scholarly journals Theory of winds from cool stars

1987 ◽  
Vol 122 ◽  
pp. 289-305
Author(s):  
Thomas E. Holzer
Keyword(s):  
Solar Wind ◽  
Stellar Winds ◽  
Late Type ◽  
Physical Processes ◽  
Specific Mass ◽  
Low Gravity ◽  
Cool Stars ◽  
Astrophysical Flows ◽  
Theoretical Considerations ◽  
Specific Mass Loss

The goal of this paper is to provide a framework for thinking about the various physical processes that may play significant roles in driving the massive winds of cool, low-gravity stars. First, some general theoretical considerations involving mass, momentum, and energy balance are discussed. Next, the value of the solar wind as an analog for these late-type stellar winds and for related astrophysical flows is briefly examined. Finally, four specific mass-loss mechanisms are discussed, and the possible importance of each of these mechanisms for massive winds from cool, low-gravity stars is evaluated.

scholarly journals Stellar Winds and Coronae in Cool Stars

1980 ◽  
Vol 51 ◽  
pp. 279-291 ◽  
Author(s):  
A.K. Dupree ◽  
L. Hartmann
Keyword(s):  
Theoretical Models ◽  
Stellar Winds ◽  
Late Type ◽  
Dwarf Stars ◽  
Giant Stars ◽  
Cool Stars ◽  
Thermally Driven ◽  
Effective Temperatures ◽  
Hot Corona ◽  
Theoretical Results

AbstractRecent observational and theoretical results are reviewed that pertain to the presence and characteristics of stellar coronae and winds in late-type stars. It is found that stars - principally dwarfs - exist with “hot” coronae similar to the Sun with thermally driven winds. For stars, at the lowest effective temperatures, and gravities characteristic of supergiant and giant stars, high temperature (~105K) atmospheres are absent (or if present are substantially weaker than in the dwarf stars), and massive winds are present. There also exist “hybrid” examples - luminous stars possessing both a “hot” corona and a supersonic stellar wind. Constraints for theoretical models are discussed.

scholarly journals Winds And Mass-Loss From Evolved, Low-Gravity Cool Stars

1998 ◽  
Vol 11 (1) ◽  
pp. 378-378
Author(s):  
K.G. Carpenter ◽  
R.D. Robinson
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Real Time ◽  
Hubble Space Telescope ◽  
Time Variability ◽  
Stellar Winds ◽  
Low Gravity ◽  
Loss Process ◽  
Cool Stars ◽  
Red Giant

The character of the winds and the amount of mass-loss from stars during the red giant and supergiant stage of evolution are critical to the progression of that evolution. We therefore summarize here the results of a series of programs utilizing the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST) to study the winds and mass-loss from the surface of evolved, low-gravity cool stars. We discuss the structure of the chromospheres in which the base of these stellar winds lie, the velocity of the wind and its acceleration with height, and what these spectra tell us about the mass-loss from these stars. Because of its relevance to this Joint Discussion, we will also discuss in some detail what we have learned about real-time variability of these phenomena and the implied somewhat erratic nature of the mass-loss process in at least some of these stars.

Observational constraints for solar-type Stellar winds

2019 ◽  
Vol 15 (S354) ◽  
pp. 313-332
Author(s):  
Manuel Güdel
Keyword(s):  
Solar Wind ◽  
Cosmic Rays ◽  
Main Sequence ◽  
Galactic Cosmic Rays ◽  
Observational Constraints ◽  
Stellar Winds ◽  
Late Type ◽  
Main Sequence Stars ◽  
Planetary Environments ◽  
Solar Type

AbstractIonized winds from late-type main-sequence stars are important for stellar spin-down and therefore the evolution of stellar activity; winds blow an “astrosphere” into the interstellar medium that absorbs a large part of galactic cosmic rays; and the winds play a key role in shaping planetary environments, in particular their upper atmospheres. These issues have been well studied for the solar wind but little is known about winds escaping from other solar-type stars. Several methods have been devised to either detect winds directly or to infer the presence of such winds from features that are shaped by the winds. This paper summarizes these methods and discusses exemplary findings. There is need for more studies using multiple methods for the same stars.

scholarly journals Physical Processes in Nebular Shells and the Interpretation of Nebular Spectra

1983 ◽  
Vol 103 ◽  
pp. 219-227
Author(s):  
J. Patrick Harrington
Keyword(s):  
Charge Transfer ◽  
Simple Model ◽  
Stellar Wind ◽  
High Velocity ◽  
Planetary Nebulae ◽  
Geometrical Parameters ◽  
Stellar Winds ◽  
Physical Processes ◽  
Rapid Cooling ◽  
Particle Distributions

Computed models are now recognized as useful tools for interpretation of the spectra of planetary nebulae. However, even the most detailed models need geometrical parameters such as filling factors which are poorly determined by observations. Some effects may be seen more clearly by modeling the stratification than by just using total fluxes. A simple model for NGC 6720 is presented which reproduces the behavior of (Ne III) λ3869 observed by Hawley and Miller (1977), clearly showing the effects of charge transfer. The behavior of C II λ4267 remains puzzling. Finally, we comment on the interaction of high velocity stellar winds with nebular shells. Non-equilibrium particle distributions at the contact between the shocked stellar wind and the nebula may result in the rapid cooling of the shocked gas.

