895 research outputs found
Chaotic diffusion of the Vesta family induced by close encounters with massive asteroids
We numerically estimate the semi-major axis chaotic diffusion of the Vesta
family asteroids induced by close encounters with 11 massive main belt
asteroids : (1) Ceres, (2) Pallas, (3) Juno, (4) Vesta, (7) Iris, (10) Hygiea,
(15) Eunomia, (19) Fortuna, (324) Bamberga, (532) Herculina, (704) Interamnia.
We find that most of the diffusion is due to Ceres and Vesta. By extrapolating
our results, we are able to constrain the global effect of close encounters
with all the main belt asteroids. A comparison of this drift estimate with the
one expected for the Yarkovsky effect shows that for asteroids whose diameter
is larger than about 40 km, close encounters dominate the Yarkovsky effect.
Overall, our findings confirm the standard scenario for the history of the
Vesta family.Comment: 9 pages, 9 figures, 1 Table, submitte
Tidal dissipation and the formation of Kepler near-resonant planets
Multi-planetary systems detected by the Kepler mission present an excess of
planets close to first-order mean-motion resonances (2:1 and 3:2) but with a
period ratio slightly higher than the resonant value. Several mechanisms have
been proposed to explain this observation. Here we provide some clues that
these near-resonant systems were initially in resonance and reached their
current configuration through tidal dissipation. The argument that has been
opposed to this scenario is that it only applies to the close-in systems and
not to the farthest ones for which the tidal effect is too weak. Using the
catalog of KOI of the Kepler mission, we show that the distributions of period
ratio among the most close-in planetary systems and the farthest ones differ
significantly. This distance dependent repartition is a strong argument in
favor of the tidal dissipation scenario.Comment: 3 pages, 3 figures, submitted for publicatio
Resonance breaking due to dissipation in planar planetary systems
We study the evolution of two planets around a star, in mean-motion resonance
and undergoing tidal effect. We derive an integrable analytical model of
mean-motion resonances of any order which reproduce the main features of the
resonant dynamics. Using this simplified model, we obtain a criterion showing
that depending on the balance of the tidal dissipation in both planets, their
final period ratio may stay at the resonant value, increase above, or decrease
below the resonant value.
Applying this criterion to the two inner planets orbiting GJ163, we deduce
that the current period ratio (2.97) could be the outcome of dissipation in the
3:1 MMR provided that the innermost planet is gaseous (slow dissipation) while
the second one is rocky (faster dissipation). We perform N-body simulations
with tidal dissipation to confirm the results of our analytical model.
We also apply our criterion on GJ581b, c (5:2 MMR) and reproduce the current
period ratio (2.4) if the inner planet is gaseous and the outer is rocky (as
for GJ163).
Finally, we apply our model to the Kepler mission's statistics. We show that
the excess of planets pairs close to first order MMR but in external
circulation, i.e., with period ratios P_out/P_in > (p+1)/p for the resonance
(p+1):p, can be reproduced by tidal dissipation in the inner planet. There is
no need for any other dissipative mechanism, provided that these systems left
the resonance with non-negligible eccentricities.Comment: 14 pages, 9 figures, submitted for publicatio
Analytical determination of orbital elements using Fourier analysis. I. The radial velocity case
We describe an analytical method for computing the orbital parameters of a
planet from the periodogram of a radial velocity signal. The method is very
efficient and provides a good approximation of the orbital parameters. The
accuracy is mainly limited by the accuracy of the computation of the Fourier
decomposition of the signal which is sensitive to sampling and noise. Our
method is complementary with more accurate (and more expensive in computer
time) numerical algorithms (e.g. Levenberg-Marquardt, Markov chain Monte Carlo,
genetic algorithms). Indeed, the analytical approximation can be used as an
initial condition to accelerate the convergence of these numerical methods. Our
method can be applied iteratively to search for multiple planets in the same
system.Comment: accepted to A&
Analytical determination of orbital elements using Fourier analysis. II. Gaia astrometry and its combination with radial velocities
The ESA global astrometry space mission Gaia has been monitoring the position
of a billion stars since 2014. The analysis of such a massive dataset is
challenging in terms of the data processing involved. In particular, the blind
detection and characterization of single or multiple companions to stars
(planets, brown dwarfs, or stars) using Gaia astrometry requires highly
efficient algorithms. In this article, we present a set of analytical methods
to detect and characterize companions in scanning space astrometric time series
as well as via a combination of astrometric and radial velocity time series. We
propose a general linear periodogram framework and we derive analytical
formulas for the false alarm probability (FAP) of periodogram peaks. Once a
significant peak has been identified, we provide analytical estimates of all
the orbital elements of the companion based on the Fourier decomposition of the
signal. The periodogram, FAP, and orbital elements estimates can be computed
for the astrometric and radial velocity time series separately or in tandem.
