To bring out the link between the observed shapes of triaxial dynamical systems (ellipticals, bulges, bars) and their orbital populations inferred from models.

We discuss the problem how to determine globally stable equilibrium states of collisionless self-gravitating matter with non-vanishing total angular momentum.

Results of dynamical, numerical simulations of self-gravitating systems are used to show the existence of non-uniform mixing in phase-space.

We study the formation of elliptical galaxies and the bulges of disk galaxies as a result of the collisionless collapse of a rotating star cloud. At small amounts of rotation, this process is accompanied by the bar mode of the radial orbit instability slightly modified by rotation. We refer this case to (giant) ellipticals. For moderate rotation, when the radial orbit instability is suppressed, another mode takes over, which is the direct continuation of a strongly damping mode at the limit of almost radial orbits; it turns into a practically non-damping and long-lived mode (for many revolutions), and even a slowly rotating bar may eventually be formed. It is natural to refer this case to bulges and dwarf elipticals. Then spirals could be formed from the clouds with large amounts of rotation.

A power series approach for solving the linearized transport equation for perturbations in the central part of flat disks is presented. The application of this method is in principle independent of the mathematical complexity of the unperturbed distribution. As an illustration, this method was used to solve the transport equation in the case of Kalnajs' Omega models.

We present evolutionary calculations which show the tumbling instability found in spherical stellar systems by Allen et al. (1992) also occurs in some initially oblate rotating systems.

The evolution of a barred galactic potential containing a central mass concentration is examined by means of a self-consistent 2-D N-body simulation. It is found that the bar weakens as the central mass grows and eventually dissolves, in agreement with earlier orbital studies of this problem.

Two mechanisms involving purely dynamical processes can lead to the formation of a bulge after its disc: 1) small bulges (1 – 2 kpc), including box-shaped bulges and mildly triaxial bulges, can result from the formation and destruction of a bar; 2) big bulges (> 2kpc) à la Sombrero can grow following the accretion of small satellites. Fully consistent N-body simulations show that the fraction of galaxy mass accreted in this way needs to be larger than about 5%. Less accretion does not create smaller bulges, but heats the whole disc. These dynamical effects transforming Hubble types from SB to SA and vice-versa over ≈ 1 – 2 Gyr also indicate, by the secular growth of bulges, a general sense of galactic evolution from Sd to Sa.

Recent 3-D N-body simulations have shown that the bars formed through the well-known global instability of discs later acquire a pronounced peanut shape when seen from the side. This paper reports a new calculation of the phenomenon using a finer grid and a slightly different initial model. The final peanut shaped bar, when viewed from within the disc, has an appearance remarkably similar to that of the Milky Way bulge. When viewed as a distant edge-on galaxy, an observer would see cylindrical rotation in the “bulge”.

Results of n-body simulations of self-gravitating systems containing 100,000 particles are presented. A program based on the particle-mesh method is used to compute the evolution of a hot stellar-disk till an oval configuration at the center is formed. The system is evolved again from this point onwards a) with halo, b) without halo, and c) with the halo but with total mass of the system reduced to that of case b. Results are presented in form of a diagram showing the development of ellipticity.

We simulate the chemical and dynamical evolution of the galactic bulge with the smoothed particle hydrodynamics (SPH) method. We calculate the early phase of galaxy formation in which the bulge is formed through a burst of star formation. The calculated abundance distribution function of stars in the bulge is consistent with the observations of bulge K giants, if the heavy element yields are three times larger than those expected from Salpeter's IMF.

Starburst phenomena in galaxies should have been common in the epoch of galaxy formation. How did the primeval starbursts affect the structure or the properties of the host galaxies?

Using basically the impulsive approximation and a modification of the method used by Alladin S.M., (1965, Ap.J.,141, 768), and described in detail in Chatterjee T.K., (1990, IAU Col.,124, 519, 569) we study the evolution of binary interacting galaxies, leading ultimately to mergers. Each collision is characterised by the initial separation between the galaxies and the relative velocity therein. In each case the orbital evolution and largescale structural changes in the galaxies are studied by taking into account the change in relative velocity due to dynamical friction, leading ultimately to mergers. The evolution is considered from a time when the gravitational interaction between the progenitor pairs is physically significant (Chatterjee, 1992, Astroph. Sp.Sc., in press).

The results of the analytical study of two disspationless non–linear models are generalized in case of rotation.

We analyze the kinematics of the gaseous ring in the central region of NGC 4736 considering an ejection mechanism for the formation of the ring in a non-axisymmetric potential. A barred spiral of strength 10 or 25 per cent of the axisymmetric background is consistent with van der Kruit (1974) observational data.

Analytic dynamic models of triaxial stellar systems, such as elliptical galaxies and galactic bulges, can be used to calculate the velocity fields of systems in a wide range of potentials without the need for orbit integrations. We present results from a first application of these models, in the form of velocity fields projected onto the sky. The appearance of the velocity field depends strongly on the viewing angle. Thin orbit models provide a theoretical upper limit to streaming in all possible kinematic models in a given potential.

Colour gradients, when due to stellar populations rather than dust, are potential diagnostics on the formation history of galaxy bulges. We have carried out measurements of colour gradients on a sample of 30 bulges, the first such study using CCD detectors.

Velocity dispersions and Mg2 indices were measured from CCD spectra of 13 S0 box-shaped galaxies and 5 ellipticals. Evidence for a different relation between velocity dispersion and metallicity, relative to ellipticals, was found for our S0 sample; we attribute this difference to the S0 disk component, affecting both the mean velocity dispersion and mean metallicity.

A bulge/disk decomposition technique using a thin and a thick disk model is applied to a sample of 11 objects. In the thick disk modeling, the profiles are obtained in five differents radial directions. The results show that the model of thick disk is more realist.