527 research outputs found
Radiative Transfer Models of a Possible Planet in the AB Aurigae Disk
Recent coronagraphic imaging of the AB Aurigae disk has revealed a region of
low polarized scattered light suggestive of perturbations from a planet at a
radius of ~100 AU. We model this darkened region using our fully
non-plane-parallel radiative-transfer code combined with a simple hydrostatic
equilibirum approximation to self-consistently solve for the structure of the
disk surface as seen in scattered light. By comparing the observations to our
models, we find that the observations are consistent with the absence of a
planet, with an upper limit of 1 Jupiter mass.Comment: Accepted to ApJ Letter
Gaps in Protoplanetary Disks as Signatures of Planets: I. Methodology and Validation
We examine the observational consequences of partial gaps being opened by
planets in protoplanetary disks. We model the disk using a static alpha-disk
model with detailed radiative transfer, parametrizing the shape and size of the
partially cleared gaps based on the results of hydrodynamic simulations.
Shadowing and illumination by stellar irradiation at the surface of the gap
leads to increased contrast as the gap trough is deepened by shadowing and
cooling and the far gap wall is puffed up by illumination and heating. In
calculating observables, we find that multiple scattering is important and
derive an approximation to include these effects. A gap produced by a 200
M_Earth (70 M_Earth) planet at 10 AU can lower/raise the midplane temperature
of the disk by up to ~-25/+29% (~-11/+19%) by shadowing in the gap trough and
illumination on the far shoulder of the gap. At the distance of Taurus, this
gap would be resolvable with ~0.01" angular resolution. The gap contrast is
most significant in scattered light and at thermal continuum wavelengths
characteristic of the surface temperature, reducing or raising the surface
brightness by up to order of magnitude. Since gaps sizes are correlated to
planet mass, this is a promising way of finding and determining the masses of
planets embedded in protoplanetary disks.Comment: 11 pages, 9 figures. Accepted to Ap
The Structure of a Self-Gravitating Protoplanetary Disk and its Implications to Direct Imaging Observations
We consider the effects of self-gravity on the hydrostatic balance in the
vertical direction of a gaseous disk and discuss the possible signature of the
self-gravity that may be captured by the direct imaging observations of
protoplanetary disks in future. In this paper, we consider a vertically
isothermal disk in order to isolate the effects of self-gravity. The specific
disk model we consider in this paper is the one with a radial surface density
gap, at which the Toomre's -parameter of the disk varies rapidly in the
radial direction. We calculate the vertical structure of the disk including the
effects of self-gravity. We then calculate the scattered light and the dust
thermal emission. We find that if the disk is massive enough and the effects of
self-gravity come into play, a weak bump-like structure at the gap edge appears
in the near-infrared (NIR) scattered light, while no such bump-like structure
is seen in the sub-mm dust continuum image. The appearance of the bump is
caused by the variation of the height of the surface in the NIR wavelength. If
such bump-like feature is detected in future direct imaging observations, with
the combination of sub-mm observations, it will bring us useful information
about the physical states of the disk.Comment: 12 pages, 9 figures, ApJ accepte
Planet Shadows in Protoplanetary Disks. I: Temperature Perturbations
Planets embedded in optically thick passive accretion disks are expected to
produce perturbations in the density and temperature structure of the disk. We
calculate the magnitudes of these perturbations for a range of planet masses
and distances. The model predicts the formation of a shadow at the position of
the planet paired with a brightening just beyond the shadow. We improve on
previous work on the subject by self-consistently calculating the temperature
and density structures under the assumption of hydrostatic equilibrium and
taking the full three-dimensional shape of the disk into account rather than
assuming a plane-parallel disk. While the excursion in temperatures is less
than in previous models, the spatial size of the perturbation is larger. We
demonstrate that a self-consistent calculation of the density and temperature
structure of the disk has a large effect on the disk model. In addition, the
temperature structure in the disk is highly sensitive to the angle of incidence
