Polytropic Relationship Research Articles

Studying the polytropic behavior of an ICME using Multi-spacecraft observation by STEREO-A, STEREO-B, and WIND

The polytropic behavior describes the relationship between macroscopic properties of plasma species and provides useful information in understanding physical mechanisms in space plasma. Through the value of the polytropic index, which governs the polytropic relationship, we can identify the energy transfer in plasma systems. In this paper, we determine the polytropic index of proton plasma within an Interplanetary Coronal Mass Ejection (ICME), which has been observed by three different spacecraft at ∼1 AU, each separated by ∼20∘ degrees in longitude during the analyzed observations. By performing this multi-spacecraft analysis, we provide evidence that the polytropic index does not vary significantly across the structure of the observed ICME. This may imply that the ICME evolution process is nearly coherent. Moreover, the polytropic index values we derive here can set boundary conditions in existing and future ICME evolution models.

Boundary Treatment for the Subsonic/Alfvénic Inner Boundary at 2.5 R ⊙ in a Time-dependent 3D Magnetohydrodynamics Solar Wind Simulation Model

A new magnetohydrodynamics (MHD) simulation model of the global solar corona and solar wind is presented. The model covers the range of heliocentric distance from 2.5 solar radii, so that coronal mass ejections at the earliest phase near the Sun can be treated in the future. This model is constructed by introducing a characteristics-based boundary treatment to an existing heliosphere 3D MHD model. In tailoring a set of characteristic equations for this new model, we assume that the coronal magnetic field is open to interplanetary space and that the solar coronal plasma is flowing outward everywhere at 2.5 solar radii. The characteristic equations for the subsonic/Alfvénic inner boundary surface are satisfied by altering the plasma density and/or temperature to maintain a polytropic relationship. In this article, the details of the characteristics-based boundary treatment for the middle of the corona (named CharM) are provided. The quasi-steady states of the solar wind derived from simulations with various choices of a parameter in the boundary treatments are compared and examined. Although further improvements are needed, we apply the new boundary treatment to simulations for three Carrington rotation periods from the minimum to maximum phase of the solar activity cycle, and show that an optimal choice yields a reasonable quasi-steady state of the transonic/Alfvénic solar wind matching the specified subsonic/Alfvénic plasma speed at 2.5 R ⊙.

Using Parker Solar Probe observations during the first four perihelia to constrain global magnetohydrodynamic models

Context.Parker Solar Probe (PSP) is providing an unprecedented view of the Sun’s corona as it progressively dips closer into the solar atmosphere with each solar encounter. Each set of observations provides a unique opportunity to test and constrain global models of the solar corona and inner heliosphere and, in turn, use the model results to provide a global context for interpreting such observations.Aims.In this study, we develop a set of global magnetohydrodynamic (MHD) model solutions of varying degrees of sophistication for PSP’s first four encounters and compare the results with in situ measurements from PSP, Stereo-A, and Earth-based spacecraft, with the objective of assessing which models perform better or worse. We also seek to understand whether the so-called ‘open flux problem’, which all global models suffer from, resolves itself at closer distances to the Sun.Methods.The global structure of the corona and inner heliosphere is calculated using three different MHD models. The first model (“polytropic”), replaced the energy equation as a simple polytropic relationship to compute coronal solutions and relied on an ad hoc method for estimating the boundary conditions necessary to drive the heliospheric model. The second model (“thermodynamic”) included a more sophisticated treatment of the energy equation to derive the coronal solution, yet it also relied on a semi-empirical approach to specify the boundary conditions of the heliospheric model. The third model (“WTD”) further refines the transport of energy through the corona, by implementing the so-called wave-turbulence-driven approximation. With this model, the heliospheric model was run directly with output from the coronal solutions. All models were primarily driven by the observed photospheric magnetic field using data from Solar Dynamics Observatory’s Helioseismic and Magnetic Imager instrument.Results.Overall, we find that there are substantial differences between the model results, both in terms of the large-scale structure of the inner heliosphere during these time periods, as well as in the inferred timeseries at various spacecraft. The “thermodynamic” model, which represents the “middle ground”, in terms of model complexity, appears to reproduce the observations most closely for all four encounters. Our results also contradict an earlier study that had hinted that the open flux problem may disappear nearer the Sun. Instead, our results suggest that this “missing” solar flux is still missing even at 26.9RS, and thus it cannot be explained by interplanetary processes. Finally, the model results were also used to provide a global context for interpreting the localized in situ measurements.Conclusions.Earlier studies suggested that the more empirically-based polytropic solutions provided the best matches with observations. The results presented here, however, suggest that the thermodynamic approach is now superior. We discuss possible reasons for why this may be the case, but, ultimately, more thorough comparisons and analyses are required. Nevertheless, it is reassuring that a more sophisticated model appears to be able to reproduce observations since it provides a more fundamental glimpse into the physical processes driving the structure we observe.

