48 research outputs found
Warp evidences in precessing galactic bar models
Most galaxies have a warped shape when they are seen from an edge-on point of
view. The reason for this curious form is not completely known so far and in
this work we apply dynamical system tools to contribute to its explanation.
Starting from a simple, but realistic, model formed by a bar and a disc, we
study the effect produced by a small misalignment between the angular momentum
of the system and its angular velocity. To this end, a precession model is
developed and considered, assuming that the bar behaves like a rigid body.
After checking that the periodic orbits inside the bar keep being the skeleton
of the inner system, even after inflicting a precession to the potential, we
compute the invariant manifolds of the unstable periodic orbits departing from
the equilibrium points at the ends of the bar to get evidences of their warped
shapes. As it is well known, the invariant manifolds associated with these
periodic orbits drive the arms and rings of barred galaxies and constitute the
skeleton of these building blocks. Looking at them from a side-on viewpoint, we
find that these manifolds present warped shapes as those recognized in
observations. Lastly, test particle simulations have been performed to
determine how the stars are affected by the applied precession, confirming this
way the theoretical results obtained.Comment: 14 pages, 21 figures, Accepted for publication in A&A (15th Jan 2016
Com les varietats invariants formen espirals i anells en galaxies barrades
L'espectacularitat de les galĂ xies barrades consisteix no solament en la
presència de la barra, allargada en el centre de la galà xia, sinó també en els braços
espirals o anells que es desenvolupen en les parts exteriors. No hi ha una teoria clara
per a la formació d'anells i, fins fa poc, només n'hi havia una que explicava l'origen dels
braços espirals en galà xies no barrades. En els darrers anys hem desenvolupat una teoria
basada en els sistemes dinà mics que relaciona els braços espirals i els anells amb les
varietats invariants hiperbòliques associades a òrbites periòdiques i quasiperiòdiques
al voltant de punts d'equilibri colineals del sistema.The spectacularity of barred galaxies resides not only in the presence of their bars, extended in the center of the galaxy, but also in the rings and spiral
arms developed in the exterior regions. There is no clear theory on the rings formation and, until recently, there was only one explaining the origin of spiral arms in non-barred galaxies. In recent years, and based on dynamical systems, we have developed a theory that relates rings and spiral arms with hyperbolic invariant manifolds associated with periodic and quasiperiodic orbits about the collinear points of the system
A Motivating Exploration on Lunar Craters and Low-Energy Dynamics in the Earth -- Moon System
It is known that most of the craters on the surface of the Moon were created
by the collision of minor bodies of the Solar System. Main Belt Asteroids,
which can approach the terrestrial planets as a consequence of different types
of resonance, are actually the main responsible for this phenomenon. Our aim is
to investigate the impact distributions on the lunar surface that low-energy
dynamics can provide. As a first approximation, we exploit the hyberbolic
invariant manifolds associated with the central invariant manifold around the
equilibrium point L_2 of the Earth - Moon system within the framework of the
Circular Restricted Three - Body Problem. Taking transit trajectories at
several energy levels, we look for orbits intersecting the surface of the Moon
and we attempt to define a relationship between longitude and latitude of
arrival and lunar craters density. Then, we add the gravitational effect of the
Sun by considering the Bicircular Restricted Four - Body Problem. As further
exploration, we assume an uniform density of impact on the lunar surface,
looking for the regions in the Earth - Moon neighbourhood these colliding
trajectories have to come from. It turns out that low-energy ejecta originated
from high-energy impacts are also responsible of the phenomenon we are
considering.Comment: The paper is being published in Celestial Mechanics and Dynamical
Astronomy, vol. 107 (2010
High-fidelity trajectory design to flyby near-Earth asteroids using CubeSats
Fast development of CubeSat technology now enables the first interplanetary missions. The potential application of CubeSats to flyby near-Earth asteroids is explored in this paper in consideration of CubeSats' limited propulsive capabilities and systems constraints. Low-energy asteroid flyby trajectories are designed assuming a CubeSat is initially parked around to the Sun-Earth Lagrange points. High-impulse and low-thrust trajectories with realistic thrusting models are computed first in the Circular Restricted Three-Body Problem (CR3BP), and then in a high-fidelity ephemeris model. Analysis in the ephemeris model is used to confirm that trajectories computed in the CR3BP model also exist in a more realistic dynamical model, and to verify the validity of the results obtained in CR3BP analysis. A catalogue of asteroid flyby opportunities between years 2019 and 2030 is provided, with 80 m/s of available ΔV and departure from halo orbits around the first and second Sun-Earth Lagrange points (of similar size to those typically used by scientific missions). Results show that the CR3BP model can serve as an effective tool to identify reachable asteroids and can provide an initial estimation of the ΔV cost in the ephemeris model (with ±15 m/s accuracy). An impulsive maneuver model can also provide an accurate estimation of the ΔV requirement for a CubeSat equipped with a high-impulse thruster (with 4 m/s accuracy), even if its thrust magnitude is small and requires duty cycling; low-thrust ΔV requirements, however, may differ significantly from the impulsive results (±15 m/s)
Design of Ganymede-synchronous frozen orbit around Europa
A Ganymede-synchronous frozen orbit around Europa provides a stable spatial geometry between a Europa probe and a Ganymede lander, which facilitates the observation of Ganymede and data transmission between probes. However, the third-body gravitation perturbation of Ganymede continues to accumulate and affect the long-term evolution of the Europa probe. In this paper, the relative orbit of Ganymede with respect to Europa is considered to accurately capture the perturbation potential. The orbital evolution behaviors of the Europa probe under the non-spherical gravitation of Europa and the third-body gravitation of Jupiter and Ganymede are studied based on a double-averaging framework. Then, the initial orbital conditions of the Ganymede-synchronous frozen orbit are developed. A station-keeping maneuver was performed to maintain the orbital elements to achieve the Ganymede-synchronous and frozen behaviors. A numerical simulation showed that the consumption for orbital maintenance is acceptable