Hydrostatic equilibrium

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

Be Star Disk Models in Consistent Vertical Hydrostatic Equilibrium

Abstract: A popular model for the circumstellar disks of Be stars is that of a geometrically thin disk with a density in the equatorial plane that drops as a power law of distance from the star. It is usually assumed that the vertical structure of such a disk (in the direction parallel to the stellar rotation axis) is governed by the hydrostatic equilibrium set by the vertical component of the star's gravitational acceleration. Previous radiative equilibrium models for such disks have usually been computed assuming a fixed density structure. This introduces an inconsistency as the gas density is not allowed to respond to temperature changes and the resultant disk model is not in vertical, hydrostatic equilibrium. In this work, we modify the {\sc bedisk} code of \citet{sig07} so that it enforces a hydrostatic equilibrium consistent with the temperature solution. We compare the disk densities, temperatures, H$\alpha$ line profiles, and near-IR excesses predicted by such models with those computed from models with a fixed density structure. We find that the fixed models can differ substantially from the consistent hydrostatic models when the disk density is high enough that the circumstellar disk develops a cool ($T\lesssim10,000 $K) equatorial region close to the parent star. Based on these new hydrostatic disks, we also predict an approximate relation between the (global) density-averaged disk temperature and the $T_{\rm eff}$ of the central star, covering the full range of central Be star spectral types.

Study of stellar structures in f(R,T) gravity

Abstract: This paper is devoted to study the compact objects whose pressure and density are related through polytropic equation-of-state (EoS) and MIT bag model (for quark stars) in the background of f(R,T) gravity We solve the field equations together with the hydrostatic equilibrium equation numerically for the model f(R,T) = R + αR2 + λT and discuss physical properties of the resulting solution It is observed that for both types of stars (polytropic and quark stars), the effects of model parameters α and λ remain the same We also obtain that the energy conditions are satisfied and stellar configurations are stable for both EoS

Shear instability for stratified hydrostatic flows

Abstract: Stratified flows in hydrostatic balance are studied in both their multilayer and continuous formulations. A novel stability criterion is proposed for stratified flows, which reinterprets stability in terms not of growth of small perturbations but of the well-posedness of the time evolution. This reinterpretation allows one to extend the classic results of Miles and Howard concerning steady and planar flows to the realm of flows that are nonuniform and unsteady.

Pressure and Stress Effects on Diffusion in Si

Abstract: The thermodynamics of diffusion under hydrostatic pressure and nonhydrostatic stress is presented for single crystals free of extended defects. The thermodynamic relationships obtained permit the direct comparison of hydrostatic and biaxial stress experiments and of atomistic calculations under hydrostatic stress for any proposed mechanism. Atomistic calculations of the volume changes upon point defect formation and migration, and experiments on the effects of pressure and stress on the diffusivity, are reviewed. For Sb in Si, using as input the results of ab initio calculations of the effect of hydrostatic pressure on diffusion by the vacancy mechanism, the thermodynamic relationships successfully account for the measured effect of biaxial stress on diffusion with no free parameters. For other cases, missing parameters are enumerated and experimental and calculational procedures outlined.