A method for modelling compressor bleed in gas turbine analysis software

The modelling of compressor interstage bleed in a gas turbine is required at all phases of the engine design cycle. The effect of the physical geometry of the bleed offtake on compressor flow is an important consideration, but of equal importance is the analysis of the effect of bleed air on compressor work requirements and overall gas turbine cycle efficiency. Knowledge of bleed air properties (temperature, pressure, work) is of paramount importance to carry out a reliable preliminary cycle analysis.While interstage bleed modelling may be regarded as a small detail in the overall gas turbine cycle, it is of increasing importance in modern engine design due to the requirement to obtain performance optimisation in engines that have already had significant development. Consequently, even small improvements to the modelling process can yield beneficial improvements to the engine cycle.Current methods to identify these effects vary in terms of complexity and accuracy; in this paper, a novel method is proposed, which offers an innovative -yet simple- way to simulate any number of interstage bleeds within a compressor, without the need to compromise on model accuracy. This is achieved through implementation of two methods - 1) properties of the bleed air are calculated by utilising the polytropic relationship between pressure and temperature, and 2) compressor work requirements are calculated by use of the “superposition principle” by implementing the work requirements of the bleed into an initial ‘no bleed’ calculation. This method has been implemented in the Cranfield modelling software Turbomatch, and validated against test data from an industrial gas turbine. Analyses so far show that the method is quick, accurate, and compares extremely well to the test data.This novel, ‘integrated’ method has been shown to calculate interstage bleed properties in a gas turbine compressor without the need for complex modelling or artificial ‘splitting’ of components. This method is partially dependent on the assumption that stage pressure ratio can be estimated using constant stage temperature rise and compressor overall polytropic efficiency (although the use of overall isentropic efficiency was also investigated). Case studies performed on a number of Siemens industrial gas turbines suggest this is indeed the case, with calculated stage inlet/outlet pressure typically within 3% of the real engine comparison, although older technology compressors tend to be modelled less accurately than newer ones.For compressor work and overall cycle calculation, comparison of this method against test data shows that accuracies between 0.5% and 1% can be obtained down to low load conditions. Compared to compressor ‘splitting’ methods, which demonstrated relatively poor accuracy levels (above 20%), likely due to inaccurate compressor map selection, the alternative method is shown to be a suitable method to model bleed without the need for extensive manual model adjustment. It is also shown how this method can be used to quickly assess the effect of bleed stage and mass flow on the compressor running line, as well as on the surge margin.It should be noted that, while the engines used in the case study represent different engine designs and technology levels, they are from the same engine manufacturer and represent a gradual evolution of compressor technology using a similar design philosophy.

On the origin of the polytropic behavior in space plasmas

The paper addresses the connection between the polytropic behavior – the specific power-law relationship among the thermal plasma moments– and the functional form of the distribution of particle velocities and energies. Surprisingly, the polytropic behavior requires the statistical mechanics of the plasma particles to turn to the framework of kappa distributions. While it was already known that kappa distributions can lead to the polytropic relationship, the new result shows that the reverse derivation is also true; thus, the polytropic behavior has the role of a mechanism generating kappa distributions. Therefore, when observations confirm the existence of a polytropic behavior in plasma particles, then the framework of kappa distributions for describing particle velocities and energies can be indirectly confirmed.

Estimating the Porosity Structure of Granular Bodies Using the Lane–Emden Equation Applied to Laboratory Measurements of the Pressure–Density Relation of Fluffy Granular Samples

Abstract The porosity structure of a granular body is an important characteristic that affects evolutionary changes in the body. We conducted compression experiments using fluffy granular samples with various particle sizes, shapes, and compositions. We approximated the pressure-filling factor relationship of each sample with a power law (a modified polytropic relationship). We also fit our previous data and literature data for fluffy granular samples using a power-law equation. The fitting with a power-law form was as good as that achieved with the equations used for powders in previous studies. The polytropic indices obtained in the current study ranged from ∼0.01 to ∼0.3 and tended to decrease with increasing particle size for samples of similar porosities. We calculated the radial porosity structure and bulk porosity of granular bodies with various radii using the Lane–Emden equation. The results provide the initial, most porous structures of accreted primordial bodies, or re-accumulated rubble-pile bodies consisting of particles that have compression properties similar to those of the assumed granular materials. A range of porosity structures is allowed for a body of given size and macroporosity, depending on the compression properties of the constituent granular material.

