100 research outputs found
Impact flux of asteroids and water transport to the habitable zone in binary star systems
By now, observations of exoplanets have found more than 50 binary star
systems hosting 71 planets. We expect these numbers to increase as more than
70% of the main sequence stars in the solar neighborhood are members of binary
or multiple systems. The planetary motion in such systems depends strongly on
both the parameters of the stellar system (stellar separation and eccentricity)
and the architecture of the planetary system (number of planets and their
orbital behaviour). In case a terrestrial planet moves in the so-called
habitable zone (HZ) of its host star, the habitability of this planet depends
on many parameters. A crucial factor is certainly the amount of water. We
investigate in this work the transport of water from beyond the snow-line to
the HZ in a binary star system and compare it to a single star system
Disc-protoplanet interaction Influence of circumprimary radiative discs on self-gravitating protoplanetary bodies in binary star systems
Context. More than 60 planets have been discovered so far in systems that
harbour two stars, some of which have binary semi-major axes as small as 20 au.
It is well known that the formation of planets in such systems is strongly
influenced by the stellar components, since the protoplanetary disc and the
particles within are exposed to the gravitational influence of the binary.
However, the question on how self-gravitating protoplanetary bodies affect the
evolution of a radiative, circumprimary disc is still open. Aims. We present
our 2D hydrodynamical GPU-CPU code and study the interaction of several
thousands of self-gravitating particles with a viscous and radiative
circumprimary disc within a binary star system. To our knowledge this program
is the only one at the moment that is capable to handle this many particles and
to calculate their influence on each other and on the disc. Methods. We
performed hydrodynamical simulations of a circumstellar disc assuming the
binary system to be coplanar. Our gridbased staggered mesh code relies on ideas
from ZEUS-2D, where we implemented the FARGO algorithm and an additional energy
equation for the radiative cooling according to opacity tables. To treat
particle motion we used a parallelised version of the precise Bulirsch - Stoer
algorithm. Four models in total where computed taking into account (i) only
N-body interaction, (ii) N-body and disc interaction, (iii) the influence of
computational parameters (especially smoothing) on N-body interaction, and (iv)
the influence of a quiet low-eccentricity disc while running model (ii). The
impact velocities where measured at two different time intervals and were
compared. Results. We show that the combination of disc- and N-body
self-gravity can have a significant influence on the orbit evolution of roughly
Moon sized protoplanets
Spectral properties of near-Earth and Mars-crossing asteroids using Sloan photometry
The nature and origin of the asteroids orbiting in near-Earth space,
including those on a potentially hazardous trajectory, is of both scientific
interest and practical importance. We aim here at determining the taxonomy of a
large sample of near-Earth (NEA) and Mars-crosser (MC) asteroids and analyze
the distribution of these classes with orbit. We use this distribution to
identify their source regions and to study the strength of planetary encounters
to refresh asteroid surfaces. We measure the photometry of these asteroids over
four filters at visible wavelengths on images taken by the SDSS. These colors
are used to classify the asteroids into a taxonomy consistent with the widely
used Bus-DeMeo taxonomy based on spectroscopy. We report here on the taxonomic
classification of 206 NEAs and 776 MCs determined from SDSS photometry,
representing an increase of 40% and 663% of known taxonomy classifications in
these populations. Using the source region mapper by Greenstreet et al. (2012),
we compare the taxonomic distribution among NEAs and main-belt asteroids of
similar diameters. Both distributions agree at the few percent level for the
inner part of the Main Belt and we confirm this region as a main source of
near-Earth objects. The effect of planetary encounters on asteroid surfaces are
also studied by developing a simple model of forces acting on a surface grain
during planetary encounter, which provides the minimum distance at which a
close approach should occur to trigger resurfacing events. By integrating
numerically the orbit of the 519 S-type and 46 Q-type asteroids back in time
and monitoring their encounter distance with planets, we seek to understand the
conditions for resurfacing events. The population of Q-type is found to present
statistically more encounters with Venus and the Earth than S-types, although
both types present the same amount of encounters with Mars.Comment: Accepted for publication in Icarus. 45 pages, 11 figures, 4 tables, 2
tables in appendix (supplementary material
The shape evolution of cometary nuclei via anisotropic mass loss
Context. Breathtaking imagery recorded during the European Space Agency's
Rosetta mission confirmed the bilobate nature of comet
67P/Churyumov-Gerasimenko's nucleus. Its peculiar appearance is not unique
among comets. The majority of cometary cores imaged at high resolution exhibit
a similar build. Various theories have been brought forward as to how cometary
nuclei attain such peculiar shapes.
Aims. We illustrate that anisotropic mass loss and local collapse of
subsurface structures caused by non-uniform exposure of the nucleus to solar
irradiation can transform initially spherical comet cores into bilobed ones.
Methods. A mathematical framework to describe the changes in morphology
resulting from non-uniform insolation during a nucleus' spin-orbit evolution is
derived. The resulting partial differential equations that govern the change in
the shape of a nucleus subject to mass loss and consequent collapse of depleted
subsurface structures are solved analytically for simple insolation
configurations and numerically for more realistic scenarios.
