5,210 research outputs found
Predicting the Configuration of Planetary System: KOI-152 Observed by Kepler
The recent Kepler discovery of KOI-152 reveals a system of three hot
super-Earth candidates that are in or near a 4:2:1 mean motion resonance. It is
unlikely that they formed in situ, the planets probably underwent orbital
migration during the formation and evolution process. The small semimajor axes
of the three planets suggest that migration stopped at the inner edge of the
primordial gas disk. In this paper we focus on the influence of migration
halting mechanisms, including migration "dead zones", and inner truncation by
the stellar magnetic field. We show that the stellar accretion rate, stellar
magnetic field and the speed of migration in the proto-planetary disk are the
main factors affecting the final configuration of KOI-152. Our simulations
suggest that three planets may be around a star with low star accretion rate or
with high magnetic field. On the other hand, slow type I migration, which
decreases to one tenth of the linear analysis results, favors forming the
configuration of KOI-152. Under such formation scenario, the planets in the
system are not massive enough to open gaps in the gas disk. The upper limit of
the planetary masses are estimated to be about , and ,
respectively. Our results are also indicative of the near Laplacian
configurations that are quite common in planetary systems.Comment: 11 pages, 8 figures, accepted for publication in Ap
Transit Timing Variation of Near-Resonance Planetary Pairs: Confirmation of Twelve Multiple Planet Systems
We extract Transit Timing Variation (TTV) signals for 12 pairs of transiting
planet candidates that are near first-order Mean Motion Resonances (MMR), using
publicly available Kepler light curves (Q0-Q14). These pairs show significant
sinusoidal TTVs with theoretically predicted periods, which demonstrate these
planet candidates are orbiting and interacting in the same system. Although
individual masses cannot be accurately extracted based only on TTVs because of
the well known degeneracy between mass and eccentricity, TTV phases and
amplitudes can still place upper limits on the masses of the candidates,
confirming their planetary nature. Furthermore, the mass ratios of these planet
pairs can be relatively tight constrained using these TTVs. The planetary pair
in Kepler-82 (KOI-880) seems to have a particularly high mass ratio and density
ratio, which might indicate very different internal compositions of these two
planets. Some of these newly confirmed planets are also near MMR with other
candidates in the system, forming unique resonance chains, e.g., Kepler-80
(KOI-500).Comment: Accepted to ApJS. 17 pages, 11 figures, 3 tables. KOI 869 is replaced
with KOI 2038. Kepler numbers are assigne
A Hybrid Mechanism Forming a 2:1 Librating-Circulating Resonant Configuration in the Planetary System
A diversity of resonance configurations may be formed under different
migration of two giant planets. And the researchers show that the HD 128311 and
HD 73526 planetary systems are involved in a 2:1 mean motion resonance but not
in apsidal corotation, because one of the resonance argument circulates over
the dynamical evolution. In this paper, we investigate potential mechanisms to
form the 2:1 librating-circulating resonance configuration.