Using Kappa Distributions to Identify the Potential Energy

AbstractThis paper reports on the properties of kappa distributions in the presence of a potential energy. The constructed phase space kappa distribution leads to a polytropic relationship between the local density and temperature. The kappa and polytropic indices are connected via a characteristic and universal relationship: their sum is a constant depending specifically on the potential features. Determining this constant comprises a method essential for revealing the functional form and understanding the nature of the particle potential energy. The method is applied to the solar wind proton plasma at 1 AU. It is shown that a satisfactory physical interpretation of the potential affecting solar wind protons can be given by the interplanetary radial electric field.

Conceptual analogy for modelling entrapped air action in hydraulic systems

ABSTRACTHydraulic systems are dynamically susceptible in the presence of entrapped air pockets, leading to amplified transient reactions. In order to model the dynamic action of an entrapped air pocket in a confined system, a heuristic mathematical formulation based on a conceptual analogy to a mechanical “spring-damper“ system is proposed. The formulation is based on the polytropic relationship of an ideal gas and includes an additional term, which encompasses the combined damping effects associated with the thermodynamic deviations from the theoretical transformation, as well as those arising from the transient vorticity developed in both fluid domains (air and water). These effects represent the key factors that account for flow energy dissipation and pressure damping. Model validation was completed via numerical simulation of experimental measurements.

Electron flow properties in the far-field plume of a Hall thruster

The plasma properties were investigated in the far-field plume of a 1.5 kW class Hall thruster using a single, cylindrical Langmuir probe. The plasma potential, the electron temperature and the electron density were measured at 191 positions, providing a detailed map of the plume pattern. This map shows that the plasma plume of a Hall thruster is an expanding jet that is symmetric about the thruster axis. The large data set was also used for a detailed analysis of the electron flow properties. This analysis reveals that the plasma plume of a Hall thruster is an isentropic expansion. In addition, the momentum conservation equation shows there is a polytropic relationship between the plasma potential and the electron density with a γ smaller than that for an atomic gas due to ionization.

The process of isothermal compression of gasses at sub-atmospheric pressures through regulated water injection in Braysson cycles

Although the Braysson cycle constitutes the ideal limit for the Combined Cycle Power Plants, its actual implementation has not been achieved due to the difficulty in building the required isothermal compressor. The present study proposes the incorporation of regulated water injection during the final compression, which could maintain the temperature constant due to the evaporation. The analysis for the thermodynamic implications of the injection on the ideal version of the Braysson cycle indicates that the (ideal cycle) efficiency reduction will be minimal. The study provides an analysis for the water injection rate that will permit such a process and shows that the additional work needed to drive the process will not be affected significantly by the injection. In addition, it shows that the minimum temperature of the Braysson cycle will be lower than the corresponding level of the conventional (Gas–Steam turbine Combined cycle plants), something that could improve the efficiency as well. Finally it shows that the process may be expressed by a polytropic relationship of the type pvβ = constant, where β ≈ 1.06.

Overspray and Interstage Fog Cooling in Gas Turbine Compressor Using Stage-Stacking Scheme—Part II: Case Study

A stage-by-stage wet compression theory and algorithm have been developed for overspray and interstage fogging in the compressor. These theory and algorithm are used to calculate the performance of an eight-stage compressor under both dry and wet compressions. A 2D compressor airfoil geometry and stage setting at the mean radius are employed. Six different cases with and without overspray are investigated and compared. The stage pressure ratio enhances during all fogging cases as does the overall pressure ratio, with saturated fogging (no overspray) achieving the highest pressure ratio. Saturated fogging reduces specific compressor work, but increases the total compressor power due to increased mass flow rate. The results of overspray and interstage spray unexpectedly show that both the specific and overall compressor power do not reduce but actually increase. Analysis shows that this increased power is contributed by the increased pressure ratio and, for interstage overspray, “recompression” contributes to more power consumption. Also it is unexpected to see that air density actually decreases, instead of increases, inside the compressor with overspray. Analysis shows that overspray induces an excessive reduction in temperature that leads to an appreciable reduction in pressure, so the increment of density due to reduced temperature is less than the decrement of air density affected by reduced pressure as air follows the polytropic relationship. In contrast, saturated fogging results in increased density as expected. After the interstage spray, the local blade loading immediately showed a significant increase. Fogging increases axial velocity, flow coefficient, blade inlet velocity, incidence angle, and tangential component of velocity. The analysis also assesses the use of an average shape factor in the generalized compressor stage performance curve when the compressor stage information and performance map are not available. The result indicates that using a constant shape factor might not be adequate because the compressor performance map may have changed with wet compression. The results of nonstage-stacking simulation are shown to underpredict the compressor power by about 6% and the net gas turbine output by about 2% in the studied cases.

