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Chaotic Orbits (chaotic + orbit)
Selected AbstractsAxisymmetric orbit models of N -body merger remnants: a dependency of reconstructed mass on viewing angleMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007J. Thomas ABSTRACT We model mock observations of collisionless N -body disc,disc mergers with the same axisymmetric orbit superposition program that has been used to model elliptical galaxies in Coma. The remnants sample representatively the shape distribution of disc,disc mergers, including the most extreme cases, like highly prolate, maximally triaxial and dominantly oblate objects. The aim of our study is to better understand how the assumption of axial symmetry affects reconstructed masses and stellar motions of systems which are intrinsically not axisymmetric, whether the axisymmetry assumption then leads to a bias and how such a potential bias can be recognized in models of real galaxies. The mass recovery at the half-light radius depends on viewing angle and intrinsic shape: edge-on views allow to reconstruct total masses with an accuracy between 20 per cent (triaxial/prolate remnants) and 3 per cent (oblate remnant). Masses of highly flattened, face-on systems are underestimated by up to 50 per cent. Deviations in local mass densities can be larger where remnants are strongly triaxial or prolate. Luminous mass-to-light ratios are sensitive to box orbits in the remnants. Box orbits cause the central value of the Gauss,Hermite parameter H4 to vary with viewing angle. Reconstructed luminous mass-to-light ratios, as well as reconstructed central masses, follow this variation. Luminous mass-to-light ratios are always underestimated (up to a factor of 2.5). Respective dark haloes in the models can be overestimated by about the same amount, depending again on viewing angle. Reconstructed velocity anisotropies , depend on viewing angle as well as on the orbital composition of the remnant and are mostly accurate to about ,,= 0.2. Larger deviations can occur towards the centre or the outer regions, respectively. We construct N -body realizations of the Schwarzschild models to discuss chaotic orbits and the virial equilibrium in our models. In this study we explore the extreme limits of axisymmetric models. Apparently flattened, rotating ellipticals of intermediate mass are likely close to both, axial symmetry and edge-on orientation. Our results imply that Schwarzschild models allow a reconstruction of their masses and stellar anisotropies with high accuracy. [source] Invariant manifolds, phase correlations of chaotic orbits and the spiral structure of galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006N. Voglis ABSTRACT In the presence of a strong m= 2 component in a rotating galaxy, the phase-space structure near corotation is shaped to a large extent by the invariant manifolds of the short-period family of unstable periodic orbits terminating at L1 or L2. The main effect of these manifolds is to create robust phase correlations among a number of chaotic orbits large enough to support a spiral density wave outside corotation. The phenomenon is described theoretically by soliton-like solutions of a Sine,Gordon equation. Numerical examples are given in an N -body simulation of a barred spiral galaxy. In these examples, we demonstrate how the projection of unstable manifolds in configuration space reproduces essentially the entire observed bar,spiral pattern. [source] Mass components in ordered and in chaotic motion in galactic N -body modelsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002N. Voglis ABSTRACT Two self-consistent (N -body) non-rotating equilibrium models of elliptical galaxies with smooth central density profiles (called ,Q' and ,C' models) are constructed, starting from quiet and clumpy cosmological initial conditions, respectively. Both models are triaxial. The Q model has an E7 maximum ellipticity in the inner parts and tends to E6 or E5 maximum ellipticity in the outer parts. The C model has a maximum ellipticity E4 in the inner parts and tends to an E2 or E1 in the outer parts. For each model, we identify the particles moving in chaotic orbits with the Lyapunov number exceeding a particular threshold (namely, 10,2.8, in units of the inverse radial periods of the particular orbits). At energy levels in the deepest 30 per cent of the potential well, no chaotic orbits were detected in the above limit of chaoticity. In the Q model, the detected chaotic part is 32 per cent of the total mass. This part has a nearly spherical distribution. It imposes limitations on the maximum ellipticity of the system, in spite of the fact that only a part of less than about 8 per cent of the total mass moves in chaotic orbits and is able to develop chaotic diffusion within a Hubble time. In the C model, the detected chaotic part is about 26 per cent of the total mass, but only less than 2 per cent can develop chaotic diffusion within a Hubble time. These chaotic components produce surface density profiles flatter than the profiles of the rest of the mass, particularly in the Q model. The two profiles intersect at a given distance, where the overall profile forms an observable hump, especially if the surface density profiles are taken along the shortest axis of the projection. [source] The stellar dynamics of spiral arms in barred spiral galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2006P. A. Patsis ABSTRACT A dynamical mechanism is proposed that explains the spiral structure observed frequently as a continuation of the bars in barred spiral galaxies. It is argued that the part of the spirals attached to the bar is due to chaotic orbits. These are chaotic orbits that exhibit for long time intervals a 4:1-resonance orbital behaviour. They are of the same type of orbit as is responsible for the boxiness of the outer isophotes of the bar in cases like NGC 4314, as indicated by Patsis, Athanassoula & Quillen. The spirals formed this way are faint with respect to the bar, open as they wind out, and do not extend over an angle larger than ,/2. A possible continuation of the spiral structure towards larger angles can be due to orbits trapped around stable periodic orbits at the corotation region. We present a family of stable, banana-like periodic orbits, precessing as EJ increases, that can play this role. [source] Determining the character of motion in quiet and active galaxies with a satellite companionASTRONOMISCHE NACHRICHTEN, Issue 1 2009N.D. Caranicolas Abstract A galaxy model with a satellite companion is used to study the character of motion for stars moving in the x - y plane. It is observed that a large part of the phase plane is covered by chaotic orbits. The percentage of chaotic orbits increases when the galaxy has a dense nucleus of massMn. The presence of the dense nucleus also increases the stellar velocities near the center of the galaxy. For small values of the distance R between the two bodies, low energy stars display a chaotic region near the centre of the galaxy, when the dense nucleus is present, while for larger values of R the motion in active galaxies is regular for low energy stars. Our results suggest that in galaxies with a satellite companion, the chaotic character of motion is not only a result of galactic interaction but also a result caused by the dense nucleus. Theoretical arguments are used to support the numerical outcomes. We follow the evolution of the galaxy, as mass is transported adiabatically from the disk to the nucleus. Our numerical results are in satisfactory agreement with observational data from M51-type binary galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||