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Hydrostatic equilibrium

About: Hydrostatic equilibrium is a research topic. Over the lifetime, 2451 publications have been published within this topic receiving 62172 citations.


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Journal ArticleDOI
TL;DR: In this article, the shape of the gas in the Lambda CDM cosmology has been analyzed in the context of cosmological simulations of the LDM cosmology, and the authors found that the gas and potential shapes differ significantly at smaller radii.
Abstract: We present analysis of the three-dimensional shape of intracluster gas in clusters formed in cosmological simulations of the Lambda CDM cosmology and compare it to the shape of dark matter distribution and the shape of the overall isopotential surfaces. We find that in simulations with radiative cooling, star formation, and stellar feedback (CSF), intracluster gas outside the cluster core (r >= 0.1r(500)) is more spherical compared to non-radiative (NR) simulations, while in the core the gas in the CSF runs is moretriaxial and has a distinctly oblate shape. The latter reflects the ongoing cooling of gas, which settles into a thick oblate ellipsoid as it loses thermal energy. The shape of the gas in the inner regions of clusters can therefore be a useful diagnostic of gas cooling. We find that gas traces the shape of the underlying potential rather well outside the core, as expected in hydrostatic equilibrium. At smaller radii, however, the gas and potential shapes differ significantly. In the CSF runs, the difference reflects the fact that gas is partly rotationally supported. Interestingly, we find that in NR simulations the difference between gas and potential shape at small radii is due to random gas motions, which make the gas distribution more spherical than the equipotential surfaces. Finally, we use mock Chandra X-ray maps to show that the differences in shapes observed in a three-dimensional distribution of gas are discernible in the ellipticity of X-ray isophotes. Contrasting the ellipticities measured in simulated clusters against observations can therefore constrain the amount of cooling in the intracluster medium and the presence of random gas motions in cluster cores.

79 citations

Journal ArticleDOI
TL;DR: In this paper, solar flare model atmospheres are computed under the assumption of energetic equilibrium in the chromosphere by the corona by using a static, one-dimensional plane parallel geometry and are designed within a physically self-consistent coronal loop.
Abstract: Solar flare model atmospheres computed under the assumption of energetic equilibrium in the chromosphere are presented. The models use a static, one-dimensional plane parallel geometry and are designed within a physically self-consistent coronal loop. Assumed flare heating mechanisms include collisions from a flux of non-thermal electrons and x-ray heating of the chromosphere by the corona. The heating by energetic electrons accounts explicitly for variations of the ionized fraction with depth in the atmosphere. X-ray heating of the chromosphere by the corona incorporates a flare loop geometry by approximating distant portions of the loop with a series of point sources, while treating the loop leg closest to the chromospheric footpoint in the plane-parallel approximation. Coronal flare heating leads to increased heat conduction, chromospheric evaporation and subsequent changes in coronal pressure; these effects are included self-consistently in the models. Cooling in the chromosphere is computed in detail for the important optically thick HI, CaII and MgII transitions using the non-LTE prescription in the program MULTI. Hydrogen ionization rates from x-ray photo-ionization and collisional ionization by non-thermal electrons are included explicitly in the rate equations. The models are computed in the 'impulsive' and 'equilibrium' limits, and in a set of intermediate 'evolving' states. The impulsive atmospheres have the density distribution frozen in pre-flare configuration, while the equilibrium models assume the entire atmosphere is in hydrostatic and energetic equilibrium. The evolving atmospheres represent intermediate stages where hydrostatic equilibrium has been established in the chromosphere and corona, but the corona is not yet in energetic equilibrium with the flare heating source. Thus, for example, chromospheric evaporation is still in the process of occurring.

79 citations

Journal ArticleDOI
15 Jul 2014-Icarus
TL;DR: In this article, the second-degree gravity field coefficients, the shape, the tidal Love number, the electric field, and the orientation of its rotation axis are used together to constrain the density profile assuming a four-layer interior model.

79 citations

Journal ArticleDOI
TL;DR: In this article, the interarm-to-arm transition for gas flow in the Galactic disk is considered and it is shown that flow passing through it builds dense, long-lived vertical structures with high velocity flow over the top, followed by a downstream shock, and sometimes secondary jumps.
Abstract: We consider the interarm-to-arm transition for gas flow in the Galactic disk, modeled as a thick, magnetized, cloudless layer of gas in hydrostatic equilibrium with external gravity from stars, and having parameters appropriate to the solar neighborhood. We neglect the self-gravity of the gas and shear, and radial variations in gravity. We show that such a transition, if supersonic, must present characteristics of both a hydraulic jump (or bore) and a shock. Our numerical simulations confirm this prediction. Modeling the spiral perturbation as local, we find that flow passing through it builds dense, long-lived vertical structures with high velocity flow over the top, followed by a downstream shock, and sometimes secondary jumps. In addition, gravity waves generated in the thick disk appear to promote the formation of marked density enhancements in the midplane.

79 citations

Journal ArticleDOI
TL;DR: Based on a grid of hydrostatic spherical COMARCS models for cool stars, this article calculated observable properties of these objects, which will be mainly used in combination with stellar evolution tracks and population synthesis tools.
Abstract: Based on a grid of hydrostatic spherical COMARCS models for cool stars, we have calculated observable properties of these objects, which will be mainly used in combination with stellar evolution tracks and population synthesis tools. The high-resolution opacity sampling and low-resolution convolved spectra as well as bolometric corrections for a large number of filter systems are made electronically available. We exploit those data to study the effect of mass, C/O ratio and nitrogen abundance on the photometry of K and M giants. Depending on effective temperature, surface gravity and the chosen wavelength ranges, variations of the investigated parameters cause very weak to moderate and, in the case of C/O values close to 1, even strong shifts of the colours. For the usage with stellar evolution calculations, they will be treated as correction factors applied to the results of an interpolation in the main quantities. WhenwecomparethesyntheticphotometrytoobservedrelationsandtodatafromtheGalactic bulge, we find in general a good agreement. Deviations appear for the coolest giants showing pulsations, mass-loss and dust shells, which cannot be described by hydrostatic models.

78 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023282
2022708
202167
202089
201998
201893