Velocity dispersion in N‐body simulations of CDM models

AbstractThis work reports on a study of the spatially coarse‐grained velocity dispersion in cosmological N‐body simulations (OCDM and ΛCDM models) as a function of time (redshifts z = 0–4) and of the coarsening length (0.6–20 h−1 Mpc). The main result is the discovery of a polytropic relationship ℐ1 ∝ ϱ2–η between the velocity‐dispersion kinetic energy density of the coarsening cells, ℐ1, and their mass density, ϱ. The exponent η, dependent on time and coarsening scale, is a compact measure of the deviations from the naive virial prediction ηvirial = 0. This relationship supports the “polytropic assumption” which has been employed in theoretical models for the growth of cosmological structure by gravitational instability. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of the polytropic relationship between density and temperature within interplanetary coronal mass ejections using numerical simulations

Single‐point spacecraft measurements within coronal mass ejections (CMEs) often exhibit a negative correlation between electron density and temperature. At least two opposing interpretations have been suggested for this relationship. If, on one hand, these single spacecraft observations provide direct measures of the polytropic properties of the plasma, then they imply that the polytropic index for the electrons γe is often < 1. Moreover, since the electrons carry the bulk of the pressure (via their significantly higher temperature), this further implies that the dynamics of CME evolution are dominated by an effective polytropic index γeƒƒ < 1. On the other hand, γ < 1 implies that as the ejecta propagate away from the Sun and expand, they also heat up; a result clearly at odds with in situ observations. In contrast to these CME intervals, many studies have shown that the quiescent solar wind exhibits a positive correlation between electron density and temperature, suggesting that γe > 1. In this study we simulate the evolution of a variety of CME‐like disturbances in the solar wind using a one‐dimensional, single‐fluid model, to address the interpretation of the relationship between electron density and temperature within CMEs at fixed locations in space. Although we strictly impose a polytropic relationship (with γ = constant) throughout our simulations, we demonstrate that a variety of correlations can exist between density and temperature at fixed points. Furthermore, we demonstrate that the presence of only local uncorrelated random fluctuations in density and temperature can produce a negative correlation. Consequently, we conclude that these single‐point observations of negative correlations between electron density and temperature cannot be used to infer the value of γe. Instead, we suggest that entropy variations, together with the plasma's tendency to achieve pressure balance with its surroundings, are responsible for the observed profiles.

Nonlinear evolution of magnetic flux ropes: 2. Finite beta plasma

In this second paper on the evolution of magnetic flux ropes we study the effects of gas pressure. We assume that the energy transport is described by a poly tropic relationship and reduce the set of ideal MHD equations to a single, second‐order, nonlinear, ordinary differential equation for the evolution function. For this conservative system we obtain a first integral of motion. To analyze the possible motions, we use a mechanical analogue—a one‐dimensional, nonlinear oscillator. We find that the effective potential for such an oscillator depends on two parameters: the polytropic index γ and a dimensionless quantity κ the latter being a function of the plasma beta, the strength of the azimuthal magnetic field relative to the axial field of the flux rope, and γ. Through a study of this effective potential we classify all possible modes of evolution of the system. In the main body of the paper, we focus on magnetic flux ropes whose field and gas pressure increase steadily towards the symmetry axis. In this case, for γ>1 and all values of κ, only oscillations are possible. For γ<1, however, both oscillations and expansion are allowed. For γ<1 and κ below a critical value, the energy of the nonlinear oscillator determines whether the flux rope will oscillate or expand to infinity. For γ<1 and κ above critical, however, only expansion occurs. Thus by increasing κ while keeping γ fixed (<1), a phase transition occurs at κ = κcritical and the oscillatory mode disappears. We illustrate the above theoretical considerations by the example of a flux rope of constant field line twist evolving self‐similarly. For this example, we present the full numerical MHD solution. In an appendix to the paper we catalogue all possible evolutions when (1) either the magnetic field or (2) the gas pressure decreases monotonically toward the axis. We find that in these cases critical conditions can occur for γ>1. While in most cases the flux rope collapses, there are notable exceptions when, for certain ranges of κ and γ, collapse may be averted.

