scholarly journals Evolution of stellar winds from the Sun to red giants

2008 ◽  
Vol 4 (S257) ◽  
pp. 589-599
Author(s):  
Takeru K. Suzuki
Keyword(s):  
Ad Hoc ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Radiative Cooling ◽  
Stellar Winds ◽  
Red Giants ◽  
The Sun ◽  
Compressive Wave ◽  
Stellar Radius ◽  
Red Giant

AbstractBy performing global 1D MHD simulations, we investigate the heating and acceleration of solar and stellar winds in open magnetic field regions. Our simulation covers from photosphere to 20-60 stellar radii, and takes into account radiative cooling and thermal conduction. We do not adopt ad hoc heating function; heating is automatically calculated from the solutions of Riemann problem at the cell boundaries. In the solar wind case we impose transverse photospheric motions with velocity ~1 km/s and period between 20 seconds and 30 minutes, which generate outgoing Alfvén waves. We have found that the dissipation of Alfvén waves through compressive wave generation by decay instability is quite effective owing to the density stratification, which leads to the sufficient heating and acceleration of the coronal plasma. Next, we study the evolution of stellar winds from main sequence to red giant phases. When the stellar radius becomes ~10 times of the Sun, the steady hot corona with temperature 106K, suddenly disappears. Instead, many hot and warm (105– 106K) bubbles are formed in cool (T< 2 × 104K) chromospheric winds because of the thermal instability of the radiative cooling function; the red giant wind is not a steady stream but structured outflow.

scholarly journals Evolution of Alfvén wave-driven solar winds to red giants

2007 ◽  
Vol 3 (S247) ◽  
pp. 201-207
Author(s):  
Takeru K. Suzuki
Keyword(s):  
Solar Wind ◽  
Mode Conversion ◽  
Alfven Waves ◽  
Alfven Wave ◽  
Alfvén Waves ◽  
Stellar Winds ◽  
Red Giants ◽  
Giant Stars ◽  
Solar Winds ◽  
Red Giant

AbstractIn this talk we introduce our recent results of global 1D MHD simulations for the acceleration of solar and stellar winds. We impose transverse photospheric motions corresponding to the granulations, which generate outgoing Alfvén waves. The Alfvén waves effectively dissipate by 3-wave coupling and direct mode conversion to compressive waves in density-stratified atmosphere. We show that the coronal heating and the solar wind acceleration in the open magnetic field regions are natural consequence of the footpoint fluctuations of the magnetic fields at the surface (photosphere). We also discuss winds from red giant stars driven by Alfvén waves, focusing on different aspects from the solar wind. We show that red giants wind are highly structured with intermittent magnetized hot bubbles embedded in cool chromospheric material.

scholarly journals The Hertzsprung-Russell Diagram of Metal-Poor Disk Stars

1978 ◽  
Vol 80 ◽  
pp. 273-276
Author(s):  
Sidney van den Bergh
Keyword(s):  
Velocity Field ◽  
Globular Cluster ◽  
High Velocity ◽  
Population Model ◽  
Open Cluster ◽  
Ultraviolet Excess ◽  
Red Giants ◽  
The Sun ◽  
The Galaxy ◽  
Red Giant

A quarter of a century ago Keenan and Keller (1953) showed that the majority of high-velocity stars near the Sun outline a Hertzsprung-Russell diagram similar to that of old Population I. This result, which did not appear to fit into Baade's (1944) two-population model of the Galaxy was ignored (except by Roman 1965) for the next two decades. Striking confirmation of the results of Keenan and Keller was, however, obtained by Hartwick and Hesser (1972). Their work appears to show that high-velocity field stars with an ultraviolet excess (which measures Fe/H) of δ(U-B) ≃ +0m.11 lie on a red giant branch that is more than a magnitude fainter than the giant branch of the strong-lined globular cluster 47 Tuc for which δ(U-B) ≃ +0m.10. Furthermore Demarque and McClure (1977) show that the red giants in the old metal poor [δ(U-B) ≃ +0m.11] open cluster NGC 2420 are significantly fainter than are those in 47 Tuc. Calculations by these authors show that the observed differences between the giants in 47 Tuc and in NGC 2420 can be explained if either (1) 47 Tuc is richer in helium than NGC 2420 by ΔY ≃ 0.1 or (2) if 47 Tuc has a ten times lower value of Z(CNO) than does NGC 2420.

