scholarly journals Molecular Cooling in the Outer Atmospheres of Red Giants

1989 ◽  
Vol 106 ◽  
pp. 381-381
Author(s):  
David Muchmore
Keyword(s):  
Shock Waves ◽  
Dissociation Energy ◽  
Convection Zone ◽  
Radiative Cooling ◽  
Red Giants ◽  
Post Shock ◽  
Molecular Cooling

In the outer atmospheres of cool giants and supergiants there is a competition between heating by shock waves which develop from noise lower down in the convection zone and radiative cooling. The post-shock cooling is most effective in keeping temperatures low and in damping shocks if molecules (especially CO) form. CO is important both because of its high dissociation energy (11 eV) and its large IR opacity.

scholarly journals Shocked Molecular Hydrogen from Star Forming Regions

1987 ◽  
Vol 115 ◽  
pp. 181-181 ◽  
Author(s):  
Adair P. Lane ◽  
John Bally
Keyword(s):  
Shock Waves ◽  
High Velocity ◽  
Molecular Hydrogen ◽  
Near Infrared ◽  
Young Stars ◽  
Emission Lines ◽  
Molecular Gas ◽  
Star Forming ◽  
Star Forming Regions ◽  
Post Shock

Near infrared (2 micron) emission lines from molecular hydrogen provide a powerful probe of the morphology and energetics of outflows associated with stellar birth. The H2 emission regions trace the location of shock waves formed when the high velocity outflow from young stars encounters dense quiescent gas. Since H2 is the dominant coolant of the hot post-shock molecular gas, the H2 lines provide a measure of the fraction of the total mechanical luminosity radiated away from the cloud.

scholarly journals On the Accretion Disk Models by Stationary and Non-Stationary Shock Waves

1994 ◽  
Vol 159 ◽  
pp. 477-477
Author(s):  
Sandip K. Chakrabarti
Keyword(s):  
Angular Momentum ◽  
Shock Waves ◽  
Accretion Disk ◽  
Line Emission ◽  
Centrifugal Barrier ◽  
Complex Behaviour ◽  
Hard Radiation ◽  
Particle Hydrodynamics ◽  
Post Shock ◽  
Smoothed Particle

An important point which emerged from this meeting is that disks in AGNs are not simply thin, Keplerian type; they show more complex behaviour. Chakrabarti (1990a and references therein) has shown that in an inviscid accretion disk with significant angular momentum, the centrifugal barrier is strong enough to produce axisymmetric standing shock wave. Subsequently, this work was extended to include the non-axisymmetric and viscous disks (Chakrabarti, 1990b). Particularly important are the solutions with viscosity, as they show that as the viscosity is increased, the stable becomes weaker and weaker till it disappears completely. This solution has a unifying character that inviscid pressure driven disks have almost constant angular momentum and can have shock discontinuities, but viscous driven disks dissipate angular momentum quick enough not to have centrifugal barrier and therefore no shock waves. Chakrabarti & Molteni (1993), using Smoothed Particle Hydrodynamics have shown that shocks are produced in inviscid disks, exactly where they are predicted.Unlike a Keplerian disk, a disk with a shock has basically two temperature zones. The post shock solution is responsible for the Big Blue Bump and UV excess (Chakrabarti and Wiita, 1992). At the shock location, the disk is ‘bulged’ the hard radiation from this region is intercepted by the cooler pre-shock flow. The shock strength and location are sensitive to input specific energy of the flow. This configuration might be responsible for the ‘zero-lag’ correlated variability of, say, NGC 5548 (Chakrabarti, Haardt, Maraschi & Molendi, AA, submitted) discussed in this meeting. Spiral shocks which may be produced in disks in a binary system can also appear in disks around AGNs; the perturbation may be due to passage of massive objects (Chakrabarti & Wiita, 1993a). They also cause time variations in the double horned pattern from disk line emission (Chakrabarti & Wiita 1993b) as observed in, say ARP 102B. All these observations point that shocks are probably important ingredients in any accretion disk in AGNs

scholarly journals Small-scale structure and dynamics of the lower solar atmosphere

