52 research outputs found
Probing the Protosolar Disk Using Dust Filtering at Gaps in the Early Solar System
Jupiter and Saturn formed early, before the gas disk dispersed. The presence
of gap-opening planets affects the dynamics of the gas and embedded solids and
halts the inward drift of grains above a certain size. A drift barrier can
explain the absence of calcium aluminium rich inclusions (CAIs) in chondrites
originating from parent bodies that accreted in the inner solar system.
Employing an interdisciplinary approach, we use a -X-Ray-fluorescence
scanner to search for large CAIs and a scanning electron microscope to search
for small CAIs in the ordinary chondrite NWA 5697. We carry out long-term,
two-dimensional simulations including gas, dust, and planets to characterize
the transport of grains within the viscous -disk framework exploring
the scenarios of a stand-alone Jupiter, Jupiter and Saturn \textit{in situ}, or
Jupiter and Saturn in a 3:2 resonance. In each case, we find a critical grain
size above which drift is halted as a function of the physical conditions in
the disk. From the laboratory search we find four CAIs with a largest size of
200m. \Combining models and data, we provide an estimate for
the upper limit of the -viscosity and the surface density at the
location of Jupiter, using reasonable assumptions about the stellar accretion
rate during inward transport of CAIs, and assuming angular momentum transport
to happen exclusively through viscous effects. Moreover, we find that the
compound gap structure in the presence of Saturn in a 3:2 resonance favors
inward transport of grains larger than CAIs currently detected in ordinary
chondrites.Comment: 16 pages, 10 figures, updated to match published version in
Astrophysical Journa
Low-mass planet migration in three-dimensional wind-driven inviscid discs: a negative corotation torque
We present simulations of low-mass planetâdisc interactions in inviscid three-dimensional discs. We show that a wind-driven laminar accretion flow through the surface layers of the disc does not significantly modify the migration torque experienced by embedded planets. More importantly, we find that 3D effects lead to a dramatic change in the behaviour of the dynamical corotation torque compared to earlier 2D theory and simulations. Although it was previously shown that the dynamical corotation torque could act to slow and essentially stall the inward migration of a low-mass planet, our results in 3D show that the dynamical corotation torque has the complete opposite effect and speeds up inward migration. Our numerical experiments implicate buoyancy resonances as the cause. These have two effects: (i) they exert a direct torque on the planet, whose magnitude relative to the Lindblad torque is measured in our simulations to be small; (ii) they torque the gas librating on horseshoe orbits in the corotation region and drive evolution of its vortensity, leading to the negative dynamical corotation torque. This indicates that at low turbulent viscosity, the detailed vertical thermal structure of the protoplanetary disc plays an important role in determining the migration behaviour of embedded planets. If this result holds up under a more refined treatment of disc thermal evolution, then it has important implications for understanding the formation and early evolution of planetary systems
Origin and Detectability of coorbital planets from radial velocity data
We analyze the possibilities of detection of hypothetical exoplanets in
coorbital motion from synthetic radial velocity (RV) signals, taking into
account different types of stable planar configurations, orbital eccentricities
and mass ratios. For each nominal solution corresponding to small-amplitude
oscillations around the periodic solution, we generate a series of synthetic RV
curves mimicking the stellar motion around the barycenter of the system. We
then fit the data sets obtained assuming three possible different orbital
architectures: (a) two planets in coorbital motion, (b) two planets in a 2/1
mean-motion resonance, and (c) a single planet. We compare the resulting
residuals and the estimated orbital parameters.
For synthetic data sets covering only a few orbital periods, we find that the
discrete radial velocity signal generated by a coorbital configuration could be
easily confused with other configurations/systems, and in many cases the best
orbital fit corresponds to either a single planet or two bodies in a 2/1
resonance. However, most of the incorrect identifications are associated to
dynamically unstable solutions.
We also compare the orbital parameters obtained with two different fitting
strategies: a simultaneous fit of two planets and a nested multi-Keplerian
model. We find that the nested models can yield incorrect orbital
configurations (sometimes close to fictitious mean-motion resonances) that are
nevertheless dynamically stable and with orbital eccentricities lower than the
correct nominal solutions.
Finally, we discuss plausible mechanisms for the formation of coorbital
configurations, by the interaction between two giant planets and an inner
cavity in the gas disk. For equal mass planets, both Lagrangian and
anti-Lagrangian configurations can be obtained from same initial condition
depending on final time of integration.Comment: 14 pages, 16 figures.2012. MNRAS, 421, 35
The mass-period distribution of close-in exoplanets
The lower limit to the distribution of orbital periods P for the current
population of close-in exoplanets shows a distinctive discontinuity located at
approximately one Jovian mass. Most smaller planets have orbital periods longer
than P~2.5 days, while higher masses are found down to P~1 day.
We analyze whether this observed mass-period distribution could be explained
in terms of the combined effects of stellar tides and the interactions of
planets with an inner cavity in the gaseous disk.
We performed a series of hydrodynamical simulations of the evolution of
single-planet systems in a gaseous disk with an inner cavity mimicking the
inner boundary of the disk. The subsequent tidal evolution is analyzed assuming
that orbital eccentricities are small and stellar tides are dominant.
