80 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
Mean-Motion Resonances of High Order in Extrasolar Planetary Systems
Many multi-planet systems have been discovered in recent years. Some of them
are in mean-motion resonances (MMR). Planet formation theory was successful in
explaining the formation of 2:1, 3:1 and other low resonances as a result of
convergent migration. However, higher order resonances require high initial
orbital eccentricities in order to be formed by this process and these are in
general unexpected in a dissipative disk. We present a way of generating large
initial eccentricities using additional planets. This procedure allows us to
form high order MMRs and predict new planets using a genetic N-body code.Comment: To appear in Proceedings: Extrasolar Planets in Multi-body Systems:
Theory and Observations; Editors K. Gozdziewski, A. Niedzielski and J.
Schneider; 5 pages, 2 figures
Dynamical architectures of planetary systems induced by orbital migration
The aim of this talk is to present the most recent advances in establishing
plausible planetary system architectures determined by the gravitational tidal
interactions between the planets and the disc in which they are embedded during
the early epoch of planetary system formation. We concentrate on a very well
defined and intensively studied process of the disc-planet interaction leading
to the planet migration. We focus on the dynamics of the systems in which
low-mass planets are present. Particular attention is devoted to investigation
of the role of resonant configurations. Our studies, apart from being
complementary to the fast progress occurring just now in observing the whole
variety of planetary systems and uncovering their structure and origin, can
also constitute a valuable contribution in support of the missions planned to
enhance the number of detected multiple systems.Comment: 10 pages with 5 figures, pdflatex, to appear in the proceedings of
the conference "Extra-solar Planets in Multi-body Systems: Theory and
Observations"; eds. K. Gozdziewski, A. Niedzielski and J. Schneider, EAS
Publication Serie
Hydrodynamic Simulations of the Bardeen-Petterson Effect
We present SPH simulations of accretion discs in orbit about rotating compact
objects such as black holes and neutron stars, and study the structure of
warped discs produced by the Bardeen-Petterson effect. We calculate the
transition radius out to which the disc specific angular momentum vector is
aligned with that of the black hole. We focus on the parameter regime where the
warp dynamics are controlled by bending wave propagation, but also consider
models in which warps are subject to diffusion rather than wave transport, and
are able to consider the fully nonlinear regime. Because of hydrodynamic or
pressure effects, for the parameter range investigated, the transition radius
is always found to be much smaller than that obtained by Bardeen & Petterson
(1975). For discs with midplane Mach numbers of about 10, the transition occurs
between 10 - 16 gravitational radii, whereas for a Mach number of about 30 it
occurs at around 30 gravitational radii. A thicker disc with a Mach number of 5
is found to produce no discernible warped structure. The rate of black hole -
disc alignment is found to be consistent with the ideas of Ress (1978), with
the alignment torque behaving as if it arises from the accreted material
transferring its misaligned component of angular momentum at the larger
transition radius of Bardeen & Petterson (1975). The inclusion of Einstein
precession in the calculations modified both the warped disc structure and,
consistent with linear analysis, produced an increased alignment rate by up to
a factor of 4 because of the effect that a non Keplerian potential has on the
propagation of warps.Comment: 18 pages, 14 figures. Accepted for publication in M.N.R.A.S. A
version with posctcript figures included can be obtained from
http://www.maths.qmw.ac.uk/~rp
Bending Instabilities in Magnetized Accretion Discs
We study the global bending modes of a thin annular disc subject to both an
internally generated magnetic field and a magnetic field due to a dipole
embedded in the central star with axis aligned with the disc rotation axis.
When there is a significant inner region of the disc corotating with the star,
we find spectra of unstable bending modes. These may lead to elevation of the
disc above the original symmetry plane facilitating accretion along the
magnetospheric field lines. The resulting non-axisymmetric disc configuration
may result in the creation of hot spots on the stellar surface and the periodic
photometric variations observed in many classical T Tauri stars (CTTS).
Time-dependent behaviour may occur including the shadowing of the central
source in magnetic accretors even when the dipole and rotation axes are
aligned.Comment: Accepted by MNRAS. 18 pages, 11 figures. LaTeX2e in the MN style.
PostScript and HTML files are also available from
http://www-star.qmw.ac.uk/~va/ or by e-mail: [email protected]
The TRAPPIST-1 system: Orbital evolution, tidal dissipation, formation and habitability
We study the dynamical evolution of the TRAPPIST-1 system under the influence
of orbital circularization through tidal interaction with the central star. We
find that systems with parameters close to the observed one evolve into a state
where consecutive planets are linked by first order resonances and consecutive
triples, apart from planets c, d and e, by connected three body Laplace
resonances. The system expands with period ratios increasing and mean
eccentricities decreasing with time. This evolution is largely driven by tides
acting on the innermost planets which then influence the outer ones. In order
that deviations from commensurability become significant only on time
scales or longer, we require that the tidal parameter associated with the
planets has to be such that At the same time, if we start
with two subsystems, with the inner three planets comprising the inner one,
associated with the planets has to be on the order (and not significantly
exceeding) for the two subsystems to interact and end up in the
observed configuration. This scenario is also supported by modelling of the
evolution through disk migration which indicates that the whole system cannot
have migrated inwards together. Also in order to avoid large departures from
commensurabilities, the system cannot have stalled at a disk inner edge for
significant time periods. We discuss the habitability consequences of the tidal
dissipation implied by our modelling, concluding that planets d, e and f are
potentially in habitable zones.Comment: 27 pages, 15 figures, accepted for publication in MNRA
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