A linear stability study of stellar rotating spheres

2019 ◽  
Vol 14 (S351) ◽  
pp. 494-497
Author(s):  
Simon Rozier ◽  
Jean-Baptiste Fouvry ◽  
Philip G. Breen ◽  
Anna Lisa Varri ◽  
Christophe Pichon ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Linear Stability ◽  
Globular Clusters ◽  
Stability Study ◽  
Velocity Space ◽  
Rotating Systems ◽  
Radial Orbit ◽  
Anisotropic Systems ◽  
Fast Rotating

AbstractRecent observations of globular clusters imposed major revisions to the previous paradigm, in which they were considered to be isotropic in velocity space and non-rotating. However, the theory of collisionless spheroids with some kinematic richness has seldom been studied. We present here a first step in this direction, owing to new results regarding the linear stability of rotating Plummer spheres, with varying anisotropy in velocity space and total amount of angular momentum. We extend the well-known radial orbit instability to rotating systems, and discover a new regime of instability in fast rotating, tangentially anisotropic systems.

Linear stability of stellar rotating spheres

2019 ◽  
Vol 14 (S353) ◽  
pp. 246-247
Author(s):  
Simon Rozier ◽  
Jean-Baptiste Fouvry ◽  
Philip G. Breen ◽  
Anna Lisa Varri ◽  
Christophe Pichon ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Linear Stability ◽  
Globular Clusters ◽  
Velocity Space ◽  
Rotating Systems ◽  
Radial Orbit ◽  
Anisotropic Systems ◽  
Traditional Paradigm ◽  
Fast Rotating

AbstractRecent observations of globular clusters encourage to revise some aspects of the traditional paradigm, in which they were considered to be isotropic in velocity space and non-rotating. However, the theory of collisionless spheroids with some kinematic richness has seldom been studied. We present here a further step in this direction, owing to new results regarding the linear stability of rotating Plummer spheres, with varying anisotropy in velocity space and total amount of angular momentum. We extend the well-known radial orbit instability to rotating systems, and discover a new regime of instability in fast rotating, tangentially anisotropic systems.

Kinematical evolution of Globular Clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 524-527
Author(s):  
Maria A. Tiongco ◽  
Enrico Vesperini ◽  
Anna Lisa Varri
Keyword(s):  
Angular Momentum ◽  
Structural Properties ◽  
Globular Clusters ◽  
Velocity Dispersion ◽  
Three Dimensional ◽  
Stellar Populations ◽  
Velocity Space ◽  
Fundamental Understanding

AbstractWe present several results of the study of the evolution of globular clusters’ internal kinematics, as driven by two-body relaxation and the interplay between internal angular momentum and the external Galactic tidal field. Via a large suite of N-body simulations, we explored the three-dimensional velocity space of tidally perturbed clusters, by characterizing their degree of velocity dispersion anisotropy and their rotational properties. These studies have shown that a cluster’s kinematical properties contain distinct imprints of the cluster’s initial structural properties, dynamical history, and tidal environment. Building on this fundamental understanding, we then studied the dynamics of multiple stellar populations in globular clusters, with attention to the largely unexplored role of angular momentum.

scholarly journals An overview of the rotational behavior of metal-poor stars

2009 ◽  
Vol 5 (S266) ◽  
pp. 374-374
Author(s):  
C. Cortés ◽  
J. R. P. Silva ◽  
A. Recio–Blanco ◽  
M. Catelan ◽  
J. D. Do Nascimento ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Globular Clusters ◽  
Main Sequence ◽  
Rotational Velocity ◽  
Transport Mechanisms ◽  
Rotation Rates ◽  
Blue Straggler ◽  
Low Metallicity ◽  
Red Giant ◽  
Fast Rotating