2007 ◽  
Vol 3 (S247) ◽  
pp. 66-73 ◽  
Author(s):  
Sven Wedemeyer-Böhm ◽  
Friedrich Wöger
Keyword(s):  
Shock Waves ◽  
Three Dimensional ◽  
Small Scale ◽  
Solar Chromosphere ◽  
Hydrodynamic Simulations ◽  
Comprehensive Picture ◽  
Post Shock ◽  
Lower Solar Atmosphere ◽  
Shock Fronts ◽  
Dynamic Interplay

AbstractThe chromosphere of the quiet Sun is a highly intermittent and dynamic phenomenon. Three-dimensional radiation (magneto-)hydrodynamic simulations exhibit a mesh-like pattern of hot shock fronts and cool expanding post-shock regions in the sub-canopy part of the inter-network. This domain might be called “fluctosphere”. The pattern is produced by propagating shock waves, which are excited at the top of the convection zone and in the photospheric overshoot layer. New high-resolution observations reveal a ubiquitous small-scale pattern of bright structures and dark regions in-between. Although it qualitatively resembles the picture seen in models, more observations – e.g. with the future ALMA – are needed for thorough comparisons with present and future models. Quantitative comparisons demand for synthetic intensity maps and spectra for the three-dimensional (magneto-)hydrodynamic simulations. The necessary radiative transfer calculations, which have to take into account deviations from local thermodynamic equilibrium, are computationally very involved so that no reliable results have been produced so far. Until this task becomes feasible, we have to rely on careful qualitative comparisons of simulations and observations. Here we discuss what effects have to be considered for such a comparison. Nevertheless we are now on the verge of assembling a comprehensive picture of the solar chromosphere in inter-network regions as dynamic interplay of shock waves and structuring and guiding magnetic fields.

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.

The relaxation zone behind normal shock waves in a reacting dusty gas. Part 1. Monatomic gases

1982 ◽  
Vol 27 (3) ◽  
pp. 377-395 ◽  
Author(s):  
G. Ben-Dor ◽  
O. Igra
Keyword(s):  
Shock Waves ◽  
Thermal Relaxation ◽  
Normal Shock ◽  
Dust Particles ◽  
Relaxation Length ◽  
Degree Of Ionization ◽  
Relaxation Zone ◽  
Post Shock ◽  
Free Case ◽  
Mach Numbers

The conservation equations for a suspension composed of an ionized gas and small solid dust particles are formulated and solved numerically. Such flows can be found downstream of strong normal shock waves propagating into dusty gases. The solution indicates that the presence of the dust has a significant effect on the post-shock flow field. Owing to the dust, the relaxation zone will be longer than in the pure plasma case; the equilibrium values for the suspension pressure and density will be higher than in the dust-free case, while the obtained values for the temperature, degree of ionization and velocity will be lower. The numerical solution was executed for shock Mach numbers ranging from 10 to 17. It was found that the thermal relaxation length for the plasma decreases rapidly with increasing shock Mach number, while the thermal relaxation length for the suspension mildly increases with increasing M. The kinematic relaxation length passes through a pronounced maximum at i M = 12·5. Throughout the investigated range of Mach numbers, the kinematic relaxation is longer than the suspension thermal relaxation length.

scholarly journals Non-Radial Oscillations in Red Giants

1980 ◽  
Vol 5 ◽  
pp. 497-500
Author(s):  
Douglas Keeley
Keyword(s):  
Convection Zone ◽  
Normal Modes ◽  
Wave Number ◽  
Red Giants ◽  
Radial Wave ◽  
Giant Stars ◽  
Oscillation Modes ◽  
Red Giant ◽  
Image Position ◽  
Very High

The structure of red giant stars allows non-radial oscillation modes which propagate as p-modes near the surface, to propagate below the convection zone as g-modes with very high radial wave number [Dziembowski (1971, 1977), Shibahashi and Osaki (1976)]. Under some conditions the oscillations in these two propagation regions can be treated as virtually independent normal modes [Shibahashi and Osaki (1976)]. This paper examines the situation in which this approximation is not good, and discusses possible observational consequences of the interaction of the two propagation regions.The linearized differential equations describing non-radial adiabatic oscillations in stars can be written in the form, 1a1b

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