26 research outputs found
Disk-planets interactions and the diversity of period ratios in Kepler's multi-planetary systems
The Kepler mission is dramatically increasing the number of planets known in
multi-planetary systems. Many adjacent planets have orbital period ratios near
resonant values, with a tendency to be larger than required for exact
first-order mean-motion resonances. This intriguing feature has been shown to
be a natural outcome of orbital circularization of resonant planetary pairs due
to star-planet tidal interactions. However, this feature holds in
multi-planetary systems with periods longer than ten days, for which tidal
circularization is unlikely to provide efficient divergent evolution of the
planets orbits. Gravitational interactions between planets and their parent
protoplanetary disk may instead provide efficient divergent evolution. For a
planet pair embedded in a disk, we show that interactions between a planet and
the wake of its companion can reverse convergent migration, and significantly
increase the period ratio from a near-resonant value. Divergent evolution due
to wake-planet interactions is particularly efficient when at least one of the
planets opens a partial gap around its orbit. This mechanism could help account
for the diversity of period ratios in Kepler's multiple systems comprising
super-Earth to sub-jovian planets with periods greater than about ten days.
Diversity is also expected for planet pairs massive enough to merge their gap.
The efficiency of wake-planet interactions is then much reduced, but convergent
migration may stall with a variety of period ratios depending on the density
structure in the common gap. This is illustrated for the Kepler-46 system, for
which we reproduce the period ratio of Kepler-46b and c.Comment: 15 pages, 11 figures, accepted for publication in Ap
Protoplanetary disks including radiative feedback from accreting planets
While recent observational progress is converging on the detection of compact
regions of thermal emission due to embedded protoplanets, further theoretical
predictions are needed to understand the response of a protoplanetary disk to
the planet formation radiative feedback. This is particularly important to make
predictions for the observability of circumplanetary regions. In this work we
use 2D hydrodynamical simulations to examine the evolution of a viscous
protoplanetary disk in which a luminous Jupiter-mass planet is embedded. We use
an energy equation which includes the radiative heating of the planet as an
additional mechanism for planet formation feedback. Several models are computed
for planet luminosities ranging from to Solar luminosities.
We find that the planet radiative feedback enhances the disk's accretion rate
at the planet's orbital radius, producing a hotter and more luminous
environement around the planet, independently of the prescription used to model
the disk's turbulent viscosity. We also estimate the thermal signature of the
planet feedback for our range of planet luminosities, finding that the emitted
spectrum of a purely active disk, without passive heating, is appreciably
modified in the infrared. We simulate the protoplanetary disk around HD 100546
where a planet companion is located at about 68 au from the star. Assuming the
planet mass is 5 Jupiter masses and its luminosity is , we find that the radiative feedback of the planet increases the
luminosity of its au circumplanetary disk from (without feedback) to , corresponding to an
emission of in band after radiative transfer
calculations, a value that is in good agreement with HD 100546b observations.Comment: 12 pages, 12 figures. Accepted for publication in The Astrophysical
Journa
Influence of the circumbinary disk gravity on planetesimal accumulation in the Kepler 16 system
Recent observations from NASA's Kepler mission detected the first planets in
circumbinary orbits. The question we try to answer is where these planets
formed in the circumbinary disk and how far inside they migrated to reach their
present location. We investigate the first and more delicate phase of planet
formation when planetesimals accumulate to form planetary embryos. We use the
hydrodynamical code FARGO to study the evolution of the disk and of a test
population of planetesimals embedded in it. With this hybrid
hydrodynamical--N--body code we can properly account for the gas drag force on
the planetesimals and for the gravitational force of the disk on them. The
numerical simulations show that the gravity of the eccentric disk on the
planetesimal swarm excites their eccentricities to values much larger than
those induced by the binary perturbations only within 10 AU from the stars.
Moreover, the disk gravity prevents a full alignment of the planetesimal
pericenters. Both these effects lead to large impact velocities, beyond the
critical value for erosion. Planetesimals accumulation in circumbinary disks
appears to be prevented close to the stellar pair by the gravitational
perturbations of the circumbinary disk. The observed planets possibly formed in
the outer regions of the disk and then migrated inside by tidal interaction
with the disk.Comment: Accepted for publication in A&
Forming Circumbinary Planets: N-body Simulations of Kepler-34
Observations of circumbinary planets orbiting very close to the central stars
have shown that planet formation may occur in a very hostile environment, where
the gravitational pull from the binary should be very strong on the primordial
protoplanetary disk. Elevated impact velocities and orbit crossings from
eccentricity oscillations are the primary contributors towards high energy,
potentially destructive collisions that inhibit the growth of aspiring planets.
In this work, we conduct high resolution, inter-particle gravity enabled N-body
simulations to investigate the feasibility of planetesimal growth in the
Kepler-34 system. We improve upon previous work by including planetesimal disk
self-gravity and an extensive collision model to accurately handle
inter-planetesimal interactions. We find that super-catastrophic erosion events
are the dominant mechanism up to and including the orbital radius of
Kepler-34(AB)b, making in-situ growth unlikely. It is more plausible that
Kepler-34(AB)b migrated from a region beyond 1.5 AU. Based on the conclusions
that we have made for Kepler-34 it seems likely that all of the currently known
circumbinary planets have also migrated significantly from their formation
location with the possible exception of Kepler-47(AB)c.Comment: 6 pages, 5 figures, accepted for publication in ApJ
A substitute for the singular Green kernel in the Newtonian potential of celestial bodies
The "point mass singularity" inherent in Newton's law for gravitation
represents a major difficulty in accurately determining the potential and
forces inside continuous bodies. Here we report a simple and efficient
analytical method to bypass the singular Green kernel 1/|r-r'| inside the
source without altering the nature of the interaction. We build an equivalent
kernel made up of a "cool kernel", which is fully regular (and contains the
long-range -GM/r asymptotic behavior), and the gradient of a "hyperkernel",
which is also regular. Compared to the initial kernel, these two components are
easily integrated over the source volume using standard numerical techniques.
