148 research outputs found
Evolution of the eccentricity and inclination of low-mass planets subjected to thermal forces: a numerical study
By means of three dimensional, high resolution hydrodynamical simulations we
study the orbital evolution of weakly eccentric or inclined low-mass
protoplanets embedded in gaseous discs subject to thermal diffusion. We
consider both non-luminous planets, and planets that also experience the
radiative feedback from their own luminosity. We compare our results to
previous analytical work, and find that thermal forces (the contribution to the
disc's force arising from thermal effects) match those predicted by linear
theory within %. When the planet's luminosity exceeds a threshold
found to be within % of that predicted by linear theory, its eccentricity
and inclination grow exponentially, whereas these quantities undergo a strong
damping below this threshold. In this regime of low luminosity indeed, thermal
diffusion cools the surroundings of the planet and allows gas to accumulate in
its vicinity. It is the dynamics of this gas excess that contributes to damp
eccentricity and inclination. The damping rates obtained can be up to
times larger than those due to the resonant interaction with the disc, where
is the disc's aspect ratio. This suggests that models that incorporate
planet-disc interactions using well-known formulae based on resonant
wave-launching to describe the evolution of eccentricity and inclination
underestimate the damping action of the disc on the eccentricity and
inclination of low-mass planets by an order of magnitude.Comment: Accepted for publication in MNRA
The Lopsidedness of Present-Day Galaxies: Results from the Sloan Digital Sky Survey
Large-scale asymmetries in the stellar mass distribution in galaxies are
believed to trace non-equilibrium situations in the luminous and/or dark matter
component. These may arise in the aftermath of events like mergers, accretion,
and tidal interactions. These events are key in the evolution of galaxies. In
this paper we quantify the large-scale lopsidedness of light distributions in
25155 galaxies at z < 0.06 from the Sloan Digital Sky Survey Data Release 4
using the m = 1 azimuthal Fourier mode. We show that the lopsided distribution
of light is primarily due to a corresponding lopsidedness in the stellar mass
distribution. Observational effects, such as seeing, Poisson noise, and
inclination, introduce only small errors in lopsidedness for the majority of
this sample. We find that lopsidedness correlates strongly with other basic
galaxy structural parameters: galaxies with low concentration, stellar mass,
and stellar surface mass density tend to be lopsided, while galaxies with high
concentration, mass, and density are not. We find that the strongest and most
fundamental relationship between lopsidedness and the other structural
parameters is with the surface mass density. We also find, in agreement with
previous studies, that lopsidedness tends to increase with radius. Both these
results may be understood as a consequence of several factors. The outer
regions of galaxies and low-density galaxies are more susceptible to tidal
perturbations, and they also have longer dynamical times (so lopsidedness will
last longer). They are also more likely to be affected by any underlying
asymmetries in the dark matter halo.Comment: 42 pages, 13 figures, 3 tables, accepted to Ap
Simultaneous formation of Solar System giant planets
In the last few years, the so-called "Nice model" has got a significant
importance in the study of the formation and evolution of the solar system.
According to this model, the initial orbital configuration of the giant planets
was much more compact than the one we observe today. We study the formation of
the giant planets in connection with some parameters that describe the
protoplanetary disk. The aim of this study is to establish the conditions that
favor their simultaneous formation in line with the initial configuration
proposed by the Nice model. We focus in the conditions that lead to the
simultaneous formation of two massive cores, corresponding to Jupiter and
Saturn, able to achieve the cross-over mass (where the mass of the envelope of
the giant planet equals the mass of the core, and gaseous runway starts) while
Uranus and Neptune have to be able to grow to their current masses. We compute
the in situ planetary formation, employing the numerical code introduced in our
previous work, for different density profiles of the protoplanetary disk.
