Influence of Steering Angle Profiles on the Orbit Transfer Trajectory

This paper considers a planar orbit transfer trajectory design problem using finite thrust modeling. In this problem, the steering angles associated with the thrust direction are calculated from the predetermined profile format, and the unknown parameters in the profile are directly optimized. Three profile formats that were implemented in previous lunar exploration missions are considered. In addition, a steering angle profile defined in the rotating frame and the optimal steering angle profile are newly studied to compare the performances. To this end, the direct parameter optimization problem and the indirect optimization problem are formulated, and the characteristics of the steering angle profile and its influence on the transfer trajectory are analyzed.

ALMA study of the HD 100453 AB system and the tidal interaction of the companion with the disk

Context. The complex system HD 100453 AB with a ring-like circumprimary disk and two spiral arms, one of which is pointing to the secondary, is a good laboratory in which to test spiral formation theories. Aims. We aim to resolve the dust and gas distribution in the disk around HD 100453 A and to quantify the interaction of HD 100453 B with the circumprimary disk. Methods. Using ALMA band 6 dust continuum and CO isotopologue observations we have studied the HD 100453 AB system with a spatial resolution of 0′′.09 × 0′′.17 at 234 GHz. We used smoothed particle hydrodynamics (SPH) simulations and orbital fitting to investigate the tidal influence of the companion on the disk. Results. We resolve the continuum emission around HD 100453 A into a disk between 0′′.22 and 0′′.40 with an inclination of 29.5° and a position angle of 151.0°, an unresolved inner disk, and excess mm emission cospatial with the northern spiral arm which was previously detected using scattered light observations. We also detect CO emission from 7 au (well within the disk cavity) out to 1′′.10, overlapping with HD 100453 B at least in projection. The outer CO disk position angle (PA) and inclination differ by up to 10° from the values found for the inner CO disk and the dust continuum emission, which we interpret as due to gravitational interaction with HD 100453 B. Both the spatial extent of the CO disk and the detection of mm emission at the same location as the northern spiral arm are in disagreement with the previously proposed near co-planar orbit of HD 100453 B. Conclusions. We conclude that HD 100453 B has an orbit that is significantly misaligned with the circumprimary disk. Because it is unclear whether such an orbit can explain the observed system geometry we highlight an alternative scenario that explains all detected disk features where another, (yet) undetected, low mass close companion within the disk cavity, shepherds a misaligned inner disk whose slowly precessing shadows excite the spiral arms.

Interactions in Barred Galaxies: Effects of a Companion on the Bar Pattern Speed

We study the effects of a companion in a parabolic co-planar orbit on the bar pattern speed. Unlike previous simulations, we use fully self-consistent 3D N-body simulations with live haloes, which are known to be important for bar evolution.

Simulations of Gas Clouds in Interacting Galaxies

A companion can induce a varitey of morphological changes in a galaxy. I use N-body simulations to study the effects of different kinds of perturbations on the dynamics of a disk galaxy. The model is two-dimensional, with a disk consisting of about 60,000 particles. Most of the particles (80 %) represent the old stellar population with a high velocity dispersion, while the rest (20 %) represent gas clouds with a low velocity dispersion. Initially, the velocity dispersion corresponds to Q = 1 for the “star” particles, and Q = 0 for the “gas” particles, where Q is Toomre’s (1964) stability parameter. The gas clouds can collide inelastically. The disk is stabilized by a rigid halo potential, and by the random motions of the old “star” particles. To simulate the effect of an encounter on the disk, a companion galaxy, modelled as a point mass, can move in a co-planar orbit around the disk. A complete description of the N-body code is found in Thomasson (1989).