Instabilities in line-driven stellar winds. I - Dependence on perturbation wavelength

1984 ◽  
Vol 284 ◽  
pp. 337 ◽  
Author(s):  
S. P. Owocki ◽  
G. B. Rybicki
Keyword(s):  
Stellar Winds ◽  
Perturbation Wavelength

Introduction to Stellar Winds

1999 ◽  
Author(s):  
Henny J. G. L. M. Lamers ◽  
Joseph P. Cassinelli
Keyword(s):  
Stellar Winds

Realistic Line Models for Pulsating B Stars

1980 ◽  
Vol 4 (1) ◽  
pp. 80-83
Author(s):  
P. A. Stamford ◽  
R. D. Watson
Keyword(s):  
Detailed Examination ◽  
Stellar Disk ◽  
Stellar Winds ◽  
Line Profiles ◽  
Stellar Rotation ◽  
B Stars ◽  
Pulsating Stars ◽  
Velocity Gradients ◽  
Expanding Atmospheres ◽  
Realistic Line

Spectral line profiles in pulsating stars are affected by the interplay of a number of velocity fields. In addition to the basic velocities associated with the pulsation mode, the complications of stellar rotation, atmospheric velocity gradients, stellar winds and varying scales of turbulence may also be present. Initial modelling for line profiles in variables assumed a constant ‘intrinsic profile’ which was integrated over the limb-darkened stellar disk. This approach has been used even in recent work for nonradial pulsations (Stamford and Watson 1977; Kubiak 1978) because of computational ease. Employing an LTE analysis to predict centre-to-limb profile variations, which are then integrated over the disk, represents an improvement on this. This has been done, for example, by Parsons (1972) for radial pulsations in cepheids and by Smith (1978) for nonradial oscillations in B stars. Mihalas (1979) has recently made an even more detailed examination of profiles in expanding atmospheres which involved consideration of velocity gradients, departures from LTE and rotation.

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.

Self-similar solutions to stellar winds with cosmic rays

2005 ◽  
Vol 35 (12) ◽  
pp. 2115-2118 ◽  
Author(s):  
Chung-Ming Ko ◽  
Min-Hsu Chu
Keyword(s):  
Cosmic Rays ◽  
Stellar Winds ◽  
Self Similar ◽  
Similar Solutions

scholarly journals Stellar wind effects on the atmospheres of close-in giants: a possible reduction in escape instead of increased erosion

2020 ◽  
Vol 494 (2) ◽  
pp. 2417-2428 ◽  
Author(s):  
A A Vidotto ◽  
A Cleary
Keyword(s):  
Parameter Space ◽  
Stellar Wind ◽  
Planetary Atmospheres ◽  
External Pressure ◽  
Stellar Winds ◽  
Wind Effects ◽  
Atmospheric Escape ◽  
Large Pressure ◽  
Ram Pressure ◽  
Host Stars

ABSTRACT The atmospheres of highly irradiated exoplanets are observed to undergo hydrodynamic escape. However, due to strong pressures, stellar winds can confine planetary atmospheres, reducing their escape. Here, we investigate under which conditions atmospheric escape of close-in giants could be confined by the large pressure of their host star’s winds. For that, we simulate escape in planets at a range of orbital distances ([0.04, 0.14] au), planetary gravities ([36, 87 per cent] of Jupiter’s gravity), and ages ([1, 6.9] Gyr). For each of these simulations, we calculate the ram pressure of these escaping atmospheres and compare them to the expected stellar wind external pressure to determine whether a given atmosphere is confined or not. We show that although younger close-in giants should experience higher levels of atmospheric escape, due to higher stellar irradiation, stellar winds are also stronger at young ages, potentially reducing escape of young exoplanets. Regardless of the age, we also find that there is always a region in our parameter space where atmospheric escape is confined, preferably occurring at higher planetary gravities and orbital distances. We investigate confinement of some known exoplanets and find that the atmosphere of several of them, including π Men c, should be confined by the winds of their host stars, thus potentially preventing escape in highly irradiated planets. Thus, the lack of hydrogen escape recently reported for π Men c could be caused by the stellar wind.