We find that most of the close-in exoplanet population is consistent with an
inner edge of the protoplanetary disk being located at approximately P>2 days
for solar-type stars, in addition to orbital decay having been caused by
stellar tides with a specific tidal parameter on the order of Q'*=10^7. The
data is broadly consistent with planets more massive than one Jupiter mass
undergoing type II migration, crossing the gap, and finally halting at the
interior 2/1 mean-motion resonance with the disk edge. Smaller planets do not
open a gap in the disk and remain trapped in the cavity edge. CoRoT-7b appears
detached from the remaining exoplanet population, apparently requiring
additional evolutionary effects to explain its current mass and semimajor axis.Comment: 8 Pages, 8 figures, accepted for publication in A&
Giant planet formation in radially structured protoplanetary discs
This article has been accepted for publication in MNRAS ©: 2016: The authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We acknowledge the comments received from an anonymous referee,
which helped to improve the quality of this paper. GALC acknowledges
the support of an STFC PhD studentship. This research
utilised Queen Maryâs MidPlus computational facilities, supported
by QMUL Research-IT and funded by EPSRC grant EP/K000128/
Low-mass planets in nearly inviscid disks: Numerical treatment
Embedded planets disturb the density structure of the ambient disk and
gravitational back-reaction will induce possibly a change in the planet's
orbital elements. The accurate determination of the forces acting on the planet
requires careful numerical analysis. Recently, the validity of the often used
fast orbital advection algorithm (FARGO) has been put into question, and
special numerical resolution and stability requirements have been suggested. In
this paper we study the process of planet-disk interaction for small mass
planets of a few Earth masses, and reanalyze the numerical requirements to
obtain converged and stable results. One focus lies on the applicability of the
FARGO-algorithm. Additionally, we study the difference of two and
three-dimensional simulations, compare global with local setups, as well as
isothermal and adiabatic conditions. We study the influence of the planet on
the disk through two- and three-dimensional hydrodynamical simulations. To
strengthen our conclusions we perform a detailed numerical comparison where
several upwind and Riemann-solver based codes are used with and without the
FARGO-algorithm.
With respect to the wake structure and the torque density acting on the
planet we demonstrate that the FARGO-algorithm yields correct results, and that
at a fraction of the regular cpu-time. We find that the resolution requirements
for achieving convergent results in unshocked regions are rather modest and
depend on the pressure scale height of the disk. By comparing the torque
densities of 2D and 3D simulations we show that a suitable vertical averaging
procedure for the force gives an excellent agreement between the two. We show
that isothermal and adiabatic runs can differ considerably, even for adiabatic
indices very close to unity.Comment: accepted by Astronomy & Astrophysic
SELF-DESTRUCTING SPIRAL WAVES: GLOBAL SIMULATIONS OF A SPIRAL-WAVE INSTABILITY IN ACCRETION DISKS
This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575. The authors acknowledge the San Diego Supercomputer Center at University of California, San Diego and the Texas Advanced Computing Center at The University of Texas at Austin for providing HPC resources that have contributed to the research results reported within this paper. This work used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility (www.dirac.ac.uk). The equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC Operations grant ST/K0003259/1. DiRAC is part of the national E-Infrastructure
Planetary population synthesis
In stellar astrophysics, the technique of population synthesis has been
successfully used for several decades. For planets, it is in contrast still a
young method which only became important in recent years because of the rapid
increase of the number of known extrasolar planets, and the associated growth
of statistical observational constraints. With planetary population synthesis,
the theory of planet formation and evolution can be put to the test against
these constraints. In this review of planetary population synthesis, we first
briefly list key observational constraints. Then, the work flow in the method
and its two main components are presented, namely global end-to-end models that
predict planetary system properties directly from protoplanetary disk
properties and probability distributions for these initial conditions. An
overview of various population synthesis models in the literature is given. The
sub-models for the physical processes considered in global models are
described: the evolution of the protoplanetary disk, the planets' accretion of
solids and gas, orbital migration, and N-body interactions among concurrently
growing protoplanets. Next, typical population synthesis results are
illustrated in the form of new syntheses obtained with the latest generation of
the Bern model. Planetary formation tracks, the distribution of planets in the
mass-distance and radius-distance plane, the planetary mass function, and the
distributions of planetary radii, semimajor axes, and luminosities are shown,
linked to underlying physical processes, and compared with their observational
counterparts. We finish by highlighting the most important predictions made by
population synthesis models and discuss the lessons learned from these
predictions - both those later observationally confirmed and those rejected.Comment: 47 pages, 12 figures. Invited review accepted for publication in the
'Handbook of Exoplanets', planet formation section, section editor: Ralph
Pudritz, Springer reference works, Juan Antonio Belmonte and Hans Deeg, Ed
The RESOLVE Survey Atomic Gas Census and Environmental Influences on Galaxy Gas Reservoirs
We present the H i mass inventory for the REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey, a volume-limited, multi-wavelength census of >1500 z = 0 galaxies spanning diverse environments and complete in baryonic mass down to dwarfs of ~109 . This first 21 cm data release provides robust detections or strong upper limits (1.4M H i 1012 ) halos, suggesting that gas stripping and/or starvation may be induced by interactions with larger halos or the surrounding cosmic web. We find that the detailed relationship between G/S and environment varies when we examine different subvolumes of RESOLVE independently, which we suggest may be a signature of assembly bias
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