These methods are complementary with more accurate and more computationally
intensive numerical algorithms (e.g., least-squares minimization, Markov chain
Monte Carlo, genetic algorithms). In particular, our analytical approximations
can be used as an initial condition to accelerate the convergence of numerical
algorithms. Our formalism has been partially implemented in the Gaia exoplanet
pipeline for the third Gaia data release. Since the Gaia astrometric time
series are not yet publicly available, we illustrate our methods on the basis
of Hipparcos data, together with on-ground CORALIE radial velocities, for three
targets known to host a companion: HD 223636 (HIP 117622), HD 17289 (HIP
12726), and HD 3277 (HIP 2790).Comment: Accepted in A&
Planets in Mean-Motion Resonances and the System Around HD45364
In some planetary systems, the orbital periods of two of its members present
a commensurability, usually known by mean-motion resonance. These resonances
greatly enhance the mutual gravitational influence of the planets. As a
consequence, these systems present uncommon behaviors, and their motions need
to be studied with specific methods. Some features are unique and allow us a
better understanding and characterization of these systems. Moreover,
mean-motion resonances are a result of an early migration of the orbits in an
accretion disk, so it is possible to derive constraints on their formation.
Here we review the dynamics of a pair of resonant planets and explain how their
orbits evolve in time. We apply our results to the HD 45365 planetary system.Comment: invited review, 17 pages, 6 figure
DREAM II. The spin-orbit angle distribution of close-in exoplanets under the lens of tides
The spin-orbit angle, or obliquity, is a powerful observational marker that
allows us to access the dynamical history of exoplanetary systems. Here, we
have examined the distribution of spin-orbit angles for close-in exoplanets and
put it in a statistical context of tidal interactions between planets and their
stars. We confirm the observed trends between the obliquity and physical
quantities directly connected to tides, namely the stellar effective
temperature, the planet-to-star mass ratio, and the scaled orbital distance. We
further devised a tidal efficiency factor combining critical parameters that
control the strength of tidal effects and used it to corroborate the strong
link between the spin-orbit angle distribution and tidal interactions. In
particular, we developed a readily usable formula to estimate the probability
that a system is misaligned, which will prove useful in global population
studies. By building a robust statistical framework, we reconstructed the
distribution of the three-dimensional spin-orbit angles, allowing for a sample
of nearly 200 true obliquities to be analyzed for the first time. This
realistic distribution maintains the sky-projected trends, and additionally
hints toward a striking pileup of truly aligned systems. The comparison between
the full population and a pristine subsample unaffected by tidal interactions
suggests that perpendicular architectures are resilient toward tidal
realignment, providing evidence that orbital misalignments are sculpted by
disruptive dynamical processes that preferentially lead to polar orbits. On the
other hand, star-planet interactions seem to efficiently realign or quench the
formation of any tilted configuration other than for polar orbits, and in
particular for antialigned orbits.Comment: Accepted in A&
Dissipation in planar resonant planetary systems
Close-in planetary systems detected by the Kepler mission present an excess
of periods ratio that are just slightly larger than some low order resonant
values. This feature occurs naturally when resonant couples undergo dissipation
that damps the eccentricities. However, the resonant angles appear to librate
at the end of the migration process, which is often believed to be an evidence
that the systems remain in resonance.
Here we provide an analytical model for the dissipation in resonant planetary
systems valid for low eccentricities. We confirm that dissipation accounts for
an excess of pairs that lie just aside from the nominal periods ratios, as
observed by the Kepler mission. In addition, by a global analysis of the phase
space of the problem, we demonstrate that these final pairs are non-resonant.
Indeed, the separatrices that exist in the resonant systems disappear with the
dissipation, and remains only a circulation of the orbits around a single
elliptical fixed point. Furthermore, the apparent libration of the resonant
angles can be explained using the classical secular averaging method. We show
that this artifact is only due to the severe damping of the amplitudes of the
eigenmodes in the secular motion.Comment: 18 pages, 20 figures, accepted to A&
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