In the late stage of planetary formation, scattering or colliding among
planetesimals and planetary embryos can frequently occur. Hence, in our model,
we consider a planetary configuration of two giants together with few
terrestrial planets. We find that both colliding or scattering events at very
early stage of dynamical evolution can influence the configurations trapped
into resonance. A planet-planet scattering of a moderate terrestrial planet, or
multiple scattering of smaller planets in a crowded planetary system can change
the resonant configuration. In addition, collision or merging can alter the
masses and location of the giant planets, which also play an important role in
shaping the resonant configuration during the dynamical evolution. In this
sense, the librating-circulating resonance configuration is more likely to form
by a hybrid mechanism of scattering and collision.Comment: 8 pages, 5 figures, 2 Tables, accepted for publication in MNRA
Secular Evolution of HD 12661: A System Caught at an Unlikely Time
The eccentricity evolution of multiple planet systems can provide valuable
constraints on planet formation models. Unfortunately, the inevitable
uncertainties in the current orbital elements can lead to significant
ambiguities in the nature of the secular evolution. Integrating any single set
of orbital elements inadequately describes the full range of secular evolutions
consistent with current observations. Thus, we combine radial velocity
observations of HD 12661 with Markov Chain Monte Carlo sampling to generate
ensembles of initial conditions for direct n-body integrations. We find that
any mean motion resonances are quite weak and do not significantly impact the
secular evolution, and that current observations indicate circulation or large
amplitude libration of the periapses. The eccentricity of the outer planet
undergoes large oscillations for nearly all of the allowed two-planet orbital
solutions. This type of secular evolution would arise if planet c had been
impulsively perturbed, perhaps due to strong scattering of an additional planet
that was subsequently accreted onto the star. Finally, we note that the secular
evolution implied by the current orbital configuration implies that planet c
spends ~96% of the time following an orbit more eccentric than that presently
observed. Either this system is being observed during a relatively rare state,
or additional planets are affecting the observed radial velocities and/or the
system's secular eccentricity evolution.Comment: 5 pages, 2 figures, 1 table, accepted for publication in ApJ
Dynamical Ne K Edge and Line Variations in the X-Ray Spectrum of the Ultra-compact Binary 4U 0614+091
We observed the ultra-compact binary candidate 4U 0614+091 for a total of 200
ksec with the high-energy transmission gratings onboard the \chandra X-ray
Observatory. The source is found at various intensity levels with spectral
variations present. X-ray luminosities vary between 2.0 \ergsec
and 3.5 \ergsec. Continuum variations are present at all times
and spectra can be well fit with a powerlaw component, a high kT blackbody
component, and a broad line component near oxygen. The spectra require
adjustments to the Ne K edge and in some occasions also to the Mg K edge. The
Ne K edge appears variable in terms of optical depths and morphology. The edge
reveals average blue- and red-shifted values implying Doppler velocities of the
order of 3500 \kms. The data show that Ne K exhibits excess column densities of
up to several 10 cm. The variability proves that the excess is
intrinsic to the source. The correponding disk velocities also imply an outer
disk radius of the order of cm consistent with an ultra-compact binary
nature. We also detect a prominent soft emission line complex near the \oviii
L position which appears extremely broad and relativistic effects from
near the innermost disk have to be included. Gravitationally broadened line
fits also provide nearly edge-on angles of inclination between 86 and
89. The emissions appear consistent with an ionized disk with
ionization parameters of the order of 10 at radii of a few 10 cm. The
line wavelengths with respect to \oviiia\ are found variably blue-shifted
indicating more complex inner disk dynamics.Comment: 24 pages, 8 figures, submitted to the Astrophyscial Main Journa
Secondary resonances of co-orbital motions
The size distribution of the stability region around the Lagrangian point L4
is investigated in the elliptic restricted three-body problem as the function
of the mass parameter and the orbital eccentricity of the primaries. It is
shown that there are minimum zones in the size distribution of the stability
regions, and these zones are connected with secondary resonances between the
frequencies of librational motions around L4. The results can be applied to
hypothetical Trojan planets for predicting values of the mass parameter and the
eccentricity for which such objects can be expected or their existence is less
probable.Comment: 9 pages, 7 figures, accepted for publication in MNRA
On the Eccentricity Distribution of Short-Period Single-Planet Systems
We apply standard Markov chain Monte Carlo (MCMC) analysis techniques for 50
short- period, single-planet systems discovered with radial velocity technique.
