9,530 research outputs found
A semi-empirical stability criterion for real planetary systems
We test a crossing orbit stability criterion for eccentric planetary systems,
based on Wisdom's criterion of first order mean motion resonance overlap
(Wisdom, 1980).
We show that this criterion fits the stability regions in real exoplanet
systems quite well. In addition, we show that elliptical orbits can remain
stable even for regions where the apocenter distance of the inner orbit is
larger than the pericenter distance of the outer orbit, as long as the initial
orbits are aligned.
The analytical expressions provided here can be used to put rapid constraints
on the stability zones of multi-planetary systems. As a byproduct of this
research, we further show that the amplitude variations of the eccentricity can
be used as a fast-computing stability indicator.Comment: 11 pages, 11 figures. MNRAS accepte
Stellar wobble caused by a nearby binary system: eccentric and inclined orbits
Most extrasolar planets currently known were discovered by means of an
indirect method that measures the stellar wobble caused by the planet. We
previously studied a triple system composed of a star and a nearby binary on
circular coplanar orbits. We showed that although the effect of the binary on
the star can be differentiated from the stellar wobble caused by a planet,
because of observational limitations the two effects may often remain
indistinguishable. Here, we develop a model that applies to eccentric and
inclined orbits. We show that the binary's effect is more likely to be mistaken
by planet(s) in the case of coplanar motion observed equator-on. Moreover, when
the orbits are eccentric, the magnitude of the binary's effect may be larger
than in the circular case. Additionally, an eccentric binary can mimic two
planets with orbital periods in the ratio 2/1. However, when the star's orbit
around the binary's center of mass has a high eccentricity and a reasonably
well-constrained period, it should be easier to distinguish the binary's effect
from a planet.Comment: 10 pages, 9 figures, 2 table
Spin-orbit resonances and rotation of coorbital bodies in quasi-circular orbits
The rotation of asymmetric bodies in eccentric Keplerian orbits can be
chaotic when there is some overlap of spin-orbit resonances. Here we show that
the rotation of two coorbital bodies (two planets orbiting a star or two
satellites of a planet) can also be chaotic even for quasi-circular orbits
around the central body. When dissipation is present, the rotation period of a
body on a nearly circular orbit is believed to always end synchronous with the
orbital period. Here we demonstrate that for coorbital bodies in quasi-circular
orbits, stable non-synchronous rotation is possible for a wide range of mass
ratios and body shapes. We further show that the rotation becomes chaotic when
the natural rotational libration frequency, due to the axial asymmetry, is of
the same order of magnitude as the orbital libration frequency
On the equilibrium rotation of Earth-like extra-solar planets
The equilibrium rotation of tidally evolved "Earth-like" extra-solar planets
is often assumed to be synchronous with their orbital mean motion. The same
assumption persisted for Mercury and Venus until radar observations revealed
their true spin rates. As many of these planets follow eccentric orbits and are
believed to host dense atmospheres, we expect the equilibrium rotation to
differ from the synchronous motion. Here we provide a general description of
the allowed final equilibrium rotation states of these planets, and apply this
to already discovered cases in which the mass is lower than twelve
Earth-masses. At low obliquity and moderate eccentricity, it is shown that
there are at most four distinct equilibrium possibilities, one of which can be
retrograde. Because most presently known "Earth-like" planets present eccentric
orbits, their equilibrium rotation is unlikely to be synchronous.Comment: 4 pages, 2 figures. accepted for publication in Astronomy and
Astrophysics. to be published in Astronomy and Astrophysic
Dynamical stability analysis of the HD202206 system and constraints to the planetary orbits
Long-term precise Doppler measurements with the CORALIE spectrograph revealed
the presence of two massive companions to the solar-type star HD202206.
Although the three-body fit of the system is unstable, it was shown that a 5:1
mean motion resonance exists close to the best fit, where the system is stable.
We present here an extensive dynamical study of the HD202206 system aiming at
constraining the inclinations of the two known companions, from which we derive
possible ranges of value for the companion masses.
We study the long term stability of the system in a small neighborhood of the
best fit using Laskar's frequency map analysis. We also introduce a numerical
method based on frequency analysis to determine the center of libration mode
inside a mean motion resonance.
We find that acceptable coplanar configurations are limited to inclinations
to the line of sight between 30 and 90 degrees. This limits the masses of both
companions to roughly twice the minimum. Non coplanar configurations are
possible for a wide range of mutual inclinations from 0 to 90 degrees, although
configurations seem to be favored. We also confirm the
5:1 mean motion resonance to be most likely. In the coplanar edge-on case, we
provide a very good stable solution in the resonance, whose does not
differ significantly from the best fit. Using our method to determine the
center of libration, we further refine this solution to obtain an orbit with a
very low amplitude of libration, as we expect dissipative effects to have
dampened the libration.Comment: 14 pages, 18 figure
Simulation of gain stability of THGEM gas-avalanche particle detectors
Charging-up processes affecting gain stability in Thick Gas Electron
Multipliers (THGEM) were studied with a dedicated simulation toolkit.
Integrated with Garfield++, it provides an effective platform for systematic
phenomenological studies of charging-up processes in MPGD detectors. We
describe the simulation tool and the fine-tuning of the step-size required for
the algorithm convergence, in relation to physical parameters. Simulation
results of gain stability over time in THGEM detectors are presented, exploring
the role of electrode-thickness and applied voltage on its evolution. The
results show that the total amount of irradiated charge through electrode's
hole needed for reaching gain stabilization is in the range of tens to hundreds
of pC, depending on the detector geometry and operational voltage. These
results are in agreement with experimental observations presented previously
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