Understanding the assembly of Kepler's compact planetary systems

The Kepler mission has recently discovered a number of exoplanetary systems, such as Kepler-11 and Kepler-32, in which ensembles of several planets are found in very closely packed orbits (often within a few percent of an AU of one another). These compact configurations present a challenge for traditional planet formation and migration scenarios. We present a dynamical study of the assembly of these systems, using an N-body method which incorporates a parametrized model of planet migration in a turbulent protoplanetary disc. We explore a wide parameter space, and find that under suitable conditions it is possible to form compact, close-packed planetary systems via traditional disc-driven migration. We find that simultaneous migration of multiple planets is a viable mechanism for the assembly of tightly-packed planetary systems, as long as the disc provides significant eccentricity damping and the level of turbulence in the disc is modest. We discuss the implications of our preferred parameters for the protoplanetary discs in which these systems formed, and comment on the occurrence and significance of mean-motion resonances in our simulations.Comment: 12 pages, 4 figures, 2 tables. Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Billiard representation for multidimensional multi-scalar cosmological model with exponential potentials

Multidimensional cosmological-type model with n Einstein factor spaces in the theory with l scalar fields and multiple exponential potential is considered. The dynamics of the model near the singularity is reduced to a billiard on the (N-1)-dimensional Lobachevsky space H^{N-1}, N = n+l. It is shown that for n > 1 the oscillating behaviour near the singularity is absent and solutions have an asymptotical Kasner-like behavior. For the case of one scale factor (n =1) billiards with finite volumes (e.g. coinciding with that of the Bianchi-IX model) are described and oscillating behaviour of scalar fields near the singularity is obtained.Comment: 19 pages, Latex, 2 figures; to be published in GR

The Galactic Kinematics of Mira Variables

The galactic kinematics of Mira variables derived from radial velocities, Hipparcos proper motions and an infrared period-luminosity relation are reviewed. Local Miras in the 145-200day period range show a large asymmetric drift and a high net outward motion in the Galaxy. Interpretations of this phenomenon are considered and (following Feast and Whitelock 2000) it is suggested that they are outlying members of the bulge-bar population and indicate that this bar extends beyond the solar circle.Comment: 7 pages, 2 figure, to be published in Mass-Losing Pulsating Stars and their Circumstellar Matter, Y. Nakada & M. Honma (eds) Kluwer ASSL serie

Phase Space Structure in the Solar Neighbourhood

We examine the idea that dynamical parameters can be estimated by identifying locations in the solar neighbourhood where simulated velocity distributions match the observed local distribution. Here, the dynamical influence of both the Galactic bar and the outer spiral pattern are taken into account. The Milky Way disc is stirred by analytical potentials that are chosen to represent the two perturbations, the ratio of pattern speeds of which is explored, rather than held constant. The velocity structure of the final configuration is presented as heliocentric velocity distributions at different locations. These model velocity distributions are compared to the observed distribution in terms of a goodness-of-fit parameter that has been formulated here. We monitor the spatial distribution of the maximal value of this parameter, in order to constrain the solar position from a model. Efficiency of a model is based on a study of this distribution as well as on other independent dynamical considerations. We reject the bar only and spiral only models and arrive at the following bar parameters from the bar+spiral simulations: bar pattern speed of 57.4^{+2.8}_{-3.3} km/s/kpc and a bar angle in [0^\circ$, 30^\circ$]. However, extracting information in this way is no longer viable when the dynamical influence of the spiral pattern does not succumb to that of the bar. Orbital analysis indicates that even though the basic bimodality in the local velocity distribution can be attributed to scattering off the Outer Lindblad Resonance of the bar, it is the interaction of irregular orbits and orbits of other resonant families, that is responsible for the other moving groups; it is realised that such interaction increases with the warmth of the background disk.Comment: 23 pages, 17 figures, accepted for publication in A&

Dynamics of the Narrow-Line Region in the Seyfert 2 Galaxy NGC 1068

We present dynamical models based on a study of high-resolution long-slit spectra of the narrow-line region (NLR) in NGC 1068 obtained with the Space Telescope Imaging Spectrograph (STIS) aboard The Hubble Space Telescope (HST). The dynamical models consider the radiative force due to the active galactic nucleus (AGN), gravitational forces from the supermassive black hole (SMBH), nuclear stellar cluster, and galactic bulge, and a drag force due to the NLR clouds interacting with a hot ambient medium. The derived velocity profile of the NLR gas is compared to that obtained from our previous kinematic models of the NLR using a simple biconical geometry for the outflowing NLR clouds. The results show that the acceleration profile due to radiative line driving is too steep to fit the data and that gravitational forces along cannot slow the clouds down, but with drag forces included, the clouds can slow down to the systemic velocity over the range 100--400 pc, as observed. However, we are not able to match the gradual acceleration of the NLR clouds from ~0 to ~100 pc, indicating the need for additional dynamical studies.Comment: Paper prepared by emulateapj version 10/09/06 and accepted for print in Ap