scholarly journals The kinematic richness of star clusters – II. Stability of spherical anisotropic models with rotation

2021 ◽  
Vol 502 (4) ◽  
pp. 4762-4778
Author(s):  
Philip G Breen ◽  
Simon Rozier ◽  
Douglas C Heggie ◽  
Anna Lisa Varri
Keyword(s):  
Growth Rate ◽  
Phase Space ◽  
Star Clusters ◽  
Stellar Systems ◽  
Complementary Series ◽  
Orbital Inclination ◽  
Anisotropic Models ◽  
Resonant Interactions ◽  
The Matrix ◽  
Pattern Speed

ABSTRACT We study the bar instability in collisionless, rotating, anisotropic, stellar systems, using N-body simulations and also the matrix technique for calculation of modes with the perturbed collisionless Boltzmann equation. These methods are applied to spherical systems with an initial Plummer density distribution, but modified kinematically in two ways: the velocity distribution is tangentially anisotropic, using results of Dejonghe, and the system is set in rotation by reversing the velocities of a fraction of stars in various regions of phase space, à la Lynden-Bell. The aim of the N-body simulations is first to survey the parameter space, and, using those results, to identify regions of phase space (by radius and orbital inclination) that have the most important influence on the bar instability. The matrix method is then used to identify the resonant interactions in the system that have the greatest effect on the growth rate of a bar. Complementary series of N-body simulations examine these processes in relation to the evolving frequency distribution and the pattern speed. Finally, the results are synthesized with an existing theoretical framework, and used to consider the old question of constructing a stability criterion.

scholarly journals Instability Through Anisotropy in Spherical Stellar Systems

1987 ◽  
Vol 127 ◽  
pp. 515-516
Author(s):  
P.L. Palmer ◽  
J. Papaloizou
Keyword(s):  
Growth Rate ◽  
Eigenvalue Problem ◽  
Growth Rates ◽  
Stellar Systems ◽  
Matrix Eigenvalue Problem ◽  
Simple Method ◽  
Anisotropic Models ◽  
Poisson Equations ◽  
Degree Of Anisotropy ◽  
The Stability

We consider the linear stability of spherical stellar systems by solving the Vlasov and Poisson equations which yield a matrix eigenvalue problem to determine the growth rate. We consider this for purely growing modes in the limit of vanishing growth rate. We show that a large class of anisotropic models are unstable and derive growth rates for the particular example of generalized polytropic models. We present a simple method for testing the stability of general anisotropic models. Our anlysis shows that instability occurs even when the degree of anisotropy is very slight.

Phase space complexity of star clusters: Fresh observables for old and new questions

2019 ◽  
Vol 14 (S351) ◽  
pp. 389-394
Author(s):  
Anna Lisa Varri ◽  
Philip G. Breen ◽  
Douglas C. Heggie
Keyword(s):  
Phase Space ◽  
Globular Clusters ◽  
Star Clusters ◽  
Stellar Dynamics ◽  
Stellar Systems ◽  
Internal Dynamics ◽  
The Rich ◽  
Evolving Context ◽  
New Generation ◽  
Precision Astrometry

AbstractThe blooming era of precision astrometry for Galactic studies truly brings the rich internal dynamics of globular clusters to the centre stage. But several aspects of our current understanding of fundamental collisional stellar dynamics cannot match such new-generation data and the theoretical ambitions they trigger. This rapidly evolving context offers the stimulus to address a number of old and new questions concerning the phase space properties of this class of stellar systems.

