113 research outputs found
Growing dust grains in protoplanetary discs - I. Radial drift with toy growth models
In a series of papers, we present a comprehensive analytic study of the
global motion of growing dust grains in protoplanetary discs, addressing both
the radial drift and the vertical settling of the particles. Here we study how
the radial drift of dust particles is affected by grain growth. In a first
step, toy models in which grain growth can either be constant, accelerate or
decelerate are introduced. The equations of motion are analytically integrable
and therefore the grains dynamics is easy to understand.
The radial motion of growing grains is governed by the relative efficiency of
the growth and migration processes which is expressed by the dimensionless
parameter Lambda, as well as the exponents for the gas surface density and
temperature profiles, denoted p and q respectively. When Lambda is of order
unity, growth and migration are strongly coupled, providing the most efficient
radial drift. For the toy models considered, grains pile up when -p+q+1/2<0.
Importantly, we show the existence of a second process which can help discs to
retain their solid materials. For accelerating growth, grains end up their
migration at a finite radius, thus avoiding being accreted onto the central
star.Comment: 12 pages, 9 figures. Accepted for publication in MNRAS. v2: typos
correcte
Stable habitable zones of single Jovian planet systems
With continued improvement in telescope sensitivity and observational
techniques, the search for rocky planets in stellar habitable zones is entering
an exciting era. With so many exoplanetary systems available for follow-up
observations to find potentially habitable planets, one needs to prioritise the
ever-growing list of candidates. We aim to determine which of the known
planetary systems are dynamically capable of hosting rocky planets in their
habitable zones, with the goal of helping to focus future planet search
programs. We perform an extensive suite of numerical simulations to identify
regions in the habitable zones of single Jovian planet systems where Earth mass
planets could maintain stable orbits, specifically focusing on the systems in
the Catalog of Earth-like Exoplanet Survey Targets (CELESTA). We find that
small, Earth-mass planets can maintain stable orbits in cases where the
habitable zone is largely, or partially, unperturbed by a nearby Jovian, and
that mutual gravitational interactions and resonant mechanisms are capable of
producing stable orbits even in habitable zones that are significantly or
completely disrupted by a Jovian. Our results yield a list of 13 single Jovian
planet systems in CELESTA that are not only capable of supporting an Earth-mass
planet on stable orbits in their habitable zone, but for which we are also able
to constrain the orbits of the Earth-mass planet such that the induced radial
velocity signals would be detectable with next generation instruments.Comment: 15 pages, 12 figures, Accepted for publication by MNRA
Planet gaps in the dust layer of 3D proto-planetary disks: Observability with ALMA
Among the numerous known extrasolar planets, only a handful have been imaged
directly so far, at large orbital radii and in rather evolved systems. The
Atacama Large Millimeter/submillimeter Array (ALMA) will have the capacity to
observe these wide planetary systems at a younger age, thus bringing a better
understanding of the planet formation process. Here we explore the ability of
ALMA to detect the gaps carved by planets on wide orbits.Comment: 2 pages, 2 figures, to appear in the Proceedings of IAU Symp. 299:
Exploring the Formation and Evolution of Planetary Systems (Victoria, Canada
Predicting Dust Distribution in Protoplanetary Discs
We present the results of three-dimensional numerical simulations that
include the effects of hydrodynamical forces and gas drag upon an evolving
dusty gas disk. We briefly describe a new parallel, two phase numerical code
based upon the smoothed particle hydrodynamics (SPH) technique in which the gas
and dust phases are represented by two distinct types of particles. We use the
code to follow the dynamical evolution of a population of grains in a gaseous
protoplanetary disk in order to understand the distribution of grains of
different sizes within the disk. Our ``grains'' range from metre to
submillimetre in size.Comment: 2 pages, LaTeX with 1 ps figure embedded, using newpasp.sty
(supplied). To appear in the proceedings of the XIXth IAP colloquium
"Extrasolar Planets: Today and Tomorrow" held in Paris, France, 2003, June 30
-- July 4, ASP Conf. Se