The demonstration is presented for three-dimensional distributions in
cylindrical coordinates, which are well-suited to describing rotating bodies
(stars, discs, asteroids, etc.) as commonly found in the Universe. An example
of implementation is given. The case of axial symmetry is treated in detail,
and the accuracy is checked by considering an exact potential/surface density
pair corresponding to a flat circular disc. This framework provides new tools
to keep or even improve the physical realism of models and simulations of
self-gravitating systems, and represents, for some of them, a conclusive
alternative to softened gravity.Comment: Accepted for publication in A&A; 7 pages, color figure
Dust Traps in the Protoplanetary Disk MWC 758: Two Vortices Produced by Two Giant Planets?
Resolved ALMA and VLA observations indicate the existence of two dust traps in the protoplanetary disc MWC 758. By means of two-dimensional gas+dust hydrodynamical simulations post-processed with three-dimensional dust radiative transfer calculations, we show that the spirals in scattered light, the eccentric, asymmetric ring and the crescent-shaped structure in the (sub)millimetre can all be caused by two giant planets: a 1.5-Jupiter mass planet at 35 au (inside the spirals) and a 5-Jupiter mass planet at 140 au (outside the spirals). The outer planet forms a dust-trapping vortex at the inner edge of its gap (at âŒ85 au), and the continuum emission of this dust trap reproduces the ALMA and VLA observations well. The outer planet triggers several spiral arms that are similar to those observed in polarized scattered light. The inner planet also forms a vortex at the outer edge of its gap (at âŒ50 au), but it decays faster than the vortex induced by the outer planet, as a result of the discâs turbulent viscosity. The vortex decay can explain the eccentric inner ring seen with ALMA as well as the low signal and larger azimuthal spread of this dust trap in VLA observations. Finding the thermal and kinematic signatures of both giant planets could verify the proposed scenario
The potential of discs from a "mean Green function"
By using various properties of the complete elliptic integrals, we have
derived an alternative expression for the gravitational potential of axially
symmetric bodies, which is free of singular kernel in contrast with the
classical form. This is mainly a radial integral of the local surface density
weighted by a regular "mean Green function" which depends explicitly on the
body's vertical thickness. Rigorously, this result stands for a wide variety of
configurations, as soon as the density structure is vertically homogeneous.
Nevertheless, the sensitivity to vertical stratification | the Gaussian profile
has been considered | appears weak provided that the surface density is
conserved. For bodies with small aspect ratio (i.e. geometrically thin discs),
a first-order Taylor expansion furnishes an excellent approximation for this
mean Green function, the absolute error being of the fourth order in the aspect
ratio. This formula is therefore well suited to studying the structure of
self-gravitating discs and rings in the spirit of the "standard model of thin
discs" where the vertical structure is often ignored, but it remains accurate
for discs and tori of finite thickness. This approximation which perfectly
saves the properties of Newton's law everywhere (in particular at large
separations), is also very useful for dynamical studies where the body is just
a source of gravity acting on external test particles.Comment: Accepted for publication in MNRAS, 11 page
The beta Pictoris system: Setting constraints on the planet and the disk structures at mid-IR wavelengths with NEAR
[abridged] We analyzed mid-infrared high-contrast coronagraphic images of the
beta Pictoris system, taking advantage of the NEAR experiment using the
VLT/VISIR instrument. The goal of our analysis is to investigate both the
detection of the planet beta Pictoris b and of the disk features at mid-IR
wavelengths. In addition, by combining several epochs of observation, we expect
to constrain the position of the known clumps and improve our knowledge on the
dynamics of the disk. To evaluate the planet b flux contribution, we extracted
the photometry and compared it to the flux published in the literature. In
addition, we used previous data from T-ReCS and VISIR, to study the evolution
of the position of the southwest clump that was initially observed in the
planetary disk back in 2003. While we did not detect the planet b, we were able
to put constraints on the presence of circumplanetary material, ruling out the
equivalent of a Saturn-like planetary ring around the planet. The disk presents
several noticeable structures, including the known southwest clump. Using a
16-year baseline, sampled with five epochs of observations, we were able to
examine the evolution of the clump: the clump orbits in a Keplerian motion with
an sma of 56.1+-0.4 au. In addition to the known clump, the images clearly show
the presence of a second clump on the northeast side of the disk and fainter
and closer structures that are yet to be confirmed. We found correlations
between the CO clumps detected with ALMA and the mid-IR images. If the
circumplanetary material were located at the Roche radius, the maximum amount
of dust determined from the flux upper limit around beta Pictoris b would
correspond to the mass of an asteroid of 5 km in diameter. Finally, the
Keplerian motion of the southwestern clump is possibly indicative of a
yet-to-be-detected planet or signals the presence of a vortex.Comment: Accepted in Astronomy and Astrophysic