Results. The here proposed mechanism is capable of explaining why a large
fraction of periodic comets appear to have peanut-shaped cores and why
light-curve amplitudes of comet nuclei are on average larger than those of
typical main belt asteroids of the same size.Comment: 4 pages of the main text, 2 pages of appendix, 4 figure
High order three part split symplectic integrators: Efficient techniques for the long time simulation of the disordered discrete nonlinear Schroedinger equation
While symplectic integration methods based on operator splitting are well
established in many branches of science, high order methods for Hamiltonian
systems that split in more than two parts have not been studied in great
detail. Here, we present several high order symplectic integrators for
Hamiltonian systems that can be split in exactly three integrable parts. We
apply these techniques, as a practical case, for the integration of the
disordered, discrete nonlinear Schroedinger equation (DDNLS) and compare their
efficiencies. Three part split algorithms provide effective means to
numerically study the asymptotic behavior of wave packet spreading in the DDNLS
- a hotly debated subject in current scientific literature.Comment: 5 Figures, Physics Letters A (accepted
Colliding Winds in Low-Mass Binary Star Systems: wind interactions and implications for habitable planets
Context. In binary star systems, the winds from the two components impact
each other, leading to strong shocks and regions of enhanced density and
temperature. Potentially habitable circumbinary planets must continually be
exposed to these interactions regions.
Aims. We study, for the first time, the interactions between winds from
low-mass stars in a binary system, to show the wind conditions seen by
potentially habitable circumbinary planets.
Methods. We use the advanced 3D numerical hydrodynamic code Nurgush to model
the wind interactions of two identical winds from two solar mass stars with
circular orbits and a binary separation of 0.5 AU. As input into this model, we
use a 1D hydrodynamic simulation of the solar wind, run using the Versatile
Advection Code. We derive the locations of stable and habitable orbits in this
system to explore what wind conditions potentially habitable planets will be
exposed to during their orbits.
Results. Our wind interaction simulations result in the formation of two
strong shock waves separated by a region of enhanced density and temperature.
The wind-wind interaction region has a spiral shape due to Coriolis forces
generated by the orbital motions of the two stars. The stable and habitable
zone in this system extends from approximately 1.4 AU to 2.4 AU. (TRUNCATED)Comment: 15 pages, 11 figures, to be published in A&
Efficient integration of the variational equations of multi-dimensional Hamiltonian systems: Application to the Fermi-Pasta-Ulam lattice
We study the problem of efficient integration of variational equations in
multi-dimensional Hamiltonian systems. For this purpose, we consider a
Runge-Kutta-type integrator, a Taylor series expansion method and the so-called
`Tangent Map' (TM) technique based on symplectic integration schemes, and apply
them to the Fermi-Pasta-Ulam (FPU-) lattice of nonlinearly
coupled oscillators, with ranging from 4 to 20. The fast and accurate
reproduction of well-known behaviors of the Generalized Alignment Index (GALI)
chaos detection technique is used as an indicator for the efficiency of the
tested integration schemes. Implementing the TM technique--which shows the best
performance among the tested algorithms--and exploiting the advantages of the
GALI method, we successfully trace the location of low-dimensional tori.Comment: 14 pages, 6 figure
Asteroid flux towards circumprimary habitable zones in binary star systems: I. Statistical Overview
So far, multiple stellar systems harbor more than 130 extra solar planets.
Dynamical simulations show that the outcome of planetary formation process can
lead to various planetary architecture (i.e. location, size, mass and water
content) when the star system is single or double. In the late phase of
planetary formation, when embryo-sized objects dominate the inner region of the
system, asteroids are also present and can provide additional material for
objects inside the habitable zone (hereafter HZ). In this study, we make a
comparison of several binary star systems and their efficiency to move icy
asteroids from beyond the snow-line into orbits crossing the HZ. We modeled a
belt of 10000 asteroids (remnants from the late phase of planetary formation
process) beyond the snow-line. The planetesimals are placed randomly around the
primary star and move under the gravitational influence of the two stars and a
gas giant. As the planetesimals do not interact with each other, we divided the
belt into 100 subrings which were separately integrated. In this statistical
study, several double star configurations with a G-type star as primary are
investigated. Our results show that small bodies also participate in bearing a
non-negligible amount of water to the HZ. The proximity of a companion moving
on an eccentric orbit increases the flux of asteroids to the HZ, which could
result into a more efficient water transport on a short timescale, causing a
heavy bombardment. In contrast to asteroids moving under the gravitational
perturbations of one G-type star and a gas giant, we show that the presence of
a companion star can not only favor a faster depletion of our disk of
planetesimals but can also bring 4 -- 5 times more water into the whole HZ.Comment: Accepted for publication in A&
High order three part split symplectic integrators: Efficient techniques for the long time simulation of the disordered discrete nonlinear Schrödinger equation
While symplectic integration methods based on operator splitting are well established in many branches of science, high order methods for Hamiltonian systems that split in more than two parts have not been studied in great detail. Here, we present several high order symplectic integrators for Hamiltonian systems that can be split in exactly three integrable parts. We apply these techniques, as a practical case, for the integration of the disordered, discrete nonlinear Schrödinger equation (DDNLS) and compare their efficiencies. Three part split algorithms provide effective means to numerically study the asymptotic behavior of wave packet spreading in the DDNLS – a hotly debated subject in current scientific literature
Prospects of the Detection of Circumbinary Planets With Kepler and CoRoT Using the Variations of Eclipse Timing
In close eclipsing binaries, measurements of the variations in binary's
eclipse timing may be used to infer information about the existence of
circumbinary objects. To determine the possibility of the detection of such
variations with CoRoT and Kepler space telescopes, we have carried out an
extensive study of the dynamics of a binary star system with a circumbinary
planet, and calculated its eclipse timing variations (ETV) for different values
of the mass-ratio and orbital elements of the binary and the perturbing body.
Here, we present the results of our study and assess the detectability of the
planet by comparing the resulting values of ETVs with the temporal sensitivity
of CoRoT and Kepler. Results point to extended regions in the parameter-space
where the perturbation of a planet may become large enough to create measurable
variations in the eclipse timing of the secondary star. Many of these
variations point to potentially detectable ETVs and the possible existence of
Jovian-type planets.Comment: 8 pages, 6 figures, submitted for publicatio
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