scholarly journals Density sensitive C II lines in cool stars of low gravity

1981 ◽  
Vol 196 (1) ◽  
pp. 47P-53P ◽  
Author(s):  
R. E. Stencel ◽  
J. L. Linsky ◽  
A. Brown ◽  
C. Jordan ◽  
K. G. Carpenter ◽  
...  
Keyword(s):  
Low Gravity ◽  
Cool Stars

Synergistic effect of Al2O3/TiO2 reinforcements on slurry erosion performance of nickel-based composite coatings

2017 ◽  
Vol 232 (8) ◽  
pp. 974-986 ◽  
Author(s):  
Rajeev Kumar ◽  
Sanjeev Bhandari ◽  
Atul Goyal
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Mass Loss ◽  
Erosion Resistance ◽  
Slurry Erosion ◽  
Specific Mass ◽  
Operational Parameter ◽  
X Ray ◽  
Specific Mass Loss ◽  
Scanning Electron

Various aspects such as development, experimentation, and analysis have been covered in the present work to examine the behavior of test coatings under slurry erosion. The primary objective of the present study was to establish the specific mass loss from the test coatings under various slurry environmental conditions and highlights the importance of the addition of alumina in improving the slurry erosion resistance of Ni-TiO2 coating. To attain this objective, two powder compositions, viz. Ni-20TiO2 and Ni-15TiO2-5Al2O3 were deposited onto the CA6NM grade hydro-turbine steel using high velocity frame spray process. The microstructural characterization of the coatings was done by employing surface roughness tester, scanning electron microscope/energy-dispersive X-ray spectroscopy, and X-ray diffraction techniques, whereas mechanical analysis was carried out using micro-hardness and bond strength tester. The slurry erosion tests were performed using an indigenously fabricated high speed slurry erosion test rig at different levels of rotational speed, average particle size of erodent, and slurry concentration in order to explore their effects on slurry erosion performance of test coatings. The slurry erosion results, as well as scanning electron microscope observations of eroded specimens, revealed higher slurry erosion resistance of Ni-15TiO2-5Al2O3 coating in comparison with Ni-20TiO2 coating. Furthermore, each operational parameter was found to have a proportional effect on specific mass loss in case of both the coatings.

scholarly journals Flare-Like Activity of Red Giant Stars

1983 ◽  
Vol 71 ◽  
pp. 251-254 ◽  
Author(s):  
Robert E. Stencel
Keyword(s):  
Surface Activity ◽  
Magnetic Surface ◽  
Low Gravity ◽  
Giant Stars ◽  
Cool Stars ◽  
Red Giant Stars ◽  
Red Giant

ABSTRACTEvidence for magnetic surface activity among cool stars of low gravity is discussed.

Ca II Emission from Late-type Stars

1983 ◽  
Vol 5 (2) ◽  
pp. 152-157 ◽  
Author(s):  
L. E. Cram
Keyword(s):  
Line Profile ◽  
Strong Correlation ◽  
Velocity Fields ◽  
Line Profiles ◽  
Late Type ◽  
Wide Range ◽  
Cool Stars ◽  
Visual Magnitude ◽  
The Absolute ◽  
Emission Core

Two recent observational surveys of the Ca II resonance lines (Zarro and Rodgers 1983; Linsky et al. 1979) illustrate the great diversity of line profile shapes found in the spectra of cool stars. This diversity reflects a corresponding wide range in the underlying chromospheric properties of the stars. There are, however, three well-marked systematic trends in the shapes of Ca II line profiles which presumably reflect systematic trends in chromospheric properties. One of these, the Wilson-Bappu effect (Wilson and Bappu 1957), describes the strong correlation betweeen the width of the emission core (see Figure 1) and the absolute visual magnitude of the star. Despite much work, it is still not clear whether this is due primarily to systematic changes of velocity fields (e.g. Hoyle and Wilson 1958) or optical depths (e.g. Jefferies and Thomas 1959) in stellar chromospheres.

Evolution of the MHD turbulence properties in the inner heliosphere with the PSP/SolO alignment data

2021 ◽  
Author(s):  
Daniele Telloni ◽  
Keyword(s):  
Solar Wind ◽  
High Frequency ◽  
Interplanetary Space ◽  
Solar Wind Plasma ◽  
Radial Dependence ◽  
Physical Processes ◽  
Temperature Anisotropy ◽  
Mhd Turbulence ◽  
Radial Evolution ◽  
Inner Heliosphere

<p>Radial alignments between pairs of spacecraft is the only way to observationally investigate the turbulent evolution of the solar wind as it expands throughout interplanetary space. On September 2020 Parker Solar Probe (PSP) and Solar Orbiter (SolO) were nearly perfectly radially aligned, with PSP orbiting around its perihelion at 0.1 au (and crossing the nominal Alfvén point) and SolO at 1 au. PSP/SolO joint observations of the same solar wind plasma allow the extraordinary and unprecedented opportunity to study how the turbulence properties of the solar wind evolve in the inner heliosphere over the wide distance of 0.9 au. The radial evolution of (i) the MHD properties (such as radial dependence of low- and high-frequency breaks, compressibility, Alfvénic content of the fluctuations), (ii) the polarization status, (iii) the presence of wave modes at kinetic scale as well as their distribution in the plasma instability-temperature anisotropy plane are just few instances of what can be addressed. Of furthest interest is the study of whether and how the cascade transfer and dissipation rates evolve with the solar distance, since this has great impact on the fundamental plasma physical processes related to the heating of the solar wind. In this talk I will present some of the results obtained by exploiting the PSP/SolO alignment data.</p>

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