49 research outputs found
Apocenter glow in eccentric debris disks: implications for Fomalhaut and epsilon Eridani
Debris disks often take the form of eccentric rings with azimuthal
asymmetries in surface brightness. Such disks are often described as showing
"pericenter glow", an enhancement of the disk brightness in regions nearest the
central star. At long wavelengths, however, the disk apocenters should appear
brighter than their pericenters: in the long wavelength limit, we find the
apocenter/pericenter flux ratio scales as 1+e for disk eccentricity e. We
produce new models of this "apocenter glow" to explore its causes and
wavelength dependence and study its potential as a probe of dust grain
properties. Based on our models, we argue that several far-infrared and
(sub)millimeter images of the Fomalhaut and epsilon Eridani debris rings
obtained with Herschel, JCMT, SHARC II, ALMA, and ATCA should be reinterpreted
as suggestions or examples of apocenter glow. This reinterpretation yields new
constraints on the disks' dust grain properties and size distributions.Comment: 20 pages, 7 figures; accepted to Ap
A Collisional Algorithm for Modeling Circumstellar Debris Disks
Many planetary systems harbor circumstellar disks of dust and planetesimals thought to be debris left over from planet formation. These debris disks exhibit a range of morphological features which can arise from the gravitational perturbations of planets. Accurate models of these features, accounting for the interactions of the particles in a disk with each other and with whatever planets they contain, can act as signposts for planets in debris disks that otherwise could not be detected. Such models can also constrain the planet's mass and orbital parameters. Current models for many disks consider the gravitational and radiative effects of the star and planets on the disk, but neglect the morphological consequences of collisional interactions between the planetesimals. Many observed disk features are not satisfactorily explained by the current generation of models. I am developing a new kind of debris disk model that considers both the gravitational shaping of the disk by planets and the inelastic collisions between particles. I will use a hybrid N-body integrator to numerically solve the equations of motion for the particles and planets in the disk. To include the collisional effects, I begin with an algorithm that tests for collisions at each step of the orbit integration and readjusts the velocities of colliding particles. I am adapting this algorithm to the problem at hand by allowing each particle to represent a "swarm" of planetesimals with a range of masses. When the algorithm detects an encounter between swarms, two or three swarms are produced to approximate the range of possible trajectories of the daughter planetesimals. Here I present preliminary results from my collisional algorithm
SMACK: A New Algorithm for Modeling Collisions and Dynamics of Planetesimals in Debris Disks
We present the Superparticle Model/Algorithm for Collisions in Kuiper belts and debris disks (SMACK), a new method for simultaneously modeling, in 3-D, the collisional and dynamical evolution of planetesimals in a debris disk with planets. SMACK can simulate azimuthal asymmetries and how these asymmetries evolve over time. We show that SMACK is stable to numerical viscosity and numerical heating over 10(exp 7) yr, and that it can reproduce analytic models of disk evolution. We use SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit. Differential precession creates a spiral structure as the ring evolves, but collisions subsequently break up the spiral, leaving a narrower eccentric ring
Formation History of HD106906 and the Vertical Warping of Debris Disks by an External Inclined Companion
HD106906 is a planetary system that hosts a wide-orbit companion, as well as
an eccentric and flat debris disk, which hold important constraints on its
formation and subsequent evolution. The recent observations of the companion
constrain its orbit to be eccentric and inclined relative to the plane of the
debris disk. Here, we show that, in the presence of the inclined companion, the
debris disk quickly ( Myr) becomes warped and puffy. This suggests
that the current configuration of the system is relatively recent. We explore
the possibility that a recent close encounter with a free floating planet could
produce a companion with orbital parameters that agree with observations of
HD106906b. We find that this scenario is able to recreate the structure of the
debris disk while producing a companion in agreement with observation.Comment: 13 pages, 7 figures. Accepted for publication in Ap
Finding the Needles in the Haystacks: High-Fidelity Models of the Modern and Archean Solar System for Simulating Exoplanet Observations
We present two state-of-the-art models of the solar system, one corresponding
to the present day and one to the Archean Eon 3.5 billion years ago. Each model
contains spatial and spectral information for the star, the planets, and the
interplanetary dust, extending to 50 AU from the sun and covering the
wavelength range 0.3 to 2.5 micron. In addition, we created a spectral image
cube representative of the astronomical backgrounds that will be seen behind
deep observations of extrasolar planetary systems, including galaxies and Milky
Way stars. These models are intended as inputs to high-fidelity simulations of
direct observations of exoplanetary systems using telescopes equipped with
high-contrast capability. They will help improve the realism of observation and
instrument parameters that are required inputs to statistical observatory yield
calculations, as well as guide development of post-processing algorithms for
telescopes capable of directly imaging Earth-like planets.Comment: Accepted for publication in PAS
Millimeter Dust Emission and Planetary Dynamics in the HD 106906 System
Debris disks are dusty, optically thin structures around main sequence stars.
HD 106906AB is a short-period stellar binary, host to a wide separation planet,
HD 106906b, and a debris disk. Only a few known systems include a debris disk
and a directly imaged planet, and HD 106906 is the only one in which the planet
is exterior to the disk. The debris disk is edge-on and highly asymmetric in
scattered light. Here we resolve the disk structure at a resolution of 0.38"
(39 au) with the Atacama Large Millimeter/submillimeter Array (ALMA) at a
wavelength of 1.3 mm. We model the disk with both a narrow and broad ring of
material, and find that a radially broad, axisymmetric disk between radii of
50100 au is able to capture the structure of the observations without
evidence of any asymmetry or eccentricity, other than a tentative stellocentric
offset. We place stringent upper limits on both the gas and dust content of a
putative circumplanetary disk. We interpret the ALMA data in concert with
scattered light observations of the inner ring and astrometric constraints on
the planet's orbit, and find that the observations are consistent with a
large-separation, low-eccentricity orbit for the planet. A dynamical analysis
indicates that the central binary can efficiently stabilize planetesimal orbits
interior to 100 au, which relaxes the constraints on eccentricity and
semimajor axis somewhat. The observational constraints are consistent with in
situ formation via gravitational instability, but cannot rule out a scattering
event as the origin for HD 106906b's current orbit