5,191 research outputs found
HD60532, a planetary system in a 3:1 mean motion resonance
In a recent paper it was reported a planetary system around the star HD60532,
composed by two giant planets in a possible 3:1 mean motion resonance, that
should be confirmed within the next decade. Here we show that the analysis of
the global dynamics of the system allows to confirm this resonance. The present
best fit to data already corresponds to this resonant configuration and the
system is stable for at least 5Gry. The 3:1 resonance is so robust that
stability is still possible for a wide variety of orbital parameters around the
best fit solution and also if the inclination of the system orbital plane with
respect to the plane of the sky is as small as 15 deg. Moreover, if the
inclination is taken as a free parameter in the adjustment to the observations,
we find an inclination ~ 20 deg, which corresponds to M_b =3.1 M_Jup and M_c =
7.4 M_Jup for the planetary companions.Comment: 4 Pages, 4 Figures, accepted by A&
La2010: A new orbital solution for the long term motion of the Earth
We present here a new solution for the astronomical computation of the
orbital motion of the Earth spanning from 0 to -250 Myr. The main improvement
with respect to the previous numerical solution La2004 (Laskar et al. 2004) is
an improved adjustment of the parameters and initial conditions through a fit
over 1 Myr to a special version of the high accurate numerical ephemeris
INPOP08 (Fienga et al. 2009). The precession equations have also been entirely
revised and are no longer averaged over the orbital motion of the Earth and
Moon. This new orbital solution is now valid over more than 50 Myr in the past
or in the future with proper phases of the eccentricity variations. Due to
chaotic behavior, the precision of the solution decreases rapidly beyond this
time span, and we discuss the behavior of various solutions beyond 50 Myr. For
paleoclimate calibrations, we provide several different solutions that are all
compatible with the most precise planetary ephemeris. We have thus reached the
time where geological data are now required to discriminate among planetary
orbital solutions beyond 50 Myr.Comment: 17 pages, 14 figure
Statistics and Universality in Simplified Models of Planetary Formation
In this paper, we modify Laskar's simplified model of planetary evolution and
accretion [J. Laskar, Phys. Rev. Lett, vol 84, p 3240 (2000)] to account for
the full conservation of the total angular momentum of the system, and extend
it to incorporate an accretion probability that depends on the mass and
relative velocity of the colliding particles. We present statistical results
for the mass and eccentricity of the planets formed, in terms of their
semi-major axes, for a large number of realisations of different versions of
the model. In particular, we find that by combining the mass-dependent
accretion probability and the velocity-selection mechanism, the planets formed
display a systematic occurrence at specific locations. By introducing properly
scaled variables, our results are universal with respect to the total angular
momentum of the system, the mass of the planetesimal disc, and the mass of the
central star.Comment: 13 pages, 21 figures, some in colour. Accepted in MNRA
Frequency map analysis and quasiperiodic decompositions
Frequency Map Analysis is a numerical method based on refined Fourier
techniques which provides a clear representation of the global dynamics of many
multi-dimensional systems, and which is particularly adapted for systems of
3-degrees of freedom and more. This method relies heavily on the possibility of
making accurate quasiperiodic approximations of of quasiperiodic signal given
in a numerical way. In the present paper, we will describe the basis of the
frequency analysis method, focussing on the quasi periodic approximation
techniques. Application of these methods for the study of the global dynamics
and chaotic diffusion of Hamiltonian systems and symplectic maps in different
domains can be found in (Laskar, 1988, 1990, Laskar and Robutel, 1993, Robutel
and Laskar, 2001, Nesvorny and Ferraz-Mello, 1997) for solar system dynamics,
and in (Papaphilippou and Laskar, 1996, 1998, Laskar, 2000, Wachlin and
Ferraz-Mello, 1998, Valluri and Merritt, 1998, Merritt and Valluri, 1999) for
galactic dynamics. The method has been particularly successful for its
application in particle accelerators (Dumas and Laskar, 1993, Laskar and Robin,
1996, Robin et al., 2000, Comunian et al., 2001, Papaphilippou and Zimmermann,
2002, Steier et al., 2002), and was also used for the understanding of atomic
physics (Milczewski et al., 1997), or more general dynamical system issues
(Laskar et al., 1992, Laskar, 1993, 1999, Chandre et al., 2001).Comment: 13 march 200
Andoyer construction for Hill and Delaunay variables
Andoyer variables are well known for the study of rotational dynamics. These
variables were derived by Andoyer through a procedure that can be also used to
obtain the Hill variables of the Kepler problem. Andoyer construction can also
forecast the Delaunay variables which canonicity is then obtained without the
use of a generating function.Comment: 8 pages, 2 figures, revised versio
Stability analysis of the Martian obliquity during the Noachian era
We performed numerical simulations of the obliquity evolution of Mars during
the Noachian era, at which time the giant planets were on drastically different
orbits than today. For the preferred primordial configuration of the planets we
find that there are two large zones where the Martian obliquity is stable and
oscillates with an amplitude lower than 20. These zones occur at
obliquities below 30 and above 60; intermediate values show
either resonant or chaotic behaviour depending on the primordial orbits of the
terrestrial planets
Imprecision of Central Bank Announcements and Credibility
We consider a model where the central bank faces a credibility problem in its announcements, but also cares about its credibility and, therefore, wants to make truthful announcements. We show that, although the central bank would be able to perfectly transmit its information to the private sector through precise announcements, the central bank may nonetheless prefer to make imprecise announcements. This choice of the central bank would be suboptimal from the point of view of society. However, if the central bank gives enough weight to making truthful announcements, this suboptimality disappears, because the central bank would then prefer precise announcements to imprecise announcements.central bank transparency; central bank announcements; imprecise announcements; credibility
Determination of the threshold of the break-up of invariant tori in a class of three frequency Hamiltonian systems
We consider a class of Hamiltonians with three degrees of freedom that can be
mapped into quasi-periodically driven pendulums. The purpose of this paper is
to determine the threshold of the break-up of invariant tori with a specific
frequency vector. We apply two techniques: the frequency map analysis and
renormalization-group methods. The renormalization transformation acting on a
Hamiltonian is a canonical change of coordinates which is a combination of a
partial elimination of the irrelevant modes of the Hamiltonian and a rescaling
of phase space around the considered torus. We give numerical evidence that the
critical coupling at which the renormalization transformation starts to diverge
is the same as the value given by the frequency map analysis for the break-up
of invariant tori. Furthermore, we obtain by these methods numerical values of
the threshold of the break-up of the last invariant torus.Comment: 18 pages, 4 figure
Central Bank Transparency and Shocks
According to the literature, in an expectations-augmented Phillips curve model, opacity is always preferred to transparency on central bank forecasts. By modelling the private sector's behavior explicitly, we show that transparency reduces the shocks. Consequently, transparency can be preferred.central bank, transparency, Phillips curve, shocks.
- …