AbstractWe describe the behavior of the rotational velocity in metal-poor stars ([Fe/H] ~ −0.5 dex) at different evolutionary stages, based on v sin i values from the literature. Our sample is composed of stars in the field and in some Galactic globular clusters, including stars on the main sequence (MS), red-giant branch (RGB), and horizontal branch (HB). The metal-poor stars are mainly slow rotators, and their v sin i distribution along the Hertzsprung–Russell diagram is quite homogeneous. Nevertheless, a few moderate to high values of v sin i are found for stars located on the MS and the HB. We show that the overall distribution of v sin i values is basically independent of metallicity for the stars in our sample. In particular, the fast-rotating MS stars in our sample exhibit similar rotation rates as their metal-rich counterparts, suggesting that some may actually be fairly young, in spite of their low metallicity, or else that at least some would be better classified as blue straggler stars. We do not find significant evidence of evolution in v sin i values as a function of position on the RGB. In particular, we do not confirm previous suggestions that stars close to the RGB tip rotate faster than their less-evolved counterparts. While the presence of fast rotators among moderately cool blue-HB stars has been suggested as due to angular-momentum transport from a stellar core that has retained significant angular momentum during its prior evolution, we find that any such transport mechanisms must likely operate very fast as the star arrives on the zero-age HB (ZAHB), since we do not find a link between evolution off the ZAHB and v sin i values.

scholarly journals Effects of initial density profiles on massive star cluster formation in giant molecular clouds

2021 ◽  
Author(s):  
Yingtian Chen ◽  
Hui Li ◽  
Mark Vogelsberger
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Molecular Clouds ◽  
Globular Clusters ◽  
Cluster Formation ◽  
Initial Density ◽  
Giant Molecular Clouds ◽  
Density Profiles ◽  
Stellar Feedback ◽  
Gas Accretion

Abstract We perform a suite of hydrodynamic simulations to investigate how initial density profiles of giant molecular clouds (GMCs) affect their subsequent evolution. We find that the star formation duration and integrated star formation efficiency of the whole clouds are not sensitive to the choice of different profiles but are mainly controlled by the interplay between gravitational collapse and stellar feedback. Despite this similarity, GMCs with different profiles show dramatically different modes of star formation. For shallower profiles, GMCs first fragment into many self-gravitation cores and form sub-clusters that distributed throughout the entire clouds. These sub-clusters are later assembled ‘hierarchically’ to central clusters. In contrast, for steeper profiles, a massive cluster is quickly formed at the center of the cloud and then gradually grows its mass via gas accretion. Consequently, central clusters that emerged from clouds with shallower profiles are less massive and show less rotation than those with the steeper profiles. This is because 1) a significant fraction of mass and angular momentum in shallower profiles is stored in the orbital motion of the sub-clusters that are not able to merge into the central clusters 2) frequent hierarchical mergers in the shallower profiles lead to further losses of mass and angular momentum via violent relaxation and tidal disruption. Encouragingly, the degree of cluster rotations in steeper profiles is consistent with recent observations of young and intermediate-age clusters. We speculate that rotating globular clusters are likely formed via an ‘accretion’ mode from centrally-concentrated clouds in the early Universe.

scholarly journals Structure in the velocity space of globular clusters

2001 ◽  
Vol 370 (3) ◽  
pp. L45-L48 ◽  
Author(s):  
E. J. Alfaro ◽  
A. J. Delgado ◽  
M. A. Gómez-Flechoso ◽  
F. Ferrini ◽  
I. Castro
Keyword(s):  
Globular Clusters ◽  
Velocity Space

scholarly journals Dynamical Evolution of Rotating Globular Clusters

1996 ◽  
Vol 174 ◽  
pp. 375-376
Author(s):  
P.-Y. Longaretti ◽  
C. Lagoute
Keyword(s):  
Angular Momentum ◽  
Stellar Evolution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Dynamical Evolution

