International Summer Institute for Modeling in Astrophysics

The transitional disks around young stars are protoplanetary disks with inner holes that are relatively empty of small dust grains, as inferred from the excess of far-infrared emission in their spectral energy distribution (SED) (Espaillat et al. 2007,2010). Recently, a new class of 'pre-transitional disks' are identified as exhibiting substantial emission from an optically thick inner disk separated from an optically thick outer disk by an optically thin gap (Espaillat et al. 2010). One plausible model for gap opening in these disks is by multiple giant planets (Zhu et al. 2011). However, two major problems remain to be solved. Firstly, micron-sized dust grains are not removed efficiently enough from the giant planet's gap to explain the observed low disk emission at near/mid-infrared wavelengths. Secondly, the presence of multiple Jupiter mass planets in resonance is not likely in standard disk models. We have developed a simple but robust coagulation-fragmentation model showing that piled-up material at the outer gap edge acts as a very efficient filter for micron-sized grains. Its reduction of the particle flow by two orders of magnitude provides excellent agreement with observational data. We can also produce high local surface density of particles at the outer edge of the gap, which may trigger planet formation in the outer disk.

Observations of T-Tauri circumstellar discs show the presence of mm or cm size dust grains at large distances from the central star (r > 10s AU). There empirical data challenge the currently mainstream grain growth theory, that disfavours the formation of such large grains in the outer disc and, despite formation, predicts their rapid inward migration due to coupling with the gas on short timescales. In this work, we develop some improvements in the grain growth theory and implement them in GrOG (Growth Of Grains), a new numerical solver for the coagulation and fragmentation of grains inside a circumstellar disc. Our results revise conclusions from previous theoretical models, as we are able to growth particles of significantly larger size.

We examine the dynamical mechanisms that control heat transport in atmospheres of tidally locked planets. Current estimates of heat redistribution in atmospheres of hot Jupiters generally only consider the equilibrium of stellar irradiation and advection. In this work, we show that gravity waves can effectively transport heat on global scales in atmospheres of tidally locked planets. A simple 1D atmospheric shallow-water model is used to study the day/night temperature contrast as a function of the radiative, advective, frictional, and wave-travel timescales of the atmosphere. We qualitatively compare our results with those made by 2D non-linear shallow-water simulations.

We present simulations of the collapse of a massive rotating protostellar core assuming conditions characteristic of Population III star formation. Starting with an initially weak magnetic field, we find that the combined action of compression and dynamo processes amplify the field to nearly equipartition levels. At late times, we find the magnetic field is able to buoyantly rise above and below the protostellar disk, producing a large-scale magnetic field.

A simple, fast algorithm which simulates collisions between inelastic particles in an optically thin disk orbiting a central mass is implemented to the N-body simulation code MERCURY. The hybrid symplectic integrator is used to simulate a moonlet in the Saturn ring scenario, and produced a propeller structure around the moonlet which opens a partial gap in the ring.

We revisit the destruction of resonance between Neptune and Kuiper Belt Objects (KBOs) by random planetesimal scatterings, which has been studied by Murray-Clay and Chiang (2006) previously. In this work, we consider the encounters between Neptune's resonant KBOs and planetesimals and the Levy flight behavior of resonant KBOs corresponding to a single big kick. The analysis in this work is based on order-of-magnitude estimation.

We have studied the stability of the thin dust-rich midplane in a protostellar disk. The layer tends to be broken apart by the Kelvin-Helmholtz instability due to differential velocities in the vertical direction, but is stabilized by the stretching of this instability thanks to the Coriolis force and radial shear. We found two trends depending on the metallicity at the midplane, which support previous studies and go further on which criteria is relevant to study these layers numerically.

In this document, we report our recent study on the turbulence inside the multi-phase ISM. First, we quantify the turbulence inside the molecular phase ISM by adopting a pixel-by-pixel line fitting strategy and studying the statistics of the fittings results of the ¹³CO lines. The histogram of the ¹³CO line amplitude and ¹³CO line FWHM show power-law behavior, indicative of turbulence. Especially, the histogram of the FWHM of the ¹³CO line show a dN/dv proportional to v^-2.45 at high velocity end, which seems to be universal. By plotting the 2D histogram of the ¹³CO line strength versus the ¹³CO line width, a lower limit of the ¹³CO line width for a given ¹³CO line strength can be identified. We argue that such a lower limit is due to the self-gravity of the molecular cloud. Second, with the combination of ¹³CO data from the GRS survey and the Hi 21cm data from the VGPS survey, we study the connection between the molecular gas probed with the ¹³CO line emission and the cold Hi gas probed by the Hi 21cm self-absorption feature. We found that the Hi gas that is associated with the molecular clouds is also turbulent. The molecular clouds that have detectable Hi envelope are more turbulent than clouds that do not show such envelope. Our results support the idea the molecular cloud turbulence is driven from outside, e.g. by the large-scale converging flow.

Using Whitney’s Monte Carlo radiative transfer code, we simulate the near IR scattered light images in both intensity and polarized intensity for a series of axisymmetric protoplanetary disk models. By measuring the properties of the images, we study the detectability of both the disks and the features of giant planet formation at early stage (i.e. gaps opened by the planets) in real observations, and the connection between the detected disk structure and the intrinsic properties of the system. We use real point spread functions of the Subaru telescope to convolve the images, in order to synthesize realistic images with the smallest spatial resolution and inner working angle which ground based instruments can provide at present. In the models without gaps, the effects of the disk depletion factor, mass, and flareness on the images are investigated, while for the models with a gap, we focus on the dependence of the detectability of the gap on the gap position, width, and depletion factor. Qualitatively, the more massive and more flared the disk is, the brighter the disk is. The gap is only visible when the disk is visible, and the deeper and wider the gap is, the larger the contrast level of the gap is.

Temperature inversion leading to a hot stratosphere have been observed in some hot-Jupiter. Theoretical models predict that such a temperature inversion can be caused by the presence of a strong absorber in the visible in the high atmosphere. Titanium oxide have been proposed to be a good candidate for being this extra-absorber. Although the temperature in the day side of these planets can be high enough to maintain titanium oxide in a gaseous phase, it is not the case in the night side. In this work we discuss how the day/night temperature contrast can lead to the depletion of titanium oxide in the high atmosphere of hot-Jupiter. Using 1D and 3D models we found some constraints on the vertical diffusion coefficient needed to maintain enough titanium oxide in the upper atmosphere to create a temperature inversion. These constraints are similar to the ones given by Spiegel et al. (2009) for the vertical cold trap but hold for all the planets, even the ones that are too hot to be affected by the vertical cold trap.