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eScholarship
Open Access Publications from the University of California

UCSC is one of the world's leading centers for both observational and theoretical research in astronomy and astrophysics. The department was recently ranked first in the country in research impact, based on citation studies. Faculty and students in the department and our affiliated research centers are building and using first-rank telescopes and instrumentation—on Earth and in space—extending humanity’s vision to planets orbiting nearby stars and the first stirrings of the Universe.

The department includes 24 faculty members, whose research interests range from our solar system and the Milky Way to the most distant galaxies in the Universe and the most fundamental questions of cosmology.

UCSC is a leader in astrophysics education, and we attract some the best graduate students in the country, enrolling approximately 40 students working towards the Ph.D. degree.

Currently this page is for hosting only ISIMA (International Summer Institute for Modeling in Astrophysics) conference proceedings.

Cover page of Detecting the earliest stages of giant planet formation in scattered light

Detecting the earliest stages of giant planet formation in scattered light

(2011)

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.

Cover page of Improving the grain growth model in the outer part of circumstellar disks

Improving the grain growth model in the outer part of circumstellar disks

(2011)

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.

Cover page of Abundance and evolution of gas around Beta Pictoris

Abundance and evolution of gas around Beta Pictoris

(2011)

Recent observations have shown that carbon in the gas around beta Pictoris is more than 100 times over- abundant with respect to the solar abundance. Although it is thought that such an overabundance in carbon is crucial to retain the metal elements in the disk, its origin is however unclear. In this paper, we establish a simple analytical model to study gas the removal process and thus calculate the abundance of various elements in the gas disk around beta Pictoris. The gas removal rate is controlled by the inward flow from viscous accretion and the outward radiation-induced drift. If the disk viscosity (using classical alpha-disk model) is low, radiation drift dominates the gas loss, and carbon can become highly overabundant. In order to produce the observed overabundance of carbon, a low viscosity of alpha < 10-3 and a gas production with solar abundance are preferred.

Cover page of Convectively generated zonal jets by thunderstorms on Jupiter

Convectively generated zonal jets by thunderstorms on Jupiter

(2011)

A forced-dissipative shallow water model is adopted to simulate the jet streams, especially the equatorial ow, on Jupiter. Two types of forcing, the local mass pulse and vorticity pulse, are used to parameterize the small scale moist convection such as thunderstorms, respectively. In the mass-forced dissipative model without the frictional drag, it is unable to produce a prograde ow at equator. The reason could be that the anticyclonic features are favored by the off-equator positive mass forcing. In the simulations with the vorticity-type forcing, equatorial superrotation could be produced under some condition, although the physical mechanism is not fully understood.

Cover page of A simple model for understanding the day-night temperature constrast on Hot Jupiters

A simple model for understanding the day-night temperature constrast on Hot Jupiters

(2011)

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.

Cover page of Ohmic dissipation in hot Jupiters

Ohmic dissipation in hot Jupiters

(2011)

We present an isolated analytical model for the ohmic heating in the interior of hot jupiters, treating the wind zone as a parameterized boundary condition. Under a conserved estimation of the strength of induced field and the assumption of an isothermal-convective planet model, we conclude that the mechanism of ohmic heating may not explain the over-inflated radius of hot jupiters along. We also develop a new time dependent evolution model for hot jupiters with ohmic heating, further show that ohmic heating is important only when the planet mass is small or the planet is at late stage of evolution.

Cover page of Day-night cold traps for TiO in hot Jupiter atmospheres

Day-night cold traps for TiO in hot Jupiter atmospheres

(2011)

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.

Cover page of Planetary dynamics in collisional particle disks

Planetary dynamics in collisional particle disks

(2011)

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.

Cover page of Planetesimal formation: shear instabilities at the dust-rich mid-plane

Planetesimal formation: shear instabilities at the dust-rich mid-plane

(2011)

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.

Cover page of Analytical studies of fragmentation during gravitational collapse

Analytical studies of fragmentation during gravitational collapse

(2011)

We investigate the growth of linear perturbations on self-similar gravitational collapse solutions of an isothermal sphere. The perturbation equations are derived analytically, for exponentially growing modes, as well as oscillatory modes and the resulting system of differential equations is solved numerically, using different algorithms.