scholarly journals Solar wind and kinetic heliophysics

2018 ◽  
Vol 36 (6) ◽  
pp. 1607-1630 ◽  
Author(s):  
Eckart Marsch
Keyword(s):  
Solar Wind ◽  
Interplanetary Space ◽  
Coronal Holes ◽  
Heavy Ion ◽  
Alfven Waves ◽  
Distribution Functions ◽  
Slow Solar Wind ◽  
Alfvén Waves ◽  
The Sun ◽  
Collisionless Dissipation

Abstract. This paper reviews recent aspects of solar wind physics and elucidates the role Alfvén waves play in solar wind acceleration and turbulence, which prevail in the low corona and inner heliosphere. Our understanding of the solar wind has made considerable progress based on remote sensing, in situ measurements, kinetic simulation and fluid modeling. Further insights are expected from such missions as the Parker Solar Probe and Solar Orbiter. The sources of the solar wind have been identified in the chromospheric network, transition region and corona of the Sun. Alfvén waves excited by reconnection in the network contribute to the driving of turbulence and plasma flows in funnels and coronal holes. The dynamic solar magnetic field causes solar wind variations over the solar cycle. Fast and slow solar wind streams, as well as transient coronal mass ejections, are generated by the Sun's magnetic activity. Magnetohydrodynamic turbulence originates at the Sun and evolves into interplanetary space. The major Alfvén waves and minor magnetosonic waves, with an admixture of pressure-balanced structures at various scales, constitute heliophysical turbulence. Its spectra evolve radially and develop anisotropies. Numerical simulations of turbulence spectra have reproduced key observational features. Collisionless dissipation of fluctuations remains a subject of intense research. Detailed measurements of particle velocity distributions have revealed non-Maxwellian electrons, strongly anisotropic protons and heavy ion beams. Besides macroscopic forces in the heliosphere, local wave–particle interactions shape the distribution functions. They can be described by the Boltzmann–Vlasov equation including collisions and waves. Kinetic simulations permit us to better understand the combined evolution of particles and waves in the heliosphere.

scholarly journals Coronal heating and wind acceleration by nonlinear Alfvén waves – global simulations with gravity, radiation, and conduction

2008 ◽  
Vol 15 (2) ◽  
pp. 295-304 ◽  
Author(s):  
T. K. Suzuki
Keyword(s):  
Solar Wind ◽  
Alfven Waves ◽  
Coronal Heating ◽  
Alfvén Waves ◽  
Flux Tubes ◽  
Giant Stars ◽  
Solar Winds ◽  
Dynamical Simulations ◽  
Consistent Manner ◽  
Red Giant

Abstract. We review our recent results of global one-dimensional (1-D) MHD simulations for the acceleration of solar and stellar winds. We impose transverse photospheric motions corresponding to the granulations, which generate outgoing Alfvén waves. We treat the propagation and dissipation of the Alfvén waves and consequent heating from the photosphere by dynamical simulations in a self-consistent manner. Nonlinear dissipation of Alfven waves becomes quite effective owing to the stratification of the atmosphere (the outward decrease of the density). We show that the coronal heating and the solar wind acceleration in the open magnetic field regions are natural consequence of the footpoint fluctuations of the magnetic fields at the surface (photosphere). We find that the properties of the solar wind sensitively depend on the fluctuation amplitudes at the solar surface because of the nonlinearity of the Alfvén waves, and that the wind speed at 1 AU is mainly controlled by the field strength and geometry of flux tubes. Based on these results, we point out that both fast and slow solar winds can be explained by the dissipation of nonlinear Alfvén waves in a unified manner. We also discuss winds from red giant stars driven by Alfvén waves, focusing on different aspects from the solar wind.