Planetesimal migration is taken into account and planetesimals are considered
to follow a size distribution between (free parameter) and
km. The core's growth is computed according to the oligarchic
growth regime. The simultaneous formation of the giant planets was successfully
completed for several initial conditions of the disk. We find that for
protoplanetary disks characterized by a power law (),
smooth surface density profiles () favor the simultaneous
formation. However, for steep slopes (, as previously proposed by
other authors) the simultaneous formation of the solar system giant planets is
unlikely ...Comment: Accepted for publication in Astronomy and Astrophysic
The role of the initial surface density profiles of the disc on giant planet formation: comparing with observations
In order to explain the main characteristics of the observed population of
extrasolar planets and the giant planets in the Solar System, we need to get a
clear understanding of which are the initial conditions that allowed their
formation. To this end we develop a semi-analytical model for computing
planetary systems formation based on the core instability model for the gas
accretion of the embryos and the oligarchic growth regime for the accretion of
the solid cores. With this model we explore not only different initial discs
profiles motivated by similarity solutions for viscous accretion discs, but we
also consider different initial conditions to generate a variety of planetary
systems assuming a large range of discs masses and sizes according to the last
results in protoplanetary discs observations. We form a large population of
planetary systems in order to explore the effects in the formation of assuming
different discs and also the effects of type I and II regimes of planetary
migration, which were found to play fundamental role in reproducing the
distribution of observed exoplanets. Our results show that the observed
population of exoplanets and the giant planets in the Solar System are well
represented when considering a surface density profile with a power law in the
inner part characterized by an exponent of -1, which represents a softer
profile when compared with the case most similar to the MMSN model case.Comment: 14 pages, 12 figures, MNRAS, 412, 211
The role of the initial surface density profiles of the disc on giant planet formation: comparing with observations
In order to explain the main characteristics of the observed population of
extrasolar planets and the giant planets in the Solar System, we need to get a
clear understanding of which are the initial conditions that allowed their
formation. To this end we develop a semi-analytical model for computing
planetary systems formation based on the core instability model for the gas
accretion of the embryos and the oligarchic growth regime for the accretion of
the solid cores. With this model we explore not only different initial discs
profiles motivated by similarity solutions for viscous accretion discs, but we
also consider different initial conditions to generate a variety of planetary
systems assuming a large range of discs masses and sizes according to the last
results in protoplanetary discs observations. We form a large population of
planetary systems in order to explore the effects in the formation of assuming
different discs and also the effects of type I and II regimes of planetary
migration, which were found to play fundamental role in reproducing the
distribution of observed exoplanets. Our results show that the observed
population of exoplanets and the giant planets in the Solar System are well
represented when considering a surface density profile with a power law in the
inner part characterized by an exponent of -1, which represents a softer
profile when compared with the case most similar to the MMSN model case.Comment: 14 pages, 12 figures, MNRAS, 412, 211
Interaction of Close-in Planets with the Magnetosphere of their Host Stars. II. Super-Earths as Unipolar Inductors and their Orbital Evolution
Planets with several Earth masses and a few day orbital periods have been
discovered through radial velocity and transit surveys. Regardless of their
formation mechanism, a key evolution issue is the efficiency of their retention
near their host stars. If these planets attained their present-day orbits
during or shortly after the T Tauri phase of their host stars, a large fraction
would have encountered intense stellar magnetic field. Since these planets have
a higher conductivity than the atmosphere of their stars, the magnetic flux
tube connecting the planet and host star would slip though the envelope of the
star faster than across the planet. The induced electro-motive force across the
planet's diameter leads to a potential drop which propagates along a flux tube
away from the planet with an Alfven speed. The foot of the flux tube sweeps
across the stellar surface and the potential drop drives a DC current analogous
to that proposed for the Io-Jupiter electrodynamic interaction. The ohmic
dissipation of this current produces potentially observable hot spots in the
star envelope. The current heats the planet and leads to a Lorrentz torque
which drives the planet's orbit to evolve toward circularization and
synchronization with the star's spin. The net effect is the damping of the
planet's orbital eccentricity. Around slowly (rapidly) spinning stars, this
process also causes rocky planets with periods less than a few days to undergo
orbital decay (expansion/stagnation) within a few Myr. In principle, this
effect can determine the retention efficiency of short-period hot Earths. We
also estimate the ohmic dissipation in these planets and show that it can lead
to severe structure evolution and potential loss of volatile material. However,
these effects may be significantly weakened by the reconnection of the induced
field [Slightly shortened abstract]
Planet formation in Binaries
Spurred by the discovery of numerous exoplanets in multiple systems, binaries
have become in recent years one of the main topics in planet formation
research. Numerous studies have investigated to what extent the presence of a
stellar companion can affect the planet formation process. Such studies have
implications that can reach beyond the sole context of binaries, as they allow
to test certain aspects of the planet formation scenario by submitting them to
extreme environments. We review here the current understanding on this complex
problem. We show in particular how each of the different stages of the
planet-formation process is affected differently by binary perturbations. We
focus especially on the intermediate stage of kilometre-sized planetesimal
accretion, which has proven to be the most sensitive to binarity and for which
the presence of some exoplanets observed in tight binaries is difficult to
explain by in-situ formation following the "standard" planet-formation
scenario. Some tentative solutions to this apparent paradox are presented. The
last part of our review presents a thorough description of the problem of
planet habitability, for which the binary environment creates a complex
situation because of the presence of two irradation sources of varying
distance.Comment: Review chapter to appear in "Planetary Exploration and Science:
Recent Advances and Applications", eds. S. Jin, N. Haghighipour, W.-H. Ip,
Springer (v2, numerous typos corrected
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
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