15 research outputs found
A new analysis of the GJ581 extrasolar planetary system
We have done a new analysis of the available observations for the GJ581
exoplanetary system. Today this system is controversial due to choices that can
be done in the orbital determination. The main ones are the ocurrence of
aliases and the additional bodies - the planets f and g - announced in Vogt et
al. 2010. Any dynamical study of exoplanets requires the good knowledge of the
orbital elements and the investigations involving the planet g are particularly
interesting, since this body would lie in the Habitable Zone (HZ) of the star
GJ581. This region,for this system, is very attractive of the dynamical point
of view due to several resonances of two and three bodies present there. In
this work, we investigate the conditions under which the planet g may exist. We
stress the fact that the planet g is intimately related with the orbital
elements of the planet d; more precisely, we conclude that it is not possible
to disconnect its existence from the determination of the eccentricity of the
planet d. Concerning the planet f, we have found one solution with period
days, but we are judicious about any affirmation concernig this
body because its signal is in the threshold of detection and the high period is
in a spectral region where the ocorruence of aliases is very common. Besides,
we outline some dynamical features of the habitable zone with the dynamical map
and point out the role played by some resonances laying there.Comment: 12 pages, 9 figure
Characterizing Multi-planet Systems with Classical Secular Theory
Classical secular theory can be a powerful tool to describe the qualitative
character of multi-planet systems and offer insight into their histories. The
eigenmodes of the secular behavior, rather than current orbital elements, can
help identify tidal effects, early planet-planet scattering, and dynamical
coupling among the planets, for systems in which mean-motion resonances do not
play a role. Although tidal damping can result in aligned major axes after all
but one eigenmode have damped away, such alignment may simply be fortuitous. An
example of this is 55 Cancri (orbital solution of Fischer et al., 2008) where
multiple eigenmodes remain undamped. Various solutions for 55 Cancri are
compared, showing differing dynamical groupings, with implications for the
coupling of eccentricities and for the partitioning of damping among the
planets. Solutions for orbits that include expectations of past tidal evolution
with observational data, must take into account which eigenmodes should be
damped, rather than expecting particular eccentricities to be near zero.
Classical secular theory is only accurate for low eccentricity values, but
comparison with other results suggests that it can yield useful qualitative
descriptions of behavior even for moderately large eccentricity values, and may
have advantages for revealing underlying physical processes and, as large
numbers of new systems are discovered, for triage to identify where more
comprehensive dynamical studies should have priority.Comment: Published in Celestial Mechanics and Dynamical Astronomy, 25 pages,
10 figure
On the dynamics of Extrasolar Planetary Systems under dissipation. Migration of planets
We study the dynamics of planetary systems with two planets moving in the
same plane, when frictional forces act on the two planets, in addition to the
gravitational forces. The model of the general three-body problem is used.
Different laws of friction are considered. The topology of the phase space is
essential in understanding the evolution of the system. The topology is
determined by the families of stable and unstable periodic orbits, both
symmetric and non symmetric. It is along the stable families, or close to them,
that the planets migrate when dissipative forces act. At the critical points
where the stability along the family changes, there is a bifurcation of a new
family of stable periodic orbits and the migration process changes route and
follows the new stable family up to large eccentricities or to a chaotic
region. We consider both resonant and non resonant planetary systems. The 2/1,
3/1 and 3/2 resonances are studied. The migration to larger or smaller
eccentricities depends on the particular law of friction. Also, in some cases
the semimajor axes increase and in other cases they are stabilized. For
particular laws of friction and for special values of the parameters of the
frictional forces, it is possible to have partially stationary solutions, where
the eccentricities and the semimajor axes are fixed.Comment: Accepted in Celestial Mechanics and Dynamical Astronom
The Relativistic Factor in the Orbital Dynamics of Point Masses
There is a growing population of relativistically relevant minor bodies in
the Solar System and a growing population of massive extrasolar planets with
orbits very close to the central star where relativistic effects should have
some signature. Our purpose is to review how general relativity affects the
orbital dynamics of the planetary systems and to define a suitable relativistic
correction for Solar System orbital studies when only point masses are
considered. Using relativistic formulae for the N body problem suited for a
planetary system given in the literature we present a series of numerical
orbital integrations designed to test the relevance of the effects due to the
general theory of relativity in the case of our Solar System. Comparison
between different algorithms for accounting for the relativistic corrections
are performed. Relativistic effects generated by the Sun or by the central star
are the most relevant ones and produce evident modifications in the secular
dynamics of the inner Solar System. The Kozai mechanism, for example, is
modified due to the relativistic effects on the argument of the perihelion.