scholarly journals The Violent Interstellar Medium of Nearby Dwarf Galaxies

1999 ◽  
Vol 16 (1) ◽  
pp. 106-112 ◽  
Author(s):  
Fabian Walter
Keyword(s):  
Interstellar Medium ◽  
Gamma Ray ◽  
Dwarf Galaxies ◽  
Young Star ◽  
Stellar Winds ◽  
Star Forming ◽  
Star Forming Regions ◽  
Supernova Explosions ◽  
High Velocity Clouds ◽  
Ob Associations

AbstractHigh resolution HI observations of nearby dwarf galaxies (most of which are situated in the M81 group at a distance of about 3·2 Mpc) reveal that their neutral interstellar medium (ISM) is dominated by hole-like features most of which are expanding. A comparison of the physical properties of these holes with the ones found in more massive spiral galaxies (such as M31 and M33) shows that they tend to reach much larger sizes in dwarf galaxies. This can be understood in terms of the galaxy's gravitational potential. The origin of these features is still a matter of debate. In general, young star forming regions (OB-associations) are held responsible for their formation. This picture, however, is not without its critics and other mechanisms such as the infall of high velocity clouds, turbulent motions or even gamma ray bursters have been recently proposed. Here I will present one example of a supergiant shell in IC 2574 which corroborates the picture that OB associations are indeed creating these structures. This particular supergiant shell is currently the most promising case to study the effects of the combined effects of stellar winds and supernova explosions which shape the neutral interstellar medium of (dwarf) galaxies.

scholarly journals What Do We Really Know About the Winds of Massive Stars?

2007 ◽  
Vol 3 (S250) ◽  
pp. 89-96
Author(s):  
D. John Hillier
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Standard Theory ◽  
Stellar Winds ◽  
X Rays ◽  
X Ray ◽  
Stellar Photosphere ◽  
Weak Winds ◽  
Ionization Balance ◽  
Loss Rates

AbstractThe standard theory of radiation driven winds has provided a useful framework to understand stellar winds arising from massive stars (O stars, Wolf-Rayet stars, and luminous blue variables). However, with new diagnostics, and advances in spectral modeling, deficiencies in our understanding of stellar winds have been thrust to the forefront of our research efforts. Spectroscopic observations and analyses have shown the importance of inhomogeneities in stellar winds, and revealed that there are fundamental discrepancies between predicted and theoretical mass-loss rates. For late O stars, spectroscopic analyses derive mass-loss rates significantly lower than predicted. For all O stars, observed X-ray fluxes are difficult to reproduce using standard shock theory, while observed X-ray profiles indicate lower mass-loss rates, the potential importance of porosity effects, and an origin surprisingly close to the stellar photosphere. In O stars with weak winds, X-rays play a crucial role in determining the ionization balance, and must be taken into account.

scholarly journals Bimodal regime in young massive clusters leading to subsequent stellar generations

2015 ◽  
Vol 12 (S316) ◽  
pp. 294-301
Author(s):  
Richard Wünsch ◽  
Jan Palouš ◽  
Guillermo Tenorio-Tagle ◽  
Casiana Muñoz-Tuñón ◽  
Soňa Ehlerová
Keyword(s):  
Stellar Evolution ◽  
Column Density ◽  
First Generation ◽  
Massive Stars ◽  
Ionising Radiation ◽  
Cluster Center ◽  
Stellar Winds ◽  
Hot Gas ◽  
Massive Clusters ◽  
By Products

AbstractMassive stars in young massive clusters insert tremendous amounts of mass and energy into their surroundings in the form of stellar winds and supernova ejecta. Mutual shock-shock collisions lead to formation of hot gas, filling the volume of the cluster. The pressure of this gas then drives a powerful cluster wind. However, it has been shown that if the cluster is massive and dense enough, it can evolve in the so–called bimodal regime, in which the hot gas inside the cluster becomes thermally unstable and forms dense clumps which are trapped inside the cluster by its gravity. We will review works on the bimodal regime and discuss the implications for the formation of subsequent stellar generations. The mass accumulates inside the cluster and as soon as a high enough column density is reached, the interior of the clumps becomes self-shielded against the ionising radiation of stars and the clumps collapse and form new stars. The second stellar generation will be enriched by products of stellar evolution from the first generation, and will be concentrated near the cluster center.

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