Atmospheric Dynamics of Short-period Extra Solar Gas Giant Planets I: Dependence of Night-Side Temperature on Opacity

More than two dozen short-period Jupiter-mass gas giant planets have been discovered around nearby solar-type stars in recent years, several of which undergo transits, making them ideal for the detection and characterization of their atmospheres. Here we adopt a three-dimensional radiative hydrodynamical numerical scheme to simulate atmospheric circulation on close-in gas giant planets. In contrast to the conventional GCM and shallow water algorithms, this method does not assume quasi hydrostatic equilibrium and it approximates radiation transfer from optically thin to thick regions with flux-limited diffusion. In the first paper of this series, we consider synchronously-spinning gas giants. We show that a full three-dimensional treatment, coupled with rotationally modified flows and an accurate treatment of radiation, yields a clear temperature transition at the terminator. Based on a series of numerical simulations with varying opacities, we show that the night-side temperature is a strong indicator of the opacity of the planetary atmosphere. Planetary atmospheres that maintain large, interstellar opacities will exhibit large day-night temperature differences, while planets with reduced atmospheric opacities due to extensive grain growth and sedimentation will exhibit much more uniform temperatures throughout their photosphere's. In addition to numerical results, we present a four-zone analytic approximation to explain this dependence.Comment: 35 Pages, 13 Figure

Radiative Hydrodynamic Simulations of HD209458b: Temporal Variability

We present a new approach for simulating the atmospheric dynamics of the close-in giant planet HD209458b that allows for the decoupling of radiative and thermal energies, direct stellar heating of the interior, and the solution of the full 3D Navier Stokes equations. Simulations reveal two distinct temperature inversions (increasing temperature with decreasing pressure) at the sub-stellar point due to the combined effects of opacity and dynamical flow structure and exhibit instabilities leading to changing velocities and temperatures on the nightside for a range of viscosities. Imposed on the quasi-static background, temperature variations of up to 15% are seen near the terminators and the location of the coldest spot is seen to vary by more than 20 degrees, occasionally appearing west of the anti-solar point. Our new approach introduces four major improvements to our previous methods including simultaneously solving both the thermal energy and radiative equations in both the optical and infrared, incorporating updated opacities, including a more accurate treatment of stellar energy deposition that incorporates the opacity relevant for higher energy stellar photons, and the addition of explicit turbulent viscosity.Comment: Accepted for publication in Ap

Simulating the impact of the Smith Cloud

We investigate the future evolution of the Smith Cloud by performing hydrodynamical simulations of the cloud impact onto the gaseous Milky Way Galactic disk. We assume a local origin for the cloud and thus do not include a dark matter component to stabilize it. Our main focus is the cloud's influence on the local and global star formation rate (SFR) of the Galaxy and whether or not it leads to an observable event in the far future. Our model assumes two extremes for the mass of the Smith Cloud, an upper mass limit of 10$^7$ M$_{\odot}$ and a lower mass limit of 10$^6$ M$_{\odot}$, compared to the observational value of a few 10$^6$ M$_{\odot}$. In addition, we also make the conservative assumption that the entirety of the cloud mass of the extended Smith Cloud is concentrated within the tip of the cloud. We find that the impact of the low-mass cloud produces no noticeable change in neither the global SFR nor the local SFR at the cloud impact site within the galactic disk. For the high-mass cloud we find a short-term (roughly 5 Myr) increase of the global SFR of up to 1 M$_{\odot}$ yr$^{-1}$, which nearly doubles the normal Milky Way SFR. This highly localized starburst should be observable.Comment: 14 pages, 5 figure

Some closure operations in Zariski-Riemann spaces of valuation domains: a survey

In this survey we present several results concerning various topologies that were introduced in recent years on spaces of valuation domains

Tidal Barrier and the Asymptotic Mass of Proto Gas-Giant Planets

Extrasolar planets found with radial velocity surveys have masses ranging from several Earth to several Jupiter masses. While mass accretion onto protoplanetary cores in weak-line T-Tauri disks may eventually be quenched by a global depletion of gas, such a mechanism is unlikely to have stalled the growth of some known planetary systems which contain relatively low-mass and close-in planets along with more massive and longer period companions. Here, we suggest a potential solution for this conundrum. In general, supersonic infall of surrounding gas onto a protoplanet is only possible interior to both of its Bondi and Roche radii. At a critical mass, a protoplanet's Bondi and Roche radii are equal to the disk thickness. Above this mass, the protoplanets' tidal perturbation induces the formation of a gap. Although the disk gas may continue to diffuse into the gap, the azimuthal flux across the protoplanets' Roche lobe is quenched. Using two different schemes, we present the results of numerical simulations and analysis to show that the accretion rate increases rapidly with the ratio of the protoplanet's Roche to Bondi radii or equivalently to the disk thickness. In regions with low geometric aspect ratios, gas accretion is quenched with relatively low protoplanetary masses. This effect is important for determining the gas-giant planets' mass function, the distribution of their masses within multiple planet systems around solar type stars, and for suppressing the emergence of gas-giants around low mass stars

Transient thermal effects in solid noble gases as materials for the detection of Dark Matter

