnetic Field

Serpens is a region of low mass star formation where the magnetic field seems to play a fundamental role. The major axis of the Serpens outflows are aligned with the magnetic field. The most outstanding object in the region is the Serpens Reflection Nebula, SRN. This is characterized by a rather complex bipolar structure with several knots of gas and dust embedded in both nebular lobes. The western lobe is directed out of the cloud toward the observer. The SRN is illuminated by the PMS star Serpens/SVS 2. The star is surrounded by a dust disk; the polarization pattern of the disk can be interpreted as produced by dust grains aligned by the magnetic field frozen-in with the disk.

scholarly journals Magnetic field evolution in dwarf and Magellanic-type galaxies

2018 ◽  
Vol 611 ◽  
pp. A7 ◽  
Author(s):  
H. Siejkowski ◽  
M. Soida ◽  
K. T. Chyży
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Large Scale ◽  
Magnetic Energy ◽  
Galactic Disk ◽  
Cosmic Ray ◽  
Dark Matter Halo ◽  
Field Evolution ◽  
Low Mass ◽  
The Magnetic Field

Aims. Low-mass galaxies radio observations show in many cases surprisingly high levels of magnetic field. The mass and kinematics of such objects do not favour the development of effective large-scale dynamo action. We attempted to check if the cosmic-ray-driven dynamo can be responsible for measured magnetization in this class of poorly investigated objects. We investigated how starburst events on the whole, as well as when part of the galactic disk, influence the magnetic field evolution. Methods. We created a model of a dwarf/Magellanic-type galaxy described by gravitational potential constituted from two components: the stars and the dark-matter halo. The model is evolved by solving a three-dimensional (3D) magnetohydrodynamic equation with an additional cosmic-ray component, which is approximated as a fluid. The turbulence is generated in the system via supernova explosions manifested by the injection of cosmic-rays. Results. The cosmic-ray-driven dynamo works efficiently enough to amplify the magnetic field even in low-mass dwarf/Magellanic-type galaxies. The e-folding times of magnetic energy growth are 0.50 and 0.25 Gyr for the slow (50 km s−1) and fast (100 km s−1) rotators, respectively. The amplification is being suppressed as the system reaches the equipartition level between kinetic, magnetic, and cosmic-ray energies. An episode of star formation burst amplifies the magnetic field but only for a short time while increased star formation activity holds. We find that a substantial amount of gas is expelled from the galactic disk, and that the starburst events increase the efficiency of this process.

scholarly journals Non-stationarity of the quasi-perpendicular bow shock: comparison between Cluster observations and simulations

2011 ◽  
Vol 29 (2) ◽  
pp. 263-274 ◽  
Author(s):  
H. Comişel ◽  
M. Scholer ◽  
J. Soucek ◽  
S. Matsukiyo
Keyword(s):  
Magnetic Field ◽  
Bow Shock ◽  
Field Profile ◽  
Mass Ratio ◽  
Poynting Flux ◽  
Magnetic Field Profile ◽  
Low Mass ◽  
Low Mass Ratio ◽  
The Waves ◽  
The Magnetic Field

Abstract. We have performed full particle electromagnetic simulations of a quasi-perpendicular shock. The shock parameters have been chosen to be appropriate for the quasi-perpendicular Earth's bow shock observed by Cluster on 24 January 2001 (Lobzin et al., 2007). We have performed two simulations with different ion to electron mass ratio: run 1 with mi/me=1840 and run 2 with mi/me=100. In run 1 the growth rate of the modified two-stream instability (MTSI) is large enough to get excited during the reflection and upstream gyration of part of the incident solar wind ions. The waves due to the MTSI are on the whistler mode branch and have downstream directed phase velocities in the shock frame. The Poynting flux (and wave group velocity) far upstream in the foot is also directed in the downstream direction. However, in the density and magnetic field compression region of the overshoot the waves are refracted and the Poynting flux in the shock frame is directed upstream. The MTSI is suppressed in the low mass ratio run 2. The low mass ratio run shows more clearly the non-stationarity of the shock with a larger time scale of the order of an inverse ion gyrofrequency (Ωci): the magnetic field profile flattens and steepens with a period of ~1.5Ωci−1. This non-stationarity is different from reformation seen in previous simulations of perpendicular or quasi-perpendicular shocks. Beginning with a sharp shock ramp the large electric field in the normal direction leads to high reflection rate of solar wind protons. As they propagate upstream, the ion bulk velocity decreases and the magnetic field increases in the foot, which results in a flattening of the magnetic field profile and in a decrease of the normal electric field. Subsequently the reflection rate decreases and the whole shock profile steepens again. Superimposed on this 'breathing' behavior are in the realistic mass ratio case the waves due to the MTSI. The simulations lead us to a re-interpretation of the 24 January 2001 bow shock observations reported by Lobzin et al. (2007). It is suggested that the high frequency waves observed in the magnetic field data are due to the MTSI and are not related to a nonlinear phase standing whistler. Different profiles at the different spacecraft are due to the non-stationary behavior on the larger time scale.

scholarly journals The early evolution of low mass stars and brown dwarfs

2009 ◽  
Vol 5 (H15) ◽  
pp. 755-755
Author(s):  
Isabelle Baraffe
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Brown Dwarfs ◽  
Early Evolution ◽  
Evolutionary Models ◽  
Low Mass Stars ◽  
Low Mass ◽  
Effects Of Rotation ◽  
Star Formation Regions

My talk will focus on the early evolution of low mass objects. I will discuss the main uncertainties on current evolutionary models and the effects of rotation, magnetic field and early accretion history on young object's structure. I will also present possible solutions to the well known spread in HRD observed in star formation regions for objects of a few Myr old.

scholarly journals The rotation of very low-mass stars and brown dwarfs

2007 ◽  
Vol 3 (S243) ◽  
pp. 241-248
Author(s):  
Jochen Eislöffel ◽  
Alexander Scholz
Keyword(s):  
Angular Momentum ◽  
Brown Dwarfs ◽  
Magnetic Interaction ◽  
Stellar Winds ◽  
Solar Mass ◽  
Low Mass Stars ◽  
Angular Momentum Loss ◽  
Rotational Evolution ◽  
Solar Type ◽  
Low Mass

AbstractThe evolution of angular momentum is a key to our understanding of star formation and stellar evolution. The rotational evolution of solar-mass stars is mostly controlled by magnetic interaction with the circumstellar disc and angular momentum loss through stellar winds. Major differences in the internal structure of very low-mass stars and brown dwarfs – they are believed to be fully convective throughout their lives, and thus should not operate a solar-type dynamo – may lead to major differences in the rotation and activity of these objects. Here, we report on observational studies to understand the rotational evolution of the very low-mass stars and brown dwarfs.

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