Magnetic flux rope versus the Spheromak as models for interplanetary magnetic clouds

Magnetic clouds form a subset of interplanetary ejecta with well‐defined magnetic and thermodynamic properties. Observationally, it is well established that magnetic clouds expand as they propagate antisunward. The aim of this paper is to compare and contrast two models which have been proposed for the global magnetic field line topology of magnetic clouds: a magnetic flux tube geometry, on the one hand, and a spheromak geometry (including possible higher multiples), on the other. Traditionally, the magnetic structure of magnetic clouds has been modeled by force‐free configurations. In a first step, we therefore analyze the ability of static force‐free models to account for the asymmetries observed in the magnetic field profiles of magnetic clouds. For a cylindrical flux tube the magnetic field remains symmetric about closest approach to the magnetic axis on all spacecraft orbits intersecting it, whereas in a spheromak geometry one can have asymmetries in the magnetic field signatures along some spacecraft trajectories. The duration of typical magnetic cloud encounters at 1 AU (1 to 2 days) is comparable to their travel time from the Sun to 1 AU and thus magnetic clouds should be treated as strongly nonstationary objects. In a second step, therefore, we abandon the static approach and model magnetic clouds as self‐similarly evolving MHD configurations. In our theory, the interaction of the expanding magnetic cloud with the ambient plasma is taken into account by a drag force proportional to the density and the velocity of expansion. Solving rigorously the full set of MHD equations, we demonstrate that the asymmetry in the magnetic signature may arise solely as a result of expansion. Using asymptotic solutions of the MHD equations, we least squares fit both theoretical models to interplanetary data. We find that while the central part of the magnetic cloud is adequately described by both models, the “edges” of the cloud data are modeled better by the magnetic flux tube. Further comparisons of the two models necessarily involve thermodynamic properties, since real magnetic configurations are never exactly force‐free and gas pressure plays an essential role. We consider a poly tropic gas. Our theoretical analysis shows that the self‐similar expansion of a magnetic flux tube requires the poly tropic index γ to be less than unity. For the spheromak, however, self‐similar, radially expanding solutions are known only for γ equal to 4/3. This difference, therefore, yields a good way of distinguishing between the two geometries. It has been shown recently (Osherovich et al., 1993a) that the polytropic relationship is applicable to magnetic clouds and that the corresponding polytropic index is ∼0.5. This observational result is consistent with the self‐similar model of the magnetic flux rope but is in conflict with the self‐similar spheromak model.

Polytropic relationship in interplanetary magnetic clouds

Interplanetary magnetic clouds are expanding MHD configurations characterized by strong magnetic fields, large rotations of the field vector, and low ion temperatures. In this paper we present high time resolution data from the ISEE 3 and IMP 8 spacecraft on the magnetic field and the proton and electron populations in a number of magnetic clouds. Our objective is to study aspects of the thermodynamics of magnetic clouds and the relation between their thermodynamic and magnetic structures. Our analysis suggests the following features of the thermodynamics of magnetic clouds: (1) The electron and ion populations are not in thermal equilibrium with each other, the electron temperature, Te, being in general up to an order of magnitude higher than the proton temperature, Tp. The temperature ratio Te/Tp in these magnetic clouds is larger than typical values of this quantity in the solar wind at comparable heliocentric distances. (2) For the proton component we find that a polytropic law with γp in the range 1.1 < γp < 1.3 is probably adequate to describe the relation between Tp and density. (3) For the electrons (E < 1.18 keV) the energetics are likewise governed by a polytropic law. Unlike the protons the polytrope that describes the electrons has an index that is less than unity, implying anticorrelation between Te and the number density. For the two clouds analyzed where electron data are available, γe ≈ 0.48 ± 0.2. (4) As a corollary of case 3, the variation of Te with density in magnetic clouds is the reverse of that generally found in the inner heliosphere. (5) Electron temperatures are well correlated with the magnetic field strength, the highest values being reached where the field strength maximizes. We interpret these experimental findings along the following lines. While the magnetic field of the cloud expands, the ions are cooled (though not so effectively as in the adiabatic case (γad = 5/3), indicating some exchange of energy with the ambient solar wind). In contrast, since γe < 1, when the density drops as a result of expansion, Te increases and, consequently, a temperature difference develops between the two species. The hot electrons are trapped by the magnetic field in the core of the magnetic cloud. If magnetic clouds originate in the region near the Sun where Tp < Te, the subsequent expansion accentuates this temperature disparity further. Such conditions are favorable for the generation of ion acoustic waves.