We develop a new method for accessing the significance of a non-zero orbital
eccentricity, namely {\Gamma} analysis, which combines frequentist bootstrap
approach with Bayesian analysis of each simulated data set. We find the
eccentricity estimations from {\Gamma} analysis are generally consistent with
results from both standard MCMC analysis and previous references. The {\Gamma}
method is particular useful for assessing the significance of small
eccentricities. Our results suggest that the current sample size is
insufficient to draw robust conclusions about the roles of tidal interaction
and perturbations in shaping the eccentricity distribution of short-period
single-planet systems. We use a Bayesian population analysis to show that a
mixture of analytical distributions is a good approximation of the underlying
eccentricity distribution. For short-period planets, we find the most probable
values of parameters in the analytical functions given the observed
eccentricities. These analytical functions can be used in theoretical
investigations or as priors for the eccentricity distribution when analyzing
short-period planets. As the measurement precision improves and sample size
increases, the method can be applied to more complex parametrizations for the
underlying distribution of eccentricity for extrasolar planetary systems.Comment: 13 pages, 11 figures, 4 tables, accepted by MNRA
LinkMind: Link Optimization in Swarming Mobile Sensor Networks
A swarming mobile sensor network is comprised of a swarm of wirelessly connected mobile robots equipped with various sensors. Such a network can be applied in an uncertain environment for services such as cooperative navigation and exploration, object identification and information gathering. One of the most advantageous properties of the swarming wireless sensor network is that mobile nodes can work cooperatively to organize an ad-hoc network and optimize the network link capacity to maximize the transmission of gathered data from a source to a target. This paper describes a new method of link optimization of swarming mobile sensor networks. The new method is based on combination of the artificial potential force guaranteeing connectivities of the mobile sensor nodes and the max-flow min-cut theorem of graph theory ensuring optimization of the network link capacity. The developed algorithm is demonstrated and evaluated in simulation
Tidal evolution of exo-planetary systems: WASP-50, GJ 1214 and CoRoT-7
We perform numerical simulations to investigate tidal evolution of two
single-planet systems, that is, WASP-50 and GJ 1214 and a two-planet system
CoRoT-7. The results of orbital evolution show that tidal decay and
circularization may play a significant role in shaping their final orbits,
which is related to the initial orbital data in the simulations. For GJ 1214
system, different cases of initial eccentricity are also considered as only an
upper limit of its eccentricity (0.27) is shown, and the outcome suggests a
possible maximum initial eccentricity (0.4) in the adopted dynamical model.
Moreover, additional runs with alternative values of dissipation factor
are carried out to explore tidal evolution for GJ 1214b, and these
results further indicate that the real of GJ 1214b may be much
larger than its typical value, which may reasonably suggest that GJ 1214b bears
a present-day larger eccentricity, undergoing tidal circularization at a slow
rate. For the CoRoT-7 system, tidal forces make two planets migrating towards
their host star as well as producing tidal circularization, and in this process
tidal effects and mutual gravitational interactions are coupled with each
other. Various scenarios of the initial eccentricity of the outer planet have
also been done to investigate final planetary configuration. Tidal decay
arising from stellar tides may still work for each system as the eccentricity
decreases to zero, and this is in association with the remaining lifetime of
each planet used to predict its future.Comment: 9 pages, 12 figures, accepted for publication in "SCIENCE CHINA
Physics,Mechanics & Astronomy
Equilibria in the secular, non-coplanar two-planet problem
We investigate the secular dynamics of a planetary system composed of the
parent star and two massive planets in mutually inclined orbits. The dynamics
are investigated in wide ranges of semi-major axes ratios (0.1-0.667), and
planetary masses ratios (0.25-2) as well as in the whole permitted ranges of
the energy and total angular momentum. The secular model is constructed by
semi-analytic averaging of the three-body system. We focus on equilibria of the
secular Hamiltonian (periodic solutions of the full system), and we analyze
their stability. We attempt to classify families of these solutions in terms of
the angular momentum integral. We identified new equilibria, yet unknown in the
literature. Our results are general and may be applied to a wide class of
three-body systems, including configurations with a star and brown dwarfs and
sub-stellar objects. We also describe some technical aspects of the
semi-numerical averaging. The HD 12661 planetary system is investigated as an
example configuration.Comment: 18 pages, 17 figures, accepted to Monthly Notices of the Royal
Astronomical Societ
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