Correlations for Interaction Layer Growth in U-Mo/Al Dispersion Fuels

2017 ◽  
Vol 375 ◽  
pp. 29-39
Author(s):  
Boris A. Tarasov ◽  
Stepan N. Nikitin ◽  
Dmitry P. Shornikov ◽  
Maria S. Tarasova ◽  
Igor I. Konovalov
Keyword(s):  
Growth Rate ◽  
Growth Process ◽  
Aluminum Matrix ◽  
Layer Growth ◽  
Radiation Diffusion ◽  
Fission Rate ◽  
Interaction Layer ◽  
The Matrix ◽  
Mechanism And Kinetics ◽  
Kinetics Of

Paper presents the results of the growth rate of the interaction layer of uranium-molybdenum dispersed fuel in aluminum matrix and influence of silicon alloying on it. The growth process of amorphous interaction layer depends on the radiation diffusion which is proportional to the fission rate in the power of 1⁄4. The alloying of the matrix by silicon does not lead to a change in the mechanism and kinetics of the interaction layer growth, but only slows it down.

One-Dimensional Harmonic Oscillator in Quantum Phase Space

2011 ◽  
Vol 110-116 ◽  
pp. 3750-3754
Author(s):  
Jun Lu ◽  
Xue Mei Wang ◽  
Ping Wu
Keyword(s):  
Phase Space ◽  
Harmonic Oscillator ◽  
Quantum Phase ◽  
Space Representation ◽  
Wave Mechanics ◽  
One Dimensional ◽  
Matrix Mechanics ◽  
The Matrix ◽  
Quantum Wave ◽  
The One

Within the framework of the quantum phase space representation established by Torres-Vega and Frederick, we solve the rigorous solutions of the stationary Schrödinger equations for the one-dimensional harmonic oscillator by means of the quantum wave-mechanics method. The result shows that the wave mechanics and the matrix mechanics are equivalent in phase space, just as in position or momentum space.

Effect of Two-Stage Aging on Microstructure and Properties of Al-Mg-Si Alloys

2022 ◽  
Vol 905 ◽  
pp. 51-55
Author(s):  
Li Wang ◽  
Ya Ya Zheng ◽  
Shi Hu Hu
Keyword(s):  
Growth Rate ◽  
Grain Boundary ◽  
Tensile Properties ◽  
Tensile Testing ◽  
Diffusion Rate ◽  
Two Stage ◽  
Precipitated Phase ◽  
Transmission Electron ◽  
The Matrix ◽  
Microstructure Characteristic

The effects of two-stage aging on the microstructures, tensile properties and intergranular corrosion (IGC) sensitivity of Al-Mg-Si alloys were studied by tensile testing and IGC experiments and transmission electron microscope (TEM). The results show that the two-stage aging (180°C, 2h+160°C, 120h) can reduce the IGC sensitivity without decrease the tensile properties. The grain is distributed with high-density β′′ phases, and the grain boundary phases are spherical and intermittently distributed. The formation of the microstructure characteristic is due to the lower re-aging temperature, which results in a decline differences in the diffusion rate between the matrix and grain boundaries. As a result, the pre-precipitated phase can maintain a better strengthening effects due to the slower growth rate. The pre-precipitated phase of the grain boundary presents a spherical and intermittent distribution due to the fast coarsening speed.

scholarly journals Observed Variations in the Density Profiles of Star Clusters in the LMC

1988 ◽  
Vol 126 ◽  
pp. 571-572 ◽  
Author(s):  
M. Kontizas ◽  
D. Hatzidimitriou ◽  
M. Metaxa
Keyword(s):  
Observational Data ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Stellar Systems ◽  
Density Profiles ◽  
Valuable Source ◽  
Dynamical Properties ◽  
Source Of Information

Several dynamical theories have been developed in order to approach the dynamical evolution of stellar systems and explain the observational data. The observed density profiles of the clusters can be a valuable source of information towards the understanding of their dynamical properties. King in a series of papers has connected the established theories with the observed profiles in clusters of our own Galaxy (King, 1962, 1966; etc.). Density profiles can be obtained by means of star counts and/or by means of photometric photometry. So far the observations for clusters in our Galaxy and the MCs appear to fit well the so called King models and provide information of their tidal radii, total masses and concentration parameters (Kontizas, 1984).