of stellar irradition at the surface, so accurately calculating the shape of
the disk surface is crucial for modeling the thermal structure of the disk.Comment: 14 pages, 14 figures. To appear in Ap
Some Moral and Ethical Dilemmas of Science in the 1970\u27s
Some critics of the scientific community - scientists and non-scientists - believe that scientists should become more socially responsible, that science should be tolerated only as long as its results are socially beneficial, and that science must be constitutionalized and controlled if it is not to destroy civilization
Radiative Transfer on Perturbations in Protoplanetary Disks
We present a method for calculating the radiative tranfer on a protoplanetary
disk perturbed by a protoplanet. We apply this method to determine the effect
on the temperature structure within the photosphere of a passive circumstellar
disk in the vicinity of a small protoplanet of up to 20 Earth masses. The
gravitational potential of a protoplanet induces a compression of the disk
material near it, resulting in a decrement in the density at the disk's
surface. Thus, an isodensity contour at the height of the photosphere takes on
the shape of a well. When such a well is illuminated by stellar irradiation at
grazing incidence, it results in cooling in a shadowed region and heating in an
exposed region. For typical stellar and disk parameters relevant to the epoch
of planet formation, we find that the temperature variation due to a
protoplanet at 1 AU separation from its parent star is about 4% (5 K) for a
planet of 1 Earth mass, about 14% (19 K) for planet of 10 Earth masses, and
about 18% (25 K) for planet of 20 Earth masses, We conclude that even such
relatively small protoplanets can induce temperature variations in a passive
disk. Therefore, many of the processes involved in planet formation should not
be modeled with a locally isothermal equation of state.Comment: 23 pages, 8 figures (including 3 color figs). Submitted to Ap
Radiatively heated, protoplanetary discs with dead zones. I. Dust settling and thermal structure of discs around M stars
The irradiation of protoplanetary discs by central stars is the main heating
mechanism for discs, resulting in their flared geometric structure. In a series
of papers, we investigate the deep links between 2D self-consistent disc
structure and planetary migration in irradiated discs, focusing particularly on
those around M stars. In this first paper, we analyse the thermal structure of
discs that are irradiated by an M star by solving the radiative transfer
equation by means of a Monte Carlo code. Our simulations of irradiated
hydrostatic discs are realistic and self-consistent in that they include dust
settling with multiple grain sizes (N=15), the gravitational force of an
embedded planet on the disc, and the presence of a dead zone (a region with
very low levels of turbulence) within it. We show that dust settling drives the
temperature of the mid-plane from an distribution (well mixed dust
models) toward an . The dead zone, meanwhile, leaves a dusty wall at
its outer edge because dust settling in this region is enhanced compared to the
active turbulent disc at larger disc radii. The disc heating produced by this
irradiated wall provides a positive gradient region of the temperature in the
dead zone in front of the wall. This is crucially important for slowing
planetary migration because Lindblad torques are inversely proportional to the
disc temperature. Furthermore, we show that low turbulence of the dead zone is
self-consistently induced by dust settling, resulting in the Kelvin-Helmholtz
instability (KHI). We show that the strength of turbulence arising from the KHI
in the dead zone is .Comment: 19 pages, 20 figures, 3 tables, accepted for publication in MNRA
Constraints on the Formation of the Planet Around HD188753A
The claimed discovery of a Jupiter-mass planet in the close triple star
system HD 188753 poses a problem for planet formation theory. A circumstellar
disk around the planet's parent star would be truncated close to the star,
leaving little material available for planet formation. In this paper, we
attempt to model a protoplanetary disk around HD 188753A using a fairly simple
alpha-disk model, exploring a range of parameters constrained by observations
of T Tauri-type stars. The disk is truncated to within 1.5 to 2.7 AU, depending
on model parameters. We find that the in situ formation of the planet around HD
188753A is implausible.Comment: Accepted version, to appear in ApJ. 23 pages, 5 figures (3 in color
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