We have computed simplified globular cluster evolutionary tracks which take into account the effects of internal relaxation, of the cluster rotation, of the galactic tidal field, and, in a cruder way, of stellar evolution and of gravitational shocking. The objectives are first to quantify the influence of rotation in the dynamical evolution of globular clusters; and second, to investigate the evolution of globular cluster angular momentum and flattening (Lagoute and Longaretti 1995a, Longaretti and Lagoute 1995b,c).

scholarly journals Rotation and Flattening of Globular Clusters

1985 ◽  
Vol 113 ◽  
pp. 285-296 ◽  
Author(s):  
S. Michael Fall ◽  
Carlos S. Frenk
Keyword(s):  
Angular Momentum ◽  
Internal Rotation ◽  
Globular Clusters ◽  
Pressure Support ◽  
Initial Conditions ◽  
Anisotropic Pressure ◽  
Stellar Systems ◽  
Galactic Globular Clusters

Pease and Shapley (1917) first remarked on the apparent flattening of several Galactic globular clusters, a view that has been confirmed by many subsequent studies. Tidal stresses, internal rotation, and velocity anisotropies can cause deviations from sphericity in stellar systems. In general, we might expect globular clusters to have some angular momentum at the time of formation and, if they collapsed from flattened initial conditions, to have anisotropic pressure support. Since the velocity distributions within the clusters can be altered by a variety of internal and external processes, their shapes are expected to evolve. In this article, we review the methods for measuring ellipticities and the results that have emerged from such studies. Our main purpose, however, is to discuss the processes that determine the shapes of globular clusters and the ways in which they change with time.

scholarly journals On the Dynamical Evolution of Clusters of Galaxies

1978 ◽  
Vol 79 ◽  
pp. 357-375 ◽  
Author(s):  
Jeremiah P. Ostriker
Keyword(s):  
Globular Clusters ◽  
Normal Modes ◽  
Dynamical Evolution ◽  
Second Law Of Thermodynamics ◽  
Elliptical Galaxies ◽  
Second Law ◽  
Clusters Of Galaxies ◽  
Physical Processes ◽  
Rotating Systems ◽  
Accurate Picture

The theory of the dynamics of star clusters (cf. Spitzer 1975 for a review) is by now so well developed that we have, or think we have, a moderately accurate picture of the physical processes acting in and the overall evolution of spherical systems. in contrast, flattened and/or rotating systems are apparently subject to a variety of ill-understood instabilities which ultimately are a manifestation of the second law of thermodynamics; at given total energy, a system will tend to increase the fraction of its kinetic energy in disordered rather than ordered form. But spherical systems (globular clusters, elliptical galaxies, Morgan cD clusters of galaxies) are relatively smooth and featureless; they show little substructure indicating, presumably, that they are quite stable to perturbations of their fundamental normal modes, and they are normally modeled as rather “hot”, pressure supported systems.

scholarly journals Dynamical evolution of rotating globular clusters with embedded black holes

2006 ◽  
Vol 2 (S238) ◽  
pp. 363-364 ◽  
Author(s):  
José Fiestas ◽  
Rainer Spurzem
Keyword(s):  
Black Holes ◽  
Angular Momentum ◽  
Globular Clusters ◽  
Structural Parameters ◽  
Dynamical Evolution ◽  
Meridional Plane ◽  
Angular Momentum Transport ◽  
Dimensional Distribution ◽  
Velocity Diffusion ◽  
Parent Galaxy

AbstractEvolution of rotating globular clusters with embedded black holes is presented. The interplay between velocity diffusion due to relaxation and black hole star accretion is followed together with cluster rotation, using 2-dimensional, in energy and z-component of angular momentum, Fokker Planck numerical methods. Gravogyro and gravothermal instabilities drive the system to a faster evolution leading to shorter collapse times and a faster cluster dissolution in the tidal field of a parent galaxy.Angular momentum transport and star accretion support the development of central rotation in relaxation time scales. Two-dimensional distribution (in the meridional plane) of kinematical and structural parameters (density, dispersions, rotation) are reproduced, with the aim to enable the use of set of models for comparison with observational data.

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