High-resolution N-body Simulations of Galactic Cannibalism: The Magellanic Stream
Hierarchical clustering represents the favoured paradigm for galaxy formation
throughout the Universe; due to its proximity, the Magellanic system offers one
of the few opportunities for astrophysicists to decompose the full
six-dimensional phase-space history of a satellite in the midst of being
cannibalised by its host galaxy. The availability of improved observational
data for the Magellanic Stream and parallel advances in computational power has
led us to revisit the canonical tidal model describing the disruption of the
Small Magellanic Cloud and the consequent formation of the Stream. We suggest
improvements to the tidal model in light of these recent advances.Comment: 6 pages, 4 figures, LaTeX (gcdv.sty). Refereed contribution to the
5th Galactic Chemodynamics conference held in Swinburne, July 2003. Accepted
for publication in PASA. Version with high resolution figures available at
http://astronomy.swin.edu.au/staff/tconnors/publications.htm
SPH Simulations of Accretion Disks and Narrow Rings
We model a massless viscous disk using Smoothed Particle Hydrodynamics (SPH)
and note that it evolves according to the Lynden-Bell \& Pringle theory (1974)
until a non-axisymmetric instability develops at the inner edge of the disk.
This instability may have the same origin as the instability of initially
axisymmetric viscous disks discussed by Lyubarskij et al. (1994). To clarify
the evolution we evolved single and double rings of particles. It is actually
inconsistent with the SPH scheme to set up a single ring as an initial
condition because SPH assumes a smoothed initial state. As would be expected
from an SPH simulation, the ring rapidly breaks up into a band. We analyse the
stability of the ring and show that the predictions are confirmed by the
simulation.Comment: 11 pages, uuencoded compressed postscript with 2 figs, accepted PASA.
Also available at http://www.maths.monash.edu.au/~maddison/me/papers.htm
A dynamical test for terrestrial planets in the habitable zone of HD 204313
With improvements in exoplanet detection techniques, the number of multiple planet systems discovered is increasing, while the detection of potentially habitable Earth-mass planets remains complicated and thus requires new search strategies. Dynamical studies of known multiple planet systems are therefore a vital tool in the search for stable and habitable planet candidates. Here, we present a dynamical study of the three-planet system HD 204313 to determine whether it could harbour an Earth-like planet within its habitable zone for a sufficient time to develop life. We found two semi-stable regions in the system, but neither prove stable for long enough for a terrestrial planet to develop life. Our investigations suggest that overlapping weak and high order resonances may be responsible for these semi-stable regions. This study established a framework for a larger project that will study the dynamical stability of the habitable zone of multiple planet systems, providing a list of interesting targets for future habitable low-mass planet searches
SPH simulations of grain growth in protoplanetary disks
6 pages, 6 figures, accepted to A&AInternational audienceAims: In order to understand the first stages of planet formation, when tiny grains aggregate to form planetesimals, one needs to simultaneously model grain growth, vertical settling and radial migration of dust in protoplanetary disks. In this study, we implement an analytical prescription for grain growth into a 3D two-phase hydrodynamics code to understand its effects on the dust distribution in disks. Methods: Following the analytic derivation of Stepinski & Valageas (1997), which assumes that grains stick perfectly upon collision, we implement a convenient and fast method of following grain growth in our 3D, two-phase (gas+dust) SPH code. We then follow the evolution of the size and spatial distribution of a dust population in a classical T Tauri star disk. Results: We find that the grains go through various stages of growth due to the complex interplay between gas drag, dust dynamics, and growth. Grains initially grow rapidly as they settle to the mid-plane, then experience a fast radial migration with little growth through the bulk of the disk, and finally pile-up in the inner disk where they grow more efficiently. This results in a bimodal distribution of grain sizes. Using this simple prescription of grain growth, we find that grains reach decimetric sizes in 10^5 years in the inner disk and survive the fast migration phase
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