The transient phenomena produced in solid noble gases by the stopping of the recoils resulting from the elastic scattering processes of WIMPs from the galactic halo were modelled, as dependencies of the temperatures of lattice and electronic subsystems on the distance to the recoil's trajectory, and time from its passage. The peculiarities of these thermal transients produced in Ar, Kr and Xe were analysed for different initial temperatures and WIMP energies, and were correlated with the characteristics of the targets and with the energy loss of the recoils. The results were compared with the thermal spikes produced by the same WIMPs in Si and Ge. In the range of the energy of interest, up to tens of keV for the self-recoil, local phase transitions solid - liquid and even liquid - gas were found possible, and the threshold parameters were established.Comment: Minor corrections and updated references; accepted to JCA

Three-dimensional atmospheric circulation of hot Jupiters on highly eccentric orbits

Of the over 800 exoplanets detected to date, over half are on non-circular orbits, with eccentricities as high as 0.93. Such orbits lead to time-variable stellar heating, which has implications for the planet's atmospheric dynamical regime. However, little is known about this dynamical regime, and how it may influence observations. Therefore, we present a systematic study of hot Jupiters on highly eccentric orbits using the SPARC/MITgcm, a model which couples a three-dimensional general circulation model with a plane-parallel, two-stream, non-grey radiative transfer model. In our study, we vary the eccentricity and orbit-average stellar flux over a wide range. We demonstrate that the eccentric hot Jupiter regime is qualitatively similar to that of planets on circular orbits; the planets possess a superrotating equatorial jet and exhibit large day-night temperature variations. We show that these day-night heating variations induce momentum fluxes equatorward to maintain the superrotating jet throughout its orbit. As the eccentricity and/or stellar flux is increased, the superrotating jet strengthens and narrows, due to a smaller Rossby deformation radius. For a select number of model integrations, we generate full-orbit lightcurves and find that the timing of transit and secondary eclipse viewed from Earth with respect to periapse and apoapse can greatly affect what we see in infrared (IR) lightcurves; the peak in IR flux can lead or lag secondary eclipse depending on the geometry. For those planets that have large day-night temperature variations and rapid rotation rates, we find that the lightcurves exhibit "ringing" as the planet's hottest region rotates in and out of view from Earth. These results can be used to explain future observations of eccentric transiting exoplanets.Comment: 20 pages, 18 figures, 2 tables; Accepted to Ap

On the chains of star complexes and superclouds in spiral arms

The relation is studied between occurrence of a regular chain of star complexes and superclouds in a spiral arm, and other properties of the latter. A regular string of star complexes is located in the north-western arm of M31; they have about the same size 0.6 kpc with spacing of 1.1 kpc. Within the same arm segment the regular magnetic field with the wavelength of 2.3 kpc was found by Beck et al. (1989). We noted that this wavelength is twice as large as the spacing between complexes and suggested that they were formed in result of magneto-gravitational instability developed along the arm. In this NW arm, star complexes are located inside the gas-dust lane, whilst in the south-western arm of M31 the gas-dust lane is upstream of the bright and uniform stellar arm. Earlier, evidence for the age gradient has been found in the SW arm. All these are signatures of a spiral shock, which may be associated with unusually large (for M31) pitch-angle of this SW arm segment. Such a shock may prevent the formation of the regular magnetic field, which might explain the absence of star complexes there. Anti-correlation between shock wave signatures and presence of star complexes is observed in spiral arms of a few other galaxies. Regular chains of star complexes and superclouds in spiral arms are rare, which may imply that a rather specific mechanism is involved in their formation, and the most probable one is the Parker-Jeans instability. The spiral pattern of our Galaxy is briefly discussed; it may be of M101 type in the outer parts. The regular bi-modal spacing of HI superclouds is found in Carina and Cygnus (Outer) arms, which may be an indirect evidence for the regular magnetic field along these arms.Comment: 20 pages, 12 figures, accepted for publication in MNRA

Epitaxial Growth Kinetics with Interacting Coherent Islands

The Stranski-Krastanov growth kinetics of undislocated (coherent) 3-dimensional islands is studied with a self-consistent mean field rate theory that takes account of elastic interactions between the islands. The latter are presumed to facilitate the detachment of atoms from the islands with a consequent decrease in their average size. Semi-quantitative agreement with experiment is found for the time evolution of the total island density and the mean island size. When combined with scaling ideas, these results provide a natural way to understand the often-observed initial increase and subsequent decrease in the width of the coherent island size distribution.Comment: 4 pages, 4 figure

The influence of surface stress on the equilibrium shape of strained quantum dots

The equilibrium shapes of InAs quantum dots (i.e., dislocation-free, strained islands with sizes >= 10,000 atoms) grown on a GaAs (001) substrate are studied using a hybrid approach which combines density functional theory (DFT) calculations of microscopic parameters, surface energies, and surface stresses with elasticity theory for the long-range strain fields and strain relaxations. In particular we report DFT calculations of the surface stresses and analyze the influence of the strain on the surface energies of the various facets of the quantum dot. The surface stresses have been neglected in previous studies. Furthermore, the influence of edge energies on the island shapes is briefly discussed. From the knowledge of the equilibrium shape of these islands, we address the question whether experimentally observed quantum dots correspond to thermal equilibrium structures or if they are a result of the growth kinetics.Comment: 7 pages, 8 figures, submitted to Phys. Rev. B (February 2, 1998). Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm