1,260 research outputs found
Circumstellar Disk Evolution: Constraining Theories of Planet Formation
Observations of circumstellar disks around stars as a function of stellar
properties such as mass, metallicity, multiplicity, and age, provide
constraints on theories concerning the formation and evolution of planetary
systems. Utilizing ground- and space-based data from the far-UV to the
millimeter, astronomners can assess the amount, composition, and location of
circumstellar gas and dust as a function of time. We review primarily results
from the Spitzer Space Telescope, with reference to other ground- and
space-based observations. Comparing these results with those from exoplanet
search techniques, theoretical models, as well as the inferred history of our
solar system, helps us to assess whether planetary systems like our own, and
the potential for life that they represent, are common or rare in the Milky Way
galaxy.Comment: To appear in IAU Symposium No. 258, Eds. E. Mamajek, D.R. Soderblom,
and R.F.G. Wys
An Overview of the 13:8 Mean Motion Resonance between Venus and Earth
It is known since the seminal study of Laskar (1989) that the inner planetary
system is chaotic with respect to its orbits and even escapes are not
impossible, although in time scales of billions of years. The aim of this
investigation is to locate the orbits of Venus and Earth in phase space,
respectively to see how close their orbits are to chaotic motion which would
lead to unstable orbits for the inner planets on much shorter time scales.
Therefore we did numerical experiments in different dynamical models with
different initial conditions -- on one hand the couple Venus-Earth was set
close to different mean motion resonances (MMR), and on the other hand Venus'
orbital eccentricity (or inclination) was set to values as large as e = 0.36 (i
= 40deg). The couple Venus-Earth is almost exactly in the 13:8 mean motion
resonance. The stronger acting 8:5 MMR inside, and the 5:3 MMR outside the 13:8
resonance are within a small shift in the Earth's semimajor axis (only 1.5
percent). Especially Mercury is strongly affected by relatively small changes
in eccentricity and/or inclination of Venus in these resonances. Even escapes
for the innermost planet are possible which may happen quite rapidly.Comment: 14 pages, 11 figures, submitted to CMD
Detecting chaos in particle accelerators through the frequency map analysis method
The motion of beams in particle accelerators is dominated by a plethora of
non-linear effects which can enhance chaotic motion and limit their
performance. The application of advanced non-linear dynamics methods for
detecting and correcting these effects and thereby increasing the region of
beam stability plays an essential role during the accelerator design phase but
also their operation. After describing the nature of non-linear effects and
their impact on performance parameters of different particle accelerator
categories, the theory of non-linear particle motion is outlined. The recent
developments on the methods employed for the analysis of chaotic beam motion
are detailed. In particular, the ability of the frequency map analysis method
to detect chaotic motion and guide the correction of non-linear effects is
demonstrated in particle tracking simulations but also experimental data.Comment: Submitted for publication in Chaos, Focus Issue: Chaos Detection
Methods and Predictabilit
Local control of Hamiltonian chaos
We review a method of control for Hamiltonian systems which is able to create
smooth invariant tori. This method of control is based on an apt modification
of the perturbation which is small and localized in phase space
On the Dynamical Stability of the Solar System
A long-term numerical integration of the classical Newtonian approximation to
the planetary orbital motions of the full Solar System (sun + 8 planets),
spanning 20 Gyr, was performed. The results showed no severe instability
arising over this time interval. Subsequently, utilizing a bifurcation method
described by Jacques Laskar, two numerical experiments were performed with the
goal of determining dynamically allowed evolutions for the Solar System in
which the planetary orbits become unstable. The experiments yielded one
evolution in which Mercury falls onto the Sun at ~1.261Gyr from now, and
another in which Mercury and Venus collide in ~862Myr. In the latter solution,
as a result of Mercury's unstable behavior, Mars was ejected from the Solar
System at ~822Myr. We have performed a number of numerical tests that confirm
these results, and indicate that they are not numerical artifacts. Using
synthetic secular perturbation theory, we find that Mercury is destabilized via
an entrance into a linear secular resonance with Jupiter in which their
corresponding eigenfrequencies experience extended periods of commensurability.
The effects of general relativity on the dynamical stability are discussed. An
application of the bifurcation method to the outer Solar System (Jupiter,
Saturn, Uranus, and Neptune) showed no sign of instability during the course of
24Gyr of integrations, in keeping with an expected Uranian dynamical lifetime
of 10^(18) years.Comment: 37 pages, 18 figures, accepted for publication in the Astrophysical
Journa
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