The acceleration of the nonsymmetric and nonpolytropic MHD solar wind

Abstract A method for obtaining analytically several classes of solutions of the full MHD equations for steady, rotating, nonspherically symmetric and nonpolytropic collimated magnetized outflows from a gravitating central object is outlined. These solutions correspond to a polytropic relationship between pressure and density but with a variable polytropic index, while their topology is governed by several hydromagnetic critical points that select a unique wind-type outflow solution. The deviation of the solutions from the original Parker model is parameterized with the introduction of appropriate parameters, such as the deviation of the density from the spherically symmetric case, ω, the deviation of the pressure from a spherically symmetric pressure distribution, κ, the deviation of the streamlines from the spherically symmetric case, s , the effects of rotation, λ and the effects of the magnetic field, β. If ω = κ = λ = β = s = 0, a dipolar, spherically symmetric in density and pressure, nonrotating and nonmagnetized radial Parker-type wind outflow is obtained. We find that the higher is the deviation of the density distribution from the spherically symmetric case, the larger is the initial acceleration. On the other hand, the more magnetically dominated is the outflow and the larger is the pressure inhomogeneity, the rotation amplitude and the flaring, the smaller is the initial acceleration. These results are at variance with attempts to generalize to nonpolytropic outflows the well established result of polytropic outflows wherein, for example, large flaring is usually associated with higher initial acceleration; in nonpolytropic flows exactly the opposite holds. Such properties should be considered in modelling the initial acceleration of the hydromagnetic solar wind.

Ionospheric outflow of plasma and compression relationship in the plasma sheet

We are concerned in this article with the curious finding of Huang et al. [1989] which suggests a polytropic index of plasma compression of about 0.7 in the quiet time central plasma sheet. We show that the reduction of this index from its adiabatic value (=5/3) can be achieved through an ionospheric outflow of plasma which lowers the plasma temperature by virtue of energy partition. The observed correlation between the plasma temperature and density is best reproduced by an ionospheric source of ∼5×1025 ions/s, consistent with independent experinental estimates and smaller than the average solar wind source by a factor of two or more. Despite the change in the polytropic relationship, we find that the global energy equation PV5/3=constant (V=volume of a unit flux tube) still holds approximately (in the absence of other energy‐loss mechanisms).

Self‐Modulation and Envelope Solitons of Spiral Density Waves

AbstractA nonlinear evolution equation describing the modulation of the LIN‐SHU density waves in the tight winding approximation is discussed. A fluid dynamical model with a polytropic relationship between the pressure and the density is used. The equilibrium state is assumed to be homogeneous in the considered radial range. As in the case of plane density waves (IKEUCHI and NAKAMURA 1976) the modulation of spiral density waves is governed by the nonlinear SCHRödinger equation. For large wave numbers the process of self‐modulation generates envelope solitons and could explain the permanent renewal of the spiral design of galaxies.

Mass and angular momentum effluxes of stellar winds

view Abstract Citations (13) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Mass and angular momentum effluxes of stellar winds. Yeh, T. Abstract The mass and angular-momentum effluxes of a stellar wind are determined by the mass and radius of the star and the mass density, temperature, rotation, and magnetic field of the stellar corona. A parametric study, under the assumption of a polytropic relationship, indicates that the mass efflux will be large if the star has small mass and large radius and the stellar corona has high mass density and temperature. The angular-momentum efflux increases in more than linear proportion to the stellar rotation and magnetic field. Publication: The Astrophysical Journal Pub Date: June 1976 DOI: 10.1086/154437 Bibcode: 1976ApJ...206..768Y Keywords: Angular Momentum; Efflux; Stellar Mass Ejection; Stellar Winds; Polytropic Processes; Stellar Atmospheres; Stellar Magnetic Fields; Stellar Rotation; Astrophysics full text sources ADS |