Energy Flux of Alfvén Waves in Weakly Ionized Plasma and Coronal Heating of the Sun

Solar Physics ◽  
2011 ◽  
Vol 270 (1) ◽  
pp. 205-211 ◽  
Author(s):  
Y. T. Tsap ◽  
A. V. Stepanov ◽  
Y. G. Kopylova
Keyword(s):  
Energy Flux ◽  
Alfven Waves ◽  
Coronal Heating ◽  
Alfvén Waves ◽  
The Sun ◽  
Weakly Ionized ◽  
Weakly Ionized Plasma

scholarly journals Solar Wind and Kinetic Heliophysics

2018 ◽  
Author(s):  
Eckart Marsch
Keyword(s):  
Solar Wind ◽  
Interplanetary Space ◽  
Coronal Holes ◽  
Heavy Ion ◽  
Alfven Waves ◽  
Distribution Functions ◽  
Slow Solar Wind ◽  
Alfvén Waves ◽  
The Sun ◽  
Collisionless Dissipation

Abstract. This lecture reviews recent aspects of solar wind physics and elucidates the role Alfvén waves play in solar wind acceleration and turbulence, which prevail in the low corona and inner heliosphere. Our understanding of the solar wind has made considerable progress based on remote sensing, in-situ measurements, kinetic simulation and fluid modeling. Further insights are expected from such missions as the Parker Solar Probe and Solar Orbiter. The sources of the solar wind have been identified in the chromospheric network, Transition region and corona of the sun. Alfvén waves excited by reconnection in the network contribute to the driving of turbulence and plasma flows in funnels and coronal holes. The dynamic solar magnetic field causes solar wind variations over the solar cycle. Fast and slow solar wind streams, as well as transient coronal mass ejections are generated by the sun’s magnetic activity. Magnetohydrodynamic turbulence originates at the sun and evolves into interplanetary space. The major Alfvén waves and minor magnetosonic waves, with an admixture of pressurebalanced structures at various scales, constitute heliophysical turbulence. Its spectra evolve radially and develop anisotropies. Numerical simulations of turbulence spectra have reproduced key observational features. Collisionless dissipation of fluctuations remains a subject of intense research. Detailed measurements of particle velocity distributions have revealed non-maxwellian electrons, strongly anisotropic protons and heavy ion beams. Besides macroscopic forces in the heliosphere local wave-particle interactions shape the distribution functions. They can be described by the Boltzmann–Vlasov equation including collisions and waves. Kinetic simulations permit us to better understand the combined evolution of particles and waves in the heliosphere.

scholarly journals Alfvén waves as a driving mechanism in stellar winds

2010 ◽  
Vol 46 (4) ◽  
pp. 509-513 ◽  
Author(s):  
A.A. Vidotto ◽  
V. Jatenco-Pereira
Keyword(s):  
Alfven Waves ◽  
Alfvén Waves ◽  
Driving Mechanism ◽  
Stellar Winds

scholarly journals Evolution of Supernova Remnants with Cosmic Rays and Radiative Cooling

1994 ◽  
Vol 142 ◽  
pp. 841-844
Author(s):  
E. A. Dorfi
Keyword(s):  
Cosmic Rays ◽  
Thermal Plasma ◽  
Supernova Remnants ◽  
Numerical Models ◽  
High Energy ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Radiative Cooling ◽  
Fermi Acceleration ◽  
Wave Heating

AbstractRecent numerical models for SNR evolution are presented, including first-order Fermi acceleration with injection of suprathermal particles at the shock wave, heating due to dissipation of Alfvén waves in the precursor region and radiative cooling of the thermal plasma. The X-ray fluxes obtained from these SNR models show significant differences depending on the acceleration efficiency of cosmic rays. γ-ray fluxes are calculated originating from π0-decay of pions generated by collisions of the high-energy particles with the thermal plasma. Cooling of the thermal plasma and dissipation of Alfvén waves in the precursor are important to determine the final amount of the explosion energy ESN which is transferred into cosmic rays.Subject headings: acceleration of particles — cosmic rays — gamma rays: theory — shock waves — supernova remnants

scholarly journals Low-threshold instabilities of kinetic alfven waves in the chromosphere of an active region on the Sun

2012 ◽  
Vol 18 (5(78)) ◽  
pp. 29-40 ◽  
Author(s):  
A.N. Kryshtal ◽  
◽  
S.V. Gerasimenko ◽  
A.D. Voitsekhovska ◽  
◽  
...  
Keyword(s):  
Active Region ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
The Sun ◽  
Low Threshold ◽  
Kinetic Alfvén Waves
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