Relativistic effects generated by planets instead are of very low relevance but
detectable in numerical simulations
Angular momentum exchange during secular migration of two-planet systems
We investigate the secular dynamics of two-planet coplanar systems evolving
under mutual gravitational interactions and dissipative forces. We consider two
mechanisms responsible for the planetary migration: star-planet (or
planet-satellite) tidal interactions and interactions of a planet with a
gaseous disc. We show that each migration mechanism is characterized by a
specific law of orbital angular momentum exchange. Calculating stationary
solutions of the conservative secular problem and taking into account the
orbital angular momentum leakage, we trace the evolutionary routes followed by
the planet pairs during the migration process. This procedure allows us to
recover the dynamical history of two-planet systems and constrain parameters of
the involved physical processes.Comment: 20 pages, 9 figures, accepted for publication in Celestial Mechanics
and Dynamical Astronomy (special issue on Exoplanets
Resonances of low orders in the planetary system of HD37124
The full set of published radial velocity data (52 measurements from Keck +
58 ones from ELODIE + 17 ones from CORALIE) for the star HD37124 is analysed.
Two families of dynamically stable high-eccentricity orbital solutions for the
planetary system are found. In the first one, the outer planets c and d are
trapped in the 2/1 mean-motion resonance. The second family of solutions
corresponds to the 5/2 mean-motion resonance between these planets. In both
families, the planets are locked in (or close to) an apsidal corotation
resonance. In the case of the 2/1 MMR, it is an asymmetric apsidal corotation
(with the difference between the longitudes of periastra ), whereas in the case of the 5/2 MMR it is a symmetric antialigned
one ().
It remains also possible that the two outer planets are not trapped in an
orbital resonance. Then their orbital eccentricities should be relatively small
(less than, say, 0.15) and the ratio of their orbital periods is unlikely to
exceed .Comment: 28 pages, 10 figures, 3 tables; Accepted to Celestial Mechanics and
Dynamical Astronom
A resonant-term-based model including a nascent disk, precession, and oblateness: application to GJ 876
Investigations of two resonant planets orbiting a star or two resonant
satellites orbiting a planet often rely on a few resonant and secular terms in
order to obtain a representative quantitative description of the system's
dynamical evolution. We present a semianalytic model which traces the orbital
evolution of any two resonant bodies in a first- through fourth-order
eccentricity or inclination-based resonance dominated by the resonant and
secular arguments of the user's choosing. By considering the variation of
libration width with different orbital parameters, we identify regions of phase
space which give rise to different resonant ''depths,'' and propose methods to
model libration profiles. We apply the model to the GJ 876 extrasolar planetary
system, quantify the relative importance of the relevant resonant and secular
contributions, and thereby assess the goodness of the common approximation of
representing the system by just the presumably dominant terms. We highlight the
danger in using ''order'' as the metric for accuracy in the orbital solution by
revealing the unnatural libration centers produced by the second-order, but not
first-order, solution, and by demonstrating that the true orbital solution lies
somewhere ''in-between'' the third- and fourth-order solutions. We also present
formulas used to incorporate perturbations from central-body oblateness and
precession, and a protoplanetary or protosatellite thin disk with gaps, into a
resonant system. We quantify these contributions to the GJ 876 system, and
thereby highlight the conditions which must exist for multi-planet exosystems
to be significantly influenced by such factors. We find that massive enough
disks may convert resonant libration into circulation; such disk-induced
signatures may provide constraints for future studies of exoplanet systems.Comment: 39 pages of body text, 21 figures, 5 tables, 1 appendix, accepted for
publication in Celestial Mechanics and Dynamical Astronom