scholarly journals 3D gas dynamics in triaxial systems

1993 ◽  
Vol 153 ◽  
pp. 273-274
Author(s):  
D. Friedli ◽  
S. Udry
Keyword(s):  
Gas Dynamics ◽  
Elliptical Galaxies ◽  
Stellar Systems ◽  
Gas Temperature ◽  
3D Simulations ◽  
Hot Gas ◽  
Chaotic Orbits ◽  
Self Consistent ◽  
Triaxial Stellar Systems ◽  
Pattern Speed

Depending on the nature of the various components (stars, gas) present in triaxial stellar systems (elliptical galaxies, bulges and bars), the dynamics is expected to be rather different. The stars are collisionless, dissipationless, and dynamically hot; they are mainly trapped by quasi-periodic or chaotic orbits. On the contrary, the gas is collisional, dissipational, and dynamically cold; the cold or warm gas (≲ 104 K) is a powerful orbital tracer, however shocks prevent it from following self-crossing orbits. The hot gas (≲ 106 K) is influenced by “repulsive” pressure forces which prevent in close encounters the flow from being strongly shocked; it rather follows chaotic trajectories. By means of fully self-consistent 3D simulations with stars and gas using PM (Pfenniger & Friedli 1992) and SPH (Friedli & Benz 1992) techniques, we investigate the response of gaseous components in the following situations: 1) slow or fast pattern speed Ωp, 2) direct or retrograde gas motion with respect to the stars, and 3) warm or hot gas temperature T. Initial parameters and final characteristics of each runs are reported in Table I.

scholarly journals Photographic Photometry With Schmidt Plates of Star Clusters in the SMC

1984 ◽  
Vol 78 ◽  
pp. 355-357
Author(s):  
M. Kontizas
Keyword(s):  
Stellar Evolution ◽  
Initial Conditions ◽  
Star Clusters ◽  
Magellanic Clouds ◽  
Large Field ◽  
Stellar Systems ◽  
Nearest Neighbour ◽  
Photographic Photometry

The star clusters have always been the most important tools of testing the stellar evolution theories and when these stellar systems belong to other galaxies, then our knowledge on stellar evolution can be extended for different initial conditions than those of our Galaxy. The Magellanic Clouds being our nearest neighbour galaxies offer ideal conditions for such studies.Since the powerful southern telescope came into operation deep plates of these two galaxies revealed a large number of new star clusters. The Schmidt plates are most useful since they have the advantage of large field where many objects can be investigated homogeneously on the same plate.

scholarly journals Evolution of fractality and rotation in embedded star clusters

2020 ◽  
Vol 496 (1) ◽  
pp. 49-59 ◽  
Author(s):  
Alessandro Ballone ◽  
Michela Mapelli ◽  
Ugo N Di Carlo ◽  
Stefano Torniamenti ◽  
Mario Spera ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Molecular Clouds ◽  
Star Clusters ◽  
Young Star ◽  
Direct Result ◽  
Molecular Gas ◽  
Stellar Systems ◽  
Small Scales ◽  
Hydrodynamical Simulations ◽  
Young Star Clusters

ABSTRACT More and more observations indicate that young star clusters could retain imprints of their formation process. In particular, the degree of substructuring and rotation are possibly the direct result of the collapse of the parent molecular cloud from which these systems form. Such properties can, in principle, be washed-out, but they are also expected to have an impact on the relaxation of these systems. We ran and analysed a set of 10 hydrodynamical simulations of the formation of embedded star clusters through the collapse of turbulent massive molecular clouds. We systematically studied the fractality of our star clusters, showing that they are all extremely substructured (fractal dimension D = 1.0–1.8). We also found that fractality is slowly reduced, with time, on small scales, while it persists on large scales on longer time-scales. Signatures of rotation are found in different simulations at every time of the evolution, even for slightly supervirial substructures, proving that the parent molecular gas transfers part of its angular momentum to the new stellar systems.

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