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A major weakness in one-dimensional (1D) stellar structure and evolution modeling is the simplified treatment of convection, which leads to erroneous near-surface stratification and considerable uncertainties in predicted effective…

Based on detailed 2D and 3D numerical radiation-hydrodynamics (RHD) simulations of time-dependent compressible convection, we have studied the dynamics and thermal structure of the convective surface layers of a prototypical late-type…

Astrophysics · Physics 2009-11-07 H. -G. Ludwig , F. Allard , P. H. Hauschildt

A one-dimensional mixing model, incorporating the effects of laser ablation and initial perturbations, is developed to study the influence of ablative Rayleigh-Taylor instability on compression dynamics. The length of the mixing region is…

Fluid Dynamics · Physics 2025-02-11 Dongxue Liu , Tao Tao , Jun Li , Qing Jia , Rui Yan , Jian Zheng

We compute the emergent stellar spectra from the UV to far infrared for different viewing angles using realistic 3D model atmospheres for a large range in stellar parameters to predict the stellar limb darkening. We have computed full 3D…

Solar and Stellar Astrophysics · Physics 2014-12-24 Zazralt Magic , Andrea Chiavassa , Remo Collet , Martin Asplund

Nonlinear evolution of one-dimensional planar perturbations in an optically thin radiatively cooling medium in the long-wavelength limit is studied numerically. The accepted cooling function generates in thermal equilibrium a bistable…

Astrophysics · Physics 2009-10-31 I. G. Kovalenko , Yu. A. Shchekinov

We consider the phase stability of a local oscillator (or laser) locked to a cavity QED system comprised of atoms with an ultra-narrow optical transition. The atoms are cooled to millikelvin temperatures and then released into the optical…

Quantum Physics · Physics 2015-06-30 D. A. Tieri , J. Cooper , Bjarke T. R. Christensen , J. W. Thomsen , M. J. Holland

Condensable species are crucial in shaping planetary climate. A wide range of planetary climate systems involve understanding non-dilute condensable substances and their influence on climate dynamics. There has been progress on large-scale…

Earth and Planetary Astrophysics · Physics 2021-12-22 Xianyu Tan , Maxence Lefevre , Raymond Pierrehumbert

We present results of a fully non-local, compressible model of convection for A-star envelopes. This model quite naturally reproduces a variety of results from observations and numerical simulations which local models based on a mixing…

Astrophysics · Physics 2009-11-07 F. Kupka , M. H. Montgomery

We investigate the impact of 3D hydrodynamical model atmospheres of red giant stars at different metallicities on the formation of spectral lines of a number of ions and molecules. We carry out realistic 3D simulations of surface convection…

Astrophysics · Physics 2009-11-13 Remo Collet , Martin Asplund , Regner Trampedach

[Abridged] Recently we have found that a family of models of partially relaxed, anisotropic stellar systems, inspired earlier by studies of incomplete violent relaxation, exhibits some interesting thermodynamic properties. Here we present a…

Astrophysics · Physics 2009-11-10 M. Trenti , G. Bertin

Context. Clumping is a common property of stellar winds and is being incorporated to a solution of the radiative transfer equation coupled with kinetic equilibrium equations. However, in static hot model atmospheres, clumping and its…

Solar and Stellar Astrophysics · Physics 2021-11-10 Jiří Kubát , Brankica Kubátová

Convection is the most important physical process that determines the structure of the envelopes of cool stars. It influences the surface radiation flux and the shape of observed spectral line profiles and is responsible for both generating…

Solar and Stellar Astrophysics · Physics 2009-12-03 F. Kupka

Current state-of-the-art computational modeling makes it possible to build realistic models of stellar convection zones and atmospheres that take into account chemical composition, radiative effects, ionization, and turbulence. The standard…

Solar and Stellar Astrophysics · Physics 2021-07-28 Irina N. Kitiashvili , Alan A. Wray

Convective motions in solar-type stellar atmospheres induce Doppler shifts that affect the strengths and shapes of spectral absorption lines and create slightly asymmetric line profiles. 1D LTE studies of elemental abundances are not able…

Solar and Stellar Astrophysics · Physics 2018-10-10 G. Harutyunyan , M. Steffen , A. Mott , E. Caffau , G. Israelian , J. I. González Hernández , K. G. Strassmeier

The adiabatic index Gamma_1 for perturbations of dense matter is studied under various physical conditions which can prevail in neutron star cores. The dependence of Gamma_1 on the composition of matter (in particular, on the presence of…

Astrophysics · Physics 2009-11-07 P. Haensel , K. P. Levenfish , D. G. Yakovlev

(Abridged) We describe the results of three-dimensional (3D) numerical simulations designed to study turbulent convection in the stellar interiors, and compare them to stellar mixing-length theory (MLT). Simulations in 2D are significantly…

Astrophysics · Physics 2011-02-11 Casey A. Meakin , David Arnett

We explore how observations relate to the physical properties of the emitting galaxies by post-processing a pair of merging $z\sim2$ galaxies from the cosmological, hydrodynamical simulation NewHorizon using LCARS (Light from Cloudy Added…

We perform the nonlinear stability analysis of a chemotaxis model of bacterial self-organization, assuming that bacteria respond sharply to chemical signals. The resulting discontinuous advection speed represents the key challenge for the…

Analysis of PDEs · Mathematics 2020-09-24 Vincent Calvez , Franca Hoffmann

We study the effect of turbulence on a sedimenting layer of particles by means of direct numerical simulations. A Lagrangian model in which particles are considered as tracers with an additional downward settling velocity is integrated…

Fluid Dynamics · Physics 2020-07-08 Alessandro Sozza , Gabor Drotos , Emilio Hernández-García , Cristóbal López

Massive sets of stellar spectroscopic observations are rapidly becoming available and these can be used to determine the chemical composition and evolution of the Galaxy with unprecedented precision. One of the major challenges in this…